title: Constitutive expression of AhR and BRCA-1 promoter CpG hypermethylation as biomarkers of ERα-negative breast tumorigenesis.
abstract: BACKGROUND
  Only 5-10% of breast cancer cases is linked to germline mutations in the BRCA-1 gene and occurs early in life. Conversely, sporadic breast tumors, which represent 90-95% of breast malignancies, have lower BRCA-1 expression, but not mutated BRCA-1 gene, and tend to occur later in life in combination with other genetic alterations and/or environmental exposures. The latter may include environmental and dietary factors that activate the aromatic hydrocarbon receptor (AhR). Therefore, understanding if changes in expression and/or activation of the AhR are associated with somatic inactivation of the BRCA-1 gene may provide clues for breast cancer therapy.
  
  
  METHODS
  We evaluated Brca-1 CpG promoter methylation and expression in mammary tumors induced in Sprague-Dawley rats with the AhR agonist and mammary carcinogen 7,12-dimethyl-benzo(a)anthracene (DMBA). Also, we tested in human estrogen receptor (ER)α-negative sporadic UACC-3199 and ERα-positive MCF-7 breast cancer cells carrying respectively, hyper- and hypomethylated BRCA-1 gene, if the treatment with the AhR antagonist α-naphthoflavone (αNF) modulated BRCA-1 and ERα expression. Finally, we examined the association between expression of AhR and BRCA-1 promoter CpG methylation in human triple-negative (TNBC), luminal-A (LUM-A), LUM-B, and epidermal growth factor receptor-2 (HER-2)-positive breast tumor samples.
  
  
  RESULTS
  Mammary tumors induced with DMBA had reduced BRCA-1 and ERα expression; higher Brca-1 promoter CpG methylation; increased expression of Ahr and its downstream target Cyp1b1; and higher proliferation markers Ccnd1 (cyclin D1) and Cdk4. In human UACC-3199 cells, low BRCA-1 was paralleled by constitutive high AhR expression; the treatment with αNF rescued BRCA-1 and ERα, while enhancing preferential expression of CYP1A1 compared to CYP1B1. Conversely, in MCF-7 cells, αNF antagonized estradiol-dependent activation of BRCA-1 without effects on expression of ERα. TNBC exhibited increased basal AhR and BRCA-1 promoter CpG methylation compared to LUM-A, LUM-B, and HER-2-positive breast tumors.
  
  
  CONCLUSIONS
  Constitutive AhR expression coupled to BRCA-1 promoter CpG hypermethylation may be predictive markers of ERα-negative breast tumor development. Regimens based on selected AhR modulators (SAhRMs) may be useful for therapy against ERα-negative tumors, and possibly, TNBC with increased AhR and hypermethylated BRCA-1 gene.
authors.affiliation: Department of Nutritional Sciences, The University of Arizona, 303 Shantz Bldg, Tucson, AZ, 85721-0038, USA. donato@u.arizona.edu.|The University of Arizona Cancer Center, 1515 N. Campbell Avenue, 3999A, Tucson, AZ, 85724-5024, USA. donato@u.arizona.edu.
authors.forename: Donato F
authors.initials: DF
authors.lastname: Romagnolo
authors.affiliation: Department of Nutritional Sciences, The University of Arizona, 303 Shantz Bldg, Tucson, AZ, 85721-0038, USA. inmytree9@hotmail.com.
authors.forename: Andreas J
authors.initials: AJ
authors.lastname: Papoutsis
authors.affiliation: Department of Nutritional Sciences, The University of Arizona, 303 Shantz Bldg, Tucson, AZ, 85721-0038, USA. CLaukaitis@uacc.arizona.edu.|The University of Arizona Cancer Center, 1515 N. Campbell Avenue, 3999A, Tucson, AZ, 85724-5024, USA. CLaukaitis@uacc.arizona.edu.|Department of Medicine, University of Arizona College of Medicine, The University of Arizona, Tucson, AZ, USA. CLaukaitis@uacc.arizona.edu.
authors.forename: Christina
authors.initials: C
authors.lastname: Laukaitis
authors.affiliation: Department of Nutritional Sciences, The University of Arizona, 303 Shantz Bldg, Tucson, AZ, 85721-0038, USA. selmin@u.arizona.edu.|The University of Arizona Cancer Center, 1515 N. Campbell Avenue, 3999A, Tucson, AZ, 85724-5024, USA. selmin@u.arizona.edu.
authors.forename: Ornella I
authors.initials: OI
authors.lastname: Selmin
mesh_terms: D000818:Animals; D019313:BRCA1 Protein / Q000235:genetics*; D051792:Basic Helix-Loop-Helix Proteins / Q000378:metabolism*; D014408:Biomarkers, Tumor / Q000235:genetics; D001943:Breast Neoplasms / Q000139:chemically induced / Q000235:genetics* / Q000378:metabolism; D045744:Cell Line, Tumor; D018899:CpG Islands; D019175:DNA Methylation; D047628:Estrogen Receptor alpha / Q000235:genetics*; D005260:Female; D015972:Gene Expression Regulation, Neoplastic; D006801:Humans; D061986:MCF-7 Cells; D011401:Promoter Regions, Genetic; D051381:Rats; D017207:Rats, Sprague-Dawley; D018336:Receptors, Aryl Hydrocarbon / Q000378:metabolism*
chemical_list: D019313:BRCA1 Protein; D051792:Basic Helix-Loop-Helix Proteins; D014408:Biomarkers, Tumor; D047628:Estrogen Receptor alpha; D018336:Receptors, Aryl Hydrocarbon; C111235:AHR protein, human; C492913:BRCA1 protein, human