Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound

---

Query: EC:2.7.11.1 (protein kinase)
81,284 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The activity of rat liver 3-hydroxy-3-methylglutaryl-coenzyme A reductase [HMG-CoA reductase; mevalonate:NADP(+) oxidoreductase (CoA-acylating), EC 1.1.1.34] can be modulated in vitro by a phosphorylation-dephosphorylation reaction sequence. A microsomal reductase kinase catalyzes the phosphorylation of HMG-CoA reductase and histones. Histone phosphorylation was enhanced 2- to 3-fold by cyclic AMP. Reductase kinase exists in interconvertible active and inactive forms. Incubation of reductase kinase with phosphoprotein phosphatase resulted in a time-dependent decrease in the ability of reductase kinase to catalyze the phosphorylation of histones and to inactivate HMG-CoA reductase. Incubation of phosphoprotein phosphatase-inactivated reductase kinase with [gamma-(32)P]ATP plus Mg(2+) and a partially purified protein kinase designated reductase kinase kinase resulted in parallel increases in protein-bound (32)P radioactivity and ability to inactivate HMG-CoA reductase. Incubation of (32)P-labeled reductase kinase with phosphoprotein phosphatase resulted in a time-dependent loss of protein-bound (32)P radioactivity and a decrease in the ability to inactivate HMG-CoA reductase. Polyacrylamide gel electrophoresis of purified reductase kinase incubated with reductase kinase kinase and [gamma-(32)P]ATP plus Mg(2+) revealed that the (32)P radioactivity and reductase kinase enzymic activity were located in a single electrophoretic position. Dephosphorylation of (32)P-labeled purified reductase kinase with phosphoprotein phosphatase was associated with significant loss of radioactivity and enzymic activity in the protein band ascribed to reductase kinase. These results provide evidence that the activity of reductase kinase, like HMG-CoA reductase, is modulated by a reversible phosphorylation-dephosphorylation reaction sequence.
...
PMID:Characterization and regulation of reductase kinase, a protein kinase that modulates the enzymic activity of 3-hydroxy-3-methylglutaryl-coenzyme A reductase. 29 71

3-Hydroxy-3-methylglutaryl coenzyme A (HMG CoA) reductase is the limiting enzyme step in cholesterol formation in mammalian liver and other tissues. It is a glycoprotein of 97,000 daltons embedded in the endoplasmic reticulum with a long cytoplasmic extension that is the site of catalytic conversion of HMG CoA to mevalonate. The enzyme is subject to both long-term (induction/repression; degradation) and short-term control (reversible phosphorylation) mediated by endocrine signaling (insulin, glucagon) and through negative feedback by metabolic products of mevalonate (e.g., cholesterol). The catalytic capacity of microsomal reductase falls rapidly in the presence of several protein kinases (reductase kinase, protein kinase-C, calmodulin-dependent protein kinase). Activity is restored with various protein phosphatases. Increased phosphorylation of reductase in intact cells after addition of glucagon or mevalonate is followed by enhanced degradation of the enzyme. In an in vitro model system, phosphorylated, native microsomal reductase is more rapidly cleaved by the calcium-dependent, neutral protease calpain than the dephosphorylated from of reductase. Our present research which centers on the mechanism of the in vitro model system is reviewed. Calpain in the presence of Ca2+ cleaves the cytosolic domain of phosphorylated 97 kDa reductase at two points giving rise to two fragments of nearly the same size that appear as a 52-56,000 dalton doublet by electrophoresis and immunoblotting. In the same system native reductase labeled with [gamma-32P]ATP generates a doublet with 32P solely in the upper (heavier) band. This indicates that serine phosphorylation sites lie between the two calpain cleavage loci. These are positioned in the "linker" region of the long carboxy-terminal cytosolic domain near the membrane. This segment possesses five invariant serine residues and two PEST sequences (constellations of proline, glutamate, serine and threonine) that are characteristic of proteins with short half-lives. If phosphorylation of HMG CoA reductase is confined to the linker region, we must look to this domain in order to interpret the resulting conformational changes that markedly influence reductase catalytic activity and prepare the enzyme for degradation.
...
PMID:Phosphorylation and degradation of HMG CoA reductase. 262 76

