Adhesion contact kinetics of HepG2 cells during Hepatitis B virus replication: Involvement of SH3-binding motif in HBX

The HBV web: An insight into molecular interactomes between the hepatitis B virus and its host en route to hepatocellular carcinoma

Hepatitis B virus (HBV) is a major aetiology associated with the development and progression of hepatocellular carcinoma (HCC), the most common primary liver malignancy. Over the past few decades, direct and indirect mechanisms have been identified in the pathogenesis of HBV-associated HCC which include altered signaling pathways, genome integration, mutation-induced genomic instability, chromosomal deletions and rearrangements. Intertwining of the HBV counterparts with the host cellular factors, though well established, needs to be systemized to understand the dynamics of host-HBV crosstalk and its consequences on HCC progression. Existence of a vast array of protein-protein and protein-nucleic acid interaction databases has led to the uncoiling of the compendia of genes/gene products associated with these interactions. This review covers the existing knowledge about the HBV-host interplay and brings it down under one canopy emphasizing on the HBV-host interactomics; and thereby highlights new strategies for therapeutic advancements against 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.

Screening of the HBx transactivation domain interacting proteins and the function of interactor Pin1 in HBV replication

Hepatitis B virus (HBV) X protein (HBx) has been determined to play a crucial role in the replication and transcription of HBV, and its biological functions mainly depend on the interaction with other host proteins. This study aims at screening the proteins that bind to the key functional domain of HBx by integrated proteomics. Proteins that specifically bind to the transactivation domain of HBx were selected by comparing interactors of full-length HBx and HBx-D5 truncation determined by glutathione-S-transferase (GST) pull-down assay combined with mass spectrometry (MS). The function of HBx interactor Pin1 in HBV replication was further investigated by in vitro experiments. In this study, a total of 189 proteins were identified from HepG2 cells that specifically bind to the transactivation domain of HBx by GST pull-down and subsequent MS. After gene ontology (GO) analysis, Pin1 was selected as the protein with the highest score in the largest cluster functioning in protein binding, and also classified into the cluster of proteins with the function of structural molecule activity, which is of great potential to be involved in HBV life cycle. The interaction between Pin1 and HBx has been further confirmed by Ni²⁺-NTA pulldown assay, co-immunoprecipitation, and immunofluorescence microscopy. HBsAg and HBeAg levels significantly decreased in Pin1 expression inhibited HepG2.2.15 cells. Besides, the inhibition of Pin1 expression in HepG2 cells impeded the restored replication of HBx-deficient HBV repaired by ectopic HBx expression. In conclusion, our study identified Pin1 as an interactor binds to the transactivation domain of HBx, and suggested the potential association between Pin1 and the function of HBx in HBV replication.

Bioinformatics analysis on multiple Gene Expression Omnibus datasets of the hepatitis B virus infection and its response to the interferon-alpha therapy

Background

Hepatitis B virus (HBV) infection is a global health problem and interferon-alpha (IFN-α) is one of the effective therapies. However, little is known about the genetic background of the HBV infection or the genetic determinants of the IFN-α treatment response. Thus, we aim to explore the possible molecular mechanisms of HBV infection and its response to the IFN-α therapy with a comprehensive bioinformatics analysis.

Methods

The Gene Expression Omnibus datasets (GSE83148, GSE84044 and GSE66698) were collected and the differentially expressed genes (DEGs), key biological processes and intersecting pathways were analyzed. The expression of the co-expressed DEGs in the clinical samples was verified by quantitative real time polymerase chain reaction (qRT-PCR).

Results

Analysis of all the 3 datasets revealed that there were eight up-regulated and one down-regulated co-expressed DEGs following the HBV infection and after IFN-α treatment. In clinical samples, the mRNA level of HKDC1, EPCAM, GSN, ZWINT and PLD3 were significantly increased, while, the mRNA level of PLEKHA2 was significantly decreased in HBV infected liver tissues compared to normal liver tissues. PI3K-Akt signaling pathway, focal adhesion, HTLV-I infection, cytokine-cytokine receptor interaction, metabolic pathways, NF-κB signaling pathway were important pathways associated with the HBV infection and the response of IFN-α treatment.

