Mutation of p53, inherited in some individuals with Li-Fraumeni syndrome (LFS), is a critical event in the elaboration of many tumors of diverse origin. Most mutations of p53 are single nucleotide changes that alter critical amino acids in the DNA-binding domain rather than alterations that delete the p53 gene. The prevalence of p53 missense mutations coupled with in vitro data has led to the hypothesis that mutant p53 has additional properties that make it more detrimental for proper cell cycle regulation and more advantageous to the dividing cell. To test this hypothesis in vivo and model human LFS more accurately, we have generated mouse models inheriting the p53R172H mutation (corresponding to the p53R175H hotspot in human cancers). This mutation disrupts the conformation of p53 resulting in a protein that is tumorigenic in cooperation with ras, and readily immortalizes cells. Mice with the p53R172H mutation have gained additional tumorigenic properties and also exhibit a dominant-negative phenotype. Metastasis is rampant in p53R172H/+ mice as opposed to mice lacking one p53 allele. Additional experiments are needed to ascertain the events leading to tumorigenesis, metastasis, stability of the mutant p53, and the dominantnegative nature of the mutation. To examine the ability of p53R172H to cooperate with Brcal deletion, another common alteration that leads to breast cancer, crosses with Brca1+/- mice in a background sensitive to beast cancer will be performed. An important question that will be addressed in these studies is what other molecular changes, examined by CGH and Affymetric arrays, cooperate with mutant p53 in the genesis of different kinds of cancers. Lastly, since the type of p53 missense mutation may also contribute to different phenotypes, another p53 missense mutation will be generated in mice. The p53R245W mutation represents a DMA contact mutant that alters an arginine amino acid involved in direct contact to DNA. p53R245W is also transcriptionally inactive, but cannot immortalize cells. The p53R245W mutation in another hot spot mutation inherited in LFS patients. Comparison of the two classes of p53 mutants (conformation versus contact) should yield insights into the role of these mutants in tumorigenesis. Our studies suggest that treatment of a patient will have to be tailored not only to the kind of tumor that develops, but to the specific p53 missense mutation identified in the tumor as well. The research outlined in this application is directly relevant to public health in that it proposes to study a gene, p53, that is often altered in different kinds of cancers. The study aims to understand the nature of p53 mutations and of other changes that cooperate with this defect. These studies may identify novel therapeutic targets.