Cathepsin B activity in human blood monocytes during differentiation in vitro

Monocytes: super cells for bone regeneration

Monocytes are progenitor cells that lead the inflammatory cascade reaction responsible for guiding revascularization and regeneration of tissue at injury sites. They do this by secreting inductive cytokines responsible for endothelial cell migration. When released into the peripheral blood, monocytes enter tissues and become macrophages. Monocytes also trigger the body's defense mechanism against microbial invasion by lysing and removing cell debris and dead tissue. The aim of this article is to explain the role of monocytes in the processes of bone healing and regeneration and describe their interaction with stem cells and other entities. Results of a pilot histomorphometric study in which concentrated monocytes were combined with demineralized allograft material to augment implant-placement sites in 2 patients also are presented.

Fine-tuning nucleophosmin in macrophage differentiation and activation

M-CSF-driven differentiation of peripheral blood monocytes is one of the sources of tissue macrophages. In humans and mice, the differentiation process involves the activation of caspases that cleave a limited number of proteins. One of these proteins is nucleophosmin (NPM1), a multifunctional and ubiquitous protein. Here, we show that caspases activated in monocytes exposed to M-CSF cleave NPM1 at D213 to generate a 30-kDa N-terminal fragment. The protein is further cleaved into a 20-kDa fragment, which involves cathepsin B. NPM1 fragments contribute to the limited motility, migration, and phagocytosis capabilities of resting macrophages. Their activation with lipopolysaccharides inhibits proteolytic processes and restores expression of the full-length protein that negatively regulates the transcription of genes encoding inflammatory cytokines (eg, NPM1 is recruited with NF-κB on the MCP1 gene promoter to decrease its transcription). In mice with heterozygous npm gene deletion, cytokine production in response to lipopolysaccharides, including CXCL1 (KC), MCP1, and MIP2, is dramatically enhanced. These results indicate a dual function of NPM1 in M-CSF-differentiated macrophages. Proteolysis of the protein participates in the establishment of a mature macrophage phenotype. In response to inflammatory stimuli, the full-length protein negatively regulates inflammatory cytokine production.

The significance of cathepsins, thrombin and aminopeptidase in diffuse interstitial lung diseases

To determine the significance of proteases in interstitial lung diseases, we examined the activity of cathepsins, thrombin, and aminopeptidase in bronchoalveolar lavage (BAL) fluid from patients with these disorders. Significantly increased activities of cathepsin H and aminopeptidase were detected in BAL fluid from patients with idiopathic pulmonary fibrosis (IPF), cryptogenic organizing pneumonia (COP), chronic eosinophilic pneumonia (CEP) and hypersensitivity pneumonitis (HP). Significantly higher activity of cathepsin B was found in BAL fluid from patients with CEP. The activity of thrombin was significantly higher in patients with IPF and CEP. In patients with IPF, there were significant correlations between neutrophil number and the activity of cathepsin B, cathepsin H or aminopeptidase. In patients with COP and HP, the activity of the proteases was significantly higher in patients with higher number of lymphocytes than in those with lower number of lymphocytes. The present study suggests that the activity of the proteases is a useful marker in activity of the interstitial lung diseases, and may have a role in the pathogenesis of these disorders.

Evidence that E-box promoter elements and MyoD transcription factors play a role in the induction of cathepsin B gene expression during human myoblast differentiation

