Isolation, characterization, and amino-terminal amino acid sequence analysis of human neutrophil cathepsin G from normal donors

Cathepsin G deficiency reduces periaortic calcium chloride injury-induced abdominal aortic aneurysms in mice

OBJECTIVE

Cathepsin G (CatG) is a serine protease that mediates angiotensin I to angiotensin II (Ang-II) conversion and is highly expressed in human abdominal aortic aneurysms (AAAs). However, it remains untested whether this protease participates in the pathogenesis of AAA.

METHODS AND RESULTS

Immunofluorescent double staining demonstrated the expression of CatG in smooth muscle cells (SMCs), macrophages, and endothelial cells in human AAA lesions (n = 12) but not in AAA-free aortas (n = 10). Whereas inflammatory cytokines induced CatG expression, high glucose concentration increased CatG activity in producing Ang-II and angiotensin-converting enzyme in SMCs, which could be fully blocked by a CatG-selective inhibitor or its small interfering RNA. To test whether CatG contributes to AAA development, we generated CatG and low-density lipoprotein receptor double deficient (Ldlr(-/-)Ctsg(-/-)) mice and their littermate controls (Ldlr(-/-)Ctsg(+/+)). Absence of CatG did not affect Ang-II infusion-induced AAAs. In contrast, in Ang-II-independent AAAs induced by periaortic CaCl2 injury (n = 12 per group), CatG deficiency significantly reduced aortic diameter increase (58.33% ± 6.83% vs 31.67% ± 5.75%; P = .007), aortic lesion area (0.35 ± 0.04 mm(2) vs 0.21 ± 0.02 mm(2); P = .005), and aortic wall elastin fragmentation grade (2.75 ± 0.18 vs 1.58 ± 0.17; P = .002) along with reduced lesion collagen content grade (2.80 ± 0.17 vs 2.12 ± 0.17; P = .009) without affecting indices of lesion inflammation, angiogenesis, cell proliferation, or apoptosis. In vitro elastin degradation assays demonstrated that CaCl2-induced AAA lesions from Ldlr(-/-)Ctsg(-/-) mice contained much lower elastinolytic activity than in those from littermate control mice. Gelatin gel zymogram assay suggested that absence of CatG in CaCl2-induced AAA lesions also reduced the activity of elastinolytic matrix metalloproteinases 2 and 9.

CONCLUSIONS

CatG may contribute to CaCl2-induced experimental AAAs directly through its elastinolytic activity and indirectly by regulating lesion matrix metalloproteinases 2 and 9 activities. Increased expression of CatG in vascular and inflammatory cells of human AAAs and its increased activity in producing Ang-II and angiotensin-converting enzyme by SMCs suggest an additional mechanism by which CatG contributes to AAA lesion progression.

Mass spectroscopic characteristics of low molecular weight proteins extracted from calcium oxalate stones: preliminary study

It is believed that boundary compositions of matrix proteins might play a role in stone formation; however, few proteomic studies concerning matrix proteins in urinary stones have been conducted. In this study, we extracted low molecular weight proteins from calcium oxalate stones and measured their characteristic patterns by mass spectroscopy. A total of 10 stones were surgically removed from patients with urolithiasis. Proteins were extracted from the stones and identified by one-dimensional electrophoresis (sodium dodecyl sulfate buffer [SDS]-polyacrylamide gel electrophoresis [SDS-PAGE]). After in-gel digest, samples were analyzed by the surface-enhanced laser desorption ionization-time of flight (SELDI-TOF) technique. The peptide sequences were analyzed from the data of mass spectroscopy. Proteins were identified from Database Search (SwissProt Protein Database; Swiss Institute of Bioinformatics; http://www.expasy.org/sprot) on a MASCOT server (Matrix Science Ltd.; http://www.matrixscience.com). A total of three bands of proteins (27, 18, and 14 kDa) were identified from SDS-PAGE in each stone sample. A database search (SwissProt) on a MASCOT server revealed that the most frequently seen proteins from band 1 (27 kDa) were leukocyte elastase precursor, cathepsin G precursor, azurocidin precursor, and myeloblastin precursor (EC 3.4.21.76) (leukocyte proteinase 3); band 2 (18 kDa) comprised calgranulin B, eosinophil cationic protein precursor, and lysozyme C precursor; band 3 (14 kDa) showed neutrophil defensin 3 precursor, calgranulin A, calgranulin C, and histone H4. The modifications and deamidations found from the mass pattern of these proteins may provide information for the study of matrix proteins. Various lower molecular weight proteins can be extracted from calcium oxalate stones. The characteristic patterns and their functions of those proteins should be further tested to investigate their roles in stone formation.

