Human von Willebrand factor (vWF): isolation of complementary DNA (cDNA) clones and chromosomal localization

Human thrombomodulin gene is intron depleted: nucleic acid sequences of the cDNA and gene predict protein structure and suggest sites of regulatory control

We have isolated a human thrombomodulin cDNA, and a human genomic clone containing the putative promoter domain, as well as the translated and untranslated regions of the endothelial cell receptor. The nucleotide sequence of the thrombomodulin cDNA allows us to provide a complete picture of the structure of this endothelial cell receptor, and to confirm its homology to the human low density lipoprotein receptor. The nucleotide sequence of the thrombomodulin gene suggests areas within the putative promoter domain that may be critical for regulating expression of the human endothelial cell receptor, indicates a potential signal peptide, and shows that no introns are present within the coding region. The overall organization of the human thrombomodulin gene is surprising because it represents an example of a gene that contains epidermal growth factor type B repeats and a membrane spanning region, which are not isolated within discrete exons.

A primary genetic linkage map for human chromosome 12

A primary genetic map for human chromosome 12 has been constructed from data on 23 restriction fragment length polymorphic systems collected in 38 normal families with large sibships. Linkage analysis of the genotypic data has ordered 16 loci into a continuous genetic map of 111 cM in males and 258 cM in females. Although most of the genetic map reflects a higher rate of recombination in females relative to males, significantly more frequent recombination was observed in males than in females in intervals between loci on the distal portion of the short arm of the chromosome. The mapping data shown here will serve as a first step toward a high-resolution genetic map for human chromosome 12.

Molecular cloning of the cDNA for tissue factor, the cellular receptor for the initiation of the coagulation protease cascade

We have isolated cDNA clones encoding the complete sequence of the heavy chain of tissue factor (TF), the high-affinity receptor responsible for cellular initiation of the coagulation protease cascade. An 885 bp open reading frame encodes a 295 amino acid polypeptide including a leader sequence with alternative cleavage sites. A single 2.3 kb mRNA is identified, and Southern blotting is consistent with a single gene. The coding sequence defines a protein with features characteristic of an integral membrane protein. This receptor appears novel, lacking significant homology with other proteins; however, TF contains the uncommon tryptophan-lysine-serine (WKS) sequence repeated three times, a sequence we find in some serine protease-binding proteins and suggest may represent a functional sequence motif.

Molecular cloning of the human gene for von Willebrand factor and identification of the transcription initiation site

A series of overlapping cosmid genomic clones have been isolated that contain the entire coding unit of the human gene for von Willebrand factor (vWf), a major component of the hemostatic system. The cloned segments span approximately 175 kilobases of human DNA sequence, and hybridization analysis suggests that the vWf coding unit is approximately 150 kilobases in length. Within one of these clones, the vWf transcription initiation site has been mapped and a portion of the vWf promoter region has been sequenced, revealing a typical "TATA box," a downstream "CCAAT box," and a perfect downstream repeat of the 8 base pairs containing the transcription start site. Sequencing of a segment of another genomic clone has revealed the vWf translation termination codon. Where tested, comparative restriction analysis of cloned and chromosomal DNA segments strongly suggests that no major alterations occurred during cloning and that there is only one complete copy of the vWf gene in the human haploid genome. Similar analyses of DNA from vWf-producing endothelial cells and nonexpressing leukocytes suggest that vWf gene expression is not accompanied by gross genomic rearrangements. In addition, there is significant homology of C-terminal coding sequences among the vWf genes of several vertebrate species.

Composition of the von Willebrand factor storage organelle (Weibel-Palade body) isolated from cultured human umbilical vein endothelial cells

von Willebrand factor (VWF) is a large, adhesive glycoprotein that is biosynthesized and secreted by cultured endothelial cells (EC). Although these cells constitutively release VWF, they also contain a storage pool of this protein that can be rapidly mobilized. In this study, a dense organelle fraction was isolated from cultured umbilical vein endothelial cells by centrifugation on a self-generated Percoll gradient. Stimulation of EC by 4-phorbol 12-myristate 13-acetate (PMA) resulted in the disappearance of this organelle fraction and the synchronous loss of Weibel-Palade bodies as judged by immunoelectron microscopy. Electrophoretic and serologic analyses of biosynthetically labeled dense organelle fraction revealed that it is comprised almost exclusively of VWF and its cleaved pro sequence. These two polypeptides were similarly localized exclusively to Weibel-Palade bodies by ultrastructural immunocytochemistry. The identity of the dense organelle as the Weibel-Palade body was further established by direct morphological examination of the dense organelle fraction. The VWF derived from this organelle is distributed among unusually high molecular weight multimers composed of fully processed monomeric subunits and is rapidly and quantitatively secreted in unmodified form after PMA stimulation. These studies: establish that the Weibel-Palade body is the endothelial-specific storage organelle for regulated VWF secretion; demonstrate that in cultured EC, the VWF concentrated in secretory organelles is of unusually high molecular weight and that this material may be rapidly mobilized in unmodified form; imply that proteolytic processing of VWF involved in regulated secretion takes place after translocation to the secretory organelle; provide a basis for further studies of intracellular protein trafficking in EC.

