L13 - cell migration + invasion

flashcards

how does cytoskeletal organisation contribute to cell motility

mesenchymal cell migration is promoted by remodelling of actin cytoskeleton

actin cytoskeleton

composed of actin filament (microfilaments) + accessory proteins (RhoGTPase, myosin) crucial for cell structure + cell migration

actin cytoskeleton remodelling

• drives membrane protrusion

• cell shape changes

• maintaining cell-ECM linkages

• cell contraction

cellular regulators of actin cytoskeleton

TGFb1 receptor

how does TBFb1 receptor activation contribute to changes in actin cytoskeleton

downstream pathways of TGF1b receptor drives alterations in Rho GTPase proteins (RhoA, cdc42, Rac1)

leads to disassembly of adherent junctions + remodelling of actin cytoskeleton

Rho GTPase cycle

binary molecular switch

inactive form: Rho bound to GDP

effector proteins drives activation (GTPase activating protein)

active form: Rho bound to GTP

conformational change allows interactions with downstream effectors

cdc42

actin polymerisation, filopodia formation

Rac

actin polymerisation, actin branching (lamellipodia formation)

Rho

drives actin polymerisation, stress fibre formation and contraction

focal adhesions

• multi-protein complex that connect the extracellular matrix to the actin cytoskeleton in cells.

• consists of actin-binding proteins, signalling proteins, structural proteins, integrin receptor (mediated interaction with ECM)

• provides tensile strength, cell shape, facilitates membrane protrusions

focal contact proteins

• FAK - structural support

• Src - signalling platform

• vinculin and talin - actin binding proteins

• paxillin - adaptor protein

integrin receptors

heterodimeric transmembrane proteins that link internal actin cytoskeleton to ECM (alpha + beta chain)

how does coordinated cellular movement occur

• extension - actin polymerisation (addition of G-actin monomers at + end of actin filament) and branching sends out filopodia extensions to local environment

• adhesion - forms focal adhesions that anchor the cell, pull it forward

• translocation - retraction is facilitated by increased tension/contraction of motor proteins (actin, myosin, sliding filament theory)

• de-adhesion - breaking of focal adhesions at the rear of the cell, allowing for forward movement.

actin cytoskeleton organisation at leading edge of migrating cell

filopodia

bundles of parallel actin filaments that form thin, finger-like projections from the cell surface. facilitates membrane protrusions

two actin fibres linked together by actin cross-linking protein

lamellipodium

branched actin filaments that form ruffles facilitated by Arp2/3 complex. push celll membrane outward so it can make attachment sites.

actin cytoskeleton regulators

Arp2/3 - mediates actin branching + actin polymerisation - driven by Rac1 + Cdc42 effector proteins

Rho GTPase

leading edge of migration

presence of focal adhesions (cell-ECM attachments)

collective cell migration

group of cells linked by cell-cell junctions/adhesions migrating in a certain direction with leader cells that drive movement and pull the cell colony in one direction (facilitated by cell-ECM attachments)

types of cell migration

• collective migration - cell-cell + cell-ECM interactions

• mesenchymal cell migration (single cell)- cell-ECM interactions

• amoeboid migration (single cell) - cytoskeletal + membrane protrusion/constriction (don’t interact well with ECM, weaves their way through gaps and holes)

• scaffold cell-dependent migration - dependent on cell-cell interaction, migration along cells

difference between collective and single cell migration

collective: sheets, strands, clusters of cells

single: amoeboid or mesenchymal

mesenchymal vs collective cell migration

both path-generating

collective - retains cadherin cell-cell junctions, only exhibits focal cell-matrix adhesions + ECM degradation in leader cells

amoeboid vs mesenchymal cell migration

mesenchymal migration: path generating by degrading ECM, uses integral focal adhesions to anchor + interact with ECM

amoeboid migration: path finding by constricting their membrane to fit into gaps in ECM, relies on signalling events that shape their membrane. no cell-ECM interactions, less anchorage to ECM.

matrix metalloproteinases (MMPs)

• zinc-dependent proteases secreted by cells into Extracellular space

• secreted as inactive pro-form and activated in extracellular space

• following activation, they cleave ECM proteins or activate latent TGFb1

• regulate migration, invasion, proliferation, differentiation, angiogenesis

the action of MT1-MMP (membrane type) in cancer cells

transmembrane MT1-MMP directly degrades ECM (basal lamina)→ allows cells to invade into underlying tissue layer

indirectly remodels through MMP-2 activation

can activate MMP-2 (soluble) within connective tissue layer (pro-MMP-2 → activated MMP-2) → facilitates ability to migrate and invade surrounding tissue

(TIMP)2

natural inhibitor of MMP activity. levels of TIMP2 regulate MMP2 activation

when TIMP2 levels are low - activation of MMP2

• homodimerisation of MT1-MMP (one subunit acts as binding site, other acts as protease)

• addition of TIMP-2 that recruits pro-MMP-2 to one MT1-MMP subunit

• the free MT1-MMP subunit acts as protease, able to cleave and activate pro-MMP-2

• release of active MMP-2

when TIMP2 levels are high - MMP2 inactive

• TIMP2 binds on both monomers / subunits of MT1-MMP

• TIMP2 inactivates protease

• MT1-MMP unable to cleave and activate MMP2

invadopodia

actin-rich, filopodia-like structures that protrude from the plasma membrane, secretes MMPs and degrades ECM

invadopodia formation

initiation

• cell senses local environment signals (TGFb)

• integrins link to ECM by focal adhesions

assembly

• Arp2/3 recruitment

• drives actin polymerisation - helps membrane protrusion

maturation

• secretion and activation of MMPs

• MT1-MMP sent to tip to degrade ECM