scholarly journals Identification of surface residues mediating tissue factor binding and catalytic function of the serine protease factor VIIa

1996 ◽  
Vol 93 (25) ◽  
pp. 14379-14384 ◽  
Author(s):  
C. D. Dickinson ◽  
C. R. Kelly ◽  
W. Ruf
Keyword(s):  
Serine Protease ◽  
Tissue Factor ◽  
Factor Viia ◽  
Factor Binding ◽  
Catalytic Function

An Anti-Tissue Factor Monoclonal Antibody which Inhibits TF Vlla Complex Is a Potent Anticoagulant in Plasma

1991 ◽  
Vol 66 (05) ◽  
pp. 529-533 ◽  
Author(s):  
Wolfram Ruf ◽  
Thomas S Edgington
Keyword(s):  
Monoclonal Antibody ◽  
Cell Surface ◽  
Tissue Factor ◽  
Slow Rate ◽  
Factor Viia ◽  
Plasma Binding ◽  
Cell Surfaces ◽  
Therapeutic Principle ◽  
Catalytic Function

SummaryTissue factor (TF) functions as the receptor and cofactor for factor VIIa (VIIa) to form a proteolytically active TFVIIa complex on cell surfaces. We here demonstrate that most MAbs against human TF were poor inhibitors of TF function in plasma and that they inhibited preformed TF-VIIa complex at a slow rate which was dependent on dissociation of VIIa from the cell surface TF. An exception was defined by one MAb (TF8-5G9) which was an effective immediate anticoagulant in plasma. Binding of TF8-5G9 to TF-VIIa inhibited catalytic function prior to dissociation of the TF-VIIa complex. This analysis thus establishes two distinct mechanisms by which MAbs interfere with TF function. The MAb TF8-5G9 introduces a therapeutic principle for rapid arrest of inappropriate triggering of coagulation by TF as well as the TF-VIIa complex in vivo.

scholarly journals Tissue Factor residue Asp44 regulates catalytic function of the bound proteinase Factor VIIa

1996 ◽  
Vol 315 (1) ◽  
pp. 145-151 ◽  
Author(s):  
Curtis R. KELLY ◽  
John R. SCHULLEK ◽  
Wolfram RUF ◽  
Thomas S. EDGINGTON
Keyword(s):  
Tissue Factor ◽  
Factor Viia ◽  
Coagulation Factor ◽  
Serine Proteinase ◽  
Cell Surface Receptor ◽  
Side Chain ◽  
Factor X ◽  
Catalytic Function ◽  
Surface Receptor ◽  
Binding Residues

The coagulation pathways are initiated by the cell-surface receptor Tissue Factor (TF), which binds the serine proteinase coagulation Factor VIIa (VIIa), resulting in enhanced catalytic function, both amidolytic, towards small pseudo-substrates, and proteolytic, towards macromolecular substrates. Here we implicate Asp44 in TF as a ligand-interactive residue that, in contrast with previously characterized binding residues, is involved in the enhancement of VIIa catalytic function. Whereas charge neutralization by replacement of Asp44 with Asn did not reduce function of human TF, the exchange by Ala resulted in mutants with 8-fold reduced affinity for binding of VIIa. Enhancement of VIIa amidolytic function by TF Ala44 was reduced by 20–25% relative to wild-type and support of proteolytic function was diminished 6-fold indicating that this cofactor residue is significantly enhancing proteolysis of the macromolecular substrate by VIIa. Replacement of Asp44 by Glu, Thr and Arg exhibited a less severe phenotype with an approx. 4-fold reduced affinity for VIIa and a 2–3-fold diminished activation of Factor X. The improved activity of these mutants as compared with the Ala replacement is consistent with functional importance of an extended side chain at this position. The specific influence of the Asp44 exchange on catalytic function of the TF·VIIa complex indicates fine specificity of the TF ligand interface in mediating receptor and cofactor function.

