Elastase inhibitor. Characterization of the human elastase inhibitor molecule associated with monocytes, macrophages, and neutrophils

A systematic review identifying seminal plasma biomarkers and their predictive ability on IVF and ICSI outcomes

The diverse nature and high molecule concentration of seminal plasma (SP) makes this fluid a good potential source for a potential biomarker that could predict assisted reproductive technology (ART) outcomes. Currently, semen quality parameters cannot accurately predict ART outcomes. A systematic literature search was conducted to identify human SP biomarkers with potential predictive ability for the outcomes of IVF and intracytoplasmic sperm injection. Observational cohort and case-control studies describing the association between biomarkers in human SP and the outcome of infertile men attending for ART were included. Forty-three studies were selected, reporting on 89 potential SP biomarkers (grouped as oxidative stress, proteins glycoproteins, metabolites, immune system components, metals and trace elements and nucleic acids). The present review supports 32 molecules in SP as potentially relevant biomarkers for predicting ART outcomes; 23 molecules were reported once and nine molecules were reported in more than one study; IL-18 and TGF-β1-IL-18 ratio were confirmed in distinct studies. This review presents the most comprehensive overview of relevant SP biomarkers to predict ART outcomes to date, which is of clinical interest for infertility investigations and assisted reproduction; nevertheless, its potential is under-exploited. This review could serve as starting point for designing an all-encompassing study for biomarkers in SP and their predictive ability for ART outcomes, and for developing a non-invasive diagnostic tool.

Physics-driven identification of clinically approved and investigation drugs against human neutrophil serine protease 4 (NSP4): A virtual drug repurposing study

Neutrophils synthesize four immune associated serine proteases: Cathepsin G (CTSG), Elastase (ELANE), Proteinase 3 (PRTN3) and Neutrophil Serine Protease 4 (NSP4). While previously considered to be immune modulators, overexpression of neutrophil serine proteases correlates with various disease conditions. Therefore, identifying novel small molecules that can potentially control or inhibit the proteolytic activity of these proteases is crucial to revert or temper the aggravated disease phenotype. To the best of our knowledge, although there is limited data for inhibitors of other neutrophil protease members, there is no previous clinical study of a synthetic small molecule inhibitor targeting NSP4. In this study, an integrated molecular modeling algorithm was performed within a virtual drug repurposing study to identify novel inhibitors for NSP4, using clinically approved and investigation drugs library (∼8000 compounds). Based on our rigorous filtration, we found that following molecules Becatecarin, Iogulamide, Delprostenate and Iralukast are predicted to block the activity of NSP4 by interacting with core catalytic residues. The selected ligands were energetically more favorable compared to the reference molecule. The result of this study identifies promising molecules as potential lead candidates.

Cathepsin G Inhibition by Serpinb1 and Serpinb6 Prevents Programmed Necrosis in Neutrophils and Monocytes and Reduces GSDMD-Driven Inflammation

Neutrophil granule serine proteases contribute to immune responses through cleavage of microbial toxins and structural proteins. They induce tissue damage and modulate inflammation if levels exceed their inhibitors. Here, we show that the intracellular protease inhibitors Serpinb1a and Serpinb6a contribute to monocyte and neutrophil survival in steady-state and inflammatory settings by inhibiting cathepsin G (CatG). Importantly, we found that CatG efficiently cleaved gasdermin D (GSDMD) to generate the signature N-terminal domain GSDMD-p30 known to induce pyroptosis. Yet GSDMD deletion did not rescue neutrophil survival in Sb1a.Sb6a^-/- mice. Furthermore, Sb1a.Sb6a^-/- mice released high levels of pro-inflammatory cytokines upon endotoxin challenge in vivo in a CatG-dependent manner. Canonical inflammasome activation in Sb1a.Sb6a^-/- macrophages showed increased IL-1β release that was dependent on CatG and GSDMD. Together, our findings demonstrate that cytosolic serpins expressed in myeloid cells prevent cell death and regulate inflammatory responses by inhibiting CatG and alternative activation of GSDMD.

Expression and purification of recombinant human serpin B1 yields novel molecules with altered protease inhibitory activities: Functional implications

Serpin B1 regulates the innate immune system by inhibiting serine and cysteine proteases that control programmed cell death and proliferation pathways. To provide recombinant human proteins for in vitro and in vivo studies we expressed and purified wild-type human serpin B1 and a C344A variant in the yeast S. cerevisiae. Both proteins expressed well and inhibited elastase and chymotrypsin. However, purification of wild-type serpin B1 in the absence of a reducing agent resulted in the specific loss of elastase - but not chymotrypsin - inhibition, concomitant with the formation of two higher molecular weight forms of the protein - a modified monomer and a dimer created via an intermolecular disulfide bond formed between C344 in respective serpin B1 monomers. In contrast to fully reduced serpin B1, both modified forms were good elastase substrates and catalytically cleaved at multiple adjacent sites within the reactive site loop. In contrast, purification of the C344A variant in the absence of a reducing agent yielded only one form of the protein which retained elastase and chymotrypsin inhibitory properties when purified. Furthermore, the elastase inhibitory activity of wild-type serpin B1, but not the C344A variant, was sensitive to oxidation. Thus, wild-type human serpin B1 should be formulated with a pharmaceutically acceptable reducing agent to protect C344 against post-translational oxidative modifications. Alternatively, the C344A variant of this protein may prove to be a suitable drug development candidate. These findings also suggest that inactivation of serpin B1 by oxidation may have a physiological role to play during inflammation.

