HBx-expressing Cells Research Articles

Hepatitis B Virus X Protein Contributes to Hepatocellular Carcinoma via Upregulation of KIAA1429 Methyltransferase and mRNA m6A Hypermethylation of HSPG2/Perlecan.

Chronic hepatitis B virus (HBV) remains to be the most common risk factor of hepatocellular carcinoma (HCC). While previous work has primarily focussed on understanding the direct and indirect mechanisms of Hepatitis B virus X protein (HBx)-mediated hepatocarcinogenesis, from genetic and epigenetic perspectives, its influence on RNA modification mediated onset of liver malignancies is less well understood. This study explored the role of HBV-encoded HBx in altering the m6A methylome profile and its implications on the pathogenesis of HCC. We established HBx-expressing stable HCC cell lines, Huh7-HBx and HepG2-HBx, and explored the transcriptomic and epitranscriptomic profiles by RNA-seq and MeRIP-seq, respectively. Preliminary results suggest that HBx promotes liver cell proliferation, migration, survival and overall m6A methylation in HCC cells and is involved in modulating the extracellular matrix. We show that HBx mediates liver cell transformation by upregulating KIAA1429 methyltransferase. HBx also drives the expression and hypermethylation of the extracellular matrix protein HSPG2/Perlecan and promotes tumourigenesis. Furthermore, we observed a potential interaction between KIAA1429 and HSPG2 in HCC liver cancer cells and demands further investigation.

HBx induced upregulation of FATP2 promotes the development of hepatic lipid accumulation

The hepatitis B Virus X (HBx) protein plays a crucial role in the HBV-induced hepatic steatosis. Fatty acid transport protein 2 (FATP2) is a key protein that is involved in hepatic lipogenesis, and it was found to be highly expressed in various metabolic diseases. However, Whether FATP2 is a key factor in the pathogenesis of HBx-induced hepatic steatosis remains unclear. In this study, we found that FATP2 was up-regulated by HBx in vitro and in vivo and participated in HBx-induced hepatic lipid accumulation. Treatment of HBx-expressing cell lines and mice with FATP2 inhibitor (FATP2i) lipofermata ameliorated HBx-induced lipid accumulation and reduced oxidative stress and inflammation caused by lipid accumulation. Moreover, the liver injury of mouse was restored after FATP2i treatment. In summary, our results reveal that FATP2 is a key driver factor for HBx-induced hepatic lipid accumulation, and inhibition of FATP2 can ameliorates lipid accumulation caused by HBx. This study provides new insights into the mechanism of HBV-induced hepatic steatosis.

Hepatitis B virus X protein promotes MAN1B1 expression by enhancing stability of GRP78 via TRIM25 to facilitate hepatocarcinogenesis.

GRP78 has been implicated in hepatocarcinogenesis. However, the clinical relevance, biological functions and related regulatory mechanisms of GRP78 in hepatitis B virus (HBV)-associated hepatoma carcinoma (HCC) remain elusive. The association between GRP78 expression and HBV-related HCC was investigated. The effects of HBV X protein (HBX) on GRP78 and MAN1B1 expression, biological functions of GRP78 and MAN1B1 in HBX-mediated HCC cells and mechanisms related to TRIM25 on GRP78 upregulation to induce MAN1B1 expression in HBX-related HCC cells were examined. GRP78 expression was correlated with poor prognosis in HBV-positive HCC. HBX increased MAN1B1 protein expression depending on GRP78, and HBX enhanced the levels of MAN1B1 to promote proliferation, migration and PI3-K/mTOR signalling pathway activation in HCC cells. GRP78 activates Smad4 via its interaction with Smad4 to increase MAN1B1 expression in HBX-expressing HCC cells. TRIM25 enhanced the stability of GRP78 by inhibiting its ubiquitination. HBX binds to GRP78 and TRIM25 and accelerates their interaction of GRP78 and TRIM25, leading to an increase in GRP78 expression. HBX enhances the stability of GRP78 through TRIM25 to increase the expression of MAN1B1 to facilitate tumorigenesis, and we provide new insights into the molecular mechanisms underlying HBV-induced malignancy.