Gene deletions correlate with the development of alloantibodies in von Willebrand disease

Among all patients with von Willebrand disease (vWD), alloantibodies to von Willebrand factor (vWF) have been described only in severe vWD (type III). The relationship between the development of alloantibodies and the nature of the genetic lesion in vWD is not known. In hemophilia B, large deletions within the factor IX gene appear to correlate with the occurrence of alloantibodies, whereas in hemophilia A no such correlation is apparent. We have studied 19 patients with severe recessive vWD (type III) and 19 with autosomal dominant vWD (type I) by Southern blotting with probes encompassing the full 9 kilobases (kb) of the vWF cDNA. Two apparently unrelated patients were shown to have large deletions within the vWF gene. Both patients had severe vWD (type III) and were the only patients among those studied that had inhibitory alloantibodies to vWF. The extent of deletion was similar in both patients, corresponding to at least the 3'-7.4 kb of the vWF cDNA. The deletion in each patient was estimated to exceed 110 kb. In addition, the localization of the vWF gene to chromosome 12 was confirmed, and a homologous sequence on chromosome 22 was identified.

Treatment of severe platelet dysfunction and hemorrhage after cardiopulmonary bypass: reduction in blood product usage with desmopressin

Impairment of platelet function commonly occurs after cardiopulmonary bypass, and may result in substantial bleeding. Because desmopressin acetate (a synthetic analogue of vasopressin) shortens bleeding time in a variety of platelet disorders, a controlled clinical trial of intravenous desmopressin was performed in 39 patients with excessive mediastinal bleeding (greater than 100 ml/h) and a prolonged template bleeding time (greater than 10 minutes) more than 2 hours after termination of cardiopulmonary bypass. Twenty-three desmopressin recipients and 16 control patients (no desmopressin) were similar in surgical procedure, pump time, platelet count, template bleeding time and amount of bleeding before therapy (p = NS). Compared with the control group, the patients receiving desmopressin (20 micrograms; mean 0.3 micrograms/kg) utilized fewer blood products (29 +/- 19 versus 15 +/- 13 units/patient; p less than 0.05), especially platelets (12 +/- 9 versus 4 +/- 7 units/patient; p = 0.004), while achieving a similarly effective reduction in mediastinal bleeding (4.8- and 4.3-fold, p = 0.001 for both). Severe platelet dysfunction was partially corrected within 1 hour after desmopressin infusion, during which interval no blood products were administered: the template bleeding time shortened (from 17 to 12.5 minutes, p less than 0.05), whereas the platelet count remained unchanged (at 96 +/- 35 and 105 +/- 31 X 10(3)/mm3, p = NS). The plasma levels of two factor VIII components increased: procoagulant activity (VIII:C) from 0.97 +/- 0.43 to 1.52 +/- 0.74 units/ml (p less than 0.05) and von Willebrand factor (VIII:vWF) from 1.28 to 1.78 units/ml (p less than 0.05); these increases correlated with the shortening of the bleeding time (p less than 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)

Evolution of human von Willebrand factor: cDNA sequence polymorphisms, repeated domains, and relationship to von Willebrand antigen II

Four cDNAs extending into the 5'-noncoding region of the human von Willebrand factor cDNA have been characterized. Thirty-four residues of amino-terminal protein sequence for von Willebrand antigen II matched that predicted from the cDNA sequence, confirming that the propeptide of von Willebrand factor is von Willebrand antigen II. Among the known cDNA sequences there are four confirmed single nucleotide differences, of which two may be in linkage disequilibrium, and two would alter the protein sequence. Based on comparisons among the four repeated D domains, an evolutional model has been proposed to account for the distribution of these sequence elements in prepro-von Willebrand factor.

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.

