DETERMINING THE ROLE OF THE AhR IN IMMUNOGLOBULIN EXPRESSION AND CLASS SWITCH RECOMBINATION A thesis submitted in partial fulfillment of the requirements for the degree of Master of Science By BASSAM F. KASHGARI B.S., King Abdul-Aziz University 2015 WRIGHT STATE UNIVERSITY
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DETERMINING THE ROLE OF THE AhR IN IMMUNOGLOBULIN
EXPRESSION AND CLASS SWITCH RECOMBINATION
A thesis submitted in partial fulfillment
of the requirements for the degree of
Master of Science
By
BASSAM F. KASHGARI
B.S., King Abdul-Aziz University
2015
WRIGHT STATE UNIVERSITY
WRIGHT STATE UNIVERSITY
GRADUATE SCHOOL
August 31st, 2015
I HEREBY RECOMMEND THAT THE THESIS PREPARED UNDER MY SUPERVISION BY Bassam Kashgari ENTITLED Determining the Role of the AhR in Immunoglobulin Expression and Class Switch Recombination BE ACCEPTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF Master of Science.
Courtney E.W. Sulentic, Ph.D. Thesis Director
Barbara E. Hull, Ph.D. Director of Microbiology and Immunology Program
College of Science and Mathematics
Committee on Final Examination
Courtney E. W. Sulentic, Ph.D.
Barbara E. Hull, Ph.D.
Nancy J. Bigley, Ph.D.
Katherine Excoffon, Ph.D.
Robert E. W. Fyffe, Ph.D.
Vice President for Research and Dean of the Graduate
School
iii
ABSTRACT
Kashgari, Bassam. M.S., Microbiology and Immunology Graduate Program, Wright State University, 2015. Determining the Role of the AhR in Immunoglobulin Expression and Class Switch Recombination.
The aryl hydrocarbon receptor (AhR) is a ligand-activated cytosolic transcription factor
that regulates xenobiotic-metabolizing enzymes. It mediates the toxicity of various
environmental chemicals such as 2,3,7,8-tetracholorodibenzo-p-dioxin (TCDD). TCDD
inhibits the differentiation of B cells into antibody-secreting cells and inhibits
immunoglobulin (Ig) expression in various animal models. We have previously
determined that TCDD-induced inhibition of the mouse Ig heavy chain gene (mo-Igh) is
AhR-dependent. This inhibition may be mediated by binding of the AhR to dioxin
response elements (DREs) within the 3’Igh regulatory region (3’IghRR) and inhibition of
3’IghRR activity, a significant transcriptional regulator of Ig expression. However, there
are structural differences between the mouse and human 3’IghRR. The mouse contains
four enhancers (hs3A; hs1,2; hs3B; and hs4), whereas the human contains three (hs3;
hs1,2; and hs4). In addition, the human hs1,2 is known to be highly polymorphic and has
been associated with several autoimmune diseases. The current study focuses on
elucidating the role of the AhR in human Ig expression and class switch recombination
(CSR). We disrupted the AhR signaling pathway in a human B-cell line (CL-01) using
two different shRNA constructs or with the chemical AhR antagonist (CH-223191).
iv
Although the CL-01 AhR has three heterozygous single nucleotide polymorphisms
(SNPs) that results in loss of CYP1A1 gene induction, TCDD significantly inhibits IgG
expression, whereas IgM expression has very low sensitivity to TCDD. Interestingly,
decreased AhR protein levels results in low IgG expression, while there was no change in
IgM expression. In contrast, the AhR antagonist induced greater IgG secretion in
stimulated B cells, which was not replicated by the AhR knockdown suggesting a
mechanistic difference between the chemical antagonist and AhR knockdown. Reduced
AhR levels caused an isotype-specific inhibition of the CSR to IgG1, but not to IgG2,
IgA or IgE. These results demonstrate that there are different mechanisms regulating
different Ig isotypes. With the growing number of human immune-related disorders
correlating with the polymorphic hs1,2 enhancer, understanding the role of the AhR in
3’IGHRR activity and Ig expression could provide insight into potential therapeutic
interventions.
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TABLE OF CONTENTS
Page
I. INTRODUCTION…………………………………......………………………….1
The Aryl Hydrocarbon Receptor (AhR)……....…………………………..1
2,3,7,8-Tetrachlorodibenzo-p-dioxon (TCDD)………..………….……....4
The Immune System………………………………………………………7
B-cells & Immunoglobulins………………………………………………8
TCDD-induced Immunotoxicity.…….…………………………….…….13
The Mouse Immunoglobulin Heavy Chain Regulatory Region.………...14
The Human Immunoglobulin Heavy Chain Regulatory Region.……..…15
The Mouse AhR and B-cell Dysfunction.……………………..…………20
The Human AhR and B-cell Dysfunction.…………………..…………...21
Significance……………………………..…………………..…….……...24
II. MATERIALS AND METHODS...........................................................................27
Chemicals and Reagents............................................................................27
Cell Line Model & Cell Culture Conditions..............................................27
shAhR Constructs.…………….…..……………………………….…….28
Stable AhR Knockdown..…………….……..………………….………..29
Protein Isolation and Western Blot.…..……..…………………………...29
Reporter Plasmid Constructs…......…..……..…………………………...30
Transient Transfection...………….…..……..…………………………...31
Luciferase Assay System…………..…..……..……..…………………...31
vi
Enzyme-Linked Immunosorbent Assay (ELISA)……………..…………31
RNA Isolation………..………………………..……..…………………..33
cDNA Synthesis and Real-Time PCR…………..…………………..…...33
Statistical Analysis.…..………………………..……..…………………..34
III. RESULTS……………………………………………………………………......37
Characterization of a stable knockdown of the AhR levels and function in
the human CL-01 B-cell line……..…………………………........………37
Knocking down the AhR inhibits the overall basal activity of IgG
expression and has no effect on IgM expression…………………......….44
Knocking down the AhR has no effect on expression of Cε de novo
germline transcripts....................................................................................51
IV. DISCUSSION........................................................................................................53
V. LITERATURE CITED…………………………......……………………………62
viii
LIST OF FIGURES
Figure 1: Aryl hydrocarbon receptor signaling pathway……………….……….…...3
Figure 2: Chemical structure of 2, 3, 7, 8-tetrachlorodibenzo-p-dioxin (TCDD).......6
Figure 3: Structure of an immunoglobulin (Ig) protein………………………….…12
Figure 4: Immunoglobulin heavy chain (IGH) gene locus........................................18
Figure 5: Human polymorphic hs1,2 reporter plasmid constructs............................19
Figure 6: Verifying the knock down of the AhR protein in the CL-01 human B-cell
line.………..……………………………………………………….……..39
Figure 7: Schematic of Cytochrom P4501A1 reporter plasmid................................41
Figure 8: The AhR polymorphisms in the CL-01 cell line results in a loss of TCDD-
inducible CYP1A1 promoter activation.……....…………………………41
Figure 9: The chromatograph for CL-01 AhR sequencing results showing where the
heterozygous SNPs fall within the transactivation domain………….......42
Figure 10: The AhR polymorphisms in the CL-01 cell line result in a loss of CYP1A1
induction but has no affect on ligand and DRE binding.....………..….....43
Figure 11: Reduced AhR levels inhibit basal IgG secretion and completely abrogate
stimulation-induced IgG secretion.……………………………..……..…45
Figure 12: Reduced AhR levels inhibit Cγ1 germline transcript mRNA expression in
the shAhR11 and shAhR12 and completely abrogate expression in the
shAhR11 and shAhR12 clones…………………………………………..46
Figure 13: Spontaneous CSR and AhR-dependent expression of Cγ1...…..………..47
ix
Figure 14: No difference in IgM protein secretion between WT CL-01 cells and
shAhR cell lines with or without TCDD treatment …...………..….....…49
Figure 15: No difference in expression of μ IGH functional transcripts between WT
CL-01 cells and shAhR cell lines with or without TCDD treatment
……………………………………………………………………………50
Figure 16: Reduced AhR levels have no change on expression of Cε de novo
germline…………....……………………………………….…………....52
x
LIST OF TABLES
Table 1: Forward and reverse primers and product sizes for μ IGH and γ1 IGH
functional transcripts, Cγ1, Cγ2, and Cε germline transcripts, AhR sequencing primers,
and β–actin loading control respectively………...................................……………..…..35
Table 2: PCR cycling conditions for μ IGH and γ1 IGH functional transcripts, Cγ1,
Cγ2, and Cε germline transcripts, AhR sequencing primers, and β–actin loading control
respectively………................................................................................……………..…..36
xi
LIST OF ABBREVVIATIONS
AhR: Aryl Hydrocarbon Receptor
ARNT: AhR Nuclear Translocator
bHLH/PAS: Basic Helix-Loop-Helix/Per-ARNT-Sim
BCR: B-Cell Receptor
CSR: Class Switch Recombination
Cyp1A1: Cytochrome P4501A1
CH: Heavy Chain Constant Region
DMSO: Dimethyl Sulfoxide
DRE: Dioxin Responsive Element
Eµ: Intronic Enhancer
HS: DNase I Hypersensitivity
IS: Invariant Sequence
IgH: Immunoglobulin Heavy Chain
IgL: Immunoglobulin Light Chain
IghRR: mouse Ig Heavy Chain Regulatory Region
IGHRR: human Ig Heavy Chain Regulatory Region
xii
Ig: Immunoglobulin
LPS: Lipopolysaccharide
MCS: Multiple Cloning Site
MHC: Major Histocompatibility Complex
NFκB: Nuclear Factor κB
Oct: Octamer Transcription Factor
PCDD: Polychlorinated Dibenzo-p-Dioxins
PCDF: Polychlorinated Dibenzofurans
PCB: Polychlorinated Biphenyls
Pax5: Paired Box Protein
RLU: Relative Light Units
SHM: Somatic Hypermutation
SNP: Single Nucleotide Polymorphism
TLR: Toll like Receptor
TCDD: 2,3,7,8-Tetrachlorodibenzo-p-Dioxin
VH promoter: Variable Heavy Chain Promoter
xiii
ACKNOWLEDGMENTS
I would like to thank all the great people who have contributed to the work
described in this thesis. First and foremost, my deepest gratitude is to my advisor Dr.
Courtney Sulentic. I have been fortunate to have an advisor who cares so much about her
students and their success. Dr. Sulentic taught me how to ask questions, think critically,
and express ideas. Her patience and great skills in communicating with her students have
helped me overcome many situations during my master’s journey. In addition, I would
like to thank my committee Dr. Nancy Bigley, Dr. Katherine Excoffon, and Dr. Barbara
Hull for their valuable suggestions and support. All the results in this thesis were
accomplished with the help and support of the members of Dr. Sulentic's lab. They are a
great team and awesome friends, who I will always remember. Lastly, I would like to
thank all of my friends and family, especially my parents, for their continuous
encouragement and help throughout my life.
1
I. INTRODUCTION
The Aryl Hydrocarbon Receptor (AhR)
The aryl hydrocarbon receptor (AhR) is a ligand-activated transcription factor of
the basic helix-loop-helix/Per-ARNT-Sim family (bHLH/PAS) that is known to mediate
the biochemical effects of polyaromatic hydrocarbons. In the cytosol, the AhR is inactive
and bound to protective proteins that help stabilize the whole complex (Abel &
Haarmann-Stemmann, 2010) and include two chaperone heat shock proteins (Hsp90),
which protects from elevation in cell temperature (Feder & Hofmann, 1999); the hepatitis
B virus X-associated protein 2 (XAP-2), which prevents the C terminus of Hsc70-
interacting protein (CHIP)-mediated degradation of the AhR (Lees, Peet, & Whitelaw,
2003); and p23, which protect from proteolysis (Nguyen et al., 2012). The AhR can be
activated by a wide range of ligands, dioxins and some other non-dioxin compounds (e.g.
dietary or pharmaceutical), leading to up-regulation of xenobiotic-metabolizing enzymes
such as cytochrome P4501A1 (CYP1A1). The majority of high-affinity AhR ligands are
halogenated aromatic hydrocarbons (HAHs) and polycyclic aromatic hydrocarbons
(PAHs). 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), which belongs to the HAH family,
has the highest AhR binding affinity, and is the prototypical AhR ligand used in AhR
studies (Abel & Haarmann-Stemmann, 2010; Mandal, 2005a). When the AhR interacts
with its ligand, it translocates into the nucleus. Once the AhR gets into the nucleus, the
AhR nuclear translocator (ARNT) competes for the XAP2 and hsp90 binding sites
leading to a dissociation of all the protective proteins and heterodimerizing of the AhR
2
with the ARNT to form a functional transcription factor. The protective proteins get
exported back to the cytosol, and the AhR-ARNT heterodimer binds to DNA at the
dioxin responsive element (DRE) upregulating or downregulating transcription (Meyer &
Perdew, 1999; Kazlauskas, Poellinger, & Pongratz, 1999). (Fig.1). The AhR signaling
pathway gets inactivated by phosphorylation/dephosphorylation processes resulting in the
AhR being exported out of the nucleus then degraded in the cytosol (Abel & Haarmann-
Stemmann, 2010).
The AhR is an intracellular molecule that plays a significant role in the regulation
of xenobiotic-metabolizing enzymes. One of the most characterized genes regulated by
the AhR is the gene for the xenobiotic-metabolizing enzyme CYP1A1, which catalyzes
reactions involved in drug metabolism (Stejskalova & Pavek, 2011). In addition, the AhR
plays a role in regulating genes involved in apoptosis, proliferation, differentiation and
cell growth (Abel & Haarmann-Stemmann, 2010). The AhR also cross-talks with steroid
receptors and can alter gene expression profiles for androgen, estrogen, or progesterone
hormones (Ohtake, 2008). AhR activation also plays an important role for immunological
responses and has been shown to inhibit inflammation through the upregulation of
interleukin 22 (Monteleone et al., 2011) and the down-regulation of Th17 and CD4+ T
cell response (Wei et al., 2014). The AhR also plays a pivotal role in mediating
inflammation and detoxification pathways by interacting with NF-κB (Tian, 2009).
3
Figure 1. Aryl hydrocarbon receptor signaling pathway. Upon ligand-binding, the
AhR-complex translocates into the nucleus where it sheds the chaperone proteins and
binds to ARNT. The AhR/ARNT complex modulates transcription by binding to DREs
within the promoter or the enhancer region of genes sensitive to AhR ligands (Meyer &
Perdew, 1999; Kazlauskas, Poellinger, & Pongratz, 1999).
4
2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD)
Dioxins are a group of toxic chemicals that are composed of halogenated aromatic
hydrocarbons. They share similar mechanisms and properties. They have a long half-life,
which means that they have high-resistance to get metabolized, and they break down
slowly. Thus, this makes them more dangerous, especially in the case of long-term
exposure, when they can bioaccumulate in fat tissues. The dioxin family includes
polychlorinated dibenzodioxins (PCDDs), polychlorinated dibenzofurans (PCDFs), and
polychlorinated biphenyls (PCBs). The biological effects of dioxin especially to human
health have been an area of intensive investigation. The prototypical and most toxic
dioxin is 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), which has been extensively
studied (Malisch & Kotz, 2014; Mandal, 2005b) (Fig 2).
TCDD is a polychlorinated dibenzo-p-dioxin that has no color or odor at room
temperature. It is formed as a stable by-product or contaminant from the incineration of
municipal & medical waste, coal-fired utilities, metal smelting, diesel trucks, burning
treated wood, misapplication of sewage sludge, and bleaching of paper fibers and textiles
(Malisch & Kotz, 2014; Struciński et al., 2011). It was first known as a hazard during the
Vietnam War (1961-1971) when the U.S military sprayed the herbicide Agent Orange,
which was contaminated with TCDD, to defoliate the forest and expose their enemies and
destroy their food resources (Karch, 2004). Then in 1976, an explosion at a chemical
plant in Seveso, Italy resulted in the highest known residential exposure to TCDD
(Eskenazi et al., 2003). Other incidents in the 1970s led to evacuation of Love Canal,
Niagra Falls, NY and Missouri after roads were sprayed for dust control with TCDD-
contaminated waste oil (Tiernan et al., 1985).
