DNA topoisomerase II (TOP2) is a major DNA metabolic enzyme, with important roles in replication, transcription, chromosome segregation and spatial organisation of the genome. TOP2 is the target of a class of anticancer drugs that poison the DNA-TOP2 transient complex to generate TOP2-linked DNA double-strand breaks (DSBs). The accumulation of DSBs kills tumour cells but can also result in genome instability. The way in which topoisomerase activity contributes to transcription remains unclear. In this work we have investigated how transcription contributes to TOP2-dependent DSB formation, genome instability and cell death. Our results demonstrate that gene transcription is an important source of abortive TOP2 activity. However, transcription does not contribute significantly to apoptosis or cell death promoted by TOP2-induced DSBs. On the contrary: transcription-dependent breaks greatly contribute to deleterious mutations and translocations, and can promote oncogenic rearrangements. Importantly, we show that TOP2-induced genome instability is mediated by mutagenic canonical non-homologous end joining whereas homologous recombination protects cells against these insults. Collectively, these results uncover mechanisms behind deleterious effects of TOP2 abortive activity during transcription, with relevant implications for chemotherapy.

中文翻译：

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规范的非同源末端连接促进转录相关 DNA 拓扑异构酶 2 活性诱导的基因组突变和易位。

DNA拓扑异构酶II (TOP2)是一种主要的DNA代谢酶，在基因组的复制、转录、染色体分离和空间组织中发挥重要作用。TOP2 是一类抗癌药物的靶标，它会毒害 DNA-TOP2 瞬时复合物，从而产生 TOP2 连接的 DNA 双链断裂 (DSB)。DSB 的积累会杀死肿瘤细胞，但也会导致基因组不稳定。拓扑异构酶活性促进转录的方式仍不清楚。在这项工作中，我们研究了转录如何促进 TOP2 依赖性 DSB 形成、基因组不稳定和细胞死亡。我们的结果表明基因转录是 TOP2 活性失效的重要来源。然而，转录对 TOP2 诱导的 DSB 促进的细胞凋亡或细胞死亡没有显着影响。相反：转录依赖性断裂极大地导致有害突变和易位，并且可以促进致癌重排。重要的是，我们发现 TOP2 诱导的基因组不稳定性是由诱变规范非同源末端连接介导的，而同源重组可以保护细胞免受这些损伤。总的来说，这些结果揭示了转录过程中 TOP2 无效活性的有害影响背后的机制，并对化疗具有相关意义。