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Philip Cohen - One of the best experts on this subject based on the ideXlab platform.
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Glycogen Synthase kinase 3
Handbook of Cell Signaling, 2020Co-Authors: Philip Cohen, Sheelagh FrameAbstract:Publisher Summary The chapter provides a short summary of the structure, substrate specificity, functions, and regulation of Glycogen Synthase kinase 3 protein. Glycogen Synthase kinase 3 (GSK3) is a protein that phosphorylates and inhibits Glycogen Synthase, the enzyme that catalyzes the transfer of glucose from UDPG to Glycogen. GSK3 is a key player in two distinct signal transduction pathways: the phosphatidylinositol-3–kinase-dependent pathway that is triggered by insulin and growth factors, and the Wnt signaling pathway that is required for embryonic development. Insulin induces the activation of Glycogen Synthase, mainly by stimulating the dephosphorylation of the serine residues in Glycogen Synthase that are targeted by GSK3, and stimulates the activation of eIF2B by promoting the dephosphorylation of Ser535. GSK3 appears to play a role in the insulin-regulated transcription of the genes. Inhibitors of GSK3 may lower the levels of blood glucose in vivo by suppressing the production of glucose as well as by enhancing the conversion of glucose to Glycogen. There is considerable evidence that the inhibition of GSK3 triggered by growth factors contributes to the anti-apoptotic effects of these signals. It is a therapeutic target for the design of inhibitory drugs to treat diseases such as head trauma, stroke, epilepsy, and motor neuron disease. GSK3 plays a key role in embryonic development as a central player in the Wnt signaling pathway. It mimics the Wnt signaling pathway and stimulates the accumulation of β-catenin.
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Glycogen Synthase kinase 3 from rabbit skeletal muscle
FEBS Journal, 2005Co-Authors: Noor Embi, Dennis Brian Rylatt, Philip CohenAbstract:Publisher Summary This chapter discusses Glycogen Synthase kinase-3 from rabbit skeletal muscle. Glycogen Synthase kinase-3 is one of the five Glycogen Synthase kinases that are identified in skeletal muscle, and is of major importance in determining the kinetic properties of Glycogen Synthase in vivo. It catalyzes the phosphorylation of three serine residues on Glycogen Synthase, converting the enzyme from a form that is almost fully active in the absence of glucose-6P, to one that is largely dependent on this allosteric activator. Glycogen Synthase kinase-3 also has a second activity that is not shared by any other protein kinase—namely, the ability to activate an enzyme termed the MgATP-dependent protein phosphatase. Glycogen Synthase may also contain traces of a modified form of phosphorylase kinase that has lost its sensitivity to regulation by calcium ions, and is therefore, no longer inhibited by ethylene glycol tetraacetic acid (EGTA). This is largely removed by passing Glycogen Synthase through phosphocellulose.
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Glycogen Synthase from Rabbit Skeletal Muscle
FEBS Journal, 2005Co-Authors: Dennis Brian Rylatt, Noor Embi, Alastair Aitken, Terence Bilham, Gerard D. Condon, Philip CohenAbstract:Glycogen Synthase has been shown to be phosphorylated in vitro by five protein kinases, cyclic-AMP-dependent protein kinase (sites la, 1b and 2). phosphorylase kinase (site 2), Glycogen Synthase kinase 3 (sites 3a,3b and 3c), Glycogen Synthase kinase 4 (site 2) and Glycogen Synthase kinase 5 (site 5) [Cohen,P. et al. (1982)Eur. J. Biochem. 124, 21–35; Picton, C. et al. (1982) Eur. J. Biocliem. 