Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:2.7.11.11 (AMPK)
 12,425 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

An inositol phosphoglycan that is the polar head group of a glycosyl phosphatidylinositol has been considered as a putative mediator of insulin action. To gain insight into the functions of this hormone during development, the relationships between insulin, insulin receptors, glycosyl phosphatidylinositol, and inositol phosphoglycan were studied. Glycosyl phosphatidylinositol was isolated and characterized in fetal liver as early as day 15 of intrauterine life. In isolated hepatocytes from fetal and adult rats labeled with [3H]glucosamine, [3H]galactose, or [3H]myo-inositol, these molecules were incorporated into glycosyl phosphatidylinositol. In hepatocytes labeled with [3H]glucosamine and then allowed to react with [1-14C]IAI, the [3H]glycosyl phosphatidylinositol was purified as the 14C-labeled amidinated lipid. Glycosyl phosphatidylinositol molecules from fetal and adult cells were sensitive to hydrolysis by a phosphatidylinositol-specific phospholipase C from B. cereus. The product of this hydrolysis inhibits the activity of a cAMP-dependent protein kinase, whereas this effect was abolished by nitrous acid deamination. In isolated hepatocytes from adult animals, an inverse correlation between extracellular insulin and the number of insulin receptors and the cellular content of glycosyl phosphatidylinositol was observed. However, in fetal hepatocytes insulin failed to reduce the glycosyl-phosphatidylinositol content when labeled either with [1-14C]isethionyl acetimidate or [3H]glucosamine, whereas insulin-like growth factor I produced a significant hydrolysis of glycosyl phosphatidylinositol. Fetal and adult hepatocytes were incubated with insulin or inositol phosphoglycan after which glycogen phosphorylase activities were determined. Inositol phosphoglycan mimicked the action of insulin on both forms of the enzyme from adult hepatocytes, whereas in fetal cells insulin did not change, and purified inositol phosphoglycan reduced the activities of glycogen phosphorylase. These findings suggest a dissociation between insulin receptor occupancy and the expected hormonal effects in fetal hepatocytes. This could be related to alterations at a postreceptor level.
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PMID:Insulin does not induce the hydrolysis of a glycosyl phosphatidylinositol in rat fetal hepatocytes. 834 37

The present study was designed to investigate the effect of phospholipase C and compounds known to promote synthesis of cAMP on System A transport activity under basal and insulin-stimulated conditions in the incubated muscle. In parallel, we also examined the effect of these agents on muscle glucose transport activity. Phospholipase C caused marked stimulation of alpha-(methyl)-aminoisobutyric acid (MeAIB--a System-A-specific analogue) uptake uptake and that of 3-O-methylglucose by the incubated muscle. In contrast, the activatory effect of insulin on System A was largely inhibited by phospholipase C. The effects of phospholipase C on transport processes differed from the effects provoked by phorbol esters (TPA), indicating that they are not just a consequence of TPA-sensitive protein kinase C activation. Agents such as isoproterenol, cholera toxin or forskolin, known cAMP inducers, caused glycogen depletion and stimulation of lactate production in the incubated muscle. However, these agents did not alter basal or insulin-stimulated MeAIB uptake. Isoproterenol and cholera toxin did not affect maximal stimulation of 3-O-methylglucose uptake caused by insulin. Our data indicate that System A transport is activated by phospholipase C in skeletal muscle, and that this effect is not due simply to activation of TPA-sensitive isoforms of protein kinase C. The effect of insulin on System A is reduced by either phospholipase C or TPA, which suggests the mediation of protein kinase C. On the basis of the lack of effect of cAMP-inducing agents on insulin-stimulated System A and glucose transport activities, we conclude that cAMP-dependent protein kinase does not cause any generalized blockade of insulin action in skeletal muscle, in contrast to what has been reported in other cell types.
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PMID:Regulation of System A amino-acid transport activity by phospholipase C and cAMP-inducing agents in skeletal muscle: modulation of insulin action. 838 2

