Regulation of Protein Kinase C in A-549 Cells by Phorbol Ester

Protein kinase C, a family of serine-threonine protein kinases, mediates a variety of intracellular signaling events. Here, the regulatory effect of phorbol 12-myristate 13-acetate(PMA)on the several PKC isozymes in the human lung carcinoma cells A-549 was studied. The expression of PKC-alpha PKC-betaII PKC-gamma PKC-delta and PKC-epsilon in A-549 cells was examined. No detectable PKC-zeta was observed. Short-term treatment of cells with PMA led to the translocation of these PKC isozymes, to different extent, from cytosol to cell membrane. Whereas, prolonged treatment of cells with PMA pronouncedly reduced the levels of PKC-alpha PKC-gamma PKC-delta and PKC-epsilon, but the intracellular level of PKC-betaII was not affected. Furthermore, PMA was observed to have differential effects on the down-regulation of PKC isozymes located in the cytosol and of those located in the membrane. Prolonged PMA treatment caused extensive decrease in the levels of cytosolic PKC-delta and PKC-gamma, and depleted cytosolic PKC-alpha and PKC-betaII. However, the amount levels of membrane PKC-alpha PKC-betaII PKC-gamma PKC-delta isozymes were not decreased. In contrast, PKC-epsilon in both cytosol and membrane fraction was obviously down-regulated by prolonged PMA treatment. This study provided novel evidence on the PMA-mediated activation and down-regulation of different PKC isozymes, which might be helpful in deepening our understanding on the roles of PKC activation and the alterations of their intracellular levels in processes of chemical carcinogenesis.