Acts as a component of the WASH core complex that functions as a nucleation-promoting factor (NPF) 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 (PubMed:19922875, PubMed:20498093). May be involved in axonal outgrowth. Involved in cellular localization of ADRB2 (PubMed:23085491). Involved in cellular trafficking of BLOC-1 complex cargos such as ATP7A and VAMP7 (PubMed:23676666). {ECO:0000269|PubMed:19922875, ECO:0000269|PubMed:20833645, ECO:0000269|PubMed:23085491, ECO:0000269|PubMed:23676666}. This is the function of ENSG00000164961 (WASHC5, WASH complex subunit 5).