Identification of Estradiol Benzoate as an Inhibitor of HBx Using Inducible Stably Transfected HepG2 Cells Expressing HiBiT Tagged HBx.

HBx plays a significant role in the cccDNA epigenetic modification regulating the hepatitis B virus (HBV) life cycle and in hepatocyte proliferation and carcinogenesis. By using the sleeping-beauty transposon system, we constructed a tetracycline-induced HBx-expressing stable cell line, SBHX21. HBx with a HiBiT tag can be quickly detected utilizing a NanoLuc-based HiBiT detection system. By screening a drug library using SBHX21 cells, we identified estradiol benzoate as a novel anti-HBx agent. Estradiol benzoate also markedly reduced the production of HBeAg, HBsAg, HBV pgRNA, and HBV DNA in a dose-dependent manner, suggesting that estradiol benzoate could be an anti-HBV agent. Docking model results revealed that estradiol benzoate binds to HBx at TRP87 and TRP107. Collectively, our results suggest that estradiol benzoate inhibits the HBx protein and HBV transcription and replication, which may serve as a novel anti-HBV molecular compound for investigating new treatment strategies for HBV infection.

Intracellular antibody targeting HBx suppresses invasion and metastasis in hepatitis B virus-related hepatocarcinogenesis via protein phosphatase 2A-B56γ-mediated dephosphorylation of protein kinase B.

Hepatitis B virus X (HBx) is closely associated with HBV-related hepatocarcinogenesis via the inactivation of tumour suppressors. Protein phosphatase 2A (PP2A) regulatory subunit B56 gamma (B56γ), as a tumour suppressor, plays a critical role in regulating cellular phosphorylation signals via dephosphorylation of signalling proteins. However, the underlying mechanism that B56γ involved in regulating HBx-associated hepatocarcinogenesis phenotypes and mediating anti-HBx antibody-mediated tumour suppression remains unknown. We used bioinformatics analysis, paired HCC patient specimens, HBx transgenic (HBx-Tg) mice, xenograft nude mice, HBV stable replication in the HepG2.2.15 cells, and anti-HBx antibody intervention to systematically evaluate the biological function of protein kinase B (AKT) dephosphorylation through B56γ in HBx-associated hepatocarcinogenesis. Bioinformatics analysis revealed that AKT, matrix metalloproteinase 2 (MMP2), and MMP9 were markedly upregulated, while cell migration and viral carcinogenesis pathways were activated in HBV-infected liver tissues and HBV-associated HCC tissues. Our results demonstrated that HBx-expression promotes AKT phosphorylation (p-AKTThr308/Ser473 ), mediating the migration and invasion phenotypes in vivo and in vitro. Importantly, in clinical samples, HBx and B56γ were downregulated in HBV-associated HCC tumour tissues compared with peritumor tissues. Moreover, intervention with site-directed mutagenesis (AKTT308A , AKTS473A ) of p-AKTThr308/Ser473 mimics dephosphorylation, genetics-based B56γ overexpression, and intracellular anti-HBx antibody inhibited cell growth, migration, and invasion in HBx-expressing HCC cells. Our results demonstrated that B56γ inhibited HBV/HBx-dependent hepatocarcinogenesis by regulating the dephosphorylation of p-AKTThr308/Ser473 in HCC cells. The intracellular anti-HBx antibody and the activator of B56γ may provide a multipattern chemopreventive strategy against HBV-related HCC.

