Jansen J G, Vrieling H, van Teijlingen C M, Mohn G R, Tates A D, van Zeeland A A
MGC-Department of Radiation Genetics and Chemical Mutagenesis, State University of Leiden, The Netherlands.
Cancer Res. 1995 May 1;55(9):1875-82.
The role of DNA alkylation at the O6 position of guanine in the induction of gene mutations in vivo was studied in the hprt gene of rat T-lymphocytes from spleen exposed in vivo to the monofunctional ethylating agents ethylmethanesulfonate (EMS) and N-ethyl-N-nitrosourea (ENU), or the hydroxyethylating agent N-(2-hydroxyethyl)-N-nitrosourea (HOENU). All chemicals showed an exposure-dependent increase in hprt mutant frequency. HOENU and ENU, however, were much more mutagenic than EMS when compared at equimolar levels. DNA sequence analysis was performed on PCR products of hprt cDNA from 40 EMS-, 35 HOENU-, and 46 ENU-induced 6-thioguanine-resistant T-lymphocyte clones. Thirty EMS-induced mutants contained a single base pair substitution with GC to AT transitions being the predominant type of mutation (26 of 30) which are probably caused by mispairing of O6-ethylguanine with T during DNA replication. No strand specificity of mutated G's among GC to AT transitions was observed. Twenty-three HOENU- and 42 ENU-induced mutants contained a single base pair substitution. In contrast to EMS, GC to AT transitions were found at a low frequency, 4 of 23 for HOENU and 5 of 42 for ENU, indicating that O6-hydroxyethylguanine and O6-ethylguanine are less important in HOENU- and ENU-induced mutagenesis in vivo, respectively. Also here no strand bias for mutated G's was observed, although the number of this type of mutation was limited. The most frequently induced base pair alterations by HOENU and ENU were transversions at AT base pairs, 16 of 23 and 28 of 42, respectively, with AT to TA being the predominant type of mutation. In both ENU and HOENU mutational spectra, an extreme strand bias for mutated T's toward the nontranscribed strand was found. The results suggest that DNA damage induced in rat T-lymphocytes in vivo by HOENU and ENU is processed in similar ways.
研究了体内鸟嘌呤O6位的DNA烷基化在诱导基因突变中的作用，该研究以大鼠脾脏T淋巴细胞的hprt基因为对象，这些细胞在体内暴露于单功能乙基化剂甲磺酸乙酯（EMS）和N-乙基-N-亚硝基脲（ENU），或羟乙基化剂N-（2-羟乙基）-N-亚硝基脲（HOENU）。所有化学物质均显示hprt突变频率随暴露量增加。然而，在等摩尔水平比较时，HOENU和ENU的致突变性比EMS高得多。对来自40个EMS诱导、35个HOENU诱导和46个ENU诱导的6-硫鸟嘌呤抗性T淋巴细胞克隆的hprt cDNA的PCR产物进行了DNA序列分析。30个EMS诱导的突变体包含单个碱基对替换，其中GC到AT的转换是主要的突变类型（30个中有26个），这可能是由于在DNA复制过程中O6-乙基鸟嘌呤与T错配所致。在GC到AT的转换中，未观察到突变G的链特异性。23个HOENU诱导的突变体和42个ENU诱导的突变体包含单个碱基对替换。与EMS相反，GC到AT的转换频率较低，HOENU为23个中的4个，ENU为42个中的5个，这表明O6-羟乙基鸟嘌呤和O6-乙基鸟嘌呤在HOENU和ENU诱导的体内诱变中分别不太重要。同样，尽管这种突变类型的数量有限，但也未观察到突变G的链偏向。HOENU和ENU最常诱导的碱基对改变是AT碱基对的颠换，分别为23个中的16个和42个中的28个，其中AT到TA是主要的突变类型。在ENU和HOENU的突变谱中，均发现突变T向非转录链存在极端的链偏向。结果表明，HOENU和ENU在体内诱导大鼠T淋巴细胞的DNA损伤以相似的方式处理。
