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)

The cellular signaling events leading to the systemic inflammatory response syndrome and sepsis in monocytes/macrophages activated by lipopolysaccharide (LPS) are well understood. LPS is a glycolipid component of Gram-negative bacterial cell wall. It exerts its effect through the lipid A moiety. LPS binds to monocytes/macrophages via a membrane-bound receptor, CD14, an interaction which is optimized in the presence of plasma factors, LPS-binding protein, and septin. Although LPS is known to bind to other receptors, the roles of these receptors in transmembrane signaling and activation of monocytes/macrophages are not as well understood as is that of the CD14 receptor. Intracellular events in response to LPS stimulation are mediated by phospholipase (PL) C, protein kinases, PLA2, and PLD. Activation of PLC by LPS results in the release of diacylglycerol and inositol 1,4,5-trisphosphate. The former mediates the stimulation of protein kinase C, and the latter induces an increase in intracellular calcium concentration. LPS stimulation of monocytes/macrophages also results in the phosphorylation and activation of several protein kinases, including protein tyrosine kinases which mediate cytokine production, and mitogen-activated protein kinase which activates cytosolic PLA2 to release arachidonate. LPS also plays a role in cellular proliferation and differentiation. Upregulation of the secretory form of PLA2 has also been documented in response to LPS. PLD is stimulated by LPS to release phosphatidic acid (PA). PA can activate the respiratory burst by increasing diacylglycerol production and by modulating the effects of guanine nucleotide-binding proteins. Therapeutic strategies to decrease the clinical effects of sepsis would logically include agents which block at initial receptor-ligand interaction, as well as those which attenuate the intracellular events that follow LPS stimulation. Early in vivo studies are promising, but clearly much work remains to be done.
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PMID:Signaling events in monocytes and macrophages. 758 75

Group I pancreatic phospholipase A2 (PLA2 I) is primarily a digestive enzyme. Recently, however, in addition to its catalytic activity a receptor-mediated function has been described for this enzyme. PLA2 I binding to its receptor induces cellular chemokinesis, proliferation, and smooth muscle contraction. This enzyme also induces the production of prostaglandin E2 in certain cells and may have a proinflammatory role. However, despite its ability to hydrolyze phospholipids in in vitro assays, PLA2-I does not efficiently catalyze release of AA from intact cells. Here, we demonstrate that while short-term exposure of NIH 3T3 cells to PLA2-I is ineffective, exposure of 6 h or longer significantly increases the basal release of AA. Dose-response curve of PLA2-I-induced AA release was saturable with an EC50 of 14.01 +/- 1.36 nM (n = 3). [3H]-AA was preferentially released over [3H]-oleic acid by PLA2-I. PLA2-I, inactivated with 4-bromophenacyl bromide, was fully capable of mediating AA release. These data suggest that a non-catalytic, receptor-mediated mechanism is involved in PLA2-I-induced AA release in NIH-3T3 cells. This release of AA is not dependent on protein kinase C or Ca2+ concentration. Comparison of the effect of PLA2-I with those of ATP and platelet-derived growth factor indicates that each of these agonists regulates AA release via independent pathways. Neither the basal enzymatic activity of the 85-kDa cytosolic PLA2 nor the protein level of this enzyme was affected by treatment of cells with PLA2-I. However, the increase in basal enzymatic activity of 85 kDa PLA2 due to protein kinase C activation was further enhanced by pretreatment of cells with PLA2-I. We conclude that: (1) short-term exposure of cells to PLA2 I does not cause measurable AA release; (2) release of AA from intact cells by this enzyme requires long-term exposure; (3) AA release is not mediated by a direct catalytic effect of PLA2 I; and (4) AA release by PLA2 I is accomplished via a receptor-mediated process. Taken together, these results raise the possibility that PLA2 I, in addition to its digestive function, may also contribute to aggravate preexisting inflammatory processes and/or to initiate new ones when chronic exposure of cells to this enzyme occurs.
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PMID:Arachidonic acid release from NIH 3T3 cells by group-I phospholipase A2: involvement of a receptor-mediated mechanism. 759 36