124, 37–45]. All seven serine residues have now been found to be phosphorylated in vivo. Glycogen Synthase purified from rabbits that had been injected with l-propranolol contained 0.33 mol of phosphate/mol subunit in site la, 0.38 in site Ib, 0.39 in site 2, 1.27 in sites 3a+3b+3c and 0.65 in site 5, totalling 3.0 mol/mol subunit. The activity ratio (∓ glucose-6 P) for these preparations was 0.21 and their Ka for glucose-6-P was 1.4mM. Glycogen Synthase purified from animals that had been injected with I-adrenaline contained 0.59 mol phosphate/mol subunit in site la, 0.65 in site lb, 1.03 in site 2, 2.43 in sites 3a + 3b + 3c and 0.65 in site 5, totalling 5.3 mol/mol subunit. The activity ratio of these preparations was 0.04 and their Ka for glucose-6-P was 6.0mM. The results show that cyclic-AMP-dependent protein kinase, Glycogen Synthase kinase 3 and Glycogen Synthase kinase 5 act as Glycogen Synthase kinases in vivo. Glycogen Synthase kinase 4 may be largely responsible for the phosphorylation of site 2 in propranolol-treated animals, and cyclic-AMP-dependent protein kinase and phos- phorylase kinase for the increased phosphorylation of site 2 in response to adrenaline. The activity of Glycogen Synthase in vivo in propranolol-treated animals is largely determined by the state of phosphorylation of sites 3a, 3b and 3c, while the inactivation in response to adrenaline is due to increased phosphorylation at site 2 as well as at sites 3a, 3b and 3c. The finding that the phosphorylation of sites 3a, 3b and 3c is increased from 1.27 mol/mol subunit to 2.43 mol/mol subunit by adrenaline was unexpected, since this enzyme is not regulated by cyclic AMP. Possible explanations for this result are discussed. Phosphofructokinase was isolated as a byproduct of the purification of Glycogen Synthase. The phosphate content of this enzyme did not differ significantly between l−propranolol-treated (0.15 mol/mol subunit) and adrenaline-treated (0.18 mol/mol subunit) animals. These results indicate that muscle phosphofructokinase is not a substrate for cyclic-AMP-dependent protein kinase in vivo.
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Phosphorylation of the type-II regulatory subunit of cyclic-AMP-dependent protein kinase by Glycogen Synthase kinase 3 and Glycogen Synthase kinase 5.
FEBS Journal, 2005Co-Authors: Brian A. Hemmings, Philip Cohen, Alastair Aitken, Michael Rymond, Franz HofmannAbstract:The regulatory (RII) subunit of type-II cyclic-AMP-dependent protein kinase from bovine heart is phosphorylated at a significant rate in vitro by Glycogen Synthase kinase 3 and Glycogen Synthase 5, but not by Glycogen Synthase kinase 4 or phosphorylase kinase. The regulatory (RI) subunit of type-I cyclic-AMP-dependent protein kinase from rabbit skeletal muscle is not phosphorylated by any of these four protein kinases. Glycogen Synthase kinase 3 phosphorylates two serine residues on the RII subunit located 44 and 47 amino acids from the N terminus of the polypeptide chain. Glycogen Synthase kinase 5 phosphorylates serine-74 and serine-76. These sites are distinct from the residue phosphorylated by the catalytic subunit of cyclic-AMP-dependent protein kinase (serine-95). The RII subunit, as normally isolated, contains 1.5–1.8 mol alkali-labile phosphate per subunit. At least 80% of this phosphate (∼ 1.3 mol/subunit) is located in the thermolytic peptide containing serine-74 and serine-76, demonstrating that phosphorylation of the RII subunit by Glycogen Synthase kinase 5 occurs in vivo. Only small amounts of phosphate (∼ 0.1 mol/subunit) are associated with the thermolytic peptides containing serine-44/serine-47 and serine-95. The phosphorylation sites on the RII subunit are organised in a strikingly similar manner to those of Glycogen Synthase, the amino acid sequences in the immediate vicinity of the phosphorylation sites showing a particular resemblance. These include the presence of a number of proline residues near the sites phosphorylated by Glycogen Synthase kinase 3, five consecutive acidic residues C-terminal to the sites phosphorylated by Glycogen Synthase kinase 5, and two adjacent arginine residues just N-terminal to the sites phosphorylated by the catalytic subunit of cyclic-AMP-dependent protein kinase. Glycogen Synthase kinase 5 is very similar or identical to the enzyme that has been variously termed casein kinase TS, casein kinase 2, casein kinase G, casein kinase N-II or troponin-T kinase. The biological role of this enzyme is reviewed.
