title: Effects of 2,3,7,8-tetrachlorodibenzo-p-dioxin, 12-O-tetradecanoylphorbol-13-acetate and 17 beta-estradiol on estrogen receptor regulation in MCF-7 human breast cancer cells.
abstract: 2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) exhibits remarkably potent antiestrogenic activity. To further elucidate the role of estrogen receptor (ER) regulation in this response, we examined the effects of exposure to TCDD in MCF-7 human breast cancer cells on ER mRNA levels by using an RNase protection assay, on ER accumulation by using an ER immunocytochemical essay (ER-ICA), and on ER function by competitive binding assays under conditions of saturating 17 beta-estradiol (E2). Comparative studies were conducted with E2 and 12-O-tetradecanoylphorbol-13-acetate (TPA), as both compounds are known to suppress ER expression. Our results indicate that 1 nM E2 and 100 nM TPA both suppress ER mRNA levels as early as 4 h after exposure and to 33.6% and 16.5% of control levels, respectively, after 72 h. In contrast, no significant effect on ER mRNA levels was attributed to exposure to 10 nM TCDD. A greater than 50% reduction in positive staining was observed by ER-ICA after 72 h exposure to 1 nM E2 and to 100 nM TPA, while only an 11% reduction in positive staining was observed with 10 nM TCDD. Specific binding of [3H]E2 under saturating conditions (10 nM E2) in whole cells was reduced by 50% in cultures exposed to 100 nM TPA, although no effect on binding was observed with exposure to 10 nM TCDD. In contrast, specific binding using subsaturating 1 nM [3H]E2 was depressed by 49% in MCF-7 cells exposed to 10 nM TCDD for 72 h. This depression was inhibited by a 1-h treatment with 5 microM alpha-naphthoflavone, which inhibits TCDD-induced, P450-mediated, E2 metabolism, and subsequent E2 depletion. In conclusion, while TPA and E2 effectively down-regulate ER expression, TCDD, under antiestrogenic conditions, has little if any effect on total ER levels in MCF-7 cells, and thus ER modulation is probably not necessary for the suppression of estrogenic activity in MCF-7 cells by TCDD.
authors.affiliation: Wadsworth Center, New York State Department of Health, Albany 12201-0509, USA.
authors.forename: J F
authors.initials: JF
authors.lastname: Gierthy
authors.forename: B C
authors.initials: BC
authors.lastname: Spink
authors.forename: H L
authors.initials: HL
authors.lastname: Figge
authors.forename: B T
authors.initials: BT
authors.lastname: Pentecost
authors.forename: D C
authors.initials: DC
authors.lastname: Spink
mesh_terms: D001943:Breast Neoplasms / Q000378:metabolism*; D002273:Carcinogens / Q000494:pharmacology*; D004958:Estradiol / Q000494:pharmacology*; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects*; D006801:Humans; D007150:Immunohistochemistry; D000072317:Polychlorinated Dibenzodioxins / Q000494:pharmacology*; D012333:RNA, Messenger / Q000378:metabolism; D011960:Receptors, Estrogen / Q000187:drug effects* / Q000235:genetics / Q000378:metabolism; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology*
chemical_list: D002273:Carcinogens; D000072317:Polychlorinated Dibenzodioxins; D012333:RNA, Messenger; D011960:Receptors, Estrogen; D004958:Estradiol; D013755:Tetradecanoylphorbol Acetate