Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:2.7.11.27 (AMPK)
 6,299 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Ghrelin is a gastric hormone increased during caloric restriction and fat depletion. A role of ghrelin in the regulation of lipid and energy metabolism is suggested by fat gain independent of changes in food intake during exogenous ghrelin administration in rodents. We investigated the potential effects of peripheral ghrelin administration (two times daily 200-micrograms [DOSAGE ERROR CORRECTED] sc injection for 4 days) on triglyceride content and mitochondrial and lipid metabolism gene expression in rat liver and muscles. Compared with vehicle, ghrelin increased body weight but not food intake and circulating insulin. In liver, ghrelin induced a lipogenic and glucogenic pattern of gene expression and increased triglyceride content while reducing activated (phosphorylated) stimulator of fatty acid oxidation, AMP-activated protein kinase (AMPK, all P < 0.05), with unchanged mitochondrial oxidative enzyme activities. In contrast, triglyceride content was reduced (P < 0.05) after ghrelin administration in mixed (gastrocnemius) and unchanged in oxidative (soleus) muscle. In mixed muscle, ghrelin increased (P < 0.05) mitochondrial oxidative enzyme activities independent of changes in expression of fat metabolism genes and phosphorylated AMPK. Expression of peroxisome proliferator-activated receptor-gamma, the activation of which reduces muscle fat content, was selectively increased in mixed muscle where it paralleled changes in oxidative capacities (P < 0.05). Thus ghrelin induces tissue-specific changes in mitochondrial and lipid metabolism gene expression and favors triglyceride deposition in liver over skeletal muscle. These novel effects of ghrelin in the regulation of lean tissue fat distribution and metabolism could contribute to metabolic adaptation to caloric restriction and loss of body fat.
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PMID:Ghrelin regulates mitochondrial-lipid metabolism gene expression and tissue fat distribution in liver and skeletal muscle. 1532 73

We recently identified a novel human AMPK family member, ARK5, and discovered that is a major factor in Akt-dependent cancer cell survival and migration activity through activation of MT1-MMPs in vitro. The mRNA expression of other AMPK family members and ARK5 was measured using RT-PCR in human colorectal carcinoma cell lines DLD-1, WiDr, HCT-15, SW620, LoVo, SW480, and mRNA expression of AMPK-alpha1, SNARK, MELK and ARK5, but not AMPK-alpha2, was detected in every line. Quantitative-PCR (Q-PCR) to estimate the amount of ARK5 mRNA expression in the cell lines showed that there is a variety of ARK5 expressions among the cell lines and high expression was observed in a cell line derived from the metastatic lesion, LoVo. To determine the effect of ARK5 overexpression on metastasis in vivo, we established human pancreas cancer cell line PANC-1 stably transfected with ARK5 full-length expression vector (P/ARK) and DLD-1 stably transfected with the same vector (D/ARK). Migration assay showed a remarkable increase in the activity both in P/ARK and D/ARK, and an in vivo metastasis assay showed a marked increase of P/ARK in liver metastasis. Based on these observations, it is suggested that ARK5 expression is involved in cancer invasion and metastasis.
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PMID:Strong association of ARK5 with tumor invasion and metastasis. 1535 11

AMPK (AMP-activated protein kinase) is a key sensor of energy status within the cell. Activated by an increase in the AMP/ATP ratio, AMPK acts to limit cellular energy depletion by down-regulating selective ATP-dependent processes. The purpose of the present study was to determine the role of AMPK in regulating intestinal glucose transport. [3H]3-O-methyl glucose fluxes were measured in murine jejunum in the presence and absence of the AMPK activators AICAR (5-aminoimidazole-4-carboxamide riboside) and metformin and the p38 inhibitor, SB203580. To differentiate between a sodium-coupled (SGLT1) and diffusive (GLUT2) route of entry, fluxes were measured in the presence of the SGLT1 and GLUT2 inhibitors phloridzin and phloretin. Glucose transporter mRNA levels were measured by reverse transcriptase-PCR, and localization by Western blotting. Surface-expressed GLUT2 was assessed by luminal biotinylation. Activation of p38 mitogen-activated protein kinase was analysed by Western blotting. We found that treatment of jejunal tissue with AICAR resulted in enhanced net glucose uptake and was associated with phosphorylation of p38 mitogen-activated protein kinase. Inhibition of p38 abrogated the stimulation of AICAR-stimulated glucose uptake. Phloretin abolished the AICAR-mediated increase in glucose flux, whereas phloridzin had no effect, suggesting the involvement of GLUT2. In addition, AICAR decreased total protein levels of SGLT1, concurrently increasing levels of GLUT2 in the brush-border membrane. The anti-diabetic drug metformin, a known activator of AMPK, also induced the localization of GLUT2 to the luminal surface. We conclude that the activation of AMPK results in an up-regulation of non-energy requiring glucose uptake by GLUT2 and a concurrent down-regulation of sodium-dependent glucose transport.
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PMID:5-aminoimidazole-4-carboxamide riboside (AICAR) enhances GLUT2-dependent jejunal glucose transport: a possible role for AMPK. 1536 3

