THE AMINO-TERMINUS OF INSULIN-RESPONSIVE AMINOPEPTIDASE CAUSES GLUT4 TRANSLOCATION IN 3T3-L1 ADIPOCYTES

The insulin-responsive aminopeptidase (IRAP) is a constituent of the v esicles that contain the insulin-regulated glucose transporter (Glut4) . Like Glu4, IRAP translocates to the cell surface in response to insu lin, Microinjection into 3T3-L1 adipocytes of a glutathione S-transfer ase (GST) fusion protein containing the cytosolic portion of IRAP (GST -IRAP-(1-109)), resulted in translocation of Glut4 to the cell surface , Immunostaining of 3T3-L1 adipocytes for Glut4 showed that the percen tage of cells with substantial cell surface Glut4 was 10% in unstimula ted cells, 8% following injection of GST, and 27% following injection of GST-IRAP-(1-109). Increased cell surface Glut4 occurred within 5-10 min following injection and was maintained for at least 4 h, A fusion protein containing only 28 amino acids from IRAP (GST-IRAP-(55-82)) w as as effective in increasing cell surface Glut4 as stimulation with 1 00 nM insulin (44% versus 43%, respectively), In contrast to insulin-s timulated Glut4 translocation, the redistribution of Glut4 following i njection of GST-IRAP-(55-82) was not blocked by wortmannin or co-injec tion with a SH2 domain from the regulatory subunit of phosphatidylinos itol 3-kinase. These data suggest that the amino terminus of IRAP inte racts with a retention/sorting protein that also regulates the distrib ution of Glut4 in insulin-responsive cells.