Functional and physical cross-talk between PAR1 and PAR2 in human microvascular endothelial cells

Protease-activated receptors (PARs) are a novel family of G-protein coupled receptors (GPCRs). Rather then being stimulated through ligand receptor occupancy, activation is initiated by cleavage of receptor N-terminus by a serine protease, resulting in the generation of a new tethered ligand, that interacts with the receptor within the extracellular loop-2. Both PAR1 and PAR2 are involved in several diseases, but any antagonist of them is still unavailable for therapy. The aim of this research project was to investigate whether functional and physical interactions occur between PAR1 and PAR2 and/or their signal transduction pathways in human microvascular endothelial cells (HMEC-1). Indeed, a wide knowledge of receptor biology constitutes the first step in the drug discovery process. For this purpose, immunoprecipitation studies were performed and the effects of PAR agonists on intracellular second messenger production (cAMP and calcium) were examined. Results indicated that in HMEC-1 PAR1 and PAR2 form hetero-oligomers but they also interact at the level of signal transduction pathways leading to functional cross-talks. Moreover, both PAR1 and PAR2 exhibit “functional selectivity” for G protein coupling. Our observation open new interesting strategies within the drug discovery process and help in the development of PAR selective antagonists useful for the treatment of several diseases.