Physiological concentrations of progesterone stimulate the activity of the endocannabinoid-degrading enzyme fatty acid amide hydrolase (FAAH) in human T lymphocytes, up to a ∼270% over the untreated controls. Stimulation of FAAH occurred through up-regulation of gene expression at transcriptional and translational level and was specific. Indeed, neither the activity of the anandamide-synthesizing N-acyltransferase and phospholipase D, nor the activity of the anandamide transporter, nor the binding to cannabinoid receptors were affected by progesterone under the same experimental conditions. The activation of FAAH by progesterone was paralleled by a decrease (down to 60%) of the cellular levels of anandamide and involved increased nuclear levels of the transcription factor Ikaros. Analysis of the FAAH promoter showed an Ikaros binding site, and mutation of this site prevented FAAH activation by progesterone in transient expression assays. Electrophoretic mobility shift and supershift assays further corroborated the promoter activity data. Furthermore, the effect of progesterone on FAAH promoter was additive to that of physiological amounts of leptin, which binds to a cAMP response element-like site in the promoter region. Taken together, these results suggest that progesterone and leptin, by up-regulating the FAAH promoter at different sites, enhance FAAH expression, thus tuning the immunomodulatory effects of anandamide. These findings might also have critical implications for human fertility.
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