Induction of ornithine decarboxylase (ODC) is one of the earliest changes in gene expression elicited by phorbol ester tumor promoters such as 12-O-tetradecanoylphorbol-13-acetate (TPA), and is a common feature of multiple classes of tumor promoters. Inhibition of ODC blocks tumor progression in experimental models, and may have clinical applicability. In addition, aberrant overexpression of ODC can be tumorigenic in vitro. The overall goal of this proposal is to understand how the transcription of ODC is regulated by tumor promoters and oncogenes. Towards this goal, the following specific aims will be pursued: 1. Identify DNA sequence elements required for transcriptional regulation of ODC by TPA and oncogenes. This will be accomplished by transient expression analysis of ODC reporter genes containing linker-scanning or point-mutations of the proximal promoter region. 2. Characterize the role of TAFII250 in regulation of ODC promoter activity. The major emphasis of this Aim will be characterization of the putative role of TAFII250 in determining responses of the ODC promoter to tumor promoters. 3. Determine the relationship between histone acetylation and ODC induction. The rationale for this aim is based on the effects we observed with the histone deacetylase inhibitor trichostatin A, as well as the apparent involvement of TAFII250 and a p300-related protein (both of which are histone acetylases) in ODC regulation. 4. Determine the role of transcriptional cofactors in ODC regulation. This Aim will use mutants of the Adenovirus 12S E1A protein as a tool to determine the role of the p300/CBP family of co-activators in ODC transcription. In addition, we will analyze ODC expression in cells co-transfected with p300. Taken together, these studies should provide new insight into the mechanisms by which tumor promoters and oncogenes influence ODC regulation and corrupt patterns of gene expression during carcinogenesis.