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50 terms

Cell Junctions and Cell Adhesion

T/F: cell junctions are relatively permanent and strong sites of cell-cell and cell-ECM attachment
What are the four classes of cell junctions?
1. anchoring
2. occluding
3. channel forming
4. signal relaying
What is the function of anchoring junctions?
to attach the cytoskeleton of one cell to the cytoskeleton of another cell or to the ECM
What is the basic design of anchoring junctions?
actin or intermediate filaments bind to attachment proteins on a different cell that are attached to transmembrane glycoproteins or to the ECM
What are the four forms of anchoring junctions?
1. adherens junction(cell-cell)
2. desmosome (cell-cell)
3. actin linked cell-matrix adhesion (cell matrix)
4. hemidesmosome (cell matrix)
What is a cadherin and what does it attach to?
a cadheren is a calcium dependent, homophillic glycoprotein (binds to other cadherin) transmembrane adhesion protein found in adherens junctions
Describe the cadherin family
a complex superfamily of proteins with diverse expession patterins. regulation of cadherin expression is important in developing tissues, especially in the epithelial-mesenchymal transition
What type of intracellular cytoskeletal attachment to adherens junctions utilize?
cadherins bind to catenins which bind to actin
Where are adherens junctions usually located?
in many epithelia, they are located near the apical surface or the ADHESION BELT OR ONULA ADHERENS
zonula adherens or adhesion belt
adherens junction
epithelial mesenchymal transition
different cadherins are expressed at different time during neural tube differentiation
Which cadherins are usualy used in adherens?
E, N, P, VE
used in adherens junctions. bind to cadherins and actin
What is the function of adherens junctions?
use actin to utilize purse string contraction involved in morphogenetic movements (invaginations, formations of tubes)
What is the primary function of desmosomes?
act to provide mechanical integrity to tissues
Describe desmosomes
button like plaques on lateral surfaces of epithelial cells
T/F: desmosomes are involved with cadherens as well
desmoglein or desmocollin are what?
cadhereins associated with desmosomes
Describe the desmosomal connections
desmosomes connect to desmoglein/desmocollin which connect to plakoglobin, plakophilin and desmoplakin intermediate filaments(keratins-epithelia or desmin-cardiomyocytes
plakoglobin, plakophilin, and desmoplakin
connect to desmosomal cadherins (desmoglein and desmocollin) in desmosomes
What is pemphigus?
autoimmune skin blistering disease
what causes pemphigus?
individuals with this disease develop antibodies against desmosomal cadherins (desmoglein) in their skin resulting in desmosomes being disrupted. this causes blistering because the skin cells are not firmly attached to one another.
What are integrins main functions?
most of them act as cell-MATRIX adhesion molecules. control cell survival and proliferation in response to binding to ECM- can recruit intracellular signaling molecules
describe the structure of integrins
transmembrane heterodimers with multiple combinations
What minerals do integrins need in order to bind to ECM?
calcium and magnesium?
focal adhesions
actin linked cell-matrix adhesions
Describe the basic design of focal adhesions
integrins (on a cell surface) bind to linker proteins (talin and vinculin) which then bind to the Actin cytoskeleton
describe integrin regulation
integrin activity can be moduled by factors outside of the cell or inside the cell. integrins can switch between active and inactive conformation-important for cell motility( integrins activated by g protein coupled receptor and tyrosine kinase)
major function of hemidesmosome
attach the basal surface of epithelial cells to the ECM (basal lamina). provide mechanical integrity to many epithelia
Describe the connections of hemidesmisomes
a6b4 integrin connects the ECM to the keratin intermediate filaments. a6b4 integrin binds to linker protein (plectin and dystonin) which connects to keratin intermediate filaments which connects to ECM
linking protein for hemidesmisomes to keratin intermediate filaments
linking protein for hemidesmisomes to keratin intermediate filaments
T/F: the orientation of the interaction of the intermediate filaments in hemidesmisomes and desmisomes is the same
False, it is lateral in desmisomes and direct in hemidesmisomes
epidermolysis bullosa
a genetic disease in which the attachment of the basal cells to the epidermis between the epidermis and dermis is interrupted. results in blisters and very fragile skin. problem with hemidesmisomes: could be defect in integrin, keratin, or laminin)
zona occludens
occluding or tight junction
tight junction
occluding junction
function of tight junctions?
anchor epithelial cells to one another while acting as a selective barrier to diffusion of molecules between cells and to proteins in plasma membrane. confer polarity to epithelial cells (apical and basolateral). paracellular transport and transcellular transport
Where are tight junctions usually formed?
near the apical surface of the epithelial cells
Describe the basic design of tight junctions
many strands formed by transmembrane junctional proteins that bind each other and form the seal. the more strands the tighter the seal. require calcium.
major transmembrane proteins which link to the actin skeleten through zona occludens (adherens junction) proteins
major transmembrane proteins which link to the actin skeleten through zona occludens (adherens junction) proteins
paracellular transport
function of tight junctions-selective permeability barriers
What regulates cell polarity?
adherens junctions, tight junctions, and basal lamina
Gap junctions usually located where?
below adherens junction
channel forming proteins used by gap junctions. make connexon. can form hetero and homo heamers with different biochemical properties
What is the function of gap junctions?
allow selective passage of small molecules between cytoplasm of neighboring cells. coupling of cells electrically and metabolically. permeability can be regulated (generally by Mw)
can be caused by a mutation in connexin 37. ovarian follicle development depends on gap junction mediated communication between the oocyte and surround granulosa cells. connexin 37 is important for the exchange of nutrients and signals in oocyte maturation
signal relaying junctions
utilize adherens and focal adhesions
transmembrane proteins that bind to carbs on cell surfaces. heterophellic. calcium INDEPENDENT. involved in leukocyte trafficing (weak adhesion and rolling)
aLB2 expressed on leukocytes and T-cells, involved in strong adhesion and extravasation. interaction between t-cells and antigen presenting cells