4-Hydroxy-2-nonenal-modified glyceraldehyde-3-phosphate dehydrogenase is degraded by cathepsin G

Degradation of oxidized or oxidatively modified proteins is an essential part of the antioxidant defenses of cells. 4-Hydroxy-2-nonenal (HNE), a major reactive aldehyde formed by lipid peroxidation, causes many types of cellular damage. It has been reported that HNE-modified proteins are degraded by the ubiquitin-proteasome pathway or, in some cases, by the lysosomal pathway. However, our previous studies using U937 cells showed that HNE-modified glyceraldehyde-3-phosphate dehydrogenase (GAPDH) is degraded by an enzyme that is sensitive to a serine protease inhibitor, diisopropyl fluorophosphate (DFP), but not a proteasome inhibitor, MG-132, and that its degradation is not catalyzed in the acidic pH range where lysosomal enzymes are active. In the present study, we purified an HNE-modified GAPDH-degrading enzyme from a U937 cell extract to a final active fraction containing two proteins of 28 kDa (P28) and 27 kDa (P27) that became labeled with [(3)H]DFP. Using peptide mass fingerprinting and a specific antibody, P28 and P27 were both identified as cathepsin G. The degradation activity was inhibited by cathepsin G inhibitors. Furthermore, a cell extract from U937 cells transfected with a cathepsin G-specific siRNA hardly degraded HNE-modified GAPDH. These results suggest that cathepsin G plays a role in the degradation of HNE-modified GAPDH.

Renal cathepsin G and angiotensin II generation

BACKGROUND

Alternative pathways of angiotensin II biosynthesis play a significant role in the renin-angiotensin system. In this study porcine renal tissue was investigated for angiotensin II-generating enzymes.

METHODS AND RESULTS

Protein extracts from porcine renal tissue were fractionated by liquid chromatography and tested for their angiotensin II-generating activity by the mass-spectrometry-assisted enzyme screening system (MES) and the active fractions were purified to near homogeneity. In one of these active fractions, inhibitable by an angiotensin-converting enzyme specific inhibitor, purified by anion-exchange chromatography, followed by hydroxyapatite chromatography, lectin affinity chromatography, size-exclusion chromatography and two-dimensional electrophoresis, angiotensin-converting enzyme was identified by a tryptic peptide matrix-assisted-laser-desorption/ionization (MALDI) mass fingerprint analysis. In a second active fraction, which was inhibited by chymostatin and antipain, yielded by anion-exchange chromatography, followed by hydroxyapatite chromatography, lectin affinity chromatography, chymostatin-antipain chromatography and one-dimensional electrophoresis, cathepsin G was identified by electro-spray ionization (ESI)-ion-trap mass spectrometry. The angiotensin-generating activities of the fraction containing angiotensin-converting enzyme and the fraction containing cathepsin G were in the same order of magnitude, thus showing that the contribution of cathepsin G towards the production of angiotensin II is significant.

CONCLUSION

This is the first time that cathepsin G has been identified in mammalian renal tissue.

Identification of constituents of human neutrophil azurophil granules that mediate fungistasis against Histoplasma capsulatum

Previously we demonstrated that human neutrophils mediate potent and long-lasting fungistasis against Histoplasma capsulatum yeasts and that all of the fungistatic activity resides in the azurophil granules. In the present study, specific azurophil granule constituents with fungistatic activity were identified by incubation with H. capsulatum yeasts for 24 h and by quantifying the subsequent growth of yeasts via the incorporation of [(3)H]leucine. Human neutrophil defensins HNP-1, HNP-2, and HNP-3 inhibited the growth of H. capsulatum yeasts in a concentration-dependent manner with maximum inhibition at 8 microg/ml. At a concentration of 4 microg/ml, all possible paired combinations of defensins exhibited additive fungistatic activity against H. capsulatum yeasts. Cathepsin G and bactericidal-permeability-increasing protein (BPI) also mediated fungistasis against H. capsulatum in a concentration-dependent manner. The fungistatic activities of combinations of cathepsin G and BPI were additive, as were those of combinations of cathepsin G or BPI with HNP-1, HNP-2, and HNP-3. Lysozyme and elastase exhibited modest antifungal activity, and azurocidin and proteinase 3 exhibited no significant fungistasis against H. capsulatum yeasts. Thus, defensins, cathepsin G, and BPI are the major anti-H. capsulatum effector molecules in the azurophil granules of human neutrophils.

