Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UMLS:C0011860 (type 2 diabetes)
 57,723 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Inactivating mutations in the protein kinase LKB1 lead to a dominantly inherited cancer in humans termed Peutz-Jeghers syndrome. The role of LKB1 is unclear, and only one target for LKB1 has been identified in vivo [3]. AMP-activated protein kinase (AMPK) is the downstream component of a protein kinase cascade that plays a pivotal role in energy homeostasis. AMPK may have a role in protecting the body from metabolic diseases including type 2 diabetes, obesity, and cardiac hypertrophy. We previously reported the identification of three protein kinases (Elm1, Pak1, and Tos3 [9]) that lie upstream of Snf1, the yeast homologue of AMPK. LKB1 shares sequence similarity with Elm1, Pak1, and Tos3, and we demonstrated that LKB1 phosphorylates AMPK on the activation loop threonine (Thr172) within the catalytic subunit and activates AMPK in vitro [9]. Here, we have investigated whether LKB1 corresponds to the major AMPKK activity present in cell extracts. AMPKK purified from rat liver corresponds to LKB1, and blocking LKB1 activity in cells abolishes AMPK activation in response to different stimuli. These results identify a link between two protein kinases, previously thought to lie in unrelated, distinct pathways, that are associated with human diseases.
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PMID:LKB1 is the upstream kinase in the AMP-activated protein kinase cascade. 2462 16

AMP-activated protein kinase (AMPK) is the downstream component of a protein kinase cascade that acts as an intracellular energy sensor maintaining the energy balance within the cell. This pivotal role of AMPK places it in an ideal position for regulating whole-body energy metabolism, and AMPK might play a part in protecting the body from metabolic diseases such as type 2 diabetes and obesity. Mutations in AMPK cause cardiac hypertrophy and arrhythmia. Recent findings have identified LKB1--a protein kinase that is mutated in a hereditary form of cancer--as a candidate for the upstream kinase in the AMPK cascade. AMPK could provide a link in human diseases of which the underlying cause is due to defects in energy metabolism.
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PMID:The AMP-activated protein kinase cascade--a unifying system for energy control. 1472 28

Activation of AMP-activated protein kinase (AMPK) by exercise and metformin is beneficial for the treatment of type 2 diabetes. We recently found that, in cultured cells, the LKB1 tumor suppressor protein kinase activates AMPK in response to the metformin analog phenformin and the AMP mimetic drug 5-aminoimidazole-4-carboxamide-1-beta-D-ribofuranoside (AICAR). We have also reported that LKB1 activates 11 other AMPK-related kinases. The activity of LKB1 or the AMPK-related kinases has not previously been studied in a tissue with physiological relevance to diabetes. In this study, we have investigated whether contraction, phenformin, and AICAR influence LKB1 and AMPK-related kinase activity in rat skeletal muscle. Contraction in situ, induced via sciatic nerve stimulation, significantly increased AMPKalpha2 activity and phosphorylation in multiple muscle fiber types without affecting LKB1 activity. Treatment of isolated skeletal muscle with phenformin or AICAR stimulated the phosphorylation and activation of AMPKalpha1 and AMPKalpha2 without altering LKB1 activity. Contraction, phenformin, or AICAR did not significantly increase activities or expression of the AMPK-related kinases QSK, QIK, MARK2/3, and MARK4 in skeletal muscle. The results of this study suggest that muscle contraction, phenformin, or AICAR activates AMPK by a mechanism that does not involve direct activation of LKB1. 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.
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PMID:Activity of LKB1 and AMPK-related kinases in skeletal muscle: effects of contraction, phenformin, and AICAR. 1506 58

Stimulation of AMP-activated protein kinase (AMPK) in skeletal muscle and liver is seen as an exciting prospect for the treatment of type 2 diabetes. However, we have recently demonstrated that changes in AMPK activity accompany the exposure of pancreatic islet beta-cells to elevated glucose concentrations and may be involved in the activation of insulin secretion. Here, we discuss this hypothesis and explore the potential role of changes in AMPK activity in the actions of other secretagogues. Amino acids decreased AMPK activity in MIN6 beta-cells with an order of potency for inhibition: arg=leu < gln= leu + glu < glucose, which was closely correlated with the stimulation of insulin release (r2=0.76). By contrast, increases in intracellular Ca2+ concentration provoked by cell depolarization with KCl activated AMPK in the face of increased free intracellular ATP concentrations. Elevation of intracellular cAMP levels with isobutylmethylxanthine or forskolin had no effect on AMPK activity. We conclude that metabolizable amino acids regulate AMPK in the beta-cell via increases in the cytosolic ATP/AMP ratio and via phosphorylation by the upstream kinase LKB1. Intracellular Ca2+ ions may activate AMPK by calmodulin kinase 1 kinase-mediated phosphorylation. The latter may act as a novel feedback mechanism to inhibit excessive insulin secretion under some circumstances.
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PMID:AMP-activated protein kinase: a new beta-cell glucose sensor?: Regulation by amino acids and calcium ions. 1556 25