5
Exposure of TCDD can occur by ingestion, inhalation or dermal contact.
Generally, when there is no occupational or other dioxin-exposure history, 90-98% of the
human exposure to TCDD results from food, and only 2-10% is from ambient sources
(ingestion of soil or water and inhalation of air or dust) and other non-food sources
(cigarette smoking) (Malisch & Kotz, 2014). TCDD affects many organs, and the short
and long-term effects vary depending on species, age, sex, and exposure concentration. In
animal studies, toxic responses from TCDD exposure include thymic atrophy, immune
dysfunction, hepatic damage and steatosis, embryonic teratogenesis, endocrine
disruption, and tumor promotion (Mandal, 2005b). In all mammalian species that have
been tested for lethal doses of TCDD, there was an excessive loss in body weight prior to
death, which is known as wasting syndrome (Cachexia) (IARC, 1997). In humans, the
major effect seen from exposure to TCDD is the development of severe chloracne, which
is an acne-like condition characterized by follicular hyperkeratosis on the face and neck
(Ong, Stevens, Roeder, & Eckhardt, 1998; Geusau et al., 2001). In addition, TCDD has
been classified by the International Agency for Research on Cancer (IARC) as a
carcinogen for humans (IRAC, 1997). TCDD is not genotoxic but can promote
carcinogenesis. However, TCDD has also been shown to inhibit metastasis and cell
proliferation of some types of cancer (e.g. mammary tumor, ovarian cancer) (Mandal,
2005b).
6
Figure 2. Chemical structure of 2, 3, 7, 8-tetrachlorodibenzo-p-dioxin (TCDD).
7
The Immune System
The immune system is a complex system that is responsible for host defense and
provides protection against infections and foreign invaders (e.g. bacteria, viruses, fungi,
and parasites). It is crucial for survival since even infections can be fatal in the absence of
a functional immune system. The immune system depends on innate and adaptive
immunity. Innate immunity is always present and ready to fight microbes at the site of
infection. It is the first line of defense and employs a non–specific response against
pathogens. It is determined by genes that have been inherited from the parents, whereas
the adaptive (acquired) immunity depends on specificity of antibodies to certain antigens,
in which this specificity develop due to an exposure to an antigen or by transmission of
antibodies from the mother to fetus (Parham, 2005).
Each subsystem has advantages and disadvantages when it comes to its
mechanism of recognition. The innate immune response is fast, taking hours to recognize
the antigen, but it is not specific and all antigens are attacked equally. It is a non-specific
fixed system that reacts the same to all different kinds of antigens. It does not have the
ability to improve during time or during the response to antigens. The main components
of innate immunity include physical barriers, phagocytes, and natural killer cells. The
adaptive immune response has slower responses, where it takes days to weeks to
recognize antigens and mount an immune response. However, it has highly selective
specificity to antigens and generates a stronger immune response as well as
immunological memory, where each pathogen is "remembered" by a signature antigen.
Both the innate and adaptive immunity work together through cross-reaction between the
two mechanisms (Parham, 2005).
8
Adaptive immunity can be divided into cell-mediated immunity that is dominated
by T cells, which is most effective against fungi, protozoans, cancers, and intracellular
bacteria, and the humoral-mediated (antibody-mediated) immunity that is dominated by
B cells. In cell-mediated immunity, T cells bind to the surface of other cells that present
antigen via major histocompatibility complex (MHC) and trigger a response through the
T cell receptor response. CD4+ T cells (T-helper cells) respond to class II MHC (MHC II)
molecules, which are only expressed on antigen-presenting cells (B cells, dendritic cells,
macrophages), leading to cellular proliferation and differentiation into effector, memory
or regulatory T helper cells and effector T helper cells that will further differentiate into
various subtypes. Additionally, CD8 T-cells (cytotoxic T-cells) respond to an epitope
presented by MHC I molecules, which are expressed on every cell of the body, by
destroying the cell that presents the foreign intracellular antigen when they get
recognized. On the other hand, humoral-mediated immunity involves the differentiation
of B cells into plasma cells that produce and secrete antigen-specific immunoglobulins
(Ig) (Parham, 2005).
B cells & Immunoglobulins
B cells or B lymphocytes are the major effector cells of humoral immunity that
can be differentiated from other lymphocytes by the presence of the B-cell receptor
(BCR), a membrane-bound Ig. They are formed in the bone marrow and then migrate as
immature or mature cells to the spleen and other secondary lymphoid tissue. B cells
circulate in the blood and the lymphatic system in an inactive state as immune
surveillances. An antigen gets recognized by the antigen-specific BCR, leading to clonal
expansion and activation. However, B cells do not become fully activated until they
9
receive additional signals from a T-helper cell that makes them further differentiate into
plasma B-cells or memory B-cells. Plasma B-cells are the antibody (Ab) factories, where
they can produce a huge amount of Ab, the soluble form of Ig, as a response to infections
and to clear the pathogens from the body through various ways. One of these ways is
opsonization of the pathogens by tagging and coating them to increase the efficacy of the
phagocytic process and enhancing the lysosomal elimination of the infective agent in an
effort to reduce inflammation. Alternatively, memory B cells are able to live for a long
time and retain antigen-specific BCR with high affinity for the activating antigen. Re-
exposure to the same antigen results in a quicker immune response from the memory B
cell, and then B cells will proliferate and produce large amounts of specific antibodies
and generate more memory B-cells against the antigen because the time that is required to
get a high affinity class-switched antibody, to the same antigen that has been recognized
before, is reduced. Furthermore, certain antigens, such as lipopolysaccharide (LPS), an
outer membrane component of gram-negative bacteria can activate B cells independent of
T-cell help. In addition to binding an LPS-specific BCR, LPS binds the
CD14/TLR4/MD2 receptor complex, which produces activating signals for inflammatory
cytokines. Whether or not T cells are involved, antibody production may proceed once
the B cell is activated (Woof & Burton, 2004).
Antibody production is the main function of the humoral immune system. The
five main Ig isotypes (IgM, IgD, IgG, IgE, and IgA) are composed of two identical heavy
chains (IgH) and two identical light chains (IgL) connected together by disulfide bonds
(Fig 3). Both the IgH and the IgL are composed of variable region sites where they bind
to the antigen and a constant region that is less diverse in its amino acid sequence. The
10
differences between antibody isotypes are based on the constant region of the heavy
chain, which convey different structural and functional properties between the isotypes.
The heavy chains: Cμ, Cδ, Cγ, Cε, and Cα encode for IgM, IgD, IgG, IgE, and IgA
respectively. On the other hand, the light chain has only two isotypes: λ and κ, but there
are no significant functional differences between them (Parham, 2005).
V(D)J recombination, also known as somatic recombination, is a random genetic
combination of gene segments that occurs during B-cell development. The first
recombination event to occur is between one random D and one J gene segment of the
heavy chain locus. DNA between these two gene segments is deleted, so D and J gene
segments are get close to each other. This D-J recombination is followed by the joining of
one random V gene segment forming a rearranged V(D)J gene segment. This process
takes place in the bone marrow, and the light chain locus is arranged in a very similar
way, except that it lacks the D segment, so only VJ recombination takes a place. This
randomness in gene recombination results in diverse encoding for immunoglobulins that
recognize a much wide diversity of antigens. Following successful rearrangement of the
light chain and heavy chain, an immature B cell expresses IgM and IgD on its surface. B
cells that fail to pass any of the maturation steps will die by apoptosis. After maturation,
B cells stay in the peripheral tissues until they get activated; another biological
mechanism known as class switch recombination (CSR) changes Ig expression from IgM
to another isotype (i.e. IgG, IgA, or IgE). This process changes the functional properties
and antibody structure; however, it does not affect antigen specificity because CSR is
limited to the constant region of the heavy chain only, whereas the variable regions of the
11
heavy and light chains encode the antigen specificity (Parham, 2005; Woof & Burton,
2004).
12
Figure 3. Structure of an immunoglobulin (Ig) protein. Ig is composed of two
identical heavy chain and light chain proteins each with a constant region of the heavy
chain that determines the effector qualities of the Ig and a variable region that binds
antigens.
13
TCDD-induced Immunotoxicity
Exposure to TCDD at a wide range of concentrations can cause various systemic
effects, including significant immunological dysfunction. TCDD exposure suppresses
both innate and adaptive immunity and inhibits cell-mediated and humoral immunity
(Abel & Haarmann-Stemmann, 2010; Mandal, 2005; Safe 1998; Vos 1997). In animal
models, exposure to TCDD can cause thymic atrophy, hepatic damage and steatosis,
embryonic teratogenesis, endocrine disruption, immune dysfunction, tumor transplant
rejection, an increase in the susceptibility to infections, and an increase in tumor growth
and metastasis (Mandal, 2005; Holsapple, 1991; Kerkvliet, 1995, 2002, 2009). However,
humans are less sensitive than animals to the immunotoxic effects by TCDD supposedly
due to variations of TCDD sensitivity. This variation might be a result of AhR binding
affinity for TCDD, which is 10-fold lower in humans than in mice and most other animal
models (Flaveny, 2009). In humans, TCDD’s short-term effects may include: nausea,
blurred vision, skin lesions, and the development of severe chloracne, whereas the long
term effects may include: vascular ocular changes, signs of neural system damage, and
cancer (IRAC, 1997; Marinkovic et al., 2010).
B cells are an essential component of the humoral immune response and a
sensitive direct target of TCDD. It has been proven in animal models that TCDD can
suppress B-cell maturation, activation, proliferation, and differentiation, which in turn
leads to suppression in Ig production (Sulentic & Kaminski, 2011). Previous studies on
splenocytes showed a direct effect of TCDD-induced suppression on antibody secretion
in B cells, and this inhibition can occur with or without T-helper function, i.e. B cells can
get activated in a T-cell independent manner by lipopolysaccharide and/or dinitrophenyl
14
or a T-cell dependent manner by sheep red blood cells (Dooley & Holsapple, 1988;
Holsapple, 1986). Other studies showed a TCDD-induced inhibition of IgM secretion in a
mouse B-cell line, activated with LPS, that expresses high levels of AhR (CH12.LX),
whereas there was no IgM inhibition under LPS stimulation in an AhR-deficient mouse
B-cell line (BCL-1) (Sulentic, 1998). Another study with an IgA-secreting mouse B-cell
line showed a reversal of TCDD-induced inhibition after knocking down the AhR or
inhibiting the AhR using AhR antagonists (Wourms & Sulentic, 2015). Additionally, AhR-/-
mice have a normal immune response when treated with TCDD or sheep red blood cells
(Vorderstrasse, 2001). These results imply that the AhR has an essential role in TCDD-
induced inhibition of Ig.
The Mouse Immunoglobulin Heavy Chain Regulatory Region
The immunoglobulin heavy chain locus (Igh) is a region on mouse chromosome
12 and on chromosome 14 in humans that encodes the heavy chain of immunoglobulins
(Cook et al., 1994; Folch et al., 2005). It is comprised of the variable heavy chain
promoter (VH), VDJ variable region, Eμ intronic enhancer, heavy chain constant regions
(CH) with germline promoters and the 3’ immunoglobulin heavy chain regulatory region
(3’IghRR). The VH promoter, upstream of the variable region, initiates Igh transcription.
The intronic enhancer Eμ between the variable region and Cμ, has a significant role in
VDJ recombination and increasing Igh transcription. However, previous studies showed
normal levels of functional heavy chain mRNA in a myeloma cell line lacking the Eμ
enhancer (Aguilera, 1985; Eckhardt & Birshtein, 1985; Klein,1984). Other studies
showed a significant inhibition of Igh transcription in a mutant myeloma cell line that still
15
has Eμ but has a deletion in a sequence downstream of Cα leading to the discovery of the
3’IghRR (Gregor & Morrison, 1986).
The mouse 3’IghRR is composed of four different DNase I hypersensitive sites
(hs): hs3A; hs1,2; hs3B; and hs4, contained in a 40 kb DNA segment (Madisen &
Groudine, 1994). They display strong synergistic activity when all four enhancers are
linked together versus in isolation, and the individual enhancers show different profiles in
transcriptional activity dependent on B-cell maturation stage (Chauveau, 1998; Saleque et
al., 1997). The hs4 is active throughout B-cell development, being active in pre-B-cells to
plasma cells, the hs1,2 is most active in mature B-cells and plasma cells, and the hs3
enhancers have slight activity in activated B cells (Madisen & Groudine, 1994; Matthias
& Baltimore, 1993; Saleque et al., 1997; Chauveau et al., 1998). As a whole, the 3’IghRR
shows less activity in pre-B cells compared to surface Ig+ B-cells and plasma cells (Ong,
1998). Overall, The 3’IghRR plays an important role in modulating the transcription of
the Igh gene and CSR (Cogné et al., 1994; Dunnick et al., 2009; Dunnick, 2005).
Additionally, Eμ enhanced the activity of the murine 3’IghRR in pre-B-cells and plasma
B cells (Chauveau et al., 1998)
The Human Immunoglobulin Heavy Chain Regulatory Region
The human 3’IGHRR has a correlation between the regulation of its activity and
IGH gene expression, CSR, and SMH, similar to the mouse 3’IghRR (Cogné et al., 1994;
Dunnick et al., 2009; Dunnick, 2005). However, the human IGH locus has many
structural differences compared to mouse Igh; the mouse 3’IghRR is most well
characterized (Fig 4). One of the differences in the human IGH is an increase in the
number of CH regions, which results in more subclasses in human IgG (IgG1, IgG2,
IgG3, and IgG4) and IgA (IgA1 and IgA2) (Fig 4). Only one 3’IghRR in present in mice
16
while there are two 3’IGHRRs present in humans, one downstream of each Cα (Cα1 and
Cα2) forming the α1 3’IgHRR and α2 3’IGHRR respectively (Fig 4). Additionally, there are
only three enhancers in each human 3’IGHRR (hs3; hs1,2; hs4), as compared to the four
in mouse, but they show similar synergistic activity when they are linked together, as
seen in mice (Chen & Birshtein, 1996; Mills, 1997). Moreover, the human enhancers
hs1,2 and hs4 lack Pax5 binding sites and other binding motifs that are significant to the
activity of the mouse 3’IghRR. The human hs1,2 enhancer lacks the NF-αP motif as well
as both Pax5 binding sites, and the human hs4 lacks one of two Oct motifs and the only
Pax5 binding site in the mouse hs4 enhancer (Chen & Birshtein, 1996; Michaelson, 1996;
Mills et al., 1997).
One of the most interesting things that makes the human IGH gene more complex
than the murine is a polymorphic region in the human hs1,2 of the α13’IgHRR. This
region consists of a 53 bp invariant sequence (IS) that can exist one (α1A
allele), two (α1B
allele), three (α1C
allele) or four (α1D
allele) times (Fig. 5). There are several important
transcription factor binding sites in the IS: AP-1, NF1, NF-κB, and a DRE core-motif,
where the AhR may bind. Each additional IS appears to increase the basal transcriptional
activity of the enhancer presumably due to the increase in transcription factor binding
sites (Cogné et al., 1994). This polymorphism has been correlated with several
autoimmune diseases involving Ig secretion including IgA nephropathy, Celiac disease,
systemic sclerosis, and psoriasis. Of the four alleles, α1B correlates with increased
prevalence and severity of the above diseases (Cianci et al., 2008; Frezza et al., 2004;
Denizot et al., 2001). In addition, patients with IgA nephropathy and Celiac disease
17
carrying the α1B
allele were found to have higher levels of serum IgA (Aupetit et al.,
2000).