Normal Neutrophil Function in Cathepsin G-Deficient Mice

Cathepsin G is a neutral serine protease that is highly expressed at the promyelocyte stage of myeloid development. We have developed a homologous recombination strategy to create a loss-of-function mutation for murine cathepsin G. Bone marrow derived from mice homozygous for this mutation had no detectable cathepsin G protein or activity, indicating that no other protease in bone marrow cells has the same specificity. Hematopoiesis in cathepsin G−/− mice is normal, and the mice have no overt abnormalities in blood clotting. Neutrophils derived from cathepsin G−/− mice have normal morphology and azurophil granule composition; these neutrophils also display normal phagocytosis and superoxide production and have normal chemotactic responses to C5a, fMLP, and interleukin-8. Although cathepsin G has previously shown to have broad spectrum antibiotic properties, challenges of mice with Staphylococcus aureus, Klebsiella pneumoniae, or Escherichia coli yielded survivals that were not different from those of wild-type animals. In sum, cathepsin G−/− neutrophils have no obvious defects in function; either cathepsin G is not required for any of these normal neutrophil functions or related azurophil granule proteases with different specificities (ie, neutrophil elastase, proteinase 3, azurocidin, and/or others) can substitute for it in vivo.

Normal Neutrophil Function in Cathepsin G-Deficient Mice

Cathepsin G is a neutral serine protease that is highly expressed at the promyelocyte stage of myeloid development. We have developed a homologous recombination strategy to create a loss-of-function mutation for murine cathepsin G. Bone marrow derived from mice homozygous for this mutation had no detectable cathepsin G protein or activity, indicating that no other protease in bone marrow cells has the same specificity. Hematopoiesis in cathepsin G−/− mice is normal, and the mice have no overt abnormalities in blood clotting. Neutrophils derived from cathepsin G−/− mice have normal morphology and azurophil granule composition; these neutrophils also display normal phagocytosis and superoxide production and have normal chemotactic responses to C5a, fMLP, and interleukin-8. Although cathepsin G has previously shown to have broad spectrum antibiotic properties, challenges of mice with Staphylococcus aureus, Klebsiella pneumoniae, or Escherichia coli yielded survivals that were not different from those of wild-type animals. In sum, cathepsin G−/− neutrophils have no obvious defects in function; either cathepsin G is not required for any of these normal neutrophil functions or related azurophil granule proteases with different specificities (ie, neutrophil elastase, proteinase 3, azurocidin, and/or others) can substitute for it in vivo.

Cleavage of native type I collagen by human neutrophil elastase

The ability of purified human neutrophil elastase (EC 3.4.21.37) to cleave native type I collagen has been investigated. Soluble human, bovine or rat type I collagen was incubated with neutrophil elastase for 16 h at 25 degrees C before catalysis was stopped with 3, 4-dichloroisocoumarin. Analysis by SDS/PAGE of the collagen digests revealed 3/4-length fragments similar in size to those produced by interstitial collagenase. The collagenolytic activity was dose dependent and was not due to a contaminating metalloproteinase or cysteine proteinase, as it was not inhibited by 1,10-phenanthroline, EDTA or L-trans-epoxysuccinyl-leucylamido-(4-guanidino)butane. The identity of the cleavage products was confirmed using a new antibody that recognizes the unwound alpha2(I)-chain. This detected the 3/4-length fragment of type I collagen following neutrophil elastase cleavage. In addition to cleaving soluble collagen, neutrophil elastase also cleaved reconstituted, radiolabelled type I collagen fibrils, at a rate of 16 microg/min per nmol. These results indicate that neutrophil elastase can cleave native type I collagen in the helix, an activity that might contribute to its roles in connective-tissue pathology.