Glucose-dependent insulinotropic polypeptide (GIP) regulates glucose homeostasis and high-fat diet-induced obesity and insulin resistance. Therefore, elucidating the mechanisms that regulate GIP release is important. GIP is produced by K cells, a specific subtype of small intestinal enteroendocrine (EE) cell. Bombesin-like peptides produced by enteric neurons and luminal nutrients stimulate GIP release in vivo. We previously showed that PMA, bombesin, meat hydrolysate, glyceraldehyde, and methylpyruvate increase hormone release from a GIP-producing EE cell line (GIP/Ins cells). Here we demonstrate that bombesin and nutrients additively stimulate hormone release from GIP/Ins cells. In various cell systems, bombesin and PMA regulate cell physiology by activating PKD signaling in a PKC-dependent fashion, whereas nutrients regulate cell physiology by inhibiting AMPK signaling. Western blot analyses of GIP/Ins cells using antibodies specific for activated and/or phosphorylated forms of PKD and AMPK and one substrate for each kinase revealed that bombesin and PMA, but not nutrients, activated PKC, but not PKD. Conversely, nutrients, but not bombesin or PMA, inhibited AMPK activity. Pharmacological studies showed that PKC inhibition blocked bombesin- and PMA-stimulated hormone release, but AMPK activation failed to suppress nutrient-stimulated hormone secretion. Forced expression of constitutively active vs. dominant negative PKDs or AMPKs failed to perturb bombesin- or nutrient-stimulated hormone release. Thus, in GIP/Ins cells, PKC regulates bombesin-stimulated hormone release, whereas nutrients may control hormone release by regulating the activity of AMPK-related kinases, rather than AMPK itself. These results strongly suggest that K cells in vivo independently respond to neuronal vs. nutritional stimuli via two distinct signaling pathways.
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PMID:Bombesin and nutrients independently and additively regulate hormone release from GIP/Ins cells. 1538 72

Autophagic activity in isolated rat hepatocytes is strongly suppressed by OA (okadaic acid) and other PP (protein phosphatase)-inhibitory toxins as well as by AICAR (5-aminoimidazole-4-carboxamide riboside), a direct activator of AMPK (AMP-activated protein kinase). To investigate whether AMPK is a mediator of the effects of the toxin, a phosphospecific antibody directed against the activation of phosphorylation of the AMPK alpha (catalytic)-subunit at Thr172 was used to assess the activation status of this enzyme. AICAR as well as all the toxins tested (OA, microcystin-LR, calyculin A, cantharidin and tautomycin) induced strong, dose-dependent AMPKalpha phosphorylation, correlating with AMPK activity in situ (in intact hepatocytes) as measured by the AMPK-dependent phosphorylation of acetyl-CoA carboxylase at Ser79. All treatments induced the appearance of multiple, phosphatase-sensitive, low-mobility forms of the AMPK alpha-subunit, consistent with phosphorylation at several sites other than Thr172. The flavonoid naringin, an effective antagonist of OA-induced autophagy suppression, inhibited the AMPK phosphorylation and mobility shifting induced by AICAR, OA or microcystin, but not the changes induced by calyculin A or cantharidin. AMPK may thus be activated both by a naringin-sensitive and a naringin-resistant mechanism, probably involving the PPs PP2A and PP1 respectively. Neither the Thr172-phosphorylating protein kinase LKB1 nor the Thr172-dephosphorylating PP, PP2C, were mobility-shifted after treatment with toxins or AICAR, whereas a slight mobility shifting of the regulatory AMPK beta-subunit was indicated. Immunoblotting with a phosphospecific antibody against pSer108 at the beta-subunit revealed a naringin-sensitive phosphorylation induced by OA, microcystin and AICAR and a naringin-resistant phosphorylation induced by calyculin A and cantharidin, suggesting that beta-subunit phosphorylation could play a role in AMPK activation. Naringin antagonized the autophagy-suppressive effects of AICAR and OA, but not the autophagy suppression caused by cantharidin, consistent with AMPK-mediated inhibition of autophagy by toxins as well as by AICAR.
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PMID:Stimulation of hepatocytic AMP-activated protein kinase by okadaic acid and other autophagy-suppressive toxins. 1546 83

