Bioactive proteinase 3 on the cell surface of human neutrophils: quantification, catalytic activity, and susceptibility to inhibition

Neutrophil proteinase 3 acts on protease-activated receptor-2 to enhance vascular endothelial cell barrier function

OBJECTIVE

The principle role of the vascular endothelium is to present a semi-impermeable barrier to soluble factors and circulating cells, while still permitting the passage of leukocytes from the bloodstream into the tissue. The process of diapedesis involves the selective disruption of endothelial cell junctions, which could compromise vascular integrity. It is therefore somewhat surprising that neutrophil transmigration does not significantly impair endothelial barrier function. We examined whether neutrophils might secrete factors that promote vascular integrity during the latter stages of neutrophil transmigration, in particular, the role of neutrophil serine proteinase 3 (PR3).

METHODS AND RESULTS

Endothelial cells were treated with PR3 either in its soluble form or in a complex form with cell surface NB1. We observed that PR3 mediated the enhancement of endothelial cell junctional integrity and that this required its proteolytic activity, as well as endothelial cell expression of the protease-activated receptor-2. Importantly, PR3 suppressed the vascular permeability changes and disruption of junctional proteins induced by the action of protease-activated receptor-1 agonists.

CONCLUSIONS

These findings establish the potential for neutrophil-derived PR3 to play a role in reestablishing vascular integrity after leukocyte transmigration and in protecting endothelial cells from protease-activated receptor-1-induced permeability changes that occur during thrombotic and inflammatory events.

Characterization of chicken spleen transcriptome after infection with Salmonella enterica serovar Enteritidis

In this study we were interested in identification of new markers of chicken response to Salmonella Enteritidis infection. To reach this aim, gene expression in the spleens of naive chickens and those intravenously infected with S. Enteritidis with or without previous oral vaccination was determined by 454 pyrosequencing of splenic mRNA/cDNA. Forty genes with increased expression at the level of transcription were identified. The most inducible genes encoded avidin (AVD), extracellular fatty acid binding protein (EXFABP), immune responsive gene 1 (IRG1), chemokine ah221 (AH221), trappin-6-like protein (TRAP6) and serum amyloid A (SAA). Using cDNA from sorted splenic B-lymphocytes, macrophages, CD4, CD8 and γδ T-lymphocytes, we found that the above mentioned genes were preferentially expressed in macrophages. AVD, EXFABP, IRG1, AH221, TRAP6 and SAA were induced also in the cecum of chickens orally infected with S. Enteritidis on day 1 of life or day 42 of life. Unusual results were obtained for the immunoglobulin encoding transcripts. Prior to the infection, transcripts coding for the constant parts of IgM, IgY, IgA and Ig light chain were detected in B-lymphocytes. However, after the infection, immunoglobulin encoding transcripts were expressed also by T-lymphocytes and macrophages. Expression of AVD, EXFABP, IRG1, AH221, TRAP6, SAA and all immunoglobulin genes can be therefore used for the characterization of the course of S. Enteritidis infection in chickens.

Influence of DNA on the activities and inhibition of neutrophil serine proteases in cystic fibrosis sputum

Uncontrolled proteolysis by neutrophil serine proteases (NSPs) in lung secretions is a hallmark of cystic fibrosis (CF). We have shown that the active neutrophil elastase, protease 3, and cathepsin G in CF sputum resist inhibition in part by exogenous protease inhibitors. This resistance may be due to their binding to neutrophil extracellular traps (NETs) secreted by the activated neutrophils in CF sputum and to genomic DNA released from senescent and dead neutrophils. Treating CF sputum with DNase dramatically increases its elastase activity, which can then be stoichiometrically inhibited by exogenous elastase inhibitors. However, DNase treatment does not increase the activities of protease 3 and cathepsin G, indicating their different distribution and/or binding in CF sputum. Purified blood neutrophils secrete NETs when stimulated by the opportunistic CF bacteria Pseudomonas aeruginosa and Staphylococcus aureus. The activities of the three proteases were unchanged in these conditions, but subsequent DNase treatment produced a dramatic increase in all three proteolytic activities. Neutrophils activated with a calcium ionophore did not secrete NETs but released huge amounts of active proteases whose activities were not modified by DNase. We conclude that NETs are reservoirs of active proteases that protect them from inhibition and maintain them in a rapidly mobilizable status. Combining the effects of protease inhibitors with that of DNA-degrading agents could counter the deleterious proteolytic effects of NSPs in CF lung secretions.

Neutrophil serine proteases promote IL-1β generation and injury in necrotizing crescentic glomerulonephritis

The pathogenesis of anti-neutrophil cytoplasmic antibody (ANCA)-associated necrotizing crescentic GN (NCGN) is incompletely understood. Dipeptidyl peptidase I (DPPI) is a cysteine protease required for the activation of neutrophil serine proteases (NSPs) cathepsin G, neutrophil elastase, and proteinase 3, which are enzymes that modulate inflammation. We used a mouse model of anti-myeloperoxidase (MPO) antibody-induced NCGN to determine whether active NSPs contribute to its pathogenesis. MPO-deficient animals immunized with murine MPO, irradiated, and transplanted with wild-type bone marrow developed NCGN. In contrast, transplantation with bone marrow that lacked DPPI or lacked both neutrophil elastase and proteinase 3 protected mice from NCGN induced by anti-MPO antibody. The kidneys of mice reconstituted with DPPI-deficient bone marrow generated significantly less IL-1β than did those of mice reconstituted with wild-type bone marrow; similarly, in vitro, DPPI-deficient monocytes produced significantly less IL-1β in response to anti-MPO antibody than did wild-type monocytes. This reduction in IL-1β was NSP dependent; exogenous addition of PR3 restored IL-β production in DPPI-deficient monocytes. Last, the IL-1 receptor antagonist anakinra protected animals against anti-MPO antibody-induced NCGN (16.7%±6.0% versus 2.4%±1.7% crescents), suggesting that IL-1β is a critical inflammatory mediator in this model. These data suggest that the development of anti-MPO antibody-induced NCGN requires NSP-dependent IL-1β generation and that these processes may provide therapeutic targets for ANCA-mediated diseases in humans.

Measurement of neutrophil elastase, proteinase 3, and cathepsin G activities using intramolecularly quenched fluorogenic substrates

Neutrophil elastase, proteinase 3, and cathepsin G are three hematopoietic serine proteases, large quantities of which are stored in neutrophil cytoplasmic azurophilic granules. They act in combination with reactive oxygen species to degrade engulfed microorganisms inside phagolysosomes. Active forms of these proteases are also externalized during neutrophil activation at inflammatory sites, thus helping to regulate inflammatory and immune responses. A fraction of secreted neutrophil serine proteases (NSPs) remains bound to the external plasma membrane, where they remain enzymatically active. This protocol describes the spectrofluorometric measurement of NSP activities using sensitive ortho-aminobenzoyl-peptidyl-N-(2,4-dinitrophenyl) ethylenediamine fluorescence resonance energy transfer (FRET) substrates that fully discriminate between the three human NSPs. These are used to measure subnanomolar concentrations of free or membrane-bound NSPs in low-binding microplates and to quantify the activities of individual proteases in biological fluids. We describe the synthesis of FRET substrate, neutrophil purification, and kinetic experiments on activated neutrophils. The protocol for measuring NSP activity on the surface of activated neutrophils can be adapted to measure NSP activities in whole biological fluids. Such data clarify the contributions of individual NSPs to the development of inflammatory diseases. Ultimately, these proteases may be shown to be targets for therapeutic inhibitors.

