Synthesis, purification, and characterization of an Arg152----Glu site-directed mutant of recombinant human blood clotting factor VII

Structural biology of factor VIIa/tissue factor initiated coagulation

Factor VII (FVII) consists of an N-terminal gamma-carboxyglutamic acid domain followed by two epidermal growth factor-like (EGF1 and EGF2) domains and the C-terminal protease domain. Activation of FVII results in a two-chain FVIIa molecule consisting of a light chain (Gla-EGF1-EGF2 domains) and a heavy chain (protease domain) held together by a single disulfide bond. During coagulation, the complex of tissue factor (TF, a transmembrane glycoprotein) and FVIIa activates factor IX (FIX) and factor X (FX). FVIIa is structurally "zymogen-like" and when bound to TF, it is more "active enzyme-like." FIX and FX share structural homology with FVII. Three structural biology aspects of FVIIa/TF are presented in this review. One, regions in soluble TF (sTF) that interact with FVIIa as well as mapping of Ca2+, Mg2+, Na+ and Zn2+ sites in FVIIa and their functions; two, modeled interactive regions of Gla and EGF1 domains of FXa and FIXa with FVIIa/sTF; and three, incompletely formed oxyanion hole in FVIIa/sTF and its induction by substrate/inhibitor. Finally, an overview of the recognition elements in TF pathway inhibitor is provided.

Prothrombotic effect of prostasomes of metastatic cell and seminal origin

BACKGROUND

Prostasomes are secretory granules produced by the glandular epithelial cells of the prostate. Seminal prostasomes contain high amounts of Tissue Factor (TF) but no studies of TF on malignant cell prostasomes have been made. Here we compare the expression, phosphorylation, and function of TF on prostasomes of different origin.

METHODS

TF was detected on prostasomes isolated from seminal fluid and human prostate cancer cell lines (PC-3, DU145, and LNCaP) using FACS and enzyme immunoassay (EIA). Incubation of prostasomes with radioactive ATP under conditions favoring protein kinase A activity led to phosphorylation of TF as detected by immunoprecipitation and SDS-PAGE. The prothrombotic effect of prostasomes was investigated in whole blood and recalcified plasma. Blocking experiments were performed using anti-TF antibodies and corn trypsin inhibitor.

RESULTS

TF was expressed on all tested prostasome preparations with lowest values found for seminal ones. Prostasomal TF was the main endogenous substrate for prostasomal protein kinase A. All tested prostasome preparations greatly enhanced the rate of clot formation in a dose-dependent fashion, that is, the clotting capability of prostasomes seemed to be related to the extent of their expression of TF. In addition, the density of the clot varied between different prostasome preparations. When incubated in whole blood, prostasomes were found to associate to WBC thereby inducing them to express and release TF.

CONCLUSIONS

These data show that TF is overexpressed and also subjected to phosphorylation by malignant cell prostasomes. This suggests major roles for prostasomes in thrombotic events that occur in some advanced cases of prostate cancer.

Allosteric Activation of Coagulation Factor VIIa Visualized by Hydrogen Exchange

Coagulation factor VIIa (FVIIa) is a serine protease that, after binding to tissue factor (TF), plays a pivotal role in the initiation of blood coagulation. We used hydrogen exchange monitored by mass spectrometry to visualize the details of FVIIa activation by comparing the exchange kinetics of distinct molecular states, namely zymogen FVII, endoproteolytically cleaved FVIIa, TF-bound zymogen FVII, TF-bound FVIIa, and FVIIa in complex with an active site inhibitor. The hydrogen exchange kinetics of zymogen FVII and FVIIa are identical indicating highly similar solution structures. However, upon tissue factor binding, FVIIa undergoes dramatic structural stabilization as indicated by decreased exchange rates localized throughout the protease domain and in distant parts of the light chain, spanning across 50A and revealing a concerted interplay between functional sites in FVIIa. The results provide novel insights into the cofactor-induced activation of this important protease and reveal the potential for allosteric regulation in the trypsin family of proteases.

Tissue factor: (patho)physiology and cellular biology

The transmembrane glycoprotein tissue factor (TF) is the initiator of the coagulation cascade in vivo. When TF is exposed to blood, it forms a high-affinity complex with the coagulation factors factor VII/activated factor VIIa (FVII/VIIa), activating factor IX and factor X, and ultimately leading to the formation of an insoluble fibrin clot. TF plays an essential role in hemostasis by restraining hemorrhage after vessel wall injury. An overview of biological and physiological aspects of TF, covering aspects consequential for thrombosis and hemostasis such as TF cell biology and biochemistry, blood-borne (circulating) TF, TF associated with microparticles, TF encryption-decryption, and regulation of TF activity and expression is presented. However, the emerging role of TF in the pathogenesis of diseases such as sepsis, atherosclerosis, certain cancers and diseases characterized by pathological fibrin deposition such as disseminated intravascular coagulation and thrombosis, has directed attention to the development of novel inhibitors of tissue factor for use as antithrombotic drugs. The main advantage of inhibitors of the TF*FVIIa pathway is that such inhibitors have the potential of inhibiting the coagulation cascade at its earliest stage. Thus, such therapeutics exert minimal disturbance of systemic hemostasis since they act locally at the site of vascular injury.

Novel anticoagulant activity of polyamino acid offsets bacterial endotoxin-induced extrinsic hypercoagulation: downregulation of monocytic tissue factor-dependent FVII activation

The extrinsic hypercoagulation often resulting from sepsis could contribute to disseminated intravascular coagulation and cardiovascular complications. The effective prevention and intervention remained largely complex and unclear. In a cell model of human leukemia THP-1 monocytes following bacterial endotoxin (LPS) exposure, we show the novel anticoagulant ability of polyamino acid (polyAA) to suppress the extrinsic hypercoagulation. LPS-induced monocytic tissue factor (mTF) procoagulation was readily offset by poly-L-lysine (PLK), poly-L-arginine (PLR), or poly-L-ornithine (POR) included in single-stage clotting assays. IC50 was estimated at 0.35, 0.30, or 0.58 microM for PLR, POR, or PLK, respectively, whereas, poly-L-asparatic acid (PLD) remained ineffective. In a separate approach, inclusion of cationic polyAA in human plasma significantly prolonged prothrombin time, confirming the depressed extrinsic coagulation. In chromogenic assays dissecting the extrinsic pathway, we further determined the inhibitory site(s). PLK, PLR, or POR significantly inhibited LPS-induced FVII activation, which was consistent with the diminished FVIIa formation shown on Western blotting analysis. In contrast, polyAA did not show any additional effect on either FVIIa/FXa amidolytic activities or mTF/FVIIa-catalyzed FX activation. Nor did polyAA show any effect on FVII activation directly catalyzed by FXa. Taken together, PLK, PLR, or POR preferentially inhibited mTF-dependent FVII activation, accounting for their novel anticoagulant activities. PolyAA might present the specific antagonists to arrest the extrinsic hypercoagulation following inflammation.

