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

Sequestration of calcium into an intracellular storage site is an important mechanism in helping to maintain a low cytoplasmic Ca2+ level in many cells. In platelets, increasing cytoplasmic cAMP lowers the free calcium level in correlation with the phosphorylation of a 22 kD protein. This protein has been thought to enhance uptake of calcium into a platelet membrane bound storage site by activating a calcium-ATPase activity by analogy with phospholamban in cardiac muscle. The evidence for an analogue of phospholamban in platelets is unclear. A pathway involving cAMP dependent kinase also seems unlikely to account for the transience of the calcium signal following agonists in platelets, some of which inhibit the cAMP dependent kinase. Here we discuss the issue of whether activation of protein kinase C, which follows agonist action, leads to enhanced calcium sequestration in platelets and if so, what indications there are for a mechanism. The evidence from our experiments with phorbol myristate acetate treated platelets shows that such an enhancement can be produced by activating protein kinase C. Phosphorylation studies suggest the involvement of a polypeptide or polypeptides distinct from the 22 kD polypeptide. Further work to test this idea is necessary. A brief overview of research on the role of phosphoproteins in calcium regulation in platelets and comparison with their role in cardiac muscle is also presented.
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PMID:Calcium sequestration in human platelets: is it stimulated by protein kinase C? 267 Feb 38

The phorbol ester 12-O-tetradecanoyl phorbol-13-acetate (TPA) was used to examine the hypothesis that phosphoinositide turnover is involved in the regulation of myocardial contractility mediated by stimulation of alpha-adrenoceptors in the mammalian cardiac muscle. Exposure of the isolated rabbit papillary muscle electrically driven at a rate of 1 Hz at a temperature of 37 degrees C to TPA in concentrations of 10-1000 nmol/l for 30 min did not affect the basal force of contraction. The concentration-response curve for the positive inotropic effect of (-)-phenylephrine mediated by stimulation of alpha-adrenoceptors in the presence of (+/-)-bupranolol (100 nmol/l) was shifted to the right and downward by TPA in concentrations of 30-1000 nmol/l, while the effect of (-)-phenylephrine mediated by stimulation of beta-adrenoceptors in the presence of prazosin (100 nmol/l) was not decreased, but slightly enhanced by exposure of the muscle to relatively low concentrations of TPA (10-100 nmol/l). Incubation of the membrane fraction isolated from the rabbit ventricular muscle with TPA in vitro under the same condition as employed in the physiological experiments decreased the specific binding of [3H]prazosin but not that of [3H]CGP-12177, while the non-tumor promoting phorbol ester, alpha PDD, was ineffective. These results indicate that activation of protein kinase C by TPA does not mimic the positive inotropic effect of catecholamines mediated by activation of myocardial alpha-adrenoceptors.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Phorbol ester does not mimic, but antagonizes the alpha-adrenoceptor-mediated positive inotropic effect in the rabbit papillary muscle. 289 86

Protein kinase C prepared from rat brain was used to phosphorylate a calcium-activated neutral protease, purified from bovine cardiac muscle. Attempts to phosphorylate the enzyme in the presence of calcium were unsuccessful, unless the protease inhibitor leupeptin was also present. Phosphorylation of the 74K subunit of the protease was completely inhibited in the absence of phosphatidylserine and diolein, indicating that phosphorylation of the enzyme was catalysed by the calcium and phospholipid-dependent protein kinase C.
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PMID:Phosphorylation of bovine cardiac calcium-activated neutral protease by protein kinase-C. 301 95

