Receptor-regulated class I phosphoinositide 3-kinases (PI3Ks) phosphorylate the membrane lipid phosphatidylinositol 4,5-bisphosphate (PtdIns(4,5)P2) to PtdIns(3,4,5)P3, which in turn recruits and activates cytosolic effectors involved in proliferation, survival, or chemotaxis. PIK3R5 is a PI3K regulatory subunit (Brock et al., 2003 [PubMed 12507995]).