Plasminogen activator inhibitor-1 is an inhibitor of factor VII-activating protease in patients with acute respiratory distress syndrome

Factor VII Activating Protease (FSAP) and Its Importance in Hemostasis—Part I: FSAP Structure, Synthesis and Activity Regulation: A Narrative Review

Factor VII activating protease (FSAP) was first isolated from human plasma less than 30 years ago. Since then, many research groups have described the biological properties of this protease and its role in hemostasis and other processes in humans and other animals. With the progress of knowledge about the structure of FSAP, several of its relationships with other proteins or chemical compounds that may modulate its activity have been explained. These mutual axes are described in the present narrative review. The first part of our series of manuscripts on FSAP describes the structure of this protein and the processes leading to the enhancement and inhibition of its activities. The following parts, II and III, concern the role of FSAP in hemostasis and in the pathophysiology of human diseases, with particular emphasis on cardiovascular diseases.

Factor VII activating protease (FSAP) inhibits the outcome of ischemic stroke in mouse models

The outcome of ischemic stroke can be improved by further refinements of thrombolysis and reperfusion strategies. Factor VII activating protease (FSAP) is a circulating serine protease that could be important in this context. Its levels are raised in patients as well as mice after stroke and a single nucleotide polymorphism (SNP) in the coding sequence, which results in an inactive enzyme, is linked to an increased risk of stroke. In vitro, FSAP cleaves fibrinogen to promote fibrinolysis, activates protease-activated receptors, and decreases the cellular cytotoxicity of histones. Based on these facts, we hypothesized that FSAP can be used as a treatment for ischemic stroke. A combination of tissue plasminogen activator (tPA), a thrombolytic drug, and recombinant serine protease domain of FSAP (FSAP-SPD) improved regional cerebral perfusion and neurological outcome and reduced infarct size in a mouse model of thromboembolic stroke. FSAP-SPD also improved stroke outcomes and diminished the negative consequences of co-treatment with tPA in the transient middle cerebral artery occlusion model of stroke without altering cerebral perfusion. The inactive MI-isoform of FSAP had no impact in either model. FSAP enhanced the lysis of blood clots in vitro, but in the tail transection model of hemostasis, FSAP-SPD treatment provoked a faster clotting time indicating that it also has pro-coagulant actions. Thus, apart from enhancing thrombolysis, FSAP has multiple effects on stroke progression and represents a promising novel therapeutic strategy in the treatment of ischemic stroke.

Extracellular nucleic acid scavenging rescues rats from sulfur mustard analog-induced lung injury and mortality

Sulfur mustard (SM) is a highly toxic war chemical that causes significant morbidity and mortality and lacks any effective therapy. Rats exposed to aerosolized CEES (2-chloroethyl ethyl sulfide; 10% in ethanol), an analog of SM, developed acute respiratory distress syndrome (ARDS), which is characterized by increased inflammation, hypoxemia and impaired gas exchange. We observed elevated levels of extracellular nucleic acids (eNA) in the bronchoalveolar lavage fluid (BALF) of CEES-exposed animals. eNA can induce inflammation, coagulation and barrier dysfunction. Treatment with hexadimethrine bromide (HDMBr; 10 mg/kg), an eNA neutralizing agent, 2 h post-exposure, reduced lung injury, inhibited disruption of alveolar-capillary barrier, improved blood oxygenation (PaO₂/FiO₂ ratio), thus reversing ARDS symptoms. HDMBr treatment also reduced lung inflammation in the CEES-exposed animals by decreasing IL-6, IL-1A, CXCL-1 and CCL-2 mRNA levels in lung tissues and HMGB1 protein in BALF. Furthermore, HDMBr treatment also reduced levels of lung tissue factor and plasminogen activator inhibitor-1 indicating reduction in clot formation and increased fibrinolysis. Fibrin was reduced in BALF of the HDMBr-treated animals. This was further confirmed by histology that revealed diminished airway fibrin, epithelial sloughing and hyaline membrane in the lungs of HDMBr-treated animals. HDMBr completely rescued the CEES-associated mortality 12 h post-exposure when the survival rate in CEES-only group was just 50%. Experimental eNA treatment of cells caused increased inflammation that was reversed by HDMBr. These results demonstrate a role of eNA in the pathogenesis of CEES/SM-induced injury and that its neutralization can serve as a potential therapeutic approach in treating SM toxicity.

