Protease Activated Receptor (PAR)

Protease activated receptors (PARs) are a family of G-protein-coupled receptors (GPCRs) that are irreversibly activated by proteolytic cleavage of the N terminus, which unmasks a tethered peptide ligand that binds and activates the transmembrane receptor domain, eliciting a cellular cascade in response to inflammatory signals and other stimuli. There are four members of the PAR family: PAR1, PAR2, PAR3 and PAR4. PARs have important functions in the vasculature, inflammation, and cancer and are important drug targets.

PARs are expressed on nearly all cell types in the blood vessel wall (ECs, fibroblasts, myocytes) and blood (platelets, neutrophils, macrophages, leukemic white cells) with exception of red blood cells. Thrombin-activated PAR-1, PAR-3, and PAR-4 are also expressed in epithelium, neurons, astrocytes, and immune cells. PAR-2, which is activated by trypsin-like serine proteases, is found in human vascular, intestinal, neuronal, and airway cells. Its expression increases in injured tissues or after stimulation by inflammatory mediators.