Exosomal miR-221/222 enhances tamoxifen resistance in recipient ER-positive breast cancer cells

Breast Cancer Res Treat. 2014 Sep;147(2):423-31. doi: 10.1007/s10549-014-3037-0. Epub 2014 Jul 10.


Recent studies have demonstrated that specific miRNAs, such as miR-221/222, may be responsible for tamoxifen resistance in breast cancer. Secreted miRNAs enclosed in exosomes can act as intercellular bio-messengers. Our objective is to investigate the role of secreted miR-221/222 in tamoxifen resistance of ER-positive breast cancer cells. Transmission electron microscopy analysis and nanoparticle tracking analysis were performed to determine the exosomes difference between MCF-7(TamR) (tamoxifen resistant) and MCF-7(wt) (tamoxifen sensitive) cells. PKH67 fluorescent labeling assay was used to detect exosomes derived from MCF-7(TamR) cells entering into MCF-7(wt) cells. The potential function of exosomes on tamoxifen resistance transmission was analyzed with cell viability, apoptosis ,and colony formation. MiRNA microarrays and qPCR were used to detect and compare the miRNAs expression levels in the two cells and exosomes. As the targets of miR-221/222, p27 and ERα were analyzed with western blot and qPCR. Compared with the MCF-7(wt) exosomes, there were significant differences in the concentration and size distribution of MCF-7(TamR) exosomes. MCF-7(wt) cells had an increased amount of exosomal RNA and proteins compared with MCF-7(TamR) cells. MCF-7(TamR) exosomes could enter into MCF-7(wt) cells, and then released miR-221/222. And the elevated miR-221/222 effectively reduced the target genes expression of P27 and ERα, which enhanced tamoxifen resistance in recipient cells. Our results are the first to show that secreted miR-221/222 serves as signaling molecules to mediate communication of tamoxifen resistance.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Apoptosis / genetics
  • Breast Neoplasms / drug therapy*
  • Breast Neoplasms / genetics
  • Breast Neoplasms / metabolism*
  • Breast Neoplasms / pathology
  • Cell Line, Tumor
  • Cell Survival / genetics
  • Drug Resistance, Neoplasm
  • Estrogen Receptor alpha / biosynthesis*
  • Estrogen Receptor alpha / genetics
  • Exosomes / drug effects
  • Exosomes / genetics*
  • Female
  • Gene Expression Regulation, Neoplastic
  • Humans
  • MCF-7 Cells
  • MicroRNAs / genetics*
  • Proliferating Cell Nuclear Antigen / biosynthesis
  • Proliferating Cell Nuclear Antigen / genetics
  • Tamoxifen / pharmacology*


  • ESR1 protein, human
  • Estrogen Receptor alpha
  • MIRN221 microRNA, human
  • MIRN222 microRNA, human
  • MicroRNAs
  • Proliferating Cell Nuclear Antigen
  • p27 antigen
  • Tamoxifen