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BMS 242 - Advanced Cell and Molecular > Extracellular matrix integrins and cell migration > Flashcards

Extracellular matrix integrins and cell migration Flashcards

1
Q

Where is extracellular matrix secreted from?

A

Cells

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2
Q

What components make up the ECM?

A

Laminin
Collegen
Elastin

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3
Q

What are fibronectins?

A

Large, secreted proteins

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4
Q

What domains do fibronectins have?

A
  • Heparin binding domain - interact with cells
  • Collagen binding domain
  • Self-association domain
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5
Q

What is the structure of laminin?

A

Trimer

Many domains

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6
Q

What does laminin interact with at the C terminal domain?

A
  • Intergrins
  • Perlecan
  • Dystroglycan
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7
Q

What is the structure of integrins?

A
  • Alpha and beta subunits
  • Each monomer has a single transmembrane domain
  • Alpha subunit is cleaved and held together by disulphide bonds
  • Extracellular cysteine rich domain
  • Matrix binding domain at the amino terminus
  • Intracellular component is anchored to actin
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8
Q

How do intergrins interact?

A

Heterodimerically

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9
Q

In integrins, what do extracellular cysteines allow?

A
  • The formation of disulphide bridges

- To interact with different extracellular components

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10
Q

How do integrins interact with actin?

A

Using talin and vinculin

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11
Q

What does the amino terminus of integrins bind to?

What does this result in?

A

The ECM and divalent cations (Ca2+, Mg2+)

Results in activation of the integrin and activates intracellular signalling pathways that influence the behaviour of the cell

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12
Q

How many alpha and beta subunits are there of integrins?

How can they bind?

A

18 subtypes

Can be paired in many combinations - to make 24 varients

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13
Q

How are integrins acitvated?

A

In 2 ways:

1) Binding to the ECM
- Causing a conformational change (unfolding of extracellular domain)
- Become activated
- Activate the intracellular domain to bind to talin

2) If integrin interacts with intracellular domain - causes unfolding of the extracellular domain

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14
Q

What are FAKs?

A

Focal adhesion kinases

A type of tyrosine kinase

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15
Q

How are FAKs activated?

What do activated FAKs do?

A

Activated by integrin binding to the ECM, on the foramtion of adhesions

When activated - FAK phosphorylates tyrosine residues - docking regions for other proteins

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16
Q

What is the typical pathway that actin is polymerised?

A
  • Fibronectin
  • Integrin (extracellular)
  • FAK (in the cytoplasm)
  • Tyrosine phosphorylation (localised in the area of focal adhesion)
  • Actin fibre polymerisation
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17
Q

What are focal adhesions?

A
  • Protein complexes where the cell connects to the ECM

- Where mechanical force and regulatory signals are transmitted between the cytoplasm and the cell

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18
Q

What are FAKs involved with?

A
  • MIGRATION (are made and formed)

- ANOIKIS (attachment-dependant cell death)

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19
Q

What do FAKs bind to?

A

The cytosolic tail of integrin, with the assistance of other proteins

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20
Q

Where to integrins cluster to?

What does this trigger?

A

The sites of the matrix contact

This triggers the assembly of cell-matrix junctions (focal adhesions)

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21
Q

What happens to cells if they are not attached to a substrate?

A

They die

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22
Q

What is motility linked with?

A

Adhesion

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23
Q

What forms the basis of cell motility in mammals?

24
Q

What is the leading edge of a cell?

What is present in the leading edge and why?

A

The direction that the cell is moving in

Actin - pushes the cell forwards

25
Q

Where are microtubules present in the cell?

A

In the centre

26
Q

What are lamellipodium?

A

Actin projection at the leading edges

27
Q

What happens to focal adhesions as the cell migrates?

A

The focal adhesions are recycled from the back of the cell to the front

28
Q

What is the actin cortex?

What does it provide to the cell?

A

Skeleton underneath the membrane (surrounding the whole cell)

Maintains cell shape as the cell migrates
Prevents the cell becoming flat
Gives the migrating cell strength

29
Q

How is the migrating cell polarised?