Human leukocyte elastase is an endogenous ligand for the integrin CR3 (CD11b/CD18, Mac-1, alpha M beta 2) and modulates polymorphonuclear leukocyte adhesion

Integrin CR3 (CD11b/CD18, Mac-1, alpha M beta 2) mediates the transient adhesion of polymorphonuclear leukocytes (PMN) to surfaces coated with fibrinogen, C3bi, ICAM-1, and other ligands. Recent studies (Cai, T.-Q., and S.D. Wright 1995. J. Biol. Chem. 270:14358) suggest that adhesion may be favored by stimulus-dependent changes in the kinetics of ligand binding by CR3. Cell detachment, on the other hand, must occur by a different mechanism because binding kinetics cannot affect cell adhesion after binding of ligand has occurred. We have sought a mechanism that would reverse binding of ligand to CR3 and report here that lysates of PMN contain an endogenous ligand that binds CR3 and competes the binding of C3bi. Purification and sequence analysis identified the structurally homologous azurophilic granule proteins, elastase, protease 3, and azurocidin as candidates. Studies with purified elastase and azurocidin showed that each bound specifically to purified, immobilized CR3. Elastase may play a role in modulating integrin-mediated cell adhesion because it is expressed at the cell surface, and the expression level is inversely proportional to cell adhesivity. Furthermore, a monoclonal antibody against elastase prevented detachment of PMN from fibrinogen-coated surfaces and blocked chemotaxis, confirming a role for this protein in regulating integrin-mediated adhesion. These studies suggest a model for release of integrin-mediated cell adhesion in which endogenous ligands such as elastase may release adhesion by "'eluting" substrate-bound ligand. A role for the proteolytic activity of elastase appears likely but is not demonstrated in this study.

Neutrophil lysosomal nonoxidative microbicidal proteins in early-onset periodontitis

The purpose of this study was to evaluate whether the reduced microbicidal activity of polymorphonuclear leukocytes (neutrophils) in patients with early-onset periodontitis is associated with a deficiency of nonoxidative microbicidal proteins. Neutrophils from 10 patients with early-onset periodontitis and 8 healthy control subjects were assessed for elastase isozymes 1 through 4, cathepsin G isozymes 1 through 4 and defensins (HNP-1, HNP-2 and HNP-3) using cationic and acid urea polyacrylamide gel electrophoresis. The results showed that both the total content and the relative distribution of elastase and cathepsin G isozymes was normal in neutrophils of patients with early-onset periodontitis. However, the HNP-3 content was significantly reduced in neutrophils from patients with generalized early-onset periodontitis. These findings indicate that the impaired microbicidal activities of neutrophils in patients with early-onset periodontitis does not appear to be based on an elastase or cathepsin G abnormality in neutrophils. Due to the high variability of HNP-1 + 2 and HNP-3 in neutrophils of control subjects, the reduced HNP-3 content in neutrophils probably plays a minor role in the pathogenesis of generalized early-onset periodontitis.

Early myeloid cell-specific expression of the human cathepsin G gene in transgenic mice

The human cathepsin G (CG) gene is expressed only in promyelocytes and encodes a neutral serine protease that is packaged in the azurophil (primary) granules of myeloid cells. To define the cis-acting DNA elements that are responsible for promyelocyte-specific "targeting," we injected a 6-kb transgene containing the entire human CG gene, including coding sequences contained in a 2.7-kb region, approximately 2.5 kb of 5' flanking sequence, and approximately 0.8 kb of 3' flanking sequence. Seven of seven "transient transgenic" murine embryos revealed human CG expression in the fetal livers at embryonic day 15. Stable transgenic founder lines were created with the same 6-kb fragment; four of five founder lines expressed human CG in the bone marrow. The level of human CG expression was relatively low per gene copy when compared with the endogenous murine CG gene, and expression was integration-site dependent; however, the level of gene expression correlated roughly with gene copy number. The human CG transgene and the endogenous murine CG gene were coordinately expressed in the bone marrow and the spleen. Immunohistochemical analysis of transgenic bone marrow revealed that the human CG protein was expressed exclusively in myeloid cells. Expression of human CG protein was highest in myeloid precursors and declined in mature myeloid cells. These data suggest that the human CG gene was appropriately targeted and developmentally regulated, demonstrating that the cis-acting DNA sequences required for the early myeloid cell-specific expression of human CG are present in this small genomic fragment.

