Molecular cloning of a cDNA encoding human antihaemophilic factor

Detection of human DNA polymorphisms with a simplified denaturing gradient gel electrophoresis technique

Single base pair differences between otherwise identical DNA molecules can result in altered melting behavior detectable by denaturing gradient gel electrophoresis. We have developed a simplified procedure for using denaturing gradient gel electrophoresis to detect base pair changes in genomic DNA. Genomic DNA is digested with restriction enzymes and hybridized in solution to labeled single-stranded probe DNA. The excess probe is then hybridized to complementary phage M13 template DNA, and the reaction mixture is electrophoresed on a denaturing gradient gel. Only the genomic DNA probe hybrids migrate into the gel. Differences in hybrid mobility on the gel indicate base pair changes in the genomic DNA. We have used this technique to identify two polymorphic sites within a 1.2-kilobase region of human chromosome 20. This approach should greatly facilitate the identification of DNA polymorphisms useful for gene linkage studies and the diagnosis of genetic diseases.

The human insulin-like growth factor II gene contains two development-specific promoters

The insulin-like growth factors (IGF) play an important role in fetal and postnatal development. Recently, the nucleotide sequences of the cDNAs encoding IGF-I and IGF-II and part of the human IGF genes were reported. In this communication we describe two distinct IGF-II cDNAs isolated from a human adult liver and a human hepatoma cDNA library, respectively. Using these two cDNAs, we have established that the human IGF-II gene contains at least 7 exons. Two different IGF-II promoters have been identified, 19 kilobases (kb) apart, which are active in a development-specific manner. The promoter, active in the adult stage, is located only 1.4 kb downstream from the insulin gene.

Vasoactive intestinal peptide gene: putative mechanism of information storage at the RNA level

The human gene coding for vasoactive intestinal peptide was recently isolated and shown to contain seven exons. We now demonstrate that an intron-containing precursor RNA can be the major vasoactive intestinal peptide-related RNA in the cell, which is in contrast to most known genes. By RNA blot analysis using a variety of genomic and cDNA-related probes we show that in a human tumor producing vasoactive intestinal peptide, most of the RNA encoding the peptide is of the precursor type. Similar precursor transcripts were found in total rat brain RNA as well. A proof of the identity of the intron-containing RNA, cDNA clones corresponding to this RNA sequence have been isolated.

Human CSF-1: molecular cloning and expression of 4-kb cDNA encoding the human urinary protein

A 4-kilobase complementary DNA (cDNA) encoding human macrophage-specific colony-stimulating factor (CSF-1) was isolated. When introduced into mammalian cells, this cDNA directs the expression of CSF-1 that is structurally and functionally indistinguishable from the natural human urinary CSF-1. Direct structural analysis of both the recombinant CSF-1 and the purified human urinary protein revealed that these species contain a sequence of at least 40 amino acids at their carboxyl termini which are not found in the coding region of a 1.6-kilobase CSF-1 cDNA that was previously described. These results demonstrate that the human CSF-1 gene can be expressed to yield at least two different messenger RNA species that encode distinct but related forms of CSF-1.

von Willebrand disease

von Willebrand disease (vWD) is a bleeding disorder characterized by a complex hemostatic defect. Abnormal platelet function, usually reflected by a prolonged bleeding time, is the result of a quantitative or qualitative defect of von Willebrand factor (vWF). A secondary deficiency of factor VIII procoagulant protein (factor VIII) may occur leading to a coagulation defect as well. These two glycoprotein macromolecules circulate as a complex in plasma. This article will review current understanding of structures and functions of vWF factor and factor VIII as they relate to the pathogenesis, diagnosis, classification and therapy of vWD.

