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)

Previous studies have shown that certain glycosphingolipids may function as modulators of protein kinase C (PKC) activity. To study the structure-activity relationship, we examined the effects of 17 gangliosides, 10 neutral glycolipids, as well as sulfatide, psychosine and ceramide on PKC activity in PC12D cells. Using an in vitro assay system, we found that all but one (GQ1b) ganglioside inhibited PKC activity at concentrations between 25 and 100 &mgr;M, and the potency was proportional to the number of sialic acid residues. However, at lower concentrations several gangliosides, including GM1 and LM1 behaved as mild activators of PKC activity. GQ1b had no effect within the range 0.1-10 &mgr;M, but acted as a mild activator of PKC activity at 25 &mgr;M. On the other hand, fucosyl-GM1 and GM1 containing blood group B determinant, which are abundant in PC12 cells, were potent inhibitors of PKC activity. Among the neutral glycosphingolipids tested, LacCer, Gb3, GalGb3, and GA1, all of which have a terminal galactose residue, were found to be ineffective or acted as mild activators of PKC activity. In contrast, GA2, Gb4 and Gb5 which have a terminal N-acetylgalactosamine residue, were potent inhibitors of the PKC activity. Thus, the terminal sugar residue may play a pivotal role in determining the effect of glycosphingolipids in modulating PKC activity. In addition, we also found that GalCer containing normal fatty acids acted as potent activators of PKC activity. Ceramide and GlcCer appeared to be ineffective in modulating PKC activity, wheras psychosine and sulfatides appeared to be inhibitory. We conclude that the carbohydrate head groups and the hydrophobic groups of gangliosides and neutral glycolipids may modulate the PKC system in unique manners, which may in turn affect various biological processes in the cell. Copyright 1994 S. Karger AG, Basel
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PMID:Differential Effects of Glycosphingolipids n Protein Kinase C Activity in PC12D Pheochromocytoma Cells. 1172 31

Ceramide, which is an integral component of the sphingomyelin signaling pathway, can attenuate voltage-gated Ca(2+) channel (VGCC) activity in a number of cell types. The aim of the present study was to determine whether ceramide can also modulate VGCC activity, and as a consequence nicotinic receptor-dependent Ca(2+) signaling and catecholamine secretion, in rat adrenal chromaffin cells. Short-term C(6)-ceramide (CER) treatment dose-dependently inhibited nicotine (NIC)-induced peak intracellular Ca(2+) transients. Sphingomyelinase elicited similar responses, whereas the inactive ceramide analog C(2)-dihydroceramide had no effect on NIC-induced Ca(2+) transients. CER suppressed KCl- and NIC-induced Ca(2+) transients to a similar extent, suggesting that the voltage-gated Ca(2+) channel was a primary site of inhibition. In direct support of this concept, whole-cell patch-clamp analysis demonstrated that CER and sphingomyelinase significantly reduced peak Ca(2+) currents. Pretreatment with staurosporine significantly attenuated CER-dependent inhibition of both NIC-induced Ca(2+) transients and peak Ca(2+) current, suggesting that the effects of CER are mediated at least in part by protein kinase C. Consistent with suppressed Ca(2+) signaling, CER also significantly inhibited NIC-induced catecholamine secretion measured at the single-cell level by carbon fiber amperometry. This effect of CER was also significantly attenuated by pretreatment with staurosporine These data demonstrate that the sphingomyelin signaling pathway can modulate nicotinic receptor-dependent Ca(2+) signaling and catecholamine secretion in rat chromaffin cells.
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PMID:Ceramide modulates nicotinic receptor-dependent Ca(2+) signaling in rat chromaffin cells. 1174 75

