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 hepatic glucagon receptor was covalently labeled with [125I-Tyr10]-monoiodoglucagon by use of the heterobifunctional crosslinker hydroxysuccinimidyl-p-azidobenzoate and analyzed by SDS-gel electrophoresis. The autoradiogram of the gel showed one band at Mr = 63,000 that was sensitive to excess unlabeled glucagon and GTP. The labeled receptor was solubilized with Lubrol-PX and the hydrodynamic characteristics of the receptor were determined. The molecular parameters of the solubilized receptor are S20,w = 4.3 +/- 0.1, Stokes radius = 6.3 +/- 0.1 nm, frictional coefficient f/f degrees = 1.8 and a calculated Mr = 119,000. Incubation of liver membranes at 32 degrees for 15 min prior to the addition of [125I-Tyr10] permitted us to identify the high molecular weight form (Mr approximately equal to 113,000) by direct SDS-gel electrophoretic analysis. Limited elastase treatment of the hormone-occupied receptor results in the appearance of a Mr = 33,000 fragment, that retains guanine nucleotide sensitivity. Elastase treatment of vacant receptors results in a Mr = 24,000 fragment that binds hormone in a GTP-sensitive manner. The Mr = 24,000 fragment is contained within the Mr = 33,000 fragment. The Mr = 63,000 receptor upon treatment with endo-beta-N-acetylglucosamine F for 4 h yields four fragments of apparent Mr = 61,000, 56,000, 51,000, and 45,000; 24 h treatment results in the accumulation of the last two fragments. Neither Mr = 33,000 and 24,000 fragment appear to be substrates for endo-beta-N-acetylglucosaminidase F. These data allow us to conclude that the hepatic glucagon receptor in the membrane is a dimer of approximately 60,000 dalton hormone binding subunit which is a glycoprotein containing at least four N-linked glycans accounting for 18,000 daltons of its mass. Both the hormone binding function and the capacity for the interaction with the stimulatory regulator of adenylyl cyclase are contained within a fragment of only approximately 21,000 daltons that does not contain any N-linked glycans.
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PMID:Characterization of the hepatic glucagon receptor. 609 55

Continuous cell lines have been established from a variety of biopsy and postmortem species of tumor from patients with small-cell carcinoma of the lung (SCCL) and have been maintained over several years. The medium from the cultures has been assayed for peptide, glycoprotein, and steroid hormones. Significant amounts of 14 hormones including calcitonin, adrenocorticotropin (ACTH), parathormone, luteinizing hormone, chorionic gonadotropin, glucagon, growth hormone, somatostatin, prolactin, beta-endorpin, lipotropin, oxytocin-neurophysin, vasopressin-neurophysin, and estradiol have been demonstrated. Up to ten different hormones have been produced by a single cell line. Most produce ACTH and all evaluated so far produce estradiol. These studies indicate that cells from SCCL have a potential for producing a wide variety of hormones and that this characteristic can be maintained for prolonged periods of culture in vitro.
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PMID:Hormone production by cultures of small-cell carcinoma of the lung. 626 22

Bovine thyroid membranes possess both ADP ribosyltransferase and NAD glycohydrolase activities with the same Km values for NAD and the same pH optima. In intact membranes, the ADP ribosyltransferase is limited in its extent by the amount of available membrane acceptor which can be ADP-ribosylated; in membranes solubilized with lithium diiodosalicylate, an artificial acceptor, L-arginine methyl ester, can be substituted to eliminate this limitation. The product of the ADP ribosyltransferase is a mono-ADP-ribosylated acceptor whether the intact or solubilized membrane provides the enzyme activity and whether membrane or exogenous acceptor, L-arginine methyl ester, is utilized. The intact membranes and the solubilized preparation also have an enzyme activity which can release AMP from the mono-ADP-ribosylated acceptor whether formed by the action of the membrane ADP ribosyltransferase or the A promoter of cholera toxin. The NAD glycohydrolase activity appears to represent the half-reaction of the ADP ribosyltransferase, i.e. an activity measurable substituting water for a membrane acceptor or L-arginine methyl ester. Membranes from functional rat thyroid cells in culture, i.e. cells chronically stimulated by thyrotropin and unresponsive to further additions of thyrotropin, have low ADP-ribosylation but high NAD glycohydrolase activities. In contrast, membranes from nonfunctional rat thyroid cells, i.e. cells unresponsive to thyrotropin, have high ADP-ribosylation and low NAD glycohydrolase activities. NAD hydrolysis by the NAD glycohydrolase activity cannot account for the low ADP-ribosylation activity in membranes from the functioning cells, and its low level of ADP-ribosylation can be eliminated by solubilizing the membranes and substituting an artificial acceptor, L-arginine methyl ester. The ADP ribosyltransferase activity of rat thyroid cell membrane preparations can be enhanced by thyrotropin in a dose-dependent manner but not by insulin, glucagon, hydrocortisone, adrenocorticotropin, or its glycoprotein hormone analog, human chorionic gonadotropin. It is thus suggested (i) that, in analogy to cholera toxin, thyrotropin-stimulated ADP-ribosylation may be important in the regulation of the adenylate cyclase response and (ii) that the level of membrane acceptor available for ADP-ribosylation may relate both to a stable "'activated" state of the adenylate cyclase system in cells chronically stimulated with thyrotropin and/or to a desensitized state with regard to a failure of more thyrotropin to elicit additional functional responses.
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PMID:Thyroid membrane ADP ribosyltransferase activity. Stimulation by thyrotropin and activity in functioning and nonfunctioning rat thyroid cells in culture. 627 80

