Proteinases release mucin from airways goblet cells

Different mucins are produced by the surface epithelium and the submucosa in human trachea: identification of MUC5AC as a major mucin from the goblet cells

Mucins were extracted from the epithelial surface and the submucosal tissue of human trachea in order to enrich glycoproteins from the goblet cells and the submucosal glands respectively. The macromolecules were purified using density-gradient centrifugation, and the presence of the MUC5AC mucin was investigated using an antiserum raised against a synthetic peptide based on the sequence of the MUC5AC apoprotein. Mucins from the surface epithelium showed a higher reactivity with the antiserum relative to carbohydrate than those from the submucosa, and ion-exchange HPLC of reduced subunits revealed the presence of two distinct mucin populations in the samples. The predominant species from the surface epithelium was more acidic than the major population from the submucosa and showed a strong reactivity with the anti-MUC5AC anti-serum. In contrast, the major portion of the submucosal mucins were less acidic and showed no MUC5AC reactivity, although a more acidic population did react with the antibody. Rate-zonal centrifugation showed that the MUC5AC mucin from the surface epithelium is smaller than the major submucosal mucin, and that both are composed of subunits. Immunolocalization confirmed that the MUC5AC mucin from human trachea originates from the goblet cells and that this glycoprotein is not a major product of the submucosal glands.

Bacterial extracellular zinc-containing metalloproteases

Extracellular zinc-containing metalloproteases are widely distributed in the bacterial world. The most extensively studied are those which are associated with pathogenic bacteria or bacteria which have industrial significance. They are found practically wherever they are sought in both gram-negative and gram-positive microorganisms, be they aerobic or anaerobic. This ubiquity in itself implies that these enzymes serve important functions for the organisms which produce them. Because of the importance of zinc to enzymatic activity, it is not surprising that there is a pervasive amino acid sequence homology in the primary structure of this family of enzymes regardless of their source. The evidence suggests that both convergent and divergent evolutionary forces are at work. Within the large family of bacterial zinc-containing metalloendopeptidases, smaller family units are observed, such as thermolysin-like, elastase-like, and Serratia protease-like metalloproteases from various bacterial species. While this review was in the process of construction, a new function for zinc-containing metalloproteases was discovered: the neurotoxins of Clostridium tetani and Clostridium botulinum type B have been shown to be zinc metalloproteases with specificity for synaptobrevin, an integral membrane protein of small synaptic vesicles which is involved in neurotransmission. Additional understanding of the mode of action of proteases which contribute to pathogenicity could lead to the development of inhibitors, such as chelators, surrogate substrates, or antibodies, which could prevent or interrupt the disease process. Further studies of this broad family of metalloproteases will provide important additional insights into the pathogenesis and structure-function relationships of enzymes and will lead to the development of products, including "designer proteins," which might be industrially and/or therapeutically useful.

Acute lung injury induced by Pseudomonas aeruginosa elastase in hamsters

Human neutrophil elastase (HNE) is the predominant elastolytic enzyme in the sputum of cystic fibrosis (CF) patients. However, a variably small portion of the activity can be ascribed to Pseudomonas aeruginosa elastase (PaE). The purpose of these studies was to evaluate the activities of the two elastases in an in vivo model of acute lung injury (ALI). The elastolytic activity of Pseudomonas aeruginosa elastase (MW = 39K) and human neutrophil elastase (MW = 33K) were also examined using insoluble bovine neck and lung elastin. The ability of hamster serum to inhibit elastinolysis by the two elastases was also examined. On a per milligram protein basis, PaE was the more potent elastase, regardless of substrate, and it preferentially hydrolyzed lung relative to neck elastin. PaE is poorly inhibited by hamster serum compared to HNE. In vivo, PaE is much more efficient than HNE in inducing an acute lung injury in hamsters. The duration of effects induced by doses of the two proteases that produce similar acute biological effects are essentially identical. The increases of lung weight and total lavagable WBCs persist for at least 7 days. All other parameters return to baseline between 3 and 5 days. The predominant cells in the lavage 1 and 2 days post insult are PMNs. By day 7, the predominant cell is the macrophage. These data suggest that even though PaE is a minor component of the elastolytic activity in CF patients, it may still contribute significantly to the pathology of the disease.

