RRC ID 12054
Author Takagi Y, Takahashi M, Sanada M, Ito R, Yamaizumi M, Sekiguchi M.
Title Roles of MGMT and MLH1 proteins in alkylation-induced apoptosis and mutagenesis.
Journal DNA Repair (Amst.)
Abstract To examine involvement of mismatch repair system in alkylation-induced apoptosis and mutagenesis, cell lines defective in the Mgmt gene encoding a DNA repair enzyme, O(6)-methylguanine-DNA methyltransferase, and/or the Mlh1 gene encoding a protein involved in mismatch repair were established from gene-targeted mice. Mgmt(-/-) cells are hypersensitive to the killing effect of N-methyl-N-nitrosourea (MNU) and this effect of MNU was overcome by introducing an additional mutation in the Mlh1 gene. Mgmt(-/-)Mlh1(-/-) cells are more resistant to MNU than are wild-type cells. When the human Mgmt cDNA sequence with a strong promoter was introduced, the wild-type cells acquired the same high level of resistance to MNU as that of Mgmt(-/-)Mlh1(-/-) cells. Although no apparent increase in MNU-induced mutant frequency was observed in such methyltransferase-overproducing wild-type cells, mutant frequency of Mgmt(-/-)Mlh1(-/-) cells became 10-fold higher after being treated with MNU. Mgmt(-/-)Mlh1(+/-) cells carrying approximately half the normal level of MLH1 protein showed a normal level of spontaneous mutant frequency, yet were still highly responsive to the mutagenic effect of the alkylating carcinogen. This haploinsufficient character of Mlh1 mutation was also observed in cell survival assays; Mgmt(-/-)Mlh1(+/-) cells were as resistant to MNU as were Mgmt(-/-)Mlh1(-/-) cells. While caspase-3 was induced in Mgmt(-/-)Mlh1(+/+) cells after treatment with MNU, no induction occurred in Mgmt(-/-)Mlh1(+/-) cells or in Mgmt(-/-)Mlh1(-/-) cells. The cellular content of MLH1 protein seems to be critical for determining if damaged cells enter into either a death or mutation-inducing pathway. The haploinsufficient phenotype of Mlh1-heterozygous cells may be explained by competition in heterodimer formation between MLH1 homologues.
Volume 2(10)
Pages 1135-46
Published 2003-10-7
PII S1568786403001344
PMID 13679151
MeSH Adaptor Proteins, Signal Transducing Alkylating Agents / pharmacology Alkylation Animals Apoptosis* / drug effects* Base Pair Mismatch Carrier Proteins Caspase 3 Caspases / metabolism Cell Line, Tumor Cell Survival / drug effects DNA Damage Methylnitrosourea / pharmacology Mice Mice, Knockout MutL Protein Homolog 1 Mutagenesis* / drug effects* Mutation Neoplasm Proteins / genetics Neoplasm Proteins / physiology* Nuclear Proteins O(6)-Methylguanine-DNA Methyltransferase / genetics O(6)-Methylguanine-DNA Methyltransferase / physiology* Time Factors
IF 3.711
Times Cited 34
DNA material pSVtsA58 ori (-) (RDB01126)