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Paul AA, Szulc NA, Kobiela A, Brown SJ, Pokrzywa W, Gutowska-Owsiak D. In silico analysis of the profilaggrin sequence indicates alterations in the stability, degradation route, and intracellular protein fate in filaggrin null mutation carriers. Front Mol Biosci 2023; 10:1105678. [PMID: 37200867 PMCID: PMC10185843 DOI: 10.3389/fmolb.2023.1105678] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/22/2022] [Accepted: 04/19/2023] [Indexed: 05/20/2023] Open
Abstract
Background: Loss of function mutation in FLG is the major genetic risk factor for atopic dermatitis (AD) and other allergic manifestations. Presently, little is known about the cellular turnover and stability of profilaggrin, the protein encoded by FLG. Since ubiquitination directly regulates the cellular fate of numerous proteins, their degradation and trafficking, this process could influence the concentration of filaggrin in the skin. Objective: To determine the elements mediating the interaction of profilaggrin with the ubiquitin-proteasome system (i.e., degron motifs and ubiquitination sites), the features responsible for its stability, and the effect of nonsense and frameshift mutations on profilaggrin turnover. Methods: The effect of inhibition of proteasome and deubiquitinases on the level and modifications of profilaggrin and processed products was assessed by immunoblotting. Wild-type profilaggrin sequence and its mutated variants were analysed in silico using the DEGRONOPEDIA and Clustal Omega tool. Results: Inhibition of proteasome and deubiquitinases stabilizes profilaggrin and its high molecular weight of presumably ubiquitinated derivatives. In silico analysis of the sequence determined that profilaggrin contains 18 known degron motifs as well as multiple canonical and non-canonical ubiquitination-prone residues. FLG mutations generate products with increased stability scores, altered usage of the ubiquitination marks, and the frequent appearance of novel degrons, including those promoting C-terminus-mediated degradation routes. Conclusion: The proteasome is involved in the turnover of profilaggrin, which contains multiple degrons and ubiquitination-prone residues. FLG mutations alter those key elements, affecting the degradation routes and the mutated products' stability.
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Affiliation(s)
- Argho Aninda Paul
- Experimental and Translational Immunology Group, Intercollegiate Faculty of Biotechnology of University of Gdansk and Medical University of Gdansk, University of Gdansk, Gdansk, Poland
| | - Natalia A. Szulc
- Laboratory of Protein Metabolism, International Institute of Molecular and Cell Biology in Warsaw, Warsaw, Poland
| | - Adrian Kobiela
- Experimental and Translational Immunology Group, Intercollegiate Faculty of Biotechnology of University of Gdansk and Medical University of Gdansk, University of Gdansk, Gdansk, Poland
| | - Sara J. Brown
- Centre for Genomic and Experimental Medicine, Institute of Genetics and Cancer, University of Edinburgh, Edinburgh, United Kingdom
| | - Wojciech Pokrzywa
- Laboratory of Protein Metabolism, International Institute of Molecular and Cell Biology in Warsaw, Warsaw, Poland
| | - Danuta Gutowska-Owsiak
- Experimental and Translational Immunology Group, Intercollegiate Faculty of Biotechnology of University of Gdansk and Medical University of Gdansk, University of Gdansk, Gdansk, Poland
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The Proteasome Inhibitor Bortezomib Induces Apoptosis and Activation in Gel-Filtered Human Platelets. Int J Mol Sci 2021; 22:ijms22168955. [PMID: 34445660 PMCID: PMC8396574 DOI: 10.3390/ijms22168955] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/14/2021] [Revised: 08/17/2021] [Accepted: 08/17/2021] [Indexed: 11/16/2022] Open
Abstract
Bortezomib (BTZ) has demonstrated its efficacy in several hematological disorders and has been associated with thrombocytopenia. There is controversy about the effect of BTZ on human platelets, so we set out to determine its effect on various types of platelet samples. Human platelets were investigated in platelet-rich plasma (PRP) and as gel-filtered platelets (GFPs). Mitochondrial inner membrane potential depolarization and phosphatidylserine (PS) and P-selectin expression levels were studied by flow cytometry, while thrombin generation was measured by a fluorescent method. In PRP, BTZ caused negligible PS expression after 60 min of treatment. However, in GFPs, PS expression was dose- and time-dependently increased in the BTZ-treated groups, as was P-selectin. The percentage of depolarized cells was also higher after BTZ pretreatment at both time points. Peak thrombin and velocity index increased significantly even with the lowest BTZ concentration (p = 0.0019; p = 0.0032) whereas time to peak and start tail parameters decreased (p = 0.0007; p = 0.0034). The difference between PRP and GFP results can be attributed to the presence of plasma proteins in PRP, as the PS-stimulating effect of BTZ could be attenuated by supplementing GFPs with purified human albumin. Overall, BTZ induces a procoagulant platelet phenotype in an experimental setting devoid of plasma proteins.
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El-Kadiry AEH, Merhi Y. The Role of the Proteasome in Platelet Function. Int J Mol Sci 2021; 22:ijms22083999. [PMID: 33924425 PMCID: PMC8069084 DOI: 10.3390/ijms22083999] [Citation(s) in RCA: 11] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/16/2021] [Revised: 04/06/2021] [Accepted: 04/08/2021] [Indexed: 02/06/2023] Open
Abstract
Platelets are megakaryocyte-derived acellular fragments prepped to maintain primary hemostasis and thrombosis by preserving vascular integrity. Although they lack nuclei, platelets harbor functional genomic mediators that bolster platelet activity in a signal-specific manner by performing limited de novo protein synthesis. Furthermore, despite their limited protein synthesis, platelets are equipped with multiple protein degradation mechanisms, such as the proteasome. In nucleated cells, the functions of the proteasome are well established and primarily include proteostasis among a myriad of other signaling processes. However, the role of proteasome-mediated protein degradation in platelets remains elusive. In this review article, we recapitulate the developing literature on the functions of the proteasome in platelets, discussing its emerging regulatory role in platelet viability and function and highlighting how its functional coupling with the transcription factor NF-κB constitutes a novel potential therapeutic target in atherothrombotic diseases.
