p53 mutants can often transactivate promoters containing a p21 but not Baxor PIG3 responsive elements

The human p53 protein acts mainly as a stress inducible transcription facto r transactivating several genes involved in cell cycle arrest (e,g, p21) or apoptosis (e,g, Bar, PIG3), Roughly half of all human tumours contains p53 missense mutations. Virtually all tumour-derived p53 mutants are unable to activate Bax transcription but some retain the ability to activate p21 tra nscription, Identification of these mutants may have valuable clinical impl ications. We have determined the transactivation ability of 77 p53 mutants using reporter yeast strains containing a p53-regulated ADE2 gene whose pro moter is regulated by p53 responsive elements derived from the regulatory r egion of the p21, BRS and PIG3 genes, We also assessed the influence of tem perature on transactivation, Our results indicate that a significant propor tion of mutants [16/77 (21%); 10/64 (16%) considering only tumour-derived m utants] are transcriptionally active, especially with the p21 promoter. Dis criminant mutants preferentially affect less conserved (P < 0.04, Fisher's exact test), more rarely mutated (P < 0.006, Fisher's exact test) amino aci ds. Temperature sensitivity is frequently observed, but is more common amon g discriminant than non-discriminant mutants (P < 0.003, Fisher's exact tes t), Finally, we extended the analysis to a group of mutants isolated in BRC A-associated tumours that surprisingly were indistinguishable from wild typ e in standard transcription, growth suppression and apoptosis assays in hum an cells, but showed gain of function in transformation assays. The inciden ce of transcriptionally active mutations among this group was significantly higher than in the panel of mutants studied previously (P < 0.001, Fisher' s exact test), Since it is not possible to predict the behaviour of a mutan t from first principles, we propose that the yeast assay be used to compile a functional p53 database and fill the gap between the biophysical, pharma cological and clinical fields.