Department of Genome Repair Dynamics, Kyoto University, Yoshida-konoe, Sakyo, Kyoto, Japan.
Mutat Res. 2011 Nov 1;716(1-2):27-32. doi: 10.1016/j.mrfmmm.2011.07.017. Epub 2011 Aug 5.
The centrosome is a cytoplasmic organelle which duplicates once during each cell cycle, and the presence of excess centrosomes promote chromosome instability through chromosome missegregation following cytokinesis. Ionizing radiation (IR) can induce extra centrosomes by permitting the continuation of CDK2/Cyclin-A/E-mediated centrosome duplication when cells are arrested in the cell cycle after irradiation. The work described here shows that, in addition to IR, extra centrosomes were induced in human U2OS and mouse NIH3T3 cells after treatment with agents which include DNA adduct-forming chemicals: benzopyrene (BP), 4-nitroquinoline 1-oxide (4NQO), a DNA cross linker: cis-diamminedichloro-platinum (cisplatin), topoisomerase inhibitors: camptothecin, etoposide, genistein, and ultra-violet light (UV). These agents were divided into two categories with respect to the regulation of p21, which is an inhibitor of CDK2/Cyclin-A/E: specifically, p21 was up-regulated by an IR exposure and treatment with topoisomerase inhibitors. However, UV, BP, 4NQO and cisplatin down-regulated p21 below basal levels. When cells were irradiated with IR in combination with all of these agents, except genistein, enhanced induction of extra centrosomes was observed, regardless of the nature of p21 expression. Genistein significantly suppressed the frequency of IR-induced extra centrosomes in a dose-dependent manner, and 20μg/ml of genistein reduced this frequency to 66%. Consistent with this, genistein substantially up-regulated p21 expression over the induction caused by IR alone, while other agents down-regulated or marginally affected this. This suggests the inhibitory effect of genistein on the induction of extra centrosomes occurs through the inactivation of CDK2/Cyclin-A/E via p21 up-regulation. This hypothesis is supported by the observation that p21 knockdown with siRNA reduced the activity of CDK2/Cyclin-A/E and restored the enhanced effect of a combined treatment with genistein and IR. These results demonstrate the preventive effect of genistein and a crucial role for p21 in IR-induced excess centrosomes.
中心体是一种细胞质细胞器，在每个细胞周期中复制一次，多余的中心体的存在会通过细胞分裂后染色体的错误分离导致染色体不稳定。电离辐射（IR）可以通过允许 CDK2/细胞周期蛋白 A/E 介导的中心体复制在照射后细胞周期停滞时继续进行，从而诱导额外的中心体。这里描述的工作表明，除了 IR 之外，在用包括 DNA 加合物形成化学物质在内的药物处理人 U2OS 和小鼠 NIH3T3 细胞后，还会诱导额外的中心体：苯并芘（BP），4-硝基喹啉 1-氧化物（4NQO），DNA 交联剂：顺式二氨二氯铂（顺铂），拓扑异构酶抑制剂：喜树碱、依托泊苷、染料木黄酮和紫外线（UV）。这些药物根据 p21 的调节分为两类，p21 是 CDK2/细胞周期蛋白 A/E 的抑制剂：具体来说，IR 暴露和拓扑异构酶抑制剂处理上调了 p21。然而，UV、BP、4NQO 和 cisplatin 将 p21 下调至基础水平以下。当用这些药物与 IR 联合照射细胞时，除了染料木黄酮外，还观察到额外中心体的诱导增强，而与 p21 表达的性质无关。染料木黄酮以剂量依赖的方式显著抑制 IR 诱导的额外中心体的频率，而 20μg/ml 的染料木黄酮将此频率降低至 66%。与此一致的是，染料木黄酮显著上调了由 IR 单独诱导的 p21 表达，而其他药物则下调或轻微影响了 p21 的表达。这表明染料木黄酮对额外中心体诱导的抑制作用是通过 p21 上调使 CDK2/细胞周期蛋白 A/E 失活而发生的。这一假设得到了以下观察结果的支持：用 siRNA 敲低 p21 降低了 CDK2/细胞周期蛋白 A/E 的活性，并恢复了染料木黄酮和 IR 联合处理的增强作用。这些结果表明染料木黄酮具有预防作用，并且 p21 在 IR 诱导的多余中心体中起关键作用。