Conclusions

The co-expressed genes, common biological processes and intersecting pathways identified in the study might play an important role in HBV infection and response of IFN-α treatment. The dysregulated genes may act as novel biomarkers and therapeutic targets for HBV.

The regulation of proteins associated with the cytoskeleton by hepatitis B virus X protein during hepatocarcinogenesis

Hepatocellular carcinoma (HCC) is a major malignant disease worldwide, and chronic hepatitis B virus (HBV) infection is one of the primary causes for this type of cancer. Hepatitis B virus X protein (HBx) is a non-structural protein encoded by the viral genome that has significant effects on the pathogenesis of HCC. With the development of high-throughput assays and technologies, the abnormal HBx-induced expression of certain cellular proteins with assorted biological functions has been investigated. These target proteins identified by various methods include specific proteins associated with the cellular cytoskeleton, which contribute to HBx-induced hepatocarcinogenesis. In addition, the cytoskeletal proteins deregulated by HBx are involved in cell morphogenesis, adhesion, migration and proliferation. This review aims to summarize the current understanding of the expression profiles of HBx-associated cytoskeletal proteins, as well as their complex functions and underlying mechanisms in hepatocarcinogenesis. Considering that the potential therapeutics for various types of tumors may function through the stabilization of cytoskeletal proteins in order to restrict cellular movement and limit intracellular processes, clarifying the mechanisms underlying protein-associated cytoskeleton dysregulation by HBx may provide novel possibilities and potent therapeutic targets for HBV-associated HCC.

Hepatitis B Virus Protein X Induces Degradation of Talin-1

In the infected human hepatocyte, expression of the hepatitis B virus (HBV) accessory protein X (HBx) is essential to maintain viral replication in vivo. HBx critically interacts with the host damaged DNA binding protein 1 (DDB1) and the associated ubiquitin ligase machinery, suggesting that HBx functions by inducing the degradation of host proteins. To identify such host proteins, we systematically analyzed the HBx interactome. One HBx interacting protein, talin-1 (TLN1), was proteasomally degraded upon HBx expression. Further analysis showed that TLN1 levels indeed modulate HBV transcriptional activity in an HBx-dependent manner. This indicates that HBx-mediated TLN1 degradation is essential and sufficient to stimulate HBV replication. Our data show that TLN1 can act as a viral restriction factor that suppresses HBV replication, and suggest that the HBx relieves this restriction by inducing TLN1 degradation.

Proteomics based identification of cell migration related proteins in HBV expressing HepG2 cells

Proteomics study was performed to investigate the specific protein expression profiles of HepG2 cells transfected with mutant HBV compared with wildtype HBV genome, aiming to identify the specific functions of SH3 binding domain (proline rich region) located in HBx. In addition to the cell movement and kinetics changes due to the expression of HBV genome we have observed previously, here we further targeted to explore the specific changes of cellular proteins and potential intracellular protein interactions, which might provide more information of the potential cellular mechanism of the differentiated cell movements. Specific changes of a number of proteins were shown in global protein profiling in HepG2 cells expressing wildtype HBV, including cell migration related proteins, and interestingly the changes were found recovered by SH3 binding domain mutated HBV. The distinctive expressions of proteins were validated by Western blot analysis.

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.

Hepatitis B virus X protein disrupts stress fiber formation and triggers apoptosis

Cytoskeletal proteins are key participants in the cellular progression to apoptosis. In a previous study we injected nude mice with CCL13-HBx cells and identified in contrast to non-HBx transfected cells a differentially phosphorylated myosin light chain (p-MLC) by two-dimensional PAGE and mass spectrometry of the tumor material. To investigate the role of HBx in myosin light chain kinase (MLCK) signaling pathways, we analyzed the key molecules, p-MLC and MLCK, by western blotting. Immunofluorescence staining analysis showed that HBx disrupted stress fiber formation and that focal adhesion kinase (FAK) and integrin-linked kinase (ILK) were regulated by HBx-mediated phosphatase and tensin homolog (PTEN). We also used pharmacological inhibitors to explore the correlation between cytoskeletal rearrangements and HBx-mediated cell apoptosis via an MLCK and a PTEN-dependent pathway. The results showed that both ML9 and bvp restored the effects caused by HBx induction. Our findings suggest that HBx disrupts stress fiber formation and triggers apoptosis via an MLCK and a PTEN-dependent pathway.

