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1.
4-O-Glycosylation of 2-azidoethyl 2,3,6-tri-O-benzyl-4-O-(2,3-di-O-benzyl-6-O-benzoyl--D-galactopyranosyl)--D-glucopyranoside with a disaccharide donor, 4-trichloroacetamidophenyl 4,6-di-O-acetyl-2-deoxy-3-O-(2,3,4,6-tetra-O-acetyl--D-galactopyranosyl)-1-thio-2-trichloroacetamido--D-galactopyranoside, in dichloromethane in the presence of N-iodosuccinimide and trifluoromethanesulfonic acid resulted in a tetrasaccharide, 2-azidoethyl (2,3,4,6-tetra-O-acetyl--D-galactopyranosyl)-(1 3)-(4,6-di-O-acetyl-2-deoxy-2-trichloroacetamido--D-galactopyranosyl)-(1 4)-(2,3-di-O-benzyl-6-O-benzoyl--D-galactopyranosyl)-(1 4)-2,3,6-tri-O-benzyl--D-glucopyranoside, in 69% yield. The complete removal of O-protecting groups in the tetrasaccharide, the replacement of N-trichloroacetyl by N-acetyl group, and the reduction of the aglycone azide group to amine led to the target aminoethyl glycoside of -D-Gal-(1 3)--D-GalNAc-(1 4)--D-Gal-(1 4)--D-Glc-OCH2CH2NH2 containing the oligosaccharide chain of asialo-GM1 ganglioside in 72% overall yield. Selective 3-O-glycosylation of 2-azidoethyl 2,3,6-tri-O-benzyl-4-O-(2,6-di-O-benzyl--D-galactopyranosyl)--D-glucopyranoside with thioglycoside methyl (ethyl 5-acetamido-4,7,8,9-tetra-O-acetyl-3,5-dideoxy-2-thio-D-glycero--D-galacto-2-nonulopyranosyl)oate in acetonitrile in the presence of N-iodosuccinimide and trifluoromethanesulfonic acid afforded 2-azidoethyl [methyl (5-acetamido-4,7,8,9-tetra-O-acetyl-3,5-dideoxy-D-glycero--D-galacto-2-nonulopyranosyl)oate]-(2 3)-(2,6-di-O-benzyl--D-galactopyranosyl)-(1 4)-2,3,6-tri-O-benzyl--D-glucopyranoside, the selectively protected derivative of the oligosaccharide chain of GM3 ganglioside, in 79% yield. Its 4-O-glycosylation with a disaccharide glycosyl donor, (4-trichloroacetophenyl-4,6-di-O-acetyl-2-deoxy-3-O-(2,3,4,6-tetra-O-acetyl--D-galactopyranosyl) 1-thio-2-trichloroacetamido--D-galactopyranoside in dichloromethane in the presence of N-iodosuccinimide and trifluoromethanesulfonic acid gave 2-azidoethyl (2,3,4,6-tetra-O-acetyl--D-galactopyranosyl)-(1 3)-(4,6-di-O-acetyl-2-deoxy-2-trichloroacetamido--D-galactopyranosyl)-(1 4)-{[methyl (5-acetamido-4,7,8,9-tetra-O-acetyl-3,5-dideoxy-D-glycero--D-galacto-2-nonulopyranosyl)onate]-(2 3)}-(2,6-di-O-benzyl--D-galactopyranosyl)-(1 4)-2,3,6-tri-O-benzyl--D-glucopyranoside in 85% yield. The resulting pentasaccharide was O-deprotected, its N-trichloroacetyl group was replaced by N-acetyl group, and the aglycone azide group was reduced to afford in 85% overall yield aminoethyl glycoside of -D-Gal-(1 3)--D-GalNAc-(1 4)-[-D-Neu5Ac-(2 3)]--D-Gal-(1 4)--D-Glc-OCH2CH2NH2 containing the oligosaccharide chain of GM1 ganglioside.  相似文献   

2.
Phospholipase A2 (PLA2) associated with the membrane fraction of trophocytes from Periplaneta americana fat body increases by as much as 100% when the cells are incubated with hypertrehalosemic hormone (HTH-II). Activation with HTH-II is approximately halved by inclusion of the PKC inhibitor sphingosine in the incubation medium. Because activation of PLA2 by HTH-II is blocked by the GDP analogue GDP-β-S, and the unactivated enzyme is activated by the GTP analogue GTP-γ-S it is likely that a G protein is involved in activation of the enzyme. Activation of PLA2 was also achieved by treating the trophocytes with the synthetic diacylglycerol 1-oleoyl-2-acetylglycerol in the presence of thapsigargin. This supports the view that protein kinase C is also involved in the activation process.  相似文献   

