Plasma levels of soluble Fc gamma receptors II (sCD32) and III (sCD16) in patients with heparin-induced thrombocytopenia.
Explore the source record for details and available documents.
Adult↗
Biomedical subjects
F Rendu
Publications and source records attributed to F Rendu.
Association of the protein tyrosine phosphatase PTP1C with the protein tyrosine kinase c-Src in human platelets.
Protein tyrosine phosphatase 1C (PTP1C), highly expressed in hematopoietic cells, is a soluble protein tyrosine phosphatase containing two Src homology 2 (SH2) domains at the N-terminus and two putative sites of tyrosine phosphorylation at the C-terminus. This paper reports that PTP1C and c-Src could be coimmunoprecipitated during thrombin-induced platelet activation. Moreover, association between the two signalling proteins occurred only after PTP1C had been tyrosine phosphorylated. In in vitro experiments, PTP1C bound to the SH2 domain of c-Src, suggesting that association between tyrosine phosphorylated PTP1C and c-Src was mediated by the SH2 domain of c-Src. Finally, in resting platelets, PTP1C was mainly found in the Nonidet P-40 soluble fraction whereas following thrombin-induced activation, around 17% of PTP1C was associated with the insoluble fraction.
Blood Platelets↗
The phospholipase C/protein kinase C pathway is involved in cathepsin G-induced human platelet activation: comparison with thrombin.
Cathepsin G, an enzyme released by stimulated polymorphonuclear neutrophils, and thrombin are two human proteinases which potently trigger platelet activation. Unlike thrombin, the mechanisms by which cathepsin G initiates platelet activation have yet to be elucidated. The involvement of the phospholipase C (PLC)/protein kinase C (PKC) pathway in cathepsin G-induced activation was investigated and compared with stimulation by thrombin. Exposure of 5-[14C]hydroxytryptamine-labelled platelets to cathepsin G, in the presence of acetylsalicylic acid and phosphocreatine/creatine kinase, induced platelet aggregation and degranulation in a concentration-dependent manner (0.1-3.0 microM). Time-course studies (0-180 s) comparing equivalent concentrations of cathepsin G (3 microM) and thrombin (0.5 unit/ml) resulted in very similar transient hydrolysis of phosphatidylinositol 4,5-bisphosphate and steady accumulation of phosphatidic acid. In addition cathepsin G, like thrombin, initiated the production of inositol phosphates. The neutrophil-derived proteinase also induced phosphorylation of both the myosin light chain and pleckstrin, a substrate for PKC, to levels similar to those observed in platelets challenged with thrombin. Inhibition of PKC by GF 109203X, a specific inhibitor, suppressed platelet aggregation and degranulation to the same extent for both proteinases. Using fura 2-loaded platelets, the rise in the cytosolic free Ca2+ concentration induced by cathepsin G was shown to result, as for thrombin, from both mobilization of internal stores and Ca2+ entry across the plasma membrane. These findings provide evidence that cathepsin G stimulates the PLC/PKC pathway as potently as does thrombin, independently of thromboxane A2 formation and ADP release, and that this pathway is required for platelet functional responses.
Amino Acid Sequence↗
Role of chondroitin 4-sulphate as a receptor for polycation induced human platelet aggregation.