Molecular pathology and immunology of factor VIII (hemophilia A and factor VIII inhibitors)

Factor VIII is a large procoagulant glycoprotein that circulates in plasma in a noncovalent complex with von Willebrand factor. It is essential for the efficient cleavage of coagulation factor X by factor IXa, and its absence causes a severe bleeding disorder. Plasma factor VIII is reduced from the normal range of approximately 100 to 200 ng/ml in patients with the hereditary coagulation defect, hemophilia A, as well as in patients who develop autoantibodies that inactivate factor VIII. The understanding of factor VIII structure has been enhanced by recent studies that have characterized the X chromosome gene responsible for its synthesis, and preliminary information is now available about specific genetic defects. The basis for antibody formation in approximately 15 per cent of repeatedly transfused hemophilic patients is less clear at this time, however, for these individuals appear to have a variety of genetic defects that are not characteristically different from the patients who do not develop inhibitors. Although the antibodies cause a serious problem for affected individuals, they have been very useful in characterizing normal factor VIII and nonfunctional factor VIII-like protein that is found in the plasmas of 10 per cent of patients with mild hemophilia. Moreover, they are very useful reagents that can be used for immunoassay of factor VIII that has been modified in ways that have destroyed its procoagulant function.

[New possibilities of heterozygote detection of hemophilia A]

Hemophilia A is the most common inherited bleeding disorder in man. The recent isolation of the hemophilia gene has led to the identification of an intragenic restriction fragment length polymorphism (RFLP) which can be used for segregation analysis in families at risk for carrying the disease. In addition, a tightly linked extragenic RFLP can also be used for these analyses. In this paper, we exemplify the usefulness of DNA analysis in genetic counseling of families at risk for hemophilia A. Although DNA analysis allows carrier detection in the majority of families, bioassays are still required for accurate diagnosis when DNA analysis is not informative.

Construction and characterization of an active factor VIII variant lacking the central one-third of the molecule

The primary structure of factor VIII consists of 2332 amino acids that exhibit 3 distinct structural domains, including a triplicated region (A domains), a unique region of 909 amino acids (B domain), and a carboxy-terminal duplicated region (C domains), that are arranged in the order A1-A2-B-A3-C1-C2. The B domain (residues 741-1648) of factor VIII is lost when factor VIII is activated by thrombin, which proteolytically processes factor VIII to active subunits of Mr 50,000 (domain A1), 43,000 (domain A2), and 73,000 (domains A3-C1-C2). To determine if the B domain is required for factor VIII coagulant activity, a variant was constructed by using recombinant DNA techniques in which residues 797-1562 were eliminated. This shortened the B domain from 909 to 142 amino acids. This variant factor VIIIdes-797-1652 was expressed in mammalian cells and was found to be functional. The factor VIIIdes-797-1562 protein was purified and shown to be processed by thrombin in the same manner as full-length factor VIII. The factor VIIIdes-797-1562 variant also bound to von Willebrand factor (vWF) immobilized on Sepharose. These results indicate that most of the highly glycosylated B domain of factor VIII is not required for the expression of factor VIII coagulant activity and its interaction with vWF.

Overlapping cDNA clones define the complete coding region for the P210c-abl gene product associated with chronic myelogenous leukemia cells containing the Philadelphia chromosome

The Philadelphia chromosome, observed in greater than 90% of patients with chronic myelogenous leukemia, results from a reciprocal translocation between chromosomes 9 and 22. The translocation breakpoint on chromosome 9 occurs near the ABL gene and correlates with the production of a chronic myelogenous leukemia-specific 8.5-kilobase ABL-related mRNA species accompanied by a structurally altered ABL protein (P210c-abl). The N-terminal sequence of the protein is derived from the BCR gene on chromosome 22. We have isolated overlapping cDNA clones from the K-562 cell line corresponding to approximately 8.5 kilobases of mRNA and have sequenced 2550 nucleotides at the 5' end. Our results indicate that the 5' end of the 8.5-kilobase mRNA consists of greater than 400 nucleotides of noncoding sequence that are greater than 80% G + C rich. Based on our sequence analysis, we propose that initiation of translation occurs at nucleotide 471, such that the initial 927 amino acids of P210c-abl are derived from BCR sequences. Our cDNA clones thus define the complete coding sequences for the P210c-abl gene product.

