Louis M. Luttrell , Jialu Wang , Bianca Plouffe , Jeffrey S. Smith , Lama Yamani , Suneet Kaur , Pierre-Yves Jean-Charles , Christophe Gauthier , Mi-Hye Lee , Biswaranjan Pani , Jihee Kim , Seungkirl Ahn , Sudarshan Rajagopal , Eric Reiter , Michel Bouvier , Sudha K. Shenoy , Stéphane A. Laporte , Howard A. Rockman , Robert J. Lefkowitz
September 25 2018
September 25 2018
G protein–coupled receptors (GPCRs) use diverse mechanisms to regulate the mitogen-activated protein kinases ERK1/2. β-Arrestins (βArr1/2) are ubiquitous inhibitors of G protein signaling, promoting GPCR desensitization and internalization and serving as scaffolds for ERK1/2 activation. Studies using CRISPR/Cas9 to delete βArr1/2 and G proteins have cast doubt on the role of β-arrestins in activating specific pools of ERK1/2. We compared the effects of siRNA-mediated knockdown of βArr1/2 and reconstitution with βArr1/2 in three different parental and CRISPR-derived βArr1/2 knockout HEK293 cell pairs to assess the effect of βArr1/2 deletion on ERK1/2 activation by four G s-coupled GPCRs. In all parental lines with all receptors, ERK1/2 stimulation was reduced by siRNAs specific for βArr2 or βArr1/2. In contrast, variable effects were observed with CRISPR-derived cell lines both between different lines and with activation of different receptors. For β 2 adrenergic receptors (β 2ARs) and β 1ARs, βArr1/2 deletion increased, decreased, or had no effect on isoproterenol-stimulated ERK1/2 activation in different CRISPR clones. ERK1/2 activation by the vasopressin V 2 and follicle-stimulating hormone receptors was reduced in these cells but was enhanced by reconstitution with βArr1/2. Loss of desensitization and receptor internalization in CRISPR βArr1/2 knockout cells caused β 2AR-mediated stimulation of ERK1/2 to become more dependent on G proteins, which was reversed by reintroducing βArr1/2. These data suggest that βArr1/2 function as a regulatory hub, determining the balance between mechanistically different pathways that result in activation of ERK1/2, and caution against extrapolating results obtained from βArr1/2- or G protein–deleted cells to GPCR behavior in native systems.