Tumor suppressor p53 protein is a nuclear phosphoprotein that regulates cellular proliferation through its involvement in cell cycle control. Normal p53 binds to DNA and represses transcriptional activation at the G1-S boundary. Loss of this function by mutation or possible conformational change will impair interaction with its DNA binding site and permit gene activation of normally repressed off genes. Since this protein requires translocation to the nucleus, we are interested in the biochemical events that induce the synthesis, regulation and translocation of the p53 protein to the nucleus. Using the human mammary carcinoma cell line T47D we have isolated at least eleven isoforms of the p53 protein by means of immunoprecipitation and two-dimensional gel electrophoresis. We have also determined that oligomeric complexes are formed in the cytoplasm with p53 and at least two heat shock proteins, HSP70 and HSP90. These complexes may be necessary to protect against proteolysis and also to maintain a conformational state that allows passage through the nuclear membrane. We are interested in determining the reasons for multiple p53 protein isoforms as well as HSP complex association and dissociation mechanics in the release of active p53.
