Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:2.7.11.31 (AMP-activated protein kinase)
 13,065 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

AMP-activated protein kinase (AMPK) has recently been implicated in the control of preproinsulin gene expression in pancreatic islet beta-cells [da Silva Xavier, Leclerc, Salt, Doiron, Hardie, Kahn and Rutter (2000) Proc. Natl. Acad. Sci. U.S.A. 97, 4023-4028]. Using pharmacological and molecular strategies to regulate AMPK activity in rat islets and clonal MIN6 beta-cells, we show here that the effects of AMPK are exerted largely upstream of insulin release. Thus forced increases in AMPK activity achieved pharmacologically with 5-amino-4-imidazolecarboxamide riboside (AICAR), or by adenoviral overexpression of a truncated, constitutively active form of the enzyme (AMPK alpha 1.T(172)D), blocked glucose-stimulated insulin secretion. In MIN6 cells, activation of AMPK suppressed glucose metabolism, as assessed by changes in total, cytosolic or mitochondrial [ATP] and NAD(P)H, and reduced increases in intracellular [Ca(2+)] caused by either glucose or tolbutamide. By contrast, inactivation of AMPK by expression of a dominant-negative form of the enzyme mutated in the catalytic site (AMPK alpha 1.D(157)A) did not affect glucose-stimulated increases in [ATP], NAD(P)H or intracellular [Ca(2+)], but led to the unregulated release of insulin. These results indicate that inhibition of AMPK by glucose is essential for the activation of insulin secretion by the sugar, and may contribute to the transcriptional stimulation of the preproinsulin gene. Modulation of AMPK activity in the beta-cell may thus represent a novel therapeutic strategy for the treatment of type 2 diabetes mellitus.
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PMID:Role for AMP-activated protein kinase in glucose-stimulated insulin secretion and preproinsulin gene expression. 1258 7

AMP-activated protein kinase (AMPK) serves as an energy-sensing protein kinase that is activated by a variety of metabolic stresses that lower cellular energy levels. When activated, AMPK modulates a network of metabolic pathways that result in net increased substrate oxidation, generation of reduced nucleotide cofactors, and production of ATP. AMPK is activated by a high AMP:ATP ratio and phosphorylation on threonine 172 by an upstream kinase. Recent studies suggest that mechanisms that do not involve changes in adenine nucleotide levels can activate AMPK. Another sensor of the metabolic state of the cell is the NAD/NADH redox potential. To test whether the redox state might have an effect on AMPK activity, we examined the effect of beta-NAD and NADH on this enzyme. The recombinant T172D-AMPK, which was mutated to mimic the phosphorylated state, was activated by beta-NAD in a dose-dependent manner, whereas NADH inhibited its activity. We explored the effect of NADH on AMPK by systematically varying the concentrations of ATP, NADH, peptide substrate, and AMP. Based on our findings and established activation of AMPK by AMP, we proposed a model for the regulation by NADH. Key features of this model are as follows. (a) NADH has an apparent competitive behavior with respect to ATP and uncompetitive behavior with respect to AMP resulting in improved binding constant in the presence of AMP, and (b) the binding of the peptide is not significantly altered by NADH. In the absence of AMP, the binding constant of NADH becomes higher than physiologically relevant. We conclude that AMPK senses both components of cellular energy status, redox potential, and phosphorylation potential.
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PMID:Biochemical regulation of mammalian AMP-activated protein kinase activity by NAD and NADH. 1546 12

