p53 Frameshift Mutations Couple Loss-of-Function with Unique Neomorphic Activities

Area of Science:

• Molecular Biology
• Cancer Research
• Genetics

Background:

• p53 mutations are common in cancer, often leading to loss of transcriptional activity.
• Frameshift mutations in the TP53 gene can produce truncated p53 proteins with altered properties.

Purpose of the Study:

• To characterize p53 frameshift mutant proteins expressed from endogenous TP53 locus.
• To investigate the functional consequences of these mutants in cancer cell lines.

Main Methods:

• Analysis of p53 frameshift mutants in U2OS osteosarcoma and HCT116 colorectal cancer cell lines.
• Assessment of DNA-binding, oligomerization, transcriptional activity, and cellular functions (proliferation, senescence, migration).

Main Results:

• Three p53 frameshift mutants were characterized, retaining intact DNA-binding domains but showing altered oligomerization.
• Mutants were transcriptionally inactive, unable to initiate wild-type p53 programs.
• One mutant, I332fs*14, exhibited residual antiproliferative activity, induced senescence, and decreased cell motility.

Conclusions:

• p53 frameshift mutants display a mix of loss-of-gain and gain-of-function characteristics.
• These variants differ from both wild-type p53 and complete p53 loss.
• The residual and neomorphic functions of p53 frameshift mutants may be targets for novel cancer therapies.