Altered platelet proteome in lupus anticoagulant (LA)-positive patients-protein disulfide isomerase and NETosis as new players in LA-related thrombosis

Patients with antiphospholipid syndrome (APS) are at high risk of developing venous and arterial thromboembolism (TE). The role of platelets in the pathogenesis of these prothrombotic conditions is not yet fully understood. The aim of this study was to gain mechanistic insights into the role of platelets in APS by comparing the platelet proteome between lupus anticoagulant (LA)-positive patients with (LA+ TE+) and without a history of TE (LA+ TE-) and healthy controls. The platelet proteome of 47 patients with LA, 31 with a history of TE and 16 without thrombotic history, and 47 healthy controls was analyzed by two-dimensional differential in-gel electrophoresis and mass spectrometry to identify disease-related proteins. Afterward, selected LA-related platelet proteins were validated by western blot and ELISA. Alterations of 25 proteins were observed between the study groups. STRING pathway analysis showed that LA-related protein profiles were involved in platelet activation, aggregation, and degranulation. For example, protein disulfide isomerase family members, enzymes that promote thrombosis, were upregulated in platelets and plasma of LA+ TE+ patients. Leukocyte elastase inhibitor (SERPINB1), an antagonist of neutrophil extracellular trap (NET) formation, was decreased in platelets of LA+ TE+ patients compared to healthy controls. Additionally, citrullinated histone H3, a NET-specific marker, was increased in plasma of LA+ TE+ patients. These findings suggest that decreased platelet SERPINB1 levels favor prothrombotic NETosis, especially in LA+ TE+ patients. Our findings reveal protein abundance changes connected to altered platelet function in LA-positive patients, thus suggesting a pathogenic role of platelets in thrombotic complications in APS.

Saint John on Patmos: Revelations of the Role of Antineutrophil Cytoplasmic Antibody (ANCA) in Vasculitis

Diagnosis of vasculitis is based on the presence of histologic features and serological testing for antineutrophil cytoplasmic antibodies (ANCA). In patients with vasculitis, two types of ANCA have been identified: ANCA directed against the neutrophil serine protease proteinase-3 (PR3) which results in a cytoplasmic immunofluorescence pattern (c-ANCA) and ANCA directed against the neutrophil enzyme myeloperoxidase (MPO), which results in a perinuclear immunofluorescence pattern (p-ANCA). Question is if the presence of ANCA is the consequence of abnormal neutrophil adhesion, activation, and apoptosis. Or is it, through mechanisms which are not totally clear for the moment, the cause of vasculitis. In the latter case it has to be postulated that ANCA autoantigens are expressed on the cell surface of viable, or activated, or early-apoptotic neutrophils.

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

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

Inhibitors of Serine Proteases in Regulating the Production and Function of Neutrophil Extracellular Traps

Neutrophil extracellular traps (NETs), DNA webs released into the extracellular environment by activated neutrophils, are thought to play a key role in the entrapment and eradication of microbes. However, NETs are highly cytotoxic and a likely source of autoantigens, suggesting that NET release is tightly regulated. NET formation involves the activity of neutrophil elastase (NE), which cleaves histones, leading to chromatin decondensation. We and others have recently demonstrated that inhibitors of NE, such as secretory leukocyte protease inhibitor (SLPI) and SerpinB1, restrict NET production in vitro and in vivo. SLPI was also identified as a NET component in the lesional skin of patients suffering from the autoinflammatory skin disease psoriasis. SLPI-competent NET-like structures (a mixture of SLPI with neutrophil DNA and NE) stimulated the synthesis of interferon type I (IFNI) in plasmacytoid dendritic cells (pDCs) in vitro. pDCs uniquely respond to viral or microbial DNA/RNA but also to nucleic acids of “self” origin with the production of IFNI. Although IFNIs are critical in activating the antiviral/antimicrobial functions of many cells, IFNIs also play a role in inducing autoimmunity. Thus, NETs decorated by SLPI may regulate skin immunity through enhancing IFNI production in pDCs. Here, we review key aspects of how SLPI and SerpinB1 can control NET production and immunogenic function.

Regulation of Neutrophil Serine Proteases by Intracellular Serpins

Neutrophil granules contain serine proteases that are central components of the antimicrobial weapons of the innate immune system. Neutrophil proteases also contribute to the amplification and resolution of inflammatory responses through defined proteolytic cleavage of mediators, cell surface receptors, and extracellular matrix proteins. In the blood and at mucosal surfaces, neutrophil serine proteases are regulated by serpins found in plasma and by non-serpin secreted inhibitors. Distinct mechanisms leading to neutrophil cell death have been described for the granule serine proteases, neutrophil elastase, cathepsin G, and proteinase-3. Granule leakage in neutrophils triggers death pathways mediated by cathepsin G and proteinase-3, and both proteases are tightly regulated by their inhibitor SERPINB1 in a cell intrinsic manner. Although stored in the same types of granules, neutrophil elastase does not significantly contribute to cell death following intracellular release from granules into the cytoplasm. However, heterozygous mutations in ELANE, the gene encoding elastase, are the cause of severe congenital neutropenia, a life-threatening condition characterized by the death of neutrophils at an early precursor stage in the bone marrow. This chapter focuses on recent work exploring the biology of clade B intracellular serpins that inhibit neutrophil serine proteases and their functions in neutrophil homeostasis and serine protease control at sites of inflammation.

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

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

Neutrophil-derived Oxidants and Proteinases as Immunomodulatory Mediators in Inflammation

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

Secretory leukocyte proteinase inhibitor-competent DNA deposits are potent stimulators of plasmacytoid dendritic cells: implication for psoriasis

Secretory leukocyte proteinase inhibitor (SLPI) is a well-established inhibitor of serine proteases such as human neutrophil elastase (HNE) and a NF-κB regulatory agent in immune cells. In this paper, we report that SLPI plays a previously uncharacterized role in regulating activation of plasmacytoid dendritic cells (pDCs). As the main source of IFN type I (IFNI), pDCs are crucial contributors to inflammatory and likely wound-healing responses associated with psoriasis. The mechanisms responsible for activation of pDCs in psoriatic skin are therefore of substantial interest. We demonstrate that in lesional skin of psoriasis patients, SLPI together with its enzymatic target HNE and DNA, is a component of neutrophil extracellular traps (NETs). Whereas SLPI(+) neutrophils and NETs were found to colocalize with pDCs in psoriatic skin, a mixture of SLPI with neutrophil DNA and HNE induced a marked production of IFNI by pDCs. IFNI synthesis by stimulated pDCs was dependent on intracellular DNA receptor TLR9. Thus, SLPI may contribute to psoriasis by enabling pDCs to sense extracellular DNA and produce IFNI.