Exogenous C(2)-ceramide has been shown to inhibit polymorphonuclear leukocyte (PMN) phagocytosis through inhibition of phospholipase D (PLD) and downstream events, including activation of extracellular signal-regulated kinases 1 and 2, leading to the hyphothesis that the sphingomyelinase pathway is involved in termination of phagocytosis. Here it is postulated that increased PLD activity generating phosphatidic acid and diacylglycerol (DAG) is essential for superoxide release and degranulation and that ceramide, previously shown to be generated during PMN activation, inhibits PLD activation, thereby leading to inhibition of PMN function. When PMNs were primed with granulocyte colony-stimulating factor (G-CSF) and then activated with N-formyl-methionyl-leucyl-phenylalanine (FMLP), C(2)-ceramide (10 microM) completely inhibited release of superoxide, lactoferrin, and gelatinase; the DAG analog sn-1,2-didecanoylglycerol (DiC10) (10 microM) restored oxidase activation and degranulation in the ceramide-treated cells. Similarly, C(2)-ceramide inhibited oxidase activity and degranulation of PMNs treated with cytochalasin B followed by FMLP, and DiC10 restored function. In contrast, C(2)-ceramide did not inhibit phosphorylation of p47phox or p38 mitogen-activated protein kinase, or translocation of p47phox, PLD-containing organelles, adenosine diphosphate-ribosylation factor 1, RhoA, protein kinase C (PKC)-beta or PKC-alpha to the plasma membrane in G-CSF or cytochalasin B-treated, FMLP-activated PMNs. PLD activity increased by 3-fold in G-CSF-primed PMNs stimulated by FMLP and by 30-fold in cytochalasin B-treated PMNs stimulated by FMLP. Both PLD activities were completely inhibited by 10 microM C(2)-ceramide. In conclusion, superoxide, gelatinase, and lactoferrin release require activation of the PLD pathway in primed PMNs and cytochalasin B-treated PMNs. Ceramide may affect protein interactions with PLD in the plasma membrane, thereby attenuating PMN activation.
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PMID:Regulation of polymorphonuclear leukocyte degranulation and oxidant production by ceramide through inhibition of phospholipase D. 1183 Apr 97

The molecular mechanisms by which arachidonic acid (AA) and ceramide elicit translocation of protein kinase C (PKC) were investigated. Ceramide translocated epsilonPKC from the cytoplasm to the Golgi complex, but with a mechanism distinct from that utilized by AA. Using fluorescence recovery after photobleaching, we showed that, upon treatment with AA, epsilonPKC was tightly associated with the Golgi complex; ceramide elicited an accumulation of epsilonPKC which was exchangeable with the cytoplasm. Stimulation with ceramide after AA converted the AA-induced Golgi complex staining to one elicited by ceramide alone; AA had no effect on the ceramide-stimulated localization. Using point mutants and deletions of epsilonPKC, we determined that the epsilonC1B domain was responsible for the ceramide- and AA-induced translocation. Switch chimeras, containing the C1B from epsilonPKC in the context of deltaPKC (delta(epsilonC1B)) and vice versa (epsilon(deltaC1B)), were generated and tested for their translocation in response to ceramide and AA. delta(epsilonC1B) translocated upon treatment with both ceramide and AA; epsilon(deltaC1B) responded only to ceramide. Thus, through the C1B domain, AA and ceramide induce different patterns of epsilonPKC translocation and the C1B domain defines the subtype specific sensitivity of PKCs to lipid second messengers.
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PMID:Importance of C1B domain for lipid messenger-induced targeting of protein kinase C. 1187 28

The possibility that lipid-induced insulin resistance in human muscle is related to alterations in diacylglycerol (DAG)/protein kinase C (PKC) signaling was investigated in normal volunteers during euglycemic-hyperinsulinemic clamping in which plasma free fatty acid (FFA) levels were increased by a lipid/heparin infusion. In keeping with previous reports, rates of insulin-stimulated glucose disappearance (G(Rd)) were normal after 2 h but were reduced by 43% (from 52.7 +/- 8.2 to 30.0 +/- 5.3 micromol. kg(-1). min(-1), P < 0.05) after 6 h of lipid infusion. No changes in PKC activity or DAG mass were seen in muscle biopsy samples after 2 h of lipid infusion; however, at approximately 6 h, PKC activity and DAG mass were increased approximately fourfold, as were the abundance of membrane-associated PKC-betaII and -delta. A threefold increase in membrane-associated PKC-betaII was also observed at approximately 2 h but was not statistically significant (P = 0.058). Ceramide mass was not changed at either time point. To evaluate whether the fatty acid-induced insulin activation of PKC was associated with a change in the IkB kinase (IKK)/nuclear factor (NF)-kappaB pathway, we determined the abundance in muscle of IkappaB-alpha, an inhibitor of NF-kappaB that is degraded after its phosphorylation by IKK. In parallel with the changes in DAG/PKC, no change in IkappaB-alpha mass was observed after 2 h of lipid infusion, but at approximately 6 h, IkappaB-alpha was diminished by 70%. In summary, the results indicated that the insulin resistance observed in human muscle when plasma FFA levels were elevated during euglycemic-hyperinsulinemic clamping was associated with increases in DAG mass and membrane-associated PKC-betaII and -delta and a decrease in IkappaB-alpha. Whether acute FFA-induced insulin resistance in human skeletal muscle is caused by the activation of these specific PKC isoforms and the IKK-beta/IkappaB/NFkappaB pathway remains to be established.
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PMID:Lipid-induced insulin resistance in human muscle is associated with changes in diacylglycerol, protein kinase C, and IkappaB-alpha. 1208 26

