Grisham J W, Smith G J, Lee L W, Bentley K S, Fatteh M V
Department of Pathology, University of North Carolina School of Medicine, Chapel Hill 27599-7525.
Cancer Res. 1988 Nov 1;48(21):5977-83.
Exposure of synchronized C3H10T1/2 (clone 8) cell populations of various sizes to N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) at a concentration of 2 micrograms/ml for 30 min at 24 h after release from confluence-induced arrest of proliferation produced neoplastic transformation (formation of foci of morphologically altered cells) by a random but episodic process in a small fraction of the cells at risk soon after treatment. The fraction of dishes that contained type II or type III foci increased as the number of cells at risk increased. In contrast, the development of spontaneous foci is a stochastic process that depends on the number of new cells that form during population growth and is independent of the number of cells that are plated (J. W. Grisham et al., Cancer Res., 48: 5969-5976,1988). When there were small numbers of cells at risk, spontaneous formation of foci was a source of considerable error in evaluating MNNG-induced transformation frequency. In surviving cell populations of less than 1000-3000 cells/100-mm dish, the frequency of induction of foci by MNNG could not be distinguished statistically from the frequency with which foci were expected to form spontaneously. When the fraction of MNNG-treated dishes that contained foci was adjusted for the fraction of pooled control dishes that contained foci, the number of foci induced by a uniform dose of MNNG was found to vary with the number of surviving cells. However, the MNNG-induced transformation frequencies calculated by the Poisson method were independent of the size of the population of cells at risk, provided the population of cells at risk was of sufficient size to allow spontaneous and induced transformation to be distinguished statistically. The results of this study show that the frequency of MNNG-induced transformation can be quantitated in cultures of 10T1/2 cells that contain varying but sufficient numbers of cells at risk when spontaneous transformation is considered. Furthermore, these observations suggest that MNNG-induced transformation of 10T1/2 cells occurs with the frequency and characteristics of a mutation-like change involving a single gene.
将不同大小的同步化C3H10T1/2（克隆8）细胞群体，在从汇合诱导的增殖停滞中释放24小时后，于24℃下以2微克/毫升的浓度暴露于N-甲基-N'-硝基-N-亚硝基胍（MNNG）30分钟，处理后不久，一小部分处于风险中的细胞通过随机但偶发的过程发生了肿瘤转化（形态改变细胞灶的形成）。含有II型或III型灶的培养皿比例随着处于风险中的细胞数量增加而增加。相比之下，自发灶的形成是一个随机过程，它取决于群体生长过程中形成的新细胞数量，并且与接种的细胞数量无关（J.W.格里森姆等人，《癌症研究》，48:5969 - 5976,1988）。当处于风险中的细胞数量较少时，自发形成灶是评估MNNG诱导的转化频率时相当大误差的来源。在每100毫米培养皿中存活细胞少于1000 - 3000个的细胞群体中，MNNG诱导灶的频率在统计学上无法与预期自发形成灶的频率区分开来。当针对含有灶的合并对照培养皿比例调整含有灶的MNNG处理培养皿比例时，发现均匀剂量的MNNG诱导的灶数量随存活细胞数量而变化。然而，通过泊松方法计算的MNNG诱导的转化频率与处于风险中的细胞群体大小无关，前提是处于风险中的细胞群体足够大，能够在统计学上区分自发和诱导转化。本研究结果表明，当考虑自发转化时，在含有不同但足够数量处于风险中的细胞的10T1/2细胞培养物中，可以定量MNNG诱导的转化频率。此外，这些观察结果表明，MNNG诱导的10T1/2细胞转化以涉及单个基因的类似突变变化的频率和特征发生。
