beta-Arrestin scaffolding of the ERK cascade enhances cytosolic ERK activity but inhibits ERK-mediated transcription following angiotensin AT1a receptor stimulation.
beta-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 beta-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 beta-arrestins in the regulation of ERK MAP kinases, we examined the effect of beta-arrestin overexpression on ERK1/2 activation and nuclear signaling in COS-7 cells expressing angiotensin II type 1a receptors (AT1aRs). Expression of either beta-arrestin1 or beta-arrestin2 reduced angiotensin-stimulated phosphatidylinositol hydrolysis but paradoxically increased angiotensin-stimulated ERK1/2 phosphorylation. The increase in ERK1/2 phosphorylation in beta-arrestin-expressing cells correlated with activation of a beta-arrestin-bound pool of ERK2. The beta-arrestin-dependent 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 beta-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. beta-Arrestin overexpression resulted in formation of a cytoplasmic pool of beta-arrestin-bound 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 beta-arrestins facilitate GPCR-mediated ERK activation but inhibit ERK-dependent transcription by binding to phospho-ERK1/2, leading to its retention in the cytosol.
Tohgo
Akira
A
Howard Hughes Medical Institute and the Departments of Medicine and Biochemistry, Duke University Medical Center, Durham, North Carolina 27710, USA.
Pierce
Kristen L
KL
Choy
Eric W
EW
Lefkowitz
Robert J
RJ
Luttrell
Louis M
LM
D000818:Animals; D019390:Arrestins / Q000502:physiology*; D019556:COS Cells; D003600:Cytosol / Q000201:enzymology*; D019204:GTP-Binding Proteins / Q000502:physiology; D006868:Hydrolysis; D020935:MAP Kinase Signaling System / Q000187:drug effects*; D020928:Mitogen-Activated Protein Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D010716:Phosphatidylinositols / Q000378:metabolism; D010766:Phosphorylation; D011506:Proteins / Q000502:physiology; D044140:Receptor, Angiotensin, Type 1; D011945:Receptors, Angiotensin / Q000187:drug effects / Q000502:physiology*; D011956:Receptors, Cell Surface / Q000502:physiology; D048008:TNF Receptor-Associated Factor 3; D014158:Transcription, Genetic; D000071557:beta-Arrestins
D019390:Arrestins; D010716:Phosphatidylinositols; D011506:Proteins; D044140:Receptor, Angiotensin, Type 1; D011945:Receptors, Angiotensin; D011956:Receptors, Cell Surface; D048008:TNF Receptor-Associated Factor 3; D000071557:beta-Arrestins; D020928:Mitogen-Activated Protein Kinases; D019204:GTP-Binding Proteins