title: microRNA regulation of mammalian target of rapamycin expression and activity controls estrogen receptor function and RAD001 sensitivity.
abstract: BACKGROUND
  The AKT/mammalian target of rapamycin (mTOR) signaling pathway is regulated by 17α-estradiol (E2) signaling and mediates E2-induced proliferation and progesterone receptor (PgR) expression in breast cancer.
  
  
  RESULTS
  Here we use deep sequencing analysis of previously published data from The Cancer Genome Atlas to demonstrate that expression of a key component of mTOR signaling, rapamycin-insensitive companion of mTOR (Rictor), positively correlated with an estrogen receptor-α positive (ERα+) breast tumor signature. Through increased microRNA-155 (miR-155) expression in the ERα+ breast cancer cells we demonstrate repression of Rictor enhanced activation of mTOR complex 1 (mTORC1) signaling with both qPCR and western blot. miR-155-mediated mTOR signaling resulted in deregulated ERα signaling both in cultured cells in vitro and in xenografts in vivo in addition to repressed PgR expression and activity. Furthermore we observed that miR-155 enhanced mTORC1 signaling (observed through western blot for increased phosphorylation on mTOR S2448) and induced inhibition of mTORC2 signaling (evident through repressed Rictor and tuberous sclerosis 1 (TSC1) gene expression). mTORC1 induced deregulation of E2 signaling was confirmed using qPCR and the mTORC1-specific inhibitor RAD001. Co-treatment of MCF7 breast cancer cells stably overexpressing miR-155 with RAD001 and E2 restored E2-induced PgR gene expression. RAD001 treatment of SCID/CB17 mice inhibited E2-induced tumorigenesis of the MCF7 miR-155 overexpressing cell line. Finally we demonstrated a strong positive correlation between Rictor and PgR expression and a negative correlation with Raptor expression in Luminal B breast cancer samples, a breast cancer histological subtype known for having an altered ERα-signaling pathway.
  
  
  CONCLUSIONS
  miRNA mediated alterations in mTOR and ERα signaling establishes a new mechanism for altered estrogen responses independent of growth factor stimulation.
authors.forename: Elizabeth C
authors.initials: EC
authors.lastname: Martin
authors.forename: Lyndsay V
authors.initials: LV
authors.lastname: Rhodes
authors.forename: Steven
authors.initials: S
authors.lastname: Elliott
authors.forename: Adrienne E
authors.initials: AE
authors.lastname: Krebs
authors.forename: Kenneth P
authors.initials: KP
authors.lastname: Nephew
authors.forename: Erik K
authors.initials: EK
authors.lastname: Flemington
authors.forename: Bridgette M
authors.initials: BM
authors.lastname: Collins-Burow
authors.affiliation: Department of Medicine-Section of Hematology and Medical Oncology, Tulane University, New Orleans, LA, USA. mburow@tulane.edu.
authors.forename: Matthew E
authors.initials: ME
authors.lastname: Burow
mesh_terms: D000818:Animals; D001943:Breast Neoplasms / Q000235:genetics / Q000473:pathology; D047628:Estrogen Receptor alpha / Q000235:genetics / Q000378:metabolism*; D004967:Estrogens / Q000494:pharmacology; D000068338:Everolimus; D005260:Female; D015972:Gene Expression Regulation, Neoplastic; D006801:Humans; D061986:MCF-7 Cells; D000076222:Mechanistic Target of Rapamycin Complex 1; D000076225:Mechanistic Target of Rapamycin Complex 2; D051379:Mice; D035683:MicroRNAs / Q000235:genetics / Q000378:metabolism*; D046912:Multiprotein Complexes / Q000378:metabolism; D010641:Phenotype; D010766:Phosphorylation / Q000187:drug effects; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism; D011980:Receptors, Progesterone / Q000378:metabolism; D015398:Signal Transduction / Q000235:genetics; D020123:Sirolimus / Q000031:analogs & derivatives* / Q000494:pharmacology; D058570:TOR Serine-Threonine Kinases / Q000378:metabolism*
chemical_list: C506487:ESR1 protein, human; D047628:Estrogen Receptor alpha; D004967:Estrogens; C524942:MIRN155 microRNA, human; D035683:MicroRNAs; D046912:Multiprotein Complexes; D011980:Receptors, Progesterone; D000068338:Everolimus; D000076222:Mechanistic Target of Rapamycin Complex 1; D000076225:Mechanistic Target of Rapamycin Complex 2; D051057:Proto-Oncogene Proteins c-akt; D058570:TOR Serine-Threonine Kinases; D020123:Sirolimus