Acts as a nucleation-promoting factor at the surface of endosomes, where it recruits and activates the Arp2/3 complex to induce actin polymerization, playing a key role in the fission of tubules that serve as transport intermediates during endosome sorting. Component of the WASH complex. The VCA (verprolin, cofilin, acidic) domain promotes actin polymerization by the Arp2/3 complex in vitro. Belongs to the WASH1 family.