CELL-CELL INTERACTIONS : CELL-CELL INTERACTIONS ANCHORING JUNCTIONS
COMMUNICATION JUNCTIONS 1 IVMS©1999-2009 ANCHORING JUNCTIONS : ANCHORING JUNCTIONS Allow groups of cells such as those in epithelium to function as a robust structural unit by connecting the cytoskeletons.
Hemidesmosomes 2 IVMS©1999-2009 Slide 3: All are composed of an intracellular and an extracellular attachment.
Intracellular attachment proteins attach, or anchor, the proteins to an actin intermediary filament.
The extracellular attachment ties the cells together. 3 IVMS©1999-2009 A. ADHERING JUNCTIONS : A. ADHERING JUNCTIONS Resemble small punctate attachments that connect actin filaments in the cortical cytoplams of adjacent cells.
In epithelial sheets they form a continuos adhesion belt around the cell (zonula adherentes).
Transmembrane linker proteins hold the cell together (cell adhesion). 4 IVMS©1999-2009 CELL ADHESION : CELL ADHESION CALCIUM INDEPENDENT CELL ADHESION MOLECULES (CAMs)
CALCIUM DEPENDENT CELL ADHESION MOLECULES
CADHERINS 5 IVMS©1999-2009 CALCIUM-INDEPENDENT CELL ADHESION MOLECULES : CALCIUM-INDEPENDENT CELL ADHESION MOLECULES Homophilic intercation
Members of the immunoglobulin super family
Not all are transmembrane
N-cam is anchored by a glycophosphatidyl insositol in the plasma membrane 6 IVMS©1999-2009 CADHERINS : CADHERINS Homophillic cell adhesion
Most are transmembrane
The cytoplasmaic domain is bound to catenins (, , ) 7 IVMS©1999-2009 Slide 8: Although both cadherins and CAMs are expressed on the same cell, cadherin adhesion is stronger.
Cadherins play a mjor role in hold the cells together and maintaining tissue integrity.
CAMs appear to be involved in fine tuning the process of adhesion. 8 IVMS©1999-2009 ATTACHMENT PROTEINS : ATTACHMENT PROTEINS In each bundle of actin filaments are attachment proteins.
-actin 9 IVMS©1999-2009 CATENINS : CATENINS Catenins are cadherin anchoring proteins which are involved in signal transduction pathways.
There are three catenins. Catenin- and - are primarily involved in signal transduction via the G-protein Rho. Catenin- is primarily a structural protein. 10 IVMS©1999-2009 Cell-Matrix Adherens Junctions : Cell-Matrix Adherens Junctions Enables cells to get a hold on the extracellular matrix be connecting their actin filaments to the matrix.
eg. Cultured fibroblasts « grabs » the substratum at specialized regions of the plama membrane which are called focal contacts or adhesion plaques.
Linker proteins are called integrins. 11 IVMS©1999-2009 B. Desmosomes : B. Desmosomes Button-like points of attachment, or contacts, that rivet the cells together.
Inside the cell, desmosomes act as anchoring sites for rope-like intermediate filaments.
The linker proteins are cadherins and the filaments depend on the cells type.
eg. keratin for epithelial cells; desmin for cardiac cells. 12 IVMS©1999-2009 Slide 13: Pemphingus
autoimmune disease which targets desmosomes. 13 IVMS©1999-2009 C. Hemidesmosomes : C. Hemidesmosomes Similar appearance to desmosomes both is functionally different.
Conects the basal surface of the cell to the basal lamina. 14 IVMS©1999-2009 Slide 15: CELL-CELL INTERACTIONS ANCHORING JUNCTIONS
COMMUNICATION JUNCTIONS 15 IVMS©1999-2009 TIGHT JUNCTIONS : TIGHT JUNCTIONS All epithelia serve as barriers.
This is important as it allows selective transport of molecules. 16 IVMS©1999-2009 Slide 17: SMALL INTESTINE FOOD PRODUCTS Blood
Vessel transporter Epithelial cells 17 IVMS©1999-2009 Tight Junctional Proteins : Tight Junctional Proteins Occludin
localized at the TJ of many cell types
two extracellular loops projecting in the paracellular space.
Phosphorylated protein. More highly phosphorylated forms are localized at the TJ.
Associates with ZO-1 18 IVMS©1999-2009 Slide 19: Claudins
Zona Ocludens (ZO-1, -2, -3)
cytoplasmic proteins which are members of the gunylate kinase family of proteins.
140 kDa protein composed of two intertwind peptides as a « coiled-coil ». 19 IVMS©1999-2009 Slide 20: Cingulin is localized in close proximity to the vinculin rich cytoskeletal belt associated with adherens junctions.
How are tight junctions assembled ? 20 IVMS©1999-2009 Tight Junction Assembly : Tight Junction Assembly 21 IVMS©1999-2009 Slide 22: CELL-CELL INTERACTIONS ANCHORING JUNCTIONS
COMMUNICATION JUNCTIONS 22 IVMS©1999-2009 GAP JUNCTIONS : GAP JUNCTIONS Survival of multicellular organism depends on each cell type retaining its individuality, even though all cellular activities must be coordinated with other cells. 23 IVMS©1999-2009 Slide 24: MULTIPLE STRATEGIES HAVE EVOLVED TO ACHIEVE THIS:
LONG RANGE INTERACTIONS MEDIATED BY THE NERVOUS AND ENDOCRINE SYSTEMS.