1. Proteoglycans provide negatively charged sites on the surface of platelets, leukocytes and endothelial cells. Since chondroitin 4-sulphate is the main proteoglycan present on the platelet surface, the role of this molecule in mediating the activation of human platelets by polylysine was studied. 2. Platelets were desensitized with phorbol 12-myristate 13-acetate (PMA, 10 nM) 5 min before the addition of polylysine to platelet-rich plasma (PRP). Changes in the intracellular Ca2+ concentration were measured in fura2-am (2 microM) loaded platelets and protein phosphorylation was assessed by autoradiography of the electrophoretic profile obtained from [32P]-phosphate labelled platelets. The release of dense granule contents was measured in [14C]-5-hydroxytryptamine loaded platelets and the synthesis of thromboxane (TXA2) was assessed by radioimmunoassay. Surface chondroitin 4-sulphate proteoglycan was degraded by incubating platelets with different concentrations of chondroitinase AC (3 min, 37 degrees C). The amount of chondroitin 4-sulphate remaining in the platelets was then quantified after proteolysis and agarose gel electrophoresis. 3. The addition of PMA to PRP before polylysine inhibited the aggregation by 88 +/- 18% (n = 3). Staurosporine (1 microM, 5 min) prevented the PMA-induced inhibition. Chondroitinase AC (4 pu ml-1 to 400 muu ml-1, 3 min) abolished the polylysine-induced aggregation in PRP but caused only a discrete inhibition of ADP-induced aggregation. The concentration of chrondroitin 4-sulphate in PRP (0.96 +/- 0.2 microgram/10(8) platelets, n = 3) and in washed platelets (WP; 0.35 +/- 0.1 microgram/10(8) platelets, n = 3) was significantly reduced following incubation with chondroitinase AC (PRP = 0.63 +/- 0.1 microgram/10(8) platelets and WP = 0.08 +/- 0.06 microgram/10(8) platelets). 4. Washed platelets had a significantly lower concentration of chondroitin 4-sulphate than platelets in PRP. The addition of polylysine to WP induced a rapid increase in light transmission which was not accompanied by TXA2 synthesis or the release of dense granule contents. This effect was not inhibited by sodium nitroprusside (SNP), iloprost, EDTA or the peptide RGDS. This event was accompanied by the discrete phosphorylation of plekstrin and myosin light chain, which were inhibited by staurosporine (10 microM, 10 min). The hydrolysis of platelet surface chondroitin 4-sulphate strongly reduced the polylysine-induced phosphorylation. 5. Our results indicate that polylysine activates platelets through a specific receptor which could be the proteoglycan chondroitin 4-sulphate present on the platelet membrane.
Blood Platelets↗
Anti-GPIIb/IIIa antibodies: powerful tools to investigate function and regulation of an integrin.
Explore the source record for details and available documents.
Amino Acid Sequence↗
Tubulin is not phosphorylated in resting and thrombin-activated platelets.
We have investigated tubulin phosphorylation in human platelets, in order to evaluate whether it might be involved in the microtubular marginal band reorganization during platelet activation. Tubulin was identified with the use of specific monoclonal antibodies directed against alpha and beta subunits of tubulin. After metabolic 32P-labeling of platelets and analysis of separated proteins from whole cells, no phosphorylation of tubulin could be detected on autoradiography of platelet proteins either in resting platelets or during thrombin-induced activation. We also analyzed tubulin-enriched cytoskeletal fractions of resting or thrombin-stimulated platelets prepared in the presence of taxol, in comparison with tubulin-deprived cytoskeletal fractions prepared in the absence of this microtubule-stabilizing drug. Neither polymeric tubulin, assembled in microtubules and belonging to the platelet cytoskeleton, nor dimeric soluble tubulin showed significant 32P labeling. Finally, no tubulin was recovered among tyrosine-phosphorylated platelet proteins immunoprecipitated with a specific anti-phosphotyrosine protein monoclonal antibody. Thus, human platelet tubulin is not phosphorylated either in unstimulated platelets or in thrombin-stimulated platelets. The fact that both alpha and beta subunits are involved appears to be a unique feature of platelets in comparison with other cells. Microtubule-associated proteins are more likely to be involved in the unbundling of the platelet marginal band.
Blood Platelets↗
[Antiplatelet glycoprotein monoclonal antibodies: properties and practical value].
