Apoptosis and its pathway in X gene-transfected HepG2 cells

LncRNA H19/microRNA-675/PPARα axis regulates liver cell injury and energy metabolism remodelling induced by hepatitis B X protein via Akt/mTOR signalling

Emerging evidence indicates that the lncRNAs/microRNA/mRNA axis plays important roles in a variety of diseases. This study was aimed to investigate the potential roles and underlying molecular mechanisms of lncRNA H19 and H19-derived miR-675 in regulating hepatitis B virus (HBV)-associated liver injury. mRNA and miR-675 levels were determined by quantitative real-time PCR (qRT-PCR), protein levels were determined by western blot, cell viability was measured by the MTT assay, cell apoptosis was measured by flow cytometry, inflammatory cytokine production was determined by ELISA, oxidative stress and energy metabolism were assessed by commercial kits, and the target relationship between PPARα and miR-675 was confirmed by the dual-luciferase reporter assay. The results showed that the expression of lncRNA H19 and miR-675 was up-regulated in patients with chronic hepatitis B (n = 20). Inhibition of lncRNA H19 or miR-675 in L02 cells increased cell viability, suppressed hepatitis B X protein (HBx)-induced cell apoptosis, inflammatory cytokine production, and oxidative stress, and remodelled energy metabolism. Furthermore, PPARα was found to be a target gene of miR-675. The expression of PPARα was down-regulated in patients with chronic hepatitis B, and there was a negative correlation between the expression of lncRNA H19 and PPARα, or between miR-675 and PPARα. Moreover, by knocking down the expression of PPARα, the actions (apoptosis, inflammatory factors, oxidative stress, and energy metabolism) of lncRNA H19 or miR-675 inhibition in HBx-induced L02 cells were at least partially reversed. In addition, HBx-induced elevated levels of p-Akt^Ser473, p-Akt^Thr308 and p-mTOR^Ser2448 were down-regulated by lncRNA H19 or miR-675 inhibition. Furthermore, PPARα knockdown partly reversed the down-regulated effects of H19 or miR-675 inhibition. Taken together, these data indicate that the lncRNA H19/miR-675/PPARα axis regulates liver cell injury and energy metabolism remodelling induced by HBx, which may be related to the modulation of Akt/mTOR signalling.

X protein variants of the autochthonous Latin American hepatitis B virus F genotype promotes human hepatocyte death by the induction of apoptosis and autophagy

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The impact of BCP mutations on HBV-X biologic activity was analyzed.

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Genotype F wild type and mutant HBV-X induce apoptosis of human hepatocytes.

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HBV-X variants modulate the expression of Bcl-2 family proteins.

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Subgenotypes F1b and F4 HBV-X and variants induce autophagy of human hepatocytes.

The hepatitis B virus X protein (HBV-X) is a multifunctional regulatory protein associated with the pathogenesis of liver disease in chronic HBV infection. Basal core promoter mutations (BCP), associated with the clinical course of chronic HBV infection, affect HBV-X at 130–131 positions. The role of these mutations on HBV-X biological activity remains largely unknown. The aim of this study was to analyze the impact of the presence of different amino acids at 130–131 positions of HBV-X on the biological activity of the protein. Transient expression of wild type and mutant F1b and F4 HBV-X increased cell mortality by the induction of apoptosis in human hepatoma cells. The wild type and mutant HBV-X differentially modulate the expression of pro-apoptotic (Bax) and anti-apoptotic (Bcl-2 and Bcl-X) regulatory proteins of the Bcl-2 family. Furthermore, the expression of HBV-X variants of both subgenotypes induced autophagy of human tumoral hepatocytes. In conclusion, HBV-X variants of the Latin American HBV F genotype promotes human hepatocytes death by the induction of apoptosis and autophagy. The results of this work describe some of the molecular mechanisms by which HBV-X variants contribute to the pathogenesis of liver diseases in the infected liver and help to the biological characterization of genotype F, responsible of the majority of HBV infections in Argentina.

Chronic viral hepatitis and its association with liver cancer

Chronic infection with hepatitis viruses represents the major causative factor for end-stage liver diseases, including liver cirrhosis and primary liver cancer (hepatocellular carcinoma, HCC). In this review, we highlight the current understanding of the molecular mechanisms that drive the hepatocarcinogenesis associated with chronic hepatitis virus infections. While chronic inflammation (associated with a persistent, but impaired anti-viral immune response) plays a major role in HCC initiation and progression, hepatitis viruses can also directly drive liver cancer. The mechanisms by which hepatitis viruses induce HCC include: hepatitis B virus DNA integration into the host cell genome; metabolic reprogramming by virus infection; induction of the cellular stress response pathway by viral gene products; and interference with tumour suppressors. Finally, we summarise the limitations of hepatitis virus-associated HCC model systems and the development of new techniques to circumvent these shortcomings.