Formation and regulation of platelet and fibrin hemostatic plug

Formation of a hemostatic plug represents one of the earliest responses to vessel wall injury. Platelets react to any discontinuity in the vascular endothelium through initial contact, spreading, and formation of a thrombus (or aggregate). This development of a primary hemostatic plug requires platelet membrane receptors through which the adhesive macromolecules, von Willebrand factor (vWF) and fibrinogen, anchor platelets to the vessel wall and link them to each other. There are two receptor pathways--classic and alternative--for the binding of vWF to platelets; the latter induced by thrombin, and adenosine diphosphate (ADP) is shared with fibrinogen. Synthetic peptides, patterned after known binding domains of adhesive molecules, have been designed to inhibit their interactions with platelet receptors. A secondary hemostatic plug, composed of platelets enmeshed in fibrin, results from the action of thrombin, which is not only essential for formation of fibrin but also for exposure of platelet receptors for adhesive molecules and for "activation" of factors V and VIII. Thrombin generation is greatly enhanced through the activity of the prothrombinase complex formed on the surface of platelets, perturbed endothelial cells, and leukocytes. A pivotal event is activation of factor X through the intrinsic and extrinsic coagulation pathways. Binding of factors IXa and VIIa to the vascular endothelium represents a localized mechanism for factor Xa generation. Formation of a platelet and fibrin thrombus is controlled by regulatory mechanism: prostacyclin, endogenous heparin-antithrombin III complex, thrombomodulin-protein C-protein S system, and the fibrinolytic system. The balance of all components--vessel wall, platelets, adhesive and coagulation proteins, regulatory mechanisms--determines the effectiveness of the hemostatic plug in maintaining the structural and functional integrity of the circulatory system. An approach to detection of hemostatic derangements in patients at risk evolves from a full understanding of inherited and acquired deficiencies affecting each step of hemostatic plug formation and from selective use of laboratory tests.

cDNA cloning of human plasminogen activator-inhibitor from endothelial cells

Full-length cDNA for plasminogen activator inhibitor (PAI-1) was isolated from a human umbilical vein endothelial cell (HUVEC) lambda gt11 cDNA library. Three overlapping clones were identified by immunologic screening of 10(6) recombinant phage using a rabbit anti-human fibrosarcoma PAI-1 antiserum. The fusion proteins encoded by these three clones also react strongly with a monoclonal mouse anti-human fibrosarcoma PAI-1 antibody. By nucleotide sequence analysis, PAI-1 cDNA encodes a protein containing 402 amino acids with a predicted, nonglycosylated molecular mass of 45 kD. Identity of this material as authentic PAI-1 was confirmed by the presence of high level homology with the primary amino acid sequence of an internal peptide prepared from purified rat hepatoma PAI-1. The predicted amino acid sequence also reveals extensive homology with other members of the serine protease inhibitor gene family. Cultured HUVECs contain two PAI-1 mRNA species, both encoded by a single gene, differing by 1 kb in the 3' untranslated region. The PAI-1 gene is located on human chromosome 7.

Characterization of a thrombomodulin cDNA reveals structural similarity to the low density lipoprotein receptor

We have isolated a partial-length cDNA for bovine thrombomodulin from a lambda gt11 bovine adrenal capillary endothelial cell expression library. This was accomplished by immunoscreening with rabbit anti-thrombomodulin IgG heteroantibody and then rescreening with the initial positive recombinant insert. The cDNA obtained was authenticated by showing that it coded for the primary structure of two separate regions of bovine thrombomodulin. The nucleotide sequence of the largest cDNA allowed us to establish the structure of about 80% of the mature thrombomodulin transcript, which encodes the C-terminal half of the polypeptide. This membrane component is structurally similar to coated-pit receptors and is organized into domains that resemble those of the low density lipoprotein receptor.

Structure of pre-pro-von Willebrand factor and its expression in heterologous cells

Von Willebrand factor (vWF), a multifunctional haemostatic glycoprotein derived from endothelial cells and megakaryocytes, mediates platelet adhesion to injured subendothelium and binds coagulation factor VIII in the circulation. Native vWF is a disulphide-bonded homopolymer; the monomeric subunits, of apparent relative molecular mass (Mr) 220,000 (220K) are derived from an intracellular precursor estimated at 260-275K. Multimer assembly is preceded by the formation of dimers, linked near their C-termini, which then assemble into filamentous polymers. The importance of the removal of the large vWF pro-polypeptide during multimer assembly, and whether this or other stages of the complex post-translational processing require components specific to endothelial cells or megakaryocytes, is unknown. Here we report an analysis of the complete sequence of pre-pro-vWF and expression of the molecule in heterologous cells. The vWF precursor is composed of several repeated subdomains. When expressed in COS and CHO cells, it is cleaved and assembled into biologically active high relative molecular mass disulphide bonded multimers. This suggests that the information for assembly of this complex molecule resides largely within its primary structure.

