DISTINCT REGIONS OF P53 HAVE A DIFFERENTIAL ROLE IN TRANSCRIPTIONAL ACTIVATION AND REPRESSION FUNCTIONS

The wild type p53 tumor suppressor protein transactivates genes carrying p53 responsive elements and represses several TATA containing promoters. We report in vivo gene regulation assays where deletion of the N-terminal 75 residues (Delta N75) results in loss of transactivation of p53CON and repression of an HPV 6 reporter. In contrast, removal of the C-terminal 75 (Delta C75) amino acids resulted in a truncated protein capable of trans-activating p53CON but not able to repress the HPV 6 reporter. In vitro protein association assays revealed that the Delta N75 protein, but not the Delta C75 truncated protein, could oligomerize with the wild type p53 protein. Co-transfection assays with wild type p53 showed that the Delta N75 mutant protein has a dominant negative effect on trans-activation function. However, it does not affect the ability of wild type p53 to repress transcription from the HPV 6 reporter. The Delta C75 protein had no effect on the ability of the wild type p53 to activate p53CON or repress the HPV 6 reporter. These results suggest that distinct regions of p53 have a differential role in transcriptional activation and repression functions.