A cytosolic inhibitor of human neutrophil elastase and cathepsin G

Neutrophil-derived extracellular vesicles modulate the phenotype of naïve human neutrophils

Neutrophils (PMN) regulate inflammation in many ways, including communication with other immune cells via extracellular vesicles (EVs). EVs released by human neutrophils activated with N-formylmethionyl-leucyl-phenylalanine (fMLF) (PMN-fMLF EVs) had an outside-out orientation and contained functionally important neutrophil plasma membrane proteins, including flavocytochrome b558, and enzymatically active granule proteins, elastase, and myeloperoxidase. Treatment of naïve PMN with PMN-fMLF EVs primed fMLF-stimulated NADPH oxidase activity, increased surface expression of the complement receptors CD11b/CD18 and CD35, the specific granule membrane protein CD66, and flavocytochrome b₅₅₈ , and promoted phagocytosis of serum-opsonized Staphylococcus aureus. The primed oxidase activity reflected increased surface expression of flavocytochrome b558 and phosphorylation of SER345 in p47^phox , two recognized mechanisms for oxidase priming. Taken together, these data demonstrate that stimulated PMN released EVs that altered the phenotype of naïve phagocytes by priming of the NADPH oxidase activity and augmenting phagocytosis, two responses that are integral to optimal PMN host defense.

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.

Neutrophil elastase is associated with serglycin on its way to lysosomes in U937 cells

Mutations in the neutrophil elastase (NE) gene have been postulated to interfere with normal intracellular trafficking of NE as an AP3-interacting membrane integrated protein and to cause severe congenital or cyclic neutropenia in humans. Here, we show that in U937 promonocytes NE is synthesized as a predominantly soluble proenzyme and is completely secreted in the presence of phorbol esters similarly to serglycin. Using chemical cross-linking NE is shown to be associated with serglycin as 34 kDa proenzyme in the trans-Golgi region of these cells indicating that it is delivered to lysosomes associated with serglycin.

Synthesis and in-vitro evaluation of novel low molecular weight thiocarbamates as inhibitors of human leukocyte elastase

A series of novel low molecular weight thiocarbamate esters (1e-6e) were synthesized and evaluated as inhibitors of human leukocyte elastase (HLE). The thiocarbamate esters studied consist of a substituted primary or secondary aliphatic or aromatic amine and a 1-phenyl-1H-tetrazole-5-thiol (Table I). The HLE catalyzed hydrolysis of N-methoxysuccinyl- L-Ala-L-Ala-L-Pro-L-Val-p-nitroanilide substrate was utilized as the measure of inhibition. N-n-butyl, 1-phenyl-1H-tetrazole-5-thiocarbamate (1e) exhibited the highest inhibitory activity (k(obs) /[I] = 2.1 x 10(5) M(-1). min(-1) ) and N-allyl, 1-phenyl-1H-tetrazole-5-thiocarbamate (2e) (K(obs) /[I] = 6.1 x 10(4) M(-1). min(-1) ) exhibited the second highest inhibitory activity of all the thiocarbamates. The aromatic N-phenyl, 1-phenyl-1H-tetrazole-5-thiocarbamate (4e) showed the lowest inhibitory activity (K(obs) /[I] = 1.9 x 10(2) M(-1). min(-1) ) among the N-monosubstituted derivatives, similar to that of N-ethyl-N-n-butyl, 1-phenyl-1H-tetrazole-5-thiocarbamate (5e) (K(obs) /[I] = 1.8 x 10(2) M(-1).min(-1) ). The N-isopropyl, 1-phenyl-1H-tetrazole-5-thiocarbamate (3e) (K(obs) /[I] = 3.3 x 10(3) M(-1).min(-1) ) was about 10 fold more active than (4e) and N, N-diisopropyl, 1-phenyl-1H-tetrazole- 5-thiocarbamate (6e) showed no inhibitory activity against HLE. In the present work less than 3% of HLE specific activity was regained after 24 hours incubation with each of the tested N-monosubstituted thiocarbamates (1e-4e). The time-dependent inhibition of HLE by the thiocarbamate compounds (1e-5e) seems to involve the interaction and possible chemical modification of one enzyme residue. Straight chain nonpolar aliphatic substituents on the nitrogen of the thiocarbamate functionality may be essential for high inhibitory activity. As the degree of substitution (branching) on the nitrogen of the thiocarbamate functionality increases the inhibitory activity of the compounds decreases. The time-dependent inhibition of HLE and the slow deacylation rates by the N-monosubstituted thiocarbamates are consistent with irreversible inhibition.

