Regulation of PtdIns4P 5-kinase C by thrombin-stimulated changes in its phosphorylation state in human platelets.
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ABSTRACT:
SUBMITTER: Hinchliffe KA
PROVIDER: S-EPMC1219021 | biostudies-other | 1998 Jan
REPOSITORIES: biostudies-other
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Project description:Platelet activation plays a key role in normal haemostasis and pathological thrombosis. Platelet activation is rapid; within minutes of stimulation, platelets generate bioactive phospholipids, secrete their granule contents, activate integrins and aggregate together to form a haemostatic plug. These events are dependent on ATP synthesis. Mitochondrial function in platelets from healthy volunteers and patients with a range of diseases indicate an important role for oxygen consumption in oxidative phosphorylation in normal and pathological function. Platelets also consume oxygen during oxidation reactions, such as cyclooxygenase-dependent thromboxane A2 synthesis. In this study, we used high-resolution respirometry to investigate rapid changes in oxygen consumption during platelet activation. We demonstrated a rapid, transient increase in oxygen consumption rate within minutes of platelet stimulation by the physiological activator, thrombin. This was partly inhibited by aspirin and by oligomycin. This shows that high resolution respirometry can provide information regarding rapid and dynamic changes in oxygen consumption during platelet activation.
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Project description:Stimulation of platelets with thrombin leads to rapid degradation of inositol phospholipids, generation of diacylglycerol (DAG) and subsequent activation of protein kinase C (PKC). Previous studies indicated that prior activation of PKC with phorbol myristate acetate (PMA) desensitizes platelets to thrombin stimulation, as indicated by a decreased production of inositol phosphates and decreased Ca2+ mobilization. This suggests that PKC activation generates negative-feedback signals, which limit the phosphoinositide response. To test this hypothesis further, we examined the effects of PKC activators and inhibitors on thrombin-stimulated DAG mass formation in platelets. Pretreatment with PMA abolishes thrombin-stimulated DAG formation (50% inhibition at 60 nM). Pretreatment of platelets with the PKC inhibitors K252a or staurosporine potentiates DAG production in response to thrombin (3-4-fold) when using concentrations required to inhibit platelet PKC (1-10 microM). K252a does not inhibit phosphorylation of endogenous DAG or phosphorylation of a cell-permeant DAG in unstimulated platelets, indicating that DAG over-production is not due to inhibition of DAG kinase. Sphingosine, a PKC inhibitor with a different mechanism of action, also potentiates DAG formation in response to thrombin. Several lines of evidence indicate that DAG formation under the conditions employed occurs predominantly by phosphoinositide (and not phosphatidylcholine) hydrolysis: (1) PMA alone does not elicit DAG formation, but inhibits agonist-stimulated DAG formation; (2) thrombin-stimulated DAG formation is inhibited by neomycin (1-10 mM) but not by the phosphatidate phosphohydrolase inhibitor propranolol; and (3) no metabolism of radiolabelled phosphatidylcholine was observed upon stimulation by thrombin or PMA. These data provide strong support for a role of PKC in limiting the extent of platelet phosphoinositide hydrolysis.
| S-EPMC1131600 | biostudies-other
Project description:Human platelets were depleted of intracellular Ca2+ and then made selectively permeable to external Ca2+ by addition of the ionophore ionomycin. In this cell system a rapid release of arachidonic acid was seen in direct response to added Ca2+ at concentrations corresponding to cytosolic Ca2+ levels measured in thrombin-stimulated platelets. Thrombin and other activators of Ca2+/phospholipid-dependent protein kinase (C-kinase) potentiated the Ca2+-stimulated arachidonic acid release while exerting little or no effect in the absence of added Ca2+. Agents which increase (R59022) or decrease (isoquinolinesulphonylmethylpiperazine) the activation of C-kinase correspondingly enhanced or inhibited, respectively, the potentiation of arachidonic acid release caused by thrombin. These results support the hypothesis that arachidonic acid release in human platelets is regulated by a co-operative action between intracellular Ca2+ and C-kinase.