18
Figure 4. Immunoglobulin heavy chain (IGH) gene locus. VH, variable heavy chain
promoter; Eμ, intronic or μ enhancer; orange rectangles, switch regions upstream of
heavy chain constant chain regions; 3ˊ IghRR, 3ˊ immunoglobulin heavy chain regulatory
region.
19
Figure 5. Human polymorphic hs1,2 reporter plasmid constructs. The asterisk (*)
represents the IS that may present one (α1A), two (α1B), three (α1C) or four (α1D) times.
20
The mouse AhR and B-cell Dysfunction
Previous mouse studies have identified B-cells as direct targets of TCDD-induced
inhibition, where it inhibits them from differentiating into antibody-forming cells, and the
AhR appears to play an essential role in this inhibition (Sulentic & Kaminski, 2011).
Other studies demonstrated an AhR-dependent inhibition of LPS induced IgM secretion
by TCDD in mouse B-cell line that expresses high levels of AhR (CH12.LX), whereas
there was no TCDD effect on an AhR-deficient B-cell line (BCL-1) (Sulentic et al., 1998;
Sulentic, 2000). In addition, AhR-/- mice were able to mount normal immune responses
when exposed to TCDD and challenged with allogeneic P815 tumor cell on sheep red
blood cells (Vorderstrasse et al., 2001). Additionally, the genes that encode the Igh and
Igl are AhR-dependent transcriptional targets of TCDD (Yoo et al., 2004).
Interestingly, the murine 3’IghRR has DRE-like motif in the two most
transcriptionally active enhancer elements hs1,2 and hs4 and TCDD induces AhR binding
to these sites (Sulentic, 2000). Additionally, the murine 3’IghRR is sensitive to a variety
of AhR agonists (Henseler, 2009). These results suggest that the murine 3’IghRR is a
transcriptional target of the AhR signaling pathway, and since this region is critical for
Igh transcription and CSR, it may mediate the TCDD-inhibitory effect on the heavy chain
expression (Sulentic et al., 2004a; Sulentic et al., 2004b). Further studies using an IgA
expressing mouse B-cell line (CH12.LX) that stably expresses a 3’IghRR-regulated γ2b-
transgene demonstrated that both the knock down of AhR protein and the
pharmacological inhibition of the AhR fully reverse the TCDD-induced inhibition of the
3’IghRR and Ig expression (Wourms & Sulentic, 2015).
21
All four enhancers or only one of them or specific transcription factor binding
sites within the enhancers could cause the overall TCDD-induced inhibition of mouse
3’IghRR by AhR-binding and/or interacting with other transcription factors to produce
the overall effect. Interestingly, the two most transcriptionally active enhancers, which
have the DRE-like binding sites (hs1,2 and hs4), react differently to TCDD when studied
separately in luciferase reporter constructs. In the CH12.LX B-cell line, the
transcriptional activation of the hs1,2 enhancer is inhibited by TCDD, whereas the hs4
enhancer is synergistically activated (Fernando et al., 2012; Sulentic et al., 2004b). The
murine hs4 activation by TCDD appears to be mediated by an overlapping DRE and κB
binding motif that is found within the enhancer (Sulentic et al., 2004a). It is postulated
that the mouse hs1,2 may mediate the inhibitory effect of TCDD on the 3’IghRR activity
although this has yet to be confirmed yet. In addition, there are genetic polymorphisms in
the mouse AhR loci leading to substantial differences in the sensitivity and biochemical
effects of TCDD. It has been shown that two different single nucleotide mutations could
cause a reduction in the AhR affinity to TCDD. One SNP (GCC to GUC) causes an
amino acid change from Ala375 to Val, and the other mutation (T to C) at the termination
codon results in an elongated read (Ema et al., 1994; Schmidt et al., 1993), which falls
within the ligand-binding site of the receptor (Whitelaw et al., 1993).
The human AhR and B-cell Dysfunction
The human AhR may mediate the biochemical and toxic effects of TCDD and
other dioxin and non-dioxin components by up/modulating regulation of gene expression.
The AhR is broadly expressed and has been identified in many tissues in humans: liver,
kidney, lung, intestine, eye, breast, prostate, cervix, uterus, ovary, lymph nodes, and brain
(McFadyen et al., 2003). Moreover, activation of B cells induces marked upregulation of
22
AhR expression (Sulentic & Kaminski, 2011). Previous investigations have shown that
CYP1A1 is a suitable mechanistically-based biomarker in the studies of human
populations exposed to dioxins and related compounds that bind to the AhR (Whitlock,
1999). Moreover, TCDD was shown to impair human B cell maturation, activation,
differentiation, and proliferation (Sulentic & Kaminski 2011; Lu et al., 2011).
Furthermore, a study on twelve human primary B cells donors showed nine donors with
reduced Ig expression, two with no response, and one with enhanced Ig expression when
treated with TCDD (Lu et al., 2010). In addition, atopic syndrome patients who are
predisposed to type 1 hypersensitive reaction have enhanced IgE expression in tonsillar B
lymphocytes when treated with TCDD (Kimata, 2003). Moreover, transient transfection
and luciferase assay studies of the isolated human hs1,2 enhancer show a concentration-
dependent increase in hs1,2 enhancer activity when exposed to TCDD (Fernando et al.,
2012). Additionally, another study on CL-01 human B-cell line showed that TCDD
inhibits IgG expression in a concentration-dependent manner under R848, a ligand for
TLR7/8, stimulation whereas IgM expression was refractory to TCDD-induced inhibition
(Brook Johnson, personal communication). These results suggest that the AhR might play
an essential role in Ig gene expression, but the mechanism is unknown.
In addition, the human AhR is a low-affinity receptor relative that requires
approximately 10-fold higher concentrations of TCDD in vitro than rodent cells to
respond with enzyme induction (Flaveny, 2009). This may explain why TCDD-exposure
has greater effects on animals rather than humans; in animals the symptoms include
immunotoxicity, tumor promotion, teratogenicity, reproductive toxicity, hepatotoxicity,
and chloracne (Abbott et al., 1999; Connor & Aylward, 2006). Additionally, in the
23
Seveso disaster, 3,300 animals were found dead within days, whereas there were no
human deaths due to exposure to TCDD (Bertazzi, Brambilla, & Pesatori, 1998).
However, expression of a human AhR in transgenic mice demonstrated that the human
and mouse AhR ligand binding pockets have differential binding properties. Based on
competitive ligand-binding experiments, the human AhR had a lower (TCDD, B[a]P,
PCB-126, and β-naphthoflavone), similar (5,7-dimethoxyflavone, and M50354), or
higher (quercetin and the plant tryptophan-derivative indirubin) binding affinity when
compared to the mouse AhR (Flaveny et al., 2009).
Moreover, polymorphisms have been discovered in exon 10, which encodes a
major portion of the transactivation domain of the AhR gene that is responsible for
transcriptional regulation (Harper, Wong, Lam, & Okey, 2002). Additionally, the human
and mouse AhR share only 58% amino acid identity in the C-terminal half, which is the
region that contains the transactivation domain. Moreover, the human and the mouse
AhR have a different binding-affinity for LXXLL-cofactor-binding motif, which may
suggest that they recruit the coactivators differently and thus may regulate unique subsets
of genes (Flaveny et al., 2008).
Transient transfection and luciferase assay studies demonstrated that in contrast to
the mouse hs1,2, the human hs1,2 acts differently with TCDD treatment and stimulation
(Fernando et al., 2012). LPS-activation of the mouse hs1,2 enhancer and 3’IghRR in the
CH12.LX cell line was inhibited when treated with TCDD, whereas the human hs1,2
enhancer was, interestingly, activated by TCDD. This difference is likely due to the
sequence differences between the human and mouse hs1,2 enhancer. For example, Pax5
binding sites exist in the mouse but not the human hs1,2 enhancer and Pax5 has an
24
important role in B-cell development and differentiation (Cobaleda et al. 2007). In LPS-
stimulated CH12.LX cells Pax5 levels decrease, but this down-regulation is inhibited
with TCDD co-treatment (Yoo et al., 2004; Schneider et al., 2008). In addition,
increasing the number of 53bp IS in the polymorphic region increases the transcription
factor binding sites and correlates with an increase in basal hs1,2 activity (Fernando et
al., 2012).
Significance
A previous study on a mouse B-cells line (CH12.LX) demonstrated that the
3’IghRR is a direct and sensitive transcriptional target of the AhR where TCDD inhibits
its capacity to increase Igh transcription leading to decreased Ig expression (Wourms &
Sulentic, 2015). In addition, TCDD impairs B cell maturation, activation, differentiation,
and proliferation (Sulentic & Kaminski 2011; Lu et al., 2011). Moreover, It has been
shown that TCDD induces the inhibition of IgM expression in a concentration-dependent
manner in primary B cells from the majority of donors; however, B cells from some
donors show no effect or an increase in Ig expression when treated with TCDD (Lu et al.,
2011). Other studies showed enhanced Ig production (IgE) by TCDD in tonsillary B
lymphocytes from atopic patients (Kimata, 2003). Moreover, transient transfection and
luciferase assay studies of the isolated human hs1,2 enhancer show a concentration-
dependent increase in hs1,2 enhancer activity when exposed to TCDD (Fernando et al.,
2012; Sulentic et al., 2004a). Other transient transfection and luciferase assay studies
have shown that mutating the human NF1 transcription factor binding-site partially
reversed TCDD-induced activation (Andrew Snyder, personal communication). In
addition, TCDD inhibits IgG secretion in a concentration-dependent manner, while it has
no effect on IgM secretion in a human B-cell line stimulated with R848, which mimics
25
the pathogen-ligand associated with TLR7/8 (Brook Johnson, personal communication).
Furthermore, there are cellular signaling and sequence differences between the mouse
and the human AhR and 3’IghRR genes. In human, the 3’IGHRR is duplicated and has
three enhancers, while in mouse, there is one 3’IghRR and four enhancers, and the human
hs1,2 is polymorphic and reacts differently to TCDD compared to mouse (Fernando et
al., 2012; Sulentic et al., 2004a). These results suggest that the mechanism by which
TCDD affects the human B cells is not clear yet, and a potential role of the AhR in the
regulation of the transcriptional activity of the human 3’IGHRR and mediating the
inhibitory effect of TCDD on Ig expression. The human AhR may possess a significant
number of contrasting properties compared with the mouse AhR, which may limit the
reliability of using animal model systems to predict the biological function of the human
AhR, and increases the need for human AhR studies.
In this study we hypothesize that the 3’IGHRR is dominantly regulated by the
AhR and mediates the inhibitory effect of TCDD on Ig expression and CSR. Thus, we
disrupted the AhR signaling pathway by using an AhR antagonist or by knocking down
the AhR receptor using two different shRNA constructs specific for AhR mRNA to
determine the role of the AhR in TCDD-induced inhibition of human IGH expression.
There are several potential significant implications from this study. First of all, the AhR
binds to a wide variety of chemicals including dietary, pharmaceutical, and
environmental ligands that can trigger the AhR signaling pathway (Mandal, 2005a).
Secondly, the 3'IghRR is an essential component of B-cell function maintaining high
levels of Ig expression in plasma cells and regulating CSR, which are fundamental to
maintaining an effective immune response. Additionally, the AhR could have a
26
physiological impact on Ig gene transcription and regulation of CSR; any dysregulation
of these processes has significant health ramifications. Furthermore, the 3’IGHRR and
the polymorphism in the human hs1,2 enhancer have been associated with a number of
autoimmune diseases, such as dermatitis herpatiforms, plaque psoriasis, psoriatic
arthritis, systemic sclerosis, coeliac disease, rheumatoid arthritis, lupus, sclerosis,
schizophrenia, and IgA nephropathy (Aupetit et al., 2000; Cianci et al., 2008; Tolusso et
al., 2009; Pinaud et al., 2011). Several lymphomas have been correlated with
chromosomal translocations between the 3’IGHRR and oncogenes (i.e. c-myc, bcl2, and
others), which may result in cancer, such as Burkitt's and diffuse large cell lymphoma
and multiple myeloma (Heckman et al., 2003; Yan et al., 2007). Therefore, elucidating
the role of the AhR in 3’IGHRR activity and the effect of TCDD on the 3’IGHRR may
provide insight into the etiology of autoimmune diseases as well as greater understanding
of Ig regulation in general. Finally, the modulation of the 3'IGHRR and/or the activity of
the human hs1,2 enhancer might be AhR-mediated, which could be important in
assessing risk of humans to exposure to AhR-ligands and potentially offering new
therapeutic avenues for diseases associated with the 3'IGHRR. Therefore, the current
study assesses the role of the human AhR in Ig expression and the effects of TCDD by
disrupting the human AhR signaling pathway.
27
II. MATERIALS AND METHODS
Chemicals and Reagents
TCDD was purchased from AccuStandard, Inc. (New Haven, CT) and dissolved
in 100% DMSO with 99.1% purity. DMSO was purchased from Sigma-Aldrich (St.
Louis, MO). R848, a TLR 7/8 ligand, was purchased from Enzo Life Sciences and
dissolved in 100% DMSO. Human IL-4 (hIL-4) was purchased from Cell Signaling
(Danvers, MA) and was dissolved in 1x sterile PBS containing 10% bovine calf serum.
Human Mega CD40L (soluble and recombinant) was purchased from Enzo Life Sciences
(San Diego, CA) and reconstituted in 100 μl sterile water and further dilutions were made
with medium containing 10% bovine calf serum. The AhR antagonist (CH-223191) 2-
methyl-2H-pyrazole-3-carboxylic acid-(2-methyl-4-o-tolyl-azo-phenyl)-amid was
purchased from Calbiochem (Carlsbad, CA) and dissolved in 100% DMSO.
Cell Line Model & Cell Culture Conditions
The CH12.LX mouse B-cell line, generously provided by Dr. Geoffrey Haughton
(University of North Carolina, Chapel Hill, NC), was derived from the murine CH12 B-
cell lymphoma arising in a B10.H-2aH-4bp/Wts (2a4b) mouse. The CH12.LX cell line
was characterized by Bishop and Haughton (1986) and has been used extensively in
immunological and toxicological research. The high expression and functionality of the
AhR in the CH12.LX cells makes it a good positive control for AhR function.
The CL-01 human B-cell line was isolated from a Burkitt’s lymphoma patient.
This cell line is a human B cell line that expresses IgM and IgD on the surface. In
28
addition, CL-01 cells can undergo somatic hypermutation, and CSR in vitro, which
makes them a suitable model for in vitro studies of human B-cell differentiation and CSR
(Cerutti, Zan et al. 1998).
A modified version of the CL-01 cell line was generated by stably integrating two
different shRNA constructs (shAhR11 & shAhR12) using lentivirus particles containing
one of two shRNA sequences complimentary to AhR mRNA (shAhR) and a puromycin
selectable marker gene. Both mixed and clonal populations of CL-01 cells stably
expressing either shAhR11 or shAhR12 were generated and analyzed. Several single-cell
clones were isolated from cells transfected with shAhR11 and shAhR12 and analyzed for
AhR knockdown. Four clones for each shAhR construct were selected for further
analysis.
All cell lines were grown in complete medium at 37°C in a 5% CO2 atmosphere.
The complete medium consisted of RPMI-1640 (Mediatech, Herndon, VA) enhanced
with 2 mM L-glutamine, 10% bovine calf serum (Hyclone, Logan, UT),
0.1 mM nonessential amino acids, 13.5 mM HEPES, 100 units/ml penicillin,
1.0 mM sodium pyruvate, 100 μg/ml streptomycin, 50 μM β-mercaptoethanol.
shRNA Constructs
Two pLKO.1 HIV-based lentiviral vector plasmids, containing shRNA sequences
complimentary to the AhR (shAhR) and puromycin selectable marker gene, were
purchased from Open Biosystems (Huntsville, AL). The shAhR sequences and the target
nucleotides in the AhR (Genbank Accession No. NM_001621.4) transcript are as
follows: shAhR11, 5’-AATTTGCTCATGTTTCAGCGC-3’, corresponding to the
29
nucleotide positions 2138-2155, and shAhR12, 5’-TAATAACATCTTGCGGGAAGG-
3’, corresponding to the nucleotide positions 779-797. Vectors were packaged into VSV-
G pseudo typed fourth generation lentiviral particles by Cincinnati Children's Viral
Vector Core (Cincinnati, OH) and stored at -80 ̊C until use.