Hepatitis B virus X protein promotes hepatocarcinogenesis via the activation of HMGA2/STC2 signaling to counteract oxidative stress-induced cell death

Chronic hepatitis B virus (HBV) infection can cause oxidative stress and induce cell death. The mechanisms by which cells overcome oxidative stress to survive remain largely unknown. Here, we used human sera, liver tissues and cell lines to study how HBV modulates cellular pathways to counteract oxidative stress-induced cell death. We found high-mobility group AT-hook 2 (HMGA2), an architectural transcription factor is upregulated in hepatocellular carcinoma (HCC) tissues and cell lines. Elevated serum HMGA2 is significantly associated with viral load in HBV carriers, and HBV-related HCC. We showed that HBV X protein (HBx) encoded by HBV-induced cell growth via HMGA2 activation. The growth-promoting effect is abolished when HMGA2 is suppressed. Ectopic HBx expression induced DNA damage and oxidative stress. HMGA2 silencing reduced oxidative stress in HBx-expressing cells. Cytoprotective stanniocalcin 2 (STC2) protein is a downstream target of HMGA2. Consistent with the findings in HMGA2, STC2 mRNA and protein expression are upregulated in HCC tissues. Elevated serum STC2 is also associated with viral load in HBV carriers, and HCC. STC2 is transcriptionally upregulated by HBx and HMGA2 to elicit cytoprotection against apoptosis. STC2 knockdown disrupted Bax/Bcl-2 balance that increased cytochrome c release, caspase 3/7 activity and apoptosis, and thus abolished the growth-promoting effect of HMGA2. Clinical relevance of HBx/HMGA2/STC2 signaling is evidenced by the significant correlation of serum HMGA2/STC2 in active HBV infection and HCC. These findings reveal a novel HBx regulatory HMGA2/STC2 pathway in counteracting reactive oxygen species-induced cell death. HMGA2 and STC2 may be therapeutic targets for prevention of hepatocarcinogenesis in chronic HBV infection.

Hepatitis B virus-associated hepatocellular carcinoma with Smc5/6 complex deficiency is susceptible to PARP inhibitors

DNA repair processes represent attractive synthetic lethal targets because many cancers exhibit impaired DNA repair pathways, which leads to dependence on specific repair proteins. The finding that poly (ADP-ribose) polymerase (PARP)-1 inhibitors are highly effective against cancers with deficient homologous recombination highlights the potential of this approach. In hepatitis B viral (HBV) infection, degradation of the structural maintenance of the chromosome 5/6 (Smc5/6) complex, which plays a key role in repairing double-stranded DNA breaks by homologous recombination, is induced by HBV regulatory protein X (HBx). Here, we hypothesized that a deficiency in the Smc5/6 complex in HBV-associated hepatocellular carcinoma (HCC) increases susceptibility to PARP inhibitors via a deficiency in homologous recombination. We confirmed impaired double-stranded DNA break repair in HBx-expressing HCC cells using a sensitive reporter to monitor homologous recombination. Treatment with a PARP inhibitor was significantly more effective against HBx-expressing HCC cells, and overexpression of Smc5/6 prevented these effects. Overall, our results suggest that homologous recombination deficiency in HBV-associated HCC leads to increased susceptibility to PARP inhibitors.

Long noncoding RNA RP11-241J12.3 targeting pyruvate carboxylase promotes hepatocellular carcinoma aggressiveness by disrupting pyruvate metabolism and the DNA mismatch repair system

Accumulating evidence indicates that hepatitis B virus X protein (HBx) plays a key role in HBV-related hepatocellular carcinoma (HCC) aggressiveness; however, the underlying mechanisms are not entirely clear. Long non-coding RNAs (lncRNAs), which participate in the regulation of diverse biological processes, may be critical for the function of HBx. Our research indicated that HBx induced changes in the expression of numerous lncRNAs and implicated the novel lncRNA RP11-241J12.3 in HBx-mediated HCC aggressiveness. Although RP11-241J12.3 expression was downregulated in transient HBx-expressing HCC cells (similar to the early stage of HBV infection), its oncogenic properties remained. The results showed that RP11-241J12.3 not only accelerated DNA synthesis and upregulated the expression of pyruvate carboxylase (PC) and MSH3, which is a key protein in pyruvate metabolism and DNA mismatch repair (MMR), but also promoted tumor growth in vitro and in vivo, thus promoting HCC aggressiveness. More importantly, we revealed that RP11-241J12.3 may interact with PC and identified its location in the cytoplasm close to the nucleus using fluorescence in situ hybridization (FISH). We also observed RP11-241J12.3 expression was upregulated in HCC tissues compared with the paracarcinomatous tissues. Furthermore, RP11-241J12.3 expression levels showed a close relationship with clinical stage and tumor size and that low RP11-241J12.3 expression was significantly correlated with longer HCC patient survival. These results further our understanding of the lncRNAs regulated by HBx in HCC, and provide evidence that dysregulation of RP11-241J12.3 contributes to HCC aggressiveness.

