Spatial encoding of cyclic AMP signaling specificity by GPCR endocytosis

Abstract

G protein‐coupled receptors (GPCRs) comprise the largest family of signaling receptors and a very important class of therapeutic targets. GPCRs are well known to signal via cyclic AMP (cAMP) production at the plasma membrane, but it is now clear that various receptors also signal after internalization. This endosome‐derived signal is already known to modify the temporal profile of downstream responsiveness but it remains unknown, particularly for signals transduced by diffusible second messengers, if there is any functional significance to the spatial segregation of initiation sites. Using the beta2‐adrenoceptor (β2‐AR) as a model, we show that endocytosis is required for the full repertoire of downstream cAMP‐dependent transcriptional control. Next, we describe an orthogonal optogenetic approach to definitively establish that the location of cAMP production is indeed the critical variable determining the transcriptional response. Further, we demonstrate that the endocytosis‐dependent transcriptional signal is highly sensitive and saturable, effectively limiting the downstream cellular response to a uniform level. These properties allow the endosome to function as a ‘noise filter’, reducing variability of the downstream response and thus enhancing reliability of cognate ligand detection. In summary, our findings reveal a discrete principle for achieving cellular signaling specificity, based on endosome‐mediated spatial encoding of intracellular second messenger production and ‘location aware’ downstream transcriptional control.Support or Funding InformationNational Institute on Drug Abuse of the NIH; American Heart Association Postdoctoral Fellowship