Cell- Cell interactions Mr. Gunjankumar Mehta, Dept. of Biotechnology, Shree M. & N. Virani Science College, Rajkot- 360005, Gujarat, India Email: [email protected] 1
Aug 19, 2014
Cell- Cell interactions
Mr. Gunjankumar Mehta,Dept. of Biotechnology,
Shree M. & N. Virani Science College, Rajkot- 360005, Gujarat, India
Email: [email protected]
1
Contents• Need of cell- cell interactions• Cell signaling overview & mechanism• A. Cell- cell interaction by direct contact• B. Paracrine signaling• C. Endocrine signaling• D. Synaptic signaling• Summary• References
2
Need of Cell- Cell interaction• Cell-to-cell communication is essential for
multicellular organisms.
• The combined effects of multiple signals determine cell response. For example, the dilation of blood vessels is controlled by multiple molecules.
• Cell-cell communication via cell adhesion molecules is critical for assembling cells into tissues, controlling cell shape and cell function (together with cell- matrix interaction).
3
Cell- cell interaction
4
Cell signaling- overview1. Reception: target cell detects a signaling molecule
coming from outside 2. Transduction: change of the receptor protein
initiating process of cellular response (enzymatic)3. Response: cellular activity: catalysis,
rearrangement of the cytoskeleton, gene activation
5
Cell signaling mechanisms
6
A. Cell- cell interaction by direct contact• Cells attach themselves to one another with long
lasting bonds called cell junctions.
• Plasma membrane areas specialized to provide contact between cells.
• Dense clusters of cell adhesion molecules on the outside linked to cytoskeleton on the inside through adapter proteins.
• Four classes of cell junctions are there.
7
Cell Junctions- types based on localizationBetween cells
– Tight junctions– Adherence
junctions and desmosomes
– gap junctionsBetween cells and
matrix– Hemidesmosomes
8
Cell junctions - types based on function
• Adhering junctions:1. Tight junctions2. Adherence junctions and
desmosomes3. Hemidesmosomes
• Communicating junctions:1. Gap junctions
9
Tight junctions (zonula occludens)• Connects plasma
membrane in a sheet.• Belts of proteins that close
extracellular space between cells
• Prevent passage of water and water-soluble substances
• Account for electrical resistance across epithelia.
• Look like honey comb
10
Tight junctions- Molecular structure• Claudins (membrane
proteins) zip two membranes together.
• Stabilized by spectrin• Connected to spectrin by
adapter proteins ZO1 and ZO2.
• The “tightness” varies according to the barrier.
• Leaky epithelia where there is need for some traffic.
11
Tight junctions- Regulation• Hormones-
Vasopressin• Cytokines• Lack of ATP causes
“leak”• Extravasating
leukocytes open tight junctions.
12
Significant example• Tight junction of intestinal epithelium
13
Adhesive/ Anchoring junctions• Adherence junctions and
desmosomes• Hold cells tightly together
confering mechanical strength.
• Common in tissue that are subject to severe stress such as skin and cardiac muscle.
• Integral membrane proteins connect a cell’s cytoskeleton to another cell or extracellular matrix.
14
Adherence junction- Molecular structure• Belt like junctions
located just below tight junction.
• Simple points of attachment, do not contain channels connecting the interiors of the two attached cells.
• Cell to cell connections are mediated by cadherins binding to other cadherins.
15
E- cadherin mediated adherens junctions• Homophilic pairing of E- cadherins• Adapter proteins (plakoglobin and α and βcatenins)
link cadherins to the belt of actin filaments.
16
E- cadherin• Ca2+ -dependent cell-cell adhesion
proteins, expressed in almost all cells of vertebrates and invertebrates.
• Transmembrane proteins. • Characteristic structural feature: Tandem repeats of homologous
domains (CAD-domains)Length of about 110 amino acids.β-sheeted structure
17
Desmosomes• Button like welds joining
opposing cell membranes• Cadherins bind the
membranes of adjacent cells in a way that gives strength and rigidity to the entire tissue.
• Cadherins attach to intermediate filaments via anchoring proteins.
18
Desmosomes- Molecular structure• Two cadherins:• Desmoglein• Desmocollin• Adapter proteins: • Plakoglobin • Desmoplakin• Linked to epidermal
keratins
19
Gap junctions• Gap junctions allow cells to exchange
electrical and/or chemical signals via direct door.
• Composed of proteins that form channels that allow small molecules to pass.
• Form electrical synapses- Direct transmission of action potential without transmitter, receptors etc.
• Integrate the metabolism of the cells- Metabolic coupling or metabolic cooperation.
20
Gap junction- Molecular structure • A ring of 6 membrane
proteins called connexins- connexons.
• Two connexons on neighboring membranes form a transmembrane channel that interconnects the cytoplasms of two cells.
• Connexons are size filters.
21
Regulation of gap junctions• Flip between open and closed states as other
channels do.• Cells may modulate the degree of coupling • Cytoplasmic levels of Ca2+and pH• Phosphorylation• Oleamide – closes gap junctions and induces
sleep
22
Significant examples• Cells that use gap junctions• Skin epithelium• Endocrine glands• GI epithelium• Smooth muscle• Cardiac muscle• Osteocytes• Glial cells
23
Hemidesmosomes- molecular structure• Similar to desmosomes but totally
different molecular structure.• Cell-matrix adhesions – attach
cells to basal lamina.• Composed of integrins (outside)
that bind to type XVII collagen and laminin-5.
• Cytosolic side consist of a plague composed of adapter proteins (plectin) attaching integrins to keratin filaments.
24
Summary- Cell junctions
25
Plasmodesmata- plants• In plants, cell walls separate
every cell from all others.• Cytoplasmic connections that
form across the touching plasma membranes.
• Plasmodesmata function much like gap junctions in animal cells- structure differs.
• Lined with plasma membrane and contain a central tubule that connects the ER of the two cells.
26
B. Paracrine signaling• Signals with such short-
lived, local effects are called paracrine signals.
• Signal molecules released by cells can diffuse through the extracellular fluid to other cells used or destroyed
• Paracrine signaling plays an important role in early development.
27
C. Endocrine signaling• Released signal molecule
remains in the extracellular fluid Circulatory flow
• Travel throughout your body Hormone
• endocrinesignaling (figure 7.3c).
• Both animals and plants use this signaling mechanism extensively.
28
D. Synaptic signaling• In animal nervous system,
signal molecules neurotransmitters, do not travel to the distant cells like hormone.
• They are secreted by long fiber like extensions of nerve cells release neurotransmitters from their tips very close to the target cells Chemical synapse.
29
30
31
References• The Cell- A Molecular Approach- 4th
edition, GEOFFREY M.COOPER, ROBERT E. HAUSMAN.
• Cell and Molecular biology- 6th edition, GERALD KARP
• Cell Biology, Genetics, Molecular Biology, Evolution and Ecology-1st Edition, Verma and Agrawal.
32