| S-EPMC1148565 | biostudies-other
Project description:Confluent human umbilical vein endothelial cells (HUVECs) were exposed to Thrombin (2 U/mL) for 2 hours. Ribosomal profiling via gradient centrifugation and fractionation was used to separate monosome, or under-translated, and polysome, or actively translated, mRNA species that were then used to probe cDNA arrays, a process known as Translation State Array Analysis (TSAA). Four samples were obtained from these experiments, Control Monosome, Control Polysome, Thrombin Monosome, and Thrombin Polysome. Using the normalized signal intensities from the GeneFilters, we calculated a translation index, or measure of movement of an mRNA molecule from the monosome to the polysome fraction upon stimulation. This calculation was made as follows: (thrombin polysome/thrombin monosome)/(control polysome/control monosome). Translational indices greater than 2.5 (upregulated) or lower than 0.4 (downregulated) were chosen for further study. TSAA data suggests that JunB is translationally regulated by thrombin stimulation. Immunocytochemistry, western blotting and RT-PCR were used to verify the results of TSAA. Keywords: Translation State Array Analysis
2006-05-31 | GSE4919 | GEO
Project description:The diacylglycerol kinase inhibitor R59022 (10 microM) potentiates secretion and aggregation responses in human platelets challenged with sub-maximal concentrations of thrombin. Potentiation correlates closely with increased formation of diacylglycerol, increased phosphorylation of a 40 kDa protein, a known substrate for protein kinase C, and with decreased formation of phosphatidic acid, the product of diacylglycerol kinase. Phosphorylation of myosin light chains, formation of inositol phosphates and the mobilization of Ca2+ by thrombin are not affected by R59022 (10 microM). These data support a role for protein kinase C in platelet aggregation and secretion, and provide further evidence that endogenous diacylglycerols bring about the activation of this enzyme. These data also add further argument against a role for phosphatidic acid in platelet activation.
| S-EPMC1147929 | biostudies-other
Project description:In this study we have examined the implication of tyrosine kinase activities in aggregation, 5-hydroxytryptamine secretion and mainly phosphoinositide metabolism in response to human platelet stimulation by thrombin. Using the potent tyrosine kinase inhibitor tyrphostin AG-213, we have observed a significant inhibition of aggregation and 5-hydroxytryptamine release; however, this percentage inhibition was lower at high thrombin concentrations. On the other hand, tyrphostin treatment of metabolically 32P-labelled platelets significantly inhibited the thrombin-dependent accumulation of PtdIns(3,4)P2, which involves at least a PtdIns 3-kinase and/or a PtdIns3P 4-kinase, whereas the synthesis of phosphatidic acid (PtdOH), a good reflection of the phospholipase C (PLC) activation in platelets, was partially blocked. Inositol phosphate production was also inhibited by about 40% when tyrphostin-treated platelets were stimulated with thrombin. In addition, we show by Western-blot analysis that PLC gamma 1, as well as the regulatory subunit (p85) of the PtdIns 3-kinase, were present in the anti-phosphotyrosine immunoprecipitate isolated from thrombin-stimulated platelets. Furthermore, tyrphostin treatment clearly decreased the PLC gamma 1 and p85 contents in such an anti-phosphotyrosine immunoprecipitate. Our results provide the first evidence for a direct or indirect regulation of PtdIns(3,4)P2 accumulation and PLC gamma 1 activity by tyrosine phosphorylation during thrombin stimulation of human platelets.
