The protein tyrosine kinase p56(lck) regulates the serine-base exchange activity in Jurkat T cells

Different classes of protein kinase inhibitors for protein kinase C, cAMP-dependent protein kinase or protein tyrosine kinases have been studied for their effect on phospholipid metabolism. The results show that among the compounds studied, only 4'-aminohydroxyflavone (AHF), previously described as a specific inhibitor of the protein tyrosine kinase p56(lck), markedly increased phosphatidylserine synthesis in Jurkat T cells. The biosyntheses of phosphatidylcholine and phosphatidylethanolamine were not affected. Also, the synthesis of phospholipids from tritium-labeled fatty acid as precursor was left unchanged by the p56(lck) inhibitor. The decreased phosphatidylserine synthesis induced when triggering the CD3-TCR complex was impaired by AHF, suggesting that p56(lck) could be implicated in the regulation of the serine-base exchange enzyme system. Direct evidence for the participation of p56(lck) in the regulation of the serine-base exchange enzyme system was obtained by using p56(lck)-deficient Jurkat cells (J.CaM 1.6) in which the basal base exchange activity was markedly increased and on the other hand AHF had no effect. In addition, transfection of J.Cam 1.6 cells with p56(lck)-cDNA allowed recovery of the AHF activity.