P53-BINDING PROTEINS IN SQUAMOUS-CELL CARCINOMA AND NORMAL HUMAN KERATINOCYTES

In squamous cell carcinomas (SCCs), the tumor suppressor protein p53 i s frequently overexpressed. The overexpression of p53 is often due to a mutation in the p53 gene; however, increased levels of p53 protein c an be observed in the tumors without p53 gene mutations. In normal hum an keratinocytes, p53 is a multiconformational protein. The different conformations of p53 can be identified by their reactivity with epitop e-specific, anti-p53 monoclonal antibodies. This study provides eviden ce that the different p53 conformations seen in human keratinocytes bi nd to distinct cellular proteins. Proteins that bind p53 in normal hum an keratinocytes were compared with p53-binding proteins from cells de rived from SCC tumors by immunoprecipitation of [S-35]methionine-label ed and P-32(i)-labeled cell lysates-using a panel of anti-p53 monoclon al antibodies. In one tumor, the SCC cells contained a protein of M(r) 30,000 bound to p53 that was not seen in normal human keratinocytes. Cells derived from a separate SCC did not have the M(r) 30,000 protein but did contain two proteins of M(r) 15,000 and M(r) 16,000, which we re not seen in normal human keratinocytes. The immunofluorescent stain ing pattern of cultured normal human keratinocytes, cells derived from two SCCs, as well as the original tumors from which the cells were de rived, was also examined. The immunofluorescent staining of the cells derived from the tumors and the tumors themselves was different from t hat seen in normal cultured keratinocytes and normal epidermis. These studies suggest that there are alterations in the proteins that bind t o p53 in SCCs.