The GGA Family Proteins Modulate the Cell Surface Transport of α_2B‐Adrenergic Receptor through Specific Interactions

Molecular mechanisms governing the cell surface transport of G‐protein‐coupled receptors (GPCRs) remain poorly elucidated. Here, we used α 2B ‐adrenergic receptor (α 2B ‐AR) as a model GPCR to determine the role of three Golgi‐localized, γ‐adaptin ear domain homology, ADP ribosylation factor‐binding proteins (GGAs), one family of adaptor proteins for clathrin‐coated vesicles involved in the trans‐Golgi network (TGN)‐to‐endosome transport. It has been well described that the function of GGAs is tightly controlled by interactions via their VHS domain with the acidic LL motifs presented in the C‐terminus of cargo molecules. We found that shRNA‐mediated depletion of individual GGAs strongly arrested α 2B ‐AR in the Golgi/TGN and significantly reduced the cell surface expression and signaling of the receptor. We further demonstrated that GGAs physically associated with α 2B ‐AR through specific domains. The GGA‐binding domains were mapped to the C‐terminal regions in the third intracellular loop of α 2B ‐AR, whereas α 2B ‐AR‐binding domains were identified to the hinge domain of GGA1, the GAE domain of GGA2 and the VHS domain of GGA3. These studies reveal a novel function of the GGA family proteins in the TGN‐to‐plasma membrane transport of α 2B ‐AR which is likely mediated through a non‐conventional mechanism. These data also suggest that the GGA adaptor proteins are important mediators of GPCR cell surface targeting.