Inhibition of neutrophil elastase by recombinant human proteinase inhibitor 9

Proteinase inhibitor PI9 (PI9) is an intracellular 42-kDa member of the ovalbumin family of serpins that is found primarily in placenta, lung and lymphocytes. PI9 has been shown to be a fast-acting inhibitor of granzyme B in vitro, presumably through the utilization of Glu(340) as the P(1) inhibitory residue in its reactive site loop. In this report, we describe the inhibition of human neutrophil elastase by recombinant human PI9. Inhibition occurred with an overall K(i)' of 221 pM and a second-order association rate constant of 1.5 x 10(5) M(-1) s(-1), indicating that PI9 is a potent inhibitor of this serine proteinase in vitro. In addition, incubation of recombinant PI9 with native neutrophil elastase resulted in the formation of an SDS-resistant 62-kDa complex. Amino-terminal sequence analyses provided evidence that inhibition of elastase occurred through the use of Cys(342) as the reactive P(1) amino acid residue in the PI9 reactive site loop. Thus, PI9 joins its close relatives PI6 and PI8 as having the ability to utilize multiple reactive site loop residues as the inhibitory P(1) residue to expand its inhibitory spectrum.

Purification and N-terminal amino acid sequence of sheep neutrophil cathepsin G and elastase

Sheep cathepsin G (CG) and neutrophil elastase (NE) were isolated from a crude leukocyte membrane preparation by elastin-Sepharose 4B and CM-Sepharose 4B chromatography, followed by native preparative PAGE. The N-termini of CG and NE were sequenced to 24 and 20 residues, showing 96 and 85% identity with human CG and NE, respectively. During SDS-PAGE, sheep CG and NE migrated parallel to human CG and NE and have apparent molecular masses of 28 and 26 kDa, respectively. Following incubation of sheep CG and NE with human alpha(1)-antichymotrypsin and alpha(1)-proteinase inhibitor, complexes with apparent molecular masses of 89 and 81 kDa respectively were observed by SDS-PAGE. Polyclonal antibodies to human CG and NE cross-reacted with purified sheep CG and NE, respectively. These results indicate that sheep neutrophils contain CG and elastase that are analogous to human CG and NE in terms of molecular mass, reactivity with endogenous inhibitors, immunocross-reactivity, and N-terminal sequence.

The Pseudomonas aeruginosa secretory product pyocyanin inactivates alpha1 protease inhibitor: implications for the pathogenesis of cystic fibrosis lung disease

Alpha1 Protease inhibitor (alpha1PI) modulates serine protease activity in the lung. Reactive oxygen species inactivate alpha1PI, and this process has been implicated in the pathogenesis of a variety of forms of lung injury. An imbalance of protease-antiprotease activity is also detected in the airways of patients with cystic fibrosis-associated lung disease who are infected with Pseudomonas aeruginosa. P. aeruginosa secretes pyocyanin, which, through its ability to redox cycle, induces cells to generate reactive oxygen species. We tested the hypothesis that redox cycling of pyocyanin could lead to inactivation of alpha1PI. When alpha1PI was exposed to NADH and pyocyanin, a combination that results in superoxide production, alpha1PI lost its ability to form an inhibitory complex with both porcine pancreatic elastase (PPE) and trypsin. Similarly, addition of pyocyanin to cultures of human airway epithelial cells to which alpha1PI was also added resulted in a loss of the ability of alpha1PI to form a complex with PPE or trypsin. Neither superoxide dismutase, catalase, nor dimethylthiourea nor depletion of the media of O2 to prevent formation of reactive oxygen species blocked pyocyanin-mediated inactivation of alpha1PI. These data raise the possibility that a direct interaction between reduced pyocyanin and alpha1PI is involved in the process. Consistent with this possibility, pretreatment of alpha1PI with the reducing agent beta-mercaptoethanol also inhibited binding of trypsin to alpha1PI. These data suggest that pyocyanin could contribute to lung injury in the P. aeruginosa-infected airway of cystic fibrosis patients by decreasing the ability of alpha1PI to control the local activity of serine proteases.

