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Brinkman HJM, Ahnström J, Castoldi E, Dahlbäck B, Marlar RA. Pleiotropic anticoagulant functions of protein S, consequences for the clinical laboratory. Communication from the SSC of the ISTH. J Thromb Haemost 2021; 19:281-286. [PMID: 33405384 DOI: 10.1111/jth.15108] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/05/2020] [Revised: 08/28/2020] [Accepted: 09/15/2020] [Indexed: 02/04/2023]
Abstract
Hereditary deficiencies of protein S (PS) increase the risk of thrombosis. However, assessing the plasma levels of PS is complicated by its manifold physiological interactions, while the large inter-individual variability makes it problematic to establish reliable cut-off values. PS has multiple physiological functions, with only two appearing to have significant anticoagulant properties: the activated protein C (APC) and tissue factor pathway inhibitor alpha (TFPIα) cofactor activities. Current clinical laboratory investigations for deficiency in PS function rely only on the APC-dependent activity. This communication presents an argument for reclassifying the qualitative PS deficiencies to differentiate the two major anticoagulant functions of PS. Reliable assays are necessary for accurate evaluation of PS function when making a specific diagnosis of PS deficiency based on the anticoagulant phenotype alone. This report emphasizes the pleiotropic anticoagulant functions of PS and presents evidence-based recommendations for their implementation in the clinical laboratory.
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Affiliation(s)
- Herm Jan M Brinkman
- Department of Molecular and Cellular Hemostasis, Sanquin Research, Amsterdam, the Netherlands
| | | | - Elisabetta Castoldi
- Department of Biochemistry, Cardiovascular Research Institute Maastricht (CARIM), Maastricht University, the Netherlands
| | - Björn Dahlbäck
- Department of Translational Medicine, Lund University, Malmō, Sweden
| | - Richard A Marlar
- Department of Pathology, University of New Mexico, TriCore Reference Laboratories, Albuquerque, NM, USA
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2
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Post-transcriptional, post-translational and pharmacological regulation of tissue factor pathway inhibitor. Blood Coagul Fibrinolysis 2018; 29:668-682. [PMID: 30439766 DOI: 10.1097/mbc.0000000000000775] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
: Tissue factor (TF) pathway inhibitor (TFPI) is an endogenous natural anticoagulant that readily inhibits the extrinsic coagulation initiation complex (TF-FVIIa-Xa) and prothrombinase (FXa, FVa and calcium ions). Alternatively, spliced TFPI isoforms (α, β and δ) are expressed by vascular and extravascular cells and regulate thrombosis and haemostasis, as well as cell signalling functions of TF complexes via protease-activated receptors (PARs). Proteolysis of TFPI plays an important role in regulating physiological roles of the TF pathway in host defense and possibly haemostasis. Elimination of TFPI inhibition has therefore been proposed as an approach to improve haemostasis in haemophilia patients. In this review, we focus on posttranscription and translational modification of TFPI and its function in thrombosis and how pharmacological inhibitors and endogenous proteases interfere with TFPI and alter haemostasis.
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3
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Plautz WE, Sekhar Pilli VS, Cooley BC, Chattopadhyay R, Westmark PR, Getz T, Paul D, Bergmeier W, Sheehan JP, Majumder R. Anticoagulant Protein S Targets the Factor IXa Heparin-Binding Exosite to Prevent Thrombosis. Arterioscler Thromb Vasc Biol 2018; 38:816-828. [PMID: 29419409 DOI: 10.1161/atvbaha.117.310588] [Citation(s) in RCA: 22] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/19/2017] [Accepted: 01/16/2018] [Indexed: 01/20/2023]
Abstract
OBJECTIVE PS (protein S) is a plasma protein that directly inhibits the coagulation FIXa (factor IXa) in vitro. Because elevated FIXa is associated with increased risk of venous thromboembolism, it is important to establish how PS inhibits FIXa function in vivo. The goal of this study is to confirm direct binding of PS with FIXa in vivo, identify FIXa amino acid residues required for binding PS in vivo, and use an enzymatically active FIXa mutant that is unable to bind PS to measure the significance of PS-FIXa interaction in hemostasis. APPROACH AND RESULTS We demonstrate that PS inhibits FIXa in vivo by associating with the FIXa heparin-binding exosite. We used fluorescence tagging, immunohistochemistry, and protein-protein crosslinking to show in vivo interaction between FIXa and PS. Importantly, platelet colocalization required a direct interaction between the 2 proteins. FIXa and PS also coimmunoprecipitated from plasma, substantiating their interaction in a physiological milieu. PS binding to FIXa and PS inhibition of the intrinsic Xase complex required residues K132, K126, and R170 in the FIXa heparin-binding exosite. A double mutant, K132A/R170A, retained full activity but could not bind to PS. Crucially, Hemophilia B mice infused with FIXa K132A/R170A displayed an accelerated rate of fibrin clot formation compared with wild-type FIXa. CONCLUSIONS Our findings establish PS as an important in vivo inhibitor of FIXa. Disruption of the interaction between PS and FIXa causes an increased rate of thrombus formation in mice. This newly discovered function of PS implies an unexploited target for antithrombotic therapeutics.
