Hepatitis B virus X protein mutants exhibit distinct biological activities in hepatoma Huh7 cells

NMI promotes hepatocellular carcinoma progression via BDKRB2 and MAPK/ERK pathway

Hepatocellular carcinoma (HCC) is one of the most prevalent and aggressive malignant tumors. The involvement of N-myc (and STAT) interactor (NMI) and its possible functional mechanisms in HCC progression still remain to be elucidated. In this study, we found that NMI was overexpressed in metastatic HCC cell lines compared with non-metastatic ones; and the expression levels of NMI in the HCC samples with metastasis were higher than that in the non-metastatic specimens. Furthermore, NMI depletion significantly decreased HCC cell proliferation and invasiveness in vitro, and also inhibited tumor growth and lung metastasis in vivo in nude mice models bearing human HCC. By contrast, NMI stable overexpression can enhance the malignant behaviors obviously. Moreover, we further verified that NMI promotes the expression of BDKRB2 and mediates the activation of MAPK/ERK signaling pathway according to the bidirectional perturbations of NMI expression in vivo or in vitro of HCC. Taken together, NMI is a pro-metastatic molecule and partially responsible for HCC tumor growth and motility. NMI could improve its downstream target BDKRB2 expression to induce ERK1/2 activation, and thereby further evoke malignant progression of HCC.

HBx triggers either cellular senescence or cell proliferation depending on cellular phenotype

Replicative senescence is a hallmark of chronic liver diseases including chronic hepatitis B virus (HBV) infection, whereas HBV-encoded oncoproteins HBx and preS2 have been found to overcome senescence. HBx possesses a C-terminal truncation mainly in hepatocellular carcinomas but also in noncancerous liver tissues. Here, by cell counting, BrdU incorporation, MTT proliferation assay, cell cycle analysis, SA-βgal staining and Western blotting in primary and malignant cells, we investigated the effect of HBx C-terminal mutants on cellular senescence. HBx C-terminal mutants were found to trigger cellular senescence in primary MRC5 cells, and malignant liver cells Huh7, and SK-Hep1. In contrast, these mutants promoted the proliferation of HepG2 malignant liver cells. The pro-senescent effect of HBx relied on an increased p16(INK4a) and p21(Waf1/Cip1) expression, and a decreased phosphorylation of Rb. Together, these results suggest that the two main variants of HBx present in HBV-infected liver possess opposite effects on cellular senescence that depend on the phenotype of infected cells.

A novel mutant 10Ala/Arg together with mutant 144Ser/Arg of hepatitis B virus X protein involved in hepatitis B virus-related hepatocarcinogenesis in HepG2 cell lines

Hepatitis B virus (HBV) infection-related hepatocellular carcinoma (HCC) represents a major health problem worldwide. HBV X (HBx) protein is the most common open reading frame that may undergo mutations, resulting in the development of HCC. This study aimed to determine specific HBx mutations that differentiate the central- and para-tumor tissues, and identify their association with HCC development. HBx gene from HCC tumor and para-tumor tissues of 47 HCC patients was amplified, sequenced and statistically analyzed. A novel combination of 2 mutations at residues 10 and 144 was identified which might play a significant role in HCC development. Expression vectors carrying HBx with the specific mutations were constructed and transfected into HepG2 and p53-null HepG2 cells. Compared to wild type (WT) and single mutation of HBx at residue 10 or 144, the 10/144 double mutations strongly up-regulated p21 expression and prolonged G1/S transition in WT- and p53-null HepG2 cells. Apoptosis was also inhibited by HBx harboring 10/44 double-mutation. Binding of 10/144 double-mutant HBx to p53 was lower than WT HBx. Conclusively, the 10/144 double mutation of HBx might play a crucial role in HCC formation.

