Neutrophil Elastase and Proteinase-3 Trigger G Protein-biased Signaling through Proteinase-activated Receptor-1 (PAR1)

Background: Proteinase-activated receptor-1 (PAR1) is a proteolytically activated G protein-coupled receptor. Neutrophil-derived enzymes might regulate PAR1 signaling. Results: Neutrophil elastase and proteinase-3 cleave and activate PAR1 signaling that is distinct from thrombin-triggered responses. Neutrophil elastase and proteinase-3 signaling through PAR1 modulates endothelial cell signaling. Conclusion: Neutrophil enzymes are G(i)-biased agonists for PAR1. Significance: Biased PAR1-activating compounds may prove of value as therapeutic agents to treat cardiovascular and inflammatory diseases. Neutrophil proteinases released at sites of inflammation can affect tissue function by either activating or disarming signal transduction mediated by proteinase-activated receptors (PARs). Because PAR1 is expressed at sites where abundant neutrophil infiltration occurs, we hypothesized that neutrophil-derived enzymes might also regulate PAR1 signaling. We report here that both neutrophil elastase and proteinase-3 cleave the human PAR1 N terminus at sites distinct from the thrombin cleavage site. This cleavage results in a disarming of thrombin-activated calcium signaling through PAR1. However, the distinct non-canonical tethered ligands unmasked by neutrophil elastase and proteinase-3, as well as synthetic peptides with sequences derived from these novel exposed tethered ligands, selectively stimulated PAR1-mediated mitogen-activated protein kinase activation. This signaling was blocked by pertussis toxin, implicating a G(i)-triggered signal pathway. We conclude that neutrophil proteinases trigger biased PAR1 signaling and we describe a novel set of tethered ligands that are distinct from the classical tethered ligand revealed by thrombin. We further demonstrate the function of this biased signaling in regulating endothelial cell barrier integrity.