Abstract 3518: Brg1 plays a critical role in PanIN formation through regulating Sox9 expression

Abstract

Abstract Background: Mutations of SWI/SNF chromatin remodeling complexes are one of the hallmarks of human pancreatic ductal adenocarcinoma (PDA). Brahma related gene 1 (Brg1) is a catalytic ATPase subunit of SWI/SNF complexes and Brg1 is silenced in about 10% of human PDA. Recent study revealed that Brg1 inhibits formation of intraductal pancreatic mucinous neoplasm (IPMN) and IPMN-derived PDA in the context of oncogenic Kras and that IPMNs originate from adult pancreatic ductal cells, demonstrating a tumor suppressive role of Brg1. However, the role of Brg1 in the formation of pancreatic intraepithelial neoplasia (PanIN) from acinar cells and PanIN-derived PDA is not fully understood. Aim: To investigate the functional role of Brg1 in the formation of PanIN Methods and Results: We generated Ptf1a-CreER; KrasG12D; Brg1f/f (KBC) mice, in which Brg1 is deleted exclusively in adult pancreatic acinar cells along with expression of oncogenic Kras upon tamoxifen induction of Cre activity and assessed spontaneous acinar-to-ductal metaplasia (ADM) and PanIN formation. We found that ADM and PanIN formation was significantly decreased in KBC mice compared with littermate controls. Next, we induced caerulein-acute pancreatitis to KBC mice and assessed for pancreatitis-induced tumorigenesis. We found that PanINs were decreased in KBC mice compared with littermate controls, although pancreatitis-induced ADMs were widely observed in KBC mice. Since Brg1 is known to critical regulator of p53, mutant p53 allele was crossed with KBC mice. Unexpectedly, even in the context of mutant p53, loss of Brg1 significantly deceased PanIN formation. These results suggest that Brg1 plays a tumor-supportive role in acinar cell-derived PanIN formation in various contexts. Primary acinar cell culture experiments revealed that ADM formation was markedly reduced in the absence of Brg1 and that Sox9 expression was downregulated in Brg1-depleted acinar cells. Furthermore, we confirmed that Sox9 expression is downregulated in Brg1-depleted ADMs/PanINs compared with Brg1-retained ADMs/PanINs by immunohistochemistry. To determine the functional relationship between Brg1 and Sox9, we generated Ptf1a-CreER; KrasG12D; Brg1f/f; Sox9OE mice, in which Sox9 is constitutively overexpressed. Remarkably, Sox9 overexpression canceled the phenotype of decrease in PanIN formation by Brg1 deletion. Furthermore, to investigate whether Brg1/Sox9 axis is observed in human PanIN-derived PDAs, we performed immunohistochemistry of Brg1 and Sox9 in human PanIN-derived PDAs. In 27 human PDAs, all of 5 PDAs with low Brg1 expression had low Sox9 expression. Conclusions: Our results suggest that Brg1 plays a critical role in acinar cell-derived PanIN formation in part through regulating Sox9 expression positively. Our data underscore a cell-type specific, context-dependent role of Brg1 in the initiation of PDA formation. Citation Format: Motoyuki Tsuda, Akihisa Fukuda, Satoshi Ogawa, Kenji Masuo, Norihiro Goto, Yukiko Hiramatsu, Yu Muta, Kozo Ikuta, Yoshito Kimura, Yoshihide Matsumoto, Yutaka Takada, Takuto Yoshioka, Takahisa Maruno, Haruhiko Akiyama, Kyoichi Takaori, Shinji Uemoto, Tsutomu Chiba, Hiroshi Seno. Brg1 plays a critical role in PanIN formation through regulating Sox9 expression [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 3518. doi:10.1158/1538-7445.AM2017-3518