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Direct evidence revealing structural elements essential for the high binding ability of bisphenol A to human estrogen-related receptor-gamma.

Okada H, Tokunaga T, Liu X, Takayanagi S, Matsushima A, Shimohigashi Y - Environ. Health Perspect. (2008)

Bottom Line: When we examined BPA derivatives to evaluate the structural essentials required for the binding of BPA to ERR-gamma , we found that only one of the two phenol-hydroxyl groups was essential for the full binding.The maximal activity was attained when one of the methyl groups was removed.These results indicate that the phenol derivatives are potent candidates for the endocrine disruptor that binds to ERR-gamma.

View Article: PubMed Central - PubMed

Affiliation: Laboratory of Structure-Function Biochemistry, Department of Chemistry, The Research-Education Centre of Risk Science, Faculty and Graduate School of Sciences, Kyushu University, Fukuoka, Japan.

ABSTRACT

Background: Various lines of evidence have shown that bisphenol A [BPA; HO-C6H4-C(CH3)2-C6H4-OH] acts as an endocrine disruptor when present in very low doses. We have recently demonstrated that BPA binds strongly to human estrogen-related receptor-gamma (ERR-gamma ) in a binding assay using [3H]4-hydroxytamoxifen ([3H]4-OHT). We also demonstrated that BPA inhibits the deactivation activity of 4-OHT.

Objectives: In the present study, we intended to obtain direct evidence that BPA interacts with ERR-gamma as a strong binder, and also to clarify the structural requirements of BPA for its binding to ERR-gamma.

Methods: We examined [3H]BPA in the saturation binding assay using the ligand binding domain of ERR-gamma and analyzed the result using Scatchard plot analysis. A number of BPA derivatives were tested in the competitive binding assay using [3H]BPA as a tracer and in the luciferase reporter gene assay.

Results: [3H]BPA showed a KD of 5.50 nM at a Bmax of 14.4 nmol/mg. When we examined BPA derivatives to evaluate the structural essentials required for the binding of BPA to ERR-gamma , we found that only one of the two phenol-hydroxyl groups was essential for the full binding. The maximal activity was attained when one of the methyl groups was removed. All of the potent BPA derivatives retained a high constitutive basal activity of ERR-gamma in the luciferase reporter gene assay and exhibited a distinct inhibitory activity against 4-OHT.

Conclusion: These results indicate that the phenol derivatives are potent candidates for the endocrine disruptor that binds to ERR-gamma.

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Related in: MedlinePlus

Chemical structure of BPA and its derivatives lacking the phenol group and their dose–response curves in the radioligand receptor binding assay for ERR-γ . (A) Chemical structure of BPA and its derivatives with the alkyl group at the position of phenol group: 4-tert-butylphenol (a methyl group); 4-tert-amylphenol (an ethyl group); and 4-tert-octylphenol (a tert-butyl methyl group). (B) Binding activities of BPA, 4-tert-butylphenol, 4-tert-amylphenol, and 4-tert-octylphenol examined by the competitive binding assay using [3H]BPA and GST-ERR-γ –LBD; representative curves indicate the IC50 value closest to the mean IC50 from at least five independent assays for each compound.
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f4-ehp0116-000032: Chemical structure of BPA and its derivatives lacking the phenol group and their dose–response curves in the radioligand receptor binding assay for ERR-γ . (A) Chemical structure of BPA and its derivatives with the alkyl group at the position of phenol group: 4-tert-butylphenol (a methyl group); 4-tert-amylphenol (an ethyl group); and 4-tert-octylphenol (a tert-butyl methyl group). (B) Binding activities of BPA, 4-tert-butylphenol, 4-tert-amylphenol, and 4-tert-octylphenol examined by the competitive binding assay using [3H]BPA and GST-ERR-γ –LBD; representative curves indicate the IC50 value closest to the mean IC50 from at least five independent assays for each compound.

Mentions: As described above, 4-α-cumylphenol is as active as BPA. The importance of the benzene B-ring can be examined by replacing the B-ring with the alkyl groups. When the benzene B-ring of 4-α-cumylphenol was substituted with either methyl or ethyl, the resulting 4-tert-butylphenol [HO-C6H4-C(CH3)2-CH3] and 4-tert-amylphenol [HO-C6H4-C(CH3)2-CH2CH3] (Figure 4A) were considerably potent (Figure 4B), with values of 26.1 nM and 33.2 nM, respectively (Table 2). This reveals that alkyl groups can be substituted for the aromatic benzene ring without affecting the basal binding capability.


