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)

The specific effect of hyperglycemia on the reported decrease in liver glycogen synthase phosphatase activity was studied in STZ-induced diabetic rats with normal fasting insulinemia. Four groups of animals were investigated: control (nondiabetic), diabetic hyperglycemic (STZ), diabetic normoglycemic (STZ followed by 3-day phloridzin treatment), and a diabetic normoglycemic group injected with glucose to reinstate hyperglycemia. None of the treatments significantly altered fasting plasma insulin and glucagon concentrations. We found that hepatic synthase phosphatase activity decreased in STZ-induced diabetic rats and was further markedly reduced when glycemia was normalized in the diabetic animals. This additional decrease in phosphatase activity was almost fully reversed when hyperglycemia was restored by acute glucose infusion of the normoglycemic diabetic rats. In parallel, the levels of liver G6P and F6P were markedly reduced in the diabetic normoglycemic rats and restored with reinstatement of hyperglycemia. In contrast, liver microsomal glucose-6-phosphatase activity was enhanced and glucokinase activity was lowered in all diabetic groups, regardless of glycemia. Our results indicate that hyperglycemia per se counteracts part of the loss of hepatic synthase phosphatase in diabetic animals and provokes the stable conversion of synthase phosphatase from a less active to a more active form.
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PMID:Opposite effects of hyperglycemia and insulin deficiency on liver glycogen synthase phosphatase activity in the diabetic rat. 838 Oct 96

Glycolysis is usually considered as a paradigm metabolic pathway, due to the fact that it is present in most organisms, and also because it is the pathway by which an important nutrient, glucose, is consumed. Far from being completely understood, the regulation of this pathway witnessed several important progresses during the last few years. One of these is the discovery of fructose 2,6-bisphosphate, a potent stimulator of phosphofructokinase and inhibitor of fructose-1,6-bisphosphatase. Originally found in the liver during the course of a study on the mechanism by which glucagon acts on gluconeogenesis, this compound is now recognized as a major element in the control of glycolysis and/or gluconeogenesis in many cell types and in various organisms. The other finding is that of a regulatory protein that modulates the activity of glucokinase, the enzyme that phosphorylates glucose in the liver and in the beta cells of pancreatic islets.
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PMID:Glycolysis revisited. 839 34

Liver insulin resistance and glucagon-stimulated hepatic glucose production are characteristics of the diabetic state. To determine the potential role of glucose toxicity in these abnormalities, we examined whether phlorizin treatment of streptozotocin-diabetic rats resulted in altered expression of genes involved in key steps of hepatic glucose metabolism. By inhibiting renal tubular glucose reabsorption, phlorizin infusion to diabetic rats induced normoglycaemia, did not significantly alter low circulating insulinaemia, but caused a marked decrease in hyperglucagonaemia. Glucokinase and L-type pyruvate kinase mRNA levels were reduced respectively by 90% and 70% in fed diabetic rats, in close correlation with changes in enzyme activities. Eighteen days of phlorizin infusion partially restored glucokinase mRNA and activity (40% of control levels), but had no effect on L-type pyruvate kinase mRNA and activity. In contrast to the glycolytic enzymes, mRNA and activity of the gluconeogenic enzyme, phosphoenolpyruvate carboxykinase were increased (10- and 2.2-fold, respectively) in fed diabetic rats. Phlorizin administration decreased phosphoenolpyruvate carboxykinase mRNA to values not different from those in control rats, while phosphoenolpyruvate carboxykinase activity remained 50% higher than that in control rats. The 50% rise in liver glucose transporter (GLUT 2) mRNA and protein, produced by diabetes, was also corrected by phlorizin treatment. In conclusion, we propose that phlorizin treatment of diabetic rats may induce a partial shift of the predominating gluconeogenesis, associated with hepatic glucose overproduction, into glycolysis, by correction of impaired pre-translational regulatory mechanisms. This could be essentially mediated through improved pancreatic alpha-cell function and subsequent lowering of hyperglucagonaemia. These observations suggest that glucagon-stimulated hepatic glucose production may result, in part, from glucose toxicity.
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PMID:Phlorizin treatment of diabetic rats partially reverses the abnormal expression of genes involved in hepatic glucose metabolism. 847 72

