Tumor-derived mutations within the DNA-binding domain of p53 that phenotypically resemble the deletion of the proline-rich domain.

The p53 tumor suppressor protein induces apoptosis through a mechanism that may involve the transcriptional activation of cellular genes, including the PIG3 gene. A p53 protein lacking the proline-rich region (p53delta62-91) induces many p53-responsive genes but not PIG3. In parallel, this mutant induces growth arrest but not apoptosis. We show here that the replacement of the N-terminal (amino acids 1-80) or C-terminal (amino acids 344-393) domains of p53 with heterologous domains does not interfere with transcription from the PIG3 promoter, but these chimeras still require the proline-rich region for PIG3 activation. The p53-homolog p73beta also activated the PIG3 promoter, but in contrast to p53, the proline-rich domain of p73beta (residues 81-113) was dispensable to induce the PIG3 promoter. Some tumor-derived p53-mutants, especially M246I, retained the ability to activate transcription of mdm2 but specifically failed to induce the PIG3 promoter, thus resembling p53delta62-91. Further, p53delta62-91 and p53M246I were defective for induction of apoptosis. Finally, p53delta62-91 and p53M246I both showed reduced binding to the DNA of the PIG3 promoter and also to the DNA of the mdm2 and p21 promoters in vitro. Correspondingly, at low expression levels, p53delta62-91 and p53M246I poorly activated the mdm2 promoter when compared to wild type p53. Our results suggest that the proline-rich domain of p53 affects the ability of the central domain to bind DNA. Moreover, some tumor-derived mutations within the central DNA binding domain of p53 mimic the loss of the proline-rich domain.