ADP-ribosylation factor 6 (ARF6) defines two insulin-regulated secretory pathways in adipocytes

ADP-ribosylation factor 6 (ARF6) appears to play an essential role in the e ndocytic/recycling pathway in several cell types. To determine whether ARF6 is involved in insulin-regulated exocytosis, 3T3-L1 adipocytes were infect ed with recombinant adenovirus expressing wildtype ARF6 or an ARF6 dominant negative mutant (D125N) that encodes a protein with nucleotide specificity modified from guanine to xanthine, Overexpression of these ARF6 proteins a ffected neither basal nor insulin-regulated glucose uptake in 3T3-L1 adipoc ytes, nor did it affect the subcellular distribution of Glut1 or Glu4. In c ontrast, the secretion of adipsin, a serine protease specifically expressed in adipocytes, was increased by the expression of wild-type ARF6 and was i nhibited by the expression of D125N, These results indicate a requirement f or ARF6 in basal and insulinregulated adipsin secretion but not in glucose transport. Our results suggest the existence of at least two distinct pathw ays that undergo insulin-stimulated exocytosis in 3T3-L1 adipocytes, one fo r adipsin release and one for glucose transporter translocation.