Palmitoylation of Protease-activated Receptor-1 Regulates Adaptor Protein Complex-2 and -3 Interaction with Tyrosine-based Motifs and Endocytic Sorting

Abstract

Protease-activated receptor-1 (PAR1) is a G protein-coupled receptor for the coagulant protease thrombin. Thrombin binds to and cleaves the N terminus of PAR1, generating a new N terminus that functions as a tethered ligand that cannot diffuse away. In addition to rapid desensitization, PAR1 trafficking is critical for the regulation of cellular responses. PAR1 displays constitutive and agonist-induced internalization. Constitutive internalization of unactivated PAR1 is mediated by the clathrin adaptor protein complex-2 (AP-2), which binds to a distal tyrosine-based motif localized within the C-terminal tail (C-tail) domain. Once internalized, PAR1 is sorted from endosomes to lysosomes via AP-3 interaction with a second C-tail tyrosine motif proximal to the transmembrane domain. However, the regulatory processes that control adaptor protein recognition of PAR1 C-tail tyrosine-based motifs are not known. Here, we report that palmitoylation of PAR1 is critical for regulating proper utilization of tyrosine-based motifs and endocytic sorting. We show that PAR1 is basally palmitoylated at highly conserved C-tail cysteines. A palmitoylation-deficient PAR1 mutant is competent to signal and exhibits a marked increase in constitutive internalization and lysosomal degradation compared with wild type receptor. Intriguingly, enhanced constitutive internalization of PAR1 is mediated by AP-2 and requires the proximal tyrosine-based motif rather than the distal tyrosine motif used by wild type receptor. Moreover, palmitoylation-deficient PAR1 displays increased degradation that is mediated by AP-3. These findings suggest that palmitoylation of PAR1 regulates appropriate utilization of tyrosine-based motifs by adaptor proteins and endocytic trafficking, processes that are critical for maintaining appropriate expression of PAR1 at the cell surface.