Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:2.7.11.1 (protein kinase)
 81,284 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Epinephrine was used to activate the heparin non-releasable lipoprotein lipase (LPL) in the 3 skeletal muscle fiber types of the perfused rat hindlimb. Following a 9 min washout of the capillary-bound lipoprotein lipase, the hindquarter of the rat was perfused with a buffer containing 10 nM of epinephrine. Activity of the residual LPL in soleus, red vastus lateralis, and white vastus lateralis muscles increased 75%, 96%, and 102% respectively, following epinephrine perfusion. These results suggest that skeletal muscle LPL is under hormonal control possibly through protein phosphorylation by cyclic AMP dependent protein kinase.
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PMID:Epinephrine-activation of heparin-nonreleasable lipoprotein lipase in 3 skeletal muscle fiber types of the rat. 281 80

Although the renal medulla is rich in triacylglycerols, the lipolysis of these intracellular triacylglycerols by a renomedullary triacylglycerol lipase has not been directly demonstrated. The present study demonstrates triacylglycerol lipase activity localized in the particulate subcellular fractions of rabbit renal medullae. Renomedullary triacylglycerol lipase activity, as determined by the hydrolysis of [14C]triolein to [14C]oleic acid, was observed to have a pH optimum of 5.8. Addition of cAMP/ATP/magnesium acetate resulted in an 80% activation of crude homogenate triacylglycerol lipase activity; addition of exogenous cAMP-dependent protein kinase resulted in a further activation of lipolysis. 3 mM CaCl2 had no effect on basal triacylglycerol lipase activity. 1 M NaCl did not inhibit lipolysis, suggesting that the lipase activity measured was not due to lipoprotein lipase. Endogenous renomedullary triacylglycerols were hydrolysed by a lipase in the 100,000 X g pellet of renomedullary homogenates, resulting in the release of free fatty acids including arachidonic and adrenic acids. Dispersed renomedullary cells were prepared to monitor hormone-sensitive triacylglycerol lipase activity in intact cells. Addition of 10 microM forskolin and 10 microM epinephrine resulted in 8-fold and 50-fold increases in triacylglycerol lipase activity, respectively, as defined by release of free glycerol from the cells. These studies demonstrate that a cAMP-dependent hormone-sensitive triacylglycerol lipase is present in the renal medulla, and is responsible for the hydrolysis of renomedullary triacylglycerols.
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PMID:Triacylglycerol lipase activity in the rabbit renal medulla. 282 29

Fatty acid metabolism in adipocytes is known to be regulated by the intracellular transducer cAMP. This study was undertaken to determine the temporal and hormonal regulation of cAMP-dependent protein kinase during the differentiation of preadipocyte mesenchymal cells to adipocytes. For this we have used a stable cell line (TA1) in which the undifferentiated preadipocyte acquires adipocyte functions and morphology after growth to confluence. We observed that synthesis of type I and II cAMP-dependent protein kinases was induced during the adipogenic conversion of growth-arrested TA1 cells. In preconfluent cells, neither mRNAs encoding regulatory subunits (RI, RII beta) and catalytic subunit (C alpha) nor the peptides themselves were detectable. Within several days of growth arrest at high cell density, mRNAs for RI, RII beta, and C alpha were detectable in total RNA extracted from cell populations. The subunits themselves were detectable in some, but not all, of the cells by indirect immunofluorescence. Immunoblotting of cytosolic extracts indicated that RI and the beta-isoform of RII (mol wt = 52,000) were expressed in these cells. Analysis of subunit presence or absence in single cells by immunofluorescence also indicated that kinase subunit expression preceded the accumulation of lipid droplets within the cells. Further, the subunits were predominantly associated with a reticular cytoplasmic structure (Golgi apparatus?) abutting the nucleus. Conversion of TA1 cells to adipocytes can be accelerated by indomethacin (125 microM) or dexamethasone (1 microM) treatment, compounds that also enhanced the accumulation of RII beta and C alpha mRNAs. Within 2-3 days of addition of indomethacin to confluent cultures, RII beta message content is increased about 20-fold, and protein content is increased about 5-fold relative to those in untreated cultures. C alpha mRNA content is increased about 5-fold relative to that in untreated cells. The response to dexamethasone requires 6-7 days, and changes in RII beta message levels were the most pronounced. We also observed the induction of mRNAs for the functionally relevant mRNA lipoprotein lipase in indomethacin-treated cells. In addition to this apparent transcriptional regulation of kinase subunit expression, we provide evidence for regulation at the posttranscriptional level. Within a differentiated culture, there exist stem cells that can be selected, will repopulate the dish, and will again differentiate into adipocytes upon growth arrest at high cell density. In preconfluent populations of these stems cells, unlike the preconfluent TA1 cells originally plated, both RII beta and C alpha messages were present.(ABSTRACT TRUNCATED AT 400 WORDS)
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PMID:Induction of adenosine 3',5'-monophosphate-dependent protein kinase subunits during adipogenesis in vitro. 284 11

