O^sup 6^-methylguanine-induced cell death involves exonuclease 1 as well as DNA mismatch recognition in vivo

• Published in: Proceedings of the National Academy of Sciences - PNAS 2009-01, Vol.106 (2), p.576
• Main Authors: Klapacz, Joanna, Meira, Lisiane B, Luchetti, David G, Calvo, Jennifer A, Bronson, Roderick T, Edelmann, Winfried, Samson, Leona D
• Format: Article
• Language: English
• Subjects: Apoptosis; Cells; Deoxyribonucleic acid; DNA; Genotype & phenotype; Mutation; Proteins; Rodents
• ISSN: 0027-8424; 1091-6490

Alkylation-induced O...-methylguanine (O...MeG) DNA lesions can be mutagenic or cytotoxic if unrepaired by the O...MeG-DNA methyltransferase (Mgmt) protein. O...MeG pairs with T during DNA replication, and if the O...MeG:T mismatch persists, a G:C to A:T transition mutation is fixed at the next replication cycle. O...MeG:T mismatch detection by MutSα and MutLα leads to apoptotic cell death, but the mechanism by which this occurs has been elusive. To explore how mismatch repair mediates O...MeG-dependent apoptosis, we used an Mgmt-null mouse model combined with either the Msh6-null mutant (defective in mismatch recognition) or the Exo1-null mutant (impaired in the excision step of mismatch repair). Mouse embryonic fibroblasts and bone marrow cells derived from Mgmt-null mice were much more alkylation-sensitive than wild type, as expected. However, ablation of either Msh6 or Exo1 function rendered these Mgmt-null cells just as resistant to alkylation-induced cytotoxicity as wild-type cells. Rapidly proliferating tissues in Mgmt-null mice (bone marrow, thymus, and spleen) are extremely sensitive to apoptosis induced by O...MeG-producing agents. Here, we show that ablation of either Msh6 or Exo1 function in the Mgmt-null mouse renders these rapidly proliferating tissues alkylation-resistant. However, whereas the Msh6 defect confers total alkylation resistance, the Exo1 defect leads to a variable tissue-specific alkylation resistance phenotype. Our results indicate that Exo1 plays an important role in the induction of apoptosis by unrepaired O...MeGs. (ProQuest: ... denotes formulae/symbols omitted.)