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Biogenesis of p53 involves cotranslational dimerization of monomers and posttranslational dimerization of dimers.
Chris D Nicholls1, Kevin G McLure, Michael A Shields
1Department of Microbiology and Infectious Diseases, Cancer Biology Research Group, University of Calgary Health Sciences Centre, Calgary, Alberta, Canada, T2N 4N1.
Abstract:
Precisely how mutant p53 exerts a dominant negative effect over wild type p53 has been an enigma. To understand how wild type and mutant p53 form hetero-oligomers, we studied p53 biogenesis in vitro. We show here that p53 dimers are formed cotranslationally (on the polysome), whereas tetramers are formed posttranslationally (by the dimerization of dimers in solution). Coexpression of wild type and mutant p53 therefore results in 50% of the p53 generated being heterotetramers comprised of a single species: wild type dimer/mutant dimer. Using hot spot mutants of p53 and a variety of natural target sites, we show that all wild type/mutant heterotetramers manifest impaired DNA binding activity. This impairment is not due to the mutant dimeric subunit inhibiting association of the complex with DNA but rather due to the lack of significant contribution (positive cooperativity) from the mutant partner. For all heterotetramers, bias in binding is particularly pronounced against those sequences in genes responsible for apoptosis rather than cell growth arrest. These results explain the molecular basis of p53 dominant negative effect and suggest a functional role in the regulation of p53 tetramerization.
Insights
Mutant p53 hinders wild type p53 function by forming non-functional heterotetramers. This dominant-negative effect impairs DNA binding, particularly for apoptosis-related genes, explaining p53
Area of Science:
- Molecular Biology
- Cancer Biology
- Protein Biochemistry
Background:
- The tumor suppressor protein p53 plays a critical role in maintaining genomic stability.
- Mutations in p53 are common in human cancers and often confer a dominant-negative effect over wild-type p53.
- The mechanism by which mutant p53 interferes with wild-type p53 function remains incompletely understood.
Purpose of the Study:
- To elucidate the molecular mechanisms underlying the dominant-negative activity of mutant p53.
- To investigate the assembly of wild-type and mutant p53 hetero-oligomers.
- To determine how these hetero-oligomers affect p53's DNA binding activity and target gene regulation.
Main Methods:
- In vitro studies of p53 biogenesis.
- Analysis of p53 dimer and tetramer formation.
- Assessment of DNA binding activity of wild-type/mutant p53 heterotetramers using various target sites.
Main Results:
- p53 dimers form cotranslationally, while tetramers form posttranslationally.
- Coexpression of wild-type and mutant p53 generates heterotetramers (wild-type dimer/mutant dimer).
- All wild-type/mutant heterotetramers exhibit impaired DNA binding due to reduced positive cooperativity from the mutant subunit, with a bias against apoptosis-related gene sequences.
Conclusions:
- The study explains the molecular basis of the p53 dominant-negative effect.
- Impaired DNA binding of heterotetramers is attributed to the mutant subunit's lack of contribution, not inhibition.
- These findings suggest a role for p53 tetramerization regulation in its dominant-negative function and cancer biology.