Protein phosphorylation by protein kinase C (PKC) has recently been shown to be a key event in the induction of the slow inward Na current observed during sustained depolarization of the Xenopus oocyte membrane. The present work investigates the possible pathways leading to PKC activation. PKC is activated by a series of phospholipid metabolites, such as diacylglycerol (DAG) and arachidonic acid produced by phospholipases C (PLC) and A2 (PLA2) respectively. To test whether PKC activation was dependent upon the phospholipid metabolites produced either by PLC or by PLA2, enzyme activity was reduced using selective inhibitors. Results indicated that inhibition of PLA2 activity and inhibition of the enzymes involved in the arachidonic acid cascade failed to affect Na current amplitude. On the other hand, PLC inhibition caused a marked decrease of Na current amplitude. In another series of experiments, Na current was fully restored, in spite of PLC inhibition, by directly enhancing PKC activity with a powerful activator phorbol 12-myristate 13-acetate. These data strongly suggest that PLC is involved in PKC activation during Na channel induction.
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PMID:Phospholipase C activates protein kinase C during induction of slow Na current in Xenopus oocytes. 760 37

Inhibition of Na+,K(+)-ATPase activity by hyperglycemia could be an important etiological factor of chronic complications in diabetic patients. The biochemical mechanism underlying hyperglycemia's inhibitory effects has been thought to involve the alteration of the protein kinase C (PKC) pathway since agonists of PKC can normalize hyperglycemia-induced inhibition of Na+,K(+)-ATPase activity. Paradoxically, elevated glucose levels and diabetes have been shown to increase PKC activities in vascular cells. The present study tested the hypothesis that the inhibition of Na+,K(+)-ATPase activity is mediated by the sequential activation of PKC and cytosolic phospholipase A2 (cPLA2). In cultured rat vascular smooth muscle cells (VSMC), increasing glucose levels in the medium from 5.5 to 22 mM elevated cPLA2 activity and increased [3H]arachidonic acid release and PGE2 production by 2.3-, 1.7- and 2-fold, respectively. Similar increases in cPLA2 activity were also induced by elevated glucose levels in human VSMC and rat capillary endothelial cells. The activation of cPLA2 was mediated by PKC since the increases in cPLA2 phosphorylation and enzymatic activity were inhibited by the PKC inhibitor GFX. In contrast, elevation of glucose levels decreased Na+,K(+)-ATPase activity as measured by ouabain-sensitive 86Rb uptake by twofold in rat VSMC. Surprisingly, both PMA, a PKC agonist, and GFX, a PKC inhibitor, were able to prevent glucose-induced decreases in 86Rb uptake. Further, the PLA2 inhibitor AACOCF3 abolished both glucose-induced activation of cPLA2 and the decrease in 86Rb uptake. These data indicated that hyperglycemia is inhibiting Na+,K(+)-ATPase activity by the sequential activation of PKC and cPLA2, resulting in the liberation of arachidonic acid and increased the production of PGE2, which are known inhibitors of Na+,K(+)-ATPase.
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PMID:Identification of the mechanism for the inhibition of Na+,K(+)-adenosine triphosphatase by hyperglycemia involving activation of protein kinase C and cytosolic phospholipase A2. 763 66

We have studied the effects of dexamethasone (dex) (i) on the level of the arachidonate-mobilizing phospholipase A2 (PLA2-85) in macrophages, (ii) on the stimulus-induced activation of this enzyme, and (iii) on the stimulus-induced release of arachidonate. Treatment of macrophages with 10 nM dex led to progressive reduction of PLA2-85 down to approx. 35% of control levels in 20 h in the absence of stimuli. This was accompanied by a partial inhibition of calcium-ionophore-induced arachidonate release. In contrast, the ability of zymosan or phorbol ester to cause both persistent activation of PLA2-85 and arachidonate release was greatly reduced or abolished. However, the protein phosphatase inhibitor okadaic acid, previously shown to cause enhanced phosphorylation and persistent activation of PLA2-85, was still able to exert this effect on the dex-suppressed PLA2-85. This suggests that the effect of okadaic acid was exerted at, or downstream of, the dex-sensitive step(s). Treatment with dex also led to inhibition of the characteristic changes in phosphoprotein labelling induced by phorbol ester or zymosan. However, phorbol-dibutyrate-binding isoforms of protein kinase C were not severely down-regulated. Thus dex was found to down-regulate PLA2-85 and, in addition, to affect one or more component(s) in the signal chain that normally leads to its activation. However, okadaic acid retained the ability to cause activation of PLA2-85.
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PMID:Dexamethasone down-regulates the 85 kDa phospholipase A2 in mouse macrophages and suppresses its activation. 773 89

