De novo DNA methyltransferases Dnmt3a and Dnmt3b primarily mediate the cytotoxic effect of 5-aza-2'-deoxycytidine

Oncogene. 2005 Apr 28;24(19):3091-9. doi: 10.1038/sj.onc.1208540.


The deoxycytidine analog 5-aza-2'-deoxycitidine (5-aza-dC) is a potent chemotherapeutic agent effective against selective types of cancer. The molecular mechanism by which 5-aza-dC induces cancer cell death, however, is not fully understood. It has been accepted that the mechanism of toxicity is due to the covalent binding between the DNA methyltransferase (Dnmt) and 5-aza-dC-substituted DNA. In order to define which member of the Dnmt family plays a dominant role in the cytotoxicity, we examined the effect of 5-aza-dC on cell growth and apoptosis in various Dnmt null mutant embryonic stem (ES) cells. Of interest, Dnmt3a-Dnmt3b double null ES cells were highly resistant to 5-aza-dC when compared to wild type, Dnmt3a null, Dnmt3b null, or Dnmt1 null ES cells. The cellular sensitivity to 5-aza-dC correlated well with the expression status of Dnmt3 in both undifferentiated and differentiated ES cells. When exogenous Dnmt3a or Dnmt3b was expressed in double null ES cells, the sensitivity to 5-aza-dC was partially restored. These results suggest that the cytotoxic effect of 5-aza-dC may be mediated primarily through Dnmt3a and Dnmt3b de novo DNA methyltransferases. Further, the ability to form Dnmt-DNA adducts was similar in Dnmt1 and Dnmt3, and the expression level of Dnmt3 was not higher than that of Dnmt1 in ES cells. Therefore, Dnmt3-DNA adducts may be more effective for inducing apoptosis than Dnmt1-DNA adducts. These results imply a therapeutic potential of 5-aza-dC to cancers expressing Dnmt3.

MeSH terms

  • Animals
  • Apoptosis
  • Azacitidine / analogs & derivatives*
  • Azacitidine / pharmacology*
  • COS Cells
  • Cell Death
  • Cell Differentiation
  • Cell Line
  • DNA (Cytosine-5-)-Methyltransferase 1
  • DNA (Cytosine-5-)-Methyltransferases / metabolism
  • DNA (Cytosine-5-)-Methyltransferases / physiology*
  • DNA / metabolism
  • DNA Adducts / metabolism
  • DNA Fragmentation
  • DNA Modification Methylases / metabolism
  • Decitabine
  • Dose-Response Relationship, Drug
  • Embryo, Mammalian / cytology
  • Immunoblotting
  • Lentivirus / genetics
  • Mice
  • Mice, Knockout
  • Microscopy, Fluorescence
  • Mutation
  • Stem Cells / cytology


  • DNA Adducts
  • Decitabine
  • DNA
  • DNA Modification Methylases
  • DNA (Cytosine-5-)-Methyltransferase 1
  • DNA (Cytosine-5-)-Methyltransferases
  • DNA methyltransferase 3A
  • DNA methyltransferase 3B
  • Dnmt1 protein, mouse
  • Azacitidine