scholarly journals Studies with a monoclonal antibody against activated platelets: evidence that a secreted 53,000-molecular weight lysosome-like granule protein is exposed on the surface of activated platelets in the circulation

Blood ◽  
1987 ◽  
Vol 70 (3) ◽  
pp. 838-845 ◽  
Author(s):  
HK Nieuwenhuis ◽  
JJ van Oosterhout ◽  
E Rozemuller ◽  
F van Iwaarden ◽  
JJ Sixma

Abstract To define the role of activated platelets we have attempted to prepare monoclonal antibodies specific for activated platelets. The IgG2b antibody of one of the clones, designated 2.28, was studied in more detail. Native platelets from normal individuals bound 650 125I-2.28 molecules/platelet, whereas thrombin-activated platelets bound 12,600 molecules/platelet with high affinity (4.6 nmol/L). Immunoelectrophoretic analysis revealed that 2.28 reacted with a 53,000- mol wt protein. Immunocytochemistry showed that the antigen is located in a special subclass of platelet granules in unstimulated platelets and is exposed on the surface of thrombin-activated platelets. Double- labeling studies with immunogold labels disclosed simultaneous localization of 2.28 binding sites and cathepsin D in the same granules both in megakaryocytes and endothelial cells, thereby indicating that the antigen may be localized in lysosomes. By using flow cytofluorometry, in vivo platelet activation was studied in patients undergoing cardiac surgery with cardiopulmonary bypass. Increased numbers of platelets that expressed the 2.28 antigen on their surface were observed after extracorporeal perfusion. The percentage of 2.28- positive platelets in the circulation was 3.9% +/- 2.7% (SD) in controls (n = 20), 5.5% +/- 3.0% in patients (n = 10) before cardiopulmonary bypass surgery, 24.6% +/- 13.5% after the bypass, and 8.5% in two patients with acute deep venous thrombosis. These data indicate that 2.28 may serve as a useful probe of in vitro and in vivo platelet activation.

Blood ◽  
1987 ◽  
Vol 70 (3) ◽  
pp. 838-845 ◽  
Author(s):  
HK Nieuwenhuis ◽  
JJ van Oosterhout ◽  
E Rozemuller ◽  
F van Iwaarden ◽  
JJ Sixma

To define the role of activated platelets we have attempted to prepare monoclonal antibodies specific for activated platelets. The IgG2b antibody of one of the clones, designated 2.28, was studied in more detail. Native platelets from normal individuals bound 650 125I-2.28 molecules/platelet, whereas thrombin-activated platelets bound 12,600 molecules/platelet with high affinity (4.6 nmol/L). Immunoelectrophoretic analysis revealed that 2.28 reacted with a 53,000- mol wt protein. Immunocytochemistry showed that the antigen is located in a special subclass of platelet granules in unstimulated platelets and is exposed on the surface of thrombin-activated platelets. Double- labeling studies with immunogold labels disclosed simultaneous localization of 2.28 binding sites and cathepsin D in the same granules both in megakaryocytes and endothelial cells, thereby indicating that the antigen may be localized in lysosomes. By using flow cytofluorometry, in vivo platelet activation was studied in patients undergoing cardiac surgery with cardiopulmonary bypass. Increased numbers of platelets that expressed the 2.28 antigen on their surface were observed after extracorporeal perfusion. The percentage of 2.28- positive platelets in the circulation was 3.9% +/- 2.7% (SD) in controls (n = 20), 5.5% +/- 3.0% in patients (n = 10) before cardiopulmonary bypass surgery, 24.6% +/- 13.5% after the bypass, and 8.5% in two patients with acute deep venous thrombosis. These data indicate that 2.28 may serve as a useful probe of in vitro and in vivo platelet activation.


2012 ◽  
Vol 449 (2) ◽  
pp. 333-341 ◽  
Author(s):  
Chiara Saggioro ◽  
Anne Olliver ◽  
Bianca Sclavi

The DnaA protein is a key factor for the regulation of the timing and synchrony of initiation of bacterial DNA replication. The transcription of the dnaA gene in Escherichia coli is regulated by two promoters, dnaAP1 and dnaAP2. The region between these two promoters contains several DnaA-binding sites that have been shown to play an important role in the negative auto-regulation of dnaA expression. The results obtained in the present study using an in vitro and in vivo quantitative analysis of the effect of mutations to the high-affinity DnaA sites reveal an additional effect of positive autoregulation. We investigated the role of transcription autoregulation in the change of dnaA expression as a function of temperature. While negative auto-regulation is lost at dnaAP1, the effects of both positive and negative autoregulation are maintained at the dnaAP2 promoter upon lowering the growth temperature. These observations can be explained by the results obtained in vitro showing a difference in the temperature-dependence of DnaA–ATP binding to its high- and low-affinity sites, resulting in a decrease in DnaA–ATP oligomerization at lower temperatures. The results of the present study underline the importance of the role for autoregulation of gene expression in the cellular adaptation to different growth temperatures.


