Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:2.7.11.13 (protein kinase C)
 49,245 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

A monoclonal antibody directed against the Ca2+-requiring proteinase (calpain) of human neutrophils was employed to assess the role of this proteinase in mediating the responses to stimuli such as phorbol 12-myristate 13-acetate or fMet-Leu-Phe. In the presence of either phorbol 12-myristate 13-acetate or fMet-Leu-Phe the antibody is taken up by the neutrophils, and a marked inhibition of intracellular calpain is observed. The decreased calpain activity is accompanied by (a) a significant decrease in the proteolytic conversion of native protein kinase C (Ca2+/phospholipid-dependent enzyme) to the soluble form that does not require Ca2+ or phospholipids for activity; (b) a marked increase in the production of superoxide anion; and (c) a decrease in the exocytosis of granule contents. The increase in superoxide production can be attributed to a more prolonged association of native protein kinase C with the plasma membrane, thus enhancing the phosphorylation of membrane proteins that precedes O(2-) production (Pontremoli, S., Melloni, E., Salamino, F., Sparatore, B., Michetti, M., Sacco, O., and Horecker, B. L. (1986), Biochem. Biophys. Res. Commun. 140, 1121-1126). The decreased exocytosis can be attributed to a decreased phosphorylation of certain cytoskeletal proteins, catalyzed by the soluble form of protein kinase C (Pontremoli, S., Melloni, E., Michetti, M., Sparatore, B., Salamino, F., Sacco, O., and Horecker, B. L. (1987) Proc. Natl. Acad. Sci. U. S. A. 84, 3604-3608); the subsequent reorganization of the cytoskeleton appears to be related to degranulation. These effects of the monoclonal anti-calpain provide direct evidence for an essential role for calpain in the activation of human neutrophils.
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PMID:Effects of a monoclonal anti-calpain antibody on responses of stimulated human neutrophils. Evidence for a role for proteolytically modified protein kinase C. 282 58

The phosphorylation of the anion-transport protein (band 3) is selectively increased in human red cell membrane, following exposure of intact cells to ionophore and micromolar calcium. The phosphorylation is catalyzed by a membrane associated protein kinase distinct from either protein kinase C or Ca2+/calmodulin dependent protein kinase. We show that the increase in phosphorylation of band 3 is abolished if red cells had been pre-loaded with an inhibitor of calpain or with an anticalpain monoclonal antibody. Our findings suggest that calpain activity may control, both at a functional and at a structural level, the activity of this important transmembrane protein through the modulation of its susceptibility as a substrate of membrane bound protein kinase(s). Based on previous observations indicating the presence in erythrocytes from hypertensive patients of an uncontrolled intracellular calpain-mediated proteolytic system accompanied by an increased phosphorylation of band 3 protein(s), we suggest that our results may shed light on the type of molecular alteration which is associated with the hypertensive state.
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PMID:The role of calpain in the selective increased phosphorylation of the anion-transport protein in red cell of hypertensive subjects. 283 93

Recent studies have demonstrated that a calcium-sensitive protease converts Ca2+/phospholipid-dependent protein kinase C to a Ca2+/phospholipid-independent form during the activation of human neutrophils. In this paper, the results of the purification and characterization of a calcium-dependent cytosolic protease from neutrophils is reported. Calcium-dependent protease has been purified 1062-fold from human neutrophils and behaves as a single species on native polyacrylamide gels. The protease is active in the neutral pH range with no observable activity amide gels. The protease is active in the neutral pH range with no observable activity at pH values greater than 8.0, has an absolute requirement for calcium for expression of activity with half-maximal activity observed at 12 microM free calcium, and has an apparent molecular weight of 110,000 based on gel filtration. The protease requires the presence of dithiothreitol for activity and is inhibited by sulfhydryl inhibitors, leupeptin, and antipain but not by serine protease inhibitors, pepstatin, or orthophenanthroline. The protease is also susceptible to inactivation by autoproteolysis. Based on the similarities of this calcium-dependent protease with calpains from a variety of other mammalian tissues, the protease isolated from human neutrophils appears to be a calpain I.
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PMID:Purification and characterization of calpain from human polymorphonuclear leukocytes. 283 20

Calpains are Ca2+ -dependent thiol proteases which have been identified in various tissues of eucaryotes, but their physiological function in the cell is uncertain. In the muscle fiber, two types of calpains are present which differ by their calcium sensitivity: calpain 1 and calpain 2, which require for their activity micro and millimolar concentrations of calcium respectively. These calpains are associated with protein kinase C activities in the differentiated fiber. The multinucleate myotube is formed by fusion of mononucleated precursor cells, myoblasts. Calpains have been reported to appear in myoblasts at around the time of fusion. Moreover, an apparent synthesis of 1,2 diacylglycerol, an activator of protein kinase C, was observed during fusion of myoblasts. However, more information is required to incriminate totally protein kinase C and calpains in the mechanism of myoblast fusion.
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PMID:[Calpains, protein kinase c and development of muscle tissue]. 284 58

In this paper we discuss recent experimental results pertinent to three unresolved issues regarding the long-term potentiation (LTP) effect: the nature of its enduring substrates, the biochemical mechanisms that produce it, and its potential role in memory. LTP appears to be triggered by a postsynaptic influx of calcium and is associated with alterations in the shape of dendritic spines and probably the formation of new synapses. We discuss the possibility that morphological reorganization also modifies membrane surface chemistry of synaptic elements. Evidence is presented that LTP is not associated with changes in presynaptic calcium currents. Activation of protein kinase C is shown to be insufficient for the induction of LTP, although it may play a modulatory role. The hypothesis that activation of a calcium-sensitive protease (calpain) is pivotal to the establishment of LTP is supported by experiments showing that a calpain inhibitor, leupeptin, blocks LTP. Furthermore, activation of NMDA receptors, an event implicated in LTP induction, is accompanied by calcium-sensitive proteolysis of spectrin, a major dendritic cytoskeletal protein. The finding that stimulation patterns designed to mimic naturally-occurring cell discharge patterns are highly effective for LTP induction greatly strengthens the hypothesis that LTP actually occurs during the encoding of information in cortical systems. Potential contributions of LTP to learning are explored using computer simulations of a simple cortical network.
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PMID:Long-term potentiation: persisting problems and recent results. 285 Aug 41

