title: Low levels of 3,3'-diindolylmethane activate estrogen receptor α and induce proliferation of breast cancer cells in the absence of estradiol.
abstract: BACKGROUND
  3,3'-diindolylmethane (DIM) is an acid-catalyzed dimer of idole-3-carbinol (I3C), a phytochemical found in cruciferous vegetables that include broccoli, Brussels sprouts and cabbage. DIM is an aryl hydrocarbon receptor (AhR) ligand and a potential anticancer agent, namely for the treatment of breast cancer. It is also advertised as a compound that regulates sex hormone homeostasis.
  
  
  METHODS
  Here we make use of RNA expression assays coupled to Chromatin Immunoprecipitation (ChIP) in breast cancer cell lines to study the effect of DIM on estrogen signaling. We further make use of growth assays, as well as fluorescence-activated cell sorting (FACS) assays, to monitor cell growth.
  
  
  RESULTS
  In this study, we report that 'physiologically obtainable' concentrations of DIM (10 μM) activate the estrogen receptor α (ERα) signaling pathway in the human breast cancer cell lines MCF7 and T47D, in a 17β-estradiol (E2)-independent manner. Accordingly, we observe induction of ERα target genes such as GREB1 and TFF1, and an increase in cellular proliferation after treatment with 10 μM DIM in the absence of E2. By using an ERα specific inhibitor (ICI 182 780), we confirm that the transcriptional and proliferative effects of DIM treatment are mediated by ERα. We further show that the protein kinase A signaling pathway participates in DIM-mediated activation of ERα. In contrast, higher concentrations of DIM (e.g. 50 μM) have an opposite and expected effect on cells, which is to inhibit proliferation.
  
  
  CONCLUSIONS
  We document an unexpected effect of DIM on cell proliferation, which is to stimulate growth by inducing the ERα signaling pathway. Importantly, this proliferative effect of DIM happens with potentially physiological concentrations that can be provided by the diet or by taking caplet supplements.
authors.forename: Maud
authors.initials: M
authors.lastname: Marques
authors.forename: Liette
authors.initials: L
authors.lastname: Laflamme
authors.forename: Ines
authors.initials: I
authors.lastname: Benassou
authors.forename: Coumba
authors.initials: C
authors.lastname: Cissokho
authors.forename: Benoit
authors.initials: B
authors.lastname: Guillemette
authors.affiliation: Département de Biologie, Université de Sherbrooke, J1K 2R1 Sherbrooke, QC, Canada. Luc.Gaudreau@USherbrooke.ca.
authors.forename: Luc
authors.initials: L
authors.lastname: Gaudreau
mesh_terms: D001943:Breast Neoplasms / Q000378:metabolism* / Q000473:pathology*; D045744:Cell Line, Tumor; D049109:Cell Proliferation / Q000187:drug effects; D004305:Dose-Response Relationship, Drug; D004958:Estradiol / Q000378:metabolism*; D047628:Estrogen Receptor alpha / Q000235:genetics / Q000378:metabolism*; D005260:Female; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects; D006801:Humans; D007211:Indoles / Q000494:pharmacology*; D061986:MCF-7 Cells; D015398:Signal Transduction / Q000187:drug effects
chemical_list: C506487:ESR1 protein, human; D047628:Estrogen Receptor alpha; D007211:Indoles; D004958:Estradiol; C016392:3,3'-diindolylmethane