2007 ◽  
Vol 98 (10) ◽  
pp. 806-812 ◽  
Author(s):  
Vandana Dole ◽  
Wolfgang Bergmeier ◽  
Ian Patten ◽  
Junichi Hirahashi ◽  
Tanya Mayadas ◽  
...  

SummaryWe have previously shown that activated platelets in circulation stimulate release of endothelial Weibel-Palade bodies thus increasing leukocyte rolling in venules. P-selectin on the activated platelets mediates adhesion to leukocytes via PSGL-1 and is rapidly shed into plasma. We were interested in studying the role of PSGL-1 in regulating expression and function of platelet P-selectin. We show here that PSGL-1 is critical for the activation of endothelial cells in venules of mice infused with activated platelets. The interaction of platelet P-selectin with PSGL-1 is also required for P-selectin shedding, as P-selectin was retained significantly longer on the surface of activated platelets infused into PSGL-1-/- compared to wild-type mice. The leukocyte integrin αMβ2 (Mac-1) was not required for P-selectin shedding. In addition to shedding, P-selectin can be downregulated from the platelet surface through internalization and this is the predominant mechanism in the absence of PSGL-1. We demonstrate that leukocyte- neutrophil elastase,known to cleave P-selectin in vitro, is not the major sheddase for P-selectin in vivo. In conclusion, interaction of platelet P-selectin with PSGL-1 is crucial for activation of the endothelium andWeibel-Palade body secretion. The interaction with PSGL-1 also results in rapid shedding of P-selectin thus downregulating the inflammatory potential of the platelet.


1998 ◽  
Vol 80 (07) ◽  
pp. 58-64 ◽  
Author(s):  
P. Ferroni ◽  
G. Speziale ◽  
G. Ruvolo ◽  
A. Giovannelli ◽  
F. M. Pulcinelli ◽  
...  

SummaryCardiopulmonary bypass (CPB) is associated with impaired platelet function and a systemic inflammatory response. The present study was designed to evaluate whether any correlation between platelet activation and inflammatory response during CPB exists. The results obtained from 8 patients undergoing hypothermic CPB for cardiac surgery showed the occurrence of a moderate degree of platelet activation during CPB, demonstrated by an increase of platelet CD62P expression in correlation with an increase of β-thromboglobulin levels, with a concomitant decrease of in vitro platelet response. Plasma IL-1β levels significantly increased during CPB, with a peak between 1 and 4 h after CPB. Similarly, IL-6 levels were elevated 30 min from CPB starting, peaked at 4 h, and remained elevated after 24 h. A direct correlation was found between plasma IL-1β and IL-6 levels. A significant correlation between plasma IL-1β and β-thromboglobulin levels was also found. In turn, plasma β-thromboglobulin levels correlated with CD62P expression on activated platelets. An inverse correlation was found between in vitro platelet aggregation and plasma IL-1β or IL-6 levels. From the present results it may be speculated that platelet activation during CPB may contribute, through the release of IL-1β, to activation of endothelial cells and subsequent release of other cytokines with chemotactic and pro-inflammatory properties, thus playing an important role in the inflammatory response associated with CPB.


2020 ◽  
Vol 4 (4) ◽  
pp. 638-643
Author(s):  
Manuel Salzmann ◽  
Sonja Bleichert ◽  
Bernhard Moser ◽  
Marion Mussbacher ◽  
Mildred Haase ◽  
...  

