A rare DNA contact mutation in cancer confers p53 gain-of-function and alters binding specificity

The p53 tumor suppressor gene encodes a sequence-specific transcription factor. Mutations in the coding sequence of p53 occur frequently in human cancer and often result in single amino acid substitutions in the DNA binding domain. These missense mutations block the normal functions of p53 by limiting its ability to bind and activate its target genes involved in tumor suppressor activities (e.g. cell cycle arrest and apoptosis). In addition to the loss of these canonical tumor suppressive functions, some missense mutations in p53 confer new or gain-of-function (GOF) activities to tumor cells, (e.g. increased metastatic potential or drug resistance). While many missense mutations in p53 cluster at 6 “hotspot” amino acids, the majority of mutations in human cancer occur elsewhere in the DNA binding domain and at a much lower frequency. We report here that mutations at K120, which is a non-hotspot site, confer p53 with the previously unrecognized ability to activate the expression of the pro-survival TNFAIP8 gene. Mutant K120 p53 binds the TNFAIP8 locus at a cryptic p53 response element that is not occupied by wild-type p53, thus providing a biochemical mechanism for this new function. Furthermore, induction of TNFAIP8 is critical for the evasion of apoptosis by tumor cells expressing mutant K120 forms of p53. These findings provide two important advances in our understanding of p53 function in human cancer. First, they identify induction of pro-survival targets as a mechanism of gain-of-function activity for mutant p53. Second, they illustrate that analysis of the gain-of-function activities conferred by non-hotspot mutations in p53, which represent the majority of human cancer mutations, will likely broaden our understanding of this phenomenon beyond the limited number of GOF activities currently reported for hotspot mutants.