Polarization restricts hepatitis C virus entry into HepG2 hepatoma cells

Tight Junction Proteins as Therapeutic Targets to Treat Liver Fibrosis and Hepatocellular Carcinoma

In the last decade tight junction proteins exposed at the surface of liver or cancer cells have been uncovered as mediators of liver disease biology: Claudin-1 and Occludin are host factors for hepatitis C virus entry and Claudin-1 has been identified as a driver for liver fibrosis and hepatocellular carcinoma (HCC). Moreover, Claudins have emerged as therapeutic targets for liver disease and HCC. CLDN1 expression is upregulated in liver fibrosis and HCC. Monoclonal antibodies (mAbs) targeting Claudin-1 have completed preclinical proof-of-concept studies for treatment of liver fibrosis and HCC and are currently in clinical development for advanced liver fibrosis. Claudin-6 overexpression is associated with an HCC aggressive phenotype and treatment resistance. Claudin-6 mAbs or chimeric antigen receptor-T cells therapies are currently being clinically investigated for Claudin-6 overexpressing tumors. In conclusion, targeting Claudin proteins offers a novel clinical opportunity for the treatment of patients with advanced liver fibrosis and HCC.

GB Virus B and Hepatitis C Virus, Distantly Related Hepaciviruses, Share an Entry Factor, Claudin-1

Due to increased and broadened screening efforts, the last decade has seen a rapid expansion in the number of viral species classified into the Hepacivirus genus. Conserved genetic features of hepaciviruses suggest that they have undergone specific adaptation and have evolved to hijack similar host proteins for efficient propagation in the liver. Here, we developed pseudotyped viruses to elucidate the entry factors of GB virus B (GBV-B), the first hepacivirus described in an animal after hepatitis C virus (HCV). GBV-B-pseudotyped viral particles (GBVBpp) were shown to be uniquely sensitive to the sera of tamarins infected with GBV-B, validating their usefulness as a surrogate for GBV-B entry studies. We screened GBVBpp infection of human hepatoma cell lines that were CRISPR/Cas9 engineered to ablate the expression of individual HCV receptors/entry factors and found that claudin-1 is essential for GBV-B infection, indicating the GBV-B and HCV share an entry factor. Our data suggest that claudin-1 facilitates HCV and GBV-B entry through distinct mechanisms since the former requires the first extracellular loop and the latter is reliant on a C-terminal region containing the second extracellular loop. The observation that claudin-1 is an entry factor shared between these two hepaciviruses suggests that the tight junction protein is of fundamental mechanistic importance during cell entry. IMPORTANCE Hepatitis C virus (HCV) is a major public health burden; approximately 58 million individuals have chronic HCV infection and are at risk of developing cirrhosis and liver cancer. To achieve the World Health Organization's target of eliminating hepatitis by 2030, new therapeutics and vaccines are needed. Understanding how HCV enters cells can inform the design of new vaccines and treatments targeting the first stage of infection. However, the HCV cell entry mechanism is complex and has been sparsely described. Studying the entry of related hepaciviruses will increase the knowledge of the molecular mechanisms of the first stages of HCV infection, such as membrane fusion, and inform structure-guided HCV vaccine design; in this work, we have identified a protein, claudin-1, that facilitates the entry of an HCV-related hepacivirus but with a mechanism not described for HCV. Similar work on other hepaciviruses may unveil a commonality of entry factors and, possibly, new mechanisms.

Natural flavonoids effectively block the CD81 receptor of hepatocytes and inhibit HCV infection: a computational drug development approach

