Mammalian PERIOD complex regulates repair of DSB in active chromatin through anchoring to the nuclear envelope

Repair of DNA Double Strand Breaks produced in transcriptionally active chromatin occurs through a mechanism, Transcription-Coupled DSB repair (TC-DSBR), that is yet poorly characterized. Here, using a screening approach scoring multiple outputs in human cells, we identified the PER complex, a key module ensuring circadian oscillations, as a novel TC-DSBR player, being enriched at DSB occurring in transcribed loci, as compared to DSB induced in un-transcribed loci. We further found that PER2 contributes to target TC-DSBs at the nuclear envelope (NE) and to foster Rad51- mediated repair. PER2 deficiency triggers decreased DSB anchoring to NE, resulting in an increase of DSB clustering, checkpoint activation and translocation frequency. In agreement, we found that the circadian clock also regulates DSB anchoring to the NE, checkpoint activation, and HR usage. Our study provides a direct link between the circadian clock and the response to DNA Damage, opening new therapeutic strategies for chemotherapies based on topoisomerase poisons that induce DSBs in active loci.

在转录活跃染色质中产生的DNA双链断裂（DNA Double Strand Break, DSB）的修复，通过一种尚未被充分阐明的机制——转录偶联DSB修复（Transcription-Coupled DSB repair, TC-DSBR）——进行。本研究通过在人类细胞中对多重检测指标进行评分的筛选策略，鉴定出调控昼夜节律振荡的核心复合物PER复合物为一种新型TC-DSBR因子；相较于在非转录位点诱导产生的DSB，该复合物会富集于转录位点的DSB处。本研究进一步发现，PER2蛋白可将TC-DSB靶向锚定至核膜（nuclear envelope, NE），并促进Rad51介导的DNA修复过程。PER2功能缺失会导致DSB向核膜的锚定作用减弱，进而引发DSB聚集、检验点激活以及染色体易位频率升高。与此一致，本研究发现昼夜节律时钟同样可调控DSB向核膜的锚定、检验点激活以及同源重组（Homologous Recombination, HR）的使用情况。本研究揭示了昼夜节律时钟与DNA损伤应答之间的直接关联，为基于拓扑异构酶毒物（可在活跃转录位点诱导DSB）的化疗方案提供了全新的治疗策略。