Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UNIPROT:P01275 (glucagon)
 26,492 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Transcription initiation of the gene encoding phosphoenolpyruvate carboxykinase (PEPCK) is stimulated by glucocorticoids and glucagon, via cAMP, and dominantly inhibited by insulin in rat liver and H4IIE cells. Lysolecithin-permeabilized H4IIE cells recover completely and continue to multiply, yet are transiently penetrable by macromolecules. These cells, after various hormonal treatments, were utilized for in situ DNase I protection studies of the PEPCK promoter. Nearly all of the sites of protein interaction observed in vitro are protected in vivo as well as several additional sites. The DNase I protection pattern is the same in cells without or with any of the hormone treatments, suggesting that hormonal modulation of transcription does not involve addition or removal of factors from the hormone response elements of the promoter. We focused on the organization and stability of the transcription initiation complex as well as the dynamic nature of distal promoter factors in their interaction with DNA. The transcription initiation complex was detected, and it appears to be co-existent with a short region of naked single-stranded DNA over the TATA box on the template strand, as determined by potassium permanganate reactivity. This complex is quite stable, even under conditions of much reduced RNA synthesis, which suggests that the complex is not broken down and reformed with each round of initiation by RNA polymerase II. Other factors bind to the PEPCK promoter with half-lives ranging from a few minutes to more than 40 min. The cAMP response element apparently involves transcriptional modulation achieved through modification of a bound factor (presumably cAMP response element-binding protein), whereas the glucocorticoid/insulin-responsive region of the promoter functions through factors which are involved in a rapid exchange, suggesting quite different modes of transcriptional regulation.
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PMID:Dynamic aspects of DNA/protein interactions in the transcriptional initiation complex and the hormone-responsive domains of the phosphoenolpyruvate carboxykinase promoter in vivo. 822 59

To maintain blood glucose levels within narrow limits, the synthesis and secretion of pancreatic islet hormones is controlled by a variety of extracellular signals. Depolarization-induced calcium influx into islet cells has been shown to stimulate glucagon gene transcription through the transcription factor cAMP response element-binding protein that binds to the glucagon cAMP response element. By transient transfection of glucagon-reporter fusion genes into islet cell lines, this study identified a second calcium response element in the glucagon gene (G2 element, from -165 to -200). Membrane depolarization was found to induce the binding of a nuclear complex with NFATp-like immunoreactivity to the G2 element. Consistent with nuclear translocation, a comigrating complex was found in cytosolic extracts of unstimulated cells, and the induction of nuclear protein binding was blocked by inhibition of calcineurin phosphatase activity by FK506. A mutational analysis of G2 function and nuclear protein binding as well as the effect of FK506 indicate that calcium responsiveness is conferred to the G2 element by NFATp functionally interacting with HNF-3beta binding to a closely associated site. Transcription factors of the NFAT family are known to cooperate with AP-1 proteins in T cells for calcium-dependent activation of cytokine genes. This study shows a novel pairing of NFATp with the cell lineage-specific transcription factor HNF-3beta in islet cells to form a novel calcium response element in the glucagon gene.
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PMID:Characterization of a novel calcium response element in the glucagon gene. 1002 8

