Abstract A43: Effects of transcriptional dysregulation on the DNA damage response in Ewing’s sarcoma

Ewing’s sarcoma is a soft-tissue bone malignancy characterized by a translocation event wherein the N-terminal low complexity domain of EWSR1 is fused with the DNA binding domain of the ETS transcription factor Fli1. The resulting EWS-Fli1 fusion protein drives expression of oncogenes and knockdown of tumor-suppressor proteins. More specifically, EWS-Fli1 acts as transcriptional regulator by helping recruit RNA Pol II to promoter regions, which is subsequently phosphorylated by CDK9 to escape initiation into elongation. Interestingly, Ewing’s sarcoma is particularly susceptible to chemotherapy compared to other cancers; however, the underlying reason for this sensitivity to DNA damage has not been elucidated. Given EWS-Fli1’s role in disrupting transcription, it was hypothesized that EWS-Fli1 is concurrently disrupting the DNA damage response. Here, a combination of CDK9 inhibition with DNA damage was found to drastically diminish cell viability in Ewing’s cell lines but not in non-Ewing’s osteosarcoma or HEK293 cells. Ordinarily, after DNA damage γH2A.X phosphorylation occurs on histones near sites of damaged DNA early during the DNA damage response to signal DNA damage repair initiation. Further work has shown Ewing’s cells undergoing the combination treatment above have a marked decrease in the DNA damage marker γH2A.X as compared to non-Ewing’s cells. Together, these results suggest Ewing’s sarcoma cells are sensitized to DNA damage due in part to transcriptional dysregulation. Citation Format: Matthew G. Rollins, Jacob C. Schwartz. Effects of transcriptional dysregulation on the DNA damage response in Ewing’s sarcoma [abstract]. In: Proceedings of the AACR Special Conference on the Advances in Pediatric Cancer Research; 2019 Sep 17-20; Montreal, QC, Canada. Philadelphia (PA): AACR; Cancer Res 2020;80(14 Suppl):Abstract nr A43.