Involvement of phosphoinositide 3‐kinase in insulin‐ or IGF‐1‐induced membrane ruffling.

Insulin, IGF‐1 or EGF induce membrane ruffling through their respective tyrosine kinase receptors. To elucidate the molecular link between receptor activation and membrane ruffling, we microinjected phosphorylated peptides containing YMXM motifs or a mutant 85 kDa subunit of phosphoinositide (PI) 3‐kinase (delta p85) which lacks a binding site for the catalytic 110 kDa subunit of PI 3‐kinase into the cytoplasm of human epidermoid carcinoma KB cells. Both inhibited the association of insulin receptor substrate‐1 (IRS‐1) with PI 3‐kinase in a cell‐free system and also inhibited insulin‐ or IGF‐1‐induced, but not EGF‐induced, membrane ruffling in KB cells. Microinjection of nonphosphorylated analogues, phosphorylated peptides containing the EYYE motif or wild‐type 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 membrane ruffling in KB cells. In addition, wortmannin, an inhibitor of PI 3‐kinase activity, inhibited insulin‐ or IGF‐1‐induced membrane ruffling. These results suggest that the association of IRS‐1 with PI 3‐kinase followed by the activation of PI 3‐kinase are required for insulin‐ or IGF‐1‐induced, but not for EGF‐induced, membrane ruffling.