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Affiliation(s)
- William E Plautz
- From the Department of Biochemistry and Molecular Biology, Louisiana State University Health Sciences Center, New Orleans (W.E.P., V.S.S.P., R.C., R.M.); Department of Biochemistry and Biophysics, University of North Carolina, Chapel Hill (B.C.C., T.G., D.P., W.B.); and Department of Medicine/Hematology-Oncology, University of Wisconsin School of Medicine and Public Health, Madison (P.R.W., J.P.S.)
| | - Vijaya Satish Sekhar Pilli
- From the Department of Biochemistry and Molecular Biology, Louisiana State University Health Sciences Center, New Orleans (W.E.P., V.S.S.P., R.C., R.M.); Department of Biochemistry and Biophysics, University of North Carolina, Chapel Hill (B.C.C., T.G., D.P., W.B.); and Department of Medicine/Hematology-Oncology, University of Wisconsin School of Medicine and Public Health, Madison (P.R.W., J.P.S.)
| | - Brian C Cooley
- From the Department of Biochemistry and Molecular Biology, Louisiana State University Health Sciences Center, New Orleans (W.E.P., V.S.S.P., R.C., R.M.); Department of Biochemistry and Biophysics, University of North Carolina, Chapel Hill (B.C.C., T.G., D.P., W.B.); and Department of Medicine/Hematology-Oncology, University of Wisconsin School of Medicine and Public Health, Madison (P.R.W., J.P.S.)
| | - Rima Chattopadhyay
- From the Department of Biochemistry and Molecular Biology, Louisiana State University Health Sciences Center, New Orleans (W.E.P., V.S.S.P., R.C., R.M.); Department of Biochemistry and Biophysics, University of North Carolina, Chapel Hill (B.C.C., T.G., D.P., W.B.); and Department of Medicine/Hematology-Oncology, University of Wisconsin School of Medicine and Public Health, Madison (P.R.W., J.P.S.)
| | - Pamela R Westmark
- From the Department of Biochemistry and Molecular Biology, Louisiana State University Health Sciences Center, New Orleans (W.E.P., V.S.S.P., R.C., R.M.); Department of Biochemistry and Biophysics, University of North Carolina, Chapel Hill (B.C.C., T.G., D.P., W.B.); and Department of Medicine/Hematology-Oncology, University of Wisconsin School of Medicine and Public Health, Madison (P.R.W., J.P.S.)
| | - Todd Getz
- From the Department of Biochemistry and Molecular Biology, Louisiana State University Health Sciences Center, New Orleans (W.E.P., V.S.S.P., R.C., R.M.); Department of Biochemistry and Biophysics, University of North Carolina, Chapel Hill (B.C.C., T.G., D.P., W.B.); and Department of Medicine/Hematology-Oncology, University of Wisconsin School of Medicine and Public Health, Madison (P.R.W., J.P.S.)
| | - David Paul
- From the Department of Biochemistry and Molecular Biology, Louisiana State University Health Sciences Center, New Orleans (W.E.P., V.S.S.P., R.C., R.M.); Department of Biochemistry and Biophysics, University of North Carolina, Chapel Hill (B.C.C., T.G., D.P., W.B.); and Department of Medicine/Hematology-Oncology, University of Wisconsin School of Medicine and Public Health, Madison (P.R.W., J.P.S.)
