MEMBRANE-PERMEANT ESTERS OF PHOSPHATIDYLINOSITOL 3,4,5-TRISPHOSPHATE

Phosphoinositide 3-OH kinases and their products, D-3 phosphorylated p hosphoinositides, are increasingly recognized as crucial elements in m any signaling cascades. A reliable means to introduce these lipids int o intact cells would be of great value for showing the physiological r oles of this pathway and for testing the specificity of pharmacologica l inhibitors of the kinases. We have stereospecifically synthesized di -C-8-PIP3/AM and di-C-12-PLP3/AM, the heptakis(acetoxymethyl) esters o f dioctanoyl- and dilauroylphosphatidylinositol 3,4,5-trisphosphate, i n 14 steps from myo-inositol. The ability of these uncharged lipophili c derivatives to deliver phosphatidylinositol 3,4,5-trisphosphate acro ss cell membranes was demonstrated on 3T3-L1 adipocytes and T-84 colon carcinoma monolayers, Insulin stimulation of hexose uptake into adipo cytes was inhibited by the kinase inhibitor wortmannin and was largely restored by di-C-8-PIP3/AM, which had no effect in the absence of ins ulin. Thus phosphatidylinositol 3,4,5-trisphosphate or a metabolite wa s necessary but not sufficient for stimulation of hexose transport, In T-84 epithelial monolayers, di-C-12-PIP3/AM mimicked epidermal growth factor in inhibiting chloride secretion and potassium efflux, suggest ing that phosphatidylinositol 3,4,5-trisphosphate was sufficient to mo dulate these fluxes and mediate epidermal growth factor's action.