Posttranscriptional regulation of ornithine decarboxylase activity.

We have used a Chinese hamster ovary cell line (DF3) that overproduces ornithine decarboxylase (ODC) to examine various parameters in the cell cycle-dependent regulation of this enzyme. Under a variety of conditions, alterations in the activity of ODC were accompanied by parallel changes in the levels of the protein, as measured by immunologically cross-reactive material (CRM). While putrescine has been known to suppress the induction of ODC, we have found that in DF3 cells 10(-4)M ornithine completely suppresses ODC activity. We also show that the levels of ODC mRNA are not modulated when the levels of ODC activity and CRM change drastically. The data can be interpreted in terms of models involving either an effect of putrescine on the translation of ODC mRNA, or on the activity of a relatively specific protease with ODC as its target.