Rat pancreatic AR42J cells possess exocrine and neuroendocrine properties. Activin A induces morphological changes and converts them into neuron-like cells. In activin-treated cells, mRNA for pancreatic polypeptide (PP) but not that for either insulin or glucagon was detected by reverse transcription-PCR. About 25% of the cells were stained by anti-PP antibody. When AR42J cells were incubated with betacellulin, a small portion of the cells were stained positively with antiinsulin and anti-PP antibodies. The effect of betacellulin was dose dependent, being maximal at 2 nM. Approximately 4% of the cells became insulin positive at this concentration, and mRNAs for insulin and PP were detected. When AR42J cells were incubated with a combination of betacellulin and activin A, approximately 10% of the cells became insulin positive. Morphologically, the insulin-positive cells were composed of two types of cells: neuron-like and round-shaped cells. Immunoreactive PP was found in the latter type of cells. The mRNAs for insulin, PP, glucose transporter 2, and glucokinase, but not glucagon, were detected. Depolarizing concentration of potassium, tolbutamide, carbachol, and glucagon-like peptide-1 stimulated the release of immunoreactive insulin. These results indicate that betacellulin and activin A convert amylase-secreting AR42J cells into cells secreting insulin. AR42J cells provide a model system to study the formation of pancreatic endocrine cells.
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PMID:Betacellulin and activin A coordinately convert amylase-secreting pancreatic AR42J cells into insulin-secreting cells. 860 30

The binding properties of hepatic aldolase (B) were determined in digitonin-permeabilized rat hepatocytes after the cells had been preincubated with either glycolytic or gluconeogenic substrates. In hepatocytes that had been preincubated in medium containing 5 mM glucose as sole carbohydrate substrate, binding of aldolase to the hepatocyte matrix was maximal at low KCl concentrations (20 mM) or bivalent cation concentrations (1 mM Mg2+) and half-maximal dissociation occurred at 50 mM KCl. Preincubation of hepatocytes (for 10-30 min) with glucose or mannose (10-40 mM), fructose, sorbitol, dihydroxyacetone or glycerol (1-10 mM), caused a leftward shift of the salt dissociation curve (maximum binding at 10 mM KCl; half-maximum dissociation at 35 mM KCl) but did not affect the proportion of bound enzyme at low or high KCl concentrations. Galactose and 2-deoxyglucose had no effect on aldolase binding. Inhibitors of glucokinase (mannoheptulose and glucosamine) suppressed the effects of glucose but not the effects of sorbitol, glycerol or dihydroxyacetone. Glucagon suppressed the effects of glucose, fructose and dihydroxyacetone but not glycerol. Poly(ethylene glycol) (PEG) (2-10%), added to the permeabilization medium, increased aldolase binding and caused a rightward shift in the salt dissociation curve. In the presence of PEG (6-8%), the effects of substrates on aldolase dissociation were shifted to higher salt concentrations (50-100 mM versus 35 mM KCl). The effects of substrates (added to the intact cell) on aldolase binding to the permeabilized cell could be mimicked by addition of the phosphorylated derivatives of these substrates to the permeabilized cell. Of the intermediates tested dihydroxyacetone phosphate and fructose 1,6-bisphosphate were the most effective at dissociating aldolase (A50 values of 20 microM and 40 microM respectively). Other effective intermediates in order of decreasing potency were fructose 1-phosphate, glycerol 3-phosphate, glucose 1,6-bisphosphate/fructose 2,6-bisphosphate. These results show that aldolase B binds to the hepatocyte matrix by a salt-dependent mechanism that is influenced by macromolecular crowding and metabolic intermediates. Maximum binding occurs when hepatocytes are incubated in the absence of glycolytic and gluconeogenic substrates and minimum binding occurs in the presence of substrates that are precursors of either fructose 1,6-bisphosphate or triose phosphates. Since the bound form of aldolase represents a kinetically less active state it is proposed that aldolase binding and dissociation may be a mechanism for buffering the concentrations of metabolic intermediates.
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PMID:Substrate modulation of aldolase B binding in hepatocytes. 861 43