Glucose transport is stimulated in a variety of cells and tissues in response to inhibition of oxidative phosphorylation. However, the underlying mechanisms and mediating steps remain largely unknown. In the present study we first tested whether a decrease in the redox state of the cell per se and the resultant increase in generation of reactive oxygen species (ROS) lead to stimulation of glucose transport. Clone 9 cells (expressing the Glut1 isoform of facilitative glucose transporters) were exposed to azide, lactate, and ethanol for 1 h. Although all three agents stimulated glucose transport and increased cell NADH-to-NAD(+) ratio and phospho-ERK1/2, signifying increased ROS generation, the response to the stimuli was not blocked by N-acetyl-l-cysteine (an agent that counteracts ROS); moreover, the response to azide was not blocked by diamide (an intracellular sulfhydryl oxidizing agent). We then found that cell AMP-to-ATP and ADP-to-ATP ratios were increased and 5'-AMP-activated protein kinase (AMPK) was stimulated by all three agents, as evidenced by increased phosphorylation of AMPK and acetyl-CoA carboxylase. We conclude that although azide, lactate, and ethanol increase NADH-to-NAD(+) ratios and ROS production, their stimulatory effect on glucose transport is not mediated by increased ROS generation. However, all three agents increased cell AMP-to-ATP ratio and stimulated AMPK, making it likely that the latter pathway plays an important role in the glucose transport response.
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PMID:Role of 5'-AMP-activated protein kinase in stimulation of glucose transport in response to inhibition of oxidative phosphorylation. 1616 57

Following stimulation of NMDA receptors, neurons transiently synthesize nitric oxide (NO) in a calcium/calmodulin-dependent manner through the activation of neuronal NO synthase. Nitric oxide acts as a messenger, activating soluble guanylyl cyclase and participating in the transduction signalling pathways involving cyclic GMP. Nitric oxide also binds to cytochrome c oxidase, and is able to inhibit cell respiration in a process that is reversible and in competition with oxygen. This action can also lead to the release of superoxide anion from the mitochondrial respiratory chain. Here, we discuss recent evidence that this mitochondrial interaction represents a molecular switch for cell signalling pathways involved in the control of physiological functions. These include superoxide- or oxygen-dependent modulation of gene transcription, calcium-dependent cell signalling responses, changes in the mitochondrial membrane potential or AMP-activated protein kinase-dependent control of glycolysis. In pathophysiological conditions, such as brain ischaemia or neurological disorders, NO is formed excessively by NMDA receptor over-activation in neurons, or by inducible NO synthase from neighbouring glia (microglial cells and astrocytes). Elevated NO concentrations can then interact with superoxide anion, generated by the mitochondria or by other mechanisms, leading to the formation of the powerful oxidant species peroxynitrite. During pathological conditions activation of the NAD(+)-consuming enzyme poly(APD-ribose) polymerase-1 (PARP-1) is also a likely mechanism for NO-mediated energy failure and neurotoxicity. Activation of PARP-1 is, however, a repair process, which in milder forms of oxidative stress protects neurons from death. Thus, whilst NO plays a physiological role in neuronal cell signalling, its over-production may cause neuronal energy compromise leading to neurodegeneration.
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PMID:Nitric oxide, cell bioenergetics and neurodegeneration. 1680 76

AMP-activated protein kinase (AMPK) is a heterotrimeric protein kinase that is crucial for cellular energy homeostasis of eukaryotic cells and organisms. Here we report on the activation of AMPK alpha1beta1gamma1 and alpha2beta2gamma1 by their upstream kinases (Ca(2+)/calmodulin-dependent protein kinase kinase-beta and LKB1-MO25alpha-STRADalpha), the deactivation by protein phosphatase 2Calpha, and on the extent of stimulation of AMPK by its allosteric activator AMP, using purified recombinant enzyme preparations. An accurate high pressure liquid chromatography-based method for AMPK activity measurements was established, which allowed for direct quantitation of the unphosphorylated and phosphorylated artificial peptide substrate, as well as the adenine nucleotides. Our results show a 1000-fold activation of AMPK by the combined effects of upstream kinase and saturating concentrations of AMP. The two AMPK isoforms exhibit similar specific activities (6 mumol/min/mg) and do not differ significantly by their responsiveness to AMP. Due to the inherent instability of ATP and ADP, it proved impossible to assay AMPK activity in the absolute absence of AMP. However, the half-maximal stimulatory effect of AMP is reached below 2 microm. AMP does not appear to augment phosphorylation by upstream kinases in the purified in vitro system, but deactivation by dephosphorylation of AMPK alpha-subunits at Thr-172 by protein phosphatase 2Calpha is attenuated by AMP. Furthermore, it is shown that neither purified NAD(+) nor NADH alters the activity of AMPK in a concentration range of 0-300 microm, respectively. Finally, evidence is provided that ZMP, a compound formed in 5-aminoimidazole-4-carboxamide-1-beta-D-ribofuranoside-treated cells to activate AMPK in vivo, allosterically activates purified AMPK in vitro, but compared with AMP, maximal activity is not reached. These data shed new light on physiologically important aspects of AMPK regulation.
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PMID:Dissecting the role of 5'-AMP for allosteric stimulation, activation, and deactivation of AMP-activated protein kinase. 1694 94

