Inhibitors of poly-ADP-ribose polymerase 1 (PARPi) are highly effective in killing cells deficient in homologous recombination (HR); thus, PARPi have been clinically utilized to successfully treat BRCA2-mutant tumors. However, positive response to PARPi is not universal, even among patients with HR-deficiency. Here, we present the results of genome-wide CRISPR knockout and activation screens which reveal genetic determinants of PARPi response in wildtype or BRCA2-knockout cells. Strikingly, we report that depletion of the ubiquitin ligase HUWE1, or the histone acetyltransferase KAT5, top hits from our screens, robustly reverses the PARPi sensitivity caused by BRCA2-deficiency. We identify distinct mechanisms of resistance, in which HUWE1 loss increases RAD51 levels to partially restore HR, whereas KAT5 depletion rewires double strand break repair by promoting 53BP1 binding to double-strand breaks. Our work provides a comprehensive set of putative biomarkers that advance understanding of PARPi response, and identifies novel pathways of PARPi resistance in BRCA2-deficient cells.

聚-ADP-核糖聚合酶 1 (PARPi) 抑制剂在杀死同源重组 (HR) 缺陷细胞方面非常有效；因此，PARPi 已在临床上成功用于治疗 BRCA2 突变肿瘤。然而，对 PARPi 的积极反应并不普遍，即使在 HR 缺陷患者中也是如此。在这里，我们展示了全基因组 CRISPR 敲除和激活筛选的结果，这些筛选揭示了野生型或 BRCA2 敲除细胞中 PARPi 反应的遗传决定因素。引人注目的是，我们报告说，泛素连接酶 HUWE1 或组蛋白乙酰转移酶 KAT5 的耗尽（我们筛选中的热门）有力地逆转了由 BRCA2 缺陷引起的 PARPi 敏感性。我们确定了不同的耐药机制，其中 HUWE1 丢失会增加 RAD51 水平以部分恢复 HR，而 KAT5 耗尽通过促进 53BP1 与双链断裂的结合来重新连接双链断裂修复。我们的工作提供了一套全面的推定生物标志物，可促进对 PARPi 反应的理解，并确定 BRCA2 缺陷细胞中 PARPi 抗性的新途径。