Ect2 links the PKCι-Par6α complex to Rac1 activation and cellular transformation

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 epithelial cell transforming sequence 2 (Ect2), a guanine nucleotide exchange factor for Rho family GTPases, is coordinately amplified and overexpressed with PKCι in NSCLC tumors. RNA interference-mediated knockdown 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. RNA interference-mediated knockdown 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.