Anticoagulant potential of an antibody against factor VII

BACKGROUND

Hypercoagulability often resulting from sepsis, trauma, and other conditions is widely associated with thrombotic and cardiovascular disorders. The development of effective and safe anticoagulation is in great demand to relieve complications and improve human health.

OBJECTIVE

We study the anticoagulant potential of a polyclonal antibody to human FVII (anti-hFVII Ab).

METHODS AND RESULTS

Preincubating FVII with anti-hFVII Ab, we showed the significantly blocked tissue factor (TF)-dependent FVII activation monitored by a two-stage chromogenic assay. Consistently, the antibody depressed TF/FVII-catalyzed FX activation was shown on Western blotting analysis. As a result, TF procoagulation derived from rabbit brain thromboplastin was prolonged significantly by the preincubation of human normal plasma with the antibody, which mimicked FVII-deficient plasma in a single-stage clotting assay. In contrast, the anti-hFVII Ab had no effect on either FVIIa amidolytic activity or TF/FVIIa binary complex.

CONCLUSIONS

Anti-hFVII Ab readily blocked clot formation, which was mediated by the upstream downregulation of the extrinsic coagulation of inhibiting FVII activation. Further research warrants establishing its in vivo application as an anticoagulant.

The pharmacokinetics of clotting factor therapy

Clotting factor preparations are expensive and not readily available in all parts of the world. We are still facing shortages due to limited production. Thus, it is obvious that clotting factor therapy should be optimised as far as possible. The judicious use of pharmacokinetic principles should be one of the fundaments of dosing. There are several pitfalls in studies of clotting factor pharmacokinetics, such as discrepancies between assays, inadequate blood sampling protocols, problems to define the administered dose, uncertainty in the estimation of plasma volume for in vivo recovery calculation, and post-infusion activation of the clotting factor. Thus, while the pharmacokinetics of factor VIII is well characterised there are some discrepancies in the literature on factor IX. Recombinant factor VIIa is useful to treat haemorrhages in haemophilia complicated by inhibitors. The pharmacokinetics of VIIa has been investigated, however, the relationship between plasma level of VIIa and effect needs further exploration. Important applications of clotting factor pharmacokinetics include optimising the treatment and improving its cost-effectiveness during long-term prophylaxis as well as during bleeding episodes and surgery.

Production of tissue factor by pancreatic islet cells as a trigger of detrimental thrombotic reactions in clinical islet transplantation

BACKGROUND

Intraportal transplantation of pancreatic islets offers improved glycaemic control and insulin independence in type 1 diabetes mellitus, but intraportal thrombosis remains a possible complication. The thrombotic reaction may explain why graft loss occurs and islets from more than one donor are needed, since contact between human islets and ABO-compatible blood in vitro triggers a thrombotic reaction that damages the islets. We investigated the possible mechanism and treatment of such thrombotic reactions.

METHODS

Coagulation activation and islet damage were monitored in four patients undergoing clinical islet transplantation according to a modified Edmonton protocol. Expression of tissue factor (TF) in the islet preparations was investigated by immunohistochemistry, immunoprecipitation, electron microscopy, and RT-PCR. To assess TF activity in purified islets, human islets were mixed with non-anticoagulated ABO-compatible blood in tubing loops coated with heparin.

FINDINGS

Coagulation activation and subsequent release of insulin were found consistently after clinical islet transplantation, even in the absence of signs of intraportal thrombosis. The endocrine, but not the exocrine, cells of the pancreas were found to synthesise and secrete active TF. The clotting reaction triggered by pancreatic islets in vitro could be abrogated by blocking the active site of TF with specific antibodies or site-inactivated factor VIIa, a candidate drug for inhibition of TF activity in vivo.

INTERPRETATION

Blockade of TF represents a new therapeutic approach that might increase the success of islet transplantation in patients with type 1 diabetes, in terms of both the risk of intraportal thrombosis and the need for islets from more than one donor.

Possible role of Marcks in the cellular modulation of monocytic tissue factor-initiated hypercoagulation

The enhanced extrinsic tissue factor (TF)-initiated coagulation, often resulting from sepsis, could lead to disseminated intravascular coagulation presenting cardiovascular complications. Using model human leukaemia THP-1 monocytes, we studied monocytic TF (mTF) hypercoagulation and its regulation. After an 8 h exposure to bacterial endotoxin [lipopolysaccharide (LPS); 100 ng/ml], mTF activity was significantly upregulated as the result of the enhanced mTF synthesis. Thereafter, LPS induction declined, exhibiting a "quiescent-desensitizing' phenomenon. Such diminished LPS induction was,however,associated with sustained LPS-enhanced mTF synthesis, revealing the possible occurrence of a post-translational downregulation. It was noted that LPS desensitization was accompanied by the increased expression of myristoylated alanine-rich C kinase substrate (Marcks). In contrast, A23187 (20 micromol/l) or Quin-2AM (20 micromol/l) drastically activated mTF activity without detectable effect on mTF synthesis; both of which showed that sustained functional upregulation during 24 h culture did not enhance Marcks expression. These inverse correlations between mTF activity upregulation and Marcks expression suggested that Marcks could be inhibitory. Marcks phosphorylation site domain (151-175) (Marcks PSD) readily inhibited mTF-dependent FVII activation and diminished FVIIa formation in LPS-challenged cells. As a result, Marcks PSD offset LPS-induced mTF hypercoagulation upon inclusion in the single-stage clotting assays. The anticoagulant activity was confirmed by showing that Marcks PSD significantly blocked rabbit brain thromboplastin (rbTF) procoagulation and inhibited rbTF-dependent FVII activation as well as FVIIa formation. Our study suggests that Marcks expression plays a role in a novel cellular modulation to downregulate mTF hypercoagulation.

