Co-planar 3,3′,4,4′,5-pentachlorinated biphenyl and non-co-planar 2,2′,4,6,6′-pentachlorinated biphenyl differentially induce recruitment of oestrogen receptor α to aryl hydrocarbon receptor target genes

摘要

pIn the present study we examined the ability of 3,3′,4,4′,5-pentachlorinated biphenyl [PCB126 (polychlorinated biphenyl 126)], a prototypical AHR (aryl hydrocarbon receptor) agonist, and 2,2′,4,6,6′-PCB (PCB104), which does not activate AHR, to induce the recruitment of ERα (oestrogen receptor α) to iCYP1A1/i (cytochrome P4501A1 gene) and iCYP1B1/i promoters in T-47D human breast cancer cells and other cell lines. PCB126 treatment strongly induced CYP1A1 and CYP1B1 mRNA expression that was unaffected by co-treatment with E2 (17β-oestradiol). PCB104 failed to induce changes in either CYP1A1 or CYP1B1 expression levels. ChIP (chromatin immunoprecipitation) assays show that PCB126, but not PCB104, increased the promoter occupancy by ERα to iCYP1A1/i and iCYP1B1/i promoters. Co-treatment with PCB126+E2 significantly enhanced the promoter occupancy of ERα at iCYP1A1/i, whereas co-treatment with PCB126+4-hydroxytamoxifen or ICI182,780 did not. Competitive binding studies revealed that neither PCB126 nor PCB104 bound to ERα. HEK-293 cells (human embryonic kidney-293 cells) stably transfected with ERα showed significantly higher PCB126-induced CYP1A1 expression compared with empty vector controls, whereas no increase was observed in cells stably transfected with ERα lacking its N-terminal AF1 (activation function-1) domain (ERαΔAF1). Despite no increase in AHR-mediated gene expression, ChIP assays revealed that ERαΔAF1 was present at iCYP1A1/i and iCYP1B1/i promoters. HC11 mouse mammary cells stably expressing shRNA (small-hairpin RNA) against ERα showed an 8-fold reduction in PCB126-dependent Cyp1a1 expression. Our results provide further evidence that AHR agonists induce ERα promoter occupancy at AHR target genes through indirect activation of ERα, and support a role for ERα in AHR transactivation./p