Intracellular Trafficking and Secretion of Adiponectin is Dependent on GGA Coated Vesicles

Adiponectin is an insulin‐sensitizing hormone secreted by adipose tissue. Our objective was to study the intracellular distribution and trafficking of this hormone in adipocytes. Confocal fluorescent microscopy demonstrated the colocalization of adiponectin with the Golgi membrane markers p115, ß‐COP and the trans‐Golgi Network marker, Syntaxin 6. Consistent with this localization, treatment of cells with Brefeldin A inhibited secretion of adiponectin. Adiponectin colocalized with the adaptor molecule GGA1myc (for Golgi‐localizing γ‐adaptin ear homology ARF binding protein‐1), but not with GGA2myc or GGA3myc isoforms. Furthermore, transmission electron microscopy demonstrated the colocalization of endogenous GGA1 with adiponectin in mice adipocytes. In addition, adiponectin containing vesicles were precipitated by a GST‐GGA1 fusion protein but not with a GST‐GGA2 or GST‐GGA3 fusion proteins. Moreover, co‐expression of adiponectin with a GGA1 dominant interfering mutant (GGA1‐VHS GAT domain) resulted in a marked inhibition of adiponectin secretion in both 3T3L1 adipocytes and HEK293 cells, whereas no inhibition was detected with the truncated mutants GGA2‐VHSGAT or GGA3‐VHSGAT. Moreover, wild type GGA1 enhanced secretion of adiponectin in HEK293 cells. Interestingly, leptin secretion was unaffected by neither the wild type form or GGA1 nutant. Taken together these results suggest that the trafficking and secretion of adiponectin is dependent on GGA1‐coated vesicles. Funding: American Diabetes Association.