Fluorescent activity-based probe for the selective detection of Factor VII activating protease (FSAP) in human plasma

The zymogen form of circulating Factor VII activating protease (FSAP) is activated by histones that are released as a consequence of tissue damage or excessive inflammation. This is likely to have consequences in a number of disease conditions such as stroke, atherosclerosis, liver fibrosis, thrombosis and cancer. To investigate the existence, as well as the concentration of active FSAP (FSAPa) in complex biological systems an active site probe is needed. We used Hybrid Combinatorial Substrate Library (HyCoSuL) to screen for natural and unnatural amino acids that specifically bind to P4-P2 pockets of FSAPa. This information was used to designing a fluorogenic substrate (Ac-Pro-DTyr-Lys-Arg-ACC) as well as an irreversible, fluorogenic activity-based probe Cy5-6-Ahx-Pro-DTyr-Lys-Arg^P(OPh)₂. In normal human plasma the probe showed very low non-specific reactivity with some plasma proteins but upon activation of pro-FSAP with histones, strong labelling of FSAPa was observed. This labelling could be inhibited by aprotinin and was not found in the plasma of a subject that was homozygous for a polymorphism, which leads to loss of activity, or in plasma that was depleted of FSAP by antibodies. This 2nd generation substrate exhibited 6-fold higher catalytic efficiency than the 1st generation substrate and a much higher selectivity for FSAPa over other plasma proteases. This substrate and probe can be useful to detect and localize FSAPa in normal and pathological tissue and plasma to gain more insight into its functions.

Origin and diversification of the plasminogen activation system among chordates

Background

The plasminogen (PLG) activation system is composed by a series of serine proteases, inhibitors and several binding proteins, which together control the temporal and spatial generation of the active serine protease plasmin. As this proteolytic system plays a central role in human physiology and pathophysiology it has been extensively studied in mammals. The serine proteases of this system are believed to originate from an ancestral gene by gene duplications followed by domain gains and deletions. However, the identification of ancestral forms in primitive chordates supporting these theories remains elusive. In addition, evolutionary studies of the non-proteolytic members of this system are scarce.

Results

Our phylogenetic analyses place lamprey PLG at the root of the vertebrate PLG-group, while lamprey PLG-related growth factors represent the ancestral forms of the jawed-vertebrate orthologues. Furthermore, we find that the earliest putative orthologue of the PLG activator group is the hyaluronan binding protein 2 (HABP2) gene found in lampreys. The prime plasminogen activators (tissue- and urokinase-type plasminogen activator, tPA and uPA) first occur in cartilaginous fish and phylogenetic analyses confirm that all orthologues identified compose monophyletic groups to their mammalian counterparts. Cartilaginous fishes exhibit the most ancient vitronectin of all vertebrates, while plasminogen activator inhibitor 1 (PAI-1) appears for the first time in cartilaginous fishes and is conserved in the rest of jawed vertebrate clades. PAI-2 appears for the first time in the common ancestor of reptiles and mammals, and represents the latest appearing plasminogen activator inhibitor. Finally, we noted that the urokinase-type plasminogen activator receptor (uPAR)—and three-LU domain containing genes in general—occurred later in evolution and was first detectable after coelacanths.

Conclusions

This study identifies several primitive orthologues of the mammalian plasminogen activation system. These ancestral forms provide clues to the origin and diversification of this enzyme system. Further, the discovery of several members—hitherto unknown in mammals—provide new perspectives on the evolution of this important enzyme system.

Electronic supplementary material

The online version of this article (10.1186/s12862-019-1353-z) contains supplementary material, which is available to authorized users.

Factor VII activating protease

Factor VII activating protease (FSAP) is a circulating serine protease with high homology to fibrinolytic enzymes. A role in the regulation of coagulation and fibrinolysis is suspected based on in vitro studies demonstrating activation of FVII or pro-urokinase plasminogen activator (uPA). However, considering the paucity of any studies in animal models or any correlative studies in humans the role of FSAP in haemostasis remains unclear. In relation to vascular remodeling processes or inflammation it has been convincingly shown that FSAP interacts with growth factors as well as protease activated receptors (PAR). Against this sparse background there are a plethora of studies which have investigated the linkage of single nucleotide polymorphisms (SNP) in the FSAP gene (HABP2) to various diseases. The G534E SNP of FSAP is associated with a low proteolytic activity due to an amino acid exchange in the protease domain. This and other SNPs have been linked to carotid stenosis, stroke as well as thrombosis in the elderly and plaque calcification. These SNP analyses indicate an important role for FSAP in the regulation of the haemostasis system as well as fibroproliferative inflammatory processes.

