Direct Evidence Revealing Structural Elements Essential for the High Binding Ability of Bisphenol A to Human Estrogen Related Receptor g
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 g (ERR g 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 g as a strong binder, and also to clarify the structural requirements of BPA for its binding to ERR g. Methods We examined [3H]BPA in the saturation binding assay using the ligand binding domain of ERR g 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 g 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 g 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 g.
Environmental health perspectives