Immortalization of cultured human fibroblasts with the mutant p53 gene and X‐rays

The mutant p53 gene (mp53; codon 273^Arg‐His) was introduced into normal human fibroblasts (OUMS‐24 strain), and a G418‐resistant clone, OUMS‐24/P6, was obtained. This clone expressed mp53 and showed an extended life span, but it senesced at the 79th population‐doubling level (PDL). When these cells were subjected to eight intermittent treatments with 2 Gy of x‐rays, they were immortalized, whereas normal fibroblasts (OUMS‐24) into which mp53 had not been introduced were not immortalized by the same x‐ray treatment. These results indicate that the introduction of mp53 alone is not sufficient for immortalization of human cells and that mutations of the remaining wild‐type p53 or other genes are also necessary. © 1995 Wiley‐Liss, Inc.