AKAP79 Controls β1‐Adrenergic Receptor Trafficking by Multiple Regulatory Mechanisms

Chronic activation of G protein‐coupled receptors promotes their endocytosis from cell membranes into intracellular endosomes. Efficient trafficking of these receptors back into the cell membrane is critical for receptor resensitization. Trafficking of many GPCR is dependent on cis ‐acting domains and trans ‐acting factors. Examples of cis ‐acting domains in the β1‐adrenergic receptor (β1‐AR) are the type‐1 PDZ domain located in the carboxy‐terminus and serine at position 312 in the 3 rd intra‐cellular loop of the β1‐AR., which is a substrate for phosphorylation by the cyclic AMP‐dependent protein kinase (PKA). In the β1‐AR, the PDZ type‐1 domain binds to a complex composed of synapse associated protein 97 (SAP97) and A‐kinase anchoring protein‐79 (AKAP79). The c‐terminus of AKAP79 in turn binds PKA, which phosphorylates Ser 312 upon the activation of the β1‐AR signaling pathway. Preliminary studies showed that AKAP79 was involved in trafficking of the β1‐AR, but its precise mechanism was obscure. In this study, we determined that selective down regulation of AKAP79 inhibited the recycling of the WT β1‐AR in HEK‐293 cells and its restoration rescued the recycling of the agonist‐internalized β1‐AR. There are several functional domains in AKAP79 including PKA and PKC binding, membrane targeting/binding, SAP79 and calcineurin binding. We analyzed by confocal microscopy the effect of deleting each of these domains on the ability of the resulting AKAP79 mutant to rescue the recycling of the β1‐AR. Our data revealed that multiple domains of AKAP79 were required, indicating that the effect of AKAP79 on recycling of the β1‐AR occurred by multiple divergent mechanisms. Therefore membrane targeting of AKAP79 and its binding to other accessory protein were all required for AKAP79‐mediated regulation of β1‐AR trafficking. Funded by NIH HL‐085848.