Factor VIIa induces tissue factor-dependent up-regulation of interleukin-8 in a human keratinocyte line

Tissue factor (TF), a transmembrane receptor for the serine protease coagulation factor VII(a) (FVIIa), is the main initiator of the coagulation cascade. Through incompletely elucidated mechanisms, TF serves additional functions in tumor-associated angiogenesis and metastasis. We have studied interleukin-8 (IL-8) as a possible link between TF-FVIIa complex formation and subsequent processes. Recombinant human FVIIa induced the up-regulation of both IL-8 mRNA and protein in a FVIIa dose- and time-dependent fashion. A neutralizing antibody to TF reduced this induction by 93 +/- 5%. Active site-inhibited FVIIa had no stimulatory effect and completely blocked that of FVIIa. This confirms that the increased IL-8 production was dependent on the formation of TF-FVIIa complexes and the proteolytic activity of FVIIa. The IL-8 promoter contains DNA binding sites for nuclear factor-kappaB (NF-kappaB) and activator protein-1 (AP-1). In response to FVIIa, the DNA binding activity of both NF-kappaB and AP-1 was enhanced in an electrophoretic mobility shift assay. In addition, the IL-8 promoter was transcriptionally activated both in a luciferase reporter system and a nuclear run-off assay. Moreover, IL-8 mRNA stability was significantly enhanced by FVIIa-induced activation of the mitogen-activated protein kinases ERK1/2 and p38. Taken together, TF-FVIIa signaling induced increased transcription as well as mRNA stabilization leading to the significant up-regulation of IL-8 protein synthesis.

Novel anticoagulant activity of polybrene: inhibition of monocytic tissue factor hypercoagulation following bacterial endotoxin induction

The enhanced extrinsic coagulation in response to inflammation could contribute to disseminated intravascular coagulation, often manifesting cardiovascular complications. The complex mechanism remains unclear. Nor is the effective anticoagulation well established. The search for arresting hypercoagulation is of antithrombotic relevance. The ability of polybrene (PB) to inhibit tissue factor (TF)-initiated extrinsic blood coagulation was demonstrated at the protein and cellular levels as well as in human plasma samples. In a single-stage clotting assay, PB dose-dependently offset bacterial endotoxin (lipopolysaccharide)-induced monocytic TF (mTF) hypercoagulation and inhibited rabbit brain thromboplastin (rbTF) procoagulation. Consistent with these findings, the significantly prolonged prothrombin time indicated the depressed extrinsic coagulation by PB. However, PB showed no effect on thrombin time. We dissected the extrinsic pathway to further determine the inhibitory site(s) of PB. A two-stage chromogenic assay monitoring S-2288 hydrolysis showed that PB readily blocked mTF-dependent or rbTF-dependent FVII activation, which was verified by the diminished activated factor VII (FVIIa) formation derived from the proteolytic cleavage of its zymogen factor VII on Western blotting analyses. PB had no effect on FVIIa and activated factor X amidolytic activity. Nor was the dissected TF/FVIIa-catalyzed factor X activation affected. In conclusion, the preferential downregulation of factor VII activation was responsible for the depressed extrinsic coagulation. PB could present a novel anticoagulant antagonizing the extrinsic hypercoagulation for the prevention of thrombotic complication following sepsis and inflammations.

Protamine inhibits tissue factor-initiated extrinsic coagulation

The enhanced extrinsic coagulation in response to inflammation could contribute to disseminated intravascular coagulation, often manifesting cardiovascular complications. The complex mechanism remains unclear and effective management is not well established. The ability of protamine to offset bacterial endotoxin (LPS)-induced tissue factor (TF)-initiated extrinsic coagulation was demonstrated in human peripheral blood monocytes and cultured human leukaemia THP-1 monocytes, which was consistent with the inhibition of rabbit brain thromboplastin (rbTF) procoagulant activity in a cell-free in vitro model. Protamine significantly prolonged prothrombin time, further confirming the downregulation of the extrinsic pathway. However, thrombin time remained unaltered. Chromogenic assays were performed to dissect the extrinsic pathway, identifying inhibitory site(s). Protamine significantly inhibited factor VII (FVII) activation but not the dissected FX activation. The amidolytic activities of FVIIa and FXa were unaffected. The inhibited FVII activation in the presence of protamine was confirmed by the diminished FVIIa formation on Western blot analyses. Protamine preferentially inhibited TF-catalysed FVII activation, downregulating the extrinsic cascade. Protamine could be of anticoagulant significance in the management of the extrinsic hypercoagulation.

Antimicrobial peptide buforin I inhibits tissue factor-initiated coagulation

The enhanced extrinsic blood coagulation following septic shock often manifests cardiovascular complications. The upregulated monocytic tissue factor (mTF) was shown to be a primary contributor to the extrinsic hypercoagulation following acute bacterial endotoxin (LPS) infection. A single-stage clotting assay monitors TF-initiated coagulation. We herein demonstrate a novel anticoagulant activity of antimicrobial peptide Buforin I (BF I) in offsetting LPS-induced mTF hypercoagulation in THP-1 cells, which was confirmed in a cell-free in vitro model, showing that BF I effectively blocked rabbit brain thromboplastin (rbTF) procoagulant activity. Upon inclusion of 25 microM BF I into human plasma, the prolonged prothrombin time (PT) was consistent with the depressed TF-initiated coagulation. In a two-stage chromogenic assay monitoring S-2288 hydrolysis, BF I significantly inhibited not only mTF- but also rbTF-catalyzed FVII activation accompanied by the diminished FVIIa formation. The inhibition by BF I of FVII activation accounted for its novel anticoagulant activity in offsetting mTF-initiated hypercoagulation.

