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Steroidogenic factor-1 (SF-1) is a key regulator of endocrine development, and mediates expression of gonadotrophin-specific genes in the pituitary. Basal and hormone stimulated transcription of the human glycoprotein hormone alpha-subunit gene (alphaGSU) in gonadotrophs involves SF-1 and its cognate binding site, the gonadotroph-specific element (GSE). In this study, we demonstrate that SF-1 significantly enhances basal and forskolin-stimulated transcription of the human alphaGSU promoter in GH(3) cells. Mutation of the GSE abolished the SF-1-mediated transactivation of basal alphaGSU promoter activity, and significantly attenuated the forskolin effect by 50%. Mutation of the Ser203 residue in SF-1 to Ala blocked basal transactivation of alphaGSU promoter activity, and halved the forskolin effect. These data collectively reveal a direct role for SF-1 and the GSE in mediating basal and forskolin-stimulated transcription of the human alphaGSU promoter in GH(3) cells. The phosphorylation site at Ser203 appears to be required for these effects.
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Search for other papers by JM Burrin in
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Search for other papers by RC Fowkes in
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The putative hypophysiotropic factor pituitary adenylate cyclase-activating polypeptide (PACAP) stimulates glycoprotein hormone alpha-subunit (alpha GSU) gene transcription and secretion in the clonal gonadotroph alpha T3-1 cell line. The specific signalling pathways regulating these actions of PACAP have not been clearly defined. We have examined the possibility that mitogen activated protein kinases (MAPKs) may play a role in mediating the effects of PACAP on alpha T3-1 gonadotrophs. Treatment of alpha T3-1 cells with PACAP (100 nM) or epidermal growth factor (EGF, 10 nM) for 5 min significantly stimulated extracellular signal-regulated kinase activity (ERK, a component of the MAPK pathway) as determined by an immunocomplex assay. Pre-treatment of alpha T3-1 cells with the specific MAPK kinase (MEK) inhibitor, U0126, blocked PACAP and EGF-induced activation of ERK. Transcriptional stimulation of a human alpha GSU-luciferase reporter construct by PACAP was unaffected by U0126 treatment. However, pre-treatment with U0126 significantly inhibited PACAP stimulation of [(3)H]-thymidine incorporation in alpha T3-1 cells. Thus our results suggest that PACAP stimulates ERK activation in alpha T3-1 cells, and that the functional effect of this ERK activation is increased DNA synthesis and cell proliferation rather then transcriptional activation of the alpha GSU gene.
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Hyperthyroidism is associated with increased bone resorption but the mechanisms by which thyroid hormone (T3) affects bone cell metabolism remain unclear. Recently it has been suggested that T3 stimulates osteoclastic resorption indirectly through the release of soluble mediators from osteoblasts. The aim of the present study was to investigate whether the T3-induced increase in bone resorption could be due to the regulation of cytokine production by human osteoblasts (hOb). The effects of T3 (1, 10, 100 nM) and IL-1 beta (100 U/ml) as the positive control were examined on cytokine protein release and mRNA levels in cultured hOb cell lines (MG63, SaOs-2), primary hOb and human bone marrow stromal (hBMS) cells. T3 increased IL-6 and IL-8 mRNA levels as well as IL-6 and IL-8 protein release into the culture media from MG63 and hBMS cells in a time- and dose-dependent manner. The maximal effect on protein release in hBMS cells occurred at 24 h with a dose of T3 10 nM (IL-6 5.5 +/- 1.1-fold above controls; IL-8 3.7 +/- 0.5-fold above controls, P < 0.05). At the same time, mRNA levels in hBMS cells were increased 6.2 +/- 0.8-fold for IL-6 (P < 0.05) and 5.7 +/- 0.8-fold for IL-8 (P < 0.05). Similar results were obtained in MG63 cells but no response was seen in SaOs-2 or hOb cells despite measurable basal production. Nor was there detectable regulation of IL-1 beta, IL-3, IL-11, IL-4 or granulocyte macrophage-colony stimulating factor by T3 in any cell type. In conclusion, T3 increases IL-6 and IL-8 production by MG63 and hBMS cells, suggesting that IL-6 and IL-8 may be T3-regulated genes in osteoblasts.
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ABSTRACT
In five healthy normal male volunteers, pretreatment with the cholinergic muscarinic antagonist pirenzepine (30 mg i.v.) almost abolished the growth hormone (GH) response to a maximal dose (120 μg i.v.) of growth hormone-releasing hormone (GHRH) (GH response at 40 min 5.6 ± 1.3 mU/l with GHRH and pirenzepine vs 40.8 ± 5.3 mU/l with GHRH alone, P <0.02). Concomitant i.v. infusion of galanin (40 pmol/kg/min) with pirenzepine not only restored but significantly potentiated the GH response to GHRH (GH at 40 min 72.2 ± 10.5 mU/l, P <0.001 vs GHRH and pirenzepine, P <0.02 vs GHRH alone). Previous studies have proposed that cholinergic pathways control GH release via samatostatin and this study suggests that galanin may act by modulating hypothalamic somatostatinergic tone either directly or, possibly, by facilitating cholinergic neurotransmission.