Serpin B1 protects colonic epithelial cell via blockage of neutrophil elastase activity and its expression is enhanced in patients with ulcerative colitis

Serpin B1 is a monocyte neutrophil elastase (NE) inhibitor and is one of the most efficient inhibitors of NE. In the present study, we investigated the role of serpin B1 in the pathogenesis of ulcerative colitis by using clinical samples and an experimental model. The colonic expression of serpin B1 was determined by real-time polymerase chain reaction (PCR), Western blot analysis, and immunohistological studies in both normal and inflamed mucosa from patients with ulcerative colitis. Serpin B1 mRNA expression was determined by real-time PCR in the mouse dextran sodium sulfate (DSS)-induced colitis model. Young adult mouse colonic epithelial (YAMC) cells were used to determine the role of serpin B1. Serpin B1 gene transfected YAMC cells were treated with H(2)O(2) to measure cell viability. The expression of NE was determined in YAMC cells treated with H(2)O(2). NE-silenced YAMC cells were also treated with H(2)O(2) and then measured for viability. Upregulated expression of serpin B1 in colonic mucosa was confirmed from patients with active ulcerative colitis. Immunohistochemical studies showed that serpin B1 expression was localized not only in inflammatory infiltration cells but also in epithelial cells. Serpin B1 mRNA expression was also increased in colonic mucosa of mouse DSS-induced colitis. Serpin B1-transfected YAMC cells were resistant against the treatment of H(2)O(2). H(2)O(2) treatment significantly induced NE in YAMC cells, and NE-silenced YAMC cells were also resistant against the treatment of H(2)O(2). These results suggest that serpin B1 may be a novel marker of active ulcerative colitis and may play an important role in the pathogenesis of inflammatory bowel disease.

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.

SerpinB1 protects the mature neutrophil reserve in the bone marrow

SerpinB1 is among the most efficient inhibitors of neutrophil serine proteases--NE, CG, and PR-3--and we investigated here its role in neutrophil development and homeostasis. We found that serpinB1 is expressed in all human bone marrow leukocytes, including stem and progenitor cells. Expression levels were highest in the neutrophil lineage and peaked at the promyelocyte stage, coincident with the production and packaging of the target proteases. Neutrophil numbers were decreased substantially in the bone marrow of serpinB1(-/-) mice. This cellular deficit was associated with an increase in serum G-CSF levels. On induction of acute pulmonary injury, neutrophils were recruited to the lungs, causing the bone marrow reserve pool to be completely exhausted in serpinB1(-/-) mice. Numbers of myeloid progenitors were normal in serpinB1(-/-) bone marrow, coincident with the absence of target protease expression at these developmental stages. Maturation arrest of serpinB1(-/-) neutrophils was excluded by the normal CFU-G growth in vitro and the normal expression in mature neutrophils of early and late differentiation markers. Normal absolute numbers of proliferating neutrophils and pulse-chase kinetic studies in vivo showed that the bone marrow deficit in serpinB1(-/-) mice was largely restricted to mature, postmitotic neutrophils. Finally, upon overnight culture, apoptosis and necrosis were greater in purified bone marrow neutrophils from serpinB1(-/-) compared with WT mice. Collectively, these findings demonstrate that serpinB1 sustains a healthy neutrophil reserve that is required in acute immune responses.

Characterization of proteins associating with 5' terminus of PGHS-1 mRNA

Induction of Prostaglandin Endoperoxide H Synthase-1 (PGHS-1) gene has been previously documented in a few studies during events such as development and cellular differentiation. However, molecular mechanisms governing the regulation of PGHS-1 gene expression and contributing to changes in protein levels are poorly understood. Using the MEG-01 cell model of PGHS-1 gene induction, our laboratory has previously demonstrated that the 5’UTR and the first two exons of PGHS-1 mRNA had a significant impact on decreasing the translational efficiency of a reporter gene and suggested that the presence of a secondary structure is required for conservation of this activity. This 5’end of PGHS-1 mRNA sequence has also been shown to associate with nucleolin protein. In the current study, we set to investigate the protein composition of the mRNP (messenger ribonucleoprotein) associating with the 5’end of PGHS-1 mRNA and to identify its protein members. RNA/protein binding assays coupled with LC-MS analysis identified serpin B1 and NF45 (nuclear factor 45) proteins as potential members of PGHS-1 mRNP complex. Immunoprecipitation experiments using MEG-01 protein extracts validated mass spectrometry data and confirmed binding of nucleolin, serpin B1, NF45 and NF90. The RNA fraction was extracted from immunoprecipitated mRNP complexes and association of RNA binding proteins, serpin B1, NF45 and NF90, to PGHS-1 mRNA target sequence was confirmed by RT-PCR. Together these data suggest that serpin B1, NF45 and NF90 associate with PGHS-1 mRNA and can potentially participate in the formation a single or a number of PGHS-1 ribonucleoprotein complexes, through nucleolin that possibly serves as a docking base for other protein complex members.

A 2D-DIGE approach to identify proteins involved in inside-out control of integrins

Leukocyte integrins are functionally regulated by "inside-out" signaling, meaning that stimulus-induced signaling pathways act on the intracellular integrin tail and induce activation of the receptor at the outside. Both a change in conformation (affinity) and in clustering (avidity/valency) of the receptors has been described to occur. This inside-out signaling is essential for adequate migration of leukocytes to inflammatory sites; however, the exact underlying mechanism is not known. We used two variants of a mouse acute lymphocytic leukemia cell line (L1210), a suspension (L1210-S) and an adherent (L1210-A) variant that were characterized by nonactivated and activated integrins (beta(1), beta(2) and beta(3)), respectively. L1210-S and L1210-A cells were compared on protein expression profiles by two-dimensional fluorescence difference in-gel electrophoresis (2D-DIGE). We found 86 protein spots that were more than 1.25-fold different between L1210-A and L1210-S. Only 4 protein spots were more than 2.5-fold different. We identified 29 proteins by mass spectrometry among which were gelsolin, L-plastin, and Rho GTPase dissociation inhibitor 2. These proteins were upregulated in the L1210-A cells versus L1210-S, which was verified by Western blot analysis. Overexpression of gelsolin in U937 resulted in increased high affinity integrin expression and cell adhesion. Comparison of functionally different cell lines from similar origin by 2D-DIGE might be a successful approach to identify regulatory proteins involved in integrin inside-out control.

