Evaluation of the Substrate Specificity of Human Mast Cell Tryptase βI and Demonstration of Its Importance in Bacterial Infections of the Lung

• Published in: The Journal of biological chemistry Vol. 276; no. 28; pp. 26276 - 26284
• Main Authors: Huang, Chifu, De Sanctis, George T., O'Brien, Peter J., Mizgerd, Joseph P., Friend, Daniel S., Drazen, Jeffrey M., Brass, Lawrence F., Stevens, Richard L.
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 13.07.2001
• Subjects: Amino Acid Sequence; Animals; Humans; Klebsiella Infections - enzymology; Klebsiella Infections - pathology; Klebsiella pneumoniae; Klebsiella pneumoniae - enzymology; Lung - enzymology; Lung - pathology; Mast Cells - enzymology; Mast Cells - pathology; Mice; Molecular Sequence Data; Neutrophils - pathology; Pneumonia, Bacterial - enzymology; Pneumonia, Bacterial - pathology; Serine Endopeptidases - metabolism; Substrate Specificity; Tryptase bI; Tryptases
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.M102356200

Human pulmonary mast cells (MCs) express tryptases α and βI, and both granule serine proteases are exocytosed during inflammatory events. Recombinant forms of these tryptases were generated for the first time to evaluate their substrate specificities at the biochemical level and then to address their physiologic roles in pulmonary inflammation. Analysis of a tryptase-specific, phage display peptide library revealed that tryptase βI prefers to cleave peptides with 1 or more Pro residues flanked by 2 positively charged residues. Although recombinant tryptase βI was unable to activate cultured cells that express different types of protease-activated receptors, the numbers of neutrophils increased >100-fold when enzymatically active tryptase βI was instilled into the lungs of mice. In contrast, the numbers of lymphocytes and eosinophils in the airspaces did not change significantly. More important, the tryptase βI-treated mice exhibited normal airway responsiveness. Neutrophils did not extravasate into the lungs of tryptase α-treated mice. Thus, this is the first study to demonstrate that the two nearly identical human MC tryptases are functionally distinct in vivo. When MC-deficientW/Wv mice were given enzymatically active tryptase βI or its inactive zymogen before pulmonary infection withKlebsiella pneumoniae, tryptase βI-treatedW/Wv mice had fewer viable bacteria in their lungs relative to zymogen-treated W/Wv mice. Because neutrophils are required to combat bacterial infections, human tryptase βI plays a critical role in the antibacterial host defenses of the lung by recruiting neutrophils in a manner that does not alter airway reactivity.