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Deguchi H, Morla S, Griffin JH. Novel blood coagulation molecules: Skeletal muscle myosin and cardiac myosin. J Thromb Haemost 2021; 19:7-19. [PMID: 32920971 PMCID: PMC7819347 DOI: 10.1111/jth.15097] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/29/2020] [Revised: 09/03/2020] [Accepted: 09/03/2020] [Indexed: 12/21/2022]
Abstract
Essentials Striated muscle myosins can promote prothrombin activation by FXa or FVa inactivation by APC. Cardiac myosin and skeletal muscle myosin are pro-hemostatic in murine tail cut bleeding models. Infused cardiac myosin exacerbates myocardial injury caused by myocardial ischemia reperfusion. Skeletal muscle myosin isoforms that circulate in human plasma can be grouped into 3 phenotypes. ABSTRACT: Two striated muscle myosins, namely skeletal muscle myosin (SkM) and cardiac myosin (CM), may potentially contribute to physiologic mechanisms for regulation of thrombosis and hemostasis. Thrombin is generated from activation of prothrombin by the prothrombinase (IIase) complex comprising factor Xa, factor Va, and Ca++ ions located on surfaces where these factors are assembled. We discovered that SkM and CM, which are abundant motor proteins in skeletal and cardiac muscles, can provide a surface for thrombin generation by the prothrombinase complex without any apparent requirement for phosphatidylserine or lipids. These myosins can also provide a surface that supports the inactivation of factor Va by activated protein C/protein S, resulting in negative feedback downregulation of thrombin generation. Although the physiologic significance of these reactions remains to be established for humans, substantive insights may be gleaned from murine studies. In mice, exogenously infused SkM and CM can promote hemostasis as they are capable of reducing tail cut bleeding. In a murine myocardial ischemia-reperfusion injury model, exogenously infused CM exacerbates myocardial infarction damage. Studies of human plasmas show that SkM antigen isoforms of different MWs circulate in human plasma, and they can be used to identify three plasma SkM phenotypes. A pilot clinical study showed that one SkM isoform pattern appeared to be linked to isolated pulmonary embolism. These discoveries enable multiple preclinical and clinical studies of SkM and CM, which should provide novel mechanistic insights with potential translational relevance for the roles of CM and SkM in the pathobiology of hemostasis and thrombosis.
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Affiliation(s)
- Hiroshi Deguchi
- Department of Molecular Medicine, The Scripps Research Institute, La Jolla, CA, USA
| | - Shravan Morla
- Department of Molecular Medicine, The Scripps Research Institute, La Jolla, CA, USA
| | - John H Griffin
- Department of Molecular Medicine, The Scripps Research Institute, La Jolla, CA, USA
- Division of Hematology, Department of Medicine, University of California, San Diego, CA, USA
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Deguchi TK, Deguchi H, Guo Z, Elias DJ, Griffin JH. Plasma skeletal muscle myosin phenotypes identified by immunoblotting are associated with pulmonary embolism occurrence in young adults. Thromb Res 2020; 189:88-92. [PMID: 32192996 DOI: 10.1016/j.thromres.2020.02.020] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/03/2019] [Revised: 02/05/2020] [Accepted: 02/26/2020] [Indexed: 11/18/2022]
Abstract
BACKGROUND Purified skeletal muscle myosin (SkM) binds factor Xa and is procoagulant. The molecular forms of SkM in human plasma have not been characterized. METHOD Human plasma SkM heavy chain (HC) isoforms of different molecular weights were detected by a newly developed immunoblotting protocol. In this pilot study, the distribution of SkM HC antigen isoforms in plasmas of healthy subjects and young adult patients with venous thrombosis was analyzed. RESULTS Multiple SkM HC antigen bands were detected in human plasmas, corresponding to full-length SkM HC, heavy meromyosin, or the S1 fragment. Plasma immunoblots of healthy subjects displayed three major phenotypes: Type I with two primary bands for full-length SkM and heavy meromyosin, and two lesser bands including S1 fragment (54%); Type II with bands primarily for full-length SkM HC (34%); and Type III with only a band for the S1 fragment (12%). Plasma SkM HC antigen Type II phenotype was associated with an increased occurrence of isolated pulmonary embolism in younger patients, respectively (≤50 years old). CONCLUSIONS Three SkM HC antigen phenotypes were identified in human plasma by immunoblotting, and Type II phenotype was correlated with the occurrence of isolated pulmonary embolisms in younger patients.
