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)

Agonist-evoked rises in [Ca2+]i were recorded from single bovine aortic endothelial cells in the middle of confluent monolayers by dual-wavelength microspectrofluorimetry. Low doses of ATP (1-5 microM) induced a transient rise in [Ca2+]i followed by a maintained plateau phase upon which were superimposed irregular fluctuations in [Ca2+]i. The mechanism underlying these fluctuations is not known. Addition of the phorbol ester, phorbol 12-myristate 13-acetate (PMA), to single cells displaying ATP-induced fluctuations reduced the amplitude and frequency of these fluctuations but the maintained plateau phase was unaffected. Elevation of intracellular cAMP by activation of adenylate cyclase with forskolin, or application of dibutyryl cAMP did not affect the ATP-induced fluctuations. These results suggest a possible role for the diacylglycerol limb of the phosphoinositide hydrolysis pathway, via activation of protein kinase C, but not cAMP, in the mechanism responsible for generating ATP-induced fluctuations in [Ca2+]i.
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PMID:Actions of the phorbol ester, PMA, on ATP-induced fluctuations in cytoplasmic calcium in single isolated bovine aortic endothelial cells. 132 92

Propranolol, a beta-adrenergic receptor antagonist, also inhibits phosphatidate phosphohydrolase, the enzyme that converts phosphatidic acid into diacylglycerol. This latter effect has prompted recent use of propranolol in studies examining the importance of diacylglycerol and phosphatidic acid in cellular signalling events. Here, we show that propranolol is also an inhibitor of protein kinase C. At concentrations greater than or equal to 20 microM, propranolol reduced [3H]phorbol dibutyrate binding (IC50 = 200 microM) and phorbol myristate acetate-stimulated superoxide anion release (IC50 = 130 microM) in human neutrophils. Scatchard analysis showed that propranolol lowers the number of phorbol diester binding sites without significantly affecting their affinity. In vitro kinetic analysis, performed in a mixed micellar assay with protein kinase C purified from human neutrophils, suggested a competitive inhibition of propranolol with the cofactor phosphatidylserine. Complex kinetic patterns were observed with respect to diacylglycerol and ATP, approximating competitive and noncompetitive inhibition, respectively. Taken together, these results suggest that the drug interacts at the level of the regulatory domain of the enzyme. Fifty % inhibition occurred at approximately 150 microM propranolol. Similar levels of inhibition were obtained using exogenous (histone) and endogenous (p47-phox, a NADPH oxidase component) substrates. Protein kinase C-alpha and protein kinase C-beta, two protein kinase C isozymes present in human neutrophils, were inhibited by propranolol in a comparable manner. In the range of concentrations tested (30-1000 microM), neither cAMP-dependent protein kinase nor neutrophil protein tyrosine kinases were affected. The racemic form of propranolol and the (+) and the (-) stereoisomers were equally active, and other beta-adrenergic receptor antagonists (pindolol) and agonists (isoproterenol) were inactive. This suggests that the inhibitory action of propranolol on protein kinase C is related to the amphipathic nature of the drug rather than to its beta-adrenergic receptor blocking ability. Analogs of propranolol were synthesized and found to be more potent protein kinase C inhibitors, with IC50 values in the 10-20 microM range. We conclude that the ability of propranolol to inhibit both protein kinase C and PA phosphohydrolase complicates interpretation of results when this drug is used in signal transduction studies. In addition, propranolol may be a useful prototype for the synthesis of new protein kinase C inhibitors.
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PMID:Propranolol, a phosphatidate phosphohydrolase inhibitor, also inhibits protein kinase C. 132

Earlier studies established that adenylyl cyclase in NCB-20 cell plasma membranes is inhibited by concentrations of Ca2+ that are achieved in intact cells. The present studies were undertaken to prove that agents such as bradykinin and ATP, which elevate the cytosolic Ca2+ concentration ([Ca2+]i) from internal stores in NCB-20 cells, could inhibit cyclic AMP (cAMP) accumulation as a result of their mobilization of [Ca2+]i and not by other mechanisms. Both bradykinin and ATP transiently inhibited [3H]cAMP accumulation in parallel with their transient mobilization of [Ca2+]i. The [Ca2+]i rise stimulated by bradykinin could be blocked by treatment with thapsigargin; this thapsigargin treatment precluded the inhibition of cAMP accumulation mediated by bradykinin (and ATP). A rapid rise in [Ca2+]i, as elicited by bradykinin, rather than the slow rise evoked by thapsigargin was required for inhibition of [3H]cAMP accumulation. Desensitization of protein kinase C did not modify the inhibitory action of bradykinin on [3H]cAMP. Effects of Ca2+ on phosphodiesterase were also excluded in the present studies. The accumulated data are consistent with the hypothesis that hormonal mobilization of [Ca2+]i leads directly to the inhibition of cAMP accumulation in these cells and presumably in other cells that express the Ca(2+)-inhibitable form of adenylyl cyclase.
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PMID:Inhibition of cyclic AMP accumulation in intact NCB-20 cells as a direct result of elevation of cytosolic Ca2+. 132 28