Abstract Platelets are small anucleate cells that release a plethora of molecules to ensure functional hemostasis. It has been reported that IκB kinase 2 (IKK2), the central enzyme of the inflammatory NF-κB pathway, is involved in platelet activation, because megakaryocyte/platelet-specific deletion of exons 6 and 7 of IKK2 resulted in platelet degranulation defects and prolonged bleeding. We aimed to investigate the role of IKK2 in platelet physiology in more detail, using a platelet-specific IKK2 knockout via excision of exon 3, which makes up the active site of the enzyme. We verified the deletion on genomic and transcriptional levels in megakaryocytes and were not able to detect any residual IKK2 protein; however, platelets from these mice did not show any functional impairment in vivo or in vitro. Bleeding time and thrombus formation were not affected in platelet-specific IKK2-knockout mice. Moreover, platelet aggregation, glycoprotein GPIIb/IIIa activation, and degranulation were unaltered. These observations were confirmed by pharmacological inhibition of IKK2 with TPCA-1 and BMS-345541, which did not affect activation of murine or human platelets over a wide concentration range. Altogether, our results imply that IKK2 is not essential for platelet function.


Blood ◽  
2006 ◽  
Vol 108 (11) ◽  
pp. 1066-1066
Author(s):  
Wenche Jy ◽  
Andrew Lin ◽  
Loreta Bidot ◽  
Jaehoon Bang ◽  
Eugene Ahn ◽  
...  

Abstract BACKGROUND: Deficiency of ADAMTS13, vWF cleaving protease, is known to be associated with TTP and some other microangiopathies, but low levels were reported in other diseases such as ITP, DIC, lupus and other thromboses. Although inhibitory autoantibodies were demonstrated in TTP, the mechanisms underlying reduced levels of ADAMTS13 in other disorders remains unclear. We tested the hypothesis that ADAMTS13 is associated with cell membranes and derived microparticles, especially from activated platelet and their microparticles (PMP), which could modulate the enzyme activities of ADAMTS13. METHODS: PRP was prepared by centrifuging citrated normal blood for 10 min at 160×g, and PPP by further centrifuging for 10 min at 3,000×g, and particle-free plasma (PFP) by further centrifuging for 15 min at 20,000×g. ADAMTS13 activity was assayed by the FRETS-VWF73 method of Kokame et al [Br J Haematol 129:93, 2005] using the Fluoroskan Ascent plate reader. Platelets were activated by ADP (10 μM) or ionophore A23187 (2 μM). RESULTS: The ADAMTS13 activity (A) of pooled PPP of 10 controls was defined as 100%. (1) In vitro study: (1a) ADAMTS13 activity was not significantly different between PPP and resting PRP. However, if the platelets in PRP were first activated by ADP for 1hr, a significant reduction of activity was observed (A = 85 ±7%, p<0.05). If the activated platelets were removed, the activity of the supernatant fell to 79 ±10% p<0.05) of the control level, and was further reduced by higher centrifugation to remove PMP (A = 66 ±12%, p<0.01). (1b) Activation by A23187, a stronger agonist producing 2–3 fold more PMP than ADP (confirmed by flow cytometry), induced a more dramatic reduction in PRP (A = 78±8%, p<0.01), and after removal of platelets (A = 71 ±11%, p<0.01), and after removal of PMP (48 ±11%, p<0.01). (1c) Interestingly, resuspending the activated platelets did not restore ADAMTS13 activity, although resuspending the PMP did partially restore the activity. (2) In vivo study: PPP from 13 patients (6 ITP, 4 APS, 3 lupus) were analyzed. The majority (11/13) of PPP samples lost activity after removal of PMP (A = 79 ±12% in PPP vs. 64 ±11% in PFP; p <0.02). CONCLUSION: These data show that a significant but variable fraction of ADAMTS13 activity is associated with activated platelets and PMP. This has several implications. First, distinguishing soluble from membrane-bound ADAMTS13 may lead to better correlation of activities with clinical findings, and may help explain low levels of ADAMTS13 in some disorders associated with platelet activation and high PMP. Second, this interaction may play a role in regulating ADAMTS13 activity. Third, membrane-bound ADAMTS13 may clear more readily from circulation, therefore inhibiting platelet activation or MP formation may have benefits for the management of microangiopathies.


Blood ◽  
2016 ◽  
Vol 128 (22) ◽  
pp. 3919-3919
Author(s):  
Peilin Ma ◽  
Yuqing Sun ◽  
Jingya Wang ◽  
Weihua Song ◽  
Tao Xu ◽  
...  