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Affiliation(s)
- Taichi K Deguchi
- Department of Molecular Medicine, The Scripps Research Institute, 10550 North Torrey Pines Rd, La Jolla, CA, USA
| | - Hiroshi Deguchi
- Department of Molecular Medicine, The Scripps Research Institute, 10550 North Torrey Pines Rd, La Jolla, CA, USA.
| | - Zihan Guo
- Department of Molecular Medicine, The Scripps Research Institute, 10550 North Torrey Pines Rd, La Jolla, CA, USA
| | - Darlene J Elias
- Department of Molecular Medicine, The Scripps Research Institute, 10550 North Torrey Pines Rd, La Jolla, CA, USA; Scripps Clinic and Scripps Green Hospital, La Jolla, CA, USA
| | - John H Griffin
- Department of Molecular Medicine, The Scripps Research Institute, 10550 North Torrey Pines Rd, La Jolla, CA, USA; Division of Hematology, Department of Medicine, University of California, San Diego, CA, USA
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Zilberman-Rudenko J, Deguchi H, Shukla M, Oyama Y, Orje JN, Guo Z, Wyseure T, Mosnier LO, McCarty OJT, Ruggeri ZM, Eckle T, Griffin JH. Cardiac Myosin Promotes Thrombin Generation and Coagulation In Vitro and In Vivo. Arterioscler Thromb Vasc Biol 2020; 40:901-913. [PMID: 32102568 DOI: 10.1161/atvbaha.120.313990] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
OBJECTIVE Cardiac myosin (CM) is structurally similar to skeletal muscle myosin, which has procoagulant activity. Here, we evaluated CM's ex vivo, in vivo, and in vitro activities related to hemostasis and thrombosis. Approach and Results: Perfusion of fresh human blood over CM-coated surfaces caused thrombus formation and fibrin deposition. Addition of CM to blood passing over collagen-coated surfaces enhanced fibrin formation. In a murine ischemia/reperfusion injury model, exogenous CM, when administered intravenously, augmented myocardial infarction and troponin I release. In hemophilia A mice, intravenously administered CM reduced tail-cut-initiated bleeding. These data provide proof of concept for CM's in vivo procoagulant properties. In vitro studies clarified some mechanisms for CM's procoagulant properties. Thrombin generation assays showed that CM, like skeletal muscle myosin, enhanced thrombin generation in human platelet-rich and platelet-poor plasmas and also in mixtures of purified factors Xa, Va, and prothrombin. Binding studies showed that CM, like skeletal muscle myosin, directly binds factor Xa, supporting the concept that the CM surface is a site for prothrombinase assembly. In tPA (tissue-type plasminogen activator)-induced plasma clot lysis assays, CM was antifibrinolytic due to robust CM-dependent thrombin generation that enhanced activation of TAFI (thrombin activatable fibrinolysis inhibitor). CONCLUSIONS CM in vitro is procoagulant and prothrombotic. CM in vivo can augment myocardial damage and can be prohemostatic in the presence of bleeding. CM's procoagulant and antifibrinolytic activities likely involve, at least in part, its ability to bind factor Xa and enhance thrombin generation. Future work is needed to clarify CM's pathophysiology and its mechanistic influences on hemostasis or thrombosis.
