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

• Published in: Molecular cell biology research communications 2000-09, Vol.4 (3), p.174-180
• Main Authors: Jana, Nihar Ranjan, Sarkar, Shubhashishi, Ishizuka, Mayumi, Yonemoto, Junzo, Tohyama, Chiharu, Sone, Hideko
• Format: Article
• Language: English
• Subjects: 2,3,7,8-tetrachlorodibenzo-p-dioxin; AhR; Azacitidine - pharmacology; CYP1A1; Cytochrome P-450 CYP1A1 - genetics; Cytochrome P-450 CYP1A1 - metabolism; Environmental Pollutants - pharmacology; Enzyme Inhibitors - pharmacology; Estradiol - pharmacology; Estrogen Receptor alpha; Estrogen Receptor beta; Gene Expression Regulation; Genes, Reporter; human cells; Humans; Plasminogen Activator Inhibitor 2 - genetics; Plasminogen Activator Inhibitor 2 - metabolism; Polychlorinated Dibenzodioxins - pharmacology; Progesterone - pharmacology; Receptors, Androgen - genetics; Receptors, Androgen - metabolism; Receptors, Aryl Hydrocarbon - genetics; Receptors, Aryl Hydrocarbon - metabolism; Receptors, Estrogen - genetics; Receptors, Estrogen - metabolism; Receptors, Progesterone - genetics; Receptors, Progesterone - metabolism; Recombinant Fusion Proteins - metabolism; Reverse Transcriptase Polymerase Chain Reaction; Serine Proteinase Inhibitors - genetics; steroid hormone; Testosterone - pharmacology; Transfection; Tumor Cells, Cultured
• ISSN: 1522-4724; 1522-4732
• DOI: 10.1006/mcbr.2001.0275

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-α (ER-α) 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 E2- 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.