Distinctive requirement of PKC[epsilon] in the control of Rho GTPases in epithelial and mesenchymally transformed lung cancer cells

Diacylglycerol (DAG)/phorbol ester-regulated protein kinase C (PKC) isozymes have been widely linked to tumor promotion and the development of a metastatic phenotype. PKC[epsilon], an oncogenic member of the PKC family, is abnormally overexpressed in lung cancer and other cancer types. This kinase plays significant roles in proliferation, survival, and migration; however, its role in epithelial-to-mesenchymal transition (EMT) has been scarcely studied. Silencing experiments in non-small lung cancer (NSCLC) cells revealed that PKC[epsilon] or other DAG-regulated PKCs (PKC[alpha] and PKC[delta]) were dispensable for the acquisition of a mesenchymal phenotype induced by transforming growth factor beta (TGF-[beta]). Unexpectedly, we found a nearly complete down-regulation of PKC[epsilon] expression in TGF-[beta]-mesenchymally transformed NSCLC cells. PMA and AJH-836 (a DAG-mimetic that preferentially activates PKC[epsilon]) promote ruffle formation in NSCLC cells via Rac1, however they fail to induce these morphological changes in TGF-[beta]-mesenchymally transformed cells despite their elevated Rac1 activity. Several Rac guanine nucleotide exchange-factors (Rac-GEFs) were also up-regulated in TGF-[beta]-treated NSCLC cells, including Trio and Tiam2, which were required for cell motility. Lastly, we found that silencing or inhibiting PKC[epsilon] enhances RhoA activity and stress fiber formation, a phenotype also observed in TGF-[beta]-transformed cells. Our studies established a distinctive involvement of PKC[epsilon] in epithelial and mesenchymal NSCLC cells, and identified a complex interplay between PKC[epsilon] and small GTPases that contributes to regulation of NSCLC cell morphology and motile activity.