Two barcodes encoded by the type-1 PDZ and by phospho-Ser regulate retromer/WASH-mediated sorting of the ß-adrenergic receptor from endosomes to the plasma membrane.

Recycling of the majority of agonist-internalized GPCR is dependent on a type I-PDZ "barcode" in their C-tail. The recycling of wild-type (WT) ß-AR is also dependent on its default "type-1 PDZ barcode", but trafficking of the ß-AR is inhibited when PKA or its substrate serine at position 312 (Ser) are inactivated. We tested the hypothesis that phospho-Ser provided a second barcode for ß-AR sorting from endosomes to the plasma membrane by determining the role of retromer/WASH complexes in ß-AR trafficking. Recycling of WT ß-AR or WT ß-AR was dependent on targeting the retromer to endosomal membranes via SNX3 and rab7a, and on complexing the retromer to the WASH pentamer via the C-tail of FAM21 (FAM21). These maneuvers however, did not inhibit the recycling of a phospho-Ser ß-AR mimic ((S312D) ß-AR). Knockdown of the trans-acting PDZ protein sorting nexin27 (SNX27) inhibited the recycling of WT ß-AR and WT ß-AR, but had no effect on (S312D) ß-AR∆PDZ or on phosphorylation of WT ß-AR by PKA at Ser. However, depletion of FKBP15, a FAM21-binding endosomal protein, selectively inhibited WT ß-AR but not ß-AR recycling, suggesting divergence might exist in GPCR trafficking roadmaps. These results indicate that two barcodes are involved in sorting WT ß-AR out of early endosomes. The first and antecedent "barcode" was the "type-1 PDZ", followed by a second reversible "phospho-Ser" verification "barcode". This organization allows tight regulation of ß-AR density to signaling intensity in conditions associated with aberrant ß-AR signaling such as in hypertension and heart failure.