D G Hardie

..These results identify a previously undetected variant of LKB1, and suggest that it has a crucial role in spermiogenesis and male fertility...

..Finally, recent studies reveal that AMPK conserves ATP levels through the regulation of processes other than metabolism, such as the cell cycle and neuronal membrane excitability...

..We recently showed that LKB1 exists as a complex with two accessory subunits, STRAD alpha/beta and MO25 alpha/beta...

..Our approaches distinguish at least six different mechanisms for AMPK activation and confirm that the widely used antidiabetic drug metformin activates AMPK by inhibiting mitochondrial respiration...

..Our results suggest the hypothesis that AMPK, as well as monitoring immediate energy availability by sensing AMP/ATP, may also be able to sense the status of cellular energy reserves in the form of glycogen...

..The aim of this study was to examine the state of AMPK phosphorylation histologically in primary breast cancer in relation to clinical and pathological parameters...

..This is abolished when expression of DmAMPK is ablated using an RNA interference approach, proving that DmAMPK is necessary for phosphorylation of DmACC in response to ATP depletion...

..Surprisingly, recent results indicate that the AMPK system is also important in functions that go beyond the regulation of energy homeostasis, such as the maintenance of cell polarity in epithelial cells...

..Three new papers providing structural information on mammalian and yeast AMPK homologs give insights into the binding of the regulatory nucleotides AMP and ATP and how mutations are associated with cardiac glycogen storage disorders...

..A study by Kuramoto and colleagues in this issue of Neuron favors the idea that AMPK activation is neuroprotective, and suggests a potential mechanism for this effect involving phosphorylation of the GABA(B) receptor...

..AMPK activators also now have potential as anticancer drugs...

....

....

..Recent work using a muscle-specific knockout of the upstream kinase, LKB1, has confirmed that the LKB1-->AMPK cascade is the signaling pathway responsible for many of these effects...

..AMPK inhibits the TOR (target of rapamycin) pathway by phosphorylating TSC2, thus inhibiting cell growth during times of stress. AMPK is also a target for adipokines that regulate energy balance at the whole-body level...

....

..Low levels of activation of AMPK are likely to play a role in the current global rise in obesity and Type 2 diabetes, and AMPK is the target for the widely used antidiabetic drug metformin...

..A survey of the range of downstream targets for this important signalling pathway is presented...

..However, activating mutations in AMPK can cause heart disease, and it will be important to look for adverse effects in the heart...

..2008) suggest a novel mechanism by which AMPK signals to mTOR, and they provide new insight into how information about cellular energy status is fed into decisions about cell growth and proliferation...

..Both tumor cells and viruses establish mechanisms to down-regulate AMPK, allowing them to escape its restraining influences on growth...

..We also discuss the role of the carbohydrate-binding module on the ? subunit and the mechanisms by which it is activated by drugs and xenobiotics such as metformin and resveratrol...

..Most of these agents activate AMPK because they inhibit mitochondrial function...

..AMPK/SNF1 homologues are found in higher plants, and this protein-kinase cascade appears to be an ancient system which evolved to protect cells against the effects of nutritional or environmental stress...

..However, if we can identify the various mechanisms by which this occurs, we may be able to find ways of overcoming it...

....

..A., Selbert, M. A., Goldstein, E. G., Edelman, A. M., Carling, D., and Hardie, D. G. (1995) J. Biol. Chem. 270, 27186-27191)...

..We are working on the hypothesis that this ensures that glycogen synthesis is rapidly activated when glycogen becomes depleted after exercise, but is switched off again as soon as glycogen stores are replenished...

..SNF1-related protein kinases in higher plants are likely to be involved in the response of plant cells to environmental and/or nutritional stress...

..Novel drugs activating AMPK may also have potential for the treatment of obesity...

..A novel mechanism has now been discovered, involving the AMP-activated protein kinase cascade, that can account for the Pasteur effect in ischaemic heart muscle...

..Dominant mutations in regulatory subunit isoforms (gamma2 and gamma3) of AMPK, which appear to increase the basal activity in the absence of AMP, lead to hypertrophy of cardiac and skeletal muscle respectively...