ATP stimulates phosphatidylcholine secretion in type II cells, an effect that is mediated by both adenosine A2 receptors coupled to adenylate cyclase and P2 receptors coupled to phosphoinositide-specific phospholipase C. Activation of these effector enzymes leads to formation of cAMP, diacylglycerols and inositol trisphosphate (IP3). cAMP in turn activates cAMP-dependent protein kinase, diacylglycerols activate protein kinase C and IP3 promotes Ca2+ mobilization. To further investigate the signal-transduction mechanisms mediating the ATP effect, we examined its action in combination with that of other surfactant secretagogues: 5'(N-ethylcarboxyamido)adenosine (NECA), a A2 agonist that activates adenylate cyclase; TPA (12-O-tetradecanoylphorbol-13-acetate), a direct activator of protein kinase C; and ionomycin, an ionophore that increases intracellular Ca2+. The effects of NECA, TPA and ionomycin were additive and thus consistent with independent signaling mechanisms. However, the effects of all combinations of three or four secretagogues that contained ATP were 10-20% less than additive. This suggested that ATP and other secretagogues act via common mechanisms. Calmodulin antagonists decreased the effects of ionomycin and ATP by approx. 60% and 30%, respectively, but did not decrease the effects of NECA, terbutaline or TPA. Complete inhibition of the effect of ATP was achieved with a combination of a calmodulin antagonist, an A2 antagonist and a protein kinase C inhibitor. These and previous data suggest that the stimulatory effect of ATP on phosphatidylcholine secretion in type II cells is mediated by three signal-transduction mechanisms: activation of cAMP-dependent protein kinase; activation of protein kinase C; and a calmodulin-dependent mechanism.
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PMID:Signal-transduction mechanisms of ATP-stimulated phosphatidylcholine secretion in rat type II pneumocytes: interactions between ATP and other surfactant secretagogues. 846 37

PTH stimulates calcium absorption by renal distal convoluted tubules. The PTH receptor is capable of coupling to adenylyl cyclase and phospholipase C. However, it is not known whether the actions of PTH require activation of both pathways. Three approaches were taken to identify the signaling pathways responsible for stimulating calcium entry in distal convoluted tubule cells: second messengers formed in response to PTH were identified, the effects on calcium uptake of inhibiting protein kinase A (PKA) or protein kinase C (PKC) with chemical or peptide blockers were determined, and calcium transport was reconstituted by the addition of exogenous second messengers. PTH increased cAMP formation in primary cultures of mouse distal and proximal tubule cells. However, PTH stimulated inositol trisphosphate formation only in proximal tubule cells. Blocking PKA with Rp-cAMPS or the cAMP-dependent protein kinase inhibitor inhibited PTH-stimulated Ca uptake. Likewise, the PKC inhibitors, calphostin C and PKC pseudosubstrate, inhibited PTH-induced calcium uptake. Addition of forskolin (30 nM) or phorbol 12-myristate 13-acetate (10 nM) alone had no effect on Ca uptake. However, when added in combination, Ca uptake was stimulated to nearly the same extent as with concentrations of PTH that maximally stimulate calcium transport. We conclude that stimulation of calcium uptake by distal convoluted tubule cells requires activation of both PKA and PKC.
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PMID:Parathyroid hormone stimulation of calcium transport is mediated by dual signaling mechanisms involving protein kinase A and protein kinase C. 853 4

ADP evoked outwardly rectifying potassium currents with a latency of 0.6 s in cultured rat medullar neurons. Purinoceptor agonists, such as 2-methylthio ATP (2-MeSATP), ATP, AMP, alpha,beta-methylene ATP (alpha,beta-MeATP), and UTP, produced similar outward currents with the order of their potencies for current amplitudes: 2-MeSATP > ADP > ATP > or = alpha,beta-MeATP > or = AMP > UTP. This order corresponds to that for a subtype of P2Y purinoceptors. ADP-evoked currents were fully blocked by a broad G-protein inhibitor, guanosine-5'-O-(2-thiodiphosphate) (GDP beta S), whereas a G(i)/G(o)-protein inhibitor, pertussis toxin (PTX) had no effect. The currents were not affected by a phospholipase C (PLC) inhibitor, neomycin. Furthermore, a selective protein kinase C inhibitor, GF109203X or a selective cAMP-dependent protein kinase inhibitor, H-89 showed no effect on the currents. These results suggest that ADP activates the potassium channel via a P2Y purinoceptor linked to a PTX-insensitive G-protein and its channel regulation may be due to a direct action of the G-protein beta gamma subunits regardless of second messenger signaling cascades. Additionally, ADP enhanced intracellular free Ca2+ concentration ([Ca2+]i) both in the presence and absence of extracellular calcium, and this [Ca2+]i increase was not inhibited by neomycin. This provides an additional evidence that ADP binds to a subtype of P2Y purinoceptors, which is not involved in PLC stimulation.
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PMID:A P2 purinoceptor activated by ADP in rat medullar neurons. 859 44

