A novel pathway of cellular phosphatidylinositol(3,4,5)-trisphosphate synthesis is regulated by oxidative stress

Background: Phosphatidylinositol-3,4,5-trisphosphate [PtdIns(3,4,5)P-3] is a key second messenger found ubiquitously in higher eukaryotic cells. The a ctivation of Class I phosphoinositide 3-kinases and the subsequent producti on of PtdIns(3,4,5)P-3 is an important cell signaling event that has been c ausally linked to the activation of a variety of downstream cellular proces ses, such as cell migration and proliferation. Although numerous proteins r egulating a variety of biological pathways have been shown to bind PtdIns(3 ,4,5)P-3, there are no data to demonstrate multiple mechanisms for PtdIns(3 ,4,5)P-3 synthesis in vivo. Results: In this study, we demonstrate an alternative pathway for the in vi vo production of PtdIns(3,4,5)P-3 mediated by the action of murine Type I a lpha phosphatidylinositol 4-phosphate 5-kinase (Type I alpha. PIPkinase), a n enzyme best characterized as regulating cellular PtdIns(4,5)P-2 levels. A nalysis of this novel pathway of PtdIns(3,4,5)P-3 synthesis in cellular mem branes leads us to conclude that in vivo, Type I alpha PiPkinase also acts as a PtdIns(3,4)P-2 5-kinase. We demonstrate for the first time that cells actually contain an endogenous PtdIns(3,4)P-2 5-kinase, and that during oxi dative stress, this enzyme is responsible for PtdIns(3,4,5)P, synthesis. Fu rthermore, we demonstrate that by upregulating the H2O2-induced PtdIns(3,4, 5)P-3 levels using overexpression studies, the endogenous PtdIns(3,4)P-2 5- kinase is likely to be Type I alpha PIPkinase. Conclusions: We describe for the first time a novel in vivo activity for Ty pe tcr PIPkinase, and a novel pathway for the in vivo synthesis of function al PtdIns(3,4,5)P-3, a key lipid second messenger regulating a number of di verse cellular processes.