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Mutant p53 Gain of Function in Two Mouse Models of Li-Fraumeni Syndrome

The p53 tumor suppressor gene is commonly altered in human tumors, predominantly through missense mutations that result in accumulation of mutant p53 protein. These mutations may confer dominant-negative or gain-of-function properties to p53. To ascertain the physiological effects of p53 point mutation, the structural mutant p53(R172H) and the contact mutant p53(R270H) (codons 175 and 273 in humans) were engineered into the endogenous p53 locus in mice. p53(R270H/+) and p53(R172H/+) mice are models of Li-Fraumeni Syndrome; they developed allele-specific tumor spectra distinct from p53(+/-) mice. In addition, p53(R270H/)(-) and p53(R172H/)(-) mice developed novel tumors compared to p53(-/-) mice, including a variety of carcinomas and more frequent endothelial tumors. Dominant effects that varied by allele and function were observed in primary cells derived from p53(R270H/+) and p53(R172H/+) mice. These results demonstrate that point mutant p53 alleles expressed under physiological control have enhanced oncogenic potential beyond the simple loss of p53 function.