Cell-Matrix Adhesion Flashcards
What is fibronectin
Large glycoprotein
Helps organise ECM and cell attachment
How is fibronectin structured?
Multiple type I-III repair domains in a beads on a string conformation
What is the role of fibronectin molecules in blood clotting?
After blood clot forms, fibrin clot forms.
FIbronectin forms bridges between fibrin strands.
What cell adheres to fibronectin in wound healing?
fibroblast
Fibroblasts lead to granular tissue formation in wound healing.
What does the granular tissue matrix convert fibroblasts to?
And what is their fucntion?
myofibroblasts
Contract which help pull the wound edges closer together
What happens to fibronectin conformation under applied force?
FN Type 3 has no disulphide bonds so unfolds under applied force
Why does T3 fibronectin unfold?
Allows FN molecules to bind to each other
When a cell (like a fibroblast) starts to move, where does fibronectin get deposited?
at the leading edge
What are the areas of a moving cell in which fibronectin is highly concentrated called?
focal complexes
What happens to focal complexes when actin filaments attach?
Focal complexes become focal adhesions
How does tensile strength cause formation of fibronectin fibrils?
Tensile strength causes unfolding of fibronectin to reveal new sites.
Other fibronectins bind to these newly exposed sites.
What is the role of integrins in focal complexes/adhesions?
Integrins act as a bridge between fibronectin (ECM compomnent) and the cell
What are integrins?
Integrins are a family of transmembrane proteins that function as cell surface receptors.
What is the role of integrin heterodimers in hemidesmosomes?
Integrin mediates the attachment of the epithelial cell to the basement membrane.
Integrin binds to laminin on BM.
How do hemidesmosomal integrins aid in mediating attachment of epithelial cell to BM?
Creates stable bridge between ECM and epithelial cell.
What does intracellular and extracellular portion of hemidesmosomal integrin bind?
Extracellular domain binds laminin.
Intracellular domain binds intermediate filaments cytoskeleton.
Are hemidesmosomes static or dynamic?
usually static, but become dynamic when endothelial cells need to move (like to a wound).
How many subunits does integrin have?
Two
Alpha and beta
Not covalently attached
what is the structure of intracellular domain of integrin?
C terminal tails (on both subunits)
Which ions are important in the specificity of binding of integrins to ECM ligands?
calcium and magnesium ions
Do all human integrins bind to actin filaments?
23 do, 1 doesn’t
What does alpha6beta4 integrin bind to?
laminin
Where is alpha5beta4 integrin found?
hemidesmosomes
Which integrin beta subunit has a large intracellular domain?
beta4
(in hemidesmosomes) Integrin beta4 binds to keratin intermediate filament through which two cytoskeletal adapter proteins?
plectin and BPAG1
(both Plakin protein family)
What other transmembrane component is alongside integrin in hemidesmosomes?
BPAG2
(collagen 17)
Which two components make up the outer plaque structure of hemidesmosomes?
integrin and collagen 17
Which two components make up the inner plaque structure of hemidesmosomes?
Plectin and BPAG1
What do alpha6beta4 integrin and collagen 17 bind to on the ECM’s basement membrane?
Laminin 332
Where is laminin 332 found?
In the lamina densa in basement membrane
What connects the laminin 332 in the lamina densa to the connective tissue in the dermis layer?
collagen VII
Which integrin is expressed on the surface of T cells?
LFA1
(Lymphocyte function-associated antigen 1)
What does LFA1 on T cell bind to when it encounters an APC?
LFA1 weakly binds to ICAM on APC
Under what situation does LFA1 on T cell bind STRONGLY to ICAM on APC?
If T cell receptor recognises an antigen on MHC of APC.
When do rolling leukocytes encounter Platelet Activating Factor (PAF) ?
From endothelial cells when they reach closer to the site of inflammation
What does Platelet Activating Factor (PAF) on endothelial cells trigger in leukocytes?
Outside-in signalling
activation of LFA1(leukocyte function associated antigen 1) integrin.
What does strong LFA1 integrin (on T cell) and ICAM1 (on endothelial cell) lead to during leukocyte recruitment?
Leads to extravasation of T cells from blood stream to site of inflammation.
Difference in structure between active and inactive integrins ?
when inactive they are compact and the cytoplasmic tails are locked together
Which type of integrin activation involves Talin?
Inside-out signalling
How does Talin activate integrin during inside-out signalling?
Talin binds to cytoplasmic domains (inactive conformation).
Unhooks the cytoplasmic domain.
Causes unfolding of extracellular domains.
What do the C terminal and N terminal of Talin bind to?
C terminal: binds integrin
N-terminal: binds actin filaments
What actin regulatory protein can bind to Talin (in areas that are hidden when Talin is folded)?
vinculin
Which integrin is important in the development of blood clots?
alpha2beta3 integrin
Which integrin does thombrin activate, and which molecules mediate this activation?
Integrin alpha2beta3
Mediated by Rap1, RIAM, Talin, kindlin.
What happens to platelets as a result of integrin alpha2beta3 activation?
the platelets become sticky
What type of blood clots are created during wound healing?
insoluble blood clots
As well as being transmembrane receptors for ECM proteins, integrins are also signalling molecules/environmental sensors.
What type of signals do integrins transduce?
- tissue stiffness
- matrix composition
- presence of growth factors
Where Focal Adhesion Kinase (FAK) phosphorylated and what does it do?
FAK is phosphorylated at focal adhesion sites.
FAK creates docking sites for RhoGTPases like RhoA.
This leads to actin filaments becoming contractile stress fibres.
What recruits FAK to focal contacts?
Talin
What is anchorage dependence?
Where cells need to be attached to ECM in order to survive
Can cells survive when attached to ECM in only one patch?
NO.
Must be distributed in multiple spots.