Production of recombinant human monocyte/neutrophil elastase inhibitor (rM/NEI)

Recombinant human monocyte/neutrophil elastase inhibitor (rM/NEI) was expressed with a baculovirus expression system. The purified recombinant protein was shown to inhibit human neutrophil elastase by the formation of a stable equimolar complex, as had been shown for M/NEI isolated from monocyte-derived cell lines. rM/NEI was remarkably stable in aqueous buffers from pH 6 to pH 8, but not in buffers below pH 6. rM/NEI activity was stable when subjected to freeze-thaw cycles and low temperature storage in Tris or phosphate buffers. rM/NEI could also be lyophilized without significant loss of activity. A 1.6-g batch of greater than 95% purity in rM/NEI was obtained by anion exchange and size exclusion chromatography with yields of 7 to 8 mg per liter of cultured insect cells. Methods and protocols were chosen for compatibility with large-scale cGMP production and were suitable for biochemical characterization and preclinical evaluation of rM/NEI as a therapeutic agent for cystic fibrosis. The availability of large amounts of purified rM/NEI will facilitate clinical evaluation of rM/NEI for prevention of the elastase-mediated destruction of lung tissue associated with the morbidity and mortality of cystic fibrosis.

Structure and sequence of human M/NEI (monocyte/neutrophil elastase inhibitor), an Ov-serpin family gene

Human monocyte/neutrophil Elastase Inhibitor (M/NEI) is a proteinase inhibitor that regulates the activity of the neutrophil proteases: elastase, cathepsin G and proteinase-3. Evidence indicates that M/NEI belongs to the Ov-serpin family (ovalbumin-related serpins), functionally diverse proteins with shared structural features. Recombinant lambda phage clones were isolated that encompass the full-length M/NEI gene plus upstream and downstream regions. The gene, 9.5kb long, consists of 7 exons and 6 introns. The 5' transcription start site identified by primer extension corresponds to a 60bp exon 1; the translation start site is in exon 2. Southern blots established a gene copy number of one. The 3' untranslated region (UTR) contains three AATAAA/AATTAA sites; these were shown to function as alternative polyadenylation signals. A 14-nucleotide upstream motif including the atypical TATA box TATAAGAG otherwise occurs only twice in GenBank, in the genes encoding neutrophil elastase and proteinase-3, target proteases inhibited by M/NEI. Comparison of M/NEI and previously characterized related genes strongly suggests that all Ov-serpins, despite a difference in chromosomal localization and exon number, nonetheless, share a common basic gene structure.

Alpha-naphthylisothiocyanate causes neutrophils to release factors that are cytotoxic to hepatocytes

Administration of alpha-naphthylisothiocyanate (ANIT) to rats causes acute liver injury characterized in part by hepatocellular damage and marked neutrophil infiltration, effects that resemble drug-induced cholangiolitic hepatitis in people. ANIT-induced liver injury is neutrophil dependent. Moreover, ANIT can activate neutrophils in vitro. Since neutrophil-derived proteases can mediate hepatocellular killing, we hypothesized that ANIT stimulates neutrophils to release proteolytic enzymes that are cytotoxic to hepatic parenchymal cells. To test this hypothesis, neutrophils were isolated from Sprague-Dawley rats and incubated with ANIT for 6-24 h. ANIT (6-50 microM) was not toxic to neutrophils as indicated by the lack of lactate dehydrogenase release into the incubation medium. The conditioned medium from ANIT-treated neutrophils (ANCM) was collected, centrifuged, added to isolated hepatocytes, and incubated for 8, 16, or 24 h. Conditioned medium collected from neutrophils exposed to 25 or 50 microM ANIT for 16-24 h caused hepatocellular damage as indicated by the release of alanine aminotransferase into the culture medium. The concentration of ANIT in ANCM was nondetectable (0.5 microM). Analysis of ANCM indicated the presence of both cathepsin G and elastase activities. Inhibitors of these enzymes afforded protection against ANCM-induced hepatocellular injury. These results indicate that ANIT causes neutrophils to release toxic proteases which cause hepatocellular damage in vitro.