Upregulation of PP2Ac predicts poor prognosis and contributes to aggressiveness in hepatocellular carcinoma

Protein phosphatase 2A (PP2A) is a heterotrimeric protein phosphatase consisting of a 36-kD catalytic C subunit (PP2Ac). This study aimed to explore the prognostic and biological significance of PP2Ac in human hepatocellular carcinoma (HCC). High PP2Ac expression was significantly (P < 0.01) associated with serum hepatitis B surface antigen positivity, serum hepatitis B e antigen positivity, liver cirrhosis, moderate to poor differentiation grade, advanced disease stage, intrahepatic metastasis, and early recurrence in HCC. Multivariate analysis revealed PP2Ac as an independent prognostic factor for overall survival. Enforced expression of hepatitis B virus X protein (HBx) and its carboxyl-terminal truncated isoform induced PP2Ac expression in HCC cells. Co-immunoprecipitation assay revealed a direct interaction between PP2Ac and HBx. Small interfering RNA-mediated knockdown of PP2Ac significantly inhibited in vitro cell proliferation, colony formation, migration, and invasion and reduced tumor growth in an xenograft mouse model. In contrast, overexpression of PP2Ac promoted HCC cell proliferation, colony formation, and tumorigenesis. Additionally, silencing of PP2Ac impaired the growth-promoting effects on HepG2 HCC cells elicited by overexpression of carboxyl-terminal truncated HBx. Gene expression profiling analysis showed that PP2Ac downregulation modulated the expression of numerous genes involved in cell cycle and apoptosis regulation. Collectively, PP2Ac upregulation has a poor prognostic impact on the overall survival of HCC patients and contributes to the aggressiveness of HCC. PP2Ac may represent a potential therapeutic target for HCC.

Molecular mechanism of hepatitis B virus X protein function in hepatocarcinogenesis

Many factors are considered to contribute to hepatitis B virus (HBV)-associated hepatocellular carcinoma (HCC), including products of HBV, HBV integration and mutation, and host susceptibility. HBV X protein (HBx) can interfere with several signaling pathways associated with cell proliferation and invasion, and HBx C-terminal truncation has been suggested to impact the development of HCC. This review focuses on the pathological functions of HBx in HBV-induced hepatocarcinogenesis. As a transactivator, HBx can affect regulatory non-coding RNAs (ncRNAs), including microRNAs and long ncRNAs. HBx is also involved in epigenetic modification and DNA repair. HBx interacts with various signal-transduction pathways, such as the p53, Wnt, and nuclear factor-κB pathways. We conclude that HBx hastens the development of hepatoma.

C-terminal-truncated hepatitis B virus X protein enhances the development of diethylnitrosamine-induced hepatocellular carcinogenesis

Hepatitis B virus X protein (HBx) is involved in the development of hepatocellular carcinoma (HCC). The HBx sequence is a preferential site of integration into the human genome, leading to the formation of C-terminal-truncated HBx proteins (Ct-HBx). We previously reported that Ct-HBx proteins were able to potentiate cell transformation in vitro. Our present goal was to compare the ability of Ct-HBx and full-length HBx (FL-HBx) proteins to develop or enhance HCC in transgenic mice. In the absence of treatment, neither Ct-HBx- nor FL-HBx-transgenic mice developed HCC. In young mice treated with diethylnitrosamine (DEN) at 8 months of age, a significantly higher incidence and number of liver lesions were observed in Ct-HBx mice than in FL-HBx and control mice. The earlier development of tumours in Ct-HBx-transgenic mice was associated with increased liver inflammation. At 10 months, macroscopic and microscopic analyses showed that, statistically, FL-HBx mice developed more liver lesions with a larger surface area than control mice. Furthermore, during DEN-induced initiation of HCC, Ct-HBx- and FL-HBx-transgenic mice showed higher expression of IL-6, TNF-α and IL-1β transcripts, activation of STAT3, ERK and JNK proteins and an increase in cell apoptosis. In conclusion, in DEN-treated transgenic mice, the expression of Ct-HBx protein causes a more rapid onset of HCC than does FL-HBx protein. HBV genome integration leading to the expression of a truncated form of HBx protein may therefore facilitate HCC development in chronically infected patients.

