A novel interaction between adrenergic receptors and the alpha-subunit of eukaryotic initiation factor 2B

The alpha-subunit of eukaryotic initiation factor 2B (eIF-2B), a guanine nucleotide exchange protein that functions in regulation of translation, was observed to associate with the carboxyl-terminal cytoplasmic domains of the alpha(2A)- and alpha(2B)-adrenergic receptors in a yeast two-hybrid screen of a cDNA library prepared from 293 cells, This protein association was confirmed in vitro by affinity chromatography and was shown to be specific for a subset of G protein-coupled receptors, including the alpha(2A)-, alpha(2B)-, alpha(2C)-, and beta(2)-adrenergic receptors, but not the vasopressin (V-2) receptor. Association of these proteins in vivo was confirmed by specific co-immunoprecipitation of eIF-2B alpha with full-length beta(2)-adrenerse receptors expressed in transfected 293 cells and by fluorescence microscopy showing co-localization of these proteins in intact cells. Remarkably, eIF-2B alpha co-localized with receptors exclusively in regions of the plasma membrane that are in contact with the extracellular medium, but failed to associate with membranes making cell-cell contacts, Overexpression of eIF-2B alpha in 293 cells caused a small (similar to 15%) but significant enhancement of beta(2)-adrenergic receptor-mediated activation of adenylyl cyclase, without affecting forskolin or V-2 receptor-mediated activation, These observations suggest a new role for a previously identified guanine nucleotide exchange protein in membrane biology and cell signaling.