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Affiliation(s)
- Jevgenia Zilberman-Rudenko
- From the Department of Molecular Medicine, The Scripps Research Institute, La Jolla, CA (J.Z.-R., H.D., M.S., J.N.O., Z.G., T.W., L.O.M., Z.M.R., J.H.G.).,Department of Biomedical Engineering (J.Z.-R., O.J.T.M.), School of Medicine, Oregon Health & Science University, Portland
| | - Hiroshi Deguchi
- From the Department of Molecular Medicine, The Scripps Research Institute, La Jolla, CA (J.Z.-R., H.D., M.S., J.N.O., Z.G., T.W., L.O.M., Z.M.R., J.H.G.)
| | - Meenal Shukla
- From the Department of Molecular Medicine, The Scripps Research Institute, La Jolla, CA (J.Z.-R., H.D., M.S., J.N.O., Z.G., T.W., L.O.M., Z.M.R., J.H.G.)
| | - Yoshimasa Oyama
- Department of Hematology-Oncology (O.J.T.M.), School of Medicine, Oregon Health & Science University, Portland
| | - Jennifer N Orje
- From the Department of Molecular Medicine, The Scripps Research Institute, La Jolla, CA (J.Z.-R., H.D., M.S., J.N.O., Z.G., T.W., L.O.M., Z.M.R., J.H.G.)
| | - Zihan Guo
- From the Department of Molecular Medicine, The Scripps Research Institute, La Jolla, CA (J.Z.-R., H.D., M.S., J.N.O., Z.G., T.W., L.O.M., Z.M.R., J.H.G.)
| | - Tine Wyseure
- From the Department of Molecular Medicine, The Scripps Research Institute, La Jolla, CA (J.Z.-R., H.D., M.S., J.N.O., Z.G., T.W., L.O.M., Z.M.R., J.H.G.)
| | - Laurent O Mosnier
- From the Department of Molecular Medicine, The Scripps Research Institute, La Jolla, CA (J.Z.-R., H.D., M.S., J.N.O., Z.G., T.W., L.O.M., Z.M.R., J.H.G.)
| | - Owen J T McCarty
- Department of Biomedical Engineering (J.Z.-R., O.J.T.M.), School of Medicine, Oregon Health & Science University, Portland
| | - Zaverio M Ruggeri
- From the Department of Molecular Medicine, The Scripps Research Institute, La Jolla, CA (J.Z.-R., H.D., M.S., J.N.O., Z.G., T.W., L.O.M., Z.M.R., J.H.G.)
| | - Tobias Eckle
- Department of Hematology-Oncology (O.J.T.M.), School of Medicine, Oregon Health & Science University, Portland
| | - John H Griffin
- From the Department of Molecular Medicine, The Scripps Research Institute, La Jolla, CA (J.Z.-R., H.D., M.S., J.N.O., Z.G., T.W., L.O.M., Z.M.R., J.H.G.).,Department of Anesthesiology, University of Colorado School of Medicine, Aurora (Y.O., T.E.)
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Borg RJ, Samson AL, Au AEL, Scholzen A, Fuchsberger M, Kong YY, Freeman R, Mifsud NA, Plebanski M, Medcalf RL. Dendritic Cell-Mediated Phagocytosis but Not Immune Activation Is Enhanced by Plasmin. PLoS One 2015; 10:e0131216. [PMID: 26132730 PMCID: PMC4488505 DOI: 10.1371/journal.pone.0131216] [Citation(s) in RCA: 37] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/10/2015] [Accepted: 05/29/2015] [Indexed: 12/31/2022] Open
Abstract
Removal of dead cells in the absence of concomitant immune stimulation is essential for tissue homeostasis. We recently identified an injury-induced protein misfolding event that orchestrates the plasmin-dependent proteolytic degradation of necrotic cells. As impaired clearance of dead cells by the innate immune system predisposes to autoimmunity, we determined whether plasmin could influence endocytosis and immune cell stimulation by dendritic cells – a critical cell that links the innate and adaptive immune systems. We find that plasmin generated on the surface of necrotic cells enhances their phagocytic removal by human monocyte-derived dendritic cells. Plasmin also promoted phagocytosis of protease-resistant microparticles by diverse mouse dendritic cell sub-types both in vitro and in vivo. Together with an increased phagocytic capacity, plasmin-treated dendritic cells maintain an immature phenotype, exhibit reduced migration to lymph nodes, increase their expression/release of the immunosuppressive cytokine TGF-β, and lose their capacity to mount an allogeneic response. Collectively, our findings support a novel role for plasmin formed on dead cells and other phagocytic targets in maintaining tissue homeostasis by increasing the phagocytic function of dendritic cells while simultaneously decreasing their immunostimulatory capacity consistent with producing an immunosuppressive state.