Biochemistry and pathology of radical-mediated protein oxidation

Radical-mediated damage to proteins may be initiated by electron leakage, metal-ion-dependent reactions and autoxidation of lipids and sugars. The consequent protein oxidation is O2-dependent, and involves several propagating radicals, notably alkoxyl radicals. Its products include several categories of reactive species, and a range of stable products whose chemistry is currently being elucidated. Among the reactive products, protein hydroperoxides can generate further radical fluxes on reaction with transition-metal ions; protein-bound reductants (notably dopa) can reduce transition-metal ions and thereby facilitate their reaction with hydroperoxides; and aldehydes may participate in Schiff-base formation and other reactions. Cells can detoxify some of the reactive species, e.g. by reducing protein hydroperoxides to unreactive hydroxides. Oxidized proteins are often functionally inactive and their unfolding is associated with enhanced susceptibility to proteinases. Thus cells can generally remove oxidized proteins by proteolysis. However, certain oxidized proteins are poorly handled by cells, and together with possible alterations in the rate of production of oxidized proteins, this may contribute to the observed accumulation and damaging actions of oxidized proteins during aging and in pathologies such as diabetes, atherosclerosis and neurodegenerative diseases. Protein oxidation may also sometimes play controlling roles in cellular remodelling and cell growth. Proteins are also key targets in defensive cytolysis and in inflammatory self-damage. The possibility of selective protection against protein oxidation (antioxidation) is raised.

Human eosinophils lack human leukocyte elastase

Recently, human leukocyte elastase has been detected in human eosinophils. Reinvestigating these findings, 2.5 pg active human leukocyte elastase (E.C. 3.4.21.37) were found per neutrophil isolated from peripheral blood, whereas the elastase activity of eosinophil preparations was linearly correlated with the content of contaminating neutrophils. Also spontaneous or stimulated release of active elastase was absent in eosinophils. By immunohistochemistry no elastase immunoreactivity could be demonstrated in human eosinophils. Therefore, we conclude that human eosinophils do not contain considerable amounts of human leukocyte elastase.

The role of lactoferrin as an anti-inflammatory molecule

The formation of hydroxyl radical via the iron catalyzed Haber-Weiss reaction has been implicated in phagocyte-mediated microbicidal activity and inflammatory tissue injury. The fact that neutrophils contain lactoferrin and mononuclear phagocytes have the capacity to acquire exogenous iron has suggested that iron bound to lactoferrin may influence the nature of free radical products generated by these cells. Over the years the iron-lactoferrin complex has been heralded as both a promoter and inhibitor of hydroxyl radical formation. This manuscript is intended to provide an overview of work performed to date related to this controversy and to present results of a number of preliminary studies which shed further light on the role of lactoferrin in inflammation.

Primary structure of a porcine leukocyte serpin

Inhibitors of neutral serine proteinases (serpins) have been shown to be colocalized with their target enzymes in leukocytes of several mammalian species. Here we report the purification and complete primary structure of a cytosolic inhibitor from porcine granulocytes which is directed against neutrophil elastase. Two molecular mass forms of the leukocyte neutral proteinase inhibitor (LNPI) were isolated by affinity and ion-exchange chromatography followed by gel filtration, and identified as the inhibitorily active monomer and homodimer of the inhibitor protein. According to the amino acid sequence the molecular mass of the non-glycosylated inhibitor was calculated to 42,597 Da (378 amino acid residues). A sequence identity of 81% was found between LNPI and the homologous elastase inhibitors from both human and equine leukocytes, whereas only 50% of the positions are identical in LNPI and human plasminogen activator inhibitor 2. These data suggest that LNPI is a member of a new group of cytosolic serpins closely related to the ovalbumin branch of the superfamily.

Inactivation of interleukin-6 in vitro by monoblastic U937 cell plasma membranes involves both protease and peptidyl-transferase activities

Human promonocytic U937 cells have previously been shown to possess at their cell surface specific transmembrane serine proteases and N-terminal amino acid proteases as well as associated enzymes including elastase and cathepsin G. In this study, purified plasma membranes from U937 cells are reported to degrade the recombinant 21-kDa 125I-interleukin-6 (125I-IL-6) into 8-kDa products with loss of biological activity, as monitored by polyacrylamide gel electrophoresis and a cell-proliferation bioassay. Degradation of 125I-IL-6 by plasma membranes was completely prevented by the serine-protease inhibitor diisopropyl fluorophosphate, but was only partially impaired by alpha 1-protease inhibitor and antibody against cathepsin G. A similar incubation of 125I-IL-6 with cathepsin G purified from U937 cells caused hydrolysis of the cytokine into similar inactive 8-kDa fragments, whereas incubation with purified U937 cell elastase failed to degrade the peptide. These findings indicate that U937 cells hydrolyze IL-6 using cell-associated serine-protease activity and that cathepsin G partially participates in this degradation. Prolonged incubation of 8-kDa 125I-IL-6 fragments with purified U937 plasma membranes, led to a complete loss of IL-6 activity related to the transformation of the 8-kDa forms into a higher-molecular-mass complex (16 kDa). This complex was stable in SDS and 2-mercaptoethanol at 100 degrees C and was not dissociated by hydroxylamine treatment, indicating the formation of a covalent non-ester bond between the 8-kDa 125I-IL-6-derived peptide and an undetermined acceptor. An initial oxidative treatment of 125I-IL-6 partially prevented complex formation, suggesting the presence of one or more oxidizable methionine residues at the binding site of 8-kDa 125I-IL-6 peptide. The kinetics of complex formation (time dependence and plasma-membrane-concentration dependence), as well as its inhibition by a specific inhibitor of N-amino-peptidase activity, bestatin, suggest the participation of peptidyl-transferase activity in complex formation. Finally, a plasma-membrane fraction, corresponding to a molecular mass > or = 30 kDa, was able to convert the 8-kDa 125I-IL-6 forms into the 125I-labeled 16-kDa complex, suggesting that a > or = 30-kDa peptidyl-transferase enzyme catalyzes the reaction and provides the 125I-labeled 16-kDa peptide by dimerization of 8-kDa 125I-IL-6-derived intermediates. Further identification of the plasma-membrane-associated peptidyl transferase as a regulator of IL-6 proteolysis may be of physiological relevance for the control of IL-6 biological activity.

