Epidermal growth factor stimulation of ornithine decarboxylase activity in a human hepatoma cell line

Epidermal growth factor (EGF) bound specifically to the human hepatoma cell line PLC/PRF/5. Treatment of these cells with nanomolar concentrations of EGF for 4-6 hr resulted in a 2- to 6-fold increase in ornithine decarboxylase (L-ornithine carboxy-lyase, EC 4.1.1.17) activity. 12-O-Tetradecanoylphorbol 13-acetate also produced an increase in enzyme activity in these cells and exhibited an additive effect with EGF. It did not inhibit the binding of 125I-labeled EGF to these cells. The stimulation of enzyme activity by EGF was not inhibited by cycloheximide or actinomycin D, although these agents did cause a significant decrease in enzyme levels when added without EGF. Also, colchicine, chloroquine, ammonium chloride, and methylamine, compounds that inhibit EGF degradation in various cells types, did not interfere with the ability of EGF to elevate enzyme levels in the human hepatoma cells.