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Affiliation(s)
- Rachael J. Borg
- Australian Centre for Blood Diseases, Monash University, Alfred Medical Research and Education Precinct, Melbourne, 3004, Victoria Australia
| | - Andre L. Samson
- Australian Centre for Blood Diseases, Monash University, Alfred Medical Research and Education Precinct, Melbourne, 3004, Victoria Australia
- Department of Biochemistry and Molecular Biology, Monash University, Clayton, 3181, Australia
| | - Amanda E.-L. Au
- Australian Centre for Blood Diseases, Monash University, Alfred Medical Research and Education Precinct, Melbourne, 3004, Victoria Australia
| | - Anja Scholzen
- Department of Immunology, Monash University, Alfred Medical Research and Education Precinct, Melbourne, 3004, Victoria, Australia
| | - Martina Fuchsberger
- Department of Immunology, Monash University, Alfred Medical Research and Education Precinct, Melbourne, 3004, Victoria, Australia
| | - Ying Y. Kong
- Department of Immunology, Monash University, Alfred Medical Research and Education Precinct, Melbourne, 3004, Victoria, Australia
| | - Roxann Freeman
- Australian Centre for Blood Diseases, Monash University, Alfred Medical Research and Education Precinct, Melbourne, 3004, Victoria Australia
| | - Nicole A. Mifsud
- Department of Medicine, Monash University, Alfred Medical Research and Education Precinct, Melbourne, 3004, Victoria, Australia
- Department of Allergy, Immunology and Respiratory Medicine, Alfred Medical Research and Education Precinct, Melbourne, 3004, Victoria, Australia
| | - Magdalena Plebanski
- Department of Immunology, Monash University, Alfred Medical Research and Education Precinct, Melbourne, 3004, Victoria, Australia
| | - Robert L. Medcalf
- Australian Centre for Blood Diseases, Monash University, Alfred Medical Research and Education Precinct, Melbourne, 3004, Victoria Australia
- * E-mail:
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Tuffy KM, Planey SL. Cytoskeleton-Associated Protein 4: Functions Beyond the Endoplasmic Reticulum in Physiology and Disease. ACTA ACUST UNITED AC 2012. [DOI: 10.5402/2012/142313] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
Cytoskeleton-associated protein 4 (CKAP4; also known as p63, CLIMP-63, or ERGIC-63) is a 63 kDa, reversibly palmitoylated and phosphorylated, type II transmembrane (TM) protein, originally identified as a resident of the endoplasmic reticulum (ER)/Golgi intermediate compartment (ERGIC). When localized to the ER, a major function of CKAP4 is to anchor rough ER to microtubules, organizing the overall structure of ER with respect to the microtubule network. There is also steadily accumulating evidence for diverse roles for CKAP4 localized outside the ER, including data demonstrating functionality of cell surface forms of CKAP4 in various cell types and of CKAP4 in the nucleus. We will review the recent studies that provide evidence for the existence of CKAP4 in multiple cellular compartments (i.e., ER, plasma membrane, and the nucleus) and discuss CKAP4’s role in the regulation of various physiological and pathological processes, such as interstitial cystitis, drug-induced cytotoxicity, pericullar proteolytic activity, and lung lipid homeostasis.
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Affiliation(s)
- Kevin M. Tuffy
- Department of Basic Sciences, The Commonwealth Medical College, Scranton, PA 18509, USA
| | - Sonia Lobo Planey
- Department of Basic Sciences, The Commonwealth Medical College, Scranton, PA 18509, USA
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Gebbink MFBG. Tissue-type plasminogen activator-mediated plasminogen activation and contact activation, implications in and beyond haemostasis. J Thromb Haemost 2011; 9 Suppl 1:174-81. [PMID: 21781253 DOI: 10.1111/j.1538-7836.2011.04278.x] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
Abstract
Due to its discovery as initiator of fibrinolysis and its well-studied activation by fibrin, tissue-type plasminogen activator (tPA) and the fibrinolytic system are generally associated with the dissolution of blood clots. However, it has been demonstrated over the years that (i) tPA can be activated by multiple proteins, (ii) plasmin has many substrates other than fibrin and (iii) tPA and plasmin have biological functions independent of fibrin and distinct from their role in blood clot lysis. We here review the data with respect to the activation of tPA by fibrin and its multiple other cofactors, in relation to tPA's role in pathophysiology, notably fibrinolysis and amyloidosis, with emphasis on Alzheimer's disease. We demonstrate a common structural element, termed cross-β structure, in misfolded proteins that is causal to tPA activation. The implications for protein misfolding diseases that are known to be associated with the deposition of amyloid and for diseases for which this has not (yet) been established are discussed.
