Signal transduction

Cellular Signal Transduction

M.Prasad NaiduMSc Medical Biochemistry,Ph.D.Research Scholar

Monad——responds directly.

Multicellular organisms——signal through elaborate system of intercellular or intracellular communication ， and consequently regulate functions of organisms.

Signaling molecule

Receptor of target cell

Intracellular molecule

biological effect

Signaltransduction

• Signaling molecules, which are released by signal-producing cells, reach and transfer biological signals to their target cells to initiate specific cellular responses.

protein & peptides: Hormone, cytokine

AA & its derivatives: Gly, Glu, adrenaline, thyroxine

Steroid: Sex Hormone, glucocorticosteroid

Fatty acid derivatives: prostaglandin

• Secreted by common cells.• Reach neighboring target cells by

passive diffusion.• Time of action is short.• Such as GF, PG

• Secreted by endocrine cells.• Reach target cells by blood

circulation.• Time of action is long.• Such as insulin, thyroxine, adrenalin

• Secreted by neuronal cells.• Reach another neuron by synaptic

gap.• Time of action is short.• Such as Acetylcholine (Ach),

noradrenaline

• Simple structure, half life is short and active in chemistry .

• Such as NO, CO.

• Act back to their own cells.• Such as GF, cytokine, interferon,

interleukin.

GAS MOLECULE

• Ca2+ ions

• DG, ceramide lipid derivatives• IP3 carbohydrate

derivatives

• cAMP cGMP nucleotides

• Ras, JAK, Raf proteins

Small molecules synthesized in cells in response to an external signal are the second messengers, which are responsible for intracellular signal transduction.

Such as Ca2+, DG, Cer, IP3, cAMP, cGMP

Third messengers are the molecules which transmit message from outside to inside of nucleous or from inside to outside of nucleous, also called DNA binding protein.

Receptors are specific membrane proteins, which are able to recognize and bind to corresponding ligand molecules, become activated, and transduce signal to next signaling molecules.

Glycoprotein or Lipoprotein

ligand 　 A small molecule that binds

specifically to a larger one; for example, a hormone is the ligand for

its specific protein receptor.

(1) Ligand-gate ion channels type

(cyclic receptor)

ligand→receptor→ion channel open or close

1) 7-helices transmembrane receptor

Cytosolicside

Oligosaccharideunit

• G protein refers to any protein which binds to GDP or GTP and act as signal transduction.

• G proteins consist of three different subunits (, , -subunit).

• -subunit carries GTPase activity, binding and hydrolysis of GTP.

G protein Coupled Receptors• The human genome encodes more than 1000 GproteinCoupled Receptors (GPCR), that transducemessages as diverse as light, smells, taste, andhormones• An example is the beta-adrenergic receptor, thatmediates the effects of epinephrine on manytissues:…

Gs→ s→AC→cAMP↑

Gi→ i→AC→cAMP↓

Gq→ q →PI-PLC→IP3+DAG

Go→ o→ion channel

Gt→ t →cGMP PDE→cGMP→

Rhodopsin

Gs vs Gi vs Gq

Gs and Gi coupled to adenylate cyclase [cAMP] G q coupled to phospholipase C [Ca2+]

Gs vs. Gi

Regulation of Adenylate Cyclase Activity

Gs stimulates adenylate cyclase

Gi inhibits adenylate cyclase

e.g. epinephrine can increase or decrease intracellular cAMP concentrations,depending upon the receptor to which it binds

adrenergic receptors couple to Gs, whereas

2 adrenergic receptors couple to Gi

Glucagon

-adrenaline →s →AC↑

ACTH

-adrenaline

angiotensin Ⅱ

acetylcholine(M2 M4)

GF release inhibitory factor

→i→AC↓

Inhibition of Gs and Gi by Bacterial Toxins

Cholera toxin effects on Gs:ADP ribosylation of an Arg residuein the s subunit of Gs inhibition ofassociated GTPase activity

Pertussis toxin effects on Gi:ADP ribosylation of a Cys residuein the i subunit of Gi an inabilityto inhibit adenylate cyclase activity.

Thus, both toxins cause increasedintracellular cAMP concentrations!

© 2000 by W. H. Freeman and Company. All rights reserved.

• Tyrosine protein kinase Receptor (catalytic receptor)

IGF － R, EGF － R

• Non tyrosine protein kinase Receptor

Growth Hormone R, interferon R

Intracellularinsulin effectsCytosol

Insulin

Membrane receptor –ANP

Soluble receptor – NO, CO

(4) Guanylate cyclase (GC) receptor

Intracellular R is trans-acting element cis-acting element gene expression

Localized in the cytosol and/or in the nucleus.

