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Pseudomonas aeruginosa Elastase Disables Proteinase-Activated Receptor 2 in Respiratory Epithelial Cells

Unité de Défense Innée et Inflammation/Inserm Equipe 336, and Plate-Forme d'Analyse et de Microséquençage des Protéines, Institut Pasteur, Paris, France; Departments of Surgery and Physiology, University of California, San Francisco, California; and Department of Pharmacology and Therapeutics and Department of Medicine, University of Calgary, Calgary, Alberta, Canada

Correspondence and requests for reprints should be addressed to Dr. Michel Chignard, Unité de Défense Innée et Inflammation, Institut National de la Santé et de la Recherche Médicale E336, Institut Pasteur, 25, rue du Dr. Roux, F-75724 Paris Cedex 15, France. E-mail: chignard{at}pasteur.fr

Pseudomonas aeruginosa, a major lung pathogen in cystic fibrosis (CF) patients, secretes an elastolytic metalloproteinase (EPa) contributing to bacterial pathogenicity. Proteinase-activated receptor 2 (PAR2), implicated in the pulmonary innate defense, is activated by the cleavage of its extracellular N-terminal domain, unmasking a new N-terminal sequence starting with SLIGKV, which binds intramolecularly and activates PAR2. We show that EPa cleaves the N-terminal domain of PAR2 from the cell surface without triggering receptor endocytosis as trypsin does. As evaluated by measurements of cytosolic calcium as well as prostaglandin E₂ and interleukin-8 production, this cleavage does not activate PAR2, but rather disarms the receptor for subsequent activation by trypsin, but not by the synthetic receptor-activating peptide, SLIGKV-NH₂. Proteolysis by EPa of synthetic peptides representing the N-terminal cleavage/activation sequences of either human or rat PAR2 indicates that cleavages resulting from EPa activity would not produce receptor-activating tethered ligands, but would disarm PAR2 in regard to any further activating proteolysis by activating proteinases. Our data indicate that a pathogen-derived proteinase like EPa can potentially silence the function of PAR2 in the respiratory tract, thereby altering the host innate defense mechanisms and respiratory functions, and thus contributing to pathogenesis in the setting of a disease like CF.

Key Words: inflammation • infection • lung • cystic fibrosis • protease

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