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insulin activates protein kinase b inhibits Glycogen Synthase kinase 3 and activates Glycogen Synthase by rapamycin insensitive pathways in skeletal muscle and adipose tissue
FEBS Letters, 1997Co-Authors: Darren Cross, Peter W Watt, Morag Shaw, Jeroen Van Der Kaay, Peter C Downes, Julie C Holder, Philip CohenAbstract:Insulin stimulated protein kinase Bα (PKBα) more than 10-fold and decreased Glycogen Synthase kinase-3 (GSK3) activity by 50±10% in skeletal muscle and adipocytes. Rapamycin did not prevent the activation of PKB, inhibition of GSK3 or stimulation of Glycogen Synthase up to 5 min. Thus rapamycin-insensitive pathways mediate the acute effect of insulin on Glycogen Synthase in the major insulin-responsive tissues. The small and very transient effects of EGF on phosphatidylinositol (3,4,5)P3 PKBα and GSK3 in adipocytes, compared to the strong and sustained effects of insulin, explains why EGF does not stimulate glucose uptake or Glycogen synthesis in adipocytes
Noor Embi - One of the best experts on this subject based on the ideXlab platform.
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Glycogen Synthase kinase 3 from rabbit skeletal muscle
FEBS Journal, 2005Co-Authors: Noor Embi, Dennis Brian Rylatt, Philip CohenAbstract:Publisher Summary This chapter discusses Glycogen Synthase kinase-3 from rabbit skeletal muscle. Glycogen Synthase kinase-3 is one of the five Glycogen Synthase kinases that are identified in skeletal muscle, and is of major importance in determining the kinetic properties of Glycogen Synthase in vivo. It catalyzes the phosphorylation of three serine residues on Glycogen Synthase, converting the enzyme from a form that is almost fully active in the absence of glucose-6P, to one that is largely dependent on this allosteric activator. Glycogen Synthase kinase-3 also has a second activity that is not shared by any other protein kinase—namely, the ability to activate an enzyme termed the MgATP-dependent protein phosphatase. Glycogen Synthase may also contain traces of a modified form of phosphorylase kinase that has lost its sensitivity to regulation by calcium ions, and is therefore, no longer inhibited by ethylene glycol tetraacetic acid (EGTA). This is largely removed by passing Glycogen Synthase through phosphocellulose.
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Glycogen Synthase from Rabbit Skeletal Muscle
FEBS Journal, 2005Co-Authors: Dennis Brian Rylatt, Noor Embi, Alastair Aitken, Terence Bilham, Gerard D. Condon, Philip CohenAbstract:Glycogen Synthase has been shown to be phosphorylated in vitro by five protein kinases, cyclic-AMP-dependent protein kinase (sites la, 1b and 2). phosphorylase kinase (site 2), Glycogen Synthase kinase 3 (sites 3a,3b and 3c), Glycogen Synthase kinase 4 (site 2) and Glycogen Synthase kinase 5 (site 5) [Cohen,P. et al. (1982)Eur. J. Biochem. 124, 21–35; Picton, C. et al. (1982) Eur. J. Biocliem. 124, 37–45]. All seven serine residues have now been found to be phosphorylated in vivo. Glycogen Synthase purified from rabbits that had been injected with l-propranolol contained 0.33 mol of phosphate/mol subunit in site la, 0.38 in site Ib, 0.39 in site 2, 1.27 in sites 3a+3b+3c and 0.65 in site 5, totalling 3.0 mol/mol subunit. The activity ratio (∓ glucose-6 P) for these preparations was 0.21 and their Ka for glucose-6-P was 1.4mM. Glycogen Synthase purified from animals that had been injected with I-adrenaline contained 0.59 mol phosphate/mol subunit in site la, 0.65 in site lb, 1.03 in site 2, 2.43 in sites 3a + 3b + 3c and 0.65 in site 5, totalling 5.3 mol/mol subunit. The activity ratio of these preparations was 0.04 and their Ka for glucose-6-P was 6.0mM. The results show that cyclic-AMP-dependent protein kinase, Glycogen Synthase kinase 3 and Glycogen Synthase kinase 5 act as Glycogen Synthase kinases in vivo. Glycogen Synthase kinase 4 may be largely responsible for the phosphorylation of site 2 in propranolol-treated animals, and cyclic-AMP-dependent protein kinase and phos- phorylase kinase for the increased phosphorylation of site 2 in response to adrenaline. The activity of Glycogen Synthase in vivo in propranolol-treated animals is largely determined by the state of phosphorylation of sites 3a, 3b and 3c, while the inactivation in response to adrenaline is due to increased phosphorylation at site 2 as well as at sites 3a, 3b and 3c. The finding that the phosphorylation of sites 3a, 3b and 3c is increased from 1.27 mol/mol subunit to 2.43 mol/mol subunit by adrenaline was unexpected, since this enzyme is not regulated by cyclic AMP. Possible explanations for this result are discussed. Phosphofructokinase was isolated as a byproduct of the purification of Glycogen Synthase. The phosphate content of this enzyme did not differ significantly between l−propranolol-treated (0.15 mol/mol subunit) and adrenaline-treated (0.18 mol/mol subunit) animals. These results indicate that muscle phosphofructokinase is not a substrate for cyclic-AMP-dependent protein kinase in vivo.