FSAP, a new player in inflammation?

Factor VII-activating protease (FSAP) is a serine protease in plasma that has a role in coagulation and fibrinolysis. FVII could be activated by purified FSAP in a tissue factor independent manner and pro-urokinase has been demonstrated to be a substrate for purified FSAP in-vitro. However, the physiological role of FSAP in haemostasis remains unclear. More recently FSAP is suggested to be involved in inflammation. It modulates vascular permeability directly and indirectly by the generation of bradykinin. Furthermore, FSAP is activated by dead cells induced by the inflammatory response and subsequently removes nucleosomes from apoptotic cells. FSAP activation can be detected in sepsis patients as well. However, whether FSAP activation upon inflammation is beneficial or detrimental remains an open question.

In this review the structure, activation mechanisms and the possible role of FSAP in inflammation are discussed.

Antihistone Properties of C1 Esterase Inhibitor Protect against Lung Injury

RATIONALE

Acute respiratory distress syndrome is characterized by alveolar epithelial cell injury, edema formation, and intraalveolar contact phase activation.

OBJECTIVES

To explore whether C1 esterase inhibitor (C1INH), an endogenous inhibitor of the contact phase, may protect from lung injury in vivo and to decipher the possible underlying mechanisms mediating protection.

METHODS

The ability of C1INH to control the inflammatory processes was studied in vitro and in vivo.

MEASUREMENTS AND MAIN RESULTS

Here, we demonstrate that application of C1INH alleviates bleomycin-induced lung injury via direct interaction with extracellular histones. In vitro, C1INH was found to bind all histone types. Interaction with histones was independent of its protease inhibitory activity, as demonstrated by the use of reactive-center-cleaved C1INH, but dependent on its glycosylation status. C1INH sialylated-N- and -O-glycans were not only essential for its interaction with histones but also to protect against histone-induced cell death. In vivo, histone-C1INH complexes were detected in bronchoalveolar lavage fluid from patients with acute respiratory distress syndrome and multiple models of lung injury. Furthermore, reactive-center-cleaved C1INH attenuated pulmonary damage evoked by intravenous histone instillation.

CONCLUSIONS

Collectively, C1INH administration provides a new therapeutic option for disorders associated with histone release.

Analysis of the substrate specificity of Factor VII activating protease (FSAP) and design of specific and sensitive peptide substrates

Factor VII (FVII) activating protease (FSAP) is a circulating serine protease that is likely to be involved in a number of disease conditions such as stroke, atherosclerosis, liver fibrosis, thrombosis and cancer. To date, no systematic information is available about the substrate specificity of FSAP. Applying phage display and positional scanning substrate combinatorial library (PS-SCL) approaches we have characterised the specificity of FSAP towards small peptides. Results were evaluated in the context of known protein substrates as well as molecular modelling of the peptides in the active site of FSAP. The representative FSAP-cleaved sequence obtained from the phage display method was Val-Leu-Lys-Arg-Ser (P4-P1'). The sequence X-Lys/Arg-Nle-Lys/Arg (P4-P1) was derived from the PS-SCL method. These results show a predilection for cleavage at a cluster of basic amino acids on the nonprime side. Quenched fluorescent substrate (Ala-Lys-Nle-Arg-AMC) (amino methyl coumarin) and (Ala-Leu-Lys-Arg-AMC) had a higher selectivity for FSAP compared to other proteases from the hemostasis system. These substrates could be used to measure FSAP activity in a complex biological system such as plasma. In histone-treated plasma there was a specific activation of pro-FSAP as validated by the use of an FSAP inhibitory antibody, corn trypsin inhibitor to inhibit Factor XIIa and hirudin to inhibit thrombin, which may account for some of the haemostasis-related effects of histones. These results will aid the development of further selective FSAP activity probes as well as specific inhibitors that will help to increase the understanding of the functions of FSAP in vivo.

