PKCi Maintains a Tumor-initiating Cell Phenotype That Is Required for Ovarian Tumorigenesis

Protein kinase Ci (PKCi) has oncogenic potential and is an attractive therapeutic target for treatment of lung cancer, particularly those tumors that express elevated PKCi. However, whether PKCi is a viable target in ovarian cancer is unknown, and virtually nothing is known about the mechanism by which PKCi drives ovarian tumorigenesis. Here, it is demonstrated that PKCi maintains a tumor-initiating cell (TIC) phenotype that drives ovarian tumorigenesis. A highly tumorigenic population of cells from human ovarian cancer cell lines exhibit cancer stem-like TIC properties, including self-renewal, clonal expansion, expression of stem-related genes, enhanced transformed growth in vitro, and aggressive tumor-initiating activity in vivo. Genetic disruption of PKCi inhibits the proliferation, clonal expansion, anchorage-independent growth, and enhanced tumorigenic properties of ovarian TICs. Biochemical analysis demonstrates that PKCi acts through its oncogenic partner Ect2 to activate a MEK/ERK signaling axis that drives the ovarian TIC phenotype. Genomic analysis reveals that PKCi and Ect2 are coordinately amplified and overexpressed in the majority of primary ovarian serous tumors, and these tumors exhibit evidence of an active PKCi-Ect2 signaling axis in vivo. Finally, this study reveals that auranofin, a potent and selective inhibitor of oncogenic PKCi signaling, inhibits the tumorigenic properties of ovarian TIC cells in vitro and in vivo. These data demonstrate that PKCi is required for a TIC phenotype in ovarian cancer, and that auranofin is an attractive therapeutic option to target deadly ovarian TICs in ovarian cancer patients. Implications: PKCi drives a tumor-initiating cell phenotype in ovarian cancer cells that can be therapeutically targeted with auranofin, a small molecule inhibitor of PKCi signaling. (C) 2013 AACR.