Summary Previous work has indicated a role for p53 in cell cycle control, genomic stability and cellular responses to DNA-damaging agents.However, few data are available for human fibroblasts heterozygous for defined germline mutations in TP53. We report studies on 25 strains derived from 12 families with Li-Fraumeni syndrome (LFS) and 18 strains from normal volunteers. The families include three that are classical LFS families, but in whom no TP53 mutation has been found. In the families with mutations, increased longevity and resistance to low-doserate ionizing radiation showed a statistically significant association with the presence of TP53 mutations. However, not all heterozygotes had increased longevity or were radioresistant, and fibroblasts from cancer-affected members of LFS families without TP53 mutations showed no significant increase in either of these end points. In contrast, all mutation-carrying strains showed evidence of genomic instability, expressed as aneuploidy, and accumulated structural chromosome aberrations in up to 100% of cells, usually accompanied by loss of the wild-type TP53 allele, immediately before senescence. Levels of aneuploidy higher than in normal cells were also observed in fibroblasts from families without TP53 mutations, suggesting that chromosome instability is a major factor in determining the cancer proneness of these families.

No abstract

Germline TP53 splicing mutations have been described infrequently (42%) in the literature, however in a series of 40 patients and families identi®ed by our group in which there are germline TP53 mutations, seven aect splicing (18%). The low ®gure reported in the literature might re¯ect the method of mutation detection, which in many studies does not include all splice junctions. These data indicate that a signi®cant proportion of TP53 germline mutations are currently unrecognized. We have carried out detailed studies of the eects of the dierent mutations on splicing, and see distinct variations in the eects of the same mutation in dierent patients. Furthermore we have identi®ed the usage of a nonconsensus splice donor site in four families with an intron 4 splice donor mutation. Oncogene (2001) 20, 2647 ± 2654.

We report an extensive Li ± Fraumeni-like family in which there is an unusual spectrum of tumours at relatively late onset. A germline TP53 splice donor mutation in exon 4 is present in all aected family members available for testing. The mutation abolishes correct splicing of intron 4 and techniques of RT ± PCR have identi®ed three dierent aberrant transcripts from the mutant TP53 allele. Using the yeast functional assay to analyse transcripts in cells from a number of family members with the mutant allele, TP53 appears wild-type. Functional studies have been carried out on cells from patients with and without cancer who carry the germline mutation, and on cells from unaected individuals from the same family who do not carry the mutation. Using a number of functional endpoints known to distinguish between cells carrying mutant or wild-type TP53 alleles, we were unable to discriminate normal (wt/wt) from heterozygous (wt/mut) cells by lymphocyte apoptosis and ®broblast survival following low dose rate ionising radiation exposure. However germline mutation carriers show increased sensitivity to radiation-induced chromosome damage in the G 2 phase of the cell cycle, and decreased transient and permanent G 1 arrest. These studies demonstrate the importance of fully characterising the eects of TP53 germline mutations, and may explain some of the phenotypic features of this family.