In tobacco (Nicotiana tabacum), hyperosmotic stress induces rapid activation of a 42-kD protein kinase, referred to as Nicotiana tabacum osmotic stress-activated protein kinase (NtOSAK). cDNA encoding the kinase was cloned and, based on the predicted amino acid sequence, the enzyme was assigned to the SNF1-related protein kinase type 2 (SnRK2) family. The identity of the enzyme was confirmed by immunoprecipitation of the active kinase from tobacco cells subjected to osmotic stress using antibodies raised against a peptide corresponding to the C-terminal sequence of the kinase predicted from the cloned cDNA. A detailed biochemical characterization of NtOSAK purified from stressed tobacco cells was performed. Our results show that NtOSAK is a calcium-independent Ser/Thr protein kinase. The sequence of putative phosphorylation sites recognized by NtOSAK, predicted by the computer program PREDIKIN, resembled the substrate consensus sequence defined for animal and yeast (Saccharomyces cerevisiae) AMPK/SNF1 kinases. Our experimental data confirmed these results, as various targets for AMPK/SNF1 kinases were also efficiently phosphorylated by NtOSAK. A range of protein kinase inhibitors was tested as potential modulators of NtOSAK, but only staurosporine, a rather nonspecific protein kinase inhibitor, was found to abolish the enzyme activity. In phosphorylation reactions, NtOSAK exhibited a preference for Mg(2+) over Mn(2+) ions and an inability to use GTP instead of ATP as a phosphate donor. 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.
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PMID:Biochemical characterization of the tobacco 42-kD protein kinase activated by osmotic stress. 1546 34

Mutations in the LKB1 tumour suppressor threonine kinase cause the inherited Peutz-Jeghers cancer syndrome and are also observed in some sporadic cancers. Recent work indicates that LKB1 exerts effects on metabolism, polarity and proliferation by phosphorylating and activating protein kinases belonging to the AMPK subfamily. In vivo, LKB1 forms a complex with STRAD, an inactive pseudokinase, and MO25, an armadillo repeat scaffolding-like protein. Binding of LKB1 to STRAD-MO25 activates LKB1 and re-localises it from the nucleus to the cytoplasm. To learn more about the inherent properties of the LKB1-STRAD-MO25 complex, we first investigated the activity of 34 point mutants of LKB1 found in human cancers and their ability to interact with STRAD and MO25. Interestingly, 12 of these mutants failed to interact with STRAD-MO25. Performing mutagenesis analysis, we defined two binding sites located on opposite surfaces of MO25alpha, which are required for the assembly of MO25alpha into a complex with STRADalpha and LKB1. In addition, we demonstrate that LKB1 does not require phosphorylation of its own T-loop to be activated by STRADalpha-MO25alpha, and discuss the possibility that this unusual mechanism of regulation arises from LKB1 functioning as an upstream kinase. Finally, we establish that STRADalpha, despite being catalytically inactive, is still capable of binding ATP with high affinity, but that this is not required for activation of LKB1. 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.
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PMID:Analysis of the LKB1-STRAD-MO25 complex. 1556 63

