Emerging paradigms of β-arrestin-dependent seven transmembrane receptor signaling

Abstract

β-arrestins, originally discovered to desensitize activated seven transmembrane receptors (7TMRs; also known as G protein-coupled receptors [GPCRs]), are now well established mediators of receptor endocytosis, ubiquitylation and G protein-independent signaling. Recent global analyses of β-arrestin interactions and β-arrestin-dependent phosphorylation events have uncovered several previously unanticipated roles of β-arrestins in a range of cellular signaling events. These findings strongly suggest that the functional roles of β-arrestins are much broader than currently understood. Biophysical studies aimed at understanding multiple active conformations of the 7TMRs and the β-arrestins have begun to unravel the mechanistic basis for the diverse functional capabilities of β-arrestins in cellular signaling.

Noncanonical GPCR signaling arising from a PTH receptor–arrestin–Gβγ complex

“…For these assays, Gβγ CFP was expressed in HEK293 cells stably expressing HA-tagged PTHR (HA-PTHR), and cell lysates were prepared at different time points after a short exposure to either M-PTH(1-28) or M-PTH (1)(2)(3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14), modified analogs of PTH that induce longer or shorter cAMP generation and biological responses, respectively (20). The difference in duration of cAMP signaling is thought to depend on the capacity of M-PTH(1-28), like PTH , to form an unusually persistent high-affinity complex with PTHR that is independent of G-protein coupling, whereas M-PTH(1-14) forms a more conventional high-affinity complex that is transient and dependent on G-protein coupling (2,20,21).…”

“…The difference in duration of cAMP signaling is thought to depend on the capacity of M-PTH(1-28), like PTH , to form an unusually persistent high-affinity complex with PTHR that is independent of G-protein coupling, whereas M-PTH(1-14) forms a more conventional high-affinity complex that is transient and dependent on G-protein coupling (2,20,21). The interactions of HA-PTHR with Gβγ CFP and β-arrestins, weakly detectable under basal conditions, increased significantly within 5 min after challenge with M-PTH (1)(2)(3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14) or M-PTH(1-28) (Fig. S1).…”

“…S3A). When PTHR was activated by M-PTH (1)(2)(3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14), the diffusion of Gβγ remained unchanged (Fig. S3B).…”

“…In either case, the classical model predicts that arrestin negatively regulates the levels of the L-R*-G complex, providing the main mechanism by which the signal of a GPCR system is turned off (4,5). This model, primarily derived from the analysis of the behavior of the β 2 -adrenergic receptor (β 2 -AR) (4,5) and many other class 1 GPCRs (6)(7)(8)(9)(10)(11)(12), is taken to be universal for GPCR biology (13). Recent findings have challenged this view.…”

Evidence that Behavioral Phenotypes of Morphine in β-arr2−/− Mice Are Due to the Unmasking of JNK Signaling

“…One of the many examples that the ubiquitously expressed arrestins serve as more than terminators of receptor signaling through initiating receptor internalization (Groer et al, 2011;Shenoy and Lefkowitz, 2011;Shukla et al, 2011) is the phenotype of mice lacking b-arrestin 2 (b-arr2À/À; Bohn et al, 1999Bohn et al, , 2002Raehal and Bohn, 2011). As morphine does not induce significant internalization of the mu opioid receptor, the effects of morphine in b-arr2À/À mice cannot be explained by this prototypical role of barrestin 2.…”