Epidermal growth factor stimulates ornithine decarboxylase activity in cultured mammalian keratinocytes

The influence of epidermal growth factor (EGF) on ornithine decarboxylase has been examined in cultured bovine keratinocytes. Keratinocyte ornithine decarboxylase activity was maximal at pH 6.3 in MES buffer in the presence of dithiothreitol and EDTA. When cultured cells, deprived of serum, were exposed to EGF, the activity of ornithine decarboxylase was stimulated severalfold. Enzyme activity increased in a dose-dependent manner with EGF. The time course of this stimulation is unlike any previously reported in cultured cells. The increase in activity was maximal by 8 h. A small dip in activity was seen between 8 and 12 h. Increased activity was sustained for as long as 24 h after exposure to EGF. The prolonged increased in enzyme activity was reduced by actinomycin D. When cycloheximide was added 1 h before EGF, ornithine decarboxylase activity was obliterated. This is the first demonstration of ornithine decarboxylase stimulation following exposure to EGF in cultured keratinocytes. The prolonged duration of ornithine decarboxylase stimulation is unexplained but may be related to processing of EGF by the keratinocytes.