SHORT RANGE INTERACTIONS THAT INCLUDE DIRECT PHYSICAL OR CELL TO CELL CONTACT. 24 IVMS©1999-2009 Slide 25: One of the direct interactions involves the passage, or transmission, of molecules from one cell to another via a specialized surface membrane structure, the gap junction.
Gap junctions contain channels that contact neighboring cells. 25 IVMS©1999-2009 Slide 26: These channels differ from other cell membrane channels in that their selectivity is based on molecular size which allows the movement of molecules 1000 da.
eg. cAMP, but prevent the movement of proteins and nucleic acids. 26 IVMS©1999-2009 Slide 27: The type of communication is an important mechanism for regulating events between cells during embryogenesis and normal function of organs such as the heart.
Apart from a few terminally differentiated cells (eg skeletal muscles, red blood cells, and lymphocytes) most cells in the body communicate via gap junctions 27 IVMS©1999-2009 STRUCTURE OF CONNEXINS AND GAP JUNCTIONS : STRUCTURE OF CONNEXINS AND GAP JUNCTIONS Gap junctions are made up of two connexons.
Each connexon is inserted into the plasma membrane of one cell.
Two connexons are connected in mirror symmetry. 28 IVMS©1999-2009 Slide 29: The gap junctional plaque, or gap junction, is formed by a gathering of a large number of connexons.
The size of the gap junction is proportional to the number of channels. 29 IVMS©1999-2009 CONNEXINS : CONNEXINS A connexon is an oligomer of six intrinsic proteins, named connexins.
Gap junctions are formed by a multigene family of proteins known as connexins (cx).
The extracellular domains of the connexins pairs the connexon. 30 IVMS©1999-2009 Slide 31: Therefore, the pore is axial and joins the cytoplasms of each cell.
PROTEIN MOLECULAR WEIGHT
There are 15 different connexins. 31 IVMS©1999-2009 STRUCTURE OF CONNEXINS : STRUCTURE OF CONNEXINS Each connexin has a transmembrane domain that contain polar amino acids which will contribute to forming the channel lining.
Reconstitution of purified connexins into artificial membranes leads to the formation of functional channels and gap junctions that are ultrastructurally identical to those naturally occuring. 32 IVMS©1999-2009 Slide 33: Each connexin has a similar general topography.
A set of three cysteine residues exist in each of the extracellular portions of the protein which is necessary to provide the tertiary rigid structure necessary for each connexon to dock into one another. 33 IVMS©1999-2009 PERMEABILITY OF GAP JUNCTIONS : PERMEABILITY OF GAP JUNCTIONS In addition to ions (Na+, K+, Ca2+ ) a number of other small molecules, including camp and inositol 1,4,5-triphosphate (ip3) can pass through gap junctions.
Dye transfer analyses suggest that gap junctions are relatively non-specific in permeability of hydrophilic molecules of 1.5 nm or less. 34 IVMS©1999-2009 CONNEXIN PERMEABILITY : CONNEXIN PERMEABILITY Cx43 Cx45 Cx45 + Cx43 LUCIFER YELLOW 35 IVMS©1999-2009 CONNEXIN PHOSPHORYLATION : CONNEXIN PHOSPHORYLATION COUPLED XENOPUS
Cx43 pp60V-SRC (tyrosine kinase) INCREASED
PHOSPHORYLATION 36 IVMS©1999-2009 Regulation of Gap Junctions : Regulation of Gap Junctions PHOSPHORYLATION
CONNEXINS, EXCEPT Cx26, ARE PHOSPHOPROTEINS
INCREASED INTRACELLULAR Ca2+ IS ASSOCIATED WITH A DECREASE IN GAP JUNCTION PERMEABILITY
LOWER pH decreases permeability 37 IVMS©1999-2009 TARGETING : TARGETING the mechanism which regulate the selective targeting of connexins is unknown.
the observation that certain connexins can form separate gap junctions with distinct membrane locations has a number of implies that there are mechanism for spatial targeting of connexins 38 IVMS©1999-2009 Slide 39: Hormonal regulation ?
ZO-1 is involved in connexin targeting. 39 IVMS©1999-2009 ENVRIONMENTAL CONTAMINANTS, CARCINOGENS AND CONNEXINS : ENVRIONMENTAL CONTAMINANTS, CARCINOGENS AND CONNEXINS -Epigenetic carcinogens such as hexachlorobenzene, TCDD ? 40 IVMS©1999-2009 DISEASE AND GAP JUNCTIONS : DISEASE AND GAP JUNCTIONS Cardiac ischemia, and cardiac hypertrophy
Psoriasis 41 IVMS©1999-2009 Cx26 Mutations : Cx26 Mutations Unlike in humans, Cx26 mutations in mice result in embryo lethality at embryonic day 11.
Suggests a role for junctional communication in transplacental movement of nutrients. 42 IVMS©1999-2009 Slide 43: In mice, nutients must pass through two layers of syncytiotrophoblast cell layers which are connected by Cx26 gap junctions.
In humans there is only one layer. 43 IVMS©1999-2009 Cx32 Knockouts : Cx32 Knockouts Mice appear normal with subtle effects in peripheral nervous system.
Dramatic abnormalities in the liver.
Lower moblization of glucose from glycogen
78% decrease in electrical stim,ul;ation to liver. 44 IVMS©1999-2009 Slide 45: Sympathetic fibers terminate at the edge of the lobules and the electrical signal is propagated through the liver. Without Cx32 this is not happening.
25-fold increased rate of spontaneous tumour formation. Indicates that inhibitory signals pass through Cx32 gap jup junctions regulating cell proliferation. 45 IVMS©1999-2009