Spermine inhibits induction of ornithine decarboxylase by cyclic AMP but not by dexamethasone in rat hepatoma cells

Abstract

POLYAMINE biosynthesis is one of the earliest events occurring during tissue growth, and the polyamines have been implicated in the control of both RNA and protein synthesis. Increased polyamine synthesis reflects a rapid elevation of the activity of ornithine decarboxylase (ODC), the rate-limiting enzyme in the biosynthesis of the polyamines spermidine and spermine1,2. Fast growing tissues exhibit the highest ODC activity, whereas in slowly growing or in non-growing tissues ODC activity is very low. ODC has been induced by various agents that affect growth processes, such as by glucocorticoids in vivo3,6, and by cyclic AMP both in vivo6,7 and in cultured baby hamster kidney cells8. There have also been conflicting reports about the efficacy of polyamines in inhibiting the induction of ODC in vivo9–11 and in activated human lymphocytes12. As most results reported so far are from whole animal studies, we felt that a more precise understanding of ODC induction may result from investigation of an isolated system. The system chosen for detailed study was rat hepatoma cells (HTC) because most in vivo studies have focused on ODC from rat liver. We now report the induction of ODC in HTC cells by both cyclic AMP and dexamethasone.