The AMP-activated protein kinase (AMPK) is an evolutionarily conserved sensor of cellular energy status, and recent data demonstrate that it also plays a critical role in systemic energy balance. AMPK integrates nutritional and hormonal signals in peripheral tissues and the hypothalamus. It mediates effects of adipokines (leptin, adiponectin, and possibly resistin) in regulating food intake, body weight, and glucose and lipid homeostasis. AMPK is regulated by upstream kinases of which the tumor suppressor, LKB1, is the first to be identified. Complex signaling networks suggest that AMPK may prevent insulin resistance, in part by inhibiting pathways that antagonize insulin signaling. 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.
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PMID:AMP-activated protein kinase: ancient energy gauge provides clues to modern understanding of metabolism. 1605 41

The Peutz-Jegher syndrome tumor-suppressor gene encodes a protein-threonine kinase, LKB1, which phosphorylates and activates AMPK [adenosine monophosphate (AMP)-activated protein kinase]. The deletion of LKB1 in the liver of adult mice resulted in a nearly complete loss of AMPK activity. Loss of LKB1 function resulted in hyperglycemia with increased gluconeogenic and lipogenic gene expression. In LKB1-deficient livers, TORC2, a transcriptional coactivator of CREB (cAMP response element-binding protein), was dephosphorylated and entered the nucleus, driving the expression of peroxisome proliferator-activated receptor-gamma coactivator 1alpha (PGC-1alpha), which in turn drives gluconeogenesis. Adenoviral small hairpin RNA (shRNA) for TORC2 reduced PGC-1alpha expression and normalized blood glucose levels in mice with deleted liver LKB1, indicating that TORC2 is a critical target of LKB1/AMPK signals in the regulation of gluconeogenesis. Finally, we show that metformin, one of the most widely prescribed type 2 diabetes therapeutics, requires LKB1 in the liver to lower blood glucose levels.
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PMID:The kinase LKB1 mediates glucose homeostasis in liver and therapeutic effects of metformin. 1630 21

AMPK is a key regulator of fat and carbohydrate metabolism. It has been postulated that defects in AMPK signaling could be responsible for some of the metabolic abnormalities of type 2 diabetes. In this study, we examined whether insulin-resistant obese Zucker rats have abnormalities in the AMPK pathway. We compared AMPK and ACC phosphorylation and the protein content of the upstream AMPK kinase LKB1 and the AMPK-regulated transcriptional coactivator PPARgamma coactivator-1 (PGC-1) in gastrocnemius of sedentary obese Zucker rats and sedentary lean Zucker rats. We also examined whether 7 wk of exercise training on a treadmill reversed abnormalities in the AMPK pathway in obese Zucker rats. In the obese rats, AMPK phosphorylation was reduced by 45% compared with lean rats. Protein expression of the AMPK kinase LKB1 was also reduced in the muscle from obese rats by 43%. In obese rats, phosphorylation of ACC and protein expression of PGC-1alpha, two AMPK-regulated proteins, tended to be reduced by 50 (P = 0.07) and 35% (P = 0.1), respectively. There were no differences in AMPKalpha1, -alpha2, -beta1, -beta2, and -gamma3 protein content between lean and obese rats. Training caused a 1.5-fold increase in AMPKalpha1 protein content in the obese rats, although there was no effect of training on AMPK phosphorylation and the other AMPK isoforms. Furthermore, training also significantly increased LKB1 and PGC-1alpha protein content 2.8- and 2.5-fold, respectively, in the obese rats. LKB1 protein strongly correlated with hexokinase II activity (r = 0.75, P = 0.001), citrate synthase activity (r = 0.54, P = 0.02), and PGC-1alpha protein content (r = 0.81, P < 0.001). In summary, obese insulin-resistant rodents have abnormalities in the LKB1-AMPK-PGC-1 pathway in muscle, and these abnormalities can be restored by training.
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PMID:LKB1-AMPK signaling in muscle from obese insulin-resistant Zucker rats and effects of training. 1635 71

