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Transforming activity of mutant human p53 alleles
1Ontario Cancer Institute, Toronto, Canada.
Abstract:
Mutant forms of the p53 gene have been shown to cooperate with an activated ras gene in transforming primary cells in culture. The aberrant proteins encoded by p53 mutants are thought to act in a dominant negative manner in these assays. In vivo data, however, reveal that where p53 has undergone genetic change in tumors, both alleles have been affected. We previously identified a case of human acute myelogenous leukemia (AML) in which both alleles of the p53 gene had undergone independent missense mutations (at codons 135 cys to ser and 246 met to val). In these blasts, p53 mutations appear to be acting recessively. We have assayed the transforming potential of these p53 mutations, as well as that of another mutation at codon 273, also identified in a human neoplasm. Both mutations from the AML blasts (codon 135 and codon 246) confer transforming ability on the mutant protein. While transformation assays may define functionally different subsets of p53 mutations, the overexpression phenotype of mutants in this assay may not accurately reflect the pathological effects of p53 mutations in vivo.
Insights
Mutant p53 genes cooperate with ras in cell transformation, but in tumors, both p53 alleles are affected. AML-derived p53 mutations (codons 135 and 246) showed transforming potential in vitro.
Area of Science:
- Oncology
- Molecular Biology
- Genetics
Background:
- Mutant p53 proteins can cooperate with activated ras to transform cells.
- In tumors, both p53 alleles are typically affected, suggesting recessive activity.
- Previous research identified independent missense mutations in both p53 alleles in acute myelogenous leukemia (AML).
Purpose of the Study:
- To investigate the transforming potential of specific p53 mutations found in human neoplasms.
- To compare in vitro transforming activity with in vivo observations of p53 mutations in cancer.
Main Methods:
- Assaying the transforming potential of p53 mutations from AML blasts (codons 135 and 246).
- Evaluating another p53 mutation (codon 273) identified in a human neoplasm.
- Cell transformation assays in culture.
Main Results:
- Both p53 mutations (codons 135 and 246) from AML blasts conferred transforming ability on the mutant protein in vitro.
- These findings suggest p53 mutations in AML may act recessively in vivo.
- Transformation assays might identify functionally distinct p53 mutation subsets.
Conclusions:
- p53 mutations at codons 135 and 246 from AML exhibit transforming potential in vitro.
- The in vitro overexpression phenotype of p53 mutants may not fully represent their in vivo pathological roles.
- Further research is needed to reconcile in vitro findings with in vivo tumor behavior of p53 mutations.