Serine/Arginine Splicing Factor 1 (Srsf1) Mediates Dna Repair And Chemo-Sensitivity And Drives Growth In Small Cell Lung Cancer

Small cell lung cancer (SCLC) is the most aggressive subtype of lung cancer. Despite a high response rate to chemotherapy, more than 95% of patients eventually die from SCLC. We have identified that Serine/Arginine Splicing Factor 1 (SRSF1) DNA copy number gain and mRNA over-expression in tumor is strongly associated with poor survival based on whole exome sequencing (WES) and transcriptomic sequencing of primary tumors from 99 Chinese SCLC patients. Here, SRSF1 is evaluated as a tumor driver in SCLC. Treatment of SCLC cell lines in vitro with a low dose of cisplatin or topotecan (two of the most common standard of care in SCLC) only induced a modest decrease of cell growth. However, knockdown of SRSF1 with siRNA along with a sub-lethal dose of cisplatin or topotecan enhanced the overall growth inhibition effect compared to the chemotherapy alone. SRSF1 siRNA alone induced modest but significant caspase-3 activation, similar to cisplatin or topotecan treatment alone. The combination of SRSF1 siRNA with chemotherapy treatments produced a significantly higher caspase induction. DNA-damage induction as a potential mechanism of SRSF1 knockdown was assessed. Phosphorylation of H2AX and Chk2, established markers of DNA-strand breaks and DNA-repair response, was consistently induced upon SRSF1 abrogation in cells, and further increased the phosphorylation of these proteins when combined with cisplatin or topotecan treatment. The knockdown of SRSF1 in SCLC cells also resulted in significant growth inhibition when cells were grown as 3D spheroids. Cells transfected with non-targeting siRNA produced large and well-organized spheroids; in contrast, cells transfected with SRSF1 siRNA did not form well-organized structures but mainly existed as single cells with poor viability. Results were confirmed by colony formation assays and could be rescued with a siRNA-resistant SRSF1 expression construct. Finally, we investigated the impact of SRSF1 loss on kinase signaling pathways in SCLC cells through phospho-kinase array profiling. Strong phospho-AKT and ERK signals were observed in control siRNA-transfected cells, and were abrogated by SRSF1 siRNA. Western blot confirmed this in several SCLC cell lines. These targeting studies demonstrate that SRSF1 plays a key role in DNA repair, chemo-sensitivity and cell proliferation. Together, these data reveal SRSF1 as a therapeutic target in SCLC and provide a rationale for personalized therapy in SCLC. Citation Format: Sarah J. Conley, Xin Yao, Jiaqi Huang, Brandon Higgs, Zhibin Hu, Zhan Xiao, Haihong Zhong, Zheng Liu, Philip Brohawn, Xiaoxiao Ge, Meggan Czapiga, Vaheh Oganesyan, Haihua Fu, David Tice, Ronald Herbst, Xinying Su, Yi Gu, Jianren Gu, Baohui Han, Laura Richman, Bahija Jallal, Liyan Jiang, Hongbing Shen, Yihong Yao. Serine/arginine splicing factor 1 (SRSF1) mediates DNA repair and chemo-sensitivity and drives growth in small cell lung cancer. [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 4954. doi:10.1158/1538-7445.AM2015-4954