HBx-induced degradation of Smc5/6 complex impairs homologous recombination-mediated repair of damaged DNA

HBV causes hepatocellular carcinoma (HCC). While it was recently shown that the ability of HBV X protein (HBx) to impair the Smc5/6 (structural maintenance of chromosome 5/6) complex is important for viral transcription, HBx is also a potent driver of HCC. However, the mechanism by which HBx expression induces hepatocarcinogenesis is unclear. Degradation of the Smc5/6 complex and accumulation of DNA damage were observed in both invivo and invitro HBV infection models. Rescue experiments were performed using nitazoxanide (NTZ), which inhibits degradation of the Smc5/6 complex by HBx. HBx-triggered degradation of the Smc5/6 complex causes impaired homologous recombination (HR) repair of DNA double-strand breaks (DSBs), leading to cellular transformation. We found that DNA damage accumulated in the liver tissue of HBV-infected humanized chimeric mice, HBx-transgenic mice, and human tissues. HBx suppressed the HR repair of DSBs, including that induced by the CRISPR-Cas9 system, in an Smc5/6-dependent manner, which was rescued by restoring the Smc5/6 complex. NTZ restored HR repair in, and colony formation by, HBx-expressing cells. Degradation of the Smc5/6 complex by HBx increases viral transcription and promotes cellular transformation by impairing HR repair of DSBs. The hepatitis B virus expresses a regulatory protein called HBV X protein (or HBx). This protein degrades the Smc5/6 complex in human hepatocytes, which is essential for viral replication. We found that this process also plays a key role in the accumulation of DNA damage, which contributes to HBx-mediated tumorigenesis.

Hepatitis B virus X Protein Promotes Liver Cancer Progression through Autophagy Induction in Response to TLR4 Stimulation.

Hepatitis B virus X (HBx) protein has been reported as a key protein regulating the pathogenesis of HBV-induced hepatocellular carcinoma (HCC). Recent evidence has shown that HBx is implicated in the activation of autophagy in hepatic cells. Nevertheless, the precise molecular and cellular mechanism by which HBx induces autophagy is still controversial. Herein, we investigated the molecular and cellular mechanism by which HBx is involved in the TRAF6-BECN1-Bcl-2 signaling for the regulation of autophagy in response to TLR4 stimulation, therefore influencing the HCC progression. HBx interacts with BECN1 (Beclin 1) and inhibits the association of the BECN1-Bcl-2 complex, which is known to prevent the assembly of the pre-autophagosomal structure. Furthermore, HBx enhances the interaction between VPS34 and TRAF6-BECN1 complex, increases the ubiquitination of BECN1, and subsequently enhances autophagy induction in response to LPS stimulation. To verify the functional role of HBx in liver cancer progression, we utilized different HCC cell lines, HepG2, SK-Hep-1, and SNU-761. HBx-expressing HepG2 cells exhibited enhanced cell migration, invasion, and cell mobility in response to LPS stimulation compared to those of control HepG2 cells. These results were consistently observed in HBx-expressed SK-Hep-1 and HBx-expressed SNU-761 cells. Taken together, our findings suggest that HBx positively regulates the induction of autophagy through the inhibition of the BECN1-Bcl-2 complex and enhancement of the TRAF6-BECN1-VPS34 complex, leading to enhance liver cancer migration and invasion.

