A 20-nucleotide (A + U)-rich element of β₂-adrenergic receptor (β₂AR) mRNA mediates binding to β₂AR-binding protein and is obligate for agonist-induced destabilization of receptor mRNA

The M(r) 35,000 β-adrenergic receptor mRNA-binding protein, termed βARB protein, is induced by β-adrenergic agonists and binds to β₂- receptor mRNAs that display agonist-induced destabilization. A cognate sequence in the mRNA was identified previously that provides for βARB protein binding in vitro. In the present work, the sequence established in vitro for binding of βARB protein to hamster β₂-adrenergic receptor mRNA was probed in vivo by site-directed mutagenesis of the 3'-untranslated region and expression in Chinese hamster ovary cells. A 20-nucleotide, (A + U)-rich region in the 3'-untranslated region consisting of an AUUUUA hexamer flanked by defined U-rich regions constitutes the binding domain for βARB protein. U to G substitution in the hexamer region attenuates the binding of βARB protein, whereas U to G substitution of hexamer and flanking U-rich domains abolishes binding of βARB protein and stabilizes β₂-adrenergic receptor mRNA levels in transfectant clones challenged with either isoproterenol or cyclic AMP. These results demonstrate that: binding of βARB protein to the 20-nucleotide, (A + U)-rich domain mediates the agonist and cyclic AMP- induced mRNA decay of G protein-linked receptors, such as the β₂-adrenergic receptor.