The activation of factor IX by the tissue factor pathway.
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Blood Coagulation↗
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Human recombinant factor IX: safety and efficacy studies in hemophilia B patients previously treated with plasma-derived factor IX concentrates.
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Clinical Trials as Topic↗
Purification of human factor IX by chromatography of a coagulation factor concentrate.
A purification procedure for, and some properties of, coagulation factor IX are described. The coagulation factor concentrate used for the treatment of hemophilia B patients was employed as the starting material. The isolation procedure consists of chromatography in DEAE-cellulose, two chromatographies in hydroxyapatite gel and two gel filtrations in Sephadex G-200. Only trace amounts of factors II, VII and X were present in the final preparation and the specific activity of factor IX was 159 corresponding 10,300 times purification from plasma. The molecular weight was estimated to be 76,000 in gel filtration and 86,000 in sodium dodecyl sulfate disc gel electrophoresis. Three activity peaks with pIs 4.15, 4.25 and 4.40 were obtained by isoelectric focusing.
Chromatography, DEAE-Cellulose↗
Activation of human factor VII by activated factors IX and X.
Factor VII clotting activity increases about five-fold when blood is clotted in glass. Prior studies suggested that this results from activation induced by activated factor IX (IXa). However, in purified systems containing phospholipid and calcium, activated factor X (Xa) is known to activate factor VII rapidly. Therefore, we studied activation of factor VII by IXa and X, in systems using purified human factors. Concentrations of IXa and Xa were calculated from total activated protein concentrations rather than from active site concentrations. In the presence of phospolipid and calcium, both IXa and Xa activated factor VII 25-fold; however, Xa was roughly 800 times more efficient than IXa. Without added phospholipid, activation of factor VII by both Xa and IXa was markedly slowed, and Xa was roughly 20 times more efficient than IXa. When both phospholipid and calcium were omitted, activation of factor VII by either enzyme was negligible. Adding normal prothrombin, but not decarboxylated prothrombin, substantially slowed activation of factor VII by both Xa and IXa. Adding thrombin-activated factor VIII and antithrombin-III did not change rates of factor VII activation by either enzyme. These results from purified systems do not provide an explanation for the prior data from plasma systems.
Blood Coagulation Tests↗
Identification of a factor IX binding site on the third apple domain of activated factor XI.
Activated factor XI (factor XIa) participates in blood coagulation by activating factor IX. Previous work has demonstrated that a binding site for factor IX is present on the noncatalytic heavy chain of factor XIa (Sinha, D., Seaman, F. S., and Walsh, P. N. (1987) Biochemistry 26, 3768-3775). Recombinant factor XI proteins were expressed in which each of the four apple domains of the heavy chain (designated A1 through A4) were individually replaced with the corresponding domain from the homologous but functionally distinct protease prekallikrein (PK). To identify the site of factor IX binding, the chimeric proteins were activated with factor XIIa and tested for their capacity to activate factor IX in plasma coagulation and purified protein assays. The chimera with the substitution in the third apple domain (factor XI/PKA3) had <1% of the coagulant activity of wild type factor XIa in a plasma coagulation assay, whereas the chimeras with substitutions in A1, A2, and A4 demonstrated significant activity (68-140% of wild type activity). The Km for activation of factor IX by factor XIa/PKA3 (12. 7 microM) is more than 30-fold higher than the Km for activation by wild type factor XIa or the other factor XI/PK chimeras (0.11-0.37 microM). Two monoclonal antibodies (2A12 and 11AE) that recognize epitopes on the factor XI A3 domain were potent inhibitors of factor IX activation by factor XIa, whereas antibodies against the A2 (1A6) and A4 (3G4) domains were poor inhibitors. The data indicate that a binding site for factor IX is present on the third apple domain of factor XIa.
Antibodies, Monoclonal↗
Molecular cloning of the gene for human anti-haemophilic factor IX.
A functional deficiency of factor IX, one of the coagulation factors involved in blood clotting, leads to the bleeding disorder known as Christmas disease, or haemophilia B. Both this disease and haemophilia A (factor VIII (C) deficiency) are X chromosome-linked and together occur at a frequency of approximately 1 in 10,000 males. The molecular basis for the functional alteration of factor IX in Christmas disease is not clearly understood. As a first step towards the elucidation of the molecular events involved, we have attempted molecular cloning of the factor IX gene. We used a bovine factor IX cDNA clone, isolated using synthetic oligonucleotides as probes, to screen a cloned human gene library. Here we report the isolation and partial characterization of a lambda recombinant phage containing the human factor IX gene.
Bacteriophage lambda↗
Analysis of the procoagulant activities of factor IX concentrates.