Dennis Brian Rylatt - One of the best experts on this subject based on the ideXlab platform.
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Glycogen Synthase kinase 3 from rabbit skeletal muscle
FEBS Journal, 2005Co-Authors: Noor Embi, Dennis Brian Rylatt, Philip CohenAbstract:Publisher Summary This chapter discusses Glycogen Synthase kinase-3 from rabbit skeletal muscle. Glycogen Synthase kinase-3 is one of the five Glycogen Synthase kinases that are identified in skeletal muscle, and is of major importance in determining the kinetic properties of Glycogen Synthase in vivo. It catalyzes the phosphorylation of three serine residues on Glycogen Synthase, converting the enzyme from a form that is almost fully active in the absence of glucose-6P, to one that is largely dependent on this allosteric activator. Glycogen Synthase kinase-3 also has a second activity that is not shared by any other protein kinase—namely, the ability to activate an enzyme termed the MgATP-dependent protein phosphatase. Glycogen Synthase may also contain traces of a modified form of phosphorylase kinase that has lost its sensitivity to regulation by calcium ions, and is therefore, no longer inhibited by ethylene glycol tetraacetic acid (EGTA). This is largely removed by passing Glycogen Synthase through phosphocellulose.
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Glycogen Synthase from Rabbit Skeletal Muscle
FEBS Journal, 2005Co-Authors: Dennis Brian Rylatt, Noor Embi, Alastair Aitken, Terence Bilham, Gerard D. Condon, Philip CohenAbstract:Glycogen Synthase has been shown to be phosphorylated in vitro by five protein kinases, cyclic-AMP-dependent protein kinase (sites la, 1b and 2). phosphorylase kinase (site 2), Glycogen Synthase kinase 3 (sites 3a,3b and 3c), Glycogen Synthase kinase 4 (site 2) and Glycogen Synthase kinase 5 (site 5) [Cohen,P. et al. (1982)Eur. J. Biochem. 124, 21–35; Picton, C. et al. (1982) Eur. J. Biocliem. 124, 37–45]. All seven serine residues have now been found to be phosphorylated in vivo. Glycogen Synthase purified from rabbits that had been injected with l-propranolol contained 0.33 mol of phosphate/mol subunit in site la, 0.38 in site Ib, 0.39 in site 2, 1.27 in sites 3a+3b+3c and 0.65 in site 5, totalling 3.0 mol/mol subunit. The activity ratio (∓ glucose-6 P) for these preparations was 0.21 and their Ka for glucose-6-P was 1.4mM. Glycogen Synthase purified from animals that had been injected with I-adrenaline contained 0.59 mol phosphate/mol subunit in site la, 0.65 in site lb, 1.03 in site 2, 2.43 in sites 3a + 3b + 3c and 0.65 in site 5, totalling 5.3 mol/mol subunit. The activity ratio of these preparations was 0.04 and their Ka for glucose-6-P was 6.0mM. The results show that cyclic-AMP-dependent protein kinase, Glycogen Synthase kinase 3 and Glycogen Synthase kinase 5 act as Glycogen Synthase kinases in vivo. Glycogen Synthase kinase 4 may be largely responsible for the phosphorylation of site 2 in propranolol-treated animals, and cyclic-AMP-dependent protein kinase and phos- phorylase kinase for the increased phosphorylation of site 2 in response to adrenaline. The activity of Glycogen Synthase in vivo in propranolol-treated animals is largely determined by the state of phosphorylation of sites 3a, 3b and 3c, while the inactivation in response to adrenaline is due to increased phosphorylation at site 2 as well as at sites 3a, 3b and 3c. The finding that the phosphorylation of sites 3a, 3b and 3c is increased from 1.27 mol/mol subunit to 2.43 mol/mol subunit by adrenaline was unexpected, since this enzyme is not regulated by cyclic AMP. Possible explanations for this result are discussed. Phosphofructokinase was isolated as a byproduct of the purification of Glycogen Synthase. The phosphate content of this enzyme did not differ significantly between l−propranolol-treated (0.15 mol/mol subunit) and adrenaline-treated (0.18 mol/mol subunit) animals. These results indicate that muscle phosphofructokinase is not a substrate for cyclic-AMP-dependent protein kinase in vivo.