AMP-activated protein kinase influences cellular metabolism, glucose-regulated gene expression, and insulin secretion of pancreatic beta cells. Its sustained activation by culture at low glucose concentrations or in the presence of 5-aminoimidazole-4-carboxamide riboside (AICAR) was shown to trigger apoptosis in beta cells. This study shows that both low glucose- and AICAR-induced apoptosis are associated with increased formation of mitochondrial superoxide-derived radicals and decreased mitochondrial activity. Mitochondrial dysfunction was reflected by an increased oxidized state of the mitochondrial flavins (FMN/FAD) but not of NAD(P)H. It was accompanied by suppression of glucose oxidation and glucose-induced insulin secretion, while palmitate oxidation appeared unaffected. When the cellular accumulation of superoxide-derived radicals was quenched by the ROS scavengers vitamin E, N-acetylcysteine, or the SOD-mimetic compound MnTBAP, apoptosis was significantly inhibited. Both low glucose and AICAR also elevated the expression of BH3-domain-only Bcl-2 antagonists, and induced caspase-3 activation, causing caspase-dependent truncation of Bcl-2. Overexpression of recombinant human Bcl-2 prevented caspase-3 activation, endogenous Bcl-2 processing, and apoptosis, but did not attenuate oxygen radical formation, AMPK activation, or JNK phosphorylation. We conclude that apoptosis by prolonged AMPK activation in beta cells results from enhanced production of mitochondria-derived oxygen radicals and onset of the intrinsic mitochondrial apoptosis pathway, followed by caspase activation and Bcl-2 cleavage which may amplify the death signal.
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PMID:Increased oxygen radical formation and mitochondrial dysfunction mediate beta cell apoptosis under conditions of AMP-activated protein kinase stimulation. 1715 94

The regulation of neuroendocrine electrical activity and gene expression by glucose is mediated through several distinct metabolic pathways. Many studies have implicated AMP and ATP as key metabolites mediating neuroendocrine responses to glucose, especially through their effects on AMP-activated protein kinase (AMPK), but other studies have suggested that glycolysis, and in particular the cytoplasmic conversion of nicotinamide adenine dinucleotide (NAD+) to reduced NAD (NADH), may play a more important role than oxidative phosphorylation for some effects of glucose. To address these molecular mechanisms further, we have examined the regulation of agouti-related peptide (AgRP) in a clonal hypothalamic cell line, N-38. AgRP expression was induced monotonically as glucose concentrations decreased from 10 to 0.5 mm glucose and with increasing concentrations of glycolytic inhibitors. However, neither pyruvate nor 3-beta-hydroxybutyrate mimicked the effect of glucose to reduce AgRP mRNA, but on the contrary, produced the opposite effect of glucose and actually increased AgRP mRNA. Nevertheless, 3beta-hydroxybutyrate mimicked the effect of glucose to increase ATP and to decrease AMPK phosphorylation. Similarly, inhibition of AMPK by RNA interference increased, and activation of AMPK decreased, AgRP mRNA. Additional studies demonstrated that neither the hexosamine nor the pentose/carbohydrate response element-binding protein pathways mediate the effects of glucose on AgRP expression. These studies do not support that either ATP or AMPK mediate effects of glucose on AgRP in this hypothalamic cell line but support a role for glycolysis and, in particular, NADH. These studies support that cytoplasmic or nuclear NADH, uniquely produced by glucose metabolism, mediates effects of glucose on AgRP expression.
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PMID:Inhibition of agouti-related peptide expression by glucose in a clonal hypothalamic neuronal cell line is mediated by glycolysis, not oxidative phosphorylation. 1797 26

