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 β-Subunit Promoter

Department of Biochemistry, The George S. Wise Faculty of Life Sciences, Tel Aviv University, Ramat Aviv 69978, Israel.
Endocrinology (Impact Factor: 4.5). 06/2004; 145(5):2228-44. DOI: 10.1210/en.2003-1418
Source: PubMed


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. Ca2+ influx, but not Ca2+ 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 Ca2+ ionophore ionomycin, stimulated FSHbeta-luciferase (LUC) activity. Furthermore, down-regulation of PKC, but not removal of Ca2+, 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 Ca2+, are involved in GnRH induction of the ovine FSHbeta gene.

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Available from: David Shahbazian, Jan 23, 2015
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    • "Pulsatile GnRH regulates the gonadotropin subunit genes in a differential manner, with faster frequencies (8 to 60 min pulse intervals) favoring mammalian LH β subunit gene expression and slower frequencies (≥ 120 min pulse intervals) favoring the expression of FSH β subunit [56]. The mechanism is through the activation of GnRH receptor and its signaling cascades including JNK and its substrate JUN [57-61]. We found that 3kPZS induced GnRH release within 15 min, and Jun and JNK gene expression after 2 h exposure, suggesting that 3kPZS can modulate GnRH release and its signaling cascades. "
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    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, 7α, 12α, 24-trihydroxy-5α-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 (χ2 = 5.042, dF = 1, p < 0.05). Exposure to 3kPZS increased plasma 15α-hydroxyprogesterone (15α-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.
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    • "This activation is supported by a pathway that involves dynamin, c-Src, and Ras and a pathway that involves calcium-signaling and possibly other signaling components [12] [13] [14]. Activation of MAPK family proteins such as ERK, c-Jun N-terminal kinase (JNK), p38 MAPK, and ERK5 has been reported to mediate GnRH-induced gonadotropin subunit expression [15] [16] [17] [18] [19]. The JNK cascade utilizes MKK4/7 to activate transcription factors such as c-Jun, ATF2, and Elk 1 [20]. "
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    ABSTRACT: The frequency of gonadotropin-releasing hormone (GnRH) pulse secreted from the hypothalamus differently regulates the expressions of gonadotropin subunit genes, luteinizing hormone β (LHβ) and follicle-stimulating hormone β (FSHβ), in the pituitary gonadotrophs. FSHβ is preferentially stimulated at slower GnRH pulse frequencies, whereas LHβ is preferentially stimulated at more rapid pulse frequencies. Several signaling pathways are activated, including mitogen-activated protein kinase (MAPK), protein kinase C, calcium influx, and calcium-calmodulin kinases, and these may be preferentially regulated under certain conditions. Previous studies demonstrated that MAPK pathways, especially the extracellular signal-regulated kinase (ERK), play an essential role for induction of gonadotropin subunit gene expression by GnRH, whereas, MAPK phosphatases (MKPs) inactivate MAPKs through dephosphorylation of threonine and/or tyrosine residues. MKPs are also induced by GnRH, and potential feedback regulation between MAPK signaling and MKPs within the GnRH signaling pathway is evident in gonadotrophs. In this paper, we reviewed and mainly focused on our observations of the pattern of ERK activation and the induction of MKP by different frequencies of GnRH stimulation.
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    • "Moreover, histamine-stimulated ERK1/2 signals were abolished in the absence of extracellular Ca 2+ , and were PKC-independent. Collectively, these data infer that Ca 2+ entry is the main driving force behind the peak phase of oxytocin and histamine ERK1/2 signalling in ULTR cells, which mirrors previous findings mediated by the gonadotropin-releasing hormone receptor in LbT-2 cells (Bonfil et al., 2004). "
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