Cloning of cDNA for proteinase 3: a serine protease, antibiotic, and autoantigen from human neutrophils

Biosensing Platform for the Detection of Biomarkers for ALI/ARDS in Bronchoalveolar Lavage Fluid of LPS Mice Model

Acute respiratory distress syndrome (ARDS) is a worldwide health concern. The pathophysiological features of ALI/ARDS include a pulmonary immunological response. The development of a rapid and low-cost biosensing platform for the detection of ARDS is urgently needed. In this study, we report the development of a paper-based multiplexed sensing platform to detect human NE, PR3 and MMP-2 proteases. Through monitoring the three proteases in infected mice after the intra-nasal administration of LPS, we showed that these proteases played an essential role in ALI/ARDS. The paper-based sensor utilized a colorimetric detection approach based on the cleavage of peptide-magnetic nanoparticle conjugates, which led to a change in the gold nanoparticle-modified paper sensor. The multiplexing of human NE, PR3 and MMP-2 proteases was tested and compared after 30 min, 2 h, 4 h and 24 h of LPS administration. The multiplexing platform of the three analytes led to relatively marked peptide cleavage occurring only after 30 min and 24 h. The results demonstrated that MMP-2, PR3 and human NE can provide a promising biosensing platform for ALI/ARDS in infected mice at different stages. MMP-2 was detected at all stages (30 min-24 h); however, the detection of human NE and PR3 can be useful for early- (30 min) and late-stage (24 h) detection of ALI/ARDS. Further studies are necessary to apply these potential diagnostic biosensing platforms to detect ARDS in patients.

Defensin Interactions in Relation to Monoclonal and Disease-Related Proteinase 3 Antibodies Binding at the Catalytic Site

Proteinase 3 (PR3) is a neutrophil granulocyte enzyme and an autoantigen found in several forms of vasculitis. Due to the diagnostic and clinical importance of antibodies (Abs) to PR3, it is important to characterize the protein and the nature of its epitopes. Here, we have characterized PR3 monoclonal antibodies (MAbs) and disease-associated Abs and their dependency on the PR3 structure and modifications, especially interactions with α-defensins. Three MAbs (HYB 172-01, 172-04, 172-05), which bind to PR3 in its native and denatured forms and provide the disulphide bridges, were intact. α-1-antitrypsin (AT) binds to purified human neutrophil granulocyte PR3 and inhibits its proteolytic activity, towards a small synthetic peptide substrate and a large protein substrate (casein). AT also inhibited the binding of the three MAbs to PR3, indicating that they bind in a region affected by AT binding. However, the MAbs did not inhibit PR3 proteolytic activity with a small substrate, showing that they bound at the active site without restricting access to the substrate cleft. Patient-derived Abs showed essentially the same characteristics as the MAbs, with important implications for vasculitis diagnostics and pathophysiology. Current findings illustrate that PR3 epitopes depend on the three-dimensional structure of the PR3/defensin complex, and that the epitopes depend to a smaller or larger degree on PR3/defensin associations.

The neutrophil: A key resourceful agent in immune‐mediated vasculitis

The term "vasculitis" refers to a group of rare immune-mediated diseases characterized by the dysregulated immune system attacking blood vessels located in any organ of the body, including the skin, lungs, and kidneys. Vasculitides are classified according to the size of the vessel that is affected. Although this observation is not specific to small-, medium-, or large-vessel vasculitides, patients show a high circulating neutrophil-to-lymphocyte ratio, suggesting the direct or indirect involvement of neutrophils in these diseases. As first responders to infection or inflammation, neutrophils release cytotoxic mediators, including reactive oxygen species, proteases, and neutrophil extracellular traps. If not controlled, this dangerous arsenal can injure the vascular system, which acts as the main transport route for neutrophils, thereby amplifying the initial inflammatory stimulus and the recruitment of immune cells. This review highlights the ability of neutrophils to "set the tone" for immune cells and other cells in the vessel wall. Considering both their long-established and newly described roles, we extend their functions far beyond their direct host-damaging potential. We also review the roles of neutrophils in various types of primary vasculitis, including immune complex vasculitis, anti-neutrophil cytoplasmic antibody-associated vasculitis, polyarteritis nodosa, Kawasaki disease, giant cell arteritis, Takayasu arteritis, and Behçet's disease.

Molecular interactions and functions of IL-32

IL-32 is a multifaceted cytokine associated with several diseases and inflammatory conditions. Its expression is induced in response to cellular stress such as hypoxia, infections, and pro-inflammatory cytokines. IL-32 can be secreted from cells and can induce the production of pro-inflammatory cytokines from several cell types but are also described to have anti-inflammatory functions. The intracellular form of IL-32 is shown to play an important role in various cellular processes, including the defense against intracellular bacteria and viruses and in modulation of cell metabolism. In this review, we discuss current literature on molecular interactions of IL-32 with other proteins. We also review data on the role of intracellular IL-32 as a metabolic regulator and its role in antimicrobial host defense.

Elastase-Positive Neutrophils Are Associated With Refractoriness of Chronic Rhinosinusitis With Nasal Polyps in an Asian Population

Purpose

Various immune cells, including eosinophils and neutrophils, are known to contribute to the development of chronic rhinosinusitis with nasal polyps (CRSwNP). However, the current understanding of the role of neutrophils in the development of CRSwNP still remains unclear. Therefore, we investigated risk factors for refractoriness of CRSwNP in an Asian population.

Methods

Protein levels of 17 neutrophil-related mediators in nasal polyps (NPs) were determined by multiplex immunoassay, and exploratory factor analysis using principal component analysis was performed. Immunofluorescence analysis was conducted to detect human neutrophil elastase (HNE) or myeloperoxidase (MPO)-positive cells. Tissue eosinophilic nasal polyp (ENP) and tissue neutrophilia (Neu^high) were defined as greater than 70 eosinophils and 20 HNE-positive cells, otherwise was classified into non-eosinophilic nasal polyp (NENP) and absence of tissue neutrophilia (Neu^low).

Results

In terms of disease control status, NENP-Neu^low patients showed the higher rate of disease control than NENP-Neu^high and ENP-Neu^high patients. Linear by linear association demonstrated the trend in refractoriness from NENP-Neu^low to NENP-Neu^high or ENP-Neu^low to ENP-Neu^high. When multiple logistic regression was performed, tissue neutrophilia (hazard ratio, 4.38; 95% confidence interval, 1.76-10.85) was found as the strongest risk factor for CRSwNP refractoriness. Additionally, exploratory factor analysis revealed that interleukin (IL)-18, interferon-γ, IL-1Ra, tumor necrosis factor-α, oncostatin M, and MPO were associated with good disease control status, whereas IL-36α and IL-1α were associated with refractory disease control status. In subgroup analysis, HNE-positive cells and IL-36α were significantly upregulated in the refractory group (P = 0.0132 and P = 0.0395, respectively), whereas MPO and IL-18 showed higher expression in the controlled group (P = 0.0002 and P = 0.0009, respectively). Moreover, immunofluorescence analysis revealed that IL-36R⁺HNE⁺-double positive cells were significantly increased in the refractory group compared to the control group. We also found that the ratio of HNE-positive cells to α1 anti-trypsin was increased in the refractory group.

Conclusions

Tissue neutrophilia had an influence on treatment outcomes in the Asian CRSwNP patients. HNE-positive cells and IL-36α may be biomarkers for predicting refractoriness in Asians with CRSwNP. Additionally, imbalances in HNE and α1 anti-trypsin may be associated with pathophysiology of neutrophilic chronic rhinosinusitis.

