ACTIVATED PHOSPHATIDYLINOSITOL 3-KINASE IS SUFFICIENT TO MEDIATE ACTIN REARRANGEMENT AND GLUT4 TRANSLOCATION IN 3T3-L1 ADIPOCYTES

Insulin stimulation of 3T3-L1 adipocytes causes rapid translocation of actin and the GLUT4 glucose transporter to the plasma membrane, Both processes depend on the activity of phosphatidylinositol 3-kinase, Usi ng single cell microinjection, we have transiently expressed a constit utively activated mutant of phosphatidylinositol 3-kinase, p110, in 3 T3-L1 adipocytes, Fluorescent detection of GLUT4 protein and actin wit hin these cells demonstrates that expression of p110 is sufficient to cause translocation of GLUT4 to the plasma membrane and the formation of actin membrane ruffles, These effects are inhibited by wortmannin in the p110-expressing cells, indicating that the phosphatidylinosito l 3-kinase activity of the protein is required, Overexpression of an i dentical protein containing a point mutation in the kinase domain, p11 0Delta kin, was incapable of mediating either action, confirming that neither the microinjection process nor a nonspecific effect of the pr otein was responsible for the observed effects, These data suggest tha t although insulin is capable of inducing numerous signaling pathways, the isolated activation of phosphatidylinositol 3-kinase can initiate the signaling cascade leading to both actin rearrangement and GLUT4 t ranslocation in the absence of insulin stimulation.