PTEN and Cancer

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PTEN is one of the most frequently mutated tumor suppressors in human cancer, and effective approaches for treating cancer with PTEN alteration is needed. Inactivation of PTEN cooperates with different oncogenic signals to stimulate tumor initiation and progression and can be mutated in early or advanced human disease. Though two hit inactivation is more penetrant than one hit for PTEN in mice, partial inactivation via haploinsufficiency is sufficient to cause tumor progression. Much of PTEN’s tumor suppressor function can be attributed to its role as a negative regulator of PI3K signaling by virtue of its ability to act as a phosphatase that catalyzes the removal of the D-3 phosphate from phosphatidylinositol-3,4,5-trisphosphate (PIP3). PIP3 binds the PH domain of AKT kinase and the PH domains of two PIP3-regulated kinases PDK1 and mTORC2, which coordinately phosphorylate AKT to activate it. PIP3 in parallel binds the PH domains of PREX1 and PREX2 to stimulate GTP loading of RAC1. The parallel PIP3-dependent activation of AKT and RAC coordinate the activation of glycolysis in the cell, and under these conditions AKT activates mTORC1. Tumors that lack PTEN have elevated PIP3 with increased AKT, TORC1, and RAC signaling, increased DNA replication and up regulated metabolic pathways involved in cell growth. In normal physiology, PTEN is a key negative regulator of the insulin signaling pathway, and loss of PTEN leads to increased glucose uptake in different tissues of the body. Acute inactivation of PTEN in normal cells leads to increased cellular PIP3 and glucose flux accompanied by increased proliferation, migration, and survival. The PTEN locus encodes multiple isoforms of PTEN, including the recently identified PTEN-L, which share common phosphatase and C2 domains. My research program focuses on the PTEN tumor suppressor. In this proposal, the broad scientific question that I will ask is: what are the tumor suppressor functions of PTEN and PTEN-L and how are they regulated? The goals of this application are to define mechanisms of PTEN regulation, determine the consequences of inactivation in tissue and on cell proliferation and metabolism, and to develop approaches for targeting tumor cells based upon their PTEN status. I expect that greater understanding of PTEN’s inactivation and regulation will lead to improved therapy for cancer.