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Bisphenol A and its analogues activate human pregnane X receptor.

Sui Y, Ai N, Park SH, Rios-Pilier J, Perkins JT, Welsh WJ, Zhou C - Environ. Health Perspect. (2012)

Bottom Line: We found that BPA and several of its analogues are potent agonists for human PXR (hPXR) but do not affect mouse PXR activity.The present study advances our understanding of the mechanism by which BPA interacts with and activates human PXR.Activation of PXR by BPA may explain some of the adverse effects of BPA in humans.

View Article: PubMed Central - PubMed

Affiliation: Graduate Center for Nutritional Sciences, University of Kentucky, Lexington, Kentucky 40536, USA.

ABSTRACT

Background: Bisphenol A (BPA) is a base chemical used extensively in many consumer products. BPA and its analogues are present in environmental and human samples. Many endocrine-disrupting chemicals, including BPA, have been shown to activate the pregnane X receptor (PXR), a nuclear receptor that functions as a master regulator of xenobiotic metabolism. However, the detailed mechanism by which these chemicals activate PXR remains unknown.

Objective: We investigated the mechanism by which BPA interacts with and activates PXR and examined selected BPA analogues to determine whether they bind to and activate PXR.

Methods: Cell-based reporter assays, in silico ligand-PXR docking studies, and site-directed mutagenesis were combined to study the interaction between BPA and PXR. We also investigated the influence of BPA and its analogues on the regulation of PXR target genes in human LS180 cells.

Results: We found that BPA and several of its analogues are potent agonists for human PXR (hPXR) but do not affect mouse PXR activity. We identified key residues within hPXR's ligand-binding pocket that constitute points of interaction with BPA. We also deduced the structural requirements of BPA analogues that activate hPXR. BPA and its analogues can also induce PXR target gene expression in human LS180 cells.

Conclusions: The present study advances our understanding of the mechanism by which BPA interacts with and activates human PXR. Activation of PXR by BPA may explain some of the adverse effects of BPA in humans.

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BPA and analogues BPB and HPP synergistically activate PXR. (A) Activation of PXR in HepG2 cells transfected with full-length hPXR together with CYP3A4-luc reporter and CMX–β-galactosidase plasmid, and then treated with BPA, BPB, HPP, or mixtures. Error bars indicate SEM. (B) Docking poses of BPA (yellow) and HPP (green) in the binding pocket of hPXR. BPA and HPP may maintain hydrogen bond with Ser247; however, the orientation of the benzene ring of HPP is better than that of BPA for π-stacking interaction toward Trp299 (red). *p < 0.05, **p < 0.01, and #p < 0.001 compared with the untreated group or groups treated with a single compound (n = 3).
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f5: BPA and analogues BPB and HPP synergistically activate PXR. (A) Activation of PXR in HepG2 cells transfected with full-length hPXR together with CYP3A4-luc reporter and CMX–β-galactosidase plasmid, and then treated with BPA, BPB, HPP, or mixtures. Error bars indicate SEM. (B) Docking poses of BPA (yellow) and HPP (green) in the binding pocket of hPXR. BPA and HPP may maintain hydrogen bond with Ser247; however, the orientation of the benzene ring of HPP is better than that of BPA for π-stacking interaction toward Trp299 (red). *p < 0.05, **p < 0.01, and #p < 0.001 compared with the untreated group or groups treated with a single compound (n = 3).

Mentions: BPA and analogues synergistically activate hPXR. Because of the large and flexible LBD of PXR, combinations of BPA and other EDCs may activate hPXR in an additive or synergistic manner. To explore this possibility, we examined mixtures of BPA with each of the analogues under study at various concentrations. These experiments revealed that BPA and HPP can activate PXR synergistically (Figure 5A). A mixture of 2 μM BPA and 2 μM HPP activated PXR and induced PXR-mediated reporter activity > 30-fold, whereas BPA or HPP alone at 4 μM induced reporter activity only 4- and 13-fold, respectively. Mixtures of BPB and HPP synergistically activated PXR in a similar manner (Figure 5A). These results show that combinations of BPA-like agonists can work synergistically to activate hPXR. In contrast, DPP, which lacks PXR agonistic activity, failed to affect the agonistic activity of BPA, BPB, or HPP [Supplemental Material, Figure 3 (http://dx.doi.org/10.1289/ehp.1104426)].


Bisphenol A and its analogues activate human pregnane X receptor.

