Department of Biochemistry and Molecular Biology, Southern Alberta Cancer Research Institute, University of Calgary, Calgary, Alberta, Canada.
Carcinogenesis. 2011 Mar;32(3):279-85. doi: 10.1093/carcin/bgq255. Epub 2010 Nov 26.
Prolonged exposure to estrogen increases breast cancer risk. Estrogen is known to induce chromosomal aberrations, yet the mechanisms by which estrogen promotes genomic instability are not fully understood. Here, we show that exposure of MCF-7 cells to 17β-estradiol (E2) induces DNA double-strand breaks (DSBs), as determined by the formation of γH2AX foci. Foci formation was dependent upon estrogen receptor-α (ERα) and the catalytic activity of the type II topoisomerase, topoisomerase IIβ (topoIIβ). Moreover, we show by chromatin immunoprecipitation that topoIIβ-dependent E2-induced γH2AX localizes to the promoter of the estrogen-inducible gene, trefoil factor 1. E2-induced foci were associated with cyclin A expression and inhibited by pre-incubation with the DNA polymerase inhibitor aphidicolin suggesting that E2-induced DSBs are mediated by progression through S phase. Furthermore, E2-induced γH2AX foci colocalized with Rad51, suggesting that E2-induced DSBs are repaired by homologous recombination. We propose that DNA DSBs formed by the strand-cleaving activity of the topoIIβ-DNA cleavage complex at estrogen-inducible genes can present a barrier to DNA replication, leading to persistent DNA DSBs in ERα-positive breast cancer cells.
雌激素暴露时间延长会增加乳腺癌的风险。已知雌激素会诱导染色体畸变，但雌激素促进基因组不稳定性的机制尚未完全阐明。在这里，我们显示 MCF-7 细胞暴露于 17β-雌二醇（E2）会诱导 DNA 双链断裂（DSB），这是通过 γH2AX 焦点的形成来确定的。焦点形成依赖于雌激素受体-α（ERα）和 II 型拓扑异构酶，拓扑异构酶 IIβ（topoIIβ）的催化活性。此外，我们通过染色质免疫沉淀显示，topoIIβ 依赖性 E2 诱导的 γH2AX 定位于雌激素诱导基因三叶因子 1 的启动子。E2 诱导的焦点与细胞周期蛋白 A 的表达有关，并且被 DNA 聚合酶抑制剂 aphidicolin 预先孵育抑制，表明 E2 诱导的 DSB 是通过 S 期进展介导的。此外，E2 诱导的 γH2AX 焦点与 Rad51 共定位，表明 E2 诱导的 DSB 是通过同源重组修复的。我们提出，拓扑异构酶 IIβ-DNA 切割复合物的链切割活性在雌激素诱导基因处形成的 DNA DSB 可以成为 DNA 复制的障碍，导致 ERα 阳性乳腺癌细胞中持续存在 DNA DSB。
