Figure 2.

The Rap GTPases are master regulators of actin dynamics, cell morphology, cell polarity and integrin-mediated adhesion. The Rap GTPases are activated subsequent to the binding of chemokines to their receptors or activated integrins to their ligands. The active GTP-bound form of Rap binds effector proteins that promote integrin activation, actin polymerization and membrane protrusion, as well as activation of the Pyk2 and FAK tyrosine kinases, which modulate cell spreading, adhesion and migration. Rap-GTP also plays a key role in establishing cell polarity and may direct membrane vesicles to the leading edge of the cell. See text for details. MTOC, microtubule-organizing center.