Inhibitors and Antibody Fragments as Potential Anti-Inflammatory Therapeutics Targeting Neutrophil Proteinase 3 in Human Disease

Proteinase 3 (PR3) has received great scientific attention after its identification as the essential antigenic target of antineutrophil cytoplasm antibodies in Wegener's granulomatosis (now called granulomatosis with polyangiitis). Despite many structural and functional similarities between neutrophil elastase (NE) and PR3 during biosynthesis, storage, and extracellular release, unique properties and pathobiological functions have emerged from detailed studies in recent years. The development of highly sensitive substrates and inhibitors of human PR3 and the creation of PR3-selective single knockout mice led to the identification of nonredundant roles of PR3 in cell death induction via procaspase-3 activation in cell cultures and in mouse models. According to a study in knockout mice, PR3 shortens the lifespan of infiltrating neutrophils in tissues and accelerates the clearance of aged neutrophils in mice. Membrane exposure of active human PR3 on apoptotic neutrophils reprograms the response of macrophages to phagocytosed neutrophils, triggers secretion of proinflammatory cytokines, and undermines immune silencing and tissue regeneration. PR3-induced disruption of the anti-inflammatory effect of efferocytosis may be relevant for not only granulomatosis with polyangiitis but also for other autoimmune diseases with high neutrophil turnover. Inhibition of membrane-bound PR3 by endogenous inhibitors such as the α-1-protease inhibitor is comparatively weaker than that of NE, suggesting that the adverse effects of unopposed PR3 activity resurface earlier than those of NE in individuals with α-1-protease inhibitor deficiency. Effective coverage of PR3 by anti-inflammatory tools and simultaneous inhibition of both PR3 and NE should be most promising in the future.

Proteinase 3 Is a Phosphatidylserine-binding Protein That Affects the Production and Function of Microvesicles

Proteinase 3 (PR3), the autoantigen in granulomatosis with polyangiitis, is expressed at the plasma membrane of resting neutrophils, and this membrane expression increases during both activation and apoptosis. Using surface plasmon resonance and protein-lipid overlay assays, this study demonstrates that PR3 is a phosphatidylserine-binding protein and this interaction is dependent on the hydrophobic patch responsible for membrane anchorage. Molecular simulations suggest that PR3 interacts with phosphatidylserine via a small number of amino acids, which engage in long lasting interactions with the lipid heads. As phosphatidylserine is a major component of microvesicles (MVs), this study also examined the consequences of this interaction on MV production and function. PR3-expressing cells produced significantly fewer MVs during both activation and apoptosis, and this reduction was dependent on the ability of PR3 to associate with the membrane as mutating the hydrophobic patch restored MV production. Functionally, activation-evoked MVs from PR3-expressing cells induced a significantly larger respiratory burst in human neutrophils compared with control MVs. Conversely, MVs generated during apoptosis inhibited the basal respiratory burst in human neutrophils, and those generated from PR3-expressing cells hampered this inhibition. Given that membrane expression of PR3 is increased in patients with granulomatosis with polyangiitis, MVs generated from neutrophils expressing membrane PR3 may potentiate oxidative damage of endothelial cells and promote the systemic inflammation observed in this disease.

Proteinase 3 on apoptotic cells disrupts immune silencing in autoimmune vasculitis

Granulomatosis with polyangiitis (GPA) is a systemic necrotizing vasculitis that is associated with granulomatous inflammation and the presence of anti-neutrophil cytoplasmic antibodies (ANCAs) directed against proteinase 3 (PR3). We previously determined that PR3 on the surface of apoptotic neutrophils interferes with induction of antiinflammatory mechanisms following phagocytosis of these cells by macrophages. Here, we demonstrate that enzymatically active membrane-associated PR3 on apoptotic cells triggered secretion of inflammatory cytokines, including granulocyte CSF (G-CSF) and chemokines. This response required the IL-1R1/MyD88 signaling pathway and was dependent on the synthesis of NO, as macrophages from animals lacking these pathways did not exhibit a PR3-associated proinflammatory response. The PR3-induced microenvironment facilitated recruitment of inflammatory cells, such as macrophages, plasmacytoid DCs (pDCs), and neutrophils, which were observed in close proximity within granulomatous lesions in the lungs of GPA patients. In different murine models of apoptotic cell injection, the PR3-induced microenvironment instructed pDC-driven Th9/Th2 cell generation. Concomitant injection of anti-PR3 ANCAs with PR3-expressing apoptotic cells induced a Th17 response, revealing a GPA-specific mechanism of immune polarization. Accordingly, circulating CD4+ T cells from GPA patients had a skewed distribution of Th9/Th2/Th17. These results reveal that PR3 disrupts immune silencing associated with clearance of apoptotic neutrophils and provide insight into how PR3 and PR3-targeting ANCAs promote GPA pathophysiology.

A metaproteomics approach to elucidate host and pathogen protein expression during catheter-associated urinary tract infections (CAUTIs)

Long-term catheterization inevitably leads to a catheter-associated bacteriuria caused by multispecies bacterial biofilms growing on and in the catheters. The overall goal of the presented study was (1) to unravel bacterial community structure and function of such a uropathogenic biofilm and (2) to elucidate the interplay between bacterial virulence and the human immune system within the urine. To this end, a metaproteomics approach combined with in vitro proteomics analyses was employed to investigate both, the pro- and eukaryotic protein inventory. Our proteome analyses demonstrated that the biofilm of the investigated catheter is dominated by three bacterial species, that is, Pseudomonas aeruginosa, Morganella morganii, and Bacteroides sp., and identified iron limitation as one of the major challenges in the bladder environment. In vitro proteome analysis of P. aeruginosa and M. morganii isolated from the biofilm revealed that these opportunistic pathogens are able to overcome iron restriction via the production of siderophores and high expression of corresponding receptors. Notably, a comparison of in vivo and in vitro protein profiles of P. aeruginosa and M. morganii also indicated that the bacteria employ different strategies to adapt to the urinary tract. Although P. aeruginosa seems to express secreted and surface-exposed proteases to escape the human innate immune system and metabolizes amino acids, M. morganii is able to take up sugars and to degrade urea. Most interestingly, a comparison of urine protein profiles of three long-term catheterized patients and three healthy control persons demonstrated the elevated level of proteins associated with neutrophils, macrophages, and the complement system in the patient's urine, which might point to a specific activation of the innate immune system in response to biofilm-associated urinary tract infections. We thus hypothesize that the often asymptomatic nature of catheter-associated urinary tract infections might be based on a fine-tuned balance between the expression of bacterial virulence factors and the human immune system.

Neutrophils and emerging targets for treatment in chronic obstructive pulmonary disease

Chronic obstructive pulmonary disease (COPD) is characterized by a decreased airflow due to airway narrowing that, once it occurs, is not fully reversible. The disease usually is progressive and associated with an enhanced inflammatory response in the lungs after exposure to noxious particles or gases. After removal of the noxious particles, the inflammation can continue in a self-sustaining manner. It has been established that improper activation of neutrophils lies at the core of the pathology. This paper provides an overview of the mechanisms by which neutrophils can induce the pulmonary damage of COPD. As the pathogenesis of COPD is slowly being unraveled, new points of intervention are discovered, some of which with promising results.

