Protein tyrosine phosphorylation activates rat splenic type II phosphatidylinositol 4-kinase in vitro

Regulation of phosphatidylinositol 4-kinase (PtdIns 4-kinase) by protein tyrosine phosphorylation has been indirect and the effects of phosphorylation are debatable. Rat splenic type II PtdIns 4-kinase was phosphorylated in vitro with protein tyrosine kinases from Con A stimulated splenic lymphocytes. Stoichiometric analysis showed one mole of phosphate was incorporated per mole of PtdIns 4-kinase. Tyrosine phosphorylation increased the enzyme activity by 3-fold. Kinetic analysis showed a reduction in Km for PtdIns and an increase in Vmax. Dephosphorylation with protein phosphotyrosine phosphatase abolished the activation of PtdIns 4-kinase while protein phosphatase 2A had no effect. Protein tyrosine phosphorylation and activation of PtdIns 4-kinase appear to be tissue specific.