The Factor VIII content of Factor IX concentrates was investigated by agarose gel electrophoresis which removed the interfering effects of stabilisers and proteolytic enzyme inhibitors. Factor VIII coagulant activity (FVIII C) as measured by clotting and amidolytic methods correlated well with the distribution of FVIII coagulant antigen (FVIII CAg). The FVIIIC activity was apparently not entirely due to the presence of activated coagulation enzymes, since none of the enzymicity patterns observed with various chromogenic substrates correlated completely with the FVIII peak. However, some enzyme activity was detected in positions coincident with the margins of the FVIII peak; these activities may represent complexes of some of the FVIII with activated coagulation factors.
Antigens↗
Covalent fixation of soluble derivatized dextrans to model proteins in low-concentration medium: application to factor IX and protein C.
Factor IX and protein C are zymogens implicated in blood clotting, and an increase in their plasmatic residence time would be of interest for the treatment of the disorders caused by their deficiency. In this context, the conjugation of these proteins to polymers such as modified dextrans could be used to approach the problem. Conjugate formation in concentrated medium ([protein] >50 g/L) is well documented, whereas drastic dilution ([protein] <1 g/L) is quite unfavorable. Before studying the binding of factor IX and protein C to polymers, the coupling of model proteins (human hemoglobin, Hb; human serum albumin, HSA) in low-concentration medium to benzenetetracarboxylate dextran (BTC-dextran) and dialdehyde dextran was investigated. To obtain soluble benzenetetracarboxylate dextran-based conjugates, the conditions of coupling were optimized; the use of sulfo-NHS was necessary to form a conjugate with benzenetetracarboxylate dextran. In fact, the O-acylurea intermediate formed between coupling agent [1-ethyl-3(3-dimethylaminopropyl) carbodiimide, EDC] and BTC-dextran must be stabilized. Concerning dialdehyde dextran, a more oxidized polymer and a higher pH of the buffer of coupling than for highly concentrated solution must be used to obtain a conjugate. Whatever polymer is used, HSA appeared clearly less reactive than Hb, which can be attributed to the better reactivity of N-terminal amino groups in this latter protein and to the marked affinity of benzenetetracarboxylate dextran for it. No soluble conjugate was formed between the same dextran derivatives and factor IX or protein C. Moreover, the activity of both coagulation factors was dramatically decreased by contact with EDC and glutaraldehyde, a small molecule. Thus, bad accessibility of protein amino groups is probably responsible for this lack of reactivity. Nevertheless, it could be shown that carboxylate and amino groups were essential to the activity of factor IX and protein C.
Blood Coagulation Factors↗
Diagnostic role of an immunoassay-detected polymorphism of factor IX for potential carriers of hemophilia B.
In hemophilia B, assays based on a monoclonal antifactor IX specific for the Thr-148 variant of an exonic polymorphism have diagnosed carriers in selected families by either establishing linkage or by indicating the presence or absence of a given normal factor IX. The sensitivity of the immunoassays for detecting heterozygous women was explored by comparing results from immunoassays with solid-phase polyclonal v the monoclonal antifactor IXs. Factor IX with the normal Ala-148 variant gave a flat dilution curve, qualitatively distinct from factor IX with the Thr-148 variant in the monoclonal assay. The two were indistinguishable in the polyclonal assay. Mixtures of equal amounts of the two types gave an intermediate result, about half as reactive in the monoclonal as compared with the polyclonal assay system. Whereas mixtures with 10% Ala-148 and 90% Thr-148 factor IXs could not readily be distinguished from Thr-148 factor IX plasma, as little as 1% of the Thr-148 protein was detected in Ala-148 factor IX plasma. The frequency of the Ala-148 variant varied in individuals with different ethnic backgrounds; it was found in 29% of white, 12% of black, and none of Asian blood donors' factor IX genes in Seattle. Only 4% of samples from South African black men were nonreactive (ie, Ala-148). The Thr/Ala-148 dimorphism is in strong linkage disequilibrium with Taql restriction fragment length polymorphisms (RFLPs). Three recombinations were noted in normal white genes and one in a normal black factor IX gene (less than 2% of those examined). In 34 white families with at least one woman being a possible carrier, genetically, the immunoassay results were informative in 18. RFLP analyses were informative in eight of the 15 families tested. In five families each, assignment of carrier status was made to a woman by only DNA or only immunoassay results, whereas the other approach was noninformative. The immunoassays provide a rapid, inexpensive screening test and complement DNA analysis in white women who are potential carriers of hemophilia B.
Factor IX↗
Factor IX is activated in vivo by the tissue factor mechanism.