Hepatitis C virus (HCV) infection is a major public health concern, and almost two million people are infected per year globally. This is occurred by the diverse spectrum of viral genotypes, which are directly associated with chronic liver disease (fibrosis, and cirrhosis). Indeed, the viral genome encodes three principal proteins as sequentially core, E1, and E2. Both E1 and E2 proteins play a crucial role in the attachment of the host system, but E2 plays a more fundamental role in attachment. The researchers have found the "E2-CD81 complex" at the entry site, and therefore, CD81 is the key receptor for HCV entrance in both humans, and chimpanzees. So, the researchers are trying to block the host CD81 receptor and halt the virus entry within the cellular system via plant-derived compounds. Perhaps that is why the current research protocol is designed to perform an in silico analysis of the flavonoid compounds for targeting the tetraspanin CD81 receptor of hepatocytes. To find out the best flavonoid compounds from our library, web-based tools (Swiss ADME, pKCSM), as well as computerized tools like the PyRx, PyMOL, BIOVIA Discovery Studio Visualizer, Ligplot+ V2.2, and YASARA were employed. For molecular docking studies, the flavonoid compounds docked with the targeted CD81 protein, and herein, the best-outperformed compounds are Taxifolin, Myricetin, Puerarin, Quercetin, and (-)-Epicatechin, and outstanding binding affinities are sequentially - 7.5, - 7.9, - 8.2, - 8.4, and - 8.5 kcal/mol, respectively. These compounds have possessed more interactions with the targeted protein. To validate the post docking data, we analyzed both 100 ns molecular dynamic simulation, and MM-PBSA via the YASARA simulator, and finally finds the more significant outcomes. It is concluded that in the future, these compounds may become one of the most important alternative antiviral agents in the fight against HCV infection. It is suggested that further in vivo, and in vitro research studies should be done to support the conclusions of this in silico research workflow.

Impact of HCV Infection on Hepatocyte Polarity and Plasticity

The hepatitis C virus (HCV) is an oncogenic virus that alters the cell polarization machinery in order to enter the hepatocyte and replicate. While these alterations are relatively well defined, their consequences in the evolution of the disease remain poorly documented. Since 2012, HCV infection can be effectively cured with the advent of direct acting antivirals (DAA). Nevertheless, patients cured of their HCV infection still have a high risk of developing hepatocellular carcinoma (HCC). Importantly, it has been shown that some of the deregulations induced by HCV are maintained despite a sustained virologic response (SVR), including the down-regulation of some hepatocyte functions such as bile acid metabolism, exemplifying cell dedifferentiation, and the up-regulation of the epithelial–mesenchymal transition (EMT). EMT is a process by which epithelial cells lose their differentiation and their specific polarity to acquire mesenchymal cell properties, including migration and extracellular matrix remodeling capabilities. Of note, epithelial cell polarity acts as a gatekeeper against EMT. Thus, it remains important to elucidate the mechanisms by which HCV alters polarity and promotes EMT that could participate in viral-induced hepatic carcinogenesis. In this review, we define the main steps involved in the polarization process of epithelial cells and recall the essential cellular actors involved. We also highlight the particularities of hepatocyte polarity, responsible for their unique morphology. We then focus on the alterations by HCV of epithelial cell polarity and the consequences of the transformation of hepatocytes involved in the carcinogenesis process.

Induction of Bile Canaliculi-Forming Hepatocytes from Human Pluripotent Stem Cells

Cell polarity and formation of bile canaliculi can be achieved in hepatocytes which are generated from patient-derived induced pluripotent stem cells. This allows for the study of endogenous mutant proteins, patient-specific pathogenesis, and drug responses for diseases where hepatocyte polarity and bile canaliculi play a key role. Here, we describe a step-by-step protocol for the generation of bile canaliculi-forming hepatocytes from induced pluripotent stem cells and their evaluation.

ROLE OF MICRO RNA IN THE REGULATION OF CELL POLARIZATION IN HEPATOCELLULAR CARCINOMA

BACKGROUND

The occurrence of tissue scarring, and architecture-modifying signalling led to a tumorigenic microenvironment. Targeting specifically the biological mediators responsible for the physiological and morphological changes accommodating Hepatocellular carcinoma (HCC) growth may be the key for identifying a future HCC cure.

METHODS

Morphological and physiological features of cultured HepG2 cells in both stimulated recombinant human vascular endothelial growth factor (VEGF165), and unstimulated (control) conditions were assessed. Quantitative RT-PCR measured endogenous VEGF expression levels. The assessment of pro-angiogenic biological mediator (miR-296, miR-31, and miR-17) profiles was achieved by polarization-inducing VEGF165 stimulation followed by quantitative RT-PCR.

