Abstract
Phosphatidylinositol-3,4,5-trisphosphate (PtdIns(3,4,5)P3) regulates diverse cellular functions including cell proliferation and apoptosis, and is related to diabetes, cancer, etc.; however, little is known about exactly when, where and how PtdIns(3,4,5)P3 is produced. We have developed fluorescent indicators for PtdIns(3,4,5)P3 to reveal spatio-temporal regulations of PtdIns(3,4,5)P3 production in single living cells. After ligand stimulations, PtdIns(3,4,5)P3 levels increased to a larger extent at the endomembranes, i.e. the ER and Golgi, than at the plasma membrane. This PtdIns(3,4,5)P3 increase at the endomembranes was found to originate from its in situ production at the endomembranes, a process stimulated directly by receptor tyrosine kinases endocytosed from the plasma membrane to the endomembranes. The demonstration of PtdIns(3,4,5)P3 production through receptor endocytosis addresses a long-lasting question about how downstream signaling pathways including Akt are activated at intracellular compartments remote from the plasma membrane. [J Physiol Sci. 2006;56 Suppl:S8]
