title: The orphan nuclear receptor LRH-1 and ERα activate GREB1 expression to induce breast cancer cell proliferation.
abstract: BACKGROUND
  Liver Receptor Homolog 1 (LRH-1, NR5A2) is an orphan nuclear receptor that is over-expressed in cancers in tissues such as the breast, colon and pancreas. LRH-1 plays important roles in embryonic development, steroidogenesis and cholesterol homeostasis. In tumor cells, LRH-1 induces proliferation and cell cycle progression. High LRH-1 expression is demonstrated in breast cancers, positively correlating with ERα status and aromatase activity. LRH-1 dependent cellular mechanisms in breast cancer epithelial cells are poorly defined. Hence in the present study we investigated the actions of LRH-1 in estrogen receptor α (ERα) positive breast cancer cells.
  
  
  RESULTS
  The study aimed to investigate LRH-1 dependent mechanisms that promote breast cancer proliferation. We identified that LRH-1 regulated the expression of Growth Regulation by Estrogen in Breast Cancer 1 (GREB1) in MCF-7 and MDA-MB-231 cells. Over-expression of LRH-1 increased GREB1 mRNA levels while knockdown of LRH-1 reduced its expression. GREB1 is a well characterised ERα target gene, with three estrogen response elements (ERE) located on its promoter. Chromatin immunoprecipitation studies provided evidence of the co-localisation of LRH-1 and ERα at all three EREs. With electrophoretic mobility shift assays, we demonstrated direct binding of LRH-1 to EREs located on GREB1 and Trefoil Factor 1 (TFF1, pS2) promoters. LRH-1 and ERα co-operatively activated transcription of ERE luciferase reporter constructs suggesting an overlap in regulation of target genes in breast cancer cells. Over-expression of LRH-1 resulted in an increase in cell proliferation. This effect was more pronounced with estradiol treatment. In the presence of ICI 182,780, an ERα antagonist, LRH-1 still induced proliferation.
  
  
  CONCLUSIONS
  We conclude that in ER-positive breast cancer cells, LRH-1 promotes cell proliferation by enhancing ERα mediated transcription of target genes such as GREB-1. Collectively these findings indicate the importance of LRH-1 in the progression of hormone-dependent breast cancer and implicate LRH-1 as a potential avenue for drug development.
authors.affiliation: Prince Henry's Institute, Monash Medical Centre, Clayton, Victoria, Australia. colin.clyne@princehenrys.org
authors.forename: Ashwini L
authors.initials: AL
authors.lastname: Chand
authors.forename: Dhilushi D
authors.initials: DD
authors.lastname: Wijayakumara
authors.forename: Kevin C
authors.initials: KC
authors.lastname: Knower
authors.forename: Kerrie A
authors.initials: KA
authors.lastname: Herridge
authors.forename: Tamara L
authors.initials: TL
authors.lastname: Howard
authors.forename: Kyren A
authors.initials: KA
authors.lastname: Lazarus
authors.forename: Colin D
authors.initials: CD
authors.lastname: Clyne
mesh_terms: D001943:Breast Neoplasms / Q000473:pathology*; D045744:Cell Line, Tumor; D049109:Cell Proliferation; D047628:Estrogen Receptor alpha / Q000502:physiology*; D005260:Female; D015972:Gene Expression Regulation, Neoplastic; D006801:Humans; D009363:Neoplasm Proteins / Q000235:genetics*; D057093:Orphan Nuclear Receptors / Q000502:physiology*; D011401:Promoter Regions, Genetic; D018160:Receptors, Cytoplasmic and Nuclear / Q000502:physiology*; D020218:Response Elements; D014158:Transcription, Genetic
chemical_list: D047628:Estrogen Receptor alpha; C416830:GREB1 protein, human; C082631:NR5A2 protein, human; D009363:Neoplasm Proteins; D057093:Orphan Nuclear Receptors; D018160:Receptors, Cytoplasmic and Nuclear