..It is a key player in the development of new treatments for obesity, type 2 diabetes, and the metabolic syndrome...

..Form B does not appear to be a proteolytic fragment of form A, and we therefore propose that it represents a closely related member of the same protein kinase sub-family...

..The function of this modification is not clear, since phosphorylation by casein kinase-2 has no direct effect on acetyl-CoA carboxylase activity...

..This system therefore represents an early eukaryotic protein kinase cascade, which is unique in that it is regulated by intracellular metabolites rather than extracellular signals or cell cycle events...

..We have also identified by amino acid sequencing the N-terminus of the catalytic fragment, which corresponds to residue 423 of the human enzyme...

..These results suggest that both the allosteric effect of AMP, and the promotion of phosphorylation and activation by the kinase kinase, are due to binding of AMP to a single site on the kinase...

..Our results do not support the idea that phosphorylation of Ser-431 increases the ability of LKB1 to phosphorylate downstream targets...

..They also open the way to experiments which could establish the physiological roles of these protein kinases in the control of fatty acid synthesis...

..Between them, these kinases may mediate the physiological effects of LKB1, including its tumour suppressor function...

..Thus, activators of AMPK could have potential as novel therapeutics both for metabolic disorders and for cancer, which together constitute two of the most prevalent groups of diseases worldwide...

..Our data strongly support a role for AMPK in the PB induction of CYP2B gene expression and provide new insights into the regulation of gene expression by barbiturate drugs...

..Although based on modelling rather than a determined structure, this represents one of the most detailed studies of the interaction between a kinase and its substrate achieved to date...

....

....

..There was a threefold increase in expression of gamma 3 after training in red quadriceps only. Our results suggest that gamma 3 might have a special role in the adaptation to endurance exercise in muscles utilizing oxidative metabolism...

..Our results suggest a potential Ca(2+)-dependent neuroprotective pathway involving phosphorylation and activation of AMPK by CaMKKbeta...

..Our results also show that AMPK can be activated by mechanisms other than changes in the cellular AMP-to-ATP ratio...

..This shows that tandem pairs of CBS domains act, in most cases, as sensors of cellular energy status and, as such, represent a newly identified class of binding domain for adenosine derivatives...

..The literature concerning AMPK, glycogen structure and glycogen-binding proteins that led us to this concept is reviewed...

..A 35 kDa polypeptide recognized by an antibody against the putative Arabidopsis beta2 subunit co-precipitates with HRK-C, but not HRK-A or D...

..These results suggest the need for caution in interpreting experiments conducted using U0126 and PD98059...

..These may be related to the abnormal glycogen storage bodies seen in heart disease patients with gamma2 mutations...

..Caution should therefore be exercised in ascribing an effect of AICA riboside to AMPK activation, especially in systems where inhibition of adenosine re-uptake has physiological consequences...

....

..Thus, although AS160 is a common target of insulin, IGF-1, EGF, PMA and AICAR, these stimuli induce distinctive patterns of phosphorylation and 14-3-3 binding, mediated by at least four protein kinases...

..Binding of AMP causes a conformational change that prevents this interaction and relieves the inhibition. We present several lines of evidence supporting this hypothesis...

..This is consistent with the effect of AMP on phosphorylation of Thr172 being due to inhibition of dephosphorylation, and confirms that the effect of AMP is independent of the upstream kinase utilized...

..Drosophila cells now represent an attractive system to study this pathway, because of the small, well-defined genome and the ability to ablate expression of specific gene products using interfering dsRNAs...

..3 +/- 0.6 to 10 +/- 0.6 mg x kg(-1) x min(-1) (P < 0.05). In healthy people, AICAR acutely stimulates muscle 2DG uptake with a minor effect on whole-body glucose disposal...

..Taken together, our findings reinforce the functional importance of the binding of LKB1 to STRAD, and provide a greater understanding of the mechanism by which LKB1 is regulated and activated through its interaction with STRAD and MO25...

