The interaction of hepatitis B virus X protein and protein phosphatase type 2 Calpha and its effect on IL-6

Regulation of Pattern-Recognition Receptor Signaling by HBX During Hepatitis B Virus Infection

As a small DNA virus, hepatitis B virus (HBV) plays a pivotal role in the development of various liver diseases, including hepatitis, cirrhosis, and liver cancer. Among the molecules encoded by this virus, the HBV X protein (HBX) is a viral transactivator that plays a vital role in HBV replication and virus-associated diseases. Accumulating evidence so far indicates that pattern recognition receptors (PRRs) are at the front-line of the host defense responses to restrict the virus by inducing the expression of interferons and various inflammatory factors. However, depending on HBX, the virus can control PRR signaling by modulating the expression and activity of essential molecules involved in the toll-like receptor (TLR), retinoic acid inducible gene I (RIG-I)-like receptor (RLR), and NOD-like receptor (NLR) signaling pathways, to not only facilitate HBV replication, but also promote the development of viral diseases. In this review, we provide an overview of the mechanisms that are linked to the regulation of PRR signaling mediated by HBX to inhibit innate immunity, regulation of viral propagation, virus-induced inflammation, and hepatocarcinogenesis. Given the importance of PRRs in the control of HBV replication, we propose that a comprehensive understanding of the modulation of cellular factors involved in PRR signaling induced by the viral protein may open new avenues for the treatment of HBV infection.

A Pleiotropic Role of the Hepatitis B Virus Core Protein in Hepatocarcinogenesis

Chronic hepatitis B virus (HBV) infection is one of the most common factors associated with hepatocellular carcinoma (HCC), which is the sixth most prevalent cancer among all cancers worldwide. However, the pathogenesis of HBV-mediated hepatocarcinogenesis is unclear. Evidence currently available suggests that the HBV core protein (HBc) plays a potential role in the development of HCC, such as the HBV X protein. The core protein, which is the structural component of the viral nucleocapsid, contributes to almost every stage of the HBV life cycle and occupies diverse roles in HBV replication and pathogenesis. Recent studies have shown that HBc was able to disrupt various pathways involved in liver carcinogenesis: the signaling pathways implicated in migration and proliferation of hepatoma cells, apoptosis pathways, and cell metabolic pathways inducing the development of HCC; and the immune system, through the expression and production of proinflammatory cytokines. In addition, HBc can modulate normal functions of hepatocytes through disrupting human host gene expression by binding to promoter regions. This HBV protein also promotes HCC metastasis through epigenetic alterations, such as micro-RNA. This review focuses on the molecular pathogenesis of the HBc protein in HBV-induced HCC.

The Hepatitis B Virus Interactome: A Comprehensive Overview

Despite the availability of a prophylactic vaccine, chronic hepatitis B (CHB) caused by the hepatitis B virus (HBV) is a major health problem affecting an estimated 292 million people globally. Current therapeutic goals are to achieve functional cure characterized by HBsAg seroclearance and the absence of HBV-DNA after treatment cessation. However, at present, functional cure is thought to be complicated due to the presence of covalently closed circular DNA (cccDNA) and integrated HBV-DNA. Even if the episomal cccDNA is silenced or eliminated, it remains unclear how important the high level of HBsAg that is expressed from integrated HBV DNA is for the pathology. To identify therapies that could bring about high rates of functional cure, in-depth knowledge of the virus' biology is imperative to pinpoint mechanisms for novel therapeutic targets. The viral proteins and the episomal cccDNA are considered integral for the control and maintenance of the HBV life cycle and through direct interaction with the host proteome they help create the most optimal environment for the virus whilst avoiding immune detection. New HBV-host protein interactions are continuously being identified. Unfortunately, a compendium of the most recent information is lacking and an interactome is unavailable. This article provides a comprehensive review of the virus-host relationship from viral entry to release, as well as an interactome of cccDNA, HBc, and HBx.

