TY - JOUR
T1 - O6-methylguanine-induced cell death involves exonuclease 1 as well as DNA mismatch recognition in vivo
AU - Klapacz, Joanna
AU - Meira, Lisiane B.
AU - Luchetti, David G.
AU - Calvo, Jennifer A.
AU - Bronson, Roderick T.
AU - Edelmann, Winfried
AU - Samson, Leona D.
PY - 2009/1/13
Y1 - 2009/1/13
N2 - Alkylation-induced O6-methylguanine (O6MeG) DNA lesions can be mutagenic or cytotoxic if unrepaired by the O6MeG-DNA methyltransferase (Mgmt) protein. O6MeG pairs with T during DNA replication, and if the O6MeG:T mismatch persists, a G:C to A:T transition mutation is fixed at the next replication cycle. O6MeG: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 O6MeG-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 O6MeG- 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 O6MeGs.
AB - Alkylation-induced O6-methylguanine (O6MeG) DNA lesions can be mutagenic or cytotoxic if unrepaired by the O6MeG-DNA methyltransferase (Mgmt) protein. O6MeG pairs with T during DNA replication, and if the O6MeG:T mismatch persists, a G:C to A:T transition mutation is fixed at the next replication cycle. O6MeG: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 O6MeG-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 O6MeG- 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 O6MeGs.
KW - Alkylation resistance
KW - Apoptosis
KW - DNA alkylation
KW - Mgmt
KW - N-methyl-N′- nitrosourea (MNU)
UR - http://www.scopus.com/inward/record.url?scp=58849124160&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=58849124160&partnerID=8YFLogxK
U2 - 10.1073/pnas.0811991106
DO - 10.1073/pnas.0811991106
M3 - Article
C2 - 19124772
AN - SCOPUS:58849124160
SN - 0027-8424
VL - 106
SP - 576
EP - 581
JO - Proceedings of the National Academy of Sciences of the United States of America
JF - Proceedings of the National Academy of Sciences of the United States of America
IS - 2
ER -