title: MicroRNA-125b upregulation confers aromatase inhibitor resistance and is a novel marker of poor prognosis in breast cancer.
abstract: BACKGROUND
  Increasing evidence indicates that microRNAs (miRNAs) are important players in oncogenesis. Considering the widespread use of aromatase inhibitors (AIs) in endocrine therapy as a first-line treatment for postmenopausal estrogen receptor α-positive breast cancer patients, identifying deregulated expression levels of miRNAs in association with AI resistance is of utmost importance.
  
  
  METHODS
  To gain further insight into the molecular mechanisms underlying the AI resistance, we performed miRNA microarray experiments using a new model of acquired resistance to letrozole (Res-Let cells), obtained by long-term exposure of aromatase-overexpressing MCF-7 cells (MCF-7aro cells) to letrozole, and a model of acquired anastrozole resistance (Res-Ana cells). Three miRNAs (miR-125b, miR-205 and miR-424) similarly deregulated in both AI-resistant cell lines were then investigated in terms of their functional role in AI resistance development and breast cancer cell aggressiveness and their clinical relevance using a cohort of 65 primary breast tumor samples.
  
  
  RESULTS
  We identified the deregulated expression of 33 miRNAs in Res-Let cells and of 18 miRNAs in Res-Ana cells compared with the sensitive MCF-7aro cell line. The top-ranked Kyoto Encyclopedia of Genes and Genomes pathways delineated by both miRNA signatures converged on the AKT/mTOR pathway, which was found to be constitutively activated in both AI-resistant cell lines. We report for the first time, to our knowledge, that ectopic overexpression of either miR-125b or miR-205, or the silencing of miR-424 expression, in the sensitive MCF-7aro cell line was sufficient to confer resistance to letrozole and anastrozole, to target and activate the AKT/mTOR pathway and to increase the formation capacity of stem-like and tumor-initiating cells possessing self-renewing properties. Increasing miR-125b expression levels was also sufficient to confer estrogen-independent growth properties to the sensitive MCF-7aro cell line. We also found that elevated miR-125b expression levels were a novel marker for poor prognosis in breast cancer and that targeting miR-125b in Res-Let cells overcame letrozole resistance.
  