Blockade by ruthenium red of tissue factor-initiated coagulation

The ability of ruthenium red (RuR) to inhibit tissue factor (TF)-initiated blood coagulation was demonstrated at the protein and cellular levels as well as in human plasma. In a single-stage clotting assay, RuR concentration-dependently inhibited rabbit brain thromboplastin (rbTF)-induced coagulation and offset bacterial endotoxin (LPS)-induced monocytic TF (mTF) hypercoagulation; the IC(50)s were estimated at 7.5 and 12.3 microM, respectively. A 15-min preincubation of RuR with rbTF or monocyte suspension resulted in the pronounced inhibition with a significantly lowered IC(50) at 1.8 or 7.7 microM for rbTF or mTF procoagulation, respectively. The differences in IC(50)s between rbTF and mTF without or with the preincubation indicated that TF was a primary target for RuR action. The effect of RuR on the physiological function of TF in FVII activation was demonstrated by the proteolytic cleavage of FVII zymogen to its active forms of serine protease on Western blotting analyses. RuR readily blocked TF-catalyzed FVII activation (diminished FVIIa formation), thus down regulating the initiation of blood coagulation. Inclusion of RuR into human plasma samples in vitro significantly prolonged prothrombin time, indicating the depressed coagulation. FVII activity was inhibited by 30 - 60% depending on the dose; as a result, FX activity also decreased. However, RuR showed no effect on thrombin time. Thus, RuR inhibited FVII activation to block the initiation of coagulation.

IV. Anticoagulant activity of compound 48/80: inhibition of factor VII activation in leukemia THP-1 monocytes

Our previous study described a novel biologic function of compound 48/80 (48/80) in the downregulation of monocytic tissue factor (TF)-initiated hypercoagulation in response to bacterial endotoxin (lipopolysaccharide; LPS). The inhibition was not due to the blockade of LPS cell signaling, as evidenced by the unaffected LPS-induced TF synthesis. We herein determined the mechanism by which 48/80 inhibits the extrinsic coagulation in agonist-challenged THP-1 monocytes. LPS as well as A23187 substantially induced TF activity. TF synthesis was enhanced by LPS but not by A23187. However, the elevated FVII binding to monocytes accompanying the upregulation of factor VII (FVII) activation was uniformly observed in both cases. A 5-min preincubation of the cells with a sheep anti-humanTF antibody (anti-hTF Ab) showed the downregulation of FVII activation, indicating a regulatory role of FVII binding in the modulation of the extrinsic coagulation. The 48/80 blocked FVII binding to monocytes, leading to the preferential inhibition of FVII activation. As the result of the diminished FVIIa formation, monocytic TF-initiated extrinsic coagulation was downregulated in agonist-challenged THP-1 monocytes.

III. Instantaneous inhibition by compound 48/80 of tissue factor-initiated extrinsic coagulation is mediated by the downregulation of factor VII activation

Our previous study has demonstrated a unique biological function of compound 48/80 (48/80) in the downregulation of monocytic tissue factor (TF)-initiated hypercoagulation in response to bacterial endotoxin (lipopolysaccharide, LPS) [A. J. Chu et al. (1999) Biochim. Biophys. Acta 1472, 386-395]. The inhibition was not due to the blockade of LPS cell signaling as evidenced by the unaffected LPS-induced TF synthesis. In the present study, we investigate the direct inhibitory action of 48/80 on the extrinsic coagulation cascade. TF-initiated coagulation was assayed by a single-stage clotting assay. Chromogenic assays dissected the extrinsic pathway to measure the activities of FVII, FX, and prothrombin by monitoring the hydrolyses of nitroaniline-conjugated substrates, identifying the inhibitory site(s). We report that 48/80 in vitro instantaneously inhibited rabbit brain thromboplastin (rbTF)-initiated coagulation in a dose-dependent manner. 48/80 preferentially inhibited FVII activation without any detectable effect on FVIIa, FXa, and thrombin activities. Neither FX activation nor prothrombin activation was affected. The significant inhibition on FVII activation was found to be noncompetitive with a fourfold reduction in the apparent Vmax of FVIIa formation from 7.1 to 1.7 nM/min, while the apparent Km (approximately 365 nM) remained unaffected. Western blotting analysis further confirmed that FVIIa formation derived from FVII was significantly diminished by 48/80, which was accompanied by blocked FVII binding to rbTF. In conclusion, 48/80 readily blocked FVII binding to rbTF, leading to diminished FVII activation and FVIIa formation. As a result, TF-initiated extrinsic coagulation was downregulated.

Probing the structural changes in the light chain of human coagulation factor VIIa due to tissue factor association

The crystallographic structure of human coagulation factor VIIa/tissue factor complex bound with calcium ions was used to model the solution structure of the light chain of factor VIIa (residues 1-142) in the absence of tissue factor. The Amber force field in conjunction with the particle mesh Ewald summation method to accommodate long-range electrostatic interactions was used in the trajectory calculations. The estimated TF-free solution structure was then compared with the crystal structure of factor VIIa/tissue factor complex to estimate the restructuring of factor VIIa due to tissue factor binding. The solution structure of the light chain of factor VIIa in the absence of tissue factor is predicted to be an extended domain structure similar to that of the tissue factor-bound crystal. Removal of the EGF1-bound calcium ion is shown by simulation to lead to minor structural changes within the EGF1 domain, but also leads to substantial relative reorientation of the Gla and EGF1 domains.

Functional consequences of mutations in Ser-52 and Ser-60 in human blood coagulation factor VII

Human blood coagulation factor VII has unique carbohydrate moieties O-glycosidically linked to serine 52 and serine 60 residues in its first epidermal growth factor-like domain. To study the functional role of these glycosyl moieties in factor VII, we constructed, expressed, and purified site-specific recombinant mutants of human factor VII in which serine 52 and serine 60 were conservatively replaced with alanine residues. S52A factor VIIa (Ser-52-->Ala), S60A factor VIIa (Ser-60-->Ala), and S52,60A factor VIIa (Ser-52, Ser-60-->Ala) exhibited 56, 73, and 44%, respectively, of the clotting activity of wild-type factor VIIa using human brain thromboplastin as a source of tissue factor/phospholipids and 32, 43, and 14% of wild-type factor VIIa using a mixture of recombinant soluble tissue factor and mixed brain phospholipids. The tissue factor-dependent and -independent amidolytic activities of these mutants were essentially indistinguishable from that of wild-type factor VIIa. In addition, equilibrium dialysis experiments indicated that the profiles of 45Ca2+ binding to these mutants were identical with that of wild-type factor VII. In the presence of either Ca2+ or EGTA, the Kd values for the interaction of the three factor VIIa mutants to full-length tissue factor were 2- to 5-fold higher than that of wild-type factor VIIa, while the Kd values for the interaction of these mutants to soluble tissue factor were 4- to 15-fold higher than that of wild-type factor VIIa. Measurement of the association and dissociation rate constants for factor VIIa binding to relipidated tissue factor apoprotein revealed that the association rate constants of the three factor VII mutants were decreased in comparison with that of wild-type factor VIIa, while the dissociation rate constants of these three mutants were virtually identical to that of wild-type factor VIIa. These findings strongly suggest that glycosyl moieties attached to Ser-52 and Ser-60 in factor VII/VIIa provide unique structural elements that are important for the rapid association of factor VII/VIIa with its cellular receptor and cofactor.

