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Cell and Molecular > L22 - Extracellular Matrix, Integrins and Cell Migration > Flashcards

L22 - Extracellular Matrix, Integrins and Cell Migration Flashcards

1
Q

What components make up the ECM?

A

Fibronectin
Laminin
Collagen
Elastin

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2
Q

What is fibronectin?

A

Large protein

Secreted into extracellular matrix

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3
Q

What are the domains of fibronectin?

A

Heparin binding
Cell binding
Collagen binding
Self-association

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4
Q

What is laminin?

A

Large protein

Trimer

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5
Q

What are domains of laminin?

A

Integrin binding
Self-assembly
Perlecan binding
Coiled coil domain

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6
Q

What do integrins form?

A

Form heterodimers

Each monomer has a single transmembrane domain

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7
Q

What is the extracellular structure of integrins?

A

Cysteine rich domains
- Form disulphide bridges
- Alpha subunit is cleaved and held together by disulphide bridges
Matrix binding domain at amino end
- Binds to ECM and divalent cations (Mg and Ca)
- Activating function

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8
Q

What is the intracellular structure of integrins?

A

Talin, filamen and a-actin binding domain at carboxyl end

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9
Q

What is the composition of integrins?

A

18 α and 8 β subtypes

24 variants

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10
Q

What do integrins interact with?

A

The cytoskeleton

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11
Q

How do integrins bind?

A

Binding is a two-way process
Activated both intracellularly and extracellularly

Outside in activation – strong ligand binding

  • Inactive integrin
  • Extracellular domain folded up in an inactive state – not binding to ECM
  • If they do bind to ECM the conformation changes

Inside out activation – strong talin binding

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12
Q

What are FAKs?

A

Focal adhesion kinases

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13
Q

When integrin binds to the ECM how does it activate FAK?

A
  1. Fibronectin interacts with integrin extracellularly
  2. Transduced intracellularly resulting in activation of FAK
  3. Results in tyrosine phosphorylation – recruitment/activation of multiple tyrosine kinases
  4. Results in polymerization of actin
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14
Q

What is FAK activated by?

A

Activated on formation of adhesions

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15
Q

What are FAKs important for?

A

Recycling focal adhesions to enable migration

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16
Q

What is attachment dependent cell death?

A

If some cell types are not adhered to appropriate substrate they will die
Act in anoikis - attachment-dependent cell death

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17
Q

How is mammalian cell motility brought about?

A

Actin based

18
Q

What is the role of lamellipodium in cell motility?

A

The cell moves its self along by extending its lamellipodium in the direction of migration

  • As cell moves it loses and create new adhesions
    • Actin reorganisation
  • Front membrane is being pushed out by actin polymerisation
    • Actin polymerisation at plus end protrudes lamellipodium
    • Action fibred are being added to at the leading edge
19
Q

Actin forms a cortex in the cell which aids in?

A

Membrane tension

20
Q

Why is a motile cell highly polarised?

A

Plus and minus end
Actin is continually recycled
Membranes are also being moved

21
Q

What molecules helps in assisted tail retraction?

A

Myosin II

22
Q

What two processes occur at the leading edge?

A

Ruffling

Actin transport

23
Q

What is the role of ruffling at the leading edge?

A

Active fibres pushing up in different directions

Involved in sensing guidance cues

24
Q

What is the role of actin transport at the leading edge?

A

Pushes out the membrane at the front

Cytochalasin binds to the plus end of actin filament and blocks more actin being added

25
Q

What is the APR complex involved in?

A

Actin polymerisation

26
Q

What is the APR complex made up of?

A

Made up of multiple proteins – Arp2 and Arp3

- Resemble the structure of actin

27
Q

What is the role of the APR complex?

A

Nucleation of actin monomers to form a filament

  1. Arp2 and Arp3 bind to form a complex
  2. This complex binds to actin monomers on the minus end
  3. New actin monomers are then added to the plus end
28
Q

What does Rac stimulate?

A

The formation of Arp2/3 complex

This then enables the cell to move forward – drives leading edge

29
Q

What are important factor of focal contacts and motility?

A

Focal contact turnover, actin interaction and microtubules are all important

30
Q

Why does recycling occur throughout the entire length of the cell?

A

Brings adhesion molecules to the front of the cell

31
Q

What is the role of focal adhesions maturing?

A

Roles for action binding proteins, small G-proteins, myosin generating force

32
Q

What are the two categories of focal adhesion?

A

Low density
- Rac1 kinase and cdcc42 kinase dependent
High density
- RhoA and actin-myosin interaction dependent

33
Q

What focal adhesions are found at the front of the cell?

A

Low density adhesions immobile

Right at the leading edge

34
Q

What focal adhesions are found at the back of the cell?

A

High density adhesions slide in the membrane

35
Q

Why do extracellular signals interact with the cytoskeleton?

A

To direct movement

36
Q

What are diffusible signals for motility?

A

Netrins

37
Q

What are insoluble signals for motility?

A

CAMs

ECM

38
Q

What are fibronectin trails?

A

Fibronectin is laid down by migratory cells for other cells to follow

39
Q

What inhibits migration by fibronectin trails?

A

Antibodies to fibronectin

Injection of arginine, glycine and asparagine

40
Q

What happens all around the cell during migration?

A

Membrane endocytosis
Deposited at the leading edge where exocytosis occurs
- Net membrane addition

41
Q

If the membrane is fixed by focal contacts the cell will?

A

Move forward

42
Q

What other roles does endocytosis have in motility?

A

Shaping chemotactic gradients
- Cell tries to reach towards higher level of signal
- To form gradient often have endocytosis of ligand
Confining signalling in migratory cells
- Confine activation to leading edge by endocytosis
Modulation of adhesive contacts and ECM
- Recycles by endocytosis to release adhesion
Polarisation of endocytosis

Cell and Molecular (24 decks)

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