Biochemical properties of an intracellular serpin from Echinococcus multilocularis

A serpin of the intracellular type from the tapeworm Echinococcus multilocularis was expressed in Escherichia coli, purified by ion exchange chromatography and tested for inhibitory activity against several proteinases. The recombinant protein, which after transcriptional induction, represents about 20 % of total cellular protein, is biochemically active and inhibits trypsin and the trypsin-like plasmin as well as pig pancreatic and human neutrophil elastase. Implications regarding its biochemistry and biological function are discussed.

Correlation of serpin–protease expression by comparative analysis of real-time PCR profiling data

Imbalanced protease activity has long been recognized in the progression of disease states such as cancer and inflammation. Serpins, the largest family of endogenous protease inhibitors, target a wide variety of serine and cysteine proteases and play a role in a number of physiological and pathological states. The expression profiles of 20 serpins and 105 serine and cysteine proteases were determined across a panel of normal and diseased human tissues. In general, expression of serpins was highly restricted in both normal and diseased tissues, suggesting defined physiological roles for these protease inhibitors. A high correlation in expression for a particular serpin-protease pair in healthy tissues was often predictive of a biological interaction. The most striking finding was the dramatic change observed in the regulation of expression between proteases and their cognate inhibitors in diseased tissues. The loss of regulated serpin-protease matched expression may underlie the imbalanced protease activity observed in pathological states.

SERPINB1 upregulation is associated with in vivo complex formation with neutrophil elastase and cathepsin G in a baboon model of bronchopulmonary dysplasia

Bronchopulmonary dysplasia (BPD) continues to be a major cause of morbidity in premature infants. An imbalance between neutrophil elastase and its inhibitors has been implicated in BPD. Serine protease inhibitor (SERPIN)B1 is an inhibitor of neutrophil proteases, including neutrophil elastase (NE) and cathepsin G (cat G). Recent studies suggest that SERPINB1 could provide protection in the airways by regulating excess protease activity associated with inflammatory lung disorders. In this study, we determined the distribution and ontogeny of SERPINB1 in the baboon lung and characterized the expression of SERPINB1 in baboon models of BPD. SERPINB1 expression was detected in the conducting airway and glandular epithelial cells in addition to neutrophils, macrophages, and mast cells. SERPINB1 mRNA and protein expression increased with advancing gestational age and in the new BPD model. In contrast, SERPINB1 expression levels were decreased in the old BPD model. Furthermore, SERPINB1 was detected as a high-molecular-mass (HMM) complex in lung tissue and bronchoalveolar lavage fluid samples from the BPD group. Analysis of the HMM complex by coimmunoprecipitation showed that these complexes were formed between SERPINB1 and NE or cat G. High-performance liquid chromatography (HPLC) ion trap mass spectrometry verified the presence of SERPINB1 in HMM complexes. Finally, NE activity level was compared between new and old baboon models of BPD and was found to be significantly lower in new BPD. Thus SERPINB1 upregulation in new BPD may be protective by contributing to the regulation of neutrophil proteases NE and cat G.

Subcellular proteomic analysis of host-pathogen interactions using human monocytes exposed toYersinia pestis andYersinia pseudotuberculosis

Yersinia pestis, the etiological agent of plague, is of concern to human health both from an infectious disease and a biodefense perspective. While Y. pestis and Yersinia pseudotuberculosis share more than 90% DNA homology, they have significantly different clinical manifestations. Plague is often fatal if untreated, yet Y. pseudotuberculosis causes severe intestinal distress but is rarely fatal. A better understanding of host response to these closely related pathogens may help explain the different mechanisms of virulence and pathogenesis that result in such different clinical outcomes. The aim of this study was to characterize host protein expression changes in human monocyte U937 cells after exposure to Y. pestis and Y. pseudotuberculosis. In order to gain global proteomic coverage of host response, proteins from cytoplasmic, nuclear and membrane fractions of host cells were studied by two-dimensional differential gel electrophoresis and relative protein expression differences were quantitated. Differentially expressed proteins, with at least 1.5-fold expression changes and p values of 0.01 or less, were identified by mass spectrometry including matrix-assisted laser desorption/ionization-MS or liquid chromatography tandem mass spectrometry. With these criteria, differential expression was detected in 16 human proteins after Y. pestis exposure and 13 human proteins after Y. pseudotuberculosis exposure, of which only two of the differentially expressed proteins identified were shared between the two exposures. Proteins identified in this study are reported to be involved in a wide spectrum of cellular functions and host defense mechanisms including apoptosis, cytoskeletal rearrangement, protein synthesis and degradation, DNA replication and transcription, metabolism, protein folding, and cell signaling. Notably, the differential expression patterns observed can distinguish the two pathogen exposures from each other and from unexposed host cells. The functions of the differentially expressed proteins identified provide insight on the different virulence and pathogenic mechanisms of Y. pestis and Y. pseudotuberculosis.

Inhibition of proteinase 3 by [alpha]1-antitrypsin in vitro predicts very fast inhibition in vivo

Neutrophil proteinase 3 (Pr3) cleaves elastin and other matrix proteins, and is thought to cause lung tissue destruction in emphysema and cystic fibrosis. Its deleterious action is theoretically prevented by alpha1-antitrypsin, a serpin present in lung secretions. We have evaluated the anti-Pr3 activity of this inhibitor to decide whether it may play a physiologic proteolysis-preventing function in vivo. We show that (i). the oxidized inhibitor does not inhibit Pr3; (ii). the inhibitor competes favorably with elastin for the binding of Pr3, but is less efficient for inhibiting elastin-bound proteinase than for complexing free enzyme; and (iii). the inhibition takes place in at least two steps: the enzyme and the inhibitor first form a high-affinity reversible inhibitory complex EI* with an equilibrium dissociation constant K*i of 38 nM; EI* subsequently transforms into an irreversible complex EI with a first-order rate constant k2 of 0.04 s-1. Because the alpha1-antitrypsin concentration in the epithelial lining fluid is much higher than K*i, any Pr3 molecule released from neutrophils will be taken up as an EI* complex within much less than 1 s, indicating very efficient inhibition in vivo.