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Affiliation(s)
- Abed El-Hakim El-Kadiry
- Laboratory of Thrombosis and Hemostasis, Montreal Heart Institute, Research Centre, Montreal, QC H1T 1C8, Canada;
- Biomedical Sciences Program, Faculty of Medicine, Université de Montréal, Montreal, QC H3T 1J4, Canada
| | - Yahye Merhi
- Laboratory of Thrombosis and Hemostasis, Montreal Heart Institute, Research Centre, Montreal, QC H1T 1C8, Canada;
- Biomedical Sciences Program, Faculty of Medicine, Université de Montréal, Montreal, QC H3T 1J4, Canada
- Correspondence: ; Tel.: +1-514-376-3330
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Račková L, Csekes E. Proteasome Biology: Chemistry and Bioengineering Insights. Polymers (Basel) 2020; 12:E2909. [PMID: 33291646 PMCID: PMC7761984 DOI: 10.3390/polym12122909] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/28/2020] [Revised: 11/22/2020] [Accepted: 11/23/2020] [Indexed: 12/12/2022] Open
Abstract
Proteasomal degradation provides the crucial machinery for maintaining cellular proteostasis. The biological origins of modulation or impairment of the function of proteasomal complexes may include changes in gene expression of their subunits, ubiquitin mutation, or indirect mechanisms arising from the overall impairment of proteostasis. However, changes in the physico-chemical characteristics of the cellular environment might also meaningfully contribute to altered performance. This review summarizes the effects of physicochemical factors in the cell, such as pH, temperature fluctuations, and reactions with the products of oxidative metabolism, on the function of the proteasome. Furthermore, evidence of the direct interaction of proteasomal complexes with protein aggregates is compared against the knowledge obtained from immobilization biotechnologies. In this regard, factors such as the structures of the natural polymeric scaffolds in the cells, their content of reactive groups or the sequestration of metal ions, and processes at the interface, are discussed here with regard to their influences on proteasomal function.
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Affiliation(s)
- Lucia Račková
- Centre of Experimental Medicine, Institute of Experimental Pharmacology and Toxicology, Slovak Academy of Sciences, Dúbravská cesta 9, 841 04 Bratislava, Slovakia;
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Colberg L, Cammann C, Greinacher A, Seifert U. Structure and function of the ubiquitin-proteasome system in platelets. J Thromb Haemost 2020; 18:771-780. [PMID: 31898400 DOI: 10.1111/jth.14730] [Citation(s) in RCA: 25] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/12/2019] [Accepted: 12/30/2019] [Indexed: 12/16/2022]
Abstract
Platelets are small anucleate blood cells with a life span of 7 to 10 days. They are main regulators of hemostasis. Balanced platelet activity is crucial to prevent bleeding or occlusive thrombus formation. Growing evidence supports that platelets also participate in immune reactions, and interaction between platelets and leukocytes contributes to both thrombosis and inflammation. The ubiquitin-proteasome system (UPS) plays a key role in maintaining cellular protein homeostasis by its ability to degrade non-functional self-, foreign, or short-lived regulatory proteins. Platelets express standard and immunoproteasomes. Inhibition of the proteasome impairs platelet production and platelet function. Platelets also express major histocompatibility complex (MHC) class I molecules. Peptide fragments released by proteasomes can bind to MHC class I, which makes it also likely that platelets can activate epitope specific cytotoxic T lymphocytes (CTLs). In this review, we focus on current knowledge on the significance of the proteasome for the functions of platelets as critical regulators of hemostasis as well as modulators of the immune response.
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Affiliation(s)
- Lisa Colberg
- Friedrich Loeffler Institut für Medizinische Mikrobiologie-Virologie, Universitätsmedizin Greifswald, Greifswald, Germany
- Institut für Immunologie und Transfusionsmedizin, Universitätsmedizin Greifswald, Greifswald, Germany
| | - Clemens Cammann
- Friedrich Loeffler Institut für Medizinische Mikrobiologie-Virologie, Universitätsmedizin Greifswald, Greifswald, Germany
| | - Andreas Greinacher
- Institut für Immunologie und Transfusionsmedizin, Universitätsmedizin Greifswald, Greifswald, Germany
| | - Ulrike Seifert
- Friedrich Loeffler Institut für Medizinische Mikrobiologie-Virologie, Universitätsmedizin Greifswald, Greifswald, Germany
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Platelet Proteasome Activity and Metabolism Is Upregulated during Bacterial Sepsis. Int J Mol Sci 2019; 20:ijms20235961. [PMID: 31783490 PMCID: PMC6928740 DOI: 10.3390/ijms20235961] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/27/2019] [Revised: 11/21/2019] [Accepted: 11/25/2019] [Indexed: 11/30/2022] Open
Abstract
Dysregulation of platelet function can contribute to the disease progression in sepsis. The proteasome represents a critical and vital element of cellular protein metabolism in platelets and its proteolytic activity has been associated with platelet function. However, the role of the platelet proteasome as well as its response to infection under conditions of sepsis have not been studied so far. We measured platelet proteasome activity by fluorescent substrates, degradation of poly-ubiquitinated proteins and cleavage of the proteasome substrate Talin-1 in the presence of living E. coli strains and in platelets isolated from sepsis patients. Upregulation of the proteasome activator PA28 (PSME1) was assessed by quantitative real-time PCR in platelets from sepsis patients. We show that co-incubation of platelets with living E. coli (UTI89) results in increased degradation of poly-ubiquitinated proteins and cleavage of Talin-1 by the proteasome. Proteasome activity and cleavage of Talin-1 was significantly increased in α-hemolysin (HlyA)-positive E. coli strains. Supporting these findings, proteasome activity was also increased in platelets of patients with sepsis. Finally, the proteasome activator PA28 (PSME1) was upregulated in this group of patients. In this study we demonstrate for the first time that the proteasome in platelets is activated in the septic milieu.