Despite significant progress in elucidating the biochemistry of the hemostatic mechanism, the process of blood coagulation in vivo remains poorly understood. Factor IX is a vitamin K-dependent glycoprotein that can be activated by factor XIa or the factor VII-tissue factor complex in vitro. To investigate the role of these two pathways in factor IX activation in humans, we have developed a sensitive procedure for quantifying the peptide that is liberated with the generation of factor IXa. The antibody population used for the immunoassay was raised in rabbits and chromatographed on a factor IX-agarose immunoadsorbent to obtain antibody populations with minimal intrinsic reactivity toward factor IX. We determined that the mean level of the factor IX activation peptide (FIXP) in normal individuals under the age of 40 years was 203 pmol/L and that levels increased significantly with advancing age. The mean concentration of FIXP was markedly reduced to 22.7 pmol/L in nine patients with hereditary factor VII deficiency (factor VII coagulant activity less than 7%) but was not significantly different from normal controls in nine subjects with factor XI deficiency (factor XI coagulant activity less than 8%). These data indicate that factor IXa generation in vivo results mainly from the activity of the tissue factor mechanism rather than the contact system (factor XII, prekallikrein, high molecular-weight kininogen, factor XI). Our results may also help to explain the absence of a bleeding diathesis in many patients with deficiencies of the contact factors of coagulation.
Adult↗
Prenatal diagnosis of hemophilia B by an immunoradiometric assay of factor IX.
An immunoradiometric assay of factor IX was developed based on homologous antibodies that arose in a hemophilic patient. With this assay, 11 of 12 patients with severe hemophilia B had factor IX antigen levels below 1 U/dl and 6 patients with mild hemophilia B had various levels. Factor IX antigen in 8 fetuses (16th-20th gestational week) aborted for therapeutic reasons ranged from 1.8 to 10.0 U/dl. Six amniotic fluids contained 0.28-1.2 U/dl factor IX antigen. Using the immunoradiometric assay, we could diagnose hemophilia B prenatally in one fetus at risk. No factor IX antigen (< 0.2 U/dl) was detectable in the fetoscopic sample. After termination of the pregnancy, analysis of blood from the abortus confirmed the diagnosis of severe hemophilia B. We conclude that very sensitive immunologic assays, such as the one described here, will prove useful in prenatal diagnosis of severe hemophilia B, since determination of factor IX activity in fetoscopic samples is unrealiable because of possible contamination with thromboplastic material.
Dose-Response Relationship, Immunologic↗
Functional domains in the heavy-chain region of factor XI: a high molecular weight kininogen-binding site and a substrate-binding site for factor IX.
To probe the molecular interactions of factor XI we have prepared two monoclonal antibodies (MoAbs; 5F7 and 3C1), each of which binds the heavy chain of reduced and alkylated factor XIa. Competitive solid phase radioimmunoassay (RIA) binding studies revealed that 5F7 and 3C1 are directed against different epitopes within factor XI. One antibody (5F7) blocked the surface-mediated proteolytic activation of factor XI and its binding to HMW kininogen, but had no effect on factor-XIa-catalyzed factor IX activation. The other antibody (3C1) is a competitive inhibitor of factor-IX activation by factor XIa, but blocked factor-XI binding to HMW kininogen only at 1,000-fold higher concentration than 5F7. Moreover, HMW kininogen had no effect on the kinetics of factor-XIa-catalyzed factor-IX activation. Furthermore, factor XI CNBr peptide fragments that bind to the 5F7 and 3C1 antibodies were isolated. The peptides that bound to the 5F7 antibody blocked the binding of HMW kininogen to factor XI but did not inhibit factor-XIa-catalyzed factor-IX activation. However, the peptides isolated by the 3C1 antibody inhibited factor-XIa-catalyzed factor-IX activation and had no effect on factor-XI binding to HMW kininogen. Our results indicate that distinct functional domains within the heavy chain region of factor XI are important for the binding of factor XI to HMW kininogen and for activation of factor IX by factor XIa.
Antibodies, Monoclonal↗
Christmas factor: dosage compensation and the production of blood coagulation factor IX.
The amount of factor IX (Christmas factor) for different genotypic classes was determined by means of a variant of the thromboplastin generation test. The mean value for females heterozygous for the Christmas gene was about half the mean values for normal males and for normal homozygous females; means for the latter two groups were about equal. This dosage compensation is interpreted as evidence in support of Lyon's hypothesis, according to which one X chromosome is inactive in mammalian females.
Animals↗
The assay of Factor IX: with a note on the use of a bentonite suspension in the preparation of an artificial substrate system for Factor IX assay.
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Adsorption↗
Expression, purification, and characterization of recombinant gamma-carboxylated factor IX synthesized in Chinese hamster ovary cells.
