Induction of apoptosis by transiently transfected metabolically stable wt p53 in transformed cell lines

Biochemical and functional properties of wild-type (wt) and mutant p53 were studied under the same cellular environment by transient transfection. Exogenous wt p53 expressed in transformed cell lines was found to be as metabolically stable as mutant p53. Yet only mutant p53 bound to hsp70 whereas wt p53 did not, suggesting that the metabolic stability of p53 does not depend on its ability to form complexes with hsp70. The wt protein was expressed essentially in the nucleus, while mutant p53 showed both nuclear and cytoplasmic expression, as determined by immunofluorescence staining with PAb122. In addition, staining with PAb1801 revealed a number of strongly fluorescent cell fragments in cultures transfected by wt p53. Morphological features of apoptosis were observed in these cultures. Quantitative analysis by flow cytometry confirmed that only the cell population expressing wt p53 had a significant amount of cell debris. Thus, transient expression of a metabolically stable wt, but not mutant, p53 induces cell death by apoptosis. The present study demonstrates a model system to investigate the functional domains of p53 in the induction of apoptosis.