THEORY OF MECHANICAL IMMUNOLOGY

Numerous autoimmune illnesses are not only caused by defects of the immune system but may also be caused by defects in anatomical barriers. Morphologically, most of these barriers consist of basal membranes combined with epithelial cells or, more precisely, their cell membranes. In many organs, these barriers are associated with specialized, phagocytizing cells (e.g. histiocytes, macrophages, microglial cells A and B cells in joints). A collapse of these anatomical barriers caused either by mechanical effects (invasion by micro-organisms) or destructive tumor growth, leads to contact between macrophages and the CD4 lymphocytes, with protein structures of the cell interior. In principle, many intracellular structures should be able to function, on this basis, as potential antigens via MHC II. Contact between intracellular structures and the immune system first leads to a restricted local immune reaction and then to local autoantibody production. In order that a systemic immune reaction can take place, the contact between macrophages, CD4 cells and intracellular structures must occur over a long period and with high intensity. As a desirable, remote target, new clinical therapeutic strategies can be developed from this theory, for example, for patients with cell damage. Examples of such illnesses are, amongst others, cardiac infarcts and strokes as well as accident traumas. An immunosuppressive therapy should reduce the immune reply in all the patients mentioned and thus reduce the volume of the cell damage, giving the patient an advantage.

The role of proteases, endoplasmic reticulum stress and SERPINA1 heterozygosity in lung disease and α-1 anti-trypsin deficiency

The serine proteinase inhibitor α-1 anti-trypsin (AAT) provides an antiprotease protective screen throughout the body. Mutations in the AAT gene (SERPINA1) that lead to deficiency in AAT are associated with chronic obstructive pulmonary diseases. The Z mutation encodes a misfolded variant of AAT that is not secreted effectively and accumulates intracellularly in the endoplasmic reticulum of hepatocytes and other AAT-producing cells. Until recently, it was thought that loss of antiprotease function was the major cause of ZAAT-related lung disease. However, the contribution of gain-of-function effects is now being recognized. Here we describe how both loss- and gain-of-function effects can contribute to ZAAT-related lung disease. In addition, we explore how SERPINA1 heterozygosity could contribute to smoking-induced chronic obstructive pulmonary diseases and consider the consequences.

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.

Loss of expression of neutrophil proteinase-3: a factor contributing to thrombotic risk in paroxysmal nocturnal hemoglobinuria

BACKGROUND

A deficiency of specific glycosylphosphatidyl inositol-anchored proteins in paroxysmal nocturnal hemoglobinuria may be responsible for most of the clinical features of this disease, but some functional consequences may be indirect. For example, the absence of certain glycosylphosphatidyl inositol-anchored proteins in paroxysmal nocturnal hemoglobinuria cells may influence expression of other membrane proteins. Membrane-bound proteinase 3 co-localizes with glycosylphosphatidyl inositol-linked neutrophil antigen 2a, which is absent in patients with paroxysmal nocturnal hemoglobinuria.

DESIGN AND METHODS

We compared expression of proteinase 3 and neutrophil antigen 2a by flow cytometry and western blotting in normal and paroxysmal nocturnal hemoglobinuria cells and measured cytoplasmic and soluble levels of proteinase 3 by enzyme-linked immunosorbent assays in controls and patients with paroxysmal nocturnal hemoglobinuria. Finally, we studied the effects of proteinase 3 on platelet activation using an in vitro aggregometry assay and flow cytometry.

RESULTS

We showed that membrane-bound proteinase 3 is deficient in patients' cells, but invariantly present in the cytoplasm regardless of disease phenotype. When we isolated lipid rafts from patients, both molecules were detected only in the rafts from normal cells, but not diseased ones. Membrane-bound proteinase 3 was associated with a decrease in plasma proteinase 3 levels, clone size and history of thrombosis. In addition, we found that treating platelets ex vivo with proteinase 3, but not other agonists, decreased the exposure of an epitope on protease activated receptor-1 needed for thrombin activation. Conversely, treatment of whole blood with serine protease inhibitor enhanced expression of this epitope on protease activated receptor-1 located C-terminal to the thrombin cleavage site on platelets.

CONCLUSIONS

We demonstrated that deficiency of glycosylphosphatidyl inositol-anchored proteins in paroxysmal nocturnal hemoglobinuria results in decreased membrane-bound and soluble proteinase 3 levels. This phenomenon may constitute another mechanism contributing to a prothrombotic propensity in patients with paroxysmal nocturnal hemoglobinuria.

Membrane-bound proteinase 3 and PAR2 mediate phagocytosis of non-opsonized bacteria in human neutrophils

The molecular mechanisms underlying the non-opsonic phagocytosis of bacteria by neutrophils are poorly understood. We previously reported the efficient uptake of Streptococcus sanguinis by human neutrophils in the absence of opsonins. To characterize the phagocytosis receptor, protein lysates from neutrophils and HL-60 cells were subjected to affinity chromatography using epoxy beads coated with S. sanguinis. Denaturing electrophoresis of the eluted proteins and subsequent mass spectrometry revealed that one of the proteins eluted from neutrophils was proteinase 3 (PR3). Enzymatic cleavage of the glycosylphosphatidylinositol linker of NB1, a co-receptor for membrane-bound PR3 (mPR3), significantly reduced the phagocytosis of S. sanguinis. In addition, the neutralization of mPR3 with antibody reduced both binding and phagocytosis of S. sanguinis. Treatment of neutrophils with a serine proteinase inhibitor indicated that protease activity is required for phagocytosis. Thus, we studied whether protease-activated receptor 2 (PAR2) is involved in signal transmission from mPR3 during this process. Indeed, neutralizing antibodies against PAR2 inhibited phagocytosis and S. sanguinis-induced calcium mobilization desensitized PAR2. Furthermore, the phagocytosis of S. sanguinis and the concomitant activation of Rho family GTPases were inhibited by the intracellular calcium chelator, BAPTA-AM. Collectively, mPR3 acts as a non-opsonic phagocytosis receptor for bacteria probably by activating PAR2 in 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.

Behavioral and structural differences in migrating peripheral neutrophils from patients with chronic obstructive pulmonary disease

RATIONALE

There are increased neutrophils in the lungs of patients with chronic obstructive pulmonary disease (COPD), but it is unclear if this is due to increased inflammatory signal or related to the inherent behavior of the neutrophils. This is critical, because inaccurate or excessive neutrophil chemotaxis could drive pathological accumulation and tissue damage.

OBJECTIVES

To assess migratory dynamics of neutrophils isolated from patients with COPD compared with healthy smoking and nonsmoking control subjects and patients with α(1)-antitryspin deficiency.

METHODS

Migratory dynamics and structure were assessed in circulating neutrophils, using phase and differential interference contrast microscopy and time-lapse photography. The effect of COPD severity was studied. Surface expression of receptors was measured using flow cytometry. The in vitro effects of a phosphoinositide 3-kinase inhibitor (LY294002) were studied.

MEASUREMENTS AND MAIN RESULTS

COPD neutrophils moved with greater speed than cells from either control group but with reduced migratory accuracy, in the presence of IL-8, growth-related oncogene α, formyl-methionyl-leucyl-phenylalanine, and sputum. This was present across all stages of COPD. Structurally, COPD neutrophils formed fewer pseudopods during migration. There were no differences in surface expression of the receptors CXCR1, CXCR2, or FPR1. LY294002 reduced COPD neutrophil migratory speed while increasing chemotactic accuracy, returning values to normal. The inhibitor did not have these effects in healthy control subjects or patients with a similar degree of lung disease.