Stable AhR Knockdown
CL-01 cells (1 x 106 cells/mL) were suspended in complete RPMI-1640 medium;
80 μL were seeded into 96-well culture plates with 10 μL of 100% concentrated
lentiviral particles containing either shAhR11 or shAhR12 and another 10 μL of
lentiviral particles were added after 8 hr of seeding. After 24 hr of seeding, 100 μL of
complete medium were added, and 24 hr after that, medium was added to adjust the cell
concentration to 1 x 105 cell/mL 0.62 μg/mL Puromycin (InvivoGene, San Diego, CA)
selective media was added 72 hr after seeding. Puromycin selective medium was replaced
every 72 hr for approximately 4 weeks until cell density and culture volumes were
sufficient to harvest whole cell lysate from 10 mL of cells and 3.0 x 106 cell stocks were
frozen in liquid nitrogen for future use. Four days after taking the cells out of the liquid
nitrogen they were treated with 0.62 μg/mL Puromycin for a week prior to experimental
use.
Protein Isolation and Western Blot
Cells were centrifuged at 500 x g for five minutes and washed with 1x PBS then
lysed with mild lysis buffer (1% NP40, 150 mM NaCl, 2 mM EDTA, 10 mM NaPO4)
containing protease inhibitors (Complete Mini Protease Inhibitor Cocktail; Roche,
Indianapolis, IN) and frozen at -80 ̊C for overnight before the protein quantification.
Protein quantification was performed by thawing whole cell lysates on ice prior to
30
centrifugation at 12,000 x g for two minutes. Then, supernatants were collected and
protein content quantified by a Bio-Rad Assay (Hercules, CA). 50 μg total protein from
naïve samples was denatured then run on 10% polyacrylamide gel at 100-150 volts for
~75 minutes. Proteins were transferred to a polyvinylidene fluoride (PVDF) membrane
(Millipore, Bedford, MA) at 90 mAMPs and ~30 volts for overnight with ice. Membranes
were blocked for ~3 hour in blocking buffer (3% non-fat milk in tris buffered
saline [TBS]) at room temperature and incubated overnight at 4 ̊C with mouse
monoclonal antibody against AhR, (Abcam lot# 2770), or with mouse monoclonal
antibody against β-actin (Sigma Aldrich) at a 1:10,000 dilution. Both antibodies cross-
react with human and were diluted in 3% non-fat milk, 0.05% tween-20 in 1X TBS at
room temperature. The membrane was washed four times with 0.05% tween-20: 1X TBS
before and after a one hour incubation at room temperature with a horse-radish-
peroxidase-conjugated donkey anti-mouse IgG secondary Ab (Thermo Scientific) at a
1:20,000 dilution with 0.05 tween-20: 1X TBS at room temperature. Proteins were
detected using SuperSignal West Femto Maximum Sensitivity substrate (Thermo
Scientific Pierce, Waltham, MA) in a Fuji LAS-3000 Bioimager (Tokyo, Japan) at 30
seconds intervals.
Reporter Plasmid Constructs
The CYP1A1 reporter plasmid was generously provided by Dr. Christoph Vogel
(University of California, Davis). The CYP1A1 reporter plasmid contains a CYP1A1
promoter, which has five DRE binding sites and a basic luciferase reporter backbone
(Promega) containing the luciferase gene (Fig. 7).
31
Transient Transfection
CL-01 cells (1.0 x 107) were collected by centrifugation at 500 x g for 5 minutes
at 4° C. The pellet was resuspended with 10 μg of plasmid and enough complete media to
make the final volume 200 μL. The 200 μL mixture was transferred to a 2 mm gap
electroporation cuvette and electroporated at 150 V, 1500 μF, and 75 ohms. Contents of
multiple transfection cuvettes were pooled and diluted to a seeding concentration of 1 x
105 cells/mL, then treated as follows: no treatment (naïve, NA), 0.01% DMSO vehicle, or
30 nM TCDD. Cells were aliquoted into 12-well plates, each well contained 2 mL of
pooled transfected cells (n=3) and was incubated at 37°C in 5% CO2 for 24 hours.
Luciferase Assay System
Following a 24 hr incubation, cell culture plates were centrifuged at 1800 x g for
5 minutes at 4°C. Supernatant was removed and cells were lysed with 1x lysis buffer
(Promega, Madison, WI) and immediately frozen at -80°C overnight. To quantify gene
expression the Luciferase Assay System (Promega, Madison, WI) was used to measure
luciferase enzyme activity. Samples were thawed at room temperature and centrifuged at
14,000 x g for 5 minutes at 4°C. 20 μL of sample lysate was mixed with 100 μL of
luciferase substrate reagent and a single-tube luminometer (Berthold Detection Systems,
Oak Ridge, TN) reported light measurements as relative light units (RLUs) following
each reaction.
Enzyme-Linked Immunosorbent Assay (ELISA)
The starting cell concentration for IgM and IgG secretion studies was 3.75 x
104 cells/mL and 1.25 x 105 cells/mL, respectively. CL-01 “Wild Type” (WT) & shAhR
32
cells were cultured in the absence of any treatment (naïve, “N”), under the activation of
1 μg/mL R848 (Control), R848 activation and 0.04% DMSO (vehicle control), or R848
activation and 10 nM TCDD. Cells were aliquoted into 12-well plates (n ≥ 3) and
incubated at 37°C in 5% CO2 for 72 and 96 hours for IgM and IgG respectively to get to
a final concentration of 1.5 x 105 cells/mL and 5 x 105 cells/mL for IgM and IgG
respectively. After the incubation, cells were removed by centrifugation at 500 x g for 5
minutes at 4°C. The supernatant was then removed and transferred to 1.5 mL
microcentrifuge tubes and stored at -80C.
96-well ELISA-plates were coated with goat anti human (GAH) poly Ig UNLB
(H+L) (Southern Biotech, Birmingham, AL) at a 1:1500 dilution with 0.1M sodium
carbonate bicarbonate buffer at 40C overnight. Plates were blocked with 3% bovine
serum albumin (BSA): 1X PBS (Calbiochem, Billerica, MA) at room temperature for
1:30 hr incubation. Samples and an appropriate standard were added and incubated for
1:30 hr in a dry incubator at 370C. Purified IgM human myeloma plasma (Athens
Research and Technology, Athens, GA) and purified human IgG (H+L) (Bethyl
Laboratories, Montgomery, TX) were used as standards for IgM and IgG respectively.
HRP conjugated secondary antibody at a 1:10,000 dilution for IgG (goat anti human IgG-
Fc HRP, Bethyl Laboratories, Montgomery, TX) and 1:4,000 dilution for IgM (goat anti
human IgM HRP, Southern Biotech, Birmingham, AL) with 3% BSA and 0.05% Tween
20: 1X PBS were added and incubated for 1:30 hr in a dry incubator at 370C. Following
each previous incubation step, plates were washed 2-3 times with 0.05% Tween 20: 1X
PBS and 3-4 times with ddH20 using ELX50 auto strip washer (Bio-Tek Instruments INC,
Winooski, VT). TMB substrate (Millipore, Temecula, CA) was used to develop the
33
enzyme-conjugated reaction and was stopped by 4N H2SO4 (Fisher Scientific, Pittsburg,
PA). Colorimetric detection was performed using a Spectramax Plus 284 automated
microplate reader with a 405-nm filter (Molecular Devices, Sunnyvale, CA). Sample
concentrations of IgM and IgG were calculated by the SOFTmax PRO analysis software
(Molecular Devices) using a standard curve generated from the absorption for known
IgM and IgG concentrations.
RNA Isolation
After a 96 hr incubation period, cells were centrifuged at 500 x g for 5 minutes,
then lysed in 0.25 mL of TRI Reagent (Sigma-Aldrich, St. Louis, MO) and stored at -
80 ̊C overnight. The samples were thawed at room temperature, centrifuged at 12,000 x g
for 10 minutes to remove cellular debris and the supernatant transferred to Phase Lock
Gel Tubes (5 PRIME, Gaithersburg, MD). After 0.1 volume of 1-bromo-3-chloropropane
was added, samples were incubated at room temperature for 10 min then centrifuged at
12,000 x g for 8 minutes at 4 ̊C. The aqueous phase was transferred into 1.5 mL tubes and
mixed with 0.125 μL isopropanol, per original 250 µl of Tri Reagent, then centrifuged at
12,000 x g for 8 minutes at 4 ̊C to precipitate RNA. The RNA pellet was washed with
0.25 mL 70% ethanol, air dried, and suspended in 50 μL of nuclease-free water. Samples
were stored at -80 ̊C until analysis.
cDNA Synthesis and Real-Time PCR
Samples were quantified using a NanoDrop ND-1000 spectrophotometer
(NanoDrop Products, Wilmington, DE) to measure the RNA and cDNA concentrations.
One microgram of total RNA was converted to cDNA using the TaqMan Reverse
Transcriptase Kit (ABI, Carlsbad, CA) and the standard manufacturer’s protocol. The
34
cycling conditions that were used for reverse transcription were as follows, 25 ̊C for 5
min, 42 ̊C for 30 min, and 85 ̊C for 5 min. Cμ expression in wild type and all shAhR cell
lines, with the treatment of DMSO and TCDD under R848 stimulation or CD40-L & IL-
4, was determined by Luminaris Color HiGreen qPCR Master Mix (Thermo Scientific,
Logan, UT) by Real Time PCR (RT-PCR). Cμ and β-actin (endogenous control)
transcripts were amplified from 100-200 ng cDNA. cDNA was combined with 6 pmol of
both FP and RP (Table 1), 2 X SYBR Green, and diluted to 25 μL with nuclease-free
water. Separate RT-PCR reactions were performed for Cμ, Cγ1, and β-actin using a
BioRad CFX Manager (Hercules, CA). Relative quantification (RQ) values (i.e. fold-
change) were determined by the BioRad CFX Manager SDS 2.0. IgM expression is
presented as a fold change (RQ) relative to naïve, which was set to one.
PCR products with <400bp were run on 1% or 1.5% agarose gels from GeneMate
LE Agarose (Kaysville, UT) using FB200 gel box from Fisher Scientific (Waltham, MA).
O’ Gene Ruler 100bp plus DNA ladder was used from Thermo Scientific (Logan, UT),
and gels were stained with 1% Ethidium Bromide solution from Fisher BioReagents
(Pittsburg, PA). Real Time PCR data were analyzed using the 2(-ΔΔCT) method.
Statistical Analysis
The mean ± S.E. was determined for each treatment group of a given experiment.
Number of experiments is clarified in figure legends. Significance of treatments from
vehicle controls was determined by a 1-way ANOVA and Dunnett post hoc test.
35
Gene of
Interest Primers
Product
Size
Cγ1 GLT
FP- 5’ GGGCTTCCAAGCCAACAGGGCAGGACA 3’
RP- 5’ GTTTTGTCACAAGATTTGGGCTC 3’
603 bp
Cγ2 GLT
FP- 5’ GGGCTTCCAAGCCAACAGGGCAGGACA 3’
RP- 5’ GTGGGCACTCGACACAACATTTGCG 3’
597 bp
Cε GLT
FP- 5’ GACGGGCCACACCATCC 3’
RP- 5’ CGGAGGTGGCATTGGAGG 3’
125 bp
μ IGH FT
FP- 5’ GACACGGCTGTGTATTACTGTGCG 3’
RP- 5’ CCGAATTCAGACGAGGGGGAAAAGGGTT 3’
152 bp
γ1 IGH FT
FP- 5’ GACACGGCTGTGTATTACTGTGCG 3’
RP- 5’ GTTTTGTCACAAGATTTGGGCTC 3’
416 bp
AhR primers
for sequencing
FP- 5’ GCACCGATGGGAAATGATAC 3’
RP- 5’ TTGACTGATCCCATGTAAGTCTG 3’
--
Loading control
β-actin
FP- 5’ ATCACCATTGGCAATGAGCGGTTC 3’
RP- 5’ GCGGATGTCCACGTCACACTTCA 3’
129 bp
Table 1: Forward and reverse primers and product sizes for Cγ1, Cγ2, and Cε germline
transcripts (GLT), μ IGH and γ1 IGH functional transcripts (FT), AhR sequencing
primers, and β–actin loading control respectively.
36
Gene of
Internist Denaturation Annealing
Final
Extension No of Cycles
Cγ1 GLT
950C for 30
seconds
610C for 1
minute
680C for 5
minutes 30
Cγ2 GLT
950C for 30
seconds
610C for 1
minute
680C for 5
minutes 30
Cε GLT 950C for 30
seconds
520C for 1
minute
680C for 5
minutes 30
μ IGH FT
950C for 30
seconds
630C for 1
minute
680C for 5
minutes 28
γ1 IGH FT
950C for 30
seconds
610C for 1
minute
680C for 5
minutes 40
AhR primers
for sequencing
950C for 30
seconds
630C for 1
minute
680C for 5
minutes 40
Loading
control β-actin
950C for 30
seconds
630C for 1
minute
680C for 5
minutes 30
Table 2: PCR cycling conditions for Cγ1, Cγ2, and Cε germline transcripts (GLT), μ IGH
and γ1 IGH functional transcripts (FT), AhR sequencing primers, and β–actin loading
control respectively
37
III. RESULTS
Characterization of a stable knockdown of the AhR levels and function
in the human CL-01 B-cell line
Previous studies using the CH12.LX mouse B-cell line have shown that knocking
down the AhR protein or inhibiting the AhR with a chemical antagonist reverses TCDD-
induced inhibition of Ig secretion (Wourms & Sulentic, 2015). Other studies
demonstrated that AhR knockout mice are resistant to TCDD toxicity-inducing inhibition
of the antibody-forming cell responses (Fernandez-Salguero, 1996; Vorderstrasse, 2004).
This indicates that the AhR mediates the toxicity of TCDD in animal models. In addition,
previous studies in our lab using the human CL-01 B-cell line, which expresses surface
IgM and IgD and can undergo somatic hypermutation and CSR, showed no consistent
effect of TCDD on IgM secretion, and a concentration-dependent inhibition of IgG
secretion by TCDD (Brooke Johnson, personal communication). This observation
suggests that TCDD inhibits CSR from IgM to IgG. To determine weather the AhR
mediates TCDD-induced inhibition of human IgG secretion and CSR, we knocked down
the AhR in the human CL-01 B-cell line by stably integrating one of two shRNA
lentiviral vectors that target AhR mRNA at different positions. AhR knockdown was
confirmed by Western blot analysis in a mixed population of cells (shAhR11 and
shAhR12) (Fig. 6A) and to select for greater, homogeneous AhR knockdown several
clones were isolated and analyzed. Four clones for each shAhR (shAhR11 clone and
38
shAhR12 clone) that demonstrated the greatest AhR knockdown were selected for further
analysis (see Fig. 6B for representative knockdown).
39
Fig. 6: Verifying the knock down of the AhR protein in the CL-01 human B-cell line.
Wild Type (WT) refers to CL-01 human B-cells and shAhR11/12 refers to CL-01 cells
that stably express shRNA specific to AhR transcripts. Whole cell lysates were collected
from WT and shAhR cells then 50μg of protein was subjected to Western blot analysis for
AhR and β-actin. A) “shAhR11” and “shAhR12” denote a mixed population of human
CL-01 cells that stably express shRNA11 or shRNA12, respectively. B) “shAhR11 clone”
and “shAhR12 clone” denote a population of human CL-01 cells originating from a
single clone that stably expresses shAhR11 or shAhR12, respectively. The above data is
representative of n = 8 for WT, n = 14 for shAhR11, n = 14 for shAhR12, n = 2 for four
different clones for shAhR11, and n = 2 for four different clones for shAhR12.