Inhibition of apoptosis by oncogenic hepatitis B virus X protein: Implications for the treatment of hepatocellular carcinoma

Hepatitis B virus X protein (HBx) plays an important role in the development of hepatocellular carcinoma (HCC). In addition, hepatoma upregulated protein (HURP) is a cellular oncogene that is upregulated in a majority of HCC cases. We highlight here recent findings demonstrating a link between HBx, HURP and anti-apoptosis effects observed in cisplatin-treated HCC cells. We observed that Hep3B cells overexpressing HBx display increased HURP mRNA and protein levels, and show resistance to cisplatin-induced apoptosis. Knockdown of HURP in HBx-expressing cells reverses this effect, and sensitizes cells to cisplatin. The anti-apoptotic effect of HBx requires activation of the p38/MAPK pathway as well as expression of SATB1, survivin and HURP. Furthermore, silencing of HURP using short-hairpin RNA promotes accumulation of p53 and reduces cell proliferation in SK-Hep-1 cells (p53^+/–), whereas these effects are not observed in p53-mutant Mahlavu cells. Similarly, HURP silencing does not affect the proliferation of H1299 lung carcinoma cells or Hep3B HCC cells which lack p53. Silencing of HURP sensitizes SK-Hep-1 cells to cisplatin. While HURP overexpression promotes p53 ubiquitination and degradation by the proteasome, HURP silencing reverses these effects. Inoculation of SK-Hep-1 cancer cells in which HURP has been silenced produces smaller tumors than control in nude mice. Besides, gankyrin, a positive regulator of the E3 ubiquitin ligase MDM2, is upregulated following HURP expression, and silencing of gankyrin reduces HURP-mediated downregulation of p53. In addition, we observed a positive correlation between HURP and gankyrin protein levels in HCC patients (r² = 0.778; n = 9). These findings suggest a role for the viral protein HBx and the host protein HURP in preventing p53-mediated apoptosis during cancer progression and establishment of chemoresistance.

Conceptual models for the initiation of hepatitis B virus-associated hepatocellular carcinoma

Although chronic hepatitis B virus (HBV) infection is a known risk factor for the development of hepatocellular carcinoma (HCC), the steps involved in the progression from normal liver to HCC are poorly understood. In this review, we apply five conceptual models, previously proposed by Vineis et al. to explain carcinogenesis in general, to explore the possible steps involved in the initiation and evolution of HBV-associated HCC. Available data suggest that the most suitable and inclusive model is based on evolution of hepatocyte subpopulations. In this evolutionary model, HCC-associated changes are driven by selection and subsequent clonal expansion of phenotypically altered hepatocyte subpopulations in the microenvironment of the HBV-infected liver. This model can incorporate the wide range of mechanisms proposed to play a role in the initiation of HCC including oncogenic HBV proteins, integration of HBV DNA and chronic inflammation of the liver. The model may assist in the early prevention, detection and treatment of HCC and may guide future studies of the initiation of HBV-associated HCC.

Effect of Hepatitis B Virus X Gene on the Expression Level of p53 Gene using Hep G2 Cell Line

BACKGROUND

The HBV-X (HBX) protein is believed to contribute to the development of HCC. However, the molecular mechanisms involved in HBX- mediated hepatocarcinogenesis remain obscure. In this study, the effect of hepatitis B virus X gene and its protein product HBxAg on expression of p53 gene in Hep G2 cell line was investigated.

METHODS

Viral DNA extracted from HBV-positive serum and HBX gene region was amplified using polymerase chain reaction (PCR). Then, PCR product was cloned into the pcDNA3 vector. After confirmation of cloning, the recombinant plasmid pcDNA3-X was transfected into HepG2 cell line using lipid-mediated DNA-transfection procedure. SDS-PAGE and western blotting methods were used to identify expression of HBX protein. Relative quantification was used to analyze the p53gene expression using the 2-(ΔΔ Ct) method.

RESULTS

Recombinant plasmid pcDNA3-HBX was confirmed by restriction endonucleases digestion and colony-PCR. The results of SDS-PAGE and western blot assays showed that HBX gene could be expressed in Hep G2 cell line. There was no significant difference between the expression levels of p53 compared with GAPDH gene as housekeeping gene (p < 0.05).