Hepatitis B Virus HBx Protein Mediates the Degradation of Host Restriction Factors through the Cullin 4 DDB1 E3 Ubiquitin Ligase Complex

The hepatitis B virus (HBV) regulatory HBx protein is required for infection, and its binding to cellular damaged DNA binding protein 1 (DDB1) is critical for this function. DDB1 is an adaptor protein for the cullin 4A Really Interesting New Gene (RING) E3 ubiquitin ligase (CRL4) complex and functions by binding cellular DDB1 cullin associated factor (DCAF) receptor proteins that recruit substrates for ubiquitination and degradation. We compared the proteins found in the CRL4 complex immunoprecipitated from uninfected versus HBV-infected hepatocytes from human liver chimeric mice for insight into mechanisms by which HBV and the cell interact within the CRL4 complex. Consistent with its role as a viral DCAF, HBx was found in the HBV CRL4 complexes. In tissue culture transfection experiments, we showed that HBx expression led to decreased levels of known restriction factor structural maintenance of chromosomes protein 6 (SMC6) and putative restriction factors stromal interaction molecule 1 (STIM1, zinc finger E-box binding homeobox 2 (ZEB2), and proteasome activator subunit 4 (PSME4). Moreover, silencing of these proteins led to increased HBV replication in the HepG2-sodium taurocholate cotransporting polypeptide (NTCP) infection model. We also identified cellular DCAF receptors in CRL4 complexes from humanized mice. Increasing amounts of HBx did not reveal competitive DCAF binding to cullin4 (CUL4)-DDB1 in plasmid-transfected cells. Our results suggest a model in which HBx benefits virus replication by directly or indirectly degrading multiple cellular restriction factors.

CRISPR/Cas9-mediated knockout of HBsAg inhibits proliferation and tumorigenicity of HBV-positive hepatocellular carcinoma cells

Chronic hepatitis B virus (HBV) infection remains the most common risk factor for hepatocellular carcinoma (HCC). High HBV surface antigen (HBsAg) levels are highly correlated with hepatocarcinogenesis and HBV‐associated HCC development. However, the role and detailed mechanisms associated with HBsAg in HCC development remain elusive. In this study, we designed specific single guide RNAs (sgRNAs) targeting the open reading frames, preS1/preS2/S, of the HBV genome and established HBsAg knockout HCC cell lines using the CRISPR/Cas9 system. We showed that knockout of HBsAg in HCC cell lines decreased HBsAg expression and significantly attenuated HCC proliferation in vitro, as well as tumorigenicity in vivo. We also found that overexpression of HBsAg, including the large (LHBs), middle (MHBs), and small (SHBs) surface proteins promoted proliferation and tumor formation in HCC cells. Moreover, we demonstrated that knockout of HBsAg in HCC cells decreased interleukin (IL)‐6 production and inhibited signal transducer and activator of transcription 3 (STAT3) signaling, while overexpression of HBsAg induced a substantial accumulation of pY‐STAT3. Collectively, these results highlighted the tumorigenic role of HBsAg and implied that the IL‐6‐STAT3 pathway may be implicated in the HBsAg‐mediated malignant potential of HBV‐associated HCC.

Hepatitis B virus X protein binding to hepsin promotes C3 production by inducing IL-6 secretion from hepatocytes

Hepatitis B virus (HBV) X protein (HBx) is an important effector for HBV-associated pathogenesis. In this study, we identified hepsin as an HBx-interacting protein and investigated the effects of hepsin on HBx-mediated complement component 3 (C3) secretion in hepatocytes. In vivo and in vitro binding between HBx and hepsin was confirmed by co-immunoprecipitation and Glutathione S-transferase pull-down assays. HBx synergized with hepsin to promote C3 production by potentiating interleukin-6 (IL-6) secretion. Knockdown of endogenous hepsin attenuated C3 and IL-6 secretion induced by HBx in hepatic cells. In addition, levels of hepsin protein correlated positively with C3 expression in human non-tumor liver tissues. Further exploration revealed that HBx and hepsin increased C3 promoter activity by up-regulating the expression and phosphorylation of the transcription factor CAAT/enhancer binding protein beta (C/EBP-β), which binds to the IL-6/IL-1 response element in the C3 promoter. HBx and hepsin synergistically enhanced IL-6 mRNA levels and promoter activity by increasing the nuclear translocation of nuclear factor kappaB (NF-κB). Our findings show for the first time that binding between HBx and hepsin promotes C3 production by inducing IL-6 secretion in hepatocytes.

