AN ALKYLATION-TOLERANT, MUTATOR HUMAN CELL-LINE IS DEFICIENT IN STRAND-SPECIFIC MISMATCH REPAIR
AN ALKYLATION-TOLERANT, MUTATOR HUMAN CELL-LINE IS DEFICIENT IN STRAND-SPECIFIC MISMATCH REPAIR
复制标题
DOI：
10.1073/pnas.90.14.6424
复制
发表时间：
1993-07-15
影响因子：
11.1
通讯作者：
MODRICH, P
中科院分区：
文献类型：
--
作者：
KAT, A;THILLY, WG;MODRICH, P
人类淋巴母细胞MT 1 B细胞系先前被分离为能够在N-甲基-N '-硝基-N-亚硝基胍（MNNG）的细胞毒性作用下存活的一系列突变细胞之一。然而，MT 1细胞仍然对MNNG的诱变敏感，并显示出突变表型。这些表型已被归因于一个单一的遗传改变，假设赋予链特异性错配修复的缺陷，一个建议，属性的DNA烷基化在野生型细胞中的细胞毒性作用，以纠正错误的徒劳尝试，出现在复制烷基化模板链。我们的研究结果支持这一观点。MNNG诱导的MT 1细胞HPRT基因突变几乎完全是G. C-> A.T转换，而在该增变细胞系中观察到的自发突变是单核苷酸插入、颠换和A.T -> G. C转换。体外测定已经证明，MT 1系实际上缺乏对所有八个碱基-碱基错配的链特异性校正。这种缺陷在反应的切除阶段或之前表现出来，是由于所需活性的简单缺乏造成的，因为MT 1核提取物可以通过部分纯化的HeLa部分来补充以恢复体外修复。这些发现证实了链特异性错配修复有助于烷基化诱导的细胞毒性的想法，并暗示该过程作为哺乳动物细胞中自发转换，颠换和插入/缺失突变的屏障。
The human lymphoblastoid MT1 B-cell line was previously isolated as one of a series of mutant cells able to survive the cytotoxic effects of N-methyl-N'-nitro-N-nitrosoguanidine (MNNG). MT1 cells nevertheless remain sensitive to mutagenesis by MNNG and display a mutator phenotype. These phenotypes have been attributed to a single genetic alteration postulated to confer a defect in strand-specific mismatch repair, a proposal that attributes the cytotoxic effect of DNA alkylation in wild-type cells to futile attempts to correct mispairs that arise during replication of alkylated template strands. Our results support this view. MNNG-induced mutations in the HPRT gene of MT1 cells are almost exclusively G.C --> A.T transitions, while spontaneous mutations observed in this mutator cell line are single-nucleotide insertions, transversions, and A.T --> G.C transitions. In vitro assay has demonstrated that the MT1 line is in fact deficient in strand-specific correction of all eight base-base mispairs. This defect, which is manifest at or prior to the excision stage of the reaction, is due to simple deficiency of a required activity because MT1 nuclear extracts can be complemented by a partially purified HeLa fraction to restore in vitro repair. These findings substantiate the idea that strand-specific mismatch repair contributes to alkylation-induced cytotoxicity and imply that this process serves as a barrier to spontaneous transition, transversion, and insertion/deletion mutations in mammalian cells.