Induction of ornithine decarboxylase in Reuber H35 rat hepatoma cells

Stimuli known to induce tyrosine aminotransferase in H35 cells were tested relative to their ability to induce ornithine decarboxylase, the initial enzyme in the polyamine biosynthetic pathway. Dibutyryl cyclic AMP (0.5 mM), parachlorophenylthio-cyclic AMP (0.1 mM) and dexamethasone (1 muM) stimulated the activity of ornithine decarboxylase 7- to 8-fold by 5 hr of induction. There was a delay of 1 hr before any increase in enzyme activity was detectable. Insulin administered alone failed to significantly change ornithine decarboxylase activity. The ability of dibutyryl cyclic AMP to elevate ornithine decarboxylase activity was found to be concentration-dependent, and a dose-response relationship very similar to that for the induction of tyrosine aminotransferase by dibutyryl cyclic AMP was observed in these cells. The ability of various 8-substituted cyclic AMP analogues to increase the activity of ornithine decarboxylase was correlated with their ability to activate purified protein kinase.