Loss of Estrogen-Regulated MIR135A1 at 3p21.1 Promotes Tamoxifen Resistance in Breast Cancer

Cancer Res. 2018 Sep 1;78(17):4915-4928. doi: 10.1158/0008-5472.CAN-18-0069. Epub 2018 Jun 26.


The dysregulation of miRNAs has been increasingly recognized as a critical mediator of cancer development and progression. Here, we show that frequent deletion of the MIR135A1 locus is associated with poor prognosis in primary breast cancer. Forced expression of miR-135a decreased breast cancer progression, while inhibition of miR-135a with a specific miRNA sponge elicited opposing effects, suggestive of a tumor suppressive role of miR-135a in breast cancer. Estrogen receptor alpha (ERα) bound the promoter of MIR135A1 for its transcriptional activation, whereas tamoxifen treatment inhibited expression of miR-135a in ERα+ breast cancer cells. miR-135a directly targeted ESR1, ESRRA, and NCOA1, forming a negative feedback loop to inhibit ERα signaling. This regulatory feedback between miR-135a and ERα demonstrated that miR-135a regulated the response to tamoxifen. The tamoxifen-mediated decrease in miR-135a expression increased the expression of miR-135a targets to reduce tamoxifen sensitivity. Consistently, miR-135a expression was downregulated in ERα+ breast cancer cells with acquired tamoxifen resistance, while forced expression of miR-135a partially resensitized these cells to tamoxifen. Tamoxifen resistance mediated by the loss of miR-135a was shown to be partially dependent on the activation of the ERK1/2 and AKT pathways by miR-135a-targeted genes. Taken together, these results indicate that deletion of the MIR135A1 locus and decreased miR-135a expression promote ERα+ breast cancer progression and tamoxifen resistance.Significance: Loss of miR-135a in breast cancer disrupts an estrogen receptor-induced negative feedback loop, perpetuating disease progression and resistance to therapy.Graphical Abstract: http://cancerres.aacrjournals.org/content/canres/78/17/4915/F1.large.jpg Cancer Res; 78(17); 4915-28. ©2018 AACR.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adult
  • Aged
  • Animals
  • Antineoplastic Agents, Hormonal / administration & dosage*
  • Apoptosis / drug effects
  • Breast Neoplasms / drug therapy*
  • Breast Neoplasms / genetics
  • Breast Neoplasms / pathology
  • Cell Proliferation / drug effects
  • Drug Resistance, Neoplasm / genetics*
  • ERRalpha Estrogen-Related Receptor
  • Estrogen Receptor alpha / genetics
  • Female
  • Gene Expression Regulation, Neoplastic / drug effects
  • Humans
  • Kaplan-Meier Estimate
  • MCF-7 Cells
  • Mice
  • MicroRNAs / genetics*
  • Middle Aged
  • Nuclear Receptor Coactivator 1 / genetics
  • Receptors, Estrogen / genetics
  • Signal Transduction / drug effects
  • Signal Transduction / genetics
  • Tamoxifen / administration & dosage*
  • Xenograft Model Antitumor Assays


  • Antineoplastic Agents, Hormonal
  • ESR1 protein, human
  • Estrogen Receptor alpha
  • MIRN135 microRNA, human
  • MicroRNAs
  • Receptors, Estrogen
  • Tamoxifen
  • NCOA1 protein, human
  • Nuclear Receptor Coactivator 1