Role of epigenetic and miR-22 and miR-29b alterations in the downregulation of Mat1a and Mthfr genes in early preneoplastic livers in rats induced by 2-acetylaminofluorene

Mol Carcinog. 2013 Apr;52(4):318-27. doi: 10.1002/mc.21861. Epub 2011 Dec 27.


Carcinogenesis is a multistep sequential process of clonal expansion of initiated cells associated with the accumulation of multiple cancer-specific heritable phenotypes. The acquisition of these heritable cancer-specific alterations may be triggered by mutational and/or non-mutational changes in the genome that affect the regulation of gene expression. Currently, cancer-specific epigenetically mediated changes in gene expression are regarded as driving events in tumorigenesis. In the present study, we investigated the role of gene-specific expression changes in the mechanism of rat hepatocarcinogenesis induced by the complete hepatocarcinogen 2-acetylaminofluorene (2-AAF). The results of the present study demonstrate significant alterations in gene expression, especially of Mat1a and Mthfr genes, during early stages of rat 2-AAF-induced liver carcinogenesis. Both of these genes were downregulated in the livers of 2-AAF-treated male rats. Inhibition of Mat1a expression was associated with an increase in histone H3 lysine 27 trimethylation and a decrease in histone H3 lysine 18 acetylation at the gene promoter/first exon region. Additionally, we demonstrate for the first time a critical contribution of miR-22 and miR-29b microRNAs in the inhibition of Mat1a and Mthfr gene expression during 2-AAF-induced rat hepatocarcinogenesis. The downregulation of Mat1a and Mthfr genes was accompanied by marked functional alterations in one-carbon metabolism. The results of the present study suggest that downregulation of the Mat1a and Mthfr genes may be one of the main driver events that promote liver carcinogenesis by causing a profound accumulation of subsequent epigenetic abnormalities during progression of the carcinogenic process.

MeSH terms

  • 2-Acetylaminofluorene
  • Acetylation
  • Animals
  • Carcinogens
  • Cell Line
  • DNA Methylation
  • Down-Regulation
  • Epigenesis, Genetic
  • Female
  • Gene Expression Regulation, Neoplastic*
  • Histones / genetics
  • Histones / metabolism
  • Liver / drug effects
  • Liver / metabolism*
  • Liver Neoplasms, Experimental / chemically induced
  • Liver Neoplasms, Experimental / genetics*
  • Liver Neoplasms, Experimental / metabolism
  • Male
  • Methionine Adenosyltransferase / genetics*
  • Methylenetetrahydrofolate Reductase (NADPH2) / genetics*
  • MicroRNAs / genetics*
  • Promoter Regions, Genetic
  • Rats
  • Rats, Sprague-Dawley
  • S-Adenosylhomocysteine / analysis
  • S-Adenosylhomocysteine / metabolism
  • S-Adenosylmethionine / analysis
  • S-Adenosylmethionine / metabolism


  • Carcinogens
  • Histones
  • MIRN22 microRNA, rat
  • MIRN29 microRNA, rat
  • MicroRNAs
  • S-Adenosylmethionine
  • S-Adenosylhomocysteine
  • 2-Acetylaminofluorene
  • Methylenetetrahydrofolate Reductase (NADPH2)
  • Mat1a protein, rat
  • Methionine Adenosyltransferase