King Ashleigh, Reichl Pia I, Metson Jean S, Parker Robert, Munro Daniella, Oliveira Catarina, Sommerova Lucia, Becker Jordan R, Biggs Daniel, Preece Chris, Davies Benjamin, Chapman J Ross
Genome Integrity laboratory, Medical Research Council Molecular Haematology Unit, MRC Weatherall Institute of Molecular Medicine, Radcliffe Department of Medicine, University of Oxford, Oxford, UK.
Centre for Immuno-Oncology, Nuffield Department of Medicine, University of Oxford, Oxford, UK.
Nat Struct Mol Biol. 2025 Jan;32(1):86-97. doi: 10.1038/s41594-024-01381-9. Epub 2024 Sep 3.
Tumor suppressor p53-binding protein 1 (53BP1) regulates DNA end joining in lymphocytes, diversifying immune antigen receptors. This involves nucleosome-bound 53BP1 at DNA double-stranded breaks (DSBs) recruiting Rap1-interacting factor 1 homolog (RIF1) and shieldin, a poorly understood DNA-binding complex. The 53BP1-RIF1-shieldin axis is pathological in BRCA1-mutated cancers, blocking homologous recombination (HR) and driving illegitimate nonhomologous end joining (NHEJ). However, how this axis regulates DNA end joining and HR suppression remains unresolved. We investigated shieldin and its interplay with the Ctc1-Stn1-Ten1 (CST) complex, which was recently implicated downstream of 53BP1. Immunophenotypically, mice lacking shieldin or CST are equivalent, with class-switch recombination coreliant on both complexes. Ataxia-telangiectasia mutated kinase-dependent DNA damage signaling underpins this cooperation, inducing physical interactions between these complexes that reveal shieldin as a DSB-responsive CST adaptor. Furthermore, DNA polymerase ζ functions downstream of shieldin, establishing DNA fill-in synthesis as the physiological function of shieldin-CST. Lastly, we demonstrate that 53BP1 suppresses HR and promotes NHEJ in BRCA1-deficient mice and cells independently of shieldin. These findings showcase the versatility of the 53BP1 pathway, achieved through the collaboration of chromatin-bound 53BP1 complexes and DNA end-processing effector proteins.
肿瘤抑制因子p53结合蛋白1（53BP1）调节淋巴细胞中的DNA末端连接，使免疫抗原受体多样化。这涉及到在DNA双链断裂（DSB）处与核小体结合的53BP1招募Rap1相互作用因子1同源物（RIF1）和shieldin，后者是一种了解较少的DNA结合复合物。53BP1-RIF1-shieldin轴在BRCA1突变的癌症中具有病理学意义，它会阻断同源重组（HR）并促使非法的非同源末端连接（NHEJ）。然而，该轴如何调节DNA末端连接以及HR抑制仍未得到解决。我们研究了shieldin及其与Ctc1-Stn1-Ten1（CST）复合物的相互作用，最近发现CST复合物在53BP1的下游发挥作用。从免疫表型上看，缺乏shieldin或CST的小鼠表现相同，类别转换重组依赖于这两种复合物。共济失调毛细血管扩张症突变激酶依赖性DNA损伤信号传导是这种合作的基础，它诱导这些复合物之间发生物理相互作用，从而揭示shieldin是一种DSB反应性CST衔接蛋白。此外，DNA聚合酶ζ在shieldin的下游发挥作用，将DNA填充合成确立为shieldin-CST的生理功能。最后，我们证明53BP1在BRCA1缺陷的小鼠和细胞中独立于shieldin抑制HR并促进NHEJ。这些发现展示了53BP1途径的多功能性，这是通过与染色质结合的53BP1复合物和DNA末端加工效应蛋白的协作实现的。