Abstract Homeobox A9 (HOXA9) is a homeodomain-containing transcription factor that is essential for hematopoietic stem cell expansion and differentiation. Deregulation of HOXA9 is commonly observed in human acute myeloid leukemia (AML). About half of AML patients overexpress HOXA9 as a result of MLL rearrangements, NUP98 translocations, NPM1 mutations or CDX2/CDX4 overexpression. Despite its central importance in leukemia, the mechanism of transcriptional regulation by HOXA9 and its downstream effectors are poorly understood. HOXA9 physically interacts with MEIS1, a cofactor that greatly accelerates leukemia development in transplanted animals. Our group recently identified a number of transcription factors as HOXA9 potential collaborators by genomic profiling of HOXA9 binding sites and mass spectroscopy. One of these putative collaborators is signal transducer and activator of transcription 5 (STAT5), which coimmunoprecipitates with HOXA9. Furthermore STAT motifs extensively overlap with HOXA9 binding sites. STAT5 is important for survival, proliferation and differentiation of hematopoietic cells and constitutive activation of STAT5 has also been observed in human leukemias bearing oncogenic mutation of Jak2, Bcr-Abl, c-Kit and Flt3. FLT3 internal tandem duplication (FLT3-ITD) is observed in 25% of patients with MLL-partial tandem duplication (MLL-PTD) and is associated with HOXA9 upregulation and unfavorable prognosis. Therefore, we hypothesized that the interaction of HOXA9 and STAT5 may play a role in HOXA9-associated leukemogenesis. Treatment of human cell lines bearing MLL-AF9 and FLT3-ITD with specific FLT3 and STAT5 inhibitors showed that suppression of the constitutive activation of STAT5 significantly inhibits the hyper-proliferation of these cells. We then overexpressed FLT3-ITD or active mutation of STAT5 (STAT5 1*6) in mouse hematopoietic stem cells /progenitor cells (HSC/PCs) transduced with MLL-AF9 or HOXA9 and found that constitutively active STAT5 enhances cell proliferation in vitro. We next transduced HOXA9 into HSC/Pcs from wild type (WT) or FLT3-ITD transgenic mice and transplanted these cells into sublethally irradiated WT mice. All of these recipients developed myeloid leukemia, with recipients transplanted with FLT3-ITD (n=4) developing leukemia significantly earlier than WT controls (n=5, p<0.05), suggesting that FLT3-ITD mediated STAT5 activation enhanced HOXA9-induced leukemogenesis in vivo. To further assess the role of STAT5 in HOXA9-mediated transformation, we performed ChIP-Seq assay with HOXA9-transformed cells and identified nearly half of STAT5 binding sites (228 out of 596) colocalized with HOXA9. Most of these cobound sites are located in distal intergenic (61.0%) and intron (35.1%) regions. Five cobound regions (Il2rα, Fgf1, Pdlim5, Pim1, Fabp5) were selected and confirmed by ChIP-qPCR. To further characterize the interaction between HOXA9 and STAT5, GST pull-down assays were performed that showed that the c-terminal of HOXA9 is critical for interaction with STAT5. Overall, the findings suggest that STAT5 promotes HOXA9-induced transformation by functionally interacting with HOXA9 at HOXA9-regulated enhancers. Disclosures No relevant conflicts of interest to declare.


Blood ◽  
1998 ◽  
Vol 92 (11) ◽  
pp. 4446-4452 ◽  
Author(s):  
Gaëtan Berger ◽  
Daqing W. Hartwell ◽  
Denisa D. Wagner

P-selectin is an adhesion receptor for leukocytes expressed by activated platelets and endothelial cells. To assess a possible role of P-selectin in platelet clearance, we adapted an in vivo biotinylation technique in mice. Wild-type and P-selectin–deficient mice were infused with N-hydroxysuccinimido biotin. The survival of biotinylated platelets was followed by flow cytometry after labeling with fluorescent streptavidin. Both wild-type and P-selectin–deficient platelets presented identical life spans of about 4.7 days, suggesting that P-selectin does not play a role in platelet turnover. When biotinylated platelets were isolated, activated with thrombin, and reinjected into mice, the rate of platelet clearance was unchanged. In contrast, storage of platelets at 4°C caused a significant reduction in their life span in vivo but again no significant differences were observed between the two genotypes. The infused thrombin-activated platelets rapidly lost their surface P-selectin in circulation, and this loss was accompanied by the simultaneous appearance of a 100-kD P-selectin fragment in the plasma. This observation suggests that the platelet membrane P-selectin was shed by cleavage. In conclusion, this study shows that P-selectin, despite its binding to leukocytes, does not mediate platelet clearance. However, the generation of a soluble form of P-selectin on platelet activation may have biological implications in modulating leukocyte recruitment or thrombus growth.


