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)

AMPK (AMP-activated protein kinase) is activated allosterically by AMP and by phosphorylation of Thr172 within the catalytic alpha subunit. Here we show that mutations in the regulatory gamma subunit reduce allosteric activation of the kinase by AMP. In addition to its allosteric effect, AMP significantly reduces the dephosphorylation of Thr172 by PP (protein phosphatase)2Calpha. Moreover, a mutation in the gamma subunit almost completely abolishes the inhibitory effect of AMP on dephosphorylation. We were unable to detect any effect of AMP on Thr172 phosphorylation by either LKB1 or CaMKKbeta (Ca2+/calmodulin-dependent protein kinase kinase beta) using recombinant preparations of the proteins. However, using partially purified AMPK from rat liver, there was an apparent AMP-stimulation of Thr172 phosphorylation by LKB1, but this was blocked by the addition of NaF, a PP inhibitor. Western blotting of partially purified rat liver AMPK and LKB1 revealed the presence of PP2Calpha in the preparations. We suggest that previous studies reporting that AMP promotes phosphorylation of Thr172 were misinterpreted. A plausible explanation for this effect of AMP is inhibition of dephosphorylation by PP2Calpha, present in the preparations of the kinases used in the earlier studies. Taken together, our results demonstrate that AMP activates AMPK via two mechanisms: by direct allosteric activation and by protecting Thr172 from dephosphorylation. On the basis of our new findings, we propose a simple model for the regulation of AMPK in mammalian cells by LKB1 and CaMKKbeta. This model accounts for activation of AMPK by two distinct signals: a Ca2+-dependent pathway, mediated by CaMKKbeta and an AMP-dependent pathway, mediated by LKB1.
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PMID:Investigating the mechanism for AMP activation of the AMP-activated protein kinase cascade. 1714 17

The SNF1/AMPK family of protein kinases is highly conserved in eukaryotes and is required for energy homeostasis in mammals, plants, and fungi. SNF1 protein kinase was initially identified by genetic analysis in the budding yeast Saccharomyces cerevisiae. SNF1 is required primarily for the adaptation of yeast cells to glucose limitation and for growth on carbon sources that are less preferred than glucose, but is also involved in responses to other environmental stresses. SNF1 regulates transcription of a large set of genes, modifies the activity of metabolic enzymes, and controls various nutrient-responsive cellular developmental processes. Like AMPK, SNF1 protein kinase is heterotrimeric. It is phosphorylated and activated by the upstream kinases Sak1, Tos3, and Elm1 and is inactivated by the Reg1-Glc7 protein phosphatase 1. Further regulation of SNF1 is achieved through autoinhibition and through control of its subcellular localization. Here we review the current understanding of SNF1 protein kinase pathways in Saccharomyces cerevisiae and other yeasts.
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PMID:SNF1/AMPK pathways in yeast. 1798 22

Lafora progressive myoclonus epilepsy (LD) is a fatal autosomal recessive neurodegenerative disorder characterized by the presence of glycogen-like intracellular inclusions called Lafora bodies. LD is caused by mutations in two genes, EPM2A and EPM2B, encoding respectively laforin, a dual-specificity protein phosphatase, and malin, an E3 ubiquitin ligase. Previously, we and others have suggested that the interactions between laforin and PTG (a regulatory subunit of type 1 protein phosphatase) and between laforin and malin are critical in the pathogenesis of LD. Here, we show that the laforin-malin complex downregulates PTG-induced glycogen synthesis in FTO2B hepatoma cells through a mechanism involving ubiquitination and degradation of PTG. Furthermore, we demonstrate that the interaction between laforin and malin is a regulated process that is modulated by the AMP-activated protein kinase (AMPK). These findings provide further insights into the critical role of the laforin-malin complex in the control of glycogen metabolism and unravel a novel link between the energy sensor AMPK and glycogen metabolism. These data advance our understanding of the functional role of laforin and malin, which hopefully will facilitate the development of appropriate LD therapies.
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PMID:Regulation of glycogen synthesis by the laforin-malin complex is modulated by the AMP-activated protein kinase pathway. 1802 86

A prediabetic phenotype of glucose intolerance, insulin resistance and obesity was observed at approximately 12 months of age in mice homozygous for a null allele of the major skeletal muscle glycogen-targeting subunit G(M) of protein phosphatase 1 (PP1) and derived from a 129/Ola donor strain. In this study, backcrossing of these G(M)-/- mice (termed obese G(M)-/- mice) onto two different genetic backgrounds gave rise to lean, glucose-tolerant, insulin-sensitive G(M)-/- mice (termed lean G(M)-/- mice), indicating that at least one variant gene in the 129/Ola background, not present in the C57BL/6 or 129s2/sV background, is required for the development of the prediabetic phenotype of obese mice. Slightly elevated AMP-activated protein kinase alpha2 activity in the skeletal muscle of lean C57BL/6 mice was also observed to a lesser extent in the obese G(M)-/- mice. Normal or slightly raised in vivo glucose transport in lean C57BL/6 G(M)-/- mice compared with decreased glucose transport in the obese G(M)-/- mice supports the tenet that adequate transport of glucose may be a key factor in preventing the development of the prediabetic phenotype. The pH 6.8/pH 8.6 activity ratio of phosphorylase kinase was increased in lean C57BL/6 G(M)-/- mice compared with controls indicating that phosphorylase kinase is an in vivo substrate of PP1-G(M).
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PMID:Disruption of the striated muscle glycogen-targeting subunit of protein phosphatase 1: influence of the genetic background. 1823 8

