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p53 mutants without a functional tetramerisation domain are not oncogenic
1Oncology Department, Novartis, Basel, CH-4002, Switzerland. patrick.chene@pharma.novartis.com
Abstract:
p53 is altered in about 50 % of cancers. Most of the p53 mutants have lost the wild-type tumour suppressor activity but show oncogenic properties. The majority of the p53 alterations are missense mutations of residues located in its DNA binding domain (DBD). Only a few mutations concern residues in its tetramerisation domain (TD). However, the study of mutant proteins identified in tumors that do not form tetramers has shown that they have lost the wild-type activity like most of the p53 DBD mutants. Here, we show that two of such mutant proteins, Arg342Pro and Leu344Pro are not dominant negative and do not stimulate the expression of a reporter gene under the control of the multi-drug resistance gene-1 (MDR-1). This suggests that to be oncogenic, p53 mutants need to form tetramers. Accordingly, the dominant negative effect and the ability of a tetrameric mutant protein, Asp281Gly, to stimulate the MDR-1 promoter are abolished when its TD is rendered non-functional by the mutation of leucine 344 to a proline residue. These results suggest that mutations in the TD, are less selected in tumors than mutations in the DBD because they do not lead to oncogenic proteins.
Insights
p53 mutations in cancer can lead to oncogenic properties. Tetramer formation is crucial for p53 mutants to exhibit dominant negative effects and oncogenic potential, suggesting a mechanism for tumor suppressor activity loss.
Area of Science:
- Molecular Biology
- Cancer Research
- Protein Structure-Function
Background:
- TP53 gene alterations occur in approximately 50% of human cancers.
- Most p53 mutants lose wild-type tumor suppressor activity and gain oncogenic properties.
- Mutations predominantly affect the DNA-binding domain (DBD), with fewer in the tetramerization domain (TD).
Purpose of the Study:
- To investigate the role of tetramer formation in the oncogenic potential of p53 mutants.
- To determine if mutations in the tetramerization domain affect p53's dominant-negative activity and oncogenic properties.
- To elucidate why mutations in the tetramerization domain are less frequently observed in tumors compared to DNA-binding domain mutations.
Main Methods:
- Analysis of specific p53 mutants (Arg342Pro, Leu344Pro, Asp281Gly) in cellular assays.
- Assessment of dominant-negative effects and reporter gene stimulation (MDR-1 promoter).
- Site-directed mutagenesis to disrupt the tetramerization domain (e.g., Leu344Pro mutation).
Main Results:
- p53 mutants Arg342Pro and Leu344Pro, lacking tetramerization, did not exhibit dominant-negative activity or stimulate the MDR-1 reporter gene.
- Disruption of the tetramerization domain in the oncogenic Asp281Gly mutant abolished its dominant-negative effect and MDR-1 promoter stimulation.
- These findings indicate that tetramer formation is essential for the oncogenic properties of p53 mutants.
Conclusions:
- Oncogenic activity of p53 mutants is dependent on their ability to form tetramers.
- Mutations in the tetramerization domain may be less selected in tumors because they do not yield oncogenic proteins.
- The structural integrity of the tetramerization domain is critical for p53's tumor suppressor function and its oncogenic transformation potential when mutated.