title: Transactivation of the PAR1-PAR2 heterodimer by thrombin elicits β-arrestin-mediated endosomal signaling.
abstract: Thrombin cleaves the N terminus of PAR1, generating a new N-terminal domain that functions as a tethered ligand that binds intermolecularly to activate PAR2 in trans. The mechanisms that regulate PAR1-PAR2 heterodimer signaling and trafficking are not known. We now report that PAR1 and PAR2 form a heterodimer that exhibits unique trafficking and signaling behaviors compared with receptor protomers. Using bioluminescence resonance energy transfer, immunofluorescence microscopy, co-immunoprecipitation, and cells expressing receptors exogenously and endogenously, we show that PAR1 and PAR2 specifically interact and form stable dimers. Intriguingly, the PAR1-PAR2 heterodimer displays constitutive internalization that is driven by PAR1 C-terminal tail sorting motifs and is a process that enhances dimer formation. Upon thrombin activation, PAR1-PAR2 dimers co-internalize and recruit β-arrestins to endosomes. Remarkably, PAR1-PAR2 heterodimers appear to utilize a distinct interface for β-arrestin interaction compared with receptor protomers. Moreover, thrombin-activated PAR1-PAR2 heterodimers enhance β-arrestin-mediated ERK1/2 activation in the cytoplasm, whereas activated ERK1/2 induced by the thrombin-activated PAR1 protomer redistributes to the nucleus. Thus, the formation of PAR1-PAR2 heterodimers provides additional modes of thrombin-stimulated signaling responses that appear to be distinctly regulated compared with the receptor protomer.
authors.affiliation: Department of Pharmacology, School of Medicine, University of California, San Diego, La Jolla, California 92093, USA.
authors.forename: Huilan
authors.initials: H
authors.lastname: Lin
authors.forename: JoAnn
authors.initials: J
authors.lastname: Trejo
mesh_terms: D020816:Amino Acid Motifs; D000818:Animals; D019390:Arrestins / Q000235:genetics / Q000378:metabolism*; D019556:COS Cells; D002522:Chlorocebus aethiops; D011992:Endosomes / Q000235:genetics / Q000378:metabolism*; D006367:HeLa Cells; D006801:Humans; D011401:Promoter Regions, Genetic / Q000502:physiology; D055503:Protein Multimerization / Q000502:physiology*; D044463:Receptor, PAR-1 / Q000235:genetics / Q000378:metabolism*; D044464:Receptor, PAR-2 / Q000235:genetics / Q000378:metabolism*; D015398:Signal Transduction / Q000502:physiology*; D013917:Thrombin / Q000235:genetics / Q000378:metabolism*; D015533:Transcriptional Activation / Q000502:physiology*; D000071557:beta-Arrestins
chemical_list: D019390:Arrestins; D044463:Receptor, PAR-1; D044464:Receptor, PAR-2; D000071557:beta-Arrestins; D013917:Thrombin