Direct evidence revealing structural elements essential for the high binding ability of bisphenol A to human estrogen-related receptor-gamma.

Okada H, Tokunaga T, Liu X, Takayanagi S, Matsushima A, Shimohigashi Y - Environ. Health Perspect. (2008)

Chemical structure of BPA and its derivatives lacking the phenol group and their dose–response curves in the radioligand receptor binding assay for ERR-γ . (A) Chemical structure of BPA and its derivatives with the alkyl group at the position of phenol group: 4-tert-butylphenol (a methyl group); 4-tert-amylphenol (an ethyl group); and 4-tert-octylphenol (a tert-butyl methyl group). (B) Binding activities of BPA, 4-tert-butylphenol, 4-tert-amylphenol, and 4-tert-octylphenol examined by the competitive binding assay using [3H]BPA and GST-ERR-γ –LBD; representative curves indicate the IC50 value closest to the mean IC50 from at least five independent assays for each compound.
© Copyright Policy - public-domain
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC2199305&req=5

f4-ehp0116-000032: Chemical structure of BPA and its derivatives lacking the phenol group and their dose–response curves in the radioligand receptor binding assay for ERR-γ . (A) Chemical structure of BPA and its derivatives with the alkyl group at the position of phenol group: 4-tert-butylphenol (a methyl group); 4-tert-amylphenol (an ethyl group); and 4-tert-octylphenol (a tert-butyl methyl group). (B) Binding activities of BPA, 4-tert-butylphenol, 4-tert-amylphenol, and 4-tert-octylphenol examined by the competitive binding assay using [3H]BPA and GST-ERR-γ –LBD; representative curves indicate the IC50 value closest to the mean IC50 from at least five independent assays for each compound.
Mentions: As described above, 4-α-cumylphenol is as active as BPA. The importance of the benzene B-ring can be examined by replacing the B-ring with the alkyl groups. When the benzene B-ring of 4-α-cumylphenol was substituted with either methyl or ethyl, the resulting 4-tert-butylphenol [HO-C6H4-C(CH3)2-CH3] and 4-tert-amylphenol [HO-C6H4-C(CH3)2-CH2CH3] (Figure 4A) were considerably potent (Figure 4B), with values of 26.1 nM and 33.2 nM, respectively (Table 2). This reveals that alkyl groups can be substituted for the aromatic benzene ring without affecting the basal binding capability.

Bottom Line: When we examined BPA derivatives to evaluate the structural essentials required for the binding of BPA to ERR-gamma , we found that only one of the two phenol-hydroxyl groups was essential for the full binding.The maximal activity was attained when one of the methyl groups was removed.These results indicate that the phenol derivatives are potent candidates for the endocrine disruptor that binds to ERR-gamma.

View Article: PubMed Central - PubMed

Affiliation: Laboratory of Structure-Function Biochemistry, Department of Chemistry, The Research-Education Centre of Risk Science, Faculty and Graduate School of Sciences, Kyushu University, Fukuoka, Japan.

ABSTRACT

Background: Various lines of evidence have shown that bisphenol A [BPA; HO-C6H4-C(CH3)2-C6H4-OH] acts as an endocrine disruptor when present in very low doses. We have recently demonstrated that BPA binds strongly to human estrogen-related receptor-gamma (ERR-gamma ) in a binding assay using [3H]4-hydroxytamoxifen ([3H]4-OHT). We also demonstrated that BPA inhibits the deactivation activity of 4-OHT.

Objectives: In the present study, we intended to obtain direct evidence that BPA interacts with ERR-gamma as a strong binder, and also to clarify the structural requirements of BPA for its binding to ERR-gamma.

Methods: We examined [3H]BPA in the saturation binding assay using the ligand binding domain of ERR-gamma and analyzed the result using Scatchard plot analysis. A number of BPA derivatives were tested in the competitive binding assay using [3H]BPA as a tracer and in the luciferase reporter gene assay.

Results: [3H]BPA showed a KD of 5.50 nM at a Bmax of 14.4 nmol/mg. When we examined BPA derivatives to evaluate the structural essentials required for the binding of BPA to ERR-gamma , we found that only one of the two phenol-hydroxyl groups was essential for the full binding. The maximal activity was attained when one of the methyl groups was removed. All of the potent BPA derivatives retained a high constitutive basal activity of ERR-gamma in the luciferase reporter gene assay and exhibited a distinct inhibitory activity against 4-OHT.

Conclusion: These results indicate that the phenol derivatives are potent candidates for the endocrine disruptor that binds to ERR-gamma.

Show MeSH
Related in: MedlinePlus