Previous, in vivo experiments have shown that an appropriate hormonal environment (high plasma insulin, low plasma glucagon) was unable to induce the accumulation of glucokinase mRNA in term fetal rat liver, whereas it was very efficient in the newly born rat. We have confirmed in the present study that insulin induced the accumulation of glucokinase mRNA in cultured hepatocytes from 1-day-old newborn rats, but not in cultured hepatocytes from 21-day-old fetuses. To identify regulatory regions of the glucokinase gene involved in the insulin response, we have scanned the glucokinase locus for DNase I hypersensitive sites in its in vivo conformation. We confirmed the presence of four liver-specific DNase I hypersensitive sites located in the 5' flanking region of the gene. Moreover, two additional hypersensitive sites, located at 2.5 kb and 3.5 kb upstream of the cap site were found but none of these new sites displayed inducibility by insulin. Finally, an increase of the sensitivity of hypersensitive site-1 and hypersensitive site-2 to DNase I correlates with the ability of insulin to induce glucokinase gene expression in cultured hepatocytes from 1-day-old rats, as observed in previous in vivo studies. This suggests that neither a prior exposure to insulin nor a simple aging of the fetal cells in the presence of the hormone in culture are instrumental for the full DNase-I hypersensitivity of the two proximal sites necessary for the neonatal response of the glucokinase gene to insulin. The proximal hypersensitive site-1, which is close to the transcription start site in the liver, does coincide with a sequence (designated IRSL) that is 80% identical to the phosphoenolpyruvate carboxykinase IRS and with a DNase-I footprint that has been identified overlapping this sequence. Nevertheless, functional analysis of this sequence suggested that it is unlikely that the insulin-response sequence like alone is sufficient to mediate the transcriptional effect of insulin on the hepatic glucokinase gene.
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PMID:Induction of the glucokinase gene by insulin in cultured neonatal rat hepatocytes. Relationship with DNase-I hypersensitive sites and functional analysis of a putative insulin-response element. 861 67

Expression of glucokinase in hepatocytes and pancreatic 6-cells is of major physiologic importance to mammalian glucose homeostasis. Liver glucokinase catalyzes the first committed step in the disposal of glucose, and beta-cell glucokinase catalyzes a rate-limiting step required for glucose-regulated insulin release. The present study reports the expression of glucokinase in rat glucagon-producing alpha-cells, which are negatively regulated by glucose. Purified rat alpha-cells express glucokinase mRNA and protein with the same transcript length, nucleotide sequence, and immunoreactivity as the beta-cell isoform. Glucokinase activity accounts for more than 50% of glucose phosphorylation in extracts of alpha-cells and for more than 90% of glucose utilization in intact cells. The glucagon-producing tumor MSL-G-AN also contained glucokinase mRNA, protein, and enzymatic activity. These data indicate that glucokinase may serve as a metabolic glucose sensor in pancreatic alpha-cells and, hence, mediate a mechanism for direct regulation of glucagon release by extracellular glucose. Since these cells do not express Glut2, we suggest that glucose sensing does not necessarily require the coexpression of Glut2 and glucokinase.
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PMID:The glucose sensor protein glucokinase is expressed in glucagon-producing alpha-cells. 869 40

