Frequent p53 mutations in chemically induced murine fibrosarcoma.

Patterns of p53 expression were investigated in chemically induced fibrosarcoma tumors and cell lines. Most, if not all, cell lines were found to carry alterations at the protein level, reflected in the overproduction of greatly stabilized p53 proteins. In many cases, this was accompanied by formation of complexes with hsc70. Hence, all of these lines may be expressing one sort or another of mutant p53. The mutant nature of the p53 gene was directly verified, in a number of cases, by PCR-amplified cDNA cloning. In one line, no p53 protein was made at all; this turned out to be because of a mutation in a splice donor site, resulting in the production of an aberrant mRNA. In all other cases, mRNAs carrying mis-sense mutations were present, and were sometimes expressed along with wt p53 mRNA. When tested in an in vitro transformation assay, all cloned mutants possessed a discrete oncogenic activity, while having lost the ability to interfere with oncogene-mediated transformation. The system described here could potentially be very helpful in elucidating the significance of p53 mutations.