Proteinase-activated receptor (PAR)-2 is cleaved within its aminoterminal extracellular domain by
serine proteinases such as
trypsin, unmasking a new aminoterminus starting with the sequence
SLIGKV, which binds intramolecularly and activates the receptor. PAR-2 has been reported to be involved in
inflammation within the lungs. We show that PAR-2 is expressed not only by human alveolar (A549), but also by bronchial (16HBE) epithelial cell lines, using RT-PCR and flow cytometry with a PAR-2 antibody whose
epitope maps over the
trypsin cleavage site. PAR-2 activation by
trypsin and by the activating
peptide SLIGKV-NH(2) leads to intracellular
calcium mobilization in both lung epithelial cells. During
lung inflammation, airspaces are burdened by neutrophils that release
elastase and
cathepsin G, two
serine proteinases. We demonstrate that these
proteinases do not activate PAR-2, but rather disarm the receptor, preventing activation by
trypsin but not by SLIGKV-NH(2). Preincubation of a PAR-2-transfected cell line, as well as 16HBE and A549 cells, with either
proteinase led to the disappearance of the cleavage/activation
epitope recognized by the PAR-2 antibody. We hypothesize that
elastase and
cathepsin G disarm PAR-2 by proteolysis of the extracellular domain downstream from the
trypsin cleavage/activation site, while leaving unmodified the SLIGKV-NH(2)-binding site. These findings suggest that the neutrophil
serine proteinases may play a role in PAR-2-mediated
lung inflammation.