Glucagon stimulation of fructose 1,6-bisphosphatase phosphorylation in rat hepatocytes

Claus, Thomas H.; Schlumpf, J.; el-Maghrabi, M R; McGrane, Molly M.; Pilkis, S J

doi:10.1016/s0006-291x(81)80234-3

Cited by 31 publications

(10 citation statements)

References 20 publications

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“…A cAMP-dependent phosphorylation has been reported to inhibit 6-phosphofructo-1-kinase (47), but this enzyme is not very active in hepatocytes from fasted rats (48). On the other hand, fructose-1,6-bisphosphatase can be activated by a c-AMP-dependent phosphorylation (49). Nevertheless, such effects of cAMP-related phosphorylation on 6-phosphofructo-1-kinase or on fructose-1,6-bisphosphatase seems to have a minor functional impact (48), and it is believed that fructose 2,6-bisphosphate is the main regulator via changes in the bifunctional enzyme: 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatase (50).…”

Section: Discussionmentioning

confidence: 99%

Exogenous Mg-ATP Induces a Large Inhibition of Pyruvate Kinase in Intact Rat Hepatocytes

Ichaï¹,

El-Mir²,

Nogueira

et al. 2001

Journal of Biological Chemistry

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Mg-ATP infusion in vivo has been reported to be beneficial both to organ function and survival rate in various models of shock. Moreover, a large variety of metabolic effects has been shown to occur in several tissues due to purinergic receptor activation. In the present work we studied the effects of exogenous Mg-ATP in rat liver cells perifused with dihydroxyacetone to investigate simultaneously gluconeogenetic and glycolytic pathways. We found a significant effect on oxidative phosphorylation as characterized by a decrease in oxygen consumption rate and in the cellular ATP-to-ADP ratio associated with an increase in lactate-to-pyruvate ratio. In addition, exogenous Mg-ATP induced rapid and reversible inhibition of both gluconeogenesis and glycolysis. The main effect on gluconeogenesis was located at the level of the fructose cycle, whereas the decrease in glycolysis was due to a strong inhibition of pyruvate kinase. Although pyruvate kinase inhibition induced by exogenous Mg-ATP was allosteric when assessed in vitro after enzyme extraction, we found a large decrease in the apparent maximal velocity when kinetics were assessed in vivo in intact perifused hepatocytes. This newly described short-term regulation of pyruvate kinase occurs only in the intact cell and may open new potentials for the pharmacological regulation of pyruvate kinase in vivo.Numerous publications have emphasized the beneficial role of Mg-ATP infusion in various models of shock or severe trauma in animals. Dysfunction of heart (1), kidney (2), muscle (3), endothelial (4), and immune cells (5, 6) are all improved by this treatment, which significantly increases the survival rate. Because such a benefit was independent of hemodynamic status (4, 7), a metabolic mechanism was proposed (8). Because the liver plays a central role in the metabolic response to such severe illnesses, it may represent a major target for Mg-ATP (9, 10).It is well known that purinergic receptor activation is responsible for a large variety of metabolic effects (11-24). ATP or adenosine or several analogues of purinergic receptors have been noted to affect liver glucose metabolism: i.e. stimulation of glycogenolysis (12, 13), increase (19,25,26) or decrease (11) of gluconeogenesis, and decrease of glycolysis (25). These effects have been related to a cAMP-dependent mechanism (12), a cAMP-independent inositol 3-phosphate/calcium-mediated signaling (13,14,16,18,21,23), a phospholipase C activation (18), or a transcriptional effect (25). It must be noted, however, that if some effects are shared among the adenine nucleotide family, others appear to be specific (12,14,18), suggesting that different signaling pathways may be involved.Because the beneficial effects were observed in vivo with Mg-ATP but not with adenosine (8, 27), we investigated the metabolic effects of exogenous Mg-ATP in rat liver cells perifused with DHA.1 Besides a significant effect on oxidative phosphorylation and on gluconeogenesis, we found that Mg-ATP was responsible for a large inhibition of pyruva...