Effects of Radiographic Contrast Agents on Thrombin Formation and Activity

1998 ◽  
Vol 80 (08) ◽  
pp. 266-272 ◽  
Author(s):  
Andrew Parker ◽  
William Fay
Keyword(s):  
Contrast Agents ◽  
Tissue Factor ◽  
Coronary Angioplasty ◽  
Molecular Mechanisms ◽  
Factor Viia ◽  
Minor Effect ◽  
Ionic Contrast ◽  
Radiographic Contrast ◽  
Inhibition Of Thrombin ◽  
Thrombin Formation

SummaryClinical trials suggest that the risk of thrombosis during coronary angioplasty is lower with ionic contrast agents than with nonionic contrast agents. However, the molecular mechanisms underlying this effect are unknown. This study examined the effects of contrast agents on thrombin formation and its interaction with substrates, inhibitors, and ligands to define potential mechanisms by which contrast agents affect thrombus formation. Two ionic agents, diatrizoate and ioxaglate, and one nonionic agent, ioversol, were studied. Ionic agents inhibited factor X activation by the tissue factor-factor VIIa complex more potently than ioversol (53 ± 3.7, 43.0 ± 1.9, and 26.5 ± 2.4% inhibition by diatrizoate, ioxaglate, and ioversol, respectively, at concentrations of 5%). Ionic contrast agents were potent inhibitors of prothrombinase function, inhibiting thrombin formation by >75% at contrast concentrations of 0.6% (p <0.005). Ioversol inhibited prothrombinase to a significantly lesser extent than ionic agents. Clotting assays suggested that ioxaglate was the most potent inhibitor of thrombin generation in plasma despite having the least effect on fibrin polymerization. Contrast agents inhibited binding of thrombin to fibrin, with ionic agents producing a more potent effect than ioversol (p <0.02). However, contrast agents did not inhibit thrombin-mediated platelet activation, had only a minor effect on inhibition of thrombin by antithrombin III, and did not affect thrombin-hirudin interactions. In summary, these studies identify specific mechanisms by which radiographic contrast agents inhibit thrombin formation and function – i.e. inhibition of tissue factor-dependent factor Xa generation, inhibition of the prothrombinase complex, and inhibition of thrombin binding to fibrin. These findings may help to explain the reduced risk of thrombosis during coronary angioplasty associated with ionic contrast agents.

Factors Affecting the lnteraction of Tissue Factor/Factor Vll with Factor X in a Heterogeneous Tubular Reactor

1991 ◽  
Vol 65 (02) ◽  
pp. 139-143 ◽  
Author(s):  
Cynthia H Gemmell ◽  
Vincet T Turitto ◽  
Yale Nemerson
Keyword(s):  
Steady State ◽  
Tissue Factor ◽  
Factor Viia ◽  
Transmembrane Protein ◽  
Strong Association ◽  
Tubular Reactor ◽  
Factor Xa ◽  
Phospholipid Bilayer ◽  
Factor Vii ◽  
Factor X

SummaryA novel reactor recently described for studying phospholipiddependent blood coagulation reactions under flow conditions similar to those occurring in the vasculature has been further charactenzed. The reactor is a capitlary whose inner wall is coated with a stable phospholipid bilayer (or two bilayers) containing tissue factor, a transmembrane protein that is required for the enzymatic activation of factor X by factor VIIa. Perfusion of the capillary at wall shear rates ranging from 25 s−1 to 1,200 s−1 with purified bovine factors X and VIIa led to steady state factor Xa levels at the outlet. Assay were performed using a chromogenic substrate, SpectrozymeTMFXa, or by using a radiometric technique. In the absence of Ca2+ or factor VIIa there was no product formation. No difference was noted in the levels of factor Xa achieved when non-activated factor VII was perfused. Once steady state was achieved further factor Xa production continued in the absence of factor VIIa implying a very strong association of factor VIIa with the tissue factor in the phospholipid membrane. In agreement with static vesicle-type studies the reactor was sensitive to wall tissue factor concentration, temperature and the presence of phosphatidylserine in the bilayer.

