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      Stimulatory Effect of Interleukin-1β on Growth Hormone Gene Expression and Growth Hormone Release from Rat GH3 Cells

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          Our previous studies demonstrated that interferon gamma increases the human (h) growth hormone (GH) gene promoter activity in rat pituitary GH3 cells, and its regulatory mechanism may be different from the classical GH-releasing hormone-induced regulatory mechanism. Interleukin-1β (IL-1β) is thought to induce the release of GH by pituitary cells, but whether or not and by which mechanisms IL-1β regulates GH synthesis remains unclear. The purpose of our study was thus to investigate the effect of IL-1β on the hGH gene expression in GH3 rat pituitary tumor cells using stable transfection of the hGH promoter fused to a luciferase reporter gene. Our results showed that IL-1β (10–10<sup>4</sup> U/ml) increased GH secretion and synthesis and that 10<sup>2</sup> to 10<sup>4</sup> U/ml IL-1β promoted the luciferase expression in stable GH3 cells, with a maximal action of 1.61 times over that of controls. Among inhibitors of intracellular signaling transduction pathways, mitogen-activated protein kinase kinase (MAPKK/MEK) inhibitor PD98059 (40 µ M) and p38 MAPK inhibitor SB203580 (5 µ M)blocked completely the stimulatory effect of IL-1β, and the phosphoinositide 3-kinase inhibitor LY294002 (10 µ M) blocked partially the induction of IL-1β. Western blot analysis demonstrated that IL-1β increased the activation of phosphorylated MEK and p38 MAPK in GH3 cells. Neither overexpression of Pit-1 nor inhibiting Pit-1 expression affected IL-1β induction of hGH promoter activity. To identify the DNA sequence that mediated the effect of IL-1β, six deletion constructs of hGH promoter were created. The stimulatory effect of IL-1β was abolished following deletion of the –196- to –132-bp fragment. In conclusion, our data show that IL-1β promotes GH secretion and synthesis by rat pituitary GH3 cells. The stimulatory effect of IL-1β on the hGH gene promoter appears to require the activation of MEK, p38 MAPK, and phosphoinositide 3-kinase and a fragment of promoter sequence that spans the –196- to –132-bp fragment of the gene, but is unrelated to the Pit-1 protein.

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          Most cited references 30

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          Functional interactions between Stat5 and the glucocorticoid receptor.

          Signal transduction pathways enable extracellular signals to activate latent transcription factors in the cytoplasm of cells. Dimerization, nuclear localization and binding to specific DNA sequences result in the induction of gene transcription by these proteins. These events are necessary for the functioning of the JAK/STAT pathway and of the glucocorticoid-receptor pathway. In the former, the protein Stat5, which is a member of a family of signal transducers and activators of transcription, is activated by cytokines, hormones and growth factors. These polypeptide ligands bind at the outside of the cell to specific transmembrane receptors and activate intracellular Janus protein tyrosine kinases (JAKs) to tyrosine-phosphorylate STAT proteins; interaction with the SH2 domain of the dimerization partner then confers the ability to bind to DNA at the STAT-response element and induce transcription. In the glucocorticoid-receptor pathway, the receptor interacts with its steroid hormone ligand in the cytoplasm, undergoes an allosteric change that enables the hormone receptor complex to bind to specific DNA-response elements (glucocorticoid response elements, or GRE) and modulate transcription. Although these pathways appear to be unrelated, we show here that the glucocorticoid receptor can act as a transcriptional co-activator for Stat5 and enhance Stat5-dependent transcription. Stat5 forms a complex with the glucocorticoid receptor which binds to DNA independently of the GRE. This complex formation between Stat5 and the glucocorticoid receptor diminishes the glucocorticoid response of a GRE-containing promoter.
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            Interleukin-1 beta and tumor necrosis factor-alpha induce MUC5AC overexpression through a mechanism involving ERK/p38 mitogen-activated protein kinases-MSK1-CREB activation in human airway epithelial cells.

            Mucin hypersecretion is commonly observed in many inflammatory diseases of the respiratory tract. MUC5AC is generally recognized to be a major airway mucin because MUC5AC is highly expressed in the goblet cells of human airway epithelium. Moreover, it is regulated by various inflammatory cytokines. However, the mechanisms by which the interleukin (IL)-1beta and tumor necrosis factor (TNF)-alpha induce MUC5AC gene expression in normal nasal epithelial cells, and the signal molecules involved, especially in the downstream signaling of mitogen-activated protein (MAP) kinases, remain unclear. Here we show that pharmacologic or genetic inhibition of either ERK or p38 MAP kinase pathway abolished IL-1beta- and TNF-alpha-induced MUC5AC gene expression in normal human nasal epithelial cells. Our results also indicate that the activation of mitogen- and stress-activated protein kinase 1 (MSK1) and cAMP-response element-binding protein and cAMP-response element signaling cascades via ERK and p38 MAP kinases are crucial aspects of the intracellular mechanisms that mediate MUC5AC gene expression. Taken together, these studies give additional insights into the molecular mechanism of IL-1beta- and TNF-alpha-induced MUC5AC gene expression and enhance our understanding on mucin hypersecretion during inflammation.
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              Interleukin-8 regulation of the Ras/Raf/mitogen-activated protein kinase pathway in human neutrophils.

              Interleukin-8 (IL-8), the prototypic member of the CXC subfamily of chemokines, induces in neutrophils chemotaxis, the respiratory burst, granule release, and increased cell adhesion. The IL-8 receptor is a seven-transmembrane spanning receptor coupled to specific heterotrimeric G proteins including Gi and G16. IL-8 stimulation of its receptor on neutrophils activates Ras GTP loading and the mitogen-activated protein kinase (MAPK) pathway including Raf-1 and B-Raf. The properties of IL-8 stimulation of the MAPK pathway differ from those observed for chemoattractants such as C5a. Even though Ras GTP loading is similar for IL-8 and C5a, the maximal activation of Raf-1 and B-Raf is approximately 2-fold and 3-7-fold, respectively, less for IL-8 than that observed for C5a. Raf-1 activation is rapid but transient, returning to near basal levels by 10 min. B-Raf activation is slower in onset and does not return to basal levels for nearly 30 min. IL-8 activation of MAPK follows a time course suggesting an involvement of both Raf-1 and B-Raf. Surprisingly, wortmannin, at low concentrations, inhibits Raf-1, B-Raf, and MAPK activation in response to IL-8 and C5a demonstrating a role for phosphatidylinositol 3-kinase in the activation of Raf kinases in G protein-coupled receptor systems in human neutrophils. Furthermore, wortmannin inhibits IL-8 stimulated granule release and neutrophil adherence. These findings demonstrate the control of Raf kinases, the MAPK pathway and specific neutrophil functions by phosphatidylinositol 3-kinase enzymes.

                Author and article information

                S. Karger AG
                September 2005
                27 September 2005
                : 81
                : 4
                : 217-228
                Department of Endocrinology, Beijing Union Medical College Hospital, Chinese Academy of Medical Sciences and Beijing Union Medical College, Beijing, China
                87160 Neuroendocrinology 2005;81:217–228
                © 2005 S. Karger AG, Basel

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                Page count
                Figures: 8, Tables: 1, References: 50, Pages: 12
                Original Paper


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