Direct Evidence Revealing Structural Elements Essential for the High Binding Ability of Bisphenol A to Human Estrogen-Related Receptor-γ

BACKGROUND: Various lines of evidence have shown that bisphenol A [BPA; HO-C(6)H(4)-C(CH(3))(2)-C(6)H(4)-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-γ (ERR-γ ) in a binding assay using [(3)H]4-hydroxytamoxifen ([(3)H]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-γ as a strong binder, and also to clarify the structural requirements of BPA for its binding to ERR-γ. METHODS: We examined [(3)H]BPA in the saturation binding assay using the ligand binding domain of ERR-γ and analyzed the result using Scatchard plot analysis. A number of BPA derivatives were tested in the competitive binding assay using [(3)H]BPA as a tracer and in the luciferase reporter gene assay. RESULTS: [(3)H]BPA showed a K(D) of 5.50 nM at a B(max) of 14.4 nmol/mg. When we examined BPA derivatives to evaluate the structural essentials required for the binding of BPA to ERR-γ , 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-γ 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-γ.