Low affinity of beta1-adrenergic receptor for beta-arrestins explains the resistance to agonist-induced internalization.

It has been reported that beta-arrestin is essential for the internalization of many G protein-coupled receptors. Since beta1-adrenergic receptor (beta1AR) shows the resistance to agonist-induced internalization, we examine the interaction of beta-arrestin with beta1AR with three different approaches: translocation of beta-arrestin to the plasma membrane, direct binding of in vitro translated beta-arrestin to intracellular domains of beta1- and beta2ARs, inhibition of beta1- and beta2AR-stimulated adenylyl cyclase activities by beta-arrestin. The enhanced green fluorescent protein (EGFP)-tagged beta-arrestin 2 (beta-arrestin 2-GFP) translocates to and stays at the plasma membrane by beta2AR stimulation. Beta-arrestin 2-GFP also translocates to the plasma membrane upon beta1AR stimulation. However, it returns to the cytoplasm 10 - 30 min after agonist stimulation. The amount of beta-arrestin bound to the third intracellular loop and the carboxyl tail of beta1AR is lower than that of beta2AR. The fusion protein of beta-arrestin 1 with glutathione-S-transferase inhibits the beta1- and beta2AR-stimulated adenylyl cyclase activities. However, inhibition of the beta1AR-stimulated activity requires a higher amount of the fusion protein than that of the beta2AR-stimulated activity. These results suggest that affinity of beta1AR for beta-arrestins is lower than that of beta2AR, and explains the resistance to agonist-induced internalization. This conclusion is further supported by the finding that beta-arrestin can induce internalization of beta1AR when beta-arrestin 1 fused to the carboxyl tail of beta1AR.