Active Site Inhibited Factor VIIa (DEGR VIIa) Attenuates the Coagulant and Interleukin-6 and -8, but not Tumor Necrosis Factor, Responses of the Baboon to LD100Escherichia coli

Antitissue factor antibody attenuated the coagulopathic and lethal responses to LD100Escherichia coli, whereas active site inhibited factor Xa inhibited only the coagulopathic response. In this study, we wished to determine: (1) whether active site inhibited factor VIIa blocks the coagulopathic and/or attenuates the lethal effects of LD100E coli and (2) whether these effects are accompanied by attenuation of the inflammatory cytokine response to LD100E coli. Eight baboons infused for 2 hours with LD100E coli also were given five bolus infusions of DEGR VIIa of 280 μg/kg at T = −10 minutes, +2, 4, 6, and 8 hours and observed for changes in vital signs, and the concentrations of hemostatic components (fibrinogen, platelets, fibrin degradation products) and inflammatory mediators (tumor necrosis factor [TNF], interleukin-6 [IL-6], IL-8) at T = 0, 1, 2, 4, 6, and 8 hours. Eight control baboons were also infused with LD100E coli alone and followed as described above. Four of the eight baboons treated with DEGR VIIa were permanent 7-day survivors versus none in the control group. The mean survival times for the treated and control groups were 116 ± 22 and 26 ± 8 hours, respectively. These values differed significantly from each other, (P = .0008). The decrease in platelet and fibrinogen concentrations and the increase in fibrin degradation products observed in the control group were significantly attenuated in the treated group, as was thrombosis of renal glomerular capillaries. Treatment with DEGR VIIa showed no effect on the peak TNF response to LD100E coli at T = 2 hours (170 ± 32 v120 ± 35 ng/mL). DEGR VIIa, however, did attenuate the IL-6 and IL-8 responses at T = 8 hours (ie, the IL-6 concentrations were 81 ± 10 for treated and 1,256 ± 236 for the control groups and the IL-8 concentrations were 28 ± 3.9 for the treated and 60 ± 8.2 for the control group). These values for IL-6 and IL-8 differed significantly from each other between the treated and control groups (P = .0001 and .0074, respectively). It should be noted that the initial responses of IL-6 and IL-8 up to T = 4 hours were not attenuated. We concluded that DEGR VIIa treatment attenuates inflammatory, as well as hemostatic system responses to LD100E coli. We hypothesize that this occurs through interference with the assembly and/or interactions of tissue factor/VIIa complexes.

Active Site Inhibited Factor VIIa (DEGR VIIa) Attenuates the Coagulant and Interleukin-6 and -8, but not Tumor Necrosis Factor, Responses of the Baboon to LD100Escherichia coli

Antitissue factor antibody attenuated the coagulopathic and lethal responses to LD100Escherichia coli, whereas active site inhibited factor Xa inhibited only the coagulopathic response. In this study, we wished to determine: (1) whether active site inhibited factor VIIa blocks the coagulopathic and/or attenuates the lethal effects of LD100E coli and (2) whether these effects are accompanied by attenuation of the inflammatory cytokine response to LD100E coli. Eight baboons infused for 2 hours with LD100E coli also were given five bolus infusions of DEGR VIIa of 280 μg/kg at T = −10 minutes, +2, 4, 6, and 8 hours and observed for changes in vital signs, and the concentrations of hemostatic components (fibrinogen, platelets, fibrin degradation products) and inflammatory mediators (tumor necrosis factor [TNF], interleukin-6 [IL-6], IL-8) at T = 0, 1, 2, 4, 6, and 8 hours. Eight control baboons were also infused with LD100E coli alone and followed as described above. Four of the eight baboons treated with DEGR VIIa were permanent 7-day survivors versus none in the control group. The mean survival times for the treated and control groups were 116 ± 22 and 26 ± 8 hours, respectively. These values differed significantly from each other, (P = .0008). The decrease in platelet and fibrinogen concentrations and the increase in fibrin degradation products observed in the control group were significantly attenuated in the treated group, as was thrombosis of renal glomerular capillaries. Treatment with DEGR VIIa showed no effect on the peak TNF response to LD100E coli at T = 2 hours (170 ± 32 v120 ± 35 ng/mL). DEGR VIIa, however, did attenuate the IL-6 and IL-8 responses at T = 8 hours (ie, the IL-6 concentrations were 81 ± 10 for treated and 1,256 ± 236 for the control groups and the IL-8 concentrations were 28 ± 3.9 for the treated and 60 ± 8.2 for the control group). These values for IL-6 and IL-8 differed significantly from each other between the treated and control groups (P = .0001 and .0074, respectively). It should be noted that the initial responses of IL-6 and IL-8 up to T = 4 hours were not attenuated. We concluded that DEGR VIIa treatment attenuates inflammatory, as well as hemostatic system responses to LD100E coli. We hypothesize that this occurs through interference with the assembly and/or interactions of tissue factor/VIIa complexes.

