P21(WAF1/CIP1) response to genotoxic agents in wild-type TP53 expressing breast primary tumours

Functional inactivation of the wild-type p53 protein has been described in different human cancers. Since a significant proportion of breast tumours express wildtype TP53, the p53 antiproliferative activity could be inactivated in transformed mammary epithelial cells by a mechanism independent on structural alteration of the gene, To test this hypothesis, we analysed the p53 activity in primary breast tumour cells. As a preliminary study, we demonstrated in breast adenocarcinoma cell lines that the nuclear accumulation of the inhibitor of cyclin dependent kinase p21(WAF1/CIP1), in response to adriamycin treatment, specifically reflected the activity of a functional wild-type p53 protein. Then, we used this strategy to study the p53 activity in 23 primary breast tumours. p21(WAF1/CIP1) accumulation was detected in all tumours expressing wild-type TP53. In contrast, no p21(WAF1/CIP1) response was detected in cells harboring a mutant TP53 gene. This report is the first functional study of p53 in primary breast tumours. The results demonstrate that TP53 mutation represents the only common mechanism leading to an irreversible inactivation of p53 functions in this cancer type.