Abstract A45: Loss of Adar1 in pancreatic acinar cells leads to cell apoptosis and inflammation
Authors: Dhwani N. Rupani, Robert W. Cowan, Andrew D. Rhim
Journal: Cancer Research (2019)

Abstract While genetic mutations have been shown to drive pancreatic ductal adenocarcinoma (PDAC), epigenomic alterations in cancer cells may also contribute to tumor initiation and progression. Adenosine-to-inosine (A-to-I) editing is the most common type of RNA editing in the cell and is mediated by the adenosine deaminase acting on RNA (ADAR) enzyme. ADAR has been shown to be upregulated in various tumor types, it improves tumor cell viability and loss of Adar1 in melanoma cells increases efficacy of checkpoint blockade therapy in vivo. However, its function in PDAC is currently not well understood. In order to investigate the role of Adar1 in PDAC we developed a mouse model with a conditional knockout of Adar1 in the pancreas using the pancreas specific ptf1a Cre. However, the CYA (ptf1a [cre/wt], Rosa26 [LSL-YFP/LSL-YFP], Adar [F/F]) mice are born runted compared to littermate controls and die preweaning. We find that a conditional loss of Adar1 in the pancreas induces acinar cell death and the pancreatic tissue degenerates over a period of fifteen days. Adar1 inhibits interferon (IFN) responses that are activated by cellular double-stranded RNA (dsRNA) sensors through mitochondrial antiviral signaling protein (Mavs). To rescue the apoptotic and inflammatory phenotype of the CYA mice, we developed a CYAM mouse (ptf1a [cre/wt], Rosa26 [LSL-YFP/LSL-YFP], Adar [F/F], Mavs [-/-]). We find that these mice develop normally and their pancreas is devoid of apoptotic cells. Furthermore, to understand the function of Adar1 in pancreas homeostasis of adult mice, we developed an inducible model wherein in adult CiYA (ptf1aCre-ERTM [cre/wt], Rosa26 [LSL-YFP/LSL-YFP], Adar [F/F]) Adar1 loss was induced with intraperitoneal tamoxifen injections. We find that loss of Adar1 in the CiYA adult pancreas induces cell death and inflammation and the mice decline rapidly. We tested expression of a panel of 5 ISGs (Mx1, Isg15, IfnB1, Ifit1, Ifit2) by RT-qPCR and show that there is an elevated expression of ISGs in the pancreas of CiYA mice compared to WT controls. In conclusion, we show that pancreatic acinar cells are extremely sensitive to Adar1 loss both during developmental stages and in adult mice. Current in vivo models to study the function of Adar1 in development and cancer are limited by the lethal phenotype caused by upregulation of interferon stimulated genes (ISGs) and cell death in tissues where Adar1 is knocked out. Our work establishes a mouse model wherein pancreas-specific role of Adar1 in development and cancer can be studied without activation of Mavs-mediated inflammation. We are currently exploring how the CYAM mouse model can be utilized to advance our understanding of Adar1’s role in pancreas development and cancer. Citation Format: Dhwani N. Rupani, Robert W. Cowan, Andrew D. Rhim. Loss of Adar1 in pancreatic acinar cells leads to cell apoptosis and inflammation [abstract]. In: Proceedings of the AACR Special Conference on Pancreatic Cancer: Advances in Science and Clinical Care; 2019 Sept 6-9; Boston, MA. Philadelphia (PA): AACR; Cancer Res 2019;79(24 Suppl):Abstract nr A45.