The ERβ ligand 5α-androstane, 3β,17β-diol (3β-diol) regulates hypothalamic oxytocin (Oxt) gene expression

The endocrine component of the stress response is regulated by glucocorticoids and sex steroids. Testosterone down-regulates hypothalamic-pituitary-adrenal (HPA) axis activity; however, the mechanisms by which it does so are poorly understood. A candidate testosterone target is the oxytocin gene (Oxt), given that it too inhibits HPA activity. Within the paraventricular nucleus of the hypothalamus, oxytocinergic neurons involved in regulating the stress response do not express androgen receptors but do express estrogen receptor-β (ERβ), which binds the dihydrotestosterone metabolite 3β,17β-diol (3β-diol). Testosterone regulation of the HPA axis thus appears to involve the conversion to the ERβ-selective ligand 5α-androstane, 3β-diol. To study mechanisms by which 3β-diol could regulate Oxt expression, we used a hypothalamic neuronal cell line derived from embryonic mice that expresses Oxt constitutively and compared 3β-diol with estradiol (E2) effects. E2 and 3β-diol elicited a phasic response in Oxt mRNA levels. In the presence of either ligand, Oxt mRNA levels were increased for at least 60 min and returned to baseline by 2 h. ERβ occupancy preceded an increase in Oxt mRNA levels in the presence of 3β-diol but not E2. In tandem with ERβ occupancy, 3β-diol increased occupancy of the Oxt promoter by cAMP response element-binding protein and steroid receptor coactivator-1 at 30 min. At the same time, 3β-diol led to the increased acetylation of histone H4 but not H3. Taken together, the data suggest that in the presence of 3β-diol, ERβ associates with cAMP response element-binding protein and steroid receptor coactivator-1 to form a functional complex that drives Oxt gene expression.     

A decline in the levels of progesterone receptor coactivators in the pregnant uterus at term may antagonize progesterone receptor function and contribute to the initiation of parturition

The molecular events that lead to the onset of labor in humans and in other mammalian species remain unclear. We propose that a decline in coactivators containing histone acetylase activity in myometrium may contribute to the onset of labor by impairing the function of the progesterone-progesterone receptor (PR) complex. As assessed by semiquantitative and real-time RT-PCR, immunohistochemistry, and immunoblotting, expression of the PR coactivators cAMP-response element-binding protein (CREB)-binding protein and steroid receptor coactivators 2 and 3 was decreased in fundal uterine tissue of women in labor. Using the mouse as an animal model, we also found decreased coactivator levels in uterine tissues at term. In both human and mouse, the levels of acetylated histone H3 were also decreased in uterine tissues at term. Administration of trichostatin A, a specific and potent histone deacetylase inhibitor, to pregnant mice late in gestation increased histone acetylation and delayed the initiation of parturition by 24-48 h, suggesting the functional importance of the decline in histone acetylation in the initiation of labor. These findings suggest that the decline in PR coactivator expression and in histone acetylation in the uterus near term may impair PR function by causing a functional progesterone withdrawal. The resulting decrease in expression of PR-responsive genes should increase sensitivity of the uterus to contractile stimuli.     

Estrogen receptor-alpha (ERalpha), but not ERbeta,modulates estrogen stimulation of the ERalpha-truncated variant,TERP-1

Estrogens regulate pituitary gene expression through two nuclear receptors (ERs), ERalpha and ERbeta. Rodent pituitary also expresses high levels of the pituitary-specific ERalpha isoform, truncated ER product-1 (TERP-1), which modulates the response of both ER forms to 17beta-estradiol (E2). Under physiological conditions, E2 stimulates TERP-1 expression from an ERalpha intronic promoter containing several potential binding sites for ERs. To evaluate the role of intact ER proteins on TERP-1 expression, we measured basal expression and steroid stimulation of TERP-1 in wild-type (WT) mice and mice in which either the ERalpha (ERalphaKO) or the ERbeta (ERbetaKO) gene was disrupted. TERP-1 mRNA expression was assessed by semiquantitative RT-PCR, and protein expression was evaluated by immunoblots. Both TERP-1 mRNA and protein were expressed in pituitaries from castrate WT, ERalphaKO, and ERbetaKO male and female mice. E2 stimulated TERP-1 mRNA expression in WT and ERbetaKO mice of both sexes, but had no effect on TERP-1 mRNA in either male or female ERalphaKO mice. Testosterone treatment also stimulated TERP-1 in WT, ERalphaKO, and ERbetaKO male mice. We conclude that ERalpha is critical for E2 stimulation, but not basal expression, of the TERP promoter, and that testosterone may act through the androgen receptor to stimulate the TERP-1 promoter in males.