R-loops lead to chronic inflammation upon DNA damage.

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Type II DNA Topoisomerases (TOP II) generate transient double-strand DNA breaks (DSBs) to resolve topological constraints during transcription. Using genome-wide mapping of DSBs and functional genomics approaches, we show that, in the absence of exogenous genotoxic stress, transcription leads to DSB accumulation and to the recruitment of the structure-specific ERCC1-XPF endonuclease on active gene promoters. Instead, we find that the complex is released from regulatory or gene body elements in UV-irradiated cells. Abrogation of ERCC1 or re-ligation blockage of TOP II-mediated DSBs aggravates the accumulation of transcription-associated γ H2Ax and 53BP1 foci, which dissolve when TOP II-mediated DNA cleavage is inhibited. An in vivo biotinylation tagging strategy coupled to a high-throughput proteomics approach reveals that ERCC1-XPF interacts with TOP IIβ and the CTCF/cohesin complex, which co-localize with the heterodimer on DSBs.Together; our findings provide a rational explanation for the remarkable clinical heterogeneity seen in human disorders with ERCC1-XPF defects. 8 indicate that, in the absence of exogenous genotoxic stimuli, transcription initiation, but not elongation, triggers an ATM-dependent DDR that is further pronounced in cells defective in the ERCC1-XPF endonuclease.