The effects of 2,3,7,8-tetrachlorodibenzo-p-dioxin on estrogen metabolism in MCF-7 breast cancer cells: evidence for induction of a novel 17 beta-estradiol 4-hydroxylase

J Steroid Biochem Mol Biol. 1994 Dec;51(5-6):251-8. doi: 10.1016/0960-0760(94)90037-x.


Rates of microsomal 17 beta-estradiol (E2) hydroxylation at the C-2, -4, -6 alpha, and -15 alpha positions are each induced greater than 10-fold by treating MCF-7 breast cancer cells with 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). The TCDD-induced activities at the C-2, -6 alpha and -15 alpha positions have been attributed to cytochrome P450 1A1 (CYP1A1); however, the low Km 4-hydroxylase induced by TCDD appears to be a distinct enzyme. We report here that antibodies to cytochrome P450-EF (mouse CYP1B1) selectivity inhibited the C-4 hydroxylation of E2 catalyzed by microsomes from TCDD-treated MCF-7 cells. Western blots probed with anti-CYP1B antibodies showed the induction of a 52 kDa microsomal protein in response to treatment with TCDD in MCF-7 cells. Western blots of microsomes from HepG2 cells did not show the TCDD-induced 52 kDa protein, and microsomes from TCDD-treated HepG2 cells did not catalyze a low Km hydroxylation of E2 at C-4. Cellular metabolism experiments also showed induction of both the C-2 and -4 hydroxylation pathways in TCDD-treated MCF-7 cells as evidenced by elevated 2- and 4-methoxyestradiol (MeOE2) formation. In contrast, TCDD-treated HepG2 cells showed 2-MeOE2 formation predominantly over 4-MeOE2. Northern blots of RNA isolated from untreated and TCDD-treated cells, when probed with the human CYP1B1 cDNA, showed induction of a 5.2 kb RNA in MCF-7 cells but not in HepG2 cells in response to treatment with TCDD. These results provide additional evidence for the induction by TCDD of a novel E2 4-hydroxylase in MCF-7 cells but not in HepG2 cells and indicate possible endocrine regulatory roles for the newly discovered group of enzymes of the CYP1B subfamily.

Publication types

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

MeSH terms

  • Aryl Hydrocarbon Hydroxylases*
  • Breast Neoplasms / metabolism*
  • Cytochrome P-450 CYP1B1
  • Cytochrome P-450 Enzyme System / biosynthesis*
  • Enzyme Induction
  • Estradiol / metabolism*
  • Humans
  • Methylation
  • Microsomes / metabolism
  • Polychlorinated Dibenzodioxins / pharmacology*
  • Steroid Hydroxylases / biosynthesis*
  • Tumor Cells, Cultured


  • Polychlorinated Dibenzodioxins
  • Estradiol
  • Cytochrome P-450 Enzyme System
  • Steroid Hydroxylases
  • Aryl Hydrocarbon Hydroxylases
  • CYP1B1 protein, human
  • Cyp1b1 protein, mouse
  • Cytochrome P-450 CYP1B1