ECHS1 acts as a novel HBsAg-binding protein enhancing apoptosis through the mitochondrial pathway in HepG2 cells

We aimed to confirm the role of ECHS1 as a binding protein of HBsAg (HBs) and investigate its function during the development of hepatocellular carcinoma (HCC). Our results show that both exogenous and endogenous ECHS1 proteins bind to HBs and co-localize in the cytoplasm in vitro. The coexistence of HBs and ECHS1 enhances HepG2 cell apoptosis, affects ECHS1 localization in the mitochondria and induces apoptosis by decreasing the mitochondrial membrane potential (MMP). These findings suggest that ECHS1 may be applied as a potential therapeutic target during the treatment of HBV-related hepatitis or HCC.

Proteomics-related biomarkers for HBV-associated hepatocellular carcinoma: current status and future prospects

HBV infection is the major cause of the development of hepatocellular carcinoma (HCC). HCC is one of the most common malignancies in the world. The morbidity rate associated with HCC is mainly linked to late diagnosis. Thus, it is very important to discover prognostic factors that can act as biomarkers for preventing HCC development, and those that can act as therapeutic targets. Proteomics analysis has been applied to identify biomarkers from clinical HCC samples. In addition, the cell-based HBV replication and viral protein overexpression system, which provides a model of the cell at an early stage of viral infection, was also used to identify biomarkers. The proteins identified at this stage may be relevant to HBV-associated HCC prognosis. In this review, we discuss the current status of proteomics analysis in the discovery of cellular proteins and prognostic HCC biomarkers, with a special focus on cell metastasis and angiogenesis.

Quantitative proteome profiling of respiratory virus-infected lung epithelial cells

Respiratory virus infections are among the primary causes of morbidity and mortality in humans. Influenza virus, respiratory syncytial virus (RSV), parainfluenza (PIV) and human metapneumovirus (hMPV) are major causes of respiratory illness in humans. Especially young children and the elderly are susceptible to infections with these viruses. In this study we aim to gain detailed insight into the molecular pathogenesis of respiratory virus infections by studying the protein expression profiles of infected lung epithelial cells. A549 cells were exposed to a set of respiratory viruses [RSV, hMPV, PIV and Measles virus (MV)] using both live and UV-inactivated virus preparations. Cells were harvested at different time points after infection and processed for proteomics analysis by 2-dimensional difference gel electrophoresis. Samples derived from infected cells were compared to mock-infected cells to identify proteins that are differentially expressed due to infection. We show that RSV, hMPV, PIV3, and MV induced similar core host responses and that mainly proteins involved in defense against ER stress and apoptosis were affected which points towards an induction of apoptosis upon infection. By 2-D DIGE analyses we have gathered information on the induction of apoptosis by respiratory viruses in A549 cells.

Proteomic analysis of HBV-associated HCC: insights on mechanisms of disease onset and biomarker discovery

The development of hepatocellular carcinoma (HCC) can be considered as an end-stage outcome of chronic hepatitis B virus (HBV) infection. Early prognostic markers are needed to allow effective treatments and prevent HCC from developing. Proteomics analysis has been used to identify markers from clinical samples from HCC patients. This approach can be further improved by identifying early biomarkers before the onset of HCC. One way would be to use the cell-based HBV replication system, which is reflective of the early stage of virus infection and thus secreted proteins identified at this stage may have relevance in HCC prognosis. In this review, we focus the discussion on the current status of proteomics analysis of cellular proteins and HCC biomarker identification, with a special highlight on the potential of the cell-based HBV replication system for the identification of prognostic HCC biomarkers.

