Implicated in both actin filament depolymerization and polymerization. May enhance chemotaxis by promoting cofilin-dependent actin assembly at cell leading edges. Interacts with cofilin and F-actin. Localizes to dynamic regions of the cell cortex that are enriched in filamentous actin and rapidly redistributes to newly formed cortical protrusions. Impairment of growth, macropinocytosis, phagocytosis and movement. Prolonged cytokinesis with exaggerated cortical protrusions and production of multinucleate cells. Suppresses the impaired F-actin assembly and defective chemotaxis characteristic of cells lacking the sodium/hydrogen exchanger nhe1. Belongs to the WD repeat AIP1 family.