Mis-splicing drives loss of function of p53E224D point mutation

Area of Science:

• Oncology
• Molecular Biology
• Genetics

Background:

• The tumor suppressor p53 (Trp53) is frequently mutated in cancer, with its canonical DNA damage response pathways traditionally linked to tumor suppression.
• Recent studies challenge this, showing p53-driven apoptosis and cell cycle arrest are not essential for tumor suppression.
• This research explores a p53 mutation found in human cancer that is predicted to activate canonical targets but behaves inversely.

Purpose of the Study:

• To investigate the functional consequences of a specific p53 mutation (p53E221D) found in human cancer.
• To determine if this mutation, despite predicted wild-type screening function, leads to a loss of tumor suppressive activity.
• To evaluate the in vitro and in vivo effects of the mouse p53E221D and analogous human p53E224D mutants.

Main Methods:

• Established a novel mouse model with a single base pair mutation (GAG>GAT, p53E221D) in the p53 DNA-Binding domain.
• Utilized mouse p53E221D and human p53E224D mutants for expression, transcriptional activation, and tumor suppression studies.
• Assessed protein expression, RNA splicing, and tumor development in homozygous mutant mice and control groups.

Main Results:

• While human p53E224D from cDNA showed full function, endogenous mouse p53E221D/E221D RNA underwent mis-splicing, leading to nonsense-mediated decay.
• Fibroblasts from p53E221D/E221D mice lacked detectable p53 protein product.
• Mice with homozygous p53E221D mutations exhibited increased tumor incidence and reduced lifespan compared to wild-type controls.

Conclusions:

• The p53E221D (mouse) and p53E224D (human) mutations result in aberrant RNA splicing.
• This splice variation leads to a biologically significant loss of p53 function, both in vitro and in vivo.
• These findings highlight a novel mechanism of p53 dysfunction in cancer relevant to Li-Fraumeni syndrome.