The photoreactive 125I-labeled glucagon-NAPS [125I-labeled 2-[2-nitro-4-azidophenyl)sulfenyl]-Trp25-glucagon] was used to label the glucagon receptor sites in rat liver plasma membranes. The proteins labeled were analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis with or without reduction with dithiothreitol. The photoaffinity peptide specifically labeled a number of bands with apparent molecular weights greater than 200000 and probably at least two protein bands in the molecular weight range 52000-70000. The relative amounts of radioactivity associated with these bands and their relative mobilities differed in samples from reduced and unreduced membranes. Their relative mobilities also differed with percent acrylamide cross-linking, suggesting a glycoprotein nature and the presence of intramolecular disulfide bonds. A nonspecifically labeled band with an apparent molecular weight of 27000-28000 also displayed a similar behavior. Photolabeling in the presence of 0.1 mM guanosine 5'-triphosphate (GTP) decreased the amount of radiolabeling of these bands, suggesting their involvement in the glucagon stimulation of adenylate cyclase. The photolabeled receptor in the membranes, solubilized with Lubrol-PX and fractionated on an Ultrogel AcA22 column, eluted with an apparent molecular weight of 200000-250000. Addition of GTP to the solubilized glucagon receptor of nonirradiated membranes caused complete dissociation of the complex. Gel electrophoresis of the partially purified radiolabeled receptor identified the same protein components observed in photolabeled membranes. These results indicate that the glucagon receptor is an oligomer probably composed of at least two different subunits that are linked together or greatly stabilized by disulfide bonds. They also show that 125I-labeled glucagon-NAPS can be used effectively to covalently label the putative glucagon receptor and thus aid in its further characterization.
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PMID:Identification of the glucagon receptor by covalent labeling with a radiolabeled photoreactive glucagon analogue. 628 11

[125I-Tyr10]Monoiodoglucagon [( 125I]MIG) was cross-linked to liver membrane glucagon receptors with hydroxysuccinimidyl-p-azidobenzoate, and the products were analyzed by sodium dodecyl sulfate-gel electrophoresis. Autoradiograms of the gel obtained after a 24-h exposure showed one major band at Mr = 63,000 that was sensitive to GTP and excess unlabeled glucagon. Exposure for 7 days showed labeling of an additional Mr = 33,000 species that was also sensitive to excess unlabeled glucagon. The Mr = 33,000 peptide can be obtained by subtilisin, trypsin, elastase, or Staphylococcus aureus V8 protease treatment of the [125I]MIG-occupied receptor in the membrane or in Lubrol-PX solution. In contrast, limited proteolysis of membranes containing vacant receptors results in labeling of a Mr = 24,000 peptide. The Mr = 24,000 peptide specifically binds [125I]MIG in a GTP-sensitive manner. The Mr = 33,000 peptide also retains GTP sensitivity since it releases bound [125I]MIG upon addition of GTP. Elastase treatment of the electroeluted Mr = 33,000 peptide yields the Mr = 24,000 and 15,000 fragments. The Mr = 15,000 peptide is the smallest fragment of the receptor as yet identified. Treatment of the Mr = 63,000 receptor with [125I]MIG cross-linked to it with endo-beta-N-acetylglucosaminidase F results in four distinct fragments with Mr values of 61,000, 56,000, 51,000, and 45,000; prolonged treatment resulted in the accumulation of the last two. Neither the Mr = 33,000 nor the Mr = 24,000 fragment appeared to be substrates for endo-beta-N-acetylglucosaminidase F. These data indicate that glucagon receptor is a glycoprotein of approximately 60,000 daltons which contains at least four N-linked glycans accounting for 18,000 daltons of its mass. Both its glucagon binding function and its capacity to interact with the stimulatory regulator of adenylyl cyclase are contained within a fragment of only approximately 21,000 daltons that does not contain any N-linked glycans. Hormone occupancy of the receptor results in a conformational change so as to expose a region that is susceptible to proteolysis by proteases of varying specificities to yield a peptide of approximately 30,000 daltons that also does not contain N-linked glycans.
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PMID:Structural analysis of the hepatic glucagon receptor. Identification of a guanine nucleotide-sensitive hormone-binding region. 632 24

