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

To provide insight into the physiological importance of 3-phosphoinositide-dependent kinase-1 (PDK-1) in the metabolic actions of insulin, we have generated mice that harbor a PDK-1 gene containing LoxP sites (PDK-1(lox/lox) mice) and established immortalized brown preadipocyte cell lines both from these animals and from wild-type mice. Exposure to appropriate hormonal inducers resulted in the differentiation of >80% of the immortalized brown preadipocytes derived from both types of mice into mature adipocytes. Introduction of the Cre recombinase with the use of adenovirus-mediated gene transfer induced a dose-dependent decrease in the abundance of PDK-1 in PDK-1(lox/lox) adipocytes but not in the wild-type cells. In Cre-expressing PDK-1(lox/lox) adipocytes in which the abundance of PDK-1 was reduced by approximately 85%, the insulin-induced phosphorylation both of Akt on threonine 308 and of p70 S6 kinase on threonine-389 was markedly inhibited. The phosphorylation both of Akt on serine 473 and of p42 and p44 isoforms of mitogen-activated protein kinase induced by insulin was not affected by Cre expression, indicating that the latter specifically inhibits PDK-1-dependent signaling. Both glucose uptake and the translocation of glucose transporter 4 to the plasma membrane induced by insulin as well as glucose uptake induced by a constitutively active form of phosphoinositide 3-kinase were also greatly inhibited by Cre expression in PDK-1(lox/lox) adipocytes. Phosphorylation of AMP-activated protein kinase and glucose uptake induced by 5-aminoimidazole-4-carboxamide ribonucleoside (AICAR) were not affected by Cre expression in PDK-1(lox/lox) adipocytes. These results indicate that PDK-1 is essential for insulin-induced glucose uptake in adipocytes.
 ...
PMID:Requirement for 3-phosphoinositide-kependent dinase-1 (PDK-1) in insulin-induced glucose uptake in immortalized brown adipocytes. 1285 88

Histamine and thrombin cause phosphorylation and activation of endothelial NO-synthase (eNOS) on Ser1177. We tested the role of various protein kinases in mediating this effect in human umbilical vein endothelial cells. Inhibition of the Ca2+/calmodulin-dependent protein kinase II or phosphoinositide 3-kinase (PI3K) had no effect. H89, an inhibitor of both protein kinase A (PKA) and 5'-AMP-activated protein kinase (AMPK), strongly inhibited phosphorylation and activity of eNOS. Conversely, the PKA inhibitor Rp-adenosine 3 '5'-cyclic monophosphate (cAMPS) had no effect and eNOS was not phosphorylated by treatments that affect cAMP levels. Thrombin and histamine caused phosphorylation of AMPK on Thr172 as well as on its downstream target acetyl-CoA carboxylase. Activation of AMPK using AICAR or CCCP also resulted in eNOS phosphorylation. We conclude that histamine and thrombin cause eNOS phosphorylation in an AMPK mediated manner, independent of P13K-Akt.
 ...
PMID:Thrombin and histamine stimulate endothelial nitric-oxide synthase phosphorylation at Ser1177 via an AMPK mediated pathway independent of PI3K-Akt. 1532 94

Glucose-sensing neurons in the ventromedial hypothalamus (VMH) are involved in the regulation of glucose homeostasis. Glucose-sensing neurons alter their action potential frequency in response to physiological changes in extracellular glucose, insulin, and leptin. Glucose-excited neurons decrease, whereas glucose-inhibited (GI) neurons increase, their action potential frequency when extracellular glucose is reduced. Central nitric oxide (NO) synthesis is regulated by changes in local fuel availability, as well as insulin and leptin. NO is involved in the regulation of food intake and is altered in obesity and diabetes. Thus this study tests the hypothesis that NO synthesis is a site of convergence for glucose, leptin, and insulin signaling in VMH glucose-sensing neurons. With the use of the NO-sensitive dye 4-amino-5-methylamino-2',7'-difluorofluorescein in conjunction with the membrane potential-sensitive dye fluorometric imaging plate reader, we found that glucose and leptin suppress, whereas insulin stimulates neuronal nitric oxide synthase (nNOS)-dependent NO production in cultured VMH GI neurons. The effects of glucose and leptin were mediated by suppression of AMP-activated protein kinase (AMPK). The AMPK activator 5-aminoimidazole-4-carboxamide-1-beta-4-ribofuranoside (AICAR) increased both NO production and neuronal activity in GI neurons. In contrast, the effects of insulin on NO production were blocked by the phosphoinositide 3-kinase inhibitors wortmannin and LY-294002. Furthermore, decreased glucose, insulin, and AICAR increase the phosphorylation of VMH nNOS, whereas leptin decreases it. Finally, VMH neurons express soluble guanylyl cyclase, a downstream mediator of NO signaling. Thus NO may mediate, in part, glucose, leptin, and insulin signaling in VMH glucose-sensing neurons.
 ...
PMID:Glucose, insulin, and leptin signaling pathways modulate nitric oxide synthesis in glucose-inhibited neurons in the ventromedial hypothalamus. 1717 Feb 37

