title: Altered nuclear receptor corepressor expression attenuates vitamin D receptor signaling in breast cancer cells.
abstract: OBJECTIVE
  We hypothesized that deregulated corepressor actions, with associated histone deacetylation activity, epigenetically suppressed vitamin D receptor (VDR) responsiveness and drives resistance towards 1alpha,25-dihydroxyvitamin D(3).
  
  
  METHODS
  Profiling, transcriptional, and proliferation assays were undertaken in 1alpha,25(OH)(2)D(3)-sensitive MCF-12A nonmalignant breast epithelial cells, a panel of breast cancer cell lines, and a cohort of primary breast cancer tumors (n = 21).
  
  
  RESULTS
  Elevated NCoR1 mRNA levels correlated with suppressed regulation of VDR target genes and the ability of cells to undergo arrest in G(1) of the cell cycle. A similar increased ratio of corepressor mRNA to VDR occurred in matched primary tumor and normal cells, noticeably in estrogen receptor alpha-negative (n = 7) tumors. 1alpha,25(OH)(2)D(3) resistance in cancer cell lines was targeted by cotreatments with either 1alpha,25(OH)(2)D(3) or a metabolically stable analogue (RO-26-2198) in combination with either trichostatin A (TSA; histone deacetylation inhibitor) or 5-aza-2'-deoxycytidine (DNA methyltransferase inhibitor). Combinations of vitamin D(3) compounds with TSA restored VDR antiproliferative signaling (target gene regulation, cell cycle arrest, and antiproliferative effects in liquid culture) to levels which were indistinguishable from MCF-12A cells.
  
  
  CONCLUSIONS
  Increased NCoR1 mRNA is a novel molecular lesion in breast cancer cells, which acts to suppress responsiveness of VDR target genes, resulting in 1alpha,25(OH)(2)D(3) resistance and seems to be particularly associated with estrogen receptor negativity. This lesion provides a novel molecular diagnostic and can be targeted by combinations of vitamin D(3) compounds and low doses of TSA.
authors.affiliation: Institute of Biomedical Research, Endocrinology and Metabolism and Division of Immunity and Infection, University of Birmingham Medical School, Edgbaston, Birmingham, United Kingdom.
authors.forename: Claire M
authors.initials: CM
authors.lastname: Banwell
authors.forename: Donia P
authors.initials: DP
authors.lastname: MacCartney
authors.forename: Michelle
authors.initials: M
authors.lastname: Guy
authors.forename: Alice E
authors.initials: AE
authors.lastname: Miles
authors.forename: Milan R
authors.initials: MR
authors.lastname: Uskokovic
authors.forename: Janine
authors.initials: J
authors.lastname: Mansi
authors.forename: Paul M
authors.initials: PM
authors.lastname: Stewart
authors.forename: Laura P
authors.initials: LP
authors.lastname: O'Neill
authors.forename: Bryan M
authors.initials: BM
authors.lastname: Turner
authors.forename: Kay W
authors.initials: KW
authors.lastname: Colston
authors.forename: Moray J
authors.initials: MJ
authors.lastname: Campbell
mesh_terms: D001374:Azacitidine / Q000031:analogs & derivatives / Q000494:pharmacology; D001943:Breast Neoplasms / Q000378:metabolism*; D002117:Calcitriol / Q000494:pharmacology; D002453:Cell Cycle / Q000187:drug effects; D045744:Cell Line, Tumor; D049109:Cell Proliferation / Q000187:drug effects; D002762:Cholecalciferol / Q000031:analogs & derivatives / Q000494:pharmacology; D000077209:Decitabine; D005260:Female; D006801:Humans; D006877:Hydroxamic Acids / Q000494:pharmacology; D009687:Nuclear Proteins / Q000187:drug effects / Q000235:genetics* / Q000378:metabolism*; D056971:Nuclear Receptor Co-Repressor 1; D012333:RNA, Messenger / Q000187:drug effects / Q000235:genetics; D018167:Receptors, Calcitriol / Q000187:drug effects / Q000378:metabolism*; D012097:Repressor Proteins / Q000187:drug effects / Q000235:genetics* / Q000378:metabolism*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D015398:Signal Transduction / Q000187:drug effects; D013329:Structure-Activity Relationship; D013997:Time Factors; D014407:Tumor Cells, Cultured
chemical_list: C408047:1,25(OH)2-16-ene-23-yne-26,27-hexafluoro-19-nor-D3; D006877:Hydroxamic Acids; C539127:NCOR1 protein, human; D009687:Nuclear Proteins; D056971:Nuclear Receptor Co-Repressor 1; D012333:RNA, Messenger; D018167:Receptors, Calcitriol; D012097:Repressor Proteins; D002762:Cholecalciferol; C012589:trichostatin A; D000077209:Decitabine; D002117:Calcitriol; D001374:Azacitidine