An Alkylation-Tolerant, Mutator Human Cell Line is Deficient in Strand-Specific Mismatch Repair

• Published in: Proceedings of the National Academy of Sciences - PNAS Vol. 90; no. 14; pp. 6424 - 6428
• Main Authors: Kat, Alexandra, Thilly, William G., Fang, Woei-Horng, Longley, Matthew J., Li, Guo-Min, Modrich, Paul
• Format: Journal Article
• Language: English
• Published: Washington, DC National Academy of Sciences of the United States of America 15.07.1993; National Acad Sciences; National Academy of Sciences
• Subjects: 550200 - Biochemistry; 550400 - Genetics; ALKYLATION; ANIMAL CELLS; B-Lymphocytes - physiology; Base pair mismatch; BASIC BIOLOGICAL SCIENCES; Biological and medical sciences; BIOLOGICAL EFFECTS; BIOLOGICAL RECOVERY; BIOLOGICAL REPAIR; CARBONIC ACID DERIVATIVES; Cell cycle; Cell Line; Cell lines; Cell Nucleus; CHEMICAL REACTIONS; cytotoxicity; DEFECTS; Deoxyribonucleic acid; DNA; DNA MISMATCH; DNA mismatch repair; DNA REPAIR; DNA Repair - genetics; Exons; Fundamental and applied biological sciences. Psychology; genes; GENETIC EFFECTS; Genetic mutation; Genetics; GUANIDINES; HeLa Cells; Human genetics; Humans; hypoxanthine phosphoribosyltransferase; Hypoxanthine Phosphoribosyltransferase - genetics; man; Molecular and cellular biology; Molecular genetics; MUTAGENESIS; Mutagenesis - genetics; Mutagenesis. Repair; Mutation; MUTATIONS; N-methyl-N'-nitro-N-nitrosoguanidine; NUCLEIC ACIDS; ORGANIC COMPOUNDS; ORGANIC NITROGEN COMPOUNDS; Phenotypes; REPAIR; SPONTANEOUS MUTATIONS; Human; Resistance; Carcinogen; Alkylating agent; Phenotype; Mutagenesis; Toxicity; DNA; Lesion; Repair; Lymphoblastoid cell; Mechanism
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.90.14.6424

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.