PARP1 (aka ARTD1) acts as a prime sensor of cellular genotoxic stress response. PARP1 detects DNA strand breaks and subsequently catalyzes the formation of poly(ADP-ribose) (PAR), which leads to the recruitment of the scaffold protein XRCC1 during base excision and single strand break repair and the assembly of multi-protein complexes to promote DNA repair. Here, we reveal that the recruitment of either protein to sites of DNA damage is impeded in the absence of the other, indicating a strong reciprocal relationship between the two DNA repair factors during genotoxic stress response. We further analyzed several cellular and molecular endpoints in HeLa PARP1 KO, XRCC1 KO, and PARP1/XRCC1 double KO (DKO) cells after genotoxic treatments, i.e., PARylation response, NAD⁺ levels, clonogenic survival, cell cycle progression, cell death, and DNA repair. The analysis of NAD⁺ levels and cytotoxicity after treatment with the topoisomerase I inhibitor camptothecin revealed a hypersensitivity phenotype of XRCC1 KO cells compared to PARP1 KO cells—an effect that could be rescued by the additional genetic deletion of PARP1 as well as by pharmacological PARP inhibition. Moreover, impaired repair of hydrogen peroxide and CPT-induced DNA damage in XRCC1 KO cells could be partially rescued by additional deletion of PARP1. Our results therefore highlight important reciprocal regulatory functions of XRCC1 and PARP1 during genotoxic stress response.

PARP1（又名 ARTD1）充当细胞遗传毒性应激反应的主要传感器。PARP1 检测 DNA 链断裂并随后催化聚 (ADP-核糖) (PAR) 的形成，这导致在碱基切除和单链断裂修复期间募集支架蛋白 XRCC1 以及多蛋白复合物的组装以促进 DNA维修。在这里，我们揭示了在缺乏另一种蛋白质的情况下，任何一种蛋白质向 DNA 损伤部位的募集都会受到阻碍，这表明在基因毒性应激反应过程中，两种 DNA 修复因子之间存在很强的相互关系。我们进一步分析了 HeLa PARP1 KO、XRCC1 KO 和PARP1 / XRCC1中的几个细胞和分子终点基因毒性处理后的双 KO (DKO) 细胞，即 PARylation 反应、NAD ⁺水平、克隆形成存活、细胞周期进程、细胞死亡和 DNA 修复。拓扑异构酶 I 抑制剂喜树碱处理后NAD ⁺水平和细胞毒性的分析表明，与PARP1 KO 细胞相比， XRCC1 KO 细胞具有超敏表型——这种效应可以通过额外的PARP1基因缺失和药理学 PARP 抑制来挽救. 此外， XRCC1 KO 细胞中过氧化氢修复受损和 CPT 诱导的 DNA 损伤可以通过额外删除PARP1来部分挽救. Our results therefore highlight important reciprocal regulatory functions of XRCC1 and PARP1 during genotoxic stress response.