Differential tyrosine phosphorylation of phospholipase D isozymes by hydrogen peroxide and the epidermal growth factor in A431 epidermoid carcinoma cells

The regulatory mechanism through which the phospholipase D (PLD) isoforms P LD1 and PLD2 are activated is poorly understood, We investigated the possib ility that the PLD isozymes are differentially regulated in response to pha rmacologic stimulants in cells, In this report, we demonstrate for the firs t time that H2O2 and EGF differentially induce tyrosine phosphorylation of the PLD isozymes in A431 cells, which express both PLD1 and PLD2, H2O2 indu ced tyrosine phosphorylation of PLD1 and PLD2, whereas EGF only caused the tyrosine phosphorylation of PLD2, Both agents also induced phosphorylation of the EGF receptor, Interestingly, the PLD isozymes were associated with t he EGF receptor and PKC-alpha in a ligand independent manner, Activation of PLD by H2O2 and EGF nearly correlated with tyrosine phosphorylation of the protein in PLD1 immune complexes. Activation of PLD by both agents was inh ibited by the PKC inhibitor, Ro 31-8220, and by the down-regulation of PI(C , Pretreatment of the cells with the tyrosine kinase inhibitor tyrphostin A G1478 resulted in inhibition of the H2O2 and EGF-induced tyrosine phosphory lation and PLD activation, These results indicate that H2O2 and EGF induce differential tyrosine phosphorylation of PLD isozymes, Also, the activation of PLD by these agonists involves tyrosine phosphorylation and PKC activat ion.