3-Hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase exists in interconvertible active and inactive forms in cultured fibroblasts from normal and familial hypercholesterolemic subjects. The inactive form can be activated by endogenous or added phosphoprotein phosphatase. Active or partially active HMG-CoA reductase in cell extracts was inactivated by a ATP-Mg-dependent reductase kinase. Incubation of phosphorylated (inactive) HMG-CoA reductase with purified phosphoprotein phosphatase was associated with dephosphorylation (reactivation) and complete restoration of HMG-CoA reductase activity. Low density lipoprotein, 25-hydroxycholesterol, 7-ketocholesterol, and mevalonolactone suppressed HMG-CoA reductase activity by a short-term mechanism involving reversible phosphorylation. 25-Hydroxycholesterol, which enters cells without the requirement of low density lipoprotein-receptor binding, inhibited the HMG-CoA reductase activity in familial hypercholesterolemic cells by reversible phosphorylation. Measurement of the short-term effects of inhibitors on the rate of cholesterol synthesis from radiolabeled acetate revealed that HMG-CoA reductase phosphorylation was responsible for rapid suppression of sterol synthesis. Reductase kinase activity of cultured fibroblasts was also affected by reversible phosphorylation. The active (phosphorylated) reductase kinase can be inactivated by dephosphorylation with phosphatase. Inactive reductase kinase can be reactivated by phosphorylation with ATP-Mg and a second protein kinase from rat liver, designated reductase kinase kinase. Reductase kinase kinase activity has been shown to be present in the extracts of cultured fibroblasts. The combined results represent the initial demonstration of a short-term regulation of HMG-CoA reductase activity and cholesterol synthesis in normal and receptor-negative cultured fibroblasts involving reversible phosphorylation of both HMG-CoA reductase and reductase kinase.
...
PMID:Regulation of 3-hydroxy-3-methylglutaryl coenzyme A reductase activity in human fibroblasts by reversible phosphorylation: modulation of enzymatic activity by low density lipoprotein, sterols, and mevalonolactone. 300 40

A calcium-activated and phospholipid-dependent protein kinase (protein kinase C) catalyzes the phosphorylation of both insoluble microsomal (Mr approximately 100,000) and purified soluble (Mr = 53,000) 3-hydroxy-3-methylglutaryl coenzyme A reductase. The phosphorylation and concomitant inactivation of enzymic activity of HMG-CoA reductase was absolutely dependent on Ca2+, phosphatidylserine, and diolein. Dephosphorylation of phosphorylated HMG-CoA reductase was associated with the loss of protein bound radioactivity and reactivation of enzymic activity. Maximal phosphorylation of purified HMG-CoA reductase was associated with the incorporation of 1.05 +/- 0.016 mol of phosphate/mol of native form of HMG-CoA reductase (Mr approximately 100,000). The apparent Km for purified HMG-CoA reductase and histone H1 was 0.08 mg/ml, and 0.12 mg/ml, respectively. The tumor-promoting phorbol ester, phorbol 12-myristate 13-acetate stimulated the protein kinase C-catalyzed phosphorylation of HMG-CoA reductase. Increased phosphorylation of HMG-CoA reductase by phorbol 12-myristate 13-acetate suggests a possible in vivo protein kinase C-mediated mechanism for the short-term regulation of HMG-CoA reductase activity. The identification of the protein kinase C system in addition to the reductase kinase-reductase kinase kinase bicyclic cascade systems for the modulation of the enzymic activity of HMG-CoA reductase may provide new insights into the molecular mechanisms involved in the regulation of cholesterol biosynthesis.
...
PMID:Phosphorylation of hepatic 3-hydroxy-3-methylglutaryl coenzyme A reductase and modulation of its enzymic activity by calcium-activated and phospholipid-dependent protein kinase. 315 37

