Abstract B24: p53 mediates reprograming of cancer-associated fibroblasts in pancreatic cancer
Authors: Ridinger Maya , Evans Ronald M. , Saghatelian Alan , Lowy Andrew M. , Wahl Geoffrey M. 
Published: December 2016

Abstract
Pancreatic ductal adenocarninoma (PDA) is one of the most aggressive human cancers and is characterized by a uniquely abundant stroma. The stroma, composed of immune and fibroblastic cells, acts both as a resource for soluble factors that sustain tumor cell growth and survival, as well as a barrier to drug delivery. The pancreatic stellate cells (PSCs) are the main fibroblastic cells in the stroma of PDA. During tumor progression, quiescent PSCs evolve into activated and proliferative myofibroblast-like cells that synthesize extracellular matrix proteins to create the desmoplasia characteristic of PDA. Identifying means to reprogram the cancer associated fibroblats (CAF) to quiescence may alter the stroma and thereby reduce PDA progression and improve therapeutic susceptibility.
Our data reveal that the tumor suppressor p53 regulates CAF quiescence/activation. We show that CAFs isolated from PDA patients express wild-type p53 that can be activated by the p53 agonist Nutlin-3a. Nutlin-3a reprogrammed CAFs to a quiescence-like state as shown by accumulation of lipid droplets, decrease of αSMA expression and growth arrest. This process is strictly p53-dependent. We also found that cell cycle arrest induced by a CDK4/6 inhibitor did not induce lipid droplet accumulation and did not decrease αSMA expression. Together, the data support the idea that growth arrest is not sufficient to reprogram CAFs toward quiescence, and that a downstream effects p53 activation are involved.
To gain insights into mechanisms of p53 induced CAF reprogramming, we investigated p53-activation induced lipid droplet accumulation. Nutlin-induced lipid droplet formation does not require lipid uptake from the media, and appears independent of growth factors since it occurs in serum-free de-lipidated medium. This implies that p53 activation may affect intracellular lipid regulation. Lipidomics and RNA-seq analysis were performed using Nutlin 3a or vehicle treated CAFs. These analyses revealed that p53 activation increases different lipid categories such as triacylglycerols, sphyngolipids and cholesterol esthers, and transcriptionaly regulates genes associated with these pathways. Further investitgations are on going to assess the importance of putative pathways identified by RNA-seq for p53-induced lipid accumulation.
RNA-seq analyses also revealed that p53 modulates expression of cytokines, growth factors, and extracellular components involved in fibrosis. Stromal p53 could therefore influence tumor growth, immune cell recruitment and therapeutic responses in vivo. We are currently testing these hypothesis using mouse models of PDA.
Citation Format: Maya Ridinger, Ronald M. Evans, Alan Saghatelian, Andrew M. Lowy, Geoffrey M. Wahl.{Authors}. p53 mediates reprograming of cancer-associated fibroblasts in pancreatic cancer. [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 B24.