Sui Y, Ai N, Park SH, Rios-Pilier J, Perkins JT, Welsh WJ, Zhou C - Environ. Health Perspect. (2012)

BPA and analogues BPB and HPP synergistically activate PXR. (A) Activation of PXR in HepG2 cells transfected with full-length hPXR together with CYP3A4-luc reporter and CMX–β-galactosidase plasmid, and then treated with BPA, BPB, HPP, or mixtures. Error bars indicate SEM. (B) Docking poses of BPA (yellow) and HPP (green) in the binding pocket of hPXR. BPA and HPP may maintain hydrogen bond with Ser247; however, the orientation of the benzene ring of HPP is better than that of BPA for π-stacking interaction toward Trp299 (red). *p < 0.05, **p < 0.01, and #p < 0.001 compared with the untreated group or groups treated with a single compound (n = 3).
© Copyright Policy - public-domain
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3295358&req=5

f5: BPA and analogues BPB and HPP synergistically activate PXR. (A) Activation of PXR in HepG2 cells transfected with full-length hPXR together with CYP3A4-luc reporter and CMX–β-galactosidase plasmid, and then treated with BPA, BPB, HPP, or mixtures. Error bars indicate SEM. (B) Docking poses of BPA (yellow) and HPP (green) in the binding pocket of hPXR. BPA and HPP may maintain hydrogen bond with Ser247; however, the orientation of the benzene ring of HPP is better than that of BPA for π-stacking interaction toward Trp299 (red). *p < 0.05, **p < 0.01, and #p < 0.001 compared with the untreated group or groups treated with a single compound (n = 3).
Mentions: BPA and analogues synergistically activate hPXR. Because of the large and flexible LBD of PXR, combinations of BPA and other EDCs may activate hPXR in an additive or synergistic manner. To explore this possibility, we examined mixtures of BPA with each of the analogues under study at various concentrations. These experiments revealed that BPA and HPP can activate PXR synergistically (Figure 5A). A mixture of 2 μM BPA and 2 μM HPP activated PXR and induced PXR-mediated reporter activity > 30-fold, whereas BPA or HPP alone at 4 μM induced reporter activity only 4- and 13-fold, respectively. Mixtures of BPB and HPP synergistically activated PXR in a similar manner (Figure 5A). These results show that combinations of BPA-like agonists can work synergistically to activate hPXR. In contrast, DPP, which lacks PXR agonistic activity, failed to affect the agonistic activity of BPA, BPB, or HPP [Supplemental Material, Figure 3 (http://dx.doi.org/10.1289/ehp.1104426)].

Bottom Line: We found that BPA and several of its analogues are potent agonists for human PXR (hPXR) but do not affect mouse PXR activity.The present study advances our understanding of the mechanism by which BPA interacts with and activates human PXR.Activation of PXR by BPA may explain some of the adverse effects of BPA in humans.

View Article: PubMed Central - PubMed

Affiliation: Graduate Center for Nutritional Sciences, University of Kentucky, Lexington, Kentucky 40536, USA.

ABSTRACT

Background: Bisphenol A (BPA) is a base chemical used extensively in many consumer products. BPA and its analogues are present in environmental and human samples. Many endocrine-disrupting chemicals, including BPA, have been shown to activate the pregnane X receptor (PXR), a nuclear receptor that functions as a master regulator of xenobiotic metabolism. However, the detailed mechanism by which these chemicals activate PXR remains unknown.

Objective: We investigated the mechanism by which BPA interacts with and activates PXR and examined selected BPA analogues to determine whether they bind to and activate PXR.

Methods: Cell-based reporter assays, in silico ligand-PXR docking studies, and site-directed mutagenesis were combined to study the interaction between BPA and PXR. We also investigated the influence of BPA and its analogues on the regulation of PXR target genes in human LS180 cells.

Results: We found that BPA and several of its analogues are potent agonists for human PXR (hPXR) but do not affect mouse PXR activity. We identified key residues within hPXR's ligand-binding pocket that constitute points of interaction with BPA. We also deduced the structural requirements of BPA analogues that activate hPXR. BPA and its analogues can also induce PXR target gene expression in human LS180 cells.

Conclusions: The present study advances our understanding of the mechanism by which BPA interacts with and activates human PXR. Activation of PXR by BPA may explain some of the adverse effects of BPA in humans.

Show MeSH