The cytoplasmic tails of protease-activated receptor-1 and substance P receptor specify sorting to lysosomes versus recycling

The G protein-coupled receptor (GPCR) for thrombin, protease-activated rece ptor-1 (PAR1), is activated when thrombin cleaves its amino-terminal exodom ain. The irreversibility of this proteolytic mechanism raises the question of how desensitization and resensitization are accomplished for thrombin si gnaling. PAR1 is phosphorylated, uncoupled from signaling, and internalized after activation like classic GPCRs, However, unlike classic GPCRs, which internalize and recycle, activated PAR1 is sorted to lysosomes. To identify the signals that specify the distinct sorting of PAR1, we constructed chim eras between PAR1 and the substance P receptor. Wild-type substance P recep tor internalized and recycled after activation; PAR1 bearing the cytoplasmi c tail of the substance P receptor (P/S) behaved similarly. By contrast, wi ld-type PAR1 and a substance P receptor bearing the cytoplasmic tail of PAR 1 (S/P) sorted to lysosomes after activation, Consistent with these observa tions, PARI and the S/P chimera were effectively downregulated by their res pective agonists as assessed by both receptor protein levels and signaling. Substance P receptor and the P/S chimera showed little down-regulation. Th ese data suggest that the cytoplasmic tails of PAR1 and substance P recepto r specify their distinct intracellular sorting patterns after activation an d internalization. Moreover, by altering the trafficking fates of PARI and substance P receptor, one can dictate the efficiency with which a cell main tains responsiveness to PAR1 or substance P receptor agonists over time.