The heterotrimeric G proteins mediate a variety of cellular processes by coupling transmembrane receptors to different effector molecules, including adenylyl cyclases and inositol-phospholipid-specific phospholipase C (PLC)1-3. Activation of adenylyl cyclases results in the production of cyclic AMP and activation of cAMP-dependent protein kinase (PKA). Phospholipase C catalyses the hydrolysis of phosphatidylinositol-4,5-bisphosphate (PtdInsP2) to generate diacylglycerol and inositol-1,4,5-triphosphate (InsP2), leading to the activation of protein kinase C (PKC) and the mobilization of intracellular calcium. The various PLC isoforms appear to be activated by different receptors, and in some cases by different G-protein components. There are four well-characterized forms of PLC-beta and all of them are activated to various extents by the G alpha q family of G proteins. Specific activation of PLC isoforms beta 2 and beta 3 by G-protein beta gamma subunits has also been reported. Although it has been suggested that PLC activity might be modulated by the adenylyl cyclase pathway, no clear link has been established between the two pathways. Here we report that cAMP-dependent protein kinase specifically inhibits G beta gamma-activated PLC-beta 2 activity but not that of the G alpha-activated PLC isoforms, and that the effect of PKA is not mimicked by PKC isozymes. Furthermore, we show that PKA directly phosphorylates serine residues of the PLC-beta 2 protein both in vivo and in vitro. Our results provide an insight into the specificity and nature of the crosstalk between the two G-protein-coupled signal transduction pathways.
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PMID:Regulation by cAMP-dependent protein kinease of a G-protein-mediated phospholipase C. 865 10

Melanophore pigment dispersion is a sensitive bioassay for activation of the adenylyl cyclase and phospholipase C second-messenger pathways. The necessity of protein kinase activation in causing pigment dispersion was confirmed for eight agonists of endogenous melanophore receptors and for two transfected receptors. All agonists and receptors previously shown to elevate intracellular cAMP in melanophores--melanocyte stimulating hormone, light, (-) norepinephrine, 5-hydroxytrptamine, and the beta2-adrenergic receptor--were able to stimulate pigment dispersion in the presence of Ro31-8220, a potent inhibitor of protein kinase C, but were blocked in the presence of H89, an inhibitor of cAMP-dependent protein kinase. The bombesin receptor, which elevates intracellular IP3 in melanophores, was unable to stimulate pigment dispersion in the presence of Ro31-8220 or H89. Agonists whose mechanism of activation of pigment dispersion are unknown were also tested. Endothelin 3 responses were blocked by both H89 and Ro31-8220, predicting coupling to phospholipase C. Vasoactive intestinal polypeptide, oxytocin, and calcitonin gene-related peptide beta responses were blocked only by H89, predicting coupling to adenylyl cyclase.
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PMID:Melanophore pigment dispersion responses to agonists show two patterns of sensitivity to inhibitors of cAMP-dependent protein kinase and protein kinase C. 869 26

Different drugs that elevate the cGMP levels inhibit the agonist-induced platelet activation. The mechanisms of action of cGMP probably include inhibition of both phospholipase C and the increase in intracellular Ca2+ concentration, and these effects seem to be mediated by cGMP-dependent protein kinases. However, in most studies, cells were preincubated with nitrovasodilators before stimulation. The effect of the preincubation with sodium nitroprusside before stimulation or the simultaneous addition of sodium nitroprusside and thrombin has been compared. The simultaneous addition of sodium nitroprusside and thrombin was able to inhibit without any significant delay the platelet aggregation. This rapid effect was correlated with an inhibition of both the maximum increase in intracellular Ca2+ concentration and the phospholipase C activity. Also, the simultaneous addition of sodium nitroprusside and thrombin clearly accelerated the decline in the Ca2+ signal, which was not observed in platelets preincubated with sodium nitroprusside. The rapid inhibition induced by sodium nitroprusside was correlated with a rapid and significant increase in the cGMP levels and reversed when platelets were pretreated with methylene blue. The inhibitor of cAMP-dependent protein kinase Rp-8-(4-chlorophenylthio)-adenosine-3',5'-cyclic monophosphorothioate was able to abolish nearly completely the inhibitory effect induced by sodium nitroprusside independent of the protocol used. Thus, the rapid inhibition induced by sodium nitroprusside seems to be induced by a rapid phosphorylation-dependent mechanism. In addition, both cGMP- and cAMP-dependent protein kinase seem to be involved; however, the cAMP-dependent protein kinase seems to be more important.
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PMID:Thrombin-stimulated phospholipase C activity is inhibited without visible delay by a rapid increase in the cyclic GMP levels induced by sodium nitroprusside. 870 Jan 45

