Protein S Deficiency: A Database of Mutations

Venous Thromboembolism: Genetics and Thrombophilias

Venous thromboembolism (VTE) is a major cause of morbidity and mortality throughout the world. Up to one half of patients who present with VTE will have an underlying thrombophilic defect. This knowledge has led to a widespread practice of testing for such defects in patients who develop VTE. However, identifying a hereditary thrombophilia by itself does not necessarily change outcomes or dictate therapy. Furthermore, family history of VTE by itself can increase an asymptomatic person's VTE risk several-fold, independent of detecting a known inherited thrombophilia. In this article, we will describe the current validated hereditary thrombophilias including their history, prevalence, and association with VTE. With a focus on evaluating both risks and benefits of testing, we will also explore the controversies of why, who, and when to test as well as discuss contemporary societal guidelines. Lastly, we will share how these tests have been integrated into clinical practice and how to best utilize them in the future.

Activated protein C suppresses osteoclast differentiation via endothelial protein C receptor, protease-activated receptor-1, sphingosine 1-phosphate receptor, and apolipoprotein E receptor 2

INTRODUCTION

Bone remodeling relies on a delicate balance between formation and resorption of bone tissues, processes in which bone-forming osteoblasts and bone-resorbing osteoclasts play central roles. Recently, we reported that anticoagulant activated protein C (APC) promotes osteoblast proliferation, but the role of the blood coagulation system in bone remodeling remains unclear. In this study, to further elucidate the relationship between bone remodeling and blood coagulation, we investigated the effect of APC on osteoclast differentiation.

MATERIALS AND METHODS

Normal human osteoclast precursor cells were cultured in their growth medium including soluble RANKL, M-CSF, and FBS, and on days 4 and 7, the culture medium was replaced with the same medium containing various concentrations of APC, protein C (PC), sphingosine 1-phosphate (S1P) receptor agonist, FTY720, or APC+various substances without FBS. On day 8, TRAP-positive multinucleated cells (≥3 nuclei) were counted manually using a light microscope. The effects of APC on NF-κB and NFATc1 activation were evaluated using specific ELISA.

RESULTS

APC suppressed RANKL-induced osteoclast differentiation, and this APC-induced suppression of osteoclast differentiation was inhibited by zymogen protein C and aprotinin, a serine protease inhibitor. Immunohistochemistry and RT-PCR analyses suggested that endothelial protein C receptor (EPCR) and protease-activated receptor-1 (PAR-1) were expressed in osteoclast precursor cells and osteoclasts. Both anti-PAR-1 antibody and anti-EPCR antibody (RCR-252), which blocks APC binding to EPCR, inhibited the APC-induced suppression of osteoclast differentiation. FTY720 had no effect on osteoclast differentiation. However, FTY 720 and S1P receptor antagonist, VP 23019, inhibited the APC-induced suppression of osteoclast differentiation. On the other hand, recombinant soluble human ApoER2 and anti-human ApoER2 inhibited the APC-induced suppression of osteoclast differentiation. Further, APC had no effect on NF-κB and NFATc1 activation.

CONCLUSIONS

APC suppresses human osteoclast differentiation mainly by inhibiting the formation of multinucleated cells via EPCR, PAR-1, S1P receptor, and ApoER2 in a manner that depends on APC protease activity.

Capture of anti-coagulant active ingredients from Moutan Cortex by platelet immobilized chromatography and evaluation of anticoagulant activity in rats

Moutan Cortex (MC) is a well-known Chinese medicine for promoting blood circulation and relieving blood stasis. The intent of this study was to evaluate the anticoagulant activity of MC and capture the bioactive compounds by platelet immobilized chromatography. Sprague Dawley (SD) rats were randomly divided into the control group, aspirin group and MC group (1.25, 2.5, 5g/kg/d). Coagulation system and platelet activity were investigated to evaluate the anti-coagulation effect of MC. The effective components of MC were captured by platelet immobilized chromatography. High performance liquid chromatography-diode array detection (HPLC-DAD) and liquid chromatography coupled to electrospray ionization tandem mass spectrometry (LC-ESI-MS/MS) analysis were used to identify the binding ingredients. Meanwhile, the efficacy of active ingredients was assessed through inhibiting platelet adhesion and regulating the expression of platelet related proteins. Principal findings showed that 2.5g/kg/d MC significantly prolonged thrombin time (TT) and 5g/kg/d MC significantly prolonged TT and prothrombin time (PT). MC exhibited an inhibitory potency on adenosine diphosphate-induced platelet aggregation. Four active compounds were found by platelet immobilized chromatography including oxypaeoniflorin, tetragalloylglucose, pentagalloyl glucose and benzoylpaeoniflorin; these active ingredients significantly up-regulated the expression of hsp-70 and coronin-1B, reduced the ratio of adhesion platelets. These results suggest that MC markedly promoted blood circulation and relieved blood stasis by inhibiting platelet activation, as an anti-coagulant, elucidating its potential capacity to treat cardiovascular diseases.

The role of hypercoagulability in ischemic colitis

OBJECTIVE

The aim of this study is to evaluate the role of thrombophilia-hypercoagulability in ischemic colitis (IC).

MATERIAL AND METHODS

Thrombophilia and fibrinogen were evaluated in 56 cases of IC and 44 controls with known predisposing factors but no evidence of IC. Thrombophilic factors tested were: protein C (PC), protein S, antithrombin (AT), resistance to activated protein C (APCR), lupus anticoagulant (LA), factor V G1691A mutation (FV Leiden), prothrombin G20210A mutation, methylenetetrahydrofolate reductase (MTHFR) gene C677T and A1298C mutations and plasminogen activator inhibitor-1 (PAI-1) gene 5G/4G and 4G/4G polymorphisms.

RESULTS

In IC group were recorded: i) low levels of PC and AT (p = 0.064 and p = 0.022, respectively); ii) low levels of APCR (normal: >2, p = 0.008); iii) high levels of fibrinogen (p = 0.0005); iv) higher number of homozygotes for MTHFR A1298C and C677T mutations (p = 0.061 and p = 0.525 (Pearson chi-square), respectively); v) greater prevalence of 5G/4G and 4G/4G polymorphisms (p = 0.031 (Pearson chi-square)) and vi) higher incidence of LA-positive individuals (p = 0.037, Fischer's exact test). Multivariate analysis was performed to determine the effects of prothrombotic factors in IC. 5G/4G polymorphism of PAI-1 gene (odds ratio (OR) 12.29; 95% confidence interval (CI) 2.26-67.00), APCR (OR 0.089; 95% CI 0.011-0.699) and fibrinogen (OR 1.013; 95% CI 1.003-1.023) were determined as predictors of IC.

CONCLUSIONS

This study suggests that hypercoagulability, hereditary or acquired, plays an essential role in the manifestation of IC.