| | - Wolfgang Bergmeier
- From the Department of Biochemistry and Molecular Biology, Louisiana State University Health Sciences Center, New Orleans (W.E.P., V.S.S.P., R.C., R.M.); Department of Biochemistry and Biophysics, University of North Carolina, Chapel Hill (B.C.C., T.G., D.P., W.B.); and Department of Medicine/Hematology-Oncology, University of Wisconsin School of Medicine and Public Health, Madison (P.R.W., J.P.S.)
| | - John P Sheehan
- From the Department of Biochemistry and Molecular Biology, Louisiana State University Health Sciences Center, New Orleans (W.E.P., V.S.S.P., R.C., R.M.); Department of Biochemistry and Biophysics, University of North Carolina, Chapel Hill (B.C.C., T.G., D.P., W.B.); and Department of Medicine/Hematology-Oncology, University of Wisconsin School of Medicine and Public Health, Madison (P.R.W., J.P.S.)
| | - Rinku Majumder
- From the Department of Biochemistry and Molecular Biology, Louisiana State University Health Sciences Center, New Orleans (W.E.P., V.S.S.P., R.C., R.M.); Department of Biochemistry and Biophysics, University of North Carolina, Chapel Hill (B.C.C., T.G., D.P., W.B.); and Department of Medicine/Hematology-Oncology, University of Wisconsin School of Medicine and Public Health, Madison (P.R.W., J.P.S.).
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4
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Tanratana P, Ellery P, Westmark P, Mast AE, Sheehan JP. Elevated Plasma Factor IXa Activity in Premenopausal Women on Hormonal Contraception. Arterioscler Thromb Vasc Biol 2017; 38:266-274. [PMID: 29097362 DOI: 10.1161/atvbaha.117.309919] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/17/2017] [Accepted: 10/12/2017] [Indexed: 01/30/2023]
Abstract
OBJECTIVE Combined oral contraceptives induce a reversible hypercoagulable state with an enhanced risk of venous thromboembolism, but the underlying mechanism(s) remain unclear. Subjects on combined oral contraceptives also demonstrate a characteristic resistance to APC (activated protein C) in the thrombin generation assay. Here, we report the potential role of plasma factor IXa (FIXa) as a mechanism for hormone-induced systemic hypercoagulability. APPROACH AND RESULTS A novel assay was used to determine FIXa activity in plasma samples from volunteer blood donors. Plasma from 36 premenopausal females on hormonal contraception and 35 not on hormonal contraception, 35 postmenopausal females, and 10 males were analyzed for FIXa activity, total PS (protein S), total tissue factor pathway inhibitor (TFPI), and TFPI-α antigen. Premenopausal females on hormonal contraception demonstrated significantly increased FIXa activity and decreased TFPI-α compared with the other groups. Remarkably, FIXa values were not normally distributed in the hormonal contraception group, but skewed toward the high end. Plasma FIXa activity inversely correlated with both TFPI-α and total PS antigen. Ex vivo determination of TF-dependent FIX activation in FV-deficient plasma demonstrated that inhibitory anti-TFPI antibodies enhanced FIXa generation by 2- to 3-fold, whereas addition of 75 nmol/L PS reduced FIXa generation by ≈2-fold. Further, increasing FIXa concentration enhanced APC resistance during TF-triggered plasma thrombin generation. CONCLUSIONS Elevation of plasma FIXa activity in association with reductions in TFPI-α and PS is a potential mechanism for systemic hypercoagulability and resistance to APC in premenopausal females on hormonal contraception.
