Regulation of RNA polymerase I activity by ornithine decarboxylase

Ornithine decarboxylase activity was elevated from 5- to 80-fold in rat liver by the administration of various methylxanthine derivatives, i.e. theophylline, aminophylline, and 3-isobutyl,1-methylxanthine. The increased activity of ornithine decarboxylase in all instances was closely followed (within 0.5 hr) by an increase in the activity of RNA polymerase I. The increment in ornithine decarboxylase activity and the increase in RNA polymerase I activity after all three drugs showed a parallel relationship. That is, theophylline administration resulted in the least stimulation of both ornithine decarboxylase and RNA polymerase I activities, and 3-isobutyl,1-methylxanthine administration produced the greatest stimulation of both enzymes. The enhanced RNA polymerase I activity resulted in a significant increase in the total RNA content of the liver within 24 hr. Administration of inhibitors of protein synthesis and RNA synthesis indicated that attenuation of the increase in ornithine decarboxylase activity was closely paralleled by attenuation of the increase in RNA polymerase I activity. RNA polymerase I activity was not stimulated by putrescine concentrations which were physiological and above. We suggest, therefore, that ornithine decarboxylase may be involved in the regulation of RNA polymerase I activity.