Translational regulation of mammalian ornithine decarboxylase by polyamines.

Ornithine decarboxylase, which catalyses the formation of putrescine, is the first and rate-limiting enzyme in the biosynthesis of polyamines in mammalian cells. The enzyme is highly regulated, as indicated by rapid changes in its mRNA and protein during cell growth. Here we report that ornithine decarboxylase is regulated at the translational level by polyamines in difluoromethylornithine-resistant mouse myeloma cells that overproduce the enzyme due to amplification of an ornithine decarboxylase gene. When such cells are exposed to putrescine or other polyamines, there is a rapid and specific decrease in the rate of synthesis of ornithine decarboxylase, assayed by pulse-labeling. Neither the cellular content of ornithine decarboxylase mRNA nor the half-life of ornithine decarboxylase protein is affected. Our results indicate that polyamines negatively regulate the translation of ornithine decarboxylase mRNA, thereby controlling their own synthesis.