RESULTS

In-vitro conditions reproduced successfully the physiological environment leading to the occurrence of HCC, including the successful HepG2 polarization following VEGF stimulation. While endogenous VEGF production only occurs if complete polarization has been reached, the quantified biological mediator profiles determined here pointed at either possible early stages of depolarization or at the lack of tumorigenic potential of the HepG2 cells. All tested micro RNAs (miRs) displayed upregulated profiles, although the miR-296 was less amplified (3.78-fold as compared to control) than miR-31 or miR-17 (6.5- and 6.6-fold, respectively).

CONCLUSIONS

The findings surrounding miR-17 reproduce similar data reported in the literature; the unexpected high miR-31 expression was intriguing. Given HepG2 cells' minimal tumorigenic potential, the unexpected multi-fold upregulation of miR-31 may be a cause or a consequence of HepG2 cells' low tumorigenic potential. The exploration of miR-31 therapeutic potential may be a future rewarding endeavor.

Effect of directly acting anti-viral agents on immunological imprints in chronic HCV-4a patients: interleukin-10 and vascular endothelial growth factor genes expression level

Background

Hepatitis C virus infection is a global health challenge with Egypt being one of the highly affected countries. IL-10 has been suggested as a suitable marker to assess necroinflammation and to monitor the progression of liver damage. Vascular endothelial growth factor (VEGF) is a potent angiogenic factor playing a central role in many physiological as well as pathological processes. Several factors can be predictive of the response to treatment and achievement of SVR; some of which are host-related, and others are virus-related. The gene expression of IL-10 and VEGF have multiple effects for treatment response. The aim of the present work was to study the effect of treatment with directly acting agents (DAA) on the expression of VEGF and IL-10 genes in chronic hepatitis C virus-infected Egyptian genotype-4a patients. Twenty-five HCV subjects where evaluated for IL-10 and VEGF gene expression before and after treatment with DAA.

Results

IL-10 expression was downregulated in 92% of the cases. VEGF expression was heterogeneous showing spreading of values along a wide range with 64% of the cases being downregulated.

Conclusion

DAAs do not completely reverse the immunological imprints established upon chronic HCV infection.

Investigating virus-host cell interactions: Comparative binding forces between hepatitis C virus-like particles and host cell receptors in 2D and 3D cell culture models

Cell cultures have been successfully used to study hepatitis C virus (HCV) for many years. However, most work has been done using traditional, 2-dimensional (2D) cell cultures (cells grown as a monolayer in growth flasks or dishes). Studies have shown that when cells are grown suspended in an extra-cellular-matrix-like material, they develop into spherical, 'organoid' arrangements of cells (3D growth) that display distinct differences in morphological and functional characteristics compared to 2D cell cultures. In liver organoids, one key difference is the development of clearly differentiated apical and basolateral surfaces separated and maintained by cellular tight junctions. This phenomenon, termed polarity, is vital to normal barrier function of hepatocytes in vivo. It has also been shown that viruses, and virus-like particles, interact very differently with cells derived from 2D as compared to 3D cell cultures, bringing into question the usefulness of 2D cell cultures to study virus-host cell interactions. Here, we investigate differences in cellular architecture as a function of cell culture system, using confocal scanning laser microscopy, and determine differences in binding interactions between HCV virus-like particles (VLPs) and their cognate receptors in the different cell culture systems using atomic force microscopy (AFM). We generated organoid cultures that were polarized, as determined by localization of key apical and basolateral markers. We found that, while uptake of HCV VLPs by both 2D and 3D Huh7 cells was observed by flow cytometry, binding interactions between HCV VLPs and cells were measurable by AFM only on polarized cells. The work presented here adds to the growing body of research suggesting that polarized cell systems are more suitable for the study of HCV infection and dynamics than non-polarized systems.

Three-Dimensional Cell Culture Systems for Studying Hepatitis C Virus

Hepatocytes, the major target of hepatitis C virus (HCV), are highly polarized. HCV infection requires extensive trafficking to distinct subcellular domains in the polarized hepatocyte. Polarized cells and three-dimensional organoids are commonly used to study liver functions and differentiation. Researchers have begun adapting these cell culture models that morphologically and physiologically resemble hepatocytes in vivo to study HCV infection. This review summarizes the use of three-dimensional cell culture systems in studies of HCV infection.