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Trugilho MRDO, Hottz ED, Brunoro GVF, Teixeira-Ferreira A, Carvalho PC, Salazar GA, Zimmerman GA, Bozza FA, Bozza PT, Perales J. Platelet proteome reveals novel pathways of platelet activation and platelet-mediated immunoregulation in dengue. PLoS Pathog 2017; 13:e1006385. [PMID: 28542641 PMCID: PMC5453622 DOI: 10.1371/journal.ppat.1006385] [Citation(s) in RCA: 62] [Impact Index Per Article: 8.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/17/2016] [Revised: 06/01/2017] [Accepted: 04/27/2017] [Indexed: 12/27/2022] Open
Abstract
Dengue is the most prevalent human arbovirus disease worldwide. Dengue virus (DENV) infection causes syndromes varying from self-limiting febrile illness to severe dengue. Although dengue pathophysiology is not completely understood, it is widely accepted that increased inflammation plays important roles in dengue pathogenesis. Platelets are blood cells classically known as effectors of hemostasis which have been increasingly recognized to have major immune and inflammatory activities. Nevertheless, the phenotype and effector functions of platelets in dengue pathogenesis are not completely understood. Here we used quantitative proteomics to investigate the protein content of platelets in clinical samples from patients with dengue compared to platelets from healthy donors. Our assays revealed a set of 252 differentially abundant proteins. In silico analyses associated these proteins with key molecular events including platelet activation and inflammatory responses, and with events not previously attributed to platelets during dengue infection including antigen processing and presentation, proteasome activity, and expression of histones. From these results, we conducted functional assays using samples from a larger cohort of patients and demonstrated evidence for platelet activation indicated by P-selectin (CD62P) translocation and secretion of granule-stored chemokines by platelets. In addition, we found evidence that DENV infection triggers HLA class I synthesis and surface expression by a mechanism depending on functional proteasome activity. Furthermore, we demonstrate that cell-free histone H2A released during dengue infection binds to platelets, increasing platelet activation. These findings are consistent with functional importance of HLA class I, proteasome subunits, and histones that we found exclusively in proteome analysis of platelets in samples from dengue patients. Our study provides the first in-depth characterization of the platelet proteome in dengue, and sheds light on new mechanisms of platelet activation and platelet-mediated immune and inflammatory responses. Dengue is the most frequent hemorrhagic viral disease and re-emergent infection in the world. Recent decades were marked by a progressive global expansion of the infection including a higher frequency of severe dengue. Currently there is no effective vaccinal coverage or specific therapies, while efforts aimed at vector control have failed to stop the progression of epidemics and expansion of the disease. An increased understanding of the molecular physiology is of paramount importance for the establishment of new therapeutic targets and better clinical management. Dengue fever is characterized by thrombocytopenia and vascular leak. Although thrombocytopenia is a hallmark of dengue, the molecular phenotype and activities of platelets in the pathogenesis of dengue is not well elucidated. This work characterizes the proteome of platelets isolated from patients with dengue and includes validation of functionally-linked protein networks that we identified, using samples from a larger cohort of dengue patients. Moreover, in vitro experiments revealed activities of platelets that have recognized importance to dengue pathogenesis, including chemokine release, antigen presentation, and proteasome activity. Finally, our results identify circulating histones as a novel mechanism of platelet activation in dengue. These findings provide new evidence for platelet immune activities in dengue illness, and mark an advance in the understanding of this disease.
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Affiliation(s)
- Monique Ramos de Oliveira Trugilho
- Laboratório de Toxinologia, Instituto Oswaldo Cruz, Fundação Oswaldo Cruz, Rio de Janeiro, Brazil
- Centro de Desenvolvimento Tecnológico em Saúde (CDTS), Fundação Oswaldo Cruz, Rio de Janeiro, Brazil
| | - Eugenio Damaceno Hottz
- Laboratório de Imunofarmacologia, Instituto Oswaldo Cruz, Fundação Oswaldo Cruz, Rio de Janeiro, Brazil
- Laboratório de Análise de Glicoconjugados, Departamento de Bioquímica, Instituto de Ciências Biológicas, Universidade Federal de Juiz de Fora (UFJF), Juiz de Fora, Minas Gerais, Brazil
| | | | - André Teixeira-Ferreira
- Laboratório de Toxinologia, Instituto Oswaldo Cruz, Fundação Oswaldo Cruz, Rio de Janeiro, Brazil
| | - Paulo Costa Carvalho
- Laboratório de Proteômica e Engenharia de Proteínas, Instituto Carlos Chagas (ICC), Fiocruz, Curitiba, Paraná, Brazil
| | - Gustavo Adolfo Salazar
- Computational Biology Group, Faculty of Health Sciences, University of Cape Town, Cape Town, South Africa
| | - Guy A. Zimmerman
- Laboratório de Imunofarmacologia, Instituto Oswaldo Cruz, Fundação Oswaldo Cruz, Rio de Janeiro, Brazil
- Department of Internal Medicine, University of Utah, Salt Lake City, UT, United States of America
| | - Fernando A. Bozza
- Instituto Nacional de Infectologia Evandro Chagas (INI), Fundação Oswaldo Cruz, Rio de Janeiro, Brazil
| | - Patrícia T. Bozza
- Laboratório de Imunofarmacologia, Instituto Oswaldo Cruz, Fundação Oswaldo Cruz, Rio de Janeiro, Brazil
- * E-mail: , (PTB); (JP)
| | - Jonas Perales
- Laboratório de Toxinologia, Instituto Oswaldo Cruz, Fundação Oswaldo Cruz, Rio de Janeiro, Brazil
- * E-mail: , (PTB); (JP)
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Yang Q, Crispino JD, Wen QJ. Kinase signaling and targeted therapy for primary myelofibrosis. Exp Hematol 2016; 48:32-38. [PMID: 28043820 DOI: 10.1016/j.exphem.2016.12.007] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/03/2016] [Revised: 12/19/2016] [Accepted: 12/20/2016] [Indexed: 01/14/2023]
Abstract
The myeloproliferative neoplasms (MPNs) are somatic mutation-driven hematologic malignancies characterized by bone marrow fibrosis and the accumulation of atypical megakaryocytes with reduced polyploidization in the primary myelofibrosis subtype of the MPNs. Increasing evidence points to a dominant role of abnormal megakaryocytes in disease initiation and progression. Here we review the literature related to kinase signaling pathways relevant to megakaryocyte differentiation and proliferation, including Aurora A kinase, RhoA/ROCK, and JAK/STAT, as well as the activities of their targeted inhibitors in models of the disease. Some of these pathway inhibitors selectively induce megakaryocyte differentiation, suppress malignant proliferation, and promote polyploidization and proplatelet formation. Moreover, combining sets of these inhibitors may be an effective approach to treat and potentially cure MPN patients. For example, preclinical studies reported significant synergistic effects of the combination of an Aurora A inhibitor and JAK1/2 inhibitor, in a murine model of the primary myelofibrosis. Future basic and clinical research into the contributions of these signaling pathways to aberrant megakaryopoiesis may lead to novel effective treatments for MPN patients.