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Affiliation(s)
- M F B G Gebbink
- Crossbeta Biosciences BV, Utrecht Department of Clinical Chemistry and Haematology, University Medical Center Utrecht, Utrecht, the Netherlands.
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Longstaff C, Thelwell C. Understanding the enzymology of fibrinolysis and improving thrombolytic therapy. FEBS Lett 2005; 579:3303-9. [PMID: 15943975 DOI: 10.1016/j.febslet.2005.03.058] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 03/17/2005] [Indexed: 11/29/2022]
Abstract
Cardiovascular disease is responsible for 17 million deaths per year but acute myocardial infarction and stroke can be treated with thrombolytics ("clot busters"), which are plasminogen activators. However, despite many years of study and huge investment from the pharmaceutical industry, clinical trials of new drugs have often been disappointing. Part of the problem may be our incomplete understanding of the regulation of plasminogen activation in vivo. We have developed precise in vitro methods and with the application of computer simulations, we hope to improve our understanding of plasminogen activation to facilitate improvements in thrombolytic therapy.
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Affiliation(s)
- Colin Longstaff
- Division of Haematology, National Institute for Biological Standards and Control, South Mimms, Herts, EN6 3QG, UK.
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Razzaq TM, Bass R, Vines DJ, Werner F, Whawell SA, Ellis V. Functional regulation of tissue plasminogen activator on the surface of vascular smooth muscle cells by the type-II transmembrane protein p63 (CKAP4). J Biol Chem 2003; 278:42679-85. [PMID: 12913003 DOI: 10.1074/jbc.m305695200] [Citation(s) in RCA: 48] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
We have demonstrated that tissue plasminogen activator (tPA) binds specifically to human vascular smooth muscle cells (VSMC) in a functionally relevant manner, both increasing plasminogen activation and decreasing tPA inhibition (Ellis, V., and Whawell, S. A. (1997) Blood 90, 2312-2322; Werner, F., Razzaq, T. M., and Ellis, V. (1999) J. Biol. Chem. 274, 21555-21561). To further understand this system we have now identified and characterized the protein responsible for this binding. Rat VSMC were surface-labeled with 125I, and cell lysates were subjected to an affinity chromatography scheme based on the previously identified tPA binding characteristics. A single radiolabeled protein of 63 kDa bound specifically and was eluted at low pH. This protein was isolated from large scale preparations of VSMC and unambiguously identified as the rat homologue of the human type-II transmembrane protein p63 (CKAP4) by matrix-assisted laser desorption ionization and nano-electrospray tandem mass spectrometry of tryptic fragments. In confirmation of this, a monoclonal antibody raised against authentic human p63 recognized the isolated protein in Western blotting. Immunofluorescence microscopy demonstrated that p63 was located principally in the endoplasmic reticulum but was also detected in significant quantities on the surface of human VSMC. In support of the hypothesis that p63 is the functional tPA binding site on VSMC, an anti-p63 monoclonal antibody was found to block tPA binding. Furthermore, heterologous expression of an N-terminally truncated mutant of p63, which targets exclusively to the plasma membrane, led to an increase in tPA-catalyzed plasminogen activation. Therefore, p63 on the surface of VSMC may contribute to the functional regulation of the plasminogen activation system in the vessel wall.
