EC:2.7.11.13 - FACTA Search

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)

Although a weak direct stimulus of superoxide anion (O2-) production, platelet-activating factor (PAF) markedly enhances responses to chemotactic peptides (such as n-formyl-met-leu-phe, FMLP) and phorbol esters (such as phorbol myristate acetate, PMA) in human neutrophils. The mechanism of priming was explored first through inhibition of steps in the signal transduction pathway at and following PAF receptor occupation. Priming was not altered by pertussis toxin or intracellular calcium chelation, but the PAF receptor antagonist WEB 2086 and the protein kinase C (PKC) inhibitors sphinganine and staurosporine significantly inhibited the primed response. In order to study the regulation of PAF priming, the effect of PAF alone was desensitized by exposure to escalating doses of PAF prior to exposure to the secondary stimuli. The priming effect of PAF was not desensitized under these conditions. The role of PKC in desensitization was also studied. Prior exposure to PAF also desensitized the increase in membrane PKC activity evoked by a single concentration of PAF. However, when the PAF response was desensitized, PKC priming of the response to FMLP or PMA still occurred, suggesting that PKC activity may play a role in the maintenance of the primed state despite PAF desensitization. These data suggest that: (1) PAF priming is receptor- and PKC-mediated but is independent of pertussis toxin-inhibitable G-proteins or intracellular calcium, (2) during migration in vivo, neutrophils may be desensitized to the direct effects of PAF but maintain the capacity for enhanced responses to other stimuli, (3) desensitization of PAF-induced particulate PKC activity also occurs, but PAF primes PKC activity despite PAF desensitization, and (4) distinct mechanisms govern the direct and priming effects of PAF on oxidative metabolism.
...
PMID:Mechanism and regulation of neutrophil priming by platelet-activating factor. 839 Oct 6

The ability of platelet activating factor (PAF), a potent endogenous inflammatory agent, to induce phenotypic transformation of primary rat embryo cells (RECs) was investigated. RECs are composed predominantly of fibroblasts, with some epithelial cells and a few neuronal and muscle cells. A 1 h period of treatment with PAF (1 x 10(-8)-1 x 10(-6) M) increased the ability of RECs to (i) form foci, (ii) reach a high saturation density in complete medium, (iii) grow in low serum-containing medium and (iv) exhibit anchorage-independent (AI) growth. Similar changes were achieved with C-PAF (1 x 10(-10)-1 x 10(-8) M), an active, non-metabolizable analog of PAF, but not by lyso-PAF (1 x 10(-10)-1 x 10(-6) M), a biologically inactive metabolite of PAF. All of the PAF-induced phenotypic changes could be inhibited by pretreatment with a PAF receptor antagonist, CV3988 (1 x 10(-6) M). Pretreatment of RECs with genestein (1 microgram/ml) also completely inhibited all four measures of PAF-induced REC transformation indicating that tyrosine kinase activity may be required for the observed changes in phenotype. Pretreatment with indomethacin (2 x 10(-7) M) blocked the PAF-induced increases in focus formation and saturation density without affecting PAF-induced alterations in growth in low serum or AI growth. This indicates that PAF may exert some of its effects through a cyclooxygenase product. Pretreatment with staurosporine (5 x 10(-8) M) failed to alter any of the PAF-induced effects, suggesting that protein kinase C activity is not involved in REC transformation by PAF. Our results provide the first evidence that PAF, released by activated phagocytes in and around areas of inflammation, may contribute to the process of malignant transformation.
...
PMID:Platelet activating factor, an endogenous mediator of inflammation, induces phenotypic transformation of rat embryo cells. 839 43

