Abstract 3319: PKCδ switches from a pro-apoptotic to a pro-survival signal in K-ras “dependent” lung cancer

Abstract

Abstract Oncogenic mutations in KRAS are found in about 25% of non-small cell lung cancers (NSCLC), however only a subset of these tumors are dependent upon K-ras for survival. We have previously shown that PKCδ is required for transformed growth of NSCLC cells that are dependent on K-ras, and for growth of K-ras driven lung tumors in vivo. PKCδ also plays an essential role in DNA damage-induced apoptosis in many cell types. Analysis of 14 mutant KRAS NSCLC cell lines that are K-ras “independent” for survival (A549, H157, H460, SW1573, H1155, H1792), or K-ras “dependent” (H2009, H727, HCC44, H2122, SW900, H1573, H358, H441) reveals that the pro-tumorigenic and pro-apoptotic functions of PKCδ segregate with the K-ras dependency status, and reflect differential regulation of survival signaling by PKCδ in these two cell populations. K-ras-independent NSCLC cells are sensitive to DNA-damage-induced apoptosis, and shRNA mediated depletion of PKCδ in these cells results in suppression of apoptosis and increased activation of the MEK/ERK pathway. In contrast, K-ras dependent NSCLC cells are resistance to DNA-damage-induced apoptosis and depletion of PKCδ enhances apoptosis and suppresses MEK/ERK activation, anchorage-independent growth, and invasion/migration. To explore why K-ras dependent NSCLC cells are resistant to apoptosis, we analyzed PKCδ Y64 phosphorylation and nuclear translocation, events we have previously shown are critical for the pro-apoptotic function of PKCδ. Surprisingly, K-ras dependent cells have an up to 7-fold increase in the nuclear:cytoplasmic ratio of PKCδ, increased phosphorylation of PKCδ Y64, and increased (1.5-3 fold) PKCδ mRNA and protein, suggesting that these cells may be refractive to PKCδ driven apoptosis. To test this we expressed a mutant of PKCδ targeted to the nucleus by the addition of a SV40 nuclear localization signal. Expression of PKCδNLS induced apoptosis and increased DNA damage-induced apoptosis in K-ras independent but not K-ras dependent NSCLC cells, confirming that the later are unable to activate apoptotic pathways downstream of PKCδ. These studies define two distinct subsets of NSCLC cell lines in the context of mutant KRAS. NSCLC cells that are “independent” of K-ras preferentially utilize PKCδ for apoptosis, while cells “dependent” on oncogenic K-ras preferentially use PKCδ for proliferation and survival. We are currently using two large, publicly available lung cancer cell line gene expression datasets (GEO accession #'s GSE4824 and GSE36133) to identify pathways and signaling networks unique to these two populations of NSCLC cells. Citation Format: Mary E. Reyland, Angela M. Ohm, Michael G. Edwards, Jennifer Symonds. PKCδ switches from a pro-apoptotic to a pro-survival signal in K-ras “dependent” lung cancer. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 3319. doi:10.1158/1538-7445.AM2014-3319