Using a Systems Pharmacology Model of the Blood Coagulation Network to Predict the Effects of Various Therapies on Biomarkers

A number of therapeutics have been developed or are under development aiming to modulate the coagulation network to treat various diseases. We used a systems model to better understand the effect of modulating various components on blood coagulation. A computational model of the coagulation network was built to match in-house in vitro thrombin generation and activated Partial Thromboplastin Time (aPTT) data with various concentrations of recombinant factor VIIa (FVIIa) or factor Xa added to normal human plasma or factor VIII-deficient plasma. Sensitivity analysis applied to the model revealed that lag time, peak thrombin concentration, area under the curve (AUC) of the thrombin generation profile, and aPTT show different sensitivity to changes in coagulation factors' concentrations and type of plasma used (normal or factor VIII-deficient). We also used the model to explore how variability in concentrations of the proteins in coagulation network can impact the response to FVIIa treatment.

Plasma protein S residues 37-50 mediate its binding to factor Va and inhibition of blood coagulation

Protein S (PS) is an anticoagulant plasma protein whose deficiency is associated with increased risk of venous thrombosis. PS directly inhibits thrombin generation by the blood coagulation pathways by several mechanisms, including by binding coagulation factors (F) Va and Xa. To identify PS sequences that mediate inhibition of FVa activity, antibodies and synthetic peptides based on PS sequence were prepared and employed in plasma coagulation assays, purified component prothrombinase assays, binding assays, and immunoblots. In the absence of activated protein C, monoclonal antibody (Mab) S4 shortened FXa-induced clotting in normal plasma but not in PS-depleted plasma. Mab S4 also blocked PS inhibition of FVa-dependent prothrombinase activity in purified component assays in the absence or presence of phospholipids and inhibited binding of PS to immobilised FVa. Epitope mapping identified N-terminal region residues 37-67 of PS as this antibody's epitope. A peptide representing PS residues 37-50 inhibited FVa-dependent prothrombinase activity in a non-competitive manner, with 50% inhibition observed at 11 µM peptide, whereas a peptide with a D-amino acid sequence of 37-50 was ineffective. FVa, but not FXa, bound specifically to the immobilised peptide representing residues 37-50, and the peptide inhibited binding of FVa to immobilised PS. These data implicate PS residues 37-50 as a binding site for FVa that mediates, at least in part, the direct inhibition of FVa-dependent procoagulant activity by PS.

Protein C anticoagulant and cytoprotective pathways

Plasma protein C is a serine protease zymogen that is transformed into the active, trypsin-like protease, activated protein C (APC), which can exert multiple activities. For its anticoagulant action, APC causes inactivation of the procoagulant cofactors, factors Va and VIIIa, by limited proteolysis, and APC's anticoagulant activity is promoted by protein S, various lipids, high-density lipoprotein, and factor V. Hereditary heterozygous deficiency of protein C or protein S is linked to moderately increased risk for venous thrombosis, while a severe or total deficiency of either protein is linked to neonatal purpura fulminans. In recent years, the beneficial direct effects of APC on cells which are mediated by several specific receptors have become the focus of much attention. APC-induced signaling can promote multiple cytoprotective actions which can minimize injuries in various preclinical animal injury models. Remarkably, pharmacologic therapy using APC demonstrates substantial neuroprotective effects in various murine injury models, including ischemic stroke. This review summarizes the molecules that are central to the protein C pathways, the relationship of pathway deficiencies to venous thrombosis risk, and mechanisms for the beneficial effects of APC.

LPS-Toll-Like Receptor-Mediated Signaling on Expression of Protein S and C4b-Binding Protein in the Liver

Protein S (PS), mainly synthesized in hepatocytes and endothelial cells, plays a critical role as a cofactor of anticoagulant activated protein C (APC). PS activity is regulated by C4b-binding protein (C4BP), structurally composed of seven α-chains (C4BPα) and a β-chain (C4BPβ). In this paper, based primarily on our previous studies, we review the lipopolysaccharide (LPS)-induced signaling which affects expression of PS and C4BP in the liver. Our in vivo studies in rats showed that after LPS injection, plasma PS levels are significantly decreased, whereas plasma C4BP levels first are transiently decreased after 2 to 12 hours and then significantly increased after 24 hours. LPS decreases PS antigen and mRNA levels in both hepatocytes and sinusoidal endothelial cells (SECs), and decreases C4BP antigen and both C4BPα and C4BPβ mRNA levels in hepatocytes. Antirat CD14 and antirat Toll-like receptor (TLR)-4 antibodies inhibited LPS-induced NFκB activation in both hepatocytes and SECs. Furthermore, inhibitors of NFκB and MEK recovered the LPS-induced decreased expression of PS in both cell types and the LPS-induced decreased expression of C4BP in hepatocytes. These data suggest that the LPS-induced decrease in PS expression in hepatocytes and SECs and LPS-induced decrease in C4BP expression in hepatocytes are mediated by MEK/ERK signaling and NFκB activation and that membrane-bound CD14 and TLR-4 are involved in this mechanism.

Past and future of genetic research in thrombosis

Genetic studies in thrombosis started with coining of the term thrombophilia by Jordan and Nandorff in 1956. Next, antithrombin deficiency was identified in 1965 as a simple genetic entity that increased thrombotic risk, albeit in a small subset of patients. This subset was enlarged when, in the 1980s, family studies showed that deficiency of protein C (PC) or its co-factor protein S (PS) increased thrombotic risk. Ten years later activated PC resistance and the underlying genetic trait of factor V Leiden were discovered in a family setting. This genetic risk factor was the first prothrombotic defect in a procoagulant protein and was also more prevalent than abnormalities in anticoagulant proteins. The high incidence induced a shift from family studies to case-control studies. Case-control studies became even more popular after the common prothrombin 20,210 mutation was discovered in 1996. In fact, in the last decade common genetic variations in almost all coagulation proteins were tested in association studies. These common variants impart a small risk, if any risk at all, thereby limiting their usefulness in furthering insight into the pathophysiology of thrombosis. Moreover, common risk factors for venous thrombosis fail to improve prediction models for thrombosis on which prophylactic treatment can be tailored. Now that large-scale sequencing techniques are becoming available that enable many genes to be studied in a single individual, one can expect a revival of the identification of private mutations that are associated with large risks, in particular in genes that have been only poorly studied.

Differential regulation of protein S expression in hepatocytes and sinusoidal endothelial cells in rats with cirrhosis

BACKGROUND

Liver dysfunction caused by intrasinusoidal microthrombi is frequently observed in patients with cirrhosis after hepatectomy, but the mechanistic pathway remains unknown.

OBJECTIVE

In the present study, we evaluated the expression of protein S (PS) in hepatocytes and sinusoidal endothelial cells (SECs) from rats with dimethylnitrosoamine-induced cirrhosis before and after hepatectomy.