Generation and characterization of mice deficient in hepsin, a hepatic transmembrane serine protease

Hepsin is a type II transmembrane serine protease highly expressed on the surface of hepatocytes. The physiological function of hepsin is not known, although in vitro studies indicate that hepsin plays a role in the initiation of blood coagulation and in hepatocyte growth. To determine the functional importance of hepsin, we generated hepsin-deficient mice by homologous recombination. Homozygous hepsin-/- mice were viable and fertile, and grew normally. In functional assays including tail bleeding time, plasma clotting times, and tissue factor- or LPS-induced disseminated intravascular coagulation models, no significant difference was found between hepsin-/- and wild-type litter mates. Liver weight and serum concentrations of liver-derived proteins or enzymes were similar in hepsin-/- and wild-type mice. Interestingly, serum concentrations of bone-derived alkaline phosphatase were approximately twofold higher in hepsin-/- mice of both sexes when compared with wild-type litter mates. No obvious abnormalities were found in major organs in hepsin-/- mice in histological examinations. Our results indicate that hepsin is not essential for embryonic development and normal hemostasis. Hepsin-/- mice will help to evaluate the long-term effects of hepsin deficiency in these animals.

Factor VII central. A novel mutation in the catalytic domain that reduces tissue factor binding, impairs activation by factor Xa, and abolishes amidolytic and coagulant activity

Factor VII is a vitamin K-dependent zymogen of a serine protease that participates in the initial phase of blood coagulation. A factor VII molecular variant (factor VII Central) was identified in a 24-year-old male with severe factor VII deficiency and whose plasma factor VII antigen was 38% of normal, but expressed <1% factor VII procoagulant activity. DNA sequence analysis of the patient's factor VII gene revealed a thymidine to cytidine transition at nucleotide 10907 in exon VIII that results in a novel amino acid substitution of Phe328 to Ser. The patient was homozygous for this mutation, whereas each parent of the patient was heterozygous for this mutation. To investigate the molecular properties of this variant, a recombinant F328S factor VII mutant was prepared and analyzed in relation to wild-type factor VII. F328S factor VII exhibited <1% factor VII procoagulant activity and a 2-fold decreased affinity for tissue factor and failed to activate factor X or IX in the presence of tissue factor following activation by factor Xa. In addition, F328S factor VIIa exhibited no detectable amidolytic activity in the presence of tissue factor. The rate of F328S factor VII activation by factor Xa was markedly decreased relative to the rate of wild-type factor VII activation as revealed by densitometry scanning of SDS gels. Temporal analysis of this reaction by SDS-polyacrylamide gel electrophoresis also revealed the formation of two novel F328S factor VII degradation products (40 and 9 kDa) resulting from factor Xa proteolysis of the Arg315-Lys316 peptide bond in intact F328S factor VII. Computer modeling and molecular dynamics simulations of the serine protease domain of factor VIIa suggested that the inability of F328S factor VIIa to cleave substrates may result from the apparent formation of a hydrogen bond between Tyr377 and Asp338, a residue at the bottom of the substrate-binding pocket important for the interaction of substrate arginine side chains with the enzyme. These findings suggest that Phe328, which is conserved in prothrombin, factor IX, factor X, factor VII, and trypsin, is important for factor VIIa catalysis.

Activation of a recombinant human factor VII structural analogue alters its affinity of binding to tissue factor

A competitive enzyme-linked immunoadsorbent assay (ELISA) technique has been developed to facilitate quantitative analysis of the earliest step in the initiation of the extrinsic pathway of coagulation, i.e., complex formation of factor VII/VIIa with tissue factor. The ELISA measures the binding of biotinylated human plasma factor VII to relipidated recombinant human tissue factor. Quantitation of the relative affinity (expressed as IC50) of any factor VII molecular population or structural analogue for tissue factor can be determined by competitive binding. Subnanomolar concentrations of both wild-type recombinant human factor VII (rFVII) and rFVII(R152Q), a mutation at the FVII activation site, competed effectively with biotinylated plasma-derived factor VII in binding to tissue factor. In contrast, the affinity of rFVII(R79Q), a mutation in the first epidermal growth factor-like domain, was 12-fold lower. Following activation of rFVII(R79Q), its affinity for tissue factor and enzymatic activity increased 4-fold and 6-fold, respectively. For wild-type rFVII, enzymatic activity rose significantly following activation. However, its affinity for tissue factor was unchanged. We conclude that both the activation state of factor VII and the mutation of amino-acid residues within the first epidermal growth factor-like domain may alter the affinity of factor VII for tissue factor.

Localization of an epitope of a calcium-dependent monoclonal antibody to the N-terminal region of the Gla domain of human factor VII

The epitope of a calcium-dependent murine monoclonal antibody specific for human factor VII (Thim et.al., Biochemistry (1988) 27, 7785-7793) has been determined. Site-directed mutagenesis of residues 3 through 10 of factor VII eliminates the binding of this antibody but does not disturb the binding of a second antibody which binds nearby.

High affinity Ca(2+)-binding site in the serine protease domain of human factor VIIa and its role in tissue factor binding and development of catalytic activity

Factor VIIa, in the presence of Ca2+ and tissue factor (TF), initiates the extrinsic pathway of blood coagulation. The light chain (amino acids 1-152) of factor VIIa consists of an N-terminal gamma-carboxyglutamic acid (Gla) domain followed by two epidermal growth factor-like domains, whereas the heavy chain (amino acids 153-406) contains the serine protease domain. In this study, both recombinant factor VIIa (rVIIa) and factor VIIa lacking the Gla domain were found to contain two high-affinity (Kd approximately 150 microM) Ca2+ binding sites. The rVIIa also contained approximately 6-7 low-affinity (Kd approximately 1 mM) Ca(2+)-binding sites. By analogy to other serine proteases, one of the two high affinity Ca(2+)-binding sites in factor VIIa may be formed involving Glu-210 and Glu-220 of the protease domain. In support of this, a synthetic peptide composed of residues 206-242 of factor VIIa bound one Ca2+ with Kd approximately 230 microM; however, Ca2+ binding was observed only in Tris buffer (pH 7.5) containing 1 M NaCl and not in buffer containing 0.1 M NaCl. In both low or high salt +/- Ca2+, the peptide existed as a monomer as determined by sedimentation equilibrium measurements and had no detectable secondary structure as determined by CD measurements. This indicates that subtle changes undetectable by CD may occur in the conformation of the peptide that favor calcium binding in high salt. In the presence of recombinant TF and 5 mM Ca2+, the peptide inhibited the amidolytic activity of rVIIa toward the synthetic substrate, S-2288. The concentration of the peptide required for half-maximal inhibition was approximately 5-fold higher in the low salt buffer than that in the high salt buffer. From direct binding and competitive inhibition assays of active site-blocked 125I-rVIIa binding to TF, the Kd for peptide-TF interaction was calculated to be approximately 15 microM in the high salt and approximately 55 microM in the low salt buffer containing 5 mM Ca2+. Moreover, as inferred from S-2288 hydrolysis, the Kd for VIIa.TF interaction was approximately 1.5 microM in the absence of Ca2+, and, as inferred from factor X activation studies, it was approximately 10 pM in the presence of Ca2+. Thus, Ca2+ decreases the functional Kd of VIIa.TF interaction approximately 150,000-fold.(ABSTRACT TRUNCATED AT 400 WORDS)

