Module 7: Interactions Between Cells and Their Environment Flashcards
What are integrins?
- Family of membrane proteins unique to animals.
- Composed of two membrane-spanning polypeptide chains, an alpha and beta chains.
What are the two conformations of integrins?
- Bent conformation: It corresponds to its inactive state,
- Upright conformation: Integrins with a bound ligand are found in an upright conformation.
- Activated integrins become clustered -> strengthens the cell-ECM interactions.
What are the major activities of integrins?
1) adhesion of cells to ECM (or to other cells).
2) transmission of signals between the external environment and the cell interior.
What do integrins bind to intracellularly?
Bind ligands such as Talin.
What do integrins bind to extracellularly?
- Different integrins bind
different ECM components such as collagen, laminin, and fibronectin (causing “Outside-in” signaling).
How does the outside-in-signals induce a conformational change in talin?
- Actin filament polymerization
- Cytoplasmic protein kinases (e.g. FAK and Src) activation to
phosphorylate other proteins à life saving signals.
What can the outside-in-signals by integrins influence?
Cell differentiation, motility, growth, and cell survival.
What is a focal adhesion?
Cultured cells are anchored to the surface of the dish only at scattered, discrete sites, called focal adhesions.
- They play a role in cell adhesion and locomotion.
What is the relation between focal adhesions and mechanical force?
Focal adhesions create mechanical forces or respond to such forces from the environment.
- Actin filaments are the source of these forces.
What are hemidesmosomes?
- Cell-ECM attachment in vivo is seen at the basal surface of epithelial cells, anchored to the underlying basement membrane.
- Hemidesmosomes contain a dense cytoplasmic plaque with keratin filaments.
- Keratin filaments are linked to the ECM by integrins.
What are cell-cell adhesions mediated by?
- Selectins
- Members of the IgSF,
- Members of the integrin family,
- Cadherins.
What are selectins?
- They are a family of membrane glycoproteins that bind to specific oligosaccharides.
- They are present in platelets, endothelial cells, leukocytes.
- They have a small cytoplasmic segment, a single membrane-spanning domain, and a large extracellular portion.
What are selectins involved in?
- Cell-cell adhesion, and
transmembrane signal transduction. - Signaling: cell growth, migration, differentiation, or survival.
What is the term “Lectin”?
It is a term used for a compound that binds to specific carbohydrate groups.
What are the Immunoglobulin superfamily?
The human genome encodes 765 different Ig domains. These are members of the immunoglobulin superfamily.
- Involved in immune functions.
- Original function likely cell-
adhesion mediators (Ca2+
independent).
- Developmental roles in neuronal growth and circuitry.
