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

J Cell Biochem. 1996 Feb;60(2):173-84. doi: 10.1002/(sici)1097-4644(19960201)60:2<173::aid-jcb2>3.0.co;2-u.


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.

Publication types

  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Breast Neoplasms / metabolism*
  • Carcinogens / pharmacology*
  • Estradiol / pharmacology*
  • Gene Expression Regulation, Neoplastic / drug effects*
  • Humans
  • Immunohistochemistry
  • Polychlorinated Dibenzodioxins / pharmacology*
  • RNA, Messenger / metabolism
  • Receptors, Estrogen / drug effects*
  • Receptors, Estrogen / genetics
  • Receptors, Estrogen / metabolism
  • Tetradecanoylphorbol Acetate / pharmacology*


  • Carcinogens
  • Polychlorinated Dibenzodioxins
  • RNA, Messenger
  • Receptors, Estrogen
  • Estradiol
  • Tetradecanoylphorbol Acetate