Proteinases and their inhibitors in the immune system

The most important roles of proteinases in the immune system are found in apoptosis and major histocompatibility complex (MHC) class II-mediated antigen presentation. A variety of cysteine proteinases, serine proteinases, and aspartic proteinases as well as their inhibitors are involved in the regulation of apoptosis in neutrophils, monocytes, and dendritic cells, in selection of specific B and T lymphocytes, and in killing of target cells by cytotoxic T cells and natural killer cells. In antigen presentation, endocytosed antigens are digested into antigenic peptides by both aspartic and cysteine proteinases. In parallel, MHC class II molecules are processed by aspartic and cysteine proteinases to degrade the invariant chain that occupies the peptide-binding site. Proteinase activity in these processes is highly regulated, particularly by posttranslational activation and the balance between active proteinases and specific endogenous inhibitors such as cystatins, thyropins, and serpins. This article discusses the regulation of proteolytic processes in apoptosis and antigen presentation in immune cells and the consequences of therapeutic interference in the balance of proteinases and their inhibitors.

Murine serpin 2A is a redox-sensitive intracellular protein

Murine serpin 2A is expressed at high levels in haemopoietic progenitors and down-regulated on differentiation. When it is constitutively expressed in the multipotent haemopoietic cell line, FDCP-Mix, it causes a delay in differentiation and increased clonogenic potential. The serpin is also dramatically up-regulated on T-cell activation. It has an unusual reactive site Cys-Cys sequence, a unique C-terminal extension and lacks a typical cleavable N-terminal signal sequence. In spite of these features, the protein is not a member of the ovalbumin-serpin family, but is instead most closely related to human antichymotrypsin. We have shown that the serpin is intracellular with prominent nuclear localization. Transverse urea gradient gels and CD studies show that the protein undergoes the stressed-relaxed conformational change typical of inhibitory serpins. However, we have not detected complex-forming activity with a set of proteases. Thermal denaturation studies also show that the protein has decreased structural stability under reducing conditions, although it lacks disulphide bonds within the core of the molecule. Our results show that serpin 2A is an intracellular protein with the potential to mediate its biological effects via interaction with non-protease intracellular targets. Furthermore, the results presented suggest a model whereby the serpin interactions could be modulated by redox conditions or conformational change induced by cleavage of the reactive-site loop.

Characterization of four murine homologs of the human ov-serpin monocyte neutrophil elastase inhibitor MNEI (SERPINB1)

The human ov-serpin monocyte neutrophil elastase inhibitor (MNEI) is encoded by a single gene SERPINB1. It is a highly efficient inhibitor of neutrophil granule proteases. Four murine genes with high sequence identity with MNEI were identified and fully sequenced, and these were named EIA, EIB, EIC, and EID. EIA, EIB and EIC showed the same seven-exon gene structure as SERPINB1. However, EIC included an additional, alternatively spliced, exon due to the insertion of an endogenous retrovirus-like sequence. EID lacked several exons and is a pseudogene. Reverse transcriptase-PCR showed that EIA, like MNEI, is expressed at high levels in many tissues. EIB is mainly expressed in brain, and EIC was only expressed as splicing variants unlikely to encode a functional serpin. Upon incubation with serine proteases, EIA formed inhibitory covalent complexes with pancreatic and neutrophil elastases, cathepsin G, proteinase-3, and chymotrypsin, as previously shown for MNEI, whereas EIB was only able to do so with cathepsin G. According to the new serpin nomenclature, the genes encoding EIA, EIB, EIC, and EID will be called Serpinb1, Serpinb1b, Serpinb1c, and Serpinb1-ps1. These data demonstrate that the four murine homologs of MNEI have met different evolutionary fates, and that EIA is the mouse ortholog of MNEI.

Characterization of a novel salivary immunosuppressive protein from Ixodes ricinus ticks

In tick salivary glands, several genes are induced during the feeding process, leading to the expression of new proteins. These proteins are typically secreted in tick saliva and are potentially involved in the modulation of the host immune and hemostatic responses. In a previous study, the construction and the analysis of a subtractive library led to the identification of Ixodes ricinus immunosuppressor (Iris), a novel protein, differentially expressed in I. ricinus salivary glands during the blood meal. In the present study, the data strongly suggest that this protein is secreted by tick salivary glands into the saliva. In addition, Iris is also found to modulate T lymphocyte and macrophage responsiveness by inducing a Th2 type response and by inhibiting the production of pro-inflammatory cytokines. In conclusion, these results suggest that Iris is an immunosuppressor, which might play an important role in the modulation of host immune response.

The serpin MNEI inhibits elastase-like and chymotrypsin-like serine proteases through efficient reactions at two active sites

MNEI (monocyte/neutrophil elastase inhibitor) is a 42 kDa serpin superfamily protein characterized initially as a fast-acting inhibitor of neutrophil elastase. Here we show that MNEI has a broader specificity, efficiently inhibiting proteases with elastase- and chymotrypsin-like specificities. Reaction of MNEI with neutrophil proteinase-3, an elastase-like protease, and porcine pancreatic elastase demonstrated rapid inhibition rate constants >10(7) M(-1) s(-1), similar to that observed for neutrophil elastase. Reactions of MNEI with chymotrypsin-like proteases were also rapid: cathepsin G from neutrophils (>10(6) M(-1) s(-1)), mast cell chymase (>10(5) M(-1) s(-1)), chymotrypsin (>10(6) M(-1) s(-1)), and prostate-specific antigen (PSA), which had the slowest rate constant at approximately 10(4) M(-1) s(-1). Inhibition of trypsin-like (plasmin, granzyme A, and thrombin) and caspase-like (granzyme B) serine proteases was not observed or highly inefficient (trypsin), nor was inhibition of proteases from the cysteine (caspase-1 and caspase-3) and metalloprotease (macrophage elastase, MMP-12) families. The stoichiometry of inhibition for all inhibitory reactions was near 1, and inhibitory complexes were resistant to dissociation by SDS, further indicating the specificity of MNEI for elastase- and chymotrypsin-like proteases. Determination of the reactive site of MNEI by N-terminal sequencing and mass analysis of reaction products identified two reactive sites, each with a different specificity. Cys(344), which corresponds to Met(358), the P(1) site of alpha1-antitrypsin, was the inhibitory site for elastase-like proteases and PSA, while the preceding residue, Phe(343), was the inhibitory site for chymotrypsin-like proteases. This study demonstrates that MNEI has two functional reactive sites corresponding to the predicted P(1) and P(2) positions of the reactive center loop. The data suggest that MNEI plays a regulatory role at extravascular sites to limit inflammatory damage due to proteases of cellular origin.

