MiR-24 tumor suppressor activity is regulated independent of p53 and through a target site polymorphism

PLoS One. 2009 Dec 24;4(12):e8445. doi: 10.1371/journal.pone.0008445.


MicroRNAs (miRNAs) are predicted to regulate approximately 30% of all human genes; however, only a few miRNAs have been assigned their targets and specific functions. Here we demonstrate that miR-24, a ubiquitously expressed miRNA, has an anti-proliferative effect independent of p53 function. Cell lines with differential p53 status were used as a model to study the effects of miR-24 on cell proliferation, cell cycle control, gene regulation and cellular transformation. Overexpression of miR-24 in six different cell lines, independent of p53 function, inhibited cell proliferation and resulted in G2/S cell cycle arrest. MiR-24 over expression in cells with wt-p53 upregulated TP53 and p21 protein; however, in p53-null cells miR-24 still induced cell cycle arrest without the involvement of p21. We show that miR-24 regulates p53-independent cellular proliferation by regulating an S-phase enzyme, dihydrofolate reductase (DHFR) a target of the chemotherapeutic drug methotrexate (MTX). Of interest, we found that a miR-24 target site polymorphism in DHFR 3' UTR that results in loss of miR-24-function and high DHFR levels in the cell imparts a growth advantage to immortalized cells and induces neoplastic transformation. Of clinical significance, we found that miR-24 is deregulated in human colorectal cancer tumors and a subset of tumors has reduced levels of miR-24. A novel function for miR-24 as a p53-independent cell cycle inhibitory miRNA is proposed.

Publication types

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

MeSH terms

  • 3' Untranslated Regions / genetics
  • Animals
  • Cell Adhesion / drug effects
  • Cell Cycle Proteins / genetics
  • Cell Cycle Proteins / metabolism
  • Cell Differentiation / drug effects
  • Cell Line, Tumor
  • Cell Proliferation / drug effects
  • Cell Shape / drug effects
  • Colorectal Neoplasms / enzymology
  • Colorectal Neoplasms / genetics
  • Colorectal Neoplasms / pathology
  • Down-Regulation / drug effects
  • Drug Resistance, Neoplasm / drug effects
  • G2 Phase / drug effects
  • Gene Expression Regulation, Neoplastic / drug effects
  • Humans
  • Methotrexate / pharmacology
  • Mice
  • MicroRNAs / genetics
  • MicroRNAs / metabolism*
  • NIH 3T3 Cells
  • Polymorphism, Single Nucleotide / genetics*
  • S Phase / drug effects
  • Tetrahydrofolate Dehydrogenase / genetics
  • Tetrahydrofolate Dehydrogenase / metabolism
  • Tumor Suppressor Protein p53 / metabolism


  • 3' Untranslated Regions
  • Cell Cycle Proteins
  • MIRN24 microRNA, human
  • MicroRNAs
  • Tumor Suppressor Protein p53
  • Tetrahydrofolate Dehydrogenase
  • Methotrexate