Signal transduction properties of exendin-4 (Ex-4) underlying its ability to stimulate rat insulin I gene promoter (RIP1) activity were assessed in the pancreatic beta-cell line INS-1. Ex-4 acted via glucagon-like peptide-1 receptors to stimulate RIP1 in a glucose-dependent manner, as measured in cells transfected with a -410-bp RIP1-luciferase construct (RIP1-Luc). The action of Ex-4 was independent of cAMP and PKA because it was not blocked by cotransfection with dominant-negative G alpha(s), was unaffected by pretreatment with the membrane-permeant cAMP antagonist 8-Br-Rp-cAMPS, and remained apparent after treatment with PKA inhibitors H-89 or KT 5720. Similarly, cotransfection with a dominant-negative isoform of the type-2 cAMP-regulated guanine nucleotide exchange factor (Epac2) failed to alter the response to Ex-4. Ro 31-8220, a serine/threonine protein kinase inhibitor that targets PKC as as well as the 90-kDa ribosomal S6 kinase (RSK) and mitogen- and stress-activated protein kinase (MSK) family of cAMP response element-binding protein (CREB) kinases, blocked the stimulatory action of Ex-4 at RIP1-Luc. However, selective inhibition of PKC using K-252c, prolonged exposure to phorbol 1,2-myristate-13-acetate, or cotransfection with dominant-negative atypical PKC-zeta, was without effect. A-CREB, a dominant-negative inhibitor of basic region-leucine zipper transcription factors (bZIPs) related in structure to CREB, inhibited the action of Ex-4 at RIP1-Luc, whereas A-ATF-2 was ineffective. Similarly, introduction of deletions at the RIP1 cAMP response element (CRE), or truncation of RIP1 to remove the CRE, nearly abolished the action of Ex-4. Inactivating mutations introduced at the A4/A3 elements, binding sites for the glucose-regulated homeodomain transcription factor PDX-1, did not diminish the response to Ex-4, although a marked reduction of basal promoter activity was observed. The glucose-dependent stimulation of RIP1-Luc by Ex-4 was reproduced using a synthetic reporter (RIP1-CRE-Luc) incorporating multimerized CREs of the RIP1 nonpalindromic sequence 5'-TGACGTCC-3'. It is concluded that the bZIP and CRE-mediated stimulation of RIP1 by Ex-4 explains, at least in part, how this insulinotropic hormone facilitates transcriptional activity of the rat insulin I gene.
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PMID:Exendin-4 as a stimulator of rat insulin I gene promoter activity via bZIP/CRE interactions sensitive to serine/threonine protein kinase inhibitor Ro 31-8220. 1202 Nov 95

Although many genes are regulated by the concerted action of several hormones, hormonal signaling to gene promoters has generally been studied one hormone at a time. The phosphoenolpyruvate carboxykinase (PEPCK) gene is a case in point. Transcription of this gene is induced by glucagon (acting by the second messenger, cAMP), glucocorticoids, and retinoic acid, and it is dominantly repressed by insulin. These hormonal responses require the presence of different hormone response units (HRUs), which consist of constellations of DNA elements and associated transcription factors. These include the glucocorticoid response unit (GRU), cAMP response unit (CRU), retinoic acid response unit (RARU), and the insulin response unit. HRUs are known to have functional overlap. In particular, the cAMP response element of the CRU is also a component of the GRU. The purpose of this study was to determine whether known GRU or RARU elements or transcription factors function as components of the CRU. We show here that the glucocorticoid accessory factor binding site 1 and glucocorticoid accessory factor binding site 3 elements, which are components of both the GRU and RARU, are an important part of the CRU. Furthermore, we find that the transcription factor, chicken ovalbumin upstream promoter-transcription factor, and two coactivators, cAMP response element-binding protein-binding protein and steroid receptor coactivator-1, participate in both the cAMP and glucocorticoid responses. This provides a further illustration of how the PEPCK gene promoter integrates different hormone responses through overlapping HRUs that utilize some of the same transcription factors and coactivators.
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PMID:Elements of the glucocorticoid and retinoic acid response units are involved in cAMP-mediated expression of the PEPCK gene. 1253 92

Glucagon-like peptide 1 (GLP-1) activates receptors coupled to cAMP production and calcium influx in pancreatic cells, resulting in enhanced glucose sensitivity and insulin secretion. Despite evidence that the GLP-1 receptor is present and active in neurons, little is known of the roles of GLP-1 in neuronal physiology. As GLP-1 modulates calcium homeostasis in pancreatic beta cells, and because calcium plays important roles in neuronal plasticity and neurodegenerative processes, we examined the effects of GLP-1 on calcium regulation in cultured rat hippocampal neurons. When neurons were pre-treated with GLP-1, calcium responses to glutamate and membrane depolarization were attenuated. Whole-cell patch clamp analyses showed that glutamate-induced currents and currents through voltage-dependent calcium channels were significantly decreased in neurons pre-treated with GLP-1. Pre-treatment of neurons with GLP-1 significantly decreased their vulnerability to death induced by glutamate. Acute application of GLP-1 resulted in a transient elevation of intracellular calcium levels, consistent with the established effects of GLP-1 on cAMP production and activation of cAMP response element-binding protein. Collectively, our findings suggest that, by modulating calcium responses to glutamate and membrane depolarization, GLP-1 may play important roles in regulating neuronal plasticity and cell survival.
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PMID:Glucagon-like peptide 1 modulates calcium responses to glutamate and membrane depolarization in hippocampal neurons. 1462 93

