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Ferreira M, Beullens M, Bollen M, Van Eynde A. Functions and therapeutic potential of protein phosphatase 1: Insights from mouse genetics. BIOCHIMICA ET BIOPHYSICA ACTA. MOLECULAR CELL RESEARCH 2019; 1866:16-30. [PMID: 30056088 PMCID: PMC7114192 DOI: 10.1016/j.bbamcr.2018.07.019] [Citation(s) in RCA: 23] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 06/08/2018] [Revised: 07/16/2018] [Accepted: 07/19/2018] [Indexed: 02/07/2023]
Abstract
Protein phosphatase 1 (PP1) catalyzes more than half of all phosphoserine/threonine dephosphorylation reactions in mammalian cells. In vivo PP1 does not exist as a free catalytic subunit but is always associated with at least one regulatory PP1-interacting protein (PIP) to generate a large set of distinct holoenzymes. Each PP1 complex controls the dephosphorylation of only a small subset of PP1 substrates. We screened the literature for genetically engineered mouse models and identified models for all PP1 isoforms and 104 PIPs. PP1 itself and at least 49 PIPs were connected to human disease-associated phenotypes. Additionally, phenotypes related to 17 PIPs were clearly linked to altered PP1 function, while such information was lacking for 32 other PIPs. We propose structural reverse genetics, which combines structural characterization of proteins with mouse genetics, to identify new PP1-related therapeutic targets. The available mouse models confirm the pleiotropic action of PP1 in health and diseases.
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Affiliation(s)
- Mónica Ferreira
- Laboratory of Biosignaling & Therapeutics, KU Leuven Department of Cellular and Molecular Medicine, University of Leuven, B-3000 Leuven, Belgium
| | - Monique Beullens
- Laboratory of Biosignaling & Therapeutics, KU Leuven Department of Cellular and Molecular Medicine, University of Leuven, B-3000 Leuven, Belgium
| | - Mathieu Bollen
- Laboratory of Biosignaling & Therapeutics, KU Leuven Department of Cellular and Molecular Medicine, University of Leuven, B-3000 Leuven, Belgium
| | - Aleyde Van Eynde
- Laboratory of Biosignaling & Therapeutics, KU Leuven Department of Cellular and Molecular Medicine, University of Leuven, B-3000 Leuven, Belgium.
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2
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Li R, Zhu LN, Ren LQ, Weng JY, Sun JS. Molecular cloning and characterization of glycogen synthase in Eriocheir sinensis. Comp Biochem Physiol B Biochem Mol Biol 2017; 214:47-56. [DOI: 10.1016/j.cbpb.2017.09.004] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/30/2017] [Revised: 08/27/2017] [Accepted: 09/19/2017] [Indexed: 01/26/2023]
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3
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Loughlin WA, Jenkins ID, Karis ND, Schweiker SS, Healy PC. 2-Oxo-1,2-dihydropyridinyl-3-yl amide-based GPa inhibitors: Design, synthesis and structure-activity relationship study. Eur J Med Chem 2016; 111:1-14. [DOI: 10.1016/j.ejmech.2016.01.031] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/08/2015] [Revised: 01/18/2016] [Accepted: 01/18/2016] [Indexed: 02/08/2023]
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4
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Role of glycogen phosphorylase in liver glycogen metabolism. Mol Aspects Med 2015; 46:34-45. [PMID: 26519772 DOI: 10.1016/j.mam.2015.09.002] [Citation(s) in RCA: 94] [Impact Index Per Article: 10.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/10/2015] [Accepted: 09/11/2015] [Indexed: 02/05/2023]
Abstract
Liver glycogen is synthesized after a meal in response to an increase in blood glucose concentration in the portal vein and endocrine and neuroendocrine signals, and is degraded to glucose between meals to maintain blood glucose homeostasis. Glycogen degradation and synthesis during the diurnal cycle are mediated by changes in the activities of phosphorylase and glycogen synthase. Phosphorylase is regulated by phosphorylation of serine-14. Only the phosphorylated form of liver phosphorylase (GPa) is catalytically active. Interconversion between GPa and GPb (unphosphorylated) is dependent on the activities of phosphorylase kinase and of phosphorylase phosphatase. The latter comprises protein phosphatase-1 in conjunction with a glycogen-targeting protein (G-subunit) of the PPP1R3 family. At least two of six G-subunits (GL and PTG) expressed in liver are involved in GPa dephosphorylation. GPa to GPb interconversion is dependent on the conformational state of phosphorylase which can be relaxed (R) or tense (T) depending on the concentrations of allosteric effectors such as glucose, glucose 6-phosphate and adenine nucleotides and on the acetylation state of lysine residues. The G-subunit, GL, encoded by PPP1R3B gene is expressed at high levels in liver and can function as a phosphorylase phosphatase and a synthase phosphatase and has an allosteric binding site for GPa at the C-terminus which inhibits synthase phosphatase activity. GPa to GPb conversion is a major upstream event in the regulation of glycogen synthesis by glucose, its downstream metabolites and extracellular signals such as insulin and neurotransmitters.