Recurrent mutations in haemophilia A give evidence for CpG mutation hotspots

Haemophilia A is a common disorder of blood coagulation caused by a deficiency of factor VIII. It is inherited as an X-linked recessive trait, and one-third of all cases are thought to result from de novo mutations. The clinical severity of haemophilia A varies markedly among different families and a subset of the patients with severe disease develop antibodies against factor VIII, called inhibitors. Because of this heterogeneity, it is likely that many different molecular lesions result in haemophilia A. Indeed, of the nine mutations described to date, all appear to be unique changes. However in this study of 83 patients with haemophilia A we have identified two different point mutations, one in exon 18 and one in exon 22, that have recurred independently in unrelated families. Each mutation produces a nonsense codon by a change of CG to TG, and each occurred de novo on the X-chromosome donated by the maternal grandfather. These observations strongly support the view that CpG dinucleotides are mutation hotspots.

Molecular cloning and expression of neuroleukin, a neurotrophic factor for spinal and sensory neurons

A novel 56,000-dalton growth factor found in mouse salivary gland was purified, molecularly cloned, and expressed in monkey COS cells. The protein is a neurotrophic factor and also, surprisingly, a lymphokine product of lectin-stimulated T cells. The factor was therefore named neuroleukin. Neuroleukin promotes the survival in culture of a subpopulation of embryonic spinal neurons that probably includes skeletal motor neurons. Neuroleukin also supports the survival of cultured sensory neurons that are insensitive to nerve growth factor, but has no effect on sympathetic or parasympathetic neurons. The amino acid sequence of neuroleukin is partly homologous to a highly conserved region of the external envelope protein of HTLV-III/LAV, the retrovirus that causes acquired immune deficiency syndrome.

Human factor VIII: purification from commercial factor VIII concentrate, characterization, identification and radiolabeling

Human factor VIII was purified from commercial factor VIII concentrate with a 12% yield. The specific coagulant activity of purified factor VIII was 8,000 units/mg. In the presence of SDS the purified factor VIII consisted of a variety of polypeptides on polyacrylamide gels, ranging between Mr 80,000 and Mr 208,000. In the absence of SDS the purified factor VIII showed an apparent molecular weight of 270,000 upon Sephadex G200 gel-filtration. The purified factor VIII could be activated by thrombin, which resulted in the disappearance of Mr 108,000-208,000 polypeptides in favor of an Mr 92,000 polypeptide. Treatment with factor Xa also activated factor VIII, whereas treatment with activated protein C resulted in the inactivation of coagulant activity. Coagulant-active 125I-factor VIII was prepared using a lactoperoxidase radioiodination procedure. This 125I-factor had the same characteristics as unlabeled factor VIII. All polypeptides could be precipitated with monoclonal antibodies directed against factor VIII. With 125I-factor VIII a pIapp of 5.7 was found in the presence of urea.

Human IL-3 (multi-CSF): identification by expression cloning of a novel hematopoietic growth factor related to murine IL-3

A cDNA clone encoding a novel hematopoietic growth factor activity produced by a gibbon T cell line has been identified using a mammalian cell expression cloning system. The sequence of this cDNA proved to have significant homology to the sequence encoding murine interleukin 3 (IL-3). The human gene, which was readily identified because of its high degree of homology to the gibbon sequence, also displayed significant homology with the murine IL-3 sequence. The recombinant gibbon IL-3 protein proved to have multipotent colony stimulating activity when tested with normal human bone marrow cells, proving that this primate hematopoietin is not only structurally but also functionally related to murine IL-3.

