INVOLVEMENT OF PHOSPHOINOSITIDE 3-KINASE IN INSULIN-INDUCED OR IGF-1-INDUCED MEMBRANE RUFFLING

Insulin, IGF-1 or EGF induce membrane ruffling through their respectiv e tyrosine kinase receptors. To elucidate the molecular link between r eceptor activation and membrane ruffling, we microinjected phosphoryla ted peptides containing YMXM motifs or a mutant 85 kDa subunit of phos phoinositide (PI) 3-kinase (Delta p85) which lacks a binding site for the catalytic 110 kDa subunit of PI 3-kinase into the cytoplasm of hum an epidermoid carcinoma KB cells. Both inhibited the association of in sulin receptor substrate-1 (IRS-1) with PI 3-kinase in a cell-free sys tem and also inhibited insulin- or IGF-1-induced, but not EGF-induced, membrane ruffling in KB cells. Microinjection of nonphosphorylated an alogues, phosphorylated peptides containing the EYYE motif or wild-typ e 85 kDa subunit (Wp85), all of which did not inhibit the association of IRS-1 with PI 3-kinase in a cell-free system, did not inhibit membr ane ruffling in KB cells. In addition, wortmannin, an inhibitor of PI 3-kinase activity, inhibited insulin- or IGF-1-induced membrane ruffli ng. These results suggest that the association of IRS-1 with PI 3-kina se followed by the activation of PI 3-kinase are required for insulin- or IGF-1-induced, but not for EGF-induced, membrane ruffling.