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5
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Juhász L, Varga G, Sztankovics A, Béke F, Docsa T, Kiss-Szikszai A, Gergely P, Kóňa J, Tvaroška I, Somsák L. Structure-Activity Relationships of Glycogen Phosphorylase Inhibitor FR258900 and Its Analogues: A Combined Synthetic, Enzyme Kinetics, and Computational Study. Chempluschem 2014. [DOI: 10.1002/cplu.201402181] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
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6
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Schweiker SS, Loughlin WA, Lohning AS, Petersson MJ, Jenkins ID. Synthesis, screening and docking of small heterocycles as Glycogen Phosphorylase inhibitors. Eur J Med Chem 2014; 84:584-94. [DOI: 10.1016/j.ejmech.2014.07.063] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/17/2013] [Revised: 07/17/2014] [Accepted: 07/19/2014] [Indexed: 10/25/2022]
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7
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von Wilamowitz-Moellendorff A, Hunter RW, García-Rocha M, Kang L, López-Soldado I, Lantier L, Patel K, Peggie MW, Martínez-Pons C, Voss M, Calbó J, Cohen PT, Wasserman DH, Guinovart JJ, Sakamoto K. Glucose-6-phosphate-mediated activation of liver glycogen synthase plays a key role in hepatic glycogen synthesis. Diabetes 2013; 62:4070-82. [PMID: 23990365 PMCID: PMC3837029 DOI: 10.2337/db13-0880] [Citation(s) in RCA: 67] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/04/2013] [Accepted: 08/27/2013] [Indexed: 12/13/2022]
Abstract
The liver responds to an increase in blood glucose levels in the postprandial state by uptake of glucose and conversion to glycogen. Liver glycogen synthase (GYS2), a key enzyme in glycogen synthesis, is controlled by a complex interplay between the allosteric activator glucose-6-phosphate (G6P) and reversible phosphorylation through glycogen synthase kinase-3 and the glycogen-associated form of protein phosphatase 1. Here, we initially performed mutagenesis analysis and identified a key residue (Arg(582)) required for activation of GYS2 by G6P. We then used GYS2 Arg(582)Ala knockin (+/R582A) mice in which G6P-mediated GYS2 activation had been profoundly impaired (60-70%), while sparing regulation through reversible phosphorylation. R582A mutant-expressing hepatocytes showed significantly reduced glycogen synthesis with glucose and insulin or glucokinase activator, which resulted in channeling glucose/G6P toward glycolysis and lipid synthesis. GYS2(+/R582A) mice were modestly glucose intolerant and displayed significantly reduced glycogen accumulation with feeding or glucose load in vivo. These data show that G6P-mediated activation of GYS2 plays a key role in controlling glycogen synthesis and hepatic glucose-G6P flux control and thus whole-body glucose homeostasis.
