lecture 10 Flashcards
what happens when cell migration goes wrong
metastatic cancer
how do cells move?
mesenchymal cell migration, amoeboid cell migration
what are both migrations driven by
lamellipodial protrusions at leading edge
what is diff b/w ameboid and mesenchymal
ameboid is less adhesive
how do cells bind to extracellular env.
integrin receptors / extracellular matrix
descibe mesenchymal migration
fibroblasts; adhesion, harder to move, stuck to environment
describe ameboid migration
immune cells; move quicker, slip through to chase down pathogens
2 main ways for cells to move
lamellipodia (high or low adhesion), blebbing migration
step 1 of cell moving
adhere to surface (integrin receptors)
step 2 of cell moving
flatten and spread (integrin, actomyosin)
step 3 of cell moving
become polarized (tell front from back; microtubules)
step 4 of cell moving
generate protrusions (actin filaments; facilitates polarization)
step 5 of cell moving
form new adhesions, release old ones (combo of all 3)
step 6 of cell moving
directionally migrate intracellular signaling
how are epithelial cells that line surface anchored to underlying matrix
integrin adhesions
what happens if you disrupt integrin adhesions
would wipe cells right off dermis
what is cell matrix adhesion mediated by
integrin receptors
what happens when u see fiber laying across cell
it’s bound by integrins entire length of filament
what are integrins
transmembrane heterodimers that link ECM to cytoskeleton
what is collagen
glue that holds tissue and organs together
what binds to collagen fiber
integrin receptors
on cytoplasmic face, what connects to adhesions
actomyosin filaments
what does this mean for contractility
as actomyosin force is applied, attached to integrin, so pulling force is gonna be applied to outside env. (ECM)
what does alpha subunit do
participates in adhesion; facilitates adheion strength
what does beta subunit do
connects complex to actin filaments inside cell
vinculin
force sensor that triggers signaling
what does actin bind to
vinculin, talin (connects everything to integrin)
what does this machinery represent
continuous mechanical connection from ECM (outside) to cytoskeleton (inside)
describe integrin activation
can be off or on
describe integrin at surface
active
what happens once integrin active
at cell surface, binds to matrix and talin
what happens through talin
binds to vinculin (adaptor protein that links integrin complex to actin filaments)
what happens when you get force/contractility
positive feedback loop, more integrins, more actomyosin filaments, bigger+stronger adhesions, more effective force
does this positive feedback loop happen in fibroblasts or immune cells
fibroblasts
what happens when integrin binds to talin
talin recriuts vinculin
how is force sensed by adhesion complexes
talin
what is talin
mechanosenser responsible for detecting pulling force on connecitions
what happens when it detects force
trigger that regruits more actomyosin contractility in positive fedback loop, to ramp up contractility to allow adhesions to grow and strengthenh
how does protein sense force
force causes change in confomration of protein, revealing a hidden binding site
what happens when they pull on talin
talin unfolds (force dependent conformational chaneg)w
what happens when talin unfolds
reveals binding site for vinculin
what happens when vinculin is binded
joins talin; more actomyosin filaments come w/ vinculin –> positive feedback loop controlled by talin
where does integrin recruit intracellular signaling proteins
sites of cell-matrix adhesion
what gives increased contractility that helps in adhesion formation
rhoA activaetes ROCK, phosphorylates myosn light chain , activates myosin 2 protein
what’s happening at bottom/back of cell
adhesions falling apart, disassembed, recycled into cytoplasmw
what wud happen if cell douln’t dissasmeble adhesions in the back
cell would get stuck;
what does myosin contraction and cell adhesoin allow
allows cell to pull itself forward
what happens if nothing to anchor the netowrk
not gonna be able to push network forward, rather it pushes it back (cuz it’s not yet attached to actomyosin machinery)
what happens when pos feedback loop
vinculin & talin grab actin filaments, harness contractile power to anchor filaments, now it can actually push it forward
retrograde flow
if filaments aren’t anchored, netowrk is pushed backward
what happens if filaments aren’t anchored
network pushed backward
what happens if filaments anchored
resist backward pushing force, exert force to make cell migration
what happens if cell bound to integrin
migrates; does work
what happens when new adheson forms
small, low contractility; need massive increase in contractility (vinculin, talin)
what needs to happen for recycling
not bound to talin; detach from it
what happens if rhoA is inhibited
contractility drops, breaks positive feedback loop, everything falls apart
what happens if vinculin mutated
you’d never get positive feedback loop initiated in first place
what happens if talin mutated
binding site always exposed; positive feedback all the time
role of myosin
help unfold talin, and strengthen adhesions through additional vinculin binding
what happens when integrins bind to ECM
talin unfolded, positive feedback loop for actomyosin contractility
what is any movement in ECM from
contractile forces in cell
what gives cell ability to propel itself forward
force is being transmitted from actomyosin filaments in cytoplasm, connected to alpha beta integrins via vinculin-talin, those integrins are connected to extracellular matrix
describe actin-integrin
continuous mechanical connection that allows cellular forces to pull on those extracellular fibers to allow for productive cell migration
2 major outcomes of force coupling
protrusion, traction forces against extracellular env.
what motor protein delivers cargo at MT tracks
kinesin 1; takes vesicles at golgi to plus ends
describe mesencyhmal cell migration
rac1 activates arp2/3, leads to actin polymerization, causes lamellipodial protrusion
what happens if RAC1 arp2/3 pathway is active W/O coupled at adhesions
no protrusion, just retrograde flow
what happene whenever rac1 activated
lamellipodia is formed
is contractility at leading or lagging edge
leading edge; adhesions
describe contractility at back of cell
RhoA, contractile forces that allow leading edge to contract and keep up w/ front
what contracts in the back?
actomyosin filaments that are attached to plasma membrane, as they are acted on by mosin 2 they become more tightly cross-linked, the spaces shrink, just continuously pulls plasma membrane forward
what is front rhoA contractility
plugs talin via vinculin to strengthen adhesions
what is back rhoA stuff
no adhesions; just contracting the actomyosin network underneath plasma membrane to contract the rear and allow it to move in synch w/ front of cell
what allows for continuous lamellipodia and cell migration
cofilin, at back of lamellipodial network (still front of cell), recycles monomers
describe how back of cell pulls itself forward
rhoA –> ROCK –> myosin 2
how does back of cell keep up w/ front
contraction in back
what does rhoA control
actomyosin contraction
what does rac1 control
lamellipodia (arp 2/3)
what does high contractility mean
low lamellipodia formation
what separates front from back of cell
cross talk b/w rac and rho
what do we need at front of cell fo r adhesion formation
rhoA
what does Rac1 do
activates arp2/3 for branched actin networks, turns on Pak, turns off actomyosin stressfibers
what does rac1 do to rhoA in front
suppresses rhoA response
describe cross-talk
chemoattractant binds GPCRs –> activate rac1 –> turn off rhoA
what happens as you get farther from cell
rac1 suppresses rhoA less and less; rhoA does actomyosin contractility more at the back
what is blebs
increase pressure to cause protrusion (no actin polymreization)
do blebs have actin
nah; just pressure driven
