title: NCOA3 is a selective co-activator of estrogen receptor α-mediated transactivation of PLAC1 in MCF-7 breast cancer cells.
abstract: BACKGROUND
  The placenta-specific 1 (PLAC1) gene encodes a membrane-associated protein which is selectively expressed in the placental syncytiotrophoblast and in murine fetal tissues during embryonic development. In contrast to its transcriptional repression in all other adult normal tissues, PLAC1 is frequently activated and highly expressed in a variety of human cancers, in particular breast cancer, where it associates with estrogen receptor α (ERα) positivity. In a previous study, we showed that ERα-signaling in breast cancer cells transactivates PLAC1 expression in a non-classical pathway. As the members of the p160/nuclear receptor co-activator (NCOA) family, NCOA1, NCOA2 and NCOA3 are known to be overexpressed in breast cancer and essentially involved in estrogen-mediated cancer cell proliferation we asked if these proteins are involved in the ERα-mediated transactivation of PLAC1 in breast cancer cells.
  
  
  METHODS
  Applying quantitative real-time RT-PCR (qRT-PCR), Western Blot analysis and chromatin immunoprecipitation, we analyzed the involvement of NCOA1, NCOA2, NCOA3 in the ERα-mediated transactivation of PLAC1 in the breast cancer cell lines MCF-7 and SK-BR-3. RNAi-mediated silencing of NCOA3, qRT-PCR, Western blot analysis and ERα activation assays were used to examine the role of NCOA3 in the ERα-mediated regulation of PLAC1 in further detail. Transcript expression of NCOA3 and PLAC1 in 48 human breast cancer samples was examined by qRT-PCR and statistical analysis was performed using Student's t-test.
  
  
  RESULTS
  We detected selective recruitment of NCOA3 but not NCOA1 or NCOA2 to the PLAC1 promoter only in ERα-positive MCF-7 cells but not in ERα-negative SK-BR-3 breast cancer cells. In addition, we demonstrate that silencing of NCOA3 results in a remarkable decrease of PLAC1 expression levels in MCF-7 cells which cannot be restored by treatment with estradiol (E₂). Moreover, significant higher transcript levels of PLAC1 were found only in ERα-positive human breast cancer samples which also show a NCOA3 overexpression.
  
  
  CONCLUSIONS
  In this study, we identified NCOA3 as a selective co-activator of ERα-mediated transactivation of PLAC1 in MCF-7 breast cancer cells. Our data introduce PLAC1 as novel target gene of NCOA3 in breast cancer, supporting the important role of both factors in breast cancer biology.
authors.forename: Meike
authors.initials: M
authors.lastname: Wagner
authors.forename: Michael
authors.initials: M
authors.lastname: Koslowski
authors.forename: Claudia
authors.initials: C
authors.lastname: Paret
authors.forename: Marcus
authors.initials: M
authors.lastname: Schmidt
authors.forename: Ozlem
authors.initials: O
authors.lastname: Türeci
authors.affiliation: Department of Internal Medicine III, Division of Translational and Experimental Oncology, University Medical Center, Johannes Gutenberg University, 55131 Mainz, Germany. ugur.sahin@tron-mainz.de.
authors.forename: Ugur
authors.initials: U
authors.lastname: Sahin
mesh_terms: D001943:Breast Neoplasms; D004958:Estradiol / Q000502:physiology; D047628:Estrogen Receptor alpha / Q000502:physiology*; D005260:Female; D015972:Gene Expression Regulation, Neoplastic; D006801:Humans; D061986:MCF-7 Cells; D056920:Nuclear Receptor Coactivator 1 / Q000502:physiology; D051958:Nuclear Receptor Coactivator 2 / Q000502:physiology; D056921:Nuclear Receptor Coactivator 3 / Q000502:physiology*; D011257:Pregnancy Proteins / Q000235:genetics* / Q000378:metabolism; D011401:Promoter Regions, Genetic; D011485:Protein Binding; D014158:Transcription, Genetic; D015533:Transcriptional Activation
chemical_list: C506487:ESR1 protein, human; D047628:Estrogen Receptor alpha; C498001:NCOA2 protein, human; D051958:Nuclear Receptor Coactivator 2; C415583:PLAC1 protein, human; D011257:Pregnancy Proteins; D004958:Estradiol; C538859:NCOA1 protein, human; C538866:NCOA3 protein, human; D056920:Nuclear Receptor Coactivator 1; D056921:Nuclear Receptor Coactivator 3