The study of hereditary tumor syndromes has laid a solid foundation toward understanding the genetic basis of cancer. One of the latest examples comes from the study of tuberous sclerosis complex (TSC). As a member of the phakomatoses, TSC is characterized by the appearance of benign tumors, most notably in the central nervous system, kidney, heart, lung, and skin. While classically described as "hamartomas," the pathology of the lesions has features suggestive of abnormal cellular proliferation, size, differentiation, and migration. Occasionally, tumors progress to become malignant (i.e., renal cell carcinoma). The genetic basis of this disease has been attributed to mutations in one of two unlinked genes, TSC1 and TSC2. Cells undergo bi-allelic inactivation of either gene to give rise to tumors in a classic tumor suppressor "two-hit" paradigm. The functions of the TSC1 and TSC2 gene products, hamartin and tuberin, respectively, have remained ill defined until recently. Genetic, biochemical, and biologic analyses have highlighted their role as negative regulators of the mTOR signaling pathway. Tuberin, serving as a substrate of AKT and AMPK, mediates mTOR activity by coordinating inputs from growth factors and energy availability in the control of cell growth, proliferation, and survival. Emerging evidence also suggests that the TSC 1/2 complex may play a role in modulating the activity of beta-catenin and TGFbeta. These findings provide novel functional links between the TSC genes and other tumor suppressors responsible for Cowden's disease (PTEN), Peutz-Jeghers syndrome (LKB1), and familial polyposis (APC). Common sporadic cancers such as prostate, lung, colon, endometrium, and breast have ties to these genes, highlighting the potential role of the TSC proteins in human cancers. Rapamycin, a specific mTOR inhibitor, has potent antitumoral activities in preclinical models of TSC and is currently undergoing phase I/II clinical studies.
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PMID:The tuberous sclerosis complex genes in tumor development. 1556 17

Increases in contraction-stimulated glucose transport in fast-twitch rat epitrochlearis muscle are mediated by AMPK- and Ca2+/calmodulin-dependent protein kinase (CAMK)-dependent signaling pathways. However, recent studies provide evidence suggesting that contraction-stimulated glucose transport in slow-twitch skeletal muscle is mediated through an AMPK-independent pathway. The purpose of the present study was to test the hypothesis that contraction-stimulated glucose transport in rat slow-twitch soleus muscle is mediated by an AMPK-independent/Ca2+-dependent pathway. Caffeine, a sarcoplasmic reticulum (SR) Ca2+-releasing agent, at a concentration that does not cause muscle contractions or decreases in high-energy phosphates, led to an approximately 2-fold increase in 2-deoxyglucose (2-DG) uptake in isolated split soleus muscles. This increase in glucose transport was prevented by the SR calcium channel blocker dantrolene and the CAMK inhibitor KN93. Conversely, 5-aminoimidazole-4-carboxamide-1-beta-D-ribofuranoside (AICAR), an AMPK activator, had no effect on 2-DG uptake in isolated split soleus muscles yet resulted in an approximately 2-fold increase in the phosphorylation of AMPK and its downstream substrate acetyl-CoA carboxylase. The hypoxia-induced increase in 2-DG uptake was prevented by dantrolene and KN93, whereas hypoxia-stimulated phosphorylation of AMPK was unaltered by these agents. Tetanic muscle contractions resulted in an approximately 3.5-fold increase in 2-DG uptake that was prevented by KN93, which did not prevent AMPK phosphorylation. Taken in concert, our results provide evidence that hypoxia- and contraction-stimulated glucose transport is mediated entirely through a Ca2+-dependent mechanism in rat slow-twitch muscle.
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PMID:Contraction- and hypoxia-stimulated glucose transport is mediated by a Ca2+-dependent mechanism in slow-twitch rat soleus muscle. 1565 88

The liver is one of the major target organs of insulin in which the expression of insulin receptor is abundant. We analyzed the effect of AICAR, an AMPK activator, on the expression of insulin receptor in a human hepatoma cell line, HepG2 cells. AICAR treatment for 48 h significantly decreased the expression of the insulin receptor protein in a dose-dependent manner, however, this same effect of AICAR was not observed in either 3T3-L1 adipocytes or CHO cells. The expression of insulin receptor mRNA also decreased after AICAR treatment. In addition, the transcriptional activity of the insulin receptor gene promoter investigated with a luciferase assay was down-regulated by AICAR treatment. Dipyridamole, an adenosine transporter inhibitor, and 5'-amino-5'-deoxyadenosine, an adenosine kinase inhibitor, blocked the effect of AICAR on the down-regulation of the insulin receptor protein, mRNA, and promoter activity. Our findings suggest, for the first time, that AMPK activation could reduce the expression of insulin receptor, at least in part, by a down-regulation of the transcriptional level, and this effect may be liver specific.
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PMID:AICAR, an activator of AMP-activated protein kinase, down-regulates the insulin receptor expression in HepG2 cells. 1569 68


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