TEMPERATURE SENSITIVITY OF HUMAN WILD-TYPE AND MUTANT P53 PROTEINS EXPRESSED IN-VIVO

p53 is activated in response to DNA damage and functions in the mainte nance of genetic integrity. Loss of p53 function because of mutation o f the p53 gene is associated with over half all human cancers. Certain human p53 mutants are conformationally flexible in vitro and are temp erature sensitive, with partial or complete recovery of wild-type (wt) properties at 32 degrees C. We have now tested the functional capacit ies of selected p53 mutants in vivo, by transfection into established human cell lines. Unexpectedly, we found that wt p53 can be temperatur e sensitive for transactivation of a co-transfected target gene in viv o. Flexible mutants retained varying degrees of functional capacity in tranfected cells, and the recipient cell line appeared to be a signif icant determinant of both wt and mutant p53 function; importantly, two p53 null cell lines commonly used to study p53 function (Saos-2 and H ep3B) differed markedly in this latter respect. We also show that the p53 mutant V272M, which exhibits sequence-specific DNA binding in vitr o, is nonetheless defective for transactivation and is unable to induc e apoptosis in vivo. The valine 272 residue may thus be crucial for pr operties (other than sequence-specific DNA binding) that are important for p53 function(s) in vivo.