Evolving concepts in the pathogenesis of chronic obstructive pulmonary disease

It is arguable that more biologic insight has been gained from the study of COPD than from any other pulmonary disorder. A vast knowledge of the biology of extracellular matrix proteins, proteinases, and proteinase inhibitors has largely stemmed from the elastase:anti-elastase hypothesis for the pathogenesis of emphysema. An equally compelling case could be made that interest in, and funding for, COPD research has been woeful, and investigators have made no significant medical breakthroughs in the treatment of this disorder, which, unfortunately, is becoming epidemic worldwide. Indeed, it cannot be argued that physicians have very little treatment to offer to the many patients with COPD. Humankind is rapidly approaching a time when all human genes will be sequenced, and genetic engineering will allow determination of the function of these proteins in vivo. Expression profiling and bioinformatics will allow clinicians to assess the spectrum of genes and proteins regulated in biologic processes, no longer limiting study to naïve candidate genes. These advances will allow investigators to decipher precise pathways of complex diseases, identify genetic and environmental interactions, and ultimately lead to specific (pre)diagnoses and rational treatment. Answers to the question as to why only a subset of smokers develop COPD will enhance the understanding of the disease process. Fortunately, there has been a resurgence of interest in COPD, led largely by the pharmaceutical industry, which has discovered the potential of this unmet need. Consequently, these state-of-the-art scientific techniques are being directly applied to COPD, lending hope for the future. Of even greater importance, the tide seems to be turning on the cigarette industry. Although difficult to imagine, perhaps cigarettes will disappear in this lifetime or at least the next generation won't be fooled by this deadly habit! Well ... the rational therapy thing could work.

Human monocyte/neutrophil elastase inhibitor (MNEI) is regulated by PU.1/Spi-1, Sp1, and NF-kappaB

Human monocyte/neutrophil elastase inhibitor (MNEI) is a specific inhibitor of the neutrophil azurophil granule proteases including elastase. To understand the physiological mechanisms that regulate expression of MNEI, we dissected a 1.0 kb region upstream of exon 1. On transient transfection, promoter activity of MNEI-luciferase constructs was highest in U937 myeloid cells, followed by K562 hematopoietic cells, followed by HeLa cervical carcinoma cells, indicating that the MNEI promoter is most active in myeloid cells and is also active in non-myeloid cells. Three transcription factor binding elements, which confer the majority of activity, are located within the first 180 base pairs of the promoter, one of which, located at -128, was active in U937 and K562 cells but inactive in non-myeloid HeLa cells. The three proximal elements were identified by transient transfection, mutation, gel shift and competition assays as Sp1 at -170, PU.1/Spi-1 at -128, and Sp1 at -66. The trans-acting factors that bind and control these elements were detected, and their identity confirmed by antibody supershift assays. Further upstream at -821, an additional regulatory element was identified controlled by NF-kappaB, which supports the highest levels of MNEI transcriptional activity. In U937 cells, reporter gene expression by the MNEI-luciferase construct that included the NF-kappaB element was two- to three-fold greater than the construct without the element. In addition, treatment of myeloid cells with lipopolysaccharide, a complex glycolipid of gram-negative bacteria, activated NF-kappaB to bind the -821 element, together suggesting that enhancement of expression of the anti-inflammatory MNEI gene is linked to innate immune responses to bacterial infection.

Nuclear translocation of a leukocyte elastase Inhibitor/Elastase complex during staurosporine-induced apoptosis: role in the generation of nuclear L-DNase II activity

Using L1210 murine leukemia cells, we have previously shown that in response to treatment with drugs having different targets, apoptotic cell death occurs through at least two different signaling pathways. Here, we present evidence that nuclear extracts from staurosporine-treated cells elicit DNase II activity that is not detected in nuclear extracts from cisplatin-treated cells. This activity correlates with the accumulation of two nuclear proteins (70 and 30 kDa) which are detected by an anti-L-DNase II antibody. Partial purification of this DNase II activity suggests that the 30-kDa protein could be the nuclease responsible for staurosporine-induced DNA fragmentation. The 70-kDa protein is also recognized by an anti-elastase antibody, suggesting that it carries residues belonging to both L-DNase II and elastase. Since previous findings showed that L-DNase II was generated from the leukocyte inhibitor of elastase, we propose that the 70-kDa protein results from an SDS-stable association between these two proteins and is translocated from the cytoplasm to the nucleus during staurosporine-induced apoptosis.

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.

