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MCB > Adhesive Interactions Between Cells > Flashcards

Adhesive Interactions Between Cells Flashcards

1
Q

What is fibronectin?

A
  • an ECM protein of connective ECM
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2
Q

What is the role of transglutaminase with fibronectin?

A

Cross-links fibronectin dimers into multimers that form fibrils around cells

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3
Q

What is the role of the RGD motif in fibronectin?

A
  • RDG motif is essential for cells to attach to fibronectin or to cell-binding fragment of fibronectin
  • Exposed position of RGD makes it accessible for binding to cell surface receptors
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4
Q

How were receptors for ECM proteins found?

A
  • Made affinity column from ECM protein fragment and identify ligand
  • Measure cell attachment to purified ECM proteins and develop monoclonal antibodies which block attachment
  • autoantibodies that recognise antigens in cell membranes used to identify protein target of antibodies
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5
Q

What proteins are receptors for ECM proteins?

A

Integrins

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6
Q

What is the structure of integrins?

A
  • Heterodimers with alpha and beta subunits
  • Each subunit has varioud exrtracellular domains as well as s single TM domain and a short cytoplasmic domain
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7
Q

What do the extracellular domains of integrins bind to for function?

A

Divalent ions

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8
Q

What is the function of integrins?

A

Bind ECM proteins outside the cell and link to the actin cytoskeleton inside the cell

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9
Q

How are the alpha and beta chains of integrins bound together?

A

Held together by non-covalent bonds

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10
Q

How can integrins bind different ECM proteins?

A

Via different heterodimers

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11
Q

Where is the ECM binding cleft of RGD-binding integrins?

A

Between alpha and beta subunits

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12
Q

How is the ECM connected to the cytoskeleton through integrins?

A
  • Connects ECM through TM helix
  • Through TM integrin to FAK to cytoskeleton
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13
Q

What happens when Talin is recruited?

A
  • Other intracellular cytoskeletal and signalling proteins are recruited to form a focal adhesion
  • This activates intracellular kinase cascades and other 2nd messengers and physically links the integrin to cytoskeleton
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14
Q

How do active integrins set up intracellular signals?

A
  • Chemical signalling via intracellular kinases and 2nd messengers
  • Responses by mechanical forces are exerted through the physical binding of ECM protein to integrin and integrin to cytoskeleton
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15
Q

How can intracellular kinases or 2nd messengers be activated by integrins?

A
  • Either through activated proteins that bind to Talin or Kindlin
  • Or by proteins that bind to the integrin alpha subunit cytoplasmic domain
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16
Q

What is laminin a major component of?

A
  • Basement membrane
  • focal adhesions
  • Hemidesmosome
17
Q

What are the 4 laminin binding integrins?

A
  • α3β1
  • α6β1
  • α7β1
  • α6β4
18
Q

Where are laminin binding integrins α3β1, α6β1, and α7β1 found?

A

In focal adhesions and linked to the cytoskeleton

19
Q

Where is α6β4 laminin binding integrin found?

A

In hemidesmosomes and linked to keratin intermediate filaments

20
Q

What are genetic skin blistering disorders called?

A

Epidermolysis bullosa

21
Q

What causes epidermolysis bullosa?

A
  • Mutations in laminin chains or alpha6 or beta4 integrin subunits that disrupt hemidesmosomes
  • This leads to epithelial cell detachment and chronic skin blisters
22
Q

What is the function of the dytroglycan complex?

A
  • Cell attachment to laminin in the basement membrane of skeletal muscle
  • Withstands changes in mechanical force as muscles contract and relax
  • Allows continuous association of the muscle with surrounding basement membrane
23
Q

What causes musclar dystrophy?

A

Mutations in components of dystroglycan complex

24
Q

How do mutations in components of dystroglycan complex cause musclar dystrophy?

A
  • Disrupts integrity of complex
  • Results in loss of mechanical force balance and loss of link to cytoskeleton and signalling pathways
  • Causes cell death and disrupts muscle tissue
25
Q

When the loosening of integrins to matrix components occurs what happens to molecular signalling complexes?

A

They fall apart on either side of membrane

26
Q

Concentration of what in extracellular medium affects the binding of integrins to matrix ligands?

A

Mg2+ and Ca2+

27
Q

What disease does a lack of alpha subunits of integrins cause?

A

Muscular dystrophy

28
Q

What disease does a lack of beta 2 subunits of integrins cause?

A

Leukocyte adhesion deficiency

29
Q

What does disruption of beta3 subunits of integrins cause?

A

Defective clotting and excessive bleeding

30
Q

What happens to integrin structure when they are inactive?

A
  • External segments of the integrin dimer are folded together in a compact structure that cannot bind matrix proteins
  • Cytoplasmic tails hooked together to prevent interaction with cytoskeletal linker proteins
31
Q

What happens to the structure of integrins when active?

A
  • 2 subunits are unhooked at the membrane to expose intracellular binding sites for cytoplasmic adaptor proteins
  • External domains unfold and extend to expose high affinity matrix binding site
32
Q

How can activation of integrin proteins occur?

A
  • Outside in activation
  • Inside out activation
33
Q

How does outside in activation of integrins occur?

A
  • Binding of an external matrix protein can drive integrins into high affinity active state
  • Binding sites for cytoplasmic adaptor proteins are exposed on tail of beta chain
  • Adaptor binding leads to actin filament attachment
  • Force can be applied at point of cell attachment
34
Q

How does inside out activation of integrins occur?

A
  • Intracellular signals stimulate proteins to interact with beta chain and compete with alpha chain of integrin for its binding site
  • When protein binds it blocks beta chain from linking
  • Alpha and beta chains spring apart
35
Q

Give an example of a cytoplasmic adaptor protein for integrin

A

Talin

36
Q

How can integrins form strong adhesions?

A
  • Once activated integrins cluster together to make dense plaque so many integrins are anchored to cytoskeletal filaments
37
Q

What does assembly of mature cell-matrix junctional complexes rely on?

A

Recruitment of dozens of scaffolding and signalling proteins

38
Q

How can the Ras/MAP kinase pathway be activated?

A
  • Either through conventional cell signalling
  • or through integrins

Cells usually need both to proliferate

39
Q

How can Talin help organise actin filaments?

A
  • Has a binding site for actin regulatory protein viculin
  • these binding sites are exposed when domains are unfolded by unstretching talin
  • When actin is pulled it unstretches Talin and exposes vinculin binding sites to recruit and organise additional actin filaments

MCB (28 decks)

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