Abstract 4625: An impact of epigenetic approaches targeting JARID1B to modulate malignant behaviors of gastrointestinal cancer.

Abstract

Abstract Background. Although there are emerging epigenetic factors that contribute to the occurrence, development and metastasis of Gastrointestinal (GI) cancer, the biological roles of epigenetic molecular modifications in different subpopulations, such as cancer stem cells, remains to be understood fully. Here we aimed to clarify the functional roles of the H3K4 demethylase, Jumonji, AT Rich Interactive Domain 1B (JARID1B), an epigenetic factor required for continuous cell growth of melanomas, in GI cancer. Materials and Methods. Based on our ptrevious expression studies showing a high expression level of JARID1B transcript, we focused on four GI cancer cell lines for the analysis: colorectal cancer Colo201 and HCT116; esophageal cancer TE4 and TE8. To study the underlined mechanism, the chromatin immunoprecipitation (ChIP) assay was performed. We performed in vitro experiments, including cell growth, invasion, sphere formation and immunocytochemistry; and in vivo ones, such as chemo-sensitivity and tumorigenesis. For specific knockdown of target genes, lentiviral mediated shRNAs and synthesize siRNA were used. To track biological behaviors of GI cancer cells, a lineage tracing technology was performed to visualize to the mode of tumor cell growth in vitro and in vivo. Result. CD44+/ALDH+ slowly proliferating immature GI cancer populations expressed relatively low levels of JARID1B and the differentiation marker CD20, with a relatively high level of the tumor suppressor p16/INK4A. Fluorescent ubiquitination-based cell cycle indicator transfections to GI cancer cells indicated that endogenous JARID1B increased in the late G1, showing a critical role in G1 to S transition checkpoint. The ChIP assay demonstrated clearly that JARID1B knockdown status leads to the methylation of p16/INK4A gene promoter. Importantly, continuous knockdown of JARID1B resulted in the loss of epithelial differentiation and suppressed cell growth, which associated with phosphorylation induction by Jnk/Sapk, and the irreversible induction of senescence (detected by SA β-galactosidase activity). Finally, green fluorescent-labeled cell tracking indicated that GI cancer cells, which reduced JARID1B expression, had lesser tumorigenicity than JARID1B-positive cells do in vivo. Conclusion. JARID1B plays a critical role in cell cycle regulation at G1/S transition of GI cancer cells. The continuous inhibition of JARID1B would contribute for tumor eradication. Taken together with melanoma study (Cell, 2011), the present study indicated that JARID1B would be a bona fide target for the eradication of chemotherapy-resistant, dormant GI cancer cells, by the induction of endogenous mechanism of cellular senescence. Learning Objective. We identified the novel function and transcriptional targets of epigenetics and verified the important biological behaviors of epigenetics in GI cancer. Citation Format: Katsuya Ohta, Yoshihiro Kano, Masamitsu Konno, Yoshinori Kagawa, Shimpei Nishikawa, Shinichiro Hasegawa, Takahito Fukusumi, Hisataka Ogawa, Atsushi Hamabe, Taroh Satoh, Naotsugu Haraguchi, Hirofumi Yamamoto, Yuichiro Doki, Masaki Mori, Hideshi Ishii. An impact of epigenetic approaches targeting JARID1B to modulate malignant behaviors of gastrointestinal cancer. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 4625. doi:10.1158/1538-7445.AM2013-4625