Modulation of elastase binding to elastin by human alveolar macrophage-derived lipids

Human neutrophil elastase (HNE), an enzyme secreted by activated neutrophils, can bind to and degrade extracellular matrix including human lung elastin. This protease is believed to play an important role in several destructive processes including pulmonary emphysema. In this study, we hypothesized that an alveolar macrophage (AM) product or products may interact with neutrophil elastase (NE) and modulate its binding to elastin. Elastase binding to elastase was evaluated by a modified elastase functional assay using a synthetic substrate. Supernatants from cultured AM inhibited elastase binding to elastin at a dose-dependent manner without inhibiting functional elastase activity. The AM products had a heterogeneous molecular weight ranging from 440,000 to 54,000. The activity was heat-stable, but was lost after ultracentrifugation. After lipid fractionation, neither the aqueous nor the lipid fractions contained activity, suggesting that the factor may be a lipid complex. Culture supernatants from smokers' AM released significantly higher amounts of the factor than nonsmokers. In addition, high-molecular-weight elastase was present in bronchoalveolar lavage fluid (BALF) obtained from patients with pneumonia. Most of the in vivo high-molecular-weight elastase was lost after lipid extraction. In conclusion, macrophages release a factor or factors, probably lipid, which can interact with NE and inhibit its binding to human lung elastin without inhibiting elastase activity. This macrophage-derived factor may play a role in protecting the lung from NE by partitioning elastase into the airspace and thus protecting the interstitial connective tissue matrix from elastase degradation.

The Intracellular Serpin Proteinase Inhibitor 6 Is Expressed in Monocytes and Granulocytes and Is a Potent Inhibitor of the Azurophilic Granule Protease, Cathepsin G

The monocyte and granulocyte azurophilic granule proteinases elastase, proteinase 3, and cathepsin G are implicated in acute and chronic diseases thought to result from an imbalance between the secreted proteinase(s) and circulating serpins such as 1-proteinase inhibitor and 1-antichymotrypsin. We show here that the intracellular serpin, proteinase inhibitor 6 (PI-6), is present in monocytes, granulocytes, and myelomonocytic cell lines. In extracts from these cells, PI-6 bound an endogenous membrane-associated serine proteinase to form an sodium dodecyl sulfate (SDS)-stable complex. Using antibodies to urokinase, elastase, proteinase 3, or cathepsin G, we demonstrated that the complex contains cathepsin G. Native cathepsin G and recombinant PI-6 formed an SDS-stable complex in vitro similar in size to that observed in the extracts. Further kinetic analysis demonstrated that cathepsin G and PI-6 rapidly form a tight 1:1 complex (ka = 6.8 ± 0.2 × 106mol/L−1s−1 at 17°C;Ki = 9.2 ± 0.04 × 10−10 mol/L). We propose that PI-6 complements 1-proteinase inhibitor and 1-antichymotrypsin (which control extracellular proteolysis) by neutralizing cathepsin G that leaks into the cytoplasm of monocytes or granulocytes during biosynthesis or phagocytosis. Control of intracellular cathepsin G may be particularly important, because it has recently been shown to activate the proapoptotic proteinase, caspase-7.

Localization and characterization of antithrombin in human kidneys

Antithrombin is a serine protease inhibitor that is critical in maintaining a thromboresistant vasculature. The association between low serum antithrombin concentration and renal disease suggests that the kidney plays a role in the conservation of plasma antithrombin. We used immunohistochemical techniques to determine the spatial distribution, heparin binding characteristics, and intracellular and intercellular localization of antithrombin in biopsy specimens (n = 53) of human donor kidneys obtained at the time of transplantation. In the renal cortex, double antibody techniques demonstrated the presence of intracellular antithrombin in proximal tubule epithelial cells. The reactivity was granular and was co-localized with vesicle-like structures. Distal and collecting tubules did not demonstrate intraepithelial antithrombin reactivity. No tubule structures in the medullary region demonstrated intracellular antithrombin, but all these structures showed intense basement membrane antithrombin reactivity. Double antibody techniques also demonstrated that the heparin binding domain of intraepithelial antithrombin was occupied. Semiquantitative scores for intraepithelial antithrombin were significantly decreased in renal biopsy specimens obtained 30 min after anastomosis compared with biopsies from the same organ obtained before anastomosis. These findings suggest that antithrombin, probably in association with heparin or heparan sulfate, is internalized by renal proximal epithelial cells. Although the ultimate fate of intraepithelial antithrombin is not known, this may represent a mechanism by which the kidney helps to maintain plasma antithrombin concentrations.

Regulation of pro-apoptotic leucocyte granule serine proteinases by intracellular serpins

Caspase activation and apoptosis can be initiated by the introduction of serine proteinases into the cytoplasm of a cell. Cytotoxic lymphocytes have evolved at least one serine proteinase with specific pro-apoptotic activity (granzyme B), as well as the mechanisms to deliver it into a target cell, and recent evidence suggests that other leucocyte granule proteinases may also have the capacity to kill if released into the interior of cells. For example, the monocyte/granulocyte proteinase cathepsin G can activate caspases in vitro, and will induce apoptosis if its entry into cells is mediated by a bacterial pore-forming protein. The potent pro-apoptotic activity of granzyme B and cathepsin G suggests that cells producing these (or other) proteinases would be at risk from self-induced death if the systems involved in packaging, degranulation or targeting fail and allow proteinases to enter the host cell cytoplasm. The purpose of the present review is to describe recent work on a group of intracellular serine proteinase inhibitors (serpins) which may function in leucocytes to prevent autolysis induced by the granule serine proteinases.

Recombinant human Monocyte/Neutrophil elastase inhibitor protects rat lungs against injury from cystic fibrosis airway secretions

Human monocyte/neutrophil elastase inhibitor (M/NEI) is a fast-acting stoichiometric inhibitor of neutrophil elastase (NE), cathepsin-G, and proteinase-3. Recombinant M/NEI (rM/NEI) was evaluated with a rat model of NE-induced lung damage. rM/NEI was found to protect against pulmonary injury caused by instilled human NE or by a preparation from airway secretions (sputum) of cystic fibrosis patients (CF sol). Human NE instilled into rat lungs produced dose-dependent hemorrhage and increased epithelial permeability, whereas NE incubated in vitro with rM/NEI did neither. Similarly, hemorrhage was induced by CF sol, but not by CF sol incubated in vitro with rM/NEI. To examine its distribution and survival time in airways, rM/NEI was labeled with the fluorochrome Texas Red (rM/NEI-TR) and instilled into rat lungs. Confocal microscopy showed that rM/NEI-TR could be detected on large airways (300 microm) at 5 min, 1 h, 4 h, and 24 h after instillation. Pretreating rats with rM/NEI was found to provide extended protection upon subsequent NE challenge, reducing hemorrhage by 98, 96, and 73%, respectively, at 1, 4, and 24 h after rM/NEI pretreatment. Pretreating rats with rM/NEI similarly conferred protection against subsequent exposure to CF sol, reducing hemorrhage by 95, 86, and 87%, respectively, at 1, 4, and 24 h after pretreatment. The findings that rM/NEI (1) mitigates protease-induced lung injury and (2) remains present and active in the lungs for 24 h after instillation strongly support its potential for treating patients with neutrophil protease-induced inflammatory lung damage, such as occurs in CF and other diseases.

