Cyclic AMP mediated induction of ornithine decarboxylase of glioma and neuroblastoma cells

The activity of ornithine decarboxylase (EC 4.1.1.17; L ornithine carboxy lyase) of C6 BU 1 glioma and N115 neuroblastoma cells increases significantly when confluent cultures are treated with compounds that increase cellular cAMP levels. These include norepinephrine or isoproterenol, and prostaglandin E₁ or adenosine, which stimulate ornithine decarboxylase activity in C6 BU 1 glioma and N115 neuroblastoma cells, respectively. Ornithine decarboxylase activity is also elevated in confluent C6 BU 1 glioma cells treated with dibutyryl cAMP and theophylline, or after the glioma cells are fed with a serum depleted medium in the presence of catecholamines and inhibitors of cyclic nucleotide phosphodiesterase. The activity of the enzyme increases 500 to 1000 fold, 1 to 6 hr after stationary phase N115 neuroblastoma cells are fed with a serum free medium, supplemented with phosphodiesterase inhibitors, adenosine, or prostaglandin E₁. This stimulation is antagonized by carbamoyl choline and is blocked by actinomycin D or cycloheximide. These results suggest that the synthesis of ornithine decarboxylase of C6 BU 1 glioma and N115 neuroblastoma cells is controlled by cAMP.