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Affiliation(s)
- Pansakorn Tanratana
- From the Department of Pathology and Laboratory Medicine (P.T.), Department of Medicine/Hematology-Oncology (P.W., J.P.S.), University of Wisconsin School of Medicine and Public Health, Madison; Department of Pharmacology, Faculty of Science, Mahidol University, Bangkok, Thailand (P.T.); Blood Research Institute, Blood Center of Wisconsin, Milwaukee (P.E., A.E.M.); and School of Biomedical Sciences, Curtin University, Perth, Western Australia, Australia (P.E.)
| | - Paul Ellery
- From the Department of Pathology and Laboratory Medicine (P.T.), Department of Medicine/Hematology-Oncology (P.W., J.P.S.), University of Wisconsin School of Medicine and Public Health, Madison; Department of Pharmacology, Faculty of Science, Mahidol University, Bangkok, Thailand (P.T.); Blood Research Institute, Blood Center of Wisconsin, Milwaukee (P.E., A.E.M.); and School of Biomedical Sciences, Curtin University, Perth, Western Australia, Australia (P.E.)
| | - Pamela Westmark
- From the Department of Pathology and Laboratory Medicine (P.T.), Department of Medicine/Hematology-Oncology (P.W., J.P.S.), University of Wisconsin School of Medicine and Public Health, Madison; Department of Pharmacology, Faculty of Science, Mahidol University, Bangkok, Thailand (P.T.); Blood Research Institute, Blood Center of Wisconsin, Milwaukee (P.E., A.E.M.); and School of Biomedical Sciences, Curtin University, Perth, Western Australia, Australia (P.E.)
| | - Alan E Mast
- From the Department of Pathology and Laboratory Medicine (P.T.), Department of Medicine/Hematology-Oncology (P.W., J.P.S.), University of Wisconsin School of Medicine and Public Health, Madison; Department of Pharmacology, Faculty of Science, Mahidol University, Bangkok, Thailand (P.T.); Blood Research Institute, Blood Center of Wisconsin, Milwaukee (P.E., A.E.M.); and School of Biomedical Sciences, Curtin University, Perth, Western Australia, Australia (P.E.)
| | - John P Sheehan
- From the Department of Pathology and Laboratory Medicine (P.T.), Department of Medicine/Hematology-Oncology (P.W., J.P.S.), University of Wisconsin School of Medicine and Public Health, Madison; Department of Pharmacology, Faculty of Science, Mahidol University, Bangkok, Thailand (P.T.); Blood Research Institute, Blood Center of Wisconsin, Milwaukee (P.E., A.E.M.); and School of Biomedical Sciences, Curtin University, Perth, Western Australia, Australia (P.E.).
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5
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Peraramelli S, Thomassen S, Heinzmann A, Rosing J, Hackeng TM, Hartmann R, Scheiflinger F, Dockal M. Inhibition of tissue factor:factor VIIa-catalyzed factor IX and factor X activation by TFPI and TFPI constructs. J Thromb Haemost 2014; 12:1826-37. [PMID: 25163770 DOI: 10.1111/jth.12713] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/04/2014] [Indexed: 11/29/2022]
Abstract
BACKGROUND TFPI is a Kunitz-type protease inhibitor that downregulates the extrinsic coagulation pathway by inhibiting factor Xa (FXa) and FVIIa. All three Kunitz domains (KD1, KD2, and KD3) and protein S are required for optimal inhibition of FXa and FVIIa. There is limited information on Kunitz domain requirements of the inhibition of TF:FVIIa-catalyzed FIX and FX activation by TFPI. AIM To investigate the role of the Kunitz domains of TFPI and protein S in the inhibition of FX and FIX activation. METHODS Inhibition of TF:FVIIa-catalyzed FX and FIX activation by full-length TFPI (TFPIFL ) and TFPI constructs was quantified from progress curves of FXa and FIXa generation measured with chromogenic substrates. RESULTS AND CONCLUSIONS TFPIFL inhibited TF:FVIIa-catalyzed FIX activation with a Ki of 16.7 nmol L(-1) . Protein S reduced the Ki to 1.0 nmol L(-1) . TFPI1-150 and KD1-KD2 had 10-fold higher Ki values and were not stimulated by protein S. Single Kunitz domains were poor inhibitors of TF:FVIIa-catalyzed FIX activation (Ki >800 nm). FX activation was measured at limiting FVIIa and excess TF or vice versa. At both conditions, TFPIFL , TFPI1-150 , and KD1-KD2 showed similar inhibition of FX activation. However, at low phospholipid concentrations, TFPIFL was ~ 15-fold more active than TFPI1-150 or KD1-KD2. Apparently, excess phospholipids act as a kind of sink for TFPIFL , limiting its availability for TF:FVIIa inhibition. Preformed FXa:TFPIFL/1-150 complexes rapidly and stoichiometrically inhibited FIX and FX activation by TF:FVIIa, indicating that binary TFPI:FXa complex formation is the limiting step in TF:FVIIa inhibition. Protein S also enhanced inhibition of TF:FVIIa-catalyzed FX activation by TFPI.
