Reciprocal regulation of microRNA-122 and c-Myc in hepatocellular cancer: role of E2F1 and transcription factor dimerization partner 2

Hepatology. 2014 Feb;59(2):555-66. doi: 10.1002/hep.26712. Epub 2013 Dec 20.


c-Myc is a well-known oncogene frequently up-regulated in different malignancies, whereas liver-specific microRNA (miR)-122, a bona fide tumor suppressor, is down-regulated in hepatocellular cancer (HCC). Here we explored the underlying mechanism of reciprocal regulation of these two genes. Real-time reverse-transcription polymerase chain reaction (RT-PCR) and northern blot analysis demonstrated reduced expression of the primary, precursor, and mature miR-122 in c-MYC-induced HCCs compared to the benign livers, indicating transcriptional suppression of miR-122 upon MYC overexpression. Indeed, chromatin immunoprecipitation (ChIP) assay showed significantly reduced association of RNA polymerase II and histone H3K9Ac, markers of active chromatin, with the miR-122 promoter in tumors relative to the c-MYC-uninduced livers, indicating transcriptional repression of miR-122 in c-MYC-overexpressing tumors. The ChIP assay also demonstrated a significant increase in c-Myc association with the miR-122 promoter region that harbors a conserved noncanonical c-Myc binding site in tumors compared to the livers. Ectopic expression and knockdown studies showed that c-Myc indeed suppresses expression of primary and mature miR-122 in hepatic cells. Additionally, Hnf-3β, a liver enriched transcription factor that activates miR-122 gene, was suppressed in c-MYC-induced tumors. Notably, miR-122 also repressed c-Myc transcription by targeting transcriptional activator E2f1 and coactivator Tfdp2, as evident from ectopic expression and knockdown studies and luciferase reporter assays in mouse and human hepatic cells.

Conclusion: c-Myc represses miR-122 gene expression by associating with its promoter and by down-regulating Hnf-3β expression, whereas miR-122 indirectly inhibits c-Myc transcription by targeting Tfdp2 and E2f1. In essence, these results suggest a double-negative feedback loop between a tumor suppressor (miR-122) and an oncogene (c-Myc).

Publication types

  • Research Support, N.I.H., Extramural

MeSH terms

  • Animals
  • Carcinoma, Hepatocellular / genetics
  • Carcinoma, Hepatocellular / pathology
  • Carcinoma, Hepatocellular / physiopathology*
  • Cell Line, Tumor
  • DNA-Binding Proteins / genetics
  • DNA-Binding Proteins / physiology*
  • Disease Models, Animal
  • Down-Regulation / genetics
  • Down-Regulation / physiology
  • E2F1 Transcription Factor / genetics
  • E2F1 Transcription Factor / physiology*
  • Gene Expression Regulation, Neoplastic / genetics
  • Gene Expression Regulation, Neoplastic / physiology*
  • Hepatocytes / metabolism
  • Hepatocytes / pathology
  • Humans
  • Liver Neoplasms / genetics
  • Liver Neoplasms / pathology
  • Liver Neoplasms / physiopathology*
  • Mice
  • Mice, Knockout
  • Mice, Transgenic
  • MicroRNAs / genetics
  • MicroRNAs / physiology*
  • Proto-Oncogene Proteins c-myc / genetics
  • Proto-Oncogene Proteins c-myc / physiology*
  • Transcription Factors / genetics
  • Transcription Factors / physiology*
  • Up-Regulation / genetics
  • Up-Regulation / physiology


  • DNA-Binding Proteins
  • E2F1 Transcription Factor
  • E2F1 protein, human
  • E2f1 protein, mouse
  • MIRN122 microRNA, human
  • MYC protein, human
  • MicroRNAs
  • Mirn122 microRNA, mouse
  • Myc protein, mouse
  • Proto-Oncogene Proteins c-myc
  • TFDP2 protein, human
  • Tfdp2 protein, mouse
  • Transcription Factors