Low affinity of β ₁ -adrenergic receptor for β-arrestins explains the resistance to agonist-induced internalization

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