Department of Radiation Genetics, Graduate School of Medicine, Kyoto University, 606-8501 Kyoto, Japan;
Department of Radiation Genetics, Graduate School of Medicine, Kyoto University, 606-8501 Kyoto, Japan.
Proc Natl Acad Sci U S A. 2018 Nov 6;115(45):E10642-E10651. doi: 10.1073/pnas.1803177115. Epub 2018 Oct 23.
Women having BRCA1 germ-line mutations develop cancer in breast and ovary, estrogen-regulated tissues, with high penetrance. Binding of estrogens to the estrogen receptor (ER) transiently induces DNA double-strand breaks (DSBs) by topoisomerase II (TOP2) and controls gene transcription. TOP2 resolves catenated DNA by transiently generating DSBs, TOP2-cleavage complexes (TOP2ccs), where TOP2 covalently binds to 5' ends of DSBs. TOP2 frequently fails to complete its catalysis, leading to formation of pathological TOP2ccs. We have previously shown that the endonucleolytic activity of MRE11 plays a key role in removing 5' TOP2 adducts in G phase. We show here that BRCA1 promotes MRE11-mediated removal of TOP2 adducts in G phase. We disrupted the gene in -deficient ER-positive breast cancer and B cells. The loss of BRCA1 caused marked increases of pathological TOP2ccs in G phase following exposure to etoposide, which generates pathological TOP2ccs. We conclude that BRCA1 promotes the removal of TOP2 adducts from DSB ends for subsequent nonhomologous end joining. -deficient cells showed a decrease in etoposide-induced MRE11 foci in G phase, suggesting that BRCA1 repairs pathological TOP2ccs by promoting the recruitment of MRE11 to TOP2cc sites. BRCA1 depletion also leads to the increase of unrepaired DSBs upon estrogen treatment both in vitro in G-arrested breast cancer cells and in vivo in epithelial cells of mouse mammary glands. BRCA1 thus plays a critical role in removing pathological TOP2ccs induced by estrogens as well as etoposide. We propose that BRCA1 suppresses tumorigenesis by removing estrogen-induced pathological TOP2ccs throughout the cell cycle.
携带 BRCA1 种系突变的女性会在乳腺和卵巢等雌激素调控组织中发生癌症，且具有高外显率。雌激素与雌激素受体（ER）结合会通过拓扑异构酶 II（TOP2）瞬时诱导 DNA 双链断裂（DSBs），并控制基因转录。TOP2 通过短暂生成 DSB 来解开连环 DNA，即 TOP2 断裂复合物（TOP2cc），其中 TOP2 与 DSB 的 5' 端共价结合。TOP2 经常无法完成其催化作用，导致形成病理性 TOP2cc。我们之前已经表明，MRE11 的内切核酸酶活性在 G 期去除 5' TOP2 加合物中发挥关键作用。我们在这里表明，BRCA1 促进 MRE11 介导的 G 期 TOP2 加合物的去除。我们在 - 缺陷的 ER 阳性乳腺癌和 B 细胞中破坏了该基因。BRCA1 的缺失导致暴露于依托泊苷后 G 期病理性 TOP2cc 的显著增加，依托泊苷会产生病理性 TOP2cc。我们得出结论，BRCA1 促进将 TOP2 加合物从 DSB 末端去除，以便随后进行非同源末端连接。在 G 期，- 缺陷细胞中依托泊苷诱导的 MRE11 焦点减少，表明 BRCA1 通过促进 MRE11 向 TOP2cc 位点募集来修复病理性 TOP2cc。BRCA1 耗竭也会导致雌激素处理后未修复的 DSB 增加，无论是在体外 G 期乳腺癌细胞中还是在体内小鼠乳腺上皮细胞中。因此，BRCA1 在去除由雌激素和依托泊苷诱导的病理性 TOP2cc 方面发挥着关键作用。我们提出，BRCA1 通过在整个细胞周期中去除雌激素诱导的病理性 TOP2cc 来抑制肿瘤发生。