CONCLUSIONS

COPD neutrophils are intrinsically different than cells from other studied populations in their chemotactic behavior and migratory structure. Differences are not due to surface expression of chemoattractant receptors but instead appear to be due to differences in cell signaling.

Tailor-made inflammation: how neutrophil serine proteases modulate the inflammatory response

Neutrophil granulocytes are important mediators of innate immunity, but also participate in the pathogenesis of (auto)inflammatory diseases. Neutrophils express a specific set of proteolytic enzymes, the neutrophil serine proteases (NSPs), which are stored in cytoplasmic granules and can be secreted into the extra- and pericellular space upon cellular activation. These NSPs, namely cathepsin G (CG), neutrophil elastase (NE), and proteinase 3 (PR3), have early been implicated in bacterial defense. However, NSPs also regulate the inflammatory response by specifically altering the function of cytokines and chemokines. For instance, PR3 and NE both inactivate the anti-inflammatory mediator progranulin, which may play a role in chronic inflammation. Here, we provide a concise update on NSPs as modulators of inflammation and discuss the biological and pathological significance of this novel function of NSPs. Mounting evidence support an important proinflammatory function for PR3, which may have been underestimated in the past.

How does proteinase 3 interact with lipid bilayers?

Proteinase 3 (PR3) is a serine protease of the neutrophils whose membrane expression is relevant in a number of inflammatory pathologies. It has been shown to strongly interact with reconstituted bilayers containing dimyristoylphosphatidylcholine (DMPC), dimyristoylphosphatidylglycerol (DMPG) or mixtures of both phospholipids. Here we present the results of molecular dynamics simulations of PR3 anchored at three different phospholipid bilayers: DMPC, DMPG and an equimolar mixture of DMPC/DMPG. We present for the first time a detailed model of membrane-bound PR3. A thorough inventory of the interaction between the lipids and the enzyme reveals three types of interactions contributing to the anchorage of PR3. Basic residues (R177, R186A, R186B, K187 and R222) interact via hydrogen bonds with the lipid headgroups to stabilize PR3 at the interfacial membrane region. Hydrophobic amino acids (V163, F165, F166, I217, L223, and F224) insert into the hydrophobic core below the carbonyl groups of the bilayers and six aromatic amino acids (F165, F192, F215, W218, F224, and F227) contribute electrostatic interaction via cation-pi interactions with the choline groups of DMPC. PR3 presents all the characteristics of a peripheral membrane protein with an ability to bind negative phospholipids. Although the catalytic triad remains unperturbed by the presence of the membrane, the ligand binding sites are located in close proximity to the membrane and amino acids K99 and I217 interact significantly with the lipids. We expect the binding of long ligands to be modified by the presence of the lipids.

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.

Elevated neutrophil membrane expression of proteinase 3 is dependent upon CD177 expression

Proteinase 3 (PR3) is a major autoantigen in anti-neutrophil cytoplasmic antibodies (ANCA)-associated systemic vasculitis (AASV), and the proportion of neutrophils expressing PR3 on their membrane (mPR3+) is increased in AASV. We have shown recently that mPR3 and CD177 are expressed on the same cells in healthy individuals. In this study we try to elucidate mechanisms behind the increased mPR3 expression in AASV and its relationship to CD177. All neutrophils in all individuals were either double-positive or double-negative for mPR3 and CD177. The proportion of double-positive neutrophils was increased significantly in AASV and systemic lupus erythematosus patients. The proportion of mPR3+/CD177+ cells was not correlated to general inflammation, renal function, age, sex, drug treatment and levels of circulating PR3. AASV patients had normal levels of granulocyte colony-stimulating factor and granulocyte-macrophage colony-stimulating factor. Pro-PR3 was found to constitute 10% of circulating PR3 but none of the mPR3. We found increased mRNA levels of both PR3 and CD177 in AASV, but they did not correlate with the proportion of double-positive cells. In cells sorted based on membrane expression, CD177-mRNA was several-fold higher in mPR3+ cells. When exogenous PR3 was added to CD177-transfected U937 cells, only CD177+ cells bound PR3 to their membrane. In conclusion, the increased membrane expression of PR3 found in AASV is not linked directly to circulating PR3 or PR3 gene transcription, but is dependent upon CD177 expression and correlated with the transcription of the CD177 gene.

Matrix metalloproteinase-8 inactivates macrophage inflammatory protein-1 alpha to reduce acute lung inflammation and injury in mice

To determine the role of matrix metalloproteinase-8 (MMP-8) in acute lung injury (ALI), we delivered LPS or bleomycin by the intratracheal route to MMP-8(-/-) mice versus wild-type (WT) mice or subjected the mice to hyperoxia (95% O(2)) and measured lung inflammation and injury at intervals. MMP-8(-/-) mice with ALI had greater increases in lung polymorphonuclear neutrophils (PMNs) and macrophage counts, measures of alveolar capillary barrier injury, lung elastance, and mortality than WT mice with ALI. Bronchoalveolar lavage fluid (BALF) from LPS-treated MMP-8(-/-) mice had more MIP-1alpha than BALF from LPS-treated WT mice, but similar levels of other pro- and anti-inflammatory mediators. MIP-1alpha(-/-) mice with ALI had less acute lung inflammation and injury than WT mice with ALI, confirming that MIP-1alpha promotes acute lung inflammation and injury in mice. Genetically deleting MIP-1alpha in MMP-8(-/-) mice reduced the increased lung inflammation and injury and mortality in MMP-8(-/-) mice with ALI. Soluble MMP-8 cleaved and inactivated MIP-1alpha in vitro, but membrane-bound MMP-8 on activated PMNs had greater MIP-1alpha-degrading activity than soluble MMP-8. High levels of membrane-bound MMP-8 were detected on lung PMNs from LPS-treated WT mice, but soluble, active MMP-8 was not detected in BALF samples. Thus, MMP-8 has novel roles in restraining lung inflammation and in limiting alveolar capillary barrier injury during ALI in mice by inactivating MIP-1alpha. In addition, membrane-bound MMP-8 on activated lung PMNs is likely to be the key bioactive form of the enzyme that limits lung inflammation and alveolar capillary barrier injury during ALI.

Anti-PR3 immune responses induce segmental and necrotizing glomerulonephritis

Wegener's granulomatosis (WG) is a life-threatening autoimmune vasculitis that affects lungs, kidneys and other organs. A hallmark of WG is the presence of classic anti-neutrophil cytoplasmic antibodies (c-ANCA) against self-proteinase 3 (PR3). Little is known about the role of these antibodies and PR3-specific immune responses in disease development. In this study, we demonstrate that PR3-specific autoimmune responses are pathogenic in non-obese diabetic (NOD) mice with an impaired regulatory arm of the immune response. Immunization of autoimmunity prone NOD mice with rmPR3 (recombinant mouse PR3) in complete Freund's adjuvant (CFA) resulted in high levels of c-ANCA, without detectable disease development. However, when splenocytes from these immunized mice were transferred into immunodeficient NOD-severe combined immunodeficiency (SCID) mice, the recipient mice developed vasculitis and severe segmental and necrotizing glomerulonephritis. No disease developed in NOD-SCID mice that received splenocytes from the CFA-alone-immunized donors (controls), indicating that disease development depends upon PR3-specific immune responses. In contrast to the pathology observed in NOD-SCID mice, no disease was observed when splenocytes from rmPR3-immunized C57BL/6 mice were transferred into immunodeficient C57BL/6-RAG-1(-/-) mice, suggesting that complex and probably multi-genetic factors play a role in the regulation of disease development.