Host-derived extracellular RNA promotes adhesion of Streptococcus pneumoniae to endothelial and epithelial cells

Streptococcus pneumoniae is the most frequent cause of community-acquired pneumonia. The infection process involves bacterial cell surface receptors, which interact with host extracellular matrix components to facilitate colonization and dissemination of bacteria. Here, we investigated the role of host-derived extracellular RNA (eRNA) in the process of pneumococcal alveolar epithelial cell infection. Our study demonstrates that eRNA dose-dependently increased S. pneumoniae invasion of alveolar epithelial cells. Extracellular enolase (Eno), a plasminogen (Plg) receptor, was identified as a novel eRNA-binding protein on S. pneumoniae surface, and six Eno eRNA-binding sites including a C-terminal 15 amino acid motif containing lysine residue 434 were characterized. Although the substitution of lysine 434 for glycine (K434G) markedly diminished the binding of eRNA to Eno, the adherence to and internalization into alveolar epithelial cells of S. pneumoniae strain carrying the C-terminal lysine deletion and the mutation of internal Plg-binding motif were only marginally impaired. Accordingly, using a mass spectrometric approach, we identified seven novel eRNA-binding proteins in pneumococcal cell wall. Given the high number of eRNA-interacting proteins on pneumococci, treatment with RNase1 completely inhibited eRNA-mediated pneumococcal alveolar epithelial cell infection. Our data support further efforts to employ RNAse1 as an antimicrobial agent to combat pneumococcal infectious diseases.

Extracellular Ribonucleic Acids (RNA) Enter the Stage in Cardiovascular Disease

Inflammatory and ischemic cardiovascular diseases, especially atherosclerosis and myocardial infarction, remain the number one cause of death in the Western world, whereas the therapeutic options currently available are still limited. Several recent findings have indicated that nucleic acids, particularly extracellular ribosomal RNA and micro-RNAs, significantly contribute to the adverse outcome of atherosclerosis, myocardial infarction, and other cardiovascular diseases. Extracellular RNAs act as novel danger-associated molecular pattern signals and potent cofactors in cardiovascular inflammation and thrombosis, particularly when accumulating in the extracellular space under tissue-damaging or pathological conditions. In this concise review article, the different entities of extracellular RNAs, their cellular sources, and their putative functional contribution to the pathogenesis of cardiovascular diseases will be discussed. In fact, it remains a tightrope walk for these polyanionic molecules outside cells to promote defense reactions on the one side but to provoke cardiovascular disease development on the other side, dependent on their concentration, the environmental conditions, and the cellular stimuli engaged. Thus, we will discuss the mechanisms and cellular responses by which extracellular RNAs operate between defense and disease. Finally, natural counteracting molecules, such as RNase1, will be focused on to elaborate their protective functions in the context of inflammatory and ischemic cardiovascular diseases with the possibility to apply them as novel interventional strategies.

Emerging targets for treating sulfur mustard-induced injuries

Sulfur mustard (SM; bis-(2-chlororethyl) sulfide) is a highly reactive, potent warfare agent that has recently reemerged as a major threat to military and civilians. Exposure to SM is often fatal, primarily due to pulmonary injuries and complications caused by its inhalation. Profound inflammation, hypercoagulation, and oxidative stress are the hallmarks that define SM-induced pulmonary toxicities. Despite advances, effective therapies are still limited. This current review focuses on inflammatory and coagulation pathways that influence the airway pathophysiology of SM poisoning and highlights the complexity of developing an effective therapeutic target.

Histone cleavage as a mechanism for epigenetic regulation: current insights and perspectives

Discovered over a century ago, histones constitute one of the oldest families of proteins and have been remarkably conserved throughout eukaryotic evolution. However, only for the past 30 years have histones demonstrated that their influence extends far beyond packaging DNA. To create the various chromatin structures that are necessary for DNA function in higher eukaryotes, histones undergo posttranslational modifications. While many such modifications are well documented, others, such as histone tail cleavage are less understood. Recent studies have discovered several proteases that cleave histones and have suggested roles for clipped histones in stem cell differentiation and aging in addition to infection and inflammation; the underlying mechanisms, however, are uncertain. One histone class in particular, histone H3, has received outstanding interest due to its numerous N-terminal modification sites and prevalence in regulating homeostatic processes. Here, with special consideration of H3, we will discuss the novel findings regarding histone proteolytic cleavage as well as their significance in the studies of immunology and epigenetics.

