Cell motility Flashcards
why is cell motility important?
aids in:
- wound healing
- chemotaxis
- development
what are Rho GTPases?
family of small signalling G proteins.
- serve as molecular switches of intracellular signal transduction
what molecules are involved in the biochemistry of Rho GTPases?
GAP: GTPase activating factor
GEF: GTPase exchange factor
GDI: GTPase dissociation inhibitor
Effectors: proteins that mediate the cellular effects of a signal transduction pathway
Rho and the cytoskeleton
participates in regulation of the actin cytoskeleton and cell adhesion through specific targets
whay regulates Rho GTPases?
growth factors and G-proteins
what is actin treadmilling?
continuous addition at one end and dissociation from the other end of the G-actin monomers.
- crucial in cell migration, endocytosis and exocytosis
what is the process of actin treadmilling?
a segment of filament ‘moves’ through a stratum or the cytosol. when one end of the filament lengthens, the other shortens.
what regulates actin cytoskeleton contractility?
MLC contracted + MP = relaxed
MLC relaxed + MLCK = contracted
molecules:
- MLC; myosin light chain
- MLCK; myosin light chain kinase
- MP; myosin phosphatase
what does RhoA do?
Ras homolog A: small GTPase protein that has a key role in actin cytoskeleton reorganisation, regulation of cell shape, adhesion and migration and transformation of cellular phenotypes
how is RhoA activated?
activation mediated by guanin nucleotide exchange factors (GEFs) that catalyse exchange of GDP for GTP
describe the RhoA cycle
RHO-GDP + serum, GFs and integrins becomes RHO-GTP.
splits into two pathways:
- actin stabilisation;
+ ROCK + LMK p -> Cof (cofilin; actin regulatory protein that severs actin filaments and accelerates actin assembly)
- actin assembly;
+ diaphanous
describe the regulation of stress fibre formation by RHOA
Rho-GTP –> ROCK –> transition of MP to MP+P which affects the MLC contraction and relaxation equilibrium
overview of the process by which RAC and CDC42 regulare actin polymerisation
- activation of RAC and CDC42
- effector proteins
- actin nucelation and polymerisation
- actin bundling and filament stability
- spatial and temporal regulation
how are RAC and CDC42 activated?
both are activated by guanine nucleotide exhcange factors (GEFs) by extracellular signalling.
GEFs cataluse the exchange of GDP for GTP thereby activating RAC and CDC42
what is the role of the effector proteins?
relay signal to downstream pathways involved in actin polymerisation.
effector proteins include; kinases, phospholipases and scaffolding proteins
what role does RAC and CDC42 play in actin nucelarion and polymerisation?
regulate actin polymerisation through their effectors by promoting formation of actin filaments.
- one key pathway: involves activation of ARP2/3 complex (actin related protein).
this promotes actin nucleation = formation of branched actin networks.
what role does RAC and CDC42 play in actin bundling and filament stability?
activate formins, proteins that facilitate elongation of actin filaments and promote formation of linear actin bundles.
- this contributes to organisation and stability of actin structures within the cell.
how is RAC and CDC42 activity regulated?
- tightly regulated spatially and temporally within the cell.
- ensures that actin polymerisation occurs in coordinated manner in response to specific signals and at precise parts of the cell.
- allowing for processes such as cell migration, adhesion and division.
what is FAK?
FAK: focal adhesion kinase is a key protein involved in regulating cell adhesion, migration and cytoskeletal dynamics.
How does FAK regulate cytoskeletal fluidity?
- activation of signalling pathways
- interaction with cytoskeletal proteins
- regulation of Rho GTPases
- stress fibre formation
- cell migration and spreading
what role does FAK have in regulating Rho GTPases?
- influences activity of Rho, Rac, CDC42 by directly phosphorylating and activating them.
what does Rac do?
- promotes formation of lamellipodia, flat sheet like membrane portrusions rich in branched actin network.
- activated Rac stimulates activationg of WAVE regulatory complex = nucleation of actin filaments and formation of branched actin networks at leading edge of migrating cells.
what is the role of CDC42?
- regulates formation of filopodia, thin, finger like portrusions with lots of actin filaments
- activated CDC42 interacts with proteins to promote actin polymerisation and bundling.
role of small GTPases in actin nucleation and polymerisation?
- regulate via interaction with actin binding proteins and actin nucleation promoting factors (NPFs)
how do Rho GTPases regulate microtubule stability?
- can influence indirectly via downstream effectors
- Rho can = phospho. and inactivation of MAPs which = microtubule destabilisation
- Rho inactivation can = microtuble stability by allowing active stathmin to bind and sequester tubulin dimers, preventing microtubule depolymerisation.
interactions of Rho GTPases and effects
- Rho > Diaphanous > stabilisation
- RAC > p65PAK > elongation
- CDC42 > Par6/PKCy > elongation
how does Rho contribute to cell proliferation?
- regulation of cell cycle
- control of cell cycle checkpoints
- influence on mitotic spindle
- regulation of cell adhesion and migration
- integration with growth factor signalling
how does Rho regulate the cell cycle?
- modulates activity of cyclin-dependent kinases and their regulators.
- RhoA signalling has been shown to promtoe expression of cyclin D1 (regulator of G1/S phases).
- RhoA inhibition = G1 cell cyle arrest
implications of Rho GTPase in cancer
- dysregulation where activation of Rho GTPases = uncontrolled cell proliferation, tumor growth and metastasis.
Rho in tumorigenesis
- inactivated Rho, RAC and CDC42 prevents RAS activation
which Rho GTPases have been found in cancers?
- RhoA; overexpressed in colon, breast, lung carcinomas
- RhoC: overexpressed in breast and pancreatic cancers
- RAC1: overexpressed in breast cancer
- RAC1B: splice variants in breast and colon cancer
- CDC42: overexpressed in breast cancer
- RhoH: rearranged in lymphomas and myelomas
what GFs are present in tumor microenvironment that can activate Rho?
- EGF
- HGF
- LPA
- PDGF
- TGF-b
Rho GTPases in maintenance of normal epithelial polarity
- cell polarity: RhoA, RAC1, CDC42
- cell junctions; RhoA, RAC1
what happens to cell polarity in bening tumours?
loss of polarity and multilayering
- loss of polarity; RAC1, RhoA
- multilayering; RhoE
what do invasive tumors present in cell polarity changes?
- loss of cell junctions: RAC1. RhoA, ROCK
- motility; RhoA, ROCK, RAC1, CDC42
- protease expression; RhoA, RAC1
what is needed for metastasis of a tumor?
- intravasation and extravasation; Rho, ROCK
- vascularisation; RhoC
Rho proteins as therapeutic targets
compounds that:
- inhibit lipid mods; geranylgeranyl transferase inhibitors (inhibit growth of tumor cells invitro & anti tumor efeects in animals)
- prevent GEF action
- inhibit Rho-GTP interaction with effectors
- inhibit effector activity; Y-27632 a ROCK inhibitor that reduces metastatic potential in vivo
what other biological process can Rho GTPases control?
- mitosis
- cytokines
- enzymatic activities; lipid metabolism & ROS
- vesicle trafficking
- phagocytosis
- endosomal transport
- apoptosis