3.
Gopee NV  Sharma RP 《Life sciences》2004,74(12):1541-1559
Fumonisin B1 (FB1), a potent and naturally occurring mycotoxin produced by the fungus Fusarium verticillioides, has been implicated in fatal and debilitating diseases in animals and humans. FB1 affects a variety of cell signaling proteins including protein kinase C (PKC); a serine/threonine kinase, involved in a number of signal transduction pathways that include cytokine induction, carcinogenesis and apoptosis. The aim of this study was to investigate the short-term temporal and concentration-dependent effects of FB1 on PKC isoforms present in LLC-PK1 cells in relation to the FB1-induced accumulation of sphinganine and sphingosine utilizing various inhibitors and activators. Our studies demonstrated that FB1 (0.1-1 μM) selectively and transiently activated PKCα at 5 min, without affecting PKC-δ, -ε and -ζ isoforms. At higher FB1 concentrations and later time points (15-120 min), PKCα membrane concentrations declined to untreated levels. The observed increase in cytosol PKCα protein expression at 15 min was not associated with an increase in its activity or protein biosynthesis. Calphostin C, a PKC inhibitor, abrogated the FB1-induced translocation of PKCα. Pre-incubation with the PKC activator, phorbol 12-myristate 13-acetate, resulted in an additive effect on membrane translocation of PKCα. Intracellular sphinganine and sphingosine concentrations were unaltered at the time points tested. Myriocin, a specific inhibitor of serine palmitoyltransferase, the first enzyme in de novo sphingolipid biosynthesis, did not prevent the FB1-induced PKCα cytosol to membrane redistribution. Altering PKCα and its signal transduction pathways may be of importance in the ability of FB1 to exert its toxicity via apoptosis and/or carcinogenesis.  相似文献   

4.
Centaurin-alpha(1) is a member of the family of ADP-ribosylation factors (ARF) GTPase activating proteins (GAPs), although ARF GAP activity has not yet been demonstrated. The human homologue, centaurin-alpha(1) functionally complements the ARF GAP activity of Gcs1 in yeast. Although Gcs1 is involved in the formation of actin filaments in vivo, the function of centaurin remains elusive. We have identified a number of novel centaurin-alpha(1) binding partners; including CKIalpha and nucleolin. In this report, we have focused on the interaction of centaurin-alpha(1) with PKC. All groups of PKC associate directly through their cysteine rich domains. Centaurin-alpha(1) is also a substrate for all PKC classes and we have identified the two sites of phosphorylation. This is the first report of a kinase that phosphorylates centaurin-alpha(1).  相似文献   

5.
6.
Protein kinase C is a serine/threonine protein kinase which is activated in the cell in response to production of diacylglycerol. Gene cloning has revealed the presence of a highly related family of enzymes, which can be sub-divided into groups on the basis of sequence conservation. Differences are seen in both isoform distribution and associated biochemical activity, for example in substrate specificity and activator requirements. Comparison of the protein sequences andin vitro activities of the protein kinase C isoforms has identified regions important for particular aspects of kinase function. Some of these regions are also found associated with other proteins, allowing confirmation of the assigned activity. Site-directed mutagenesis has confirmed the presence of an autoinhibitory sequence involved in protein kinase C regulation and generated constitutively activated proteins which can be used to study differential isoform function. These same sequences have been shown to play a role in substrate selection, perhaps by competition for binding to the active site. Protein kinase C is known to be a phosphoprotein and the identification of regulatory sites phosphorylated by a ‘PKC-kinase’ suggest a possible alternative route for regulation of protein kinase C activity.  相似文献   

7.
We have shown previously that fibroblasts derived from fat or dermal tissue differ in their functional properties, such as proliferation rate and contractile properties. To study these differences further, two-dimensional electrophoresis (2D PAGE) was performed on proteins isolated from cultured subcutaneous fat and dermal fibroblasts. The 2D gels were screened for proteins that were differentially expressed in all donors (n = 5). Five protein spots were subjected to further analysis by mass spectrometry. Two proteins could be identified: brain acid soluble protein 1 (BASP1) and cellular retinoic acid binding protein-II (CRABP-II). CRABP-II is of interest in terms of re-epithelialisation and was clearly expressed in dermal fibroblasts but not in fat fibroblasts. Real time PCR was performed to confirm the 2D data on CRABP-II. The CRABP-II mRNA level was significantly increased in dermal tissue and cultured dermal fibroblasts compared to fat tissue and cultured fat-derived fibroblasts, respectively. The mode of action of CRABP-II in skin is to mediate retinoic acid activity. Retinoic acid is known to inhibit migration and to stimulate differentiation of keratinocytes. The expression of CRABP-II by dermal fibroblasts implicates a role for these fibroblasts in wound re-epithelialisation, in contrast to subcutaneous fat-derived fibroblasts.  相似文献   