  
  CONCLUSIONS
  This study highlights that acquisition of specific deregulated miRNAs is a newly discovered alternative mechanism developed by AI-resistant breast cancer cells to achieve constitutive activation of the AKT/mTOR pathway and to develop AI resistance. It also highlights that miR-125b is a new biomarker of poor prognosis and a candidate therapeutic target in AI-resistant breast cancers.
authors: ISPB, Faculté de Pharmacie, 8 Avenue Rockefeller, 69008, Lyon, France. paul.vilquin@univ-lyon1.fr.|Université Lyon 1, 8 Avenue Rockefeller, 69008, Lyon, France. paul.vilquin@univ-lyon1.fr.|INSERM U1052, CNRS UMR5286, Centre de Recherche en Cancérologie de Lyon, 28 Rue Laennec, 69008, Lyon, France. paul.vilquin@univ-lyon1.fr.
authors: Paul
authors: P
authors: Vilquin
authors: ISPB, Faculté de Pharmacie, 8 Avenue Rockefeller, 69008, Lyon, France. caterina.donini@univ-lyon1.fr.|Université Lyon 1, 8 Avenue Rockefeller, 69008, Lyon, France. caterina.donini@univ-lyon1.fr.|INSERM U1052, CNRS UMR5286, Centre de Recherche en Cancérologie de Lyon, 28 Rue Laennec, 69008, Lyon, France. caterina.donini@univ-lyon1.fr.|Unité Cancer et Environnement, Centre Léon Bérard-Université Lyon 1, 28 Rue Laennec, 69008, Lyon, France. caterina.donini@univ-lyon1.fr.
authors: Caterina F
authors: CF
authors: Donini
authors: ISPB, Faculté de Pharmacie, 8 Avenue Rockefeller, 69008, Lyon, France. marie.villedieu@univ-lyon1.fr.|Université Lyon 1, 8 Avenue Rockefeller, 69008, Lyon, France. marie.villedieu@univ-lyon1.fr.|INSERM U1052, CNRS UMR5286, Centre de Recherche en Cancérologie de Lyon, 28 Rue Laennec, 69008, Lyon, France. marie.villedieu@univ-lyon1.fr.
authors: Marie
authors: M
authors: Villedieu
authors: ISPB, Faculté de Pharmacie, 8 Avenue Rockefeller, 69008, Lyon, France. evelyne.grisard@univ-lyon1.fr.|Université Lyon 1, 8 Avenue Rockefeller, 69008, Lyon, France. evelyne.grisard@univ-lyon1.fr.|INSERM U1052, CNRS UMR5286, Centre de Recherche en Cancérologie de Lyon, 28 Rue Laennec, 69008, Lyon, France. evelyne.grisard@univ-lyon1.fr.
authors: Evelyne
authors: E
authors: Grisard
authors: Université Lyon 1, 8 Avenue Rockefeller, 69008, Lyon, France. laura.corbo@lyon.unicancer.fr.|INSERM U1052, CNRS UMR5286, Centre de Recherche en Cancérologie de Lyon, 28 Rue Laennec, 69008, Lyon, France. laura.corbo@lyon.unicancer.fr.
authors: Laura
authors: L
authors: Corbo
authors: Centre Léon Bérard, 28 Rue Laennec, 69008, Lyon, France. thomas.bachelot@lyon.unicancer.fr.
authors: Thomas
authors: T
authors: Bachelot
authors: ISPB, Faculté de Pharmacie, 8 Avenue Rockefeller, 69008, Lyon, France. julie.vendrell@univ-lyon1.fr.|Université Lyon 1, 8 Avenue Rockefeller, 69008, Lyon, France. julie.vendrell@univ-lyon1.fr.|INSERM U1052, CNRS UMR5286, Centre de Recherche en Cancérologie de Lyon, 28 Rue Laennec, 69008, Lyon, France. julie.vendrell@univ-lyon1.fr.
authors: Julie A
authors: JA
authors: Vendrell
authors: ISPB, Faculté de Pharmacie, 8 Avenue Rockefeller, 69008, Lyon, France. pascale.cohen@univ-lyon1.fr.|Université Lyon 1, 8 Avenue Rockefeller, 69008, Lyon, France. pascale.cohen@univ-lyon1.fr.|INSERM U1052, CNRS UMR5286, Centre de Recherche en Cancérologie de Lyon, 28 Rue Laennec, 69008, Lyon, France. pascale.cohen@univ-lyon1.fr.|Unité Cancer et Environnement, Centre Léon Bérard-Université Lyon 1, 28 Rue Laennec, 69008, Lyon, France. pascale.cohen@univ-lyon1.fr.|ProfileXpert, SFR Lyon-Est, 69008, Lyon, France. pascale.cohen@univ-lyon1.fr.|ISPBL-Faculté de Pharmacie de Lyon, 8 Avenue Rockefeller, 69373, Lyon, Cedex 08, France. pascale.cohen@univ-lyon1.fr.
authors: Pascale A
authors: PA
authors: Cohen
mesh_terms: D000970:Antineoplastic Agents / Q000494:pharmacology; D018931:Antineoplastic Agents, Hormonal; D047072:Aromatase Inhibitors / Q000494:pharmacology* / Q000627:therapeutic use; D014408:Biomarkers, Tumor; D001943:Breast Neoplasms / Q000188:drug therapy / Q000235:genetics* / Q000378:metabolism / Q000401:mortality / Q000473:pathology; D016000:Cluster Analysis; D015331:Cohort Studies; D019008:Drug Resistance, Neoplasm / Q000235:genetics; D005260:Female; D020869:Gene Expression Profiling; D015972:Gene Expression Regulation, Neoplastic; D006801:Humans; D000077289:Letrozole; D061986:MCF-7 Cells; D035683:MicroRNAs / Q000235:genetics*; D009364:Neoplasm Recurrence, Local; D009570:Nitriles / Q000494:pharmacology; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D011379:Prognosis; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism; D011960:Receptors, Estrogen; D015398:Signal Transduction; D058570:TOR Serine-Threonine Kinases / Q000378:metabolism; D014230:Triazoles / Q000494:pharmacology; D014407:Tumor Cells, Cultured; D015854:Up-Regulation
chemical_list: D000970:Antineoplastic Agents; D018931:Antineoplastic Agents, Hormonal; D047072:Aromatase Inhibitors; D014408:Biomarkers, Tumor; D000077289:Letrozole; D035683:MicroRNAs; D009570:Nitriles; D019869:Phosphatidylinositol 3-Kinases; D051057:Proto-Oncogene Proteins c-akt; D011960:Receptors, Estrogen; D058570:TOR Serine-Threonine Kinases; D014230:Triazoles; C531888:MIRN125 microRNA, human
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