..They also suggest that the effects of excercise, phenformin, and AICAR on metabolic processes in muscle may be mediated through activation of AMPK rather than activation of LKB1 or the AMPK-related kinases...

..In both cases, activation requires phosphorylation at a conserved threonine residue within the activation loop of the kinase domain, but identifying the upstream kinase(s) responsible for this has been a challenging, unsolved problem...

..These are the first studies to provide a cellular signalling mechanism for the action of phenformin on ion transport processes, and also the first studies showing AMPK as a regulator of Na+ absorption in the lung...

..It is concluded that phosphodiesterase-generated AMP may serve as a transducer of the meiotic induction process through activation of AMPK...

..Our data demonstrate that AMPK not only links the orexigenic effects of endocannabinoids and ghrelin in the hypothalamus but also their effects on the metabolism of peripheral tissues...

..Here, we present evidence of a new regulatory mechanism of skeletal muscle glycogen metabolism based on glycogen enzyme intracellular compartmentalization...

..These data suggest that impaired insulin action on glycogen synthesis and lipid oxidation in skeletal muscle of obese type 2 diabetic subjects is unlikely to involve changes in AMPK expression and activity...

..Taken together, these results indicate that SCD1 deficiency reduces ceramide synthesis by decreasing SPT expression and increasing the rate of beta-oxidation in oxidative muscles...

..The higher basal IMTG content in women compared with men is therefore the best candidate to explain the higher IMTG net hydrolysis during exercise in women...

..The enzyme activity was not modulated by 5'-AMP. To our knowledge, these results represent the first detailed biochemical characterization of a kinase of the SnRK2 family...

..Apparently, HSL Ser565 phosphorylation by AMPK during exercise had no effect on HSL activity. Alternatively, other factors including ERK may have counterbalanced any effect of AMPK on HSL activity...

..001) thereby stimulating the oxidation of mitochondrial palmitoyl-CoA. Our results identify AMPK as a mediator of increased fatty acid oxidation in liver of SCD1-deficient mice...

..Thus cardiac AMPK activity increases progressively with exercise intensity, supporting the hypothesis that AMPK has a physiological role in the heart...

..Through signaling, metabolic, and gene expression effects, AMPK enhances insulin sensitivity and fosters a metabolic milieu that may reduce the risk for obesity and type 2 diabetes...

..These results suggest that aging-associated reductions in AMPK activity may be an important contributing factor in the reduced mitochondrial function and dysregulated intracellular lipid metabolism associated with aging...

..Our findings demonstrate a central role for AMPK in stimulus-response coupling by hypoxia and identify for the first time a link between metabolic stress and ion channel regulation in an O2-sensing system...

..It is concluded that muscle AMPK activity and ACCbeta Ser(221) phosphorylation at rest and during exercise are sensitive to the fuel status of the muscle. During exercise, this dependence may in part be mediated by humoral factors...

..01). In conclusion, trained human skeletal muscle has increased alpha(1)-AMPK protein levels and blunted AMPK activation during exercise...

..Our studies confirm that mutations in PRKAG2 can cause fatal infantile cardiomyopathy, often associated with apparent PHK deficiency...

..We propose that this direct and specific AMPK activator will be a valuable experimental tool to understand the physiological roles of AMPK...

....

..Except for the increase in gamma1 protein, all observed adaptations to training could be ascribed to local contraction-induced mechanisms, since they did not occur in the contralateral untrained muscle...

..Thus, metabolic sensing by AMP-activated protein kinase may mediate chemotransduction by hypoxia...

..These enzymes, which have been implicated in stress-regulated pathways in other cell types, are therefore unlikely to play a role in transport regulation by stress in Clone 9 cells...

..In conclusion, AICAR-stimulated glucose transport varies with muscle fiber type and nutritional state. AMPK is unlikely to be the sole mediator of contraction-stimulated glucose transport...

..Because the glycogen level did not affect adenine nucleotide concentrations, our data suggest that glycogen may directly affect the activation state of AMPK in skeletal muscle...