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.
Chemical Exposure and Health Effects Research Team, National Institute for Environmental Studies, 16-2 Onogawa,Tsukuba, Ibaraki 305-0053, Japan.
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Jana
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Sarkar
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Ishizuka
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Yonemoto
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Tohyama
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Sone
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