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Section: Discussionmentioning

confidence: 99%

Exogenous Mg-ATP Induces a Large Inhibition of Pyruvate Kinase in Intact Rat Hepatocytes

Ichaï¹,

El-Mir²,

Nogueira

et al. 2001

Journal of Biological Chemistry

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“…This indicates that, under our conditions, the hormone had no net effect on this part of the pathway. Glucagon affects the fructose phosphate cycle by inhibiting 6-phosphofructo-1-kinase and activating fructose-1,6-bisphosphatase (6,7). From the data at 37°C it is not possible to exclude an acute role of glucagon on this cycle, the presumed effect being more likely on fructose-1,6-bisphosphatase than on 6-phosphofructo-1-kinase, because the latter is probably inhibited in fasting conditions (42).…”

Section: Table I Effect Of Glucagon On Adenine Nucleotides In Isolatementioning

confidence: 99%

“…In addition, some effects of glucagon on the fructose phosphate cycle have been described, i.e. inhibition of 6-phosphofructo-1-kinase and activation of fructose-1,6-bisphosphatase (6,7). Apart from these indisputable effects, a stimulation of glucose-6-phosphatase, a key enzyme in glucose production, has been proposed but never proven (8 -10).…”

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confidence: 99%

Glucose 6-Phosphate Hydrolysis Is Activated by Glucagon in a Low Temperature-sensitive Manner

Ichaï

Guignot

El-Mir

et al. 2001

Journal of Biological Chemistry

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Glucagon affects liver glucose metabolism mainly by activating glycogen breakdown and by inhibiting pyruvate kinase, whereas a possible effect on glucose-6-phosphatase has also been suggested. Although such a target is of physiological importance for liver glucose production it was never proven. By using a model of liver cells, perifused with dihydroxyacetone, we show here that the acute stimulation of gluconeogenesis by glucagon (10 ؊7 M) was not related to the significant inhibition of pyruvate kinase but to a dramatic activation of the hydrolysis of glucose 6-phosphate. We failed to find an acute change in glucose-6-phosphatase activity by glucagon, but the increase in glucose 6-phosphate hydrolysis was abolished at 21°C; conversely the effect on pyruvate kinase was not affected by temperature. The activation of glucose 6-phosphate hydrolysis by glucagon was confirmed in vivo, in postabsorptive rats receiving a constant infusion of glucagon, by the combination of a 2-fold increase in hepatic glucose production and a 60% decrease in liver glucose 6-phosphate concentration. Besides the description of a novel effect of glucagon on glucose 6-phosphate hydrolysis by a temperature-sensitive mechanism, this finding could represent an important breakthrough in the understanding of type II diabetes, because glucose 6-phosphate is proposed to be a key molecule in the transcriptional effect of glucose.The metabolic effects of glucagon on liver glucose metabolism have long been described, mediated by both cAMP-and calciumdependent signalings (1-3). Besides a powerful and well documented effect on glycogen breakdown, glucagon also increases liver gluconeogenesis mainly by the allosteric inhibition of pyruvate kinase by its phosphorylation (4, 5). In addition, some effects of glucagon on the fructose phosphate cycle have been described, i.e. inhibition of 6-phosphofructo-1-kinase and activation of fructose-1,6-bisphosphatase (6, 7). Apart from these indisputable effects, a stimulation of glucose-6-phosphatase, a key enzyme in glucose production, has been proposed but never proven (8 -10). In view of a potential key role of glucose 6-phosphate as a cellular intermediate in the transcriptional effects of glucose (11,12), an effect of glucagon on glucose-6-phosphatase could be of major importance. Indeed, despite a prominent effect on liver glucose metabolism, the role of glucagon in the pathogenesis of type II diabetes is still unclear and a matter of debate (13).By studying glucose production under steady state conditions in a model of rat hepatocytes perifused with dihydroxyacetone (DHA) 1 as an exogenous source of carbohydrate, we show in the present work that despite a clear inhibitory effect of glucagon on pyruvate kinase, this effect was not responsible for the enhanced glucose production, indicating that this step is actually not controlling this pathway. Actually, the dramatic increase in the glucose production after glucagon addition was related to a substantial activation of glucose 6-phosphate hydrolysis in glucos...

