Inhibition of erythropoietin production by phorbol ester is associated with down-regulation of protein kinase C-α isoenzyme in hepatoma cells

The role of protein kinase C (PKC) in the control of erythropoietin (Epo) production was studied using the human hepatoma cell line HepG2. Inhibition of PKC by staurosporine and the selective PKC inhibitor CGP 41251 significantly reduced Epo formation. No inhibition occurred with the inactive staurosporine derivative CGP 42700. Treatment with phorbol 12-myristate 13-acetate (PMA) for 24 h dose-dependently inhibited Epo formation, thus suggesting that down-regulation of PKC might be responsible for this inhibition. Immunoblotting experiments showed that incubation of HepG2 cells with PMA for 24 h resulted in a selective and almost complete down-regulation of PKC-α. Thus, PKC-α may play a permissive role in Epo synthesis in HepG2 cells.