Subfractionation, characterization, and in-depth proteomic analysis of glomerular membrane vesicles in human urine

Urinary exosome-like vesicles (ELVs) are a heterogenous mixture (diameter 40–200nm) containing vesicles shed from all segments of the nephron including glomerular podocytes. Contamination with Tamm Horsfall protein (THP) oligomers has hampered their isolation and proteomic analysis. Here we improved ELV isolation protocols employing density centrifugation to remove THP and albumin, and isolated a glomerular membranous vesicle (GMV) enriched subfraction from 7 individuals identifying 1830 proteins and in 3 patients with glomerular disease identifying 5657 unique proteins. The GMV fraction was composed of podocin/podocalyxin positive irregularly shaped membranous vesicles and podocin/podocalyxin negative classical exosomes. Ingenuity pathway analysis identified integrin, actin cytoskeleton and RhoGDI signaling in the top three canonical represented signaling pathways and 19 other proteins associated with inherited glomerular diseases. The GMVs are of podocyte origin and the density gradient technique allowed isolation in a reproducible manner. We show many nephrotic syndrome proteins, proteases and complement proteins involved in glomerular disease are in GMVs and some were shed in the disease state (nephrin, TRPC6 and INF2 and PLA2R). We calculated sample sizes required to identify new glomerular disease biomarkers, expand the ELV proteome and provide a reference proteome in a database that may prove useful in the search for biomarkers of glomerular disease.

Inhibitors of cathepsin G: a patent review (2005 to present)

INTRODUCTION

Cathepsin G (CatG) is a neutral proteinase originating from human neutrophils. It displays a unique dual specificity (trypsin- and chymotrypsin-like); thus, its enzymatic activity is difficult to control. CatG is involved in the pathophysiology of several serious human diseases, such as chronic obstructive pulmonary disease (COPD), Crohn's disease, rheumatoid arthritis, cystic fibrosis and other conditions clinically manifested by excessive inflammatory reactions. For mentioned reasons, CatG was considered as good molecular target for the development of novel drugs. However, none of them have yet entered the market as novel therapeutic agents.

AREAS COVERED

This article presents an in-depth and detailed analysis of the therapeutic potential of CatG inhibitors based on a review of patent applications and academic publishing disclosed in patents and patent applications (1991 - 2012), with several exceptions for inhibitors retrieved from academic articles.

EXPERT OPINION

Among the discussed inhibitors of CatG, examples corresponding to derivatives of β-ketophosphonic acids, aminoalkylphosphonic esters and boswellic acids (BAs) could be regarded as the most promising. The most promising one seems to be analogues of compounds of Nature's origin (peptidic and BA derivates). Nevertheless, nothing is currently known about the clinical disposition of any of the CatG inhibitors discovered so far. This latter point suggests that there is still a lot of work to do in the design of stable, pharmacologically active compounds able to specifically regulate the in vivo activity of cathepsin G.

A monoclonal antibody (MCPR3-7) interfering with the activity of proteinase 3 by an allosteric mechanism

Proteinase 3 (PR3) is an abundant serine protease of neutrophil granules and a major target of autoantibodies (PR3 anti-neutrophil cytoplasmic antibodies) in granulomatosis with polyangiitis. Some of the PR3 synthesized by promyelocytes in the bone marrow escapes the targeting to granules and occurs on the plasma membrane of naive and primed neutrophils. This membrane-associated PR3 antigen may represent pro-PR3, mature PR3, or both forms. To discriminate between mature PR3 and its inactive zymogen, which have different conformations, we generated and identified a monoclonal antibody called MCPR3-7. It bound much better to pro-PR3 than to mature PR3. This monoclonal antibody greatly reduced the catalytic activity of mature PR3 toward extended peptide substrates. Using diverse techniques and multiple recombinant PR3 variants, we characterized its binding properties and found that MCPR3-7 preferentially bound to the so-called activation domain of the zymogen and changed the conformation of mature PR3, resulting in impaired catalysis and inactivation by α1-proteinase inhibitor (α1-antitrypsin). Noncovalent as well as covalent complexation between PR3 and α1-proteinase inhibitor was delayed in the presence of MCPR3-7, but cleavage of certain thioester and paranitroanilide substrates with small residues in the P1 position was not inhibited. We conclude that MCPR3-7 reduces PR3 activity by an allosteric mechanism affecting the S1' pocket and further prime side interactions with substrates. In addition, MCPR3-7 prevents binding of PR3 to cellular membranes. Inhibitory antibodies targeting the activation domain of PR3 could be exploited as highly selective inhibitors of PR3, scavengers, and clearers of the PR3 autoantigen in granulomatosis with polyangiitis.

Relevance of the mouse model as a therapeutic approach for neutrophil proteinase 3-associated human diseases

Proteinase 3 (PR3) is one of the four elastase-related serine proteinases stored in the azurophilic granules of neutrophils. Although it participates in the pro- and anti-inflammatory responses to infection and inflammation it also retains specific functions that make it different from neutrophil elastase in spite of their close structural resemblance. PR3 is involved in the immune response to infection and is the major autoantigen in granulomatosis with polyangiitis (GPA, formerly Wegener disease), an autoimmune systemic vasculitis with granulomas. Thus, PR3 appears to be a relevant therapeutic target in a variety of inflammatory human diseases. Animal models are required for the testing of new drugs that target PR3 specifically but differences between human and rodent neutrophil PR3 expression and substrate specificity have greatly impaired progress in this direction. This may explain that, to date, there is no spontaneous model of vasculitis associated with anti-PR3 antibodies. In this review, we will focus on the structural and functional differences between human and murine PR3, and how these differences may be by-passed in order to develop a relevant animal model.

Neutrophil-derived Oxidants and Proteinases as Immunomodulatory Mediators in Inflammation

Neutrophils generate potent microbicidal molecules via the oxygen-dependent pathway, leading to the generation of reactive oxygen intermediates (ROI), and via the non-oxygen dependent pathway, consisting in the release of serine proteinases and metalloproteinases stored in granules. Over the past years, the concept has emerged that both ROI and proteinases can be viewed as mediators able to modulate neutrophil responses as well as the whole inflammatory process. This is well illustrated by the oxidative regulation of proteinase activity showing that oxidants and proteinases acts is concert to optimize the microbicidal activity and to damage host tissues. ROI and proteinases can modify the activity of several proteins involved in the control of inflammatory process. Among them, tumour necrosis factor-α and interleukin-8, are elective targets for such a modulation. Moreover, ROI and proteinases are also able to modulate the adhesion process of neutrophils to endothelial cells, which is a critical step in the inflammatory process.

PR3 antibodies do not induce renal pathology in a novel PR3-humanized mouse model for Wegener's granulomatosis

Different murine models have been used as basis for Proteinase 3 (PR3)-associated vasculitis models, but sufficient reproduction of the human clinical manifestation has failed to this date. As a reliable animal model is needed to further elucidate the pathological value of PR3-ANCA, we developed a PR3-humanized transgenic mouse model, in order to induce a glomerulonephritis. Our huPR3-transgenic mice were injected i.v. with our monoclonal antibodies, either unlabeled or directly labeled by fluorescein isothiocyanate. For a period of 5 days, proteinuria and erythrocyte count were measured with urine dip sticks. None of the mice exhibited proteinuria and/or an abnormal number of erythrocytes in the urine. Five days after antibody treatment, the mice were killed and different organs were fixed and immunohistochemically assessed. In the case of the kidney, we could detect a glomerulonephritis. Our study is able to show that although a direct renal target was given in transgenic human PR3 mice, no renal pathology was detectable. Multifactorial mechanisms for PR3-ANCA involvement in the development of Wegener's granulomatosis must be hypothesized.