Lipolysis of intracellular triglycerides in the heart has been shown to be regulated by hormones. However, activation of myocardial triglyceride lipase in a cell-free system has not been directly demonstrated. In the present studies, initial attempts to demonstrate cAMP-dependent activation of triglyceride lipase using the 1,000 X g supernatant fraction (S1) of mouse heart homogenate were unsuccessful, presumably due to the masking effects of high levels of lipoprotein lipase activity even when assayed at pH 7.4 and in the absence of apolipoprotein C-II. Myocardial lipoprotein lipase in the 40,000 X g supernatant fraction was then removed by heparin-Sepharose affinity chromatography. The lipoprotein lipase-free fractions were shown to contain neutral triglyceride lipase and neutral cholesterol esterase of about equal activities. The triglyceride lipase and cholesterol esterase activities fell progressively during preincubation in the presence of 5 mM Mg2+. Additions of cAMP and ATP resulted in 40-70% activation of both triglyceride lipase and cholesterol esterase. The activation was blocked by protein kinase inhibitor and was restored by the addition of exogenous cAMP-dependent protein kinase. Since lipoprotein lipase has no activity toward cholesteryl oleate, activation of cholesterol esterase in untreated S1 was readily demonstrable. Both triglyceride lipase and cholesterol esterase activities were present in homogenates prepared from isolated rat heart myocytes. We conclude that the myocardium contains a hormone-sensitive lipase that is regulated in a fashion similar to that of the adipose tissue enzyme.
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PMID:Activation of myocardial neutral triglyceride lipase and neutral cholesterol esterase by cAMP-dependent protein kinase. 298 7

The effect of CAM [cyclic AMP, Mg-ATP, and 3-isobutyl, 1-methylxanthine (MIX)] on triacylglycerol (TG) lipase activity in extracts from heparin-perfused rat heart was determined. TG lipase activity in homogenate, 10,000g supernatant, 105,000g supernatant, ammonium sulfate supernatant, and the eluate from heparin-Sepharose was increased between 62 and 151% when incubated with a combination of 0.3 mM cyclic AMP, 5 mM MgCl2, and 2 mM ATP. The addition of Mg-ATP + cyclic AMP caused a greater activation of TG lipase in the various fractions than did Mg-ATP + MIX or cyclic AMP + MIX. These results suggest that activation may be mediated by the classical cyclic AMP-protein kinase cascade. Control and CAM-stimulated activities were increased by heparin and inhibited by NaCl and protamine sulfate. In the absence of serum in the assay, the CAM system caused a relatively greater stimulation of lipolytic activity in each fraction compared to when serum was present in the assay. However, the absolute values were 6.1 to 16.3-fold greater with serum in the assay than without serum. In a similar manner, TG lipase activity was stimulated by CAM between 1.75 and 4.26-fold at pH 7.4, and only between 1.62 and 2.51-fold at pH 8.1. However, the absolute values at pH 8.1 were 6.77 to 31.83-fold greater than those seen at pH 7.4. These data demonstrate, for the first time, the cyclic AMP activation of a TG lipase above basal levels in cell-free fractions of rat heart. It is intriguing to speculate that the intracellular fraction of lipoprotein lipase may play a role in the hormonal regulation of cardiac TG lipolysis.
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PMID:Cyclic AMP activation of a triglyceride lipase in broken cell preparations of rat heart. 301 40

