title: Oestrogen increases the activity of oestrogen receptor negative breast cancer stem cells through paracrine EGFR and Notch signalling.
abstract: BACKGROUND
  Although oestrogen is essential for the development of the normal breast, adult mammary stem cells are known to be oestrogen receptor alpha (ER) negative and rely on paracrine signals in the mammary epithelium for mediation of developmental cues. However, little is known about how systemic oestrogen regulates breast cancer stem cell (CSC) activity.
  
  
  METHODS
  Here, we tested the effects of oestrogen on CSC activity in vitro and in vivo and investigated which paracrine signalling pathways locally mediate oestrogen effects.
  
  
  RESULTS
  CSC-enriched populations (ESA+CD44+CD24low) sorted from ER positive patient derived and established cell lines have low or absent ER expression. However, oestrogen stimulated CSC activity demonstrated by increased mammosphere and holoclone formation in vitro and tumour formation in vivo. This effect was abrogated by the anti-oestrogen tamoxifen or ER siRNA. These data suggest that the oestrogen response is mediated through paracrine signalling from non-CSCs to CSCs. We have, therefore, investigated both epidermal growth factor (EGF) and Notch receptor signals downstream of oestrogen. We demonstrate that gefitinib (epidermal growth factor receptor (EGFR) inhibitor) and gamma secretase inhibitors (Notch inhibitor) block oestrogen-induced CSC activity in vitro and in vivo but GSIs more efficiently reduce CSC frequency.
  
  
  CONCLUSIONS
  These data establish that EGF and Notch receptor signalling pathways operate downstream of oestrogen in the regulation of ER negative CSCs.
authors.forename: Hannah
authors.initials: H
authors.lastname: Harrison
authors.forename: Bruno M
authors.initials: BM
authors.lastname: Simões
authors.forename: Lynsey
authors.initials: L
authors.lastname: Rogerson
authors.forename: Sacha J
authors.initials: SJ
authors.lastname: Howell
authors.forename: Göran
authors.initials: G
authors.lastname: Landberg
authors.forename: Robert B
authors.initials: RB
authors.lastname: Clarke
mesh_terms: D000818:Animals; D015153:Blotting, Western; D001943:Breast Neoplasms / Q000188:drug therapy* / Q000201:enzymology / Q000473:pathology; D002471:Cell Transformation, Neoplastic; D066246:ErbB Receptors / Q000235:genetics / Q000378:metabolism*; D004967:Estrogens / Q000494:pharmacology*; D005260:Female; D005434:Flow Cytometry; D015972:Gene Expression Regulation, Neoplastic; D006801:Humans; D007124:Immunoenzyme Techniques; D051379:Mice; D016688:Mice, Inbred NOD; D016513:Mice, SCID; D014411:Neoplastic Stem Cells / Q000187:drug effects* / Q000378:metabolism / Q000473:pathology; D019899:Paracrine Communication; D012333:RNA, Messenger / Q000235:genetics; D034741:RNA, Small Interfering / Q000235:genetics; D060888:Real-Time Polymerase Chain Reaction; D011960:Receptors, Estrogen / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D051880:Receptors, Notch / Q000235:genetics / Q000378:metabolism*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D014407:Tumor Cells, Cultured; D023041:Xenograft Model Antitumor Assays
chemical_list: D004967:Estrogens; D012333:RNA, Messenger; D034741:RNA, Small Interfering; D011960:Receptors, Estrogen; D051880:Receptors, Notch; C512478:EGFR protein, human; D066246:ErbB Receptors