Glia play an important role in neurotoxicity in neurodegenerative diseases. In this study, we investigated the expression of glucagon-like peptide-1 (GLP-1) and its receptor, and the effects of GLP-1 on lipopolysaccharide (LPS)-induced IL-1beta mRNA expression and IL-1beta production in glia. GLP-1-like immunoreactivity was observed in amoeboid microglia, but not ramified microglia or astrocytes. GLP-1 binding and GLP-1 receptor mRNA expression were observed in both astrocytes and microglia. GLP-1-induced morphological changes in microglia from the ramified type to the amoeboid type, suggesting an increase in production and release of endogenous GLP-1. GLP-1 prevented the LPS-induced IL-1beta mRNA expression, which effect was, in turn, inhibited by pretreatment with SQ22536, an adenylate cyclase inhibitor. GLP-1 also increased cAMP concentration and cAMP response element-binding protein phosphorylation in astrocytes. These results suggest that GLP-1 may be a modulator of inflammation in the central nervous system.
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PMID:Glucagon-like peptide-1 inhibits LPS-induced IL-1beta production in cultured rat astrocytes. 1672 54

Glucagon-like peptide-1 and its potent agonist exendin-4 induce several immediate early response genes (IEGs) that code for transcription factors implicated in cell proliferation, differentiation, and apoptosis. We recently observed that early growth response factor-1 (EGR-1), an IEG product, was required for transcriptional activation of Ccnd1 (cyclin D1) gene by exendin-4. Herein, the regulatory mechanism whereby exendin-4 activates the transcription of EGR-1 gene was investigated in the pancreatic beta-cell line INS-1. Deletion analysis of rat EGR-1 promoter identified a critical region between -73 and -46 for the activation of EGR-1 in response to exendin-4. Mutation of the proximal putative cAMP response element (CRE, 5'-GTACGTCA-3') located at -69 resulted in a significant decrease in the EGR-1 transcription, whereas the mutation of the distal putative CRE at -139 was without such an effect. In immune supershift assays using exendin-4-treated cells, binding of cAMP response element-binding protein (CREB) phosphorylated on Ser(133) to the proximal CRE was increased. Employment of a CREB mutant containing Ala substitution at Ser(133) or a dominant negative CREB mutant that inhibits the binding of endogenous CREB to DNA significantly decreased the exendin-4-induced EGR-1 transcription. In experiments using specific protein kinase inhibitors, the effect of H-89 was more prominent than PD-98059, indicating the predominance of the PKA signaling over the MEK/ERK in induction of EGR-1. Therefore, it appears that the proximal CRE site is critical and the binding with CREB phosphorylated on Ser(133) is necessary for induction of the EGR-1 transcription by exendin-4.
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PMID:Proximal cyclic AMP response element is essential for exendin-4 induction of rat EGR-1 gene. 1692 76

We previously demonstrated the dose-dependent glucagon-like peptide (GLP)-2 activation of intracellular signals associated with increased epithelial cell survival and proliferation in the neonatal intestine. Our current aim was to quantify the acute, temporal GLP-2 activation of these key intracellular signals and relate this to changes in epithelial cell survival and proliferation in the neonatal intestine. We studied 29 total parenteral nutrition-fed neonatal piglets infused intravenously with either saline (control) or human GLP-2 (420 micromol.kg(-1).h(-1)) for 1, 4, or 48 h. GLP-2 infusion increased small intestinal weight, DNA and protein content, and villus height at 48 h, but not at 1 or 4 h. Intestinal crypt and villus apoptosis decreased and crypt cell proliferation and protein synthesis increased linearly with duration of GLP-2 infusion, but were statistically different from controls only after 48 h. Before the morphological and cellular kinetic changes, GLP-2 rapidly activated putative GLP-2 receptor downstream signals within 1-4 h, including phosphorylation of protein kinase A, protein kinase B, extracellular signal-regulated kinase 1/2, and the transcription factors cAMP response element-binding protein and c-Fos. GLP-2 rapidly suppressed caspase-3 activation and upregulated Bcl-2 abundance within 1 h, whereas there was an increase in apoptosis inhibitors X-linked inhibitor of apoptosis at 1 h and cellular inhibitor of apoptosis-2 at 4 and 48 h. We also show that the increased c-Fos and reduced active caspase-3 immunostaining after GLP-2 infusion was localized in epithelial cells. We conclude that GLP-2-induced activation of intracellular signals involved in both cell survival and proliferation occurs rapidly and precedes the trophic cellular kinetic effects that occur later in intestinal epithelial cells.
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PMID:GLP-2 rapidly activates divergent intracellular signaling pathways involved in intestinal cell survival and proliferation in neonatal piglets. 1695 36

