Fox M, Rossiter B J, Brennand J
Department of Biochemical Genetics, Paterson Institute for Cancer Research, Manchester, UK.
Mutagenesis. 1988 Jan;3(1):15-21. doi: 10.1093/mutage/3.1.15.
The revertibility of three spontaneous hypoxanthine phosphoribosyl transferase (HPRT)-deficient V79 cell lines has been determined after exposure to a number of alkylating agents. TG11 and 19 reverted at frequencies ranging from 1 X 10(-5) to 1 X 10(-4) after exposure to doses of ethylmethane sulphonate (EMS) N-methyl-N-nitrosourea (MNU) and N-ethyl-N-nitrosourea (ENU) resulting in surviving fractions between 1.0 and 0.1. Reversion frequencies in TG15 ranged from 10(-7) to 5 x 10(-6) over a similar dose range. The relative efficiencies of different monofunctional alkylating agents in causing reversion of TG11 at equitoxic doses were ENU greater than EMS greater than N-ethyl-N-nitroso-guanidine greater than MNU greater than N-methyl-N-nitrosoguanidine greater than methylmethane sulphonate. Revertant frequencies for all three cell lines were maximal immediately after treatment and declined thereafter at a rate inversely proportional to dose. Such kinetics are explicable if reversion is due to miscoding opposite alkylated guanines. Reversion frequencies after N-butyl-N-nitrosourea exposure were 100-fold lower than after MNU and kinetics of expression of revertant colonies differed. Frequencies were low immediately after treatment, increased between 0 and 24 h then remained at a plateau. Similar kinetics were observed after chlorozotocin and bis-chloroethylnitrosourea exposure. This difference in expression kinetics suggests that reversion in this case is not the result of direct miscoding but of errors in excision repair. TG11, 15 and 19 had low spontaneous mutant frequencies which were either unaffected or only marginally increased by treatment with 5-azacytidine.(ABSTRACT TRUNCATED AT 250 WORDS)
在暴露于多种烷化剂后，已测定了三种自发的次黄嘌呤磷酸核糖基转移酶（HPRT）缺陷型V79细胞系的回复突变情况。在暴露于甲磺酸乙酯（EMS）、N-甲基-N-亚硝基脲（MNU）和N-乙基-N-亚硝基脲（ENU）后，TG11和19以1×10⁻⁵至1×10⁻⁴的频率回复突变，这些剂量导致存活分数在1.0至0.1之间。在相似的剂量范围内，TG15的回复突变频率在10⁻⁷至5×10⁻⁶之间。在等毒性剂量下，不同单功能烷化剂导致TG11回复突变的相对效率为：ENU＞EMS＞N-乙基-N-亚硝基胍＞MNU＞N-甲基-N-亚硝基胍＞甲磺酸甲酯。所有三种细胞系的回复突变频率在处理后立即达到最大值，此后以与剂量成反比的速率下降。如果回复突变是由于与烷基化鸟嘌呤相对的错配编码导致的，那么这种动力学是可以解释的。暴露于N-丁基-N-亚硝基脲后的回复突变频率比MNU暴露后低100倍，且回复突变菌落的表达动力学不同。处理后频率较低，在0至24小时之间增加，然后保持在平稳状态。在暴露于氯脲菌素和双氯乙基亚硝基脲后也观察到了类似的动力学。这种表达动力学的差异表明，在这种情况下，回复突变不是直接错配编码的结果，而是切除修复错误的结果。TG11、15和19具有低自发突变频率，用5-氮杂胞苷处理后这些频率要么未受影响，要么仅略有增加。
