Identifying Novel Mechanisms of Tp53-Mediated Tumor Suppression

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2023

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Abstract

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 investigate two mouse models that seek to further elucidate the necessity of p53 pathways in tumor suppression. These mutants represent a paradoxical signaling of canonical targets and incidence in human cancer. One p53 mutation is deficient in signaling, but not found in human cancer and the other represents the inverse context of a p53 mutation predicted to drive the expression of canonical targets, but is detected in human cancer.

Methods: We established novel mouse models with single amino acid substitutions (GAG>GAC, mouse p53E221D and GCC>GGG, mouse p53G259A) in the DNA-binding domain. The first represents the mouse variant of a p53 mutant that has wild-type function in screening assays, but is paradoxically found in human cancer in Li Fraumeni syndrome. The second mutation has decreased transactivation in screening assays but is not widely found in human cancer. Using mouse models and the analogous human mutants, 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, mouse p53E221D/E221D RNA transcribed from the endogenous locus is mis-spliced resulting in nonsense-mediated decay. Moreover, fibroblasts derived from p53E221D/E221D mice do not express a detectable protein product. Mice homozygous for p53E221D/E221D exhibited increased tumor penetrance and decreased life expectancy compared to p53WT/WT animals. Expression of the human p53G262A from cDNA translated into a functionally deficient p53 protein. The mouse p53G259A/G259A mutation was transcribed in mouse embryonic fibroblasts, and hyper-stabilized in untreated cells. Signaling was modestly deficient and did not result in a significant tumor burden in p53G259A/G259A mouse models.

Conclusions: Mouse p53E221D/E221D and human p53E224D mutations lead to splice variation and a biologically relevant p53 loss of function in vitro and in vivo. Mouse p53G259A/G259A and human p53G262A are deficient in transactivation, but maintenance of homeostasis is achieved through hyperstabilization of the mutant.

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Lock, Ian Charles (2023). Identifying Novel Mechanisms of Tp53-Mediated Tumor Suppression. Dissertation, Duke University. Retrieved from https://hdl.handle.net/10161/30271.

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