40
We tested the AhR function by transient transfection and luciferase assay using a
plasmid that contains the CYP1A1 promoter, which has five DRE binding sites and is
hooked up with a luciferase gene (Fig. 7). Interestingly, TCDD did not induce CYP1A1
promoter activity in the CL-01 cell, whereas the activity was significantly increased in
the positive control CH12.LX mouse cells (Fig. 8). This suggests that the CL-01 AhR
binding affinity and/or function are not normal. Thus, we sequenced the CL-01 AhR
gene, and we found three heterozygous single nucleotide polymorphisms (SNPs) (P517S,
R554K, and V570I) in exon 10, which encodes the major region within the AhR that is
responsible of transactivation of other genes (Dolwick et al., 1993) (Fig. 9). These
heterozygous SNPs are primarily found in the African-American population (Rowlands et
al., 2010), and our CL-01 cells were isolated from a Burkitt’s lymphoma in an African-
American patient. These heterozygous SNPs were shown to cause loss of AhR’s ability to
induce its marker gene (i.e. CYP1A1) (Wong et al., 2001), which can explain way TCDD
is not able to induce CYP1A1 promoter activity in the CL-01 cells. It was also shown that
these heterozygous SNPs have no effect on ligand-binding or binding to DREs (Wong et
al., 2001), and even when the transactivation domain is completely deleted, the ligand-
binding and DNA-binding domains can still function (Dolwick et al., 1993; Ko et al.,
1997). This indicates that the CL-01 AhR can be activated by TCDD, form the
AhR/ARNT complex, and bind to DREs, but it is not able to induce CYP1A1 gene
expression (Fig. 10).
41
Fig. 7: Schematic of Cytochrome P4501A1 reporter plasmid. There are five DRE
binding-sites “blue circles” within the CYP1A1 promoter. Binding of the AhR/ARNT
heterodimers to these sites induces transcription of the luciferase gene “black rectangle”.
Fig. 8: The AhR polymorphisms in the CL-01 cell line results in a loss of TCDD-
inducible CYP1A1 promoter activation. CH12.LX and CL-01 WT cells were
transiently transfected with the CYP1A1 luciferase reporter plasmid. Transfected cells
were either cultured in the absence of any additional treatment (naïve) or treated for 24 h
with 0.01% DMSO vehicle control, or with 30 nM TCDD. “N” donates the naïve control,
and “V” donates the vehicle control. Comparisons between treatment groups were
analyzed using a 1-way ANOVA followed by a Dunnett’s Multiple Comparison post test.
Asterisk “***” denote significance compared to the vehicle control DMSO at p<0.001.
42
Fig. 9: The chromatograph for CL-01 AhR sequencing results showing where the
heterozygous SNPs fall within the transactivation domain. A four-color
chromatograph showing the results of the CL-01 AhR sequencing run. Each peak
represents a single nucleotide and the color determines which nucleotide it is (Adenine:
green, Guanine: black, Cytosine: blue, Thymine: red). The heterozygous SNPs are
represented with double peaks with two different colors in exon 10 nucleotide positions
2321, 2274, and 2367 for R554K, V570I, and P517S, respectively.
43
Fig. 10: The AhR polymorphisms in the CL-01 cell line result in a loss of CYP1A1
induction but has no effect on ligand and DRE binding. Upon ligand-binding, the
AhR translocates into the nucleus where it dimerizes with ARNT. The AhR/ARNT
complex can bind to DREs within the promoter or the enhancer region of genes sensitive
to AhR ligands, but its ability to directly transactivate is abolished based on a lack of
CYP1A1 induction (Wong et al., 2001).
44
Knocking down the AhR inhibits the overall basal activity of IgG
expression and has no effect on IgM expression
To determine if the effect of TCDD on IgG secretion is AhR-dependent, the IgG
levels in the supernatant of AhR knockdown cells were measured by ELISA in mixed
populations (shAhR11 & shAhR12) and a population derived from a single clone
(shAhR11 and shAhR12 clones). Cells were stimulated with R848, a synthetic molecule
that activates B cells via the TLR7. Co-treatment with TCDD inhibited IgG expression at
96 hr, which was reversed by pre-treatment with the AhR antagonist (AhRA) as seen
previously (Brooke Johnson, personal communication). Notably, the AhRA increased
IgG expression above the stimulation alone control (Fig. 11, and Brooke Johnson). In
contrast to the effect of the AhRA, shAhR11 and shAhR12 cells showed a markedly
lower overall basal IgG activity compared to the WT (Fig. 11A), and IgG secretion could
not be detected in shAhR11 and shAhR12 clones (Fig. 11B). In addition, we measured γ1
germline transcripts (GLT) and functional transcripts (FT) and found much lower levels
of Cγ1 GLT in shAhR11 and shAhR12 cells as compared to the WT, and no detectable γ1
IGH FT or Cγ1 GLT in shAhR11 and shAhR12 clones (Figs. 12 and 13). Surprisingly,
basal Cγ1 GLT, γ1 IGH FT, and α1 IGH FT were detected in unstimulated WT cells,
suggesting that some of the CL-01 cells underwent spontaneous CSR to γ1 and α1 (Figs.
12, 13, data not shown). Although no γ1 transcripts were detected in the shAhR clones, α1
FT was detected in shAhR11 and shAhR12 clones (data not shown). These data
demonstrate a potential physiological role of the AhR in the expression of and CSR to
IgG1.
45
Fig. 11: Reduced AhR levels inhibit basal IgG secretion and completely abrogate
stimulation-induced IgG secretion. Wild Type (WT) and shAhR CL-01 cells were
activated with 1 μg/mL R848 and treated with the vehicle control (0.05% DMSO) in A
and 0.02% in B, 10 nM TCDD, 10 μM AhRA, or with both TCDD and AhRA. Cells were
incubated for 96 hours, then supernatant collected and analyzed for IgG secretion by
ELISA. “N” denotes the naïve control; “C” R848 stimulation alone; and “N.D.” not
detected. A) Mixed population of shAhR11 or shAhR12 knockdown cells; B)
representative of shAhR11 or shAhR12 clones. Comparisons between treatment groups
were analyzed using a 1-way ANOVA followed by a Dunnett’s Multiple Comparison post
test. Asterisk “*”, “**”, or “***” denote significance compared to the vehicle control
DMSO at p<0.05, p<0.01 or p<0.001, respectively. A) represents four different
experiments with an n = 4, and B) represents three different experiments on 8 different
clone with an n = 3.
46
Fig. 12: Reduced AhR levels inhibit Cγ1 germline transcript mRNA expression in
the shAhR11 and shAhR12 and completely abrogate expression in the shAhR11 and
shAhR12 clones. Wild Type (WT) and shAhR CL-01 cells were activated with 1 μg/mL
R848 or with 6.25 ng/mL CD40L & 50 ng/mL IL-4 and treated with the vehicle control
(0.01% DMSO) or 10 nM TCDD. “N” denotes the naïve control, “S” denotes CD40L &
IL-4 stimulation alone, “V” donates vehicle control, and “T” donates TCDD. Cells were
incubated for 96 hours, then total RNA was extracted, 1 μg was reverse transcribed to
cDNA, and 200 ng of cDNA was used to amplify Cγ1 germline transcripts (GLT) and β-
actin via PCR (n=3 for each treatment group). A) CL-01 WT B) shAhR11 C) shAhR12
D) three different clones of shAhR11 or shAhR12. The γ1 germline transcript is
observed at 604 bp, and β-actin, used as a loading control, is observed at 129 bp.
47
Fig. 13: Spontaneous CSR and AhR-dependent expression of IGH γ1 functional
transcripts. Wild Type (WT) CL-01 cells and clones of shAhR11 and shAhR12 were
activated with 1 μg/mL R848 and treated with the vehicle control (0.02% DMSO) or 10
nM TCDD. “N” denotes the naïve control, while “C” denotes R848 stimulation alone.
Cells were incubated for 96 hours, then total RNA was extracted, 1 μg was reverse
transcribed to cDNA, and 200 ng of cDNA was used to amplify γ1 IGH functional
transcripts (FT) and β-actin via PCR. The γ1
IGH FT is observed at 416 bp, and β-actin,
used as a loading control, was observed at 129 bp. Three different shAhR clones were
tested (n = 2 different mRNA isolation per clone).
48
Although previous results demonstrated no consistent effect of TCDD on IgM
levels in the CL-01 cells, the above results suggest a physiological role of the AhR,
independent of TCDD, on Igh expression (Brooke Johnson, personal communication).
Therefore we evaluated IgM in the AhR knockdown cells. As previously seen, no
differences were observed in IgM secretion with and without the treatment of TCDD or
AhRA in WT CL-01 cells and all shAhR cell lines (Fig. 14). μ IGH FT mRNA
expression also showed no differences between CL-01 WT and shAhR cells with and
without TCDD (Fig. 15). These data suggest that IgM is regulated differently from IgG,
and a functional AhR might be needed to mediate the effect of TCDD on IgM expression.
49
Fig. 14: No differences in IgM protein secretion between WT CL-01 cells and shAhR
cell lines with or without TCDD treatment. Wild Type (WT) and shAhR CL-01 cells
were activated with 1 μg/mL R848 and treated with the vehicle control (0.02% DMSO),
or 10 nM TCDD. Cells were incubated for 72 hours, then supernatant was collected and
analyzed for IgM secretion by ELISA analysis. “N” denotes the naïve control, while “C”
denotes R848 stimulation alone. A) Mixed population of shAhR11 or shAhR12
knockdown cells; B) representative of shAhR11 or shAhR12 clones. Comparisons
between treatment groups were analyzed using a 1-way ANOVA followed by a Dunnett’s
Multiple Comparison post test. A) represents two different experiments with an n = 4, and
B) represents four different clones of shAhR11 and shAhR12.
50
Fig. 15: No differences in expression of μ IGH functional transcripts between WT
CL-01 cells and shAhR cell lines with or without TCDD treatment. Wild Type (WT)
and shAhR CL-01 cells were activated with 6.25 ng/mL CD40L & 50 ng/mL IL-4 and
treated with the vehicle control (0.02% DMSO), or 10 μM TCDD. “N” denotes the naïve
control, while “C” denotes R848 stimulation alone. Cells were incubated for 96 hours,
then total RNA was extracted, one μg was reverse transcribed to cDNA, and 200 ng of
cDNA was used to amplify Cμ and β-actin via SYBR Green real-time PCR. The data is
representative of at least two separate experiments (n=3 for each treatment group). A)
Mixed population of shAhR11 or shAhR12 knockdown cells B) representative of
shAhR11 or shAhR12 clones. Comparisons between treatment groups were analyzed
using a 1-way ANOVA followed by a Dunnett’s Multiple Comparison post test. Two
clones for shAhR11 and two for shAhR12 were tested with an n = 3.
51
Knocking down the AhR has no effect on expression of Cε de novo
germline transcripts
We induced de novo GLT, which is a precursor to CSR to determine the role of
the AhR in CSR in CL-01 WT and shAhR cell lines. We used CD40L & IL-4, which
mimics T-cell-dependent activation of B cells, to induce CSR to IgE and IgG2 (Fig. 16,
data not shown). We measured the Cε GLT mRNA expression and found no basal
expression in unstimulated CL-01 WT and shAhR cells indicating that Cε de novo GLT
was induced to facilitate the CSR to IgE. There was no difference in Cε and Cγ2 de novo
GLT between CL-01 WT and shAhR cells with or without TCDD treatment (Fig 16 and
data not shown), indicating that the AhR does not play a significant role in Cε and Cγ2 de
novo GLT.
52
Fig. 16: Reduced AhR levels have no change on expression of Cε de novo germline
transcripts. Wild Type (WT) and shAhR CL-01 cells were activated with 6.25 ng/mL
CD40L & 50 ng/mL IL-4 and treated with the vehicle control (0.01% DMSO) or 10 nM
TCDD. “N” denotes the naïve control, “C” denotes CD40L & IL-4 stimulation alone,
“V” donates vehicle control, and “T” donates TCDD. Cells were incubated for 96 hours,
then total RNA was extracted, 1 μg was reverse transcribed to cDNA, and 200 ng of
cDNA was used to amplify Cε germline transcripts and β-actin via PCR SYBR Green
real-time PCR (n=3 for each treatment group).
53
IV. DISCUSSION
The AhR is a transcription factor that mediates the toxicity of various
environmental chemicals and regulates xenobiotic-metabolizing enzymes (Abel &
Haarmann-Stemmann, 2010). It has been shown in vitro in animal models that the AhR
mediates TCDD-induced inhibition of Ig expression by inhibiting the capacity of the
3’IghRR to increase Ig transcription (Wourms & Sulentic, 2015). However, the role of
AhR with TCDD on Ig expression remains elusive in humans. A study using primary B
cells isolated from human peripheral blood demonstrated reduced Ig expression in nine of
twelve human donor primary B cells when treated with TCDD, while cells from two
donors showed no response and one demonstrated enhanced Ig expression (Lu et al.,
2010). Additionally, IgE expression was enhanced by TCDD in tonsillar B lymphocytes
from atopic patients who are predisposed to type I hypersensitivity reactions (Kimata,
2003). Moreover, it has been shown that TCDD has no effect on IgM secretion but
induces the inhibition of IgG expression in a concentration-dependent manner in a human
B cell line CL-01 (Brooke Johnson, personal communication). Thus, we hypothesized
that the AhR mediates the effects of TCDD in human. However, it was not clear from our
experiments if TCDD's effects are mediated by the AhR because IgM expression was
refractory to TCDD in both AhR wild type (CL-01 WT) and AhR knockdown (shAhR)
cell lines (Figs. 14 and 15); and interestingly, we found a significant decrease in overall
IgG in shAhR cell lines (Figs. 11 and 13), which prevented analysis of TCDD's effects on
IgG. Expression of γ1 germline and functional transcripts were also dramatically inhibited
in the shAhR cells, but ε, α1, and γ2 transcripts were refractory to AhR knockdown (Figs.
54
12, 13, 16, data not shown). However, decreased IgG expression with decreased AhR
expression contrasts with the increase in IgG expression following treatment with the
chemical AhR antagonist (AhRA) (Fig. 11). Differing effects between the AhRA and
AhR knockdown suggests an indirect effect through the involvement of other signaling
pathways. Alternatively, the effects of AhRA could be off-target effects. Additionally,
our sequencing results and lack of CYP1A1 induction (Figs. 8, 9, 10) demonstrate that
the AhR expressed in the CL-01 cells is likely incapable of directly transactivating genes
and suggests that our studies are evaluating the effects of protein-protein interaction
between the AhR and other transcription factors in the effect of IgG1 expression. These
results suggest the need of a functional AhR in order to mediate the effect of TCDD on
IgM expression. It also suggests a potential physiological role of the AhR in the
expression of and class switching to IgG1. Therefore, based on these studies we
hypothesize that different mechanisms are involved in regulating the expression of
different Ig isotypes
In our study we used the CL-01 cell line, which is an IgM and IgD expressing cell
line indicating a naive B-cell phenotype. However, low expression of IgG1 was detected
in unstimulated CL-01 cells, which suggests a spontaneous class switch. Since TCDD’s
effect on IgM was not reproducible and IgG was not detectable in AhR knockdown cells,
it is not clear whether the AhR or TCDD are affecting only Ig expression in post-
switched cells as opposed to some effect on CSR to IgG1 as well. Knocking down the
AhR results in a significant decrease in IgG. We can say that this decrease is at the
transcriptional level since we found no detectable γ1 IGH FT mRNA expression in the
shAhR cell lines (Fig. 12). Although TCDD significantly inhibited IgG expression in CL-
55
01 WT cells we found no change in the protein and mRNA expression for IgM when
treated with TCDD, and decreased levels of the AhR also had no change on IgM
expression as well (Figs. 14 and 15). In addition, decreased levels of the AhR has no
effect on γ2, α1, and ε transcripts (Fig. 16, data not shown); however, γ1 germline and
functional transcripts were significantly inhibited in the shAhR cell lines (Figs. 12 and
13) suggesting an isotype-specific inhibition in CSR to IgG1 when knocking down the
AhR. Taken together these data support our hypothesis that different mechanisms are
involved in regulating the expression of different Ig isotypes.