Ceramide levels are strongly increased by stimulation of renal mesangial cells with nitric oxide (NO). This effect was shown previously to be due to a dual action of NO, comprising an activation of sphingomyelinases and an inhibition of ceramidase activity. In this study we show that the NO-triggered inhibition of neutral ceramidase activity is paralleled by a down-regulation at the protein level. A complete loss of neutral ceramidase protein is obtained after 24 h of stimulation. Whereas the selective proteasome inhibitor lactacystin blocked NO-evoked ceramidase degradation, several caspase inhibitors were ineffective. Moreover, the NO-induced degradation is reversed by the protein kinase C (PKC) activator, 12-O-tetradecanoylphorbol-13-acetate (TPA), and also by the physiological PKC activators platelet-derived growth factor-BB (PDGF), angiotensin II and ATP, resulting in a normalization of neutral ceramidase protein as well as activity. In vivo phosphorylation studies using (32)P(i)-labeled mesangial cells revealed that TPA, PDGF, angiotensin II, and ATP trigger an increased phosphorylation of the neutral ceramidase, which is blocked by the broad spectrum PKC inhibitor Ro-31 8220 but not by CGP 41251, which has a preferential action on Ca(2+)-dependent isoforms, thus suggesting the involvement of a Ca(2+)-independent PKC isoform. In vitro phosphorylation assays using recombinant PKC isoenzymes and neutral ceramidase immunoprecipitated from unstimulated mesangial cells show that particularly the PKC-delta isoform and to a lesser extent the PKC-alpha isoform are efficient in directly phosphorylating neutral ceramidase. In summary, our data show that NO is able to induce degradation of neutral ceramidase, thereby promoting accumulation of ceramide in the cell. This effect is reversed by PKC activation, most probably by the PKC-delta isoenzyme, which can directly phosphorylate and thereby prevent neutral ceramidase degradation. These novel regulatory interactions will provide therapeutically valuable information to target neutral ceramidase stability and subsequent ceramide accumulation.
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PMID:Nitric oxide induces degradation of the neutral ceramidase in rat renal mesangial cells and is counterregulated by protein kinase C. 1235 35

Ceramide is generated in response to inflammatory mediators and oxidative stress. Since these stimuli dramatically increase nociceptin/orphanin FQ (N/OFQ) gene expression in astrocytes we evaluated the regulation of N/OFQ by ceramide and the signaling mechanisms involved. We found that ceramide induced N/OFQ mRNA levels 22-fold after 24 h. In astrocytes ceramide stimulated the JNK, p38 and ERK MAP kinase pathways and also led to the activation of the transcription factors CREB and NFkappaB. Using specific inhibitors of signaling pathways we determined that N/OFQ gene induction is mediated by ERK and p38 MAP kinases. ERK activation may be induced by protein kinase C and it leads to CREB phosphorylation. The NFkappaB pathway also appears to be crucial for ceramide-induced N/OFQ gene expression.
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PMID:Regulation of nociceptin/orphanin FQ gene expression in astrocytes by ceramide. 1239 8

