Agapova L S, Ivanov A V, Sablina A A, Kopnin P B, Sokova O I, Chumakov P M, Kopnin B P
Institute of Carcinogenesis, Cancer Research Center, Moscow Medical Center, Russia.
Oncogene. 1999 May 20;18(20):3135-42. doi: 10.1038/sj.onc.1202386.
Mutations activating the function of ras proto-oncogenes are often observed in human tumors. Their oncogenic potential is mainly due to permanent stimulation of cellular proliferation and dramatic changes in morphogenic reactions of the cell. To learn more on the role of ras activation in cancerogenesis we studied its effects on chromosome stability and cell cycle checkpoints. Since the ability of ras oncogenes to cause cell transformation may be dependent on activity of the p53 tumor-suppressor the cells with different p53 state were analysed. Ectopic expression of N-ras(asp12) caused in p53-deficient MDAH041 cell line an augmentation in the number of chromosome breaks in mitogenic cells, significant increase in the frequency of metaphases showing chromosome endoreduplication and accumulation of polyploid cells. Similar effects were induced by different exogenous ras genes (N-ras(asp12), H-ras(leu12), N-ras proto-oncogene) in Rat1 and Rat2 cells which have a defect in p53-upstream pathways. In contrast, in REF52 and human LIM1215 cells showing ras-induced p53 up-regulation, ras expression caused only slight increase in the number of chromosome breaks and did not enhance the frequency of endoreduplication and polyploidy. Inactivation in these cells of p53 function by transduction of dominant-negative C-terminal p53 fragment (genetic suppressor element #22, GSE22) or mutant p53s significantly increased the frequency of both spontaneous and ras-induced karyotypic changes. In concordance with these observations we have found that expression of ras oncogene caused in p53-defective cells further mitigation of ethyl-metansulphonate-induced G1 and G2 cell cycle arrest, but did not abrogate G1 and G2 cell cycle checkpoints in cells with normal p53 function. These data indicate that along with stimulation of cell proliferation and morphological transformation ras activation can contribute to cancerogenesis by increasing genetic instability.
激活原癌基因ras功能的突变在人类肿瘤中经常可见。它们的致癌潜能主要归因于对细胞增殖的持续刺激以及细胞形态发生反应的显著变化。为了更深入了解ras激活在肿瘤发生中的作用，我们研究了其对染色体稳定性和细胞周期检查点的影响。由于ras癌基因导致细胞转化的能力可能取决于p53肿瘤抑制因子的活性，因此我们分析了处于不同p53状态的细胞。在p53缺陷的MDAH041细胞系中，N-ras(asp12)的异位表达导致有丝分裂细胞中染色体断裂数量增加，出现染色体核内复制的中期频率显著升高，以及多倍体细胞的积累。在p53上游通路存在缺陷的Rat1和Rat2细胞中，不同的外源性ras基因（N-ras(asp12)、H-ras(leu12)、N-ras原癌基因）也诱导了类似的效应。相比之下，在显示ras诱导p53上调的REF52和人LIM1215细胞中，ras表达仅使染色体断裂数量略有增加，并未提高核内复制和多倍体的频率。通过转导显性负性C末端p53片段（基因抑制元件#22，GSE22）或突变型p53使这些细胞中的p53功能失活，显著增加了自发和ras诱导的核型变化频率。与这些观察结果一致，我们发现ras癌基因的表达在p53缺陷细胞中进一步减轻了甲磺酸乙酯诱导的G1和G2期细胞周期阻滞，但在p53功能正常的细胞中并未消除G1和G2期细胞周期检查点。这些数据表明，除了刺激细胞增殖和形态转化外，ras激活还可通过增加遗传不稳定性促进肿瘤发生。