| S-EPMC1134192 | biostudies-other
Project description:Confluent human umbilical vein endothelial cells (HUVECs) were exposed to Thrombin (2 U/mL) for 2 hours. Ribosomal profiling via gradient centrifugation and fractionation was used to separate monosome, or under-translated, and polysome, or actively translated, mRNA species that were then used to probe cDNA arrays, a process known as Translation State Array Analysis (TSAA). Four samples were obtained from these experiments, Control Monosome, Control Polysome, Thrombin Monosome, and Thrombin Polysome. Using the normalized signal intensities from the GeneFilters, we calculated a translation index, or measure of movement of an mRNA molecule from the monosome to the polysome fraction upon stimulation. This calculation was made as follows: (thrombin polysome/thrombin monosome)/(control polysome/control monosome). Translational indices greater than 2.5 (upregulated) or lower than 0.4 (downregulated) were chosen for further study. TSAA data suggests that JunB is translationally regulated by thrombin stimulation. Immunocytochemistry, western blotting and RT-PCR were used to verify the results of TSAA. Polysome Profiling. HUVECs were stimulated with thrombin (2 U/mL) for 2 hours. Cycloheximide (CHX) was added to a final concentration of 100 ng/mL for 5 minutes and cells were then rinsed with cold HBSS containing CHX (100 ng/mL) and scraped from the dish and pelleted by centrifugation (2000 x g, 5 minutes). The supernatant was removed and cells were carefully resuspended in 375 microL Low Salt Buffer (LSB; 20 mM Tris, 10 mM NaCl, 3 mM MgCl2, pH 7.4) + RNasin (40 U/mL) + DTT (10 nM) for 3 minutes on ice. 125 microL LSB Lysis buffer (LSB containing 200 mM sucrose and 1.2% Triton-X100) was then added and cells disrupted by pipetting. The mixture was then transferred to 1.7 mL microfuge tubes and centrifuged (20,000 x g, 1 minute, 4 degrees C) to remove nuclei and cellular debris. The supernatant was transferred to a new tube containing 50 microL LSB + RNasin (40 U/mL) + DTT (10 nM) and 15 microL 5M NaCl. This mixture was then layered onto prepoured gradients (15-50% sucrose in LSB). Gradients were spun at 43,700 rpm for 90 minutes (4 degrees C) and then run on a density gradient flow cell fractionator (Isco) to obtain ribosomal profiles. Ribosomal fractions corresponding to monosomes (M) and polysomes (P) (Figure 1) were collected into Trizol LS (Invitrogen) and total RNA isolated according to the directions of the manufacturer. Total RNA was reverse transcribed using oligo dT primers in the presence of 33P dCTP to generate labeled cDNA probes from the M and P associated mRNA fractions of control and stimulated cells and these probes used to detect specific array elements on four identical Research Genetics (ResGen) Named Human Gene cDNA GeneFilters (GF 211, Invitrogen). These filters were washed using high stringency conditions and exposed to phosphorimaging screens for analysis using Pathways 3, proprietary software included with the ResGen filters. Hybridization signals were normalized to the average intensity of the hybridization signals from the particular array filter to correct for differing global hybridization efficiencies between filters. To determine if a particular hybridization signal was significantly above background levels, an initial screen of the array elements was conducted by dividing the hybridization signal of an individual cDNA spot by the background signal on particular filter. Background signal levels were determined using the Pathways 3 analysis software that measures the signal intensity of the area between cDNA spots and averages that signal over the area of the entire array. Array elements were considered to be distinguishable from background if the hybridization signal/background ratio was greater than 1.1. Signal intensities from each filter were normalized by dividing the raw signal intensity of the cDNA spot by the average signal intensity for the entire filter. The translation state (TS) of each qualifying array element was determined by dividing the normalized signal intensity of the element in the polysome fraction by the normalized signal intensity of the element in the monosome fraction: TS=P/M. The Translation Index (TLI), a measure of the change of translation states of individual genes, was determined by calculating the ratio of the treated cell TS to the control cell TS; TLI = TSe/TSc where e represents experimental or treated conditions and c represents controls. In this scenario, a gene that is not regulated by translation would have a TLI value of 1, actively translated genes would have a TLI value greater than 1, whereas a poorly translated or under-translated gene would have a TLI value less than 1. Arbitrary TLI values of 2.5 and 0.4 were used to categorize individual array elements as being translationally regulated. A measure of transcriptional activity was also determined from the signal intensities of the array elements. Summing the normalized signal intensities from the M and P fractions of the experimental cells and dividing that value by the sum of the normalized signal intensities from the control fractions calculated the Transcription Index (TCI). Therefore, TCI = (Me + Pe)/(Mc + Pc). If transcript levels for a specific gene do not change, the TCI value for that gene will be 1. Genes that are transcribed upon stimulation of the cells will have a TCI value greater than 1, while genes that are not transcribed or transcription is down-regulated upon stimulation will have a TCI value less than 1. Arbitrary values of 2 and 0.5, a doubling or halving of the amount of mRNA for that element, respectively, were used to categorize individual array elements as being transcriptionally regulated.
