Posttranscriptional regulation of ornithine decarboxylase.

Activity of the polyamine biosynthetic enzyme ornithine decarboxylase (ODC) and intracellular levels of ODC protein are controlled very tightly. Numerous studies have described ODC regulation at the levels of transcription, translation, and protein degradation in normal cells and dysregulation of these processes in response to oncogenic stimuli. Although posttranscriptional regulation of ODC has been well documented, the RNA binding proteins (RBPs) that interact with ODC mRNA and control synthesis of the ODC protein have not been defined. Using Ras-transformed rat intestinal epithelial cells (Ras12V cells) as a model, we have begun identifying the RBPs that associate with the ODC transcript. Binding of RBPs could potentially regulate ODC synthesis by either changing mRNA stability or rate of mRNA translation. Techniques for measuring RBP binding and translation initiation are described here. Targeting control of ODC translation or mRNA decay could be a valuable method of limiting polyamine accumulation and subsequent tumor development in a variety of cancers.