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Affiliation(s)
- Qiong Yang
- Beijing Key Laboratory of Gene Resource and Molecular Development, College of Life Sciences, Beijing Normal University, Beijing, China
| | - John D Crispino
- Division of Hematology and Oncology, Department of Medicine, Northwestern University, Chicago, IL
| | - Qiang Jeremy Wen
- Division of Hematology and Oncology, Department of Medicine, Northwestern University, Chicago, IL.
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9
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Srikanthan S, Li W, Silverstein RL, McIntyre TM. Exosome poly-ubiquitin inhibits platelet activation, downregulates CD36 and inhibits pro-atherothombotic cellular functions. J Thromb Haemost 2014; 12:1906-17. [PMID: 25163645 PMCID: PMC4229405 DOI: 10.1111/jth.12712] [Citation(s) in RCA: 78] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/16/2013] [Indexed: 12/12/2022]
Abstract
INTRODUCTION Activated platelets shed microparticles from plasma membranes, but also release smaller exosomes from internal compartments. While microparticles participate in athero-thrombosis, little is known of exosomes in this process. MATERIALS & METHODS Ex vivo biochemical experiments with human platelets and exosomes, and FeCl3 -induced murine carotid artery thrombosis. RESULTS Both microparticles and exosomes were abundant in human plasma. Platelet-derived exosomes suppressed ex vivo platelet aggregation and reduced adhesion to collagen-coated microfluidic channels at high shear. Injected exosomes inhibited occlusive thrombosis in FeCl3 -damaged murine carotid arteries. Control platelets infused into irradiated, thrombocytopenic mice reconstituted thrombosis in damaged carotid arteries, but failed to do so after prior ex vivo incubation with exosomes.CD36 promotes platelet activation, and exosomes dramatically reduced platelet CD36.CD36 is also expressed by macrophages, where it binds and internalizes oxidized LDL and microparticles, supplying lipid to promote foam cell formation. Platelet exosomes inhibited oxidized-LDL binding and cholesterol loading into macrophages. Exosomes were not competitive CD36 ligands, but instead sharply reduced total macrophage CD36 content. Exosomal proteins, in contrast to microparticle or cellular proteins, were highly adducted by ubiquitin. Exosomes enhanced ubiquitination of cellular proteins, including CD36, and blockade of proteosome proteolysis with MG-132 rescued CD36 expression. Recombinant unanchored K48 poly-ubiquitin behaved similarly to exosomes, inhibiting platelet function, macrophage CD36 expression and macrophage particle uptake. CONCLUSIONS Platelet-derived exosomes inhibit athero-thrombotic processes by reducing CD36-dependent lipid loading of macrophages and by suppressing platelet thrombosis. Exosomes increase protein ubiquitination and enhance proteasome degradation of CD36.
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Affiliation(s)
- S Srikanthan
- Department of Cellular and Molecular Medicine, Lerner Research Institute, Cleveland, OH, USA; Department of Molecular Medicine, Case Western Reserve University, Cleveland, OH, USA
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Klockenbusch C, Walsh GM, Brown LM, Hoffman MD, Ignatchenko V, Kislinger T, Kast J. Global proteome analysis identifies active immunoproteasome subunits in human platelets. Mol Cell Proteomics 2014; 13:3308-19. [PMID: 25146974 DOI: 10.1074/mcp.m113.031757] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023] Open
Abstract
The discovery of new functions for platelets, particularly in inflammation and immunity, has expanded the role of these anucleate cell fragments beyond their primary hemostatic function. Here, four in-depth human platelet proteomic data sets were generated to explore potential new functions for platelets based on their protein content and this led to the identification of 2559 high confidence proteins. During a more detailed analysis, consistently high expression of the proteasome was discovered, and the composition and function of this complex, whose role in platelets has not been thoroughly investigated, was examined. Data set mining resulted in identification of nearly all members of the 26S proteasome in one or more data sets, except the β5 subunit. However, β5i, a component of the immunoproteasome, was identified. Biochemical analyses confirmed the presence of all catalytically active subunits of the standard 20S proteasome and immunoproteasome in human platelets, including β5, which was predominantly found in its precursor form. It was demonstrated that these components were assembled into the proteasome complex and that standard proteasome as well as immunoproteasome subunits were constitutively active in platelets. These findings suggest potential new roles for platelets in the immune system. For example, the immunoproteasome may be involved in major histocompatibility complex I (MHC I) peptide generation, as the MHC I machinery was also identified in our data sets.