The Factor VIII Bypassing Activity of Prothrombin Complex Concentrates: The Roles of Factor VIla and of Endothelial Cell Tissue Factor

1991 ◽  
Vol 66 (05) ◽  
pp. 559-564 ◽  
Author(s):  
Jerome M Teitel
Keyword(s):  
Factor Viii ◽  
Tissue Factor ◽  
Factor Viia ◽  
Factor Xa ◽  
Procoagulant Activity ◽  
Tissue Factor Expression ◽  
Prothrombin Complex Concentrates ◽  
Cell Tissue ◽  
Factor Expression ◽  
Necrosis Factor

SummaryAn experimental model incorporating cultured endothelial cells (EC) was used to study the "factor VIII bypassing" activity of prothrombin complex concentrates (PCC), a property exploited in the treatment of hemophiliacs with alloantibodies to factor VIII. Two PCC preparations were ineffective as stimuli of tissue factor expression by EC. However, incubation with a combination of PCC plus endotoxin (lipopolysaccharide, LPS) or tumor necrosis factor (TNF) induced much greater tissue factor expression than was seen in response to either substance alone. PCC expressed an additional direct procoagulant activity at the EC surface, which could not be attributed to either thrombin or factor Xa, and which was diminished by an anti-tissue factor antibody. Therefore factor VIIa, which was detectable in both PCC preparations, likely provided this additional direct procoagulant activity at the EC surface. We also excluded the possibility that coagulation proteases contained in or generated in the presence of PCC are protected from inactivation by AT III. Therefore, PCC can indirectly bypass factor VIII by enhancing induced endothelial tissue factor expression, and also possess direct procoagulant activity, probably mediated by factor VIIa.

Studies of the Mechanism for Enhanced Cell Surface Factor VIIa/Tissue Factor Activation of Factor X on Fibroblast Monolayers after Their Exposure to N-Ethylmaleimide

1994 ◽  
Vol 72 (06) ◽  
pp. 848-855 ◽  
Author(s):  
Dzung The Le ◽  
Samuel I Rapaport ◽  
L Vijaya Mohan Rao
Keyword(s):  
Cell Surface ◽  
Tissue Factor ◽  
Factor Viia ◽  
Cell Damage ◽  
Specific Binding ◽  
Surface Membrane ◽  
Annexin V ◽  
Factor X ◽  
Binding Studies ◽  
Anionic Phospholipid

SummaryFibroblast monolayers constitutively expressing surface membrane tissue factor (TF) were treated with 0.1 mM N-ethylmaleimide (NEM) for 1 min to inhibit aminophospholipid translocase activity without inducing general cell damage. This resulted in increased anionic phospholipid in the outer leaflet of the cell surface membrane as measured by the binding of 125I-annexin V and by the ability of the monolayers to support the generation of prothrombinase. Specific binding of 125I-rVIIa to TF on NEM-treated monolayers was increased 3- to 4-fold over control monolayers after only brief exposure to 125I-rVIIa, but this difference progressively diminished with longer exposure times. A brief exposure of NEM-treated monolayers to rVIIa led to a maximum 3- to 4-fold enhancement of VIIa/TF catalytic activity towards factor X over control monolayers, but, in contrast to the binding studies, this 3- to 4-fold difference persisted despite increasing time of exposure to rVIIa. Adding prothrombin fragment 1 failed to diminish the enhanced VIIa/TF activation of factor X of NEM-treated monolayers. Moreover, adding annexin V, which was shown to abolish the ability of NEM to enhance factor X binding to the fibroblast monolayers, also failed to diminish the enhanced VIIa/TF activation of factor X. These data provide new evidence for a possible mechanism by which availability of anionic phospholipid in the outer layer of the cell membrane limits formation of functional VIIa/TF complexes on cell surfaces.