Human neutrophil cathepsin G is a potent platelet activator

PURPOSE

Neutrophil activation has been implicated in the pathophysiologic condition of ischemia-reperfusion injury, the formation of arterial aneurysms, the progression of myocardial ischemia, and the initiation of deep venous thrombosis. Activated neutrophils release cathepsin G, a serine protease, from their granules, which may cause platelet activation that leads to intravascular thrombosis, tissue infarction, and systemic release of the thrombogenic products of platelet granules. This study used flow cytometry to quantify the extent of cathepsin G-induced platelet activation and degranulation through changes in the expression of platelet surface glycoproteins.

METHODS

Increasing concentrations of human neutrophil-derived cathepsin G were incubated with washed platelets or whole blood from healthy human donors. The platelet surface expression of glycoproteins, including P-selectin, a platelet membrane glycoprotein only expressed after platelet alpha granule release, were determined by quantifying the platelet binding of a panel of fluorescently labeled monoclonal antibodies. Results were compared with the effect of a maximal dose of thrombin, the most potent known platelet activator.

RESULTS

In a washed platelet system, cathepsin G increased platelet surface expression of P-selectin (an activation-dependent neutrophil binding site), the glycoprotein IIb/IIIa complex (fibrinogen receptor), and glycoprotein IV (thrombospondin receptor), and decreased surface expression of glycoprotein Ib (von Willebrand factor receptor) to an extent comparable to maximal thrombin. However, these effects were not observed in a whole blood system. Further experiments revealed that preexposure to plasma completely inhibited cathepsin G-induced washed platelet activation and degranulation. Prostacyclin treatment of washed platelets markedly inhibited cathepsin G-induced platelet activation.

CONCLUSIONS

Cathepsin G is a very potent platelet agonist and degranulator, comparable to maximal thrombin, which alters platelet surface glycoprotein expression for enhanced neutrophil binding and effective platelet aggregation. This study helps to elucidate a possible pathway through which neutrophils may directly activate platelets, leading to intravascular thrombosis, irreversible ischemia, and tissue death in cardiovascular disease states. Patients with diseased endothelium that is deficient in prostacyclin production may be particularly prone to the detrimental effects of neutrophil-derived cathepsin G platelet activation.

Biochemical properties of aeroallergens: contributory factors in allergic sensitization?

Recent studies indicate that the majority of clinically important aeroallergens are biochemically active. A diverse range of properties have been demonstrated but most possess either enzymatic activity (principally hydrolytic), enzyme inhibitory activity, low molecular weight ligand transporting or regulatory properties. In addition, some allergens are glycosylated and/or are structurally similar to proteins which have evolved to function in the respiratory system per se. Little attention has been given to the possibility that the biochemical activity of an allergen or any post-translational modifications contribute to sensitization. In this review, mechanisms with the potential to influence immunogenicity are discussed including interaction with respiratory secretions, epithelial disruption, interactions with immunocompetent cells and receptor mediated endocytosis. Given that many aeroallergens are structurally and functionally similar to a variety of endogenous (e.g. lysosomal enzymes) and exogenous proteins (e.g. microbial enzymes and glycoproteins), particular attention has been directed to the latter. This process represents an important non-adaptive defence mechanism which has evolved to recognize and process such proteins and it is feasible that it plays a similar role in the processing of some allergens entering the respiratory system.

Binding of bovine basic pancreatic trypsin inhibitor (Kunitz) as well as bovine and porcine pancreatic secretory trypsin inhibitor (Kazal) to human cathepsin G: a kinetic and thermodynamic study

The effect of pH and temperature on kinetic and thermodynamic parameters for the binding of the bovine basic pancreatic trypsin inhibitor (Kunitz inhibitor; BPTI) as well as bovine and porcine pancreatic secretory trypsin inhibitor (Kazal inhibitor; bovine and porcine PSTI, respectively) to human cathepsin G (EC 3.4.21.20) has been investigated. The affinity of the macromolecular inhibitors examined for cathepsin G is characterized by an endothermic, entropy-driven, behaviour, and shows the following trend: BPTI > bovine PSTI > porcine PSTI. The affinity difference of BPTI as well as of bovine and porcine PSTI for cathepsin G is mostly accounted for by changes in the values of the apparent dissociation rate constant for the proteinase:inhibitor complex destabilization. On increasing the pH from 4.5 to 9.5 (at 25.0 degrees C), the affinity of BPTI, as well as bovine and porcine PSTI for cathepsin G increases thus reflecting the acidic-pK shift of the His-57 catalytic residue from approximately 6.9 in the free enzyme to approximately 5.0 in the serine proteinase:inhibitor complexes. The BPTI as well as the bovine and porcine PSTI binding properties of cathepsin G have been analyzed in parallel with those of related serine (pro)enzyme/macromolecular inhibitor systems. Considering the known molecular models, the observed binding behaviour of BPTI as well as that of bovine and porcine PSTI to cathepsin G has been related to the inferred stereochemistry of the serine proteinase/inhibitor contact region(s).