2010-07-01 | E-GEOD-4919 | biostudies-arrayexpress
Project description:VASP (vasodilator-stimulated phosphoprotein) is an actin- and profilin-binding protein that is expressed in platelets at high levels and plays a major role in negatively regulating secretory and adhesive events in these cells. VASP is a major substrate for cAMP- and cGMP-regulated protein kinases and it has been shown to be directly phosphorylated on Ser157 by PKC (protein kinase C). In the present paper, we show that, in human platelets, VASP is phosphorylated by PKC on Ser157, but not Ser239, in response to phorbol ester stimulation, in a manner blocked by the PKC inhibitor BIM I (bisindolylmaleimide I). In response to thrombin, VASP was also phosphorylated on Ser157, but this response was only partially inhibited by BIM I, indicating PKC-dependent and -independent pathways to VASP phosphorylation by thrombin. Using inhibitors, we have ruled out the possibility that the PKC-independent pathway acts through guanylate cyclase generation of cGMP, or through a phosphoinositide 3-kinase-dependent kinase. Inhibition of Rho kinase, however, substantially reduced Ser157 VASP phosphorylation, and its effects were additive with BIM I. This implicates Rho kinase and PKC as the major kinases that phosphorylate VASP Ser157 in response to thrombin in platelets.
| S-EPMC1360706 | biostudies-other
Project description:BackgroundPlatelets are small anucleated blood particles that play a key role in the control of bleeding. Platelets need to be activated to perform their functions and participate in hemostasis. The process of activation is accompanied by vast protein reorganization and posttranslational modifications. The goal of this study was to identify changes in proteins in platelets activated by different agonists. Platelets were activated by three different agonists - arachidonic acid, collagen, and thrombin. 2D SDS-PAGE (pI 4-7) was used to separate platelet proteins. Proteomes of activated and resting platelets were compared with each other by Progenesis SameSpots statistical software; and proteins were identified by nanoLC-MS/MS.Results190 spots were found to be significantly different. Of these, 180 spots were successfully identified and correspond to 144 different proteins. Five proteins were found that had not previously been identified in platelets: protein CDV3 homolog, protein ETHE1, protein LZIC, FGFR1 oncogene partner 2, and guanine nucleotide-binding protein subunit beta-5. Using spot expression profile analysis, we found two proteins (WD repeat-containing protein 1 and mitochondrial glycerol-3-phosphate dehydrogenase) that may be part of thrombin specific activation or signal transduction pathway(s).ConclusionsOur results, characterizing the differences within proteins in both activated (by various agonists) and resting platelets, can thus contribute to the basic knowledge of platelets and to the understanding of the function and development of new antiplatelet drugs.
| S-EPMC2996359 | biostudies-literature
Project description:The spleen tyrosine kinase (Syk) is essential for immunoreceptor tyrosine-based activation motif (ITAM)-dependent platelet activation, and it is stimulated by Src-family kinase (SFK)-/Syk-mediated phosphorylation of Y352 (interdomain-B) and Y525/526 (kinase domain). Additional sites for Syk phosphorylation and protein interactions are known but remain elusive. Since Syk S297 phosphorylation (interdomain-B) was detected in platelets, we hypothesized that this phosphorylation site regulates Syk activity via protein kinase C (PKC)-and cyclic adenosine monophosphate (cAMP)-dependent pathways. ADP, the GPVI-agonist convulxin, and the GPIbα-agonist echicetin beads (EB) were used to stimulate human platelets with/without effectors. Platelet aggregation and intracellular messengers were analyzed, along with phosphoproteins, by immunoblotting using phosphosite-specific antibodies or phos-tags. ADP, convulxin, and EB upregulated Syk S297 phosphorylation, which was inhibited by iloprost (cAMP pathway). Convulxin-stimulated Syk S297 phosphorylation was stoichiometric, transient, abolished by the PKC inhibitor GF109203X, and mimicked by the PKC activator PDBu. Convulxin/EB stimulated Syk S297, Y352, and Y525/526 phosphorylation, which was inhibited by SFK and Syk inhibitors. GFX and iloprost inhibited convulxin/EB-induced Syk S297 phosphorylation but enhanced Syk tyrosine (Y352/Y525/526) and substrate (linker adaptor for T cells (LAT), phospholipase γ2 (PLC γ2)) phosphorylation. GFX enhanced convulxin/EB-increases of inositol monophosphate/Ca2+. ITAM-activated Syk stimulates PKC-dependent Syk S297 phosphorylation, which is reduced by SFK/Syk/PKC inhibition and cAMP. Inhibition of Syk S297 phosphorylation coincides with enhanced Syk activation, suggesting that S297 phosphorylation represents a mechanism for feedback inhibition in human platelets.
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