Crosstalk between estradiol and NFκB signaling pathways on placental leptin expression.

Pregnancy success requires a proper fetal maternal interaction at the establishment of implantation. Leptin has been described as a multitasking cytokine in pregnancy, particularly in the placenta, where it acts as an autocrine hormone. The expression of leptin in normal trophoblastic cells is regulated by different endogenous signals. We have previously reported that 17ß-estradiol upregulates placental leptin expression through genomic and non-genomic mechanisms. To improve the knowledge of estrogen receptor mechanisms in regulating leptin gene expression, we examined transcription nuclear factor kappa B (NFκB) effect on estradiol leptin induction in human BeWo cell line and human term placental explants. We demonstrated that estradiol induction effect on leptin expression is blocked by the inhibition of NFκB signaling. We also found that the overexpression of p65 subunit, the active form of NFκB, induces leptin expression. Moreover, downregulation of estrogen receptor alpha (ERα), through a specific siRNA, abolished NFκB effect on leptin expression. We also demonstrated that ERα enhanced NFκB signaling pathway activation in trophoblastic cells. Estradiol treatment significantly increased p65 expression and phosphorylation of the inhibitory protein κB alpha (IκBα). A reporter plasmid containing NFκB elements was also induced in response to estradiol stimulation. Localization experiments revealed that estradiol treatment induced nuclear localization of overexpressed p65. Moreover, the overexpression of ERα produced a complete displacement of p65 protein to the nucleus. Finally, immunoprecipitation experiments showed the presence of a complex containing ERα and NFκB. All these evidences suggest a cooperative behavior between ERα and NFκB transcription factors to induce leptin transcription.

NF-κB transcriptional activity is modulated by FK506-binding proteins FKBP51 and FKBP52: a role for peptidyl-prolyl isomerase activity.

Hsp90 binding immunophilins FKBP51 and FKBP52 modulate steroid receptor trafficking and hormone-dependent biological responses. With the purpose to expand this model to other nuclear factors that are also subject to nuclear-cytoplasmic shuttling, we analyzed whether these immunophilins modulate NF-κB signaling. It is demonstrated that FKBP51 impairs both the nuclear translocation rate of NF-κB and its transcriptional activity. The inhibitory action of FKBP51 requires neither the peptidylprolyl-isomerase activity of the immunophilin nor its association with Hsp90. The TPR domain of FKBP51 is essential. On the other hand, FKBP52 favors the nuclear retention time of RelA, its association to a DNA consensus binding sequence, and NF-κB transcriptional activity, the latter effect being strongly dependent on the peptidylprolyl-isomerase activity and also on the TPR domain of FKBP52, but its interaction with Hsp90 is not required. In unstimulated cells, FKBP51 forms endogenous complexes with cytoplasmic RelA. Upon cell stimulation with phorbol ester, the NF-κB soluble complex exchanges FKBP51 for FKBP52, and the NF-κB biological effect is triggered. Importantly, FKBP52 is functionally recruited to the promoter region of NF-κB target genes, whereas FKBP51 is released. Competition assays demonstrated that both immunophilins antagonize one another, and binding assays with purified proteins suggest that the association of RelA and immunophilins could be direct. These observations suggest that the biological action of NF-κB in different cell types could be positively regulated by a high FKBP52/FKBP51 expression ratio by favoring NF-κB nuclear retention, recruitment to the promoter regions of target genes, and transcriptional activity.