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Affiliation(s)
| | - Roger W. Hunter
- Medical Research Council Protein Phosphorylation Unit, College of Life Sciences, University of Dundee, Dundee, Scotland, U.K
| | - Mar García-Rocha
- Institute for Research in Biomedicine and Department of Biochemistry and Molecular Biology, University of Barcelona, and CIBERDEM, Barcelona, Spain
| | - Li Kang
- Department of Molecular Physiology and Biophysics and Mouse Metabolic Phenotyping Center, Vanderbilt University School of Medicine, Nashville, Tennessee
| | - Iliana López-Soldado
- Institute for Research in Biomedicine and Department of Biochemistry and Molecular Biology, University of Barcelona, and CIBERDEM, Barcelona, Spain
| | - Louise Lantier
- Department of Molecular Physiology and Biophysics and Mouse Metabolic Phenotyping Center, Vanderbilt University School of Medicine, Nashville, Tennessee
| | - Kashyap Patel
- Medical Research Council Protein Phosphorylation Unit, College of Life Sciences, University of Dundee, Dundee, Scotland, U.K
| | - Mark W. Peggie
- Medical Research Council Protein Phosphorylation Unit, College of Life Sciences, University of Dundee, Dundee, Scotland, U.K
| | - Carlos Martínez-Pons
- Institute for Research in Biomedicine and Department of Biochemistry and Molecular Biology, University of Barcelona, and CIBERDEM, Barcelona, Spain
| | - Martin Voss
- Medical Research Council Protein Phosphorylation Unit, College of Life Sciences, University of Dundee, Dundee, Scotland, U.K
| | - Joaquim Calbó
- Institute for Research in Biomedicine and Department of Biochemistry and Molecular Biology, University of Barcelona, and CIBERDEM, Barcelona, Spain
| | - Patricia T.W. Cohen
- Medical Research Council Protein Phosphorylation Unit, College of Life Sciences, University of Dundee, Dundee, Scotland, U.K
| | - David H. Wasserman
- Department of Molecular Physiology and Biophysics and Mouse Metabolic Phenotyping Center, Vanderbilt University School of Medicine, Nashville, Tennessee
| | - Joan J. Guinovart
- Institute for Research in Biomedicine and Department of Biochemistry and Molecular Biology, University of Barcelona, and CIBERDEM, Barcelona, Spain
| | - Kei Sakamoto
- Medical Research Council Protein Phosphorylation Unit, College of Life Sciences, University of Dundee, Dundee, Scotland, U.K
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8
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Synthesis and evaluation of C8-substituted 4.5-spiro lactams as Glycogen Phosphorylase a inhibitors. Tetrahedron 2013. [DOI: 10.1016/j.tet.2012.12.004] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
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9
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Varga G, Docsa T, Gergely P, Juhász L, Somsák L. Synthesis of tartaric acid analogues of FR258900 and their evaluation as glycogen phosphorylase inhibitors. Bioorg Med Chem Lett 2013; 23:1789-92. [PMID: 23395662 DOI: 10.1016/j.bmcl.2013.01.042] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/04/2012] [Revised: 01/10/2013] [Accepted: 01/12/2013] [Indexed: 11/16/2022]
Abstract
Di-O-cinnamoylated, -p-coumaroylated, and -feruloylated d-, l- and meso-tartaric acids were synthesized as analogues of the natural product FR258900, a glycogen phosphorylase (GP) inhibitor with in vivo antihyperglycaemic activity. The new compounds inhibited rabbit muscle GP in the low micromolar range, and bound to the allosteric site of the enzyme. The best inhibitor was 2,3-di-O-feruloyl meso-tartaric acid and had Ki values of 2.0μM against AMP (competitive) and 3.36μM against glucose-1-phosphate (non-competitive).
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Affiliation(s)
- Gergely Varga
- Department of Organic Chemistry, Faculty of Science and Technology, University of Debrecen, PO Box 20, H-4010 Debrecen, Hungary
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10
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Abstract
Glycogen is a branched polymer of glucose that acts as a store of energy in times of nutritional sufficiency for utilization in times of need. Its metabolism has been the subject of extensive investigation and much is known about its regulation by hormones such as insulin, glucagon and adrenaline (epinephrine). There has been debate over the relative importance of allosteric compared with covalent control of the key biosynthetic enzyme, glycogen synthase, as well as the relative importance of glucose entry into cells compared with glycogen synthase regulation in determining glycogen accumulation. Significant new developments in eukaryotic glycogen metabolism over the last decade or so include: (i) three-dimensional structures of the biosynthetic enzymes glycogenin and glycogen synthase, with associated implications for mechanism and control; (ii) analyses of several genetically engineered mice with altered glycogen metabolism that shed light on the mechanism of control; (iii) greater appreciation of the spatial aspects of glycogen metabolism, including more focus on the lysosomal degradation of glycogen; and (iv) glycogen phosphorylation and advances in the study of Lafora disease, which is emerging as a glycogen storage disease.