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Affiliation(s)
- Cordula Klockenbusch
- From the ‡The Biomedical Research Centre, 2222 Health Sciences Mall, University of British Columbia, Vancouver, BC V6T 1Z3, Canada
| | - Geraldine M Walsh
- From the ‡The Biomedical Research Centre, 2222 Health Sciences Mall, University of British Columbia, Vancouver, BC V6T 1Z3, Canada; §The Centre for Blood Research, 2350 Health Sciences Mall, University of British Columbia, Vancouver, BC V6T 1Z3, Canada
| | - Lyda M Brown
- From the ‡The Biomedical Research Centre, 2222 Health Sciences Mall, University of British Columbia, Vancouver, BC V6T 1Z3, Canada
| | - Michael D Hoffman
- From the ‡The Biomedical Research Centre, 2222 Health Sciences Mall, University of British Columbia, Vancouver, BC V6T 1Z3, Canada; ¶The Department of Chemistry, 2036 Main Mall, University of British Columbia, Vancouver, BC V6T 1Z1, Canada
| | - Vladimir Ignatchenko
- ‖Princess Margaret Cancer Centre, University Health Network, Toronto, ON M5G 2C4, Canada
| | - Thomas Kislinger
- ‖Princess Margaret Cancer Centre, University Health Network, Toronto, ON M5G 2C4, Canada; **Department of Medical Biophysics, University of Toronto, Toronto, ON M5G 1L7, Canada
| | - Juergen Kast
- From the ‡The Biomedical Research Centre, 2222 Health Sciences Mall, University of British Columbia, Vancouver, BC V6T 1Z3, Canada; §The Centre for Blood Research, 2350 Health Sciences Mall, University of British Columbia, Vancouver, BC V6T 1Z3, Canada; ¶The Department of Chemistry, 2036 Main Mall, University of British Columbia, Vancouver, BC V6T 1Z1, Canada;
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Shi DS, Smith MCP, Campbell RA, Zimmerman PW, Franks ZB, Kraemer BF, Machlus KR, Ling J, Kamba P, Schwertz H, Rowley JW, Miles RR, Liu ZJ, Sola-Visner M, Italiano JE, Christensen H, Kahr WHA, Li DY, Weyrich AS. Proteasome function is required for platelet production. J Clin Invest 2014; 124:3757-66. [PMID: 25061876 DOI: 10.1172/jci75247] [Citation(s) in RCA: 52] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/17/2014] [Accepted: 06/05/2014] [Indexed: 01/03/2023] Open
Abstract
The proteasome inhibiter bortezomib has been successfully used to treat patients with relapsed multiple myeloma; however, many of these patients become thrombocytopenic, and it is not clear how the proteasome influences platelet production. Here we determined that pharmacologic inhibition of proteasome activity blocks proplatelet formation in human and mouse megakaryocytes. We also found that megakaryocytes isolated from mice deficient for PSMC1, an essential subunit of the 26S proteasome, fail to produce proplatelets. Consistent with decreased proplatelet formation, mice lacking PSMC1 in platelets (Psmc1(fl/fl) Pf4-Cre mice) exhibited severe thrombocytopenia and died shortly after birth. The failure to produce proplatelets in proteasome-inhibited megakaryocytes was due to upregulation and hyperactivation of the small GTPase, RhoA, rather than NF-κB, as has been previously suggested. Inhibition of RhoA or its downstream target, Rho-associated protein kinase (ROCK), restored megakaryocyte proplatelet formation in the setting of proteasome inhibition in vitro. Similarly, fasudil, a ROCK inhibitor used clinically to treat cerebral vasospasm, restored platelet counts in adult mice that were made thrombocytopenic by tamoxifen-induced suppression of proteasome activity in megakaryocytes and platelets (Psmc1(fl/fl) Pdgf-Cre-ER mice). These results indicate that proteasome function is critical for thrombopoiesis, and suggest inhibition of RhoA signaling as a potential strategy to treat thrombocytopenia in bortezomib-treated multiple myeloma patients.
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Feng W, Chang C, Luo D, Su H, Yu S, Hua W, Chen Z, Hu H, Liu W. Dissection of autophagy in human platelets. Autophagy 2014; 10:642-51. [PMID: 24458007 PMCID: PMC4091151 DOI: 10.4161/auto.27832] [Citation(s) in RCA: 66] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/18/2023] Open
Abstract
Continuous turnover of intracellular components by autophagy is necessary to preserve cellular homeostasis in all tissues. Despite recent advances in identifying autophagy-related genes and understanding the functions of autophagy in developmental and pathological conditions, so far, the role of autophagy in platelet, a specific anucleate cell type, is poorly understood. In this study, we showed that human platelets express the autophagy-related proteins ATG5, ATG7, and LC3. The same as in nucleated mammalian cells, autophagy was stimulated by cell starvation or the MTOR inhibitor rapamycin in a phosphatidylinositol 3-kinase (PtdIns3K)-dependent manner. Disruption of autophagic flux led to impairment of platelet aggregation and adhesion. Furthermore, Becn1 heterozygous knockout mice displayed a prolonged bleeding time and reduced platelet aggregation. These results suggest a potential role of autophagy in the regulation of platelet function, and imply that gene transcription may not be an essential prerequisite for adaptive autophagy.
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Affiliation(s)
- Wenfeng Feng
- Department of Biochemistry and Molecular Biology; Program in Molecular and Cell Biology; Zhejiang University School of Medicine; Hangzhou, China
| | - Chunmei Chang
- Department of Biochemistry and Molecular Biology; Program in Molecular and Cell Biology; Zhejiang University School of Medicine; Hangzhou, China
| | - Dongjiao Luo
- Department of Pathology and Pathophysiology; Zhejiang University School of Medicine; Hangzhou, China
| | - Hua Su
- Department of Biochemistry and Molecular Biology; Program in Molecular and Cell Biology; Zhejiang University School of Medicine; Hangzhou, China
| | - Shanshan Yu
- Department of Pathology and Pathophysiology; Zhejiang University School of Medicine; Hangzhou, China
| | - Wen Hua
- Department of Respiratory Medicine; Second Affiliated Hospital; Zhejiang University School of Medicine; Hangzhou, China
| | - Zhihua Chen
- Department of Respiratory Medicine; Second Affiliated Hospital; Zhejiang University School of Medicine; Hangzhou, China
| | - Hu Hu
- Department of Pathology and Pathophysiology; Zhejiang University School of Medicine; Hangzhou, China
| | - Wei Liu
- Department of Biochemistry and Molecular Biology; Program in Molecular and Cell Biology; Zhejiang University School of Medicine; Hangzhou, China; Collaborative Innovation Center for Diagnosis and Treatment of Infectious Disease; First Affiliated Hospital; Zhejiang University School of Medicine; Hangzhou, China
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Gupta N, Li W, Willard B, Silverstein RL, McIntyre TM. Proteasome proteolysis supports stimulated platelet function and thrombosis. Arterioscler Thromb Vasc Biol 2013; 34:160-8. [PMID: 24177323 DOI: 10.1161/atvbaha.113.302116] [Citation(s) in RCA: 41] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Abstract
OBJECTIVE Proteasome inhibitors used in the treatment of hematologic cancers also reduce thrombosis. Whether the proteasome participates in platelet activation or function is unclear because little is known of the proteasome in these terminally differentiated cells. APPROACH AND RESULTS Platelets displayed all 3 primary proteasome protease activities, which MG132 and bortezomib (Velcade) inhibited. Proteasome substrates are marked by ubiquitin, and platelets contained a functional ubiquitination system that modified the proteome by monoubiquitination and polyubiquitination. Systemic MG132 strongly suppressed the formation of occlusive, platelet-rich thrombi in FeCl3-damaged carotid arteries. Transfusion of platelets treated ex vivo with MG132 and washed before transfusion into thrombocytopenic mice also reduced carotid artery thrombosis. Proteasome inhibition reduced platelet aggregation by low thrombin concentrations and ristocetin-stimulated agglutination through the glycoprotein Ib-IX-V complex. This receptor was not appropriately internalized after proteasome inhibition in stimulated platelets, and spreading and clot retraction after MG132 exposure also were decreased. The effects of proteasome inhibitors were not confined to a single receptor as MG132 suppressed thrombin-stimulated, ADP-stimulated, and lipopolysaccharide-stimulated microparticle shedding. Proteasome inhibition increased ubiquitin decoration of cytoplasmic proteins, including the cytoskeletal proteins Filamin A and Talin-1. Mass spectrometry revealed a single MG132-sensitive tryptic cleavage after R1745 in an extended Filamin A loop, which would separate its actin-binding domain from its carboxy terminal glycoprotein Ibα-binding domain. CONCLUSIONS Platelets contain a ubiquitin/proteasome system that marks cytoskeletal proteins for proteolytic modification to promote productive platelet-platelet and platelet-wall interactions.