The aim of this review is (i) to classify the different monoclonal antibodies against platelet glycoproteins according to their properties and (ii) to take stock of their many diagnostic and therapeutic uses. Most of these antibodies recognize antigens on resting platelets without inducing activation, sometimes however they inhibit platelet function. Some of these antibodies, especially those against specific antigens (GPIIb/IIIa, CD9, CD36), have the capacity to activate platelets in vitro, either by direct binding of antibodies on the antigen or through the Fc domain binding to its platelet receptor Fc gamma RII. Other antibodies are directed against activation-dependent antigens that are expressed as a result of (i) a modification of a glycoprotein structure during platelet activation (as for GPIIb/IIIa), (ii) platelet release of granular antigens (GMP140, CD63, granulophysin...) or (iii) binding of soluble antigens on the activated platelet surface. Monoclonal antibodies find practical applications for both in vitro and in vivo diagnosis of bleeding or thrombotic pathology with some of them, notably anti-GPIIb/IIIa, having a promising future for antithrombotic therapy.
Antibodies, Monoclonal↗
Different abilities of thrombin receptor activating peptide and thrombin to induce platelet calcium rise and full release reaction.
Synthetic peptides (TRAP or Thrombin Receptor Activating Peptide) corresponding to at least the first five aminoacids of the new N-terminal tail generated after thrombin proteolysis of its receptor are effective to mimic thrombin. We have studied two different TRAPs (SFLLR, and SFLLRN) in their effectiveness to induce the different platelet responses in comparison with thrombin. Using Indo-l/AM-labelled platelets, the maximum rise in cytoplasmic ionized calcium was lower with TRAPs than with thrombin. At threshold concentrations allowing maximal aggregation (50 microM SFLLR, 5 microM SFLLRN and 1 nM thrombin) the TRAPs-induced release reaction was about the same level as with thrombin, except when external calcium was removed by addition of 1 mM EDTA. In these conditions, the dense granule release induced by TRAPs was reduced by over 60%, that of lysosome release by 75%, compared to only 15% of reduction in the presence of thrombin. Thus calcium influx was more important for TRAPs-induced release than for thrombin-induced release. At strong concentrations giving maximal aggregation and release in the absence of secondary mediators (by pretreatment with ADP scavengers plus aspirin), SFLLRN mobilized less calcium, with a fast return towards the basal level and induced smaller lysosome release than did thrombin. The results further demonstrate the essential role of external calcium in triggering sustained and full platelet responses, and emphasize the major difference between TRAP and thrombin in mobilizing [Ca2+]i. Thus, apart from the proteolysis of the seven transmembrane receptor, another thrombin binding site or thrombin receptor interaction is required to obtain full and complete responses.
Blood Platelets↗
Role of Fc gamma RIIA gene polymorphism in human platelet activation by monoclonal antibodies.
The aim of this study was to determine if there is a correlation between the activity of a MoAb as an agonist and its ability to bind to the Fc platelet receptor, Fc gamma RIIa. A polymorphism at amino acid 131 [arginine (Arg) or histidine (His)] of Fc gamma RIIa was first shown to be determinant for MoAb-IgG1 binding on monocytes. To clarify the role of this polymorphism in platelet activation by MoAb-IgG1 we (i) established the Fc gamma RIIa polymorphism at the gene level by adapting the denaturating gradient gel electrophoresis method, (ii) analyzed the binding affinity of the MoAbs to Fc gamma RIIa on platelets from homozygous Arg, homozygous His, and heterozygous Arg/His donors, and (iii) characterized the different reactivities of platelets according to the Fc gamma RIIA polymorphism. Among 167 caucasian donors we found 46% heterozygous Arg/His, 36% homozygous His and 18% homozygous Arg. ALB6, and anti CD9, P256 an anti GPIIb-IIIa, and AP3 an anti-GPIIIa were chosen according to their ability (ALB6, P256) or not (AP3) to activate platelets. These 3 MoAbs-IgG1 bind to Fc gamma RIIa with a stronger affinity for the Arg-form of Fc gamma RIIa, a result which was confirmed with the use of diverse MoAbs directed against various antigens. The different abilities of MoAbs to bind to the two Fc gamma RIIa forms were well correlated to the different platelet responses induced by ALB6 and P256. However, low concentrations of ALB6, which allow full activation of platelets from homozygous Arg donors, as did P256, did not induce any activation of platelets from homozygous His donors, whereas P256 is able to induce a low aggregation. The results further define the respective roles of the antigen and the Fc receptor, depending on the MoAb, and the role of the Fc gamma RIIa polymorphism in platelet activation induced by MoAbs. In addition, the results obtained with MoAbs unable to induce platelet activation provided evidence that the binding of a MoAb on Fc gamma RIIa does not predict its ability to activate platelets.