Inflammatory arthritis in caspase 1 gene-deficient mice: contribution of proteinase 3 to caspase 1-independent production of bioactive interleukin-1beta

OBJECTIVE

Caspase 1, a known cysteine protease, is a critical component of the inflammasome. Both caspase 1 and neutrophil serine proteases such as proteinase 3 (PR3) can process pro-interleukin-1beta (proIL-1beta), a crucial cytokine linked to the pathogenesis of rheumatoid arthritis. This study was undertaken to establish the relative importance of caspase 1 and serine proteases in mouse models of acute and chronic inflammatory arthritis.

METHODS

Acute and chronic arthritis were induced in caspase 1-/- mice, and the lack of caspase 1 was investigated for its effects on joint swelling, cartilage metabolism, and histopathologic features. In addition, caspase 1 activity was inhibited in mice lacking active cysteine proteases, and the effects of dual blockade of caspase 1 and serine proteases on arthritis severity and histopathologic features were evaluated.

RESULTS

Surprisingly, caspase 1-/- mice, in a model of acute (neutrophil-dominated) arthritis, developed joint swelling to an extent similar to that in wild-type control mice. Joint fluid concentrations of bioactive IL-1beta were comparable in caspase 1-/- mice and controls. In contrast, induction of chronic arthritis (characterized by minimal numbers of neutrophils) in caspase 1-/- mice led to reduced joint inflammation and less cartilage damage, implying a caspase 1-dependent role in this process. In mice lacking neutrophil serine PR3, inhibition of caspase 1 activity resulted in decreased bioactive IL-1beta concentrations in the synovial tissue and less suppression of chondrocyte anabolic function. In addition, dual blockade of both PR3 and caspase 1 led to protection against cartilage and bone destruction.

CONCLUSION

Caspase 1 deficiency does not affect neutrophil-dominated joint inflammation, whereas in chronic arthritis, the lack of caspase 1 results in reduced joint inflammation and cartilage destruction. These findings suggest that inhibitors of caspase 1 are not able to interfere with the whole spectrum of IL-1beta production, and therefore such inhibitors may be of therapeutic value only in inflammatory conditions in which limited numbers of neutrophils are present.

Caspase 1-independent activation of interleukin-1beta in neutrophil-predominant inflammation

OBJECTIVE

Interleukin-1beta (IL-1beta) is a key cytokine linked to the pathogenesis of acute arthritis. Caspase 1, neutrophil elastase, and chymase all process proIL-1beta to its biologically active form. This study was undertaken to examine the potential contributions of each of these proteases in experimental models of inflammatory arthritis.

METHODS

Caspase 1-deficient (Casp1-/-) and wild-type (WT) mice were tested for their response to arthritogenic K/BxN serum transfer for induction of arthritis or injection of monosodium urate monohydrate (MSU) crystals for induction of peritonitis. All mice were prophylactically treated with inhibitors of neutrophil elastase or chymase. Arthritic paws were tested for the presence of IL-1beta protein by enzyme-linked immunosorbent assay and Western blotting. Neutrophils and mast cells from WT and mutant mice were tested for their ability to secrete IL-1beta after in vitro stimulation, in the presence of protease inhibitors.

RESULTS

Casp1-/- and WT mice developed paw swelling to the same extent in the K/BxN serum transfer-induced arthritis model. MSU crystal injection into Casp1-/- mice also resulted in neutrophil influx and production of measurable peritoneal IL-1beta protein. Both of these responses were attenuated with neutrophil elastase inhibitors. K/BxN serum transfer-induced arthritis was also reduced by treatment with a chymase inhibitor. Casp1-/- neutrophils and mast cells, when exposed to MSU crystals, secreted similar amounts of IL-1beta protein upon in vitro stimulation with lipopolysaccharide, albeit at lower levels than that secreted by WT cells. Elastase and chymase inhibitors reduced the amount of IL-1beta released by these cells.

CONCLUSION

The production of IL-1beta by neutrophils and mast cells is not exclusively dependent on caspase 1, and other proteases can compensate for the loss of caspase 1 in vivo. These pathways might therefore compromise the caspase 1-targeted therapies in neutrophil-predominant arthritis.

Gingival crevicular fluid levels of cathelicidin LL-37 and interleukin-18 in patients with chronic periodontitis

BACKGROUND

Cathelicidin LL-37, an antimicrobial peptide, is part of the host innate immune response in the oral cavity. Interleukin (IL)-18, a proinflammatory cytokine, could play a role in the progression of the inflammatory response. The aim of the present study was to determine the levels of cathelicidin LL-37 and IL-18 in the gingival crevicular fluid (GCF) of patients with gingivitis and chronic periodontitis.

METHODS

Fifty-nine subjects were included in the present study. Probing depth (PD), clinical attachment level (CAL), plaque index (PI), bleeding on probing, and papilla bleeding index (PBI) were assessed in patients with chronic periodontitis or gingivitis and in healthy controls. GCF levels of cathelicidin LL-37 and IL-18 were analyzed by enzyme-linked immunosorbent assay.

RESULTS

GCF levels of cathelicidin LL-37 were significantly elevated in patients with chronic periodontitis compared to the other groups (P <0.05). No significant difference was found in the total amount of GCF IL-18 among the study groups (P >0.05). Spearman correlation analysis revealed a positive relationship between levels of GCF cathelicidin LL-37 and PD, CAL, PI, and PBI at the sampled sites (P <0.01), whereas no correlation was found between the total amount of GCF IL-18 and clinical periodontal parameters at the sampled sites (P >0.05).

CONCLUSION

Elevated levels of GCF cathelicidin LL-37 in chronic periodontitis suggest that it may play a role in the host innate immune response during periodontal inflammation.

Protease inhibitors derived from elafin and SLPI and engineered to have enhanced specificity towards neutrophil serine proteases

The secretory leukocyte protease inhibitor (SLPI), elafin, and its biologically active precursor trappin-2 are endogeneous low-molecular weight inhibitors of the chelonianin family that control the enzymatic activity of neutrophil serine proteases (NSPs) like elastase, proteinase 3, and cathepsin G. These inhibitors may be of therapeutic value, since unregulated NSP activities are linked to inflammatory lung diseases. However SLPI inhibits elastase and cathepsin G but not proteinase 3, while elafin targets elastase and proteinase 3 but not cathepsin G. We have used two strategies to design polyvalent inhibitors of NSPs that target all three NSPs and may be used in the aerosol-based treatment of inflammatory lung diseases. First, we fused the elafin domain with the second inhibitory domain of SLPI to produce recombinant chimeras that had the inhibitory properties of both parent molecules. Second, we generated the trappin-2 variant, trappin-2 A62L, in which the P1 residue Ala is replaced by Leu, as in the corresponding position in SLPI domain 2. The chimera inhibitors and trappin-2 A62L are tight-binding inhibitors of all three NSPs with subnanomolar K(i)s, similar to those of the parent molecules for their respective target proteases. We have also shown that these molecules inhibit the neutrophil membrane-bound forms of all three NSPs. The trappin-2 A62L and elafin-SLPI chimeras, like wild-type elafin and trappin-2, can be covalently cross-linked to fibronectin or elastin by a tissue transglutaminase, while retaining their polypotent inhibition of NSPs. Therefore, the inhibitors described herein have the appropriate properties to be further evaluated as therapeutic anti-inflammatory agents.