A

Different things happening at the front and rear:

  • Recycling of focal adhesions
  • Flow of actin to the front of the cell
30
Q

What is ruffling of the leading edge and what is it important for?

A
  • Actin polymerisation pushing the membrane up in different directions
  • Important in sensing guidance cues
31
Q

How is actin attached to the lamellipodia?

A

At the + end (distal to the cell)

32
Q

What happens at the - end of lemellipodia?

A

Actin fillaments are removed and recycled to the + end

33
Q

What is cytochalasin B?

A

A drug which binds to the + end of actin and prevents any further actin polymerisation

Can be used to study actin polymerisation

34
Q

What complex is important in actin polymerisation?

A

The ARP complex

35
Q

What is the structure of the ARP complex?

A

Made of many proteins (including Arp2 and Arp3)

36
Q

What do Arp2 and Arp3 do?

A

Nucleate actin monomers by binding at the minus end and allowing actin to polymerise

37
Q

What do Arp2 and Arp3 resemble?

38
Q

What activates ARP complex activity? How?

A

Rac kinase - initiates the formation of ARP complexes

39
Q

What is the result of Rac kinase?

A

Increase in formation of ARP complexes
Increase nucleation of actin filaments
Drive the leading edge forwards

40
Q

How do ARP complexes form a branched networks?

What does this provide to the cell?

A

ARP complexes can bind to existing actin filaments

Provides stability and strength and pushes the leading edge forwards

41
Q

What happens to focal adhesions when the cell migrates?

A
  • Focal adhesions that interact with the ECM at the rear of the cell are broken
  • Recycled to the leading edge to initiate new binding
42
Q

Where in the migrating cell is stable adhesion?

A

At the leading edge

43
Q

Where in the migrating cell is sliding adhesion?

A

At the rear

44
Q

How are focal adhesions different?

A

They are all made of different molecules

Some are stable, whereas some are transient

45
Q

What are the 2 different categories of focal adhesions?

What are the differences between the 2?

A

1) Low density
- Found around the leading edge
- Immobile (fixed within the cell)

2) High density
- Compacted
- Found away from the leading edge
- Can move within the membrane

46
Q

What are low density focal adhesions?

A

rac1

cdc42-dependant

47
Q

What are high density focal adhesions?

A

RhoA

Actin-myosin interaction-dependant

48
Q

What are 3 signals that are used for motility?

A

1) Soluble/diffusible
2) Insoluble
3) Fibronectin

49
Q

What are the soluble signals used for motility and how are they used?

A

Netrins

Released from an attraction point and diffuse away to attract cells to that point

50
Q

What are the insoluble signals used for motility and how are they used?

A
  • CAMs and components of the ECM
  • Inserted into a tissue or the ECM and don’t diffuse away
  • Act as contact attractants
51
Q

Where is fibronectin secreted from?

What is this secreted fibronetin used for?

A

Secreted by migratory cells

To lay down a trail which is followed by other migratory cells

52
Q

What 2 things inhibit fibronectin dependant migration?

A

1) Antibodies binding to fibronectin

2) RGD motif injection into migratory cels

53
Q

What is the RGD motif and why does injecting it into migratory cells block fibronectin dependant migration?

A

Arginine - Glycine - Asparagine

It is important for fibronectin dependant migration - if artificially administered, it ‘swamps’ the binding site

54
Q

What are 5 roles of endocytosis in motility?

A

1) Shaping chemotactic gradients
2) Membrane cycling
3) Confining signalling
4) Modulation of adhesive contact and ECM
5) Polarisation of endocytosis

55
Q

What happens to the membrane of the cell when it is migrating?

A
  • More membrane made to accommodate movement

- Membrane endocytosis around the cell and deposition (exocytosis) at the leading edge

56
Q

What must happen to the membrane for the cell to move forwards?

A

It must be fixed by focal contacts to the ECM

57
Q

What do integrins facilitate?

How?

A

Cell to extracellular matrix binding

Bind to components of the ECM, such as laminin and fibronectin

Bind to actin

BMS 242 - Advanced Cell and Molecular (24 decks)

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