title: Disruption of cell cycle kinetics by benzo[a]pyrene: inverse expression patterns of BRCA-1 and p53 in MCF-7 cells arrested in S and G2.
abstract: The effects of a ligand of the aromatic hydrocarbon receptor (AhR), benzo[a] pyrene (B[ a]P), and its metabolite, BPDE (7r,8t-dihydroxy-9t,10t-epoxy-7,8,9,10-tetrahydro-benzo[a]pyrene), on BRCA-1 levels and cell cycle kinetics were determined in MCF-7 breast cancer cells. Exposure of asynchronous MCF-7 cells for 72 hours to a non-cytotoxic dose of 0.5 microM B[a]P triggered a three-fold reduction in BRCA-1 protein. In MCF-7 cells resistant (20% to 30%) to genotoxic concentrations of B[a]P (1 to 5 microM), the loss of BRCA-1 protein was coupled with pausing in S-phase and G2/M, and accumulation of p53, mdm2 and p21. Treatment of MCF-7 cells synchronized in S-phase (72%) with B[a]P prolonged the arrest in S-phase, although this checkpoint was transient since cells resumed to G2/M after 12 hours with reduced levels of BRCA-1. In these cells, levels of p53 were increased, whereas the cellular content of p21 remained unaltered. In contrast, the co-treatment with the AhR antagonist, alpha-naphthoflavone (ANF), abrogated the deleterious effects of B[a]P on BRCA-1 expression, while preventing the accumulation of p53 and disruption of cell cycle profile. These findings suggest that the AhR mediated the inverse expression patterns of BRCA-1 and p53 upon exposure to B[a]P. The treatment with BPDE induced S-phase arrest and reduced BRCA-1 mRNA levels. The negative effects of BPDE on BRCA-1 expression were not transient since removal of BPDE did not allow complete reversal of the repression. These cumulative data suggest that the B[a]P metabolite, BPDE, may play a key role in disruption of BRCA-1 expression and cell cycle kinetics in breast epithelial cells.
authors.affiliation: Cancer Biology Interdisciplinary Program, Arizona Cancer Center, The University of Arizona, Tucson, USA.
authors.forename: B D
authors.initials: BD
authors.lastname: Jeffy
authors.forename: E J
authors.initials: EJ
authors.lastname: Chen
authors.forename: J M
authors.initials: JM
authors.lastname: Gudas
authors.forename: D F
authors.initials: DF
authors.lastname: Romagnolo
mesh_terms: D015123:7,8-Dihydro-7,8-dihydroxybenzo(a)pyrene 9,10-oxide / Q000494:pharmacology*; D000230:Adenocarcinoma / Q000235:genetics / Q000473:pathology*; D016590:Aphidicolin / Q000494:pharmacology; D019313:BRCA1 Protein / Q000096:biosynthesis* / Q000235:genetics; D001564:Benzo(a)pyrene / Q000494:pharmacology*; D001571:Benzoflavones / Q000494:pharmacology; D001943:Breast Neoplasms / Q000235:genetics / Q000473:pathology*; D002453:Cell Cycle / Q000187:drug effects*; D003078:Colchicine / Q000494:pharmacology; D003864:Depression, Chemical; D004305:Dose-Response Relationship, Drug; D005260:Female; D016195:G2 Phase / Q000187:drug effects; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects*; D019398:Genes, BRCA1; D016158:Genes, p53; D006801:Humans; D009363:Neoplasm Proteins / Q000096:biosynthesis* / Q000187:drug effects / Q000235:genetics / Q000502:physiology; D018336:Receptors, Aryl Hydrocarbon / Q000187:drug effects* / Q000502:physiology; D016196:S Phase / Q000187:drug effects; D014407:Tumor Cells, Cultured / Q000187:drug effects / Q000378:metabolism; D016159:Tumor Suppressor Protein p53 / Q000096:biosynthesis*
chemical_list: D019313:BRCA1 Protein; D001571:Benzoflavones; D009363:Neoplasm Proteins; D018336:Receptors, Aryl Hydrocarbon; D016159:Tumor Suppressor Protein p53; D001564:Benzo(a)pyrene; D016590:Aphidicolin; D015123:7,8-Dihydro-7,8-dihydroxybenzo(a)pyrene 9,10-oxide; C011512:alpha-naphthoflavone; D003078:Colchicine