Dissecting the effect of RNA aptamer binding on the dynamics of plasminogen activator inhibitor 1 using hydrogen/deuterium exchange mass spectrometry

RNA aptamers, selected from large synthetic libraries, are attracting increasing interest as protein ligands, with potential uses as prototype pharmaceuticals, conformational probes, and reagents for specific quantification of protein levels in biological samples. Very little is known, however, about their effects on protein conformation and dynamics. We have employed hydrogen/deuterium exchange (HDX) mass spectrometry to study the effect of RNA aptamers on the structural flexibility of the serpin plasminogen activator inhibitor-1 (PAI-1). The aptamers have characteristic effects on the biochemical properties of PAI-1. In particular, they are potent inhibitors of the structural transition of PAI-1 from the active state to the inactive, so-called latent state. This transition is one of the largest conformational changes of a folded protein domain without covalent modification. Binding of the aptamers to PAI-1 is associated with substantial and widespread protection against deuterium uptake in PAI-1. The aptamers induce protection against exchange with the solvent both in the protein-aptamer interface as well as in other specific areas. Interestingly, the aptamers induce substantial protection against exchange in α-helices B, C and I. This observation substantiates the relevance of structural instability in this region for transition to the latent state and argues for involvement of flexibility in regions not commonly associated with regulation of latency transition in serpins.

Factor seven activating protease (FSAP) expression in human placenta and its role in trophoblast migration

OBJECTIVES

Factor seven activating protease (FSAP) is a plasma serine protease known to play a critical role in hemostasis and remodeling processes: FSAP levels increase markedly during normal pregnancy. In order to define the role of FSAP in vascular pathophysiology in pregnant women and particularly in the placenta, we performed this study (i) to evaluate the FSAP expression in human placenta and (ii) to identify the role of FSAP in human trophoblast migration.

STUDY DESIGN

FSAP expression in placental tissues was analyzed by using immunohistochemistry and reverse transcriptase-polymerase chain reaction (RT-PCR). To determine whether FSAP plays any role in trophoblast migration, we used human trophoblast cells in transwell migration assays.

RESULTS

Immunohistochemistry showed that FSAP protein was expressed by syncytiotrophoblast and in the cytoplasma of invasive extravillous trophoblasts (EVT) within the maternal decidua (DC) in implantation sites of human first trimester placenta. Furthermore, FSAP mRNA and protein decreased with gestational age (p<0.05, 1st vs 3rd trimester). FSAP (10μg/ml) had a significant stimulatory effect on the migration of human trophoblast cells. This effect was abolished by addition of aprotinin to block the enzymatic activity of FSAP.

CONCLUSIONS

The high expression level of FSAP in the placenta supports a relevant role of this protease in trophoblast migration and vascular remodeling, identifies a new concept of coagulation/fibrinolysis at the feto-maternal interface and may be essential for the maintenance of pregnancy.

Tissue factor pathway inhibitor is an inhibitor of factor VII-activating protease

BACKGROUND

Factor VII-activating protease (FSAP) is a serine protease that circulates in plasma in its inactive single-chain form and can be activated upon contact with dead cells. When activated by apoptotic cells, FSAP leads to the release of nucleosomes. The serpins C1-inhibitor and α(2) -antiplasmin are reported to be the major inhibitors of FSAP. However, regulation of FSAP activity by Kunitz-type inhibitors is not well studied.

OBJECTIVES

To compare the inhibition of FSAP activity and FSAP-induced nucleosome release from apoptotic cells by tissue factor pathway inhibitor (TFPI) with that of C1-inhibitor and α(2) -antiplasmin.

METHODS

Apoptotic cells were incubated with plasma or FSAP in presence of the inhibitor, and nucleosome release was analyzed with flow cytometry. Monoclonal antibodies against TFPI and altered forms of TFPI were used to investigate which domains of TFPI contribute to FSAP inhibition.

RESULTS AND CONCLUSIONS

We show that TFPI abrogates FSAP activity and nucleosome release from apoptotic cells. TFPI is a much more efficient inhibitor than C1-inhibitor or α(2) -antiplasmin. The active site of K2 is required for inhibition of FSAP. A direct binding interaction between FSAP and the C-terminal domain of TFPI is also required for efficient inhibition. Inhibition of FSAP-induced nucleosome release by recombinant TFPI might, in part, explain the anti-inflammatory effects of recombinant TFPI infusion observed in animal and human sepsis.

