Coupling actin dynamics and membrane dynamics during endocytosis.

A convergence of cellular, genetic and biochemical studies supports the hypothesis that the actin cytoskeleton is coupled to endocytic processes, but the roles played by actin filaments during endocytosis are not yet clear. Recent studies have identified several proteins that may functionally link the endocytic machinery with actin filament dynamics. Three of these proteins, Abp1p, Pan1p and cortactin, are activators of actin assembly nucleated by the Arp2/3 complex, a key regulator of actin assembly in vivo. Two others, intersectin and syndapin, bind N-WASp, a potent activator of actin assembly via the Arp2/3 complex. All of these proteins also bind components of the endocytic machinery, and thus, could coordinately regulate actin assembly and trafficking events. Hip1R, an F-actin-binding protein that associates with clathrin-coated vesicles, may physically link endocytic vesicles to actin filaments. The GTPase dynamin is implicated in modulating actin filaments at specialized actin-rich structures of the cell cortex, suggesting that dynamin may regulate the organization of cortical actin filaments as well as regulate actin dynamics during endocytosis. Finally, myosin VI may generate actin-dependent forces for membrane invagination or vesicle movement during the early stages of endocytosis.