scholarly journals Daphnoretin, a new protein kinase C activator isolated from Wikstroemia indica C.A. Mey

1993 ◽  
Vol 295 (1) ◽  
pp. 321-327 ◽  
Author(s):  
F N Ko ◽  
Y L Chang ◽  
Y H Kuo ◽  
Y L Lin ◽  
C M Teng

Daphnoretin, a biologically active principle isolated from Wikstroemia indica C.A. Mey., caused platelet aggregation in washed rabbit platelets, platelet-rich plasma and whole blood. The aggregation of and ATP release from platelets induced by daphnoretin were similar to phorbol ester- and diacylglycerol-induced aggregation and release. The EC50 values of daphnoretin-, phorbol 12,13-dibutyrate (PDBu)- and 1-oleoyl-2-acetylglycerol (OAG)-induced platelet aggregation in washed rabbit platelets were 17.2 +/- 2.8 microM, 20.6 +/- 2.1 nM and 38.6 +/- 1.7 microM respectively. Platelet aggregation induced by daphnoretin and PDBu was not inhibited by indomethacin, BN52021 or sodium nitroprusside. ADP-scavenging systems, apyrase and phosphocreatine/creatine kinase, showed weak inhibition of the aggregation, and EGTA, triflavin, verapamil and prostaglandin E1 markedly inhibited the aggregation. Staurosporine, a potent protein kinase C inhibitor, suppressed daphnoretin-, PDBu- and OAG-induced aggregation and ATP release in a concentration-dependent manner. The IC50 values of staurosporine on daphnoretin (50 microM)-, PDBu (100 nM)- and OAG (50 microM)-induced aggregation were 37.7 +/- 8.3, 52.2 +/- 6.3 and 42.8 +/- 8.9 nM respectively. Daphnoretin did not cause significant thromboxane B2 formation in rabbit platelets. Neither daphnoretin nor PDBu caused [3H]inositol monophosphate formation or an increase in intracellular Ca2+ concentration in myo-[3H]inositol-labelled and Fura-2-loaded platelets. Platelet cytosolic protein kinase C was activated by daphnoretin and PDBu in a concentration-dependent manner with an EC50 of 12.4 +/- 1.2 microM and 18.7 +/- 1.4 nM respectively. Membrane-associated protein kinase C activity was increased by either daphnoretin or PDBu. [3H]PDBu binding to washed rabbit platelets was inhibited by daphnoretin in a concentration-dependent manner with an IC50 value of 45.2 +/- 5.2 microM. These results indicate that daphnoretin is a protein kinase C activator in rabbit platelets.

2008 ◽  
Vol 36 (03) ◽  
pp. 603-613 ◽  
Author(s):  
Yu-Min Yang ◽  
Xing-Xiang Wang ◽  
Jun-Zhu Chen ◽  
Shi-Jun Wang ◽  
Hu Hu ◽  
...  

Inappropriate platelet activation is the key point of thrombogenesis. The aim of the present study was to investigate the effects of resveratrol (RESV), a compound extracted from the Chinese medicinal herb Polygonum cuspidatum sieb et Zucc, on the platelet activation induced by adenosine diphosphate (ADP) and its possible mechanism. The percentage of platelet aggregation and surface P-selectin-positive platelets, and the activity of protein kinase C (PKC) of platelet were observed with platelet aggregometer, flow cytometry and phosphorimaging system, respectively. RESV at 25, 50 and 100 μM showed anti-platelet aggregation and inhibition of surface P-selectin-positive platelets in a concentration-dependent manner. RESV (50 μM) inhibited the activity of PKC in the membrane fraction of platelets and decreased the percentage of membrane associated PKC activity in total PKC activity. Moreover, DL-erythro-1,3-Dihydroxy-2-aminooctadecane, an elective protein kinase C inhibitor (PKCI), and RESV had additive effects of inhibiting the percentage of platelet aggregation and surface P-selectin-positive platelets. It is suggested that RESV may inhibit platelet aggregation, the percentage of surface P-selectin-positive platelets and subsequent thrombus formation. The mechanisms may be partly relative to the decrease of the activity of PKC of platelets.


