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

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 [H-3]4-hydroxytamoxifen ([H-3]4-OHT). We also demonstrated that BPA inhibits the deactivation activity v 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 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-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.