Diacylglycerol lipase and kinase activities were measured in particulate and soluble fractions from rabbit aorta (intima-media) and coronary microvessels. With rabbit aorta, the hydrolysis at the sn-1 position of 1-palmitoyl-2-oleoyl-sn-glycerol had a pH optimum of 5-6 and was greater than hydrolysis at the sn-2 position (pH optimum of 6.5). Only the 2-monoacylglycerol accumulated during incubations at pH 5 and 6.5. These results are consistent with an ordered two-step reaction sequence where the fatty acid at the sn-1 position is released first, followed by the hydrolysis of the fatty acid from the 2-monoacylglycerol by a monoacylglycerol lipase with a neutral pH optimum. Lipase activity (sn-2 hydrolysis) at pH 6.5 was greater than kinase activity at all substrate concentrations. The presence of arachidonate at the sn-2 position of the diacylglycerol increased kinase activity but had little effect on lipase activity. Kinase activity was mainly particulate, whereas 50-60% of diacylglycerol lipase and 50% of monoacylglycerol lipase activity were soluble. Diacylglycerol lipase and kinase were also present in coronary microvessel preparations. Diacylglycerol lipase (sn-2 hydrolysis) activity in coronary microvessels was not enhanced by preincubation of the enzyme preparation with cAMP-dependent protein kinase.
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PMID:Diacylglycerol lipase and kinase activities in rabbit aorta and coronary microvessels. 302 22

Three TG lipases have been identified in muscle (i.e., acid, neutral, and alkaline), but as yet we do not know which enzyme is responsible for tissue TG hydrolysis. Over the past 8 yr, work in our laboratory has focused on intracellular lipoprotein lipase (LPL). The results show that this lipase is regulated by the classical cAMP cascade and that the activity of this enzyme is inversely related to endogenous TG concentration. Using these results as a foundation we plan to examine molecular mechanisms involved in the synthesis, compartmentalization, and transport of the alkaline TG lipase. Further, the evidence suggests that this enzyme may be regulated by protein phosphorylation mediated by cyclic AMP-dependent protein kinase. We plan to test this possibility.
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PMID:Role of the alkaline TG lipase in regulating intramuscular TG content. 307 Feb 56

A model for the regulation of erythropoietin production has been presented. This model proposes that a primary O2-sensing reaction in the kidney is initiated by a decrease in ambient PO2, a rapid decrease in gas exchange in the lung, a diminished oxygen-carrying capacity of hemoglobin, a molecular deprivation of oxygen, or a decrease in renal blood flow. It is proposed that the primary oxygen-sensing reaction may trigger the release of several mediators that stimulate adenylate cyclase through a receptor-activated stimulation of a G protein in the renal cell membrane. Some of the agents that are thought to be released during hypoxia, which may trigger this cascade, are adenosine (A2 activation), eicosanoids (PGE2, PGI2, and 6-keto PGE1), oxygen-free radicals (superoxide and H2O2), and catecholamines with beta-2 adrenergic receptor agonist properties. The activation of adenylate cyclase generates cyclic AMP, which activates protein kinase A, leading to the production of a phosphoprotein that, in turn, activates a nuclear protein involved in transcription and/or translation for erythropoietin biosynthesis and/or secretion. A second part of this model concerns the effect of hypoxia on a renal cell membrane phosphodiesterase and the generation of inositol triphosphate and diacylglycerol. Diacylglycerol may interact with diacylglycerol lipase to generate arachidonic acid, which, together with arachidonic acid generated by the interaction of phospholipase A2 on membrane phospholipids, produces eicosanoids. Eicosanoids may play a secondary role in Ep production/secretion. The model further proposes that calcium levels in both renal and liver cells may be important in regulating erythropoietin biosynthesis and/or secretion. It is proposed that an increase in intracellular calcium leads to the inhibition of erythropoietin biosynthesis and/or secretion and a decrease in intracellular calcium increases erythropoietin production. The specific mechanism by which calcium regulates erythropoietin biosynthesis and secretion is not well understood. However, a good correlation is seen with several agents that decrease intracellular calcium and increase erythropoietin production as well as with other agents that increase intracellular calcium and decrease erythropoietin production. When inositol triphosphate levels are increased, an increase in the mobilization of intracellular calcium from the endoplasmic reticulum or another intracellular pool occurs. This increased intracellular calcium probably activates a calcium calmodulin kinase and produces a phosphoprotein that inhibits erythropoietin production/secretion.(ABSTRACT TRUNCATED AT 400 WORDS)
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PMID:Pharmacologic modulation of erythropoietin production. 328 82