CpsY influences Streptococcus iniae cell wall adaptations important for neutrophil intracellular survival

The ability of a pathogen to evade neutrophil phagocytic killing mechanisms is critically important for dissemination and establishment of a systemic infection. Understanding how pathogens overcome these innate defenses is essential for the development of optimal therapeutic strategies for invasive infections. CpsY is a conserved transcriptional regulator previously identified as an important virulence determinant for systemic infection of Streptococcus iniae. While orthologs of CpsY have been associated with the regulation of methionine metabolism and uptake pathways, CpsY additionally functions in protection from neutrophil-mediated killing. S. iniae does not alter neutrophil phagosomal maturation but instead is able to adapt to the extreme bactericidal environment of a mature neutrophil phagosome, a property dependent upon CpsY. This CpsY-dependent adaptation appears to involve stabilization of the cell wall through peptidoglycan O-acetylation and repression of cellular autolysins. Furthermore, S. iniae continues to be a powerful model for investigation of bacterial adaptations during systemic streptococcal infection.

Vascular ligand-receptor mapping by direct combinatorial selection in cancer patients

Molecules differentially expressed in blood vessels among organs or between damaged and normal tissues, are attractive therapy targets; however, their identification within the human vasculature is challenging. Here we screened a peptide library in cancer patients to uncover ligand-receptors common or specific to certain vascular beds. Surveying ~2.35 x 10(6) motifs recovered from biopsies yielded a nonrandom distribution, indicating that systemic tissue targeting is feasible. High-throughput analysis by similarity search, protein arrays, and affinity chromatography revealed four native ligand-receptors, three of which were previously unrecognized. Two are shared among multiple tissues (integrin α4/annexin A4 and cathepsin B/apolipoprotein E3) and the other two have a restricted and specific distribution in normal tissue (prohibitin/annexin A2 in white adipose tissue) or cancer (RAGE/leukocyte proteinase-3 in bone metastases). These findings provide vascular molecular markers for biotechnology and medical applications.

Alpha-1-antitrypsin is produced by human neutrophil granulocytes and their precursors and liberated during granule exocytosis

Alpha-1-antitrypsin (A1AT) is an important inhibitor of neutrophil proteases including elastase, cathepsin G, and proteinase 3. Transcription profiling data suggest that A1AT is expressed by human neutrophil granulocytes during all developmental stages. A1AT has hitherto only been found associated with azurophile granules in neutrophils indicative of A1AT expression being restricted to the promyelocyte stage. We examined the localization and production of A1AT in healthy donor neutrophils and found A1AT to be a constituent of all granule subtypes and to be released from neutrophils following stimulation. A1AT is produced at all stages of myeloid maturation in the bone marrow. The production increases as neutrophils enter circulation and increases further upon migration to tissues as observed in skin windows and when blood neutrophils are incubated with granulocyte colony-stimulating factor. Neutrophils from patients with A1AT-deficiency carrying the (PI)ZZ mutation in the A1AT gene appeared structurally and functionally normal, but A1AT produced in leukocytes of these patients lacked the ability to bind proteases efficiently. We conclude that A1AT generation and release from neutrophils add significantly to the antiprotease levels in tissues during inflammation. Impaired binding of neutrophil A1AT to serine proteases in patients with (PI)ZZ mutations may enhance their susceptibility to the development of emphysema.

Molecular analysis of the membrane insertion domain of proteinase 3, the Wegener's autoantigen, in RBL cells: implication for its pathogenic activity

PR3, also called myeloblastin, is a neutrophil serine protease that promotes myeloid cell proliferation by cleaving the cyclin-dependent kinase inhibitor p21(cip1/waf1). In addition, it is the target of ANCA in GPA, a necrotizing vasculitis. Anti-PR3 ANCA binding to membrane-expressed PR3 triggers neutrophil activation, potentiating vascular inflammation. This study performed in RBL cells identifies the structural motifs of PR3 membrane anchorage and examines its impact on PR3 proinflammatory and proliferative functions. With the use of MD simulations and mutagenesis, we demonstrate that the mutations of four hydrophobic (F180, F181, L228, F229) or four basic (R193, R194, K195, R227) amino acids abrogated PR3 membrane anchorage. The hydrophobic patch-deficient PR3 mutant (PR34H4A) was still able to cleave the synthetic substrate Boc-Ala-Pro-Val in cell lysates. However, in contrast to WT PR3, PR34H4A was not expressed at the plasma membrane after degranulation and failed to cleave extracellular fibronectin, was not externalized after apoptosis and did not impair macrophage phagocytosis of apoptotic cells, did not promote myeloid cell proliferation and failed to cleave p21/waf1. PR3 membrane insertion appears to be pivotal for its proinflammatory activities, such as extracellular proteolysis and impairment of apoptotic cell clearance, but also for myeloid cell proliferation. Targeting membrane-associated PR3 might constitute a novel, anti-inflammatory therapeutic strategy in inflammatory disease especially in vasculitis, but this approach has to be validated in mature neutrophils.

Neutrophil elastase, proteinase 3, and cathepsin G as therapeutic targets in human diseases

Polymorphonuclear neutrophils are the first cells recruited to inflammatory sites and form the earliest line of defense against invading microorganisms. Neutrophil elastase, proteinase 3, and cathepsin G are three hematopoietic serine proteases stored in large quantities in neutrophil cytoplasmic azurophilic granules. They act in combination with reactive oxygen species to help degrade engulfed microorganisms inside phagolysosomes. These proteases are also externalized in an active form during neutrophil activation at inflammatory sites, thus contributing to the regulation of inflammatory and immune responses. As multifunctional proteases, they also play a regulatory role in noninfectious inflammatory diseases. Mutations in the ELA2/ELANE gene, encoding neutrophil elastase, are the cause of human congenital neutropenia. Neutrophil membrane-bound proteinase 3 serves as an autoantigen in Wegener granulomatosis, a systemic autoimmune vasculitis. All three proteases are affected by mutations of the gene (CTSC) encoding dipeptidyl peptidase I, a protease required for activation of their proform before storage in cytoplasmic granules. Mutations of CTSC cause Papillon-Lefèvre syndrome. Because of their roles in host defense and disease, elastase, proteinase 3, and cathepsin G are of interest as potential therapeutic targets. In this review, we describe the physicochemical functions of these proteases, toward a goal of better delineating their role in human diseases and identifying new therapeutic strategies based on the modulation of their bioavailability and activity. We also describe how nonhuman primate experimental models could assist with testing the efficacy of proposed therapeutic strategies.

Anti-neutrophil cytoplasmic antibodies target sequential functional proteinase 3 epitopes in the sera of patients with Wegener’s granulomatosis

Many patients with Wegener’s granulomatosis (WG) have anti-neutrophil cytoplasmic antibodies (c-ANCA). Aside from being a diagnostic marker, these autoantibodies may play roles in disease pathogenesis. Proteinase 3 (PR3) is the primary target of c-ANCA in WG patient sera. Of 60 c-ANCA-positive patients, 10 patients were selected for detailed humoral epitope analysis, contingent upon serum availability, using samples with positive levels of anti-PR3 by enzyme-linked immunosorbent assay (ELISA). Sequential epitope specificities of anti-PR3 antibodies detected by screening the maximally overlapping solid-phase octapeptides of PR3 showed seven major common antigenic targets bound by WG patient sera. These include novel and previously identified sequential PR3 epitopes bound by c-ANCA. B cell epitope prediction algorithms identified all or part of the seven defined epitopes. Several epitopes share sequence and structural proximity with functional sites, including the catalytic triad and proposed binding sites of other potential proteins [PR3 complementary peptide and soluble endothelial protein C receptor (sEPCR)]. Epitope 4 (VVLGAHNVRTQ) had the highest binding prevalence (90%) and epitope 2 (AQPHSRPYMAS) has the highest average reactivity of the antigenic regions. Epitope 4 includes the interaction site between sEPCR and PR3 which may serve as an important interaction to down-regulate inflammation. Epitopes 3, 5 and 7 are in direct proximity to amino acids that form the catalytic triad of the protein. c-ANCA targets both unique and previously known sequential PR3 peptides. This information may prove useful in understanding anti-PR3-mediated disease pathogenesis in systemic vasculitides.