Direct and alternative antimicrobial mechanisms of neutrophil-derived granule proteins

Polymorphonuclear leukocytes (PMN) contribute to bacterial clearance by uptake and intracellular killing of microbes. However, antimicrobial polypeptides are released extracellularly where they are enweaved in a chromatin web that traps and eliminates bacteria. In addition, PMN-derived antimicrobial polypeptides direct monocytes and macrophages to the site of infection and activate their antimicrobial armor. Increased expression of Fcgamma receptors as well as opsonization of bacteria by PMN granule proteins support bacterial uptake by macrophages. PMN granule proteins also increase intracellular reactive oxygen species formation in macrophages. Finally, apoptotic PMN transfer parts of their antimicrobial peptides to macrophages, hence increasing killing of intracellular bacteria. Understanding mechanisms by which PMN granule proteins stimulate antimicrobial mechanisms in macrophages may open novel strategies in fighting bacterial infections.

Human neutrophils kill Streptococcus pneumoniae via serine proteases

Neutrophils, or polymorphonuclear leukocytes, comprise a crucial component of innate immunity, controlling bacterial and fungal infection through a combination of both oxidative and nonoxidative mechanisms. Indeed, neutrophils are believed to play an important role in controlling infection caused by the major human pathogen Streptococcus pneumoniae. However, the method by which neutrophils kill the pneumococcus as well as other Gram-positive bacteria, is not fully understood. We investigated human neutrophil killing of the pneumococcus in a complement-dependent opsonophagocytic assay. In contrast to other Gram-positive organisms, inhibition of the NADPH oxidase did not affect killing of S. pneumoniae. Supernatant from degranulated neutrophils killed the pneumococcus, suggesting a role for granular products. When neutrophil granule proteases were inhibited with either a protease mixture, or specific serine protease inhibitors 4-(2-Aminoethyl)benzenesulfonylfluoride and diisopropylfluorophosphate, killing by neutrophils was inhibited in a manner that correlated with increased intracellular survival. All three compounds inhibited intracellular activity of the three major neutrophil serine proteases: elastase, cathepsin G, and proteinase 3. Additionally, purified elastase and cathepsin G were sufficient to kill S. pneumoniae in a serine protease dependent-manner in in vitro assays. Inhibition studies using specific inhibitors of these serine proteases suggested that while each serine protease is sufficient to kill the pneumococcus, none is essential. Our findings show that Gram-positive pathogens are killed by human neutrophils via different mechanisms involving serine proteases.

The Influence of Different Cultivating Conditions on Polymorphonuclear Leukocyte Apoptotic Process In Vitro, II: Ultrastructural Characteristics of PMN Populations Incubated with Proteinase 3 Anti-neutrophil Autoantibodies

The present study shows the effects of proteinase 3 anti-neutrophil cytoplasmic autoantibodies (PR3 ANCA) on polymorphonuclear leukocytes (PMN) apoptotic processes in vitro. The results are part of a generalized morphological analysis of 3 identical experiments on the influence of different cultivating conditions on the apoptotic processes. As controls, the authors use the results on spontaneous PMN apoptosis (Guejes L, Zurgil N, Deutsch M, Gilburd B, Shoenfeld Y. Ultrastruct Pathol. 2003;27: 23-32) and PMN populations incubated with normal human IgG. Interaction of PR3 ANCA with the target antigen proteinase 3 (PR3) is one of the crucial pathogenic factors in Wegener granulomatosis (systemic autoimmune vasculitis). Following 40min and 12h incubation, PMN populations were evaluated by light microscopy, transmission electron microscopy, and immunogold electron microscopy. Twelve-hour cultures, either control or incubated with PR3 ANCA, contained different cell forms ranging from normal cells to cells at the final stages of apoptosis. Neutrophils at the state of complete manifestation of apoptotic phenotype were analyzed and compared. Three morphologically distinct apoptotic cell lines were characteristic for all PMN populations studied, regardless of cultivating conditions. As in spontaneous apoptosis, these cell lines are code-named "first," "second," and "third." The present study has shown, firstly, that in the presence of PR3 ANCA, all 3 apoptotic lines were modified or altered. Secondly, the modifications or alterations of apoptotic cell lines effected by PR3 ANCA are specific for each cell line: the "first" line is characterized by intensification and modification of activation; the "second" by vacuolized cell forms; and the "third" by pronounced lytic alterations of the nuclei, while the cytoplasm is fully identical to that of control cell lines.

Catalytic activity and inhibition of wegener antigen proteinase 3 on the cell surface of human polymorphonuclear neutrophils

Proteinase 3 (Pr3), the main target of anti-neutrophil cytoplasmic antibodies, is a neutrophil serine protease that may be constitutively expressed at the surface of quiescent circulating neutrophils. This raises the question of the simultaneous presence in the circulation of constitutive membrane-bound Pr3 (mPr3) and its plasma inhibitor alpha1-protease inhibitor (alpha1-Pi). We have looked at the fate of constitutive mPr3 at the surface of circulating blood neutrophils and of induced mPr3 on triggered neutrophils. We found significant Pr3 activity at the surface of activated neutrophils but not at the surface of quiescent neutrophils whatever the constitutive expression. This suggests that constitutive mPr3 is enzymatically inactive or its active site is not accessible to the substrate. Supporting this conclusion, we have not been able to demonstrate any interaction between constitutive mPr3 and alpha1-Pi, whereas induced mPr3 is cleared from the cell surface when activated cells are incubated with this inhibitor. But, unlike membrane-bound elastase that is also cleared from the surface of activated cells, mPr3 remained bound to the membrane when inhibited by elafin or by a low molecular weight chloromethyl ketone inhibitor, which shows that it binds more tightly to the neutrophil membrane. mPr3 may thus be present at the surface of circulating neutrophils in an environment replete with alpha1-Pi. The permanent presence of inactive Pr3 at the surface of quiescent neutrophils may explain why Pr3 is a major target of anti-neutrophil cytoplasmic antibodies, whose binding activates neutrophils and triggers inflammation, as in Wegener granulomatosis.

Proteinase 3 and neutrophil elastase enhance inflammation in mice by inactivating antiinflammatory progranulin

Neutrophil granulocytes form the body's first line of antibacterial defense, but they also contribute to tissue injury and noninfectious, chronic inflammation. Proteinase 3 (PR3) and neutrophil elastase (NE) are 2 abundant neutrophil serine proteases implicated in antimicrobial defense with overlapping and potentially redundant substrate specificity. Here, we unraveled a cooperative role for PR3 and NE in neutrophil activation and noninfectious inflammation in vivo, which we believe to be novel. Mice lacking both PR3 and NE demonstrated strongly diminished immune complex-mediated (IC-mediated) neutrophil infiltration in vivo as well as reduced activation of isolated neutrophils by ICs in vitro. In contrast, in mice lacking just NE, neutrophil recruitment to ICs was only marginally impaired. The defects in mice lacking both PR3 and NE were directly linked to the accumulation of antiinflammatory progranulin (PGRN). Both PR3 and NE cleaved PGRN in vitro and during neutrophil activation and inflammation in vivo. Local administration of recombinant PGRN potently inhibited neutrophilic inflammation in vivo, demonstrating that PGRN represents a crucial inflammation-suppressing mediator. We conclude that PR3 and NE enhance neutrophil-dependent inflammation by eliminating the local antiinflammatory activity of PGRN. Our results support the use of serine protease inhibitors as antiinflammatory agents.

