G protein-coupled receptor kinase 5 regulates β1-adrenergic receptor association with PSD-95

Abstract

We previously reported that the β1-adrenergic receptor (β1AR) associates with PSD-95 through a PDZ domain-mediated interaction, by which PSD-95 modulates β1AR function and facilitates the physical association of β1AR with other synaptic proteins such as N-methyl-D-aspartate receptors. Here we demonstrate that β1AR association with PSD-95 is regulated by G protein-coupled receptor kinase 5 (GRK5). When β1AR and PSD-95 were coexpressed with either GRK2 or GRK5 in COS-7 cells, GRK5 alone dramatically decreased the association of β1AR with PSD-95, although GRK2 and GRK5 both could be co-immunoprecipitated with β1AR and both could enhance receptor phosphorylation in vivo. Increasing expression of GRK5 in the cells led to further decreased β1AR association with PSD-95. Stimulation with the β1AR agonist isoproterenol further decreased PSD-95 binding to β1AR. In addition, GRK5 protein kinase activity was required for this regulatory effect since a kinase-inactive GRK5 mutant had no effect on PSD-95 binding to β1AR. Moreover, the regulatory effect of GRK5 on β1AR association with PSD-95 was observed only when GRK5 was expressed together with the receptor, but not when GRK5 was coexpressed with PSD-95. Thus, we propose that GRK5 regulates β1AR association with PSD-95 through phosphorylation of β1AR. Regulation of protein association through receptor phosphorylation may be a general mechanism used by G protein-coupled receptors that associate via PDZ domain-mediated protein/protein interactions.