A WASp-VASP complex regulates actin polymerization at the plasma membrane

Proteins of the Wiskott-Aldrich syndrome and Ena/VASP families both play es sential functions in the regulation of actin dynamics at the cell leading e dge. However, possibilities of functional interplay between members of thes e two families have not been addressed. Here we show that, in hemopoietic c ells, recruitment of the C-terminal VCA (Verprolin homology, Cofilin homolo gy, Acidic) domain of WASp at the plasma membrane by a ligand technique usi ng rapamycin as an intermediate is not sufficient to elicit efficient Arp2/ 3 complex-mediated actin polymerization. Other domains of WASp, in particul ar the proline-rich domain, are required for the formation of actin-rich st ructures. An in vitro analysis demonstrates that the proIine-rich domain of WASp binds VASP with an affinity of similar to 10(6) M-1. In addition, WAS p and VASP both accumulate in actin-rich phagocytic caps. Finally, in a rec onstituted motility medium, VASP enhances actin-based propulsion of WASp-co ated beads in a fashion reminiscent of its effect on Listeria movement. We propose that VASP and WASp cooperation is essential in stimulating actin as sembly and membrane protrusion at the leading edge.