Peter J Roach - One of the best experts on this subject based on the ideXlab platform.
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INTERACTION BETWEEN GlycogenIN AND Glycogen Synthase
Archives of Biochemistry and Biophysics, 2006Co-Authors: Alexander V. Skurat, Amy D. Dietrich, Peter J RoachAbstract:Glycogen Synthase plays a key role in regulating Glycogen metabolism. In a search for regulators of Glycogen Synthase, a yeast two-hybrid study was performed. Two Glycogen Synthase-interacting proteins were identified in human skeletal muscle, Glycogenin-1, and nebulin. The interaction with Glycogenin was found to be mediated by the region of Glycogenin which contains the 33 COOH-terminal amino acid residues. The regions in Glycogen Synthase containing both NH 2 - and COOH-terminal phosphorylation sites are not involved in the interaction. The core segment of Glycogen Synthase from Glu 21 to Gly 503 does not bind COOH-terminal fragment of Glycogenin. However, this region of Glycogen Synthase binds full-length Glycogenin indicating that Glycogenin contains at least one additional interacting site for Glycogen Synthase besides the COOH-terminus. We demonstrate that the COOH-terminal fragment of Glycogenin can be used as an effective high affinity reagent for the purification of Glycogen Synthase from skeletal muscle and liver.
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Control of mammalian Glycogen Synthase by PAS kinase
Proceedings of the National Academy of Sciences of the United States of America, 2005Co-Authors: Wayne A. Wilson, Peter J Roach, Alexander V. Skurat, Brandon L. Probst, Anna De Paoli-roach, Jared RutterAbstract:The regulation of Glycogen metabolism is critical for the maintenance of glucose and energy homeostasis in mammals. Glycogen Synthase, the enzyme responsible for Glycogen production, is regulated by multisite phosphorylation in yeast and mammals. We have previously identified PAS kinase as a physiological regulator of Glycogen Synthase in Saccharomyces cerevisiae. We provide evidence here that PAS kinase is an important regulator of mammalian Glycogen Synthase. Glycogen Synthase is efficiently phosphorylated by PAS kinase in vitro at Ser-640, a known regulatory phosphosite. Efficient phosphorylation requires a region of PAS kinase outside the catalytic domain. This region appears to mediate a direct interaction between Glycogen Synthase and PAS kinase, thereby targeting kinase activity to this substrate specifically. This interaction is regulated by the PAS kinase PAS domain, raising the possibility that this interaction (and phosphorylation event) is modulated by the cellular metabolic state. This mode of regulation provides a mechanism for metabolic status to impinge directly on the cellular decision of whether to store or use available energy.
