β-Arrestin Scaffolding of the ERK Cascade Enhances Cytosolic ERK Activity but Inhibits ERK-mediated Transcription following Angiotensin AT1a Receptor Stimulation

Abstract

␤-Arrestins are cytosolic proteins that mediate homologous desensitization of G protein-coupled receptors (GPCRs) by binding to agonist-occupied receptors and by uncoupling them from heterotrimeric G proteins. The recent finding that ␤-arrestins bind to some mitogen-activated protein (MAP) kinases has suggested that they might also function as scaffolds for GPCR-stimulated MAP kinase activation. To define the role of ␤-arrestins in the regulation of ERK MAP kinases, we examined the effect of ␤-arrestin overexpression on ERK1/2 activation and nuclear signaling in COS-7 cells expressing angiotensin II type 1a receptors (AT1aRs). Expression of either ␤-arrestin1 or ␤-arrestin2 reduced angiotensin-stimulated phosphatidylinositol hydrolysis but paradoxically increased angiotensin-stimulated ERK1/2 phosphorylation. The increase in ERK1/2 phosphorylation in ␤-arrestin-expressing cells correlated with activation of a ␤-arrestin-bound pool of ERK2. The ␤-arrestindependent increase in ERK1/2 phosphorylation was accompanied by a significant reduction in ERK1/2-mediated, Elk1-driven transcription of a luciferase reporter. Analysis of the cellular distribution of phospho-ERK1/2 by confocal immunofluorescence microscopy and cellular fractionation revealed that overexpression of ␤-arrestin resulted in a significant increase in the cytosolic pool of phospho-ERK1/2 and a corresponding decrease in the nuclear pool of phospho-ERK1/2 following angiotensin stimulation. ␤-Arrestin overexpression resulted in formation of a cytoplasmic pool of ␤-arrestinbound phospho-ERK, decreased nuclear translocation of phospho-ERK1/2, and inhibition of Elk1-driven luciferase transcription even when ERK1/2 was activated by overexpression of cRaf-1 in the absence of AT1aR stimulation. These data demonstrate that ␤-arrestins facilitate GPCR-mediated ERK activation but inhibit ERKdependent transcription by binding to phospho-ERK1/2, leading to its retention in the cytosol. The G protein-coupled receptor (GPCR)1 superfamily is composed of a diverse array of membrane receptors that share a conserved seven-transmembrane domain architecture. In response to receptor occupancy, GPCRs promote the activation of heterotrimeric G proteins by catalyzing the exchange of GDP for GTP on the G␣ subunit and dissociation of the G␣ subunit from the G␤␥ subunit heterodimer. Once dissociated, free G␣-GTP and G␤␥ subunits regulate the activity of enzymatic effectors, such as adenylyl cyclases and phospholipase C isoforms.For the majority of GPCRs, productive G protein coupling in the continued presence of agonist is terminated by receptor phosphorylation followed by the binding of arrestins (1, 2). Specialized G protein-coupled receptor kinases phosphorylate agonist-occupied GPCRs, increasing their affinity for arrestins. Upon binding the receptor, arrestins sterically block further coupling between GPCR and G protein. In addition, the two non-visual arrestins, ␤-arrestin1 and 2, target GPCRs for endocytosis by linking the GPCR to components of the cellular endocytic machi...

Arrestins and two receptor kinases are upregulated in Parkinson's disease with dementia

“…Arrestins work as scaffolds recruiting a number of components of several MAPK cascades to activated GPCRs, thereby mediating activation of the MAPK pathways. In particular, both non-visual arrestins have been shown to activate ERK [66,87,100]. Over-expression of arrestins potentiates arrestin-mediated ERK activation [100,101].…”

“…In particular, both non-visual arrestins have been shown to activate ERK [66,87,100]. Over-expression of arrestins potentiates arrestin-mediated ERK activation [100,101]. Conversely, reduction of the arrestin concentration by siRNAs inhibits ERK activation [3].…”

Reciprocal Regulation of Angiotensin Receptor-activated Extracellular Signal-regulated Kinases by β-Arrestins 1 and 2

“…This is as a signal transducer and adaptor which scaffolds a variety of signaling molecules, for example, Src family kinases (6 -8) and components of mitogen-activated protein kinase (MAPK) cascades, leading to their activation (8 -14). Such scaffolding and targeting of activated extracellular signal-regulated kinases (ERKs) to a cytoplasmic vesicular compartment has been demonstrated for angiotensin II type 1A (AT 1A ) (11,12), neurokinin 1 (8), proteinase-activated (9), and vasopressin 2 (V 2 ) receptors (13). Overexpression of ␤-arrestins enhances cytosolic ERK activation following stimulation of AT 1A or V 2 receptors (11)(12)(13).…”

“…Such scaffolding and targeting of activated extracellular signal-regulated kinases (ERKs) to a cytoplasmic vesicular compartment has been demonstrated for angiotensin II type 1A (AT 1A ) (11,12), neurokinin 1 (8), proteinase-activated (9), and vasopressin 2 (V 2 ) receptors (13). Overexpression of ␤-arrestins enhances cytosolic ERK activation following stimulation of AT 1A or V 2 receptors (11)(12)(13). In addition, studies using the RNA interference (RNAi) technique have demonstrated that ␤-arrestin2 mediates G protein-independent ERK1/2 activation following AT 1A receptor stimulation (15), as well as that ␤-arrestin2 is required for CXCR4 chemokine receptor-mediated ERK1/2 and p38 activation (16).…”

GIPC Recruits GAIP (RGS19) To Attenuate Dopamine D2Receptor Signaling

“…Clathrin-coated pits, where receptors, GIPC, GAIP, and G proteins could all meet, are important sites for the assembly of endocytosis and MAP-kinase signaling machineries (Luttrell et al, 1999). Indeed, ␤-arrestin2, which serves as a scaffold protein for GPCR endocytosis (Goodman et al, 1996) and GPCR-induced Erk activation (Tohgo et al, 2002), colocalized with GIPC in D 2 R-expressing cells stimulated by quinpirole (Supplementary Information; Figure 5). Thus, the GIPC and GAIP could take part in the GPCR-associated scaffold that connects both tightly related machineries.…”