Abstract
Protease‐activated receptor 2 (PAR~2~) is a G protein‐coupled cell surface receptor for trypsin‐like enzymes. Proteolytic cleavage at a specific site in the extracellular N‐terminus exposes a receptor‐activating sequence, the ‘tethered ligand’, which binds intramolecularly to initiate receptor signalling. Peptide or small molecule agonists for PAR~2~, devoid of the non‐specific and proteolytic effects of enzyme activators, may be promising therapeutic agents for proliferative and inflammatory diseases reportedly mediated by PAR~2~. Synthetic hexapeptides that correspond to the native tethered ligand of human or rodent PAR~2~ (SLIGKV and SLIGRL, respectively) can activate the receptor independently of proteolytic cleavage; however, known peptide agonists have much lower potency compared to protease‐mediated activation. Here, we investigated the agonist activity of 94 hepta and octapeptide derivatives of the human and rodent PAR~2~‐tethered ligand sequences in human airway epithelial (A549) cells which endogenously express PAR~2~. Thirty synthetic peptides were found to be as potent as or more potent than SLIGRL on the basis of intracellular Ca^2+^ responses. The more active peptide agonists were also examined for agonist cross‐reactivity at PAR~1~ in Chinese Hamster Ovary (CHO) cells that endogenously express functional PAR~1~ but not PAR~2~. Two potent and PAR~2~‐selective agonists were further examined for their capacity to relax phenylephrine‐contracted rat aortic rings. Our findings reveal an important role for carboxyl extensions to native PAR~2~ activating peptides in potentiating agonist activity. Copyright © 2007 European Peptide Society and John Wiley & Sons, Ltd.