8.
Gangliosides are normal constituents of the plasma membrane. Exogenous gangliosides can be incorporated into the membrane and extensive research in nervous tissue has demonstrated a beneficial effect of gangliosides on the functional recovery of lesioned neurons and protection against neurotoxins. This paper shows that the effect of gangliosides is not restricted to neurons. The monosialoganglioside GM1 efficiently increases the survival of thymocytes and protects them against both the lytic effect of the glucocorticoid prednisolone and the effect of a thymocytotoxic serum. The protective effect of GM1 was achieved bothin vitro andin vivo.  相似文献   

9.
The effects of externally applied different protein kinase C (PKC) activators on Na+ currents in mouse neuroblastoma cells were studied using the perforated-patch (nystatin-based) whole cell voltage clamp technique. Two diacylglycerol-like compounds, OAG (1-oleoyl-2-acetyl-sn-glycerol), and DOG (1-2-dioctanoyl-rac-glycerol) attenuated Na+ currents without affecting the time course of activation or inactivation. The reduction in Na+ current amplitude caused by OAG or DOG was dependent on membrane potential, being more intense at positive voltages. The steady-state activation curve was also unaffected by these substances. However, both OAG and DOG shifted the steady-state inactivation curve of Na+ currents to more hyperpolarized voltages. Surprisingly, phorbol esters did not affect Na+ currents. Cis-unsaturated fatty acids (linoleic, linolenic, and arachidonic) attenuated Na+ currents without modifying the steady-state activation. As with DOG and OAG, cis-unsaturated fatty acids also shifted the steady-state inactivation curve to more negative voltages. Interestingly, inward currents were more effectively attenuated by cis-fatty acids than outward currents. Oleic acid, also a cis-unsaturated fatty acid, enhanced Na+ currents. This enhancement was not accompanied by changes in kinetic or steady-state properties of currents. Enhancement of Na+ currents caused by oleate was voltage dependent, being stronger at negative voltages. The inhibitory or stimulatory effects caused by all PKC activators on Na+ currents were completely prevented by pretreating cells with PKC inhibitors (calphostin C, H7, staurosporine or polymyxin B). By themselves, PKC inhibitors did not affect membrane currents. Trans-unsaturated or saturated fatty acids, which do not activate PKC's, did not modify Na+ currents. Taken together, the experimental results suggest that PKC activation modulates the behavior of Na+ channels by at least three distinct mechanisms. Because qualitatively different results were obtained with different PKC activators, it is not clear how Na+ currents would respond to activation of PKC under physiological conditions.This work was supported in part by a grant-in-aid from the American Heart Association (National Center), and by Loyola University Medical Center. Dr. Godoy is a recipient of a fellowship from Conselho Nacional de Pesquisas e Desenvolvimento (Brazil).  相似文献   

10.
The expression of GABAA receptors in rat cerebellar granules in culture has been studied by β2/3 subunit immunocytochemistry and fluorescence confocal microscopy. These cells show labeling all over the cell bodies' plasma membrane and dendrites. Treatment with the protein tyrosine kinase (PTK) inhibitor genistein results in a decrease of the labeling associated with the β2/3 subunit in both cell bodies and dendrites. No effect was found with an inactive genistein analogue, daidzein. A similar effect was found with a protein kinase C (PKC) activator, phorbol myristate acetate (PMA). The effects of genistein and PMA are additive.The interpretation of the results is that PTK inhibition blocks exocytotic deposit of newly synthesized GABAA receptors onto the neuronal plasma membrane. On the other hand, PKC activation speeds up endocytotic removal of GABAA receptors.  相似文献   

