Characterization of mouse models for the Human p53 codon 72 polymorphism.

PR-8

The TP535 tumor suppressor is the most commonly mutated gene in human cancers. In addition to mutation, the activity of p53 can be altered by single nucleotide polymorphisms (SNPs), which can modify the structure and function of the protein. The TP53 gene contains a common SNP that results in either an arginine or proline encoded at position 72. Numerous epidemiology studies suggest that this R72P polymorphism modulates the risk for developing a variety of cancers. It has been previously reported that the R72P polymorphism correlates with increased incidence of lung cancer and poorer lung cancer prognosis in African-Americans as compared to Caucasian-Americans. Furthermore, African-Americans with the proline mutation have increased odds of lung cancer. Moreover, the R72P polymorphism affects several p53 activities including apoptosis. Currently this polymorphism can only be analyzed by epidemiology studies and in vitro cell culture systems, yielding some conflicting results. Genetically engineered mouse models are powerful tools for studying the function of single genes and even sites of post-translational modifications. Here, we describe the development of a humanized mouse model system, using bacterial artificial chromosome (BAC) technology to study this human p53 codon 72 polymorphism. Thus far, we have demonstrated that the human BAC transgenes encoding either the arginine or proline p53 variant can functionally rescue the murine p53 null phenotype. Both human p53 variant proteins are induced in response to DNA damage in the BAC transgenic line and their levels of expression are similar to the level of endogenous murine p53 induced in wild type mice. Furthermore, studies indicate that mice expressing the arginine variant have increased levels of apoptosis when compared to mice expressing the proline variant, which is consistent with previous in vitro findings. We intend to further elucidate the functional differences in the p53 variants within the in vivo environment and clarify the epidemiological studies with laboratory-controlled experiments. Finally, these mice can be used as a model for therapy trials since humans with these p53 variants have been shown to react differently to various therapies.