Hepatitis B Virus Entry into Cells

Hepatitis B virus (HBV), an enveloped partially double-stranded DNA virus, is a widespread human pathogen responsible for more than 250 million chronic infections worldwide. Current therapeutic strategies cannot eradicate HBV due to the persistence of the viral genome in a special DNA structure (covalently closed circular DNA, cccDNA). The identification of sodium taurocholate co-transporting polypeptide (NTCP) as an entry receptor for both HBV and its satellite virus hepatitis delta virus (HDV) has led to great advances in our understanding of the life cycle of HBV, including the early steps of infection in particular. However, the mechanisms of HBV internalization and the host factors involved in this uptake remain unclear. Improvements in our understanding of HBV entry would facilitate the design of new therapeutic approaches targeting this stage and preventing the de novo infection of naïve hepatocytes. In this review, we provide an overview of current knowledge about the process of HBV internalization into cells.

Hepatocytes Delete Regulatory T Cells by Enclysis, a CD4+ T Cell Engulfment Process

CD4+ T cells play critical roles in directing immunity, both as T helper and as regulatory T (Treg) cells. Here, we demonstrate that hepatocytes can modulate T cell populations through engulfment of live CD4+ lymphocytes. We term this phenomenon enclysis to reflect the specific enclosure of CD4+ T cells in hepatocytes. Enclysis is selective for CD4+ but not CD8+ cells, independent of antigen-specific activation, and occurs in human hepatocytes in vitro, ex vivo, and in vivo. Intercellular adhesion molecule 1 (ICAM-1) facilitates T cell early adhesion and internalization, whereas hepatocytes form membrane lamellipodia or blebs to mediate engulfment. T cell internalization is unaffected by wortmannin and Rho kinase inhibition. Hepatocytes engulf Treg cells more efficiently than non-Treg cells, but Treg cell-containing vesicles preferentially acidify overnight. Thus, enclysis is a biological process with potential effects on immunomodulation and opens a new field for research to fully understand CD4+ T cell dynamics in liver inflammation.

A CRISPR Screen Identifies the Cell Polarity Determinant Crumbs 3 as an Adeno-associated Virus Restriction Factor in Hepatocytes

Adeno-associated viruses (AAV) are helper-dependent parvoviruses that have been developed into promising gene therapy vectors. Many studies, including a recent unbiased genomic screen, have identified host factors essential for AAV cell entry, but no genome-wide screens that address inhibitory host factors have been reported. Here, we utilize a novel CRISPR screen to identify AAV restriction factors in a human hepatocyte cell line. The major hit from our gain-of-function screen is the apical polarity determinant Crumbs 3 (Crb3). Knockout (KO) of Crb3 enhances AAV transduction, while overexpression exerts the opposite effect. Further, Crb3 appears to restrict AAV transduction in a serotype- and cell type-specific manner. Particularly, for AAV serotype 9 and a rationally engineered AAV variant, we demonstrate that increased availability of galactosylated glycans on the surfaces of Crb3 KO cells, but not the universal AAV receptor, leads to increased capsid attachment and enhanced transduction. We postulate that Crb3 could serve as a key molecular determinant that restricts the availability of AAV glycan attachment factors on the cell surface by maintaining apical-basal polarity and tight junction integrity.IMPORTANCE Adeno-associated viruses (AAVs) have recently emerged at the forefront as gene therapy vectors; however, our understanding of host factors that influence AAV transduction in different cell types is still evolving. In the present study, we perform a genome-scale CRISPR knockout screen to identify cellular host factors that restrict AAV infection in hepatocyte cultures. We discover that Crumbs 3, which determines cellular polarity, also influences the distribution of certain carbohydrate attachment factors on the cell surface. This in turn affects the ability of virions to bind and enter the cells. This study underscores the importance of cell polarity in AAV transduction and provides a potential molecular basis for the differential infectious mechanism(s) in cell culture versus organ systems.