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Overexpression of Glycogen Synthase in mouse muscle results in less branched Glycogen
Biochemical and Biophysical Research Communications, 2003Co-Authors: Bartholomew A. Pederson, Anna G. Csitkovits, Renee Simon, Jill M. Schroeder, Alexander V. Skurat, Wei Wang, Peter J RoachAbstract:Glycogen, a branched polymer of glucose, serves as an energy reserve in many organisms. The degree of branching likely reflects the balance between the activities of Glycogen Synthase and branching enzyme. Mice overexpressing constitutively active Glycogen Synthase in skeletal muscle (GSL30) have elevated muscle Glycogen. To test whether excess Glycogen Synthase activity affected Glycogen branching, we examined the Glycogen from skeletal muscle of GSL30 mice. The absorption spectrum of muscle Glycogen determined in the presence of iodine was shifted to higher wavelengths in the GSL30 animals, consistent with a decrease in the degree of branching. As judged by Western blotting, the levels of Glycogenin and the branching enzyme were also elevated. Branching enzyme activity also increased approximately threefold. However, this compared with an increase in Glycogen Synthase of some 50-fold, so that the increase in branching enzyme in response to overexpression of Glycogen Synthase was insufficient to synthesize normally branched Glycogen.
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Glucose-6-P control of Glycogen Synthase phosphorylation in yeast.
Journal of Biological Chemistry, 1997Co-Authors: Dongqing Huang, Wayne A. Wilson, Peter J RoachAbstract:Abstract The SNF1 gene encodes a protein kinase necessary for expression of glucose-repressible genes and for the synthesis of the storage polysaccharide Glycogen. From a genetic screen, we have found that mutation of the PFK2 gene, which encodes the β-subunit of 6-phosphofructo-1-kinase, restores Glycogen accumulation in snf1 cells. Loss of PFK2 causes elevated levels of metabolites such as glucose-6-P, hyperaccumulation of Glycogen, and activation of Glycogen Synthase, whereas glucose-6-P is reduced in snf1 cells. Other mutations that increase glucose-6-P, deletion of PFK1, which codes for the α-subunit of 6-phosphofructo-1-kinase, or of PGI1, the phosphoglucoisomerase gene, had similar effects on Glycogen metabolism as did pfk2 mutants. We propose that elevated glucose-6-P mediates the effects of these mutations on Glycogen storage. Glycogen Synthase kinase activity was reduced in extracts from pfk2cells but was restored to that of wild type if the extract was gel-filtered to remove small molecules. Also, added glucose-6-P inhibited the Glycogen Synthase kinase activity in extracts from wild-type cells, half-maximally at ∼2 mm. We suggest that glucose-6-P controls Glycogen Synthase activity by two separate mechanisms. First, glucose-6-P is a direct activator of Glycogen Synthase, and second, it controls the phosphorylation state of Glycogen Synthase by inhibiting a Glycogen Synthase kinase.
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New Insights Into the Role and Mechanism of Glycogen Synthase Activation by Insulin
Diabetes, 1997Co-Authors: John C. Lawrence, Peter J RoachAbstract:The metabolism of the storage polysaccharide Glycogen is intimately linked with insulin action and blood glucose homeostasis. Insulin activates both glucose transport and Glycogen Synthase in skeletal muscle. The central issue of a long-standing debate is which of these two effects determines the rate of Glycogen synthesis in response to insulin. Recent studies with transgenic animals indicate that, under appropriate conditions, each process can contribute to determining the extent of Glycogen accumulation. Insulin causes stable activation of Glycogen Synthase by promoting dephosphorylation of multiple sites in the enzyme. A model linking this action to the mitogen-activated protein kinase signaling pathway via the phosphorylation of the regulatory subunit of Glycogen Synthase phosphatase gained widespread acceptance. However, the most recent evidence argues strongly against this mechanism. A newer model, in which insulin inactivates the enzyme Glycogen Synthase kinase-3 via the protein kinase B pathway, has emerged. Though promising, this model still does not completely explain the molecular basis for the insulin-mediated activation of Glycogen Synthase, which remains one of the many unknowns of insulin action.
Carlos Villar-palasi - One of the best experts on this subject based on the ideXlab platform.
