B cell CLL/lymphoma 6 member B inhibits hepatocellular carcinoma metastases in vitro and in mice.

B cell CLL/lymphoma 6 member B (BCL6B) is a novel tumor suppressor silenced in human cancer. In this study, we investigated the functional role and underlying mechanisms of BCL6B in hepatocellular carcinoma (HCC). BCL6B was expressed in normal HCC tissues, but its expression was suppressed in 6 out of 9 HCC cell lines. Loss of BCL6B expression was associated with promoter hypermethylation. Ectopic expression of BCL6B in HepG2 and Huh7 cell lines inhibited colony formation (P <0.05), cell viability (P <0.01), and tumorigenicity in nude mice (P <0.05). BCL6B expression also induced apoptosis (P <0.05), an effect associated with activation of the caspase cascade and cleavage of PARP. Stable expression of BCL6B in MHCC97L cells suppressed cell migration (P <0.05) and invasion (P <0.05), and significantly reduced the incidence and severity of lung metastasis in an orthotopic HCC mouse model. The anti-metastatic effect of BCL6B was mediated by up-regulation of cell adhesion gene E-cadherin, OB-cadherin, HIV-1 Tat interactive protein 2, and transient receptor potential cation channel, subfamily M, member 1; and down-regulation of angiogenesis gene VEGFA. BCL6B functions as a tumor suppressor that inhibits HCC metastases in vitro and in vivo.

Wang J ，Dong L ，Xu L ，Chu ES ，Chen Y ，Shen J ，Li X ，Wong CC ，Sung JJ ，Yu J ... -  《-》

Nuclear localization of BRCA1-associated protein 1 is important in suppressing hepatocellular carcinoma metastasis via CTCF and NRF1/OGT axis.

Germline mutations of the deubiquitinase BRCA1-associated protein 1 (BAP1) lead to the "BAP1 cancer syndrome" characterized by development of cancers. However, the role of BAP1 in hepatocellular carcinoma (HCC) is unclear. We found that BAP1 was upregulated at mRNA level in human HCCs and significantly correlated with a more aggressive tumour behaviour. Intriguingly, we observed cytoplasmic but no or minimal nuclear BAP1 in human HCC samples by immunohistochemistry. We observed that, while BAP1 protein was found mainly in the cytoplasm and less in the nuclei of HCC cell lines, BAP1 expression was predominantly nuclear in HepG2 cells, by cell fractionation and immunofluorescence analyses. Functionally, in the orthotopic liver injection mouse model, silencing the BAP1 predominant nuclear expression of HepG2 cells promoted intrahepatic tumor metastasis, with more frequent tumor microsatellite formation and venous invasion. With transcriptomic profiling, we identified RHOJ amongst the downregulated targets in HepG2 cells upon BAP1 knockdown. Subsequent overexpression of RHOJ suppressed cell migration in HCC cells, suggesting that BAP1 might upregulate RHOJ resulting in reduced cell migratory ability of HCC cells. Furthermore, we identified two transcription factors, CTCF and NRF1, which activated BAP1 transcription by binding to BAP1 promoter region. On the other hand, we uncovered that O-linked N-acetylglucosamine (GlcNAc) transferase (OGT) physically bound to BAP1 in the nucleus, resulting in diminished stability of the nuclear BAP1. Intriguingly, OGT transcription was upregulated and was also under the control of CTCF and NRF1 in human HCC, acting as a negative regulator of BAP1. To summarize, this study uncovered the underlying mechanisms of the regulation of BAP1 and that loss of the nuclear localization of BAP1 protein contributed to enhanced cell migration in vitro and more aggressive tumor behavior in human HCCs.

Xie X ，Tsui YM ，Zhang VX ，Yu TC ，Husain A ，Chiu YT ，Tian L ，Lee E ，Lee JM ，Ma HT ，Ho DW ，Sze KM ，Ng IO ... -  《Cell Death & Disease》

Promoter hypermethylation-mediated downregulation of PAX6 promotes tumor growth and metastasis during the progression of liver cancer.

The progression of liver cancer is a complicated process that involves genetic and epigenetic changes. Paired box 6 (PAX6) is a critical transcription factor for embryonic development. PAX6 is abnormally methylated in human cancer. The role of the PAX6 gene in the pathogenesis of hepatocellular carcinoma (HCC) is still unclear. Transcriptional silencing of PAX6 mediated by promoter methylation was confirmed using quantitative methylation-specific polymerase chain reaction (PCR) and reverse-transcription (RT)-PCR. Then we conducted gain-and-loss of function approaches to evaluate the function of PAX6 in HCC progression in vitro. Moreover, we designed xenograft mouse models to assess the effect of PAX6 on tumor growth and metastasis. Finally, we used RNA sequencing (RNA-seq) strategy and phenotypic rescue experiments to identify potential targets of PAX6 performing tumor-suppressive function. Constitutive expression of PAX6 suppressed anchorage-independent growth and cell invasion in vitro as well as tumor growth and metastasis in xenograft mouse models. In contrast, the inhibition of PAX6 using knockout and knockdown strategies increased tumor growth both in vitro and in vivo. Downregulation of PAX6 by doxycycline depletion partially reversed the malignant phenotypes of HCC cells induced by PAX6. Moreover, we identified E-cadherin (CDH1) and thrombospondin-1 (THBS1) as targets of PAX6. Ultimately, we demonstrated that the knockdown of CDH1 and overexpression of THBS1 in PAX6-expressing HCC cells partly reversed the tumor-suppressive effect. PAX6 functions as a tumor suppressor partly through upregulation of CDH1 and downregulation of THBS1. Promoter hypermethylation-mediated suppression of PAX6 reduces the tumor suppressor function in the progression of liver cancer.

Yeh CH ，Chen RY ，Wu TH ，Chang SY ，Hsieh TY ，Shih YL ，Lin YW ... -  《-》

MicroRNA-34c-3p promotes cell proliferation and invasion in hepatocellular carcinoma by regulation of NCKAP1 expression.

Xiao CZ ，Wei W ，Guo ZX ，Zhang MY ，Zhang YF ，Wang JH ，Shi M ，Wang HY ，Guo RP ... -  《-》

Downregulation of discoidin domain receptor 2 decreases tumor growth of hepatocellular carcinoma.

Park JW ，Lee YS ，Kim JS ，Lee SK ，Kim BH ，Lee JA ，Lee NO ，Kim SH ，Hong EK ... -  《-》