RESULTS

The plasma level of PS antigen was significantly decreased in cirrhotic rats as compared to control rats treated with vehicle. PS expression was significantly decreased in hepatocytes isolated from cirrhotic rats as compared to controls. In contrast, PS expression was significantly increased in SECs isolated from rats with cirrhosis as compared to controls. Interleukin-6 (IL-6) upregulated the expression of PS in hepatocytes, and tumor necrosis factor-alpha (TNF-alpha) decreased its expression in SECs from both cirrhotic and normal rats. The production of IL-6 and TNF-alpha by Kupffer cells and SECs was decreased in rats with cirrhosis as compared to controls. After hepatectomy, microthrombus formation was markedly enhanced in sinusoids from rats with cirrhosis, and the plasma levels of IL-6 and TNF-alpha were significantly increased in rats with cirrhosis as compared to controls. Furthermore, PS production in SECs was decreased, whereas that in hepatocytes was significantly increased in cirrhotic rats as compared to controls.

CONCLUSIONS

These findings suggest that PS expression is differently regulated in hepatocytes and SECs of rats with cirrhosis before and after hepatectomy, that the expression of PS is regulated by locally released inflammatory cytokines, and that decreased expression of PS in SECs may cause liver microthrombus formation, which is frequently observed in patients with cirrhosis after hepatectomy.

Mutations des protéines de la coagulation et thromboses

The coagulation system is governed by a subtle balance between clotting activators and inhibitors. Many genes can contribute to the overall phenotype, and polymorphisms may act to up regulate or down regulate the generation of thrombin, the coagulation-key enzyme. An increase in coagulation factor (gain function) or/and a decrease in coagulation inhibitors (loss of function) may favor venous thromboembolism (VTE). It has been observed since a long time that VTE may be a familial disease, but it was only in 1965 that Egeberg published the first case of inherited antithrombin (AT) deficiency. This was followed by similar reports of protein C (PC) and protein S (PS) deficiencies. Hereditary thrombophilia was thus initially considered as a rare monogenic disorder with incomplete penetrance. AT, PC and PS deficiencies are due to multiple and mostly private mutations of the corresponding genes. Most patients are heterozygous and experience VTE at adult age. Homozygosity associated with severe thrombosis at birth has been observed in newborns with undetectable PC or PS concentrations. The discovery of factor (F) V Leiden and F2 g.20210 G>A, two gain of function mutations, challenged the view of thrombophilia as a rare monogenic disorder. FV Leiden and F2 g.20210 G>A are due to a founder effect and affect populations of European descent with frequencies at 5% and 3% respectively. These two mutations are moderate of risk factor for thrombosis and paved the way for gene-gene and gene-environment interactions. Patients carrying more than one genetic risk factor are at higher risk to develop VTE. The exposition to acquired risk factors such as estrogen based oral contraception may also have a synergistic effect favoring thrombosis in patients with FV Leiden or other genetic risk factors.

Lipopolysaccharide-induced decreased protein S expression in liver cells is mediated by MEK/ERK signaling and NFkappaB activation: involvement of membrane-bound CD14 and toll-like receptor-4

BACKGROUND

The vitamin K-dependent protein S (PS), mainly synthesized in hepatocytes and endothelial cells, plays a critical role in the anticoagulant activity of plasma. The decreased plasma level of PS in sepsis is associated with thrombotic tendency, but the mechanism is unclear.

OBJECTIVES

In the present study, we examined the effect of lipopolysaccharide (LPS) on PS expression in vivo in rat liver, and in vitro in isolated hepatocytes and sinusoidal endothelial cells (SECs) from normal rats.

RESULTS

LPS induced a progressive decrease of plasma PS antigen level up to 12 h with a slight recovery at 24 h, and a transient decrease of liver PS mRNA level at 4-8 h with a complete recovery at 24 h. In the in vitro studies, LPS decreased PS antigen and mRNA levels in both hepatocytes and SECs. After LPS treatment, tumor necrosis factor-alpha (TNF-alpha), interleukin-6 (IL-6) and interferon-gamma (IFN-gamma) transiently increased in plasma. IL-6 increased the protein expression of PS from hepatocytes, while TNF-alpha decreased it from SECs. LPS increased CD14 in hepatocytes and decreased it in SECs, but did not affect toll-like receptor-4 (TLR-4) expression in both cells. Antirat CD14 and antirat TLR-4 antibodies inhibited LPS-induced NFkappaB activation, and a NFkappaB inhibitor suppressed LPS-induced decreased PS expression in both cells. Furthermore, MEK inhibitor blocked LPS-induced decreased PS expression in both cells.

CONCLUSIONS

These findings suggest that LPS-induced decreased PS expression in hepatocytes and SECs is mediated by MEK/ERK signaling and NFkappaB activation and that membrane-bound CD14 and TLR-4 are involved in this mechanism. These findings may explain in part the decreased level of plasma PS and thrombotic tendency in sepsis.

The Constitutive Expression of Anticoagulant Protein S Is Regulated through Multiple Binding Sites for Sp1 and Sp3 Transcription Factors in the Protein S Gene Promoter

Protein S (PS) is a vitamin K-dependent plasma protein that inhibits blood coagulation by serving as a nonenzymatic cofactor for activated protein C in the protein C anticoagulant pathway. Low PS levels are a risk factor for the development of deep venous thrombosis. The regulation of PS levels through transcriptional regulation of the PS gene was investigated in this report. A minimal PS gene promoter 370 bp upstream from the translational initiation codon was sufficient for maximal promoter activity in transient transfections regardless of the cell type. A pivotal role for Sp1 in the constitutive expression of the PS gene was demonstrated through electrophoretic mobility shift assay experiments, transient expression of mutant PS promoter-reporter gene constructs, and chromatin immunoprecipitations in HepG2 cells. At least four Sp-binding sites were identified. The two sites most proximal to the translational start codon were found to be indispensable for PS promoter activity, whereas mutation of the two most distal Sp-binding sites had a negligible influence on basal promoter activity. In addition, all other major promoter-binding proteins that were found by electrophoretic mobility shift assay could be positively identified in supershift assays. We identified binding sites for the hepatocyte-specific forkhead transcription factor FOXA2, nuclear factor Y, and the cAMP-response element-binding protein/activating transcription factor family of transcription factors. Their relevance was investigated using site-directed mutagenesis.

Issues concerning the laboratory investigation of inherited thrombophilia

Inherited thrombophilia, defined as an increased familial tendency to develop thrombosis, may be due to congenital deficiencies or abnormalities of antithrombin, protein C or protein S; to the presence of a point mutation in the factor V gene (G1691A, factor V Leiden) leading to a poor anticoagulant response to activated protein C; or to the presence of a mutation in the prothrombin gene (G20210A) leading to increased plasma levels of prothrombin. The laboratory investigation of inherited thrombophilia should be limited to patients with a history of venous thromboembolism and, if positive, to their family members even though they are still asymptomatic. There is no indication for indiscriminate screening of the general population or screening of asymptomatic women before prescribing oral contraceptives. Testing should be based on the phenotype for antithrombin, protein C and protein S; on the phenotype and genotype (factor V Leiden mutation) for activated protein C resistance; and on the genotype (G20210A mutation) for hyperprothrombinemia. Phenotypic testing should be performed no sooner than three months after acute thrombotic events and at least 2 weeks after discontinuation of oral anticoagulant treatment.

