Mis-splicing Drives Loss of Function of p53E224D Point Mutation

Background: Tp53 is the most commonly mutated gene in cancer. Canonical Tp53 DNA damage response pathways are well characterized and classically thought to underlie the tumor suppressive effect of Tp53. Challenging this dogma, mouse models have revealed that p53 driven apoptosis and cell cycle arrest are dispensable for tumor suppression. Here, we investigated the inverse context of a p53 mutation predicted to drive expression of canonical targets, but is detected in human cancer. Methods: We established a novel mouse model with a single base pair mutation (GAG>GAC, p53E221D) in the DNA-Binding domain that has wild-type function in screening assays, but is paradoxically found in human cancer in Li Fraumeni syndrome. Using mouse p53 E221D and the the analogous human p53E224D mutant, we evaluated expression, transcriptional activation, and tumor suppression in vitro and in vivo. Results: Expression of human p53E224D from cDNA translated to a fully functional p53 protein. However, p53 E221D/E221D RNA transcribed from the endogenous locus is mis-spliced resulting in nonsense mediated decay. Moreover, fibroblasts derived from p53 E221D/E221D mice do not express a detectable protein product. Mice homozygous for p53 E221D exhibited increased tumor penetrance and decreased life expectancy compared to p53 WT animals. Conclusions: Mouse p53 E221D and human p53 E224D mutations lead to splice variation and a biologically relevant p53 loss of function in vitro and in vivo. Wild-Type and homozygous P53E221D/E221D mutant mouse embryonic fibroblasts were sequenced without perturbation in triplicate. NCI-H716 and HCT116 cells were similarly sequenced in triplicate.