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Affiliation(s)
- Nilaksh Gupta
- From the Department of Cellular and Molecular Medicine, Lerner Research Institute, Cleveland, OH (N.G., W.L., B.W., R.L.S., T.M.M.); and Department of Biological Geological and Environmental Sciences, Cleveland State University, Cleveland, OH (N.G., T.M.M.)
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14
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Kraemer BF, Weyrich AS, Lindemann S. Protein degradation systems in platelets. Thromb Haemost 2013; 110:920-4. [PMID: 24048267 DOI: 10.1160/th13-03-0183] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/01/2013] [Accepted: 07/28/2013] [Indexed: 01/05/2023]
Abstract
Protein synthesis and degradation are essential processes that allow cells to survive and adapt to their surrounding milieu. In nucleated cells, the degradation and/or cleavage of proteins is required to eliminate aberrant proteins. Cells also degrade proteins as a mechanism for cell signalling and complex cellular functions. Although the last decade has convincingly shown that platelets synthesise proteins, the roles of protein degradation in these anucleate cytoplasts are less clear. Here we review what is known about protein degradation in platelets placing particular emphasis on the proteasome and the cysteine protease calpain.
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Affiliation(s)
- B F Kraemer
- Andrew Weyrich, MD, Eccles Institute of Human Genetics, Department of Internal Medicine, University of Utah, Salt Lake City, Building 533 Room 4220, Salt Lake City, Utah 84112, USA, Tel: +1 801 5850702, Fax: +1 801 5850701, E-mail:
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15
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Chapman LM, Aggrey AA, Field DJ, Srivastava K, Ture S, Yui K, Topham DJ, Baldwin WM, Morrell CN. Platelets present antigen in the context of MHC class I. THE JOURNAL OF IMMUNOLOGY 2012; 189:916-23. [PMID: 22706078 DOI: 10.4049/jimmunol.1200580] [Citation(s) in RCA: 159] [Impact Index Per Article: 13.3] [Reference Citation Analysis] [Abstract] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
Abstract
Platelets are most recognized for their vital role as the cellular mediator of thrombosis, but platelets also have important immune functions. Platelets initiate and sustain vascular inflammation in many disease conditions, including arthritis, atherosclerosis, transplant rejection, and severe malaria. We now demonstrate that platelets express T cell costimulatory molecules, process and present Ag in MHC class I, and directly activate naive T cells in a platelet MHC class I-dependent manner. Using an experimental cerebral malaria mouse model, we also demonstrate that platelets present pathogen-derived Ag to promote T cell responses in vivo, and that platelets can be used in a cell-based vaccine model to induce protective immune responses. Our study demonstrates a novel Ag presentation role for platelets.
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Affiliation(s)
- Lesley M Chapman
- Aab Cardiovascular Research Institute, University of Rochester School of Medicine and Dentistry, Rochester, NY 14642, USA
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Schwertz H, Rowley JW, Tolley ND, Campbell RA, Weyrich AS. Assessing protein synthesis by platelets. Methods Mol Biol 2012; 788:141-153. [PMID: 22130706 DOI: 10.1007/978-1-61779-307-3_11] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/31/2023]
Abstract
Platelets are anucleate cytoplasts that circulate in the bloodstream for approximately 9-11 days. Because they lack nuclei, platelets were considered incapable of protein synthesis. However, studies over the last decade have revealed that platelets use a variety of translational control pathways to synthesize proteins.A variety of protocols can be employed to assess protein synthesis by platelets. These protocols are scattered throughout the literature and, more often than not, lack critical details. In this chapter, we thoroughly outline methods used in our laboratory to assess protein synthesis by platelets.
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Affiliation(s)
- Hansjörg Schwertz
- Program in Molecular Medicine, Department of Surgery, University of Utah, Salt Lake City, UT, USA
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18
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Nayak MK, Kumar K, Dash D. Regulation of proteasome activity in activated human platelets. Cell Calcium 2011; 49:226-32. [PMID: 21388679 DOI: 10.1016/j.ceca.2011.02.005] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/29/2010] [Revised: 02/11/2011] [Accepted: 02/13/2011] [Indexed: 01/12/2023]
Abstract
Ubiquitin-proteasome system has emerged a central player in regulation of diverse cellular processes. However, relevance of proteasome activity in platelets, which are terminally differentiated enucleate cells, is not clear. In this report we show that activation of platelets with physiological agonists was associated with 7-10 -fold rise in proteasomal activity. Elevation of cytosolic calcium with A23187 or thapsigargin resulted in significant increase in enzymatic activity, while treatment with intracellular calcium chelator or inhibitor of inositol trisphosphate receptor attenuated proteasomal enzymes in collagen-stimulated platelets. Specific inhibitors of protein kinase C as well as calpain, too, downregulated proteasome function. To conclude, proteasomal enzymatic activity in platelets is regulated by cytosolic calcium through Ca(2+)-dependent downstream effectors like calpain and protein kinase C.
