Goncharova E I, Rossman T G
Nelson Institute of Environmental Medicine, New York University Medical Center, New York 10016.
Cancer Res. 1994 Oct 15;54(20):5318-23.
G12, a transgenic Chinese hamster V79 cell derivative which contains a single copy of the Escherichia coli gpt gene as a target for mutagenesis, has little constitutive metallothionein (MT) expression. It was transfected with a vector containing the mouse MT-I gene, and MT-I-overproducing lines were isolated. MT-I transfectants had lower spontaneous mutation frequencies compared with the G12 parental cell line. Mutagenesis by alkylating agents was unchanged. MT expression in G12 and MT transfectants could be modulated by exposure to Zn(II) or Cd(II). The spontaneous mutation frequencies in Zn(II)- and Cd(II)-treated cells was inversely related to MT expression. In G12 cells grown in concentrations of Zn(II) up to 12 microM, a significant dose-dependent increase in spontaneous mutagenesis was observed. At higher (but subtoxic) concentrations in which endogenous MT was induced, a dramatic decrease in spontaneous mutagenesis was observed. In contrast, MT-I transfectants exhibited much lower spontaneous mutagenesis after growth in all concentrations of Zn(II). These data demonstrate a possible role for MT in modulating spontaneous mutagenesis and point to a role for Zn(II) in contributing to spontaneous mutagenesis. Because there is variability in human MT expression, low MT expression might be a risk factor for cancer.
G12是一种转基因中国仓鼠V79细胞衍生物，它含有单个拷贝的大肠杆菌gpt基因作为诱变靶点，其组成型金属硫蛋白（MT）表达很少。用含有小鼠MT-I基因的载体转染该细胞，并分离出MT-I过量表达的细胞系。与G12亲本细胞系相比，MT-I转染细胞的自发突变频率较低。烷基化剂诱导的诱变作用没有变化。G12细胞和MT转染细胞中的MT表达可通过暴露于Zn(II)或Cd(II)来调节。Zn(II)和Cd(II)处理细胞中的自发突变频率与MT表达呈负相关。在浓度高达12 microM的Zn(II)中生长的G12细胞中，观察到自发诱变有显著的剂量依赖性增加。在诱导内源性MT的较高（但亚毒性）浓度下，观察到自发诱变显著降低。相比之下，MT-I转染细胞在所有浓度的Zn(II)中生长后，自发诱变率都低得多。这些数据证明了MT在调节自发诱变中的可能作用，并指出了Zn(II)在促成自发诱变中的作用。由于人类MT表达存在变异性，低MT表达可能是癌症的一个风险因素。