Mapping of conformational epitopes on human proteinase 3, the autoantigen of Wegener's granulomatosis

Anti-neutrophil cytoplasmic Abs (cANCAs) against conformational epitopes of proteinase 3 (PR3) are regarded as an important pathogenic marker in Wegener's granulomatosis (WG). Although the three-dimensional structure of PR3 is known, binding sites of mAbs and cANCAs have not been mapped to date. Competitive binding and biosensor experiments suggested the existence of four nonoverlapping areas on the PR3 surface. In this paper, we present an approach to identify these discontinuous surface regions that cannot be mimicked by linear peptides. The very few surface substitutions found in closely related PR3 homologs from primates, which were further varied by the construction of functional human-gibbon hybrids, resulted in the differential loss of three Ab binding sites, two of which were mapped to the N-terminal beta-barrel and one to the linker segment connecting the N- and C-terminal barrels of PR3. The sera from WG patients differed in their binding to gibbon PR3 and the gibbon-human PR3 hybrid, and could be divided into two groups with similar or significantly reduced binding to gibbon PR3. Binding of almost all sera to PR3-alpha1-protease inhibitor (alpha1-PI) complexes was even more reduced and often absent, indicating that major antigenic determinants overlap with the active site surface on PR3 that associates with alpha1-PI. Similarly, the mouse mAbs CLB12.8 and 6A6 also did not react with gibbon PR3 and PR3-alpha1-PI complexes. Our data strongly suggest that cANCAs from WG patients at least in part recognize similar surface structures as do mouse mAbs and compete with the binding of alpha1-PI to PR3.

Structures of human proteinase 3 and neutrophil elastase--so similar yet so different

Proteinase 3 and neutrophil elastase are serine proteinases of the polymorphonuclear neutrophils, which are considered to have both similar localization and ligand specificity because of their high sequence similarity. However, recent studies indicate that they might have different and yet complementary physiologic roles. Specifically, proteinase 3 has intracellular specific protein substrates resulting in its involvement in the regulation of intracellular functions such as proliferation or apoptosis. It behaves as a peripheral membrane protein and its membrane expression is a risk factor in chronic inflammatory diseases. Moreover, in contrast to human neutrophil elastase, proteinase 3 is the preferred target antigen in Wegener's granulomatosis, a particular type of vasculitis. We review the structural basis for the different ligand specificities and membrane binding mechanisms of both enzymes, as well as the putative anti-neutrophil cytoplasm autoantibody epitopes on human neutrophil elastase 3. We also address the differences existing between murine and human enzymes, and their consequences with respect to the development of animal models for the study of human proteinase 3-related pathologies. By integrating the functional and the structural data, we assemble many pieces of a complicated puzzle to provide a new perspective on the structure-function relationship of human proteinase 3 and its interaction with membrane, partner proteins or cleavable substrates. Hence, precise and meticulous structural studies are essential tools for the rational design of specific proteinase 3 substrates or competitive ligands that modulate its activities.

The possible role of granzyme B in the pathogenesis of chronic obstructive pulmonary disease

Chronic obstructive pulmonary disease (COPD) is a highly prevalent inflammatory lung condition characterized by airways disease and emphysema, and the precise mechanism of pathogenesis is poorly understood. The consistent features of COPD include protease-antiprotease imbalance, inflammation and accelerated aging caused by apoptosis or senescence. One family of molecules involved in all of these processes is the granzymes, serine proteases with the best-known member being granzyme B (GzmB). The majority of GzmB is released unidirectionally towards target cells, but GzmB can also be released nonspecifically and escape into the extracellular environment. GzmB is capable of cleaving extracellular matrix (ECM) proteins in vitro, and the accumulation of GzmB in the extracellular milieu during chronic inflammation in COPD could contribute to ECM degradation and remodelling and, consequently, the emphysematous phenotype in the lung. Preliminary studies suggest that increased GzmB expression is associated with increased COPD severity, and this may represent a promising new target for drug and biomarker discovery in COPD. In this paper, we review the potential pathogenic contributions of GzmB to the pathogenesis of COPD.

Reconstitution of human azurocidin catalytic triad and proteolytic activity by site-directed mutagenesis

Azurocidin belongs to the serprocidin family, but it is devoid of proteolytic activity due to a substitution of His and Ser residues in the catalytic triad. The aim of this study was to reconstitute the active site of azurocidin by site-directed mutagenesis, analyze its processing and restored proteolytic activity. Azurocidin expressed inSf9 insect cells possessing the reconstituted His41-Asp89-Ser175 triad exhibited significant proteolytic activity toward casein with a pH optimum of approximately 8–9, but a reconstitution of only one active site amino acid did not result in proteolytically active protein. Enzymatically active recombinant azurocidin caused cleavage of the C-terminal fusion tag with the primary cleavage site after lysine at Lys-Leu and after alanine at Ala-Ala, and the secondary cleavage site after arginine at Arg-Gln, as well as with low efficiency caused cleavage of insulin chain B after leucine at Leu-Tyr and Leu-Cys, and after alanine at Ala-Leu. We demonstrate that cleavage of the azurocidin C-terminal tripeptide is not necessary for its enzymatic activity. The first isoleucine present in mature azurocidin can be replaced by similar amino acids, such as leucine or valine, but its substitution by histidine or arginine decreases proteolytic activity.

Antimicrobial proteins with homology to serine proteases

The azurophil granule, a specialized lysosome of human neutrophils, contains a family of antimicrobial proteins with structural homology to serine proteases, the serprocidins. Three members of this family are serine proteases (cathepsin G, elastase and proteinase-3) and one is a proteolytically inactive homologue (azurocidin). They are synthesized as preproproteins with a characteristic leader peptide and a propiece, both of which are removed by processing enzymes to yield the mature protein. The functional genes for three serprocidins (elastase, proteinase-3 and azurocidin) are grouped in a single genetic locus on chromosome 19 and are coordinately expressed and regulated during haemopoietic differentiation. Multiple and sometimes overlapping biological functions are a feature of this family, yet they all seem to pertain to host immunity. The structural requirements for the function of one member of this group (azurocidin), particularly its antibiotic function, are under investigation.