Accumulating evidence suggests that platelet-activating factor (PAF) may play a role in renal pathophysiology. Therefore, in order to investigate this notion further, the effects of PAF on cell growth and tyrosine phosphorylation were analyzed in cultured rat mesangial cells. PAF was found to enhance a time and concentration-dependent increase in phosphotyrosine in several proteins and stimulate 3H-thymidine incorporation. Tyrosine phosphorylation was also enhanced by PAF in protein kinase C (PKC) depleted cells, whereas a tyrosine kinase inhibitor, genistein, inhibited tyrosine phosphorylation of these proteins at the concentration of 1 microgram/ml. PAF stimulated 3H-thymidine incorporation at concentrations below 10(-6) M, but exerted progressive inhibition at concentrations above 10(-6) M. Pre-treatment with phorbol 12-myristate 13-acetate (PMA) did not affect PAF-enhanced incorporation at lower concentrations of PAF, and reversed the inhibitory effects of PAF at higher concentrations. Finally, genistein pre-treatment completely inhibited PAF-induced cell growth at the concentration of 1 microgram/ml. Both tyrosine phosphorylation and 3H-thymidine incorporation induced by PAF were completely inhibited by pre-treatment with the PAF-receptor antagonist, CV-6209, at the concentration of 10(-5)M. These results suggest that PAF enhancement of tyrosine phosphorylation occurred in a PKC-independent manner and that a tyrosine kinase was associated with PAF-induced tyrosine phosphorylation. Moreover, they indicate that the phosphoinositide hydrolysis-PKC pathway is not essential for PAF-induced cell proliferation, and that PKC activation may play an inhibitory rather than a stimulatory role in mitogenesis in response to PAF. Our results indicate that the tyrosine phosphorylation pathway induced by PAF may participate critically in downstream mitogenic signaling through the PAF receptor.
...
PMID:Platelet-activating factor induces cell growth through tyrosine phosphorylation pathway in cultured rat mesangial cells. 858 98

We have recently demonstrated the existence of an autocrine growth loop driven by platelet-activating factor (PAF) in the human endometrial adenocarcinoma. cell line HEC-1A. To investigate a possible cooperation between PAF and the insulin-like growth factor (IGF) system in this cell line, the effect of PAF on insulin-like growth factor binding protein (IGFBP) production as well as binding and biological activities of IGF-I, IGFv-II, and the analog Des(1-3)IGF-I have been evaluated. Analysis of self- and cross-displacement curves of [125I]IGF-I binding to HEC-1A cells indicates the presence of a single class of binding sites, with affinity constants of 1-4 nM for IGF-I and IGF-II and 70 nM for Des(1- 3)IGF-I, which binds to IGFBPs with lower affinity. Insulin does not apparently bind to this binding site. Moreover, the addition of increasing concentrations of IGF-I leads to a paradoxical increase of binding. These results indicate a similarity of this binding site to IGFBPs. The presence of IGFBPs has been demonstrated by Western ligand blot analysis of HEC-1A conditioned medium which shows the presence of two bands of 32-34 and 40-45 kDa. By Western immunoblotting analysis, the two bands were respectively identified as IGFBP-2 and IGFBP-3. Incubation with PAF (1 microM) highly increases the release of the two IGFBPs from the cells. Such an effect is inhibited by the PAF receptor antagonist L659,989, by the PKC inhibitor sangivamycin, and by the tyrosine kinase inhibitor genistein. PAF also induces a time-dependent increase of mRNA expression for IGFBP-3, suggesting an effect on synthesis of this protein. IGF-I and IGF-II (0.1-100 nM) are almost ineffective in inducing [3H]thymidine incorporation, whereas a slight proliferative effect is observed with Des(1-3)IGF-I which also increases PAF synthesis. These data demonstrate a modulatory action of PAF on IGFBP secretion in HEC-1A cells and indicate that the IGF system plays a minor, if any, modulatory role on proliferation of this cell line.
...
PMID:Platelet-activating factor enhances production of insulin-like growth factor binding proteins in a human adenocarcinoma cell line (HEC-1A) 864 11

