Polyamines regulate both transcription and translation of the gene encoding ornithine decarboxylase antizyme in mouse

The degradation of ornithine decarboxylase (ODC) is mediated by antizyme, a protein regulated by the end-products of ODC activity, the polyamines. High levels of polyamines induce a +1 ribosomal frameshift in the translation of the rat antizyme message leading to the expression of a full-length protein. We have studied whether the regulation of antizyme expression occurs only at the level of translation or whether polyamine levels also affect the transcription of the antizyme gene. Thus, we have cloned and sequenced the mouse homologues of the rat ODC-antizyme gene and cDNA. Northern blot analysis shows that although high concentrations of polyamines do not affect the steady-state levels of antizyme message in L1210 leukemia cells, polyamine depletion using 2-(difluoromethyl)ornithine [Om(F2Me)] leads to a marked decrease in mRNA levels. Results of transient transfections of luciferase-reporter-gene constructs driven by antizyme promoter fragments in untreated and Orn(F2Me)-treated Balb/C 3T3 cells indicate that the transcription of the antizyme gene is altered upon polyamine depletion. The amount of antizyme protein on Western blots was also altered by polyamine depletion and addition, and the polysomal distribution of antizyme message suggests a general translational increase of the message when polyamine concentrations are high. These results indicate a role for polyamines in the transcriptional and translational regulation of ornithine decarboxylase antizyme.