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Affiliation(s)
- S Peraramelli
- Department of Biochemistry, Cardiovascular Research Institute Maastricht, University Maastricht, Maastricht, the Netherlands
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6
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Wood JP, Ellery PER, Maroney SA, Mast AE. Protein S is a cofactor for platelet and endothelial tissue factor pathway inhibitor-α but not for cell surface-associated tissue factor pathway inhibitor. Arterioscler Thromb Vasc Biol 2013; 34:169-76. [PMID: 24233490 DOI: 10.1161/atvbaha.113.302655] [Citation(s) in RCA: 40] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
OBJECTIVE Tissue factor pathway inhibitor (TFPI) is produced in 2 isoforms: TFPIα, a soluble protein in plasma, platelets, and endothelial cells, and TFPIβ, a glycosylphosphatidylinositol-anchored protein on endothelium. Protein S (PS) functions as a cofactor for TFPIα, enhancing the inhibition of factor Xa. However, PS does not alter the inhibition of prothrombinase by TFPIα, and PS interactions with TFPIβ are undescribed. Thus, the physiological role and scope of the PS-TFPI system remain unclear. APPROACH AND RESULTS Here, the cofactor activity of PS toward platelet and endothelial TFPIα and endothelial TFPIβ was quantified. PS enhanced the inhibition of factor Xa by TFPIα from platelets and endothelial cells and stabilized the TFPIα/factor Xa inhibitory complex, delaying thrombin generation by prothrombinase. By contrast, PS did not enhance the inhibitory activity of TFPIβ or a membrane-anchored form of TFPI containing the PS-binding third Kunitz domain (K1K2K3) although PS did function as a cofactor for K1K2K3 enzymatically released from the cell surface. CONCLUSIONS The PS-TFPI anticoagulant system is limited to plasma TFPIα and TFPIα released from platelets and endothelial cells. PS likely functions to localize solution-phase TFPIα to the cell surface, where factor Xa is bound. PS does not alter the activity of membrane-associated TFPI. Because activated platelets release TFPIα and PS, the PS-TFPIα anticoagulant system may act physiologically to dampen thrombin generation at the platelet surface.
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Affiliation(s)
- Jeremy P Wood
- From the Blood Research Institute, Blood Center of Wisconsin, Milwaukee, WI (J.P.W., P.E.R.E., S.A.M., A.E.M.); and Department of Cell Biology, Neurobiology and Anatomy, Medical College of Wisconsin, Milwaukee, WI (A.E.M.)
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7
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Chattopadhyay R, Sengupta T, Majumder R. Inhibition of Intrinsic Xase by Protein S. Arterioscler Thromb Vasc Biol 2012; 32:2387-93. [DOI: 10.1161/atvbaha.112.250928] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Objective—
Protein S is a vitamin K–dependent plasma protein that functions in the feedback regulation of thrombin generation. Our goal was to determine how protein S regulates the intrinsic pathway of blood coagulation.
Methods and Results—
We used plasma, including platelet-rich plasma, and in vitro methods to determine how the intrinsic pathway of blood coagulation is regulated by protein S. We obtained the following results: (1) activated partial thromboplastin time assays with protein S–supplemented plasma confirmed that protein S prolongs clotting time; (2) a modified activated partial thromboplastin time assay with factor IX (fIX)–deficient plasma confirmed that protein S affects fIX-initiated clotting; (3) a fIXa/factor VIIIa (fVIIIa)–mediated thrombin generation assay with either platelet-rich plasma or factor-deficient plasma, initiated with a limiting amount of tissue factor, was regulated by protein S; (4) in the presence of phosphatidylserine vesicles, protein S inhibited fIXa in the absence and presence of fVIIIa; and (5) protein S altered only the
K
M
for factor X activation by fIXa in the absence of fVIIIa and both
k
cat
and
K
M
in the presence of fVIIIa.