NB1 mediates surface expression of the ANCA antigen proteinase 3 on human neutrophils

Antineutrophil cytoplasmic antibodies (ANCAs) with specificity for proteinase 3 (PR3) are central to a form of ANCA-associated vasculitis. Membrane PR3 (mPR3) is expressed only on a subset of neutrophils. The aim of this study was to determine the mechanism of PR3 surface expression on human neutrophils. Neutrophils were isolated from patients and healthy controls, and hematopoietic stem cells from cord blood served as a model of neutrophil differentiation. Surface expression was analyzed by flow cytometry and confocal microscopy, and proteins were analyzed by Western blot experiments. Neutrophil subsets were separated by magnetic cell sorting. Transfection experiments were carried out in HEK293 and HL60 cell lines. Using neutrophils from healthy donors, patients with vasculitis, and neutrophilic differentiated stem cells we found that mPR3 display was restricted to cells expressing neutrophil glycoprotein NB1, a glycosylphosphatidylinositol (GPI)–linked surface receptor. mPR3 expression was decreased by enzymatic removal of GPI anchors from cell membranes and was absent in a patient with paroxysmal nocturnal hemoglobinuria. PR3 and NB1 coimmunoprecipitated from and colocalized on the neutrophil plasma membrane. Transfection with NB1 resulted in specific PR3 surface binding in different cell types. We conclude that PR3 membrane expression on neutrophils is mediated by the NB1 receptor.

Increased neutrophil membrane expression and plasma level of proteinase 3 in systemic vasculitis are not a consequence of the - 564 A/G promotor polymorphism

Several findings link proteinase 3 (PR3) to small vessel vasculitis. Besides being a major target of anti-neutrophil cytoplasm antibodies (ANCA), previous findings have shown increased circulating levels of PR3 in vasculitis patients, increased levels of neutrophil membrane-PR3 (mPR3) expression and a skewed distribution of the - 564 A/G polymorphism in the promotor region of the PR3 gene. In this study we elucidate how these three findings relate to each other. The plasma concentration of PR3 was measured by enzyme-linked immunosorbent assay (ELISA), mPR3 expression by fluorescence activated cell sorter (FACS) and the gene polymorphism by real-time polymerase chain reaction (PCR). We compared results from 63 patients with ANCA-associated systemic vasculitis (AASV) with 107 healthy blood donors. In accordance with previous reports, AASV patients had increased plasma concentrations of PR3 compared to healthy controls (mean 224 microg/l versus 155 microg/l, P < 0.0001). They also showed an increased number of mPR3-positive neutrophils (60%versus 42%, P < 0.001). However, contrary to a previous report, we found no skewed distribution of the polymorphism in PR3 gene. There was a weak correlation between mPR3 mean fluorescence intensity (MFI) and plasma PR3 among healthy controls and myeloperoxidase-ANCA (MPO-ANCA)-positive patients (r = 0.24, P = 0.015 and r = 0.52, P = 0.011, respectively). In conclusion, increased plasma PR3 and high expression of mPR3 are associated with small vessel vasculitis, but neither of them is a consequence of the - 564 A/G polymorphism of the PR3 gene promotor.

Interleukin-17 and airway remodelling

Interleukin (IL)-17A is emerging as important in reinforcing innate immunity by orchestrating sustained neutrophilic mobilisation. Even though there are indications of association with specific airway diseases, there is still no final proof that IL-17A plays a truly causative pathogenic role. There is evidence in mice that endogenous IL-17A contributes to the development of allergen-induced airway hyperresponsiveness and there is also evidence that IL-17A stimulates the release of several cytokines with known capacity for airway remodelling, from cells normally residing in the airways. New studies are required to determine whether these effects on local cells actually contribute to airway remodelling in vivo. If this is the case, then IL-17A may constitute a useful target for pharmacotherapeutic intervention in allergic airway disease.

Differences between human proteinase 3 and neutrophil elastase and their murine homologues are relevant for murine model experiments

Direct comparisons of human (h) and murine (m) neutrophil elastase (NE) and proteinase 3 (PR3) are important for the understanding and interpretation of inflammatory and PR3-related autoimmune processes investigated in wild-type-, mNE- and mPR3/mNE knockout mice. To this end, we purified recombinant mPR3 and mNE expressed in HMC1 and 293 cells and compared their biophysical properties, proteolytic activities and susceptibility to inhibitors with those of their human homologues, hPR3 and hNE. Significant species differences in physico-chemical properties, substrate specificities and enzyme kinetics towards synthetic peptide substrates, oxidized insulin B chain, and fibrinogen were detected. MeOSuc-AAPV-pNA and Suc-AAPV-pNA were hydrolyzed more efficiently by mPR3 than hPR3, but enzymatic activities of mNE and hNE were very similar. Fibrinogen was cleaved much more efficiently by mPR3 than by hPR3. All four proteases were inhibited by alpha(1)-antitrypsin and elafin. Eglin C inihibited mNE, hNE, mPR3, but not hPR3. SLPI inhibited both NEs, but neither PR3. The custom-designed hNE inhibitor, Val(15)-aprotinin, is a poor inhibitor for mNE. In conclusion, appropriate interpretation of experiments in murine models requires individual species-specific assessment of neutrophil protease function and inhibition.

Cleavage of p21/WAF1/CIP1 by Proteinase 3 Modulates Differentiation of a Monocytic Cell Line

Proteinase 3 (PR3), also called myeloblastin, is involved in the control of myeloid cell growth, but the underlying molecular mechanisms have not been elucidated. In U937/PR3, stably transfected with PRCRSV/PR3 to overexpress PR3, PMA-induced p21 expression was significantly decreased as compared with control U937, and this phenomenon was reversed in the presence of the serine proteinase inhibitor, pefabloc. Conversely, when PR3 was inactivated by small interfering RNA, p21 protein was increased, and PMA-induced monocytic differentiation was potentiated. Mass spectrometry analysis identified Ala45 as the primary cleavage site on p21, and the recombinant mutated p21A45R, generated by site-directed mutagenesis and expressed in Escherichia coli, was resistant to in vitro PR3 cleavage. The U937 cells were then stably transfected with either PRCRSV/p21 or PRCRSV/p21A45R, to ectopically express wild type p21 or PR3-resistant p21, respectively. In U937/p21A45R treated with PS-341, a selective proteasome inhibitor, a significant decrease in the S phase and a blockade in the G0-G1 phase of cell cycle were observed when compared with U937/p21 or control U937. This suggested that both PR3 and the proteasome are efficiently involved in the proteolytic regulation of p21 expression in myeloid cells. Moreover, PMA-induced p21 expression was more pronounced in U937/p21A45R compared with U937/p21 and was concomitant with the morphological features of early differentiation. Our data demonstrated that p21 is one specific target of PR3 and that PR3-mediated p21 cleavage prevents monocytic differentiation.

Proteinase-3 induces procaspase-3 activation in the absence of apoptosis: potential role of this compartmentalized activation of membrane-associated procaspase-3 in neutrophils

In the present study, we provide evidence that procaspase-3 is a novel target of proteinase 3 (PR3) but not of human neutrophil elastase (HNE). Human mast cell clone 1 (HMC1) and rat basophilic leukemia (RBL) mast cell lines were transfected with PR3 or the inactive mutated PR3 (PR3S203A) or HNE cDNA. In both RBL/PR3 and HMC1/PR3, a constitutive activity of caspase-3 was measured with DEVD substrate, due to the direct processing of procaspase-3 by PR3. No caspase-3 activation was observed in cells transfected with the inactive PR3 mutant or HNE. Despite the high caspase-3 activity in RBL/PR3, no apoptosis was detected as demonstrated by an absence of 1) phosphatidylserine externalization, 2) mitochondria cytochrome c release, 3) upstream caspase-8 or caspase-9 activation, or 4) DNA fragmentation. In vitro, purified PR3 cleaved procaspase-3 into an active 22-kDa fragment. In neutrophils, the 22-kDa caspase-3 activation fragment was present only in resting neutrophils but was absent after apoptosis. The 22 kDa fragment was specific of myeloid cells because it was absent from resting lymphocytes. This 22-kDa fragment was not present when neutrophils were treated with pefabloc, an inhibitor of serine proteinase. Like in HMC1/PR3, the 22-kDa caspase-3 fragment was restricted to the plasma membrane compartment. Double immunofluorescence labeling after streptolysin-O permeabilization further showed that PR3 and procaspase-3 could colocalize in an extragranular compartment. In conclusion, our results strongly suggest that compartmentalized PR3-induced caspase-3 activation might play specific functions in neutrophil survival.

