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)

An early response to epidermal growth factor in A431 cells is the generation of diglyceride, a physiological activator of protein kinase C. By differentially prelabeling cellular phospholipids with [3H]arachidonate and [3H]myristate, which are incorporated primarily into phosphatidylinositol and phosphatidylcholine, respectively, we have found that epidermal growth factor induces an increase in diglyceride levels from both phosphatidylinositol and phosphatidylcholine via distinct mechanisms and kinetics. The epidermal growth factor-induced increase in phosphatidylinositol-derived diglyceride was transient and peaked at 5 min. As diglyceride levels dropped, there was a corresponding increase in phosphatidic acid, suggesting that the diglyceride is efficiently converted to phosphatidic acid by a diglyceride kinase. In contrast, epidermal growth factor-induced increases in phosphatidylcholine-derived diglyceride peaked at 30 min and remained elevated for greater than 2 h. The epidermal growth factor-induced increases in phosphatidic acid detected in [3H]myristate-prelabeled cells paralleled the increase in diglyceride, suggesting that the phosphatidylcholine-derived diglyceride is produced from phosphatidic acid via a phosphatidic acid phosphatase. Consistent with this hypothesis, epidermal growth factor also induced a protein kinase C-independent phospholipase D activity that was specific for phosphatidylcholine. These data suggest that epidermal growth factor induces diglyceride production from phosphatidylinositol and phosphatidylcholine via two distinct mechanisms: a rapid and transient induction of diglyceride that likely involves phospholipase c-gamma-mediated hydrolysis of phosphatidylinositol-4,5-bisphosphate and a slower, more sustained induction of diglyceride via a phospholipase D-mediated hydrolysis of phosphatidylcholine to produce phosphatidic acid, which is then converted to diglyceride by a phosphatidic acid phosphatase.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Epidermal growth factor induces the production of biologically distinguishable diglyceride species from phosphatidylinositol and phosphatidylcholine via the independent activation of type C and type D phospholipases. 812 95

Phosphatidylinositol 3-kinase (PI 3-kinase) was partially purified from rat liver cytosol and used to synthesize phosphatidylinositol 3,4,5-trisphosphate (PIP3), using phosphatidylinositol 4,5-bisphosphate (PIP2) as a substrate. Purified PIP3 (free of chromatographic oxalate) activated protein kinase C (PKC) in the presence of phosphatidylserine and calcium (PKC -cofactors) in a concentration-dependent manner. In the absence of these cofactors, effect of PIP3 was not observed. Comparison of the effects of PIP3 and PIP2 on PKC activity indicates that PIP3 is a more potent PKC-activator than PIP2. The affinity of PKC to PIP3 was 4 fold higher than that to PIP2 (KPIP3 = 0.022 and KPIP2 = 0.087 mol %), while its maximal velocity (Vmax) was similar to that of PIP2-stimulated PKC activity (0.4 - 0.5 mumol/mg/min). These results suggest a physiological role for PIP3 in signal transduction, and support the previous finding (Chauhan et al. (1991) Arch. Biochem. Biophys. 287,283) that PKC-activation by phosphoinositides increases with the state of phosphorylation of these lipids. We propose that PIP3 by activating PKC may initiate a cascade of events from PIP3-->PKC- activation-->effects on other protein kinases such as MAP-kinase-->gene expression.
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PMID:Activation of protein kinase C by phosphatidylinositol 3,4,5-trisphosphate. 839 20

Mitogen-activated protein (MAP) kinase phosphorylates tau in cell-free analyses, but whether or not it does so within intact cells remains controversial. In the present study, microinjection of MAP kinase into SH-SY-5Y human neuroblastoma cells increased tau immunoreactivity toward the phosphodependent antibodies PHF-1 and AT-8. In contrast, treatment with a specific inhibitor of MAP kinase (PD98059) did not diminish "basal" levels of these immunoreactivities in otherwise untreated cells. These findings indicate that hyperactivation of MAP kinase increases phospho-tau levels within cells, despite that MAP kinase apparently does not substantially influence intracellular tau phosphorylation under normal conditions. These findings underscore that results obtained following inhibition of kinase activities do not necessarily provide an indication of the consequences accompanying hyperactivation of that same kinase. Several studies conducted in cell-free systems indicate that exposure of tau to multiple kinases can have synergistic effects on the nature and extent of tau phosphorylation. We therefore examined whether or not such effects could be demonstrated within these cells. Site-specific phospho-tau immunoreactivity was increased in additive and synergistic manners by treatment of injected cells with TPA (which activates PKC), calcium ionophore (which activates calcium-dependent kinases), and wortmannin (which inhibits PIP3 kinase). Alteration in total tau levels was insufficient to account for the full extent of the increase in phospho-tau immunoreactivity. These additional results indicate that multiple kinase activities modulate the influence of MAP kinase on tau within intact cells.
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PMID:Hyperactivation of mitogen-activated protein kinase increases phospho-tau immunoreactivity within human neuroblastoma: additive and synergistic influence of alteration of additional kinase activities. 1008 8