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11
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Acetylation negatively regulates glycogen phosphorylase by recruiting protein phosphatase 1. Cell Metab 2012; 15:75-87. [PMID: 22225877 PMCID: PMC3285296 DOI: 10.1016/j.cmet.2011.12.005] [Citation(s) in RCA: 93] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/24/2011] [Revised: 07/07/2011] [Accepted: 12/09/2011] [Indexed: 11/23/2022]
Abstract
Glycogen phosphorylase (GP) catalyzes the rate-limiting step in glycogen catabolism and plays a key role in maintaining cellular and organismal glucose homeostasis. GP is the first protein whose function was discovered to be regulated by reversible protein phosphorylation, which is controlled by phosphorylase kinase (PhK) and protein phosphatase 1 (PP1). Here we report that lysine acetylation negatively regulates GP activity by both inhibiting enzyme activity directly and promoting dephosphorylation. Acetylation of GP Lys(470) enhances its interaction with the PP1 substrate-targeting subunit, G(L), and PP1, thereby promoting GP dephosphorylation and inactivation. We show that GP acetylation is stimulated by glucose and insulin and inhibited by glucagon. Our results provide molecular insights into the intricate regulation of the classical GP and a functional crosstalk between protein acetylation and phosphorylation.
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12
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Torres TP, Fujimoto Y, Donahue E, Printz RL, Houseknecht KL, Treadway JL, Shiota M. Defective glycogenesis contributes toward the inability to suppress hepatic glucose production in response to hyperglycemia and hyperinsulinemia in zucker diabetic fatty rats. Diabetes 2011; 60:2225-33. [PMID: 21771972 PMCID: PMC3161317 DOI: 10.2337/db09-1156] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
OBJECTIVE Examine whether normalizing net hepatic glycogenesis restores endogenous glucose production and hepatic glucose phosphorylation in response to diabetic levels of plasma glucose and insulin in Zucker diabetic fatty rats (ZDF). RESEARCH DESIGN AND METHODS Hepatic glucose and intermediate fluxes (µmol · kg(-1) · min(-1)) were measured with and without a glycogen phosphorylase inhibitor (GPI) using [2-(3)H]glucose, [3-(3)H]glucose, and [U-(14)C]alanine in 20 h-fasted conscious ZDF and their lean littermates (ZCL) under clamp conditions designed to maintain diabetic levels of plasma glucose and insulin. RESULTS With infusion of GPI into ZDF (ZDF-GPI+G), compared with vehicle infused ZDF (ZDF-V), high glycogen phosphorylase a activity was decreased and low synthase I activity was increased to that of ZCL. Low net glycogenesis from plasma glucose rose to 75% of ZCL levels (4 ± 1 in ZDF-V, 18 ± 1 in ZDF-GPI+G, and 24 ± 2 in ZCL) and phosphoenolpyruvate 260% (4 ± 2 in ZDF-V, 16 ± 1 in ZDF+GPI-G, and 6 ± 2 in ZCL). High endogenous glucose production was suppressed with GPI infusion but not to that of ZCL (46 ± 4 in ZDF-V, 18 ± 4 in ZDF-GPI+G, and -8 ± 3 in ZCL). This was accompanied by reduction of the higher glucose-6-phosphatase flux (75 ± 4 in ZDF-V, 41 ± 4 in ZDF-GPI+G, and 86 ± 12 in ZCL) and no change in low glucose phosphorylation or total gluconeogenesis. CONCLUSIONS In the presence of hyperglycemic-hyperinsulinemia in ZDF, reduced glycogenic flux partially contributes to a lack of suppression of hepatic glucose production by failing to redirect glucose-6-phosphate flux from production of glucose to glycogen but is not responsible for a lower rate of glucose phosphorylation.
