Phosphoinositide 3-kinase regulatory subunit 4, also known as PI3-kinase regulatory subunit 4 or PI3-kinase p150 subunit or phosphoinositide 3-kinase adaptor protein, or VPS15 is an enzyme that in humans is encoded by the PIK3R4 gene. The PI3-kinases regulate cellular signaling networks that are involved in processes linked to the survival, growth, proliferation, metabolism and specialized differentiated functions of cells. The subversion of this network is common in cancer and has also been linked to disorders of inflammation.