Venenastverschluss und Abduzensparese bei Protein-S-Mangel

BACKGROUND

Protein S deficiency, which exists in 0.7% of the population, is a risk factor for retinal vein branch occlusions and is inherited in an autosomal dominant manner.

METHODS

A genealogical study was carried out on three generations of one family who exhibited different venous occlusions and subsequent complications.

RESULTS

Four members of the family, spanning three generations, suffered from complications of venous thrombosis. In the first generation a great uncle died of complications from a deep leg venous thrombosis. In the second generation, the mother underwent a venous branch thrombosis at the age of 41 with a protein S activity of 18%. Subsequently, a palsy of the N. abducens developed with multiple cerebral lesions (presumably post-thrombotic) in the MRI. Fluorescein angiography showed a typical picture of a venous branch occlusion which had been treated by laser. In the third generation, the 16-year-old daughter developed iliac venous thrombosis and a pulmonary embolism with a protein S activity of 0%. The fluorescein angiography showed distinctively engorged veins. A 28-year-old daughter, with a protein S activity of 16%, remained asymptomatic, although fluorescein angiography demonstrated engorged veins. Protein C activity and APC resistance of all family members were normal. The chromosomal analysis of the family members revealed no morphological aberrations.

CONCLUSION

Protein S deficiency increases the risk of congenital thrombosis in young and middle-aged heterozygous individuals.

Normal Functional Protein S Activity Does Not Exclude Protein S Deficiency

Protein S (PS) deficiency appears to increase the risk of venous thrombosis. PS deficiency is classified into three phenotypes using antigenic levels and functional activity. By definition, all three phenotypes of PS deficiency should result in low activated protein C cofactor activity. We compared the results of functional PS activity testing to free antigenic PS testing in order to determine if a normal functional PS activity assay result could eliminate the need for free antigenic PS testing. The sensitivity of the functional assay is 45.5% (95% confidence interval, CI, 36-55%), specificity 95.3% (95% CI 93-97%), negative predictive value 88.6% (95% CI 86-91%) with a positive predictive value of 68.5% (95% CI 57-79%). In conclusion, a normal functional PS activity result does not exclude free antigenic PS deficiency. Functional PS activity testing should not be used as a screening test to eliminate free antigenic PS testing for the laboratory diagnosis of PS deficiency.

Etiology of Pulmonary Thromboembolism in the Absence of Commonly Recognized Risk Factors

Pulmonary thromboembolism is an often fatal complication of venous thrombosis. Any component or combination of the components composing Virchow's triad (venostasis, hypercoagulability, and endothelial damage) increases the propensity for a thrombophilic state. Hypercoagulable states may be inherited or acquired. While the etiology in many cases may be evident either on physical examination or on evaluation of the decedent's medical history, this is often not the case. We conducted a retrospective study of cases presenting to the Jefferson County Coroner/Medical Examiner's Office in Birmingham, Alabama, who were given a diagnosis of pulmonary embolism. A search of cases within the past 23 years yielded 81 cases. An underlying cause was determined in 70 cases (86%). The remaining 11 (14%) cases had no identifiable cause. We believe that a number of these cases may represent an underlying thrombophilic disorder. Since these disorders may be of an inherited or acquired nature, the determination of an etiology may be relevant to the decedent's family. Postmortem blood analyses may in selected cases be useful and appropriate for the detection of some of these disorders. However, such analyses are not practical in all cases, with each case having to be evaluated on its own merits.

The APC-independent anticoagulant activity of protein S in plasma is decreased by elevated prothrombin levels due to the prothrombin G20210A mutation

Protein S exhibits anticoagulant activity independent of activated protein C (APC). An automated factor Xa-based one-stage clotting assay was developed that enables quantification of the APC-independent activity of protein S in plasma from the ratio of clotting times (protein S ratio [pSR]) determined in the absence and presence of neutralizing antibodies against protein S. The pSR was 1.62 +/- 0.16 (mean +/- SD) in a healthy population (n = 60), independent of plasma levels of factors V, VIII, IX, and X; protein C; and antithrombin, and not affected by the presence of factor V Leiden. The pSR strongly correlates with the plasma level of protein S and is modulated by the plasma prothrombin concentration. In a group of 16 heterozygous protein S-deficient patients, the observed mean pSR (1.31 +/- 0.09) was significantly lower than the mean pSR of the healthy population, as was the pSR of plasma from carriers of the prothrombin G20210A mutation (1.47 +/- 0.21; n = 46). We propose that the decreased APC-independent anticoagulant activity of protein S in plasma with elevated prothrombin levels may contribute to the thrombotic risk associated with the prothrombin G20210A mutation.

Bacterial lipopolysaccharide decreases thrombomodulin expression in the sinusoidal endothelial cells of rats -- a possible mechanism of intrasinusoidal microthrombus formation and liver dysfunction

BACKGROUND/AIMS

To elucidate the mechanism of liver dysfunction occurring in patients with sepsis, we evaluated the effect of bacterial lipopolysaccharide (LPS) on the expression of thrombomodulin (TM) in rat sinusoidal endothelial cells (SECs) and the therapeutic efficacy of exogenous recombinant TM.

METHODS

We induced endotoxemia in rats by bolus intraperitoneal injection of LPS. TM antigen levels within tissues were assessed by immunohistochemistry. We measured TM in cultured SECs by enzyme immunoassay, functional analysis and real-time polymerase chain reaction (PCR).

RESULTS

TM antigen and activity levels were significantly decreased in SECs isolated from LPS-treated rats after 3 and 6 h treatment, and recovered after 12 h treatment, correlating with immunohistochemical observations. In contrast, TM messenger RNA was decreased after 6 and 12 h treatment, and slightly recovered after 24 h treatment. TM expression in cultured SECs isolated from normal rats was also reduced after treatment with LPS and tumor necrosis factor (TNF)-alpha in vitro. The increased levels of serum fibrin degradation products (FDP), fibrin deposition within liver sinusoids, injury of SECs and liver dysfunction induced by LPS in our rat model was improved by recombinant TM treatment.

CONCLUSIONS

Decreased TM expression in SECs of LPS-treated rats may result in intrasinusoidal microthrombus formation and subsequent liver dysfunction during sepsis.

A review of the technical, diagnostic, and epidemiologic considerations for protein S assays

OBJECTIVES

To review the state of the art relating to protein S deficiency as a risk factor for thrombosis and to make recommendations regarding the use of protein S measurements in the assessment of thrombotic risk in individual patients and families.