Hepatitis B Virus Middle Protein Enhances IL-6 Production via p38 MAPK/NF-κB Pathways in an ER Stress-Dependent Manner

During hepatitis B virus (HBV) infection, three viral envelope proteins of HBV are overexpressed in the endoplasmic reticulum (ER). The large S protein (LHBs) and truncated middle S protein (MHBs^t) have been documented to play roles in regulating host gene expression and contribute to hepatic disease development. As a predominant protein at the ultrastructural level in biopsy samples taken from viremic patients, the role of the middle S protein (MHBs) remains to be understood despite its high immunogenicity. When we transfected hepatocytes with an enhanced green fluorescent protein (EGFP)-tagged MHBs expressing plasmid, the results showed that expression of MHBs cause an upregulation of IL-6 at the message RNA and protein levels through activating the p38 mitogen-activated protein kinase (p38 MAPK) and nuclear factor-kappa B (NF-κB) pathways. The use of specific inhibitors of the signaling pathways can diminish this upregulation. The use of BAPTA-AM attenuated the stimulation caused by MHBs. We further found that MHBs accumulated in the endoplasmic reticulum and increased the amount of glucose regulated protein 78 (GRP78/BiP). Our results provide a possibility that MHBs could be involved in liver disease progression.

The Relationship Between Serum Interleukin-6 and the Recurrence of Hepatitis B Virus Related Hepatocellular Carcinoma after Curative Resection

The aim of this study is to assess whether preoperative serum interleukin-6 (IL-6) can predict recurrence of hepatitis B virus (HBV)-associated hepatocellular carcinoma (HCC). The association between preoperative IL-6 levels and HCC recurrence following curative hepatectomy in 146 patients with chronic HBV infection was determined. Patients were divided into groups based on the presence or absence of HCC recurrence. Serum IL-6 levels were compared between groups, and the association between serum IL-6 level and greatest tumor dimension was also analyzed. Receiver operating characteristics (ROC) curve was used to define the optimal cutoff value for predicting recurrence-free survival (RFS) and overall survival (OS) rates. The OS and RFS rates were calculated using the Kaplan-Meier method. Out of 146 patients, 80 (54.8%) patients were documented as having HCC recurrence during the follow-up period. After adjusting for potential confounders, serum IL-6 levels were significantly associated with HCC recurrence, and a saturation effect existed with serum IL-6 levels up to 3.7 pg/mL. In addition, patients with preoperative serum IL-6 levels over 3.1 pg/mL had lower RFS and OS rates (P < 0.01). There was no significant correlation between preoperative serum IL-6 levels and maximal tumor dimension (r = 0.0003, P = 0.84). Elevated serum levels of IL-6 were significantly associated with an increased risk of HBV-associated HCC recurrence suggesting that preoperative IL-6 serum level is potential biomarker for early prediction of HBV-associated HCC recurrence.

Negative regulation of RelA phosphorylation: emerging players and their roles in cancer

NF-κB signaling contributes to human disease processes, notably inflammatory diseases and cancer. Many advances have been made in understanding mechanisms responsible for abnormal NF-κB activation with RelA post-translational modification, particularly phosphorylation, proven to be critical for RelA function. While the majority of studies have focused on identifying kinases responsible for NF-κB phosphorylation and pathway activation, recently progress has also been made in understanding the negative regulators important for restraining RelA activity. Here we summarize negative regulators of RelA phosphorylation, their targeting sites in RelA and biological functions through negative regulation of RelA activation. Finally, we emphasize the tumor suppressor-like roles that these negative regulators can assume in human cancers.

Potential roles played by IL-6 in hepatitis B infection

ABSTRACT: 

Hepatitis B is a main disorder of the liver, which is induced by HBV. Hepatitis B can induce liver diseases, such as inflammation, cirrhosis and hepatocellular carcinoma (HCC). Recent studies demonstrated that several patients are unable to eradicate the virus from hepatocytes and develop chronic hepatitis B infections. The main mechanisms responsible for development of chronic hepatitis B and its related cirrhosis as well as HCC are yet to be identified. IL-6 is a proinflammatory cytokine that participates in stimulation of immune responses against viral infections. In addition, it has been documented that IL-6 can play key roles in induction of fibrosis and cancers. Therefore, the aim of this article is to clarify the main roles of IL-6 in stimulation of appropriate immune responses against hepatitis B virus and induction of hepatitis B-dependent cirrhosis as well as HCC.

