Abstract 1390: Deregulation of RNA N6-adenosine methylation contribute to liver carcinogenesis
Authors: Chen Mengnuo , Wei Larry L. , Law Cheuk Ting , Tsang Felice HC , Xu Iris MJ , Lee Joyce Lee MF , Wong Carmen Wong CL , Ng Irene OL , Wong Chun-Ming 
Published: July 2017

Primary liver cancer, particularly the most common type hepatocellular carcinoma (HCC), is the third leading cause of cancer death worldwide. Case is even worse in Asia due to extremely high prevalence of HBV/HCV infection, which enhances the risk of HCC. However, the exact mechanism of how HCC develops is still not clearly defined. Previous studies have shown strong evidence for epigenetic alterations in human carcinogenesis, which mainly focus on abnormal DNA methylation, histone modifications, and chromatin remodeling. Recent studies suggest that diverse chemical modifications on RNAs, also known as “epi-transcriptome”, constitute another layer of gene expression regulation. N-6-methyladenosine (m6A) is the most abundant modification on eukaryotic mRNA, which has been found to functionally influence mRNA stability, alternative splicing, and translation efficiency. However, the roles of m6A deregulation in human carcinogenesis remain unclear. Through whole-transcriptome sequencing, we identified that METTL3, the major component of m6A methyltransferase, was significantly up-regulated in human HCC. Up-regulation of METTL3 negatively associated with poor patient overall and disease free survival. Functionally knockdown/knockout of METTL3 dramatically inhibited HCC proliferation, migration and colony formation abilities in vitro and significantly suppressed in vivo tumorigenicity. In contrast, overexpression of METTL3 using CRISPR/dCas9 SAM system modestly but significantly enhanced HCC proliferation, migration, anchorage-independent growth in vitro and tumor formation in vivo. In order to find the downstream mechanisms which might attributed to METTL3 oncogenic function we performed RNA-Seq on two independent METTL3 knockdown cell lines to interrogated their transcriptome changes. Based on RNA-Seq data, we identified a prominent tumor suppressor SOCS2 as a potential down-stream target of METTL3. With m6A-RNA immunoprecipitation (RIP) assay, we confirmed that SOCS2 mRNA was subject to m6A modification in cancer cells. Inactivation of METTL3 by RNAi or treatment of methylation inhibitor (DAA) impaired m6A mediated mRNA degradation and thereby stabilized SOSC2 mRNA. We further confirm SOCS2 tumor suppressor function in HCC. Downregulation of SOCS2 was associated with poor patient overall survival and disease free survival of HCC patients. Knockdown of SOCS2 significantly promoted HCC proliferation, migration in HCC cells. In conclusion, our findings suggested that deregulation of METTL3 and its associated m6A modification could contribute to human carcinogenesis by imposing an epigenetic control on the stability and expressions of critical tumor suppressor genes.

Citation Format: Mengnuo Chen, Larry L. Wei, Cheuk Ting Law, Felice HC Tsang, Iris MJ Xu, Joyce Lee MF Lee, Carmen Wong CL Wong, Irene OL Ng, Chun-Ming Wong. Deregulation of RNA N6-adenosine methylation contribute to liver carcinogenesis [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 1390. doi:10.1158/1538-7445.AM2017-1390