Progressive up-regulation of genes encoding DNA methyltransferases in the colorectal adenoma-carcinoma sequence

Mol Carcinog. 2007 Sep;46(9):766-72. doi: 10.1002/mc.20307.

Abstract

Epigenetic silencing is a prominent feature of cancer. Here, we investigated the expression of DNA demethylase and three DNA methyltransferases during colorectal tumorigenesis comparing the genes encoding DNA methyltransferases 1 (DNMT1), 3A, and 3B (DNMT3A and DNMT3B) with methyl-CpG binding domain protein 2 (MBD2), recently described as the only active DNA demethylase. Total RNA isolated from normal colonic mucosa (n = 24), benign adenomas (n = 18), and malignant colorectal carcinomas (n = 32) was analyzed by reverse transcriptase-PCR with subsequent quantification by capillary gel electrophoresis. In contrast to MBD2, expression of DNMT1 and DNMT3A increased in parallel to the degree of dysplasia, with significant overexpression in the malignant lesion when compared with mucosa or with benign lesions (DNMT1). Pairwise comparisons between tumors and matched, adjacent healthy mucosa tissue (n = 13) revealed that expression of all three genes encoding DNA methyltransferases increased by two- to three-fold. Our data suggest a relevant role of the DNA methyltransferases during colorectal tumorigenesis. This increase is not counterbalanced by enhanced expression of the demethylating component MBD2. As a consequence, epigenetic regulation in the adenoma-carcinoma sequence may be driven by increased methylating activity rather than suppressed demethylation.

Publication types

  • Comparative Study

MeSH terms

  • Adenoma / enzymology*
  • Adenoma / genetics
  • Colorectal Neoplasms / enzymology*
  • Colorectal Neoplasms / genetics
  • DNA (Cytosine-5-)-Methyltransferases / genetics
  • DNA (Cytosine-5-)-Methyltransferases / metabolism
  • DNA Modification Methylases / genetics
  • DNA Modification Methylases / metabolism*
  • DNA-Binding Proteins / genetics
  • DNA-Binding Proteins / metabolism
  • Electrophoresis, Capillary / methods
  • Epigenesis, Genetic
  • Gene Expression Regulation, Neoplastic*
  • Humans
  • Repressor Proteins / genetics
  • Repressor Proteins / metabolism
  • Reverse Transcriptase Polymerase Chain Reaction / methods
  • Up-Regulation*

Substances

  • DMAP1 protein, human
  • DNA-Binding Proteins
  • MBD2 protein, human
  • Repressor Proteins
  • DNA Modification Methylases
  • DNA (Cytosine-5-)-Methyltransferases
  • DNA methyltransferase 3A
  • DNA methyltransferase 3B