A double-negative feedback loop between EZH2 and miR-26a regulates tumor cell growth in hepatocellular carcinoma

Int J Oncol. 2016 Mar;48(3):1195-204. doi: 10.3892/ijo.2016.3336. Epub 2016 Jan 13.

Abstract

Accumulating evidence demonstrates the important roles of microRNAs (miRNAs) in tumor development and progression. miR-26a has been reported to be downregulated in several types of cancers including hepatocellular carcinoma, but the underlying mechanism of how miR-26a is repressed remains largely unknown. In the present study, we performed western blot analysis, qRT-PCR, luciferase reporter assay and chromatin immunoprecipitation assay to investigate the relationship between miR-26a and the enhancer of zest homologue 2 (EZH2). CCK-8 assay and colony formation assay were carried out to explore the effect of miR-26a on HCC cells proliferation. We demonstrated that miR-26a was epigenetically repressed by EZH2-mediated H3K27 trimethylation within the miR-26a promoter. Moreover, we confirmed that EZH2 was also a direct target of miR-26a in HCC cells, thus, creating a double-negative feedback loop. Furthermore, miR-26a restoration increased the expressions of its host genes (CTDSPL and CTDSP2). Overexpression of EZH2 abrogated miR-26a induction of CTDSPL and CTDSP2. Restoring the balance of the double-negative feedback loop by miR-26a overpression or EZH2 silence significantly inhibited HCC cell growth. Overexpression of EZH2 rescued the growth inhibition effect of miR-26a. These findings suggest that an imbalanced double-negative feedback loop between EZH2 and miR-26a exists in HCC cells, which contributes to miR-26a deregulation and regulates tumor cells proliferation.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Carcinoma, Hepatocellular / metabolism*
  • Cell Cycle
  • Cell Line, Tumor
  • Cell Proliferation
  • Down-Regulation
  • Enhancer of Zeste Homolog 2 Protein
  • Epigenesis, Genetic
  • Feedback, Physiological
  • Gene Expression Regulation, Neoplastic*
  • Gene Silencing
  • Hep G2 Cells
  • Humans
  • Liver Neoplasms / metabolism*
  • MicroRNAs / metabolism*
  • Plasmids / chemistry
  • Polycomb Repressive Complex 2 / metabolism*
  • Real-Time Polymerase Chain Reaction

Substances

  • MIRN26A microRNA, human
  • MicroRNAs
  • EZH2 protein, human
  • Enhancer of Zeste Homolog 2 Protein
  • Polycomb Repressive Complex 2