Synthesis of eicosanoids is initiated by signal transduction cascades which result in the hydrolysis of free arachidonic acid from membrane phospholipids. Both a cytosolic 85 kDa and a nonpancreatic 14 kDa PLA2 may contribute to cellular arachidonate mobilization. In many cells, agonist-stimulated fatty acid release is dependent upon increases in intracellular free calcium and is enhanced by pretreatment with agents such as phorbol esters and soluble diglycerides. The response is specific for arachidonate and structurally similar polyunsaturated fatty acids containing a cis 5, 6 double bond. DMSO-differentiation of U937 cells markedly enhances the A23187-stimulated release of [3H]arachidonate, which appears to be coupled to differentiation-induced enhancement of capacitance calcium entry. Although both phorbol esters and soluble diglycerides enhance subsequent fMLP or A23187-stimulated arachidonate release in human neutrophils, several lines of evidence indicate that the effects of oleoylacetylglycerol and 1,2-dioctanoylglycerol are protein kinase C-independent. Soluble diglycerides, but not phorbol esters, enhance the coupling of arachidonate mobilization to subsequent leukotriene B4 synthesis. Further studies will be required to elucidate the mechanisms which regulate activation of cellular phospholipases and subsequent synthesis.
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PMID:Cellular regulation of arachidonate mobilization and metabolism. 778 64

We have previously demonstrated that oxysterols and calcitriol potentiate arachidonic acid (AA) release and prostaglandin (PG) synthesis when NRK cells (fibroblastic clone 49F) are activated by foetal calf serum. As serum is essential for a full oxysterol effect, we hypothesized that these compounds could act on one or more of the events triggered by serum growth factor binding to their specific receptors and leading to PLA2 activation; we showed that the oxysterol effect on AA release is synergistic with, but not fully dependent on, protein kinase C (PKC) activity and Ca2+ ion fluxes, suggesting that oxysterols could effect early events in the cell signalling pathway. In the present paper, we investigated the effect of some oxysterols and calcitriol on epidermal growth factor (EGF)-induced AA release and PGE2 synthesis in NRK cells. The clear potentiation of EGF effect by most of the oxygenated sterols--chiefly when polyoxidized--cannot be explained by a modification of EGF high affinity binding site number which was only moderately increased after a 4 h incubation of cells with these compounds, and moreover was not related to the ability of a given oxysterol to increase PLA2 activity; whatever the compound, the dissociation constant (Kd) of either a high or low affinity binding site was unchanged (respectively, 3.5 x 10(-11) M and 4.4 x 10(-10) M). Genistein, a known inhibitor of EGF receptor tyrosine kinase, changed neither the EGF effect on AA release nor its potentiation by oxysterol, whereas it inhibited PGE2 synthesis in both situations. PKC activation by phorbol ester TPA increased the effect of EGF alone as well as the oxysterol potentiating effect, whereas PKC down-regulation strongly decreased both of these effects, showing that both are dependent on PKC activity. Nevertheless staurosporine, a PKC inhibitor, did not reproduce the effects of PKC down-regulation on EGF activation: stimulatory when AA release was induced by EGF alone, inhibitory when AA release is induced by TPA alone, this compound did not modify the oxysterol potentiating effect. In conclusion, the potentiating effect of oxysterols on AA release seems to be exerted downstream to the growth factor receptor (as demonstrated here with EGF) and probably at the PKC level, but not exclusively.
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PMID:Potentiation by cholesterol and vitamin D3 oxygenated derivatives of arachidonic acid release and prostaglandin E2 synthesis induced by the epidermal growth factor in NRK 49F cells: the role of protein kinase C. 788 3

