An essential role for phosphatidylinositol transfer protein in phospholipase C-Mediated inositol lipid signaling

Transmembrane signaling by the phospholipase C-β (PLC-β) pathway is known to require at least three components: the receptor, the G protein, and the PLC. Recent studies have indicated that if the cytosol is allowed to leak out of HL60 cells, then G protein-stimulated PLC activity is greatly diminished, indicating an essential role for a cytosolic component(s). We now report the complete purification of one component based on its ability to reconstitute GTPγS-mediated PLC activity and identify it as the phosphatidylinositol transfer protein (PI-TP). Based on the in vitro effects of PI-TP, we surmise that it is involved in transporting PI from intracellular compartments for conversion to PI bisphosphate (PIP 2) prior to hydrolysis by PLC-β2 PLC-β3 , the endogenous PLC isoforms present in these cells.