The structure of human thrombospondin, an adhesive glycoprotein with multiple calcium-binding sites and homologies with several different proteins

Thrombospondin is one of a class of adhesive glycoproteins that mediate cell-to-cell and cell-to-matrix interactions. We have used two monoclonal antibodies to isolate cDNA clones of thrombospondin from a human endothelial cell cDNA library and have determined the complete nucleotide sequence of the coding region. Three regions of known amino acid sequence of human platelet thrombospondin confirm that the clones are authentic. Three types of repeating amino acid sequence are present in thrombospondin. The first is 57 amino acids long and shows homology with circumsporozoite protein from Plasmodium falciparum. The second is 50-60 amino acids long and shows homology with epidermal growth factor precursor. The third occurs as a continuous eightfold repeat of a 38-residue sequence; structural homology with parvalbumin and calmodulin indicates that these repeats constitute the multiple calcium-binding sites of thrombospondin. The amino acid sequence arg-gly-asp-ala is included in the last type 3 repeat. This sequence is probably the site for the association of thrombospondin with cells. In addition, localized homologies with procollagen, fibronectin, and von Willebrand factor are present in one region of the thrombospondin molecule.

Plasma and cytoplasmic gelsolins are encoded by a single gene and contain a duplicated actin-binding domain

Gelsolin is representative of a class of actin-modulating proteins found in lower eukaryotes to mammals, which sever actin filaments. Gelsolin found in the cytoplasm of cells is functionally similar to a mammalian plasma protein of similar size, originally called ADF or brevin. Human plasma and rabbit macrophage gelsolins differ by the presence of a 25-amino-acid residue extension on plasma gelsolin which appears to account for the difference in relative molecular mass (Mr) between the proteins as assessed by SDS-polyacrylamide gel electrophoresis (PAGE), 93,000 (93K) and 90K, respectively. Here we report the isolation of full-length human plasma gelsolin complementary DNA clones from a HepG2 library. The inferred amino-acid sequence reveals the presence of a signal peptide, a long tandem repeat that matches the actin-binding domains of gelsolin, a tetrapeptide present in actin and extended regions of identical sequence with rabbit macrophage gelsolin. Southern blot analysis indicates that a single gene in the haploid genome encodes both protein forms.

Cloning the gene for an inherited human disorder--chronic granulomatous disease--on the basis of its chromosomal location

The gene that is abnormal in the X-linked form of the phagocytic disorder chronic granulomatous disease has been cloned without reference to a specific protein by relying on its chromosomal map position. The transcript of the gene is expressed in the phagocytic lineage of haematopoietic cells and is absent or structurally abnormal in four patients with the disorder. The nucleotide sequence of complementary DNA clones predicts a polypeptide of at least 468 amino acids with no homology to proteins described previously.

Application of an enzyme-linked immunosorbent assay (ELISA) to von Willebrand factor (vWF) and its derivatives

Sandwich ELISA systems were developed to measure human von Willebrand factor (vWF). In one system the microtitre plates were coated with goat F(ab')2 to vWF. The F(ab')2 different molecular forms in the soluble phase. VWF antigen bound by the F(ab')2 antibody was subsequently determined by using horse-radish peroxidase labeled goat Fab' to vWF. In plasma 3 X 10(-4) units of vWF per ml could be detected with this system. In a different approach the antigen bound by the F(ab')2 antibody was probed by monoclonal antibodies to multimeric as well as to the reduced and carboxymethylated (RCM) form of vWF. Using these monoclonals and RCM-as well as native plasma as antigen, the total antigen and the relative proportion of multimeric forms in the sample were estimated.

Propolypeptide of von Willebrand factor circulates in blood and is identical to von Willebrand antigen II

The generally mild bleeding disorder of von Willebrand disease is associated with abnormalities of two distinct plasma proteins, the large multimeric von Willebrand factor (vWF), which mediates platelet adhesion, and von Willebrand antigen II (vW AgII), which is of unknown function. The two proteins were found to have a common biosynthetic origin in endothelial cells and megakaryocytes, which explains their simultaneous absence in the severe form of this hereditary disease. Shared amino acid sequences from a 100-kilodalton plasma glycoprotein and from vW AgII are identical to amino acid sequences predicted from a complementary DNA clone encoding the 5' end of vWF. In addition, these proteins have identical molecular weights and immunologic cross reactivities. Monoclonal antibodies prepared against both proteins recognize epitopes on the pro-vWF subunit and on a 100-kilodalton protein that are not present on the mature vWF subunit in endothelial cell lysates. In contrast, polyclonal antibodies against vWF recognize both pro-vWF and vWF subunits. Thus, the 100-kilodalton plasma glycoprotein and vW AgII are identical proteins and represent an extremely large propolypeptide that is first cleaved from pro-vWF during intracellular processing and then released into plasma.