Deep sequencing of the hepatitis B virus in hepatocellular carcinoma patients reveals enriched integration events, structural alterations and sequence variations

Chronic hepatitis B virus (HBV) infection is epidemiologically associated with hepatocellular carcinoma (HCC), but its role in HCC remains poorly understood due to technological limitations. In this study, we systematically characterize HBV in HCC patients. HBV sequences were enriched from 48 HCC patients using an oligo-bead-based strategy, pooled together and sequenced using the FLX-Genome-Sequencer. In the tumors, preferential integration of HBV into promoters of genes (P < 0.001) and significant enrichment of integration into chromosome 10 (P < 0.01) were observed. Integration into chromosome 10 was significantly associated with poorly differentiated tumors (P < 0.05). Notably, in the tumors, recurrent integration into the promoter of the human telomerase reverse transcriptase (TERT) gene was found to correlate with increased TERT expression. The preferred region within the HBV genome involved in integration and viral structural alteration is at the 3'-end of hepatitis B virus X protein (HBx), where viral replication/transcription initiates. Upon integration, the 3'-end of the HBx is often deleted. HBx-human chimeric transcripts, the most common type of chimeric transcripts, can be expressed as chimeric proteins. Sequence variation resulting in non-conservative amino acid substitutions are commonly observed in HBV genome. This study highlights HBV as highly mutable in HCC patients with preferential regions within the host and virus genome for HBV integration/structural alterations.

Hepatitis C virus sensitizes host cells to TRAIL-induced apoptosis by up-regulating DR4 and DR5 via a MEK1-dependent pathway

Background

Hepatitis C virus (HCV) is the leading cause of liver fibrosis, cirrhosis and hepatocellular carcinoma. It is believed that continuous liver cell apoptosis contributes to HCV pathogenesis. Recent studies have shown that HCV infection can sensitize host cells to TNF-related apoptosis-inducing ligand (TRAIL) induced apoptosis, but the mechanism by which HCV regulates the TRAIL pathway remains unclear.

Methods and Results

Using a sub-genomic replicon and full length virus, JFH-1, we demonstrate that HCV can sensitize host cells to TRAIL-induced apoptosis by up-regulating two TRAIL receptors, death receptor 4 (DR4) and death receptor 5 (DR5). Furthermore, the HCV replicon enhanced transcription of DR5 via Sp1, and the HCV-mediated up-regulation of DR4 and DR5 required MEK1 activity. HCV infection also stimulated the activity of MEK1, and the inhibition of MEK1 activity or the knockdown of MEK1 increased the replication of HCV.

Conclusions

Our studies demonstrate that HCV replication sensitizes host cells to TRAIL-induced apoptosis by up-regulating DR4 and DR5 via a MEK1 dependent pathway. These findings may help to further understand the pathogenesis of HCV infection and provide a therapeutic target.

Analysis of hepatitis B virus X gene (HBx) mutants in tissues of patients suffered from hepatocellular carcinoma in China

Hepatitis B virus (HBV) X (HBx) gene multi-site mutations are a frequent event in the clinical hepatocellular carcinoma (HCC) tissues. It has been reported that the mutation of the HBx plays a crucial role in the development of HBV-related HCC. To identify the novel mutations of HBx in the HCC tissues, we examined and analyzed the sequences of HBx gene in 60 cases of HCC tumor tissues and paratumor tissues from China by polymerase chain reaction (PCR). The mutation patterns of HBx were analyzed by comparing the tumor tissues with non-tumor tissues. The data showed that 44 cases of tissues out of 60 patients were HBV-positive. Our results showed that the mutations at amino acid 30, 88, 144 from tumor samples and at amino acid 31, 43, 87, 94 from non-tumor samples were highly frequent events. Interestingly, we found that a novel type of HBx linked-mutations, such as at aa L30F/S144A, was 29.5% (13/44) positive in the tumor tissues. However, the role of HBx gene mutations at aa L30F/S144A relative to wild type HBx gene is unclear in hepatocarcinogenesis. The novel HBx linked-mutations may be significant in the development of HCC.