Using proteomics to identify the HBx interactome in hepatitis B virus: how can this inform the clinic?

Hepatitis B virus (HBV) is a small and enveloped DNA virus, of which chronic infection is the main risk factor of liver cirrhosis and hepatocellular carcinoma. Hepatitis B virus X protein (HBx) is a multifunctional protein encoded by HBV genome, which have significant effects on HBV replication and pathogenesis. Through directly interacting with cellular proteins, HBx is capable to promote HBV replication, regulate transcription of host genes, disrupt protein degradation, modulate signaling pathway, manipulate cell death and deregulate cell cycle. In this review, we briefly discuss the diversified effects of HBx-interactome and their potential clinical significances.

PPM1A is a RelA phosphatase with tumor suppressor-like activity

Nuclear factor-κB (NF-κB) signaling contributes to human disease processes, notably inflammatory diseases and cancer. NF-κB has a role in tumorigenesis and tumor growth, as well as promotion of metastases. Mechanisms responsible for abnormal NF-κB activation are not fully elucidated; however, RelA phosphorylation, particularly at serine residues S536 and S276, is critical for RelA function. Kinases that phosphorylate RelA promote oncogenic behaviors, suggesting that phosphatases targeting RelA could have tumor-inhibiting activities; however, few RelA phosphatases have been identified. Here, we identified tumor inhibitory and RelA phosphatase activities of the protein phosphatase 2C (PP2C) phosphatase family member, PPM1A. We show that PPM1A directly dephosphorylated RelA at residues S536 and S276 and selectively inhibited NF-κB transcriptional activity, resulting in decreased expression of monocyte chemotactic protein-1/chemokine (C-C motif) ligand 2 and interleukin-6, cytokines implicated in cancer metastasis. PPM1A depletion enhanced NF-κB-dependent cell invasion, whereas PPM1A expression inhibited invasion. Analyses of human expression data revealed that metastatic prostate cancer deposits had lower PPM1A expression compared with primary tumors without distant metastases. A hematogenous metastasis mouse model revealed that PPM1A expression inhibited bony metastases of prostate cancer cells after vascular injection. In summary, our findings suggest that PPM1A is a RelA phosphatase that regulates NF-κB activity and that PPM1A has tumor suppressor-like activity. Our analyses also suggest that PPM1A inhibits prostate cancer metastases and as neither gene deletions nor inactivating mutations of PPM1A have been described, increasing PPM1A activity in tumors represents a potential therapeutic strategy to inhibit NF-κB signaling or bony metastases in human cancer.

Unraveling the complexity of hepatitis B virus: from molecular understanding to therapeutic strategy in 50 years

Hepatitis B virus (HBV) is a well-known hepadnavirus with a double-stranded circular DNA genome. Although HBV was first described approximately 50 years ago, the precise mechanisms of HBV infection and effective therapeutic strategies remain unclear. Here, we focus on summarizing the complicated mechanisms of HBV replication and infection, as well as genomic factors and epigenetic regulation. Additionally, we discuss in vivo models of HBV, as well as diagnosis, prevention and therapeutic drugs for HBV. Together, the data in this 50-year review may provide new clues to elucidate molecular mechanisms of HBV pathogenesis and shed new light on the future HBV therapies.