The enzymatic and release characteristics of sheep neutrophil elastase: a comparison with human neutrophil elastase

Sheep are often used to study tissue damage following shock after traumatic injury and in the course of other diseases. The processes involved are thought to be caused at least in part by elastase released from polymorphonuclear leukocytes (PMNs). Since little is known about elastase and its role as a mediator of tissue damage in sheep, we studied the biochemical properties and release characteristics to sheep leukocyte elastase (SLE) in comparison of those of human leukocyte elastase (HLE). Both enzymes showed similar molecular masses, amino-acid compositions, N-terminal amino-acid sequences, and abilities to digest elastin substrates. Differences, however, were found in kinetic parameters measured with the elastase-specific substrate N-methoxysuccinyl-(L-alanyl)2-L-prolyl-L- valine-4-nitroanilide (MeoSuc-AAPV-pNa). The Michaelis constant (Km) of ovine elastase was nearly 10 times higher (1.82 mM) than the Km of HLE (0.21 mM). Values of SLE calculated for kcat were 70% and for kcat/Km 8% of corresponding values determined for HLE. In addition, significant differences between sheep and human PMNs were found in in vitro stimulation experiments. In contrast to human PMNs, sheep neutrophils released no active elastase, and only 50 to 70% of the H2O2 produced by human PMNs. This failure to release active elastase could not be explained by a lower elastase content of sheep PMNs, as there were no significant differences found between the elastase contents of sheep and human PMNs. We conclude that elastase liberated by stimulated sheep PMNs is inactivated by a concomitantly released proteinase inhibitor also located within the sheep PMNs.(ABSTRACT TRUNCATED AT 250 WORDS)

Sequence and molecular characterization of human monocyte/neutrophil elastase inhibitor

cDNA encoding human monocyte/neutrophil elastase inhibitor (EI), a M(r) approximately 42,000 protein with serpin-like functional properties, has been sequenced. The 1316-base-pair sequence was obtained from overlapping clones and amplified DNA from libraries of monocyte-like and neutrophil-like cells. Hybridization with EI cDNA identified three EI mRNA species of 1.5, 1.9, and 2.6 kilobases in U937 monocyte-like cells and no hybridizing mRNA in lymphoblastoid cells lacking detectable EI. The cDNA open reading frame encodes a 379-amino acid protein, of which 167 residues were confirmed by tryptic peptides. Although EI may function extracellularly as well as intracellularly, its deduced sequence lacks a typical cleavable N-terminal signal sequence. Sequence analysis established that EI is a member of the serpin superfamily. EI has greatest homology (50.1% identity of amino acids) with plasminogen activator inhibitor 2, also a monocyte protein, and ovalbumin and gene Y, which were previously grouped as an ancient branch of the serpin superfamily. The extent of EI identity with the functionally related serpin alpha 1 antitrypsin is only 30.1%. Sequence alignment indicates that the reactive center P1 residue is Cys-344, consistent with abrogation of elastase inhibitory activity by iodoacetamide and making EI a naturally occurring Cys-serpin. The cleavable bond, Cys-Met, suggests an oxidation-sensitive molecule capable of inhibiting more than one serine protease. Oxidation sensitivity would limit the place of action of EI to the immediate vicinity of carrier cells. The molecular structure will help clarify the likely role of EI in regulating protease action and preventing tissue damage by phagocytic cells.