The effect of β‐agonist on expression and trafficking of β2‐adrenergic receptors with N‐terminal polymorphisms

Abstract

The β2‐Adrenergic receptor (β2AR) is an important target for asthma medications. Stimulation of β2AR by agonist inhibits contractile processes and results in bronchodilation. Studies suggest that polymorphisms of the β2AR may act as disease modifiers. We hypothesized that polymorphisms at positions 16 and 27 result in differential expression and trafficking of β2AR following β‐agonist exposure. The functional consequences of these polymorphisms of the β2AR were studied using site‐directed mutagenesis and recombinant expression in HEK293 cells. No differences in receptor density were noted between isoforms after 20 min or 2 h isoproterenol (ISO) treatment in ligand binding assays. However, after 24 h exposure to 1μM ISO, isoforms with Arg16 underwent increased downregulation or reduced receptor density (50.6±2.9% and 70.2±1.7% for R16Q27 and R16E27, respectively) compared to isoforms with Gly16 (27.7±4.2 and 23.2±5.4% for G16Q27 and G16E27, respectively). However, there was no difference between isoforms in co‐localization with Lamp1 (a lysosomal marker) in untreated cells and cells treated with ISO for 24 h. These findings are consistent with an inhibition of β2AR recycling by the Arg16 polymorphism. These results may contribute to understanding the genotype‐specific differences in humans in response to β‐agonist therapy. Support has been provided in part by the Arkansas Biosciences Institute.