Mismatch repair and differential sensitivity of mouse and human cells to methylating agents

• Published in: Carcinogenesis (New York) 1999-02, Vol.20 (2), p.205-214
• Main Authors: HUMBERT, O, FIUMICINO, S, AQUILINA, G, BRANCH, P, ODA, S, ZIJNO, A, KARRAN, P, BIGNAMI, M
• Format: Article
• Language: English
• Subjects: 3T3 Cells - drug effects; Alkylating Agents - pharmacology; Animals; Antineoplastic Agents - pharmacology; Apoptosis; Base Pair Mismatch - drug effects; Base Pair Mismatch - genetics; Biological and medical sciences; Carcinogenesis, carcinogens and anticarcinogens; Chemical agents; Chromosomes, Human, Pair 2 - genetics; DNA Methylation; DNA Repair; DNA-Binding Proteins; Drug Resistance, Neoplasm - genetics; Gene Transfer Techniques; Genotype; Guanine - analogs & derivatives; Guanine - pharmacology; HeLa Cells - drug effects; Humans; Medical sciences; Melanoma, Experimental; Methylnitronitrosoguanidine; Methylnitrosourea - pharmacology; Mice; MutS Homolog 2 Protein; Proto-Oncogene Proteins - genetics; Species Specificity; Tumor Cells, Cultured - drug effects; Tumors
• ISSN: 0143-3334; 1460-2180; 1460-2180
• DOI: 10.1093/carcin/20.2.205

The long-patch mismatch repair pathway contributes to the cytotoxic effect of methylating agents and loss of this pathway confers tolerance to DNA methylation damage. Two methylation-tolerant mouse cell lines were identified and were shown to be defective in the MSH2 protein by in vitro mismatch repair assay. A normal copy of the human MSH2 gene, introduced by transfer of human chromosome 2, reversed the methylation tolerance. These mismatch repair defective mouse cells together with a fibroblast cell line derived from an MSH2-/- mouse, were all as resistant to N-methyl-N-nitrosourea as repair-defective human cells. Although long-patch mismatch repair-defective human cells were 50- to 100-fold more resistant to methylating agents than repair-proficient cells, loss of the same pathway from mouse cells conferred only a 3-fold increase. This discrepancy was accounted for by the intrinsic N-methyl-N-nitrosourea resistance of normal or transformed mouse cells compared with human cells. The >20-fold differential resistance between mouse and human cells could not be explained by the levels of either DNA methylation damage or the repair enzyme O6-methylguanine-DNA methyltransferase. The resistance of mouse cells to N-methyl-N-nitrosourea was selective and no cross-resistance to unrelated DNA damaging agents was observed. Pathways of apoptosis were apparently intact and functional after exposure to either N-methyl-N-nitrosourea or ultraviolet light. Extracts of mouse cells were found to perform 2-fold less long-patch mismatch repair. The reduced level of mismatch repair may contribute to their lack of sensitivity to DNA methylation damage.