Mouse Mutants Reveal that Putative Protein Interaction Sites in the p53 Proline-Rich Domain Are Dispensable for Tumor Suppression

Abstract

The stability and activity of tumor suppressor p53 are tightly regulated and partially depend on the p53 proline-rich domain (PRD). We recently analyzed mice expressing p53 with a deletion of the PRD (p53^ΔP). p53^ΔP, a weak transactivator hypersensitive to Mdm2-mediated degradation, is unable to suppress oncogene-induced tumors. This phenotype could result from the loss of two motifs: Pin1 sites proposed to influence p53 stabilization and PXXP motifs proposed to mediate protein interactions. We investigated the importance of these motifs by generating mice encoding point mutations in the PRD. p53^TTAA contains mutations suppressing all putative Pin1 sites in the PRD, while p53^AXXA lacks PXXP motifs but retains one intact Pin1 site. Both mutant proteins accumulated in response to DNA damage, although the accumulation of p53^TTAA was partially impaired. Importantly, p53^TTAA and p53^AXXA are efficient transactivators and potent suppressors of oncogene-induced tumors. Thus, Pin1 sites in the PRD may modulate p53 stability but do not significantly affect function. In addition, PXXP motifs are not essential, but structure dictated by the presence of prolines, PXXXXP motifs that may mediate protein interactions, and/or the length of this region appears to be functionally significant. These results may explain why the sequence of the p53 PRD is so variable in evolution.

SUPPLEMENTAL MATERIAL

We thank G. Campbell and B. Jaroszynski for technical assistance.

This work was supported by NIH grant 100845 to G.M.W. F.T. was supported in part by a fellowship from the Association pour la Recherche sur le Cancer.