Hydroxymethylglutaryl CoA reductase catalyzes the limiting step in cholesterol synthesis in liver and other tissues. Beginning in 1973 studies with subcellular systems established that microsomal reductase is inactivated with ATP(Mg) and reductase kinase, and restored to full activity with phospho-protein phosphatase. By contrast reductase kinase is inactivated with phosphatase and reactivated with a second protein kinase (reductase kinase kinase). This bicyclic system has now been confirmed in terms of homogeneous enzyme components and by direct reversible phosphorylation with [gamma 32P]ATP in several laboratories. Short-term endocrine control of reductase and reductase kinase has been demonstrated in intact rat hepatocytes. Preincubation of cells with glucagon brought about a fall in the expressed activity of reductase and a rise in reductase kinase consistent with net phosphorylation of both enzymes. Total reductase levels were also severely depressed after glucagon. Addition of insulin to suspensions of hepatocytes had the reverse effect on expressed activity of reductase (elevated) and reductase kinase (depressed). Insulin also prevented the decay in total reductase activity. Since both protein kinases identified in this system are cAMP-insensitive, it was possible that hormonal signaling is mediated through the protein phosphatase that acts on both reductase kinase and reductase. In recent studies we have shown that the rate of activation of endogenous reductase in hepatocyte extracts (microsomes plus cytosol) is responsive to hormonal modulation. Pretreatment of hepatocytes with insulin increases apparent reductase phosphatase activity in extracts while glucagon diminishes the rate of reductase activation. HMG CoA is converted to mevalonate by the reductase enzyme. In hepatocytes mevalonate is rapidly converted to cholesterol and to a variety of isoprene derivatives. Expressed reductase activity falls precipitously when hepatocytes are incubated with mevalonate (added in the form of mevalono-lactone). As in the case with glucagon pretreatment reductase phosphatase is rapidly diminished. (Mevalonate itself is not inhibitory to reductase or reductase phosphatase activity in subcellular systems.) It is probable that a product of mevalonate metabolism generated in intact cells may act as a reductase phosphatase inhibitor. Among these added inorganic pyrophosphate inhibited reductase phosphatase at low concentrations.
...
PMID:Short-term regulation of hydroxymethylglutaryl coenzyme A reductase by reversible phosphorylation: modulation of reductase phosphatase in rat hepatocytes. 705 70

We recently reported the existence of a protein kinase cascade in higher plants, of which the central component is a 3-hydroxy-3-methylglutaryl(HMG-)-CoA reductase kinase functionally related to mammalian AMP-activated protein kinase [MacKintosh, R. W., Davies, S. P., Clarke P. R., Weekes, J., Gillespie, S. G., Gibb, B. J. & Hardie, D. G. (1992) Eur. J. Biochem. 209, 923-931]. We have now purified this protein kinase 9000-fold from cauliflower inflorescences. During the course of this work we noticed a second minor form (form B) which separated from the major form (A) on ion exchange and gel filtration. Both forms phosphorylate the catalytic fragment of mammalian HMG-CoA reductase. Both forms are markedly inactivated by incubation with the reactive ATP analogue p-fluorosulphonylbenzoyl adenosine (FSO2PhCOAdo), and also by mammalian protein phosphatase 2C, indicating that form B, like form A, is activated by phosphorylation. Form A has an apparent native molecular mass of 200 kDa by gel filtration and, after labelling with [14C]FSO2PhCOAdo, of 150 kDa by electrophoresis in non-denaturing gels. The catalytic subunit was identified as a polypeptide of 58 kDa after labelling with [14C]FSO2PhCOAdo. Form B has an apparent native molecular mass of 45 kDa by gel filtration, and was identified as a polypeptide of 45 kDa after labelling with [14C]FSO2PhCOAdo and [gamma-32P]ATP. Using a series of variants of the synthetic peptide substrate, the substrate specificities of the two forms are similar but not identical. Form B does not appear to be a proteolytic fragment of form A, and we therefore propose that it represents a closely related member of the same protein kinase sub-family.
...
PMID:Biochemical characterization of two forms of 3-hydroxy-3-methylglutaryl-CoA reductase kinase from cauliflower (Brassica oleracia). 811 24