Hepsin, a putative membrane-associated serine protease, activates human factor VII and initiates a pathway of blood coagulation on the cell surface leading to thrombin formation

Previous studies have shown that hepsin is a putative membrane-associated serine protease that is required for cell growth (Torres-Rosado, A., O'Shea, K. S., Tsuji, A., Chou, S.-H., and Kurachi, K. (1993) Proc. Natl. Acad. Sci. U.S. A. 90, 7181 7185). In the present study, we have transfected baby hamster kidney (BHK) cells with a plasmid containing the cDNA for human hepsin and examined these cells for their ability to activate several blood coagulation factors including factors X, IX, VII, prothrombin, and protein C. Little, if any, proteolytic activation of factors X, IX, prothrombin, or protein C was observed when these clotting factors were incubated with hepsin-transfected cells. On the other hand, hepsin-transfected cells proteolytically activated significant concentrations of human factor VII in a time- and calcium-dependent manner, whereas essentially no activation of factor VII was observed in BHK cells transfected with plasmid lacking the cDNA for hepsin. The factor VII activating activity in the hepsin-transfected BHK cell line was confined exclusively to the total membrane fraction and was inhibited > 95% by antibody raised against a fusion protein consisting of maltose-binding protein and the extracellular domain of human hepsin. An active site factor VII mutant, S344A factor VII, was cleaved as readily as plasma-derived factor VII by hepsin-transfected cells, indicating that factor VII was not converted to factor VIIa autocatalytically on the cell surface. In contrast, an activation cleavage site factor VII mutant, R152E factor VII, was not cleaved by hepsin-transfected cells, suggesting that factor VII and S344A factor VII were activated on these cells by cleavage of the Arg152-Ile153 peptide bond. In the copresence of factor VII and factor X, hepsin-transfected BHK cells supported the formation of factor Xa. In addition, in the copresence of factor VII, factor X, and prothrombin, hepsin-transfected BHK cells supported the formation of thrombin. These results strongly suggest that membrane-associated hepsin converts zymogen factor VII to factor VIIa, which in turn, is capable of initiating a coagulation pathway on the cell surface that ultimately leads to thrombin formation.

Tissue factor pathway

Blood coagulation is initiated in response to vessel damage in order to preserve the integrity of the mammalian vascular system. The coagulation cascade can also be initiated by mediators of the inflammatory response, and fibrin deposition has been noted in a variety of pathological states. The cascade of coagulation zymogen activations which leads to clot formation is initiated by exposure of flowing blood to tissue factor (TF), the cellular receptor and cofactor for factor VII (FVII). FVII binds to the receptor in a 1:1 stoichiometric complex and is rapidly activated. FVIIa undergoes an active site transition upon binding TF in the presence of calcium which enhances the fundamental properties of the enzyme. This results in rapid autocatalytic activation of FVII to VIIa thereby amplifying the response by generating more TF-VIIa complexes. The TF-VIIa activates both FIX and FX. Further FXa generation by the IXa-VIIIa-Ca(2+)-phospholipid complex is required to sustain the coagulation mechanism, since the TF-VIIa complex is rapidly inactivated. Structure and function studies have identified a number of regions on both TF and FVII involved in this interaction. It is clear, however, that the molecular structures of TF, FVII and the TF-VII complex will have to be solved before we fully understand this complex interaction. The activity of the TF-VIIa complex is controlled by two inhibitors:tissue factor pathway inhibitor (TFPI) and antithrombin III (AT-III). TFPI circulates in plasma, is associated with vascular cell surface and is released from platelets following stimulation by thrombin. TFPI requires the formation of an active TF-VIIa complex and FXa generation before inhibition can occur. Similarly, AT-III which is unable to inhibit circulating FVIIa requires the formation of the TF-VIIa complex. TFPI prevents further participation of TF in the coagulation process by forming a stable quaternary complex, TF-VIIa-Xa-TFPI. In contrast, the AT-III-VIIa complex is thought to dissociate from TF allowing it to interact with additional FVII-VIIa. TFPI has been considered the primary regulator of TF-VIIa activity during haemostasis. Whether AT-III in the presence of glycosaminoglycans on cell surfaces expressing TF can function as an auxiliary second physiological regulator is not known.

High-level production of human blood coagulation factors VII and XI using a new mammalian expression vector

Recombinant human proteins are generally recovered in low yields from mammalian tissue culture following transfection with commercially available vectors. We have constructed a novel vector containing both the neomycin-resistance-encoding gene (neo) as a dominant selectable marker, and the dihydrofolate reductase-encoding gene (DHFR) to enable amplification of transfected DNA followed by stable expression in mammalian cell lines. Levels of 5 micrograms/ml of the coagulation proteins, factor VII (FVII) and factor XI (FXI), have been achieved in serum-free media. N-terminal sequencing of the purified proteins, and of their separated chains after proteolytic activation, demonstrated correct processing of the recombinant products. In addition, the ratios of clotting activity to antigen for each are close to unity, and the recombinant and plasma-derived proteins had identical mobilities upon electrophoresis in the presence of SDS. The vector described will be of use for the synthesis of recombinant proteins, both wild-type and variants produced by site-directed mutagenesis, especially where complex post-translational modification of the protein makes it essential to use mammalian cells.

