Proposed to be involved in endosomal maturation implicating in part VPS33B. In epithelial cells, the VPS33B:VIPAS39 complex may play a role in the apical RAB11A-dependent recycling pathway and in the maintenance of the apical-basolateral polarity (PubMed:20190753). May play a role in lysosomal trafficking, probably via association with the core HOPS complex in a discrete population of endosomes; the functions seems to be independent of VPS33B (PubMed:19109425). May play a role in vesicular trafficking during spermatogenesis (By similarity). May be involved in direct or indirect transcriptional regulation of E-cadherin (By similarity). {ECO:0000250|UniProtKB:Q23288, ECO:0000269|PubMed:19109425, ECO:0000269|PubMed:20190753}. This is the function of ENSG00000151445 (VIPAS39, VPS33B interacting protein, apical-basolateral polarity regulator, spe-39 homolog).