B cell epitope specificity in ANCA-associated vasculitis: does it matter?

Pauci-immune idiopathic small-vessel vasculitis is strongly associated with the presence of antineutrophil cytoplasm autoantibodies (ANCA). Antibodies to PR3 predominate in patients with Wegener's granulomatosis; antibodies to myeloperoxidase (MPO) are found more frequently in patients with microscopic polyangiitis. There is increasing in vivo and in vitro evidence for a pathogenic role of ANCA in systemic vasculitis based on associations of ANCA with disease activity. If ANCA are pathogenic, why is the course of disease different from one patient to another? Antibodies can recognize different binding sites (epitopes) on their corresponding antigens. Differences in binding specificity may influence the pathogenic potential of the antibodies. Differences between epitope specificity of ANCA between patients or changes in epitope specificity of ANCA in time in an individual patient may, accordingly, result in differences in disease expression. This review will focus on epitope specificity of autoantibodies in systemic autoimmune diseases and especially on the epitope specificity of PR3- and MPO-ANCA. We will discuss whether PR3-ANCA or MPO-ANCA recognize different epitopes on PR3 and MPO, respectively, and whether the epitopes recognized by ANCA change in parallel with the disease activity of ANCA-associated vasculitis. Finally, we will speculate if the direct pathogenic role of ANCA can be ascribed to one relapse- or disease-inducing epitope. Characterization of relapse- or disease-inducing epitopes bound by PR3-ANCA and MPO-ANCA is significant for understanding initiation and reactivation of ANCA-associated vasculitis. Elucidating a disease-inducing epitope bound by ANCA may lead to the development of epitope-specific therapeutic strategies.

Neutrophil granules and secretory vesicles in inflammation

The neutrophil is a major effector cell of innate immunity. Exocytosis of granules and secretory vesicles plays a pivotal role in most neutrophil functions from early activation to the destruction of phagocytosed microorganisms. Neutrophil granules contain a multitude of antimicrobial and potentially cytotoxic substances that are delivered to the phagosome or to the exterior of the cell following degranulation. This review summarises current knowledge of granule biology and highlights the effects of neutrophil degranulation in the acute inflammatory response.

Characterisation and properties of ectosomes released by human polymorphonuclear neutrophils

Human neutrophils release vesicles when activated in vitro and in vivo, in local and systemic inflammation. We have suggested that the presence of these vesicles is due to ectocytosis, defined as the release of rightside-out oriented vesicles expressing a select set of membrane proteins. Herein we have characterised the vesicles released by neutrophils to be ectosomes with specific properties. They contained cytosolic F-actin indicating their outside-out orientation. They bound Annexin V, suggesting that they expose phosphatidylserine, similarly to platelet microparticles. They expressed a subset of cell surface proteins (selectins and integrins, complement regulators, HLA-1, FcgammaRIII, and CD66b, but not CD14, FcgammaRII, and CD87). There was no specificity for transmembrane or glycosyl-phosphatidylinositol-linked proteins and, unexpectedly, L-selectin, known to be cleaved from the surface of activated neutrophils, was present. Ectosomes exposed active enzymes released by neutrophils upon degranulation (matrix metalloproteinase-9, myeloperoxidase, proteinase 3, and elastase). In particular, released myeloperoxidase was able to bind back to ectosomes. The purified complement protein C1q and C1q from serum bound to ectosomes as well. Another aspect of ectosomes was that they became specifically adherent to monocytic and endothelial cells. These observations suggest that neutrophil-derived ectosomes have unique characteristics that make them candidates for playing roles in inflammation and cell signaling.

Diagnostic and pathogenetic role of antineutrophil cytoplasmic autoantibodies

Anti-neutrophil cytoplasmic antibodies (ANCA) are mostly known as a useful diagnostic tool in patients with small-vessel vasculitides. With the accumulating knowledge of these autoantibodies, however, it becomes clear that the role of ANCA may not be only limited to a diagnosis of such disorders. The current review addresses, in addition to classical diagnostic associations, other diseases connected with ANCA positivity, both in adults and in children. The etiology of ANCA remains unknown, but still, the importance of both genetic and environmental factors is undoubted. The role of infection and chemicals in the etiology of ANCA-associated diseases is stressed in particular. A pathogenetic role of ANCA is suggested because of clinical observations based on the correlation of the vasculitis activity and the titer of ANCA. Many experiments show the effects of ANCA in various steps of an inflammatory process, particularly on leukocyte microbicidal activity and oxidative burst. Recent findings are analyzed in the experimental field and they are correlated with clinical significance.

Cleavage of p21waf1 by proteinase-3, a myeloid-specific serine protease, potentiates cell proliferation

In this study, we present evidence for the critical role of proteinase-3 (PR3) in the proliferation of myeloid cells via the proteolytic regulation of the cyclin-dependent kinase inhibitor p21(waf1). Expression of recombinant PR3 in rat (RBL) or human (HMC1) mast cell lines increased bromodeoxyuridine incorporation and CDK2 activity compared with RBL and HMC1 cells transfected with an enzymatically inactive PR3 mutant (PR3(S203A)) or with human neutrophil elastase. Western blot analysis of p21(waf1) showed an absence of detectable protein, despite normal levels of p21 mRNA. Ectopic overexpression of p21 restored normal levels of p21 in the RBL/PR3/p21 double transfectants and reverted the proliferative effect of PR3. Inhibition of the 26 S proteasome by lactacystin or of caspases by benzyloxycarbonyl-Val-Ala-Asp-fluoromethyl ketone did not inhibit p21 proteolysis. p21 cleavage correlated with PR3 expression in HMC1 cells infected with recombinant adenoviral vector Ad/PR3. During in vitro studies, purified p21 was cleaved by PR3, resulting in a 10-kDa p21 fragment. Employing double immunofluorescence confocal microscopy, subcellular fractionation, and co-immunoprecipitation, we found that PR3 and p21 colocalized in the cytosol. In human neutrophils treated with tumor necrosis factor-alpha, which induces PR3 re-expression, we observed that p21 disappeared and was reversed by Pefabloc, a serine proteinase inhibitor. The physiopathological implications of the cleavage of p21 by PR3 have to be determined.

Expression of recombinant proteinase 3, the autoantigen in Wegener's granulomatosis, in insect cells

Proteinase 3 (PR3) is the major autoantigen for anti-neutrophil cytoplasmic antibodies (ANCA) in patients with Wegener's granulomatosis. Little is known about the major antigenic sites on PR3. To facilitate epitope mapping, PR3 was cloned in insect cells using a baculovirus expression system. Four different sequences of the PR3 cDNA were amplified by PCR: two clones containing the pro-peptide of PR3 with or without a His-tag (rproPR3-his and rproPR3, respectively) and two clones without the pro-peptide and with or without a His-tag (rPR3-his and rPR3, respectively). The PR3 sequences were cloned behind the polyhedrin promoter and the honeybee melittin signal peptide enabling secretion of rPR3. Plasmids were transposed into the genome of baculovirus, and wild types as well as PR3-containing virus genomes were transfected into Sf21 insect cells. All four rPR3 variants were secreted into the medium and were recognized by anti-neutrophil PR3 rabbit serum and by at least two anti-PR3 monoclonal antibodies. Mature forms of PR3 were recognized by almost all patient sera, whereas the pro-forms of PR3 were recognized by 14 of 18 PR3-ANCA sera tested. On SDS-PAGE, the four rPR3 forms migrated at approximately 32 kDa. RPR3-his and rproPR3-his could be purified by means of this His-tag. In conclusion, especially the mature rPR3s are well recognized by PR3-ANCA sera. The presence of a C-terminal His-tag facilitated purification of His-tagged rPR3. Thus, rPR3 expressed in insect cells can be used as a tool for diagnostic tests as well as for epitope mapping studies.

