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 PKC? is an oncogene in non-small cell lung cancer (NSCLC) the leading cause of cancer death in the United States, elucidated a major oncogenic PKC? signaling pathway, and developed a therapeutic agent that targets oncogenic PKC? signaling that is currently being evaluated in the clinic. During the current funding period we showed that: 1) PKC? forms an oncogenic PKC?/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 PKC?/Par6 complex and activates Rac1, a key downstream effector of this complex; 3) PKC? 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 PKC?/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 PKC? 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 PKC?/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 PKC?- dependent manner where it regulates ribosomal RNA (rRNA) transcription; 3) PKC? transcriptionally activates cell autonomous hedgehog (Hh) signaling in NSCLC tumor-initiating cells; and 4) PKC? 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) PKC?-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) PKC? 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 PKC?-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 PKC? and Ect2 regulate ribosomal RNA transcription; 2) assess the role of Ect2 in Kras-mediated lung tumorigenesis; 3) determine the mechanism by which PKC? regulates hedgehog acyl-transferase (HHAT) expression; and 4) assess the role of HHAT in lung tumorigenesis.
Lung cancer is the number one cause of cancer death in the United States. Protein kinase C? (PKC?) is an oncogene, prognostic marker and therapeutic target in lung cancer. This project will elucidate novel PKC? signaling mechanisms that drive lung cancer growth, assess the importance of PKC? signaling in lung cancer development, progression and spread in pre-clinical animal models in vivo, and determine the translational relevance of these findings to primary human lung cancers.
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