Initial glycosylation and acidic pH in the Golgi apparatus are required for multimerization of von Willebrand factor

Two conditions were identified that interfered with the complex polymerization process in biosynthesis of von Willebrand factor (vWf). Treatment of human umbilical vein endothelial cells with tunicamycin inhibited N-linked glycosylation of nascent vWf and the resulting pro-vWf monomers failed to dimerize. The single subunits accumulated in the endoplasmic reticulum and were neither processed further nor secreted. In the presence of a weak base (ammonium chloride or chloroquine), interdimer disulfide bond formation was inhibited in a dose-dependent manner. This process appeared therefore to be pH sensitive and likely to be initiated in the acidic trans-Golgi apparatus (Anderson, R. G. W., and R. K. Pathak, 1985, Cell, 40: 635-643). The weak base had no obvious effect on the other processing steps, i.e. dimerization, complex carbohydrate formation and sulfation, and produced only slight inhibition of prosequence cleavage. On the other hand, the weak base interfered with the targeting of newly synthesized vWf into Weibel-Palade bodies, with all of the vWf being secreted constitutively and none stored in the Weibel-Palade bodies. In summary, initial glycosylation of the nascent vWf protein and low pH in the trans-Golgi apparatus were important conditions for the successful polymerization of human vWf. Genetic defects disrupting any one of these conditions could result in the phenotype of von Willebrand disease.

Von Willebrand factor levels do not predict or diagnose radiation pneumonitis

In search for an index of endothelial injury that would provide an early diagnosis of radiation pneumonitis, we investigated the plasma levels of von Willebrand Factor (Factor VIII Related Antigen, FVIII:RAg) in 14 patients undergoing pulmonary irradiation. This study was based on observations indicating that damage to the endothelium-rich pulmonary parenchyma may produce alterations in the synthesis, storage or release of FVIII:RAg, detectable in plasma. There was no correlation between FVIII:RAg levels and radiation pneumonitis, radiation dose, volume of irradiated lung, tumor burden, or time-interval between exposure and sampling. The heterogeneity of the neoplasms and the inconstant effects of radiation in the tumor vasculature are among several variables that may explain this lack of correlation. The plasma levels of FVIII:RAg cannot be used to diagnose or predict radiation pneumonitis.

More homologies among the vertebrate plasma proteins

Many of the proteins of vertebrate blood plasma share common ancestry. As more sequences are reported, the network of relationships continues to expand in unexpected directions. Computer analysis now reveals that a minor plasma protein of unknown function, gamma-trace protein, is related to the kininogen family. Some other possible relationships have been uncovered also, including a resemblance between the histidine-rich hinge regions of high molecular weight kininogen and hemopexin and between Factor VIII and Von Willebrand Factor.

Cultured human endothelial cells express platelet-derived growth factor B chain: cDNA cloning and structural analysis

Vascular endothelial cells have a central role in various pathophysiological responses such as acute inflammation, wound healing and atherogenesis. The anatomical position of endothelial cells between blood leukocytes and the surrounding vascular smooth muscle cells or stromal fibroblasts may intensify and focus the effects of released endothelial cell products. Endothelial cells in culture produce a platelet-derived growth factor (PDGF)-like mitogen. PDGF purified from platelets is a basic protein with an apparent relative molecular mass (Mr) of approximately 30,000 (reviewed in refs 2, 3) and is believed to comprise two polypeptide chains, PDGF-A and PDGF-B (also referred to as PDGF-1 and PDGF-2; refs 5, 6). Sequence analysis of PDGF B chain has revealed a striking homology with the predicted sequence of p28sis, the transforming protein of simian sarcoma virus. sis-Homologous transcripts have been detected by Northern blot analysis of RNA from cultured endothelial cells. However, there are no structural data available on either the protein product or the messenger RNA to establish the identity of the endothelial-derived mitogen with either chain of PDGF. Here we report the isolation and complete sequence analysis of a sis-homologous complementary DNA clone from human endothelial cells, providing an opportunity to study the structure of sis as transcribed by a normal (untransformed) cell. Our results establish that normal human endothelial cells in culture express the B chain of PDGF, and that endothelial-derived PDGF B chain is synthesized as a predicted precursor polypeptide of Mr 27,281.