Cloning of a cDNA coding for human factor V, a blood coagulation factor homologous to factor VIII and ceruloplasmin

Coagulation factor V is a high molecular weight plasma glycoprotein that participates as a cofactor in the conversion of prothrombin to thrombin by factor Xa. A phage lambda gt11 Hep G2 cell cDNA expression library was screened by using an affinity-purified antibody to human factor V, and 11 positive clones were isolated and plaque-purified. The clone containing the largest cDNA insert contained 2970 nucleotides and coded for 938 amino acids, a stop codon, and 155 nucleotides of 3' noncoding sequence including a poly(A) tail. The coding region includes 651 amino acids from the carboxyl terminus that constitute the light chain of human factor Va and 287 amino acids that are part of the connecting region of the protein. The predicted amino acid sequence agreed completely with 147 amino acid residues that were identified by Edman degradation of cyanogen bromide peptides isolated from the light chain. During the activation of factor V, several peptide bonds are cleaved by thrombin, giving rise to a heavy chain, a connecting fragment(s), and a light chain. The light chain is generated by the cleavage of an Arg-Ser peptide bond. The amino acid sequence of the light chain is homologous (40%) with the carboxyl-terminal fragment (Mr, 73,000) of human factor VIII. Both fragments have a similar domain structure that includes a single ceruloplasmin-related domain followed by two C domains. The carboxyl terminus of the connecting region, however, shows no significant amino acid sequence homology with factor VIII. It is very acidic and contains a number of potential N-linked glycosylation sites. It also contains about 20 tandem repeats of nine amino acids.

Cloning and expression of multiple protein kinase C cDNAs

Three different protein kinase C related cDNA clones were isolated from a rat brain cDNA library and designated PKC-I, PKC-II, and PKC-III. These each encode very similar, but distinct, polypeptides that contain a region homologous with other protein kinases. COS cells transfected with either PKC-I or PKC-II specifically bind at least 5-fold more 3H-PDBu (phorbol ester) than control cells. An increase in Ca2+, phosphatidylserine, and diacylglycerol/phorbol-ester-dependent protein kinase activity is also observed in COS cells transfected with either PKC-I or PKC-II. The physiological implications of the discovery of three protein-kinase-C-related cDNAs are discussed.

Transcriptional interference and termination between duplicated alpha-globin gene constructs suggests a novel mechanism for gene regulation

The interesting possibility that transcriptional interference can occur between eukaryotic genes was raised by studies on the avian leukosis retrovirus (ALV) which showed that deletion of the promoter in the 5' long terminal repeat (LTR) activates the 3' LTR promoter, linked to a downstream gene. These observations provide a molecular explanation for the fact that insertional oncogenesis by the ALV promoter is invariably associated with either a rearranged or deleted 5' LTR sequence. This letter extends these findings to chromosomal RNA polymerase II genes by studying transcriptional interference between duplicated alpha-globin gene constructions. I demonstrate that transcriptional interference causes substantial inhibition of the downstream alpha gene by transcription of the upstream alpha gene. Furthermore, this inhibition is alleviated by placing transcriptional termination signals between the two alpha genes. Because many eukaryotic genes may be arranged in tandem on a chromosome, these observations suggest that transcriptional termination is an important mechanism for preventing interference between adjacent genes. The selective use of termination signals may provide a novel way of regulating the activity of eukaryotic genes.

A large region (approximately equal to 95 kDa) of human factor VIII is dispensable for in vitro procoagulant activity

Factor VIII (antihemophilic factor) is a high molecular weight plasma glycoprotein that participates in the blood clotting cascade. The recent cloning and sequence analysis of the cDNA encoding human factor VIII revealed an obvious domain structure for the protein, which can be represented as A1-A2-B-A3-C1-C2. We now report the DNA sequence analysis of porcine exons encoding the entire B domain and part of the A2 and A3 domains. We found an unusually high degree of porcine-human amino acid sequence divergence in the B region compared with the limited sequence available for other regions of the porcine factor VIII molecule. In addition to sequence divergence, there are numerous gaps in the porcine B domain totalling over 200 amino acids. Recombinant DNA techniques were used to effect the removal of large segments of DNA encoding the B domain from the full-length human factor VIII cDNA. These constructs directed the synthesis of biologically active factor VIII when introduced into mammalian cells despite the deletion of up to 38% of the factor VIII molecule.

