Cell Junctions and Adhesion Flashcards
Cell junctions are best observed in
Epithelial cells
What are the types of cell junctions?
- ) Tight junctions
- ) Zonula adherens (belt desmosomes)
- ) Macular adherens (spot desmosomes)
- ) Hemidesmosome
- ) Gap (communicating) junctions
Define cell polarityand control the passage of substances between adjacent cells
Tight junctions
Have a distribution like a ribbon internally bracing the cells and are associated with actin filaments
Tight junctions
An anchorage junction that has a beltlike distribution and is associated with actin filaments
Zonula adherens (belt desmosome)
An anchorage junction with a spotlike distribution and is associated with intermediate filaments
Macula Adherens (spot desmosomes)
Link the basal domain of an epithelial cell to the basal lamina. Intermediate filaments are associated with a plaque
Hemidesmosome
Connect functionally two adjacent cells.
-Formed by connexons
Gap junction
Channel-like structures that enable the passage of small molecules
Connexons
Gap junctions are not associated with
Cytoskeletal components
What are the two cell-cell anchorage junctions?
Belt desmosomes and spot desmosomes
What are the cell matrix junctions?
Hemidesmosomes and focal adhesions
The transmembrane proteins for the cell-cell anchor junctions (belt and spot desmosomes) are?
Cytoskeletal?
1.) Cadherins
Actin (belt) Intermediate filaments (spot)
Which two proteins make up tight junctions?
Occludins and Claudins
Encircle the entire cell like a belt
Tight junctions
The apical domain of a cell faces the
Lumen
Tight junctions are composed of “sealing strands” where the two membranes are tightly linked together by lines of
Transmembrane proteins
Mediate the adhesion at tight junctions
Occludins and Claudins
Occludins and claudins are linked to the actin cytoskeleton through adaptor proteins like
ZO-1
Also encircle the entire cell an are positioned right underneath the tight junctions
Belt desmosomes
Transmembrane proteins that mediate adhesion at the belt desmosomes
Cadherins
In order to function, cadherins need
Calcium
Cadherins are linked to the actin cytoskeleton by
Catenins
Catenins are made up of
α, β, and ƴ/plakoglobin
Binds to cadherin and ƴ-catenin/plakoglobin
β-catenin
Binds directly to actin
α-catenin
The main proteins holding epithelial cells together in a sheet
Cadherins
Important for cell-cell adhesion in the epithelia
E-cadherin
Contributes to epithelial-mesenchymal transition (EMT) during cancer progression
Loss of E-cadherin
E-caherin engagement is needed for
Tight junction formation
Spot-like cell-cell junctions
Spot Desmosomes
Cadherin family proteins that mediate the adhesion at spot desmosomes
Desmocollins and desmogleins
Spot desmosomes are linked to which cytoskeletal component?
Intermediate filaments
Transmembrane proteins that have an α subunit and a β subunit.
-interact with extracellular matrix proteins on the RGD peptide sequence
Integrins
Integrins are present in actin-linked cell-matrix adhesion sites called
Focal adhesions
Mediate the interactions between the cells and the basement membrane
Hemidesmosomes
Mediates the interaction between hemidesmosomes and the basement membrane
Integrin α6β4
Hemidesmosomes are linked to which cytoskeletal component
Intermediate filaments
Integrin mediated and are linked to the actin cytoskeleton. These adhesions are not visible under conventional EM, but can be visualized using immuno-EM.
Focal adhesions/focal contacts
Focal adhesions/focal contacts are important for many cellular processes including
Cell migration
Serve to coordinate cellular responses
Gap junctions
Formed by connexon channels, which allow small molecules like Ca2+ and cAMP to pass from cell to cell
Gap junctions
Connexons are formed by six connexin proteins. Connexon on cell A interacts with connexon on cell B to form the
Hydrophilic chanel
Connexon permeability is regulated by multiple factors including
pH, Voltage, Calcium, etc
In gap junctions, there are two plasma membranes close together, similar to tight junctions. However, unlike tight junctions, gap junctions can be
Very extensive structures
Small molecules can pass between cells through gap junctions. Gap junctions are abundant in
Cardiac, smooth muscle, and epithelial cells
In connexon channels, high calcium concentration signals
Apoptosis
Claudin 16 mutation causes an autosomal-recessive renal disorder, familial hypomagnesemia with hypercalciuria and nephrocalcinosis. This affects
Tight Junctions
P-cadherin mutation causes hypotriosis with juvenile
macular dystrophy, characterized by early hair loss and
progressive degeneration of the central retina. This affects
Belt desmosomes
Autoimmune disease with antibodies against Desmoglein such as 1-blistering disease affects
Spot desmosomes
Autoimmune disease with antibodies against BPAG1 such as 2-blistering disease affects
Hemidesmosomes
Mutations in multiple different connexins causes defects in gap desmosomes that are assoicated with which clinical phenomenon?
Deafness
There are different ways to get blistering diseases. Blistering diseases are caused by defects in either
Spot desmosomes or hemidesmosomes
Will cause splitting (vesicles) within the epidermal cell layers
Spot desmosome defects
Will cause splitting (vesicles) between the epidermis and the underlying basement membrane
Hemidesmosome defects
Usually found during cell locomotion where dynamic cell-cell and cell-matrix adhesions are needed
Non-junctional adhesions
Cell adhesion does not only happen at stable cell junctions. During cell locomotion, we also need
Dynamic adhesions
Transmembrane proteins that bind oligosaccharides
-calcium dependent
Selectins
Selectins are expressed on the surfaceof
Lymphocytes (L-selectin), endothelial cells (E-selectin), and platelets (P-selectin)
The extracellular segment of cell adhesion molecules (CAMs) are folded into 2-6 immunoglobin-like domains. As a result, CAMs belong to the
Immunoglobin (Ig) Superfamily
Immunoglobulin superfamily cell adhesion molecules (IgCAMs) have Ig-like domains on the
Extracellular side
IgCAMS are NOT dependent on
Calcium
Play important roles in T cell interactions and binding of leukocytes to activated or resting endothelial cells
ICAM and VCAM
Slow down and start rolling on the endothelial cell surface through loose adhesion with selectins on the
endothelial cell surface
Leukocytes
During rolling, integrins on the leukocytes are activated to bind to
ICAM and VCAM on endothelial surface
These stronger adhesive interactions lead to the arrest of leukocytes on the endothelial cell surface, and the subsequent integrin-mediated migration of leukocytes through the wall of the blood vessel, in between the
Endothelial cells
The lymphocyte-endothelial cell interaction requires which two types of cell adhesion proteins?
Selectins and Integrins
High Endothelial Venules (HEVs) in the deep cortex and medulla of lymph nodes allow for the transition of lymphocytes from the blood stream to
Lymph Tissue
