title: Involvement of miRNA-29a in epigenetic regulation of transforming growth factor-β-induced epithelial-mesenchymal transition in hepatocellular carcinoma.
abstract: OBJECTIVE
  Epithelial-mesenchymal transition (EMT) is a crucial process during cancer invasion and metastasis, which is accompanied by the suppressed expression of E-cadherin initiated by stimuli such as transforming growth factor (TGF)-β. Recent studies have shown that the epigenetic regulation of E-cadherin could be an alternate mechanism of EMT induction in hepatocellular carcinoma (HCC). miRNA-29a (miR-29a) is involved in the epigenetic regulation of genes by targeting DNA methyltransferases (DNMT), which methylate CpG islands to suppress the transcription of genes. We studied the involvement of miR-29a in TGF-β-induced EMT in HCC cells.
  
  
  METHODS
  We treated human HCC cell lines with TGF-β to induce EMT. To investigate DNA methylation in EMT, cells were treated with a methylation inhibitor, 5-Aza-2'-deoxycytidine (5-Aza) and methylation status of CpG islands in the E-cadherin promoter was examined using methylation-specific PCR. Precursor miR-29a (pre-miR-29a) was electroporated to force the expression of miR-29a in HCC cells in order to study the role of miR-29a in EMT.
  
  
  RESULTS
  TGF-β transformed HCC cells into a spindle-shaped morphology accompanied by a decrease of E-cadherin with the induction of methylation of its promoter. Pretreatment of the cells with 5-Aza blocked this suppression of E-cadherin, indicating the involvement of DNA methylation. TGF-β increased DNMT3B and DNMT1 and decreased miR-29a expression. The forced expression of miR-29a abrogated the suppression of E-cadherin induced by TGF-β.
  
  
  CONCLUSIONS
  miR-29a could regulate TGF-β-induced EMT by affecting DNA methylation via the suppression of DNMT. These observations reveal the epigenetic regulation of genes by miRNA as a unique mechanism of EMT in HCC.
authors.affiliation: Division of Gastroenterology, Tohoku University Graduate School of Medicine, Sendai, Japan.
authors.forename: Takayuki
authors.initials: T
authors.lastname: Kogure
authors.forename: Yasuteru
authors.initials: Y
authors.lastname: Kondo
authors.forename: Eiji
authors.initials: E
authors.lastname: Kakazu
authors.forename: Masashi
authors.initials: M
authors.lastname: Ninomiya
authors.forename: Osamu
authors.initials: O
authors.lastname: Kimura
authors.forename: Tooru
authors.initials: T
authors.lastname: Shimosegawa
keywords: E-cadherin; epithelial-mesenchymal transition; hepatocellular carcinoma; miR-29a