A calcium-stimulated serine protease from monkey brain degrades the beta-amyloid precursor protein

Amyloid deposition, a histopathological feature of Alzheimer's disease brain, may be the underlying cause of this disease. The isolation of enzymes involved in both the normal and aberrant or alternative processing of the beta-amyloid precursor protein may lead to an understanding of how beta-protein, the major component of amyloid deposits, is formed in the brain parenchyma and vasculature of Alzheimer's disease patients and aged humans. As the same kind of deposits is also found in aged primates, the use of primates will undoubtedly help to understand the mechanisms of amyloid deposition, both spatially and temporally. Here we report the partial purification from adult monkey brain of a calcium-activated serine protease that is immunoreactive with antibodies against cathepsin G and is potentially involved in the abnormal degradation of the beta-amyloid precursor protein. Moreover, immunoreactivity with cathepsin G antibodies was localised to astrocytes in both adult and aged monkey cortex, suggesting that our protease may be expressed in astrocytes.

Additive enhancement of neutrophil collagenase activity by HOCl and cathepsin G

Using preparations of latent collagenase derived from neutrophil specific granule extracts, the relative effects of cathepsin G and HOCl on activation of neutrophil collagenase were determined using a quantitative collagenase assay. Enhancement of collagenase activity by cathepsin G and physiologically relevant concentrations of HOCl were comparable, but HOCl mediated collagenase activation was reversible in the presence of HOCl scavenger. Collagenase activity in preparations treated with cathepsin G and HOCL simultaneously or sequentially was significantly greater than activity in preparations treated with HOCl or cathepsin G alone. The results indicated additive, yet independent enhancing effects of HOCl and cathepsin G on activity of neutrophil collagenase.

Comparison of granule proteins from human polymorphonuclear leukocytes which are bactericidal toward Pseudomonas aeruginosa

Killing of Pseudomonas aeruginosa by a 55-kDa bactericidal protein (BP 55), a 30-kDa protein (BP 30), cathepsin G, elastase, and proteinase 3 has been compared. P. aeruginosa was resistant to killing by elastase and proteinase 3. BP 55 at a 50% lethal dose (LD50) of 0.23 micrograms of protein per 5 x 10(6) bacteria per ml killed P. aeruginosa and was far more active than BP 30 and cathepsin G. The LD50s of BP 30 and cathepsin G were 16.9 and 28.3 micrograms of protein per 5 x 10(6) bacteria per ml, respectively. Preincubation of BP 55 or BP 30 with lipopolysaccharide (LPS) from P. aeruginosa inhibited bactericidal activity. The N-terminal amino acid sequence of BP 55 and BP 30 revealed no relationship between the two proteins. However, a monoclonal antibody (AHN-15) reacted with both proteins by Western immunoblot. The bactericidal activity of cathepsin G toward P. aeruginosa appeared to be dependent on the availability of the active site of the enzyme; bactericidal activity was inhibited by phenylmethylsulfonyl fluoride (PMSF) and by the specific cathepsin G inhibitor, Z-Gly-Leu-Phe-CH2Cl. The enzyme and bactericidal activities of cathepsin G were also inhibited by LPS from P. aeruginosa. LPS from P. aeruginosa was shown to be a competitive inhibitor of the enzyme activity of cathepsin G. Elastase enzyme activity was also inhibited noncompetitively by LPS, but the enzyme was not bactericidal. We have concluded that all three bactericidal proteins (BP 55, BP 30, and cathepsin G) may bind to the LPS of the outer membrane of P. aeruginosa. It appears that the enzyme active site must be available for cathepsin G to kill P. aeruginosa and that the active site may be involved in the binding of cathepsin G to P. aeruginosa.

