Dissecting functional roles of p53 N-terminal transactivation domains by microarray expression analysis

The p53 protein exerts its tumor suppressive function mainly by acting as a transcription activator. Two transactivation domains (TADs) located at the amino-terminus of p53 are required for transcription activation, and the activity of TADs is tightly regulated by post-translational modifications, such as phosphorylation. We attempted to dissect the functions of the two TADs and phosphorylation within the TADs by analyzing p53 target genes induced by full-length p53 (FL-p53), N-terminally deleted p53 isoform lacking the first TAD (Delta 1stTAD) and p53 carrying point mutations at all serine residues within the two TADs (TAD-S/A). By performing a comprehensive survey by employing microarray expression analysis, the induction of target genes by FL-p53, Delta 1stTAD and TAD-S/A was analyzed. All p53s showed different target gene induction patterns, suggesting the importance of the two TADs and phosphorylation within the TADs in target gene induction. Although Delta 1stTAD showed a marked decrease in the ability to induce genes induced by FL-p53, Delta 1stTAD induced many apoptosis-related genes that were not induced by FL-p53, suggesting the roles of these Delta 1stTAD-induced genes in Delta 1stTAD-dependent apoptosis. Approximately 80% of genes induced by FL-p53 were not induced by TAD-S/A, including 29 previously reported p53 target genes such as Hdm2 and Bax, emphasizing the importance of phosphorylation within the TADs. These results demonstrate the significance of the regulation and differential roles of the N-terminal TADs in p53 transcriptional activity.