The X protein of hepatitis B virus inhibits apoptosis in hepatoma cells through enhancing the methionine adenosyltransferase 2A gene expression and reducing S-adenosylmethionine production

The X protein (HBx) of hepatitis B virus (HBV) is involved in the development of hepatocellular carcinoma (HCC), and methionine adenosyltransferase 2A (MAT2A) promotes the growth of liver cancer cells through altering S-adenosylmethionine homeostasis. Thus, we speculated that a link between HBx and MAT2A may contribute to HCC development. In this study, the effects of HBx on MAT2A expression and cell apoptosis were investigated, and the molecular mechanism by which HBx and MAT2A regulate tumorigenesis was evaluated. Results from immunohistochemistry analyses of 37 pairs of HBV-associated liver cancer tissues/corresponding peritumor tissues showed that HBx and MAT2A are highly expressed in most liver tumor tissues. Our in vitro results revealed that HBx activates MAT2A expression in a dose-dependent manner in hepatoma cells, and such regulation requires the cis-regulatory elements NF-κB and CREB on the MAT2A gene promoter. Electrophoretic mobility shift assay (EMSA) and chromatin immunoprecipitation (ChIP) further demonstrated that HBx facilitates the binding of NF-κB and CREB to MAT2A gene promoter. In addition, overexpression of HBx or MAT2A inhibits cell apoptosis, whereas knockdown of MAT2A expression stimulates apoptosis in hepatoma cells. Furthermore, we demonstrated that HBx reduces MAT1A expression and AdoMet production but enhances MAT2β expression. Thus, we proposed that HBx activates MAT2A expression through NF-κB and CREB signaling pathways to reduce AdoMet production, inhibit hepatoma cell apoptosis, and perhaps enhance HCC development. These findings should provide new insights into our understanding how the molecular mechanisms underline the effects of HBV infection on the production of MAT2A and the development of HCC.

Naturally occurring hepatitis B virus X deletions and insertions among Korean chronic patients

Deletions and insertions in the hepatitis B virus (HBV) X region have been associated with severe forms of liver disease, including hepatocellular carcinoma (HCC). However, the molecular epidemiologic features of this virus have been described rarely. Deletions and insertions in the X region were determined by direct sequencing in a Korean cohort of 267 patients with different clinical statuses. Deletions and insertions were observed in two sets of six patients each (2.2%, 6/267). The prevalence of deletions or insertions was significantly higher in patients with severe liver disease, HCC, or cirrhosis of the liver (7.2%, 10/132) compared to patients who were carriers or had chronic hepatitis (1.5%, 2/135) (P = 0.017). All deletions in six strains were concentrated at the C terminal end of HBx, encompassing the 113th to 154th codons. A total of four novel types of insertions (PKLL, GM, FFN, and tt) were observed in six patients. Of particular interest, all six strains with insertions were accompanied by double mutations in the basal core promoter (BCP). In conclusion, these results suggest that deletions or insertions in the X region may contribute to disease progression in Korean patients with genotype C infection.

A mutant of hepatitis B virus X protein (HBx Delta 127) enhances hepatoma cell migration via osteopontin involving 5-lipoxygenase

AIM

To explore a novel function of a mutant of the hepatitis B virus X protein (HBx Delta 127) in the promotion of hepatoma cell migration.

METHODS

The effect of HBx Delta 127 and wild type HBx on the migration ability of hepatoblastoma HepG2 cells were examined using wound healing assays in stable transfection systems. The full-length osteopontin(OPN) promoter sequence was cloned into the pGL3-Basic plasmid. The promoter activities of OPN in stably HBx Delta 127-transfected hepatoblastoma HepG2 (HepG2-X Delta 127) and hepatocellular carcinoma H7402 (H7402-X Delta 127) cells were determined using luciferase reporter gene assays. The mRNA expression levels of OPN were detected by RT-PCR. And the effect of MK886, a specific inhibitor of 5-lipoxygenase (5-LOX), on OPN promoter activity and mRNA expression in HepG2-X Delta 127 and H7402-X Delta 127 cells were examined using luciferase reporter gene assays and RT-PCR, respectively. Finally, the migration ability of HepG2-X Delta 127 was observed after treatment with siRNA targeting OPN mRNA and HBx mRNA using wound healing assays.