Complete cDNA sequence of human preceruloplasmin

A cDNA for human ceruloplasmin (EC 1.16.3.1) was identified in a human liver cDNA library by screening with two mixtures of synthetic oligodeoxyribonucleotides that were complementary to two regions of ceruloplasmin mRNA as predicted from the amino acid sequence of plasma ceruloplasmin. The resulting clone (phCP1) contained DNA coding for amino acid residues 202-1046 of the protein, followed by a stop codon, a 3' untranslated region of 123 base pairs, and a poly(A) tail. To isolate cDNAs encoding the 5' end of ceruloplasmin mRNA, a cDNA library was constructed in lambda gt10. The cDNA for this library was synthesized by reverse transcription of human liver poly(A)+ RNA, using random oligonucleotides as primers. When this cDNA library was screened by using a 5' fragment of phCP1 as a hybridization probe, several positive clones were identified. One of these clones (lambda hCP1) contained DNA coding for a probable signal peptide of 19 amino acid residues followed by DNA coding for residues 1-380 of plasma ceruloplasmin. Blot hybridization analysis showed that ceruloplasmin mRNA from human liver and the human hepatoma cell line HepG2 is 3700 nucleotides in size. Liver contained an additional mRNA species that is like ceruloplasmin mRNA and is 4500 nucleotides in size. Comparison of the complete nucleotide sequences of human ceruloplasmin cDNA and human clotting factor VIII cDNA showed regions of sequence homology, suggesting that these two proteins have evolved from a common ancestor.

Immunohistological localization of factor VIII in placental endothelial cells

DNA-recombinant studies have established that factor VIII-mRNA is present in liver and placental tissue. In a previous immunohistological study using monoclonal antibodies we have localized factor VIII in liver sinusoidal endothelial cells. In this paper we demonstrate that also the endothelial cells lining the fetal vessels in human placenta contain factor VIII. Based on the combined results of the present study and a previous study we favour the concept that factor VIII is synthesized in placental endothelial cells.

A functional gamma gene formed from known gamma-gene segments is not necessary for antigen-specific responses of murine cytotoxic T lymphocytes

Structural similarities between surface immunoglobulins (s Ig) on B cells and antigen-specific receptors on T cells suggest that a T cell, like a B cell, should express only two immunoglobulin-like genes, one for each subunit of the disulphide-linked, heterodimeric, antigen-specific (alpha beta) T-cell receptor. However, cytotoxic T lymphocytes (Tc cells) and immature thymocytes also contain RNA transcripts of a third immunoglobulin-like gene, called gamma (refs 1-4). A polypeptide corresponding to the gamma gene has not yet been identified and the function of this gene remains an enigma. Judging from its nucleotide sequence, the rearranged gamma gene is expected to encode an integral membrane polypeptide chain, and gamma complementary DNAs from two cloned Tc cell lines have previously been found to have different sequences around the V-J (variable region-joining region) junction, suggesting that, in these cells, the gamma-gene product is a clonally diverse surface structure that may form part of an as yet unidentified, antigen-specific receptor. To analyse further the extent of diversity of the gamma-gene product, we have determined the partial sequences of 11 gamma cDNA clones from three other cloned Tc cell lines, and report here that the sequences are indeed clonally diverse, but in all instances they are out-of-phase in the region of the V-J junction. This finding and the pattern of gamma-gene rearrangements in these cell lines indicate that a polypeptide product of the previously reported gamma gene, V2J2-C2, is not expressed in them and is, therefore, not necessary for the antigen-specific cytotoxic and proliferative responses of these mature T cells.

