Silencing of MicroRNA-21 confers the sensitivity to tamoxifen and fulvestrant by enhancing autophagic cell death through inhibition of the PI3K-AKT-mTOR pathway in breast cancer cells

Biomed Pharmacother. 2016 Feb;77:37-44. doi: 10.1016/j.biopha.2015.11.005. Epub 2015 Dec 12.


Tamoxifen (TAM) and fulvestrant (FUL) represent the major adjuvant therapy to estrogen receptor-alpha positive (ER(+)) breast cancer patients. However, endocrine resistance to TAM and FUL is a great impediment for successful treatment. We hypothesized that miR-21 might alter the sensitivity of breast cancer cells to TAM or FUL by regulating cell autophagy. Using the ER(+) breast cancer cells, we knockdown transfection with miR-21 inhibitor, then the cells were exposed to TAM or FUL and the percentages of apoptosis and autophagy were determined. Knockdown of miR-21 significantly increased the TAM or FUL-induced apoptosis in ER(+) breast cancer cells. Further, silencing of miR-21 in MCF-7 cells enhanced cell autophagy at both basal and TAM or FUL-induced level. The increase of autophagy in miR-21-knockdown MCF-7 cells was also indicated by increase of beclin-1, LC3-II and increased GFP-LC3 dots. Importantly, knockdown of miR-21 contributed to autophagic cell death, which is responsible for part of TAM induced cell death in miR-21 inhibitor-transfected cells. Further analysis suggested that miR-21 inhibitor enhance autophagic cell death through inhibition of PI3K-AKT-mTOR pathway. MiR-21 coordinated the function of autophagy and apoptosis by targeting Phosphatase and tensin homolog (PTEN) through inhibition of PI3K-AKT-mTOR pathway. In conclusion, silencing of miR-21 increased the sensitivity of ER(+) breast cancer cells to TAM or FUL by increasing autophagic cell death. Targeting autophagy-related miRNAs is a potential strategy for overcoming endocrine resistance to TAM and FUL.

Keywords: Apoptosis; Autophagy; Endocrine resistance; MiR-21; PI3K-AKT-mTOR.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Antineoplastic Agents, Hormonal / pharmacology*
  • Apoptosis / drug effects
  • Apoptosis Regulatory Proteins / biosynthesis
  • Autophagy
  • Beclin-1
  • Breast Neoplasms / drug therapy*
  • Breast Neoplasms / genetics
  • Cell Line, Tumor
  • Estradiol / analogs & derivatives*
  • Estradiol / pharmacology
  • Fulvestrant
  • Gene Expression Regulation, Neoplastic
  • Humans
  • MCF-7 Cells
  • Membrane Proteins / biosynthesis
  • MicroRNAs / genetics*
  • PTEN Phosphohydrolase / biosynthesis
  • Phosphoinositide-3 Kinase Inhibitors
  • Reverse Transcriptase Polymerase Chain Reaction
  • TOR Serine-Threonine Kinases / antagonists & inhibitors
  • Tamoxifen / pharmacology*
  • Transfection


  • Antineoplastic Agents, Hormonal
  • Apoptosis Regulatory Proteins
  • BECN1 protein, human
  • Beclin-1
  • MIRN21 microRNA, human
  • Membrane Proteins
  • MicroRNAs
  • Phosphoinositide-3 Kinase Inhibitors
  • Tamoxifen
  • Fulvestrant
  • Estradiol
  • MTOR protein, human
  • TOR Serine-Threonine Kinases
  • PTEN Phosphohydrolase
  • PTEN protein, human