Comparative effects of 2,3,7,8-tetrachlorodibenzo-p-dioxin on MCF-7, RL95-2, and LNCaP cells: role of target steroid hormones in cellular responsiveness to CYP1A1 induction.
A study was conducted to investigate whether target hormones affect 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD)-inducible gene expression, using as an experimental model system three human cancer cell lines, breast (MCF-7), uterine (RL95-2), and prostate (LNCaP). Exposure to TCDD induced the CYP1A1 gene in all three cell lines. MCF-7 and RL95-2 cells showed more than 15- and 10-fold induction of EROD (7-ethoxyresorufin O-deethylase) activity, respectively, compared with the less responsive LNCaP cells. Surprisingly, however, TCDD-induced reporter gene activity driven by a single XRE element was similar in RL95-2 and LNCaP cells. The steady-state levels of expression of aryl hydrocarbon receptor (AhR) and aryl hydrocarbon receptor nuclear translocator (ARNT) were similar in all three cell lines. Expression of the CYP1B1 and PAI-2 genes was induced by TCDD in MCF-7 and RL95-2, but not in LNCaP, cells. Transient coexpression of estradiol receptor-alpha (ER-alpha) with a TCDD-responsive reporter plasmid and subsequent TCDD treatment increased responsiveness to TCDD in RL95-2 and LNCaP cells. Treatment with AZA-C, a DNA methyltransferase inhibitor, enhanced responsiveness to TCDD, in terms of EROD activity in LNCaP cells, but not in MCF-7 and RL95-2 cells, suggesting that DNA methylation in the CpG dinucleotide within the XRE core sequence is another factor involved in silencing of CYP1A1 in LNCaP cells. TCDD markedly inhibited E(2)- or testosterone-induced reporter gene activities in all three cell lines. Conversely, these target hormones inhibited TCDD-induced EROD activity in the three cell lines. These findings suggest that TCDD and the target steroid hormones negatively regulate each other's activity.
Jana
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Chemical Exposure and Health Effects Research Team, National Institute for Environmental Studies, 16-2 Onogawa,Tsukuba, Ibaraki 305-0053, Japan.
Sarkar
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Ishizuka
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Yonemoto
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Tohyama
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Sone
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D001374:Azacitidine / Q000494:pharmacology; D019363:Cytochrome P-450 CYP1A1 / Q000235:genetics / Q000378:metabolism*; D004785:Environmental Pollutants / Q000494:pharmacology*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D004958:Estradiol / Q000494:pharmacology; D047628:Estrogen Receptor alpha; D047629:Estrogen Receptor beta; D005786:Gene Expression Regulation; D017930:Genes, Reporter; D006801:Humans; D017396:Plasminogen Activator Inhibitor 2 / Q000235:genetics / Q000378:metabolism*; D000072317:Polychlorinated Dibenzodioxins / Q000494:pharmacology*; D011374:Progesterone / Q000494:pharmacology; D011944:Receptors, Androgen / Q000235:genetics / Q000378:metabolism; D018336:Receptors, Aryl Hydrocarbon / Q000235:genetics / Q000378:metabolism*; D011960:Receptors, Estrogen / Q000235:genetics / Q000378:metabolism; D011980:Receptors, Progesterone / Q000235:genetics / Q000378:metabolism; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D015842:Serine Proteinase Inhibitors / Q000235:genetics; D013739:Testosterone / Q000494:pharmacology; D014162:Transfection; D014407:Tumor Cells, Cultured
D004785:Environmental Pollutants; D004791:Enzyme Inhibitors; D047628:Estrogen Receptor alpha; D047629:Estrogen Receptor beta; D017396:Plasminogen Activator Inhibitor 2; D000072317:Polychlorinated Dibenzodioxins; D011944:Receptors, Androgen; D018336:Receptors, Aryl Hydrocarbon; D011960:Receptors, Estrogen; D011980:Receptors, Progesterone; D011993:Recombinant Fusion Proteins; D015842:Serine Proteinase Inhibitors; D013739:Testosterone; D011374:Progesterone; D004958:Estradiol; D019363:Cytochrome P-450 CYP1A1; D001374:Azacitidine