HB13 human myoblasts express physiological and biochemical markers associated with myoblast differentiation in non-human cell culture model systems. During differentiation, HB13 myoblasts also demonstrate fusion-related increases in cathepsin B activity and protein levels. These increases are associated with an increase in levels of cathepsin B mRNA suggesting the involvement of transcriptional regulatory mechanisms. To examine these mechanisms human myoblasts were transfected with cathepsin B nested deletion promoter constructs within the 1.8 kb 5' promoter 1 region of the human catB gene. Transfected myoblasts that were maintained under differentiating conditions demonstrated higher promoter activity than those maintained in proliferating conditions. The highest activity was obtained with pSCB2-3 (-1279/+56 bp), a construct containing two putative upstream E-box elements. Co-transfection experiments demonstrated that MyoD and myogenin transactivate cathepsin B promoter activity. Electrophoretic mobility shift assays of nuclear extracts incubated with an oligonucleotide containing two upstream E-box elements found within the cathepsin B promoter demonstrated two band shifts. The band shifts were abolished using an oligonucleotide with mutations in both E-box elements. Moreover, the shifted bands were super-shifted and abolished when incubated with anti-myogenin and anti-MyoD, respectively. Collectively, these data support myogenic transcription factor-mediated activation of cathepsin B expression during myogenesis.

Cathepsin B in human leukocytes

We have applied a method using the fluorigenic substrate benzoloxycarbonyl-Arg-Arg-amido-4-methylcoumarin to measure cathepsin B, a thiol proteinase, in homogenates of human leukocytes. Data like pH optimum, stability, influence of thiol groups and effects of thiol proteinase inhibitors, lack of binding to Concanavalin A and lack of contribution to the fluorescence by other cathepsins indicate that cathepsin B is the enzyme measured. Although the activity of the enzyme was linear with respect to time at all protein concentrations measured, there was an acceptable 10% deviation of the enzyme activity from linearity as a function of protein concentration. The enzyme in the homogenate was stable at 0 degrees C but was rapidly inactivated at 50 degrees C and above pH 6.5-7. Very limited activation on the one hand and variable inhibition on the other was seen by reagents containing thiol groups and thiol proteinase inhibitors respectively. Latency (60% of the enzyme activity) indicates a probable subcellular lysosomal localization. There is no affinity towards the lectin Concanavalin A and the Km value was around 1 mmol/l. Normal enzyme activity values in leukocyte homogenates were determined.

Ultrastructural localization of cathepsin B in gingival tissue from chronic periodontitis patients

Loss of tooth support during chronic periodontitis is very likely to involve tissue proteases such as cathepsin B. The distribution of this enzyme was, therefore, examined in ultrathin sections of gingival tissue embedded in acrylic resin and labelled with a sheep polyclonal antibody and gold-conjugated secondary antibody. Macrophages and fibroblasts in both inflamed and non-inflamed areas of tissue showed labelling, and this was strongest in lysosomes, corresponding to the normal intracellular location of cathepsin B. However, additional gold particles were found on the surface of these cells. Monocytes in inflamed areas also had surface labelling, some of which was present on microvilli. Labelled collagen fibres adjacent to all three cell types indicated that cathepsin B had been released into the immediate extracellular environment. Plasma membrane cathepsin B has previously been associated with cancers, but enzyme redistribution and release in the gingiva may have been linked to the inflammatory response, since fibroblasts and macrophages in non-inflamed areas showed less labelling of their surface and adjacent collagen. The collagen labelling added to evidence that cathepsin B can function extracellularly as well as intracellularly in connective tissue degradation. This destructive role for the enzyme is supported by our earlier measurements of increased biochemical activity in chronic periodontitis.

Endotoxin induces increased intracellular cathepsin B activity in THP-1 cells

Macrophage cathepsin B (CB) is implicated in tissue injury in inflammatory diseases. Lipopolysaccharide (LPS) is an activator of macrophages whose effect on CB is unknown. This study was undertaken to investigate the potential of macrophages as a source of increased CB and to determine if exposure to LPS might stimulate CB levels. As a model we chose the macrophage-like tumor line, THP-1. Incubation with LPS led to a time and dose-dependent increase in CB activity. LPS potentiated interferon-gamma (IFN-gamma)-induced elevations of CB and led to an additive increase in CB activity. Pretreatment of the cells with LPS not only caused a marked stimulation of CB activity over that seen with IFN-gamma alone, but also decreased the concentration and exposure time to the cytokine necessary to achieve maximum induction of the enzyme. The LPS and IFN-gamma induced CB increases were abolished by cycloheximide or actinomycin D in the cultures, indicating that the increases in CB required increased RNA transcription and de novo protein synthesis. Direct measurement of CB mRNA showed increases. These data indicate that although LPS alone appears to induce the production of CB in THP-1 cells, it augments IFN-gamma induced increases, suggesting that two signals are necessary for maximum CB induction in this system.