Muscarinic agonists can stimulate rather than inhibit cardiac muscle in some preparations. In left atria from hatched chicks, treatment with pertussis toxin reversed the membrane action of carbachol from hyperpolarization to depolarization and reversed the inotropic effect of carbachol from negative to positive. Acetylcholine also depolarized the membrane and increased the force of contraction in atria from pertussis-toxin-treated chicks although oxotremorine did not. These cholinergic responses were blocked by atropine but not by adrenoceptor antagonists, suggesting that they are mediated via muscarinic receptors and are not due to actions of endogenously released catecholamines. Muscarinic receptor stimulation leads to two distinct biochemical responses in chick atria: inhibition of adenylate cyclase and activation of phosphoinositide (PI) hydrolysis. The former is lost in atria from pertussis-toxin-treated chicks, whereas the PI response persists. The pharmacologic characteristics of the PI response resemble those of the depolarization and positive inotropic response. Both are insensitive to blockade by pertussis toxin, require high concentrations of carbachol, and are elicited by acetylcholine but not by oxotremorine. The present study suggests that muscarinic agonist-induced PI turnover may be responsible for the membrane depolarization and positive inotropic effects of carbachol and acetylcholine; that an increase in Na+ conductance underlies these responses; and that it is stimulated either by an increase of intracellular calcium mobilized by inositol triphosphate and/or by activation by protein kinase C.
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PMID:Pertussis toxin-insensitive phosphoinositide hydrolysis, membrane depolarization, and positive inotropic effect of carbachol in chick atria. 304 Feb 95

Previous studies have established that the terminally differentiated ventricular cardiac muscle cell of the adult rat reinitiates semiconservative DNA replication when grown in culture (W. C. Claycomb and H. D. Bradshaw, Jr., 1983, Dev. Biol. 90, 331-337). Work reported here shows that several growth factors and chemicals will stimulate this DNA synthetic activity in a concentration-dependent manner. Autoradiographic experiments establish that this stimulated DNA synthesis is due to cells not previously synthesizing DNA being induced to enter the S phase of the cell cycle. By far the greatest stimulation (250%) is observed with the tumor promoter 12-O-tetradecanoyl-phorbol-13-acetate (TPA). Fifty ng/ml is the optimal concentration, and the maximal effect is observed 5 days after adding TPA. TPA also substantially increases the protein content of the cultured myocytes. Diacylyglcerols (DAG) induce these same changes, indicating that the effect of TPA is mediated by protein kinase C. The morphology of the cultured cardiac muscle cells is profoundly altered by TPA and DAG. TPA- and DAG-treated myocytes spread more thinly on the surface of the culture flask, acquire multiple nuclei, and undergo nucleolar fragmentation. The myofibrillar ultrastructure of the treated cells becomes almost totally disorganized, and intermediate filaments and rough endoplasmic reticulum accumulate in the cytoplasm. These TPA results suggest a possible relationship between the degree of ultrastructural differentiation of the ventricular cardiac muscle cell and DNA synthetic activity. This easily altered cellular plasticity should be very useful for studies of the regulation of cardiac muscle cell proliferation and cell differentiation.
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PMID:Growth factors and TPA stimulate DNA synthesis and alter the morphology of cultured terminally differentiated adult rat cardiac muscle cells. 337 63

Phorbol esters are potent tumor promoters that have been widely used in studies of transmembrane signaling because of their ability to activate protein kinase C. To study the effect of phorbol esters (and indirectly, the role of protein kinase C) on cardiac muscle contractility, we examined the effects of phorbol myristate acetate (PMA) on contractile state, transmembrane 45Ca fluxes, and cytosolic free Ca concentration ([Ca]i) using spontaneously contracting cultured chick ventricular cells. PMA produced a concentration- and time-dependent decrease in the amplitude of cell motion [half maximum inhibitory concentration (IC50) = 130 nM] with maximal effect (54 +/- 5% of control) observed at 1 microM. PMA (1 microM) reduced 45Ca uptake rate by 16 +/- 4% (P less than 0.05) and the size of the rapidly exchangeable Ca pool by 11 +/- 2% (P less than 0.05) but did not alter the 45Ca efflux rate. In fura-2-loaded cells, PMA produced a decrease in [Ca]i from 96 +/- 7 to 72 +/- 5 nM (mean +/- SE; P less than 0.05) with a time course similar to that of alteration in contractile amplitude. PMA had no effect on cellular Na content. Phorbol didecanoate (1 microM), a phorbol diester that does not activate protein kinase C, produced no significant changes in contractile amplitude, 45Ca fluxes, or [Ca]i. These results indicate that PMA influences transsarcolemmal Ca uptake, and thus the excitation-contraction process, and suggest that protein kinase C may modulate myocardial Ca homeostasis and contractile state.
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PMID:Effect of phorbol esters on contractile state and calcium flux in cultured chick heart cells. 360 67

