Functions as a negative regulator of the PI3 kinase/PI3K activity associated with endosomal membranes via BECN1, a core subunit of the PI3K complex. By modifying the phosphatidylinositol 3-phosphate/PtdInsP3 content of endosomal membranes may regulate endosome fusion, recycling, sorting and early to late endosome transport. It is for instance, required for the delivery of cargos like BST2/tetherin from early to late endosome and thereby participates indirectly to their degradation by the lysosome (By similarity). May play a role in meiosis (PubMed:27346680). Interacts with WDR81; involved in early to late endosome cargo transport. Interacts with BECN1; negatively regulates the PI3 kinase/PI3K activity associated with endosomal membranes. Belongs to the WD repeat WDR91 family.