Macrophages express two distinct types of nucleotide (P2 purinergic) receptors for extracellular ATP: one type induces a Ca(2+)-mobilizing response via the activation of phosphatidylinositol-phospholipase C (PI-PLC) while the second type induces the rapid formation of nonselective pores which are permeated by ions and small (< 1 kDa) organic molecules. We have confirmed the presence of these two ATP receptor types in the BAC1.2F5 murine macrophage cell line and have identified 3'-O-(4-benzoyl)benzoyl-ATP (BzATP) as a selective and potent agonist for the so-called P2z or pore-forming ATP receptor type. Several lines of evidence indicated that occupation of these P2z receptors is also accompanied by a rapid and large increase in the activity of a phosphatidylcholine-selective phospholipase D (PLD) effector enzyme. In cells metabolically labeled with [3H]oleic acid or [3H]glycerol and stimulated in the presence of ethanol, ATP and BzATP induced a severalfold increase in the rate and extent of [3H]phosphatidylethanol (PEt) accumulation. These responses were stimulated only by ATP, BzATP, and ATP gamma S (adenosine 5'-O-(3-thiotriphosphate) with the rank order of potency: BzATP >> ATP > ATP gamma A; there was no response to other adenine nucleotides or to non-adenine nucleotides. Significantly, the ability of P2z receptor agonists to stimulate this PLD activity was not dependent on the presence of extracellular [Ca2+] or elevation of cytosolic [Ca2+]. The inability of ionomycin, gramicidin, digitonin, UTP, platelet-activating factor, or phorbol ester to quantitatively mimic these nucleotide effects suggested that activation of this PLD by P2z receptor agonists was not a secondary response due to: 1) enhanced Ca2+ influx; 2) membrane depolarization; 3) nonselective permeabilization of the plasma membrane; 4) stimulation of Ca(2+)-mobilizing ATP receptors; 5) stimulation of a primary PI-PLC pathway; or 6) activation of protein kinase C. These findings suggest that activation of a novel PLD-based signaling pathway may play an important role in the modulation of macrophage function by pore-forming P2z receptors for extracellular ATP.
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PMID:A novel pathway for the activation of phospholipase D by P2z purinergic receptors in BAC1.2F5 macrophages. 133 Oct 96

The human erythroleukemia cell line (HEL) has been used as a model system for studying signal transduction processes as they might relate to platelet/megakaryocyte function. We were interested in examining the role of thrombin in the regulation of adenylyl cyclase in this cell line. As opposed to its predominantly inhibitory effects on cyclic AMP production in platelets or in membranes from HEL cells, our initial experiments in intact HEL cells revealed that thrombin markedly potentiated the cyclic AMP response to prostaglandin E1 (2.9 +/- 0.2-fold), prostacyclin (1.9 +/- 0.2-fold) and carbacyclin (2.5 +/- 0.5-fold), measured either by radioimmunoassay or by the [3H]adenine preloading procedure. Thrombin, although ineffective alone, also potentiated cyclic AMP production stimulated by vasoactive intestinal peptide (1.6 +/- 0.2-fold), cholera toxin (3.0 +/- 0.6-fold) and AIF4- (2.3 +/- 0.6-fold), but not by forskolin (0.9 +/- 0.1-fold). The thrombin effect 1) produced an increase in the efficacy of the prostaglandins with no change in potency; 2) was long-lived; 3) required the proteolytic activity of thrombin; 4) was insensitive to pertussis toxin; and 5) was at least partially mimicked by trypsin, extracellular ATP and UTP, platelet activating factor and activators of protein kinase C. Down-regulation of protein kinase C or pre-exposure to the protein kinase inhibitor staurosporine blocked the potentiating effect. Together, these results suggest that in HEL cells, the mechanism of thrombin potentiation of cyclic AMP production may involve alterations in the interaction between stimulatory guanine nucleotide binding protein and the catalytic subunit of adenylyl cyclase, possibly involving protein kinase C-mediated phosphorylation.
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PMID:Potentiation of cyclic adenosine monophosphate production by thrombin in the human erythroleukemia cell line, HEL. 133 12

