Positive and negative regulatory elements in the murine p53 promoter

In order to understand the basis for regulated as well as de-regulated expression of the p53 tumor suppressor gene, we have focused on characterizing the transcriptional regulation of the p53 gene. Here we present evidence for the existence of two additional upstream regulatory elements in the murine p53 promoter. One of these sites maps to a region between -296 to -270 and the second one between -255 to -226 relative to the major transcription initiation site. These two sites are referred to as binding sites for PBF I and II, respectively. Nucleotide bases that have been found to be critical for the binding of nuclear factors to these sites are 5'-AGA-3' (-282 to -280) in binding site I and 5'-ACAG-3' (-246 to -243) in binding site II. Mutational analyses in conjunction with transient transfection assays indicated that the factor that binds to the region between -245 to -242 (PBF II) plays a positive regulatory role p53 promoter activity. This was demonstrated by the observation that promoter mutations that abolished binding to this site, showed a decreased level of activity as compared to the wild type promoter. In analogous experiments, mutational anlayses and transient transfection assays indicated that the factor that binds to the region between -282 to -280 (PBF I) plays a negative regulatory role in p53 promoter activity. This was demonstrated by the observation that promoter mutations that abolished binding to this site, showed an increased level of activity as compared to the wild type promoter.