In vitro killing of oral Capnocytophaga by granule fractions of human neutrophils is associated with cathepsin G activity

The Capnocytophaga are inhabitants of the hypoxic human gingival crevice that are normally prevented by neutrophils from causing periodontal and systemic infection. To identify potential nonoxidative bactericidal mechanisms against Capnocytophaga within human neutrophils, gel filtration chromatography was used to fractionate neutrophil granule extracts. Seven granule fractions, designated A through G, were obtained. The Capnocytophaga were most sensitive to killing by fraction D. Fraction D exhibited substantial bactericidal activity under aerobic and anaerobic conditions. The bactericidal activity associated with ion-exchange subfractions D8-D11, which contained primarily cathepsin G as assessed by enzymatic activity, amino acid composition, and NH2-terminal sequence. Heat-inactivation, diisopropylfluorophosphate, PMSF, and N-benzyloxycarbonylglycylleucylphenylalanyl-chloromethyl ketone inhibited bactericidal activity against Capnocytophaga sputigena but not Escherichia coli. We conclude that (a) human neutrophil cathepsin G is an important antimicrobial system against the Capnocytophaga, (b) the bactericidal activity of cathepsin G against Capnocytophaga is oxygen independent, and (c) an intact enzyme active site is involved in the killing of C. sputigena but not E. coli. We suggest that human neutrophil cathepsin G is an important antimicrobial system against certain oral bacteria and that cathepsin G kills bacteria by two distinct mechanisms.

The biosynthesis of endothelin-1 by human polymorphonuclear leukocytes

Human polymorphonuclear leukocytes (PMNs) converted human big endothelin (bET; 2 microM) to an endothelin-1 (ET-1) like contractile factor, as assessed by bioassay. The generation of this ET-1 like activity was rapid (minutes), time-dependent and more pronounced in non-activated cells, suggesting a partial degradation by activated PMNs. Phosphoramidon (54 micrograms/ml) inhibited the formation of this contractile factor, whereas phenylmethylsulfonylfluoride (PMSF; 25 micrograms/ml), pepstatin A (1 microgram/ml) or epoxysuccinyl-L-leucylamido-(guanidino)butane (E-64; 10 micrograms/ml) did not. Incubations of activated PMNs with PMSF significantly potentiated the generation of ET-1 like activity and selectively inhibited the degradation of [125I]ET-1 by activated PMNs. These findings indicate that human PMNs contain and/or release neutral proteases, which can both rapidly produce and degrade ET-1, an observation which may have important (patho)physiologic implications.

Neutrophil elastase and cathepsin G stimulate secretion from cultured bovine airway gland serous cells

To investigate the hypothesis that neutrophil proteases stimulate airway gland secretion, we studied the effect of human cathepsin G and elastase on secretion of 35S-labeled macromolecules from cultured bovine airway gland serous cells. Both proteases stimulated secretion in a concentration-dependent fashion with a threshold of greater than or equal to 10(-10) M. Elastase was more potent than cathepsin G, causing a maximal secretory response of 1,810 +/- 60% over baseline at 10(-8) M. The maximal response to cathepsin G (1,810 +/- 70% over baseline at 10(-7) M) was similar to the maximal response to elastase. These responses were greater than 10-fold larger than the response to other agonists such as histamine. Protease-induced secretion was noncytotoxic and required catalytically active enzymes. The predominant sulfated macromolecule released by proteases was chondroitin sulfate proteoglycan. Immunocytochemical staining demonstrated chondroitin sulfate in cytoplasmic granules and decreased granular staining after stimulation of cells with elastase. The neutrophil proteases also degraded the proteoglycan released from serous cells. Cathepsin G and elastase in supernatant obtained by degranulation of human peripheral neutrophils also caused a secretory response. Thus, neutrophil proteases stimulate airway gland serous cell secretion of chondroitin sulfate proteoglycan and degrade the secreted product. These findings suggest a potential role for neutrophil proteases in the pathogenesis of increased and abnormal submucosal gland secretions in diseases associated with inflammation and neutrophil infiltration of the airways.

Anti-neutrophil cytoplasm antibodies in Wegener's granulomatosis recognize an elastinolytic enzyme

The target antigen of anti-neutrophil cytoplasm antibodies (ACPA; also known as ANCA) was isolated by affinity chromatography from supernatants of human neutrophils, stimulated with phorbol ester to induce degranulation. Sequence analysis of the antigen revealed 17 NH2-terminal amino acids (IVGGHEAQPHIRPIYMA), which have considerable sequence homology with known serine proteinases. Investigation of the enzymatic activity showed that the antigen is a neutral serine proteinase that is able to cleave elastin. Since the molecular weight of the antigen, its substrate specificity, and its inhibitor profile reported in this study are identical with those reported recently for proteinase 3, we conclude that ACPA are most probably directed against proteinase 3.