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Affiliation(s)
- Tracy P. Torres
- Department of Molecular Physiology and Biophysics, Vanderbilt University School of Medicine, Nashville, Tennessee
| | - Yuka Fujimoto
- Department of Molecular Physiology and Biophysics, Vanderbilt University School of Medicine, Nashville, Tennessee
| | - E.P. Donahue
- Department of Molecular Physiology and Biophysics, Vanderbilt University School of Medicine, Nashville, Tennessee
| | - Richard L. Printz
- Department of Molecular Physiology and Biophysics, Vanderbilt University School of Medicine, Nashville, Tennessee
| | | | | | - Masakazu Shiota
- Department of Molecular Physiology and Biophysics, Vanderbilt University School of Medicine, Nashville, Tennessee
- Corresponding author: Masakazu Shiota,
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13
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Luo X, Zhang Y, Ruan X, Jiang X, Zhu L, Wang X, Ding Q, Liu W, Pan Y, Wang Z, Chen Y. Fasting-induced protein phosphatase 1 regulatory subunit contributes to postprandial blood glucose homeostasis via regulation of hepatic glycogenesis. Diabetes 2011; 60:1435-45. [PMID: 21471512 PMCID: PMC3292316 DOI: 10.2337/db10-1663] [Citation(s) in RCA: 49] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
OBJECTIVE Most animals experience fasting-feeding cycles throughout their lives. It is well known that the liver plays a central role in regulating glycogen metabolism. However, how hepatic glycogenesis is coordinated with the fasting-feeding cycle to control postprandial glucose homeostasis remains largely unknown. This study determines the molecular mechanism underlying the coupling of hepatic glycogenesis with the fasting-feeding cycle. RESEARCH DESIGN AND METHODS Through a series of molecular, cellular, and animal studies, we investigated how PPP1R3G, a glycogen-targeting regulatory subunit of protein phosphatase 1 (PP1), is implicated in regulating hepatic glycogenesis and glucose homeostasis in a manner tightly orchestrated with the fasting-feeding cycle. RESULTS PPP1R3G in the liver is upregulated during fasting and downregulated after feeding. PPP1R3G associates with glycogen pellet, interacts with the catalytic subunit of PP1, and regulates glycogen synthase (GS) activity. Fasting glucose level is reduced when PPP1R3G is overexpressed in the liver. Hepatic knockdown of PPP1R3G reduces postprandial elevation of GS activity, decreases postprandial accumulation of liver glycogen, and decelerates postprandial clearance of blood glucose. Other glycogen-targeting regulatory subunits of PP1, such as PPP1R3B, PPP1R3C, and PPP1R3D, are downregulated by fasting and increased by feeding in the liver. CONCLUSIONS We propose that the opposite expression pattern of PPP1R3G versus other PP1 regulatory subunits comprise an intricate regulatory machinery to control hepatic glycogenesis during the fasting-feeding cycle. Because of its unique expression pattern, PPP1R3G plays a major role to control postprandial glucose homeostasis during the fasting-feeding transition via its regulation on liver glycogenesis.
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14
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Torres TP, Sasaki N, Donahue EP, Lacy B, Printz RL, Cherrington AD, Treadway JL, Shiota M. Impact of a glycogen phosphorylase inhibitor and metformin on basal and glucagon-stimulated hepatic glucose flux in conscious dogs. J Pharmacol Exp Ther 2011; 337:610-20. [PMID: 21363927 DOI: 10.1124/jpet.110.177899] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
The effects of a glycogen phosphorylase inhibitor (GPI) and metformin (MT) on hepatic glucose fluxes (μmol · kg(-1) · min(-1)) in the presence of basal and 4-fold basal levels of plasma glucagon were investigated in 18-h fasted conscious dogs. Compared with the vehicle treatment, GPI infusion suppressed net hepatic glucose output (NHGO) completely (-3.8 ± 1.3 versus 9.9 ± 2.8) despite increased glucose 6-phosphate (G-6-P) neogenesis from gluconeogenic precursors (8.1 ± 1.1 versus 5.5 ± 1.1). MT infusion did not alter those parameters. In response to a 4-fold rise in plasma glucagon levels, in the vehicle group, plasma glucose levels were increased 2-fold, and NHGO was increased (43.9 ± 5.7 at 10 min and 22.7 ± 3.4 at steady state) without altering G-6-P neogenesis (3.7 ± 1.5 and 5.5 ± 0.5, respectively). In the GPI group, there was no increase in NHGO due to decreased glucose-6-phosphatase flux associated with reduced G-6-P concentration. A lower G-6-P concentration was the result of increased net glycogenesis without altering G-6-P neogenesis. In the MT group, the increment in NHGO (22.2 ± 4.4 at 10 min and 12.1 ± 3.6 at steady state) was approximately half of that of the vehicle group. The lesser NHGO was associated with reduced glucose-6-phosphatase flux but a rise in G-6-P concentration and only a small incorporation of plasma glucose into glycogen. In conclusion, the inhibition of glycogen phosphorylase a activity decreases basal and glucagon-induced NHGO via redirecting glucose 6-phosphate flux from glucose toward glycogen, and MT decreases glucagon-induced NHGO by inhibiting glucose-6-phosphatase flux and thereby reducing glycogen breakdown.