Elucidation of crucial structures for a catechol-based inhibitor of plasma hyaluronan-binding protein (factor VII activating protease) autoactivation

Plasma hyaluronan-binding protein (PHBP) is a serine protease the activation of which is implicated in inflammation. Previous investigations have suggested the presence of catechol-binding sites in its proenzyme form, pro-PHBP. Here we found that compounds with plural catechol groups conjugated with strong electron-withdrawing groups, such as tyrphostin AG 537 (IC(50)=18 nM), were potent inhibitors of pro-PHBP activation.

Activation of factor VII-activating protease in human inflammation: a sensor for cell death

INTRODUCTION

Cell death is a central event in the pathogenesis of sepsis and is reflected by circulating nucleosomes. Circulating nucleosomes were suggested to play an important role in inflammation and were demonstrated to correlate with severity and outcome in sepsis patients. We recently showed that plasma can release nucleosomes from late apoptotic cells. Factor VII-activating protease (FSAP) was identified to be the plasma serine protease responsible for nucleosome release. The aim of this study was to investigate FSAP activation in patients suffering from various inflammatory diseases of increasing severity.

METHODS

We developed ELISAs to measure FSAP-C1-inhibitor and FSAP-α2-antiplasmin complexes in plasma. FSAP-inhibitor complexes were measured in the plasma of 20 adult patients undergoing transhiatal esophagectomy, 32 adult patients suffering from severe sepsis and 8 from septic shock and 38 children suffering from meningococcal sepsis.

RESULTS

We demonstrate plasma FSAP to be activated upon contact with apoptotic and necrotic cells by an assay detecting complexes between FSAP and its target serpins α2-antiplasmin and C1-inhibitor, respectively. By means of that assay we demonstrate FSAP activation in post-surgery patients, patients suffering from severe sepsis, septic shock and meningococcal sepsis. Levels of FSAP-inhibitor complexes correlate with nucleosome levels and correlate with severity and mortality in these patients.

CONCLUSIONS

These results suggest FSAP activation to be a sensor for cell death in the circulation and that FSAP activation in sepsis might be involved in nucleosome release, thereby contributing to lethality.

Genetic variation in hyaluronan metabolism loci is associated with plasma plasminogen activator inhibitor-1 concentration

Elevated plasma plasminogen activator inhibitor-1 (PAI-1) concentration is associated with cardiovascular disease risk. PAI-1 is the primary inhibitor of fibrinolysis within both the circulation and the arterial wall, playing roles in both atherosclerosis and thrombosis. To define the heritable component, subjects within the population-based SHARE (Study of Health Assessment and Risk in Ethnic groups) and SHARE-AP (Study of Health Assessment and Risk Evaluation in Aboriginal Peoples) studies, composed of Canadians of South Asian (n = 298), Chinese (n = 284), European (n = 227), and Aboriginal (n = 284) descent, were genotyped using the gene-centric Illumina HumanCVD BeadChip. After imputation, more than 150,000 single nucleotide polymorphisms (SNPs) in more than 2000 loci were tested for association with plasma PAI-1 concentration. Marginal association was observed with the PAI-1 locus itself (SERPINE1; P < .05). However, 5 loci (HABP2, HSPA1A, HYAL1, MBTPS1, TARP) were associated with PAI-1 concentration at a P < 1 × 10(-5) threshold. The protein products of 2 of these loci, hyaluronan binding protein 2 (HABP2) and hyaluronoglucosaminidase 1 (HYAL1), play key roles in hyaluronan metabolism, providing genetic evidence to link these pathways.

Small-molecule modulators of zymogen activation in the fibrinolytic and coagulation systems

The coagulation and fibrinolytic systems are central to the hemostatic mechanism, which works promptly on vascular injury and tissue damage. The rapid response is generated by specific molecular interactions between components in these systems. Thus, the regulation mechanism of the systems is programmed in each component, as exemplified by the elegant processes in zymogen activation. This review describes recently identified small molecules that modulate the activation of zymogens in the fibrinolytic and coagulation systems.

