Spontaneous in vitro immortalization of breast epithelial cells from a patient with Li-Fraumeni syndrome.

Individuals with germ line mutations in the p53 gene, such as Li-Fraumeni syndrome (LFS), have an increased occurrence of many types of cancer, including an unusually high incidence of breast cancer. This report documents that normal breast epithelial cells obtained from a patient with LFS (with a mutation at codon133ofthep53gene)spontaneouslyimmortalizedincellculturewhilethebreaststromalfibroblastsfrom thissamepatientdidnot.Spontaneousimmortalizationofhumancellsinvitroisanextremelyrareevent.This is thefirst documented case of the spontaneous immortalization of breast epithelial cells from a patient with LFS in culture. LFS patient breast stromal fibroblasts infected with a retroviral vector containing human papillomavirus type 16 E7 alone were able to immortalize, whereas stromal cells obtained from patients with wild-type p53, similarly infected with human papillomavirus type 16 E7, did not. The present results indicate aprotectiveroleofnormalpRb-likefunctionsinbreaststromalfibroblastsbutnotinbreastepithelialcellsand reinforcesanimportantroleofwild-typep53intheregulationofthenormalgrowthanddevelopmentofbreast epithelial tissue. Familialcancersyndromeswithgermlinemutations,suchas the dominantly inherited p53 mutations present in Li-Fraumeni syndrome (LFS), have helped to illustrate the important role of tumor suppressor genes in the development of human cancers (3, 30, 31, 35, 36, 37, 52). The p53 gene is presently considered to be one of the most frequently mutated genes in human cancer (19, 22, 28, 29, 47, 56, 58), and the functional effects of mutations in evolutionarily conserved regions of the p53 phosphoprotein are currently a subject of intense study (24, 25, 28, 43, 46, 59‐63). While a complete understanding of wild-type p53 function is not yet known, it is generally believed that perturbations of wild-type p53 function may lead to genomic instability and permit the expansion of the pool of proliferating cells, which leads to a cascade of additional mutations,increasingtheprobabilityofneoplastictransformation. The discovery of the importance of the tumor suppressor gene p53, and the identification of germ line mutations in p53 in LFS-affected families, has led to a growing awareness of the cancer risk to such families. Even though rare bone and soft tissue sarcomas are relatively common in families affected by LFS, other, more frequently occurring forms of cancer other thanbreastcancer(suchascolorectalcarcinoma)arenotoverrepresented.AmongwomeninfamiliesaffectedbyLFS,breast tumors are the most prevalent cancer (afflicting at least 50%), with 28% of the breast cancers diagnosed before age 30 and 89% diagnosed before age 50 (21, 31, 37). A molecular explanation for the specifically increased incidence of breast cancer, particularly early-onset breast cancer, in families affected by LFS relative to other forms of cancer has not yet been elucidated (20, 41). We and others have shown that spontaneous immortalization of human cells in vitro (a cell culture term for unlimited proliferative capacity of cells) is an extremely rare event (23, 32,50)requiringalterationormutationsinseveralgeneswhich are normally involved in the regulation of cellular senescence