Abstract LB-164: Ran Binding Protein 9 (RanBP9) is a novel mediator of cellular DNA damage response in lung cancer cells

Abstract

Currently, most of the anti-neoplastic treatments for lung cancer patients are based on DNA-damaging cytotoxic therapies such as platinum-containing compounds and radiotherapy. Therefore, a better understanding of the molecular mechanisms involved in the cellular response to genotoxic stresses is required in order to improve the clinical management of lung cancer. Ran Binding Protein 9 (RanBP9, also known as RanBP-M) is a ubiquitous and evolutionary conserved scaffold protein that shuttles between the nucleus and the cytoplasm, and interacts with many major players in tumor biology. However, its biological functions are not well studied and still debated. Here, we show that RanBP9 interacts with and is phosphorylated by ATM, one of the apical activators of the DNA damage response (DDR) following DNA Double-Strand Breaks (DSBs). Following ATM-dependent phosphorylation, RanBP9 rapidly accumulates into the nucleus of lung cancer cells. By using three different lung cancer cell lines (A549, H460, and H1299), we found that stable silencing of RanBP9 (ShRanBP9) significantly affects the DDR. In fact, stable ShRanBP9 clones display a delayed and/or reduced activation of key components of the cellular response to Ionizing Radiation (IR), including ATM, Chk2, H2AX-γ and p53. Accordingly, abrogation of RanBP9 expression significantly affected Homology-Directed repair of damaged DNA. On the other hand, stable silencing of RanBP9 results in increased IR-induced senescence and apoptosis. In summary, here we present evidence that RanBP9 is a novel mediator of the cellular DDR, whose recruitment into the nucleus upon IR is dependent on ATM kinase activity. In turn, nuclear RanBP9 participates to the efficient activation of cellular DDR. On the contrary, its absence hampers the repair of damaged DNA following DSBs, resulting in enhanced lung cancer sensitivity to genotoxic stresses. Taken together, our findings suggest that targeting RanBP9 might represent a new potential approach to increase sensitivity of lung cancer cells to genotoxic anti-neoplastic treatments. Citation Format: Dario Palmieri, Mario Scarpa, Anna Tessari, Rexhep Uka, Foued Amari, Cindy Lee, Timothy Richmond, Tyler Sheetz, Jeffrey Parvin, Thomas Ludwig, Carlo M. Croce, Vincenzo Coppola. Ran Binding Protein 9 (RanBP9) is a novel mediator of cellular DNA damage response in lung cancer cells. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr LB-164. doi:10.1158/1538-7445.AM2015-LB-164