DATA SOURCES, EXTRACTION, AND SYNTHESIS

Selection criteria were developed for the inclusion of publications from 1985 to 2001 based on the relevant literature concerned with the systematic review of diagnostic tests. Minimal selection criteria were agreed on and the articles stratified into level 1 if they met these criteria and level 2 if they did not meet these criteria. The included articles were reviewed by the authors and abstracted onto predetermined data collection forms. These forms were then scored and recommendations based on level 1 studies. As described elsewhere, results of discussions at the College of American Pathologists Conference XXXVI on Diagnostic Issues in Thrombophilia were used to revise the manuscript into its final form.

CONCLUSIONS

Consensus was reached on 16 recommendations for the use of protein S assays in the assessment of thrombotic risk in individuals and families. Two themes run through the conclusions. First, protein S assays are the most technically problematic of the assays reviewed at this conference. Second, only 2 papers evaluating the diagnostic use of protein S assays met our level 1 inclusion criteria. These 2 problems point out the need for better standardized assays and rigorous studies of the diagnostic utility of these assays.

Hereditary thrombophilia in elite athletes

PURPOSE

Although under normal circumstances exercise prevents thrombosis, there are cases in the literature that indicate a connection between exercise and the onset of thrombosis. In the average population, hereditary thrombophilia is a major cause of thrombosis. However, nothing is known about the prevalence of hereditary thrombophilia in elite athletes. Because high-performance sports are known to carry an increased risk of thrombogenesis, measures to avoid thrombosis must be initiated in cases of known hereditary thrombophilia.

METHODS

Hereditary thrombophilia was checked for in 173 elite athletes, members of the German national team. Antithrombin III, protein C, protein S, and the APC ratio, followed by a molecular genetic analysis, were measured, and molecular analysis of factor II G20210A mutation was used to detect the presence of an antithrombin III-, protein C- and protein S-deficiency, as well as factor V Leiden (factor V 506Arg to Gln) and factor II G20210A mutation.

RESULTS

No definite antithrombin III-, protein C- or protein S-deficiency was found. In 12 cases, an APC resistance caused by a factor V Leiden mutation (11 heterozygous; 1 homozygous) was detected. In 10 cases, a heterozygous factor II G20210A was observed; a combination of both mutations was not found. For factor V Leiden, this corresponds to a prevalence of 6.9% (CI 95% 3.6-11.8%) in our group, similar to prevalence rates in the general population. Additionally, the observed prevalence of 5.8% (CI 95% 2.8-10.4%) of factor II G20210A is nearly within the range as reported by several authors.

CONCLUSION

Based on the observed prevalence of APC resistance and factor II G20210A mutation in our group of athletes, along with consideration of additional circumstantial risks, screening tests for elite athletes should be considered to allow the undertaking of preventive measures.

Superior mesenteric venous thrombosis associated with a familial missense mutation (Pro626Leu) in the SHBG-like domain of the protein S molecule

A 76-year-old Japanese woman was hospitalized for ileus symptoms caused by extensive thrombosis of the superior mesenteric vein. Because laboratory test results suggested type III protein S (PS) deficiency, molecular changes in PS were investigated. A single-base transition, CCG to CTG at codon 626 in exon XV, resulting in the missense mutation Pro626Leu, was identified in an allele of the patient and in her son. Reverse transcriptase polymerase chain reaction analysis indicated the presence of both normal and mutant types of PS messages in platelet-derived messenger RNAs. Our findings thus suggest that Pro626 in SHBG-like domain 7 may be crucial for in vivo antithrombotic activity of the PS molecule.

Solution structure of the LDL receptor EGF-AB pair: a paradigm for the assembly of tandem calcium binding EGF domains

BACKGROUND

From the observed structure and sequence of a pair of calcium binding (cb) epidermal growth factor-like (EGF) domains from human fibrillin-1, we proposed that many tandem cbEGF domains adopt a conserved relative conformation. The low-density lipoprotein receptor (LDLR), which is functionally unrelated to fibrillin-1, contains a single pair of EGF domains that was chosen for study in the validation of this hypothesis. The LDLR is the protein that is defective in familial hypercholesterolaemia, a common genetic disorder that predisposes individuals to cardiovascular complications and premature death.

RESULTS

Here, we present the solution structure of the first two EGF domains from the LDL receptor, determined using conventional NMR restraints and residual dipolar couplings. The cbEGF domains have an elongated, rod-like arrangement, as predicted. The new structure allows a detailed assessment of the consequences of mutations associated with familial hypercholesterolaemia to be made.

CONCLUSIONS

The validation of the conserved arrangement of EGF domains in functionally distinct proteins has important implications for structural genomics, since multiple tandem cbEGF pairs have been identified in many essential proteins that are implicated in human disease. Our results provide the means to use homology modeling to probe structure-function relationships in this diverse family of proteins and may hold the potential for the design of novel diagnostics and therapies in the future.

A novel splice acceptor site mutation of protein S gene in affected individuals with type I protein S deficiency: allelic exclusion of the mutant gene

Sequencing studies of the protein S gene (PROS1) in a Japanese patient suffering from recurrent thrombosis revealed the following. The proband and his first daughter, but not the second daughter, were having the type I protein S (PS) deficiency due to a novel point mutation from A to G at the intronic acceptor splice site in intron 13 of the PROS1. In the affected daughter, exclusion of the aberrant allele was assessed by the BstX1 dimorphism of PROS1 at Pro626 (CCG/CCA). The reduced PS activities in the proband and his first daughter were apparently due to defective production of mRNA from the mutant allele.

Protein S gene analysis reveals the presence of a cosegregating mutation in most pedigrees with type I but not type III PS deficiency

DNA sequence analysis of the protein S gene (PROS1) in 22 Spanish probands with type I or III PS deficiency, has allowed the identification of 10 different mutations and 2 new sequence variants in 15 probands. Nine of the mutations, 8 of which are novel, cosegregate with type I or quantitative PS deficiency in 12 of the 13 pedigrees analyzed. One of these mutations (Q238X) also cosegregates with both type I and III PS-deficient phenotypes coexisting in a type I/III pedigree. Another mutation identified in a pedigree with these two PS phenotypes is the missense mutation R520G, present in the homozygous form in the type I propositus and in the heterozygous form in his type III relatives. By contrast, no cosegregating PROS1 mutation has been found in any of the six families with only type III phenotypes. Three of these families, as well as the two families with type I and I/III phenotypes where no other PROS1 mutation has been identified, segregate the P allele of the S460P variant, although this allele does not always cosegregate with the deficient phenotype. From these results we conclude that while mutations in PROS1 are the main cause of type I PS deficiency, the molecular basis of the type III phenotype is probably more complex, with many cases not being explained by a PROS1 mutation.

