Cell-Cell and Cell-Matrix Adhesion

Question 1

Cell-Cell Adhesion: Examples of molecules responsible

Answer 1

Cadherins

• Link to actin filaments = Adherens Junctions
• Link to Intermediate Filaments = Desmosomes

Selectins:
- Link to actin filaments = non-junctional adhesions

Ig Family Members (e.g. I-CAM, N-CAM):
-Signalling Junctions e.g. neuronal and immune synapses

Question 2

Cell-Matrix Adhesion: Examples of molecules responsible

Answer 2

Integrins:

• Actin Filaments = Focal Adhesions
• Intermediate Filaments = Hemidesmosomes

Transmembrane Proteoglycans:
-Link to actin filaments, non-junctional

Question 3

Cadherins:

Answer 3

• A family of adhesion proteins which mediate Ca2+ dependent homophilic adhesion (binding of a receptor molecule to an identical molecule).
• Adhesions individually low affinity, but in combination give strong attachment.
• Classical cadherin = E-cadherin.
• Catenins link classical cadherins cytoplasmic domains to the actin cytoskeleton.

Question 4

Ig Family Members: Cell Adhesion

Answer 4

• Mediate Ca2+ independent adhesion.
• Extracellular domains made up of multiple Ig-like domains.
• The T cell receptor is an Ig family adhesion molecule
• Present in neuronal synapses.

Question 5

Selectins:

Answer 5

• Ca2+ dependent cell surface carbohydrate binding proteins.
• Expressed on white blood cells (L-selectin), platelets, and endothelial cells.
• Weak interactions between selectins allows the cell to attach to the blood vessel and roll, slowing down the cell. (Cell adhesion molecules control the recruitment of neutrophils to infected tissues).
• Selectins are regulated by inflammation.

Question 6

Syndecans:

Answer 6

• Cell surface proteoglycan adhesion molecules.

- Mediate cell adhesion to the ECM.

Question 7

Integrin:

Answer 7

• Non-covalently bound heterodimers.
• Mediate cell adhesion to the ECM (But can also mediate cell-cell adhesion e.g. bind to Ig family adhesion molecules such as I-CAM).
• Physically link intracellular cytoskeleton to the extracellular matrix (e.g. attachment of epithelial cells to basal lamina).
• Integrin activation via Inside-Out or Outside-In signalling.

Question 8

Integrins: Outside-In Signalling.

Answer 8

• Dimer adopts folded structure in absence of ligand.
• After activation by ligand binding, dimer has extended conformation.
• This breaks the interaction between cytoplasmic tails, exposing binding sites for cytoskeleton attachment

Question 9

Integrins: Inside-Out Signalling

Answer 9

• Intracellular signalling can activate “talin”
• “Talin” competes for binding to cytoplasmic tails, pushing subunits apart
• Extracellular portion adopts extended conformation -higher affinity for ligand