title: MiR-214 increases the sensitivity of breast cancer cells to tamoxifen and fulvestrant through inhibition of autophagy.
abstract: BACKGROUND
  Tamoxifen (TAM) and fulvestrant (FUL) are the major drugs for patients with estrogen receptor-positive (ER(+)) breast cancers. However, the development of endocrine resistance is the impediment for successful treatment. We aimed to explore the mechanisms of endocrine resistance and therapeutic strategy for overcoming resistance against TAM and FUL.
  
  
  METHODS
  Experiments were performed in ER(+) and estrogen/TAM-sensitive MCF7 cells and antiestrogen-resistant MCF7/LCC9 cells. The expression of miR-214 and uncoupling protein 2 (UCP2) was determined by RT-qPCR and Western blot in breast cancer cells and human breast cancer tissue specimens. Cell autophagy was examined by fluorescent probe monodansyl cadaverine (MDC) and GFP-LC3-II-positive punctate identified by confocal microscopy. Apoptotic cells were determined by Annexin V-FITC/PI staining. The potential regulatory target of miR-214 was determined by prediction tool, target protein expression and luciferase reporter assay.
  
  
  RESULTS
  4-OHT/FUL treatment resulted in induction of apoptosis as well as autophagy in breast cancer cells. Autophagy might be the major cause of endocrine resistance to 4-OHT or FUL. MiR-214 increased the sensitivity of breast cancer cells to the 4-OHT/FUL-induced apoptosis through inhibition of autophagy. Importantly, a negative correlation was established between miR-214 and UCP2 in human breast cancer tissue specimens assayed by RT-qPCR. UCP2 was identified to be a direct target of miR-214. Further study in MCF7/LCC9 cells indicated that endocrine resistance might arise from activation of the PI3K-Akt-mTOR pathway, thereby inducing autophagy by overexpression of UCP2.
  
  
  CONCLUSIONS
  MiR-214 increased the sensitivity of breast cancer cells to TAM and FUL through inhibition of autophagy by targeting UCP2. MiR-214 shows potential as a novel therapeutic strategy for overcoming endocrine resistance in ER(+) breast cancers.
authors.affiliation: Department of Pharmacology, School of Basic Medical Sciences, Capital Medical University, No.10, Xitoutiao, Youanmenwai Avenue, 100069, Beijing, China.
authors.forename: Xinfeng
authors.initials: X
authors.lastname: Yu
authors.affiliation: State Key Lab of Molecular Oncology, Cancer Institute & Hospital, Chinese Academy of Medical Sciences, Beijing, China.
authors.forename: Aiping
authors.initials: A
authors.lastname: Luo
authors.affiliation: Department of Pharmacology, School of Basic Medical Sciences, Capital Medical University, No.10, Xitoutiao, Youanmenwai Avenue, 100069, Beijing, China.
authors.forename: Yicong
authors.initials: Y
authors.lastname: Liu
authors.affiliation: Department of Pharmacology, School of Basic Medical Sciences, Capital Medical University, No.10, Xitoutiao, Youanmenwai Avenue, 100069, Beijing, China.
authors.forename: Shuqing
authors.initials: S
authors.lastname: Wang
authors.affiliation: Department of Pharmacology, School of Chemical Biology & Pharmaceutical Sciences, Capital Medical University, Beijing, China.
authors.forename: Ye
authors.initials: Y
authors.lastname: Li
authors.affiliation: Department of Pharmacology, School of Basic Medical Sciences, Capital Medical University, No.10, Xitoutiao, Youanmenwai Avenue, 100069, Beijing, China.
authors.forename: Wenna
authors.initials: W
authors.lastname: Shi
authors.affiliation: State Key Lab of Molecular Oncology, Cancer Institute & Hospital, Chinese Academy of Medical Sciences, Beijing, China.
authors.forename: Zhihua
authors.initials: Z
authors.lastname: Liu
authors.affiliation: Department of Pharmacology, School of Basic Medical Sciences, Capital Medical University, No.10, Xitoutiao, Youanmenwai Avenue, 100069, Beijing, China. quxj@ccmu.edu.cn.
authors.forename: Xianjun
authors.initials: X
authors.lastname: Qu
mesh_terms: D018931:Antineoplastic Agents, Hormonal / Q000494:pharmacology*; D017209:Apoptosis; D001343:Autophagy; D001483:Base Sequence; D001665:Binding Sites; D001943:Breast Neoplasms / Q000188:drug therapy*; D002470:Cell Survival / Q000187:drug effects; D019008:Drug Resistance, Neoplasm; D004958:Estradiol / Q000031:analogs & derivatives* / Q000494:pharmacology; D005260:Female; D000077267:Fulvestrant; D015870:Gene Expression; D006801:Humans; D007473:Ion Channels / Q000235:genetics / Q000378:metabolism; D061986:MCF-7 Cells; D035683:MicroRNAs / Q000502:physiology*; D024101:Mitochondrial Proteins / Q000235:genetics / Q000378:metabolism; D034622:RNA Interference; D013629:Tamoxifen / Q000494:pharmacology*; D000071246:Uncoupling Protein 2
chemical_list: D018931:Antineoplastic Agents, Hormonal; D007473:Ion Channels; C547397:MIRN214 microRNA, human; D035683:MicroRNAs; D024101:Mitochondrial Proteins; C000604389:UCP2 protein, human; D000071246:Uncoupling Protein 2; D013629:Tamoxifen; D000077267:Fulvestrant; D004958:Estradiol