Division of Radiation and Cancer Biology, Department of Radiation Oncology, Stanford University School of Medicine, Stanford, CA 94305, USA.
Nucleic Acids Res. 2024 May 22;52(9):5048-5066. doi: 10.1093/nar/gkae140.
Two DNA repair pathways, non-homologous end joining (NHEJ) and alternative end joining (A-EJ), are involved in V(D)J recombination and chromosome translocation. Previous studies reported distinct repair mechanisms for chromosome translocation, with NHEJ involved in humans and A-EJ in mice predominantly. NHEJ depends on DNA-PKcs, a critical partner in synapsis formation and downstream component activation. While DNA-PKcs inhibition promotes chromosome translocations harboring microhomologies in mice, its synonymous effect in humans is not known. We find partial DNA-PKcs inhibition in human cells leads to increased translocations and the continued involvement of a dampened NHEJ. In contrast, complete DNA-PKcs inhibition substantially increased microhomology-mediated end joining (MMEJ), thus bridging the two different translocation mechanisms between human and mice. Similar to a previous study on Ku70 deletion, DNA-PKcs deletion in G1/G0-phase mouse progenitor B cell lines, significantly impairs V(D)J recombination and generated higher rates of translocations as a consequence of dysregulated coding and signal end joining. Genetic DNA-PKcs inhibition suppresses NHEJ entirely, with repair phenotypically resembling Ku70-deficient A-EJ. In contrast, we find DNA-PKcs necessary in generating the near-exclusive MMEJ associated with Lig4 deficiency. Our study underscores DNA-PKcs in suppressing illegitimate chromosome rearrangement while also contributing to MMEJ in both species.
两种 DNA 修复途径，非同源末端连接（NHEJ）和替代末端连接（A-EJ），参与 V(D)J 重组和染色体易位。先前的研究报告了染色体易位的不同修复机制，其中 NHEJ 涉及人类，A-EJ 主要涉及小鼠。NHEJ 依赖于 DNA-PKcs，它是联会形成和下游组件激活的关键伴侣。虽然 DNA-PKcs 抑制促进了小鼠中含有微同源性的染色体易位，但在人类中其相同的效果尚不清楚。我们发现，人类细胞中部分 DNA-PKcs 的抑制导致易位增加，并持续涉及减弱的 NHEJ。相比之下，完全的 DNA-PKcs 抑制显著增加了微同源介导的末端连接（MMEJ），从而在人类和小鼠之间架起了两种不同的易位机制之间的桥梁。与 Ku70 缺失的先前研究相似，G1/G0 期小鼠祖 B 细胞系中 DNA-PKcs 的缺失，严重损害了 V(D)J 重组，并由于编码和信号末端连接的失调导致易位率增加。遗传 DNA-PKcs 的抑制完全抑制了 NHEJ，其修复表型类似于 Ku70 缺陷的 A-EJ。相比之下，我们发现 DNA-PKcs 在产生与 Lig4 缺陷相关的几乎专有的 MMEJ 中是必需的。我们的研究强调了 DNA-PKcs 在抑制不合法的染色体重排的同时，也在两种物种中促进 MMEJ。