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Affiliation(s)
- Tracy P Torres
- Molecular Physiology and Biophysics, Vanderbilt University School of Medicine, 2215 Garland Ave., Nashville, TN 37232-0615, USA
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15
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Ros S, Zafra D, Valles-Ortega J, García-Rocha M, Forrow S, Domínguez J, Calbó J, Guinovart JJ. Hepatic overexpression of a constitutively active form of liver glycogen synthase improves glucose homeostasis. J Biol Chem 2010; 285:37170-7. [PMID: 20841354 DOI: 10.1074/jbc.m110.157396] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
In this study, we tested the efficacy of increasing liver glycogen synthase to improve blood glucose homeostasis. The overexpression of wild-type liver glycogen synthase in rats had no effect on blood glucose homeostasis in either the fed or the fasted state. In contrast, the expression of a constitutively active mutant form of the enzyme caused a significant lowering of blood glucose in the former but not the latter state. Moreover, it markedly enhanced the clearance of blood glucose when fasted rats were challenged with a glucose load. Hepatic glycogen stores in rats overexpressing the activated mutant form of liver glycogen synthase were enhanced in the fed state and in response to an oral glucose load but showed a net decline during fasting. In order to test whether these effects were maintained during long term activation of liver glycogen synthase, we generated liver-specific transgenic mice expressing the constitutively active LGS form. These mice also showed an enhanced capacity to store glycogen in the fed state and an improved glucose tolerance when challenged with a glucose load. Thus, we conclude that the activation of liver glycogen synthase improves glucose tolerance in the fed state without compromising glycogenolysis in the postabsorptive state. On the basis of these findings, we propose that the activation of liver glycogen synthase may provide a potential strategy for improvement of glucose tolerance in the postprandial state.
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Affiliation(s)
- Susana Ros
- Department of Biochemistry and Molecular Biology, Institute for Research in Biomedicine, University of Barcelona, Baldiri Reixac 10, E-08028 Barcelona, Spain
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16
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Zhang L, Liu H. Novel therapeutics based on inhibiting the interaction of glycogen phosphorylase and GL-subunit of glycogen-associated protein phosphatase 1: WO2009127723. Expert Opin Ther Pat 2010; 20:969-73. [DOI: 10.1517/13543771003781923] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
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17
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Disruption of the allosteric phosphorylase a regulation of the hepatic glycogen-targeted protein phosphatase 1 improves glucose tolerance in vivo. Cell Signal 2009; 21:1123-34. [DOI: 10.1016/j.cellsig.2009.03.001] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/15/2009] [Accepted: 03/02/2009] [Indexed: 11/17/2022]
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18
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Karis ND, Loughlin WA, Jenkins ID, Healy PC. Glycogen phosphorylase inhibitory effects of 2-oxo-1,2-dihydropyridin-3-yl amide derivatives. Bioorg Med Chem 2009; 17:4724-33. [DOI: 10.1016/j.bmc.2009.04.049] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/31/2009] [Revised: 04/22/2009] [Accepted: 04/23/2009] [Indexed: 10/20/2022]
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19
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Schweiker SS, Loughlin WA, Brown CL, Pierens GK. Synthesis of new modified truncated peptides and inhibition of glycogen phosphorylase. J Pept Sci 2009; 15:442-50. [DOI: 10.1002/psc.1140] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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20
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Danos AM, Osmanovic S, Brady MJ. Differential regulation of glycogenolysis by mutant protein phosphatase-1 glycogen-targeting subunits. J Biol Chem 2009; 284:19544-53. [PMID: 19487702 DOI: 10.1074/jbc.m109.015073] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
PTG and G(L) are hepatic protein phosphatase-1 (PP1) glycogen-targeting subunits, which direct PP1 activity against glycogen synthase (GS) and/or phosphorylase (GP). The C-terminal 16 amino residues of G(L) comprise a high affinity binding site for GP that regulates bound PP1 activity against GS. In this study, a truncated G(L) construct lacking the GP-binding site (G(L)tr) and a chimeric PTG molecule containing the C-terminal site (PTG-G(L)) were generated. As expected, GP binding to glutathione S-transferase (GST)-G(L)tr was reduced, whereas GP binding to GST-PTG-G(L) was increased 2- to 3-fold versus GST-PTG. In contrast, PP1 binding to all proteins was equivalent. Primary mouse hepatocytes were infected with adenoviral constructs for each subunit, and their effects on glycogen metabolism were investigated. G(L)tr expression was more effective at promoting GP inactivation, GS activation, and glycogen accumulation than G(L). Removal of the regulatory GP-binding site from G(L)tr completely blocked the inactivation of GS seen in G(L)-expressing cells following a drop in extracellular glucose. As a result, G(L)tr expression prevented glycogen mobilization under 5 mm glucose conditions. In contrast, equivalent overexpression of PTG or PTG-G(L) caused a similar increase in glycogen-targeted PP1 levels and GS dephosphorylation. Surprisingly, GP dephosphorylation was significantly reduced in PTG-G(L)-overexpressing cells. As a result, PTG-G(L) expression permitted glycogenolysis under 5 mm glucose conditions that was prevented in PTG-expressing cells. Thus, expression of constructs that contained the high affinity GP-binding site (G(L) and PTG-G(L)) displayed reduced glycogen accumulation and enhanced glycogenolysis compared with their respective controls, albeit via different mechanisms.
