Münzel P A, Pfohl-Leszkowicz A, Röhrdanz E, Keith G, Dirheimer G, Bock K W
Institute of Toxicology, University of Tübingen, Federal Republic of Germany.
Biochem Pharmacol. 1991 Jul 5;42(2):365-71. doi: 10.1016/0006-2952(91)90724-j.
The protooncogene c-myc was investigated in N-nitrosomorpholine-induced rat liver nodules to elucidate the role of altered DNA methylation in chemical carcinogenesis. Furthermore, Micrococcus luteus DNA and chicken erythrocyte DNA were modified in vitro by reactive metabolites of N-nitrosomorpholine, generated by P450-dependent monooxygenases. The modified DNAs were less methylated in vitro than control DNAs by DNA-(cytosine-5)-methyltransferase (DNA methylase). The DNA methylase assay and 32P-postlabeling analysis revealed lowered levels of DNA methylation in nodular DNA. In nodular tissue, c-myc messenger RNA levels were found to be increased compared to normal liver. DNA methylation analysis using the restriction endonucleases HpaII/MspI indicated hypomethylation in the first intron of c-myc DNA in liver nodules. The results suggest that genotoxic lesions may cause stably inherited, aberrant DNA methylation patterns which may be responsible for site-specific hypomethylation of the c-myc protooncogene in liver nodules.
对原癌基因c-myc在N-亚硝基吗啉诱导的大鼠肝结节中进行了研究，以阐明DNA甲基化改变在化学致癌过程中的作用。此外，通过P450依赖的单加氧酶产生的N-亚硝基吗啉的活性代谢产物，在体外对藤黄微球菌DNA和鸡红细胞DNA进行了修饰。与对照DNA相比，经修饰的DNA在体外被DNA-(胞嘧啶-5)-甲基转移酶（DNA甲基化酶）甲基化的程度更低。DNA甲基化酶测定和32P后标记分析显示结节性DNA中的DNA甲基化水平降低。在结节组织中，发现与正常肝脏相比，c-myc信使RNA水平升高。使用限制性内切酶HpaII/MspI进行的DNA甲基化分析表明，肝结节中c-myc DNA的第一个内含子存在低甲基化。结果表明，遗传毒性损伤可能导致稳定遗传的异常DNA甲基化模式，这可能是肝结节中c-myc原癌基因位点特异性低甲基化的原因。