We report a novel signaling pathway linking M2 muscarinic receptors to metabotropic ion channels. Stimulation of heterologously expressed M2 receptors, but not other Gi/Go-associated receptors (M4 or alpha2c), activates a calcium- and voltage-independent chloride current in Xenopus oocytes. We show that the stimulatory pathway linking M2 receptors to these chloride channels consists of Gbeta gamma stimulation of phosphoinositide 3-kinase gamma (PI-3Kgamma), formation of phosphatidylinositol 3,4,5-trisphosphate (PIP3), and activation of atypical protein kinase C (PKC). The chloride current is activated in the absence of M2 receptor stimulation by the injection of PIP3, and PIP3 current activation is blocked by a pseudosubstrate inhibitory peptide of atypical PKC but not other PKCs. Moreover, the current is activated by injection of recombinant PKCzeta at concentrations as low as 1 nM. M2 receptor-current coupling was disrupted by inhibiton of PI-3K and by injection of beta gamma binding peptides, but it was not affected by expression of dominant negative p85 cRNA. We also show that this pathway mediates M2 receptor coupling to metabotropic nonselective cation channels in mammalian smooth muscle cells, thus demonstrating the broad relevance of this signaling cascade in neurotransmitter signaling.
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PMID:Coupling of M2 muscarinic receptors to membrane ion channels via phosphoinositide 3-kinase gamma and atypical protein kinase C. 1031 93

The human high affinity receptor for immunoglobulin G, FcgammaRI, in dibutyryl cyclic AMP (dbcAMP)-differentiated U937 cells, is coupled to the activation of phospholipase C (PLC) and the conventional protein kinase C (PKC) isoforms, alpha, beta, and gamma. Here we demonstrate that aggregation of FcgammaRI activates the tyrosine-kinase regulated form of phosphatidylinositol-3-kinase (PI-3-kinase) and that an increase of phosphatidylinositol trisphosphate (PIP3) is essential for the activation and translocation of PLCgamma1 in these cells. In addition, activation of the PKC isoforms was ablated by specific inhibitors of PI3-kinase or by overexpression of a dominant negative p85 subunit of PI3-kinase. The findings reported here demonstrate that PLCgamma1 and PKC activation by FcgammaRI are downstream of PI3-kinase, and that in contrast to cytokine primed cells, only the tyrosine-kinase activated isoform of PI3-kinase is coupled to FcgammaRI in dbcAMP-differentiated cells.
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PMID:FcgammaRI activation of phospholipase Cgamma1 and protein kinase C in dibutyryl cAMP-differentiated U937 cells is dependent solely on the tyrosine-kinase activated form of phosphatidylinositol-3-kinase. 1046 27

Abnormal glucose handling in the proximal tubule may play an important role in the development of diabetic nephropathy. Thus, the present study was designed to examine the effect of high glucose on alpha-methyl-D-glucopyranoside (alpha-MG) uptake and its signaling pathways in the primary cultured rabbit renal proximal tubule cells (PTCs). When PTCs were preincubated with 25 or 50 mM glucose for 4 h, 25 or 50 mM glucose significantly inhibited alpha-MG uptake, while 25 or 50 mM mannitol and L-glucose did not affect. Actinomycin D and cycloheximide did not block the effect of high glucose on alpha-MG uptake. Twenty-five millimoles glucose-induced inhibition of alpha-MG uptake was blocked by mepacrine and AACOCF(3), phospholipase A(2) (PLA(2)) inhibitors. Twenty-five millimoles of glucose, not mannitol or L-glucose, significantly increased the [(3)H]-arachidonic acid (AA) release compared to control. In addition, the 25 mM glucose-induced [(3)H]-AA release was completely blocked by mepacrine or AACOCF(3). Indomethacin, a cyclooxygenase inhibitor, blocked the high glucose-induced inhibition of alpha-MG uptake, although econazole, cytochrome P-450 a epoxygenase inhibitor, and nordihydroguaiaretic acid (NDGA), a lipoxygenase inhibitor, did not. On the other hand, staurosporine and bisindolylmaleimide I, protein kinase C (PKC) inhibitors, blocked 25 mM glucose-induced increase of [(3)H]-AA release and inhibition of alpha-MG uptake. However, neomycin, U 73122, and phospholipase c(PLC) inhibitors did not block the effect of 25 mM glucose on [(3)H]-AA release and alpha-MG uptake. Pretreatment of methoxyverapamil, an L-type Ca(2+) channel blocker, abolished 25 mM glucose-induced increase of [(3)H]-AA release. Indeed, 25 mM glucose increased translocation of cPLA(2) from cytosolic fraction to membrane fraction. In conclusion, the present results demonstrate that high glucose inhibits alpha-MG uptake by the increase of AA release via the activation of PKC.
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PMID:High glucose-induced inhibition of alpha-methyl-D-glucopyranoside uptake is mediated by protein kinase C-dependent activation of arachidonic acid release in primary cultured rabbit renal proximal tubule cells. 1079 10