An integrated proteomics and bioinformatics analyses of hepatitis B virus X interacting proteins and identification of a novel interactor apoA-I

HBx is well-known to be a multifunctional protein encoded by HBV and its biological functions are mainly dependent on pleiotropic protein-protein interactions (PPIs); however, the global mapping of HBx-interactome has not been established so far. Thus, in this study, we have identified 127 HBx-interacting proteins by a profound GST pull-down assay coupled with mass spectrometry, and constructed an HBx-interactome network and core apoA-I pathways with a series of bioinformatics approaches. One of the identified HBx-binding partners is apolipoprotein A-I (apoA-I), which has a specific role in lipid and cholesterol metabolism. The HBx-apoA-I protein interaction was confirmed by both GST pull-down and co-immunoprecipitation. The ectopic overexpression of apoA-I can lead to a significant inhibition on HBV secretion concomitant with the reduction of cellular cholesterol level. In addition, HBV can modulate the function of apoA-I through HBx which might interact with the 44-189 residues of apoA-I and result in dysfunction of apoA-I such as decreased self-association ability, increased carbonyl level and impaired lipid-binding ability. Our results demonstrate an integrated physical association of HBx and host proteins, especially a novel interactor apoA-I that may influence the HBV secretion, which would shed new light on exploring the complicated mechanisms of HBV manipulation on host cellular functions.

BIOLOGICAL SIGNIFICANCE

HBx is well-known to be a multifunctional protein encoded by HBV and its biological functions are mainly dependent on pleiotropic protein-protein interactions. Although a series of HBx-interacting proteins have been identified, a global characterization of HBx interactome has not been reported. In this study, we have identified a total of 127 HBx-interacting proteins by a profound GST pull-down assay coupled with mass spectrometry, and constructed an HBx-interactome network with a series of bioinformatics approaches. Our results demonstrate an integrated physical association of HBx and host proteins which may help us explore the complicated mechanisms of HBV manipulation on host cellular functions. In addition, we validated one of the identified HBx-binding partners, apolipoprotein A-I (apoA-I), which played a significant inhibitory effect on HBV secretion, indicating a crucial role of the HBx-apoA-I axis in HBV life cycle.

Hepatitis B virus X protein stimulates IL-6 expression in hepatocytes via a MyD88-dependent pathway

BACKGROUND & AIMS

Hepatitis B virus (HBV) X protein (HBx) has been implicated in HBV-associated carcinogenesis by activating signal transduction pathways and influencing gene transcription in liver cells. We aimed to investigate the underlying mechanisms for HBx-induced production of interleukin-6 (IL-6), one of the major inflammatory mediators that stimulate hepatocellular carcinoma development.

METHODS

HBx was overexpressed in hepatic and hepatoma cell lines and IL-6 expression levels were measured by quantitative RT-PCR and ELISA. The activation of IRAK-1, ERKs/p38, and NF-κB was determined by Western blotting using specific anti-phosphoprotein antibodies. The role of MyD88 in these processes was analyzed by MyD88 RNAi and expression of an inactive MyD88 mutant.

RESULTS

Expression of HBx in hepatic and hepatoma cells led to a dramatic enhancement of IL-6 synthesis and secretion. Dysfunction of MyD88 in these cells prevented the HBx-triggered IL-6 production. HBx expression also activated downstream signaling proteins of MyD88 including IRAK-1, ERKs/p38, and NF-κB. Inactivation of these signaling molecules blocked IL-6 synthesis as well. HBx-stimulated the expression of MyD88.

CONCLUSIONS

In hepatocytes and hepatoma cells, HBx stimulates the production of IL-6 in a MyD88-dependent manner, indicating that parenchymal liver cells are an additional source of high levels of IL-6 in the HBV-infected liver microenvironment. HBx could be involved in HBV-mediated liver carcinogenesis, through this mechanism of action.

Advances in understanding the role of STAT3 in the pathogenesis of hepatocellular carcinoma

Signal transducer and activator of transcription 3 (STAT3) is an important nuclear transcription factor that, once activated, can regulate the transcription of target genes. STAT3 is overexpressed in hepatocellular carcinoma (HCC). It has been demonstrated that STAT3 can be activated by HBV, HCV and diverse oncoproteins. The dysregulation of STAT/SOCS signaling also results in constitutive activation of STAT3. Aberrantly activated STAT3 can contribute to the malignant transformation of liver cells and result in the occurrence of HCC by inducing dysregulation of c-Myc, EGFR, TGF, survivin and VEGF. This paper summarizes the critical role of STAT3 in the pathogenesis of HCC and explores the possibility of using STAT3 as a target for HCC therapy.

