PARP1-mediated PARylation of TonEBP prevents R-loop-associated DNA damage.

Lack of coordination between the DNA replication and transcription machineries can increase the frequency of transcription-replication conflicts, leading ultimately to DNA damage and genomic instability. A major source of these conflicts is the formation of R-loops, which consist of a transcriptionally generated RNA-DNA hybrid and the displaced single-stranded DNA. R-loops play important physiological roles and have been implicated in human diseases. Although these structures have been extensively studied, many aspects of R-loop biology and R-loop-mediated genome instability remain unclear. We found that in cancer cells, tonicity-responsive enhancer-binding protein (TonEBP, also called NFAT5) interacted with PARP1 and localized to R-loops in response to DNA-damaging agent camptothecin (CPT), which is associated with R-loop formation. PARP1-mediated PARylation was required for recruitment of TonEBP to the sites of R-loop-associated DNA damage. Loss of TonEBP increased levels of R-loop accumulation and DNA damage, and promoted cell death in response to CPT. These findings suggest that TonEBP mediates resistance to CPT-induced cell death by preventing R-loop accumulation in cancer cells.