The activity on ARF of the guanine nucleotide exchange factor ARNO depends on its membrane recruitment, induced by binding of its PH domain to phosphoinositides. A polycationic C-terminal extension to the PH domain might also contribute to its specific binding to phosphatidylinositol 4,5-bisphosphate [(4,5)PIP2] and to phosphatidylinositol 3,4,5-trisphosphate [(3,4,5)PIP3], and to ionic binding to other acidic lipids. We have analyzed in vitro the relative contributions to phospholipid binding of the PH domain and C-terminal extension by cosedimentation of "PH+C domain" and "nominal PH domain" protein constructs including or not including the polycationic C-terminus, with sucrose-loaded unilamellar vesicles made of equal proportions of the neutral lipids phosphatidylcholine and phosphatidylethanolamine, and supplemented or not with 30% acidic phosphatidylserine (PS) and 2% of various phosphoinositides. Binding was measured as a function of the vesicle concentration and of the medium ionic strength. Both proteins bound with higher affinity to (3,4,5)PIP3 than to (4,5)PIP2, the selectivity for (3,4,5)PIP3 being highest for the nominal PH domain. We observed also a clear selectivity of (3,4,5)PIP3 over (4,5)PIP2 for stimulating the activity of ARNO on ARF with vesicles containing 10% PS and 1% PIP2 or PIP3. Our data suggest that the PH domain provides the specific phosphoinositide binding site and some unspecific ionic interaction with acidic PS, whereas the polybasic C domain contributes to binding mainly by unspecific ionic interactions vith PS. Phosphorylation by protein kinase C of a serine in the C domain reduces the ionic affinity of the PH+C domain for PS, but does not affect the phosphoinositide specificity.
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PMID:Binding of the PH and polybasic C-terminal domains of ARNO to phosphoinositides and to acidic lipids. 1080 41

Antigen-presenting cells internalize antigen by fluid-phase pinocytosis or by endocytosis via surface receptors such as the B cell receptor (BCR) and Fc receptors for IgG, IgA and IgE (FcR). While both modes of internalization lead to antigen presentation it is recognized that receptor-mediated endocytosis greatly enhances the efficiency of processing and antigen presentation. Receptors facilitate the entry of antigen into the endocytic pathway by interaction of their internalization motifs with the endocytic machinery. These motifs include tyrosine-based, dileucine and casein kinase-like motifs. However these structures appear insufficient to support processing of cryptic epitopes, leading to a limited immune response. Cryptic epitope processing appears dependent on receptor signaling which is mediated by immunoreceptor tyrosine activation motifs (ITAMs). The signaling cascade which follows receptor crosslinking promotes reorganization and acidification of the late endocytic compartment or MIIC. Signaling events downstream of Syk, in particular calcium flux and protein kinase C activation, are necessary for MIIC induction. PI(3) kinase is also involved at multiple steps in antigen presentation, including production of PIP3 and transport of cathepsins. PIP3 is crucial both as a binding substrate for proteins implicated in vesicle transport and for the recruitment of signaling molecules to the plasma membrane. Among PIP3 activated molecules, protein kinase B (PKB) has been linked to endocytic function. We observe association of activated PKB with the MIIC after signaling through antigen presentation-competent receptors, but not mutant, presentation-defective receptors.
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PMID:The ins and outs of getting in: structures and signals that enhance BCR or Fc receptor-mediated antigen presentation. 1099 20