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Affiliation(s)
- Arpad M Danos
- Department of Medicine, Section of Endocrinology, Diabetes and Metabolism, University of Chicago, Chicago, Illinois 60637, USA
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21
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MacAulay K, Woodgett JR. Targeting glycogen synthase kinase-3 (GSK-3) in the treatment of Type 2 diabetes. Expert Opin Ther Targets 2008; 12:1265-74. [PMID: 18781825 DOI: 10.1517/14728222.12.10.1265] [Citation(s) in RCA: 84] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
Abstract
BACKGROUND In spite of its rather specific name, glycogen synthase kinase-3 (GSK-3) is an eclectic cellular regulator that modulates an array of processes from nuclear transcription, to neurological functions and metabolism. The enzyme is also a focal point for diverse signaling pathways that act to suppress its activity. OBJECTIVES To review recent evidence supporting the important role GSK-3 plays in glucose homeostasis and discuss the therapeutic potential of inhibiting this enzyme in the treatment of diabetes and insulin resistance. RESULTS/CONCLUSION Despite its pleiotropic nature, GSK-3 has significant promise as a target for diabetes due to functional partitioning of the enzyme, tissue-selectivity and acute dosage-dependency of effects of inhibition, suggesting useful therapeutic windows.
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Affiliation(s)
- Katrina MacAulay
- Samuel Lunenfeld Research Institute, Mount Sinai Hospital, Toronto, Ontario M5G 1X5, Canada
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22
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Bjelić S, Jelesarov I. A survey of the year 2007 literature on applications of isothermal titration calorimetry. J Mol Recognit 2008; 21:289-312. [PMID: 18729242 DOI: 10.1002/jmr.909] [Citation(s) in RCA: 56] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
Elucidation of the energetic principles of binding affinity and specificity is a central task in many branches of current sciences: biology, medicine, pharmacology, chemistry, material sciences, etc. In biomedical research, integral approaches combining structural information with in-solution biophysical data have proved to be a powerful way toward understanding the physical basis of vital cellular phenomena. Isothermal titration calorimetry (ITC) is a valuable experimental tool facilitating quantification of the thermodynamic parameters that characterize recognition processes involving biomacromolecules. The method provides access to all relevant thermodynamic information by performing a few experiments. In particular, ITC experiments allow to by-pass tedious and (rarely precise) procedures aimed at determining the changes in enthalpy and entropy upon binding by van't Hoff analysis. Notwithstanding limitations, ITC has now the reputation of being the "gold standard" and ITC data are widely used to validate theoretical predictions of thermodynamic parameters, as well as to benchmark the results of novel binding assays. In this paper, we discuss several publications from 2007 reporting ITC results. The focus is on applications in biologically oriented fields. We do not intend a comprehensive coverage of all newly accumulated information. Rather, we emphasize work which has captured our attention with originality and far-reaching analysis, or else has provided ideas for expanding the potential of the method.