Activation of Factor X by Factor VIIa Complexed with Human-mouse Tissue Factor Chimeras Requires Human Exon 3

1996 ◽  
Vol 76 (03) ◽  
pp. 361-368 ◽  
Author(s):  
Carrie H Fang ◽  
T-C Lin ◽  
Arabinda Guha ◽  
Yale Nemerson ◽  
William H Konigsberg
Keyword(s):  
Tissue Factor ◽  
Human Factor ◽  
Factor Viia ◽  
Mouse Tissue ◽  
Factor X ◽  
Lower Affinity ◽  
E Coli ◽  
Sequence Elements ◽  
Specific Activities ◽  
Human And Mouse

SummaryIn an attempt to define sequence elements in human and mouse tissue factor (TF) that are responsible for the species specificity observed in their interaction with human factor VIIa (HVIIa), we constructed human-mouse chimeric TF cDNAs, inserted them into plasmid vectors, and induced their expression in E.coli. Assays for procoagulant activity were carried out with the resulting E. coli lysates using (HVIIa) human and mouse (MVIIa). The ratio of the procoagulant activities, HVIIa/MVIIa, revealed that human TF exon 3 was essential for activity when the TF:VIIa complex was formed with HVIIa. By ligating the maltose binding protein (MBP) gene to TF cDNAs it was possible to construct, express and purify MBP-TF chimeras as well as to estimate their specific activities. With selected MBP-TF chimeras and HVIIa we determined kinetic parameters for the activation of human factor X. Replacement of exon 3 in human TF cDNA with the corresponding exon from mouse TF cDNA resulted in both lower affinity for HVIIa and failure to convert bound HVIIa into a potent protease

The Effect of Active Site-inhibited Factor VIIa on Tissue Factor-initiated Coagulation Using Platelets before and after Aspirin Administration

1997 ◽  
Vol 78 (04) ◽  
pp. 1202-1208 ◽  
Author(s):  
Marianne Kjalke ◽  
Julie A Oliver ◽  
Dougald M Monroe ◽  
Maureane Hoffman ◽  
Mirella Ezban ◽  
...  
Keyword(s):  
Tissue Factor ◽  
Active Site ◽  
Large Scale ◽  
Thrombin Generation ◽  
Factor Viia ◽  
Dependent Manner ◽  
Antithrombotic Agent ◽  
Before And After ◽  
Ic50 Values

SummaryActive site-inactivated factor VIIa has potential as an antithrombotic agent. The effects of D-Phe-L-Phe-L-Arg-chloromethyl ketone-treated factor VIla (FFR-FVIIa) were evaluated in a cell-based system mimicking in vivo initiation of coagulation. FFR-FVIIa inhibited platelet activation (as measured by expression of P-selectin) and subsequent large-scale thrombin generation in a dose-dependent manner with IC50 values of 1.4 ± 0.8 nM (n = 8) and 0.9 ± 0.7 nM (n = 7), respectively. Kd for factor VIIa binding to monocytes ki for FFR-FVIIa competing with factor VIIa were similar (11.4 ± 0.8 pM and 10.6 ± 1.1 pM, respectively), showing that FFR-FVIIa binds to tissue factor in the tenase complex with the same affinity as factor VIIa. Using platelets from volunteers before and after ingestion of aspirin (1.3 g), there were no significant differences in the IC50 values of FFR-FVIIa [after aspirin ingestion, the IC50 values were 1.7 ± 0.9 nM (n = 8) for P-selectin expression, p = 0.37, and 1.4 ± 1.3 nM (n = 7) for thrombin generation, p = 0.38]. This shows that aspirin treatment of platelets does not influence the inhibition of tissue factor-initiated coagulation by FFR-FVIIa, probably because thrombin activation of platelets is not entirely dependent upon expression of thromboxane A2.

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