Protein Kinase C Signaling Mechanisms in Cancer

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DESCRIPTION (provided by applicant): Our long-term goals are to elucidate protein kinase C (PKC) signaling mechanisms that contribute to cancer and translate these mechanistic insights into better prognostic and treatment strategies. In previous funding periods, we discovered that PKCι is an oncogene in non-small cell lung cancer (NSCLC) the leading cause of cancer death in the United States, elucidated a major oncogenic PKCι signaling pathway, and developed a therapeutic agent that targets oncogenic PKCι signaling that is currently being evaluated in the clinic. During the current funding period we showed that: 1) PKCι forms an oncogenic PKCι/Par6 signaling complex in the cytoplasm of NSCLC cells that is necessary for cell proliferation and invasion in vitro, and tumor formation in vivo; 2) the guanine nucleotide exchange factor (GEF) Ect2 binds the PKCι/Par6 complex and activates Rac1, a key downstream effector of this complex; 3) PKCι regulates the intracellular location and oncogenic activity of Ect2 through direct binding and phosphorylation; 4) matrix metalloproteinase 10 (Mmp10) is a critical downstream effector of the PKCι/Ect2/Par6/Rac1 signaling axis that is required for NSCLC cell proliferation and invasion in vitro, and Kras-mediated lung tumorigenesis in vivo; and 5) both PKCι and Mmp10 are required for Kras-mediated transformation of bronchio-alveolar stem cells (BASCs), putative lung tumorinitiating cells (TICs) in vivo. Our preliminary studies indicate that: 1) the PKCι/Ect2/Par6/Rac1/Mmp10 signaling axis maintains a tumor-initiating cell phenotype in NSCLC cells characterized by stem-like behavior and enhanced tumorigenicity; 2) a significant pool of cellular Ect2 localizes to the nucleolus in a PKCι- dependent manner where it regulates ribosomal RNA (rRNA) transcription; 3) PKCι transcriptionally activates cell autonomous hedgehog (Hh) signaling in NSCLC tumor-initiating cells; and 4) PKCι regulates recruitment of the stem cell pluripotency factor Sox2 to th promoter region of the gene encoding Hedgehog Acyl Transferase (HHAT), an enzyme that catalyzes a key step in the production of Hh ligand. Based on these data, we hypothesize that: 1) PKCι-mediated transformation involves regulation of Ect2 nucleolar localization and pre-ribosomal RNA synthesis; 2) Ect2 signaling is required for Kras-mediated BASC transformation and lung tumorigenesis in vivo; 3) PKCι maintains a lung tumor-initiating cell phenotype, at least in part, through Sox2-mediated induction of HHAT transcription and activation of a cell autonomous Hh signaling axis; and 4) HHAT, a PKCι-dependent transcriptional target, plays a key role in lung tumor-initiating activity in vivo. These hypotheses will be tested through completion of four interrelated specific aims to: 1) determine the mechanism by which PKCι and Ect2 regulate ribosomal RNA transcription; 2) assess the role of Ect2 in Kras-mediated lung tumorigenesis; 3) determine the mechanism by which PKCι regulates hedgehog acyl-transferase (HHAT) expression; and 4) assess the role of HHAT in lung tumorigenesis.