Both the shAhR and the AhRA lower the AhR activity but through different
mechanisms, and they have an opposite effect on IgG expression. The AhRA inhibits the
AhR by blocking and keeping the AhR in the cytosol, and shAhR targets the AhR mRNA
for cleavage. Since the AhRA keeps AhR in the cytosol, the AhR is likely not directly
mediating the increase in IgG, but AhRA may increase IgG secretion through the
activation of signaling proteins associated with the cytosolic AhR, such as c-Src.
Alternatively, the increased IgG levels might due to off-target effects of the AhRA. The
inactive AhR is found as a cytosolic complex associated with different proteins, such as
p23, Hsp90, and XAP2 (Feltz et al., 2003; Meyer et al.,1999). Knocking down the AhR
may result in more AhR-associated proteins that can be free in the cytosol or bound to
other molecules. The AhR-associated proteins play roles in cell signaling and gene
expression, that can affect Ig expression and/or CSR, and these roles are not fully
understood (Cai, et al., 2011; Felts & Toft, 2003; Pearl & Prodromou, 2006).
We hypothesized a mechanism by which that the AhR-associated proteins might
lead to an isotype-specific inhibition of class switching to IgG1. Several studies human
56
cell lines have shown that the AhR-associated proteins: p23, XAP2, and Hsp90, inhibit
the activation of the glucocorticoid receptor (GR), its transcriptional activity, its
occupancy of DNA, and the recruitment of its co-activators (Dalman et al., 1991;
Hutchison et. al., 1995; Freeman & Yamamoto, 2002; Wochnik et al., 2004; Laenger et
al., 2009). In addition, the GR pathway was shown to inhibit NF-κB activity in humans
(Nelson et al., 2003; Scheinman et al., 1995). Additionally, a study on a mouse cell-line
showed that NF-κB inhibits class switching to IgG1 (Bhattacharya et al., 2002).
Therefore, knocking down the AhR could release more AhR-associated proteins that can
be free in the cytosol that may inhibit GR, leaving GR more readily available to inhibit
NFkB whereas. In addition, the AhRA is known to inhibit the TCDD binding to the AhR
and the AhR translocation into the nucleus (Choi et al., 2012), but it is not known
whether it allows the activation of c-Src, a protein associated with the AhR. Activating c-
Src could activate a signaling cascade that activates the cell and increases Ig expression
(Enan & Matsumura, 1996). Moreover, there are several pathways that cross-talk with the
AhR that could be affected differently when knocking down (i.e. decreased AhR) versus
inhibiting the AhR (retained in cytosol), such as nuclear receptors, i.e. androgen,
estrogen, and progesterone (Ohtake et al., 2008) and NF-κB pathway (Vogel et al., 2013;
Sulentic et al., 2004a; Sulentic et al., 2004b), which inhibits the CSR to IgG1 in mice
(Bhattacharya et al., 2002).
Preliminary studies using a cytokine protein multiplex assay demonstrated some
differences in cytokine expression between the WT and the shAhR cell lines (data not
shown). For example, interleukin 7 (IL-7) was found in the WT cells but not the shAhR
cell lines. The role of IL-7 is well studied in the development of B cells, where it is
57
required as an extrinsic signal for somatic recombination (Biuips et al., 1995; Corcoran
et al., 1998). However, mature B cells lack the IL-7 receptor (Oldham, 2012), and there
are no studies on mature B cells. In addition, Eotaxins, which are a CC chemokine
subfamily of eosinophil chemotactic proteins, were not found in the AhR WT B cells, but
were expressed in the shAhR B-cell lines (data not shown). They are known as
chemotactic, but they are not fully understood. In addition, recent studies on AhR-/-
knockout mice demonstrated significantly higher expression of IL-1β and IL-6 in AhR-/-
mice compared to WT in the liver and lung (Wu at el., 2011). Interestingly, our data do
not show a significant difference in IL-1β or IL-6 expression between the CL-01 WT and
shAhR cell lines. Another study showed an AhR-dependent regulation of IL-8 in
response to benzo(a)pyrene in macrophages (Podechard at el., 2008). These data
demonstrate the involvement of the AhR in cytokine expression, which may affect cell
signaling directly and/or indirectly, and potentially could affect the Ig expression.
Clearly, the AhR has distinct roles in B cells other than mediating the xenobiotic
metabolism. It is also showing a potential species differences in the way the AhR affects
the cytokine expression between human and mouse.
Although TCDD induces inhibition of IgM expression in a concentration-
dependent manner in mouse (Sulentic et.al., 1998; North et al., 2009), we could not see a
reproducible TCDD-induced effect on human IgM expression in the CL-01 B cells. In
total IgM protein expression was slightly inhibited by TCDD six times and had no effect
11 times (data not shown). Moreover, Cμ GLT mRNA expression was refractory to
TCDD. These data demonstrate that IgM expression in the CL-01 cell line is less
sensitive to TCDD. These different responses to TCDD could be a result of AhR
58
polymorphisms, where some AhR isoforms show significantly less function in inducting
its marker gene (CYP1A1) compared to other isoforms. The CL-01 AhR has three SNPs
on exon 10 that abolished its ability to induce CYP1A1 promoter activity, which may
suggest that a functional AhR is needed to mediate TCDD-induced inhibition on IgM
expression. Additionally, the hs1,2 enhancer is polymorphic, where there is a 53 bp
invariant sequence (IS) within that enhancer that can exist one, two, three, or four times
(Fig. 5). There are several transcription factor binding sites in the IS including a DRE-
like motif, and the increase in the number of IS leads to an increase in the number of
binding sites, which may sensitivity. Our results demonstrate a reproducible inhibition of
IgG, which may be a result of an inhibition of CSR to IgG or perhaps the transcriptional
enhancers controlling Cμ versus Cγ expression have differential sensitivity to TCDD.
We used two different shAhR constructs for knocking down the AhR to avoid off-
target gene effects; however, this does not exclude possible indirect effects on the cellular
signaling pathways. Additionally, knocking down the AhR using shRNA requires a
continuous expression of shRNA, which brings the possibility of variability in
knockdown over time and the potential of off-target effects. Another limitation for this
study is that it has been conducted on only one cell line, which is a cancer cell line
bearing an abnormal chromosomal translocation. It is uncertain how definitive it is since
there are no other studies evaluating a physiological role of the AhR on human Ig
expression, and studies with AhR-/- knockout mice did not show a decrease in IgG levels
(Lawrence & Vorderstrasse, 2004). However, there are significant species differences
regarding the human and mouse AhR, Igh, and the 3’IghRR in gene sequence and likely
cellular signaling (Fernando et al., 2012; Sulentic & Kaminski, 2011; Sulentic et al.,
59
2004a). Moreover, to the best of our knowledge, this is the first human AhR inactivation
study evaluating Ig expression and CSR with TCDD. For future studies, we can further
investigate the ligand-independent role of the AhR in the expression of and CSR to IgG1.
This study showed a ligand-independent role of the AhR in IgG1 expression and CSR to
IgG1, but the mechanisms behind this effect is unclear. The AhR pathway cross-talks
with many other signaling pathways and can change cytokines expression (Wu at el.,
2011; Biuips et al., 1995; Corcoran et al., 1998; Vogel et al., 2013; Sulentic et al., 2004a;
Sulentic et al., 2004b; Ohtake et al., 2008), which may affect Ig expression and/or CSR
directly and/or indirectly. For example, the NF-κB pathway cross-talks with the AhR
pathway and can inhibit CSR to IgG1 in mouse B-cell lines (Vogel et al., 2013; Sulentic
et al., 2004a; Sulentic et al., 2004b). Thus, a future study could determine if NF-κB cross-
talks with the AhR and affects CSR in human B-cell lines. By using co-
immunoprecipitation and electrophoretic shift assays (EMSA), we can determine if the
AhR and NF-κB physically interact and associate with each other when AhR and NF-κB
are activated by TCDD and R848 respectively. Additionally, by knocking out NF-κB and
inducing CSR to different isotypes, using different B-cell stimuli, we can determine if
NF-κB plays a role in CSR to IgG1, as seen in mouse, or to any other isotype. In addition,
there are ongoing efforts in our laboratory to knockout the AhR using the genome-editing
system CRISPR, which should provide a more direct and permanent AhR knockout with
hopefully limited chances of off-target effects particularly those associated with
continuous expression foreign gene. We can also determine if the increase of IgG
expression by the AhRA is due to a completely off-target effect. Since there is no residual
AhR in the AhR-/- cell line, an increase in IgG expression could indicate a complete off-
60
target effect. Our CL-01 B-cell line showed an increase in IgG expression by the AhRA
that may be a result of residual AhR (Fig 11). Moreover, to our knowledge, all of the
AhR polymorphism studies test for AhR functionality using upregulation of CYP1A1,
and the studies that showed variation in human Ig expression with TCDD did not test the
functionality of the AhR. Thus, developing human B-cell models expressing different
AhR polymorphisms would allow us to directly test if AhR polymorphisms impact Ig
expression and/or sensitivity of Ig expression to TCDD.
This study revealed for the first time a significant physiological, TCDD-
independent, role of the AhR and/or its associated proteins on the regulation of the
expression of and CSR to IgG1, but not to IgG2 or IgE. Inhibition of IgG1 was not seen
in AhR knockout mice, which indicated a species difference (Lawrence & Vorderstrasse,
2004). IgM expression was not affected by TCDD in CL-01 WT and shAhR cell lines.
These results support our hypothesis that different mechanisms are involved in regulating
the expression of different Ig isotypes. These results also support the limitation in
translating mouse AhR studies into human, which increases the need for more human
AhR studies, especially since the AhR cross-talks with other pathways and molecules. In
addition, understanding how the AhR-ligands modulate Ig expression and CSR and its
relation to the 3’IGHRR will provide insight into how chemically-induced immunotoxic
effects are mediated. The human hs1,2 enhancer in the 3’IGHRR is sensitive to chemical-
induced modulation and associated with a number of lymphomas and Ig-secreting
diseases (Fernando et al., 2012; Cianci et al., 2008; Heckman et al., 2003; Yan et al.,
2007; Aupetit et al., 2000; Tolusso et al., 2009; Pinaud et al., 2011). Understanding the
role of the AhR in mediating TCDD and Ig expression and class switching may provide
61
insight into the etiology of certain disease states and how they can be altered along with
how these diseases could be influenced by environmental exposures. Thus, further
elucidation of the AhR may also provide valuable insight into the identification and
quantification of humans health risks and opportunities for therapeutic intervention in
many immune-related disorders. Although human cell seem less sensitive to TCDD,
maybe due to the lower affinity of human AhR to TCDD, the AhR has a large number of
dietary, pharmaceutical and endogenous ligands that differ in affinity for human versus
mouse AhR and therefore may produce species-specific effects (Denison et al., 2011;
Flaveny et al., 2009). Finally, this study suggests potential off-target effects of the AhRA
on IgG expression and underscores the need for further studies to determine whether the
effects of the commonly used AhRA is truly an off-target effect or a novel alternative
signaling mechanism initiated through the inhibition of AhR nuclear translocation.
62
V. LITERATURE CITED
Abbott, B. D., Schmid, J. E., Pitt, J. A., Buckalew, A. R., Wood, C. R., Held, G. A., & Diliberto, J. J. (1999). Adverse reproductive outcomes in the transgenic Ah receptor-deficient mouse. Toxicology and Applied Pharmacology, 155(1), 62–70. http://doi.org/10.1006/taap.1998.8601
Abel, J., & Haarmann-Stemmann, T. (2010). An introduction to the molecular basics of aryl hydrocarbon receptor biology. Biological Chemistry, 391(11), 1235–48. http://doi.org/10.1515/BC.2010.128
Aguilera, R. J., Hope, T. J., & Sakano, H. (1985). Characterization of immunoglobulin enhancer deletions in murine plasmacytomas. The EMBO Journal, 4(13B), 3689–93. Retrieved from http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=554719&tool=pmcentrez&rendertype=abstract
Aupetit, C., Drouet, M., Pinaud, E., Denizot, Y., Aldigier, J. C., Bridoux, F., & Cogné, M. (2000). Alleles of the alpha1 immunoglobulin gene 3’ enhancer
control evolution of IgA nephropathy toward renal failure. Kidney International, 58(3), 966–71. http://doi.org/10.1046/j.1523-1755.2000.00253.x
Bankoti, J., Rase, B., Simones, T., & Shepherd, D. M. (2010). Functional and phenotypic effects of AhR activation in inflammatory dendritic cells. Toxicology and Applied Pharmacology, 246(1-2), 18–28. http://doi.org/10.1016/j.taap.2010.03.013
Bertazzi, P. A., Bernucci, I. Brambilla, G., Consonni D., & Pesatori, A. C. (1998). The Seveso Studies on Early and Long-Term Effects of Dioxin Exposure : A
Review. Environmental Heath Perspectives, 106(Suppl2), 625–633. Retrieved from http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1533388/
Bhattacharya, D., Lee, D. U., & Sha, W. C. (2002). Regulation of Ig class switch recombination by NF- k B : Retroviral expression of RelB in activated B cells inhibits switching to IgG1, but not to IgE, International Immunology, 14(9), 983–991. http://doi: 10.1093/intimm/dxf066
Biuips, B. L. G., Nufiez, C. A., Iii, E. B., Stankovic, A. K., Gartland, G. L., Burrows, P. D., & Cooper, M. D. (1995). Immunoglobulin Recombinase Gene Activity Is Modulated Reciprocally by Interleukin 7 and CD19 in B Cell Progenitors, The Journal of Experimental Medicine, 1;182(4), 973-82. Retrieved from http://www.ncbi.nlm.nih.gov/pubmed/7561700
Cai, W., Kramarova, T. V, Berg, P., Korbonits, M., & Pongratz, I. (2011). The immunophilin-like protein XAP2 is a negative regulator of estrogen signaling through interaction with estrogen receptor α. PloS One, 6(10), e25201. http://doi.org/10.1371/journal.pone.0025201
63
Chauveau, C., Pinaud, E., & Cogne, M. (1998). Synergies between regulatory elements of the immunoglobulin heavy chain locus and its palindromic 3’ locus
control region. European Journal of Immunology, 28(10), 3048–56. http://doi.org/10.1002/(SICI)1521-4141(199810)28:10<3048::AID-IMMU3048>3.0.CO;2-V
Chen, C., & Birshtein, B. K. (1996). A region of the 20 bp repeats lies 3’ of human Ig
Calpha1 and Calpha2 genes. International Immunology, 8(1), 115–22. Retrieved from http://www.ncbi.nlm.nih.gov/pubmed/8671595
Choi, E.-Y., Lee, H., Dingle, R. W. C., Kim, K. B., & Swanson, H. I. (2012). Development of novel CH223191-based antagonists of the aryl hydrocarbon receptor. Molecular Pharmacology, 81(1), 3–11. http://doi.org/10.1124/mol.111.073643
Cianci, R., Giambra, V., Mattioli, C., Esposito, M., Cammarota, G., Scibilia, G., …
Frezza, D. (2008). Increased frequency of Ig heavy-chain HS1,2-A enhancer *2 allele in dermatitis herpetiformis, plaque psoriasis, and psoriatic arthritis. The Journal of Investigative Dermatology, 128(8), 1920–4. http://doi.org/10.1038/jid.2008.40
Cobaleda, C., Schebesta, A., Delogu, A., & Busslinger, M. (2007). Pax5: the guardian of B cell identity and function. Nature Immunology, 8(5), 463-70. http://doi:10.1038/ni1454
Cogné, M., Lansford, R., Bottaro, A., Zhang, J., Gorman, J., Young, F., … Alt, F. W.
