Session 7: ECM

Question 1

What are integrins?

Answer 1

Heterodimers that form from transmembrane proteins to act as receptors for ECM proteins
- different alpha/beta dimers recognize different ECM proteins (collagen, fibronectin, laminin)

Question 2

Name the various types of proteins in the ECM.

Answer 2

fibrous proteins - collagens, elastin and fibrillin (BULK of ECM)
adhesive proteins - fibronectin and laminin (cell:cell and cell:matrix interactions)
gel proteins - proteoglycans (holds water for hydration)

Question 3

Is the ECM organized or random?

Answer 3

Organized
- info. for how cells align in tissue
- hold gradient of factors to induce haptotactic migration

Question 4

Explain what durotaxis is.

Answer 4

Durotaxis is cell migration toward higher ECM stiffness (density)
- increased capacity for deposited factors

Question 5

What is the most abundant ECM protein?

Answer 5

Collagen - fibrous protein

Question 6

Describe collagen: structure, amino acid sequence.

Answer 6

collagen has a distinctive repeating amino acid sequence = GLY-X-Y
- gly –> allows tight helical packing
- X and Y –> usually proline and hydroxyl proline

intra/extracellular processing controls triple helix formation (stability)
- central region similar but N- and C- termini vary –> different function

Question 7

What would happen as a result of mutation in collagen gene?

Answer 7

Osteogenesis Imperfecta (OI) = brittle bone disease
- when collagen doesn’t properly form because of mutation –> bone matrix won’t form properly

Question 8

Describe the characteristics of elastin and fibrillin

Answer 8

Elastin - brings stretch
Fibrillin - brings structure and allow for retraction

Question 9

What effect would a mutation in fibrillin have on blood vessels?

Answer 9

Marfan syndrome - large arteries are weakened
- may result in aortic dissection and sudden death (heart can rupture)
- mutation causes decreased flexibility in blood vessels
- diagnosis: heart abnormality

Question 10

Name the two major types of adhesive proteins.

Answer 10

Laminin and Fibronectin
- promote cell:cell and cell:matrix interaction
- soluble plasma fibronectin participates in blood clots

Question 11

What is the amino acid sequence within laminin and fibronectin?

Answer 11

RGD
arginine-glycine-aspartic acid
- recognized by SOME integrin dimers

Question 12

How can RGD peptide be used within chemotherapy? platelet aggregation?

Answer 12

Chemotherapy:
RGD peptide (mimetic) competes with RGD within ECM protein and can inhibit migration
- Lowers metastasis

Platelet aggregation:
RGD peptide inhibits platelet aggregation –> lowers blood clotting

Question 13

How do disintegrins work? What could they be used for?

Answer 13

Disintegrins are 3 mimics of RGD and “occupy” integrins –> blocking site of cell attachment to ECM (competitive)

Application:
- disruption/prevention of cell integrin-ECM interactions
- prevent blood clotting

Question 14

Explain how Eptifibatide works as a drug.

Answer 14

Reduces blood clots by binding to a ring formation to get rid of N- and C- termini.

Question 15

Explain how Tirofiban works as a drug.

Answer 15

Reduces platelet clotting - peptidomimetic
- synthetic
- protein-like chain used to mimic a peptide (competitively bind to integrin –> blocks RGD)

Question 16

What is one major example of a gel protein? What is its function?

Answer 16

Proteoglycans - proteins with sugar residues, covalently linked to R groups
- repeating disaccharide unit: GAG (ex. D-glucuronic acid and N-acetyl- D-galactosamine
- attracts positive ions bc of its negative charge
- ions attract water –> proteoglycans swell
- PG loss –> arthritis

Question 17

What is the basal lamina?

Answer 17

The basement membrane (thin)
- good at separating compartments of tissues
- contains all 3 ECM components (collagen, laminins, proteoglycans)

Question 18

How does Emphysema relate to ECM-degradation?

Answer 18

Caused by uncontrolled release of ECM-degrading enzymes
- ex. matrix metallo-proteases (MMPs) break down collagen; dependent on Ca2+ and Zn 2+
solution: blocking MMPs function

Question 19

How does the ECM, intracellular networks, and cell motility contribute to metastasis?

Answer 19

• MMP degradation of collagen and other matrix proteins
• actin-based cell movement
• integrin-based cell attachment to the ECM

Question 20

Explain how bat-tPA (Activase) works to break fibrin/fibronectin-based blood clots.

Answer 20

Activase is a recombinant human tissue plasminogen activator
- it will activate plasminogen to plasmin
- plasmin will breakdown a fibrin clot