Measuring elastase, proteinase 3 and cathepsin G activities at the surface of human neutrophils with fluorescence resonance energy transfer substrates

The neutrophil serine proteases (NSPs) elastase, proteinase 3 and cathepsin G are multifunctional proteases involved in pathogen destruction and the modulation of inflammatory processes. A fraction of secreted NSPs remains bound to the external plasma membrane, where they remain enzymatically active. This protocol describes the spectrofluorometric measurement of NSP activities on neutrophil surfaces using highly sensitive Abz-peptidyl-EDDnp fluorescence resonance energy transfer (FRET) substrates that fully discriminate between the three human NSPs. We describe FRET substrate synthesis, neutrophil purification and handling, and kinetic experiments on quiescent and activated cells. These are used to measure subnanomolar concentrations of membrane-bound or free NSPs in low-binding microplates and to quantify the activities of individual proteases in biological fluids like expectorations and bronchoalveolar lavages. The whole procedure, including neutrophil purification and kinetic measurements, can be done in 4-5 h and should not be longer because of the lifetime of neutrophils. Using this protocol will help identify the contributions of individual NSPs to the development of inflammatory diseases and may reveal these proteases to be targets for therapeutic inhibitors.

Roles for proteinases in the pathogenesis of chronic obstructive pulmonary disease

Since the early 1960s, a compelling body of evidence has accumulated to show that proteinases play critical roles in airspace enlargement in chronic obstructive pulmonary disease (COPD). However, until recently the causative enzymes and their exact roles in pathologic processes in COPD have not been clear. Recent studies of gene-targeted mice in murine models of COPD have confirmed roles for proteinases not only in airspace enlargement, but also in airway pathologies in COPD. These studies have also shed light on the specific proteinases involved in COPD pathogenesis, and the mechanisms by which these proteinases injure the lung. They have also identified important interactions between different classes of proteinases, and between proteinases and other molecules that amplify lung inflammation and injury. This review will discuss the biology of proteinases and the mechanisms by which they contribute to the pathogenesis of COPD. In addition, I will discuss the potential of proteinase inhibitors and anti-inflammatory drugs as new treatment strategies for COPD patients.

Neutrophil surface presentation of the anti-neutrophil cytoplasmic antibody-antigen proteinase 3 depends on N-terminal processing

The neutrophil serine protease proteinase 3 (PR3) is a main autoantigen in anti-neutrophil cytoplasmic antibody-associated vasculitis. PR3 surface presentation on neutrophilic granulocytes, the main effector cells, is pathogenically important. PR3 is presented by the NB1 (CD177) glycoprotein, but how the presentation develops during neutrophil differentiation is not known. An N-terminally unprocessed PR3 (proPR3) is produced early during neutrophil development and promotes myeloid cell differentiation. We therefore investigated if PR3 presentation depended on NB1 during neutrophil differentiation and if PR3 and proPR3 could both be presented by NB1. In contrast to mature neutrophils, differentiating neutrophils showed an early NB1-independent PR3 surface display that was recognized by only two of four monoclonal anti-PR3 antibodies and occurred in parallel with proPR3, but not PR3 secretion, suggesting that the NB1-independent surface PR3 was proPR3. PR3 gene expression preceeded NB1. When the NB1 receptor was detected on the surface, a mode of PR3 surface display similar to mature neutrophils developed together with the degranulation system. Ectopic expression studies showed that NB1 was a sufficient receptor for PR3 but not proPR3. ProPR3 display on the plasma membrane may influence the bone marrow microenvironment. NB1-mediated PR3 presentation depended on PR3 N-terminal processing implicating the PR3-N-terminus as NB1-binding site.

The membrane proteinase 3 expression on neutrophils was downregulated after treatment with infliximab in patients with rheumatoid arthritis

Proteinase 3 (PR3) expression on neutrophils was examined in rheumatoid arthritis (RA) patients before and after antitumor necrosis factor (TNF)-alpha therapy. Membrane PR3 expression from patients with either an infection or RA significantly increased. Membrane PR3 expression on neutrophils from RA patients treated with infliximab (anti-TNF-alpha antibody) therapy was less than in those without such treatment in a resting state, but the expression later increased after stimulation in vitro. Membrane PR3 expression increased because of the stimulation of TNFalpha, whereas it was significantly suppressed by plasma or alpha(1)-proteinase inhibitor. The condition of patients with RA improved after treatment with infliximab. Membrane PR3 expression on neutrophils in RA patients was downregulated by infliximab. As a result, PR3 might play an important role in the neutrophil-mediated inflammatory reaction in patients with either RA or an infection.

Targeting neutrophil elastase in cystic fibrosis

BACKGROUND

Cystic fibrosis (CF) is a lethal hereditary disease characterised by neutrophil-dominated lung inflammation. These abundant neutrophils produce neutrophil elastase (NE), a destructive serine protease that has direct actions on extracellular matrix proteins and has a role in the host response to inflammation and infection.

OBJECTIVE

This review examines the prospect of developing novel therapies for CF by targeting NE. The authors explore the functions of NE and of naturally-occurring and synthetic NE inhibitors.

METHODS

A literature search was conducted exploring the functions of NE and inhibitors of NE; naturally occurring and synthetic.

CONCLUSIONS

Targeting NE in CF offers therapeutic potential, but optimal inhibitors that can be delivered safely and effectively to the lung are still under development.

Leukocyte cell surface proteinases: regulation of expression, functions, and mechanisms of surface localization

A number of proteinases are expressed on the surface of leukocytes including members of the serine, metallo-, and cysteine proteinase superfamilies. Some proteinases are anchored to the plasma membrane of leukocytes by a transmembrane domain or a glycosyl phosphatidyl inositol (GPI) anchor. Other proteinases bind with high affinity to classical receptors, or with lower affinity to integrins, proteoglycans, or other leukocyte surface molecules. Leukocyte surface levels of proteinases are regulated by: (1) cytokines, chemokines, bacterial products, and growth factors which stimulate synthesis and/or release of proteinases by cells; (2) the availability of surface binding sites for proteinases; and/or (3) internalization or shedding of surface-bound proteinases. The binding of proteinases to leukocyte surfaces serves many functions including: (1) concentrating the activity of proteinases to the immediate pericellular environment; (2) facilitating pro-enzyme activation; (3) increasing proteinase stability and retention in the extracellular space; (4) regulating leukocyte function by proteinases signaling through cell surface binding sites or other surface proteins; and (5) protecting proteinases from inhibition by extracellular proteinase inhibitors. There is strong evidence that membrane-associated proteinases on leukocytes play critical roles in wound healing, inflammation, extracellular matrix remodeling, fibrinolysis, and coagulation. This review will outline the biology of membrane-associated proteinases expressed by leukocytes and their roles in physiologic and pathologic processes.

Neutrophil serine proteases fine-tune the inflammatory response

Neutrophil serine proteases are granule-associated enzymes known mainly for their function in the intracellular killing of pathogens. Their extracellular release upon neutrophil activation is traditionally regarded as the primary reason for tissue damage at the sites of inflammation. However, studies over the past several years indicate that neutrophil serine proteases may also be key regulators of the inflammatory response. Neutrophil serine proteases specifically process and release chemokines, cytokines, and growth factors, thus modulating their biological activity. In addition, neutrophil serine proteases activate and shed specific cell surface receptors, which can ultimately prolong or terminate cytokine-induced responses. Moreover, it has been proposed that these proteases can impact cell viability through their caspase-like activity and initiate the adaptive immune response by directly activating lymphocytes. In summary, these studies point to neutrophil serine proteases as versatile mediators that fine-tune the local immune response and identify them as potential targets for therapeutic interventions.