2011 ◽  
Vol 39 (01) ◽  
pp. 145-159 ◽  
Author(s):  
Yumin Yang ◽  
Xiaoling Wang ◽  
Li Zhang ◽  
Huiping An ◽  
Zhigao Zao

Resveratrol (RSVL), a polyphenolic compound found in red wine is believed to be a contributor in decreasing the incidence of coronary heart disease. Although its primary target is unknown, it blocks platelet aggregation by an ill-defined mechanism. Protein kinase C (PKC), which would redistribute from the cytosol to the platelet membrane upon platelet stimulation, plays a key role in the signal transduction system of platelets in human. In this study, we investigated the effect of RSVL and a PKC inhibitor (DL-erythro-1,3-Dihydroxy-2-aminooctadecane, PKCI) on platelet aggregation induced by a thromboxane A2receptor agonist (U46619, 9,11-Dideoxy-11α, 9α-epoxymethanoprostaglandin F2α) using a platelet aggregometer. We also studied the platelet membranebound fibrinogen (PFig) content and the activity of protein kinase C (PKC) in platelets from healthy volunteers using flow cytometry, and a phosphorimaging system, respectively. Our results showed that RSVL blocked platelet aggregation and PFig content induced by U46619 in a concentration-dependent manner. PKCI and RSVL had an additive effect in inhibiting platelet aggregation and PFig content. Furthermore, RSVL (final concentration 50 μM) remarkably depressed the activity of PKC in the membrane of platelets and the percentage of membrane PKC activity in total PKC activity. Taken together, these results suggested that RSVL suppressed U46619-induced platelet aggregation and PFig content partially through the inhibition of the activity of PKC in platelets.


1987 ◽  
Author(s):  
J A Ware ◽  
M Smith ◽  
E W Salzman

Platelet aggregation and secretion induced by phorbol ester (PMA) or diacylglycerol (DAG) are preceded by an increase in [Ca++] that is detected byaequorin, but not by quin2, fura-2, or indo-1, suggesting that these indicatorsreflect different aspects of Ca++ homeostasis, possibly different functional Ca++ pools. Addition of two conventional agonists in subthreold concentrations synergistically enhances the [Ca++] rise and aggregation.However, if PMA or DAG is the first agonist the subsequent quin2-indicated [Ca++] rise after thrombin is reduced.Whether aequorin-indicated [Ca++] is similarly affected is unknown. We studied gel-filtered platelets loaded with aequorin or a fluorophore and added PMA, DAG, thrombin or ADP, alone or in combination. Either PMA or DAG alone caused a concentration-dependent increase in [Ca++] detectable with aequorin but not with the fluorophores; simultaneous addition of thrombin or ADP with DAG or PMA produced a larger [Ca++] rise than either alone. However, addition of DAG or PMA as a first agonist reduced subsequent aequorin-indicated [Ca++] rises following thrombin or ADP in a concentration and time-dependent manner. Inhibition of ADP or thrombin-induced [Ca++] rise was not always accompanied by inhibition of aggregation or secretion. Combination of subthreshold concentrations of ADP and thrombin produced an enhanced [Ca++] rise and aggregation. However, this synergistic effect was inhibited by preincubation with DAG or PMA. Neither this effect nor DAG-induced [Ca++] rise was inhibited by the protein kinase C inhibitor H-7. In genera^ preincubation of platelets with an agonist enhances Ca rise and aggregation in response to a second agonist; in contrasl protein kinase C activators, which themselves elevate [Ca++] as shown by aequorin, inhibit aequorin-indicated Ca rises after ADP or thrombin, and limit synergism between these two agonists.


1993 ◽  
Vol 264 (5) ◽  
pp. F845-F853
Author(s):  
M. M. Friedlaender ◽  
D. Jain ◽  
Z. Ahmed ◽  
D. Hart ◽  
R. L. Barnett ◽  
...  

