Abstract 3405: E12 and E47 are essential for TWIST1 dependent suppression of oncogene-induced senescence in NSCLC

Lung cancer is the leading cause of cancer death in the United States and in the world. Non-small cell lung cancer (NSCLC) is not a single disease entity, but a collection of distinct oncogene driven neoplasms. The most common driver oncogene in NSCLC is mutant-KRAS, which is present in 20-25% of all NSCLC and for which no effective therapies exist. In addition, acquired resistance to the current therapy for the two most frequently observed targetable driver oncogenes in NSCLC, mutant-EGFR and the ALK translocations, is inevitable. Clearly there is a need for novel therapeutic strategies to target these oncogene driven lung cancers. The basic helix-loop-helix (bHLH) transcription factor TWIST1 plays several critical roles in promoting tumorigenesis through inhibition of apoptosis, promotion of metastasis through induction of epithelial-mesenchymal transition (EMT) and inhibition of oncogene-induced senescence (OIS). We recently demonstrated that TWIST1 is essential for tumor maintenance in human NSCLC containing mutant KRAS, mutant EGFR, or amplified cMET. Moreover we have shown that Twist1 cooperates with Kras to induce adenocarcinoma of the lung in mouse models and that inhibition of Twist1 in both a murine model and in human cell lines causes OIS or in some cases apoptosis. We have previously demonstrated that reactivation of OIS after inhibition of TWIST1 occurs independently of the RB/p16, p53/p21 or p27 pathways. In the current study, we examined the role of the TWIST1 binding partners E12 and E47, which are encoded by the E2A locus, in mediating TWIST1 dependent suppression of OIS. E2A encoded proteins have previously been demonstrated to act as tumor suppressors through inhibition of cell proliferation. However, E12 and E47 are overexpressed in several tumor types and this expression can lead to chemoresistance. Furthermore, previous studies have demonstrated that the E12-TWIST1 heterodimerization stabilizes both proteins and in some cases, enhances TWIST1 activity. In our study we have shown that in human KRAS mutant NSCLC cell lines the silencing of the E2A gene products phenocopies the silencing of TWIST1 by inducing either OIS or apoptosis. Furthermore, we have observed significant downregulation of TWIST1 after silencing the E2A gene products. Conversely, overexpression of either E12 or E47 leads to increased TWIST1 protein levels. Interestingly, TWIST1 overexpression leads to E12/E47 stabilization suggesting that heterodimer formation results in a reciprocal stabilization of the binding partner. Finally, we have shown that harmine, a harmala alkaloid that leads to degradation of TWIST1, inhibits NSCLC cell line growth and decreases both E12/E47 levels as well. These data suggest that E12/E47 are essential for TWIST mediated suppression of OIS and that targeting of the TWIST1-E12/E47 axis may be an effective therapeutic strategy against oncogene driven NSCLC. Citation Format: Lucia Mazzacurati, Sarah NH Chatley, Zachary Yochum, Charles M. Rudin, Phuoc T. Tran, Timothy F. Burns. E12 and E47 are essential for TWIST1 dependent suppression of oncogene-induced senescence in NSCLC. [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 3405. doi:10.1158/1538-7445.AM2014-3405