C-protein, a thick filament-associated protein, has been isolated from bovine myocardium and found to be a substrate in vitro of the Ca2+- and phospholipid-dependent protein kinase (protein kinase C). Incorporation of approximately 1.6 mol Pi/mol C-protein was observed. This phosphorylation was dependent on both Ca2+ and a phospholipid (L-alpha-phosphatidyl-L-serine was used). Phosphate incorporation specifically into C-protein was verified by SDS-polyacrylamide gel electrophoresis and autoradiography and was almost exclusively into serine residues (86.9%), with only a small amount of phosphothreonine (13.1%) and no phosphotyrosine being detected. Two-dimensional thin-layer electrophoresis of a chymotryptic digest of phosphorylated C-protein indicated site specificity of phosphorylation. Cardiac C-protein is known to be a substrate of cAMP-dependent protein kinase both in vitro and in vivo (Jeacocke, S.A. and England, P.J. (1980) FEBS Lett. 122, 129-132). Isolated bovine cardiac C-protein was rapidly phosphorylated, to the extent of 5 mol/mol, by the purified catalytic subunit of cAMP-dependent protein kinase. Phosphorylation catalyzed by these two protein kinases was not additive, suggesting that the sites phosphorylated by protein kinase C are also phosphorylated by cAMP-dependent protein kinase. Chicken cardiac muscle has also been shown to contain a Ca2+, calmodulin-dependent protein kinase which phosphorylates C-protein (Hartzell, H.C. and Glass, D.B. (1984) J. Biol. Chem. 259, 15587-15596). The physiological role of cardiac C-protein may therefore be subject to regulation by multiple protein kinases.
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PMID:Phosphorylation of bovine cardiac C-protein by protein kinase C. 384 Sep 98

The enzymatic activity of mitogen-activated protein kinases (MAP kinases) increases in response to agents acting on a variety of cell surface receptors, including receptors linked to heterotrimeric G proteins of the Gi and Gq family. Recently, it has been shown that stimulation of beta-adrenergic receptors, which are typical of those that act through Gs to activate adenylyl cyclases, potently activates MAP kinases in the heart, resulting in the hypertrophy of the cardiac muscle (Lazou, A., Bogoyevitch, M.A., Clerk, A., Fuller, S.J., Marshall, C.J., and Sudgen, P.H. (1994) Circ. Res. 75, 938-941). We have observed that exposure of COS-7 cells to a beta-adrenergic agonist, isoproterenol, raises intracellular levels of cAMP and effectively activates protein kinase A (PKA) and an epitope-tagged MAP kinase. However, MAP kinase stimulation by isoproterenol was neither mimicked by expression of an activated mutant of G alpha s, nor by treatment with PKA-stimulating agents. Moreover, pretreatment of COS-7 with a permeable cAMP analog, 8-Br-cAMP, markedly decreased MAP kinase activation by either isoproterenol or epidermal growth factor. Thus, in COS-7 cells cAMP and PKA do not appear to mediate MAP kinase activation by beta-adrenergic receptors. Signaling from beta-adrenergic receptors to MAP kinase was inhibited by transfection of a chimeric molecule consisting of the CD8 receptor and the carboxyl terminus of the beta-adrenergic receptor kinase, which includes the beta gamma-binding domain. MAP kinase activation by isoproterenol was not affected by depletion of protein kinase C, but it was completely abolished by expression of Ras-inhibiting molecules. We conclude that signaling from beta-adrenergic receptors to MAP kinase involves an activating signal mediated by beta gamma subunits acting on a Ras-dependent pathway and a G alpha s-induced inhibitory signal mediated by cAMP and PKA. The balance between these two opposing mechanisms of regulation would be expected to control the MAP kinase response to beta-adrenergic agonists as well as to other biologically active agents known to act on Gs coupled receptors, including a number of hormones, neurotransmitters, and lipid mediators.
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PMID:Dual effect of beta-adrenergic receptors on mitogen-activated protein kinase. Evidence for a beta gamma-dependent activation and a G alpha s-cAMP-mediated inhibition. 755 65