Amino Acid Sequence↗
Platelet procoagulant activity is independent of aggregation.
Platelet prothrombinase activity and aggregation were studied in parallel in the same platelet suspensions with the aim of determining the relationship between these two responses. Stimulation of platelets with thrombin (0.12 U/ml) plus collagen (20 mu g/ml) led to maximum thrombin generation when the aggregation intensity was still only 30%. Since the rate of thrombin formation then remained constant as aggregation intensity was still only 30%. Since the rate of thrombin formation then remained constant as aggregation increased up to its maximum intensity, the aggregation processes did not appear to result in partial masking of any procoagulant surface. This was confirmed by the fact that thrombin generation was the same on aggregated platelets as on activated platelets prevented from aggregating by addition of RGDS. Finally, maximum 5-hydroxy-tryptamine release could be obtained in the absence of thrombin generation. Thus platelet procoagulant activity did not appear to be related to aggregation or secretion and thrombin formation on the surface of activated platelets was in fact two to three times more important in the absence of stirring than under the conditions of continuous stirring required for aggregation. In conclusion, these results suggest procoagulant activity and aggregation to be two independent platelet responses which occur in different physiological situations.
Blood Coagulation Factors↗
An autoantibody directed against human thrombin anion-binding exosite in a patient with arterial thrombosis: effects on platelets, endothelial cells, and protein C activation.
An autoantibody, developed by a patient with severe and recurrent arterial thrombosis, was characterized to be directed against the anion-binding exosite of thrombin, and inhibited all thrombin interactions requiring this secondary binding site without interfering with the catalytic site. The effect of the antibody was studied on thrombin interactions with platelets and endothelial cells from human umbilical veins (HUVEC). The autoantibody specifically and concentration-dependently inhibited alpha-thrombin-induced platelet activation and prostacyclin (PGI2) synthesis from HUVEC. It had no effect when gamma-thrombin or the thrombin receptor activation peptide SFLLR were the inducers. The effect of the antibody on protein C activation has been studied. The antibody blocked the thrombin-thrombomodulin activation of protein C. The inhibition of the activation was maximal with a low concentration of thrombomodulin. The fact that the autoantibody inhibited concentration-dependent alpha-thrombin-induced platelet and endothelial cell functions emphasizes the crucial role of the anion-binding exosite of thrombin to activate its receptor. In regard to the pathology, the antibody inhibited two vascular processes implicated in thrombin-antithrombotic functions, PGI2 secretion, and protein C activation, which could be implicated in this arterial thrombotic disease.
Anions↗
Calcium mobilisation controls tyrosine protein phosphorylation independently of the activation of protein kinase C in human platelets.
We have investigated the regulation of tyrosine proteins phosphorylation by intracellular Ca2+ level ([Ca2+]i) and protein kinase C (PKC) during platelet stimulation. We found that chelation of extracellular calcium completely prevented phosphorylation of tyrosine proteins induced by thapsigargin and phorbol 12-myristate 13-acetate (PMA), whereas, when induced by thrombin, it prevented a subset of tyrosine proteins. The selective inhibition of PKC by GF 109203X did not abolish tyrosine protein phosphorylation when induced by thrombin and thapsigargin. The results suggest that in human platelets tyrosine protein phosphorylation is dependent on [Ca2+]i, although direct PKC activation can also induce phosphorylation of tyrosine proteins.
Blood Platelets↗
Influence of a 12-hour, 22 degrees C holding period for buffy coats on the preparation of platelet concentrates stored in plasma.