Role of the cytosolic domain of occludin in trafficking and hepatitis C virus infection

The role of the tight-junction (TJ) protein occludin (OCLN) in hepatitis C virus (HCV) entry remains elusive. Here, we investigated the OCLN C-terminal cytosolic domain in HCV infection. We expressed a series of C-terminal deletion mutants in Huh-7 cells KO for OCLN and characterized their functionality in HCV infection and trafficking. Deleting the OCLN cytosolic domain led to protein instability and intracellular retention. The first 15 residues (OCLN-C15 mutant) of the cytosolic domain were sufficient for OCLN stability, but led to its accumulation in the trans-Golgi network (TGN) due to a deficient cell surface export after synthesis. In contrast, the OCLN-C18 mutant, containing the first 18 residues of the cytosolic domain, was expressed at the cell surface and could mediate HCV infection. Point mutations in the context of C18 showed that I279 and W281 are crucial residues for cell surface expression of OCLN-C18. However, in the context of full-length OCLN, mutation of these residues only partially affected infection and cell surface localization. Importantly, the characterization of OCLN-C18 in human-polarized hepatocytes revealed a defect in its TJ localization without affecting HCV infection. These data suggest that TJ localization of OCLN is not a prerequisite for HCV infection in polarized hepatocytes.

Bacterial flagellin promotes viral entry via an NF-kB and Toll Like Receptor 5 dependent pathway

Viruses and bacteria colonize hosts by invading epithelial barriers. Recent studies have shown that interactions between the microbiota, pathogens and the host can potentiate infection through poorly understood mechanisms. Here, we investigated whether diverse bacterial species could modulate virus internalization into host cells, often a rate-limiting step in establishing infections. Lentiviral pseudoviruses expressing influenza, measles, Ebola, Lassa or vesicular stomatitis virus envelope glycoproteins enabled us to study entry of viruses that exploit diverse internalization pathways. Salmonella Typhimurium, Escherichia coli and Pseudomonas aeruginosa significantly increased viral uptake, even at low bacterial frequencies. This did not require bacterial contact with or invasion of host cells. Studies determined that the bacterial antigen responsible for this pro-viral activity was the Toll-Like Receptor 5 (TLR5) agonist flagellin. Exposure to flagellin increased virus attachment to epithelial cells in a temperature-dependent manner via TLR5-dependent activation of NF-ΚB. Importantly, this phenotype was both long lasting and detectable at low multiplicities of infection. Flagellin is shed from bacteria and our studies uncover a new bystander role for this protein in regulating virus entry. This highlights a new aspect of viral-bacterial interplay with significant implications for our understanding of polymicrobial-associated pathogenesis.

Tight junction proteins in gastrointestinal and liver disease

Over the past two decades a growing body of evidence has demonstrated an important role of tight junction (TJ) proteins in the physiology and disease biology of GI and liver disease. On one side, TJ proteins exert their functional role as integral proteins of TJs in forming barriers in the gut and the liver. Furthermore, TJ proteins can also be expressed outside TJs where they play important functional roles in signalling, trafficking and regulation of gene expression. A hallmark of TJ proteins in disease biology is their functional role in epithelial-to-mesenchymal transition. A causative role of TJ proteins has been established in the pathogenesis of colorectal cancer and gastric cancer. Among the best characterised roles of TJ proteins in liver disease biology is their function as cell entry receptors for HCV-one of the most common causes of hepatocellular carcinoma. At the same time TJ proteins are emerging as targets for novel therapeutic approaches for GI and liver disease. Here we review our current knowledge of the role of TJ proteins in the pathogenesis of GI and liver disease biology and discuss their potential as therapeutic targets.