Detection of lysosomal cysteine proteinases in microglia: flow cytometric measurement and histochemical localization of cathepsin B and L

The activation and differentiation of microglia is a prominent pathophysiological process in numerous inflammatory and demyelinating diseases of the central nervous system, including Alzheimer's disease and the AIDS encephalopathy. The tissue damage during these diseases has partly been attributed to lipid peroxidating reactive oxygen intermediates for which activated microglia are a major source. The destruction of tissue may also involve the release of proteolytic enzymes, such as the lysosomal cysteine proteinases cathepsin B and L, which are present notably in phagocytic cells. The cathepsins B and L are endopeptidases with a substrate specificity including important proteins, like myelin basic protein, extracellular matrix components, or the class II major histocompatibility complex. Because of this pathophysiological relevance the cathepsins B and L were chosen for histochemical demonstration in isolated and cultured rat microglia and measurement by a new flow cytometric method. Cathepsin B/L activity was measured flow cytometrically in single viable cells by the intracellular cleavage of non-fluorescent (Z-Phe-Arg)2-rhodamine 110 to the green fluorescent monoamide Z-Phe-Arg-rhodamine 110 and rhodamine 110. In microglia we measured a cathepsin B/L activity that was 2.5 times higher than in thioglycolate-elicited, i.e., inflammatory peritoneal rat macrophages. In elicited peritoneal macrophages the formation of fluorescent product was 6.2 times higher than in unstimulated resident peritoneal macrophages, demonstrating that the activation and differentiation of mononuclear phagocytes is accompanied by an increased cathepsin B/L enzyme activity. The subcellular localization of cathepsin B/L activity in plated viable microglia was demonstrated histochemically by the use of Z-Ala-Arg-Arg-4-methoxy-2-naphthylamide. Its blue fluorescent cleavage product 4-methoxy-2-naphthylamide was found in lysosomes. Our study shows that activated microglia are an important potential source of cathepsin B/L. This is particularly interesting as enzymatically active cathepsins have recently been found extracellularly at high levels in the senile plaques of Alzheimer's disease, which are known to contain many activated microglia. The release of proteinases by microglia may play a crucial role in the pathomechanism of tissue-destructing diseases in the brain.

Role of enzyme receptors and inhibitors in regulating proteolytic activities of macrophages

Expression of proteases by neutrophils and other cells with a prominent regulated secretory pathway is determined largely by stimulus-response secretion of proteins prepackaged in high concentration. The regulated secretory pathway is apparently minor in macrophages, and instead proteases are either channeled into lysosomes or secreted constitutively. Posttranslational regulation of macrophage proteases then depends on compartmentalizing enzymes to their sites of primary function. Available data suggest that cells use both specific receptors and inhibitors to accomplish this. Viewed in this context protease inhibitors primarily function to inhibit enzyme not bound to their receptor. Consonant with this model of regulation, connective tissue turnover by macrophages is a contact-dependent process relatively resistant to exogenous macromolecular inhibitors. Although limited information is available regarding determinants that modulate matrix metabolism by human macrophages, this model suggests that determinants of adhesion and colocalization of enzyme and substrate would be as or more important than alterations of inhibitors in the microenvironment of the cell.