(1994). A class switch control region at the 3’ end of the immunoglobulin heavy
chain locus. Cell, 77(5), 737–47. Retrieved from http://www.ncbi.nlm.nih.gov/pubmed/8205622
Connor, K. T., & Aylward, L. L. (n.d.). Human response to dioxin: aryl hydrocarbon receptor (AhR) molecular structure, function, and dose-response data for enzyme induction indicate an impaired human AhR. Journal of Toxicology and Environmental Health. Part B, Critical Reviews, 9(2), 147–71. http://doi.org/10.1080/15287390500196487
Cook, G. P., Tomlinson, I. M., Walter, G., Riethman, H., Carter, N. P., Buluwela, L., … Rabbitts, T. H. (1994). A map of the human immunoglobulin VH locus
completed by analysis of the telomeric region of chromosome 14q. Nature Genetics, 7(2), 162–8. http://doi.org/10.1038/ng0694-162
Corcoran, A. E., Riddell, A., Krooshoop, D., & Venkitaraman, A. R. (1998). Impaired immunoglobulin gene rearrangement in mice lacking the IL-7 receptor, Nature, 26;391(6670), 904–907.Rerieved from http://www.ncbi.nlm.nih.gov/pubmed/9495344
Dalmans, F. C., Scherrerg, L. C., Taylor, L. P., Akilg, H., & Prattsv, W. B. (1991). Localization of the 90-kDa Heat Shock Protein-binding Site within the Hormone-binding Domain of the Glucocorticoid Receptor by Peptide
64
Competition, The Journal of Biological Chemistry, 266(6), 3482–3490. Retrieved from http://www.ncbi.nlm.nih.gov/pubmed/1995612
Denison, M. S., Soshilov, A. A., He, G., DeGroot, D. E., & Zhao, B. (2011). Exactly the same but different: promiscuity and diversity in the molecular mechanisms of action of the aryl hydrocarbon (dioxin) receptor. Toxicological Sciences : An
Official Journal of the Society of Toxicology, 124(1), 1–22. http://doi.org/10.1093/toxsci/kfr218
Denizot, Y., Pinaud, E., Aupetit, C., Le Morvan, C., Magnoux, E., Aldigier, J. C., & Cogné, M. (2001). Polymorphism of the human alpha1 immunoglobulin gene 3’
enhancer hs1,2 and its relation to gene expression. Immunology, 103(1), 35–40. Retrieved from http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=1783220&tool=pmcentrez&rendertype=abstract
Dolwick, K. M., Swanson, H. I., Bradfield, C. A. (1993). In vitro analysis of Ah receptor domains involved in ligand-activated DNA recognition. Proceedings of the National Acadimy of Science of the United States of America. 5;90(18), 8566-8570. Retrieved from http://www.ncbi.nlm.nih.gov/pubmed/8397410
Dooley, R. K., & Holsapple, M. P. (1988). Elucidation of cellular targets responsible for tetrachlorodibenzo-p-dioxin (TCDD)-induced suppression of antibody responses: I. The role of the B lymphocyte. Immunopharmacology, 16(3), 167–
80. Retrieved from http://www.ncbi.nlm.nih.gov/pubmed/3267010
Dunnick, W. A., Collins, J. T., Shi, J., Westfield, G., Fontaine, C., Hakimpour, P., & Papavasiliou, F. N. (2009). Switch recombination and somatic hypermutation are controlled by the heavy chain 3’ enhancer region. The Journal of Experimental Medicine, 206(12), 2613–23. http://doi.org/10.1084/jem.20091280
Dunnick, W. A., Shi, J., Graves, K. A., & Collins, J. T. (2005). The 3’ end of the
heavy chain constant region locus enhances germline transcription and switch recombination of the four gamma genes. The Journal of Experimental Medicine, 201(9), 1459–66. http://doi.org/10.1084/jem.20041988
Eckhardt, L. A., & Birshtein, B. K. (1985). Independent immunoglobulin class-switch events occurring in a single myeloma cell line. Molecular and Cellular Biology, 5(4), 856–68. Retrieved from http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=366791&tool=pmcentrez&rendertype=abstract
Enan, E., & Matsumura, F. (1996). Identification of c-Src as the integral component of the cytosolic Ah receptor complex, transducing the signal of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) through the protein phosphorylation pathway. Biochemical Pharmacology, 52(10), 1599–612. Retrieved from http://www.ncbi.nlm.nih.gov/pubmed/8937476
Ema, M., Ohe, N., Suzuki, M., Mimura, J., Sogawa, K., Ikawa, S., & Fujii-Kuriyama, Y. (1994). Dioxin binding activities of polymorphic forms of mouse and human
65
arylhydrocarbon receptors. The Journal of Biological Chemistry, 269(44), 27337–43. Retrieved from http://www.ncbi.nlm.nih.gov/pubmed/7961644
Eskenazi, B., Mocarelli, P., Warner, M., Needham, L., Patterson, D. G., Samuels, S., … Brambilla, P. (2003). Relationship of Serum TCDD Concentrations and Age
at Exposure of Female Residents of Seveso, Italy. Environmental Health Perspectives, 112(1), 22–27. http://doi.org/10.1289/ehp.6573
Feder, M. E., & Hofmann, G. E. (1999). Heat-shock proteins, molecular chaperones, and the stress response: evolutionary and ecological physiology. Annual Review of Physiology, 61, 243–82. http://doi.org/10.1146/annurev.physiol.61.1.243
Felts, S. J., & Toft, D. O. (2003). P23, a Simple Protein With Complex Activities. Cell Stress & Chaperones, 8(2), 108. http://doi.org/10.1379/1466-1268(2003)008<0108:PASPWC>2.0.CO;2
Fernandez-Salguero, P. M., Hilbert, D. M., Rudikoff, S., Ward, J. M., & Gonzalez, F. J. (1996). Aryl-hydrocarbon receptor-deficient mice are resistant to 2,3,7,8-tetrachlorodibenzo-p-dioxin-induced toxicity. Toxicology and Applied Pharmacology, 140(1), 173–9. http://doi.org/10.1006/taap.1996.0210
Fernando, T. M., Ochs, S. D., Liu, J., Chambers-Turner, R. C., & Sulentic, C. E. W. (2012). 2,3,7,8-tetrachlorodibenzo-p-dioxin induces transcriptional activity of the human polymorphic hs1,2 enhancer of the 3’Igh regulatory region. Journal of Immunology (Baltimore, Md. : 1950), 188(7), 3294–306. http://doi.org/10.4049/jimmunol.1101111
Flaveny, C. A., Murray, I. A., Chiaro, C. R., & Perdew, G. H. (2009). Ligand selectivity and gene regulation by the human aryl hydrocarbon receptor in transgenic mice. Molecular Pharmacology, 75(6), 1412–20. http://doi.org/10.1124/mol.109.054825
Flaveny, C., Reen, R. K., Kusnadi, A., & Perdew, G. H. (2008). The mouse and human Ah receptor differ in recognition of LXXLL motifs. Archives of Biochemistry and Biophysics, 471(2), 215–23. http://doi.org/10.1016/j.abb.2008.01.014
Folch, G., Giudicelli, V., Jean, C., Ginestoux, C., Lefranc, G., & Lefranc, M. (2005). IMGT overview : The mouse immunoglobulin heavy IGH genes,
Immunogenetics, 210(2004), 34396. Retrieved from http://www.imgt.org/IMGTposters/IMGC_IGK.pdf
Freeman, B. C., & Yamamoto, K. R. (2002). Disassembly of transcriptional regulatory complexes by molecular chaperones, Science, 21;296(5576):2232-2235. Retrieved from http://www.ncbi.nlm.nih.gov/pubmed/12077419
Frezza, D., Giambra, V., Cianci, R., Fruscalzo, A., Giufrè, M., Cammarota, G., …
Pandolfi, F. (2004). Increased frequency of the immunoglobulin enhancer HS1,2 allele 2 in coeliac disease. Scandinavian Journal of Gastroenterology, 39(11), 1083–7. http://doi.org/10.1080/00365520410007999
66
Geusau, A., Abraham, K., Geissler, K., Sator, M. O., Stingl, G., & Tschachler, E. (2001). Severe 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) intoxication: clinical and laboratory effects. Environmental Health Perspectives, 109(8), 865–869. Retrieved from http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1240417/
Gregor, P. D., & Morrison, S. L. (1986). Myeloma mutant with a novel 3’ flanking
region: loss of normal sequence and insertion of repetitive elements leads to decreased transcription but normal processing of the alpha heavy-chain gene products. Molecular and Cellular Biology, 6(6), 1903–16. Retrieved from http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=367728&tool=pmcentrez&rendertype=abstract
Harper, P. A., Wong, J. m Y., Lam, M. S. M., & Okey, A. B. (2002). Polymorphisms in the human AH receptor. Chemico-Biological Interactions, 141(1-2), 161–87. Retrieved from http://www.ncbi.nlm.nih.gov/pubmed/12213390
Heckman, C. A., Cao, T., Somsouk, L., Duan, H., Mehew, J. W., Zhang, C., & Boxer, L. M. (2003). Critical elements of the immunoglobulin heavy chain gene enhancers for deregulated expression of bcl-2. Cancer Research, 63(20), 6666–
73. Retrieved from http://www.ncbi.nlm.nih.gov/pubmed/14583460
Henseler, R. A., Romer, E. J., & Sulentic, C. E. (2009). Diverse chemicals including aryl hydrocarbon receptor ligands modulate transcriptional activity of the 3'immunoglobulin heavy chain regulatory region. Toxicology, 261(1-2), 9-18. http://doi: 10.1016/j.tox.2009.03.015.
Holsapple, M. P., Snyder, N. K., Wood, S. C., & Morris, D. L. (1991). A review of 2,3,7,8-tetrachlorodibenzo-ρ−dioxin-induced changes in immunocompetence: 1991 update. Toxicology, 69(3), 219-255. Retrieved from http://www.ncbi.nlm.nih.gov/pubmed/1949050
Holsapple, M. P., Dooley, R. K., McNerney, P. J., & McCay, J. A. (1986). Direct suppression of antibody responses by chlorinated dibenzodioxins in cultured spleen cells from (C57BL/6 x C3H)F1 and DBA/2 mice. Immunopharmacology, 12(3), 175–86. Retrieved from http://www.ncbi.nlm.nih.gov/pubmed/3818259
Hu, W., C. Sorrentino, M. S. Denison, K. Kolaja and M. R. Fielden (2007). Induction of cyp1a1 is a nonspecific biomarker of aryl hydrocarbon receptor activation: results of large scale screening of pharmaceuticals and toxicants in vivo and in vitro. Molecular Pharmacology, 71(6): 1475-1486. http://doi: 10.1124
Hutchison, K. A., Stancato, L. F., Owens-Grillo, J. K., Johnson, J. L., Krishna, P., Toft, D. O., & Pratt, W. B. (1995). The 23-kDa acidic protein in reticulocyte lysate is the weakly bound component of the hsp foldosome that is required for assembly of the glucocorticoid receptor into a functional heterocomplex with hsp90. The Journal of Biological Chemistry, 270(32), 18841–18847. Retrieved from http://www.ncbi.nlm.nih.gov/pubmed/7642537
IARC (1997). IARC Working Group on the Evaluation of Carcinogenic Risks to Humans: Polychlorinated Dibenzo-Para-Dioxins and Polychlorinated
67
Dibenzofurans. Lyon, France, 4-11 February 1997. IARC Monogr Eval Carcinog Risks Hum, 69, 1-631.
Karch, J. Nathan, D. K. Watkins, A. L. Young, M. E. Ginevan. (2004). Environmental Fate of TCDD and Agent Orange and Bioavailability to Troops in Vietnam. Organohalogen Compounds,66, 3689-3694. Retrieved from http://www.dnrec.delaware.gov/dwhs/SiteCollectionDocuments/AWM%20Gallery/Hercules/Environmental%20Fate%20and%20Bioavailablity%20of%20TCDD%20and%20Agent%20Orange001.pdf
Kazlauskas, a., Poellinger, L., & Pongratz, I. (1999). Evidence That the Co-chaperone p23 Regulates Ligand Responsiveness of the Dioxin (Aryl Hydrocarbon) Receptor. Journal of Biological Chemistry, 274(19), 13519–13524. http://doi.org/10.1074/jbc.274.19.13519
Kerkvliet, N. I. (1995). Immunological effects of chlorinated dibenzo-ρ-dioxins. Environmental Health Perspectives, 103 Suppl 9, 47-53.
Kerkvliet, N. I. (2002). Recent advances in understanding the mechanisms of TCDD immunotoxicity. International Immunopharmacology, 2(2-3), 277-291. http://doi:10.1016/S1567-5769(01)00179-5
Kerkvliet, N. I. (2009). AHR-mediated immunomodulation: The role of altered gene transcription. Biochemical Pharmacology, 77(4), 746-760. htpp:// doi: 10.1016/j.bcp.2008.11.021
Kimata, H. (2003). 2,3,7,8-tetrachlorodibenzo-p-dioxin selectively enhances spontaneous IgE production in B cells from atopic patients. International Journal of Hygiene and Environmental Health, 206(6), 601-604. http://doi: 10.1078/1438-4639-00248
Klein, S., Sablitzky, F., & Radbruch, A. (1984). Deletion of the IgH enhancer does not reduce immunoglobulin heavy chain production of a hybridoma IgD class switch variant. The EMBO Journal, 3(11), 2473–6. Retrieved from http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=557714&tool=pmcentrez&rendertype=abstract
Ko, H. P., Okino, S. T., Ma, Q., Whitlock, J. P. (1997). Transactivation domains facilitate promoter occupancy for the dioxin-inducible CYP1A1 gene in vivo. Molecular and Cell Biology. 17(7), 3497-507. Retrieved from http://www.ncbi.nlm.nih.gov/pubmed/9199285
Laenger, A., Lang-Rollin, I., Kozany, C., Zschocke, J., Zimmermann, N., Rüegg, J., … Rein, T. (2009). XAP2 inhibits glucocorticoid receptor activity in mammalian
cells. FEBS Letters, 583(9), 1493–8. http://doi.org/10.1016/j.febslet.2009.03.072
Lawrence, B. P., & Vorderstrasse, B. a. (2004). Activation of the aryl hydrocarbon receptor diminishes the memory response to homotypic influenza virus infection but does not impair host resistance. Toxicological Sciences : An Official Journal
of the Society of Toxicology, 79(2), 304–14. http://doi.org/10.1093/toxsci/kfh094
68
Lees, M. J., Peet, D. J., & Whitelaw, M. L. (2003). Defining the role for XAP2 in stabilization of the dioxin receptor. The Journal of Biological Chemistry, 278(38), 35878–88. http://doi.org/10.1074/jbc.M302430200
Lu, H., Crawford, R. B., Suarez-Martinez, J. E., Kaplan, B. L., & Kaminski, N. E. (2010). Induction of the aryl hydrocarbon receptor-responsive genes and modulation of the immunoglobulin M response by 2,3,7,8- tetrachlorodibenzo-p-dioxin in primary human B cells. Toxicological Science, 118(1), 86-97. http://doi: 10.1093/toxsci/kfq234
Lu, H., Crawford, R. B., Kaplan, B. L. F., & Kaminski, N. E. (2011). 2,3,7,8-Tetrachlorodibenzo-p-dioxin-mediated disruption of the CD40 ligand-induced activation of primary human B cells. Toxicology and Applied Pharmacology, 255(3), 251–60. http://doi.org/10.1016/j.taap.2011.06.026
Madisen, L., & Groudine, M. (1994). Identification of a locus control region in the immunoglobulin heavy-chain locus that deregulates c-myc expression in plasmacytoma and Burkitt’s lymphoma cells. Genes & Development, 8(18), 2212–26. Retrieved from http://www.ncbi.nlm.nih.gov/pubmed/7958890
Malisch, R., & Kotz, A. (2014). Dioxins and PCBs in feed and food - review from European perspective. The Science of the Total Environment, 491-492, 2–10. http://doi.org/10.1016/j.scitotenv.2014.03.022
Mandal, P. K. (2005a). Dioxin: a review of its environmental effects and its aryl hydrocarbon receptor biology. Journal of Comparative Physiology. B, Biochemical, Systemic, and Environmental Physiology, 175(4), 221–30. http://doi.org/10.1007/s00360-005-0483-3
Mandal, P. K. (2005b). Dioxin: a review of its environmental effects and its aryl hydrocarbon receptor biology. Journal of Comparative Physiology. B, Biochemical, Systemic, and Environmental Physiology, 175(4), 221–30. http://doi.org/10.1007/s00360-005-0483-3
Matthias, P., & Baltimore, D. (1993). The immunoglobulin heavy chain locus contains another B-cell-specific 3’ enhancer close to the alpha constant region.