Protein kinase isoenzymes belonging to the protein kinase C (PK-C) family present in rat mammary tissue have been resolved from one another by chromatography on hydroxyapatite, and characterized. PK-C alpha is the predominant isoenzyme and is present at a constant level of activity throughout mammary-gland development and differentiation. In contrast, marked changes in the relative abundance of other mammary PK-C isoenzymes accompany the transition from pregnancy to lactation. The sensitivity of mammary PK-C alpha to Ca2+ is greater in tissue from pregnant than from lactating rats. This isoenzyme has other atypical properties consistent with its being more highly phosphorylated than PK-C alpha in rat brain and spleen. One of the protein kinase isoenzymes resolved from mammary tissue recognizes the peptide substrate used to assay AMP-activated kinase and may thus interfere in the determination of this activity. Another is fully active in the absence of Ca2+ and is more than 80% active in the absence of added lipid effectors. A 'housekeeping' role is proposed for PK-C alpha in mammary tissue, whereas the less abundant PK-C isoenzymes may be involved in mammary cell proliferation and differentiation.
...
PMID:Isoenzymes of protein kinase C in rat mammary tissue: changes in properties and relative amounts during pregnancy and lactation. 848 8

We have developed a sensitive assay for the AMP-activated protein kinase kinase, the upstream component in the AMP-activated protein kinase cascade. Phosphorylation and activation of the downstream kinase by the upstream kinase absolutely requires AMP and is antagonized by high (millimolar) concentrations of ATP. We have purified the upstream kinase >1000-fold from rat liver; a variety of evidence indicates that the catalytic subunit may be a polypeptide of 58 kDa. The physical properties of the downstream and upstream kinases, e.g. catalytic subunit masses (63 versus 58 kDa) and native molecular masses (190 versus 195 kDa), are very similar. However, unlike the downstream kinase, the upstream kinase is not inactivated by protein phosphatases. The upstream kinase phosphorylates the downstream kinase at a single major site on the alpha subunit, i.e. threonine 172, which lies in the "activation segment" between the DFG and APE motifs. This site aligns with activating phosphorylation sites on many other protein kinases, including Thr177 on calmodulin-dependent protein kinase I. As well as suggesting a mechanism of activation of AMP-activated protein kinase, this finding is consistent with our recent report that the AMP-activated protein kinase kinase can slowly phosphorylate and activate calmodulin-dependent protein kinase I, at least in vitro (Hawley, S. A., Selbert, M. A., Goldstein, E. G., Edelman, A. M., Carling, D., and Hardie, D. G. (1995) J. Biol. Chem. 270, 27186-27191).
...
PMID:Characterization of the AMP-activated protein kinase kinase from rat liver and identification of threonine 172 as the major site at which it phosphorylates AMP-activated protein kinase. 891 Mar 87

The ability of cells to react appropriately to nutritional cues is of fundamental importance, and in budding yeast, a small number of intracellular protein kinases, PKA, Snf1p/AMP-activated kinase, TOR, Gcn2p, and the cyclin-dependent kinase Pho85p have key roles. A recently characterized enzyme, PAS kinase, may be a new member of this group of nutritional transducers.
...
PMID:Nutrient-regulated protein kinases in budding yeast. 1240 59

Enkephalin modulates striatal function, thereby affecting motor performance and addictive behaviors. The proenkephalin gene is also used as a model to study cyclic AMP-mediated gene expression in striatal neurons. The second messenger pathway leading to proenkephalin expression demonstrates how cyclic AMP pathways are synchronized with depolarization. We show that cyclic AMP-mediated regulation of the proenkephalin gene is dependent on the activity of L-type Ca2+ channels. Inhibition of L-type Ca2+ channels blocks forskolin-mediated induction of proenkephalin. The Ca2+-activated kinase, Ca2+/calmodulin kinase, as well as the cyclic AMP-activated kinase, protein kinase A (PKA), are both necessary for the induction of the proenkephalin promoter. Similarly, both kinases are needed for the L-type Ca2+ channel-mediated induction of proenkephalin. This synchronization of second messenger pathways provides a coincidence mechanism that gates proenkephalin synthesis in striatal neurons, ensuring that levels are increased only in the presence of activated PKA and depolarization.
...
PMID:Striatal proenkephalin gene induction: coordinated regulation by cyclic AMP and calcium pathways. 1287 86


1 2 3 4 5 Next >>

---