CONCLUSION

There was no significant difference in the protein levels between the transfected cells with X gene containing HBX130 and HBX131 double mu-tations and p53 gene. It is necessary to do more studies on Hepatitis B virus to understand the role of HBX on the development of liver cancer and its function on p53 tumor suppressor protein.

HBx activates FasL and mediates HepG2 cell apoptosis through MLK3-MKK7-JNKs signal module

AIM

To investigate the possible mechanism by which hepatitis B virus X protein (HBx) mediates apoptosis of HepG2 cells.

METHODS

HBx expression vector pcDNA3.1-X was transfected into HepG2 cells to establish an HBx high-expression cellular model as pcDNA3.1-X transfected group. The pcDNA3.1-X and pSilencer3.1-shHBX (HBx antagonist) were cotransfected into HepG2 cells to establish an HBx low-expression model as RNAi group. Untransfected HepG2 cells and HepG2 cells transfected with negative control plasmid were used as controls. Apoptosis rate, the expression of Fas/FasL signaling pathway-related proteins and the phosphorylation levels of MLK3, MKK7 and JNKs, which are upstream molecules of death receptor pathways and belong to the family of mitogen-activated protein kinases (MAPKs), were measured in each group.

RESULTS

Compared with HepG2 cell group and RNAi group, apoptosis rate, the expression of Fas and FasL proteins, and the activation of MLK3, MKK7 and JNKs were increased in the pcDNA3.1-X transfected group. The activation of JNKs and expression of FasL protein were inhibited in the pcDNA3.1-X transfected group when treated with a known JNK inhibitor, SP600125. When authors treated pcDNA3.1-X transfected group with K252a, a known MLK3 inhibitor, the activation of MLK3, MKK7 and JNKs as well as expression of FasL protein was inhibited. Furthermore, cell apoptosis rate was also significantly declined in the presence of K252a in the pcDNA3.1-X transfected group.

CONCLUSION

HBx can induce HepG2 cell apoptosis via a novel active MLK3-MKK7-JNKs signaling module to upregulate FasL protein expression.

Effect of antiviral therapy on the immunohistochemical expression of bcl-xL and bax protein in patients with HBeAg-negative chronic hepatitis B

The effect of antiviral treatment on apoptosis in chronic hepatitis B (CHB) has not been clarified. We evaluated the hepatic immunohistochemical expression of the pro-apoptotic bax and the antiapoptotic bcl-xL protein in HBeAg-negative CHB patients before and after treatment. In our study we included 72 paired biopsies from 36 HBeAg-negative CHB patients: 29 treated (interferon-alfa: 17, adefovir: 12) and 7 untreated. Changes in expression of apoptotic proteins (D-bax, D-bcl-xL), necroinflammation and fibrosis (D-grade/D-stage) (Ishak classification) were evaluated. We found that Bax-positive compared to bax-negative biopsies had worse necroinflammation (8.2 vs. 6.7, P = 0.05) and fibrosis score (3.9 vs. 3, P = 0.036). bcl-xL-positive compared to bcl-xL-negative biopsies had lower intralobular inflammation (1.6 vs. 2.2, P = 0.03). Decreased compared to stable/increased D-bax was associated with greater improvement in necroinflammation only in treated patients (D-grade: -4.6 vs. -1.6, P = 0.05) and greater fibrosis improvement in interferon treated patients (D-stage: -0.4 vs. 0.55, P = 0.05). Increased compared to stable/decreased total apoptotic trend [D-apoptosis: (D-bax)-(D-bcl-xL)], was associated with worsening fibrosis, particularly in adefovir treated patients (D-stage: 2.3 vs. 0, P = 0.004). In the 11 patients without significant changes from 1st to 2nd biopsy, increased apoptosis was more frequent in treated than untreated cases (P = 0.046). In multivariate analysis, bax change was independently associated with change of grade (P = 0.038) and antiviral therapy (P = 0.015). In conclusions, in HBeAg-negative CHB, histological improvement after treatment is associated with decreased hepatocyte apoptosis. In patients without substantial histological changes, treatment seems to increase the apoptosis of hepatocytes, thus having a possible protective effect on hepatocarcinogenesis.