The recent discovery that the tumour suppressor LKB1 is an upstream kinase in the AMP-activated protein kinase (AMPK) cascade provided a molecular link between energy metabolism and cancer. A recent study by Shaw and colleagues elucidated the role of LKB1 in type 2 diabetes. Deletion of the gene encoding LKB1 in the liver leads to marked hyperglycaemia as a consequence of increased gluconeogenic gene expression and hepatic glucose output. Importantly, the absence of LKB1 in the liver abolishes the effect of lowering glucose level caused by metformin, a drug that is widely used for the treatment of type 2 diabetes. These findings should help solve the mystery surrounding the function of metformin, which has lasted for >30 years.
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PMID:LKB1: a sweet side to Peutz-Jeghers syndrome? 1653 14

The AMP-activated protein kinase (AMPK) system acts as a sensor of cellular energy status that is conserved in all eukaryotic cells. It is activated by increases in the cellular AMP:ATP ratio caused by metabolic stresses that either interfere with ATP production (eg, deprivation for glucose or oxygen) or that accelerate ATP consumption (eg, muscle contraction). Activation in response to increases in AMP involves phosphorylation by an upstream kinase, the tumor suppressor LKB1. In certain cells (eg, neurones, endothelial cells, and lymphocytes), AMPK can also be activated by a Ca(2+)-dependent and AMP-independent process involving phosphorylation by an alternate upstream kinase, CaMKKbeta. Once activated, AMPK switches on catabolic pathways that generate ATP, while switching off ATP-consuming processes such as biosynthesis and cell growth and proliferation. The AMPK complex contains 3 subunits, with the alpha subunit being catalytic, the beta subunit containing a glycogen-sensing domain, and the gamma subunits containing 2 regulatory sites that bind the activating and inhibitory nucleotides AMP and ATP. Although it may have evolved to respond to metabolic stress at the cellular level, hormones and cytokines such as insulin, leptin, and adiponectin can interact with the system, and it now appears to play a key role in maintaining energy balance at the whole body level. The AMPK system may be partly responsible for the health benefits of exercise and is the target for the antidiabetic drug metformin. It is a key player in the development of new treatments for obesity, type 2 diabetes, and the metabolic syndrome.
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PMID:AMP-activated protein kinase in metabolic control and insulin signaling. 1730 71

Activation of AMP-activated protein kinase (AMPK) by exercise induces several cellular processes in muscle. Exercise activation of AMPK is unaffected in lean (BMI approximately 25 kg/m(2)) subjects with type 2 diabetes. However, most type 2 diabetic subjects are obese (BMI >30 kg/m(2)), and exercise stimulation of AMPK is blunted in obese rodents. We examined whether obese type 2 diabetic subjects have impaired exercise stimulation of AMPK, at different signaling levels, spanning from the upstream kinase, LKB1, to the putative AMPK targets, AS160 and peroxisome proliferator-activated receptor coactivator (PGC)-1alpha, involved in glucose transport regulation and mitochondrial biogenesis, respectively. Twelve type 2 diabetic, eight obese, and eight lean subjects exercised on a cycle ergometer for 40 min. Muscle biopsies were done before, during, and after exercise. Subjects underwent this protocol on two occasions, at low (50% Vo(2max)) and moderate (70% Vo(2max)) intensities, with a 4-6 week interval. Exercise had no effect on LKB1 activity. Exercise had a time- and intensity-dependent effect to increase AMPK activity and AS160 phosphorylation. Obese and type 2 diabetic subjects had attenuated exercise-stimulated AMPK activity and AS160 phosphorylation. Type 2 diabetic subjects had reduced basal PGC-1 gene expression but normal exercise-induced increases in PGC-1 expression. Our findings suggest that obese type 2 diabetic subjects may need to exercise at higher intensity to stimulate the AMPK-AS160 axis to the same level as lean subjects.
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PMID:Effect of acute exercise on AMPK signaling in skeletal muscle of subjects with type 2 diabetes: a time-course and dose-response study. 1732 55


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