Lecture 29 - Cell migration Flashcards
Describe the 3 steps of cell migration and the cell at rest
Cell migration is dynamic
At rest - cell has focal adhesions to anchor it to the surface
Step 1 - Lamellopodia protrudes forward
Step 2 - Adhesion (via new focal points) is generated, providing traction and establishing forward movement.
Step 3 - Breakdown of old focal adhesions.
How is the supply of free actin monomers for polymerisation maintained?
Depolymerisation of actin at the back end of the moving cell supplies actin subunits for polymerisation at the front end of the cell.
What is needed for stress fibres to form (besides actin monomers)?
Active integrin is needed to establish focal adhesion.
Activation factors bind to β integrin, also act as a scaffold, allowing the stress fibre to form.
What are the components of focal adhesion?
Abundant in phosphotyrosine.
Two tyrosine kinases colocalise to the focal adhesion. Reciprocal phosphorylation occurs (they phosphorylate each other) and the focal adhesion.
What are FERMs?
band 4.1, Ezrin, Radixin and Moesin (4ERM or FERM)
All attach actin filaments to the cell membrane.
What is talin, and what is its relationship with FERMs?
Talin is a FERM domain containing protein.
Binding of talin to integrin is mutually exclusive to FERM binding to integrin
ie. compete with one another. This allows for competitive inhibition of talin.
Describe talin, and its active/inactive forms
Talin head - contains several FERM domains, bound by an α-helix. Binds to β-integrin when active, as well as focal adhesion kinases and PI-4,5-BP.
Talin rod - linker region (neck) links it to the head.
Talin is normally inactive, rod region masks the head region. Activated by binding to PI-4,5-BP, and dimerising, exposing the β-integrin binding site (FERMs).
It cannot bind inactive β-integrin. Binding to β-integrin stabilises its active form. Very tight binding, high affinity. An equilibrium forward shift occurs when talin binds to integrin.
What are paxillin and vinculin?
They are additional scaffold proteins that bind to talin to enable actin stress fibre formation.
How are actin filaments disassembled?
Disassembly achieved by inhibiting integrin activation.
If the active and inactive form ar ein equilibrium, must be shifted backward, done by phosphorylating the talin binding site on β-integrin by Src. Talin can no longer bind and stabilise β-integrin.
This alone isn’t sufficient.
Moesin displaces talin off of β-integrin, acting as a competitive inhibitor. Moesin must be phosphorylated to do so.
What proteins are involved with the different actin structures?
Stress fibres (or fibers, as a certain yankee likes to call them): Rho protein
Lamellopodia: Rac protein
Fillopodia: cdc42 protein
Differential distribution of the three allows for directionality.
Inactive if bound to GDP, active when bound to GTP,
GEF exchange activity needed for activation.
Active forms bind to effector proteins.
GAP returns them to the inactive form.
GDI prevents binding to GEF.
What happens with moesin dysfunction?
Retraction inability.
What is the effector protein of Rho, and what is its mechanisms?
Rho effector - ROCK
it phosphorylates LIM domain kinase (LIMK) to activate it.
ROCK also binds and phosphorylates myosin light chain phosphatase (MLCK phosphatase), leading to its inactivation.
Another effector protein called mDia1 (formin), binding to Rho activates formin, inducing actin nucleation and elongation.
Activated LIMK can inactivate cofilin, stabilising actin further.
Where are Rac, cdc42, and Rho found within a migrating cell?
Rac and cdc42 are found at the front end. They activate Arp2/Arp3 complex.
Rho is at the rear end.
What activates Rac?
PTEN contributes to PI3 activation, as does PIP3.
PI3 activates Rac.
How can EMT contribute to a mesenchymal-like state?
EMT induced by c-Src contributes to a mesenchymal-like state.
