ALYREF binds to poly-ADP-ribose at double strand breaks impairing repair in tumoral cells.

DNA-RNA hybrids cause genome instability by promoting transcription-replication conflicts. However, as they are stimulated at double-stranded breaks (DSBs), they can also impact DSB repair. We investigated whether the RNA chaperon ALYREF and its RNA helicase partner UAP56/DDX39B, both of which regulate RNA biogenesis and R-loops, also act at DSBs. We found that ALYREF, but not UAP56/DDX39B, is recruited to DSBs. Recruitment is partially dependent on transcription and hybrids, and fully dependent on polyADP-ribose (PAR). Consistently, we show that ALYREF, but not UAP56/DDX39B, binds PAR in vitro. Notably, ALYREF overexpression delays DSB repair by retaining PAR levels and interfering with the loading dynamics of early DSB repair factors that regulate DNA resection. Interestingly, we detect high ALYREF levels in numerous cancer subtypes by database analysis. We propose that ALYREF, when overexpressed, induces genome instability in tumoral cells by interfering with DSB repair.