Abstract 1374: Frequent up-regulation of histone methyltransferase G9a contributed to liver carcinogenesis by epigenetically silencing of tumor suppressor RARRES3
Authors: wei lai , Tsang Felice Ho-Ching , Law Dicky Cheuk-Ting , Au Sandy Leung-Kuen , Lee Joyce Man-Fong , Wong Carmen Chak-Lui , Ng Irene Oi-Lin , Wong Jack Chun-Ming 
Published: July 2017

Hepatocellular carcinoma (HCC) is the second leading cause of cancer death worldwide and is the most common type of cancer in sub-Saharan Africa and Southeast Asia area where hepatitis B infections are common. The initiation and progression of HCC was attributed to alternations in genetics and disruptions of epigenetic processes which lead to altered gene functions in both oncogenes and tumor suppressors. Recent advancements in the field of cancer epigenetics increasingly emphasize the important role of every component in the epigenetic machinery. However, the alternations of epigenetic mechanisms involved in HCC are still largely unknown. Using transcriptome sequencing, we examined the expression of 591 epigenetic regulators in hepatitis B-associated human HCC and found that most of the epigenetic regulators are deregulated especially the histone modification enzymes. Among all of them, we identified G9a (Euchromatic histone-lysine N-methyltransferase 2, EHMT2), a histone H3 lysine 9 (H3K9) specific histone methyltransferases, as one of the most significantly up-regulated epigenetic regulators in human HCCs. Previous studies about epigenetic alternations primarily focused on promoter DNA hypermethylation. However, little is known about the pathological implications of histone modifications. Herein, we hypothesis the frequent up-regulation of G9a causes epigenetic aberrations which contribute liver carcinogenesis, and targeting G9a could be a potential epigenetic therapeutic method for HCC treatment. In this study, we found that G9a was frequently up-regulated in different HCC sample cohorts. Up-regulation of G9a was significantly associated with HCC disease progression, cancer aggressiveness, and more malignant tumor phenotypes. Functionally, we demonstrated that shRNA knockdown and CRISPR/Cas9 knockout of G9a suppressed HCC cell proliferation in vitro and inhibited subcutaneously xenograft HCC tumorigenicity in vivo. Depletion of G9a significantly reduced HCC cell migration ability and induced cell senescence. Pharmacological inhibition of G9a by small molecule inhibitors, UNC0638 and BIX01294, also suppressed HCC cell growth and altered cell morphology. Mechanistically, we showed that the frequent up-regulation of G9a in human HCC was attributed to gene copy number gain at chromosome 6p21 and loss of miR-1. Furthermore, up-regulation of G9 also epigenetically repressed miR-1 expression and thus formed a feedforward regulation loop between them. By utilizing RNA-Seq and GSEA analysis, we identified a potential tumor suppressor RARRES that was epigenetically silenced by G9a and promoted tumor cells proliferation in human HCC. Taken together, we showed that G9a are novel oncogenes in human HCCs and G9a could be novel therapeutic targets for HCC treatment.

Citation Format: lai wei, Felice Ho-Ching Tsang, Dicky Cheuk-Ting Law, Sandy Leung-Kuen Au, Joyce Man-Fong Lee, Carmen Chak-Lui Wong, Irene Oi-Lin Ng, Jack Chun-Ming Wong. Frequent up-regulation of histone methyltransferase G9a contributed to liver carcinogenesis by epigenetically silencing of tumor suppressor RARRES3 [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 1374. doi:10.1158/1538-7445.AM2017-1374