Tumor-derived p53 mutant C174Y is a gain-of-function mutant which activates the fos promoter and enhances colony formation

Abstract

SV40 large T antigen-induced primitive neuroectodermal tumors of the rat provide a model system to study induction and progression of primitive neuroectodermal tumors at the molecular level. A cell line derived from such a tumor reproducibly gave rise to malignant derivatives that ceased large T-antigen expression but harbored a mutant p53 allele with a common mutation at Cys(174) to Tyr (C174Y). To determine whether this p53 mutation contributes to tumor progression, we analyzed mutant C174Y functionally. Co-transfection experiments in Saos-2 cells with mutant or wild-type p53 and reporter genes linked to various p53-responsive promoters revealed that mutant C174Y failed to transcriptionally transactivate the Mdm2, Waf1, Cyclin G and Bax promoters. Loss of transcriptional activation correlated with loss of DNA-binding activity. Moreover, mutant C174Y exhibited a dominant negative effect on co-expressed wild-type p53. The ability of mutant p53 to repress the viral RSV, LTR or SV40 early promoters or the cellular fos promoter was likewise impaired. In contrast, it showed even induction of the fos promoter. Consistent with these observations, mutant C174Y was non-functional in the suppression of Saos-2 cell growth and even conferred a growth advantage to the cells. Surprisingly, mutant C174Y was also impaired in nuclear transport, as revealed by immunofluorescence analyses. Taken together, our results demonstrate that mutant C174Y possesses features that can positively contribute to cancer progression.