Core promoter involvement in the induction of rat ornithine decarboxylase by phorbol esters.

Biwei Zhao and Andrew P. Butler
(2001) Molec. Carcinogenesis 32:92-99

Overexpression of ornithine decarboxylase (ODC) is an important oncogenic event in tumorigenesis. Although ODC was one of the first genes described whose product is inducible by 12-O-tetradecanoylphorbol-13-acetate (TPA), the mechanisms of ODC transcriptional regulation have remained elusive. In this study, we systematically analyzed the rat ODC core promoter region for novel TPA response elements. Analysis of linker scanning mutants of the ODC promoter from the TATA box to the transcription start site demonstrated that mutation of the TATA box reduced the TPA induction ratio by 40%, while the basal ODC promoter activity was not significantly changed. A novel region between nt -20 to -10 was shown to be critical for both basal promoter activity and induction by TPA. Random mutagenesis of this region showed that conversion of the GC-rich wild-type sequence into a T-rich sequence could either substantially increase the basal promoter activity and decrease the TPA induction ratio, or dramatically reduce the basal promoter activity, depending on the T-content. Mutant R5, containing an ATTT sequence at nt -15 to -12, caused a more than 2-fold increase of basal promoter activity and 80% reduction of TPA induction ratio. We suggest that this region interacts with components of the general transcription machinery, and that the strength of this interaction is mediated by the T-content in this region.