Lipid bodies, lipid rich cytoplasmic inclusions, are characteristically abundant in vivo in leukocytes associated with inflammation. Because lipid bodies are potential reservoirs of esterified arachidonate and sites at which eicosanoid-forming enzymes may localize, we evaluated mechanisms of lipid body formation in neutrophils (PMN). Among receptor-mediated agonists, platelet activating factor (PAF), but not C5a, formyl-methyl-phenylalanine, interleukin 8, or leukotriene (LT) B4, induced the rapid formation of lipid bodies in PMN. This action of PAF was receptor mediated, as it was dose dependently inhibited by the PAF receptor antagonist WEB 2086 and blocked by pertussis toxin. Lipid body induction by PAF required 5-lipoxygenase (LO) activity and was inhibited by the 5-lipoxygenase-activating protein antagonist MK 886 and the 5-LO inhibitor zileuton, but not by cyclooxygenase inhibitors. Corroborating the dependency of PAF-induced lipid body formation on 5-LO, PMN and macrophages from wild-type mice, but not from 5-LO genetically deficient mice, formed lipid bodies on exposure to PAF both in vitro and in vivo within the pleural cavity. The 5-LO product inducing lipid body formation was not LTB4 but was 5(S)-hydroxyeicosatetraenoic acid [5(S)-HETE], which was active at 10-fold lower concentrations than PAF and was also inhibited by pertussis toxin but not by zileuton or WEB 2086. Furthermore, 5-HETE was equally effective in inducing lipid body formation in both wild-type and 5-LO genetically deficient mice. Both PAF- and 5(S)-HETE-induced lipid body formation were inhibited by protein kinase C (PKC) inhibitors staurosporine and chelerythrine, the phospholipase C (PLC) inhibitors D609 and U-73122, and by actinomycin D and cycloheximide. Prior stimulation of human PMN with PAF to form lipid bodies enhanced eicosanoid production in response to submaximal stimulation with the calcium ionophore A23187; and the levels of both prostaglandin (PG) E2 and LTB4 correlated with the number of lipid bodies. Furthermore, pretreatment of cells with actinomycin D or cycloheximide inhibited not only the induction of lipid body formation by PAF, but also the PAF-induced "priming" for enhanced PGE2 and LTB4 in PMN. Thus, the compartmentalization of lipids to form lipid bodies in PMN is dependent on specific cellular responses that can be PAF receptor mediated, involves signaling through 5-LO to form 5-HETE and then through PKC and PLC, and requires new protein synthesis. Since increases in lipid body numbers correlated with priming for enhanced PGE2 and LTB4 production in PMN, the induction of lipid bodies may have a role in the formation of eicosanoid mediators by leukocytes involved in inflammation.
...
PMID:Mechanisms of platelet-activating factor-induced lipid body formation: requisite roles for 5-lipoxygenase and de novo protein synthesis in the compartmentalization of neutrophil lipids. 866 9

Platelet-activating factor (PAF) is a potent proinflammatory phospholipid mediator of the lung. In this study, we demonstrate that PAF receptor mRNA and protein is expressed by human lung fibroblasts. Interaction of PAF with its specific receptor resulted in increases of tyrosine phosphorylation of several intracellular proteins, indicating that the PAF-receptor might be functionally active. PAF-induced transcription of protooncogenes c-fos and c-jun as well as of interleukin (IL)-6 and IL-8 genes in human fibroblasts. Transcription of the interleukins was followed by secretion of the respective proteins. Moreover, PAF enhanced proliferation of fibroblasts in a concentration-dependent manner. Using signaling inhibitors, we demonstrate that PAF-induced transcription of the c-fos, IL-6, and IL-8 genes, as well as proliferation, require activation of pertussis toxin-sensitive G proteins, tyrosine kinases, and protein kinase C (PKC). In contrast, transcription of c-jun was blocked by pertussis toxin, but not by inhibitors for tyrosine kinases or PKC. These data suggest that PAF stimulates distinct signaling pathways in human lung fibroblasts. In addition, the activation of human fibroblasts by PAF leads to enhanced proliferation and to the expression of proinflammatory cytokines, which may contribute to the pathophysiological changes in pulmonary inflammation.
...
PMID:Platelet-activating factor exerts mitogenic activity and stimulates expression of interleukin 6 and interleukin 8 in human lung fibroblasts via binding to its functional receptor. 869 Nov 34