Optimization of a simple and rapid single-strand conformation analysis for detection of mutations in the PROS1 gene: identification of seven novel mutations and three novel, apparently neutral, variants

Anticoagulant protein S (PS) deficiency is a known risk factor for thrombophilia. The structure and high allelic heterogeneity of the PS gene (PROS1), together with the presence of a 97% homologous pseudogene, complicates PROS1 analysis. We have optimized a simple, fast, and non-isotopic Single-Strand Conformation Analysis (SSCA or SSCP) method for PROS1 mutation detection. This is accomplished through the analysis of the single-stranded and heteroduplex DNA fragments corresponding to 15 PCR segments that include part of the 5'-upstream region and the 15 PROS1 exons with their intron boundaries. To standardize the method, 13 known PROS1 mutations or allele variants in 10 different fragments were analyzed under different electrophoretic conditions. The results indicated that, using a combination of two different electrophoretic settings, all the allele variants could be detected as a single-strand band shift and/or by the presence of a heteroduplex. This method was used to analyze the PROS1 gene in 31 propositi with different types of PS deficiency and thrombosis. Ten different cosegregating mutations, seven of which are novel (143C->G, L-27H, G96X, M599T, P626L, 1418delA, and 1877delT), were identified in the five families suffering from type I or quantitative PS deficiency and in four of the nine families with coexistence of type I and type III phenotypes. No clearly co-segregating PROS1 mutations were identified in any of the 17 type III propositi analyzed, although eight of them were heterozygotes for the uncommon P460 allele of the S/P460 variant. Furthermore, five apparently neutral allelic variants, three of which are novel (-296C->T, 182G->C and T57S), were identified in a normal control, two type I/III and two type III PS-deficient pedigrees.

Detection of protein S deficiency: a new functional assay compared to an antigenic technique

Congenital protein S (PS) deficiency is associated with increased risk of venous thrombosis. To investigate the possibility of automating PS testing with decreased turnaround time, a clotting-based functional protein S assay was evaluated and compared to an antigenic method. Samples were collected from 126 patients within 5 days of their first acute cerebral infarction, from 62 controls and from 47 consecutive samples for thrombophilia investigation. The normal range for the clotting-based kit, calculated from the results of 20 healthy controls, was 62-136% (mean +/- 2 SD). Intra- and inter-assay co-efficients of variation were < 3.0 and 10.0% respectively. There was no significant correlation between the two methods (r = 0.30, P > 0.05). Two patients had low PS antigen results with normal functional levels. Both techniques were used to compare a further group of 53 patients with defined abnormalities which included nine antigenic protein S deficiencies, five protein C deficient patients, 10 patients with a lupus anticoagulant (LA), 17 Factor V Leiden (FVL) heterozygotes, two FVL homozygotes and 10 patients on therapeutic levels of heparin. In this group we found that four of nine antigenic PS deficient patients had normal functional PS levels. The test was susceptible to the FVL mutation with four of 17 FVL heterozygotes and both of two FVL homozygotes giving low levels. One of five protein C-deficient patients also had a low functional PS result with a normal antigenic level. Normal results were obtained by both methods for all of the LA and patients on therapeutic heparin. We concluded that the automated protein S clotting assay was rapid and simple to perform but appeared to be influenced by factors other than PS deficiency. Results need to be interpreted with caution but may be useful as part of a full thrombophilia investigation.

Genetic analysis, phenotypic diagnosis, and risk of venous thrombosis in families with inherited deficiencies of protein S

Protein S deficiency is a recognized risk factor for venous thrombosis. Of all the inherited thrombophilic conditions, it remains the most difficult to diagnose because of phenotypic variability, which can lead to inconclusive results. We have overcome this problem by studying a cohort of patients from a single center where the diagnosis was confirmed at the genetic level. Twenty-eight index patients with protein S deficiency and a PROS1 gene defect were studied, together with 109 first-degree relatives. To avoid selection bias, we confined analysis of total and free protein S levels and thrombotic risk to the patients' relatives. In this group of relatives, a low free protein S level was the most reliable predictor of a PROS1gene defect (sensitivity 97.7%, specificity 100%). First-degree relatives with a PROS1 gene defect had a 5.0-fold higher risk of thrombosis (95% confidence interval, 1.5-16.8) than those with a normal PROS1 gene and no other recognized thrombophilic defect. Although pregnancy/puerperium and immobility/trauma were important precipitating factors for thrombosis, almost half of the events were spontaneous. Relatives with splice-site or major structural defects in the PROS1 gene were more likely to have had a thrombotic event and had significantly lower total and free protein S levels than those relatives having missense mutations. We conclude that persons withPROS1 gene defects and protein S deficiency are at increased risk of thrombosis and that free protein S estimation offers the most reliable way of diagnosing the deficiency.

The prothrombin nt20210 A allele as a risk factor for venous thromboembolism: detection of heterozygous and homozygous carriers by alternative methods

The A allele of a G/A dimorphism at position nt20210 in the 3'-untranslated region of the prothrombin gene has been recently identified as a common risk factor for venous thrombosis. It is detected mostly by PCR amplification using a mutagenic primer and subsequent restriction analysis. We have applied two alternative methods--DGGE and SSCP-to analyse the nt20210 dimorphism in a series of 383 consecutive patients with deep venous thrombosis and in 144 controls. Both screening methods resulted in the unambiguous identification of carriers of the nt20210 A allele not only in heterozygotes but in two cases as well in homozygous state. The frequency of the A allele was 0.7% in the control group but 3.7% in the patient group, demonstrating a substantial increase in risk for venous thrombosis in carriers of the 20210 A allele. Both methods have the potential to detect other DNA sequence variations in the vicinity of the 20210 G/A dimorphism. This was demonstrated by the identification of a new mutation T20122G in the 3'-untranslated region of the prothrombin gene in a single patient.