BACKGROUND: The preparation of platelet concentrates (PCs) from buffy coats (BCs) stored at room temperature is controversial, because of the strong metabolic activity of cells in BCs and the possible detrimental effect of neutrophil enzymes on platelets when the holding time before separation is prolonged. Despite good in vitro and in vivo behavior of BC-PCs stored in synthetic solution, little is known of the quality of BC-PCs stored in plasma. STUDY DESIGN AND METHODS: Comparison was made of PCs prepared from BCs held at 22 degrees C for 3 hours (3-hour BC-PCs) or overnight (12-hour BC-PCs) and stored in plasma. Platelet and white cell counts, pH, response to osmotic shock, and morphologic scores were determined on 20 PCs of each type. The decrease in dense granule and alpha granule content, a marker of platelet activation, were estimated by mepacrine counting and beta-thromboglobulin measurement, respectively (n = 8-10). Platelet function was studied in terms of aggregation and thromboxane production in response to various concentrations of collagen and thrombin (n = 8-17). PCs prepared from unstored BCs (n = 15) and from BCs held for 90 minutes (n = 15) were used as controls. RESULTS: Platelet yield was increased from 53 +/- 10 percent of donated platelets to 73 +/- 4 percent by increasing the BC holding time from 0 to 90 minutes to 3 hours (p < 0.001). Similar yields (7.8 +/- 1.8 vs. 7.9 +/- 2 x 10(10) platelets) and white cell contamination (0.9 +/- 0.8 vs. 1.0 +/- 0.9 x 10(7)) were obtained with 3-hour and 12-hour BC-PCs. At the end of the storage period (Day 5), all variables known to correlate with platelet survival in vivo were well maintained in both 3-hour and 12-hour BC-PCs: pH > or = 6.9, response to osmotic shock > or = 70 percent, and morphology scores always > or = 240. During storage, the dense granule content decreased moderately (30% after 5 days), whatever the conditions. By contrast, the total platelet beta-thromboglobulin content was better preserved in 12-hour BC-PCs than in 3-hour BC-PCs (p < 0.04). No significant differences were observed in collagen-induced aggregation and thromboxane production in the two PC preparations. However, aggregation responses to thrombin were higher in 12-hour BC-PCs on Day 5 of storage (p < 0.01). CONCLUSION: BCs can be held at 22 degrees C for up to 12 hours, with no detrimental effect on the quality of PCs stored for up to 5 days in plasma. Such a holding time might help overcome logistic problems in blood banks.
Blood Platelets↗
[Cellular receptor of thrombin].
Thrombin is a serine protease able to evoke biological responses from a variety of cells, including platelets, endothelial cells, fibroblasts and smooth muscle cells. The structure of the thrombin receptor present in the human megakaryoblastic cell line and in hamster fibroblasts has recently been deduced by expression in the Xenopus laevis oocyte. The cloned receptor is a new member of the seven transmembrane domain receptor family that interacts with G proteins. A large amino-terminal extracellular extension has a cleavage site for thrombin (Leu Asp Pro Arg/Ser Phe Leu Leu,/representing the cleavage site). Thrombin cleaves at this site, unmasking a new amino terminus, that functions like a ligand, binding to an as yet undefined site and eliciting receptor activation. Peptides similar to a new amino terminus created after cleavage are able to mimic thrombin cellular effects. These agonist peptides are used to analyse the role of the cloned receptor in the thrombin-specific response.
Animals↗
Parkia biglobosa seeds possess anti platelet activity.
Explore the source record for details and available documents.
Blood Platelets↗
Translocation of spin-labeled phospholipids through plasma membrane during thrombin- and ionophore A23187-induced platelet activation.
