Integrins are Cell Surface Receptors That Bind ECM Constituents

Question 1

What are integrins?

Answer 1

Cell surface receptors that bind to fibronectins or laminins

Question 2

What do integrins do?

Answer 2

-integrate the cytoskeleton (integrin tails interact with cytosolic proteins that link integrins to cytoskeleton) with the ECM (integrins recognize the RGD sequences in the ECM glycoproteins)

Question 3

Composition of integrins?`

• what do the extracellular parts of the a and B subunits do?-specificity is mainly dependent on what?
• how many types of a and B subunits?

Answer 3

• consists of two large transmembrane polypeptides, a and B
• the extracellular parts of a and B subunits form the binding sites of the integrin, the specificity is mainly dependent on the a unit
• there are multiple types of a and B subunits, resulting in many types of integrin heterodimers

Question 4

what do focal adhesions do?

what do they contain?

Answer 4

• migratory and nonepithelial cells such as fibroblasts attach to the ECM molecules via focal adhesions
• these contain clustered integrins that interact with bundles of actin filaments via talin, vinculin, and a-actin

Question 5

• where are hemidesmosomes found?
• what integrin do they contain?
• what are integrins attached to in this case?
• what do linker proteins in the hemisedmosomes do?

Answer 5

• found in epithelial cells
• contain integrin a6B4
• keratin
• linker proteins in the hemidesmosomes form a dense plague, connecting the integrins to the cytoskeleton

Question 6

• what are prominent linker proteins in hemidesmosomes?
• what does plectin do?
• what are BPAGs and what do they do?

Answer 6

• members of the plakin family
• a plakin, called plectin, attaches keratin filaments to integrins
• another transmembrane protein BPAG2 and its associated plakin BPAG1 serve as a bridge between keratin and laminin

Question 7

• what else do integrins do?

- explain “inside out signalling”

Answer 7

• play important roles in regulating cell movement and attachment
• integrins also interact with intracellular signalling pathways
• signals such as growth factors that lead to MAP kinase activation can induce integrin clustering

Question 8

• explain “outside in signalling”
• what else is “outside in signalling” referred to as?
• what does anchorage dependent growth involve?

Answer 8

• intgrins can also act as receptors that activate intracellular signaling
• anchorage dependent growth, which involves activation of intracellular pathways following integrin clustering

Question 9

Integrins:
what is a costamere?
what do costameres contain?

Answer 9

• an attachment structure at the surface of striated muscle

- costameres contain many of the same proteins found at focal contracts in addition to the protein dystrophin

Question 10

Integrins ->costamers->dystrophin
-what do mutations in the dystrophin locus cause?
-

Answer 10

• Duchenne muscular dystrophy (DMD)
• interacts with a complex that includes integral membrane protein dystroglycan and the sarcoglycansarcospan complexes
• interacts with cytosolic proteins such as dystrobrevins and syntrophins

Question 11

Glycocalyx and animal cells

• where is glycocalyx?
• roles of glycocalyx?

Answer 11

• the glycocalyx is a carbohydrate rich zone at the periphery of animal cells
• around the plasma membrane
• cell adhesion, recognition, protection of the surface, creation of permeability barriers