Institute of Medical Radiation Biology, University Hospital Essen, University of Duisburg-Essen, 45147 Essen, Germany.
Division of Experimental Radiation Biology, Department of Radiation Therapy, University Hospital Essen, University of Duisburg-Essen, 45147 Essen, Germany.
Cells. 2022 Jul 2;11(13):2099. doi: 10.3390/cells11132099.
The load of DNA double-strand breaks (DSBs) induced in the genome of higher eukaryotes by different doses of ionizing radiation (IR) is a key determinant of DSB repair pathway choice, with homologous recombination (HR) and ATR substantially gaining ground at doses below 0.5 Gy. Increased resection and HR engagement with decreasing DSB-load generate a conundrum in a classical non-homologous end-joining (c-NHEJ)-dominated cell and suggest a mechanism adaptively facilitating resection. We report that ablation of DNA-PKcs causes hyper-resection, implicating DNA-PK in the underpinning mechanism. However, hyper-resection in -deficient cells can also be an indirect consequence of their c-NHEJ defect. Here, we report that all tested mutants show hyper-resection, while mutants with defects in all other factors of c-NHEJ fail to do so. This result rules out the model of c-NHEJ versus HR competition and the passive shift from c-NHEJ to HR as the causes of the increased resection and suggests the integration of DNA-PKcs into resection regulation. We develop a model, compatible with the results of others, which integrates DNA-PKcs into resection regulation and HR for a subset of DSBs. For these DSBs, we propose that the kinase remains at the break site, rather than the commonly assumed autophosphorylation-mediated removal from DNA ends.
由不同剂量电离辐射（IR）在高等真核生物基因组中诱导的 DNA 双链断裂（DSB）负载是 DSB 修复途径选择的关键决定因素，同源重组（HR）和 ATR 在低于 0.5 Gy 的剂量下显著增加。随着 DSB 负载的减少，增加的切除和 HR 与 DSB 的结合产生了一个经典的非同源末端连接（c-NHEJ）为主的细胞中的难题，并提出了一种适应性促进切除的机制。我们报告说，DNA-PKcs 的消融会导致过度切除，这表明 DNA-PK 参与了基础机制。然而，-缺陷细胞中的过度切除也可能是其 c-NHEJ 缺陷的间接后果。在这里，我们报告说所有测试的 -/- 突变体都表现出过度切除，而其他 c-NHEJ 因子缺陷的突变体则不能。这一结果排除了 c-NHEJ 与 HR 竞争的模型以及从 c-NHEJ 到 HR 的被动转变作为增加切除的原因，并表明 DNA-PKcs 被整合到切除调节中。我们提出了一个模型，该模型与其他人的结果兼容，将 DNA-PKcs 整合到一部分 DSB 的切除调节和 HR 中。对于这些 DSB，我们提出激酶仍然留在断裂部位，而不是通常假设的通过自动磷酸化从 DNA 末端移除。