Extracellular ATP (7 microM-14 mM) induced monolayer Chang liver cells (ATCC CCL 13) to retract and round up in dose-dependent and time-dependent manners. ATP-induced rounding was concomitant with raised intracellular pH (7.3 to 7.8) and suppressed (a) in sodium-free medium (250 mM sucrose), (b) with the addition of 1 mM quinidine, an inhibitor of Na+/H+ exchanges, and (c) with the addition of 10 nM staurosporine, a potent inhibitor of protein kinase C that is known to activate Na+/H+ exchanges. These findings suggest that ATP-induced cell rounding is due to activation of Na+/H+ antiporters.
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PMID:Extracellular ATP induces rapid cell rounding in cultured human Chang liver cells. 133 82

Activation of protein kinase C (PKC) modulates the mobilization of intracellular Ca2+ induced by extracellular ATP in rat ventricular myocytes. Pretreatment of myocytes with PKC activators attenuated both the ATP-induced Ca2+ transient and the noradrenergic potentiation of the Ca2+ response. Various PKC activators decreased both the basal cAMP level and the cAMP levels that had been elevated by norepinephrine, forskolin, or 3-isobutyl-1-methylxanthine. The inhibitory effects of PKC activators were reversed by the PKC inhibitor staurosporine. The ATP-induced Ca2+ response is an integrated response resulting from ATP eliciting an inward cation current (IATP), cellular depolarization, Ca2+ influx through Ca2+ channels, and Ca2+ release from the sarcoplasmic reticulum. We used the whole cell voltage-clamp technique to investigate which steps of this integrated response are affected by PKC. PKC activators did not significantly affect the IATP. In contrast, PKC activators decreased the basal Ca2+ current (ICa) or Ba2+ current and the beta-adrenergic-stimulated ICa. These results suggest that PKC-induced suppression of the ATP-induced Ca2+ response and the beta-adrenergic-potentiated Ca2+ response is achieved at least partially by decreasing the intracellular cAMP level and ICa.
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PMID:Ca2+ mobilization by extracellular ATP in rat cardiac myocytes: regulation by protein kinase C and A. 133 93

Stimulation of isolated rat olfactory cilia in the presence of [gamma-32P]ATP leads to a significantly enhanced incorporation of [32P]phosphate. Depending on the type of odorants applied, the induced phosphorylation is completely blocked by specific inhibitors of either protein kinase A or protein kinase C. Time-course experiments indicate that the odor-induced modification of ciliary proteins is transient; the intensity of labeling decayed over time (1-10 sec). Separation of ciliary proteins by SDS/polyacrylamide gel electrophoresis followed by autoradiography demonstrated that upon stimulation with lilial, a single polypeptide (50,000 Da) was phosphorylated; the size of the modified protein is in line with the hypothesis that odorant receptors are phosphorylated subsequent to activation by specific odors.
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PMID:Odor-induced phosphorylation of olfactory cilia proteins. 133 54

There is increasing evidence that the calcium ion plays a critical role in both toxic cell killing and programmed cell death. Thus, in a variety of experimental systems a perturbation of intracellular Ca2+ homeostasis due to increased Ca2+ influx and/or inhibition of Ca2+ extrusion has been found to be an early event in the development of cell injury. It is clear that sustained increases in intracellular Ca2+ can activate cytotoxic mechanisms which result in perturbations of cellular structure and function. For example, the stimulation of Ca(2+)-dependent proteases can result in a disruption of cytoskeletal organization and the formation of surface protrusions (blebs) and Ca(2+)-mediated phospholipase activation can result in an impairment of mitochondrial function with collapse of membrane potential and cessation of ATP synthesis. The activation of a Ca2+, Mg(2+)-dependent nuclear endonuclease is associated with chromatin cleavage and appears to play a crucial role in programmed cell death (apoptosis) in the immune system and other tissues. There is also recent evidence that this process may be responsible for the immunotoxicity of dioxins and organotin compounds and involved in the killing of adenocarcinoma cells by tumor necrosis factor alpha. Although calcium ions appear to be required for endonuclease activity during apoptosis, this process is also influenced by other factors, e.g. protein kinase C activity, intracellular polyamine and Zn2+ levels, chromatin structure, etc. Thus, the regulation of endonuclease activity under both physiological and toxicological conditions appears to be complex and to involve multiple factors.
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PMID:Ca(2+)-dependent mechanisms of cytotoxicity and programmed cell death. 133 78

We investigated the effects of protein kinase C modulations and calcium mobilization on GSH efflux in Hep G2 cells. GSH efflux from Hep G2 cells was increased by a phorbol ester. Staurosporine, an inhibitor of protein kinase C, diminished phorbol ester-stimulated GSH efflux from the cells. GSH efflux was negatively correlated with extracellular calcium concentrations. Verapamil enhanced GSH efflux, whereas ATP decreased GSH efflux. The latter effect was diminished in the absence of extracellular calcium. Protein kinase C and calcium mobilization may be crucial factors in GSH efflux from human hepatocytes.
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PMID:Possible involvement of protein kinase C and calcium in GSH efflux from Hep G2 cells. 133 37


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