Heterologous phosphorylation–induced formation of a stability lock permits regulation of inactive receptors by β-arrestins

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β-Arrestins are key regulators and signal transducers of G protein–coupled receptors (GPCRs). The interaction between receptors and β-arrestins is generally believed to require both receptor activity and phosphorylation by GPCR kinases. In this study, we investigated whether β-arrestins are able to bind second messenger kinase–phosphorylated, but inactive receptors as well. Because heterologous phosphorylation is a common phenomenon among GPCRs, this mode of β-arrestin activation may represent a novel mechanism of signal transduction and receptor cross-talk. Here we demonstrate that activation of protein kinase C (PKC) by phorbol myristate acetate, G q/11 -coupled GPCR, or epidermal growth factor receptor stimulation promotes β-arrestin2 recruitment to unliganded AT 1 angiotensin receptor (AT 1 R). We found that this interaction depends on the stability lock, a structure responsible for the sustained binding between GPCRs and β-arrestins, formed by phosphorylated serine–threonine clusters in the receptor's C terminus and two conserved phosphate-binding lysines in the β-arrestin2 N-domain. Using improved FlAsH-based serine-threonine clusters β-arrestin2 conformational biosensors, we also show that the stability lock not only stabilizes the receptor–β-arrestin interaction, but also governs the structural rearrangements within β-arrestins. Furthermore, we found that β-arrestin2 binds to PKC-phosphorylated AT 1 R in a distinct active conformation, which triggers MAPK recruitment and receptor internalization. Our results provide new insights into the activation of β-arrestins and reveal their novel role in receptor cross-talk.