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. Component of the WASH core complex also described as WASH regulatory complex (SHRC) composed of WASH (WASHC1, WASH2P or WASH3P), WASHC2 (WASHC2A or WASHC2C), WASHC3, WASHC4 and WASHC5. The WASH core complex associates via WASHC2 with the F-actin-capping protein dimer (formed by CAPZA1, CAPZA2 or CAPZA3 and CAPZB) in a transient or substoichiometric manner which was initially described as WASH complex. Belongs to the CCDC53 family. One study reported a nucleation-promoting factor (NPF) activity towards the Arp2/3 complex using partially purified samples of the WASH complex (PubMed:19922875). In another study, the in vitro reconstituted and purified recombinant WASH core complex, consisting of WASHC3, WASHC4, WASHC5, WASHC1 and the N-terminal residues 1-356 of WASHC2, did not show activity toward Arp2/3 complex (PubMed:20498093).