Skeletal muscle fibers differ considerably in their metabolic and physiological properties. Skeletal muscle displays a high degree of metabolic flexibility, which allows the myofibers to adapt to various physiological demands by shifting energy substrate utilization. Transcriptional events play a pivotal role in the metabolic adaptations of skeletal muscle. The expression of genes essential for skeletal muscle glucose and lipid metabolism is tightly coordinated in support of a shift in substrate utilization. AMP-activated protein kinase (AMPK) and calcineurin (a calcium-regulated serine/threonine protein phosphatase) regulate skeletal muscle metabolic gene expression programs in response to changes in the energy status and levels of neuronal input, respectively. AMPK and calcineurin activate transcriptional regulators such as peroxisome proliferator-activated receptor-gamma coactivator-1alpha and myocyte enhancer factor as well as increase skeletal muscle oxidative capacity and mitochondrial gene expression. Activation of either the AMPK or calcineurin pathway can also enhance the glycogen storage capacity and insulin sensitivity in skeletal muscle. Characterization of pathways governing skeletal muscle metabolism offers insight into physiological and pharmacological strategies to prevent or ameliorate peripheral insulin resistance associated with metabolic disorders such as type 2 diabetes.
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PMID:Influence of AMP-activated protein kinase and calcineurin on metabolic networks in skeletal muscle. 1854 43

Ischemic postconditioning (IPCD) significantly reduces infarct size in healthy animals and protects the human heart. Because obesity is a major risk factor of cardiovascular diseases, the effects of IPCD were investigated in 8- to 10-wk-old leptin-deficient obese (ob/ob) mice and compared with wild-type C57BL/6J (WT) mice. All animals underwent 30 min of coronary artery occlusion followed by 24 h of reperfusion associated or not with IPCD (6 cycles of 10-s occlusion, 10-s reperfusion). Additional mice were killed at 10 min of reperfusion for Western blotting. IPCD reduced infarct size by 58% in WT mice (33+/-1% vs. 14+/-3% for control and IPCD, respectively, P<0.05) but failed to induce cardioprotection in ob/ob mice (53+/-4% vs. 56+/-5% for control and IPCD, respectively). In WT mice, IPCD significantly increased the phosphorylation of Akt (+77%), ERK1/2 (+41%), and their common target p70S6K1 (+153% at Thr389 and +57% at Thr421/Ser424). In addition, the phosphorylated AMP-activated protein kinase (AMPK)-to-total AMPK ratio was also increased by IPCD in WT mice (+64%, P<0.05). This was accompanied by decreases in phosphatase and tensin homolog deleted on chromosome 10 (PTEN), MAP kinase phosphatase (MKP)-3, and protein phosphatase (PP)2C levels. In contrast, IPCD failed to increase the phosphorylation state of all these kinases in ob/ob mice, and the level of the three phosphatases was significantly increased. Thus, although IPCD reduces myocardial infarct size in healthy animals, its cardioprotective effect vanishes with obesity. The lack of enhanced phosphorylation by IPCD of Akt, ERK1/2, p70S6K1, and AMPK might partly explain the loss of cardioprotection in this experimental model of obese mice.
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PMID:Myocardial ischemic postconditioning against ischemia-reperfusion is impaired in ob/ob mice. 1868 99

AMP-activated protein kinase (AMPK) is a heterotrimeric complex playing a crucial role in maintaining cellular energy homeostasis. Recently, homodimerization of mammalian AMPK and yeast ortholog SNF1 was shown by us and others. In SNF1, it involved specific hydrophobic residues in the kinase domain alphaG-helix. Mutation of the corresponding AMPK alpha-subunit residues (Val-219 and Phe-223) to glutamate reduced the tendency of the kinase to form higher order homo-oligomers, as was determined by the following three independent techniques in vitro: (i) small angle x-ray scattering, (ii) surface plasmon resonance spectroscopy, and (iii) two-dimensional blue native/SDS-PAGE. Recombinant protein as well as AMPK in cell lysates of primary cells revealed distinct complexes of various sizes. In particular, the assembly of very high molecular mass complexes was dependent on both the alphaG-helix-mediated hydrophobic interactions and kinase activation. In vitro and when overexpressed in double knock-out (alpha1(-/-), alpha2(-/-)) mouse embryonic fibroblast cells, activation of mutant AMPK was impaired, indicating a critical role of the alphaG-helix residues for AMPK activation via its upstream kinases. Also inactivation by protein phosphatase 2Calpha was affected in mutant AMPK. Importantly, activation of mutant AMPK by LKB1 was restored by exchanging the corresponding and conserved hydrophobic alphaG-helix residues of LKB1 (Ile-260 and Phe-264) to positively charged amino acids. These mutations functionally rescued LKB1-dependent activation of mutant AMPK in vitro and in cell culture. Our data suggest a physiological role for the hydrophobic alphaG-helix residues in homo-oligomerization of heterotrimers and cellular interactions, in particular with upstream kinases, indicating an additional level of AMPK regulation.
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PMID:Homo-oligomerization and activation of AMP-activated protein kinase are mediated by the kinase domain alphaG-helix. 1965 72

