Ewing sarcoma breakpoint region 1 prevents transcription-associated genome instability at its own translocation-prone locus

Ewing Sarcoma break point region 1 (EWSR1) is a multi-functional RNA-binding protein that is involved in many cellular processes, from gene expression to RNA processing and transport. Translocations into its locus lead to chimeric proteins with tumorigenic activity, that lack the RNA binding domain. With crosslinking and immunoprecipitation we have found that EWSR1 binds to intronic regions that are present in polyadenylated nuclear RNAs, which include the translocation-prone region of its own locus. Reduced EWSR1 expression leads to gene expression changes that indicate reduced proliferation. By fluorescence in situ hybridization (FISH) with break-apart probes that flanked the translocation-prone region within the EWSR1 locus we found that reduced EWSR1 expression increases the frequency of split signals, indicative of DNA double strand breaks (DSB). The response in phosphorylated histone H2AX and p53-binding protein 1 (53BP1) double-stained foci to the topoisomerase poison camptothecin in cells treated with a control shRNA and with sh-EWSR1 further suggests that EWSR1 functions in the prevention of DNA DSBs. Our data reveals a new function of the EWSR1 member of the FET family and connect the RNA-binding activity of EWSR1 with the translocations that affects its own locus in malignancies.