Evidence for diversity of substrate specificity among members of the chymase family of serine proteases

The term chymase is used to signify a chymotrypsin-like protease stored within the secretory granules of mast cells. Primarily based on amino acid sequence homology, 18 chymases have been identified among different animals. This study, which compares the structure of the primary specificity pocket (S1 subsite), defines a subgroup of four chymases likely to have a substrate specificity with more elastase- than chymotrypsin-like qualities. This difference is due, primarily, to finding a Val instead of a Gly at residue 199, a position corresponding to Gly216 in bovine chymotrypsin and Val216 in neutrophil and porcine elastases. Chymases with Val at 199 are found only in animals expressing multiple chymases, consistent with the premise that their substrate specificity differs from that of chymases with Gly at 199.

Proteinase-3 as the major autoantigen of c-ANCA is strongly expressed in lung tissue of patients with Wegener's granulomatosis

Proteinase-3 (PR-3) is a neutral serine proteinase present in azurophil granules of human polymorphonuclear leukocytes and serves as the major target antigen of antineutrophil cytoplasmic antibodies with a cytoplasmic staining pattern (c-ANCA) in Wegener's granulomatosis (WG). The WG disease appears as severe vasculitis in different organs (e.g. kidney, nose and lung). Little is known about the expression and distribution of PR-3 in the lung. We found that PR-3 is expressed in normal lung tissue and is upregulated in lung tissue of patients with WG. Interestingly, the parenchymal cells (pneumocytes type I and II) and macrophages, and not the neutrophils, express PR-3 most strongly and may contribute to lung damage in patients with WG via direct interaction with antineutrophil cytoplasmic antobodies (ANCA). These findings suggest that the PR-3 expression in parenchymal cells of lung tissue could be at least one missing link in the etiopathogenesis of pulmonary pathology in ANCA-associated disease.

Immobilised metal-ion affinity chromatography purification of histidine-tagged recombinant proteins: a wash step with a low concentration of EDTA

Immobilised metal-ion affinity chromatography (IMAC) is widely used for the purification of recombinant proteins in which a poly-histidine tag is introduced. However, other proteins may also bind to IMAC columns. We describe the use of a washing buffer with a low concentration of EDTA (0.5 mM) for the removal of proteins without histidine tag from IMAC columns. Four histidine-tagged recombinant proteins/protein complexes were purified to homogeneity from cell culture medium of insect cells by using an EDTA washing buffer. The presence of a low concentration of EDTA in washing buffers during IMAC may have a general application in the purification of histidine-tagged proteins.

Antineutrophil cytoplasmic antibodies to proteinase 3 in Wegener's granulomatosis: epitope analysis using synthetic peptides

BACKGROUND

Antineutrophil cytoplasmic antibodies (ANCA) to proteinase 3 (PR3) are strongly associated with Wegener's granulomatosis (WG) and are thought to be involved in its pathogenesis. Levels of PR3-ANCA do not always correspond to clinical disease activity nor to functional effects of these antibodies in vitro, suggesting differences in epitope specificity. To define relevant epitopes for PR3-ANCA, sera of WG patients were analyzed on their reactivity to linear peptides of PR3.

METHODS

Fifty linear peptides of 15 amino acids in length with an overlap of 10 aa spanning the entire PR3 sequence were synthesized. Sera of 27 WG patients with active disease and 27 age- and sex-matched healthy controls, eight anti-PR3 monoclonal antibodies (mAbs), and a rabbit anti-PR3 serum were tested by enzyme-linked immunosorbent assay for reactivity to PR3 peptides.

RESULTS

Rabbit anti-PR3 serum recognized three distinct peptide areas, whereas none of the anti-PR3 mAbs bound PR3 peptides. Sera of both WG patients and healthy controls recognized a restricted number of PR3 peptides. Four of these peptide areas were recognized significantly more strongly by WG sera than by control sera. Sera drawn at the initial presentation of WG mainly recognized these peptides. Two of the recognized peptide areas were located near the active center of PR3.

CONCLUSION

A restricted number of epitope areas of PR3 are recognized both by WG patient sera and control sera. Four peptide areas were bound stronger by sera of WG patients at initial presentation than by healthy controls.

In vitro T lymphocyte responses to proteinase 3 (PR3) and linear peptides of PR3 in patients with Wegener's granulomatosis (WG)

T cell-mediated immunity is thought to play an important role in the pathogenesis of WG. In previous studies a minority of WG patients as well as some healthy controls showed in vitro proliferation of their peripheral blood mononuclear cells (PBMC) to PR3, the main autoantigen in WG. The relevant peptides responsible for this in vitro proliferation have not been identified. In order to define immunogenic peptides, PBMC of 13 WG patients in remission and 10 healthy controls were tested for proliferation to linear peptides of PR3 and to whole PR3. Fifty overlapping peptides spanning the whole PR3 sequence were synthesized. Peptides were tested in pools of five peptides and as single peptide. PBMC of two WG patients and one healthy control proliferated to whole PR3 and to peptide pools. In addition, 10 WG patients and eight healthy controls that did not proliferate to whole PR3 did proliferate to pools of PR3 peptides. Although more WG patients tended to react to particular peptide pools, no significant difference was seen between lymphocyte proliferation to PR3 peptides of WG patients and that of healthy controls. The pools of peptides recognized were mainly located at the N- and C-terminus of PR3. No correlation was observed between HLA type and proliferation on particular peptide pools. No proliferation of PBMC was observed to single peptides. In conclusion, T cells of WG patients proliferate in vitro more frequently to PR3 peptides than to the whole PR3 protein. Peptides derived from the signal sequence, the propeptide or peptides located at the C-terminus of PR3 induce highest levels of proliferation. No specific PR3 sequence could be identified that was preferentially recognized by PBMC of WG patients compared with controls.

Reactive oxygen and nitrogen intermediates in the relationship between mammalian hosts and microbial pathogens

This review summarizes recent evidence from knock-out mice on the role of reactive oxygen intermediates and reactive nitrogen intermediates (RNI) in mammalian immunity. Reflections on redundancy in immunity help explain an apparent paradox: the phagocyte oxidase and inducible nitric oxide synthase are each nonredundant, and yet also mutually redundant, in host defense. In combination, the contribution of these two enzymes appears to be greater than previously appreciated. The remainder of this review focuses on a relatively new field, the basis of microbial resistance to RNI. Experimental tuberculosis provides an important example of an extended, dynamic balance between host and pathogen in which RNI play a major role. In diseases such as tuberculosis, a molecular understanding of host-pathogen interactions requires characterization of the defenses used by microbes against RNI, analogous to our understanding of defenses against reactive oxygen intermediates. Genetic and biochemical approaches have identified candidates for RNI-resistance genes in Mycobacterium tuberculosis and other pathogens.