Abstract 5220: Reciprocal regulation of MYC and LKB1 modulates cell survival and differentiation in lung cancer

Abstract

Abstract MYC and LKB1 are important regulators of cell survival and differentiation. Although recent studies have been shown oncogenic cooperation between MYC and LKB1 loss, their relationship is unclear. In this study, we report a reciprocal regulation between MYC and LKB1 which modulates cell survival and differentiation in non-small cell lung cancer (NSCLC). We found that MYC regulates LKB1 expression via miR-17. Specifically, luciferase activity was reduced in cells transfected with miR-17, LKB1 3′ UTR constructs compared with scrambled control. Mutation of miR-17 interaction sites rescued the luciferase activity, thus confirming that miR-17 directly interacts with the LKB1 3´ UTRs. In agreement with our reporter gene assay results, enforced overexpression of miR-17 decreased the expression of LKB1 mRNA and protein levels compared with scrambled control. Conversely, miR-17 inhibition promoted upregulation of LKB1 expression in NSCLC cells. Furthermore, miR-17 expression was inversely correlated with LKB1 expression in 532 patients with NSCLC from The Cancer Genome Atlas data (TCGA). MYC and miR-17 overexpression promoted mTOR pathway activation, increased cell proliferation and colony formation in NSCLC cells. In line with these findings, similar results were obtained when we knockdown LKB1 expression, suggesting that MYC promotes mTOR pathway and cell survival, at least in part, via LKB1 regulation. Reciprocally, we found upregulation of MYC expression in NSCLC cell lines with LKB1 mutation or low expression compared to LKB1 wild-type (total n=78) via reverse phase protein array (RPPA) analysis. We validated these findings by analyzing MYC expression via western blotting in LKB1-knockdown and LKB1-ovexpressing stable cell lines. Mechanistically, we found that LKB1 downmodulates MYC expression via Yes-Associated protein 1 (YAP) phosphorylation at Ser127 site, which results in YAP cytoplasmic retention inhibiting transcription activation of its targets. In addition, we found that LKB1 also regulates ID2, a negative regulator of cell differentiation, via YAP/MYC axis. Taken together, our study reveals a reciprocal regulation between MYC and LKB1 offering additional mechanistic insights how MYC promotes cell survival and differentiation in lung cancer. Citation Format: Maria A. Cortez, Chao Yang, Lauren Averett Byers, Lixia Diao, Thaddeus Allen, Uma Giri, Jing Wang, James Welsh, John Victor Heymach. Reciprocal regulation of MYC and LKB1 modulates cell survival and differentiation in 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 5220. doi:10.1158/1538-7445.AM2014-5220