Previous work from this laboratory has identified an endothelin (ET) type A (ETA) receptor on cultured rat renal medullary interstitial cells (RMIC), coupled to phosphatidylinositol-specific phospholipase C (PI-PLC), dihydropyridine-insensitive receptor-operated Ca2+ channels, and phospholipase A2. The current studies explored a role for ET stimulation of phosphatidylcholine-specific phospholipase D (PC-PLD) in intracellular signaling of this cell type. ET stimulated PLD activation, as measured by phosphatidic acid (PA) or phosphatidylethanol (PEt) accumulation, in a time- and concentration-dependent manner. Inhibition of diacylglycerol (DAG) kinase by ethylene glycol dioctanoate or 6-(2)4-[(4-fluorophenyl)-phenylmethylene]-1-piperadinyl]ethy l-7-methyl-5H - thiaxolo-[3,2-alpyrimidin]-5-one (R 59022) failed to blunt PA accumulation, indicating that PLD, and not DAG, was the source of PA. Inhibition of PA phosphohydrolase (PAP) by propranolol increased late accumulation of PA, suggesting that the prevailing metabolic flow was in the direction of PA to DAG. Phorbol 12-myristate 13-acetate (PMA) augmented ET-evoked PEt accumulation, whereas downregulation of protein kinase C (PKC) obviated agonist-induced PEt production. PMA augmentation of PLD activity proceeded independent of cytosolic free Ca2+ concentration. Ca2+ derived from either intracellular or extracellular sources enhanced ET-related PEt accumulation but was without effect in PKC-downregulated cells. Collectively, these observations indicate that ET stimulates PLD production in RMIC. PKC is the major regulator of this process, with Ca2+ playing a secondary, modulatory role. In addition, these data suggest that PC-PLD is coupled to the ETA receptor.


Blood ◽  
1993 ◽  
Vol 82 (9) ◽  
pp. 2704-2713 ◽  
Author(s):  
R Vezza ◽  
R Roberti ◽  
GG Nenci ◽  
P Gresele

Abstract Prostaglandin E2 (PGE2) is produced by activated platelets and by several other cells, including capillary endothelial cells. PGE2 exerts a dual effect on platelet aggregation: inhibitory, at high, supraphysiologic concentrations, and potentiating, at low concentrations. No information exists on the biochemical mechanisms through which PGE2 exerts its proaggregatory effect on human platelets. We have evaluated the activity of PGE2 on human platelets and have analyzed the second messenger pathways involved. PGE2 (5 to 500 nmol/L) significantly enhanced aggregation induced by subthreshold concentrations of U46619, thrombin, adenosine diphosphate (ADP), and phorbol 12-myristate 13-acetate (PMA) without simultaneously increasing calcium transients. At a high concentration (50 mumol/L), PGE2 inhibited both aggregation and calcium movements. PGE2 (5 to 500 nmol/L) significantly enhanced secretion of beta-thromboglobulin (beta TG) and adenosine triphosphate from U46619- and ADP-stimulated platelets, but it did not affect platelet shape change. PGE2 also increased the binding of radiolabeled fibrinogen to the platelet surface and increased the phosphorylation of the 47-kD protein in 32P- labeled platelets stimulated with subthreshold doses of U46619. Finally, the amplification of U46619-induced aggregation by PGE2 (500 nmol/L) was abolished by four different protein kinase C (PKC) inhibitors (calphostin C, staurosporine, H7, and TMB8). Our results suggest that PGE2 exerts its facilitating activity on agonist-induced platelet activation by priming PKC to activation by other agonists. PGE2 potentiates platelet activation at concentrations produced by activated platelets and may thus be of pathophysiologic relevance.


2009 ◽  
Vol 29 (6) ◽  
pp. 477-487
Author(s):  
Pochuen Shieh ◽  
Chih-Hung Lee ◽  
Ng Ling Yi ◽  
Chung-Ren Jan

