Correlation between DNA methylation and expression of O6-methylguanine-DNA methyltransferase gene in cultured human tumor cells

Yi Wang, Tomohisa Kato, Hitoshi Ayaki, Kanji Ishizaki, Keizo Tano, Sankar Mitra, Mituo Ikenaga

Research output: Contribution to journalArticlepeer-review

43 Scopus citations


Approximately 20% of human tumor cell strains are deficient in a DNA repair protein, O6-methylguanine-DNA methyltransferase (MGMT), and are called Mer- strains. In an attempt to determine the molecular basis for the extinction of MGMT expression in Mer- human cells, the distribution of DNA methylation sites in and around the exon sequences of the repair gene was compared in 6 Mer+ (repair-proficient) and 12 Mer- cell lines. Southern blot analysis of the genomic DNA digested with isoschizomeric restriction endonucleases MspI and HpaII to detect 5-methylcytosine in CCGG sequences indicated that the DNA of all the Mer+ cells but of none of the Mer- cells is heavily methylated in the exon-containing regions. The methylation pattern contradicts the general belief that inactive genes are hypermethylated compared to hypomethylation of transcriptionally active genes. It appears that the regulation of the MGMT gene in human cells is much more complex than simply dictated by its methylation level.

Original languageEnglish (US)
Pages (from-to)221-230
Number of pages10
JournalMutation Research-DNA Repair
Issue number2
StatePublished - Mar 1992

ASJC Scopus subject areas

  • Molecular Biology
  • Toxicology
  • Genetics


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