Dietary fat induces changes in factor VII coagulant activity through effects on plasma free stearic acid concentration

Previous studies have demonstrated activation of the contact system of coagulation and an increase in factor VII coagulant activity (VIIc) when citrated plasma is incubated in the presence of micellar stearate. The products of contact activation, factors XIIa and IXa, were responsible in this system for the activation of factor VII, thereby increasing factor VIIc. To obtain evidence that these in vitro interactions also operate in vivo, factor VIIc was examined in relation to plasma free fatty acid concentrations in five healthy individuals during the consumption of isocaloric high-saturated fat, high-unsaturated fat, and low-fat diets, each taken for 4 weeks in random order and separated by intervals of 12 weeks. For all but the final 3 days of each phase, subjects selected appropriate foods from prepared lists to meet the dietary requirements. Experimental diets of predetermined fat content and composition were fed on days 26 through 28 in each phase. Fat supplied on average 62% of energy in two of the experimental diets and less than 20% of energy in the third. On the final day of each dietary phase, the concentrations of the various free fatty acids and factor VIIc were measured before breakfast and at three 150-minute intervals thereafter. Plasma factor VIIc was, respectively, 6.5% and 13.1% of standard higher on the unsaturated and saturated fat diets than on the low-fat diet. Furthermore, the plasma concentration of stearic acid was strongly associated with factor VIIc (r = .58; P < .0001), and this relation remained significant (P = .003) after allowance for the plasma concentrations of palmitic, oleic, and linoleic acids.(ABSTRACT TRUNCATED AT 250 WORDS)

Tissue factor as a tumor procoagulant

Tissue factor is a cell surface glycoprotein responsible for initiating the extrinsic pathway of coagulation. Many tumor cell homogenates and intact tumor cells have been shown to contain tissue factor activity. Immunohistochemical studies show that many tumors associated with Trousseau's syndrome express tissue factor on their cell surfaces. Tumor cells shed membrane fragments which carry tissue factor that can account for the activation of the clotting system. Tumor cells also produce soluble substances that can induce tissue factor expression on host cells, such as endothelium and monocytes, at sites distant from the tumor. Although, all the functional TF molecules are localized on the outer cell membrane in many tumor cells, the procoagulant activity on the intact cell surface is largely dormant and can be greatly enhanced upon cell injury or damage. Tissue factor procoagulant activity on the cell surface can be modulated by alterations in the plasma membrane without loss of cell viability. Tissue factor activity on cell surfaces is largely regulated by a plasma inhibitor, tissue factor pathway inhibitor. This inhibitor binds to both functional and non-functional tissue factor/VIIa complexes on the cell surface and prevents non-functional tissue factor/VIIa complexes from becoming functional after cell injury or lysis. Heparin, but not warfarin, therapy is effective in preventing the occurrence of devastating thrombotic events in patients with Trousseau's syndrome and the reason(s) for this are still unknown.

Lipolysis of triglyceride-rich lipoproteins activates coagulant factor XII: a study in familial lipoprotein-lipase deficiency

A high factor VII coagulant activity (VIIc), a marker of increased risk of coronary heart disease, is frequently found in types IIb and IV hyperlipidaemia, but its cause is not fully understood. Factor VII can be activated by factor XIIa, generated from factor XII upon activation of the contact system of coagulation. Ten patients with familial lipoprotein-lipase (LPL) deficiency and 10 healthy control subjects were therefore compared to explore the hypothesis that high concentrations of unesterified fatty acids (UFA), released from triglyceride-rich lipoproteins by LPL, are a source of factor XII activation and hence the increased VIIc that is observed post-prandially and in non-LPL-deficient hypertriglyceridaemic states. Mean plasma cholesterol and triglyceride concentrations were, respectively, 1.5- and 19-fold higher in the patients than controls, due to increases in very-low-density lipoproteins and chylomicrons. The concentration and composition of plasma UFA were similar in both groups. In conformity with the hypothesis, VIIc was not increased in the LPL-deficient group, despite their massive hypertriglyceridaemia. Furthermore, when the patients' plasma was treated with LPL, factor XII was activated promptly and substantially, whereas no similar effect was observed in the controls. These results suggest that high concentrations of circulating triglyceride-rich lipoproteins will increase VIIc in the presence of LPL.

Activation of human factor VII by the prothrombin activator from the venom of Oxyuranus scutellatus (Taipan snake)

The crude venom of Oxyuranus scutellatus (Taipan snake) was found to cleave single-chain human factor VII to yield a two-chain molecule indistinguishable from authentic factor VIIa by SDS-polyacrylamide gel electrophoresis. A protease that activates factor VII was purified from this venom by a combination of gel permeation and ion-exchange chromatography. Characterization of the venom factor VII activator revealed its apparent identity with the Oxyuranus scutellatus prothrombin activator. The purified venom prothrombin activator was observed to activate factor VII by limited proteolysis in a reaction that was greatly potentiated by calcium and phospholipids (75% phosphatidyl choline/25% phosphatidylserine). Treatment of the venom protease with 0.8 M NaSCN weakly inhibited its ability to activate factor VII indicating that, in contrast to prothrombin activation, the factor Va-like component of this oligomeric enzyme complex was not essential for the activation of factor VII.

Coupling of the adhesive receptor CD11b/CD18 to functional enhancement of effector macrophage tissue factor response

Initiation and regulation of localized selective proteolysis is an important effector property of cells of macrophage (Mo) lineage. Among such effector responses is the induced expression of tissue factor (TF) by cells of Mo lineage. In characterizing the regulation of the Mo responses that may influence the magnitude of the effector phase of the cellular immune response, we have identified a role for the cell surface adhesive receptor CD11b/CD18 (Mac-1, CR3) to amplify the induced TF response. Occupancy of CD11b/CD18 by MAb as surrogate ligands does not directly initiate a TF response. In contrast, after either T cell-derived cytokine or LPS as initial signals, engagement of CD11b/CD18 by MAb induces a two- to eight-fold functional enhancement of the TF response in murine and human Mo. This pathway of CD11b/CD18 enhancement of this Mo effector response was also confirmed with recognized ligands for CD11b/CD18 by exposure of Mo to immobilized fibrinogen. A quantitative increase of Mo surface expression of TF was validated by flow cytometry. We suggest that engagement of CD11b/CD18 by complementary ligands including adherence to extracellular matrix, and possibly in antigen-driven TH:Mo collaborative responses, results in the transduction of cellular signals that quantitatively enhance the expression of TF per se and thereby enhance the inflammatory component of Mo mediated response.