What have animal models taught us about the p53 pathway?

Mouse models have provided important insight into the in vivo significance of upstream and downstream signals that regulate the p53 tumour suppressor. One important lesson learned from these models is that negative regulators of p53 are critical in vivo modulators of p53 activity. Additionally, upstream regulators of p53 activity, such as p19^Arf and Atm, are themselves critical tumour modifiers/suppressors. The presence of multiple positive regulators of p53 and numerous downstream targets indicates a redundancy that ensures activation of the p53 pathway. Importantly, p53 plays a prominent role as a tumour suppressor in vivo by virtue of its ability both to block cell cycle progression and to induce cell death. Finally, different p53 mutants have different properties in vivo. Three missense mutations have been generated at the p53 locus and all three exhibit unique differences in their ability to contribute to the tumour phenotype. Clearly, determining the levels of p53 inhibitors, and the typing of p53 mutations in human tumours should be performed to determine the best avenue for treatment.