Stabilization of stalled replication forks is a prominent mechanism of PARP (Poly(ADP-ribose) Polymerase) inhibitor (PARPi) resistance in BRCA-deficient tumors. Epigenetic mechanisms of replication fork stability are emerging but remain poorly understood. Here, we report the histone acetyltransferase PCAF (p300/CBP-associated) as a fork-associated protein that promotes fork degradation in BRCA-deficient cells by acetylating H4K8 at stalled replication forks, which recruits MRE11 and EXO1. A H4K8ac binding domain within MRE11/EXO1 is required for their recruitment to stalled forks. Low PCAF levels, which we identify in a subset of BRCA2-deficient tumors, stabilize stalled forks, resulting in PARPi resistance in BRCA-deficient cells. Furthermore, PCAF activity is tightly regulated by ATR (ataxia telangiectasia and Rad3-related), which phosphorylates PCAF on serine 264 (S264) to limit its association and activity at stalled forks. Our results reveal PCAF and histone acetylation as critical regulators of fork stability and PARPi responses in BRCA-deficient cells, which provides key insights into targeting BRCA-deficient tumors and identifying epigenetic modulators of chemotherapeutic responses.

停滞复制叉的稳定是BRCA缺陷肿瘤中 PARP（聚（ADP-核糖）聚合酶）抑制剂（PARPi）抗性的一个突出机制。复制叉稳定性的表观遗传机制正在出现，但仍知之甚少。在这里，我们报告了组蛋白乙酰转移酶 PCAF（p300/CBP 相关）作为一种叉相关蛋白，它通过在停滞的复制叉处乙酰化 H4K8 来促进 BRCA 缺陷细胞中的叉降解，从而招募 MRE11 和 EXO1。MRE11/EXO1 中的 H4K8ac 结合域是将它们招募到停滞的分叉所必需的。低 PCAF 水平，我们在BRCA2 的一个子集中识别- 缺陷肿瘤，稳定停滞的叉，导致 BRCA 缺陷细胞中的 PARPi 抗性。此外，PCAF 活动受到 ATR（共济失调毛细血管扩张症和 Rad3 相关）的严格调控，ATR 使丝氨酸 264（S264）上的 PCAF 磷酸化，以限制其在停滞叉上的关联和活动。我们的结果揭示了 PCAF 和组蛋白乙酰化是 BRCA 缺陷细胞中叉稳定性和 PARPi 反应的关键调节因子，这为靶向BRCA缺陷肿瘤和鉴定化疗反应的表观遗传调节剂提供了关键见解。