Changes in the expression of elastase and cathepsin B with differentiation of U937 promonocytes by GMCSF

The human promonocytic cell line, U937, when treated for up to 72h with 12,O,tetradecanoyl-phorbol-13-acetate or granulocyte-macrophage colony-stimulating factor, exhibited increased phagocytic activity and expression of the marker p150/95. There was an associated increase in the monocyte proteinase cathepsin B and its mRNA but decreased cellular levels of neutrophil elastase and elastase mRNA. Granulocyte-macrophage colony-stimulating factor therefore causes differentiation of U937 cells, with appropriate effects on the synthesis of leukocyte proteinases.

Identification of cystatin C, a cysteine proteinase inhibitor, as a major secretory product of human alveolar macrophages in vitro

The major inhibitor of the cysteine class of proteinases found in human body fluids, such as spinal fluid, milk, and seminal plasma, is cystatin C. In this study we show that human bronchoalveolar fluid also contains cystatin C and examine cystatin C expression by alveolar macrophages in vitro. Immunoprecipitation of extracts of metabolically labeled cells and immunoblotting of cellular extracts and culture media show that cystatin C is synthesized as a 14 (+/- 0.5) kilodalton (kD) protein and that greater than 90% of the protein is released as the 14 kD product into the culture supernatant (26.5 +/- 6.8 ng per 10(6) cells per 24 h). Cystatin C is not one of the most abundant proteins secreted during the first 24 h in vitro, representing approximately 10 to 12% of the total protein released by normal nonsmoker macrophages. Alveolar macrophages obtained from cigarette smokers or nonsmoker macrophages exposed to zymosan in vitro released 10 to 55% less cystatin C than nonsmoker macrophages. We also assayed culture supernatants from macrophages of smokers and nonsmokers for functional cystatin C. Supernatants of nonsmoker macrophages inhibited cathepsin B-like amidolytic activity in a fluorometric assay at pH 5.5. The inhibition was blocked by adsorption with Sepharose-coupled cystatin C antibodies and the inhibitor subsequently recovered from the Sepharose beads. In contrast, supernatants from smoker macrophages had obvious cathepsin B-like activity.(ABSTRACT TRUNCATED AT 250 WORDS)

Tuberculin sensitivity and an interaction of leucocyte and plasma factors involving fibrinogen

Lysates of blood leucocytes from strong tuberculin-positive reactors contained smaller particles of insoluble protein-rich material than did similar preparations from negative donors. The phenomenon was dependent on the presence of small quantities of plasma in the original leucocyte suspensions: when this was removed or replaced by serum both groups of donors produced particles of the smaller size. When the experiments were repeated in the presence of 125I-fibrinogen, larger particle size was found to be associated with an increased proportion of radioactivity becoming firmly bound to the insoluble material. These findings are likely to reflect differences in the levels of procoagulant, proteolytic enzymes or associated activities in the cells or plasma of the two groups.

Synthesis and processing of cathepsin L, an elastase, by human alveolar macrophages

Cathepsin L was partially purified from lysates of freshly isolated macrophages lavaged from lungs of apparently healthy adults and found to be chromatographically and catalytically identical with liver cathepsin L. Western-blotting analysis showed that lung macrophages contain significant levels of a precursor of cathepsin L (43 kDa) in addition to mature enzyme (25 kDa). After culturing for a further 24 h, the precursor disappeared and a new band, corresponding to 34 kDa, appeared, suggesting that the precursor had been processed to an intermediate form of cathepsin L. Biosynthetic labelling of macrophages in vitro with [35S]methionine followed by immunoprecipitation with the cathepsin L antibody confirmed that the cells synthesize cathepsin L as a 43 kDa precursor that is then processed to the mature form (25 kDa) via a 34 kDa intermediate. The precursor, but not the processed forms, was released into the culture medium. During culture in vitro the 34 kDa intermediate accumulated, and little enzyme was processed to the 24 kDa form, consistent with the immunoblot data. Human lung macrophages contain a 1.5 kb transcript of cathepsin L mRNA, whereas none is detectable in human monocytes. These results establish that differentiation of human macrophages within the lung is accompanied by synthesis and expression of an elastinolytic enzyme, cathepsin L. The altered processing of cathepsin L observed during cultivation in vitro suggests caution in the assessment of the elastinolytic potential of human macrophages based on assay in vitro.