Factor IX has been expressed to high levels within a recombinant host cell and the biologically active fraction subsequently purified to homogeneity for characterization. The coding sequence for Factor IX was inserted into a mammalian cell expression vector and transfected into dihydrofolate reductase-deficient Chinese hamster ovary cells. The integrated DNA was amplified to a high copy number by selection for increasingly higher expression levels of the marker gene, dihydrofolate reductase, contained within a co-transfected plasmid. Cloned cell lines secreting over 100 micrograms/ml Factor IX antigen and up to 1.5 microgram/ml native Factor IX antigen have been obtained. Expression of biologically active Factor IX was dependent on the presence of vitamin K in the culture media. The gamma-carboxylated Factor IX was isolated from cell culture fluid by immunoaffinity chromatography using antibodies conformation-specific for the metal-stabilized conformer of Factor IX. This conformation is dependent upon metal ions and gamma-carboxyglutamic acid. Purified recombinant Factor IX migrated as a single band on sodium dodecyl sulfate-polyacrylamide gel electrophoresis with an electrophoretic mobility equivalent to plasma-derived Factor IX. The purified recombinant Factor IX demonstrated Factor IX coagulant activity, measured in Factor IX-deficient plasma, of 35-75 units/mg. Amino acid analysis of the alkaline hydrolysate of recombinant Factor IX demonstrated an average of 6-7 mol of gamma-carboxyglutamic acid per mol of Factor IX. NH2-terminal sequence analysis of the first 17 residues revealed equivalent amino acid sequences for both purified recombinant and plasma-derived Factor IX. The results represent the first purification and characterization of a biologically active, gamma-carboxylated vitamin K-dependent protein expressed in a recombinant DNA system.
Amino Acid Sequence↗
Transcriptional regulation of the human factor IX promoter by the orphan receptor superfamily factor, HNF4, ARP1 and COUP/Ear3.
A study of the human clotting factor IX promoter by DNase I footprinting and gel shifts in vitro, and by functional analysis of HepG2 cells in vivo, suggests that the liver-enriched transcription factor, HNF4, is involved in transactivating two cis-acting elements, i.e. X (nucleotides -15 to +3) and Y (nucleotides +15 to +36), in addition to the well-known element centred around nucleotide -20. Other members of the orphan receptor superfamily, e.g. ARP1 and COUP/Ear3, repress the factor IX promoter possibly by competition with HNF4 binding sites in the X and Y elements, but probably not at the -20 element. Mutations at -6 in the promoter, similar to those found in patients with haemophilia B, hinder HNF4 binding and transactivation of the X element, suggesting that impaired HNF4 binding contributes to the down-regulation of the factor IX expression in these patients, but is unlikely to be the only factor involved.
Base Sequence↗
Construction and its expression of a new retroviral vector containing a human blood coagulation factor IX cDNA.
We constructed a new factor IX expression vector containing a full length factor IX cDNA. The Moloney Murine Leukemia Virus (MoMLV)-based retroviral vector pLRNL was cloned with the entire coding region of human factor IX down stream of the promoter of Rous sarcoma virus, giving rise to the construct pL9RNL. The GP+E 86 packaging cell was transfected with pL9RNL and two mouse fibroblast cell lines (PA317 and NIH3T3) were infected with the virus generated from PA317 cell. During the 24 hr culture period, the maximum 1.2 micrograms of factor IX was secreted into the medium from 10(6) of GP+E 86 cells. Factor IX in the culture media had the relatively normal procoagulant activity and was barium-citrate precipitated. Western blotting analysis of the barium-citrate precipitates revealed that a single chain 50Kd protein indistinguishable from the plasma-derived factor IX was produced in these three cells. The retroviral expression system that we utilized herein may contribute to the study of recombinant wild type or various mutant factor IX, and to the basic study for the future gene therapy.
Animals↗
Characteristics and thrombogenicity of factor IX concentrate.
Thrombogenicity of the factor IX concentrate and its clinical use for stoppage of the bleeding in the case of hemophilia A with inhibitor were reported. (1) Factor IX concentrate contained the coagulation factors as prothrombin complex (factors II, VII, IX and X); Thrombin and factor Xa. (2) Prothrombin in the factor IX concentrate could be converted to thrombin without any additional procoagulant such as thromboplastin or factor V, but in just 2.5M glycine solution by the effect of factor Xa. (3) The infusion of factor IX concentrate into a rabbit induced DIC promptly which was proved by autopsy and coagulation-fibrinolytic studies. (4) Factor IX concentrate showed a great efficacy in stopping the bleeding in the case of hemophilia A with inhibitor.
Adult↗