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“…4) was initially surprising as this reaction has been reported to be catalyzed by cyclic-AMP-dependent protein kinase [ZX]. A recent report by Pilkis and co-workers [29] described a 60 '!,, maximum stimulation of phosphorylation of fructose-1,6-bisphosphatase in hepatocytes by glucagon. They also showed that this occurred at a high glucagon concentration and was superimposed upon a considerable basal protein phosphorylation.…”

Section: Hepatic Biosynthesis Of Fatty Acidsmentioning

confidence: 99%

Glucocorticoid Hormones Have a Permissive Role in the Phosphorylation of L‐Type Pyruvate Kinase by Glucagon

Postle¹,

Bloxham²

1982

European Journal of Biochemistry

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The incorporation of [32P]phosphate into L-type pyruvate kinase in response to glucagon was studied in hepatocytes isolated from control and adrenalectomized rats. In control cells, pyruvate kinase phosphorylation was maximally stimulated by 210 % by glucagon. Adrenalectomy reduced both the basal extent of phosphorylation and the response to glucagon to 25 % of those measured in control hepatocytes. This impaired pyruvate kinase phosphorylation was associated with altered kinetic properties of L-type pyruvate kinase. Glucagon injected in vivo (1 mg/kg) into adrenalectomized rats did not increase the substrate co-operativity of L-type pyruvate kinase. These results suggest a molecular basis for the well-recognised glucocorticoid hormone-dependence for the stimulation by glucagon of hepatic gluconeogenesis. Further effects of this defective enzyme regulation on hepatic metabolism are suggested by the observation that adrenalectomy abolished the ability of glucagon to inhibit hepatic fatty acid biosynthesis both in vivo and in isolated hepatocytes.The hepatic responses to glucagon and to glucocorticoid hormones are mediated by two different mechanisms. Glucagon modulates the catalytic activities of enzymes by rapid and reversible changes in cyclic-AMP-dependent phosphorylation [I]. Glucocorticoid hormones act over a longer time scale by changes in protein synthesis [2, 31. Nevertheless a number of interactions between the two types of hormone have long been recognised [3]. Hepatic responses to glucagon that are either diminished or abolished after adrenalectomy include the stimulations of gluconeogenesis [4], glycogenolysis [5] and ketogenesis [6]. The nature of this so-called 'permissive' interaction remains largely unclear. There is no impairment in livers from adrenalectomized animals of cyclic AMP production in response to glucagon stimulation [3,5]. Moreover, it is not certain which target enzymes for glucagon action are affected by adrenalectomy. Some evidence suggests that L-type pyruvate kinase might be one such enzyme. Inhibition of L-type pyruvate kinase by increased cyclic-AMP-dependent protein phosphorylation [7] is a well recognized requirement for the stimulation of hepatic gluconeogenesis by glucagon [8]. The defect in the gluconeogenic response to glucagon in the perfused liver of adrenalectomized rats was located between phosphoenolpyruvate and pyruvate by metabolite cross-over analysis [S]. Such a result would be consistent with a decreased inhibition of pyruvate kinase in these livers. We therefore decided to investigate more directly whether the action of glucagon on L-type pyruvate kinase was altered by adrenalectomy.The inactivation of L-type pyruvate kinase correlates not only with activation of hepatic gluconeogenesis but also with inhibition of hepatic fatty acid biosynthesis in a variety of metabolic states [9, 101. The inhibition of hepatic fatty acid biosynthesis by glucagon has been attributed to an 'antiglycolysis' effect as it was largely relieved by incubating hormone-treated hepato...

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Glucagon stimulation of fructose 1,6-bisphosphatase phosphorylation in rat hepatocytes

Cited by 31 publications

References 20 publications

Exogenous Mg-ATP Induces a Large Inhibition of Pyruvate Kinase in Intact Rat Hepatocytes

Exogenous Mg-ATP Induces a Large Inhibition of Pyruvate Kinase in Intact Rat Hepatocytes

Glucose 6-Phosphate Hydrolysis Is Activated by Glucagon in a Low Temperature-sensitive Manner

Glucocorticoid Hormones Have a Permissive Role in the Phosphorylation of L‐Type Pyruvate Kinase by Glucagon

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