Primary cultures of rat hepatocytes respond to hormones or amino acid deprivation by increasing System A-mediated neutral amino acid transport. Previous reports have shown this stimulation to be dependent on RNA and protein synthesis, whereas the present report describes the inhibition of System A by tunicamycin (TM), an inhibitor of asparagine-linked glycoprotein biosynthesis. The basal System A activity, as monitored by Na+-dependent 2-aminoisobutyric acid uptake, was decreased by TM when hepatocytes were cultured for 24 h in the presence of the antibiotic. System Gly activity was also sensitive to TM, whereas the activities of Systems L1, L2, and N were relatively resistant and that of System ASC was only moderately affected. The increase in System A-mediated uptake after incubation of hepatocytes in the absence of amino acids (i.e. adaptive control) was almost completely abolished by including TM. Likewise, stimulation of hepatic 2-aminoisobutyric acid transport by glucagon, dexamethasone, insulin, or vasopressin was also blocked by the inhibitor. When glucagon alone or glucagon plus dexamethasone was added, the inhibition by TM was transient such that the degree of inhibition decreased with incubation time after the initial 2 h. Addition of TM to cells which had been treated previously for 2 h to 4 h with glucagon and dexamethasone blocked any further increase in transport indicating that the glycoprotein component of System A must be continually synthesized to sustain the increase in activity. Treatment of hepatocytes with various lectins did not inhibit 2-aminoisobutyric acid transport.
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PMID:Induction of amino acid transport system A in rat hepatocytes is blocked by tunicamycin. 635 4

Goblet-cell carcinoids are particular mucus-producing tumors combining features of typical carcinoids and adenocarcinomas. The immunoreactivity of five goblet-cell carcinoids of the appendix and one tumor of the ileum for 5-hydroxytryptamine (5-HT, serotonin), glucagon, somatostatin, substance P (SP), neuron-specific enolase (NSE), lysozyme, secretory component (SC) and carcino-embryonic antigen (CEA) was compared with that of the mucosa of the appendix (n = 24) and ileum (n = 12), and of typical carcinoids (appendix: n = 10; ileum: n = 3). The goblet-cell carcinoids were consistently lysozyme-, SC- and CEA-reactive and contained weakly NSE reactive endocrine cells, while typical carcinoids were lysozyme-, SC- and CEA-negative, but strongly NSE- reactive. Two goblet-cell carcinoids were glucagon-reactive, one displayed SP-reactivity, one malignant tumor was reactive to the alpha-chain of glycoprotein hormones; six of ten typical appendix carcinoids were SP reactive, as were the three typical ileum carcinoids. Using the immunogold technique combined with the alcian-blue reaction, the presence of 5-hydroxytryptamine (5-HT) and mucus was demonstrated within the same cell. These findings suggest histogenetic differences between goblet-cell carcinoids and typical carcinoids; the former are possibly derived from undifferentiated stem cells, whereas the latter probably arise from endocrine cells in the mucosal stroma.
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PMID:Combined production of mucus, amines and peptides by goblet-cell carcinoids of the appendix and ileum. 648 83

