INHIBITORS OF PHOSPHOINOSITIDE 3-KINASE BLOCK EXOCYTOSIS BUT NOT ENDOCYTOSIS OF TRANSFERRIN RECEPTORS IN 3T3-L1 ADIPOCYTES

The role of PI 3-kinase in transferrin receptor recycling was investig ated in 3T3-L1 adipocytes. Wortmannin, a specific PI 3-kinase inhibito r, blocked insulin stimulated recruitment of transferrin receptors to the plasma membrane (IC50 approximate to 5-15 nM) with a similar poten cy to its inhibitory effects on PI 3-kinase and glucose transport. Wor tmannin also blocked insulin stimulated recruitment of IGF-2 receptors to the cell surface. However, wortmannin (up to 200 nM) and another P I 3-kinase inhibitor, LY294002 (3 mu g/ml), did not block transferrin receptor endocytosis. This demonstrates that while PI 3-kinase may be necessary for insulin stimulated exocytosis, it is not necessary for e ndocytosis of transferrin receptors. (C) 1995 Academic Press, Inc.