The endothelial isoform of nitric-oxide synthase (eNOS), a key determinant of vascular homeostasis, is a calcium/calmodulin-dependent phosphoprotein regulated by diverse cell surface receptors. Vascular endothelial growth factor (VEGF) and sphingosine 1-phosphate (S1P) stimulate eNOS activity through Akt/phosphoinositide 3-kinase and calcium-dependent pathways. AMP-activated protein kinase (AMPK) also activates eNOS in endothelial cells; however, the molecular mechanisms linking agonist-mediated AMPK regulation with eNOS activation remain incompletely understood. We studied the role of AMPK in VEGF- and S1P-mediated eNOS activation and found that both agonists led to a striking increase in AMPK phosphorylation in pathways involving the calcium/calmodulin-dependent protein kinase kinase beta. Treatment with tyrosine kinase inhibitors or the phosphoinositide 3-kinase inhibitor wortmannin demonstrated differential effects of VEGF versus S1P. Small interfering RNA (siRNA)-mediated knockdown of AMPKalpha1or Akt1 impaired the stimulatory effects of both VEGF and S1P on eNOS activation. AMPKalpha1 knockdown impaired agonist-mediated Akt phosphorylation, whereas Akt1 knockdown did not affect AMPK activation, thus suggesting that AMPK lies upstream of Akt in the pathway leading from receptor activation to eNOS stimulation. Importantly, we found that siRNA-mediated knockdown of AMPKalpha1 abrogates agonist-mediated activation of the small GTPase Rac1. Conversely, siRNA-mediated knockdown of Rac1 decreased the agonist-mediated phosphorylation of AMPK substrates without affecting that of AMPK, implicating Rac1 as a molecular link between AMPK and Akt in agonist-mediated eNOS activation. Finally, siRNA-mediated knockdown of caveolin-1 significantly enhanced AMPK phosphorylation, suggesting that AMPK is negatively regulated by caveolin-1. Taken together, these results suggest that VEGF and S1P differentially regulate AMPK and establish a central role for an agonist-modulated AMPK --> Rac1 --> Akt axis in the control of eNOS in endothelial cells.
 ...
PMID:Agonist-modulated regulation of AMP-activated protein kinase (AMPK) in endothelial cells. Evidence for an AMPK -> Rac1 -> Akt -> endothelial nitric-oxide synthase pathway. 1751 30

AS160 (Akt substrate of 160 kDa) mediates insulin-stimulated GLUT4 (glucose transporter 4) translocation, but is widely expressed in insulin-insensitive tissues lacking GLUT4. Having isolated AS160 by 14-3-3-affinity chromatography, we found that binding of AS160 to 14-3-3 isoforms in HEK (human embryonic kidney)-293 cells was induced by IGF-1 (insulin-like growth factor-1), EGF (epidermal growth factor), PMA and, to a lesser extent, AICAR (5-aminoimidazole-4-carboxamide-1-b-D-ribofuranoside). AS160-14-3-3 interactions were stabilized by chemical cross-linking and abolished by dephosphorylation. Eight residues on AS160 (Ser318, Ser341, Thr568, Ser570, Ser588, Thr642, Ser666 and Ser751) were differentially phosphorylated in response to IGF-1, EGF, PMA and AICAR. The binding of 14-3-3 proteins to HA-AS160 (where HA is haemagglutinin) was markedly decreased by mutation of Thr642 and abolished in a Thr642Ala/Ser341Ala double mutant. The AGC (protein kinase A/protein kinase G/protein kinase C-family) kinases RSK1 (p90 ribosomal S6 kinase 1), SGK1 (serum- and glucocorticoid-induced protein kinase 1) and PKB (protein kinase B) displayed distinct signatures of AS160 phosphorylation in vitro: all three kinases phosphorylated Ser318, Ser588 and Thr642; RSK1 also phosphorylated Ser341, Ser751 and to a lesser extent Thr568; and SGK1 phosphorylated Thr568 and Ser751. AMPK (AMP-activated protein kinase) preferentially phosphorylated Ser588, with less phosphorylation of other sites. In cells, the IGF-1-stimulated phosphorylations, and certain EGF-stimulated phosphorylations, were inhibited by PI3K (phosphoinositide 3-kinase) inhibitors, whereas the RSK inhibitor BI-D1870 inhibited the PMA-induced phosphorylations. The expression of LKB1 in HeLa cells and the use of AICAR in HEK-293 cells promoted phosphorylation of Ser588, but only weak Ser341 and Thr642 phosphorylations and binding to 14-3-3s. Paradoxically however, phenformin activated AMPK without promoting AS160 phosphorylation. The IGF-1-induced phosphorylation of the novel phosphorylated Ser666-Pro site was suppressed by AICAR, and by combined mutation of a TOS (mTOR signalling)-like sequence (FEMDI) and rapamycin. 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.
 ...
PMID:Regulation of multisite phosphorylation and 14-3-3 binding of AS160 in response to IGF-1, EGF, PMA and AICAR. 1761 58

