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 (PubMed:26783301). 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 (PubMed:27126989). May also play a role in aggrephagy, the macroautophagic degradation of ubiquitinated protein aggregates. In this process, may regulate the interaction of SQSTM1 with ubiquitinated proteins and also recruit MAP1LC3C (PubMed:28404643). May also be involved in maintenance of normal mitochondrial structure and organization (By similarity). Interacts with WDR91; involved in early to late endosome cargo transport (PubMed:26783301, PubMed:27126989). Interacts with BECN1; negatively regulates the PI3 kinase/PI3K activity associated with endosomal membranes (PubMed:26783301). Interacts with SQSTM1; the interaction is direct and regulates the interaction of SQSTM1 with ubiquitinated proteins (PubMed:28404643). Interacts with MAP1LC3C; recruits MAP1LC3C to ubiquitinated protein aggregates in the aggrephagy process (PubMed:28404643). Widely expressed. In the brain, highest levels in cerebellum and corpus callosum. The disease is caused by variants affecting the gene represented in this entry. The disease is caused by variants affecting the gene represented in this entry. Belongs to the WD repeat WDR81 family. Truncated N-terminus.