Abstract 4825: Functional role of Ring Finger Protein 43 in intestinal stem cell during colorectal tumorigenesis

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Abstract Background: Colorectal cancer is one of the most general causes of cancer related death. Ring Finger Protein 43(RNF43) is an E3 ubiquitin ligase that suppresses the Wint signaling pathway and is known as a tumor suppressor gene. Previous studies reported RNF43 mutation leads to inactivation of RNF43 in pancreatic, ovarian, colorectal cancer and so on. Subsequently, Wnt signaling activation is associtated with tumor progression in these types of cancers. However, functional role of RNF43 for tumor formation is not clear in colorectal cancer. Aim: To investigate the functional role of RNF43 in colorectal cancer by using RNF43 knockout mice. Method: We prepared RNF43 knockout mice by using CRISPR/Cas9 system. To induce colorectal tumor in mice, we used Azoxymethane-Dextran sulfate sodium (AOM-DSS) model. First, we injected AOM 10mg/kg into the peritoneal cavity. After 7days from injection, drunk 2% DSS water to mice for 7days. We sacrificed the mice and evaluated the tumor incidence and tumor size after 8, 10, 12, and 16 weeks from injection. Next, we prepared the small intestine organoid from RNF43 wild and knockout mice. Then we compared the organoid size and formation rate. In vitro analysis, we prepared colon cancer cell lines (COLO205, SW620, HCT116) and evaluated the effect on cell proliferation in suppression of RNF43 and normal condition. Result: There was no significant difference in the tumor incidence and tumor size at 8, 10, and 12weeks after AOM injection. However, at 16 weeks, the tumor size of RNF43 knockout mice was significantly bigger than that of RNF43 wild type mice. (p<0.001) Further examination of the intestinal organoid revealed that the organoids derived from RNF43 knockout mice tended to get bigger than those from wild type mice. In vitro analysis, cell proliferation of RNF43 mutant cell line (HCT116) was significantly increased compared with RNF43 wild type cell lines (COLO205, SW620). RNF43 silencing significantly increased cell proliferation in RNF43 wild type cell lines (p<0.001), whereas did not affected in RNF43 mutant cell line. Conclusion: Our results suggest that RNF43 expression suppresses epithelial cell growth in the intestine, and the dysregulation of Wint signaling via RNF43 disruption promote intestinal stem cell expansion and colorectal tumorigenesis. Citation Format: Tsugio Eto, Takatsugu Ishimoto, Eri Oda, Daisuke Kuroda, Kota Arima, Mayuko Ohuchi, Kenichi Nakamura, Hiroshi Sawayama, Koichi Kinoshita, Masaaki Iwatsuki, Yoshifumi Baba, Yasuo Sakamoto, Naoya Yoshida, Hideo Baba. Functional role of Ring Finger Protein 43 in intestinal stem cell during colorectal tumorigenesis [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 4825. doi:10.1158/1538-7445.AM2017-4825