ligand: Steroid H, Vit D3, Thyroxine

• Phosphorylation or dephosphorylation of R

• Phospholipid of membrane

• Enzyme catalyzed hydrolysis

• G protein regulation

(1) Recognize the special ligand

(2) Binding to special ligand

(3) Signal transduction biological effect

• cAMP dependent-protein kinase A pathway

• cGMP dependent PKG pathway 　

• Ca2+ dependent PK pathway • 　• Tyrosine protein Kinase pathway

• NF-κB pathway 　

H R

G protein

Phosphorylation of Es or functional proteins

Biological effects

PKA

cAMPAC

ATP

Mg2+

PPi

cAMP

H2OMg2+ 5'-AMP

AC PDE

AC ： Adenylate cyclase

PDE ： Phosphodiesterase

PDE

H2O

N

N N

N

NH2

O

H

OHOH

CH2

H

H H

OPO

O

O

PO

O

O

P

O

O

O ATP

ACPPi

N

N N

N

NH2

O

H

OHO

CH2

H

H H

O

PO

O

cAMP

N

N N

N

NH2

O

H

OHOH

CH2

H

H H

OPO

O

O

5'-AMP

(3) PKA effect

Phosphorylate specifically Ser/Thr residues in several proteins

（ 1 ） Regulation of metabolism

（ 2 ） Regulation of gene

expression

hormons: glucagon, epinephrine

inactive AC active AC

ATP cAMP

inactive PKA active PKA

phosphorylase b kinase

phosphorylase b kinase

P

ATP

ADP

H2O

Pi

phosphorylase b

P

P

ATP ADP

Pi

H2OATP ADP

glycogen synthase

glycogen synthase

P

H2OPi protein phosphatase-1

(active) (inactive)

inhibitor-1 (active)

inhibitor-1 (inactive)

phosphorylase a

ATP

(1) Ca2+ -DAG -dependent PKC pathway

H R

PIP2

G protein PLC

IP3 DG

ERPKC

Ca2+

Biological effects

Phosphorylation of Es or functional proteins

IP3 + R→open of Ca2 ＋ channel →[Ca2 ＋ ]↑ from ER

[Ca 2+]i 0.01-1 mol/L （ 10-7 mol/L ）

[Ca 2+]o 2.5mmol/L （ 10-3 mol/L ）

5000~10000×

Ca2 ＋DG PKC ↑

• regulation of metabolism

PKC →Ser/Thr-P of R, enzyme,

Protein of Mb.

• Gene expression 　

H R G protein PLC

IP3

Ca2+ CaM

CaMK

Biological effects

Phosphorylation of Es or functional proteins

Ca2 ＋ binding protein 4 Ca2 ＋ + CaM → Ca2 ＋ - CaM

↓ CaM kinase↑

↓ 　 Ser/Thr - P ↓

Ca2 ＋ pump, AC ↑ GC ↑ Es (glycogen synthase, phosphorylase

kinase)

Biological effects

Phosphorylation of Es or functional proteins

ANPNO, CO

Soluble GC

PKG

cGMPReceptor-linked GC

(2) Function of PKG

Ser/Thr- P of protein and E

Mg2+

PPi H2O

Mg2+GTP cGMP 5'-GMP

GC PDE

GC: Guanylate cyclase

ANP （ atrial natriuretic peptides ） ↓

GC NO

↓

cGMP

↓

PKG

↓

Vascular dilatation

cis-acting elementnucleus

expression

cell memberane

phosphorylation of enzymes or proteins effects

CaM-PK

Ca2+-CaMCa2+

IP3DGcAMP cGMP

PKA PKG PKC

ATP GTP PIP2(PC)

G AC GC G PL

peptide hormonesneurotransmitters AFP

neurotransmittershypothalamic pituitrin

Ptrans-acting factor

• TPK receptor is related to proliferation, differentiation, dissociation, carcinomatous change.

• TPK：receptor TPK ： Membrane.

non receptor TPK ： cytosol

• GRB2, SOS, Ras, Raf• Small G protein: Ras• MAPK (mitogen-activated protein kinase)：

MAPK 、 MAPKK 、 MAPKKK

• MAPKs belong to a family of serine/threonine kinases (kinases add

phosphate groups to/phosphorylate other proteins)

• They participate in cell growth, differentiation, transformation,

apoptosis (controlled cell death) and others

ÊÜÌå ÐÍTPKϸ°ûĤ

EGF, PDGF

receptor TPK Ras － GTPSOS － PGRB2 － P

Raf － P

MAPKK － P

MAPK － Ptrans-acting factor

expression

nucleus

－ P

(2) JAKs － STAT pathway

• JAKs(JANUS KINASES)

• STAT: Signal transductors and

activator of transcription

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ºËĤ

»ùÒò

£ PP£

JAK

11391

84

48

113

P

91P 84 P

48

113

91 84P P

P

interferons & GH

inactive STAT

Plasma membrane

STAT complex

Nuclear membrane

geneInterferons response element

transcription

• Steroid H, VD3, Thyroxine

• Cytosolic R: glycocorticosteroid H

• Nuclear R: thyroxine, estrogen, androgen, progesterone

Effect by membrane receptors

Effect by intracellular receptors

Intracellular molecules

Extracellular molecules

Signal molecules

cAMP, cGMP, IP3, DG, Ca2+

Proteins and peptides:

Hormones, cytokines

Amino acid derivatives:

Catecholamines

Fatty acid derivatives:

Prostaglandins

Steroid hormones, Thyroxine, VD3