Interleukin 4 (IL-4) diminishes cytokine activation of human macrophage. IL-4 binding to monocyte IL-4R is associated with protein kinase C (PKC) translocation to a nuclear fraction. The cleavage of diacyglycerol (DAG), an activator of PKC, from membrane phospholipids was investigated to define the proximal events of IL-4R signaling. IL-4 induced a statistically significant time-and dose-dependent generation of DAG. The IL-4-triggered production of DAG was not derived from phosphatidylinositol 4,5-bisphosphate (PIP2) hydrolysis, since neither cytosolic calcium flux nor liberation of inositol phosphates was detected in response to IL-4. Experiments were performed using [14C-methyl]choline-labeled U937 cells and monocytes to determine whether IL-4R activated phospholipase C (PLC), PLD, or PLA2 to use membrane phosphatidylcholine (PC) to form DAG. IL-4 induced a time- and dose-dependent increase of phosphocholine (pchol) with concomitant degradation of membrane PC (p < 0.05 compared with control). The finding that the peak reduction of PC was equivalent to peak production of pchol suggested that IL-4R signaling involved the activation of a PC-specific PLC. Changes in choline (chol) or lyso-PC and glycerolphosphocholine, the respective products of PC cleavage by PLD or PLA2, were not detected in IL-4-treated cells. In contrast, exogenous PLD induced an increase in chol and concomitant loss of membrane PC. Additional investigation suggested that IL-4R signaling does not involve PLD. In cells labeled with L-lyso-3-PC 1-[1-14C]palmitoyl, PLD but not IL-4, increased the production of phosphatidic acid (PA) and phosphatidyl-ethanol when pretreated with ethanol. Propranolol, an inhibitor of phosphatidate phosphohydrolase, and calyculin A, a phosphatase 1 and 2A inhibitor, blocked DAG production in response to FMLP but not to IL-4. In propranolol pretreated cells, PMA but not IL-4 triggered the production of PA and lowered the amount of DAG. Evidence that PLA2 is not coupled to IL-4R is the detection of arachidonate production in response to FMLP but not to IL-4. Furthermore, IL-4R is not coupled to sphingomyelinase (SMase) since IL-4, unlike exogenous SMase, did not generate ceramide but induced the hydrolysis of PC to pchol that was comparable to exogenous PLC. In summary, IL-4R signaling in monocytes and U937 cells involves PLC and not PLD, PLA2, or SMase, and it uses PC and not PIP2 to form DAG.
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PMID:Interleukin 4 receptor signaling in human monocytes and U937 cells involves the activation of a phosphatidylcholine-specific phospholipase C: a comparison with chemotactic peptide, FMLP, phospholipase D, and sphingomyelinase. 793 Oct 78

Xenopus laevis oocytes are a powerful tool for the characterization of signal transduction pathways leading to the induction of DNA synthesis. Since activation of PLA2, PLC, or PLD has been postulated as a mediator of ras function, we have used the oocyte system to study the putative functional relationship between ras-p21 and these phospholipases. A rapid generation of PA and DAG was observed after ras-p21 microinjection, suggesting the activation of both PLC and PLD enzymes. However, production of DAG was sensitive to inhibition of the PA-hydrolase by propranolol, indicating that PLD is the enzyme responsible for the generation of both PA and DAG. Microinjection of PLD or ras-p21 induced the late production of lysophosphatidylcholine on a p42MAPK-dependent manner, an indication of the activation of a PLA2. Inhibition of this enzyme by quinacrine does not inhibit PLD- or ras-induced GVBD, suggesting that PLA2 activation is not needed for ras or PLD function. Contrary to 3T3 fibroblasts, where ras-p21 is functionally dependent for its mitogenic activity on TPA- and staurosporine-sensitive PKC isoforms, in Xenopus oocytes, induction of GVBD by ras-p21 was independent of PKC, while PLC-induced GVBD was sensitive to PKC inhibition. Thus, our results demonstrate the activation of PLD and PLA2 by ras-p21 proteins, while no effect on PLC was observed.
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PMID:ras-p21 activates phospholipase D and A2, but not phospholipase C or PKC, in Xenopus laevis oocytes. 801 97

An assay has been developed to quantitatively measure the tension and elasticity of the cytoskeleton in living plant cells. The cell optical displacement assay (CODA) uses a focused laser beam to optically trap and displace transvacuolar and cortical strands through a defined distance within the cell. Results from these experiments provide evidence for the classification of at least two rheologically distinct cytoskeletal assemblies, cortical and transvacuolar, that differ in their tension and response to both signaling molecules and reagents that perturb the cytoskeleton. It is further demonstrated that the tension of the transvacuolar strands can be significantly decreased by the addition of either linoleic acid, 1,2 dioctanoyl-sn-glycerol, or 1,3 dioctanoylglycerol. These decreases in tension could also be induced by lowering the cytoplasmic pH. In contrast, addition of Ca2+, Mg2+, or the ionophore A23187 to the cells caused a considerable increase in the tension of the transvacuolar strands. The data provides evidence that: (a) linoleic acid may be a signaling molecule in plant cells; (b) diacylglycerol functions as a signaling molecule through a protein kinase C-independent pathway mediated by PLA2; and (c) Ca2+ and pH have regulatory roles for controlling cytoskeleton tension and organization.
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PMID:Lipids trigger changes in the elasticity of the cytoskeleton in plant cells: a cell optical displacement assay for live cell measurements. 804 35


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