METTL3 is frequently up-regulated in human HCC and contributes to HCC progression. METTL3 represses SOCS2 expression in HCC through an m6A-YTHDF2-dependent mechanism. Our findings suggest an important mechanism of epigenetic alteration in liver carcinogenesis. (Hepatology 2018;67:2254-2270).

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Epigenetic alterations and microRNA (miRNA) deregulation are common in hepatocellular carcinoma (HCC). The histone H3 lysine 27 (H3K27) tri-methylating enzyme, enhancer of zeste homolog 2 (EZH2) mediates epigenetic silencing of gene expression and is frequently up-regulated in human cancers. In this study we aimed to delineate the implications of EZH2 up-regulation in miRNA deregulation and HCC metastasis. Expressions of a total of 90 epigenetic regulators were first determined in 38 pairs of primary HCCs and their corresponding nontumorous livers. We identified EZH2 and its associated polycomb repressive complex 2 (PRC2) as one of the most significantly deregulated epigenetic regulators in primary HCC samples. Up-regulation of EZH2 was next confirmed in 69.5% (41/59) of primary HCCs. Clinicopathologically, EZH2 up-regulation was associated with HCC progression and multiple HCC metastatic features, including venous invasion (P 5 0.043), direct liver invasion (P 5 0.014), and absence of tumor encapsulation (P 5 0.043). We further demonstrated that knockdown of EZH2 in HCC cell lines reduced the global levels of tri-methylated H3K27, and suppressed HCC motility in vitro and pulmonary metastasis in a nude mouse model. By interrogating the miRNA expression profile in EZH2-knockdown cell lines and primary HCC samples, we identified a subset of miRNA that was epigenetically suppressed by EZH2 in human HCC. These included well-characterized tumor-suppressor miRNAs, such as miR- 139-5p, miR-125b, miR-101, let-7c, and miR-200b. Pathway enrichment analysis revealed a common regulatory role of these EZH2-silenced miRNAs in modulating cell motility and metastasis-related pathways. Our findings suggest that EZH2 exerts its prometastatic function by way of epigenetic silencing of multiple tumor suppressor miRNAs. Conclusion: Our study demonstrated that EZH2 epigenetically silenced multiple miRNAs that negatively regulate HCC metastasis. (HEPATOLOGY 2012;56:622-631)

AMP-activated protein kinase (AMPK), a biologic sensor for cellular energy status, has been shown to act upstream and downstream of known tumor suppressors. However, whether AMPK itself plays a tumor suppressor role in cancer remains unclear. Here, we found that the a2 catalytic subunit isoform of AMPK is significantly downregulated in hepatocellular carcinoma (HCC). Clinicopathologic analysis revealed that underexpression of AMPK-a2 was statistically associated with an undifferentiated cellular phenotype and poor patient prognosis. Loss of AMPK-a2 in HCC cells rendered them more tumorigenic than control cells both in vitro and in vivo. Mechanistically, ectopic expression of AMPK enhanced the acetylation and stability of p53 in HCC cells. The p53 deacetylase, SIRT1, was phosphorylated and inactivated by AMPK at Thr344, promoting p53 acetylation and apoptosis of HCC cells. Taken together, our findings suggest that underexpression of AMPK is frequently observed in HCC, and that inactivation of AMPK promotes hepatocarcinogenesis by destabilizing p53 in a SIRT1-dependent manner. Cancer Res; 72(17); 4394-404. Ó2012 AACR.

ObjectiveWe investigated the effect and mechanism of hypoxic microenvironment and hypoxia-inducible factors (HIFs) on hepatocellular carcinoma (HCC) cancer stemness.DesignHCC cancer stemness was analysed by self-renewal ability, chemoresistance, expression of stemness-related genes and cancer stem cell (CSC) marker-positive cell population. Specific small ubiquitin-like modifier (SUMO) proteases 1 (SENP1) mRNA level was examined with quantitative PCR in human paired HCCs. Immunoprecipitation was used to examine the binding of proteins and chromatin immunoprecipitation assay to detect the binding of HIFs with hypoxia response element sequence. In vivo characterisation was performed in immunocompromised mice and stem cell frequency was analysed.ResultsWe showed that hypoxia enhanced the stemness of HCC cells and hepatocarcinogenesis through enhancing HIF-1α deSUMOylation by SENP1 and increasing stabilisation and transcriptional activity of HIF-1α. Furthermore, we demonstrated that SENP1 is a direct target of HIF-1/2α and a previously unrecognised positive feedback loop exists between SENP1 and HIF-1α.ConclusionsTaken together, our findings suggest the significance of this positive feedback loop between HIF-1α and SENP1 in contributing to the increased cancer stemness in HCC and hepatocarcinogenesis under hypoxia. Drugs that specifically target SENP1 may offer a potential novel therapeutic approach for HCC.

Epigenetic deregulation plays an important role in liver carcinogenesis. Using transcriptome sequencing, we examined the expression of 591 epigenetic regulators in hepatitis B-associated human hepatocellular carcinoma (HCC). We found that aberrant expression of epigenetic regulators was a common event in HCC. We further identified SETDB1 (SET domain, bifurcated 1), an H3K9-specific histone methyltransferase, as the most significantly up-regulated epigenetic regulator in human HCCs. Up-regulation of SETDB1 was significantly associated with HCC disease progression, cancer aggressiveness, and poorer prognosis of HCC patients. Functionally, we showed that knockdown of SETDB1 reduced HCC cell proliferation in vitro and suppressed orthotopic tumorigenicity in vivo. Inactivation of SETDB1 also impeded HCC cell migration and abolished lung metastasis in nude mice. Interestingly, SETDB1 protein was consistently up-regulated in all metastatic foci found in different organs, suggesting that SETDB1 was essential for HCC metastatic progression. Mechanistically, we showed that the frequent up-regulation of SETDB1 in human HCC was attributed to the recurrent SETDB1 gene copy gain at chromosome 1q21. In addition, hyperactivation of specificity protein 1 transcription factor in HCC enhanced SETDB1 expression at the transcriptional level. Furthermore, we identified miR-29 as a negative regulator of SETDB1. Down-regulation of miR-29 expression in human HCC contributed to SETDB1 up-regulation by relieving its post-transcriptional regulation. Conclusion: SETDB1 is an oncogene that is frequently up-regulated in human HCCs; the multiplicity of SETDB1 activating mechanisms at the chromosomal, transcriptional, and posttranscriptional levels together facilitates SETDB1 up-regulation in human HCC. (HEPATOLOGY 2016;63:474-487)

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Interaction between tumor cells and immune cells in the tumor microenvironment is important in cancer development. Immune cells interact with the tumor cells to shape this process. Here, we use single-cell RNA sequencing analysis to delineate the immune landscape and tumor heterogeneity in a cohort of patients with HBV-associated human hepatocellular carcinoma (HCC). We found that tumor-associated macrophages suppress tumor T cell infiltration and TIGIT-NECTIN2 interaction regulates the immunosuppressive environment. The cell state transition of immune cells towards a more immunosuppressive and exhaustive status exemplifies the overall cancer-promoting immunocellular landscape. Furthermore, the heterogeneity of global molecular profiles reveals co-existence of intra-tumoral and inter-tumoral heterogeneity, but is more apparent in the latter. This analysis of the immunosuppressive landscape and intercellular interactions provides mechanistic information for the design of efficacious immune-oncology treatments in hepatocellular carcinoma.