Dissociation of β-Arrestin-Dependent Desensitization and Signaling Using 'Biased' Parathyroid Hormone Receptor Ligands

While structurally distinct ligands can “bias” the efficiency with which G protein-coupled receptors (GPCRs) activate different downstream effectors, it is thought that the events downstream of a single effector are inseparable. We tested a panel of type 1 parathyroid hormone receptor (PTH1R) ligands for their effects on two β-arrestin-mediated processes, receptor desensitization and β-arrestin-dependent signaling. Unlike conventional agonists, which caused desensitization while activating β-arrestin-dependent signaling, we found that β-arrestin biased agonists that did not activate G protein signaling or desensitize the receptor paradoxically retained the ability to signal via β-arrestins. Total internal fluorescence microscopy, bimolecular fluorescent complementation between PTH1R and β-arrestin2, and intramolecular β-arrestin2 FlAsH-BRET conformational profiling demonstrated that these ligands transiently recruit β-arrestin2 to the receptor and induced distinctive changes in β-arrestin2 conformation without a requirement for stable binding. Our results demonstrate that β-arrestin-dependent signaling can be dissociated from receptor desensitization and establish a novel profile of β-arrestin-dependent efficacy.