MicroRNA-221/222 confers tamoxifen resistance in breast cancer by targeting p27Kip1

J Biol Chem. 2008 Oct 31;283(44):29897-903. doi: 10.1074/jbc.M804612200. Epub 2008 Aug 15.


We explored the role of microRNAs (miRNAs) in acquiring resistance to tamoxifen, a drug successfully used to treat women with estrogen receptor-positive breast cancer. miRNA microarray analysis of MCF-7 cell lines that are either sensitive (parental) or resistant (4-hydroxytamoxifen-resistant (OHT(R))) to tamoxifen showed significant (>1.8-fold) up-regulation of eight miRNAs and marked down-regulation (>50%) of seven miRNAs in OHT(R) cells compared with parental MCF-7 cells. Increased expression of three of the most promising up-regulated (miR-221, miR-222, and miR-181) and down-regulated (miR-21, miR-342, and miR-489) miRNAs was validated by real-time reverse transcription-PCR. The expression of miR-221 and miR-222 was also significantly (2-fold) elevated in HER2/neu-positive primary human breast cancer tissues that are known to be resistant to endocrine therapy compared with HER2/neu-negative tissue samples. Ectopic expression of miR-221/222 rendered the parental MCF-7 cells resistant to tamoxifen. The protein level of the cell cycle inhibitor p27(Kip1), a known target of miR-221/222, was reduced by 50% in OHT(R) cells and by 28-50% in miR-221/222-overexpressing MCF-7 cells. Furthermore, overexpression of p27(Kip1) in the resistant OHT(R) cells caused enhanced cell death when exposed to tamoxifen. This is the first study demonstrating a relationship between miR-221/222 expression and HER2/neu overexpression in primary breast tumors that are generally resistant to tamoxifen therapy. This finding also provides the rationale for the application of altered expression of specific miRNAs as a predictive tamoxifen-resistant breast cancer marker.

Publication types

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

MeSH terms

  • Antineoplastic Agents, Hormonal / pharmacology
  • Biomarkers, Tumor / metabolism
  • Breast Neoplasms / metabolism*
  • Cell Line, Tumor
  • Cyclin-Dependent Kinase Inhibitor p27 / metabolism*
  • Drug Resistance, Neoplasm*
  • Female
  • Gene Expression Profiling
  • Humans
  • MicroRNAs / metabolism*
  • Models, Biological
  • Tamoxifen / pharmacology*
  • Time Factors


  • Antineoplastic Agents, Hormonal
  • Biomarkers, Tumor
  • MIRN221 microRNA, human
  • MIRN222 microRNA, human
  • MicroRNAs
  • Tamoxifen
  • Cyclin-Dependent Kinase Inhibitor p27