11.
Fumonisin B1 induces cytotoxicity in sensitive cells by inhibiting ceramide synthase due to its structural similarity to the long-chain backbones of sphingolipids. The resulting accumulation of sphingoid bases has been established as a mechanism for fumonisin B1 cytotoxicity. We found that despite the accumulation of sphinganine, human embryonic kidney (HEK-293) cells are resistant to fumonisin B1 toxicity; 25 microM fumonisin B1 exposure for 48 h did not increase apoptosis in these cells, while it did so in sensitive porcine kidney epithelial (LLC-PK1) cells. In this study, DL-threo-dihydrosphingosine, the sphingosine kinase inhibitor (SKI), considerably increased the sensitivity of HEK-293 cells to fumonisin B1. Treatment of these cells with 25 microM fumonisin B1 and 2.5 microM SKI increased apoptosis. Sphingoid bases, sphinganine or sphingosine, added to cell cultures induced apoptosis by themselves and their effects were potentiated by SKI or fumonisin B1. Addition of physiological amounts of sphingosine-1-phosphate prevented the toxic effects induced by SKI inhibition and fumonisin B1. Results indicated that HEK-293 cells are resistant to fumonisin B1 due to rapid formation of sphingosine-1-phosphate that imparts survival properties. Taken together, these findings suggest that sphingoid base metabolism by sphingosine kinase may be a critical event in rendering the HEK-293 cells relatively resistant to fumonisin B1-induced apoptosis.  相似文献   

12.
In order to determine if protein kinase C (PKC) plays a significant role in the stimulant action of thromboxane A2 (TxA2) on pulmonary vascular smooth muscle, TxA2-induced contractile responses were measured following inhibition of PKC. Rabbits were sacrificed and segments of the main trunk of the pulmonary artery were removed and placed within a temperature-controlled (37 °C) organ bath. Contractile responses that were evoked by a TxA2 mimetic (U46,619, 0.5 µM) decreased by 27 and 35% following treatment with the PKC inhibitors, calphostin C (2 µM) and staurosporine (200 nM), respectively. These results account for the effect of the vehicle, DMSO, which was also found to have a concentration-dependent inhibitory effect on the U46,619-induced contractions. The effects of DMSO alone was subsequently subtracted from the previously measured responses to PKC inhibitors that were dissolved in DMSO to obtain effects attributable to the PKC inhibitor alone. It can therefore be concluded that inhibition of PKC results in partial attenuation of U46,619-induced responses supporting the hypothesis that activation of PKC plays a partial role in TxA2-induced contraction of pulmonary arterial smooth muscle.  相似文献   

13.
14.
15.
16.
Ganglioside GM3 was reported to induce the differentiation of HL-60 cells to differentiate along the macrophage-monocytic route. We used human monocytoid leukemia J6-2 cells and successfully induced differentiation by GM3. Because differentiation is accompanied by retarded growth rate and cell cycle is intimately related to phospholipid metabolism, so we explored how GM3 was related to phospholipid metabolism. By using [32P]Pi, [3H-CH3]choline, [3H-CH3]SAM, and [3H]inositol as radioactive tracers, we studied the turnover changes of phospholipids and their metabolites induced by GM3. For the morphological changes of differentiation to occur, the cells had to be treated with GM3 at a concentration of 50 M for 5-6 days, but the phospholipid changes occurred at a very early stage of GM3 treatment (only 1 h). Our results indicate that GM3 stimulated PE methylation pathway inhibited both CDP-choline pathway and PI cycle. The phospholipid changes may constitute the early events in differentiation induced by GM3.  相似文献   

17.
The D(1) dopamine receptor (D(1) DAR) is robustly phosphorylated by multiple protein kinases, yet the phosphorylation sites and functional consequences of these modifications are not fully understood. Here, we report that the D(1) DAR is phosphorylated by protein kinase C (PKC) in the absence of agonist stimulation. Phosphorylation of the D(1) DAR by PKC is constitutive in nature, can be induced by phorbol ester treatment or through activation of Gq-mediated signal transduction pathways, and is abolished by PKC inhibitors. We demonstrate that most, but not all, isoforms of PKC are capable of phosphorylating the receptor. To directly assess the functional role of PKC phosphorylation of the D(1) DAR, a site-directed mutagenesis approach was used to identify the PKC sites within the receptor. Five serine residues were found to mediate the PKC phosphorylation. Replacement of these residues had no effect on D(1) DAR expression or agonist-induced desensitization; however, G protein coupling and cAMP accumulation were significantly enhanced in PKC-null D(1) DAR. Thus, constitutive or heterologous PKC phosphorylation of the D(1) DAR dampens dopamine activation of the receptor, most likely occurring in a context-specific manner, mediated by the repertoire of PKC isozymes within the cell.  相似文献   