Pancreatic AR42J cells are derived from acinar cells and express both exocrine and neuroendocrine properties. We have recently shown that these cells convert into insulin-producing cells in vitro after treatment with activin A and betacellulin. Here, we investigated the effect of hepatocyte growth factor (HGF) in those cells. When AR42J cells were incubated with HGF, DNA synthesis was attenuated, and the amylase content was reduced in a concentration-dependent manner. HGF-treated cells extended processes, but bundle formation was not observed using an antibody against tubulin. Reverse both insulin and pancreatic polypeptide (PP) were expressed in HGF-treated, but not naive, AR42J cells. Immunocytochemical analysis indicated that approximately 3% of the HGF-treated cells were stained with antiinsulin antibody, and some were also stained with anti-PP antibody. When AR42J cells were exposed to a combination of activin A and HGF, cells extended longer processes, and over 10% of them were stained with antiinsulin antibody. In these cells, messenger RNAs for insulin, PP, glucose transporter 2, and glucokinase, but not those for glucagon or somatostatin, were expressed. A subclone of AR42J cells, AR42J-B13, was obtained. Most of the AR42J-B13 cells converted to insulin-producing cells after the incubation with activin A and HGF. Insulin secretion was augmented by tolbutamide, depolarizing concentrations of potassium, carbachol, and glucagon-like peptide-1 in these cells. These results indicate that HGF reduces the acinar cell-like property of AR42J cells and converts them into insulin-producing cells. The effect of HGF was markedly enhanced by activin A.
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PMID:Formation of insulin-producing cells from pancreatic acinar AR42J cells by hepatocyte growth factor. 875 73

Evidence that glucagon-like peptide-1 (GLP-1) (7-36) amide functions as a novel neuropeptide prompted us to study the gene expression of its receptor in rat brain. Northern blot analysis showed transcripts of similar size in RINm5F cells, hypothalamus, and brain-stem. First-strand cDNA was prepared by using RNA from hypothalamus, brainstem, and R1Nm5F cells and subsequently amplified by PCR. Southern blot analysis of the PCR products showed a major 1.4-kb band in all these preparations. PCR products amplified from hypothalamus were cloned, and the nucleotide sequence of one strand was identical to that described in rat pancreatic islets. In situ hybridization studies showed specific labeling in both neurons and glia of the thalamus, hypothalamus, hippocampus, primary olfactory cortex, choroid plexus, and pituitary gland. In the hypothalamus, ventromedial nuclei cells were highly labeled. These findings indicate that GLP-1 receptors are actually synthesized in rat brain. In addition, the colocalization of GLP-1 receptors, glucokinase, and GLUT-2 in the same areas supports the idea that these cells play an important role in glucose sensing in the brain.
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PMID:Expression of the glucagon-like peptide-1 receptor gene in rat brain. 876 50

Aging is an etiologic factor in non-insulin-dependent diabetes mellitus. While the effect of aging on insulin secretion has been described by several classic studies, the characterization of the molecular basis of beta-cell abnormalities is still under way. We recently demonstrated in rats that aging is associated not only with a reduction in insulin secretion but also with diminished levels of intracellular insulin content and the mRNA for insulin. In this study, we investigated whether the molecular abnormalities previously described in the rat beta cell were also present in the mouse (C57BL/6J). Total cellular RNA was isolated from individual pancreata of 3-, 9-, and 30-month-old mice (n = 6 per age group). Samples were subjected to slot-blot analysis by using homologous probes for insulin, glucagon, somatostatin, glucose transporter-2 (glut-2), glucokinase, elastase-I, and beta-actin. We observed a progressive age-dependent decrease in insulin mRNA levels: insulin mRNA levels decreased by 40% with age (p = .007). This paralleled decreases in glut-2 (p = .001) mRNA levels, but it was in contrast with glucokinase mRNA levels which increased markedly (p = .0003). Somatostatin mRNA levels were unchanged, glucagon mRNA levels decreased modesty (p = .01), and mRNA levels for elastase-I and beta-actin increased with age (p = .0001 for either one). In summary, it appears that in the mouse a progressive decline in the activity of the endocrine pancreas occurs with aging. This phenomenon seems to affect only the beta cells and not the alpha or delta cells of the islet of Langerhans or the exocrine pancreas. This progressive decline may represent the biological features of the age-dependent risk for the development of diabetes.
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PMID:Molecular investigation of age-related changes in mouse endocrine pancreas. 880 81


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