Journal of hepatology

Histone methyltransferase G9a promotes liver cancer development by epigenetic silencing of tumor suppressor gene RARRES3.

PMID 28532996


Hepatocellular carcinoma (HCC) is a major leading cause of cancer mortality worldwide. Epigenetic deregulation is a common trait of human HCC. G9s is an important epigenetics regulator. However, its roles in liver carcinogenesis remain to be investigated. Gene expressions were determined by RNA-Seq and qRT-PCR. G9a knockdown and knockout cell lines were established by lentiviral-based shRNA and CRISPR/Cas9 gene editing system. Tumor promoting functions of G9a was studied by both in HCC cell lines and nude mice model. The down-stream targets of G9a were identified by RNA-Seq and confirmed by ChIP assay. The therapeutic value of G9a inhibitors was evaluated both in vitro and in vivo. We identified G9a as a frequently up-regulated histone methyltransferase in human HCCs. Up-regulation of G9a was significantly associated with HCC progression and aggressive clinicopathological features. Functionally, we demonstrated that inactivation of G9a by RNAi knockdown, CRISPR/Cas9 knockout, and pharmacological inhibition remarkably abolished H3K9 di-methylation and suppressed HCC cell proliferation and metastasis in both in vitro and in vivo models. Mechanistically, we showed that the frequent up-regulation of G9a in human HCCs was attributed to gene copy number gain at chromosome 6p21. In addition, we identified miR-1 as a negative regulator of G9a. Loss of miR-1 relieved the post-transcriptional repression on G9a and contributed to its up-regulation in human HCC. Utilizing RNA-sequencing, we identified the tumor suppressor RARRES3 as a critical target of G9a. Epigenetic silencing of RARRES3 contributed to the tumor-promoting function of G9a. Our findings discovered a frequent deregulation of miR-1/G9a/RARRES3 axis in liver carcinogenesis. Our findings also highlighted the pathological significance of G9a and its therapeutic potential in HCC treatment. In this study, we identified G9a histone methylation was frequently up-regulated in human HCC and contribute to epigenetic silencing of tumor suppressor genes RARRES3 in liver cancer. Targeting G9a may be a novel approach for HCC treatment.