Conclusion—
From our findings, it can be concluded that protein S inhibits fIXa in the presence or absence of fVIIIa in an activated protein C–independent way.
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Affiliation(s)
- Rima Chattopadhyay
- From the Department of Biochemistry and Biophysics, University of North Carolina, Chapel Hill, NC
| | - Tanusree Sengupta
- From the Department of Biochemistry and Biophysics, University of North Carolina, Chapel Hill, NC
| | - Rinku Majumder
- From the Department of Biochemistry and Biophysics, University of North Carolina, Chapel Hill, NC
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9
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Activated protein C cofactor function of protein S: a novel role for a γ-carboxyglutamic acid residue. Blood 2011; 117:6685-93. [PMID: 21508412 DOI: 10.1182/blood-2010-11-317099] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Protein S has an important anticoagulant function by acting as a cofactor for activated protein C (APC). We recently reported that the EGF1 domain residue Asp95 is critical for APC cofactor function. In the present study, we examined whether additional interaction sites within the Gla domain of protein S might contribute to its APC cofactor function. We examined 4 residues, composing the previously reported "Face1" (N33S/P35T/E36A/Y39V) variant, as single point substitutions. Of these protein S variants, protein S E36A was found to be almost completely inactive using calibrated automated thrombography. In factor Va inactivation assays, protein S E36A had 89% reduced cofactor activity compared with wild-type protein S and was almost completely inactive in factor VIIIa inactivation; phospholipid binding was, however, normal. Glu36 lies outside the ω-loop that mediates Ca(2+)-dependent phospholipid binding. Using mass spectrometry, it was nevertheless confirmed that Glu36 is γ-carboxylated. Our finding that Gla36 is important for APC cofactor function, but not for phospholipid binding, defines a novel function (other than Ca(2+) coordination/phospholipid binding) for a Gla residue in vitamin K-dependent proteins. It also suggests that residues within the Gla and EGF1 domains of protein S act cooperatively for its APC cofactor function.
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10
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Andersson HM, Arantes MJ, Crawley JTB, Luken BM, Tran S, Dahlbäck B, Lane DA, Rezende SM. Activated protein C cofactor function of protein S: a critical role for Asp95 in the EGF1-like domain. Blood 2010; 115:4878-85. [PMID: 20308596 PMCID: PMC2884152 DOI: 10.1182/blood-2009-11-256610] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/26/2009] [Accepted: 02/20/2010] [Indexed: 11/20/2022] Open
Abstract
Protein S has an established role in the protein C anticoagulant pathway, where it enhances the factor Va (FVa) and factor VIIIa (FVIIIa) inactivating property of activated protein C (APC). Despite its physiological role and clinical importance, the molecular basis of its action is not fully understood. To clarify the mechanism of the protein S interaction with APC, we have constructed and expressed a library of composite or point variants of human protein S, with residue substitutions introduced into the Gla, thrombin-sensitive region (TSR), epidermal growth factor 1 (EGF1), and EGF2 domains. Cofactor activity for APC was evaluated by calibrated automated thrombography (CAT) using protein S-deficient plasma. Of 27 variants tested initially, only one, protein S D95A (within the EGF1 domain), was largely devoid of functional APC cofactor activity. Protein S D95A was, however, gamma-carboxylated and bound phospholipids with an apparent dissociation constant (Kd(app)) similar to that of wild-type (WT) protein S. In a purified assay using FVa R506Q/R679Q, purified protein S D95A was shown to have greatly reduced ability to enhance APC-induced cleavage of FVa Arg306. It is concluded that residue Asp95 within EGF1 is critical for APC cofactor function of protein S and could define a principal functional interaction site for APC.
