Abstract 764: Characterization Of A Novel Receptosome Involved In Signaling, Trafficking And Networking Of The Human Beta-1-adrenergic Receptor
The beta1-adrenergic receptor (beta1-AR) mediates many of the cardiovascular actions of catecholamines and its down-regulation is a hallmark of cardiac failure. Persistent activation of the human beta1-AR causes its selective internalization, while its recycling and resensitization requires two domains. One is the serine at position 312 (Ser312) in the 3rd intracellular loop of the beta1-AR and the other is the type-1 PDZ-binding sequence (ESKV) at the extreme carboxy-terminus of the human beta1-AR. Ser312 is phosphorylated by the cyclic AMP-dependent protein kinase (PKA), which imparts a recycling signal to the beta1-AR. Anchorage of PKA to A-kinase anchoring protein-79 (AKAP79) is required for efficient phosphorylation of Ser312 and recycling of the beta1-AR. Using co-immunoprecipitations and FRET microscopy, we determined that the type-1 PDZ of the beta1-AR binds to the membrane-associated guanylate-kinase (MAGUK) protein SAP97. SAP97 in turn binds to the AKAP79-PKA complex to target PKA to the carboxy-tail of the human beta1-AR. The contribution of the type-1 PDZ to recycling can be overcome either by overexpression of the catalytic subunit of PKA (cPKA) or mutagenesis of Ser312 to the phosphoserine mimic aspartic acid. Thus, Ser312 occupies a hierarchical position to the type-1 PDZ in setting the trafficking itinerary of the human beta1-AR. The data presented here show that a novel beta1-adrenergic receptosome is organized at the type-1 PDZ of the human beta1-AR to generate a scaffold essential for trafficking and networking of the beta1-AR. This novel beta1-AR signalosome might explain unique aspects of beta1-AR signaling in the heart that underlie some of the aberrant beta1-AR signaling events observed in the failing human myocardium.