The effect of the cardiovascular drug carvedilol on cytosolic free Ca2+ concentrations ([Ca 2+]i) and viability was examined in Statens Seruminstitut rabbit cornea (SIRC) corneal epithelial cells. [Ca2+]i and cell viability were measured using the fluorescent dyes fura-2 and 4-[3-[4-lodophenyl]-2-4(4-nitrophenyl)-2H-5-tetrazolio-1,3-benzene disulfonate] (WST-1), respectively. Carvedilol at concentrations between 1 and 30 μM increased [Ca 2+]i in a concentration-dependent manner. The Ca2+ signal was reduced partly by removing extracellular Ca2+. Carvedilol induced Mn2+ quench of fura-2 fluorescence implicating Ca2+ influx. The Ca2+ influx was inhibited by suppression of protein kinase C activity. In Ca2+-free medium, after pretreatment with 1 μM thapsigargin (an endoplasmic reticulum Ca 2+ pump inhibitor), carvedilol-induced [Ca2+]i rise was reduced; and conversely, carvedilol pretreatment inhibited a major part of thapsigargin-induced [Ca 2+]i rise. Addition of the phospholipase C inhibitor 1-[6-[[17 beta-3-methoxyestra-1,3,5(10)-trien-17-yl]amino] hexyl]-1H-pyrrole-2,5-dione (U73122; 2 μM) did not change carvedilol-induced [Ca2+]i rise. At concentrations between 5 and 70 μM, carvedilol killed cells in a concentration-dependent manner. The cytotoxic effect of 20 μM carvedilol was not reversed by prechelating cytosolic Ca2+ with BAPTA/AM. Apoptosis was induced by 5—70 μM carvedilol. Collectively, in SIRC corneal epithelial cells, carvedilol-induced [Ca2+]i rises by causing Ca2+ release from the endoplasmic reticulum in a phospholipase C-independent manner, and Ca 2+ influx via protein kinase C-regulated Ca2+ channels. Carvedilol-caused cytotoxicity was mediated by Ca2+-independent apoptosis in a concentration-dependent manner.


1997 ◽  
Vol 326 (3) ◽  
pp. 701-707 ◽  
Author(s):  
Irene LITOSCH

Protein kinase C (PKC) isoforms phosphorylated phospholipase C-β1 (PLC-β1) in vitro as follows: PKCα ≫ PKCϵ; not PKCζ. PLC-β3 was not phosphorylated by PKCα. G-protein βγ subunits inhibited the PKCα phosphorylation of PLC-β1 in a concentration-dependent manner. Half-maximal inhibition occurred with 500 nM βγ. G-protein βγ subunits also antagonized the PKCα-mediated inhibition of PLC-β1 enzymic activity. PKCα, in turn, inhibited the stimulation of PLC-β1 activity by βγ. There was little effect of PKCα on the stimulation of PLC-β1 by αq/11–guanosine 5′[γ-thio]triphosphate (GTP[S]). These findings demonstrate that G protein βγ subunits antagonize PKCα regulation of PLC-β1. Thus βγ subunits might have a role in modulating the negative feedback regulation of this signalling system by PKC.


1988 ◽  
Vol 116 (2) ◽  
pp. 231-239 ◽  
Author(s):  
M. S. Johnson ◽  
R. Mitchell ◽  
G. Fink

ABSTRACT We have investigated the role of protein kinase C (PKC) in LHRH-induced LH and FSH secretion and LHRH priming. Hemipituitary glands from pro-oestrous rats were incubated with agents known to affect PKC and with or without LHRH, during which time the secretion of gonadotrophins was measured. Phorbol esters and phospholipase C, activators of PKC, released LH and FSH in a concentration-dependent manner and potentiated the LHRH-induced secretion of gonadotrophins in parallel with their ability to release these hormones alone. Inhibitors of PKC had either no effect on LH release (1-(5-isoquinolinesulphonyl)-2-methylpiperazine hydrochloride) or they augmented LHRH-induced gonadotrophin release (polymyxin B and 8-(N,N-diethylamino) octyl-3,4,5-trimethoxybenzoate). Neither the activators nor the inhibitors of PKC, when present with LHRH, caused any change in LHRH priming, even though the activators alone produced a release of gonadotrophins that showed a temporal pattern similar to that produced by LHRH priming. The profiles of effects on LH and FSH secretion were always qualitatively similar. These results show that PKC may be involved in general regulation of gonadotrophin release but that it is not important in acute responses to LHRH nor in LHRH self-priming. J. Endocr. (1988) 116, 231–239


1990 ◽  
Vol 267 (3) ◽  
pp. 689-696 ◽  
Author(s):  
H Salari ◽  
V Duronio ◽  
S Howard ◽  
M Demos ◽  
S L Pelech