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Affiliation(s)
- Manasa K Nayak
- Department of Biochemistry, Institute of Medical Sciences, Banaras Hindu University, Varanasi 221005, India
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19
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Proteome of platelets in patients with coronary artery disease. Exp Hematol 2010; 38:341-50. [PMID: 20226836 DOI: 10.1016/j.exphem.2010.03.001] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/06/2009] [Revised: 02/26/2010] [Accepted: 03/02/2010] [Indexed: 11/21/2022]
Abstract
OBJECTIVE This study aimed at investigating the protein patterns of platelets from patients with stable or acute coronary atherosclerosis (CAD), in which platelets play a key role. MATERIALS AND METHODS A proteomic approach was adopted to investigate specific protein patterns in platelets of patients with non-ST elevation acute coronary syndrome, stable angina, or of subjects with no history of CAD. RESULTS Six differentially expressed proteins were identified: two involved in energy metabolism (2-oxoglutarate dehydrogenase [OGDH], and lactate dehydrogenase [LDH]); three were associated with cytoskeleton-based processes (gamma-actin, coronin 1B, and pleckstrin); and one involved in protein degradation (proteasome subunit type 8). Expression levels of OGDH and a cleaved form of gamma-actin were significantly higher in the platelets of patients than in controls, whereas that of LDH was higher only in the platelets of patients with acute coronary disease. The increases in protein expression of OGDH and LDH are paralleled by changes in their functional activities. Coronin and proteasome subunit type 8 were less expressed in the platelets of patients, as were the basic isoforms of pleckstrin. CONCLUSION The platelet proteome is altered in CAD patients with stable or acute coronary syndrome possibly because of the ongoing atherosclerotic process. The identified protein changes not previously connected with CAD were an increase in the energy metabolism enzymes and alterations in the proteins associated with cytoskeleton-based processes, both of which indicate platelet activation.
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Shi C, Rui Q, Xu LL. Enzymatic properties of the 20S proteasome in wheat endosperm and its biochemical characteristics after seed imbibition. PLANT BIOLOGY (STUTTGART, GERMANY) 2009; 11:849-858. [PMID: 19796362 DOI: 10.1111/j.1438-8677.2009.00193.x] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/28/2023]
Abstract
The 20S proteasome from wheat (Triticum aestivum L., Yangmai 158) endosperm was purified to apparent homogeneity by three sequential centrifugations and gradient PAGE (GPAGE). The purified 20S proteasome clearly cleaved peptidyl-arylamide bonds in the model synthetic substrates Z-GGL-AMC and Z-GGR-AMC, which are used to reflect chymotrypsin-like and trypsin-like activity, respectively. For both substrates, the optimum pH was 8.0, but the optimum temperatures for chymotrypsin-like and trypsin-like activity were 55 degrees C and 37 degrees C, respectively. Both enzyme activities were clearly inhibited by MG115 and PMSF. Polyubiquitinated proteins remained constant from 0 to 7 days after seed imbibition, but caseinolytic activity and the amount of the 20S proteasome associated with the aleurone layer decreased from 1 to 2 days after imbibition (DAI), then increased from 2 to 4 DAI, and reached a maximum at 4 DAI that was retained until 7 DAI. An increase was seen in the mRNA level of the beta5 subunit of the 20S proteasome from 2 DAI, and caseinolytic activity and the amount of the 20S proteasome increased from 3 DAI onwards. In addition, the main storage proteins of the wheat endosperm could not be hydrolyzed by the 20S proteasome. The evidence suggests that the main role of the 20S proteasome may not be to degrade massive proteins of the wheat endosperm after seed imbibition.
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Affiliation(s)
- C Shi
- College of Life Sciences, Nanjing Agricultural University, Nanjing, China
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Li Y, Wang YS, Shen XF, Hui YN, Han J, Zhao W, Zhu J. Alterations of activity and intracellular distribution of the 20S proteasome in ageing retinal pigment epithelial cells. Exp Gerontol 2008; 43:1114-22. [PMID: 18817863 DOI: 10.1016/j.exger.2008.08.052] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/06/2008] [Revised: 08/24/2008] [Accepted: 08/25/2008] [Indexed: 11/17/2022]
Abstract
Age-related macular degeneration (AMD) remains high incidence and accounts for a main cause of blindness in ageing people, but its mechanism is still poorly understood. Ageing and associated dysfunction of retinal pigment epithelial (RPE) cells were believed to be the pathological onset of AMD. 20S proteasome has been tightly correlated with cell ageing due to its fundamental role in maintaining cellular homeostasis, but its implication in the ageing process of human RPE cells was seldom concerned. This study aimed to demonstrate the interconnections between 20S proteasome and ageing RPE cells by characterizing age-dependent alterations of the 20S proteasome in primarily cultured human RPE cells. For this purpose, a replicative ageing RPE cell model was established and validated through testing the cell viability, beta-galactosidase activity and cellular autofluorescence. Decline in chymotrypsin-like, peptidylglutamyl-peptide hydrolase and trypsin-like activities of the 20S proteasome was detected in aged RPE cells through degradation of fluorogenic substrates. Immunofluorescence assay revealed that the 20S proteasome was concentrated in RPE nucleus, and redistributed partly to the peri-nuclear regions in old RPE passages. These age-dependent changes of the 20S complex were accompanied with a significantly increased fluorescent intensity of intracellular oxidized proteins. Further analysis of the proteasome-to-oxidized protein ratio indicated a preferred protection of the RPE nuclear proteins by the 20S proteasome, which also subsided remarkably as a function of the cell ageing. In conclusion, we demonstrated functional impairment and redistribution of the 20S proteasome with age in human RPE cells and supposed these alterations impactful on the process of RPE cell ageing and furthermore on the pathogenesis of AMD. Future researches on the mechanism of these alterations and the pathways to manipulate their effects are still strongly recommended.
