Abstract LB034: EWSR1, Ewing sarcoma breakpoint region 1, maintains centromere identity by binding to centromeric R-loops

Abstract The centromere DNA-kinetochore complex is the specialized chromatin structure that mediates chromosome attachment to microtubules and is required for high-fidelity chromosome transmission. CENP-A is the centromere-specific histone H3 variant that epigenetically determines centromere position on the chromosome to ensure kinetochore assembly. Despite its importance, the precise mechanism of maintenance of CENP-A, i.e., the maintenance of centromere identity, remains obscure. In this study, we found that EWSR1 (Ewing Sarcoma Breakpoint Region 1) is required for CENP-A deposition at centromeres by binding to centromeric RNA. We determined that the CENP-A binding domain of EWSR1 is the SYGQ2 region within the prion-like domain, which plays an important role in phase separation for chromatin remodeling. Our data suggest that EWSR1 guards CENP-A in centromeric chromatins by binding to centromeric RNA. This is a novel mechanism to maintain the position of the centromere on the chromosome i.e., centromere identify. As EWSR1-FLI1 is the oncogenic fusion protein in Ewing sarcoma and as it inhibits EWSR1 function as a dominant negative mutant, it contributes to chromosome instability in Ewing sarcoma, which may lead to therapy resistance and metastasis. Citation Format: Risa Kitagawa, Argentina Becker, Peter Houghton, Katsumi Kitagawa. EWSR1, Ewing sarcoma breakpoint region 1, maintains centromere identity by binding to centromeric R-loops [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 2 (Clinical Trials and Late-Breaking Research); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(8_Suppl):Abstract nr LB034.