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Affiliation(s)
- Helena M Andersson
- Department of Haematology, Faculty of Medicine, Imperial College London, London, UK
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11
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Abstract
In the last decades evidence was obtained that protein S not only acts as cofactor of activated protein C (APC) in the downregulation of coagulation, but also expresses anticoagulant activity in the absence of APC. The search for the mechanism(s) underlying the APC-independent anticoagulant activity of protein S was hampered by the fact that protein S exhibited 2 seemingly identical anticoagulant activities in model systems and in plasma. Later it was shown that the anticoagulant activity of purified protein S in model systems was dependent on the concentration of phospholipid vesicles and was explained by low amounts of protein S multimers generated during purification that effectively inhibited phospholipid-dependent coagulation reactions via competition for phospholipid binding sites. Plasma does not contain multimers, and the anticoagulant activity of protein S in plasma was not affected by the phospholipid concentration but was dependent on the amount of tissue factor (TF) used for initiation of thrombin generation. This led to the discovery that protein S acts as cofactor of tissue factor pathway inhibitor (TFPI) which stimulates the inhibition of factor Xa by TFPI approximately 10-fold. The current review describes the background of the TFPI-cofactor activity of protein S as well as the rationale for the observation that the TFPI/protein S system particularly inhibits the TF pathway at low procoagulant stimuli.
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Affiliation(s)
- Tilman M Hackeng
- Department of Biochemistry, Cardiovascular Research Institute Maastricht, University Maastricht, Maastricht, The Netherlands
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12
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Abstract
Protein S is an anticoagulant cofactor of full-length tissue factor pathway inhibitor (TFPI) that facilitates optimal factor Xa-inhibition and efficient down-regulation of thrombin generation in plasma. Protein S and TFPI are constitutively active in plasma and therefore provide an effective anticoagulant barrier against unwanted procoagulant activity in the circulation. In this review, we describe the current status on how TFPI-activity depends on protein S, and show that TFPI and protein S are major regulators of thrombin generation both in the absence and presence of activated protein C (APC). As there is covariation of plasma TFPI and protein S levels both in health and in disease, these findings suggest that the risk of venous thrombosis associated with protein S deficiency states might be in part explained by the accompanying low plasma TFPI levels.
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Affiliation(s)
- T M Hackeng
- Department of Biochemistry, Cardiovascular Research Institute Maastricht (CARIM), Maastricht University, Maastricht, The Netherlands.
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Heeb MJ, Radtke KP, Fernández JA, Tonnu L. Plasma contains protein S monomers and multimers with similar direct anticoagulant activity. J Thromb Haemost 2006; 4:2215-22. [PMID: 16824189 DOI: 10.1111/j.1538-7836.2006.02117.x] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
BACKGROUND Protein S (PS) has activated protein C-independent, direct anticoagulant activity (PS-direct). We reported that both multimers and monomers of affinity-purified PS have PS-direct similar to that in plasma, in contrast to another report. OBJECTIVE We extended our studies to establish the molecular forms and activity of plasma PS. METHODS Novel ELISAs were developed that could detect only multimeric, not monomeric, PS because they employed the same monoclonal antibody for capture and detection. PS forms were also examined on native PAGE immunoblots. A new activity assay for PS-direct was applied to plasma and gel-filtered plasma fractions. RESULTS Plasma PS multimers were clearly demonstrated using the ELISAs; 30-60% of free plasma PS appeared to be multimeric, a proportion similar to that of affinity-purified PS. On immunoblots, plasma PS multimers were more easily detected after gel filtration; plasma PS monomers and several apparent multimers comigrated with respective forms of affinity-purified PS. Antigen elution profiles after gel filtration of plasma revealed at least one major peak of apparent PS multimers (40-55% of free PS appeared multimeric). Biotin-factor Xa could bind to both plasma PS monomers and multimers. Strong plasma PS-direct was demonstrated, and plasma PS monomers, multimers, and PS-C4b-binding protein complexes each reconstituted PS-depleted plasma to similar levels of PS-direct. CONCLUSION Our data are in disagreement with a report that monomeric purified PS has little PS-direct and that only monomeric PS exists in plasma. We find that both affinity-purified and plasma PS exist as monomers and multimers with similar PS-direct.
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Affiliation(s)
- M J Heeb
- Department of Molecular and Experimental Medicine, The Scripps Research Institute, La Jolla, CA 92037, USA.
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