Evidence for a role for ADP-ribosylation factor 6 in insulin-stimulated glucose transporter-4 (GLUT4) trafficking in 3T3-L1 adipocytes

ADP-ribosylation factors (ARFs) play important roles in both constitutive a nd regulated membrane trafficking to the plasma membrane in other cells. He re we have examined their role in insulin-stimulated GLUT4 translocation in 3T3-L1 adipocytes. These cells express ARF5 and ARF6. ARF5 was identified in the soluble protein and intracellular membranes; in response to insulin some ARF5 was observed to re-locate to the plasma membrane. In contrast, AR F6 was predominantly localized to the plasma membrane and did not redistrib ute in response to insulin. We employed myristoylated peptides correspondin g to the NH, termini of ARF5 and ARF6 to investigate the function of these proteins. Myr-ARF6 peptide inhibited insulin-stimulated glucose transport a nd GLUT4 translocation by similar to 50% in permeabilized adipocytes. In co ntrast, myr-BRF1 and myr-ARF5 peptides were without effect. Myr-ARF5 peptid e also inhibited the insulin stimulated increase in cell surface levels of GLUT1 and transferrin receptors. Myr-ARF6 peptide significantly decreased c ell surface levels of these proteins in both basal and insulin-stimulated s tates, but did not inhibit the fold increase in response to insulin. These data suggest an important role for ARF6 in regulating cell surface levels o f GLUT4 in adipocytes, and argue for a role for both ARF5 and ARF6 in the r egulation of membrane trafficking to the plasma membrane.