Protein profile in HBx transfected cells: a comparative iTRAQ-coupled 2D LC-MS/MS analysis

The x protein of HBV (HBx) has been involved in the development of hepatocellular carcinoma (HCC), with a possible link to individual genotypes. Nevertheless, the underlying mechanism remains obscure. In this study, we aim to identify the HBx-induced protein profile in HepG2 cells by LC-MS/MS proteomics analysis. Our results indicated that proteins were differentially expressed in HepG2 cells transfected by HBx of various genotypes. Proteins associated with cytoskeleton were found to be either up-regulated (MACF1, HMGB1, Annexin A2) or down-regulated (Lamin A/C). These may in turn result in the decrease of focal adhesion and increase of cell migration in response to HBx. Levels of other cellular proteins with reported impact on the function of extracellular matrix (ECM) proteins and cell migration, including Ca(2+)-binding proteins (S100A11, S100A6, and S100A4) and proteasome protein (PSMA3), were affected by HBx. The differential protein profile identified in this study was also supported by our functional assay which indicated that cell migration was enhanced by HBx. Our preliminary study provided a new platform to establish a comprehensive cellular protein profile by LC-MS/MS proteomics analysis. Further downstream functional assays, including our reported cell migration assay, should provide new insights in the association between HCC and HBx.

Hepatitis B virus induced coupling of deadhesion and migration of HepG2 cells on thermo-responsive polymer

The unique physical property of thermo-responsive polymer (TRP) has recently prompted its increasing applications in tissue engineering. On the other hand, TRP has not been exploited for potential applications in quantitative cell screening against external stimulations. In this study, TRP is applied as a model system for elucidating the effect of HBV replication on the biophysical responses of HepG2 cells transfected by wild type HBV genome. Moreover, mutant HBV genome is designed to assess the specific activity of the SH3-binding domain of HBx during HBV replication. The adhesion contact recession and geometry transformation of HepG2 cells transfected with empty vector (pcDNA3.1 cells), wild type HBV (wtHBV cells) and mutant HBV genome (mHBV cells) are probed during the thermal transformation across lower solution critical temperature of TRP. In comparison with pcDNA3.1 cells and mHBV cells, the initial rate of reduction in degree of deformation and average adhesion energy for wtHBV cells is significantly increased. Interestingly, migration speed and persistence time of cells are found to be correlated with the cell deadhesion kinetics. Immuno-fluorescence microscopy demonstrates that HBV replication reduces the actin concentration and focal adhesions at cell periphery during the initial 30 min cell deadhesion. The results strongly suggested that HBV infection triggers the dynamic responses of HepG2 cells through the cytoskeleton remodeling and subsequent mechanochemical transduction. Overall, it is shown that TRP provides a convenient platform for quantifying biological stimulations on adherent cells.

HBX-mediated migration of HBV-replicating HepG2 cells: insights on development of hepatocellular carcinoma

Hepatitus B virus (HBV) is a major cause of the development of hepatpcellular carcinoma (HCC). One of the significant characteristics of tumor progression is cell migration which is reflective of cytoskeletal dynamics. The Rho GTPases contribute to a multiple cellular processes, including the cellular cytoskeletal reorganization and motility. It has been found that some Rho GTPases have oncogenic activity and can promote cancer cell invasion. Here we discuss one of the Rho GTPases, Rac1 can be activated by HBV replication and such activation results in the high motility of HBV-replicating cells. The enhanced cell motility can be interestingly alleviated by the mutation at the sites of proline rich domain located in HBX. Our findings may provide new insights on the mechanism of HCC development associated with chronic HBV infection.

Rac1 GTPase is activated by hepatitis B virus replication--involvement of HBX

Hepatitis B virus (HBV) is a causative agent for liver diseases including hepatocellular carcinoma. Understanding its interactions with cellular proteins is critical in the elucidation of the mechanisms of disease progression. Using a cell-based HBV replication system, we showed that HBV replication in HepG2 cells resulted in a cellular morphological changes displaying membrane rufflings and lamellipodia like structures reminiscent of cells expressing constitutively activated Rac1. We also showed that activated Rac1 resulted in increased viral replication. HBV replication specifically activated wild type Rac1, but not Cdc42. The Rac1 activation by HBV replication also resulted in the phosphorylation of ERK1/2 and AKT, the downstream targets of Rac1 signaling cascade. The smallest HBV viral protein, HBX, was able to activate the endogenous Rac1 and induce membrane ruffling when transfected into cells. Significantly, HBX was found to directly interact with a Rac1 nucleotide exchange factor (betaPIX) through a SH3 binding motif. Taken together, we have shown the interaction of HBV with the Rho GTPase, affecting cell morphology through the Rac1 activation pathway. HBV may possibly make use of an activated Rac1 signaling pathway for increased replication and resultant metastatic effects.