Increased p53 transcription prior to DNA synthesis is regulated through a novel regulatory element within the p53 promoter.

p53 mRNA levels are tightly regulated during the cell cycle with its transcription being induced prior to DNA synthesis. However, the mechanism controlling this regulation is not well defined. Through characterizing an additional 1000 bp of upstream DNA sequences of the murine p53 gene, we identified new positive and negative regulatory elements. Furthermore, we found a trans-acting factor(s) that binds within a positive cis-acting element (-972/-953) in a manner indicative of regulation during the cell cycle. When Swiss3T3 cells are arrested by serum depletion p53 mRNA levels decrease and binding of this regulatory factor(s) to the promoter is reduced. Upon serum stimulation, the regulatory factor(s) binds the promoter and p53 mRNA levels increase prior to the cells entering S phase. When the factors are experimentally sequestered from the promoter or when the regulatory element is deleted from the promoter, p53 promoter activity is reduced. There is no further reduction in p53 promoter activity upon serum depletion and the kinetics of induction upon serum stimulation is delayed by approximately 5 h. These findings indicate that a factor(s) binding within the -972/-953 regulatory element on the p53 promoter is important for the proper regulation of p53 mRNA expression in response to mitogen stimulation. Our initial findings indicate that a member of the C/EBP family of transcription factors may play a role in this regulation.