In response to energy stress (and elevated AMP), the AMP-activated protein kinase (AMPK) coordinates the restoration of energy homeostasis. We determined that AMPK is activated in a model system (desert snail Otala lactea) during a physiological state of profound metabolic rate depression (estivation) in the absence of a rise in AMP. Kinetic characterization indicated a strong increase in AMPK activity and phosphorylation in estivation, consistent with an increase in P-Ser428 LKB, an established regulator of AMPK. Accordingly, approximately 2-fold increases in AMPKalpha1 protein and activity were observed with LKB1 immunoprecipitates from estivating snails. In vitro studies determined that AMPK in crude extracts was activated in the presence of cGMP and deactivated in conditions that permitted protein phosphatase type-2A (PP2A) activity. Furthermore, AMPKalpha1 protein and activity increased in PKG immunoprecipitates from estivating tissues, suggesting a novel role for PKG in the regulation of AMPK in vivo. We evaluated several downstream targets of AMPK. Acetyl-CoA carboxylase (ACC) activity was strongly inhibited in estivation, consistent with increased P-Ser79 content, and in vitro stimulation of AMPK negated citrate's ability to stimulate ACC aggregation. Analysis of other targets revealed a strong decrease in PPARgamma-coactivator 1alpha expression in both tissues, which was related to decreased gluconeogenic protein expression in hepatic tissue, but no changes in mitochondrial biogenesis markers in muscle. We concluded that AMPK activation in O. lactea aids in facilitating the suppression of anabolic pathways, without necessarily activating ATP-generating catabolism.
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PMID:The regulation of AMPK signaling in a natural state of profound metabolic rate depression. 1975 61

The plant hormone abscisic acid (ABA) orchestrates plant adaptive responses to a variety of stresses, including drought. This signaling pathway is regulated by reversible protein phosphorylation, and genetic evidence demonstrated that several related protein phosphatases 2C (PP2Cs) are negative regulators of this pathway in Arabidopsis thaliana. Here, we developed a protein phosphatase profiling strategy to define the substrate preferences of the HAB1 PP2C implicated in ABA signaling and used these data to screen for putative substrates. Interestingly, this analysis designated the activation loop of the ABA activated kinase OST1, related to Snf1 and AMPK kinases, as a putative HAB1 substrate. We experimentally demonstrated that HAB1 dephosphorylates and deactivates OST1 in vitro. Furthermore, HAB1 and the related PP2Cs ABI1 and ABI2 interact with OST1 in vivo, and mutations in the corresponding genes strongly affect OST1 activation by ABA. Our results provide evidence that PP2Cs are directly implicated in the ABA-dependent activation of OST1 and further suggest that the activation mechanism of AMPK/Snf1-related kinases through the inhibition of regulating PP2Cs is conserved from plants to human.
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PMID:Protein phosphatases 2C regulate the activation of the Snf1-related kinase OST1 by abscisic acid in Arabidopsis. 1985 47

The AMPK-related kinases NUAK1 and NUAK2 are activated by the tumor suppressor LKB1. We found that NUAK1 interacts with several myosin phosphatases, including the myosin phosphatase targeting-1 (MYPT1)-protein phosphatase-1beta (PP1beta) complex, through conserved Gly-Ile-Leu-Lys motifs that are direct binding sites for PP1beta. Phosphorylation of Ser(445), Ser(472), and Ser(910) of MYPT1 by NUAK1 promoted the interaction of MYPT1 with 14-3-3 adaptor proteins, thereby suppressing phosphatase activity. Cell detachment induced phosphorylation of endogenous MYPT1 by NUAK1, resulting in 14-3-3 binding to MYPT1 and enhanced phosphorylation of myosin light chain-2. Inhibition of the LKB1-NUAK1 pathway impaired cell detachment. Our data indicate that NUAK1 controls cell adhesion and functions as a regulator of myosin phosphatase complexes. Thus, LKB1 can influence the phosphorylation of targets not only through the AMPK family of kinases but also by controlling phosphatase complexes.
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PMID:New roles for the LKB1-NUAK pathway in controlling myosin phosphatase complexes and cell adhesion. 2035 25


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