ACTIVATION OF PROTEIN-KINASE-C BY TYROSINE PHOSPHORYLATION IN RESPONSE TO H2O2

Protein kinase C (PKC) isoforms, alpha, beta I, and gamma of cPKC subg roup, delta and epsilon of nPKC subgroup, and zeta of aPKC subgroup, w ere tyrosine phosphorylated in COS-7 cells in response to H2O2. These isoforms isolated from the H2O2-treated cells showed enhanced enzyme a ctivity to various extents. The enzymes, PKC alpha and delta, recovere d from the cells were independent of lipid cofactors for their catalyt ic activity. Analysis of mutated molecules of PKC delta showed that ty rosine residues, which are conserved in the catalytic domain of the PK C family, are critical for PKC activation induced by H2O2. These resul ts suggest that PKC isoforms can be activated through tyrosine phospho rylation in a manner unrelated to receptor-coupled hydrolysis of inosi tol phospholipids.