Abstract 1255: Protein kinase C epsilon (PKCε) as a target for lung cancer treatment: Essential role of PKCε in tumor growth and metastatic dissemination of non-small cell lung cancer (NSCLC) cells

Abstract

Abstract Protein Kinase C epsilon (PKCε), a member of the PKC family of phorbol ester/diacylglycerol receptors, has been recently shown to be highly overexpressed in non-small cell lung carcinomas (NSCLCs) compared to normal lung epithelium. The fact that several of the most common genetic alterations in lung cancer, such as EGFR, K-Ras, or PI3K mutations, could signal through PKCs, led us to hypothesize that PKCε may contribute to lung tumorigenesis. We found that the expression of PKCε was markedly up-regulated in NSCLC cell lines (H358, H441, H322, H1299, and A459) relative to immortalized non-tumorigenic cells (HBEC-3). Stable knockdown of PKCε in NSCLC cells using shRNA lentiviruses impaired cell survival in response to serum starvation, as well as it increased the sensitivity to senescence induction by phorbol esters. Moreover, anchorage-dependent and -independent growth were markedly reduced in PKCε-depleted NSCLC cells. Notably, silencing of PKCε-expression in NSCLC impaired motility in response to PMA, FBS or TGFα. Treatment of NSCLC cells with PMA led to a significant enhancement in cell motility as well as it promoted ruffle formation. Both ruffle formation and migration were mediated by PKCε. Moreover, PMA caused a marked enhancement in Rac1-GTP levels in NSCLC cells, but this effect was lost when PKCε was knocked down using RNAi. To address the relevance of our findings in an in vivo setting, we examined the requirement of PKCε in tumorigenesis and metastasis. Remarkably, PKCε-depleted H358 cells have impaired tumorigenic potential when inoculated into nude mice. At early time points during tumor formation (6-15 days) we observed a significant increase in apoptotic cells in PKCε-depleted H358 xenografts compared to controls, as determined by TUNEL. These in vivo results were validated pharmacologically by means of a specific inhibitor of PKCε translocation/activation. Indeed, delivery of the specific PKCε inhibitor εV1-2 by osmotic minipumps greatly reduced the rate of tumor growth in nude mice. Finally, we sought to study whether PKCε is implicated in tumor dissemination. Using a tail vein injection assay, we found that stable depletion of PKCε essentially impaired the appearance of lung metastatic foci in nude mice. In summary, our results established PKCε as a key mediator of lung tumorigenesis and provided strong evidence that elevated PKCε levels in NSCLC cells play a key role in metastatic dissemination. We speculate that PKCε is an attractive pharmacological target for lung cancer treatment. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 1255.