Regulation of human type II phosphatidylinositol kinase activity by epidermal growth factor-dependent phosphorylation...

Epidermal growth factor (EGF) stimulates phosphatidylinositol PtdIns) hydrolysis in many cell types by effecting the specific interaction between the EGF receptor and phospholipase C gamma. Several studies have suggested that PtdIns 4-kinase activity can also be regulated by EGF, but the mechanism of this stimulation was unclear. We report here that EGF treatment of intact A431 cells increased the association of type II PtdIns kinase with the EGF receptor within 1 min at 37 degrees C. Phosphorylation of immunoprecipitated EGF receptor also increased the association of PtdIns 4-kinase. Furthermore dephosphorylation of phosphoserine residues on the stimulated receptor immune complex led to inactivation of the bound PtdIns 4-kinase, while dephosphorylation of phosphotyrosine residues led to activation. Unlike the stimulated activity measured in total cell and plasma membrane lysates, the changes in activity of the immunoprecipitates were apparent at high substrate concentration. Metabolic labeling was used to show that a 55-kDa phosphoserine and phosphotyrosine-containing protein comigrated with renatured PtdIns 4-kinase activity on SDS-polyacrylamide gel electrophoresis, while in vitro labeling revealed only serine phosphorylation. These data are discussed with reference to the direct regulation of PtdIns 4-kinase by phosphorylation, PtdIns compartmentalization, and the formation of a multienzyme signal transduction complex.