Biological and Molecular Analysis of P53 Cellular-Encoded Tumor Antigen

Abstract

Publisher Summary p53 was originally observed as a cellular product that formed a stable complex with the viral large T antigen expressed in Simian Virus 40 (SV40)-transformed cells. p53 is found in tumor cells in its phosphorylated form. The addition of radioactive phosphorus yields a phosphorylated p53 that immunoprecipitates with anti-p53 monoclonal antibodies. Under in vivo conditions, p53 phosphorylates onto a serine amino acid. Experiments showed that immunoprecipitation of p53 with a specific anti-p53 monoclonal antibody yields a p53 protein that also autokinases under in vitro conditions. In these experiments, p53 immunoprecipitated with several other anti-p53 monoclonal antibodies apparently did not bind the radioactive phosphate of γ-ATP under in vitro conditions. These conflicting results, concerning autokinase of p53 in vitro after immunoprecipitation with one reagent and not with another could be explained by the assumption that some monoclonal antibodies bind directly to the site of phosphorylation. The assumption that p53 is encoded by the normal cellular genome is based on the observation that it is expressed in several types of nontransformed cells. Several investigations suggest that the basis for the quantitative difference of p53 in transformed and nontransformed cells is due to posttranslational regulatory mechanisms.