Molecular and Cellular Biology, 13(3), 1547–53. Retrieved from http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=359466&tool=pmcentrez&rendertype=abstract
McFadyen, M. C. E., Rooney, P. H., Melvin, W. T., & Murray, G. I. (2003). Quantitative analysis of the Ah receptor/cytochrome P450 CYP1B1/CYP1A1 signalling pathway. Biochemical Pharmacology, 65(10), 1663–74. Retrieved from http://www.ncbi.nlm.nih.gov/pubmed/12754102
Meyer, B. K., & Perdew, G. H. (1999). Characterization of the AhR - hsp90 - XAP2 Core Complex and the Role of the Immunophilin-Related Protein XAP2 in AhR Stabilization, Biochemistry, 13;38(28),8907–8917.http:// doi: 10.1021/bi982223w
69
Michaelson, J. S., Singh, M., & Birshtein, B. K. (1996). B cell lineage-specific activator protein (BSAP). A player at multiple stages of B cell development. Journal of Immunology, 156(7), 2349–2351. Retrieved from http://www.jimmunol.org/content/156/7/2349.abstract
Mills, F. C., Harindranath, N., Mitchell, M., & Max, E. E. (1997). Enhancer complexes located downstream of both human immunoglobulin Calpha genes. The Journal of Experimental Medicine, 186(6), 845–58. Retrieved from http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=2199054&tool=pmcentrez&rendertype=abstract
Monteleone, I., Rizzo, A., Sarra, M., Sica, G., Sileri, P., Biancone, L., … Monteleone,
G. (2011). Aryl hydrocarbon receptor-induced signals up-regulate IL-22 production and inhibit inflammation in the gastrointestinal tract. Gastroenterology, 141(1), 237–48, 248.e1. http://doi.org/10.1053/j.gastro.2011.04.007
Morris, D. L., & Holsapple, M. P. (n.d.). Effects of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) on humoral immunity: II. B cell activation. Immunopharmacology, 21(3), 171–81. Retrieved from http://www.ncbi.nlm.nih.gov/pubmed/1917439
Nelson, G., Wilde, G. J. C., Spiller, D. G., Kennedy, S. M., Ray, D. W., Sullivan, E., … White, M. R. H. (2003). NF-kappaB signalling is inhibited by glucocorticoid receptor and STAT6 via distinct mechanisms. Journal of Cell Science, 116(Pt 12), 2495–503. http://doi.org/10.1242/jcs.00461
Nguyen, P. M., Wang, D., Wang, Y., Li, Y., Uchizono, J. A., & Chan, W. K. (2012). p23 co-chaperone protects the aryl hydrocarbon receptor from degradation in mouse and human cell lines. Biochemical Pharmacology, 84(6), 838–50. http://doi.org/10.1016/j.bcp.2012.06.018
North, C. M., Crawford, R. B., Lu, H., & Kaminski, N. E. (2009). Simultaneous In Vivo Time Course and Dose Response Evaluation for TCDD-Induced Impairment of the LPS-stimulated Primary IgM Response. Toxicological Sciences, 112(1), 123–132. http://doi:10.1093/toxsci/kfp187
Ohtake, F., Baba, A., Fujii-Kuriyama, Y., & Kato, S. (2008). Intrinsic AhR function underlies cross-talk of dioxins with sex hormone signalings. Biochemical and Biophysical Research Communications, 370(4), 541–6. http://doi.org/10.1016/j.bbrc.2008.03.054
Oldham Robert K. “ Principles of Cancer Biotherapy”. (2009) (p. 742). Springer Science & Business Media. Retrieved from https://books.google.com/books?id=emGC_fRJH_IC&pgis=1
Ong, J., Stevens, S., Roeder, R. G., & Eckhardt, L. A. (1998). 3’ IgH enhancer
elements shift synergistic interactions during B cell development. Journal of Immunology (Baltimore, Md. : 1950), 160(10), 4896–4903. Retrieved from http://www.ncbi.nlm.nih.gov/pubmed/9590237
70
Parham, P. (2005). The immune system, third ed. New York, NY: Garland Science.
Pearl, L. H., & Prodromou, C. (2006). Structure and mechanism of the Hsp90 molecular chaperone machinery. Annual Review of Biochemistry, 75, 271–94. http://doi.org/10.1146/annurev.biochem.75.103004.142738
Pinaud, E., Marquet, M., Fiancette, R., Péron, S., Vincent-Fabert, C., Denizot, Y., & Cogné, M. (2011). The IgH locus 3’ regulatory region: pulling the strings from
behind. Advances in Immunology, 110, 27–70. http://doi.org/10.1016/B978-0-12-387663-8.00002-8
Rowlands, C. J., Staskal, D. F., Gollapudi, B., Budinsky, R. (2010). The human AHR: identification of single nucleotide polymorphisms from six ethnic populations. Pharmacogenetics and Genomics. 20(5), 283-290. Retrieved from http://www.ncbi.nlm.nih.gov/pubmed/20401977
Podechard, N., Lecureur, V., Le Ferrec, E., Guenon, I., Sparfel, L., Gilot, D., ... Fardel, O. (2008). Interleukin-8 induction by the environmental contaminant benzo(a)pyrene is aryl hydrocarbon receptor-dependent and leads to lung inflammation. Toxicology Letters, 177(2), 130–7. http://doi.org/10.1016/j.toxlet.2008.01.006
Safe, S. H. (1998). Development validation and problems with the toxic equivalency factor approach for risk assessment of dioxins and related compounds. Journal of Animal Science, 76(1): 134-141. http:// doi:/1998.761134x
Saleque, S., Singh, M., Little, R. D., Giannini, S. L., Michaelson, J. S., & Birshtein, B. K. (1997). Dyad symmetry within the mouse 3’ IgH regulatory region
includes two virtually identical enhancers (C alpha3'E and hs3). Journal of Immunology, 158(10), 4780–7. Retrieved from http://www.ncbi.nlm.nih.gov/pubmed/9144492
Scheinman, R. I., Gualberto, A., Jewell, C. M., Cidlowski, J. A., & Baldwin, A. S. (1995). Characterization of mechanisms involved in transrepression of NF-kappa B by activated glucocorticoid receptors. Molecular and Cellular Biology, 15(2), 943–53. Retrieved from http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=231982&tool=pmcentrez&rendertype=abstract
Schneider, D., M. A. Manzan, et al. (2008). 2,3,7,8-Tetrachlorodibenzo-p-dioxin- mediated impairment of B cell differentiation involves dysregulation of paired box 5 (Pax5) isoform, Pax5a. The Journal of Pharmacology and Experimental Therapeutics, 326(2): 463-74. http:// doi: 10.1124/jpet.108.139857
Schmidt, J. V, Carver, L. A., & Bradfield, C. A. (1993). Molecular characterization of the murine Ahr gene. Organization, promoter analysis, and chromosomal assignment. The Journal of Biological Chemistry, 268(29), 22203–9. Retrieved from http://www.ncbi.nlm.nih.gov/pubmed/8408082
71
Stejskalova, L., & Pavek, P. (2011). The Function of Cytochrome P450 1A1 Enzyme (CYP1A1) and Aryl Hydrocarbon Receptor (AhR) in the Placenta. Current Pharmaceutical Biotechnology, 12(5), 715–730. http://doi.org/10.2174/138920111795470994
Struciński, P., Piskorska-Pliszczyńska, J., Góralczyk, K., Warenik-Bany, M., Maszewski, S., Czaja, K., & Ludwicki, J. K. (2011). Dioxins and food safety. Roczniki Państwowego Zakładu Higieny, 62(1), 3–17. Retrieved from http://www.ncbi.nlm.nih.gov/pubmed/21735973
Sulentic, C. E., Holsapple, M. P., & Kaminski, N. E. (1998). Aryl hydrocarbon receptor-dependent suppression by 2,3,7, 8-tetrachlorodibenzo-p-dioxin of IgM secretion in activated B cells. Molecular Pharmacology, 53(4), 623–9. Retrieved from http://www.ncbi.nlm.nih.gov/pubmed/9547351
Sulentic, C. E., Holsapple, M. P., & Kaminski, N. E. (2000). Putative link between transcriptional regulation of IgM expression by 2,3,7,8-tetrachlorodibenzo-p-dioxin and the aryl hydrocarbon receptor/dioxin-responsive enhancer signaling pathway. The Journal of Pharmacology and Experimental Therapeutics, 295(2), 705–16. Retrieved from http://www.ncbi.nlm.nih.gov/pubmed/11046109
Sulentic, C. E. W., & Kaminski, N. E. (2011). The long winding road toward understanding the molecular mechanisms for B-cell suppression by 2,3,7,8-tetrachlorodibenzo-p-dioxin. Toxicological Sciences : An Official Journal of the
Society of Toxicology, 120 Suppl , S171–91. http://doi.org/10.1093/toxsci/kfq324
Sulentic, C. E. W., Kang, J. S., Na, Y. J., & Kaminski, N. E. (2004b). Interactions at a dioxin responsive element (DRE) and an overlapping kappaB site within the hs4 domain of the 3’alpha immunoglobulin heavy chain enhancer. Toxicology, 200(2-3), 235–46. http://doi.org/10.1016/j.tox.2004.03.015
Sulentic, C. E. W., Zhang, W., Na, Y. J., & Kaminski, N. E. (2004a). 2,3,7,8-tetrachlorodibenzo-p-dioxin, an exogenous modulator of the 3’alpha
immunoglobulin heavy chain enhancer in the CH12.LX mouse cell line. The Journal of Pharmacology and Experimental Therapeutics, 309(1), 71–8. http://doi.org/10.1124/jpet.103.059493
Tian, Y. (2009). Ah receptor and NF-kappaB interplay on the stage of epigenome. Biochemical Pharmacology, 77(4), 670–80. http://doi.org/10.1016/j.bcp.2008.10.023
Tiernan, T., Taylor, M. L., Garrett, J. H., Vanness, G. F., Solch, J. G., Wagel, D. J., … Schecter, A. (1985). Sources And Fate of Polychiorinated Dibenzodioxins , Dibenzofurans and Related Compounds in Human Environments, Environmental Health Perspectives, 59, 145–158. Retrieved from http://www.ncbi.nlm.nih.gov/pubmed/9464894
Tolusso, B., Frezza, D., Mattioli, C., Fedele, A.L., Bosello, S., Faustini, F., . . . Ferraccioli, G.F. (2009). Allele *2 of the HS1,2A enhancer of the Ig regulatory
72
region associates with rheumatoid arthritis. Annals of the Rheumatic Diseases, 68(3): 416-419. http:// doi: 10.1136/ard.2008.095414
Vogel, C. F. a, Wu, D., Goth, S. R., Baek, J., Lollies, A., Domhardt, R., … Pessah, I.
N. (2013). Aryl hydrocarbon receptor signaling regulates NF-κB RelB activation
during dendritic-cell differentiation. Immunology and Cell Biology, 91(9), 568–
75. http://doi.org/10.1038/icb.2013.43
Vorderstrasse, B. A., Steppan, L. B., Silverstone, A. E., & Kerkvliet, N. I. (2001). Aryl hydrocarbon receptor-deficient mice generate normal immune responses to model antigens and are resistant to TCDD-induced immune suppression. Toxicology and Applied Pharmacology, 171(3), 157–64. http://doi.org/10.1006/taap.2000.9122
Vos, J.G., De, H. C., Van. L. H. (1997). Immunotoxic effects of TCDD and toxic equivalency factors. Teratogenesis, Carcinogenesis, and Mutagenwsis, 17(4-5): 275-284.http:// DOI: 10.1002/(SICI)1520-6866(1997)17
Wei, P., Hu, G.-H., Kang, H.-Y., Yao, H.-B., Kou, W., Liu, H., … Hong, S.-L. (2014). An aryl hydrocarbon receptor ligand acts on dendritic cells and T cells to suppress the Th17 response in allergic rhinitis patients. Laboratory Investigation; a Journal of Technical Methods and Pathology, 94(5), 528–35. http://doi.org/10.1038/labinvest.2014.8
Whitelaw, M. L., Göttlicher, M., Gustafsson, J. A., & Poellinger, L. (1993). Definition of a novel ligand binding domain of a nuclear bHLH receptor: co-localization of ligand and hsp90 binding activities within the regulable inactivation domain of the dioxin receptor. The EMBO Journal, 12(11), 4169–
79. Retrieved from http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=413711&tool=pmcentrez&rendertype=abstract
Whitlock, J. P., Jr. (1999). Induction of cytochrome P4501A1. Annual Review of Pharmacology Toxicology, 39, 103-125. http:doi: 10.1146/annurev.pharmtox.39.1.103
Wong, J. M., Okey, A. B., Harper, P. A. (2001) Human aryl hydrocarbon receptor polymorphisms that result in loss of CYP1A1 induction. Biochemistry and Biophysical Research Communication. 9;288(4), 990-996. Retrieved from http://www.ncbi.nlm.nih.gov/pubmed/11689007
Wochnik, G. M., Young, J. C., Schmidt, U., Holsboer, F., Hartl, F. U., & Rein, T. (2004). Inhibition of GR-mediated transcription by p23 requires interaction with Hsp90. FEBS Letters, 560(1-3), 35–8. http://doi.org/10.1016/S0014-5793(04)00066-3
Woof, J. M., & Burton, D. R. (2004). Human antibody-Fc receptor interactions illuminated by crystal structures. Nature Reviews. Immunology, 4(2), 89–99. http://doi.org/10.1038/nri1266
73
Wourms, M. J., & Sulentic, C. E. W. (2015). The aryl hydrocarbon receptor regulates an essential transcriptional element in the immunoglobulin heavy chain gene. Cellular Immunology, 295(1), 60–6. http://doi.org/10.1016/j.cellimm.2015.02.012
Wu, D., Li, W., Lok, P., Matsumura, F., & Vogel, C. F. A. (2011). AhR deficiency impairs expression of LPS-induced inflammatory genes in mice. Biochemical and Biophysical Research Communications, 410(2), 358–63. http://doi.org/10.1016/j.bbrc.2011.06.018
Yan, Y., S. S. Park, et al. (2007). In a model of immunoglobulin heavy-chain (IGH)/MYC translocation, the Igh 3′ regulatory region induces MYC expression
at the immature stage of B cell development. Genes, Chromosomes and Cancer, 46(10), 950-959. http://doi: 10.1002/gcc.20480
Yoo, B. S., Boverhof, D. R., Shnaider, D., Crawford, R. B., Zacharewski, T. R., & Kaminski, N. E. (2004). 2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) alters the regulation of Pax5 in lipopolysaccharide-activated B cells. Toxicological Sciences : An Official Journal of the Society of Toxicology, 77(2), 272–9. http://doi.org/10.1093/toxsci/kfh013
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