These and earlier findings suggest that certain neutrophil biochemical responses induced by external stimuli are mediated by the reorganization of the cytoskeletal-membrane interactions. This rearrangement of the intracellular architecture appears to result from a coordinated and integrated operation of two enzymes, namely PKC and calpain. This conclusion is schematically represented in a comprehensive model, discussed in the introduction and derived from a number of experimental observations. In focusing the importance of cytoskeletal reorganization, signal-directed proteolysis, induced by specific PKC-mediated phosphorylation, appears to play a fundamental role in cell functions such as positioning and fusion of organelles with plasma membranes and possibly locomotion and transport.
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PMID:The role of calpain and protein kinase C in activation of human neutrophils. 285 70

Calpains are Ca2+-dependent serine proteases that can regulate protein kinase C-mediated cellular events by cleaving the membrane-bound native enzyme to yield an activated cytosolic fragment. Inhibition of calpain by leupeptin may cause enhancement or inhibition of cellular functions depending on the nature of the protein kinase C reaction involved. We have studied the effects of leupeptin on platelet responses (aggregation, secretion, thromboxane B2 formation and intracellular Ca2+ and pH changes) induced by either thrombin, collagen or phorbol 12-myristate 13-acetate (TPA), which are known to activate protein kinase C by different mechanisms. Only thrombin-induced responses were inhibited by leupeptin. This suggests that the inhibitory effect of leupeptin is not due to antagonism of calpain in this system, but to direct interference with the proteolytic effect of thrombin.
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PMID:Leupeptin does not affect the normal signal transduction mechanism in platelets. 292 Aug 37

Low concentrations of phorbol 12-myristate 13-acetate (PMA) elicit a specific response in human neutrophils, characterized by the production of oxygen radicals and the release into the medium of a membrane-bound serine proteinase (Pontremoli, S., Melloni, E., Michetti, M., Sacco, O., Sparatore, B., Salamino, F., Damiani, G. and Horecker, B. L. (1986) Proc. Natl. Acad. Sci. U. S. A., 83, 1685-1689). The following evidence indicates that this response is mediated by membrane-bound protein kinase C: 1) it is blocked by inhibitors of protein kinase C; and 2) it is enhanced in cells preloaded with leupeptin which prevents proteolysis of protein kinase C and its subsequent dissociation from the cell membrane. This response is not accompanied by significant exocytosis of granule enzymes. With higher concentrations of PMA, and more particularly on stimulation with formylmethionyl-leucyl-phenylalanine (fMLP) plus cytochalasin B, a substantial exocytosis of constituents of both specific and azurophil granules is observed. With fMLP, exocytosis of granule enzymes is the predominant event, with little production of H2O2 and negligible release of membrane-bound serine proteinase. Exocytosis promoted either by a high concentration of PMA or by fMLP is inhibited by leupeptin, indicating that it is due to the action of an intracellular Ca2+-dependent thiol proteinase (calpain), either directly or by conversion by calpain of membrane-bound protein kinase C to the soluble Ca2+/phospholipid-independent form. Intracellular mobilization of Ca2+ is also observed following stimulation with either PMA or fMLP, but only the latter results in a net increase in the intracellular concentration of free Ca2+; under these conditions maximum exocytosis of granule contents is observed.
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PMID:Biochemical responses in activated human neutrophils mediated by protein kinase C and a Ca2+-requiring proteinase. 301 47

Incubation of the cytoskeletal fraction from human neutrophils with the proteolytically activated form of protein kinase C results in the phosphorylation of several components, including a 20-kDa polypeptide, probably consisting of myosin light chains. The 20-kDa polypeptide is also specifically phosphorylated by activated protein kinase C in a solubilized 20-kDa/80-kDa complex that was obtained after sonication of the insoluble cytoskeletal fraction. Phosphorylation of this polypeptide, in either the insoluble cytoskeletal fraction or the soluble 20-kDa/80-kDa complex, greatly enhances its susceptibility to digestion by the Ca2+-requiring proteinase (calpain, EC 3.4.22.17) of human neutrophils. Thus, signals that activate calpain by mobilizing intracellular calcium would lead to proteolytic activation of protein kinase C, phosphorylation of cytoskeletal proteins, and remodeling of the cytoskeleton by proteolysis of at least one cytoskeletal component.
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PMID:Phosphorylation by protein kinase C of a 20-kDa cytoskeletal polypeptide enhances its susceptibility to digestion by calpain. 302 69

Calpains 1 and 2 co-eluted with protein kinase C activities after hydrophobic (phenyl-Sepharose) and anion-exchange (Mono Q) chromatographies of a 100,000 X g supernatant which was defined as cytosol. After centrifugation of the cytosol at 200,000 X g for 16 h, the major part of calpain 1 and of its associated protein kinase C activity was recovered in the pellet, when the major part of calpain 2, also associated to a protein kinase C activity, was present in the resulting supernatant. Polyacrylamide gel electrophoresis of the fractions eluted from the Mono Q column, which contained calpains 1 or 2 and their associated protein kinase C activities, revealed two main bands with a molecular mass of 80 and 28 kDa.
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PMID:Association of calpains 1 and 2 with protein kinase C activities. 303 71


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