The sphingolipid ceramide has proven to be a powerful second-signal effector molecule that regulates diverse cellular processes including apoptosis, cell senescence, the cell cycle, and cellular differentiation. Ceramide has been shown to activate a number of enzymes involved in stress signaling cascades including both protein kinases and protein phosphatases. Ceramide kinase targets include stress-activated protein kinases (SAPKs) such as the jun kinases (JNKs), kinase suppressor of Ras (KSR), and the atypical protein kinase C (PKC) isoform, PKC zeta. Ceramide also is capable of activating protein phosphatases such as protein phosphatase 1 (PP1) and protein phosphatase 2A (PP2A). It is through these protein phosphatases that ceramide can indirectly inhibit kinases that are key components of pro-growth signaling processes such as the classical and novel PKC isoforms and protein kinase B (PKB; also known as Akt). However, the mechanisms how ceramide directly activates enzymes such as JNK and PP2A are still not clear. Elucidation of these mechanisms will reveal how ceramide functions in stress signaling cascades and will provide important information on cellular processes such as apoptosis. It is becoming clear that the ceramide generation is a near universal feature of programmed cell death. It is possible that during at least some apoptotic events, ceramide may be required to activate stress-signal cascades that lead to cell death, while concurrently, suppressing growth and survival pathways in the dying cell. Such a versatile role for ceramide is not unreasonable since ceramide has been implicated as having a role in both intrinsic (i.e. mitochondrial) and extrinsic (i.e. death receptor-mediated) apoptotic pathways. The recent data suggesting that aberrant glycosylation of ceramide (i.e. inactivation of the molecule) may be an important cause of drug resistance in certain cancers suggests that ceramide-mediated signaling cascades are critical components of chemotherapy-induced cell killing. Taken together, these properties of ceramide suggest that this important second-signal molecule may be an important target in anti-neoplastic strategies.
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PMID:Intracellular signal transduction pathways activated by ceramide and its metabolites. 1267 12

Ceramide is generated in response to numerous stress-inducing stimuli and has been implicated in the regulation of diverse cellular responses, including cell death, differentiation, and insulin sensitivity. Recent evidence indicates that ceramide may regulate these responses by inhibiting the stimulus-mediated activation of protein kinase B (PKB), a key determinant of cell fate and insulin action. Here we show that inhibition of this kinase involves atypical PKCzeta, which physically interacts with PKB in unstimulated cells. Insulin reduces the PKB-PKCzeta interaction and stimulates PKB. However, dissociation of the kinase complex and the attendant hormonal activation of PKB were prevented by ceramide. Under these circumstances, ceramide activated PKCzeta, leading to phosphorylation of the PKB-PH domain on Thr(34). This phosphorylation inhibited phosphatidylinositol 3,4,5-trisphosphate (PIP(3)) binding to PKB, thereby preventing activation of the kinase by insulin. In contrast, a PKB-PH domain with a T34A mutation retained the ability to bind PIP(3) even in the presence of a ceramide-activated PKCzeta and, as such, expression of PKB T34A mutant in L6 cells was resistant to inhibition by ceramide treatment. Inhibitors of PKCzeta and a kinase-dead PKCzeta both antagonized the inhibitory effect of ceramide on PKB. Since PKB confers a prosurvival signal and regulates numerous pathways in response to insulin, suppressing its activation by a PKCzeta-dependent process may be one mechanism by which ceramide promotes cell death and induces insulin resistance.
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PMID:Ceramide disables 3-phosphoinositide binding to the pleckstrin homology domain of protein kinase B (PKB)/Akt by a PKCzeta-dependent mechanism. 1456 23

Ceramide is a lipid second messenger produced by sphingolipid metabolism in cells exposed to a limited number of agonists and in turn triggers important cell responses including protein kinase C (PKC)-alpha activation. Using a fusion protein comprising bovine PKCalpha and the green fluorescent protein (GFP), we transfected human embryonic kidney (HEK) cells and investigated to which subcellular compartment ceramide triggers PKCalpha redistribution. Stimulation of HEK cells with exogenous C16-ceramide or bacterial sphingomyelinase (bSMase), which leads to increased endogenous ceramide formation, evokes a translocation of PKCalpha to the Golgi compartment. By using deletion mutants of PKCalpha lacking distinct domains in the regulatory region, it is shown that the Ca(2+)-dependent lipid binding C2 domain, but not one of the C1 domains is essentially required for the ceramide-triggered translocation of PKCalpha to the Golgi complex. In contrast, the C2 domain is not required for phorbol ester (TPA) binding and translocation of PKCalpha to the plasma membrane. In addition, evidence is provided that TPA requires only one of the two C1 subdomains to trigger translocation to the plasma membrane.In summary, our data provide evidence that ceramide either directly or indirectly interacts with the Ca(2+)-dependent lipid binding C2 domain of PKCalpha and thereby induces translocation of the enzyme to the Golgi compartment.
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PMID:Ceramide induces translocation of protein kinase C-alpha to the Golgi compartment of human embryonic kidney cells by interacting with the C2 domain. 1456 11


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