DNA-Binding Ability of NF-κB is Affected Differently by ERα and ERβ and Its Activation Results in Inhibition of Estrogen Responsiveness

Estrogenic effects involve interactions between estrogen receptors (ERs), response elements, and nuclear proteins. It is hypothesized that interaction between ER and NF-κ B may affect the regulation of responsive genes. Electrophoretic mobility shift assay (EMSA) was performed to assess if the interaction of ERs and NF- κB affect their respective DNA-binding activities, and alkaline phosphatase assay was done to evaluate estrogenic activity. EMSA revealed that ERs inhibit DNA-binding of p50 and p65, whereas p50 did not impair ER α binding. Stimulation with estradiol inhibited DNA binding of NF-κB in ERα-transfected endometrial stromal cells (ESCs). Moreover, activation of NF-κB significantly decreased estrogen responsiveness of Ishikawa cells and ERα-transfected ESC. Our results suggest that ERs downregulate NF-κB-dependent gene activation by directly preventing DNA binding. However, NF-κB-mediated inhibition of ER-dependent gene activation may be carried out indirectly rather than through a direct inhibition of ER-DNA binding. These findings offer new insight into the specific role of ERα and could eventually help in developing therapeutics for endometriosis.