Platelet-activating factor (PAF) is a potent activator of angiogenesis and controls the motility and the shape of vascular endothelium. The mechanism(s) whereby PAF exerts its action are in part known. Here we report that the biological active (R)PAF enantiomer administrated to cultured endothelial cells induces the early phosphorylation in tyrosine residues of focal adhesion kinase (p125FAX) and paxillin, two molecules involved in the early signaling and cytoskeleton assembly in cells that undergo integrin-mediated adhesion or are challenged by neuropeptides or lysophosphatidic acid. The phenomenon is rapidly turned on, lasts for a few minutes and is adhesion-independent indicating that the chain of events induced by (R)PAF, including p125FAK activation, precedes adhesion. The inhibitory effect of WEB2086, a PAF receptor antagonist, and the lack of activity exerted by the (S)PAF enantiomer, indicate that (R)PAF-mediated p125FAK activation, is PAF receptor-dependent. Calphostin C, an inhibitor of protein kinase C blocks the effect of (R)PAF on p125FAK phosphorylation suggesting that protein kinase C activation is up-stream the activation of this tyrosine kinase. When endothelial cells are exposed to a substratum that allows adhesion and spreading. (R)PAF-stimulated cells, change their adhesive phenotype and start migrating. Inhibitors of tyrosine kinases, like 3-(1,4,-dihydroxytetralyl) methylen-2-oxindole and herbimycin A, reduce the cells migration, the transendothelial flux of albumin and the enhancement of p125FAK activity induced by (R)PAF. The observation that increased tyrosine phosphorylation of p125FAK and its ensuring association with focal adhesion occurs rapidly upon (R)PAF challenge indicates that this signaling molecule has a primary and independent role also in the signaling cascade initiated by (R)PAF.
...
PMID:Platelet-activating factor (PAF) induces the early tyrosine phosphorylation of focal adhesion kinase (p125FAK) in human endothelial cells. 876 Feb 93

The expression of cytokine-induced neutrophil chemoattractants (CINC-1 and CINC-2) mRNA was studied in rat peritoneal cells stimulated with insoluble IgG/ovalbumin immune complexes. A dose- and time-dependent induction was observed in adherent cells, which was more prominent than that induced by the lipid mediator platelet-activating factor (PAF), comparable to that observed in response to 10 micrograms endotoxin in the absence of lipopolysaccharide (LPS)-binding protein, but lower than that produced by 1 mM dibutyryl cyclic AMP, a compound which stabilized transiently expressed genes containing AU-rich sequences in the 3' untranslated region. Analysis of CINC-1 protein by specific enzyme-linked immunosorbent assay confirmed the presence of CINC-1 in the supernatants at concentrations of approximately 4 nM, 4 h after addition of 100 micrograms/ml immune complexes. CINC-2 beta protein was detectable at a lower concentration (approximately 0.3 nM) under the same conditions. Attempts to relate CINC-1 induction with the pathways for cytoplasmic signaling showed a dissociation of Ca2+ mobilization and protein kinase C activation as judged from the small effect of thapsigargin and the lack of effect of phorbol ester. In contrast, these agents produced a marked mobilization of arachidonate linked to the MAP kinase-dependent activation of cytosolic phospholipase A2. The possible dependence of CINC-1 induction on the autocrine generation of lipid mediators was ruled out by a set of experiments including the use of the PAF receptor antagonist BB823, and the analysis of the effect of free arachidonate and leukotriene B4 on CINC-1 induction. Surprisingly, the inhibitor of leukotriene synthesis MK-886 in the range of concentration 1-10 microM inhibited CINC-1 induction by a mechanism that appears to be independent of its effect on eicosanoid production. Interestingly, CINC-1 induction appeared to be related to protein tyrosine phosphorylation reactions on the basis of both the appearance of several tyrosine-phosphorylated protein bands in lysates from adherent peritoneal cells treated with immune complexes and the complete blockade of CINC-1 induction by treatment with 1 microM herbimycin A, an inhibitor of src protein tyrosine kinases.
...
PMID:The expression of cytokine-induced neutrophil chemoattractants (CINC-1 and CINC-2) in rat peritoneal macrophages is triggered by Fc gamma receptor activation: study of the signaling mechanism. 881 63