Liver biomatrix contains a group of connective tissue components needed for attachment, survival, and maintenance of liver-specific functions of adult rat hepatocytes in culture. An acidic extract of liver biomatrix that contains a group of glycoproteins can replace intact biomatrix in promoting attachment and survival of hepatocytes. However, except for albumin synthesis, liver-specific functions have not been tested. Acidic extracts of biomatrices prepared from heart, kidney, lung, and spleen (heterologous) contain a similar group of glycoproteins, but differ with respect to liver glycoproteins in their capacity to sustain hepatocyte binding. Normal hepatocytes attach poorly to heterologous glycoprotein extracts, although regenerating and tumoral hepatocytes attach to liver glycoproteins and adhere equally well or with greater efficiency to heterologous glycoprotein extracts. The increased efficiency of hepatocytes to attach to kidney biomatrix-derived glycoproteins showed a linear correlation with the decreased glucagon binding capacity of their isolated plasma membranes. An epithelioid cell-line derived from kidney (MDCK) attached with higher efficiency to kidney than to liver glycoproteins. These results suggest that biomatrices may contain specific glycoproteins needed for attachment and survival of their epithelial cells. This specificity is lost during the proliferative state of regenerating and tumoral hepatocytes and could be important in the general mechanism of tumor dissemination and metastases.
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PMID:Abnormal matrix recognition by Morris hepatomas correlates with low glucagon binding capacity. 684 Jun 76

Adult mouse hepatocytes respond in vivo to experimentally induced acute inflammation by an increased synthesis and secretion of alpha 1-acid glycoprotein, haptoglobin, hemopexin, and serum amyloid A. Concurrently, the production of albumin and apolipoprotein A-1 is reduced. To define possible mediators of this response and to study their action in tissue culture, we established primary cultures of hepatocytes. Various hormones and factors that have been proposed to regulate the hepatic acute phase reaction were tested for their ability to modulate the expression of plasma proteins in these cells. Acute phase plasma and conditioned medium from activated monocytes influenced the production of most acute phase plasma proteins, and the regulation appears to occur at the level of functional mRNA. Purified hormones produced a significant anabolic response in only a few cases: dexamethasone was found to be effective in maintaining differentiated expression of the cells; and glucagon produced a specific inhibition of haptoglobin synthesis. When cells were treated with a combination of conditioned monocyte medium and dexamethasone, secretion of proteins was markedly reduced. The carbohydrate moieties of all plasma glycoproteins were incompletely modified, apparently as a result of decreased intracellular transport of newly synthesized plasma proteins. Although primary hepatocytes were not phenotypically stable in tissue culture, the cells nevertheless retained a broad response spectrum to exogenous signals. We propose this as a useful system to study the production of plasma proteins and thereby pinpoint the nature and activity of effectors mediating the hepatic acute phase reaction.
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PMID:Synthesis and regulation of acute phase plasma proteins in primary cultures of mouse hepatocytes. 688 23

The glycoproteinic nature of the insulin receptor was indicated using two different approaches: 1. [125I] insulin binding to soluble receptors from mouse liver was inhibited by digestion with beta-galactosidase or pretreatment with Ricinus communis I or concanavalin A. An other enzyme (neuraminidase) and lectins (wheat germ agglutinin, Dolichos biflorus) did not affect the binding reaction. These data confirmed that insulin directly interacts with the galactoglycoproteins of liver membranes. 2. The galactose oxidase-sodium boro[3H] hydride technique, previously used for labeling accessible membrane galactoglycoproteins, was again utilized to discern the components that interact with insulin. When liver membranes were equilibrated with 10-7 M insulin prior to labeling, the SDS gel radioactive profiles were specifically modified with two galactoglycoprotein of apparent molecular sizes 195 000 and 145 000, compatible with their participation in the insulin binding interaction. Membrane pretreatment with beta-galactosidase or Sophora japonica lectin reduced the labeling in most peaks, thus supporting the argument for labeling sensitivity. Preincubation of membranes with 10-7 M proinsulin slightly hindered labeling, while pretreatment with 10-7 M glucagon was ineffective, suggesting a specificity of the insulin effect. These data indicate that glycoprotein nature of the insulin receptor for two reasons: alteration of insulin binding after modification of the galactoglycoproteins, and alteration of galactoglycoprotein labeling after insulin binding. Two galactoglycoproteins, with apparent molecular weights 145 000 and 195 000, respectively, were identified and they are suggested to have insulin binding properties.
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PMID:Identification of liver cell membrane galactoglycoproteins involved in the process of insulin binding. 703 Mar 99


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