Protein S secretion differences of missense mutants account for phenotypic heterogeneity

To elucidate the molecular background for the heterogeneity in protein S plasma concentrations observed in protein S deficient individuals, the in vitro synthesis of recombinant protein S missense mutants was investigated. Six different naturally occurring mutations identified in the protein S gene (PROS1) of thrombosis patients were reproduced in protein S cDNA by site directed mutagenesis. Two mutants, G441C and Y444C (group A), were associated with low total plasma concentration of protein S. Modestly low protein S was found in families with R520G and P626L (group B) mutants. T57S and I518M (group C), which was associated with marginally low protein S, did not segregate with protein S deficiency in the respective families, raising doubts as to whether they were causative mutations or rare neutral variants. The 6 protein S mutants were transiently expressed in COS 1 cells. The Y444C mutant showed the lowest level of secretion (2.5%) followed by the G441C mutant (40%). Group B demonstrated around 50% reduction in secretion, whereas group C mutants showed normal secretion. Pulse-chase experiments demonstrated impaired protein S processing with intracellular degradation and decreased secretion into the culture media of group A and B mutants. Interestingly, there was a good correlation between in vitro secretion and the concentration of free protein S in the plasma of heterozygous carriers. These results demonstrate impaired protein S secretion to be an important mechanism underlying hereditary protein S deficiency and that variations in protein secretion is a major determinant of the phenotypic heterogeneity observed in protein S deficiency. (Blood. 2000;95:173-179)

Protein S secretion differences of missense mutants account for phenotypic heterogeneity

To elucidate the molecular background for the heterogeneity in protein S plasma concentrations observed in protein S deficient individuals, the in vitro synthesis of recombinant protein S missense mutants was investigated. Six different naturally occurring mutations identified in the protein S gene (PROS1) of thrombosis patients were reproduced in protein S cDNA by site directed mutagenesis. Two mutants, G441C and Y444C (group A), were associated with low total plasma concentration of protein S. Modestly low protein S was found in families with R520G and P626L (group B) mutants. T57S and I518M (group C), which was associated with marginally low protein S, did not segregate with protein S deficiency in the respective families, raising doubts as to whether they were causative mutations or rare neutral variants. The 6 protein S mutants were transiently expressed in COS 1 cells. The Y444C mutant showed the lowest level of secretion (2.5%) followed by the G441C mutant (40%). Group B demonstrated around 50% reduction in secretion, whereas group C mutants showed normal secretion. Pulse-chase experiments demonstrated impaired protein S processing with intracellular degradation and decreased secretion into the culture media of group A and B mutants. Interestingly, there was a good correlation between in vitro secretion and the concentration of free protein S in the plasma of heterozygous carriers. These results demonstrate impaired protein S secretion to be an important mechanism underlying hereditary protein S deficiency and that variations in protein secretion is a major determinant of the phenotypic heterogeneity observed in protein S deficiency. (Blood. 2000;95:173-179)

EGF-like module pair 3-4 in vitamin K-dependent protein S: modulation of calcium affinity of module 4 by module 3, and interaction with factor X

Calcium-binding epidermal growth factor (EGF)-like modules are found in numerous extracellular and membrane proteins involved in such diverse processes as blood coagulation, lipoprotein metabolism, determination of cell fate, and cell adhesion. Vitamin K-dependent protein S, a cofactor of the anticoagulant enzyme activated protein C, has four EGF-like modules in tandem with the three C-terminal modules each harbouring a Ca(2+)-binding consensus sequence. Recombinant fragments containing EGF modules 1-4 and 2-4 have two Ca(2+)-binding sites with dissociation constants ranging from 10(-8) to 10(-5) M. Module-module interactions that greatly influence the Ca(2+) affinity of individual modules have been identified. As a step towards an analysis of the structural basis of the high Ca(2+) affinity, we expressed the Ca(2+)-binding EGF pair 3-4 from human protein S. Correct folding was shown by (1)H NMR spectroscopy. Calcium-binding properties of the C-terminal module were determined by titration with chromophoric chelators; binding to the low-affinity N-terminal site was monitored by (1)H-(15)N NMR spectroscopy. At physiological pH and ionic strength, the dissociation constants for Ca(2+) binding were 1.0x10(-6) M and 4. 8x10(-3) M for modules 4 and 3, respectively, i.e. the calcium affinity of the C-terminal site was about 5000-fold higher than that of the N-terminal site. Moreover, the Ca(2+) affinity of EGF 4, in the pair 3-4, was about 9000-fold higher than that of synthetic EGF 4. The EGF modules in protein S are known to mediate the interaction with factor Xa. We have now found modules 3-4 to be involved in this interaction. However, the individual modules 3 and 4 manifested no measurable activity.

Organization and chromosomal localization of the human endothelial protein C receptor gene

Endothelial protein C receptor (EPCR), present on endothelial cells of relatively large veins and arteries, plays a role in the enhancement of protein C activation by the thrombin-thrombomodulin complex. In the present study, we determined the organization and the complete nucleotide sequence of the human EPCR gene using polymerase chain reaction-direct sequencing method. The transcription initiation site of the EPCR gene was also determined by the cap site hunting method, using a cap site cDNA prepared from human placenta. The human EPCR gene spanned approx. 6 kb and was composed of four exons and three introns. All exon-intron boundaries agreed with the GT-AG rule. The 5'-flanking region (300 bp) of the EPCR gene contained a putative AP1-binding site, two Sp1-binding sites and two AP2-binding sites, but not definite TATAA or CCAAT sequences. Fluorescence in situ hybridization analysis showed that the EPCR gene is located in chromosome 20q11.2.

The molecular genetics of familial venous thrombosis

In the past few years, important advances have been made in the identification of factors predisposing to familial thrombophilia. Particular attention has been paid to the characterization of known inherited defects and their genotype-phenotype relationship, and to studying the interaction between single or multiple inherited conditions and acquired risk factors for venous thrombosis. The recent discovery of 'new' and very common genetic lesions predisposing to thrombosis has greatly expanded the interest in this field. Hereditary predisposition to venous thrombosis may be related to lesions in one or more of 10-15 genes encoding antithrombin, Protein C, Protein S, Factor V, prothrombin, enzymes of the homocysteine metabolic pathway, fibrinogen, heparin cofactor II, plasminogen and thrombomodulin. About 500 different gene lesions (substitutions, deletions, insertions) have so far been reported to affect these genes in patients with thrombotic disease. Because there are potentially multiple interactions between genetic and environmental factors, familial thrombophilia is now considered to be a multifactorial disease. The aim of this chapter is to review aspects of the molecular genetics of familial thrombophilia. In particular, those gene/protein defects for which there is convincing evidence of an association with familial thrombosis will be examined in detail.

Thrombomodulin with the Asp468Tyr mutation is expressed on the cell surface with normal cofactor activity for protein C activation

Thrombomodulin (TM) is an endothelial cell glycoprotein that acts as an anticoagulant. Mutation in the TM gene is a potential risk factor for thrombosis. The first TM mutation identified was a heterozygous substitution of T for G at nucleotide position 1456, which predicted Asp468 with Tyr in a Ser/Thr-rich domain. To evaluate the reported TM gene mutation as a possible cause of thrombosis, we transiently tranfected a vector for TM gene carrying the mutation to mammalian COS7 cells. TM antigen levels in lysates of cells transfected with variant TM were comparable to those in preparations of normal TM. The TM cofactor activity for protein C (PC) activation on the variant TM-expressing cells was similar to that of the control. The Michaelis constant Km and Vmax. of variant TM for PC activation were shown to be similar compared to those of normal TM. The affinity of each TM for thrombin in PC activation was also similar. We obtained several stable cell lines expressing normal and variant TM. Lysate of the cell lines with normal and variant TM genes had a similar expression level of TM antigen. Pulse-chase analysis showed that normal and variant TM were glycosylated and resistant to endoglycosidase H, indicating that the variant TM was expressed on the cell surface in a mature form. Variant TM protein is apparently expressed on the cell surface with normal cofactor activity for PC activation. It is unlikely that the TM variant directly causes thrombosis by mechanism of reduced expression or impaired cofactor activity for PC activation, which comprises a major anticoagulant activity of TM.