Polyamine-promoted autoactivation of plasma hyaluronan-binding protein

BACKGROUND

Plasma hyaluronan-binding protein (PHBP), a protease implicated in extracellular proteolysis, consists of multiple domains: an N-terminal region (NTR), three epidermal growth factor (EGF)-like domains, a kringle domain, and a protease domain. PHBP circulates as a single-chain proenzyme (pro-PHBP), which is converted to an active, two-chain form through autoproteolysis.

OBJECTIVE

To understand the mechanism of autoactivation. Here, we report that polyamine induces the formation of pro-PHBP autoactivation complex, in which an intermolecular interaction between NTR and the third EGF-like domain (E3) plays a role.

METHODS

Using a series of pro-PHBP mutants that partially lack functional domains, polyamine-induced pro-PHBP autoactivation was investigated in terms of enzyme activity, protein interaction, and inhibition by carminic acid, an anthraquinone compound identified in this study.

RESULTS

Polyamine enhanced intermolecular binding of pro-PHBP, but not of mutant pro-PHBP that partially lacked NTR (DeltaN). Carminic acid inhibited intermolecular pro-PHBP binding and specifically abolished polyamine-induced autoactivation. NTR bound to pro-PHBP and DeltaN, but its binding was minimal to a mutant that lacked E3. The NTR-DeltaN binding was inhibited by a combination of polyamine and carminic acid, but each compound alone was ineffective.

CONCLUSIONS

We infer from the data that (i) polyamine modulates intramolecular NTR-E3 interaction to allow intermolecular binding between NTR and E3 in another pro-PHBP molecule to form an autoactivation complex, and (ii) carminic acid inhibits polyamine-modulated intermolecular NTR-E3 binding. Polyamine concentrations are higher in cells and tissues with inflammation and malignancy. Polyamine leakage from legions through cell death or tissue injury may account for physiologically relevant pro-PHBP activation.

Hyaluronic Acid binding protein 2 is a novel regulator of vascular integrity

OBJECTIVE

The disruption of the endothelial cell barrier is a critical feature of inflammation and an important contributing factor to acute lung injury (ALI), an inflammatory condition that is a major cause of morbidity and mortality in critically ill patients. We evaluated the role of the extracellular serine protease, hyaluronic acid binding protein 2 (HABP2), in vascular barrier regulation.

METHODS AND RESULTS

By using immunoblot and immunohistochemical analysis, we observed that lipopolysaccharide (LPS) induces HABP2 expression in murine lung endothelium in vivo and in human pulmonary microvascular endothelial cells (ECs) in vitro. High-molecular-weight hyaluronan (HMW-HA, approximately 1x10(6) Da) decreased HABP2 protein expression in human pulmonary microvascular ECs and decreased purified HABP2 enzymatic activity, whereas low-molecular-weight HA (LMW-HA, approximately 2500 Da) increased these activities. The effects of LMW-HA, but not HMW-HA, on HABP2 activity were inhibited with a peptide of the polyanion-binding domain of HABP2. Silencing (small interfering RNA) HABP2 expression augmented HMW-HA-induced EC barrier enhancement and inhibited LPS and LMW-HA-mediated EC barrier disruption, results that were reversed with overexpression of HABP2. Silencing protease-activated receptor 1 and 3, RhoA, or Rho kinase expression attenuated LPS-, LMW-HA-, and HABP2-mediated EC barrier disruption. By using murine models of acute lung injury, we observed that LPS- and ventilator-induced pulmonary vascular hyperpermeability was significantly reduced with vascular silencing (small interfering RNA) of HABP2.

CONCLUSIONS

HABP2 negatively regulates vascular integrity via activation of protease-activated receptor/RhoA/Rho kinase signaling and represents a potentially useful therapeutic target for syndromes of increased vascular permeability.