Single Particle Imaging of Polarized Hepatoma Organoids upon Hepatitis C Virus Infection Reveals an Ordered and Sequential Entry Process

Hepatitis C virus (HCV) enters hepatocytes via various entry factors, including scavenger receptor BI (SR-B1), cluster of differentiation 81 (CD81), epidermal growth factor receptor (EGFR), claudin-1 (CLDN1), and occludin (OCLN). As CLDN1 and OCLN are not readily accessible due to their tight junctional localization, HCV likely accesses them by either disrupting cellular polarity or migrating to the tight junction. In this study, we image HCV entry into a three-dimensional polarized hepatoma system and reveal that the virus sequentially engages these entry factors through actin-dependent mechanisms. HCV initially localizes with the early entry factors SR-B1, CD81, and EGFR at the basolateral membrane and then accumulates at the tight junction in an actin-dependent manner. HCV associates with CLDN1 and then OCLN at the tight junction and is internalized via clathrin-mediated endocytosis by an active process requiring EGFR. Thus, HCV uses a dynamic and multi-step process to engage and enter host cells.

Human iPS derived progenitors bioengineered into liver organoids using an inverted colloidal crystal poly (ethylene glycol) scaffold

Generation of human organoids from induced pluripotent stem cells (iPSCs) offers exciting possibilities for developmental biology, disease modelling and cell therapy. Significant advances towards those goals have been hampered by dependence on animal derived matrices (e.g. Matrigel), immortalized cell lines and resultant structures that are difficult to control or scale. To address these challenges, we aimed to develop a fully defined liver organoid platform using inverted colloid crystal (ICC) whose 3-dimensional mechanical properties could be engineered to recapitulate the extracellular niche sensed by hepatic progenitors during human development. iPSC derived hepatic progenitors (IH) formed organoids most optimally in ICC scaffolds constructed with 140 μm diameter pores coated with type I collagen in a two-step process mimicking liver bud formation. The resultant organoids were closer to adult tissue, compared to 2D and 3D controls, with respect to morphology, gene expression, protein secretion, drug metabolism and viral infection and could integrate, vascularise and function following implantation into livers of immune-deficient mice. Preliminary interrogation of the underpinning mechanisms highlighted the importance of TGFβ and hedgehog signalling pathways. The combination of functional relevance with tuneable mechanical properties leads us to propose this bioengineered platform to be ideally suited for a range of future mechanistic and clinical organoid related applications.

Hypoxia inducible factors in hepatocellular carcinoma

Hepatocellular carcinoma is one of the most prevalent and lethal cancers with limited therapeutic options. Pathogenesis of this disease involves tumor hypoxia and the activation of hypoxia inducible factors. In this review, we describe the current understanding of hypoxia signaling pathway and summarize the expression, function and target genes of hypoxia inducible factors in hepatocellular carcinoma. We also highlight the recent progress in hypoxia-targeted therapeutic strategies in hepatocellular carcinoma and discuss further the future efforts for the study of hypoxia and/or hypoxia inducible factors in this deadly disease.

Humanisation of a claudin-1-specific monoclonal antibody for clinical prevention and cure of HCV infection without escape

OBJECTIVE

HCV infection is a leading cause of chronic liver disease and a major indication for liver transplantation. Although direct-acting antivirals (DAAs) have much improved the treatment of chronic HCV infection, alternative strategies are needed for patients with treatment failure. As an essential HCV entry factor, the tight junction protein claudin-1 (CLDN1) is a promising antiviral target. However, genotype-dependent escape via CLDN6 and CLDN9 has been described in some cell lines as a possible limitation facing CLDN1-targeted therapies. Here, we evaluated the clinical potential of therapeutic strategies targeting CLDN1.

DESIGN

We generated a humanised anti-CLDN1 monoclonal antibody (mAb) (H3L3) suitable for clinical development and characterised its anti-HCV activity using cell culture models, a large panel of primary human hepatocytes (PHH) from 12 different donors, and human liver chimeric mice.

RESULTS

H3L3 pan-genotypically inhibited HCV pseudoparticle entry into PHH, irrespective of donor. Escape was likely precluded by low surface expression of CLDN6 and CLDN9 on PHH. Co-treatment of a panel of PHH with a CLDN6-specific mAb did not enhance the antiviral effect of H3L3, confirming that CLDN6 does not function as an entry factor in PHH from multiple donors. H3L3 also inhibited DAA-resistant strains of HCV and synergised with current DAAs. Finally, H3L3 cured persistent HCV infection in human-liver chimeric uPA-SCID mice in monotherapy.

