MTOR and neoplasm: PIP3 subsequently binds to phosphoinositide-dependent kinase 1 (PDK1), thus phosphorylating and activating the serine/threonine kinase AKT.193,194 PTEN (phosphatase and tensin homolog), a tumor suppressor, is a phosphatase that dephosphorylates PIP3 into inactive PIP2, thereby dampening AKT and PDK1.195,196 Activated AKT can phosphorylate and activate mTOR or indirectly promote mTOR activity by phosphorylation and inactivation of tuberous sclerosis complex 1/2, a mTOR inhibitor.