Signal Termination by PHLPP, PH domain Leucine-rich repeat Protein Phosphatase

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DESCRIPTION (provided by applicant): The long-term goal of this proposal is to understand the molecular, cellular and physiological mechanisms of signal termination mediated by the novel phosphatase PHLPP (PH domain Leucine- rich repeat Protein Phosphatase; pronounced 'flip') that we discovered. PHLPP terminates signaling by two oncogenic kinases, Akt and protein kinase C, by specifically dephosphorylating a key regulatory residue, the hydrophobic motif, which we originally identified on protein kinase C. PHLPP is frequently deleted in diverse human cancers and its deletion in mice promotes prostate tumors. Thus, the central hypothesis driving this proposal is that PHLPP terminates growth signaling pathways and that deregulation leads to pathophysiological states, notably cancer. Three Aims are proposed: 1. Molecular Mechanisms of PHLPP. The goals are to identify small molecule inhibitors or activators of PHLPP to use as tools in cellular studies in Aims 2 and 3. In addition, we will test the hypothesis that cancer-associated mutations in PHLPP are inactivating and thus confer a survival advantage to tumor cells. 2. Cellular Mechanisms of PHLPP. The goal of this section is to understand the mechanisms that control the function of PHLPP in cells. First, we will use innovative live cell imaging technologies to test the hypothesis that spatial coordination on the PDZ scaffold NHERF increases the ability of PHLPP to control the amplitude and duration of Akt signaling. Second, we will address the mechanism by which PHLPP suppresses the levels of growth factor receptors in cells. 3. PHLPP in pathophysiology. This Aim addresses the role of PHLPP in cancer. Specifically, we will test that hypothesis that deregulation of PHLPP by the E3 ligase 2-TrCP contributes to glioblastoma. In addition, we will address the roles of PHLPP1 and PHLPP2 in prostate cancer using a mouse model and in breast cell growth using a 3D culture model.