The size of human factor VIII heterodimers and the effects produced by thrombin

The heterodimeric structure of factor VIII was demonstrated by two approaches. First, the native molecular weights of several partially purified fractions of factor VIII were determined by measurement of Stokes radii and sedimentation coefficients to be approx. 237 500, 201 000 and 141 000. These measured molecular weights correlated with those derived from polypeptide chain composition, in which each molecule would consist of a doublet polypeptide of Mr 83 000/81 000 plus one predominant high-Mr polypeptide of either 146 000, 120 000 or 93 000. In addition, immunoadsorption using a monoclonal antibody specific for the light-chain doublet removed all of the heavy chains. Separation of the heavy chains from the light chain by EDTA further illustrated the non-covalent nature of the heterodimers. All forms had coagulant activity which was potentiated 13-15-fold by an equimolar amount of human alpha-thrombin. Thrombin converted the Mr 83 000/81 000 doublet to one of Mr 73 000/71 000, and cleaved the largest polypeptides to a transient intermediate form of Mr 93 000 which was further cleaved to polypeptides of Mr 51 000 and 43 000. Potentiation of coagulant activity was correlated with proteolytic cleavage of either or both the doublet and the Mr 93 000 polypeptides. These data indicate that human factor VIII purified from plasma consists of a group of heterodimers, composed of a light chain of Mr 83 000 (81 000) and a heavy chain which varies in size between Mr 170 000 and 93 000, each form of which is similarly potentiated and cleaved by thrombin.

Identification of a missense mutation in the factor VIII gene of a mild hemophiliac

DNA probes derived from the cloned factor VIII gene can be used to detect mutations in the factor VIII gene of hemophiliacs. DNA hybridization analysis led to the identification of two contrasting point mutations in the same codon. In a severe hemophiliac with no detectable factor VIII activity, the normal arginine codon (number 2307) is converted to a stop codon, while in a mild hemophiliac with 10 percent of normal activity, this same codon is converted to glutamine.

A new polymorphism in the factor VIII gene for prenatal diagnosis of hemophilia A

A restriction fragment length polymorphism (RFLP) has been found in the gene for clotting factor VIII. Defects in this gene are the cause of hemophilia A. The DNA polymorphism affects an XbaI site in intron 22 of the gene. Two alleles occur in a frequency of 59 and 41 percent of the X chromosomes tested. Furthermore, about 25 percent of females who are homozygous for the previously reported BclI RFLP in the factor VIII gene are heterozygous for the XbaI polymorphism. This new RFLP thus represents a significant addition to available probes for the DNA-based prenatal diagnosis and carrier detection of this disease.

Correlations between T-cell specificity and the structure of the antigen receptor

The derived amino-acid sequences of the heterodimeric antigen receptors expressed by a series of murine T-cell clones are presented. A comparison of the receptor sequences indicates that several mechanisms for generating receptor diversity can influence T-cell specificity, including junctional diversity, combinatorial joining, and combinatorial chain associations.

Isolation and characterization of human factor VIII: molecular forms in commercial factor VIII concentrate, cryoprecipitate, and plasma

Human factor VIII has been isolated from a high purity factor VIII concentrate by immunoaffinity chromatography and HPLC on Mono Q gel. Two fractions of factor VIII were obtained with a specific activity of approximately equal to 7000 units/mg. The major fraction contained eight peptide chains of 200, 180, 160, 150, 135, 130, 115, and 105 kDa plus one doublet chain of 80 kDa. The minor fraction contained one peptide chain of 90 kDa plus the chain of 80 kDa. Both fractions were activated by thrombin to the same extent. Amino-terminal amino acid sequence analysis was performed on the 180-kDa, 130-kDa, and 90-kDa chains and showed an identical amino-terminal sequence in these chains. Each chain from 200 kDa to 90 kDa was linked to one 80-kDa chain by a metal-ion bridge(s). Studies on factor VIII in plasma and cryoprecipitate, prepared and gel filtered in the presence of protease inhibitors, showed that one 200-kDa plus one 80-kDa chain were the only or dominating chains in the materials and may represent native factor VIII. The results indicated that all chains from 180 kDa to 90 kDa are fragments of the 200-kDa chain. All of these more or less fragmented chains form active factor VIII complexes with the 80-kDa chain.