Biochemical quantitation and histochemical localization of cathepsin B, dipeptidyl peptidases I and II, and acid phosphatase in pulmonary granulomatosis and fibrosis in rats

The purpose of this study was to quantitate biochemically and to localize histochemically the proteases cathepsin B (Cath B), dipeptidyl peptidase I (DPP I), and dipeptidyl peptidase II (DPP II) in experimental pulmonary granulomatosis and fibrosis. These were compared to the prototypical lysosomal hydrolase acid phosphatase (AP). Granulomatosis was induced by the intravenous injection of complete Freund's adjuvant (CFA, 0.2 ml) and fibrosis was induced by the intratracheal instillation of bleomycin sulfate (1 unit) in rats (Wistar, 200 g). Total Cath B, DPP I, and AP activities were markedly elevated over control values five days following both treatments when expressed as activity per lung or as specific activity per milligram protein or milligram DNA. By 14 and 28 days, total activity was elevated for all three enzymes, and activity per milligram DNA remained elevated for Cath B following both treatments and for DPP I 28 days following CFA treatment. Total lung activity of DPP II was significantly elevated at 28 days for both treatments. Histochemical staining indicated that these changes are due, in part, to the influx of inflammatory monocytes and their maturation to macrophages. This study provides a basis for examining the role of these proteases in connective tissue matrix injury during inflammatory processes in the lungs.

The effect of recombinant interferons on cathepsin B activity in human monocytes

Blood monocytes isolated from healthy human donors were cultivated for 3 days in the presence of recombinant human interferons (rHuIFN) alpha, beta, gamma. Intracellular activity of cathepsin B was recorded. All rHuIFNs suppressed the cathepsin B activity in the monocytes, rHuIFNs alpha and beta suppressed in a dose-dependent manner, whereas rHuIFN-gamma was suppressive only at low concentrations (1-10 U/ml). In parallel experiments, monocytes were stimulated with carrageenan, which caused increased cathepsin B activity in the cells. This increase was reduced to the level of activity in nonstimulated cells by all rHuIFNs. We have previously reported that cathepsin B may be involved in the pathogenesis of rheumatoid arthritis, and the present results may have a bearing on the effects of HuIFNs on the immune system.

Cathepsin B synthesis by the HL60 promyelocytic cell line: effects of stimulating agents and anti-inflammatory compounds

Cathepsin B synthesis by the human HL60 promyelocyte cell line was investigated by immunohistochemistry and by the assay of the enzyme in cell lysates using a fluorimetric substrate. HL60 cells were shown to produce cathepsin B in response to treatment with 12-O-tetradecanoylphorbol 13-acetate (TPA). Intracellular levels of cathepsin B and immunohistochemical staining of the enzyme were related to time in culture with increasing concentrations of TPA from 1 nmol/1 to 8.0 nmol/1. Synthesis of cathepsin B was associated with TPA-induced phagocytic activity of cells in culture, expression of alpha-naphthyl acetate esterase and reduced cell division. Cathepsin B production was, therefore, related to differentiation of the HL60 promyelocytes into mature macrophage-like cells. Cathepsin B activity in HL60 cell lysates was significantly increased by incubation of the cells with 10 micrograms/ml endotoxin (lipopolysaccharide) from Escherichia coli, but not carrageenan. The production of cathepsin B by TPA-induced HL60 cells was significantly reduced by 0.25 mumol/1 dexamethasone and the non-steroidal anti-inflammatory compound 4-(6-methoxy-2-naphthyl)-butan-2-one but not by indomethacin. The HL60 promyelocytic cell line is a useful model for the study of factors affecting proteinase synthesis by human mononuclear phagocytes.