Blood ◽  
2009 ◽  
Vol 114 (16) ◽  
pp. 3464-3472 ◽  
Author(s):  
Frauke May ◽  
Ina Hagedorn ◽  
Irina Pleines ◽  
Markus Bender ◽  
Timo Vögtle ◽  
...  

Abstract Damage to the integrity of the vessel wall leads to exposure of the subendothelial extracellular matrix (ECM), triggering platelet activation and aggregation. This process is essential for primary hemostasis but it may also lead to arterial thrombosis. Although the mechanisms underlying platelet activation on the ECM are well explored, it is less clear which receptors mediate cellular activation in a growing thrombus. Here we studied the role of the recently identified C-type lectin-like receptor 2 (CLEC-2) in this process. We show that anti–CLEC-2 antibody treatment of mice leads to complete and highly specific loss of CLEC-2 in circulating platelets for several days. CLEC-2–deficient platelets displayed normal adhesion under flow, but subsequent aggregate formation was severely defective in vitro and in vivo. As a consequence, CLEC-2 deficiency was associated with increased bleeding times and profound protection from occlusive arterial thrombus formation. These results reveal an essential function of CLEC-2 in hemostasis and thrombosis.


Blood ◽  
2018 ◽  
Vol 132 (Supplement 1) ◽  
pp. 1133-1133
Author(s):  
Qi Yingxue ◽  
Wenchun Chen ◽  
Ke Xu ◽  
Fengying Wu ◽  
Xuemei Fan ◽  
...  

Abstract Background: Platelet glycoprotein Ibα (GPIbα) extracellular domain, which is part of the receptor complex GPIb-IX-V, plays an important role in tumor metastasis. However, the mechanism through which GPIbα participates in the metastatic process remains unclear. In addition, potential bleeding complication remains an obstacle for the clinical use of anti-platelet agents in cancer therapy. Methods and Results: To generate antibodies that bind to mouse platelet GPIbα, washed mouse platelet lysate was used as the antigen for rat immunization. Obtained hybridoma clones were screened in ELISA for binding affinity to the GPIb-IX complex. Positive clones were further screened for their abilities to inhibit platelet-cancer cell adhesion. Finally, at static condition, two antibodies, 2B4 and 1D12, had virtually no effect on the activation of integrin αIIbβ3, which is used to indicate platelet activation. Then, we characterized the binding sites of 2B4 and 1D12 by 20 purified recombinant GPIbα fragments binding. Results showed that 2B4 and 1D12 shared the same binding sites with vWF. To determine whether 2B4 and 1D12 affect vWF binding, we tested the binding by flow cytometry using recombined mouse vWF, and then, we investigated platelet aggregation induced by several agonists, including vWF binding agonist ristocetin. Our data demonstrated clearly that 2B4 and 1D12 could inhibit vWF binding. To investigate whether the inhibition of vWF-GPIbα interaction was associated with tumor metastasis, we examined the effect of 2B4 and 1D12 in each of the following interactions in vitro: between activated platelets and tumor cells, platelets and endothelial cells. Meanwhile, We further investigated the inhibitory effect of these antibodies in vivo using the experimental metastasis model and the spontaneous metastasis model. Results showed that 2B4 and 1D12 could potently inhibit the adhesion of cancer cells in vitro, and metastasisin vivo. We next investigated whether 2B4 and 1D12 could affect platelet activation and/or induce thrombocytopenia in vivo. Results showed that the addition of 2B4 or 1D12 to PRP did not induce platelet aggregation and injection of 2B4 or 1D12 Fab at appropriate dose did not affect tail-bleeding time and platelet count. Based on the above findings, we obtained anti-human platelet GPIbα monoclonal antibody YQ3 using the same approach to explore the role of human GPIbα in cancer metastasis. As expected, YQ3 inhibited lung cancer adhesion and demonstrated similar value in metastasis. More importantly, for all three mAbs in our study, none of their Fabs induced thrombocytopenia. Conclusion: Our results therefore supported the hypothesis that GPIbα contributes to tumor metastasis, and suggested potential value of using anti-GPIbα mAb to suppress cancer metastasis. Disclosures Li: Neoletix: Consultancy, Equity Ownership.


Sign in / Sign up

Export Citation Format

Share Document