MUTANT P53-INDUCED IMMORTALIZATION OF PRIMARY HUMAN MAMMARY EPITHELIAL-CELLS

Mutations of the p53 gene are the most frequent genetic lesions in bre ast cancer, suggesting a critical role for p53 protein in normal mamma ry cell growth control. Indeed, the p53-targeting human papillomavirus oncogene E6 induces efficient immortalization of normal human mammary epithelial cells (MECs). To assess whether selective loss of p53 is s ufficient for MEC immortalization, we introduced seven missense mutant s and one single-amino acid deletion mutant (del239) of p53 into the 7 6N normal MEC strain. Although the missense mutants failed to immortal ize MECs, the del239 mutant reproducibly immortalized these cells. The immortal cells were anchorage dependent and nontumorigenic, indicatin g a preneoplastic transformation. gamma-Irradiation of these cells fai led to induce G(1) cell cycle arrest and did not lead to an increase i n WAF1 and mdm-2 mRNA levels, demonstrating a loss of the endogenous p 53 function. These results demonstrate that selective ablation of p53 function by a dominant-negative mutant is sufficient for immortalizati on of MECs. Availability of an immortalizing as well as several nonimm ortalizing p53 mutants should help identify functions critical for cel l growth control by p53 in mammary epithelial cells.