Goncharova E I, Nádas A, Rossman T G
New York University Medical Center, Nelson Institute of Environmental Medicine, New York 10016, USA.
Cancer Res. 1996 Feb 15;56(4):752-6.
Spontaneous mutagenesis is thought to play a crucial role in spontaneous carcinogenesis. We recently described a new mathematical model for estimation of the spontaneous mutation rate (mutation/gene/generations) based on the assumption that mutations are fixed in the S-phase of the cell cycle. With this definition, the spontaneous mutation rate should be independent of the growth rate. In the present study, we tested this hypothesis, using cell line G12, a transgenic Chinese hamster V79 derivative, which contains a single copy of the Escherichia coli gpt gene as a target for mutagenesis. The growth rate was modulated by varying the serum concentration or the seeding density, or by addition of suramin, transforming growth factor beta, or dichlorobenzimidazole riboside to the medium. Significant increases in the spontaneous mutation rate occurred when cell proliferation was blocked by serum deprivation. Density-dependent inhibition of growth and inhibition of growth by suramin, transforming growth factor beta, or dichlorobenzimidazole riboside did not result in significant increases in spontaneous mutation rates. The level of oxidants in cells cultivated in the presence of low concentrations of serum was higher compared to control cells, suggesting that the increases in the spontaneous mutation rates under low serum conditions may be partly a result of oxidative stress due to a lack of serum antioxidants. This was shown to be the case, because spontaneous mutation rates were significantly reduced in serum-depleted cells when antioxidants were added to the medium. We suggest that during carcinogenesis, when tumors are in a prevascularized state, the spontaneous mutation rate may be elevated, and this process may contribute to the genetic instability of the tumor cells.
自发诱变被认为在自发致癌过程中起着关键作用。我们最近描述了一种新的数学模型，用于估计自发突变率（突变/基因/世代），该模型基于突变在细胞周期的S期固定的假设。根据这个定义，自发突变率应该与生长速率无关。在本研究中，我们使用细胞系G12（一种转基因中国仓鼠V79衍生物）来检验这一假设，该细胞系含有单个大肠杆菌gpt基因拷贝作为诱变靶点。通过改变血清浓度或接种密度，或向培养基中添加苏拉明、转化生长因子β或二氯苯并咪唑核糖核苷来调节生长速率。当血清剥夺导致细胞增殖受阻时，自发突变率显著增加。苏拉明、转化生长因子β或二氯苯并咪唑核糖核苷对生长的密度依赖性抑制和生长抑制并未导致自发突变率显著增加。与对照细胞相比，在低浓度血清中培养的细胞中氧化剂水平更高，这表明低血清条件下自发突变率的增加可能部分是由于缺乏血清抗氧化剂导致的氧化应激所致。事实证明的确如此，因为向培养基中添加抗氧化剂后，血清缺乏细胞中的自发突变率显著降低。我们认为，在致癌过程中，当肿瘤处于血管生成前期状态时，自发突变率可能会升高，这一过程可能会导致肿瘤细胞的遗传不稳定性。
