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Conformational effects in the p53 protein of mutations induced during chemical carcinogenesis: molecular dynamic and
P W Brandt-Rauf1, J M Chen, M J Marion
1Division of Environmental Health Sciences, Columbia University School of Public Health, New York, New York 10032, USA.
Abstract:
The tumor suppressor gene p53 has been identified as the most frequent target of genetic alterations in human cancers. Vinyl chloride, a known human carcinogen that induces the rare sentinel neoplasm angiosarcoma of the liver, has been associated with specific A-->T transversions at the first base of codons 249 and 255 of the p53 gene. These mutations result in an Arg-->Trp amino acid substitution at residue 249 and an Ile-->Phe amino acid substitution at residue 255 in a highly conserved region in the DNA-binding core domain of the p53 protein. To determine the effects of these substitutions on the three-dimensional structure of the p53 protein, we have performed molecular dynamics calculations on this core domain of the wild-type and the Trp-249 and Phe-255 mutants to compute the average structures of each of the three forms. Comparisons of the computed average structures show that both mutants differ substantially from the wild-type structure in certain common, discrete regions. One of these regions (residues 204-217) contains the epitope for the monoclonal antibody PAb240, which is concealed in the wild-type structure but accessible in both mutant structures. In order to confirm this conformational shift, tumor tissue and serum from vinyl chloride-exposed individuals with angiosarcomas of the liver were examined by immunohistochemistry and enzyme-linked immunosorbent assay. Individuals with tumors that contained the p53 mutations were found to have detectable mutant p53 protein in their tumor tissue and serum, whereas individuals with tumors without mutations and normal controls did not.
Insights
Vinyl chloride exposure causes specific p53 gene mutations, altering the p53 protein structure. These structural changes allow detection of mutant p53 in cancer patients exposed to this carcinogen.
Area of Science:
- Molecular Biology
- Cancer Research
- Toxicology
Background:
- The p53 tumor suppressor gene is frequently altered in human cancers.
- Vinyl chloride, a carcinogen, induces specific p53 mutations linked to angiosarcoma of the liver.
- These mutations lead to amino acid substitutions in the p53 DNA-binding core domain.
Purpose of the Study:
- To investigate the structural impact of p53 mutations (Trp-249 and Phe-255) induced by vinyl chloride.
- To determine if these structural changes affect the accessibility of specific p53 epitopes.
- To correlate structural findings with the detectability of mutant p53 in affected individuals.
Main Methods:
- Molecular dynamics calculations were used to model the wild-type and mutant p53 core domains.
- Computed average structures were compared to identify conformational differences.
- Immunohistochemistry and enzyme-linked immunosorbent assays were employed to detect mutant p53 in patient samples.
Main Results:
- Both Trp-249 and Phe-255 p53 mutants exhibited significant structural deviations from the wild-type.
- A key region (residues 204-217), including the PAb240 antibody epitope, became accessible in both mutants, unlike the wild-type.
- Mutant p53 protein was detectable in tumor tissue and serum of vinyl chloride-exposed individuals with angiosarcomas, but not in controls.
Conclusions:
- Vinyl chloride-induced p53 mutations cause distinct structural alterations in the p53 protein.
- These conformational changes, particularly epitope accessibility, may have diagnostic implications.
- Detection of mutant p53 in serum and tissue confirms the biological impact of vinyl chloride exposure and associated mutations.