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 guani ne nucleotide exchange protein that functions in regulation of transla tion, was observed to associate with the carboxyl-terminal cytoplasmic domains of the alpha(2A)- and alpha(2B)-adrenergic receptors in a yea st two-hybrid screen of a cDNA library prepared from 293 cells, This p rotein association was confirmed in vitro by affinity chromatography a nd was shown to be specific for a subset of G protein-coupled receptor s, including the alpha(2A)-, alpha(2B)-, alpha(2C)-, and beta(2)-adren ergic receptors, but not the vasopressin (V-2) receptor. Association o f these proteins in vivo was confirmed by specific co-immunoprecipitat ion of eIF-2B alpha with full-length beta(2)-adrenerse receptors expre ssed in transfected 293 cells and by fluorescence microscopy showing c o-localization of these proteins in intact cells. Remarkably, eIF-2B a lpha 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 sign ificant enhancement of beta(2)-adrenergic receptor-mediated activation of adenylyl cyclase, without affecting forskolin or V-2 receptor-medi ated activation, These observations suggest a new role for a previousl y identified guanine nucleotide exchange protein in membrane biology a nd cell signaling.