SUMMARY We report that two oncogenes co-amplified on chromosome 3q26, PRKCI and SOX2, cooperate to drive a stem-like phenotype in lung squamous cell carcinoma (LSCC). PKCι phosphorylates SOX2, a master transcriptional regulator of stemness, and recruits it to the promoter of Hedgehog Acyl Transferase (HHAT), which catalyzes the rate-limiting step in Hh ligand production. PKCι-mediated SOX2 phosphorylation is required for HHAT promoter occupancy, HHAT expression, and maintenance of a stem-like phenotype. Primary LSCC tumors coordinately overexpress PKCι, SOX2, and HHAT, and require PKCι-SOX2-HHAT signaling to maintain a stem-like phenotype. Thus, PKCι and SOX2 are genetically, biochemically and functionally linked in LSCC, and together they drive tumorigenesis by establishing a cell autonomous Hh signaling axis.

Protein kinase Cι (PKCι) promotes non-small cell lung cancer (NSCLC) by binding to Par6α and activating a Rac1-Pak-Mek1,2-Erk1,2 signaling cascade. The mechanism by which the PKCι-Par6α complex regulates Rac1 is unknown. Here we show that Ect2, a guanine nucleotide exchange factor (GEF) for Rho family GTPases, is coordinately amplified and overexpressed with PKCι in NSCLC tumors. RNAi-mediated knock down of Ect2 inhibits Rac1 activity and blocks transformed growth, invasion and tumorigenicity of NSCLC cells. Expression of constitutively active Rac1 (RacV12) restores transformation to Ect2-deficient cells. Interestingly, the role of Ect2 in transformation is distinct from its well-established role in cytokinesis. In NSCLC cells, Ect2 is mislocalized to the cytoplasm where it binds the PKCι-Par6α complex. RNAi-mediated knock down of either PKCι or Par6α causes Ect2 to redistribute to the nucleus, indicating that the PKCι-Par6α complex regulates the cytoplasmic localization of Ect2. Our data indicate that Ect2 and PKCι are genetically and functionally linked in NSCLC, acting to coordinately drive tumor cell proliferation and invasion through formation of an oncogenic PKCι-Par6α-Ect2 complex.

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