Epithelial Cells and their adhesions Flashcards
What are the functions of the basement membrane?
- Organisation and mechanical resilience of epithelium
- Receptors provide adhesion and signalling cures to sheets of epi/endothelial cells
- Act as barrier so prevent invasion of cancer/pathogens
- Mutations give rise to skin blistering diseases
What are the 4 major proteins which build the basement membrane?
- Laminin
- Collagen IV
- Perlecan
- Nidogen
What are the features of the alpha subunit of laminin?
- alpha subunit is longer and has globular domains with cell surface receptors
- Has main integrin binding sites
What is the structure of laminin?
- Made up of alpha, beta, and gamma subunit
- 3 subunit proteins assembled via extended alpha helical coiled-coil domain
What are the features of the beta and gamma subunits of laminin?
- Globular domains important for binding other components
What are the features of collagen IV?
- Assembles into flat meshworks
- No cleavage of 7s or NC1 domains on secretion
- 7s associations build tetramers and associate tail to tail via NC1
Why does collagen IV have a different structure?
There is no cleavage of globular domains so it produces a different structure as it can form different crosslinks
What is the function of perdegan and nidogen?
- Add more protein-protein interactions that reinforce and stabilise structure
What are the different types of cell-cell junctions?
- Tight junction
- Adherens junction
- Desmosome
What are the types of Cell-ECM junction?
- Focal adhesions
- Hemidesmosome
What proteins form tight junctions?
- Clausdin
- Occuldin
- JAM1
What are the features of tight junctions?
- Upper region of 2 epithelial cells
- Short extracellular domains between 2 TM domains
- Interact end to end with molecules on other cell and allows cells to be very close together
What is the function of tight junctions?
Acts as a protective barrier
how are adherens junctions formed?
- By end to end interaction of cadherin molecules on adjacent cells
What domains does the extracellular part of cadherin contain?
- 5 CAD domains
- 3 of which contain Ca2+ binding sites
What does the 1st CAD domain of cadherin contain a binding domain for?
- 1st CAD domain contains the binding site for an eqivalent CAD domain
What is the function of adherens junctions?
They attach epithelial cells into sheets
What are cadherins involved in?
- The sorting of cell layers in tissues
- Involved in binding of adheren junction
What are the features of an adherens junction?
- Adjacent cells interact via cadherin molecules
- Multiple proteins inlcuding catenins are involved in coupling cadherins and catenins to actin filaments
What are desmosomes?
- Mechanically rigid connections near the base of epithelial cells
What makes up desomosomes?
- Desmosomal cadherins
- keratin intermediate filaments
- linker proteins
What is the function of the desmosome?
Enables epithelial cells to resist mechanical stresses on tissue
What are the desmosomal cadherins?
- Desmocollin
- Desmoglycin
What are gap junctions?
Channels between the cytoplasms of epithelial cells
What are gap junctions made up of?
- 6 connexin proteins
What is the function of gap junctions?
- molecules with molecular mass of less than 1000 Da can diffuse through gap
- Allows local communication and co-ordination of intracellular signalling between neighbouring cells
What are the features of gap junctions?
- The channels bind head to head
- Opening and closing is regulated by phosphprylation of connexin subunits
