We have previously shown that the loss of IWS1 phosphorylation promotes the alternative RNA splicing of U2 Associated-Factor 2 (U2AF2), resulting in transcripts lacking exon 2 in lung adenocarcinoma cells. This exon encodes part of the U2AF65 Serine-Rich (SR) Domain, which is required for its binding with pre-mRNA Processing factor 19 (Prp19). We have also shown that inhibition of the pathway results in the downregulation of cell cycle division associated 5 (CDCA5), and its protein product Sororin, a phosphorylation target and regulator of ERK and member of the cohesin complex, leading to G2/M phase arrest, sister-chromatid cohesion defects, impaired cell proliferation and tumor growth in mouse xenografts models. Here, we show that the loss of IWS1 results in genomic instability and accumulation of cytosolic dsDNA, an effect rescued by the expression of Sororin. The dsDNA is censored by cyclic GMP-AMP synthetase (cGAS), activating the STING/TBK1 pathway. The latter leads to increased expression of Interferon Regulatory Factor-3 (IRF-3) targets along with PD-L1. More importantly, IWS1 phosphorylation, U2AF2 RNA splicing pattern and Sororin expression negatively correlate with the cGAS/STING pathway and PD-L1 expression in lung adenocarcinoma patients. These results highlight the role of IWS1 phosphorylation-dependent RNA splicing in governing genomic stability, and proposes this axis as a novel drug target for a synergy with PD-L1/PD-1 blockade in lung adenocarcinoma patients.

Citation Format: Georgios I. Laliotis, Evangelia Chavdoula, Abdul Kaba, Alessandro La Ferlita, Vollter Anastas, Arturo Orlacchio, Lalit Sehgal, David P. Carbone, Vincenzo Coppola, Philip N. Tsichlis. The inhibition of IWS1 phosphorylation promotes genomic instability, the cGAS/STING pathway activation and PD-L1 levels, through the U2AF2 alternative RNA splicing and Sororin expression [abstract]. In: Abstracts: AACR Virtual Special Conference: Tumor Immunology and Immunotherapy; 2020 Oct 19-20. Philadelphia (PA): AACR; Cancer Immunol Res 2021;9(2 Suppl):Abstract nr PO010.