High serum interleukin-6 level predicts future hepatocellular carcinoma development in patients with chronic hepatitis B

Increased interleukin-6 (IL-6) production is implicated in the pathogenesis of hepatocellular carcinoma (HCC) in animal models. Although previous studies showed that HCC patients had higher serum IL-6 level at the time of diagnosis, it is unclear if the cytokine contributes to the development of HCC or is just a reaction to cancer. To address this question, we performed a nested case-control study. Consecutive chronic hepatitis B patients were recruited from 1997 to 2000 and followed till 2008. Profiling of 27 cytokines, chemokines and growth factors was performed at baseline, date of peak alanine aminotransferase (ALT) level and the last visit. Thirty-seven patients developed HCC at a median follow-up of 62 months (interquartile range: 41-110). Serum IL-6 was higher in patients with HCC than controls both during peak ALT and at the last visit (both p = 0.02). Patients with IL-6 above 7 pg/ml during peak ALT had increased risk of HCC or death (adjusted hazard ratio 3.0; 95% confidence interval 1.2, 7.8; p = 0.02). The sensitivity, specificity, positive and negative predictive values of this cutoff to predict future HCC development were 70%, 73%, 72% and 71%, respectively. Combination of IL-6 and AFP improved the sensitivity in diagnosing HCC or predicting future HCC development. In conclusion, high serum IL-6 level predates the development of HCC in chronic hepatitis B patients, and has moderate accuracy in predicting future cancer. This may assist clinicians in selecting high-risk patients for HCC surveillance program.

HBV X gene transfection upregulates IL-1beta and IL-6 gene expression and induces rat glomerular mesangial cell proliferation

The X gene of HBV encodes a 17-kD protein, termed HBx, which has been shown to function as a transcriptional trans-activator of a variety of viral and cellular promoter/enhancer elements. The aim of this study was to investigate the effect of HBx on gene expression of interleukin (IL)-1 and IL-6, and proliferation of rat mesangial cells in vitro. The X gene of HBV was amplified by PCR assay, and inserted into the eukaryotic expression vector pCI-neo. The structure of recombinant pCI-neo-X plasmid was proved by restrict endonuclease digestion and sequencing analysis. pCI-neo-X was transfected into cultured rat mesangial cell line in vitro via liposome. HBx expression in transfected mesangial cells was detected by Western blot. The IL-1beta and IL-6 mRNA expression in those cells was assayed by semiquantitative RT-PCR. Mesangial cell proliferation was tested by MTT. The results showed that HBx was obviously expressed in cultured mesangial cell line at 36th and 48th h after transfection. The expression of IL-1beta and IL-6 mRNA was simultaneously increased. The cell proliferation was also obvious at the same time. It was concluded that HBx gene transfection could induce IL-1beta and IL-6 gene expression and mesangial cell proliferation. HBx may play a critical role in mesangial cell proliferation through upregulation of the IL-1beta and IL-6 gene expression.

Viral hepatocarcinogenesis: from infection to cancer

Hepatocellular carcinoma (HCC) is a worldwide health issue that has started receiving attention but is still poorly understood. However, the hepatitis B virus (HBV) and the hepatitis C virus (HCV) are known to be two major causative agents of HCC. They differ in their modes of infection, their treatment options, their genomes and their carcinogenic abilities. However, both share a link with HCC through alterations of the host genome. In order to continue in our search for the mechanisms behind viral hepatocarcinogenesis, the individual entities (HBV, HCV, HCC and host), their natural history, treatment options and genomic properties must be further understood. Additionally, an understanding of the genomics, the link between the entities, is crucial for the success of the ongoing search for therapeutic options for HCC. Similar to most types of cancer, hepatocarcinogenesis is a multistep process involving different genetic alterations that ultimately lead to malignant transformation of the hepatocyte. As technology advances and research continues, the genetic changes and influences among these entities will prove essential to improved diagnostic and therapeutic options. It remains a challenge to provide a clear picture of the connection between virus and cancer. We review (i) the epidemiological link between HBV/HCV infection to HCC; (ii) prevention and control of chronic hepatitis B or C in reducing HCC risk; and (iii) genetic characters of viruses and hosts and the mechanisms associated with HCC susceptibilities, with the intention of providing a direction for future research and treatment.