Developmental Biology Program, Memorial Sloan-Kettering Cancer Center and Weill Cornell Graduate School of Medical Sciences, New York, New York, USA.
Nat Struct Mol Biol. 2010 Apr;17(4):410-6. doi: 10.1038/nsmb.1773. Epub 2010 Mar 7.
Chromosomal translocations in hematologic and mesenchymal tumors form overwhelmingly by nonhomologous end-joining (NHEJ). Canonical NHEJ, essential for the repair of radiation-induced and some programmed double-strand breaks (DSBs), requires the Xrcc4-ligase IV complex. For other DSBs, the requirement for Xrcc4-ligase IV is less stringent, suggesting the existence of alternative end-joining (alt-NHEJ) pathways. To understand the contributions of the canonical NHEJ and alt-NHEJ pathways, we examined translocation formation in cells deficient in Xrcc4-ligase IV. We found that Xrcc4-ligase IV is not required for but rather suppresses translocations. Translocation breakpoint junctions have similar characteristics in wild-type cells and cells deficient in Xrcc4-ligase IV, including an unchanged bias toward microhomology, unlike what is observed for intrachromosomal DSB repair. Complex insertions in some junctions show that joining can be iterative, encompassing successive processing steps before joining. Our results imply that alt-NHEJ is the primary mediator of translocation formation in mammalian cells.
染色体重排主要通过非同源末端连接（NHEJ）形成于血液系统肿瘤和间叶性肿瘤中。经典 NHEJ 对于辐射诱导的和某些程序性双链断裂（DSB）的修复至关重要，需要 Xrcc4-连接酶 IV 复合物。对于其他 DSB，对 Xrcc4-连接酶 IV 的需求不那么严格，这表明存在替代的末端连接（alt-NHEJ）途径。为了了解经典 NHEJ 和 alt-NHEJ 途径的贡献，我们研究了 Xrcc4-连接酶 IV 缺陷细胞中的易位形成。我们发现，Xrcc4-连接酶 IV 不是必需的，而是抑制易位。野生型细胞和 Xrcc4-连接酶 IV 缺陷细胞中转位断点连接具有相似的特征，包括微同源性的偏好没有改变，与染色体内 DSB 修复不同。一些连接点的复杂插入表明连接可以是迭代的，在连接之前包含连续的处理步骤。我们的结果表明，alt-NHEJ 是哺乳动物细胞中易位形成的主要介导者。