Characterization of a cDNA coding for human factor VII

Factor VII is a precursor to a serine protease that is present in mammalian plasma. In its activated form, it participates in blood coagulation by activating factor X and/or factor IX in the presence of tissue factor and calcium. Clones coding for factor VII were obtained from two cDNA libraries prepared from poly(A) RNA from human liver and Hep G2 cells. The amino acid sequence deduced from the cDNAs indicates that factor VII is synthesized with a prepro-leader sequence of 60 or 38 amino acids. The mature protein that circulates in plasma is a single-chain polypeptide composed of 406 amino acids. The amino acid sequence analysis of the protein and the amino acid sequence deduced from the cDNAs indicate that factor VII is converted to factor VIIa by the cleavage of a single internal bond between arginine and isoleucine. This results in the formation of a light chain (152 amino acids) and a heavy chain (254 amino acids) that are held together by a disulfide bond. The light chain contains a gamma-carboxyglutamic acid (Gla) domain and two potential epidermal growth factor domains, while the heavy chain contains the serine protease portion of the molecule. Factor VII shows a high degree of amino acid sequence homology with the other vitamin K-dependent plasma proteins.

Cloning of a portion of the chromosomal gene for human erythrocyte alpha-spectrin by using a synthetic gene fragment

A region of minimal codon degeneracy was selected from the amino acid sequence of the amino-terminal alpha I domain of human erythrocyte spectrin to design a 90-base-pair DNA probe for the screening of a human genomic library. Five complementary oligonucleotides were assembled to form a full-length double-stranded DNA, which was then cloned in an M13 phage vector to generate hybridization probes. Under stringent conditions, a single hybridizing clone was isolated from a total human genomic library. Partial DNA sequence analysis established the 16.8-kilobase-pair isolate as erythrocyte alpha-spectrin by correlation to a known sequence of 131 amino acids. The spectrin 106 amino acid repeat segment is encoded by multiple exons separated by introns of various sizes. Of the 3074 base pairs of DNA sequenced thus far, 12.8% code for amino acids.

Monoclonal antibodies and the haemostasis laboratory: current position

In recent years research laboratories have produced a wide variety of monoclonal antibodies to haemostatic proteins. While these have proven very useful in fundamental research they have not, as yet, been widely used as routine reagents. This article reviews the range of monoclonal antibodies currently available and discusses their potential applications in routine laboratory practice.

A new member of the plasma protease inhibitor gene family

A 2.1-kb cDNA clone representing a new member of the protease inhibitor family was isolated from a human liver cDNA library. The inhibitor, named human Leuserpin 2 (hLS2), comprises 480 amino acids and contains a leucine residue at its putative reactive center. HLS2 is about 25-28% homologous to three human members of the plasma protease inhibitor family: antithrombin III, alpha 1-antitrypsin and alpha 1-antichymotrypsin. A comparison with published partial amino acid sequences shows that hLS2 is closely related to the thrombin inhibitor heparin cofactor II.

The physiology and pathophysiology of the factor VIII complex

The factor VIII complex consists of two noncovalently linked proteins: von Willebrand factor (VWF) and factor VIII (FVIII). VWF plays an important role in primary hemostasis by mediating the adherence of blood platelets to the damaged vessel wall. A review of the literature on VWF is given with regard to its physicochemical properties and mode of action. FVIII acts as a cofactor in the factor Xa-generating enzyme complex of the intrinsic coagulation cascade. Starting with the recently published primary structure of FVIII, the literature is reviewed for structural information on FVIII. Also, an effort is made to characterize the interaction of FVIII with VWF and to discuss the possible physiological significance of FVIII-VWF complex formation. Interaction of FVIII with the clotting factors of the intrinsic pathway of coagulation is described in detail. Hemophilia and von Willebrand's disease (VWD) are both congenital bleeding disorders affecting a great many people. The different variants of these diseases are described with some reference to therapy and detection.