Caffeic acid phenethyl ester (CAPE), a flavonoid-like compound, is one of the major components of honeybee propolis. In the present study, we investigated the metabolic effects of CAPE in skeletal muscle cells and found that CAPE stimulated glucose uptake in differentiated L6 rat myoblast cells and also activated AMPK (AMP-activated protein kinase). In addition, the inhibition of AMPK blocked CAPE-induced glucose uptake, and CAPE activated the Akt pathway in a PI3K (phosphoinositide 3-kinase)-dependent manner. Furthermore, CAPE enhanced both insulin-mediated Akt activation and glucose uptake. In summary, our results suggest that CAPE may have beneficial roles in glucose metabolism via stimulation of the AMPK pathway.
 ...
PMID:CAPE (caffeic acid phenethyl ester) stimulates glucose uptake through AMPK (AMP-activated protein kinase) activation in skeletal muscle cells. 1768 96

Mutation of LKB1 is the key molecular event underlying Peutz-Jeghers syndrome, a dominantly inherited condition characterized by a predisposition to a range of malignancies, including those of the reproductive system. We report here the use of a Cre-LoxP strategy to directly address the role of Lkb1 in prostate neoplasia. Recombination of a LoxP-flanked Lkb1 allele within all four murine prostate lobes was mediated by spontaneous activation of a p450 CYP1A1-driven Cre recombinase transgene (termed AhCre). Homozygous mutation of Lkb1 in males expressing AhCre reduced longevity, with 100% manifesting atypical hyperplasia and 83% developing prostate intraepithelial neoplasia (PIN) of the anterior prostate within 2 to 4 months. We also observed focal hyperplasia of the dorsolateral and ventral lobes (61% and 56% incidence, respectively), bulbourethral gland cysts associated with atypical hyperplasia (100% incidence), hyperplasia of the urethra (39% incidence), and seminal vesicle squamous metaplasia (11% incidence). PIN foci overexpressed nuclear beta-catenin, p-Gsk3 beta, and downstream Wnt targets. Immunohistochemical analysis of foci also showed a reduction in Pten activation and up-regulation of both p-PDK1 (an AMPK kinase) and phosphorylated Akt. Our data are therefore consistent with deregulation of Wnt and phosphoinositide 3-kinase/Akt signaling cascades after loss of Lkb1 function. For the first time, this model establishes a link between the tumor suppressor Lkb1 and prostate neoplasia, highlighting a tumor suppressive role within the mouse and raising the possibility of a similar association in the human.
 ...
PMID:Lkb1 deficiency causes prostate neoplasia in the mouse. 1838 28