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Effect of glucose phosphorylation on the activation by insulin of skeletal muscle Glycogen Synthase
Biochimica et Biophysica Acta, 1995Co-Authors: Carlos Villar-palasiAbstract:Abstract The effect of insulin injection on skeletal muscle Glycogen Synthase activation was studied in anesthetized, normal, fed rats. Insulin stimulated the conversion of Glycogen Synthase to the active I form, increased the concentration of glucose 6-phosphate, and activated Glycogen Synthase phosphatase. A close correlation between glucose 6-phosphate concentrations, per cent Glycogen Synthase in the active I form, and phosphatase activity was found. When boiled extracts of muscle from control and insulin-injected animals were added to Glycogen pellets containing phosphatase 1G, the difference in phosphatase activity between muscle extracts from insulin-injected and control rats was restored, indicating that the phosphatase was activated by heat-stable factors. Deproteinized muscle extracts from control and insulin-injected rats, at concentrations equivalent to those present in muscle, were tested for the activation of Glycogen Synthase by purified protein phosphatases 1 and 2A. The activation with the insulin extracts was four-fold larger than with the control extracts. When the extracts from insulin-injected rats were treated with glucose 6-phosphatase, the difference in activation with the control rat extracts was canceled. It would appear that, as in other insulin sensitive tissues, in skeletal muscle the increase in glucose 6-phosphate subsequent to the activation of glucose transport by insulin contributes to the activation of Glycogen Synthase.
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Substrate specific activation by glucose 6-phosphate of the dephosphorylation of muscle Glycogen Synthase.
Biochimica et Biophysica Acta, 1991Co-Authors: Carlos Villar-palasiAbstract:Abstract The activation of Glycogen Synthase by insulin is in many instances stimulated by the presence of extracellular glucose. Previous observations in cell extracts, Glycogen pellets and other crude systems suggest that this stimulation may be due to an increase in glucose 6-phosphate, which activates the dephosphorylation of Glycogen Synthase by protein phosphatases. Using purified rabbit muscle Glycogen Synthase D adn protein phosphateses 1 and 2A, the types responsible for the activation of muscle Synthase, it was found that glucose 6-phosphate, at low, physiological concentrations, stimulated the dephosphorylation of Glycogen Synthase. Both types of phosphatase were stimulated to the same extent when acting on Glycogen Synthase. The dephosphorylation of other protein substrates of the phosphatases was either not affected or inhibited by glucose 6-phosphate. It appears that the stimulatory effect of glucose 6-phosphate at physiological concentrations is apparently specific for Glycogen Synthase, and most likely due to an allosteric configuration change of this enzyme which facilitates its dephosphorylation. In addition, the effects of other reported modulators of Glycogen Synthase dephosphorylation, AMP, ATP and Mg2+, were studied in this ‘in vitro’ system.
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Long-term effects of insulin on the enzyme activity and messenger RNA of Glycogen Synthase in rat hepatoma H4 cells: an effect of insulin on Glycogen Synthase mRNA stability.
Archives of Biochemistry and Biophysics, 1991Co-Authors: Masashi Okubo, Carlos Villar-palasi, Yuji Nagasaka, Joseph Larner, Andrew C. LarnerAbstract:Abstract Insulin induced Glycogen Synthase activity and decreased Glycogen Synthase mRNA concentrations in rat hepatoma H4 cells. Total enzyme activity measured with glucose 6-phosphate gradually increased during a 24-h insulin incubation. The time course of Glycogen Synthase activation measured by the activity ratio (low G-6-P/high G-6-P) in response to insulin was biphasic with the first peak at 15 min and the second peak at 4 to 6 h. When cells were incubated with insulin and cycloheximide, the first peak persisted while the second peak was abolished. These data suggest that the first activation peak derives from the classic effect of insulin via dephosphorylation and the second peak from an insulin-induced protein synthesis of a Glycogen Synthase activator. Ribonuclease protection assays with a cloned rat liver Glycogen Synthase cDNA were used to quantitate Glycogen Synthase mRNA. Insulin unexpectedly decreased Glycogen Synthase mRNA in a time- and a dose-dependent manner. After incubation with the RNA synthesis inhibitor, 5,6-dichloro-1-β- d -ribofuranosyl benzimidazole (DRB) without and with insulin, the half time of Glycogen Synthase mRNA decreased from 6.0 ± 0.80 to 3.9 ± 0.75 h, respectively. Nuclear run-off experiments with isolated nuclei showed no change of transcription of Glycogen Synthase mRNA. These data suggest that insulin in this system affects Glycogen Synthase mRNA stability rather than transcription.