Platelet-activating factor (PAF) stimulates a diverse array of cellular responses through receptors coupled to G proteins that activate phospholipase C (PLC). Truncation of the cytoplasmic tail of the receptor to remove phosphorylation sites (mutant PAF receptor, mPAFR) results in enhancement of PAF-stimulated responses. Here we demonstrate that PAF or phorbol 12-myristate 13-acetate (PMA) pretreatment inhibited wild type PAFR-induced PLC-mediated responses by approximately 90%, whereas these responses to the phosphorylation-deficient mPAFR were inhibited by approximately 50%, despite normal G protein coupling, suggesting a distal inhibitory locus. PAF and PMA, as well as a membrane permeable cyclic AMP analog, stimulated phosphorylation of PLCbeta3. A protein kinase C (PKC) inhibitor blocked phosphorylation of PLCbeta3 stimulated by PAF and PMA but not by cAMP. Activation of protein kinase A (PKA) by cAMP did not result in inhibition of Ca2+ mobilization stimulated by PAF. In contrast, cAMP did inhibit the response to formylpeptide chemoattractant receptor. These data suggest that homologous desensitization of PAF-mediated responses is regulated via phosphorylation at two levels in the signaling pathway, one at the receptor and the other at PLCbeta3 mediated by PKC but not by PKA. Phosphorylation of PLCbeta3 by PKA could explain the inhibition of formylpeptide chemoattractant receptor signaling by cAMP. As PAF and formylpeptide chemoattractant receptors activate PLC via different G proteins, phosphorylation of PLCbeta3 by PKC and PKA could provide distinct regulatory control for classes of G protein-coupled receptors.
...
PMID:Role of phospholipase Cbeta3 phosphorylation in the desensitization of cellular responses to platelet-activating factor. 911 22

The different platelet-activating factor (PAF) receptor subtypes were identified in alveolar macrophages of hamster and guinea pig, based on the distinct characteristics of PAF-induced Ca++ responses and PAF antagonist potencies to these responses. PAF, but not lyso-PAF (inactive PAF), induced Ca++ release from intracellular Ca++ stores and the influx of extracellular Ca++ in a dose-dependent manner in both hamster and guinea pig alveolar macrophages. The potency for PAF-stimulated Ca++ release, however, was significantly different between the two species with EC50 values being 30- and 50-fold higher in Ca++ release and Ca++ influx responses in guinea pig than hamster, respectively. In addition, there were distinct differences in Ca++ influx characteristics between the two species; guinea pig macrophages exhibiting a rapid Ca++ extrusion and high sensitivity to thapsigargin (depletion of intracellular Ca++ store). The PAF-induced Ca++ response was sensitive to G-protein inhibitor pertussis toxin in hamster but not in guinea pig, suggesting the coupling of different types of G-proteins to PAF receptors. Pretreatment of macrophages with tyrosine kinase inhibitor, herbimycin A, caused a dose-dependent decrease in PAF-induced Ca++ response in guinea pig but surprisingly an increased response in hamster. These observations suggest the possibility of a dual mechanism, for G-protein and tyrosine kinase, in PAF-induced phospholipase C activation of macrophages from both species and thus Ca++ signaling in response to PAF-mediated receptor signal transduction cascade. The PAF-induced Ca++ response was desensitized by repetitive stimulation with PAF or pretreatment with protein kinase C activator, mitogen-activated protein kinase, which had a slightly greater potency in guinea pig than hamster. Importantly, three structurally distinct PAF antagonists, WEB2086, L659,989 and CL184005, blocked PAF-induced Ca++ responses in a dose-dependent manner with a markedly different potencies between the two species. The IC50 values for inhibiting PAF-induced Ca++ release were 2.5- (WEB2086), 650- (L659,989) and 120- (CL184005) fold less in hamster than in guinea pig. The relative potencies of these PAF antagonists in hamster macrophages were L659,989 > CL184005 > WEB2086. However, in guinea pig these three antagonists showed roughly the same potency. Interestingly, the opposite inhibitory effects of these antagonists on PAF-induced Ca++ influx were found in the two species, in which the IC50 were 15- (WEB2086) and 5- (CL184005) fold greater in hamster than in guinea pig but no difference in the IC50 value of L659,989 between the two species. Pretreatment of macrophages from both species with these antagonists had no effect on ATP-induced Ca++ response, suggesting that the antagonism is specific to PAF receptors. Based on our data, it was concluded that the alveolar macrophages isolated from the bronchoalveolar lavage of hamsters contain a distinct subtype PAF receptor that differs from that of guinea pigs in modulating a different signal transduction pathway.
...
PMID:Differences in platelet-activating factor receptor mediated Ca++ response between hamster and guinea pig alveolar macrophages. 919 Aug 35

<< Previous 1 2 3 4 5 6 Next >>