Protein kinase B (PKB) is known to mediate a number of biological responses to insulin and growth factors, its role in glucose uptake being one of the most extensively studied. In this work, we have employed a recently described allosteric inhibitor of PKB, Akti, to clarify the role of PKB in lipid metabolism in adipocytes-a subject that has received less attention. Pretreatment of primary rat and 3T3L1 adipocytes with Akti resulted in dose-dependent inhibition of PKB phosphorylation and activation in response to insulin, without affecting upstream insulin signaling [insulin receptor (IR), insulin receptor substrate (IRS)] or the insulin-induced phosphoinositide 3-kinase (PI3K)-dependent activation of the ERK/p90 ribosomal kinase (RSK) pathway. PKB activity was required for the insulin-induced activation of phosphodiesterase 3B (PDE3B) and for the antilipolytic action of insulin. Moreover, inhibition of PKB activity resulted in a reduction in de novo lipid synthesis and in the ability of insulin to stimulate this process. The regulation of the rate-limiting lipogenic enzyme acetyl-CoA carboxylase (ACC) by insulin through dephosphorylation of S79, which is a target for AMP-activated protein kinase (AMPK), was dependent on the presence of active PKB. Finally, AMPK was shown to be phosphorylated by PKB on S485 in response to insulin, and this was associated with a reduction in AMPK activity. In summary, we propose that PKB is required for the positive effects of insulin on lipid storage and that regulation of PDE3B and AMPK by PKB is important for these effects.
 ...
PMID:Protein kinase B activity is required for the effects of insulin on lipid metabolism in adipocytes. 1915 25

Visfatin is an adipokine highly expressed in visceral AT (adipose tissue) of humans and rodents, the production of which seems to be dysregulated in excessive fat accumulation and conditions of insulin resistance. EPA (eicosapentaenoic acid), an n-3 PUFA (polyunsaturated fatty acid), has been demonstrated to exert beneficial effects in obesity and insulin resistance conditions, which have been further linked to its reported ability to modulate adipokine production by adipocytes. TNF-alpha (tumour necrosis factor-alpha) is a pro-inflammatory cytokine whose production is increased in obesity and is involved in the development of insulin resistance. Control of adipokine production by some insulin-sensitizing compounds has been associated with the stimulation of AMPK (AMP-activated protein kinase). The aim of the present study was to examine in vitro the effects of EPA on visfatin production and the potential involvement of AMPK both in the absence or presence of TNF-alpha. Treatment with the pro-inflammatory cytokine TNF-alpha (1 ng/ml) did not modify visfatin gene expression and protein secretion in primary cultured rat adipocytes. However, treatment of these primary adipocytes with EPA (200 mumol/l) for 24 h significantly increased visfatin secretion (P<0.001) and mRNA gene expression (P<0.05). Moreover, the stimulatory effect of EPA on visfatin secretion was prevented by treatment with the AMPK inhibitor Compound C, but not with the PI3K (phosphoinositide 3-kinase) inhibitor LY294002. Similar results were observed in 3T3-L1 adipocytes. Moreover, EPA strongly stimulated AMPK phosphorylation alone or in combination with TNF-alpha in 3T3-L1 adipocytes and pre-adipocytes. The results of the present study suggest that the stimulatory action of EPA on visfatin production involves AMPK activation in adipocytes.
 ...
PMID:Eicosapentaenoic acid stimulates AMP-activated protein kinase and increases visfatin secretion in cultured murine adipocytes. 1929 27

alpha-Lipoic acid (alpha-LA), an antioxidant used for diabetic polyneuropathy, was reported to induce AMP-activated protein kinase activation and reductions in insulin secretion in pancreatic beta-cells at high concentrations (> or = 500 micromol/l). This study investigated whether alpha-LA has a protective role under oxidative stress in beta-cells and its effect is dose-related. In INS-1 cells treated with alpha-LA (150-1200 micromol/l) for 24 h, alpha-LA itself (> or = 300 micromol/l) induced apoptotic death dose-dependently. However, pre-treatment with 150 and 300 micromol/l alpha-LA reduced the hydrogen peroxide-induced apoptosis in INS-1 cells and isolated islets. alpha-LA alleviated hydrogen peroxide-induced reactive oxygen species production, mitochondrial membrane depolarization and c-JNK activation in beta-cells. alpha-LA induced phosphoinositide 3-kinase-dependent Akt phosphorylation in INS-1 cells. While alpha-LA is harmful to beta-cells at high concentrations in vitro, it has potential cytoprotective effects on beta-cells under oxidative stress as in diabetes by its antioxidant properties and possibly by Akt phosphorylation at clinically relevant concentrations.
 ...
PMID:Dose-related cytoprotective effect of alpha-lipoic acid on hydrogen peroxide-induced oxidative stress to pancreatic beta cells. 1935 2


1 2 3 4 5 6 7 8 Next >>