CONCLUSIONS

Overall, these findings underscore the clinical potential of CLDN1-targeted therapies and describe the functional characterisation of a humanised anti-CLDN1 antibody suitable for further clinical development to complement existing therapeutic strategies for HCV.

Disruption of Claudin-1 Expression by miRNA-182 Alters the Susceptibility to Viral Infectivity in HCV Cell Models

HCV entry involves a complex interplay between viral and host molecules. During post-binding interactions, the viral E2 complexes with CD81 receptor for delivery to the tight junction proteins CLDN1 and OCLN, which aid in viral internalization. Targeting HCV entry receptors represents an appealing approach to inhibit viral infectivity. This study aimed at investigating the impact of targeting CLDN1 by microRNAs on HCV infectivity. miR-155 was previously shown to target the 3′UTR of CLDN1 mRNA. Therefore, miR-155 was used as a control in this study. In-silico analysis and luciferase reporter assay were utilized to identify potential targeting miRNAs. The impact of the identified miRNAs on CLDN1 mRNA and protein expression was examined by qRT-PCR, indirect immunofluorescence and western blotting, respectively. The role of the selected miRNAs on HCV infectivity was assessed by measuring the viral load following the ectopic expression of the selected miRNAs. miR-182 was identified in-silico and by experimental validation to target CLDN1. Both miR-155 and miR-182 inhibited CLDN1 mRNA and protein expression in infected Huh7 cells. Ectopic expression of miR-155 increased, while miR-182 reduced the viral load. In conclusion, despite repressing CLDN1, the impact of miR-155 and miR-182 on HCV infectivity is contradictory. Ectopic miR-182 expression is suggested as an upstream regulator of the entry factor CLDN1, harnessing HCV infection.

Productive HBV infection of well-differentiated, hNTCP-expressing human hepatoma-derived (Huh7) cells

Feasible and effective cell models for hepatitis B virus (HBV) infection are required for investigating the complete lifecycle of this virus, including the early steps of viral entry. Resistance to dimethyl sulfoxide/polyethylene glycol (DMSO/PEG), hNTCP expression, and a differentiated state are the limiting factors for successful HBV infection models. In the present study, we used a hepatoma cell line (Huh7D^hNTCP) to overcome these limiting factors so that it exhibits excellent susceptibility to HBV infection. To achieve this goal, different hepatoma cell lines were tested with 2.5% DMSO / 4% PEG8000, and one resistant cell line (Huh7D) was used to construct a stable hNTCP-expressing cell line (Huh7D^hNTCP) using a recombinant lentivirus system. Then, the morphological characteristics and differentiation molecular markers of Huh7D^hNTCP cells with or without DMSO treatment were characterized. Finally, the susceptibility of Huh7D^hNTCP cells to HBV infection was assessed. Our results showed that Huh7D cells were resistant to 2.5% DMSO / 4% PEG8000, whereas the others were not. Huh7D^hNTCP cells were established to express a high level of hNTCP compared to liver extracts, and Huh7D^hNTCP cells rapidly transformed into a non-dividing, well-differentiated polarized phenotype under DMSO treatment. Huh7D^hNTCP cells fully supported the entire lifecycle of HBV infection. This cell culture system will be useful for the analysis of host-virus interactions, which should facilitate the discovery of antiviral drugs and vaccines.

