title: Progressive up-regulation of genes encoding DNA methyltransferases in the colorectal adenoma-carcinoma sequence.
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.
authors.affiliation: Department of Clinical Pharmacology, Section of Cardiovascular Medicine, Medical University of Vienna, Währinger Gürtel, Vienna, Austria.
authors.forename: Wolfgang M
authors.initials: WM
authors.lastname: Schmidt
authors.forename: Roland
authors.initials: R
authors.lastname: Sedivy
authors.forename: Birgit
authors.initials: B
authors.lastname: Forstner
authors.forename: Günther G
authors.initials: GG
authors.lastname: Steger
authors.forename: Sabine
authors.initials: S
authors.lastname: Zöchbauer-Müller
authors.forename: Robert M
authors.initials: RM
authors.lastname: Mader
mesh_terms: D000236:Adenoma / Q000201:enzymology* / Q000235:genetics; D015179:Colorectal Neoplasms / Q000201:enzymology* / Q000235:genetics; D004248:DNA (Cytosine-5-)-Methyltransferases / Q000235:genetics / Q000378:metabolism; D000090205:DNA Methyltransferase 3A; D015254:DNA Modification Methylases / Q000235:genetics / Q000378:metabolism*; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism; D019075:Electrophoresis, Capillary / Q000379:methods; D044127:Epigenesis, Genetic; D015972:Gene Expression Regulation, Neoplastic; D006801:Humans; D012097:Repressor Proteins / Q000235:genetics / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction / Q000379:methods; D015854:Up-Regulation; D000097584:DNA Methyltransferase 3B
chemical_list: D004248:DNA (Cytosine-5-)-Methyltransferases; D000090205:DNA Methyltransferase 3A; D015254:DNA Modification Methylases; D004268:DNA-Binding Proteins; D012097:Repressor Proteins; D000097584:DNA Methyltransferase 3B; C411744:DMAP1 protein, human; C000717967:DNMT3A protein, human; C489325:MBD2 protein, human