Phosphoinositide 3-kinase regulates phospholipase Cγ-mediated calcium signaling

It has been demonstrated that the lipid products of the phosphoinositide a-kinase (PI3K) can associate with the Src homology 2 (SH2) domains of specific signaling molecules and modify their actions. In the current experiments, phosphatidylinositol 3,4,5-trisphosphate (Pt-dIns-3,4,5-P-3) was found to bind to the C-terminal SH2 domain of phospholipase C gamma (PLC gamma) with an apparent K-d of 2.4 pra and to displace the C-terminal SH2 domain from the activated platelet-derived growth factor receptor (PDGFR). To investigate the in vivo relevance of this observation, intracellular inositol trisphosphate (IP3) generation and calcium release were examined in HepGB cells expressing a series of PDGFR mutants that activate PLC gamma with or without receptor association with PI3K. Coactivation of PLC gamma and PI3K resulted in an similar to 40% increase in both intracellular IF, generation and intracellular calcium release as compared with selective activation of PLC gamma. Similarly, the addition of wortmannin or LY294002 to cells expressing the wild-type PDGFR inhibited the release of intracellular calcium. Thus, generation of PtdIns-3,4,5-P-3 by receptor-associated PI3K causes an increase in IP3 production and intracellular calcium release, potentially via enhanced PtdIns-4,5-P-2 substrate availability due to PtdIns-3,4,5-P-3-mediated recruitment of PLC gamma to the lipid bilayer.