Klein J C, Bleeker M J, Roelen H C, Rafferty J A, Margison G P, Brugghe H F, van den Elst H, van der Marel G A, van Boom J H, Kriek E
Division of Molecular Carcinogenesis, The Netherlands Cancer Institute, Amsterdam.
J Biol Chem. 1994 Oct 14;269(41):25521-8.
O4-Alkylthymines have been implicated as potential carcinogenic DNA lesions. We have studied the effects of O4-methylthymine, O4-ethylthymine, and O4-n-propylthymine in a model system in which a single lesion was located at a defined position on a SV40-based shuttle vector and have found large differences in the effects of these lesions in repair-proficient and nucleotide excision repair-deficient cells. In repair-competent human HeLa cells, normal fibroblasts, and XP-A (2OS) revertant cells, all 3 residues were highly mutagenic; a mutation frequency of approximately 20% was found for both O4-methylthymine and O4-ethylthymine, whereas that of O4-n-propylthymine was approximately 12%. These frequencies were independent of the activity of the O6-alkylguanine DNA alkyltransferase. All three O4-alkylthymines induced T-->C transitions exclusively. In nucleotide excision repair-deficient XP-A cells, however, these lesions were not mutagenic but strongly inhibited plasmid replication (> 90%). These results indicate that O4-alkylthymines are efficiently recognized by the nucleotide excision repair system and cause a complete cessation of plasmid replication if this system is deficient. Nevertheless, proficiency in the nucleotide excision repair pathway correlates with a high frequency of mutation induction by these lesions.
O4-烷基胸腺嘧啶被认为是潜在的致癌性DNA损伤。我们在一个模型系统中研究了O4-甲基胸腺嘧啶、O4-乙基胸腺嘧啶和O4-正丙基胸腺嘧啶的作用，在该模型系统中，单个损伤位于基于SV40的穿梭载体上的特定位置，并且发现这些损伤在修复 proficient 和核苷酸切除修复缺陷细胞中的作用存在很大差异。在具有修复能力的人宫颈癌HeLa细胞、正常成纤维细胞和XP-A（2OS）回复细胞中，所有3个残基都具有高度致突变性；O4-甲基胸腺嘧啶和O4-乙基胸腺嘧啶的突变频率约为20%，而O4-正丙基胸腺嘧啶的突变频率约为12%。这些频率与O6-烷基鸟嘌呤DNA烷基转移酶的活性无关。所有三种O4-烷基胸腺嘧啶仅诱导T→C转换。然而，在核苷酸切除修复缺陷的XP-A细胞中，这些损伤没有致突变性，但强烈抑制质粒复制（>90%）。这些结果表明，O4-烷基胸腺嘧啶被核苷酸切除修复系统有效识别，如果该系统缺陷，则会导致质粒复制完全停止。尽管如此，核苷酸切除修复途径的 proficiency 与这些损伤诱导的高突变频率相关。