After incorporation of spin-labeled phosphatidylcholine, phosphatidylserine, and phosphatidylethanolamine analogues in the outer leaflet of the plasma membrane in resting platelets, more than 90% amino-head analogues accumulated within 30 min in the inner leaflet by aminophospholipid translocase activity, while choline analogues mostly remained on the outer leaflet. Platelets were then activated by thrombin or Ca2+ ionophore A23187. No outward movement of internally located spin-labeled aminophospholipids was observed during thrombin-induced activation, whereas the influx of externally located probes increased slightly. During A23187-mediated activation, similar slightly increased influx was observed, while 40-50% of the initially internally located aminophospholipids could then be extracted from the outer leaflet. This sudden exposure on the outer face was dependent on an increase in intracellular Ca2+ and achieved in less than 2 min at 37 degrees C. Inhibition of translocase activity by N-ethylmaleimide did not induce any aminophospholipid outflux. When probes were incorporated on the outer face of the plasma membrane in resting platelets, they were still fully accessible from the extracellular medium after A23187-induced activation. Moreover, they were distributed between the vesicles and remnant platelets in proportion to the external membrane phospholipidic content in each structure. This suggested that no scrambling of plasma membrane leaflets occurred during the vesicle blebbing. Moreover, the spin-labeled aminophospholipids exposure rate and amplitude were unchanged when vesicle formation was inhibited by the calpain inhibitor calpeptin. These results indicate that loss of asymmetry thus inducing generation of a catalytic surface is not the consequence of vesicle formation. Conversely, we propose that vesicle shedding is an effect of PL transverse redistribution and calpain-mediated proteolysis during activation.
Biological Transport↗
Indapamide inhibits human platelet aggregation in vitro: comparison with hydrochlorothiazide.
Among antihypertensive drugs with diuretic properties, indapamide was shown to inhibit platelet growth factors production in diabetic hypertensive patients, suggesting an antiplatelet activity. The present study aimed to demonstrate the antiaggregating properties of indapamide. The effect of indapamide on platelet function was compared in vitro to that of hydrochlorothiazide. Indapamide (100 microM) inhibited the second wave of adenosine diphosphate-induced aggregation and inhibited collagen-induced aggregation of platelet rich plasma by 50%. Using isolated platelets, indapamide also inhibited aggregation induced by low doses of thrombin (70% inhibition with 0.035 U/ml). This inhibition was dose-dependent and was still observed in presence of high thrombin concentrations, although the inhibition was moderate. Inhibitory effect of indapamide was more pronounced on the release reaction. Indapamide inhibited the thrombin-induced release of serotonin from dense granules by up to 80%. Hydrochlorothiazide at the same concentrations had no effect on platelet aggregation, and the inhibitory effect on the secretion was inconsistent and never exceeded 30%. By contrast, when the aggregation inducer was arachidonic acid, indapamide had no effect either on aggregation or on thromboxane formation, indicating that it was not acting on arachidonic catabolism. Calcium mobilization evoked by thrombin stimulation and measured with the fluorescent dye Indo 1 was also reduced in presence of indapamide by 30%. Myosin light chain and pleckstrin phosphorylation induced by thrombin were also reduced. These results demonstrate that indapamide inhibits platelet responses by inhibiting calcium mobilization. The anti-aggregating properties of indapamide could contribute to normalize the hyperresponsiveness of platelets from hypertensive patients.
Adenosine Diphosphate↗
Phospholipid transverse mobility modifications in plasma membranes of activated platelets: an ESR study.
Spin labeled phospholipid analogs were used to directly study changes in aminophospholipid translocase activity in activated platelets. In thrombin-activated platelets, the translocase activity was slightly stimulated, whereas no vesicle formation or proteolysis of cytoskeletal protein occurred. Ca2+ ionophore A23187-mediated activation produced vesiculation and proteolysis. Additionally, the translocase activity was completely inhibited, probably due to a sharp rise the intracellular Ca2+ concentration, as shown when platelets were activated in the presence of various A23187 and Ca2+ concentrations and by the recovery of the translocase activity when Ca2+ was complexed with EGTA. No translocase activity was found in vesicles. Whereas vesiculation and translocase inhibition can occur independently of proteolysis, this later accentuated the shedding phenomenon.
Blood Platelets↗