Abstract 5339: Epigenetic silencing of ANGPTL4 in tumor tissues and its overexpression in the urothelial carcinoma microenvironment

Abstract

Abstract Urothelial carcinoma (UC) carcinogenesis has been hypothesized to occur through epigenetic repression of tumor suppressor genes (TSGs). By qRT-PCR array, we found that one potential TSG, ANGPTL4, was expressed at very low levels in all UC cell lines we examined. Previous studies had demonstrated that ANGPTL4 is highly expressed in some cancers, but downregulated, by DNA methylation, in others. Consequently, due to these seemingly conflicting functions in distinct cancers, the precise role of ANGPTL4 in the etiology of UC remains unclear. In this study, using methylation-specific PCR and bisulfite pyrosequencing, we show that ANGPTL4 is transcriptionally repressed by promoter hypermethylation in UC cell lines and primary tumor samples, as compared to adjacent noncancerous bladder urothelium. Functional studies further demonstrated that ectopic expression of ANGPTL4 potently suppressed UC cell proliferation, monolayer colony formation in vitro, and invasion, migration, and xenograft formation in vivo. As ANGPTL4 is a secreted factor, we therefore examined the circulating ANGPTL4 (cir-ANGPTL4) level in UC patients. Surprisingly, cir-ANGPTL4 was significantly higher in plasma samples from UC patients than normal control, suggesting it might be secreted from other cell types. More importantly, exogenous c-terminal fragment of ANGPTL4 (cANGPTL4) could promote cell proliferation and cell migration via activation of signaling through the Erk/FAK axis. We further confirmed that mouse xenograft tumor growth could be promoted by administration of exogenous cANGPTL4. Finally, immunohistochemistry demonstrated that ANGPTL4 was downregulated in tumor cells but overexpressed in tumor-adjacent stromal tissues including muscle and macrophages of muscle-invasive UC tissue samples. In conclusion, our data supports dual roles for ANGPTL4 in urothelial carcinoma progression, either as a tumor suppressor or oncogene, in response to microenvironmental context. Citation Format: Michael WY Chan, Hsiao-Yen Hsieh, Yeong-Chin Jou, Chun-Liang Tung, Yuh-Shyan Tsai, Yuan-Hung Wang, Chen-Lin Chi, Ru-Inn Lin, Shih-Kai Hung, Yu-Ming Chuang, Shu-Fen Wu, Chin Li, Cheng-Huang Shen, Cheng-Da Hsu. Epigenetic silencing of ANGPTL4 in tumor tissues and its overexpression in the urothelial carcinoma microenvironment [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 5339.