Hepatitis B virus X protein prevents apoptosis of hepatocellular carcinoma cells by upregulating SATB1 and HURP expression

Protein X from hepatitis B virus (HBV) appears to play a critical role in the development of hepatocellular carcinoma (HCC). The hepatoma upregulated protein (HURP) is also upregulated in a majority of HCC cases, therefore suggesting that HURP represents an oncogene. In this study, we describe a link between the viral protein HBx, HURP, and the establishment of cisplatin chemoresistance in HCC cells. Hep3B cells which express HBx displayed increased levels of HURP mRNA and protein, and showed resistance to cisplatin-induced apoptosis. Knockdown of HURP in HBx-expressing cells reversed this effect and sensitized Hep3B cells to cisplatin. Interestingly, SATB1, a global gene regulator which is often overexpressed in malignant breast cancer, was also induced following expression of HBx. The anti-apoptotic effect of HBx was shown to require activation of the p38/MAPK pathway in Hep3B cells. In addition, the expression of survivin, an anti-apoptotic protein, was also upregulated by HBx in an HURP-dependent manner. Taken together, these results indicate that HBx activates the expression of HURP via the p38/MAPK pathway and the SATB1 protein, culminating with the accumulation of the anti-apoptotic protein survivin. Our findings illustrate the role of the viral protein HBx in preventing apoptosis during cancer progression and establishment of chemoresistance.

Progressive changes in hepatoma cells stably transfected with hepatitis B virus X gene

OBJECTIVE

The aim of this study is to investigate the molecular mechanism of hepatocellular carcinoma (HCC) development induced by hepatitis B virus X protein (HBx).

METHODS

We previously established a H7402-X cell line that constitutively expresses HBx protein. In the present study, H7402-X gene expression profiles and proteins were examined using cDNA microarrays and Western blot analysis. Apoptosis was induced by adriamycin in H7402-X cells. The transcriptional activities of NF-kappaB and AP-1 were examined using a luciferase reporter gene.

RESULTS

The DNA expression profiles identified candidate genes showing aberrant expression in cells overexpressing HBx. Western blot analysis showed that cyclin D, cyclin E, survivin, Bcl-2, and PCNA were up-regulated, whereas p27 was down-regulated in H7402-X cells. Treatment with RNAi targeting HBx mRNA led to the down-regulation of these genes. H7402-X cells were resistant to adriamycin-induced apoptosis. Luciferase reporter gene analysis revealed that HBx induces the transcriptional activities of NF-kappaB and AP-1.

CONCLUSION

Our data provide additional insight into cellular targets of HBx, which allows a better understanding of HBx function and the progressive changes during HBx-mediated hepatocarcinogenesis.

Hepatitis B virus sensitizes hepatocytes to TRAIL-induced apoptosis through Bax

Hepatitis B virus (HBV) infection afflicts >300 million people worldwide and is a leading cause of hepatocyte death, cirrhosis, and hepatocellular carcinoma. While the morphological characteristics of dying hepatocytes are well documented, the molecular mechanisms leading to the death of hepatocytes during HBV infection are not well understood. TRAIL, the TNF-related apoptosis-inducing ligand, has recently been implicated in the death of hepatocytes under certain inflammatory but not normal conditions. To determine the potential roles of TRAIL in HBV-induced hepatitis, we examined the effects of HBV and its X protein (HBx) on TRAIL-induced hepatocyte apoptosis both in vivo and in vitro. We found that hepatitis and hepatic cell death in HBV transgenic mice were significantly inhibited by a soluble TRAIL receptor that blocks TRAIL function. We also found that HBV or HBx transfection of a hepatoma cell line significantly increased its sensitivity to TRAIL-induced apoptosis. The increase in TRAIL sensitivity were associated with a dramatic up-regulation of Bax protein expression. Knocking down Bax expression using Bax-specific small interference RNA blocked HBV-induced hepatitis and hepatocyte apoptosis. The degradation of caspases 3 and 9, but not that of Bid or caspase-8, was preferentially affected by Bax knockdown. These results establish that HBV sensitizes hepatocytes to TRAIL-induced apoptosis through Bax and that Bax-specific small interference RNA can be used to inhibit HBV-induced hepatic cell death.

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Human hepatitis B virus X protein induces apoptosis in HepG2 cells: Role of BH3 domain

The smallest protein of hepatitis B virus, HBX, has been implicated in the development of liver diseases by interfering with normal cellular processes. Its role in cell proliferation has been unclear as both pro-apoptotic and anti-apoptotic activities have been reported. We showed molecular evidence that HBX induced apoptosis in HepG2 cells. A Bcl-2 Homology Domain 3 was identified in HBX, which interacted with anti-apoptotic but not pro-apoptotic members of the Bcl-2 family of proteins. HBX induced apoptosis when transfected into HepG2 cells, as demonstrated by both flow cytometry and caspase-3 activity. However, HBX protein may not be stable in apoptotic cells triggered by its own expression as only its mRNA or the fusion protein with the glutathione-S-transferase was detected in transfected cells. Our results suggested that HBX behaved as a pro-apoptotic protein and was able to induce apoptosis.