Localization of human factor FVIII inhibitor epitopes to two polypeptide fragments

Epitopes for 22 alloantibodies that inhibit factor VIII procoagulant protein (FVIII) from multitransfused individuals with severe hemophilia A and three autoantibodies from nonhemophilic individuals appeared to be restricted to two specific regions of the FVIII molecule. Immunoblotting of purified FVIII and purified thrombin-degraded FVIII, followed by reaction with inhibitor plasma samples, monoclonal anti-human IgG3 and IgG4 antibodies, and radiolabeled affinity-purified rabbit anti-mouse IgG, revealed that inhibitor epitopes could be localized to the Mr 72,000 and Mr 44,000 thrombin fragments of FVIII. These two chains are located at the carboxyl terminus and near the amino terminus of the FVIII molecule, respectively. The pattern of reactivity of the inhibitor alloantibodies could be divided into three types: 10 reacted with the Mr 72,000 chain, 3 reacted with the Mr 44,000 chain, and 9 reacted with both of these chains. Among the 3 inhibitor autoantibodies, 1 of each type was found. Ten normal plasmas, as well as 14 plasmas from multitransfused individuals with severe hemophilia A and no inhibitor, were not reactive with the FVIII immunoblots. However, one multitransfused individual with severe hemophilia A and no detectable inhibitor revealed the presence of an antibody reactive with the middle section of the FVIII molecule. The existence of FVIII inhibitor epitopes on both the Mr 72,000 and Mr 44,000 chains raises the possibility that these epitopes might be further restricted to regions of homology between the two chains. These data suggest the possibility of designing inhibitor blocking polypeptides for use as therapeutic agents.

Distribution of factor VIII mRNA and antigen in human liver and other tissues

The cellular site of synthesis of factor VIII (FVIII:C; anti-haemophilic factor) has long been sought. Previous studies suggested the liver as a major site of synthesis, but extrahepatic sources such as spleen and lung have been implicated. Using an immunoradiometric assay (IRMA), we recently localized factor VIII antigen (FVIII:Ag, formerly FVIII:CAg), to whole perfused guinea pig liver and spleen, and to isolated hepatocytes, with lesser or trace amounts in other tissues. Using an immunohistological technique, Stel et al. detected FVIII:Ag in normal human liver sinusoidal endothelial cells, while Exner et al. detected FVIII:Ag by IRMA in extracts of human lymph nodes, lung, liver and spleen. The localization of antigen in tissues does not, however, distinguish sites of factor VIII synthesis from those of storage, and such experiments are subject to misinterpretation due to entrapment of plasma factor VIII in tissues. The recent cloning of the human factor VIII gene provides hybridization probes for the detection of factor VIII messenger RNA in cells, thus directly determining sites of synthesis. During complementary DNA cloning, we detected factor VIII mRNA in liver, and it has been localized by others in liver and placenta and in liver and kidney. In the present study, we detected factor VIII mRNA in isolated human hepatocytes, in spleen and in numerous tissues including lymph nodes and kidney, but not in white blood cells or cultured endothelial cells. We also found that the factor VIII, factor VII, factor IX and protein C antigens in liver are predominantly localized in hepatocytes, while very little von Willebrand factor antigen (vWF:Ag, formerly FVIIIR Ag) is detectable in this organ.

Gene synthesis machines: DNA chemistry and its uses

Deoxyoligonucleotides can now be synthesized rapidly and in high yield because of recent advances in nucleic acid chemistry. Key innovations include solid-phase synthesis on silica-based supports and the development of stable deoxynucleoside phosphoramidites as synthons. When incorporated into manual, semiautomatic, or automatic instruments, these new procedures can be used to prepare probes, mixed probes, deoxyoligonucleotides for priming DNA synthesis, analogues of deoxyoligonucleotides, and DNA segments containing more than 100 deoxynucleotides.