Protease-activated receptors: novel PARtners in innate immunity

Protease-activated receptors (PARs) belong to a family of G protein-coupled receptors activated by serine proteases via proteolytic cleavage. PARs are expressed on epithelial cells, endothelial cells, and leukocytes, indicating a role in controlling barrier function against external danger. During inflammation, microorganisms as well as host immune cells release various proteases activating PARs. Thus, PARs can be viewed as an integral component of the host antimicrobial alarm system. When stimulated, PARs regulate various functions of leukocytes in vivo and in vitro, revealing a novel pathway by which proteases affect innate immune responses. Understanding protease-immune interactions could lead to novel strategies for the treatment of infectious and immune-related diseases.

Pro-inflammatory feedback activation cycle evoked by attack of Vibrio cholerae cytolysin on human neutrophil granulocytes

Vibrio cholerae cytolysin (VCC) is a pore-forming toxin that is secreted in precursor form (pro-VCC) and requires proteolytic cleavage in order to attain membrane-permeabilizing properties. Pro-VCC can be activated both in solution and membrane-bound state. Processing of membrane-bound pro-VCC can in turn be achieved through the action of both cell-associated and soluble proteases. The current investigation describes the interaction of VCC with human neutrophil granulocytes. It is shown that pro-VCC binds to these cells and is cleaved by cell-bound serine proteases. Membrane permeabilization leads to granulocyte activation, as witnessed by the generation of reactive oxygen metabolites and liberation of granule constituents. A mutant toxin with unaltered binding properties but devoid of pore-forming activity did not elicit these effects. The secreted proteases cleave and activate further bound- and non-bound pro-VCC. A positive feedback loop is thus created that results in enhanced cytotoxicity towards both the targeted granulocytes and towards bystander cells that are not primarily killed by the protoxin. Thus, activation of neutrophil granulocytes by VCC fuels a positive feedback cycle that will cripple immune defence, augment inflammation, and enhance the cytotoxic action of the toxin on neighbouring tissue cells.

Proteinase 3, the Wegener autoantigen, is externalized during neutrophil apoptosis: evidence for a functional association with phospholipid scramblase 1 and interference with macrophage phagocytosis

Proteinase 3 (PR3), a serine proteinase contained in neutrophil azurophilic granules, is considered a risk factor for vasculitides and rheumatoid arthritis when expressed on the outer leaflet of neutrophil plasma membrane and is the preferred target of antineutrophil cytoplasm autoantibodies (ANCA) in Wegener granulomatosis. ANCA binding to PR3 expressed at the surface of neutrophils activates them. Evidence is provided that neutrophil apoptosis induced significantly more membrane PR3 expression without degranulation (but no enhanced membrane CD35, CD66b, CD63, myeloperoxidase, or elastase expression). This observation was confirmed on cytoplasts, a model of granule-free neutrophils. We hypothesized that PR3 could interact with proteins involved in membrane flip-flop (eg, phospholipid scramblase 1 [PLSCR1]). PR3-PLSCR1 interaction in neutrophils was demonstrated by confocal microscopy and coimmunoprecipitation. In the RBL-2H3 rat mast-cell line stably transfected with PR3 or its inactive mutant (PR3S203A), PR3 externalization depended on PLSCR1, as shown by less PR3 externalization in the presence of rPLSCR1 siRNA, but independently of its serine-proteinase activity. Finally, apoptosis-externalized PR3 decreased the human macrophage-phagocytosis rate of apoptotic PR3 transfectants. Therefore, in addition to ANCA binding in vasculitis, the proinflammatory role of membrane PR3 expression may involve interference with macrophage clearance of apoptotic neutrophils.

Apoptosis of human neutrophils induced by protein phosphatase 1/2A inhibition is caspase-independent and serine protease-dependent

Protein phosphatase (PP) activity is associated with the regulation of apoptosis in neutrophils. However, the underlying regulatory mechanism(s) in apoptosis remain unclear. The type of cell death induced by okadaic acid (OA), the inhibitor of PP1 and PP2A, is characterized by apoptotic morphological changes of the cells and annexin V-positive staining without DNA fragmentation. The apoptotic effects of OA and calyculin A on neutrophils were observed at concentrations ranging from 50 to 200 nM, or 10 to 50 nM, respectively. Cyclosporine A (a PP2B specific inhibitor), however, did not exhibit any pro-apoptotic effects. OA and calyculin A, but not cyclosporine A, exhibited significant effects on protein levels and on the electrophoretic mobility of Mcl-1. zVAD-fmk, a pancaspase inhibitor, failed to inhibit the effect of OA on the caspase-3 activity, procaspase-3 processing, and the apoptotic rate of neutrophils. However, 4-(2-aminoethyl) benzenesulfonylfluoride (AEBSF), a general serine protease inhibitor, significantly abrogated the OA-induced mobility shift in procaspase-3, caspase-3 activation, and the apoptotic morphological changes in neutrophils. Moreover, OA enhanced the serine protease activity of the neutrophils. The addition of the proteinase-3 protein increased the rate of neutrophil apoptosis, which was also blocked by AEBSF but not by zVAD-fmk. These results suggest that OA induces procaspase-3 processing but that OA-induced apoptosis is caspase-independent and serine protease-dependent.

Tumor necrosis factor alpha activates release of B lymphocyte stimulator by neutrophils infiltrating the rheumatoid joint

OBJECTIVE

The tumor necrosis factor (TNF) family member B lymphocyte stimulator (BLyS) is an important regulator of B cell-dependent autoimmunity. Similar to other TNF family members, it is generally expressed as a transmembrane protein and cleaved from the surface to release its active soluble form. This study was undertaken to investigate the expression of BLyS and regulation of BLyS release from the surface of neutrophils infiltrating the rheumatoid joint.

METHODS

BLyS expression was studied in neutrophils from the synovial fluid and peripheral blood of patients with rheumatoid arthritis (RA) and healthy controls, by flow cytometry, Western blotting, and immunofluorescence analyses. Peripheral blood neutrophils cultured with 50% RA synovial fluid were study for membrane expression of BLyS. Neutrophils were exposed to a range of proinflammatory cytokines to study the mechanisms of surface loss of BLyS.

RESULTS

Expression of BLyS was detected on the surface of peripheral blood neutrophils from both RA patients and healthy controls, whereas BLyS expression on synovial fluid neutrophils was very low. Constitutive expression of BLyS was observed in neutrophils, both on the cell membrane and in intracellular stores; however, BLyS release from each of these sites was found to be regulated independently. Of the various cytokine stimuli, only TNFalpha triggered release of BLyS from the neutrophil membrane. This process led to release of physiologically relevant quantities of soluble BLyS, which was dependent on the presence of the pro-protein convertase furin. In contrast, stimulation of neutrophils with granulocyte colony-stimulating factor induced BLyS release from the intracellular stores. Incubation of peripheral blood neutrophils with RA synovial fluid led to TNFalpha-dependent shedding of BLyS from the cell surface.

CONCLUSION

These findings indicate that as neutrophils enter the site of inflammation, they release surface-expressed BLyS in a TNFalpha-dependent manner, and thus may contribute to local stimulation of autoimmune B cell responses.

