THE M(R) 35,000 BETA-ADRENERGIC-RECEPTOR MESSENGER RNA-BINDING PROTEIN-INDUCED BY AGONISTS REQUIRES BOTH AN AUUUA PENTAMER AND U-RICH DOMAINS FOR RNA RECOGNITION

Delineating the molecular basis for agonist-induced destabilization of mRNA of G-protein-linked receptors that contributes to receptor down- regulation is fundamental to our understanding of long-term regulation of receptors by agonist. Previously we identified a prominent, M(r) 3 5,000 cytosolic RNA-binding protein that (i) binds selectively to beta 1- and beta2-adrenergic receptor mRNAs, both of which undergo agonist- induced down-regulation; (ii) does not bind either to alpha1b-adrenerg ic receptor mRNA, which does not undergo agonist-induced down-regulati on, or to beta-globin mRNA; (iii) displays binding to beta2-adrenergic receptor mRNA that is selectively competed by poly(U) RNA, but not po ly(A), -(C), or -(G) RNA; and (iv) its abundance varies inversely with the level of receptor mRNA, being induced by agonists that down-regul ate receptor mRNA (Port, J. D., Huang, L.-y., and Malbon (1992) J. Bio l. Chem. 267,24103-24108). We demonstrate here that the binding of bet a-adrenergic receptor mRNA by this protein, termed beta-ARB protein, i s sensitive to competition by AU-rich domains of the 3'-untranslated r egions of c-fos, c-myc, and human granulocyte-macrophage colony-stimul ating factor. Using the AU-rich 3'-untranslated regions of wild-type a denovirus IVa2 mRNA and variants with defined mutations in the AUUUA p entamer, AU-rich, and U-rich domains, we were able to define sequences critical to the binding of the beta2-receptor mRNA by the beta-ARB pr otein. Recognition of beta-ARB protein requires not only an AUUUA dest abilization pentamer, but also a flanking U-rich domain(s). Using radi olabeled 3'-untranslated regions of short-lived mRNA, we were able to identify this same M(r) 35,000 cytosolic RNA-binding protein(s), beta- ARB protein, as selective for beta2-adrenergic receptor mRNA.