TYROSINE PHOSPHORYLATION OF PROTEIN-KINASE C-DELTA IN RESPONSE TO ITSACTIVATION

Retroviral vectors containing five different protein kinase C (PKC) is oenzymes (alpha, delta, epsilon, eta, xeta) were expressed in 32D hema topoietic cells and NIH-3T3 fibroblasts. In an effort to investigate s ignaling events regulated by PKC activation, we analyzed whether tyros ine phosphorylation of cellular proteins would occur after 12-O-tetrad ecanoylphorbol-13-acetate (TPA) treatment of the various transfectants . While no detectable tyrosine-specific phosphorylation was observed a fter treatment of the majority of the transfectants, pronounced TPA-de pendent tyrosine phosphorylation of an 82-kDa protein was detected in the 32D/PKC-delta and NIH-3T3/PKC-delta lines. Interestingly, the 82-k Da substrate proved to be PKC-delta itself. Tyrosine phosphorylation o f purified PKC-delta by src family or receptor tyrosine kinases in vit ro enhanced PKC-delta activity, suggesting that tyrosine phosphorylati on of PKC-delta may positively affect its function.