Centrosomal protein TAX1BP2 inhibits centrosome-microtubules aberrations induced by hepatitis B virus X oncoprotein.

Liver cancer (hepatocellular carcinoma, HCC) is one of the most prevalent cancers worldwide. Several etiological factors of HCC, including hepatitis B or hepatitis C virus infection, liver cirrhosis and aflatoxin B1 intake has been identified. HBx, which is an oncogenic protein encoded by the hepatitis B virus, is strongly associated with hepatocarcinogenesis. Using stable HBx-expressing cell, we showed that HBx induced chromosome gain, with amplification of centrosomes numbers and deregulation of centrosome ultrastructure. To dissect the mechanism for chromosome instability, our result revealed that HBx contributed to a hyperactive centrosome-microtubule dynamics by accelerating microtubule nucleation and polymerization. Further investigations suggested that HBx interacted with a centrosome linker protein TAX1BP2, which has previously been shown to function as an intrinsic block of centrosome amplification and a tumour suppressor in HCC. Restoring TAX1BP2 was able to block HBx-mediated centrosome amplification and abolish the HBx-mediated centrosome aberration, thereby suppressing chromosome instability. Thus, we demonstrate here a mechanism by which HBx deregulates centrosome-microtubule dynamics through interacting with TAX1BP2, which underlines the possibility of restoration of TAX1BP2 to rescue cells from chromosome instability.

BNIP3L-Dependent Mitophagy Promotes HBx-Induced Cancer Stemness of Hepatocellular Carcinoma Cells via Glycolysis Metabolism Reprogramming.

Hepatitis B virus (HBV) is one of predisposing factors for hepatocellular carcinoma (HCC). The role of HBV x protein (HBx) in mediating the induction and maintenance of cancer stemness during HBV-related HCC attracts considerable attention, but the exact mechanism has not been clearly elucidated. Here, ABCG2-dependent stem-like side population (SP) cells, which are thought to be liver cancer stem cells (LCSCs), were present in HCC cells, and the fraction of this subset was increased in HBx-expressing HCC cells. In addition, glycolysis was upregulated in LCSCs and HBx-expressing HCC cells, and intervention of glycolysis attenuated cancer stem-like phenotypes. Mitochondria play an important role in the maintenance of energy homeostasis, BNIP3L-dependent mitophagy was also activated in LCSCs and HBx-expressing HCC cells, which triggered a metabolic shift toward glycolysis. In summary, we proposed a positive feedback loop, in which HBx induced BNIP3L-dependent mitophagy which upregulated glycolytic metabolism, increasing cancer stemness of HCC cells in vivo and in vitro. BNIP3L might be a potential therapeutic target for intervention of LCSCs-associated HCC. Anti-HBx, a monoclonal antibody targeting intracellular HBx, had the potential to delay the progression of HBV infection related-HCC.

Hepatitis B virus infection is not associated with fatty liver disease: Evidence from a cohort study and functional analysis.

Chronic hepatitis B virus (HBV) infection has been reported to be associated with the prevalence of non-alcoholic fatty liver disease (NAFLD). However, the present study demonstrated that the incidence of fatty liver disease in HBV-infected subjects (16/152, 10.5%) was not significantly different from in non-HBV-infected subjects (292/1,714, 17%), following adjustment for age (odds ratio=0.656; 95% confidence interval=0.379–1.134; P=0.131). Hepatitis B protein X (HBx) is considered a key regulator in HBV infection and several studies have confirmed that HBx serves a pivotal role in the process of fatty liver disease. In the present study, it was demonstrated that HBx-expressing cells exhibited increased mitochondrial membrane potential, ATP generation, and endogenous mitochondrial respiration. In addition, higher levels of mitochondrial reactive oxygen species (ROS) were detected in HBx-expressing cells compared with in control cells. Increased ROS production may contribute to increased lipid droplet formation in HBx-expressing cells, whereas the removal of ROS with N-acetylcysteine may decrease the accumulation of lipid droplets in a time-dependent manner. In conclusion, the present findings indicated that HBV, and perhaps more specifically HBx, was not a protective factor against NAFLD. HBx may function as a risk factor for fatty liver disease, based on the findings of the present functional study; however, further studies are required to clarify the effects of HBx on hepatic steatosis.

