Medical Research Council (MRC) Molecular Haematology Unit, Weatherall Institute of Molecular Medicine, University of Oxford, Oxford, UK.
Wellcome Centre for Human Genetics, University of Oxford, Oxford, UK.
Nature. 2021 Aug;596(7872):433-437. doi: 10.1038/s41586-021-03776-w. Epub 2021 Jul 28.
Protein ubiquitination at sites of DNA double-strand breaks (DSBs) by RNF168 recruits BRCA1 and 53BP1, which are mediators of the homologous recombination and non-homologous end joining DSB repair pathways, respectively. Non-homologous end joining relies on 53BP1 binding directly to ubiquitinated lysine 15 on H2A-type histones (H2AK15ub) (which is an RNF168-dependent modification), but how RNF168 promotes BRCA1 recruitment and function remains unclear. Here we identify a tandem BRCT-domain-associated ubiquitin-dependent recruitment motif (BUDR) in BRCA1-associated RING domain protein 1 (BARD1) (the obligate partner protein of BRCA1) that, by engaging H2AK15ub, recruits BRCA1 to DSBs. Disruption of the BUDR of BARD1 compromises homologous recombination and renders cells hypersensitive to PARP inhibition and cisplatin. We further show that BARD1 binds nucleosomes through multivalent interactions: coordinated binding of H2AK15ub and unmethylated H4 lysine 20 by its adjacent BUDR and ankyrin repeat domains, respectively, provides high-affinity recognition of DNA lesions in replicated chromatin and promotes the homologous recombination activities of the BRCA1-BARD1 complex. Finally, our genetic epistasis experiments confirm that the need for BARD1 chromatin-binding activities can be entirely relieved upon deletion of RNF168 or 53BP1. Thus, our results demonstrate that by sensing DNA-damage-dependent and post-replication histone post-translation modification states, BRCA1-BARD1 complexes coordinate the antagonization of the 53BP1 pathway with promotion of homologous recombination, establishing a simple paradigm for the governance of the choice of DSB repair pathway.
蛋白质在 DNA 双链断裂（DSBs）部位的泛素化由 RNF168 完成，它可募集 BRCA1 和 53BP1，分别作为同源重组和非同源末端连接 DSB 修复途径的介质。非同源末端连接依赖于 53BP1 直接结合于组蛋白 H2A 型上的赖氨酸 15 上的泛素化（这是一种 RNF168 依赖性修饰）（H2AK15ub），但 RNF168 如何促进 BRCA1 的募集和功能仍不清楚。在这里，我们在 BRCA1 相关 RING 结构域蛋白 1（BARD1）（BRCA1 的必需伴侣蛋白）中鉴定出一个串联 BRCT 结构域相关的泛素依赖性募集基序（BUDR），该基序通过结合 H2AK15ub，将 BRCA1 募集到 DSB 部位。BARD1 的 BUDR 缺失会损害同源重组，并使细胞对 PARP 抑制剂和顺铂敏感。我们进一步表明，BARD1 通过多价相互作用与核小体结合：其相邻的 BUDR 和锚蛋白重复结构域分别通过协调结合 H2AK15ub 和未甲基化的 H4 赖氨酸 20，为复制染色质中的 DNA 损伤提供高亲和力识别，并促进 BRCA1-BARD1 复合物的同源重组活性。最后，我们的遗传上位性实验证实，在删除 RNF168 或 53BP1 后，完全可以解除 BARD1 染色质结合活性的需要。因此，我们的结果表明，通过感知 DNA 损伤依赖性和复制后组蛋白翻译后修饰状态，BRCA1-BARD1 复合物协调了 53BP1 途径的拮抗作用与同源重组的促进作用，为 DSB 修复途径的选择建立了一个简单的范例。