Oxytocin increases myometrial intracellular free calcium by promotion of calcium entry and release of calcium from intracellular stores. Calcium release from intracellular stores is secondary to an increase in phosphoinositide (PI) turnover and generation of IP3. We have explored the biochemical basis for the coupling of oxytocin (OT) to phospholipase C (PLC). Rat myometrial membranes contain PLC beta, gamma, and delta isoforms as well as the GTP-binding proteins G alpha(q) and G alpha(11). Oxytocin stimulates both GTPase and PLC activity in rat and human myometrial membranes. These data and available structural information suggest that the oxytocin receptor couples to PLC through a GTP-binding protein. In support of this hypothesis, an antibody generated against the specific C-terminal region of G alpha(q) and G alpha(11) inhibits both the oxytocin-stimulated GTPase and PLC activities. This inhibition is reversed by neutralization of the antibody with the antigenic peptide. The data indicate that the oxytocin receptor couples to PLC, presumably of the beta subclass, via interaction with proteins of the G alpha(q/11) subclass. In the nonpregnant, estrogen-primed rat, the stimulation of PI turnover by oxytocin is inhibited by the hormone relaxin and by pertussis toxin. The effects of both of these agents are mediated by the action of cAMP-dependent protein kinase. In plasma membranes, GTP-stimulated PLC activity can also be inhibited by treatment with protein kinase A. These data suggest that cAMP-dependent phosphorylation at a step involving GTP-binding protein/PLC coupling can exert a negative effect on the stimulation of IP3 formation by oxytocin and thereby affect contraction/relaxation in the myometrium.
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PMID:Mechanisms regulating oxytocin receptor coupling to phospholipase C in rat and human myometrium. 871 99

The effects of increases in intracellular adenosine 3',5'-cyclic monophosphate (cAMP) on carbachol-induced generation of inositol phosphates (IPs) and increases in intracellular Ca2+ ([Ca2+]i) were investigated in canine cultured tracheal smooth muscle cells (TSMCs). The cAMP elevating agents, cholera toxin (CTX) and forskolin, induced concentration- and time-dependent cAMP formation with half-maximal effects (-logEC50) at concentrations of 7.6 +/- 1.3 g/ml and 4.8 +/- 0.9 M, respectively. Forskolin caused a concentration-dependent inhibition of carbachol-induced increase in [Ca2+]i with half-maximal inhibition (-logEC50) at 5.2 +/- 0.7 M. Pretreatment of TSMCs with either CTX (10 micrograms/ml, 4 h), forskolin (10-100 microM, 30 min), or dibutyryl cAMP (1 mM, 30 min) inhibited carbachol-stimulated Ca2+ mobilization and IPs accumulation. The inhibitory effects of these agents produced both depression of the maximal response and a shift to the right of the concentration-response curve of carbachol without changing the EC50 values. After treatment with forskolin for 24 h, carbachol-induced IPs accumulation and Ca2+ mobilization were close to those of control group. SQ-22536 [9-(tetrahydro-2-furanyl)-9H-purin-6-amine, 10 microM], an inhibitor of adenylate cyclase, and HA-1004 [N-(2-guanidinoethyl)-5-isoquinolinesulfonamide hydrochloride, 50 microM], an inhibitor of cAMP-dependent protein kinase (PKA), attenuated the ability of forskolin to inhibit carbachol-induced IPs accumulation. Moreover, the inactive analogue of forskolin, 1,9-dideoxy forskolin, did not inhibit these responses evoked by carbachol, suggesting that activation of cAMP/PKA was involved in these inhibitory effects of forskolin. The KD and Bmax values of the muscarinic receptor (mAChR) for [3H]-N-methyl scopolamine binding were not significantly changed by forskolin treatment for 30 min and 24 h, suggesting that the inhibitory effect of forskolin is distal to the mAChR. The locus of this inhibition was further investigated by examining the effect of forskolin treatment on AIF4(-)-stimulated IPs accumulation in canine TSMCs. The AIF4(-)-induced response was inhibited by forskolin, supporting the notion that G protein(s) are directly activated by AIF4- and uncoupled to phospholipase C by forskolin treatment. We conclude that cAMP elevating agents inhibit carbachol-stimulated generation of IPs and Ca2+ mobilization in canine cultured TSMCs. Since generation of IPs and increases in [Ca2+]i are very early events in the activation of mAChRs, attenuation of these events by cAMP elevating agents might well contribute to the inhibitory effect of cAMP on tracheal smooth muscle formation.
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PMID:Effect of cAMP elevating agents on carbachol-induced phosphoinositide hydrolysis and calcium mobilization in cultured canine tracheal smooth muscle cells. 873 64


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