High Estradiol Concentrations Induce Heat Shock Protein 70 Expression and Suppress Nuclear Factor Kappa B Activation...

The high serum estradiol (E₂) concentrations induced during in vitro fertilization are detrimental to endometrial receptivity and may result in lower embryo implantation rates. We have previously found that high E₂ concentrations inhibit the activation of nuclear factor kappa B (NF-kappa B), which led to endometrial epithelial cells (EECs) apoptosis. The objective of this study is to investigate the signaling pathways through which high E₂ results in NF-kappa B downregulation in EECs. Isolated human EECs were cultured in different concentrations of E₂ (10^-10, 10^-9, 10^-8, 10^-7 M). The expression of heat shock protein 70 (Hsp70) and heat shock factor 1 (HSF-1) were upregulated under supraphysiological E₂ (10^-7 M) concentration, whereas phosphorylated inhibitory kappa B-alpha (pI kappa B-alpha) and NF-kappa B p65 subunits were downregulated. Immunohistochemistry of C57BL/6 mouse EECs, that were exposed in vivo to high serum E₂ from the administration of 20 IUs of equine chorionic gonadotropin, also demonstrated the same increase in HSF-1 and Hsp70 expression, and decrease in NF-kappa B. Immunoprecipitation of the induced Hsp70 proteins was achieved with the addition of inhibitory kappa B kinase gamma (IKK-gamma) antibodies, and elimination of this reaction occurred after addition of hsp70 siRNA. In conclusion, high E₂ concentrations enhance HSF-1 and Hsp70 expression in EECs. The induced Hsp70 forms a complex with IKK-gamma and inhibits pI kappa B-alpha, which consequently suppresses NF-kappa B activation.