18.
Woolcock K  Specht SC 《Life sciences》2006,78(15):1653-1661
Adenylyl cyclase is activated by prostaglandin E and inhibited by mu-opioids. Since cAMP-related events influence the activity of the Na Pump and its biochemical correlate Na,K-ATPase in many systems, we tested the hypothesis that prostaglandin E1 and [D-Ala2,N-Me-Phe4,Gly5-ol]-enkephalin (DAMGO), a mu-opioid agonist, have opposing actions on Na,K-ATPase activity. Studies were conducted with alamethicin-permeabilized SH-SY5Y human neuroblastoma cells. Prostaglandin E1 (1 microM) transiently inhibited Na,K-ATPase activity for 10-15 min. A direct activator of protein kinase A, 8-Br-cAMP (150 and 500 microM), also inhibited, but more rapidly and for a shorter duration. Both DAMGO (1 microM) and Rp-adenosine 3',5'-cyclic monophosphorothioate (500 microM), a protein kinase A-inhibitor, reversed the inhibitory effect of prostaglandin E1. DAMGO alone (1 microM) stimulated Na,K-ATPase activity up to nearly three-fold control activity. The stimulatory action of DAMGO was blocked by cyclosporine A (2 microM), an inhibitor of calcineurin, and was dependent on Ca2+ entry through nifedipine-sensitive Ca2+ channels. In the presence of 1 mM EGTA, DAMGO inhibited Na,K-ATPase activity. DAMGO-induced inhibition was blocked by the inositol 1,4,5-trisphosphate receptor antagonist xestospongin C (1 microM). Na,K-ATPase is poised to modulate neuronal excitability through its roles in maintaining the membrane potential and transmembrane ion gradients. The differential effects of prostaglandin E1 and opioids on Na,K-ATPase activity may be related to their actions in hyperalgesia.  相似文献   

19.
Rat pancreatic islet homogenates display protein kinase C activity. This phospholipid-dependent and calcium-sensitive enzyme is activated by diacylglycerol or the tumor-promoting phorbol ester 12-O-tetradecanoylphorbol-13-acetate (TPA). In the presence of TPA, the Ka for Ca2+ is close to 5 microM. TPA does not affect phosphoinositide turnover but stimulates [32P]- and [3H]choline-labelling of phosphatidylcholine in intact islets. Exogenous phospholipase C stimulates insulin release, in a sustained and glucose-independent fashion. The secretory response to phospholipase C persists in media deprived of CaCl2. It is proposed that protein kinase C participates in the coupling of stimulus recognition to insulin release evoked by TPA, phospholipase C and, possibly, those secretatogues causing phosphoinositide breakdown in pancreatic islets.  相似文献   

20.
We investigated the effects of different protein kinase C (PKC) activators on Na+ currents using the conventional whole-cell and the inside-out macropatch voltage-clamp techniques in mouse neuroblastoma cells (N1E-115). Two different categories of PKC activators were investigated: the cis-unsaturated fatty acids (CUFAs): oleic (cis-9-octadecenoic), linoleic (cis-9-12-octadecadienoic), and linolenic acid (cis-9-12-15-octadecatrienoic), and, the diacylglycerol (DAG) derivative 1-2-dioctanoyl-sn-glycerol (DOG). These substances caused the following alterations on Na+ currents: (i) Na+ currents were attenuated as a function of voltage. While DOG attenuated both inward and outward Na+ currents in a monotonic and continuous voltage-dependent manner, CUFAs preferentially attenuated inward currents; (ii) the steady-state activation curve of Na+ currents shifted to more depolarized voltages; (iii) opposite to the activation curve, the steady-state inactivation curve of Na+ channels (h curve) shifted to more hyperpolarized voltages; (iv) the time course of inactivation development was accelerated by PKC activators, while the recovery from inactivation was not affected; (v) substances that inhibit different metabolic pathways (PKC activation, cyclooxygenase, lipooxygenase, and P-450 pathways) did not prevent the effects of PKC activators on Na+ currents. One fully saturated fatty acid (octadecanoic acid), a trans-unsaturated fatty acid (trans-9-octadecenoic), and different phorbol esters did not affect Na+ currents; (vi) effects of different PKC activators on Na+ currents were completely reversible. These observations suggest that PKC activators might interact with Na+ channels directly. These direct effects must be taken into consideration in evaluating the overall effect of PKC activation on Na+ channels. Moreover, it is likely that this direct interaction could account, at least in part, for the diversity of effects of PKC activators on Na+ channels.This work was supported in part by a grant-in-aid from the American Heart Association (National Center).  相似文献   

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