Abstract PR07: Deconstructing p53 transcriptional networks in pancreatic cancer suppression
Authors: Attardi Laura D. , Mello Stephano Spano , Valente Elizabeth J. , Mazur Pawel K. , Raj Nitin , Bieging-Rolett Kathryn , Vogel Hannes 
Published: December 2016

Abstract
The p53 transcription factor is mutated in the majority of human pancreatic cancers, underscoring its critical role in suppressing pancreatic cancer development. Although p53 can restrain neoplastic cell expansion by inducing cell-cycle arrest or apoptosis in response to diverse stress signals, the molecular pathways through which p53 acts in tumor suppression remain largely elusive. To define the transcriptional networks underlying p53 tumor suppressor function, we have used mouse genetic and genomic approaches. We generated a set of p53 knock-in mouse strains expressing mutants in the first (p53 25,26), second (p5353,54), or both (p5325,26,53,54) of two transcriptional activation domains (TADs). Using a combination of ChIP-sequencing and expression profiling on cells expressing these mutants, we have been able to define a limited list of direct p53 target genes whose expression is tightly correlated with tumor suppression. Specifically, we found that p5325,26 is severely compromised for transactivation of most classical p53 target genes (e.g. p21, Puma), but retains the ability to activate a subset of p53 target genes, while p5325,26,53,54 lacks transactivation activity completely. The p5325,26,53,54 mutant is completely inactive in tumor suppression, highlighting the importance of transactivation for p53-mediated tumor suppression. Interestingly, however, p5325,26 retains full activity in suppressing various cancers, including pancreatic cancer, indicating that efficient transactivation of most canonical p53 targets is dispensable for tumor suppression. As p5325,26 activates only a subset of p53-dependent genes, yet retains tumor suppressor activity, it has helped pinpoint a small set of novel, direct p53-inducible tumor suppression-associated genes (TSAGs) whose functions we are currently interrogating through genetic screens. In addition, we have made the surprising discovery that the p5353,54 mutant suppresses pancreatic cancer more effectively than wild-type p53, and that this capacity correlates with the ability of p5353,54 to hyperactivate a subset of p53 target genes. Indeed, our analysis of these genes has unveiled p53 targets critical for mediating p53 function in suppressing mouse and human pancreatic cancer cell growth, including a protein tyrosine phosphatase that negatively regulates Yap signaling. Collectively, these approaches will delineate the transcriptional networks fundamental for p53 function in tumor suppression, an approach that will ultimately facilitate the design of novel therapies for pancreatic cancers with p53 mutation.
Citation Format: Laura D. Attardi, Stephano Spano Mello, Elizabeth J. Valente, Pawel K. Mazur, Nitin Raj, Kathryn Bieging-Rolett, Hannes Vogel.{Authors}. Deconstructing p53 transcriptional networks in pancreatic cancer suppression. [abstract]. In: Proceedings of the AACR Special Conference on Pancreatic Cancer: Advances in Science and Clinical Care; 2016 May 12-15; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2016;76(24 Suppl):Abstract nr PR07.