Structural and Functional Implications of the Intron/Exon Organization of the Human Endothelial Cell Protein C/Activated Protein C Receptor (EPCR) Gene: Comparison With the Structure of CD1/Major Histocompatibility Complex 1 and 2 Domains

The endothelial cell protein C/activated protein C receptor (EPCR) is located primarily on the surface of the large vessels of the vasculature. In vitro studies suggest that it is involved in the protein C anticoagulant pathway. We report the organization and nucleotide sequence of the human EPCR gene. It spans approximately 6 kbp of genomic DNA, with a transcription initiation point 79 bp upstream of the translation initiation (Met) codon in close proximity to a TATA box and other promoter element consensus sequences. The human EPCR gene has been localized to 20q11.2 and consists of four exons interrupted by three introns, all of which obey the GT-AG rule. Exon I encodes the 5′ untranslated region and the signal peptide, and exon IV encodes the transmembrane domain, the cytoplasmic tail, and the 3′ untranslated region. Exons II and III encode most of the extracellular region of the EPCR. These exons have been found to correspond to those encoding the 1 and 2 domains of the CD1/major histocompatibility complex (MHC) class I superfamily. Flanking and intervening introns are of the same phase (phase I) and the position of the intervening intron is identically located. Secondary structure prediction for the amino acid sequence of exons II and III corresponds well with the actual secondary structure elements determined for the 1 and 2 domains of HLA-A2 and murine CD1.1 from crystal structures. These findings suggest that the EPCR folds with a β-sheet platform supporting two -helical regions collectively forming a potential binding pocket for protein C/activated protein C.

Structural and Functional Implications of the Intron/Exon Organization of the Human Endothelial Cell Protein C/Activated Protein C Receptor (EPCR) Gene: Comparison With the Structure of CD1/Major Histocompatibility Complex 1 and 2 Domains

The endothelial cell protein C/activated protein C receptor (EPCR) is located primarily on the surface of the large vessels of the vasculature. In vitro studies suggest that it is involved in the protein C anticoagulant pathway. We report the organization and nucleotide sequence of the human EPCR gene. It spans approximately 6 kbp of genomic DNA, with a transcription initiation point 79 bp upstream of the translation initiation (Met) codon in close proximity to a TATA box and other promoter element consensus sequences. The human EPCR gene has been localized to 20q11.2 and consists of four exons interrupted by three introns, all of which obey the GT-AG rule. Exon I encodes the 5′ untranslated region and the signal peptide, and exon IV encodes the transmembrane domain, the cytoplasmic tail, and the 3′ untranslated region. Exons II and III encode most of the extracellular region of the EPCR. These exons have been found to correspond to those encoding the 1 and 2 domains of the CD1/major histocompatibility complex (MHC) class I superfamily. Flanking and intervening introns are of the same phase (phase I) and the position of the intervening intron is identically located. Secondary structure prediction for the amino acid sequence of exons II and III corresponds well with the actual secondary structure elements determined for the 1 and 2 domains of HLA-A2 and murine CD1.1 from crystal structures. These findings suggest that the EPCR folds with a β-sheet platform supporting two -helical regions collectively forming a potential binding pocket for protein C/activated protein C.

Screening for aetiology of thrombophilia: a high prevalence of protein S abnormality

We systematically screened for the aetiology of thrombophilia in 115 patients with venous, arterial and small vessel thromboses. Forty-one patients (36% of those we examined) suffering from a variety of thromboses, including deep vein thrombosis, pulmonary embolism, arterial occlusion, cerebral infarction, Moyamoya disease and ulcerative colitis, were characterized either with positive lupus anticoagulants or with decreased activities of protein S, protein C, antithrombin III and/or plasminogen. Eight mutation sites were confirmed in 11 thrombotic patients using gene analysis. Decreased protein S activity was found with a high incidence (23 out of 115) in Japanese patients who suffered from not only venous thrombosis but also arterial and small vessel thrombosis. We emphasize here the important role of protein S in the pathogenesis of thrombosis in the Japanese population.

A Mutation of the Active Protein S Gene Leading to an EGF1-Lacking Protein in a Family With Qualitative (Type II) Deficiency

The genomic analysis of a 70-year-old man with recurrent deep venous thrombosis having a protein S (PS)-deficient phenotype corresponding to both type III and type II evidenced two different mutations: a +5 g→a mutation in the donor splice site of intron e (ivs e) and a ser 460 to Pro mutation. The propositus' son, who had a type II PS deficiency phenotype, only bore the ivs e +5 g→a mutation. The study of platelet PS mRNA prepared from this subject showed that the ivs e, +5 g→a mutation led to the generation of two abnormal transcripts, one lacking exon 5 and the other lacking exons 5 and 6. The presence of an additional PS band with a decreased molecular mass on immunoblots performed in reducing conditions suggested the presence of truncated PS lacking EGF1 (encoded by exon 5). Two monoclonal antibodies (MoAbs) were used to further characterize the nonfunctional plasma PS. Comparison of PS levels measured with each of these MoAbs and PS levels in conventional assays was consistent with the presence of an abnormal inactive protein in the plasma of both patients bearing the ivs e, +5 g→a mutation, suggesting that variant PS lacking EGF1 is secreted but is devoid of activated protein C cofactor activity.

A Mutation of the Active Protein S Gene Leading to an EGF1-Lacking Protein in a Family With Qualitative (Type II) Deficiency

The genomic analysis of a 70-year-old man with recurrent deep venous thrombosis having a protein S (PS)-deficient phenotype corresponding to both type III and type II evidenced two different mutations: a +5 g→a mutation in the donor splice site of intron e (ivs e) and a ser 460 to Pro mutation. The propositus' son, who had a type II PS deficiency phenotype, only bore the ivs e +5 g→a mutation. The study of platelet PS mRNA prepared from this subject showed that the ivs e, +5 g→a mutation led to the generation of two abnormal transcripts, one lacking exon 5 and the other lacking exons 5 and 6. The presence of an additional PS band with a decreased molecular mass on immunoblots performed in reducing conditions suggested the presence of truncated PS lacking EGF1 (encoded by exon 5). Two monoclonal antibodies (MoAbs) were used to further characterize the nonfunctional plasma PS. Comparison of PS levels measured with each of these MoAbs and PS levels in conventional assays was consistent with the presence of an abnormal inactive protein in the plasma of both patients bearing the ivs e, +5 g→a mutation, suggesting that variant PS lacking EGF1 is secreted but is devoid of activated protein C cofactor activity.