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.

An ultrastructural study of the response of hamster bronchial epithelium to human neutrophil elastase

The central intrapulmonary bronchi of hamsters were examined by transmission electron microscopy at varying times following intratracheal instillation of human neutrophil elastase (HNE) or its vehicle, saline. Two hours after HNE treatment, there was a marked irregularity of the surfaces of many nonciliated epithelial cells; a differential count of transepithelial cells (those with both a basal lamina and luminal border) demonstrated a significant decrease in the proportion of granule-containing (granulated) secretory cells and a corresponding increase in nongranulated secretory cells. By 3 days after HNE injection, the differential count had returned to control levels and cell surface alterations were less evident. By 8 days, the proportion of granulated secretory cells had significantly increased, while that of nongranulated secretory cells had decreased. Many Clara cells developed the characteristics of mucous cells so that mucous cells constituted 57% of the secretory cells compared to 14% for the saline controls. The mucous cells contained an increased number of mucous granules including bizarre forms never seen in controls. By day 16, the average mucous cell proportion had increased to 75%; the mucous cells were larger and contained many more secretory granules than at day 8. At no time was there evidence of overt cell injury or alteration of extracellular connective tissue due to HNE. Basal and pseudobasal cells, distinguished by the presence or absence of hemidesmosomes, did not change as a percentage of total nucleated epithelial cells. Saline had no effect on the differential cell count compared to untreated values. Our results indicate a strong likelihood that HNE causes early discharge of secretory granules and alters the phenotypic expression of Clara cells so that they produce abundant, often abnormal mucous granules. The mechanism of HNE-induced disturbance of epithelial homeostasis is unknown, but the early irregularity of nonciliated epithelial cell surfaces may signify an important event in the evolution of the resultant lesion.

Dog tracheal epithelial cells in culture synthesize sulfated macromolecular glycoconjugates and release them from the cell surface upon exposure to extracellular proteinases

To determine whether glycoconjugates can be released into airways by surface epithelial cells that do not contain secretory granules and, if so, whether extracellular proteinases can affect this release, we studied dog tracheal epithelial cells after 8-10 days in culture. Ultrastructurally, these cells showed an extensive cell surface coat and no secretory granules. Cells were pulse labeled with radioactive sulfate (Na2 35SO4, 50 microCi/ml/24 h) and washed free of the unbound label. Release of sulfated products was then measured at 20-min intervals under basal conditions and again after 20 min of incubation with various extracellular proteinase. We found that these cells synthesized sulfated products and released them spontaneously and continuously into the medium. In addition, trypsin, Pseudomonas aeruginosa elastase, thermolysin, Staphylococcus aureus proteinase, mast cell chymase, plasmin, and kallikrein (each at 10(-7) M except plasmin, at 5 X 10(-6) M) increased the release of sulfated products to 77-667% over baseline release (p less than 0.01, n = 5 dogs for each); preliminary results showed that human neutrophil elastase was also very potent. The sulfated products released by trypsin had an apparent molecular weight of greater than or equal to 10(6) da as determined by gel filtration on Sepharose Cl-4B. Over 50% of these 35S-labeled products were digested to low-molecular-weight products (500-2000 da) upon incubation with endo-beta-galactosidase or with keratanase, suggesting that they are glycoconjugates containing poly(N-acetyllactosamine)-type carbohydrate chains. Decrease in cell staining by lectins specific for poly(N-acetyllactosamine), which accompanied the release of glycoconjugates, indicates that these sulfated glycoconjugates were released by proteinases from the apical cell surface. We conclude that cultured tracheal epithelial cells synthesize and transport sulfated macromolecular glycoconjugates to apical cell surfaces. These glycoconjugates are released from cell surfaces when exposed to extracellular proteinases. We therefore suggest that macromolecular glycoconjugates in airway secretions can originate not only from secretory granules but also from epithelial cell surfaces during airway inflammation.