BIOCHEMICAL AND PHARMACOLOGICAL STUDIES WITH KT7692 AND LY294002 ON THE RARE OF PHOSPHATIDYLINOSITOL 3-KINASE IN FC-EPSILON-RI-MEDIATED SIGNAL-TRANSDUCTION

Wortmannin inhibited phosphatidylinositol 3-kinase (P13-kinase) and Fc epsilon RI-mediated histamine secretion in RBL-2H3 cells to a similar degree, with IC50 values of 3 and 2nM, respectively. Although P13-kinase is an acknowledged regulator of intracellular trafficking and secretion, wortmannin has proved to be a difficult drug to use in assessing the role of P13-kinase because it inhibits another important enzyme, myosin light-chain kinase (MLCK; IC50=200 nM). In the present study we synthesized a unique derivative of wortmannin, O-acetyld-Delta(16)-wortmannin-17-ol (KT7692), that has an inhibitory potency against P13-kinase one-hundredth that of wortmannin, but retains a similar potency to wortmannin against MLCK. Histamine secretion was influenced 100-fold more by wortmannin than by KT7692. 2-(4-Morpholinyl)-8-phenyl-4H-1-benzopyran-4-one (LY294002), a structurally different P13-kinase inhibitor from wortmannin, inhibited P13-kinase with an IC50 of 2 mu M but had little effect on MLCK activity in this concentration range. LY294002 also inhibited histamine secretion in RBL-2H3 cells with an IC50 of 5 mu M. These results provide further evidence that P13-kinase is involved in the signal transduction pathway responsible for histamine secretion after stimulation of Fc epsilon RI. Furthermore KT7692 in combination with wortmannin and LY294002 would be a powerful tool for clarifying the involvement of P13-kinase as distinct from that of MLCK in signal transduction systems of various cellular responses.