Orexin-A (OXA) regulates food intake and energy homeostasis. It increases insulin secretion in vivo and in vitro, although controversial effects of OXA on plasma glucagon are reported. We characterized the effects of OXA on glucagon secretion and identify intracellular target molecules in glucagon-producing cells. Glucagon secretion from in situ perfused rat pancreas, isolated rat pancreatic islets, and clonal pancreatic A-cells (InR1-G9) were measured by RIA. The expression of orexin receptor 1 (OXR1) was detected by Western blot and immunofluorescence. The effects of OXA on cAMP, adenylate-cyclase-kinase (AKT), phosphoinositide-dependent kinase (PDK)-1, forkhead box O-1 (Foxo1), and cAMP response element-binding protein were measured by ELISA and Western blot. Intracellular calcium (Ca(2+)(i)) concentration was detected by fura-2and glucagon expression by real-time PCR. Foxo1 was silenced in InR1-G9 cells by transfecting cells with short interfering RNA. OXR1 was expressed on pancreatic A and InR1-G9 cells. OXA reduced glucagon secretion from perfused rat pancreas, isolated rat pancreatic islets, and InR1-G9 cells. OXA inhibited proglucagon gene expression via the phosphatidylinositol 3-kinase-dependent pathway. OXA decreased cAMP and Ca(2+)(i) concentration and increased AKT, PDK-1, and Foxo1 phosphorylation. Silencing of Foxo1 caused a reversal of the inhibitory effect of OXA on proglucagon gene expression. Our study provides the first in vitro evidence for the interaction of OXA with pancreatic A cells. OXA inhibits glucagon secretion and reduces intracellular cAMP and Ca(2+)(i) concentration. OXA increases AKT/PDK-1 phosphorylation and inhibits proglucagon expression via phosphatidylinositol 3-kinase- and Foxo-1-dependent pathways. As a physiological inhibitor of glucagon secretion, OXA may have a therapeutic potential to reduce hyperglucagonemia in type 2 diabetes.
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PMID:Orexin-A inhibits glucagon secretion and gene expression through a Foxo1-dependent pathway. 1816 14

Terminally ill insulin-deficient rodents with uncontrolled diabetes due to autoimmune or chemical destruction of beta-cells were made hyperleptinemic by adenoviral transfer of the leptin gene. Within approximately 10 days their severe hyperglycemia and ketosis were corrected. Despite the lack of insulin, moribund animals resumed linear growth and appeared normal. Normoglycemia persisted 10-80 days without other treatment; normal physiological conditions lasted for approximately 175 days despite reappearance of moderate hyperglycemia. Inhibition of gluconeogenesis by suppression of hyperglucagonemia and reduction of hepatic cAMP response element-binding protein, phoshoenolpyruvate carboxykinase, and peroxisome proliferator-activated receptor-gamma-coactivator-1alpha may explain the anticatabolic effect. Up-regulation of insulin-like growth factor 1 (IGF-1) expression and plasma levels and increasing IGF-1 receptor phosphorylation in muscle may explain the increased insulin receptor substrate 1, PI3K, and ERK phosphorylation in skeletal muscle. These findings suggest that leptin reverses the catabolic consequences of total lack of insulin, potentially by suppressing glucagon action on liver and enhancing the insulinomimetic actions of IGF-1 on skeletal muscle, and suggest strategies for making type 1 diabetes insulin-independent.
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PMID:Making insulin-deficient type 1 diabetic rodents thrive without insulin. 1877 78


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