The wild-type p53 protein plays a central role in regulating growth, G1/S boundary arrest, transactivation and apoptosis. Mutations in the p53 gene are found in half of human tumors. Circulating autoantibodies to p53 are found in 10-15 percent of cancer patients. Although the presence of p53 autoantibodies coincides with p53 mutations, these autoantibodies are not specific to a particular p53 mutant and recognize both wild type and mutant proteins therefore indicating that the immunogenicity of p53 is not a direct consequence of the mutations. p53 is a phosphoprotein that contains a large number of proposed or potential phosphorylation sites. Additionally, one or more O-linked glycosylation sites have been identified. In spite of extensive research to correlate phosphorylation and tumor suppression or lack thereof, knowledge of which phosphate acceptor sites are utilized and the ultimate biological significance of phosphorylation is very limited. Previous studies on mutated proteins have been complicated because of potential anomalies in the phosphorylation machinery in cell lines used for protein production. The goal of the proposal is to unambiguously identify phosphorylation and glycosylation sites in wild type and mutant p53. To this end well-characterized single and multiply phosphorylated and glycosylated peptides will be synthesized and used as immunogens in mice to generate monoclonal antibodies with high titer and specificity for the modified forms of the antigens. The antibodies will be tested for antigen recognition of a wide range of p53 alleles. The synthetic peptides will serve as valuable tools for screening p53 autoantibodies from cancer patients to determine whether the autoantibodies recognize simple or more complex modifications in antigen structure. After identifying the actual phosphorylation sites in normal and cancerous cells future research may target (i) the activation or deregulation of appropriate kinases and phosphatases and (ii) design protocols for immunization and immunotherapy against modified p53.
| Varadi, Gyorgyi; Otvos Jr, Laszlo (2002) Synthesis of complex phosphopeptides as mimics of p53 functional domains. J Pept Sci 8:621-33 |
| Otvos Jr, L; Hoffmann, R; Xiang, Z Q et al. (1998) A monoclonal antibody to a multiphosphorylated, conformational epitope at the carboxy-terminus of p53. Biochim Biophys Acta 1404:457-74 |
| Hoffmann, R; Craik, D J; Pierens, G et al. (1998) Phosphorylation of the C-terminal sites of human p53 reduces non-sequence-specific DNA binding as modeled with synthetic peptides. Biochemistry 37:13755-64 |
