The long-term objective of the proposed research is to develop a biomarker for the study of carcinogenesis in occupational cohorts exposed to vinyl chloride (VC) based on the immunologic detection of mutant forms of the tumor suppressor gene protein p53 in serum. Mutational inactivation of the p53 gene appears to be common in the angiosarcomas of the liver (ASL) that develop in VC-exposed workers, occurring in 50 percent of cases studied. The specific mutation (A-T transversion at the first base of codons 249 and 255) is consistent with the known mutational properties of VC's carcinogenic metabolites and results in amino acid substitutions at residues 249 and 255 in the encoded p53 protein. Such mutant p53 proteins are conformationally altered resulting in the exposure of a common epitope and they have greatly prolonged half-lives resulting in accumulation of the protein in the cell and in the extracellular environment. Monoclonal antibodies are available that can specifically identify the revealed common epitope of these mutant p53 proteins and thus demonstrate increased amounts of the mutant p53 in cells and in the extracellular supernatant. Using such antibodies in a previously developed enzyme-linked immunosorbent assay (ELISA) for serum, preliminary studies have shown that it is possible to identify mutant p53 in the serum of VC- exposed workers with ASLs where the corresponding tumor DNA contains the mutant p53 gene. Furthermore, mutant p53 has been identified in a significant proportion (18 percent) of VC-exposed workers without ASLs compared to none (0 percent) of matched unexposed controls.
The specific aims of the proposed research are to confirm and extend these findings by: (1) examining the tissue expression by immunohistochemistry and the serum expression by ELISA of mutant p53 protein in 13 additional cases of ASL in VC-exposed workers to confirm the relationship between serum and tumor tissue results; (2) determining the serum expression of mutant p53 protein in an additional 201 VC- exposed workers without tumors stratified by degree of VC exposure and 200 matched unexposed controls to establish the relationship between VC exposure and serum mutant p53 expression.
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