Radioimmunoassay of the cellular protein p53 in mouse and human cell lines.

Abstract

Quantitative radioimmunological solid phase assays were developed for the host protein p53 from mouse cells and from human cells. The first assy, for mouse p53, depends on having 2 monoclonal antibodies reacting with different determinants on the p53 molecule. SV40-transformed cells have .apprx. 100-fold more p53 that untransformed mouse cells and other transformed cells have intermediate levels. Embryonal carcinoma cell lines have .apprx. 50-fold less p53 than SV40-transformed cells. This is in contrast to the high levels of incorporation of [35S]Met into p53 in these cells and indicates that metabolic labeling is not a valid approach for measuring p53 levels. The 2nd assay, for human p53, required a different approach and made use of the anti-p53 antibodies detected in the sera of some breast cancer patients. Human tumor cell lines contained amounts of p53 varying from the high level seen in SV40-transformed human fibroblasts down to < 1/100 of this amount. Normal human cells showed low levels of p53. Evidently, many, but not all human tumor cell lines contain more p53 than normal cells.