Molecular Pharmacology, Vol 14, 431-441, Copyright © 1978 by the American Society for Pharmacology and Experimental Therapeutics

Ornithine Decarboxylase Induction in Mitogen-Stimulated Lymphocytes is Related to the Specific Activation of Type I Adenosine Cyclic 3',5'-Monophosphate-Dependent Protein Kinase

¹ Departments of Pharmacology and Microbiology, University of Arizona Health Sciences Center, Tucson, Arizona 85724

The induction of ornithine decarboxylase was studied following the stimulation of human peripheral blood lymphocytes with concanavalin A (ConA) (10 µg/ml). Following treatment with ConA, ornithine decarboxylase activity increased 4-5-fold between 6 and 12 hr of incubation and reached a peak level 10-12-fold above control (unstimulated) values by 48 hr. Increases in incorporation of [³H]uridine into acid-insoluble material followed a similar time course after the addition of ConA to lymphocytes. The rate of incorporation of [³H]thymidine into acid-insoluble material was maximal at 72 hr. The degree of activation of soluble cyclic 3',5'-AMP-dependent protein kinase(s) was determined at various times following ConA stimulation. Between 1 and 2 hr after mitogen administration, the cyclic AMP-dependent protein kinase activity ratio increased markedly and was 0.23 unit above control values by 4 hr. The activity ratio decreased between 4 and 8 hr and returned to higher values after incubation with the mitogen for 12, 24, and 48 hr. Separation of the free catalytic subunit from type I and type II protein kinase holoenzyme isozymes via C₆-aminoalkyl agarose chromatography revealed that only type I protein kinase was activated 4 hr following incubation of lymphocytes with a mitogenic concentration of ConA (10 µg/ml). The addition of dibutyryl cyclic AMP at the same time as ConA (10 µg/ml) resulted in nearly total activation of both type I and type II protein kinases at 4 hr but was inhibitory to the later induction of ornithine decarboxylase and to increased synthesis of RNA and DNA. A high concentration of ConA (100 µg/ml), which also activated both isozyme forms of the kinase at 4 hr, produced only a small increase in ornithine decarboxylase activity and RNA synthesis at later times and no elevation in DNA synthesis. The data suggest that while the early activation of type I cyclic AMP-dependent protein kinase may mediate in a positive manner the induction of ornithine decarboxylase and the mitogenic response of lymphocytes to ConA, concomitant activation of type II protein kinase may inhibit this process.