PTEN, Fig. 1

PTEN and the PI3K signaling pathway. A schematic diagram of PI3K-dependent signaling pathway is shown. Upon receptor-driven activation of Class I PI3K enzymes, these lipid kinases phosphorylate PtdIns(4,5)P₂ to form the lipid second messenger PtdIns(3,4,5)P₃. This lipid in turn activates downstream responses, generally including cellular growth, proliferation, survival, and motility through direct effector proteins including the AKT and BTK groups of protein kinases and activating exchange factors (GEFs) for the RAC and ARF families of small GTPases. PtdIns(3,4,5)P₃ is in turn metabolized either by the 3-phosphatase PTEN or by members of a family of phopshoinositide 5-phosphatases