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Affiliation(s)
- Sasa Bjelić
- Biochemisches Institut der Universität Zürich, Winterthurerstrasse 190, Zürich, Switzerland
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23
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Abstract
Conversion of glucose into glycogen is a major pathway that contributes to the removal of glucose from the portal vein by the liver in the postprandial state. It is regulated in part by the increase in blood-glucose concentration in the portal vein, which activates glucokinase, the first enzyme in the pathway, causing an increase in the concentration of glucose 6-P (glucose 6-phosphate), which modulates the phosphorylation state of downstream enzymes by acting synergistically with other allosteric effectors. Glucokinase is regulated by a hierarchy of transcriptional and post-transcriptional mechanisms that are only partially understood. In the fasted state, glucokinase is in part sequestered in the nucleus in an inactive state, complexed to a specific regulatory protein, GKRP (glucokinase regulatory protein). This reserve pool is rapidly mobilized to the cytoplasm in the postprandial state in response to an elevated concentration of glucose. The translocation of glucokinase between the nucleus and cytoplasm is modulated by various metabolic and hormonal conditions. The elevated glucose 6-P concentration, consequent to glucokinase activation, has a synergistic effect with glucose in promoting dephosphorylation (inactivation) of glycogen phosphorylase and inducing dephosphorylation (activation) of glycogen synthase. The latter involves both a direct ligand-induced conformational change and depletion of the phosphorylated form of glycogen phosphorylase, which is a potent allosteric inhibitor of glycogen synthase phosphatase activity associated with the glycogen-targeting protein, GL [hepatic glycogen-targeting subunit of PP-1 (protein phosphatase-1) encoded by PPP1R3B]. Defects in both the activation of glucokinase and in the dephosphorylation of glycogen phosphorylase are potential contributing factors to the dysregulation of hepatic glucose metabolism in Type 2 diabetes.
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Inhibition of the interaction between protein phosphatase 1 glycogen-targeting subunit and glycogen phosphorylase increases glycogen synthesis in primary rat hepatocytes. Biochem J 2008; 412:359-66. [DOI: 10.1042/bj20071483] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/23/2023]
Abstract
In Type 2 diabetes, increased glycogenolysis contributes to the hyperglycaemic state, therefore the inhibition of GP (glycogen phosphorylase), a key glycogenolytic enzyme, is one of the possibilities to lower plasma glucose levels. Following this strategy, a number of GPis (GP inhibitors) have been described. However, certain critical issues are associated with their mode of action, e.g. an impairment of muscle function. The interaction between GP and the liver glycogen targeting subunit (termed GL) of PP1 (protein phosphatase 1) has emerged as a new potential anti-diabetic target, as the disruption of this interaction should increase glycogen synthesis, potentially providing an alternative approach to counteract the enhanced glycogenolysis without inhibiting GP activity. We identified an inhibitor of the GL–GP interaction (termed GL–GPi) and characterized its mechanism of action in comparison with direct GPis. In primary rat hepatocytes, at elevated glucose levels, the GL–GPi increased glycogen synthesis similarly to direct GPis. Direct GPis significantly reduced the cellular GP activity, caused a dephosphorylation of the enzyme and decreased the amounts of GP in the glycogen-enriched fraction; the GL–GPi did not influence any of these parameters. Both mechanisms increased glycogen accumulation at elevated glucose levels. However, at low glucose levels, only direct GPis led to increased glycogen amounts, whereas the GL–GPi allowed the mobilization of glycogen because it did not block the activity of GP. Due to this characteristic, GL–GPi in comparison with GPis could offer an advantageous risk/benefit profile circumventing the potential downsides of a complete prevention of glycogen breakdown while retaining glucose- lowering efficacy, suggesting that inhibition of the GL–GP interaction may provide an attractive novel approach for rebalancing the disturbed glycogen metabolism in diabetic patients.
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25
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Pautsch A, Stadler N, Wissdorf O, Langkopf E, Moreth W, Streicher R. Molecular recognition of the protein phosphatase 1 glycogen targeting subunit by glycogen phosphorylase. J Biol Chem 2008; 283:8913-8. [PMID: 18198182 DOI: 10.1074/jbc.m706612200] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Disrupting the interaction between glycogen phosphorylase and the glycogen targeting subunit (G(L)) of protein phosphatase 1 is emerging as a novel target for the treatment of type 2 diabetes. To elucidate the molecular basis of binding, we have determined the crystal structure of liver phosphorylase bound to a G(L)-derived peptide. The structure reveals the C terminus of G(L) binding in a hydrophobically collapsed conformation to the allosteric regulator-binding site at the phosphorylase dimer interface. G(L) mimics interactions that are otherwise employed by the activator AMP. Functional studies show that G(L) binds tighter than AMP and confirm that the C-terminal Tyr-Tyr motif is the major determinant for G(L) binding potency. Our study validates the G(L)-phosphorylase interface as a novel target for small molecule interaction.
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Affiliation(s)
- Alexander Pautsch
- Department of Lead Discovery, Boehringer Ingelheim GmbH & Co. KG, Birkendorferstrasse 65, Biberach, Germany.
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