Assembly of an SAP97-AKAP79-cAMP-dependent protein kinase scaffold at the type 1 PSD-95/DLG/ZO1 motif of the human β1-adrenergic receptor generates a receptosome involved in receptor recycling and networking

Appropriate trafficking of the beta(1)-adrenergic receptor (beta(1)-AR) after agonist-promoted internalization is crucial for the resensitization of its signaling pathway. Efficient recycling of the beta(1)-AR required the binding of the protein kinase A anchoring protein-79 (AKAP79) to the carboxyl terminus of the beta(1)-AR (Gardner, L. A., Tavalin, S. A., Goehring, A., Scott, J. D., and Bahouth, S. W. (2006) J. Biol. Chem. 281, 33537-33553). In this study we show that AKAP79 forms a complex with the type 1 PDZ-binding sequence (ESKV) at the extreme carboxyl terminus of the beta(1)-AR, which is mediated by the membrane-associated guanylate kinase (MAGUK) protein SAP97. Thus, the PDZ and its associated SAP97-AKAP79 complex are involved in targeting the cyclic AMP-dependent protein kinase (PKA) to the beta(1)-AR. The PDZ and its scaffold were required for efficient recycling of the beta(1)-AR and for PKA-mediated phosphorylation of the beta(1)-AR at Ser(312). Overexpression of the catalytic subunit of PKA or mutagenesis of Ser312 to the phosphoserine mimic aspartic acid both rescued the recycling of the trafficking-defective beta(1)-ARAPDZ mutant. Thus, trafficking signals transmitted from the PDZ-associated scaffold in the carboxyl terminus of the beta(1)-AR to Ser312 in the 3rd intracellular loop (3rd IC) were paramount in setting the trafficking itinerary of the beta(1)-AR. The data presented here show that a novel beta(1)-adrenergic receptosome is organized at the beta(1)-AR PDZ to generate a scaffold essential for trafficking and networking of the beta(1)-AR.