Optical biosensor differentiates signaling of endogenous PAR1 and PAR2 in A431 cells

Background: Protease activated receptors (PARs) consist of a family of four G protein-coupled receptors. Many types of cells express several PARs, whose physiological significance is mostly unknown. Results: Here, we show that non-invasive resonant waveguide grating (RWG) biosensor differentiates signaling of endogenous protease activated receptor subtype 1 (PAR(1)) and 2 (PAR(2)) in human epidermoid carcinoma A431 cells. The biosensor directly measures dynamic mass redistribution ( DMR) resulted from ligand-induced receptor activation in adherent cells. In A431, both PAR(1) and PAR(2) agonists, but neither PAR(3) nor PAR(4) agonists, trigger dose-dependent Ca2+ mobilization as well as G(q)-type DMR signals. Both Ca2+ flux and DMR signals display comparable desensitization patterns upon repeated stimulation with different combinations of agonists. However, PAR1 and PAR2 exhibit distinct kinetics of receptor re-sensitization. Furthermore, both trypsin- and thrombin- induced Ca2+ flux signals show almost identical dependence on cell surface cholesterol level, but their corresponding DMR signals present different sensitivities. Conclusion: Optical biosensor provides an alternative readout for examining receptor activation under physiologically relevant conditions, and differentiates the signaling of endogenous PAR(1) and PAR(2) in A431.