GPCR endocytosis confers uniformity in responses to chemically distinct ligands

This study shows that chemically and pharmacodynamically distinct agonists acting on the same GPCR can produce indistinguishable cellular responses and that this uniformity is conferred by endosomal signaling The ability of chemically distinct ligands to produce different effects on the same G protein-coupled receptor (GPCR) has interesting therapeutic implications but, if excessively propagated downstream, would introduce biological 'noise' compromising cognate ligand detection We asked if cells have the ability to limit the degree to which chemical diversity imposed at the ligand-GPCR interface is propagated to the downstream signal We carried out an unbiased analysis of the integrated cellular response elicited by two chemically and pharmacodynamically diverse β-adrenoceptor agonists, isoproterenol and salmeterol We show that both ligands generate an identical integrated response, and that this stereotyped output requires endocytosis We further demonstrate that the endosomal β2-AR signal confers uniformity on the downstream response because it is highly sensitive and saturable Based on these findings, we propose that GPCR signaling from endosomes functions as a biological noise filter to enhance reliability of cognate ligand detection This study includes a total of 6 microarray experiments, each condition is done in triplicate