RESULTS

HepG2-X Delta 127 cells exhibited a greater capacity for wound repair compared to HepG2-X cells. The promoter activity and mRNA expression levels of OPN were also increased in HepG2-X Delta 127 and H7402-X Delta 127 cells. Moreover, MK886 abolished the HBx Delta 127-mediated upregulation of OPN. Wound healing assays demonstrated that the migration ability of HepG2-X Delta 127 cells can be suppressed by treatment with siRNA targeting OPN mRNA and siRNA targeting HBx mRNA.

CONCLUSION

HBx Delta 127 strongly promotes hepatoma cell migration via activation of OPN involving 5-LOX.

A mutant of hepatitis B virus X protein (HBxDelta127) promotes cell growth through a positive feedback loop involving 5-lipoxygenase and fatty acid synthase

Hepatocellular carcinoma (HCC) is one of the most common malignant tumors worldwide. Hepatitis B virus X protein (HBx) contributes to the development of HCC, whereas HBx with COOH-terminal deletion is a frequent event in the HCC tissues. Previously, we identified a natural mutant of HBx-truncated 27 amino acids at the COOH-terminal (termed HBxDelta127), which strongly enhanced cell growth. In the present study, we focused on investigating the mechanism. Accordingly, fatty acid synthase (FAS) plays a crucial role in cancer cell survival and proliferation; thus, we examined the signaling pathways involving FAS. Our data showed that HBxDelta127 strongly increased the transcriptional activities of FAS in human hepatoma HepG2 and H7402 cells. Moreover, we found that 5-lipoxygenase (5-LOX) was responsible for the up-regulation of FAS by using MK886 (an inhibitor of 5-LOX) and 5-LOX small interfering RNA. We observed that HBxDelta127 could upregulate 5-LOX through phosphorylated extracellular signal-regulated protein kinases 1/2 and thus resulted in the increase of released leukotriene B4 (LTB4, a metabolite of 5-LOX) by ELISA. The additional LTB4 could upregulate the expression of FAS in the cells as well. Interestingly, we found that FAS was able to upregulate the expression of 5-LOX in a feedback manner by using cerulenin (an inhibitor of FAS). Collectively, HBxDelta127 promotes cell growth through a positive feedback loop involving 5-LOX and FAS, in which released LTB4 is involved in the up-regulation of FAS. Thus, our finding provides a new insight into the mechanism involving the promotion of cell growth mediated by HBxDelta127.

A mutant of HBx (HBxDelta127) promotes hepatoma cell growth via sterol regulatory element binding protein 1c involving 5-lipoxygenase

AIM

Previously, we identified a natural mutant of hepatitis B virus X gene (HBx) with a deletion from 382 to 401 base pairs (termed HBxDelta127), which could potently enhance growth of hepatoma cells. In this study, we further investigated the mechanism of increased hepatoma cell growth that was mediated by HBxDelta127.

METHODS

We examined the effect of HBxDelta127 on the transcription factor sterol regulatory element-binding protein 1c (SREBP-1c) and fatty acid synthase (FAS) in a model of HepG2-XDelta127 (or H7402-XDelta127) cells, which was stably transfected with HBxDelta127 gene in a human hepatoma HepG2 (or H7402) cell line.

RESULTS

Relative to wild type HBx, HBxDelta127 was able to potently activate SREBP-1c at the levels of promoter activity, mRNA and protein by a luciferase reporter gene assay, RT-PCR and Western blot analysis. Then, using the treatment with MK886, a specific 5-lipoxygenases (5-LOX) inhibitor, (or 5-LOX siRNA) we identified that 5-LOX was responsible for the upregulation of SREBP-1c by luciferase reporter gene assay, RT-PCR and Western blot analysis. Because FAS was a target gene of SREBP-1c, we further showed that HBxDelta127 was able to strongly activate the promoter activity of FAS and upregulated the mRNA expression level of FAS as well, by luciferase reporter gene assay and RT-PCR. In function, flow cytometry analysis revealed that FAS contributed to the growth of hepatoma cells that was mediated by HBxDelta127, using cerulenin (a FAS inhibitor).

CONCLUSION

HBxDelta127 promotes hepatoma cell growth through activating SREBP-1c involving 5-LOX.