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.

The proteinase-antiproteinase theory of emphysema: a speculative analysis of recent advances into the pathogenesis of emphysema

This review concerns the reasons why only an estimated 10-15% of patients with alpha-1-antitrypsin (A1AT) deficiency develop the destructive lung disease known as emphysema. The arguments presented revolve around the proteinase-antiproteinase balance in the 'microenvironment' of the epithelial space of the lung. Attention is focused on the balance between destructive enzymes such as neutrophil elastase and protective proteins such as A1AT, secretory leucocyte proteinase inhibitor (SLPI), human elastase inhibitor (HEI) and elafin. When neutrophil elastase is already attached to the elastin fibres the smaller molecules SLPI and elafin appear to be better inhibitors of this enzyme than larger inhibitors such as A1AT and HEI. Furthermore, SLPI and elafin may provide the first line of defence against proteinase attack from neutrophil elastase. In trying to explain the variability in the clinical expression of A1AT-deficiency and the development of emphysema, the importance of changes to A1AT, SLPI and elafin molecules induced by smoking and/or oxygen free radicals has been considered. It is possible that emphysema only develops in patients who have SLPI/elafin deficiency as well as A1AT deficiency.

A serpin from human tumor cells with direct lymphoid immunomodulatory activity: mitogenic stimulation of human tumor-infiltrating lymphocytes

A serum-free supernatant from an epidermal carcinoma cell line has previously been shown to contain mitogenic activity for human tumor infiltrating lymphocytes in culture [1]. From this conditioned medium we have now purified to homogeneity, as determined by SDS-PAGE analysis, a ca. 45 kDa protein which stimulates [3H]thymidine incorporation into the DNA of these human T-lymphocytes. Amino acid composition data and immunoreactivity of the purified protein as well as sequence analyses of 7 tryptic fragments obtained therefrom suggest a strong similarity with human monocyte/neutrophil elastase inhibitor, which is a member of the serine protease inhibitor (serpin) superfamily. We have previously identified and purified from the same conditioned medium a 36 kDa protein with myeloid immunomodulatory activity [2]. Taken together, these two reports support the role of tumor-derived soluble factors in tumor immunosurveillance.

A qualitative and quantitative protein database approach identifies individual and groups of functionally related proteins that are differentially regulated in simian virus 40 (SV40) transformed human keratinocytes: an overview of the functional changes associated with the transformed phenotype

A qualitative and quantitative two-dimensional (2-D) gel database approach has been used to identify individual and groups of proteins that are differentially regulated in simian virus 40 (SV40) transformed human keratinocytes (K14). Five hundred and sixty [35S]methionine-labeled proteins (462 isoelectric focusing, IEF; 98 nonequilibrium pH gradient electrophoresis, NEPHGE), out of the 3038 recorded in the master keratinocyte database, were excised from dry, silver-stained gels of normal proliferating primary keratinocytes and K14 cells and the radioactivity was determined by liquid scintillation counting. Two hundred and thirty five proteins were found to be either up- (177) or down-regulated (58) in the transformed cells by 50% or more, and of these, 115 corresponded to known proteins in the keratinocyte database (J.E. Celis et al., Electrophoresis 1993, 14, 1091-1198). The lowest abundance acidic protein quantitated was present in about 60,000 molecules per cell, assuming a value of 10(8) molecules per cell for total actin. The results identified individual, and groups of functionally related proteins that are differentially regulated in K14 keratinocytes and that play a role in a variety of cellular activities that include general metabolism, the cytoskeleton, DNA replication and cell proliferation, transcription and translation, protein folding, assembly, repair and turnover, membrane traffic, signal transduction, and differentiation. In addition, the results revealed several transformation sensitive proteins of unknown identity in the database as well as known proteins of yet undefined functions. Within the latter group, members of the S100 protein family--whose genes are clustered on human chromosome 1q21--were among the highest down-regulated proteins in K14 keratinocytes. Visual inspection of films exposed for different periods of time revealed only one new protein in the transformed K14 keratinocytes and this corresponded to keratin 18, a cytokeratin expressed mainly by simple epithelia. Besides providing with the first global overview of the functional changes associated with the transformed phenotype of human keratinocytes, the data strengthened previous evidence indicating that transformation results in the abnormal expression of normal genes rather than in the expression of new ones.

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.

Cloning and molecular characterization of a human intracellular serine proteinase inhibitor

We describe a cDNA encoding a serine proteinase inhibitor present in placental tissue and the cytosolic fraction of K562 cells. On the basis of its interaction with thrombin, through which it was discovered, the inhibitor has been operationally named the placental thrombin inhibitor (PTI). Amino acid sequence comparisons suggest that its reactive center is located at Arg-341 and Cys-342, that it lacks a classical N-terminal signal sequence, and that it has the highest degree of similarity to intracellular serine proteinase inhibitors (serpins), such as the human monocyte/neutrophil elastase inhibitor and the equine leukocyte elastase inhibitor. PTI also resembles these inhibitors in that it contains oxidation-sensitive residues adjacent to the reactive site. The PTI cDNA was expressed in rabbit reticulocyte lysate and in COS-7 cells and a 42-kDa protein was produced. Recombinant PTI formed a 67-kDa complex when incubated with thrombin. The ability of native PTI to bind thrombin was destroyed by incubation with iodoacetamide. Analysis of human tissue mRNA indicated that PTI is expressed widely with the highest levels in cardiac and skeletal muscle and placenta. We conclude that PTI is a member of an emerging class of intracellular serpins.