In the mammalian myocardium, an active triglyceride synthesis pathway is operating, (re)esterifying activated fatty acids from endogenous or exogenous sources, with the glycolytically derived three-carbon intermediates dihydroxyacetone-phosphate and glycerol-3-phosphate by the so-called Kennedy pathway. The seven enzymes of triglyceride synthesis are membrane bound and located at the sarcoplasmic reticulum. The first enzyme in the glycerol-3-phosphate pathway, glycerol-3-phosphate acyltransferase, is proposed to be rate limiting for triglyceride formation. This microsomal enzyme is regulated by phosphorylation (inactiycation)-dephosphorylation (activation) coupled to the beta-receptor--adenyl cyclase--protein kinase system. Additional regulatory steps in triglyceride formation are the reactions catalyzed by the microsomal phosphatidic acid phosphatase and diglyceride acyltransferase. Intracellular triglycerides occur as free floating cytosolic droplets, membrane-bound particles and lipid-filled lysosomes. No consensus exists about the metabolically active portion of myocardial triglycerides. Various lipases have been proposed to be involved in endogenous lipolysis: the lysosomal acid, microsomal and soluble neutral triglyceride, intracellular lipoprotein lipases and the microsomal di- and monoglyceridase. It has been acknowledged that the bulk of the intracellular neutral lipase represents the precursor of vascular lipoprotein lipase. The presence of a neutral lipase, as distinct from lipoprotein lipase, in the rat heart was recently advocated. Endogenous lipolysis is a hormone-sensitive process. Hormone-sensitivity may involve direct alteration of enzyme activity by protein phosphorylation-dephosphorylation but is also dependent on the removal rate of product fatty acids, since feedback inhibition is a common property of all lipases in the heart.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Synthesis, storage and degradation of myocardial triglycerides. 331 Oct 5

An attempt was made to activate the capillary-bound fraction of lipoprotein lipase (LPL) with cAMP-dependent protein kinase catalytic subunit (PKC). Following a 30s washout period, hearts were perfused for 1 min with buffer containing heparin. Medium was collected during the second 30s of heparin perfusion. Addition of PKC+Mg-ATP to this capillary bed perfusate increased LPL activity from 6.84 +/- 0.72 nmol/ml/min to 13.76 +/- 1.12 nmol/ml/min (P less than 0.001). A similar 2-fold increase in activity was observed when results were expressed on a mg protein basis. Removal of serum from, or addition of 1.0M NaCl to, the assay system inhibited PKC-stimulated LPL activity approximately 85%. These results indicate that capillary alkaline LPL can be activated by PKC assayed under experimental conditions free of other TG lipases. Moreover, these findings suggest that the intracellular fraction of LPL can be activated by cAMP and that this activation is mediated through protein phosphorylation by cAMP-dependent protein kinase.
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PMID:Protein kinase activation of heparin-releasable lipoprotein lipase in rat heart. 395 70


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