Cathepsin G is a strong platelet agonist released by neutrophils

The present studies were undertaken to characterize a serine protease released by N-formyl-L-Met-L-Leu-L-Phe (fMet-Leu-Phe)-stimulated neutrophils that rapidly induces platelet calcium mobilization, secretion and aggregation. The biological activity associated with this protease was unaffected by leupeptin, was only weakly diminished by N-p-tosyl-L-Lys-chloromethane, but was strongly inhibited by alpha 1-antitrypsin, soyabean trypsin inhibitor, N-tosyl-L-Phe-chloromethane and benzoyloxycarbonyl-Gly-Leu-Phe-chloromethane (Z-Gly-Leu-PheCH2Cl). These observations indicated that the biological activity of neutrophil supernatants could be attributed to a chymotrypsin-like enzyme such as cathepsin G. Furthermore, platelet aggregation and 5-hydroxytryptamine release induced by cell-free supernatants from fMet-Leu-Phe-stimulated neutrophils were found to be blocked by antiserum to cathepsin G in a concentration-dependent manner but were unaffected by antiserum to elastase. The biological activity present in neutrophil supernatants co-purified with enzymic activity for cathepsin G during sequential Aprotinin-Sepharose affinity chromatography and carboxymethyl-Sephadex chromatography. SDS/polyacrylamide-gel electrophoresis of the reduced, purified protein, demonstrated three polypeptides with apparent Mr values of 31,500, 29,000 and 28,000 and four polypeptides were resolved on acid-gel electrophoresis. Purified cathepsin G from neutrophils cross-reacted with anti-(cathepsin G) serum in a double immunodiffusion assay and elicited platelet calcium mobilization, 5-hydroxytryptamine secretion and aggregation. Calcium mobilization and secretion induced by low concentrations of cathepsin G were partially dependent on arachidonic acid metabolites and ADP, while stimulation by higher enzyme concentrations was independent of amplification pathways, indicating that cathepsin G is a strong platelet agonist. These results suggest that pathological processes which stimulate neutrophils and release cathepsin G can in turn result in the recruitment and activation of platelets.

Dog mastocytoma tryptase: affinity purification, characterization, and amino-terminal sequence

A tryptic protease with the characteristics of a mast cell tryptase was purified from dog mastocytoma cells propagated in nude mice. Partial amino acid sequence of the mastocytoma tryptase revealed unexpected differences in comparison with other mast cell and leukocyte granule protease sequences. Extraction from mastocytoma homogenates at high ionic strength, followed by gel filtration and benzamidine affinity chromatography yielded a product with several closely spaced bands (Mr 30,000-32,000) on gel electrophoresis and a single N-terminal sequence. Nondenaturing analytical gel filtration revealed an apparent Mr of 132,000, suggesting noncovalent association as a tetramer. Studies with peptide p-nitroanilides indicated pronounced substrate preferences, with P1 arginine preferred to lysine. Benzoyl-L-Lys-Gly-Arg-p-nitroanilide was the best of the substrates screened. Inhibition by diisopropyl fluorophosphate and tosyllysine chloromethyl ketone indicated that the enzyme is a serine protease. Like the tryptases of human mast cells, mastocytoma tryptic protease was inhibited by NaCl, resistant to inactivation by alpha 1-proteinase inhibitor and plasma, and stabilized by heparin. Comparison of the N-terminal 24 residues of mastocytoma tryptase revealed 80% identity with the more limited sequence reported for human lung tryptase, and surprisingly, closer homology to serine proteases of digestion and clotting than to other leukocyte granule proteases sequenced to date, including mast cell chymase. The N-terminal isoleucine is the homolog of trypsinogen Ile-16 which becomes the new N-terminus upon cleavage of the activation peptide. Thus, the tryptase N-terminus is related to the catalytic domain of activated serine proteases, and lacks the N-terminal regulatory domains found in most clotting and complement serine proteases. These findings provide further evidence that tryptases are unique serine proteases and that they may be less closely related in evolution and function than are other leukocyte granule proteases described to date.