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Affiliation(s)
- Yue Li
- Department of Ophthalmology, Xijing Hospital, The Fourth Military Medical University and Eye Institute of PLA, Chang-le Road 17, Xi'an, Shaanxi 710032, China
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Avcu F, Ural AU, Cetin T, Nevruz O. Effects of bortezomib on platelet aggregation and ATP release in human platelets, in vitro. Thromb Res 2007; 121:567-71. [PMID: 17910980 DOI: 10.1016/j.thromres.2007.06.013] [Citation(s) in RCA: 46] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/13/2007] [Revised: 06/07/2007] [Accepted: 06/12/2007] [Indexed: 01/08/2023]
Abstract
INTRODUCTION Proteasome inhibitor bortezomib (PS-341) has been the first proteasome inhibitor that has entered clinical trials with its antiproliferative and proapoptotic effects in patients with multiple myeloma. Recent studies indicate that proteasome inhibitors can be useful in prevention of experimental arterial thrombosis in renovascular hypertensive rat models. The aim of the present study is to investigate the effect of bortezomib on in vitro platelet aggregation and adenosine triphosphate (ATP) release of human platelets. MATERIALS AND METHODS For this purpose, platelet aggregation was induced in the platelet-rich plasma (PRP) using 3 microg ml(-1) collagen, 5 microM adenosine diphosphate (ADP), 10 microM epinephrine and 1 U ml(-1) thrombin and ATP release was induced by collagen. RESULTS AND CONCLUSIONS Bortezomib showed an inhibitory effect on platelet aggregation induced by ADP in human PRP in a dose- and time-dependent manner, whereas it had no effect on collagen-, epinephrin and thrombin-induced aggregation. ATP-release reaction induced by collagen was inhibited dose- and time-dependently by bortezomib, even though collagen-induced platelet aggregation was apparently not affected in human PRP. These findings indicate that bortezomib may be an antiaggregating agent and its' effects may be related to adenine nucleotide receptor dependent regulatory proteins which are important for physiological and pathophysiological cellular processes. However, our in vitro studies suggest that this hypothesis is inadequate to explain the observations completely. This phenomenon and its clinical implication justify further clinical investigations.
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Affiliation(s)
- Ferit Avcu
- Gulhane Military Medical Academy, Department of Haematology, Medical and Cancer Research Center, Ankara, Turkey.
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Hopkins LM, Davis JM, Buchli R, Vangundy RS, Schwartz KA, Gerlach JA. MHC Class I–Associated Peptides Identified From Normal Platelets and From Individuals With Idiopathic Thrombocytopenic Purpura. Hum Immunol 2005; 66:874-83. [PMID: 16216671 DOI: 10.1016/j.humimm.2005.06.004] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/14/2005] [Indexed: 11/22/2022]
Abstract
Major histocompatibility complex (MHC) class I molecules bind and display peptide antigens on the cell surface. CD8(+) T lymphocytes recognize peptides in association with class I proteins to initiate a cytotoxic immune response. To understand the specificity of such immune responses and to facilitate the development of therapies for disease, it is important to identify MHC-presented peptides. In this study, platelets, easily obtainable and often associated with immune-mediated disease, were selected to identify MHC class I-associated peptides. MHC-associated peptides presented on platelets of normal individuals and individuals with idiopathic thrombocytopenic purpura (ITP) were characterized. ITP is characterized by the premature immune destruction of platelets. It is associated with the production of antiplatelet autoantibodies, most often targeting platelet membrane GPIIb/IIIa or GPIb/IX. In addition to characterizing five fully and several partially sequenced peptides from platelets, the peptide GPRGA(L/I)S(L/I)(L/I) was identified from four of the five ITP patients. The anchor motif of this peptide correlates with the presence of the HLA-B7 allele. A BLAST search identified this peptide as GPIb (4-12). In conclusion, platelets from normal and ITP individuals can present peptides from general cellular proteins and platelet specific proteins, such as GPIb, to the immune system via MHC class I.
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Affiliation(s)
- Leann M Hopkins
- Department of Pathobiology and Diagnostic Investigation, Michigan State University, East Lansing, MI, USA
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Dangelmaier CA, Quinter PG, Jin J, Tsygankov AY, Kunapuli SP, Daniel JL. Rapid ubiquitination of Syk following GPVI activation in platelets. Blood 2005; 105:3918-24. [PMID: 15701717 PMCID: PMC1895068 DOI: 10.1182/blood-2004-09-3689] [Citation(s) in RCA: 54] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Spleen tyrosine kinase (Syk) activation is a key intermediate step in the activation of platelets by the physiologic agonist collagen. We have found that Syk is rapidly ubiquitinated upon activation of platelets by collagen, collagen-related peptide (CRP), and convulxin. The Src family kinase inhibitors prevented Syk phosphorylation and its ubiquitination, indicating that the process is downstream of Src kinases. The ubiquitination of Syk did not cause degradation of the protein as evidenced by the lack of effect of proteasomal and lysosomal inhibitors. We separated ubiquitinated Syk from its nonubiquitinated counterpart and used an in vitro kinase assay to compare their activities. We found that the ubiquitinated Syk appeared to be about 5-fold more active. Using a phosphospecific antibody to Syk (Tyr525/Tyr526) that measures activated Syk, we found that most (60%-75%) of the active Syk is in the ubiquitinated fraction. This result explains the apparent high specific activity of ubiquitinated Syk. In c-Cbl-deficient mice, Syk is not ubiquitinated, implicating c-Cbl as the E3 ligase involved in Syk ubiquitination. Furthermore, Syk is not dephosphorylated in these mice. We propose that c-Cbl plays a regulatory role in glycoprotein VI (GPVI)/Fc receptor gamma (FcRgamma)-chain-dependent platelet activation through its interaction with Syk.
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Affiliation(s)
- Carol A Dangelmaier
- Department of Pharmacology, Temple University School of Medicine, 3420 N Broad St, Philadelphia, PA 19140, USA
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