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miR-449a and miR-449b are direct transcriptional targets of E2F1 and negatively regulate pRb-E2F1 activity through a

Xiaojing Yang1, Min Feng, Xia Jiang

  • 1Cancer Biology and Pharmacology, Genome Institute of Singapore, A*STAR (Agency for Science, Technology, and Research), Singapore 138672.

Genes & Development
|October 17, 2009
PubMed

Insights

The Rb-E2F pathway is regulated by miR-449a/b, which inhibits cell proliferation. Epigenetic repression of miR-449a/b in cancer allows uncontrolled cell growth, highlighting its tumor suppressor role.

Area of Science:

  • Molecular Biology
  • Epigenetics
  • Cancer Biology

Background:

  • The Retinoblastoma (Rb)-E2F pathway is crucial for cell cycle progression and proliferation.
  • Mechanisms maintaining Rb-E2F pathway activity are not fully elucidated.
  • Dysregulation of this pathway is implicated in human cancers.

Purpose of the Study:

  • To investigate the regulatory role of microRNAs in the Rb-E2F pathway.
  • To identify novel feedback mechanisms controlling cell cycle progression.
  • To explore the epigenetic regulation of microRNAs in cancer.

Main Methods:

  • Luciferase reporter assays to confirm E2F1-mediated transactivation of miR-449a/b.
  • Western blotting to assess protein levels of CDK6, CDC25A, and phosphorylated Rb.
  • Quantitative PCR to measure miR-449a/b expression.
  • Chromatin immunoprecipitation assays to analyze histone modifications.
  • Treatment of cancer cells with epigenetic drugs targeting histone methylation.

Main Results:

  • E2F1 directly activates the transcription of miR-449a/b.
  • miR-449a/b targets and inhibits oncogenic CDK6 and CDC25A.
  • This inhibition leads to pRb dephosphorylation and G1 cell cycle arrest, establishing negative feedback.
  • miR-449a/b expression is epigenetically silenced in cancer cells via H3K27 trimethylation.
  • Epigenetic drug treatment restores miR-449a/b expression and inhibits cell proliferation.

Conclusions:

  • miR-449a/b acts as a tumor suppressor by negatively regulating the Rb/E2F1 pathway.
  • Aberrant epigenetic silencing of miR-449a/b contributes to E2F1 deregulation in cancer.
  • Targeting epigenetic mechanisms offers a potential therapeutic strategy for cancers with deregulated E2F1 activity.

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