Inhibition of ornithine decarboxylase and S-adenosylmethionine decarboxylase activities of S49 lymphoma cells by agents increasing cyclic AMP

Abstract

We have examined the regulation of two key enzymes that control polyamine biosynthesis-L-ornithine decarboxylase (ODC) and S-adenosylmethionine decarboxylase (SAMDC) - by agents increasing cAMP in S49 lymphoma cells. Incubation of wild type S49 cells with beta-adrenergic agonists (terbutaline or isoproterenol) inhibited ODC and SAMDC activities rapidly (less than 2 hr). more quickly than these agents arrested the cells in the G1 phase of the cell cycle. The beta-adrenergic antagonist propranolol blocked inhibition of ODC activity produced by isoproterenol, but only if added simultaneously or less than 4 hr after the agonist. Incubation of wild type S49 cells with cholera toxin or PGE1 also inhibited ODC activity. Decreases in ODC activity produced by beta-adrenergic agonists, cholera toxin, PGE1 or dibutyryl cAMP were all enhanced by the phosphodiesterase inhibitor Ro 20-1724. Results of studies of ODC and SAMDC activity in S49 variants having lesions in the pathway of cAMP generation and action were as follows: kin- cells (which lack cAMP-dependent protein kinase activity) showed no inhibition of ODC by any agent; AC- cells (which have absent nucleotide coupling units in their adenylate cyclase system) only demonstrated inhibition in response to dibutyryl cAMP; UNC cells (which have deficient coupling of hormone receptors and adenylate cyclase) only demonstrated inhibition in response to dibutyryl cAMP and cholera toxin, and beta-depleted cells (which have a decreased number of beta-adrenergic receptors) responded as did wild type cells except for absent response to isoproterenol. We conclude that inhibition of ODC and SAMDC activity in S49 cells is an early response to agents that increase cAMP and that this action occurs via the "classical" pathways of activation of adenylate cyclase and protein kinase. These results in S49 cells contrast with evidence in other systems in which cAMP has been suggested to enhance polyamine biosynthesis, perhaps through alternative mechanisms.