Letter | Published:

DNMT1 is required to maintain CpG methylation and aberrant gene silencing in human cancer cells

Nature Genetics volume 33, pages 6165 (2003) | Download Citation

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Abstract

Transcriptional silencing by CpG island methylation is a prevalent mechanism of tumor-suppressor gene suppression in cancers1,2,3,4. Genetic experiments have defined the importance of the DNA methyltransferase Dnmt1 for the maintenance of methylation in mouse cells5 and its role in neoplasia6. In human bladder cancer cells, selective depletion of DNMT1 with antisense inhibitors has been shown to induce demethylation and reactivation of the silenced tumor-suppressor gene CDKN2A7. In contrast, targeted disruption of DNMT1 alleles in HCT116 human colon cancer cells produced clones that retained CpG island methylation and associated tumor-suppressor gene silencing8, whereas HCT116 clones with inactivation of both DNMT1 and DNMT3B showed much lower levels of DNA methylation, suggesting that the two enzymes are highly cooperative9. We used a combination of genetic (antisense and siRNA) and pharmacologic (5-aza-2′-deoxycytidine) inhibitors of DNA methyl transferases to study the contribution of the DNMT isotypes to cancer-cell methylation. Selective depletion of DNMT1 using either antisense or siRNA resulted in lower cellular maintenance methyltransferase activity, global and gene-specific demethylation and re-expression of tumor-suppressor genes in human cancer cells. Specific depletion of DNMT1 but not DNMT3A or DNMT3B markedly potentiated the ability of 5-aza-2′-deoxycytidine to reactivate silenced tumor-suppressor genes, indicating that inhibition of DNMT1 function is the principal means by which 5-aza-2′-deoxycytidine reactivates genes. These results indicate that DNMT1 is necessary and sufficient to maintain global methylation and aberrant CpG island methylation in human cancer cells.

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Author notes

    • Marie-France Robert
    •  & Steves Morin

    These authors contributed equally to this work.

Affiliations

  1. Department of Molecular Biology, MethylGene, 7220 Frederick-Banting, Montreal, Canada H4S 2A1.

    • Marie-France Robert
    • , Steves Morin
    • , Normand Beaulieu
    • , France Gauthier
    • , Ian C. Chute
    • , Annie Barsalou
    •  & A. Robert MacLeod

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Competing interests

All authors are employees of MethylGene, a privately owned biotechnology company. MethylGene does not have company stock, but employees have company-issued options to purchase MethylGene shares.

Corresponding author

Correspondence to A. Robert MacLeod.

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DOI

https://doi.org/10.1038/ng1068