Location-Biased Activation of the Proton-Sensor GPR65 is Uncoupled from Receptor Trafficking

Abstract

<b>Abstract ID 17708</b> <b>Poster Board 290</b> The canonical view of G protein-coupled receptors (GPCR) function is that receptor trafficking is tightly coupled to signaling. GPCRs remain on the cell surface until they are activated, after which they are desensitized and internalized into endosomal compartments. This canonical view presents an interesting context for proton-sensing GPCRs because they are more likely to be activated in acidic endosomal compartments than at the cell surface. However, whether proton-sensing receptors are active in intracellular compartments, and whether trafficking is coupled to this signaling, are not known. Here we show that the trafficking of the prototypical proton-sensor GPR65 is fully uncoupled from signaling, unlike that of other known mammalian GPCRs. GPR65 internalizes and localizes to early and late endosomes, from where they signal at steady state, irrespective of extracellular pH. Acidic extracellular environments stimulate surface receptor signaling in a dose-dependent manner, although endosomal GPR65 is still required for a full cAMP response. Receptor mutants that were incapable of activating cAMP trafficked normally and were internalized and localized to endosomal compartments. Our results suggest a model where GPR65 is constitutively active in endosomes. Changes in extracellular pH reprogram the spatial pattern of receptor signaling and bias the location of signaling to the cell surface. This material is based upon work supported by the Rackham Merit Fellowship (RMF) and the National Science Foundation Graduate Research Fellowship Program (NSF-GRFP) under Grant No. DGE 1256260. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the National Science Foundation.