Pancreatic cancer is the 4th leading cause of cancer-associated deaths, and it is virtually always a fatal disease. The progression of this cancer from a preinvasive state to a metastatic, invasive state is associated with mutation of the p53 tumor suppressor gene. While p53 suppresses cancer by inducing cell cycle arrest, senescence or apoptosis in response to stress signals, its molecular mechanism of action in vivo remains unclear. p53 displays activity as a transcriptional activator, but it also has a variety of other biochemical activities, in regulating transcriptional repression, DNA replication and recombination, mitochondrial membrane integrity, and centrosome duplication. To begin to define the p53 molecular activities important for suppressing pancreatic cancer progression, we propose to address the importance of p53 transcriptional activation and repression functions for tumor suppression through the generation and analysis of a panel of p53 knock-in mouse strains expressing different p53 mutants. The use of knock-in mice, in which mutants are expressed under the control of the native p53 promoter, and in which normal cells can be studied both ex vivo and in the physiological context of the organism, should provide definitive insight into the mechanism of p53 action in tumor suppression. We previously generated knock-in mice expressing a p53 mutant, p5325,26, that is severely impaired for the transactivation of most, but not all, p53 target genes and that retains the ability to suppress lung cancer development. These observations suggest that p5325,26 tumor suppressor function is accounted for by either residual p53 transactivation or another p53 activity. We will first examine the ability of this mutant to inhibit pancreatic cancer progression using a well-characterized mouse model of pancreatic cancer driven by activated KRas expression, and we will thus determine if full p53 transactivation potential is required for tumor suppression in the pancreas. If p5325,26 displays activity, the importance of limited transactivation versus another p53 function for tumor suppression will be distinguished by examining knock-in mice expressing a mutant totally defective for transactivation, p5325,26,53,54. In addition, the importance of transcriptional repression for p53 function in blocking pancreatic cancer progression will be assessed by generating mice expressing a repression-defective variant of p53. We propose further to develop a cellular culture model system for more detailed mechanistic studies of p53-mediated tumor suppression in the pancreas. Together, these studies will determine whether genes must be activated and/or repressed by p53, or whether other p53 activities are essential for its ability to suppress pancreatic cancer development, and will have great utility for the future development of better cancer therapies for this deadly disease. PUBLIC HEALTH RELEVANCE: Pancreatic cancer is the 4th leading cause of cancer deaths in the US and is nearly always fatal. It is therefore very important to understand the basis of this disease in order to be able to more effectively treat and cure it. This research aims to elucidate how a gene known as p53 acts to prevent the development of pancreatic cancer, with the ultimate goal of devising better prevention and treatment strategies for cancer.