A novel protein, MAPO1, that functions in apoptosis triggered by O6-methylguanine mispair in DNA

Oncogene. 2009 Feb 26;28(8):1142-50. doi: 10.1038/onc.2008.462. Epub 2009 Jan 12.


O(6)-Methylguanine produced in DNA induces mutation due to its ambiguous base-pairing properties during DNA replication. To suppress such an outcome, organisms possess a mechanism to eliminate cells carrying O(6)-methylguanine by inducing apoptosis that requires the function of mismatch repair proteins. To identify other factors involved in this apoptotic process, we performed retrovirus-mediated gene-trap mutagenesis and isolated a mutant that acquired resistance to a simple alkylating agent, N-methyl-N-nitrosourea (MNU). However, it was still sensitive to methyl methanesulfonate, 1-(4-amino-2-methyl-5-pyrimidinyl)methyl-3-(2-chloroethyl)-3-nitrosourea, etoposide and ultraviolet irradiation. Moreover, the mutant exhibited an increased mutant frequency after exposure to MNU. The gene responsible was identified and designated Mapo1 (O(6)-methylguanine-induced apoptosis 1). When the expression of the gene was inhibited by small interfering RNA, MNU-induced apoptosis was significantly suppressed. In the Mapo1-defective mutant cells treated with MNU, the mitochondrial membrane depolarization and caspase-3 activation were severely suppressed, although phosphorylation of p53, CHK1 and histone H2AX was observed. The orthologs of the Mapo1 gene are present in various organisms from nematode to humans. Both mouse and human MAPO1 proteins expressed in cells localize in the cytoplasm. We therefore propose that MAPO1 may play a role in the signal-transduction pathway of apoptosis induced by O(6)-methylguanine-mispaired lesions.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adaptor Proteins, Signal Transducing / physiology
  • Animals
  • Antineoplastic Agents, Alkylating / pharmacology
  • Antineoplastic Agents, Phytogenic / pharmacology
  • Apoptosis / genetics*
  • Base Pair Mismatch / genetics*
  • Caspase 3 / metabolism
  • DNA / genetics*
  • DNA Modification Methylases / physiology
  • DNA Repair Enzymes / physiology
  • Etoposide / pharmacology
  • Fibroblasts / drug effects
  • Fibroblasts / metabolism
  • Fibroblasts / radiation effects
  • Gene Expression Regulation / physiology*
  • Guanine / analogs & derivatives*
  • Guanine / metabolism
  • Humans
  • Lung / drug effects
  • Lung / metabolism
  • Lung / radiation effects
  • Methyl Methanesulfonate / pharmacology
  • Methylnitrosourea / pharmacology
  • Mice
  • Mice, Knockout / genetics*
  • MutL Protein Homolog 1
  • Mutagenesis
  • Mutation / genetics
  • Nuclear Proteins / physiology
  • RNA, Small Interfering / pharmacology
  • Tumor Suppressor Proteins / physiology
  • Ultraviolet Rays


  • Adaptor Proteins, Signal Transducing
  • Antineoplastic Agents, Alkylating
  • Antineoplastic Agents, Phytogenic
  • Mlh1 protein, mouse
  • Nuclear Proteins
  • RNA, Small Interfering
  • Tumor Suppressor Proteins
  • Guanine
  • Methylnitrosourea
  • Etoposide
  • DNA
  • O-(6)-methylguanine
  • Methyl Methanesulfonate
  • DNA Modification Methylases
  • MGMT protein, mouse
  • Casp3 protein, mouse
  • Caspase 3
  • MutL Protein Homolog 1
  • DNA Repair Enzymes