ER stress regulating protein phosphatase 2A-B56\u03b3, targeted by hepatitis B virus X protein, induces cell cycle arrest and apoptosis of hepatocytes

Hepatitis B virus X (HBx) protein contributes to the progression of hepatitis B virus (HBV)-related hepatic injury and diseases, but the exact mechanism remains unclear. Protein phosphatase 2 A (PP2A) is a major serine/threonine phosphatase involved in regulating many cellular phosphorylation signals that are important for regulation of cell cycle and apoptosis. Does HBx target to PP2A-B56γ and therefore affect HBx-induced hepatotoxicity? In the present study, the expression of B56γ positively correlated with the level of HBx in HBV-infected primary human hepatocytes in human-liver-chimeric mice, HBx-transgenic mice, HBV-infected cells, and HBx-expressing hepatic cells. B56γ promoted p53/p21-dependent cell cycle arrest and apoptosis. Mechanistically, B56γ was transactivated by AP-1, which was under the regulation of endoplasmic reticulum (ER) stress induced CREBH signaling in HBx-expressing hepatic cells. B56γ dephosphorylated p-Thr55-p53 to trigger p53/p21 pathway-dependent cell cycle G1 phase arrest, resulting in apoptosis of hepatic cells. In conclusion, this study provides a novel insight into a mechanism of B56γ mediating cell cycle arrest and apoptosis of HBx-expressing hepatic cells and a basis for B56γ being a potential therapeutic target for HBV-infected hepatic cells.

The expression and role of lncRNA AX800134 in hepatitis B virus-related hepatocellular carcinoma.

Chronic infection with hepatitis B virus (HBV) is one of most important risk factors for the development of hepatocellular carcinoma (HCC). Several long non-coding RNAs (lncRNAs) have been shown to be involved in the etiology of HBV-related HCC. AX800134 is one recently identified lncRNA associated with HCC. In this study, we validated the upregulated expression of AX800134 in HBV-positive HCC compared with HBV-negative HCC. Furthermore, we found that HBV X protein (HBx) directly triggered AX800134 expression in human hepatoma HepG2 cells. Pro-inflammatory cytokine TNFα also induced AX800134 upregulation in HBx-expressing HepG2 cells, which could be reversed by reactive oxygen species (ROS) scavenger pyrrolidine dithiocarbamate (PDTC). Additionally, silencing AX800134 with siRNA interference remarkably inhibited the growth and invasion of HBx-expressing HepG2 cells. AX800134 antagonism also enhanced spontaneous apoptosis of HepG2 cells under serum deprivation condition. Therefore, our results indicate that highly expressed AX800134 acts as an oncogenic factor in HCC, and its upregulation is related with the viral product HBx and chronic inflammation.

HBV infection potentiates resistance to S-phase arrest-inducing chemotherapeutics by inhibiting CHK2 pathway in diffuse large B-cell lymphoma

