SAP97 Controls β1‐Adrenergic Receptor Trafficking in a PDZ Dependent Manner

Efficient trafficking of the β1‐adrenergic receptor (β1AR) after agonist‐induced internalization is critical for receptor resensitization. Trafficking of many GPCR is dependent on their type‐1 PDZ domains located in the carboxy‐terminus (β1AR‐CT) of these receptors. In the β1‐AR, SAP97 binds to the type‐1 PDZ sequence and acts as an organizer of the scaffold composed of AKAP79 and PKA, which we have termed as the β1‐adrenergic receptosome. In this study we show by far‐Western studies that β1AR‐CT binds only one of the three PDZ domains of SAP97. Moreover, association between the SAP97 PDZ domain and the full‐length β1AR was confirmed by GST‐fusion protein pull‐down and by co‐immunoprecipitations. Since the major function of the type‐1 PDZ sequence of the β1AR is to facilitate the recycling of the agonist‐internalized β1AR, we investigated if other members of the β1‐adrenergic receptosome were also involved. In this report we focused on SAP97. Our data shows that knock down of SAP97 by shRNA inhibited the recycling of the β1‐AR in HEK‐293 cells. Through overexpression of individual SAP97 PDZ proteins we determined that the PDZ domain of SAP97 which binds to the β1‐AR inhibited its recycling, while the other PDZ domains did not. These and other data to be presented reveal that other members of the receptosome were necessary for efficient recycling and resensitization of the agonist‐internalized GPCR. Funded by NIH HL‐085848.