Abstract LB-183: Sensitivity of cancer cells to oncolytic viruses is defined by IWS1 phosphorylation dependent epigenetic regulation of U2AF2 splicing and nucleocytoplasmic export of type I IFN transcripts

Abstract

Abstract We have previously shown that phosphorylation of IWS1 by AKT (primarily AKT3) at Ser720/Thr721 promotes the binding of SETD2 to an Spt6/IWS1/Aly-Ref transcription elongation complex. This complex is bound via Spt6 to the Ser2-phosphorylated CTD of RNA Pol II. We have also shown that this results in the AKT-dependent trimethylation of Histone H3 at K36, a histone modification that contributes to the regulation of alternative splicing, and that this splicing pathway plays an important role in lung cancer. Here, we show that one of the genes targeted for alternative splicing via this mechanism is U2AF2, which encodes the splicing factor U2AF65. The predominant alternatively spliced U2AF2 transcript in cells which have lost IWS1, and in cells in which IWS1 is not phosphorylated, lacks exon 2, which encodes the SR domain of U2AF65. U2AF65 lacking the SR domain does not bind Prp19, a member of a seven-protein complex, which also contributes to RNA processing. U2AF65 and Prp19, along with the TREX complex, bind Cytoplasmic Accumulation Response Elements (CAR-E) in naturally intronless mRNAs and promotes their nucleocytoplasmic export. Examples of mRNAs whose transport is regulated by this mechanism include IFNα1, IFNβ1, HSPBP3 and c-Jun. Based on these data, we predicted that the production of type I IFNs would be dependent on IWS1 phosphorylation by AKT and that inhibition of this pathway would lead to increased sensitivity of cells to virus infection. Indeed, type I IFN production was decreased in such cells and infection with Vesicular Stomatitis Virus (VSV) was accordingly increased. In addition, whereas U2AF65 binds CAR-E elements in the RNA of type I interferons independent of IWS1 phosphorylation, the binding of Prp19 to the same RNA elements occured only in cells expressing AKT-phosphorylated IWS1. These data identify a mechanism by which AKT inhibits viral infection and suggest that inhibition of the AKT/IWS1 axis will increase the sensitivity of cancer cells to infection by oncolytic viruses. Citation Format: Georgios I. Laliotis, Adam D. Kenney, Arturo Orlacchio, Vincenzo Coppola, Jacob S. Yount, Philip N. Tsichlis. Sensitivity of cancer cells to oncolytic viruses is defined by IWS1 phosphorylation dependent epigenetic regulation of U2AF2 splicing and nucleocytoplasmic export of type I IFN transcripts [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr LB-183.