Increased membrane expression of proteinase 3 during neutrophil adhesion in the presence of anti proteinase 3 antibodies

We investigated membrane proteinase 3 (mPR3) expression during TNF-alpha-induced adhesion of neutrophils in the presence of anti-PR3 antibodies, a situation occurring during anti-neutrophil cytoplasmic autoantibodies (ANCA)-associated vasculitis. Three increasing levels of mPR3 expression were observed on the mPR3(+) neutrophil subset after stepwise cell activation. TNF-alpha activation without adhesion, TNF-alpha-induced adhesion, and adhesion in the presence of anti-PR3 mAb or human anti-PR3 ANCA resulted, respectively, in a two-, seven-, and 24-fold increase of mPR3 levels. In plasma, anti-PR3 antibodies poorly recognized suspended neutrophils, whereas they bound to mPR3 on adherent cells. mPR3 upregulation was also triggered by IL-8, formyl-methionyl-leucyl-phenylalanine (fMLP), and neutrophil adhesion to activated human umbilical vein endothelial cells. It involved beta2 integrins and Fcgamma receptor, because it was prevented by anti-CD18 antibodies and was not observed with anti-PR3 F(ab')(2). Furthermore, it was specific to anti-PR3 mAb, and no mPR3 upregulation was observed with anti-myeloperoxidase or anti-HLA-ABC mAb. Newly expressed mPR3 molecules, after TNF-induced adhesion, were mobilized from secretory vesicles (CD35(+)) and secondary granules (CD11b(+)). The adhesion- and antibody-dependent upregulations of mPR3 expression occurred with little azurophilic granule degranulation, no sign of apoptosis, and no further CD177 upregulation. In conclusion, this study describes an amplifying loop in polymorphonuclear neutrophil activation process, whereby ANCA are involved in the membrane expression of their own antigen during cell adhesion. This could explain the restriction of ANCA-associated vasculitis to small vessels, the main site of neutrophil adhesion.

Inhibition of the Activation of Multiple Serine Proteases with a Cathepsin C Inhibitor Requires Sustained Exposure to Prevent Pro-enzyme Processing

Cathepsin C is a cysteine protease required for the activation of several pro-inflammatory serine proteases and, as such, is of interest as a therapeutic target. In cathepsin C-deficient mice and humans, the N-terminal processing and activation of neutrophil elastase, cathepsin G, and proteinase-3 is abolished and is accompanied by a reduction of protein levels. Pharmacologically, the consequence of cathepsin C inhibition on the activation of these serine proteases has not been described, due to the lack of stable and non-toxic inhibitors and the absence of appropriate experimental cell systems. Using novel reversible peptide nitrile inhibitors of cathepsin C, and cell-based assays with U937 and EcoM-G cells, we determined the effects of pharmacological inhibition of cathepsin C on serine protease activity. We show that indirect and complete inhibition of neutrophil elastase, cathepsin G, and proteinase-3 is achievable in intact cells with selective and non-cytotoxic cathepsin C inhibitors, at concentrations approximately 10-fold higher than those required to inhibit purified cathepsin C. The concentration of inhibitor needed to block processing of these three serine proteases was similar, regardless of the cell system used. Importantly, cathepsin C inhibition must be sustained to maintain serine protease inhibition, because removal of the reversible inhibitors resulted in the activation of pro-enzymes in intact cells. These findings demonstrate that near complete inhibition of multiple serine proteases can be achieved with cathepsin C inhibitors and that cathepsin C inhibition represents a viable but challenging approach for the treatment of neutrophil-based inflammatory diseases.

Proteolysis of the endothelial cell protein C receptor by neutrophil proteinase 3

BACKGROUND

The endothelial cell protein C receptor (EPCR) presents protein C to the thrombin:thrombomodulin complex on the endothelium of large vessels, and enhances the generation of activated protein C (APC) and activation of protease-activated receptor-1. A previous report has demonstrated binding of soluble (s) EPCR to activated neutrophils via surface proteinase 3 (PR3).

METHODS

We now report further characterization of this interaction. Activated neutrophils and purified PR3 both decrease endothelial cell (EC) surface EPCR, suggestive of its proteolysis.

RESULTS

When added to purified recombinant sEPCR, PR3 produced multiple cleavages, with early products including 20 kDa N-terminal and C-terminal (after Lys(176)) fragments. The binding of active site blocked PR3 to sEPCR was studied by surface plasmon resonance. Estimates of the K(D) of 18.5-102 nM were obtained with heterogeneous binding, suggestive of more than a single interaction site.

CONCLUSIONS

This work demonstrates PR3 binding to and proteolysis of EPCR and suggests a mechanism by which anticoagulant and cell protective pathways can be down-regulated during inflammation.

Standardised assessment of membrane proteinase 3 expression. Analysis in ANCA-associated vasculitis and controls

OBJECTIVES

Increased numbers of neutrophils expressing proteinase 3 on their membrane (mPR3) have been reported in anti-neutrophil cytoplasm antibody (ANCA)-associated vasculitis (AAV) and are suggested to be involved in AAV immunopathogenesis. In most studies, neutrophils were analysed for mPR3 expression without priming with TNFalpha, suggesting that mPR3 expression on neutrophils is dependent on other priming events, such as isolation procedures . These priming events can be variable. Therefore, we analysed mPR3 expression on neutrophils before and after priming with TNFalpha to assess whether standardised assessment of mPR3 expression requires priming. Using neutrophils before and after priming with TNFalpha, we assessed percentages of mPR3(+) neutrophils in patients with AAV and in disease and healthy controls.

METHODS

Neutrophils from patients with PR3-AAV and MPO-AAV, systemic lupus erythematosus (SLE) and rheumatoid arthritis (RA), and from healthy controls were analysed before and after priming with TNFalpha for mPR3 expression.

RESULTS

42% of all individuals analysed showed minimal expression for mPR3 on all neutrophils before priming with TNFalpha, whereas after priming a clear mPR3(+) subset was observed next to mPR3(-) neutrophils, corresponding to bimodal mPR3 expression. In patients with PR3-AAV or MPO-AAV, the percentage of mPR3(+) neutrophils after priming with TNFalpha was significantly increased (p<0.01 and p<0.05, respectively) compared with healthy controls. Percentages of mPR3(+) PMN were also increased in patients with SLE (p<0.01) but not in RA.

CONCLUSION

Standardised assessment of proteinase 3 on the membrane of neutrophils requires priming with TNFalpha. Percentages of mPR3(+) PMN are increased in AAV and SLE, but not in RA.

The sulfate groups of chondroitin sulfate- and heparan sulfate-containing proteoglycans in neutrophil plasma membranes are novel binding sites for human leukocyte elastase and cathepsin G

Human leukocyte elastase (HLE) and cathepsin G (CG) are expressed at high levels on the surface of activated human neutrophils (PMN) in catalytically active but inhibitor-resistant forms having the potential to contribute to tissue injury. Herein we have investigated the mechanisms by which HLE and CG bind to PMN plasma membranes. (125)I-Labeled HLE and CG bind to PMN at 0 degrees C in a saturable and reversible manner (K(D) = 5.38 and 4.36 x 10(-7) m and 11.5 and 8.1 x 10(6) binding sites/cell, respectively). Incubation of PMN with radiolabeled HLE and CG in the presence of a 200-fold molar excess of unlabeled HLE, CG, myeloperoxidase, lactoferrin, proteinase 3, phenylmethylsulfonyl fluoride (PMSF)-inactivated HLE, or PMSF-inactivated CG inhibited binding of radiolabeled ligands. This indicates that these PMN granule proteins share binding sites on PMN and that functional active sites of HLE and CG are not required for their binding to PMN. The sulfate groups of heparan sulfate- and chondroitin sulfate-containing proteoglycans are the PMN binding sites for HLE and CG since binding of HLE and CG to PMN was inhibited by incubating PMN with 1) trypsin, chondroitinase ABC, and heparitinases, but not other glycanases, and 2) purified chondroitin sulfates, heparan sulfate, and other sulfated molecules, but not with non-sulfated glycans. Thus, heparan sulfate- and chondroitin sulfate-containing proteoglycans are low affinity, high volume PMN surface binding sites for HLE and CG, which are well suited to bind high concentrations of active serine proteinases released from degranulating PMN.