Transforming growth factor-β1 induces expression of human coagulation factor XII via Smad3 and JNK signaling pathways in human lung fibroblasts

Coagulation factor XII (FXII) is a liver-derived serine protease involved in fibrinolysis, coagulation, and inflammation. The regulation of FXII expression is largely unknown. Transforming growth factor-beta1 (TGF-beta1) is a multifunctional cytokine that has been linked to several pathological processes, including tissue fibrosis by modulating procoagulant and fibrinolytic activities. This study investigated whether TGF-beta1 may regulate FXII expression in human lung fibroblasts. Treatment of human lung fibroblasts with TGF-beta1 resulted in a time-dependent increase in FXII production, activation of p44/42, p38, JNK, and Akt, and phosphorylation and translocation into the nucleus of Smad3. However, TGF-beta1-induced FXII expression was repressed only by the JNK inhibitor and JNK and Smad3 antisense oligonucleotides but not by MEK, p38, or phosphoinositide 3-kinase blockers. JNK inhibition had no effect on TGF-beta1-induced Smad3 phosphorylation, association with Smad4, and its translocation into the nucleus but strongly suppressed Smad3-DNA complex formation. FXII promoter analysis revealed that the -299/+1 region was sufficient for TGF-beta1 to induce FXII expression. Sequence analysis of this region detected a potential Smad-binding element at position -272/-269 (SBE-(-272/-269)). Chromatin immunoprecipitation and streptavidin pulldown assays demonstrated TGF-beta1-dependent Smad3 binding to SBE-(-272/-269). Mutation or deletion of SBE-(-272/-269) substantially reduced TGF-beta1-mediated activation of the FXII promoter. Clinical relevance was demonstrated by elevated FXII levels and its co-localization with fibroblasts in the lungs of patients with acute respiratory distress syndrome. Our results show that JNK/Smad3 pathway plays a critical role in TGF-beta1-induced FXII expression in human lung fibroblasts and implicate its possible involvement in pathological conditions characterized by elevated TGF-beta1 levels.

Purpurin as a specific inhibitor of spermidine-induced autoactivation of the protease plasma hyaluronan-binding protein

Plasma hyaluronan-binding protein (PHBP), a serine protease that can activate coagulation factor VII and prourokinase, circulates as a single-chain form (pro-PHBP), and is autoproteolytically converted to an active two-chain form with the aid of an effector such as spermidine and heparin. In this study, we screened natural sources for inhibitors of spermidine-induced pro-PHBP autoactivation. As an active agent, we purified bikaverin from a culture of a fungus. Bikaverin inhibited spermidine-induced autoactivation with an IC(50) of 0.45 microM, while it also inhibited the active form of PHBP (IC(50)=0.8 microM). Additional screening of related compounds led to the identification of purpurin, a plant anthraquinone, as a specific inhibitor: IC(50)=6.6 microM for spermidine-induced autoactivation; no inhibition of heparin-induced autoactivation and active PHBP. Alizarin and emodin, which structurally differed from purpurin in the position or the number of the hydroxyl groups, were less active and nonspecific. Thus, the position and/or the number of the hydroxyl group affect both the potency and selectivity of the anthraquinone inhibitors.

Factor VII-activating protease in patients with acute deep venous thrombosis

Factor VII-activating protease (FSAP) is involved in haemostasis and inflammation. FSAP cleaves single chain urokinase-type plasminogen activator (scu-PA). The 1601GA genotype of the 1601G/A polymorphism in the FSAP gene leads to the expression of a FSAP variant with reduced ability to activate scu-PA, without affecting the ability to activate coagulation Factor VII (FVII). Previous studies have investigated the association of the 1601GA genotype with incidence and progression of carotid stenosis and deep venous thrombosis (DVT). The present study is the first to evaluate the potential association between the FSAP phenotype and DVT. We studied the association between the 1601G/A polymorphism, FSAP activity, FSAP antigen, Factor VIIa (FVIIa), prothrombin fragment 1+2 (F1+2), and C-reactive protein (CRP) in plasmas of 170 patients suspected for DVT. FSAP genotypes were equally distributed in patients with (n=64) and without DVT (n=106), (P=0.94). The 1601GA genotype was associated with significant reduction of FSAP activity (P<0.001) and FSAP antigen levels (P=0.04). Patients with DVT showed significantly higher FSAP activity (P=0.008), FSAP antigen (P=0.003), and F1+2 levels (P<0.001) than patients without DVT. The association between the FSAP measures and DVT disappeared when adjusted for CRP levels. F1+2 correlated positively to FSAP antigen (P=0.01), while FVIIa-levels were comparable in patients with and without DVT. We conclude that even though FSAP measures are significantly increased in patients with acute DVT, alterations in the scu-PA activating properties of FSAP are presumably not markedly involved in the development of acute DVT, and that the association between FSAP and DVT disappears after adjustment for CRP.