Extracellular signal-regulated kinase, Jun N-terminal kinase, p38, and c-Src are involved in gonadotropin-releasing hormone-stimulated activity of the glycoprotein hormone follicle-stimulating hormone beta-subunit promoter.
ABSTRACT The role of ERK, Jun N-terminal kinase (JNK), p38, and c-Src in GnRH-stimulated FSHbeta-subunit promoter activity was examined in the LbetaT-2 gonadotroph cell line. Incubation of the cells with a GnRH agonist resulted in activation of ERK, JNK, p38, and c-Src. The peak of ERK activation was observed at 5 min, whereas that of JNK, p38, and c-Src at 30 min, declining thereafter. ERK activation by GnRH is dependent on protein kinase C (PKC), as evident by activation, inhibition, and depletion of 12-O-tetradecanoylphorbol-13-acetate-sensitive PKC subspecies. Ca(2+) influx, but not Ca(2+) mobilization, is required for ERK activation. GnRH signaling to ERK is partially mediated by dynamin and a protein tyrosine kinase, apparently c-Src. ERK activation by GnRH in LbetaT-2 cells does not involve transactivation of epidermal growth factor receptor or mediation via Gbetagamma or beta-arrestin. Once activated by GnRH, ERK translocates to the nucleus. We examined the role of ERK, JNK, p38, and c-Src in GnRH-stimulated ovine FSHbeta promoter, linked to a luciferase reporter gene (-4741oFSHbeta-LUC). The PKC activator 12-O-tetradecanoylphorbol-13-acetate, but not the Ca(2+) ionophore ionomycin, stimulated FSHbeta-luciferase (LUC) activity. Furthermore, down-regulation of PKC, but not removal of Ca(2+), inhibited the GnRH response. Cotransfection of FSHbeta-LUC and the constitutively active forms of Raf-1 and MEK stimulated FSHbeta-LUC activity, whereas the dominant negatives of Ras, Raf-1, and MEK and the selective MEK inhibitor PD98059, abolished GnRH-induced FSHbeta-LUC activity. The dominant negatives of CDC42 and JNK reduced the GnRH response by 36 and 49%, respectively. Incubation of the cells with the p38 or the c-Src inhibitors SB203580 and PP1 also reduced the GnRH response. Surprisingly, two proximal activator protein-1 sites contribute very little to the GnRH response. Thus, PKC, ERK, JNK, p38, and c-Src, but not Ca(2+), are involved in GnRH induction of the ovine FSHbeta gene.
- SourceAvailable from: Yu-Wen Chung-Davidson[show abstract] [hide abstract]
ABSTRACT: BACKGROUND: Vertebrate pheromones are known to prime the endocrine system, especially the hypothalamic-pituitary-gonadal (HPG) axis. However, no known pheromone molecule has been shown to modulate directly the synthesis or release of gonadotropin releasing hormone (GnRH), the main regulator of the HPG axis. We selected sea lamprey (Petromyzon marinus) as a model system to determine whether a single pheromone component alters the output of GnRH.Sea lamprey male sex pheromones contain a main component, 7alpha, 12alpha, 24-trihydroxy-5alpha-cholan-3-one 24-sulfate (3 keto-petromyzonol sulfate or 3kPZS), which has been shown to modulate behaviors of mature females. Through a series of experiments, we tested the hypothesis that 3kPZS modulates both synthesis and release of GnRH, and subsequently, HPG output in immature sea lamprey. RESULTS: The results showed that natural male pheromone mixtures induced differential steroid responses but facilitated sexual maturation in both sexes of immature animals (chi2 = 5.042, dF = 1, p < 0.05). Exposure to 3kPZS increased plasma 15alpha-hydroxyprogesterone (15alpha-P) concentrations (one-way ANOVA, p < 0.05) and brain gene expressions (genes examined: three lamprey (l) GnRH-I transcripts, lGnRH-III, Jun and Jun N-terminal kinase (JNK); one-way ANOVA, p < 0.05), but did not alter the number of GnRH neurons in the hypothalamus in immature animals. In addition, 3kPZS treatments increased lGnRH peptide concentrations in the forebrain and modulated their levels in plasma. Overall, 3kPZS modulation of HPG axis is more pronounced in immature males than in females. CONCLUSIONS: We conclude that a single male pheromone component primes the HPG axis in immature sea lamprey in a sexually dimorphic manner.BMC Neuroscience 01/2013; 14(1):11. · 3.00 Impact Factor
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ABSTRACT: Gonadotropin-releasing hormone (GnRH) is the primary regulator of mammalian reproductive function in both males and females. It acts via G-protein coupled receptors on gonadotropes to stimulate synthesis and secretion of the gonadotropin hormones luteinizing hormone and follicle-stimulating hormone. These receptors couple primarily via G-proteins of the Gq/ll family, driving activation of phospholipases C and mediating GnRH effects on gonadotropin synthesis and secretion. There is also good evidence that GnRH causes activation of other heterotrimeric G-proteins (Gs and Gi) with consequent effects on cyclic AMP production, as well as for effects on the soluble and particulate guanylyl cyclases that generate cGMP. Here we provide an overview of these pathways. We emphasize mechanisms underpinning pulsatile hormone signaling and the possible interplay of GnRH and autocrine or paracrine regulatory mechanisms in control of cyclic nucleotide signaling.Frontiers in Endocrinology 01/2013; 4:180.
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ABSTRACT: The GnRH receptor (GnRHR) mediates the pituitary functions of GnRH, as well as its anti-proliferative effects in sex hormone-dependent cancer cells. Here we compare the signaling of GnRHR in pituitary gonadotrope cell lines vs. prostate cancer cell lines. We first noticed that the expression level of PKCα, PKCβII and PKCε is much higher in αT3-1 and LβT2 gonadotrope cell lines vs. LNCaP and DU-145 cell lines, while the opposite is seen for PKCδ. Activation of PKCα, PKCβII and PKCε by GnRH is relatively transient in αT3-1 and LβT2 gonadotrope cell lines and more prolonged in LNCaP and DU-145 cell lines. On the otherhand, the activation and redistribution of the above PKCs by PMA was similar for both gonadotrope cell lines and prostate cancer cell lines. Activation of ERK1/2 by GnRH and PMA was robust in the gonadotrope cell lines, with a smaller effect observed in the prostate cancer cell lines. The Ca(2+) ionophore A23187 stimulated ERK1/2 in gonadotrope cell lines but not in prostate cancer cell lines. GnRH, PMA and A23187 stimulated JNK activity in gonadotrope cell lines, with a more sustained effect in prostate cancer cell lines. Sustained activation of p38 was observed for PMA and A23187 in Du-145 cells, while p38 activation by GnRH, PMA and A23187 in LβT2 cells was transient. Thus, differential expression and redistribution of PKCs by GnRH and the transient vs. the more sustained nature of the activation of the PKC-MAPK cascade by GnRH in gonadotrope cell lines vs. prostate cancer cell lines respectively, may provide the mechanistic basis for the cell context-dependent differential biological responses observed in GnRH interaction with pituitary gonadotropes vs. prostate cancer cells.Molecular and Cellular Endocrinology 02/2013; · 4.04 Impact Factor