title: Suppression of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD)-mediated CYP1A1 and CYP1B1 induction by 12-O-tetradecanoylphorbol-13-acetate: role of transforming growth factor beta and mitogen-activated protein kinases.
abstract: The phorbol ester 12-O-tetradecanoylphorbol-13-acetate (TPA) enhances or suppresses the transcriptional activation of CYP1A1 by 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) in a cell/tissue-specific manner. The basis for these effects is not known. Exposure of the immortalized human breast epithelial cell line MCF10A-Neo to TPA at the time of, or up to 12 hr prior to, the addition of TCDD strongly suppressed the transcriptional activation of CYP1A1 and CYP1B1 (IC(50) approximately 0.5 nM). A recent study (Carcinogenesis 2000;21:1303-12) demonstrated that TPA-treated MCF10A-Neo cells rapidly activate the latent transforming growth factor beta (TGFbeta) in the serum used to supplement the culture medium. The suppressive effects of TPA on CYP1A1 induction by TCDD in MCF10A-Neo cultures could be partially suppressed by: (a) co-incubation of TCDD + TPA-treated cultures with a neutralizing TGFbeta pan antibody; (b) prior removal of latent TGFbeta from the culture medium; or (c) switching cultures to serum- and growth factor-free medium immediately before the addition of TPA and TCDD. Exposure of cultures to TPA 24-48 hr prior to subsequent TPA + TCDD treatment not only inhibited the suppressive effects of TPA, but markedly enhanced CYP1A1 mRNA accumulation. TPA caused a rapid and protracted activation of extracellular signal-regulated kinases (ERKs). Pretreatment of cultures with the mitogen-activated protein kinase kinase (MEK) inhibitor PD184352 [2-(2-chloro-4-iodo-phenylamino)-N-cyclopropyl-methoxy-3,4-difluoro-benzamide] completely inhibited ERK activation by TPA. However, PD184352 did not prevent the suppressive effects of TPA on CYP1A1 activation by TCDD. These studies demonstrate that TPA initiates protein kinase C-dependent, ERK-independent processes that suppress CYP1A1 activation by TCDD in MCF10A-Neo cells. Furthermore, TGFbeta mediates a small portion of this suppressive activity.
authors.affiliation: Institute of Environmental Health Sciences, Wayne State University, 2727 Second Ave., Rm. 4000, Detroit, MI 48201, USA.
authors.forename: M
authors.initials: M
authors.lastname: Guo
authors.forename: A
authors.initials: A
authors.lastname: Joiakim
authors.forename: D T
authors.initials: DT
authors.lastname: Dudley
authors.forename: J J
authors.initials: JJ
authors.lastname: Reiners
mesh_terms: D001189:Aryl Hydrocarbon Hydroxylases; D001549:Benzamides / Q000494:pharmacology; D002273:Carcinogens / Q000494:pharmacology; D002478:Cells, Cultured; D019363:Cytochrome P-450 CYP1A1 / Q000096:biosynthesis* / Q000187:drug effects / Q000235:genetics; D065633:Cytochrome P-450 CYP1B1; D003577:Cytochrome P-450 Enzyme System / Q000096:biosynthesis* / Q000187:drug effects / Q000235:genetics; D004347:Drug Interactions; D004789:Enzyme Activation; D004790:Enzyme Induction / Q000187:drug effects; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006801:Humans; D020928:Mitogen-Activated Protein Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism / Q000502:physiology*; D000072317:Polychlorinated Dibenzodioxins / Q000494:pharmacology*; D011493:Protein Kinase C / Q000037:antagonists & inhibitors / Q000502:physiology; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology*; D015533:Transcriptional Activation / Q000187:drug effects; D016212:Transforming Growth Factor beta / Q000502:physiology*
chemical_list: C120227:2-(2-chloro-4-iodophenylamino)-N-cyclopropylmethoxy-3,4-difluorobenzamide; D001549:Benzamides; D002273:Carcinogens; D004791:Enzyme Inhibitors; D000072317:Polychlorinated Dibenzodioxins; D016212:Transforming Growth Factor beta; D003577:Cytochrome P-450 Enzyme System; D001189:Aryl Hydrocarbon Hydroxylases; C585496:CYP1B1 protein, human; D019363:Cytochrome P-450 CYP1A1; D065633:Cytochrome P-450 CYP1B1; D011493:Protein Kinase C; D020928:Mitogen-Activated Protein Kinases; D013755:Tetradecanoylphorbol Acetate