Purification and characterization of beta-adrenergic receptor mRNA-bindingproteins

beta-Adrenergic receptors (beta-ARs), like other G-protein-coupled receptor s, can undergo post-transciptional regulation at the level of mRNA stabilit y. In particular, the human beta(1)- and beta(2)-ARs and the hamster beta(2 )-AR mRNA undergo beta-agonist-mediated destabilization. By UV cross-linkin g, we have previously described an similar to M-r 36,000 mRNA-binding prote in, beta ARB, that binds to A/C+U-rich nucleotide regions within 3'-untrans lated regions. Further, we have demonstrated previously that beta ARB is im munologically distinct from AUF1/heterogeneous nuclear ribonucleoprotein (h nRNP) D, another mRNA-binding protein associated with destabilization of AU-rich mRNAs (Pende, A., Tremmel, K. D., De-Maria, C. T., Blaxall, B. C., M inobe, W., Sherman, J. A., Bisognano, J., Bristow, M. R., Brewer, G., and P ort, J. D. (1996) J. Biol. Chem. 271, 8493-8501). In this report, we descri be the peptide composition of beta ARB. Mass spectrometric analysis of an s imilar to M-r 36,000 band isolated from ribosomal salt wash proteins reveal ed the presence of two mRNA-binding proteins, hnRNP Al, and the elav-like p rotein, HuR, both of which are known to bind to A+U-rich nucleotide regions . By immunoprecipitation, HuR appears to be the biologically dominant RNA b inding component of beta ARB. Although hnRNP Al and HuR can both be immunop recipitated from ribosomal salt wash proteins, the composition of beta ARB (HuR alone versus HuR and hnRNP Al) appears to be dependent on the mRNA pro be used. The exact role of HuR and hnRNP Al in the regulation of beta-AR mR NA stability remains to be determined.