Selective inhibition of α1A-adrenergic receptor signaling by RGS2 association with the receptor third intracellular loop

Abstract

Regulators of G-protein signaling (RGS) proteins act directly on Gα subunits to increase the rate of GTP hydrolysis and to terminate signaling. However, the mechanisms involved in determining their specificities of action in cells remain unclear. Recent evidence has raised the possibility that RGS proteins may interact directly with G-protein-coupled receptors to modulate their activity. By using biochemical, fluorescent imaging, and functional approaches, we found that RGS2 binds directly and selectively to the third intracellular loop of the α1A-adrenergic receptor (AR) in vitro, and is recruited by the unstimulated α1A-AR to the plasma membrane in cells to inhibit receptor and Gq/11 signaling. This interaction was specific, because RGS2 did not interact with the highly homologous α1B- or α1D-ARs, and the closely related RGS16 did not interact with any α1-ARs. The N terminus of RGS2 was required for association with α1A-ARs and inhibition of signaling, and amino acids Lys219, Ser220, and Arg238 within the α1A-AR i3 loop were found to be essential for this interaction. These findings demonstrate that certain RGS proteins can directly interact with preferred G-protein-coupled receptors to modulate their signaling with a high degree of specificity. © 2005 by The American Society for Biochemistry and Molecular Biology, Inc.