A considerable number of diffuse large B-cell lymphoma (DLBCL) patients are infected with hepatitis B virus (HBV), which is correlated with their poor outcomes. However, the role of HBV infection in DLBCL treatment failure remains poorly understood. Here, our data demonstrated that HBV infection was closely associated with poorer clinical prognosis independent of its hepatic dysfunction in germinal center B-cell type (GCB type) DLBCL patients. Interestingly, we found that DLBCL cells expressing hepatitis B virus X protein (HBX) did not exhibit enhanced cell growth but did show reduced sensitivity to methotrexate (MTX) and cytarabine (Ara-C), which induced S-phase arrest. Mechanism studies showed that HBX specifically inhibited the phosphorylation of checkpoint kinase 2 (CHK2, a key DNA damage response protein). CHK2 depletion similarly conferred resistance to the S-phase arrest-inducing chemotherapeutics, consistent with HBX overexpression in DLBCL cells. Moreover, overexpression of wild-type CHK2 rather than its unphosphorylated mutant (T68A) significantly restored the reduced chemosensitivity in HBX-expressing cells, suggesting that HBV infection conferred resistance to chemotherapeutics that induced S-phase arrest by specifically inhibiting the activation of CHK2 response signaling in DLBCL.

간염바이러스 X단백질 유전자를 핵산전달감염시킨 간암세포주에서 17-DMAG의 항종양효과 상승 효과

Background/Aims: Hepatitis B viral protein X (HBx) is implicated in the pathogenesis of hepatocellular carcinoma (HCC) as well as the elevation of heat shock proteins (HSPs) after hepatitis B virus (HBV) infection. We thus investigated the anticancer effects of an HSP90 inhibitor 17-Dimethylaminoethylamino-17-demethoxygeldanamycin (17-DMAG) in HBxtransfected hepatocellular carcinoma cells. MethodspcDNA-HBx was made by inserting the HBx gene derived from the HBV-infected patient into pcDNA3.1 using the restriction enzymes (XbaI/HindIII). HBx-expressing HepG2 cells were then generated by transfecting HepG2 cells with pcDNA containing HBx gene. To compare the anticancer effects of 17-DMAG between pcDNA-HBx transfected HepG2 cells and the control cells (pcDNA-transfected HepG2 cells), we performed various molecular studies, including Ez-cytox proliferation assay, Western blot analysis, and flow cytometry. Results17-DMAG inhibited the proliferation of pcDNA-HBx transfected HepG2 cells better than control cells (P<0.05). After treating with a various concentration of 17-DMAG (50–1,000 nM), pcDNA-HBx transfected HepG2 cells exhibited higher expression of pro-apoptotic proteins (c-caspase-3, c-caspase-8, and c-caspase-9) than did control cells (P<0.05). pcDNAHBx transfected HepG2 cells showed higher activities of caspase-3, caspase-8, and caspase-9 than did control cells (P<0.05). Finally, we found that the expression of pro-apoptotic proteins (PARP and c-caspase-3) was considerably decreased by the use of a caspase inhibitor suggesting that 17-DMAG induces the cell death of HepG2 cells caspase-dependently. ConclusionsOur study strongly suggests that 17-DMAG has antiviral effects against HBV as well as anticancer effects against HepG2 cells. Thus, the application of 17-DMAG appears to be particularly advantageous to the HCC patients related with HBV infection.

The HBx gene of hepatitis B virus can influence hepatic microenvironment via exosomes by transferring its mRNA and protein

The cellular secretory vesicles known as ‘exosomes’ have emerged as key player in intercellular transport and communication between different eukaryotic in order to maintain body homeostasis. Many pathogenic viruses utilize exosome pathway to efficiently transfer bioactive components from infected cells to naïve cells. Here, we show that HBx can tweak the exosome biogenesis machinery both by enhancing neutral sphingomyelinase2 activity as well as by interacting with exosomal biomarkers such as neutral sphingomyelinase2, CD9 and CD81. The nano particle tracking analysis revealed enhanced secretion of exosomes by the HBx-expressing cells while confocal studies confirmed the co-localization of HBx with CD9 and CD63. Importantly, we observed the encapsulation of HBx mRNA and protein in these exosomes besides some other qualitative changes. The exosomal cargo secreted by HBx-expressing cells had a profound effect on the recipient hepatic cells including creation of a milieu conducive for cellular-transformation. Thus, the present study unfolds a novel role of HBx in intercellular communication by facilitating horizontal transfer of viral gene products and other host factors via exosomes in order to support viral spread and pathogenesis.

