¹Department of Cancer Biology, Mayo Clinic College of Medicine, Jacksonville, FL, USA

Correspondence: Dr AP Fields, Department of Cancer Biology, Mayo Clinic College of Medicine, Griffin Cancer Research Building, Rm 212, 4500 San Pablo Road, Jacksonville, FL 32224, USA. E-mail: fields.alan@mayo.edu

Received 24 March 2009; Revised 23 May 2009; Accepted 24 May 2009; Published online 20 July 2009.

Abstract

Protein kinase C (PKC) promotes non-small cell lung cancer (NSCLC) by binding to Par6 and activating a Rac1-Pak-Mek1,2-Erk1,2 signaling cascade. The mechanism by which the PKC–Par6 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 PKC 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 PKC–Par6 complex. RNA interference-mediated knockdown of either PKC or Par6 causes Ect2 to redistribute to the nucleus, indicating that the PKC–Par6 complex regulates the cytoplasmic localization of Ect2. Our data indicate that Ect2 and PKC are genetically and functionally linked in NSCLC, acting to coordinately drive tumor cell proliferation and invasion through formation of an oncogenic PKC–Par6-Ect2 complex.