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Affiliation(s)
- Tahir M Razzaq
- School of Biological Sciences, University of East Anglia, Norwich NR4 7TJ, United Kingdom
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Kolev K, Tenekedjiev K, Ajtai K, Kovalszky I, Gombas J, Váradi B, Machovich R. Myosin: a noncovalent stabilizer of fibrin in the process of clot dissolution. Blood 2003; 101:4380-6. [PMID: 12543859 DOI: 10.1182/blood-2002-10-3227] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Myosin modulates the fibrinolytic process as a cofactor of the tissue plasminogen activator and as a substrate of plasmin. We report now that myosin is present in arterial thrombi and it forms reversible noncovalent complexes with fibrinogen and fibrin with equilibrium dissociation constants in the micromolar range (1.70 and 0.94 microM, respectively). Competition studies using a peptide inhibitor of fibrin polymerization (glycl-prolyl-arginyl-proline [GPRP]) indicate that myosin interacts with domains common in fibrinogen and fibrin and this interaction is independent of the GPRP-binding polymerization site in the fibrinogen molecule. An association rate constant of 1.81 x 10(2) M(-1) x s(-1) and a dissociation rate constant of 3.07 x 10(-4) s(-1) are determined for the fibrinogen-myosin interaction. Surface plasmon resonance studies indicate that fibrin serves as a matrix core for myosin aggregation. The fibrin clots equilibrated with myosin are stabilized against dissolution initiated by plasminogen and tissue-type plasminogen activator (tPA) or urokinase (at fibrin monomer-myosin molar ratio as high as 30) and by plasmin under static and flow conditions (at fibrin monomer-myosin molar ratio lower than 15). Myosin exerts similar effects on the tPA-induced dissolution of blood plasma clots. Covalent modification involving factor XIIIa does not contribute to this stabilizing effect; myosin is not covalently attached to the clot by the time of complete cross-linking of fibrin. Thus, our in vitro data suggest that myosin detected in arterial thrombi binds to the polymerized fibrin, in the bound form its tPA-cofactor properties are masked, and the myosin fibrin clot is relatively resistant to plasmin.
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Affiliation(s)
- Krasimir Kolev
- Department of Medical Biochemistry, Semmelweis University, Budapest, Hungary
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Machovich R, Komorowicz E, Kolev K, Owen WG. Facilitation of plasminogen activation by denatured prothrombin. Thromb Res 1999; 94:389-94. [PMID: 10390134 DOI: 10.1016/s0049-3848(99)00003-1] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/17/2022]
Affiliation(s)
- R Machovich
- Semmelweis University of Medicine, Department of Medical Biochemistry, Budapest, Hungary
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Abstract
Activation of covalently intact plasminogen by tissue-type plasminogen activator (tPA) is facilitated by a majority of proteins subjected to denaturing conditions. Except for heat-denatured apoferritin, the denatured proteins examined require partial proteolysis by plasmin for cofactor activity. The same proteins in their native state are resistant to proteolysis with plasmin and develop no activity. Denatured preparations of apoferritin, antithrombin, alpha1-protease inhibitor, alpha2-macroglobulin, and albumin also accelerate des(1-77)-plasminogen activation by tPA. The rate enhancements are comparable with that of the fibrin(ogen) fragments on a w/w basis. The cofactor activities are inhibited by 6-aminohexanoate and inactivated by pepsin. Analysis of heat-denatured apoferritin and albumin preparations by ultracentrifugation and gel chromatography indicates that cofactor is associated predominately with aggregates, which have binding capacity for both tPA and zymogen. Heat-denatured albumin pretreated with plasmin decreases K(M) and increases k(cat) for both intact plasminogen and des(1-77)-plasminogen activation by tPA, yielding catalytic efficiencies in excess of 8 x 10(3) M(-1) s(-1) and 2 x 10(4) M(-1) s(-1), respectively. Because of enhanced plasmin-catalyzed proteolysis of plasminogen to des(1-77)-plasminogen, activation by urokinase-type plasminogen activator is also facilitated by denatured proteins; activation of des(1-77)-plasminogen is not affected. It is concluded that denatured proteins serve as both cofactors and substrates in the fibrinolytic system, and that enhancement of plasminogen activation by denatured proteins is mechanistically indistinguishable from that observed with fibrin.
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Affiliation(s)
- R Machovich
- Department of Biochemistry and Molecular Biology, Mayo Clinic and Foundation, Rochester, Minnesota 55905, USA
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