HDM2 Promotes NEDDylation of Hepatitis B Virus HBx To Enhance Its Stability and Function.

Hepatitis B virus (HBV)-encoded X protein (HBx) plays a critical role in HBV-related hepatocarcinoma development. In this study, we demonstrate that HBx is specifically modified by NEDD8. We found that E3 ligase HDM2 promotes NEDDylation of HBx to enhance HBx stability by preventing its ubiquitination-mediated degradation. Consistently, analysis of 160 hepatocellular carcinoma patient specimens indicated that the amount of HDM2 protein correlates with HBx protein level. We identified that HBx K91 and K95 as the key HBx NEDDylation sites and observed that the NEDDylation-deficient HBx has shorter half-life. We generated Huh7 cell lines which ectopically express wild-type and NEDDylation-deficient HBx and found that NEDDylation-deficient HBx showed less chromatin localization and less DDB1 binding. Consistently, the expression of HBx-regulated genes (IL-8, MMP9, and YAP) and HBV transcription (the activity of HBV enhancer and the amount of pgRNA transcribed from cccDNA) were significantly higher in cells expressing wild-type (WT) HBx than that in cells expressing mutant HBx. In addition, HBx-expressing cells proliferated faster than control and mutant HBx-expressing cells. We also showed that the ability of WT HBx-expressing cells to form tumors in nude mice was significantly higher than that of mutant HBx-expressing cells. In conclusion, we revealed that E3 ligase HDM2 promotes NEDDylation of HBx to enhance HBx stability and chromatin localization, which in turn favors HBx-dependent transcriptional regulation, cell proliferation, and HBV-driven tumor growth.IMPORTANCE Hepatitis B virus (HBV) HBx protein plays a critical role in viral replication and hepatocarcinogenesis. However, the regulation of HBx stability is not well understood. We found that HBx is modified by NEDD8 and that the HDM2 E3 ligase promotes HBx NEDDylation to enhance HBx stability by inhibiting its ubiquitination. We provide a new evidence to show the positive correlation between HDM2 and HBx in clinical hepatocellular carcinoma (HCC) samples. We also identified the major NEDDylation sites on HBx. Our studies indicate that the defective NEDDylation of HBx negatively affects its ability to activate the transcription of downstream genes and promote cell proliferation and tumor growth in vivo Taken together, our findings reveal a novel posttranslational modification of HBx by HDM2 which regulates its stability, subcellular localization, and functions. These findings indicate that HDM2 is an important regulator on HBx and a potential diagnosis/therapeutic marker for HBV-associated HCC.

Integrated analysis of microRNA and mRNA expression profiles in HBx-expressing hepatic cells.

AIMTo identify the miRNA-mRNA regulatory network in hepatitis B virus X (HBx)-expressing hepatic cells.METHODSA stable HBx-expressing human liver cell line L02 was established. The mRNA and miRNA expression profiles of L02/HBx and L02/pcDNA liver cells were identified by RNA-sequencing analysis. Kyoto Encyclopedia of Genes and Genomes pathway enrichment analysis was performed to investigate the function of candidate biomarkers, and the relationship between miRNA and mRNA was studied by network analysis.RESULTSCompared with L02/pcDNA cells, 742 unregulated genes and 501 downregulated genes were determined as differentially expressed in L02/HBx cells. Gene ontology analysis suggested that the differentially expressed genes were relevant to different biological processes. Concurrently, 22 differential miRNAs were also determined in L02/HBx cells. Furthermore, integrated analysis of miRNA and mRNA expression profiles identified a core miRNA-mRNA regulatory network that is correlated with the carcinogenic role of HBx.CONCLUSIONCollectively, the miRNA-mRNA network-based analysis could be useful to elucidate the potential role of HBx in liver cell malignant transformation and shed light on the underlying molecular mechanism and novel therapy targets for hepatocellular carcinoma.