The relationship between polyphosphoinositide hydrolysis and protein kinase C (PKC) activation was explored in rabbit platelets treated with the agonists platelet-activating factor (PAF), thrombin and 12-O-tetradecanoylphorbol 13-acetate (TPA), and with the anti-aggregant prostacyclin (PGI2). Measurement of the hydrolysis of radiolabelled inositol-containing phospholipids relied upon the separation of the products [3H]inositol mono-, bis- and tris-phosphates by Dowex-1 chromatography. PKC activity, measured in platelet cytosolic and Nonidet-P40-solubilized particulate extracts that were fractionated by MonoQ chromatography, was based upon the ability of the enzyme to phosphorylate either histone H1 in the presence of the activators Ca2+, diacylglycerol and phosphatidylserine, or protamine in the absence of Ca2+ and lipid. Treatment of platelets for 1 min with PAF (2 nM) or thrombin (2 units/ml) led to the rapid hydrolysis of inositol-containing phospholipids, a 2-3-fold stimulation of both cytosolic and particulate-derived PKC activity, and platelet aggregation. Exposure to TPA (200 nM) for 5 min did not stimulate formation of phosphoinositides, but translocated more than 95% of cytosolic PKC into the particulate fraction, and induced a slower rate of aggregation. PGI2 (1 microgram/ml) did not enhance phosphoinositide production, and at higher concentrations (50 micrograms/ml) it antagonized the ability of PAF, but not that of thrombin, to induce inositol phospholipid turnover, even though platelet aggregation in response to both agonists was blocked by PGI2. On the other hand, PGI2 alone also appeared to activate (by 3-5-fold) cytosolic and particulate PKC by a translocation-independent mechanism. The activation of PKC by PGI2 was probably mediated via cyclic AMP (cAMP), as this effect was mimicked by the cAMP analogue 8-chlorophenylthio-cAMP. It is concluded that this novel mechanism of PKC regulation by platelet agonists may operate independently of polyphosphoinositide turnover, and that activation of cAMP-dependent protein kinase represents another route leading to PKC activation.


1999 ◽  
Vol 18 (2) ◽  
pp. 91-96 ◽  
Author(s):  
I. Pala ◽  
A. Srinivasan ◽  
P. J. S. Vig ◽  
D. Desaiah

Calmodulin (CaM), a calcium-binding protein, is found in high concentrations in mammalian brain where it plays a pivotal role in a large number of cellular functions. Protein kinase C (PKC), a multifunctional cytosolic enzyme, in the presence of both Ca2+ and phospholipids, transduce extracellular signals into intracellu-lar events. Both CaM and PKC are partially involved in maintaining Ca2+ homeostasis in the cell. Any fluctuations in the intracel-lular Ca2+ can modulate cellular functions and may contribute to neuronal dysfunction. Hence, the present investigation was initiated to study the effects of some selected penicillium (naturally occurring tremorgenic) mycotoxins like secalonic acid, citreoviridin, and verruculogen on CaM activity, active conformation of CaM and PKC activity. Stimulation of CaM-deflcient bovine brain 3′-5′ phosphodieste rase (PDE) indicated CaM activity. The modification of CaM active conformation was studied by the binding of fluorescent probe N-phenyl-1-napthylamine (NPN) to CaM. Alterations in the fluorescence of dansyl-CaM was used to study the effect of these compounds on complex formation between CaM and PDE. Rat brain cytosolic PKC was studied using 32P-ATP as a measure of altered protein phosphorylation. The concentrations of mycotoxins used were in the range of 10 to 50 μM. All three mycotoxins inhibited CaM-stimulated PDE activity in a concentration-dependent manner. Citreoviridin and secalonic acid inhibited NPN fluorescence and Ca2+-dependent complex formation of dansyl-CaM and PDE. The IC50 values for NPN fluorescence of citreoviridin and secalonic acid were 13 μM and 19 μM respectively. However, verruculogen showed little effect on NPN fluorescence and the Ca2+-dependent complex formation of dansyl-CaM and PDE. These mycotoxins also inhibited PKC activity in a concentration-dependent manner with IC50 values of 19.8, 25.7, and 38.4 μM for secalonic acid, citreoviridin, and verruculogen, respectively. The results of our study suggest that these mycotoxins at very low concentrations are interacting with CaM and PKC. Such an effect could lead to impairment of neurotransmission and result in neurotoxicity.


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