SIRT1, the mammalian homolog of SIR2 in Saccharomyces cerevisiae, is an NAD-dependent deacetylase implicated in regulation of lifespan. By designing effective short hairpin RNAs and a silent shRNA-resistant mutant SIRT1 in a genetically defined system, we show that efficient inhibition of SIRT1 in telomerase-immortalized human cells enhanced cell growth under normal and nutrient limiting conditions. Hematopoietic stem cells obtained from SIRT1-deficient mice also showed increased growth capacity and decreased dependency on growth factors. Consistent with this, SIRT1 inhibition was associated with increased telomerase activity in human cells. We also observed a significant increase in AMPK levels up on SIRT1 inhibition under glucose limiting conditions. Although SIRT1 suppression cooperated with hTERT to promote cell growth, either overexpression or suppression of SIRT1 alone had no effect on life span of human diploid fibroblasts. Our findings challenge certain models and connect nutrient sensing enzymes to the immortalization process. Furthermore, they show that in certain cell lineages, SIRT1 can act as a growth suppressor gene.
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PMID:SIRT1 acts as a nutrient-sensitive growth suppressor and its loss is associated with increased AMPK and telomerase activity. 1818 47

The metabolic syndrome (MetS) encompasses a constellation of cardio-metabolic abnormalities associated with a high risk of developing type 2 diabetes and cardiovascular disease (CVD), the top killer in the ageing population. Recent studies have demonstrated multiple beneficial effects of moderate wine consumption in the protection against development of the MetS and its related medical complications. The association of moderate wine consumption with lower incidence of the MetS and atherosclerotic heart disease has been repeatedly documented in numerous epidemiological studies on diverse ethnic groups. In addition to the favorable effects of moderate ethanol intake on lipid profiles, polyphenols enriched in red wine possess multiple benefits on the MetS beyond alcohol through their anti-oxidant, anti-inflammatory, vascular-protective and insulin-sensitizing properties. Notable among these red wine polypheolic compounds is resveratrol, a phytoalexin that has recently attracted great attention due to its role in mimicking calorie restriction. This compound can act as a potent activator of the NAD(+)-dependent deacetylases sirtuins to expand the life span and to prevent the deleterious effects of excess intake on insulin resistance and metabolic derangement. In addition, resveratrol exerts its multiple protective effects against the MetS through stimulating AMP-activated protein kinase and promoting mitochondria biogenesis. In this review, we highlight the recent epidemiological and experimental evidences supporting the protective effects of moderate wine intake against the MetS and its associated cardio-metabolic complications, and discuss the molecular mechanisms underlying the multiple beneficial actions of red wine polyphenols with the focus on resveratrol.
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PMID:Moderate wine consumption in the prevention of metabolic syndrome and its related medical complications. 1853 95

The ability to adapt and respond to nutrients is an ancient cellular function, conserved from unicellular to the most complex multicellular organisms, including mammals. Mammals adapt to changes in nutritional status through the modulation of tissue-specific metabolic pathways so as to maintain energy homeostasis. At least two proteins are activated in response to reduced nutrient availability: AMP-activated protein kinase (AMPK) and NAD(+)-dependent deacetylase SIRT1. AMPK functions as a sensor of cellular energy status and as a master regulator of metabolism. When ATP levels decrease, AMPK is activated to boost ATP production and to inhibit ATP usage, thus restoring energy balance. Similarly, SIRT1 is activated in response to changes in the energy status to promote transcription of genes that mediate the metabolic response to stress, starvation or calorie restriction. Several observations support a model where, in response to stress and reduced nutrients, a metabolic pathway is activated within which AMPK and SIRT1 concordantly function to ensure an appropriate cellular response and adaptation to environmental modifications. In this perspective, we compare and contrast the roles of SIRT1 and AMPK in several metabolic tissues and propose a working model of how the AMPK-SIRT1 axis may be regulated to control functions relevant to organismal physiology and pathophysiology.
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PMID:Comparing and contrasting the roles of AMPK and SIRT1 in metabolic tissues. 1902 11


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