Cell Signaling and Migration

Erich LidstoneApril 29, 2009

Cell Signaling and Migration

• Importance of cell migration• Major steps of migration• Signaling pathways• Lipid rafts• Adhesion-dependent trafficking

Importance of Cell Migration

• Embryonic development• Chemotaxis• Tissue turnover• Wound healing• Immunity

Cell Migration and the Immune Response

• http://www.youtube.com/watch?v=MgVPLNu_S-w

Importance of Cell Migration

• Pathological processes– Vascular disease– Osteoporosis

• Chronic inflammatory diseases– Rheumatoid arthritis– Multiple sclerosis– Cancer– Mental retardation

Cell Migration Cycle

Polarize, extend protrusion

Migration-promoting event

Adhere to ECM or TM receptor proteins

Move forward over proteins

Disassemble adhesions

Transport necessary proteins to

movement front

Microtubule dynamics promote efficient exploration of the peripheral cytoplasmic domain of a neuronal growth cone. An example of a single dynamically unstable microtubule undergoing assembly followed by disassembly (bottom). Microtubule behavior integrated over 10 minutes in the peripheral growth cone lamellipodium (top).

Forscher Lab, Yale, Department of Molecular, Cellular, and Developmental Biology

Actin Polymerization• FAST-growing “barbed” end• SLOW-growing “pointed” end

• Lamellipodia – branching dendritic network configuration

• Filipodia – long parallel bundles of filaments

• Mediated by Arp2/3 complex• Causes branching of existing

filaments

Movement

• Leading edge moves by “Brownian ratchet”• Uses thermal energy built up by deforming

existing filaments• Does not derive energy directly from actin

polymerization

Cell migration detection

• Akt/PKB-GFP fusion• 4-integrin staining• PTEN-GFP fusion• FRET of GFP-V12Rac

with an effector molecule

Cell Migration Effectors•Profilin•Thymosin•Cofilin•Capping proteins•Cortactin stabilizes branches•Cross-linkers•filamin A•-actinin

Cell Polarization

•Polarity intrinsic to migrating cell•Vesicle trafficking toward the leading edge•Localization of the MTOC and golgi apparatus•PTEN resides at cell margins•PI3K resides at the leading edge•PIP3 production at the leading edge

Protrusion and Adhesion Formation

Integrins and Adhesion in Migration

• Integrins support adhesion to ECM or neighboring cells• Activate migration-related signaling molecules• - and - subunits interact with signaling proteins ,

undergo conformational changes• Integrin clustering• Downstream intracellular signaling– Tyrosine phosphorylation– GTPase activation– Phospholipid biosynthesis– Adhesion complex integrity

Tractional Forces

• Integrins also function as sites of traction• Cell uses them as a substrate over which it

moves during migration• Balance between adhesion at the leading edge

and disassembly at the trailing edge• Junction density• Rate of disassembly

Adhesion Disassembly

• Important at both the front and the rear of the cell

• Front – junctions disassembled as new ones are assembled in the formation of the protrusion

• Rear – junctions must be disassembled to provide materials and release cell from rear direction

Cell Migration Summary

• Migration is promoted• Cell undergoes polarization• Leading edge reconfigures junctions, actin

filaments, and microtubules• Trailing edge undergoes junction disassembly• Cell uses integrins for a combination of

traction and intracellular signaling• Cell reevaluates direction of migration

Arf6 and Microtubules in Adhesion-Dependent Trafficking of Lipid Rafts

• Detailed analysis of adhesion modulation• Lipid raft movement• Cell movement

Cytoskeletal Regulation of Raft Endocytosis

Identification of the Intracellular Compartment

Identification of the Intracellular Compartment

Role of Arf6 in Raft Trafficking

Role of Arf6 in Raft Trafficking

Role of Arf6 in Raft Trafficking

Inhibition of Arf6 Function

Inhibition of Arf6 Function

Adhesion-dependent Activation of Arf6 Promotes Raft Exocytosis

Adhesion-dependent Activation of Arf6 Promotes Raft Exocytosis

Microtubules in Raft Exocytosis

Lipid Raft Trafficking Summary

References