The modulation of GnT-V activity by signaling molecules in PI-3-K/PKB pathway in human hepatocarcinoma cell line 7721 was studied. GnT-V activity was determined after the transfection of sense or antisense cDNA of PKB into the cells, as well as the addition of activators, specific inhibitors, and the antibodies to the enzyme assay system or culture medium. It was found that the basal activity of GnT-V was up regulated by the sense and down regulated by the antisense cDNA of PKB transfected into 7721 cells. GnT-V was activated by PIP2, PIP3 or GTPgamma[S] added to the assay system, and the activation of PIP2 or GTPgamma[S] was abolished by LY2940002, a specific inhibitor of PI-3-K, but the activation of PIP3 was not attenuated by LY2940002. In addition, GnT-V activity in cultured parental or H-ras transfected cells was inhibited by the antibody against PKB or PI-3-K. These findings demonstrated the involvement of PI-3-K/PKB signaling pathway in the regulation of GnT-V. Moreover, ET18-OCH3, an inhibitor of Raf translocation and PI-PLC enzyme, which produces the activator of PKC, as well as the antibodies against Raf-1 or MEK also inhibited GnT-V activity in the parental and H-ras transfected cells. The inhibitory rates, however, were less in the transfected cells than those in the parental cells. These results reveal that in parental and H-ras transfected 7721 cells, the basal activity of GnT-V is also regulated by the Ras/Raf-1/MEK/MAPK cascade in addition to PI-3-K/PKB signaling pathway. The significance of these two pathways in the regulation of GnT-V and their relations to the activation of PKC previously reported by our laboratory (Ju TZ et al., 1995 Glyconjugate J 12, 767-772) was discussed.
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PMID:Modulation of the basal activity of phosphatidylinositol-3-kinase/protein kinase B signaling pathway in human hepatocarcinoma cells. 1126 40

Escherichia coli, the most common Gram-negative bacterium that causes meningitis in neonates, invades human brain microvascular endothelial cells (HBMEC) by rearranging host cell actin via the activation of phosphatidylinositol 3-kinase (PI3K) and PKC-alpha. Here, further, we show that phospholipase (PLC)-gamma1 is phosphorylated on tyrosine 783 and condenses at the HBMEC membrane beneath the E. coli entry site. Overexpression of a dominant negative (DN) form of PLC-gamma, the PLC-z fragment, in HBMEC inhibits PLC-gamma1 activation and significantly blocks E. coli invasion. PI3K activation is not affected in PLC-z/HBMEC upon infection, whereas PKC-alpha phosphorylation is completely abolished, indicating that PLC-gamma1 is downstream of PI3K. Concomitantly, the phosphorylation of PLC-gamma1 is blocked in HBMEC overexpressing a dominant negative form of the p85 subunit of PI3K but not in HBMEC overexpressing a dominant negative form of PKC-alpha. In addition, the recruitment of PLC-gamma1 to the cell membrane in both PLC-z/HBMEC and DN-p85/HBMEC is inhibited. Activation of PI3K is associated with the conversion of phosphatidylinositol 4,5-bisphosphate (PIP2) to phosphatidylinositol 1,4,5-trisphosphate (PIP3), which in turn recruits PLC-gamma1 to the cell membrane via its interaction with pleckstrin homology domain of PLC-gamma1. Utilizing the pleckstrin homology domains of PKC-delta and Btk proteins fused to green fluorescent protein (GFP), which specifically interact with PIP2 and PIP3, respectively, we show herein that E. coli invasion induces the breakdown of PIP2 at the plasma membrane near the site of E. coli interaction. PIP3, on the other hand, recruits the GFPBkt to the cell membrane beneath the sites of E. coli attachment. Our studies further show that E. coli invasion induces the release of Ca2+ from intracellular pools as well as the influx of Ca2+ from the extracellular medium. This elevation in Ca2+ levels is completely blocked both in PLC-z/HBMEC and DN-p85/HBMEC, but not in DN-PKC/HBMEC. Taken together, these results suggest that E. coli infection of HBMEC induces PLC-gamma1 activation in a PI3K-dependent manner to increase Ca2+ levels in HBMEC. This is the first report demonstrating the recruitment of activated PLC-gamma1 to the sites of bacterial entry.
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PMID:Escherichia coli K-1 interaction with human brain micro-vascular endothelial cells triggers phospholipase C-gamma1 activation downstream of phosphatidylinositol 3-kinase. 1295 50


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