PATHWAY FOR THE FORMATION OF D-3-PHOSPHATE CONTAINING INOSITOL PHOSPHOLIPIDS IN PDGF STIMULATED NIH 3T3 FIBROBLASTS

PtdIns (3,4,5)P3 is formed rapidly in NIH-3T3 cells stimulated with platelet derived growth factor (PDGF). We have determined the pathway of formation of this lipid in these cells. Cells were labeled briefly with 32PO4 and then stimulated with PDGF under conditions where the specific activity of each phosphate group determines the order of its addition. The D-5 phosphate of this lipid contained ∼42% of the total radioactivity present in the molecule, while ∼32% was in the D-4 position, 25% in the D-3 position, and ∼2% in the D-1 position. This indicates that PtdIns(3,4)P2 and not PtdIns(4,5)P2 is the immediate precursor of PtdIns(3,4,5)P3, and defines the pathway of formation of these lipids to be PtdIns(3)P → PtdIns(3,4)P2 → PtdIns(3,4,5)P3. This pathway is the same as that in thrombin-stimulated platelets and infers that the pathways are not different in non-growing and proliferating cells. © 1991.