Distinct Phosphorylation Sites on the β ₂ -Adrenergic Receptor Establish a Barcode That Encodes Differential Functions of β-Arrestin

Abstract

Phosphorylation of G protein–coupled receptors (GPCRs, which are also known as seven-transmembrane spanning receptors) by GPCR kinases (GRKs) plays essential roles in the regulation of receptor function by promoting interactions of the receptors with β-arrestins. These multifunctional adaptor proteins desensitize GPCRs, by reducing receptor coupling to G proteins and facilitating receptor internalization, and mediate GPCR signaling through β-arrestin–specific pathways. Detailed mapping of the phosphorylation sites on GPCRs targeted by individual GRKs and an understanding of how these sites regulate the specific functional consequences of β-arrestin engagement may aid in the discovery of therapeutic agents targeting individual β-arrestin functions. The β2-adrenergic receptor (β2AR) has many serine and threonine residues in the carboxyl-terminal tail and the intracellular loops, which are potential sites of phosphorylation. We monitored the phosphorylation of the β2AR at specific sites upon stimulation with an agonist that promotes signaling by both G protein–mediated and β-arrestin–mediated pathways or with a biased ligand that promotes signaling only through β-arrestin–mediated events in the presence of the full complement of GRKs or when either GRK2 or GRK6 was depleted. We correlated the specific and distinct patterns of receptor phosphorylation by individual GRKs with the functions of β-arrestins and propose that the distinct phosphorylation patterns established by different GRKs establish a “barcode” that imparts distinct conformations to the recruited β-arrestin, thus regulating its functional activities.

Elucidation of G-protein and β-arrestin functional selectivity at the dopamine D2 receptor

“…G protein-mediated signaling is rapid and transient, and engagement of β-arrestin inhibits the G-protein pathways. In addition, formation of the GPCR/β-arrestin complex normally depends upon phosphorylation of the receptor (32). Moreover, G proteins and β-arrestins can engage the same pathway but with distinct cellular consequences.…”

Structural dynamics and energetics underlying allosteric inactivation of the cannabinoid receptor CB 1

“…Arrestin recruitment and MAPK signaling by the G-protein inactive receptor could be triggered by interactions of an arrestin signaling complex with a distinct receptor phosphorylation pattern that may occur for the Org 27569 bound receptor, analogous to the effect of carvedilol on the β 2 -adrenoreceptor (46). Such a distinct phosphorylation pattern could be instigated by GRK5 (or GRK6), which has recently been shown to phosphorylate inverse agonist bound β 2 -adrenoreceptor and even rhodopsin (47).…”

A stress response pathway in mice upregulates somatostatin level and transcription in pancreatic delta cells through Gs and β-arrestin 1

“…In addition, β2ARs can also activate Gi signalling or form receptor-arrestin complexes to initiate the 'second wave' of signalling [16,17]. We investigated the expression of key effectors downstream of the β-adrenergic receptors.…”