The regulation of cardiac muscle glycogen metabolism is not well understood. Previous studies have indicated that heart glycogen synthase is heavily phosphorylated in vivo on multiple sites. Using purified enzymes, we have investigated the effect of phosphorylation of different sites on the activity of rat heart glycogen synthase. A convenient procedure was developed for the purification of rat heart glycogen synthase. The enzyme was phosphorylated by selected kinases, and glycogen synthase activity, extent of phosphorylation, and phosphopeptide maps were analyzed. Rat heart glycogen synthase, purified to apparent homogeneity (M(r) 87,000 on SDS-PAGE), had a specific activity of 18 U/mg protein and had an activity ratio of 0.74 (activity in the absence divided by the activity in the presence of glucose 6-P). cAMP-dependent protein kinase, glycogen synthase kinase 3, Ca2+/calmodulin-dependent protein kinase II, protein kinase C, and phosphorylase kinase phosphorylated the enzyme with a concomitant decrease in the activity ratio to values ranging from 0.1 to 0.4. Casein kinase II phosphorylated but did not inactivate glycogen synthase. Six tryptic phosphopeptides, obtained from heart glycogen synthase phosphorylated by the various kinases, were separated by reverse-phase chromatography. The phosphopeptide(s) obtained with each kinase eluted at the same position(s) as corresponding phosphopeptides obtained from rat skeletal muscle glycogen synthase. The study shows that the pattern of phosphorylation and effects on activity are very similar for cardiac and skeletal muscle glycogen synthase. It is suggested that the well known differences in heart and glycogen metabolism may be due to the interplay of kinases and phosphatases which could lead to different phosphorylation and activity states of glycogen synthase.
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PMID:Phosphorylation and inactivation of rat heart glycogen synthase by cAMP-dependent and cAMP-independent protein kinases. 767 Nov 34

At least seven bacteriophage lambda clones encoding structurally related but unique polypeptides with PKC activity have been isolated from mammalian brain, epidermis, and lung cDNA libraries. The possibility that additional isoenzymes are expressed in human blood platelets or megakaryoblastoid human erythroleukemia cells was examined by polymerase chain reaction amplification of reverse transcribed RNA employing oligonucleotide primers corresponding to conserved peptide sequences. cDNAs encoding a novel PKC-related sequence, designated PKC-theta, and four (alpha, beta, delta, and eta) previously identified isoenzymes were isolated from reverse transcribed total RNA of human erythroleukemia cells and platelets. PKC-theta lacks a conserved region (C2) that is present in the calcium-dependent isoenzymes and therefore belongs to the group of novel, or nPKC, isoenzymes. Significantly increased [3H] phorbol 12,13-dibutyrate binding and cytoskeleton-associated calcium-independent PKC activity were found in COS cells expressing the transfected cDNA. Northern transfer analysis of mRNA from various human tissues revealed high level expression of PKC-theta in skeletal muscle, lung, and brain, and minimal expression in cardiac muscle, placenta, and liver. These findings extend the PKC family and suggest a novel approach to the study of diversity within this pathway of intracellular signal transduction.
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PMID:Molecular cloning and expression of a cDNA encoding a novel isoenzyme of protein kinase C (nPKC). A new member of the nPKC family expressed in skeletal muscle, megakaryoblastic cells, and platelets. 1696 35


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