Entry and Release of Hepatitis C Virus in Polarized Human Hepatocytes

Hepatitis C virus (HCV) primarily infects hepatocytes, which are highly polarized cells. The relevance of cell polarity in the HCV life cycle has been addressed only in distantly related models and remains poorly understood. Although polarized epithelial cells have a rather simple morphology with a basolateral and an apical domain, hepatocytes exhibit complex polarization structures. However, it has been reported that some selected polarized HepG2 cell clones can exhibit a honeycomb pattern of distribution of the tight-junction proteins typical of columnar polarized epithelia, which can be used as a simple model to study the role of cell polarization in viral infection of hepatocytes. To obtain similar clones, HepG2 cells expressing CD81 (HepG2-CD81) were used, and clones were isolated by limiting dilutions. Two clones exhibiting a simple columnar polarization capacity when grown on a semipermeable support were isolated and characterized. To test the polarity of HCV entry and release, our polarized HepG2-CD81 clones were infected with cell culture-derived HCV. Our data indicate that HCV binds equally to both sides of the cells, but productive infection occurs mainly when the virus is added at the basolateral domain. Furthermore, we also observed that HCV virions are released from the basolateral domain of the cells. Finally, when polarized cells were treated with oleic acid and U0126, a MEK inhibitor, to promote lipoprotein secretion, a higher proportion of infectious viral particles of lower density were secreted. This cell culture system provides an excellent model to investigate the influence of cell polarization on the HCV life cycle.IMPORTANCE Hepatitis C is a major health burden, with approximately 170 million persons infected worldwide. Hepatitis C virus (HCV) primarily infects hepatocytes, which are highly polarized cells with a complex organization. The relevance of cell polarity in the HCV life cycle has been addressed in distantly related models and remains unclear. Hepatocyte organization is complex, with multiple apical and basolateral surfaces. A simple culture model of HepG2 cells expressing CD81 that are able to polarize with unique apical and basolateral domains was developed to study HCV infection. With this model, we demonstrated that HCV enters and exits hepatocytes by the basolateral domain. Furthermore, lower-density viral particles were produced under conditions that promote lipoprotein secretion. This cell culture system provides a useful model to study the influence of cell polarization on HCV infection.

Regulated Entry of Hepatitis C Virus into Hepatocytes

Hepatitis C virus (HCV) is a model for the study of virus–host interaction and host cell responses to infection. Virus entry into hepatocytes is the first step in the HCV life cycle, and this process requires multiple receptors working together. The scavenger receptor class B type I (SR-BI) and claudin-1 (CLDN1), together with human cluster of differentiation (CD) 81 and occludin (OCLN), constitute the minimal set of HCV entry receptors. Nevertheless, HCV entry is a complex process involving multiple host signaling pathways that form a systematic regulatory network; this network is centrally controlled by upstream regulators epidermal growth factor receptor (EGFR) and transforming growth factor β receptor (TGFβ-R). Further feedback regulation and cell-to-cell spread of the virus contribute to the chronic maintenance of HCV infection. A comprehensive and accurate disclosure of this critical process should provide insights into the viral entry mechanism, and offer new strategies for treatment regimens and targets for HCV therapeutics.

TNF superfamily members promote hepatitis C virus entry via an NF-κB and myosin light chain kinase dependent pathway

Preventing virally induced liver disease begins with an understanding of the host factors that define susceptibility to infection. Hepatitis C virus (HCV) is a global health issue, with an estimated 170 million infected individuals at risk of developing liver disease including fibrosis and hepatocellular carcinoma. The liver is the major reservoir supporting HCV replication and this hepatocellular tropism is defined by HCV engagement of cellular entry receptors. Hepatocytes are polarized in vivo and this barrier function limits HCV entry. We previously reported that activated macrophages promote HCV entry into polarized hepatocytes via a TNF-α-dependent process; however, the underlying mechanism was not defined. In this study, we show that several TNF superfamily members, including TNF-α, TNF-β, TWEAK and LIGHT, promote HCV entry via NF-κB-mediated activation of myosin light chain kinase (MLCK) and disruption of tight junctions. These observations support a model where HCV hijacks an inflammatory immune response to stimulate infection and uncovers a role for NF-κB-MLCK signalling in maintaining hepatocellular tight junctions.

Low-dose acetaminophen induces early disruption of cell-cell tight junctions in human hepatic cells and mouse liver

Dysfunction of cell-cell tight junction (TJ) adhesions is a major feature in the pathogenesis of various diseases. Liver TJs preserve cellular polarity by delimiting functional bile-canalicular structures, forming the blood-biliary barrier. In acetaminophen-hepatotoxicity, the mechanism by which tissue cohesion and polarity are affected remains unclear. Here, we demonstrate that acetaminophen, even at low-dose, disrupts the integrity of TJ and cell-matrix adhesions, with indicators of cellular stress with liver injury in the human hepatic HepaRG cell line, and primary hepatocytes. In mouse liver, at human-equivalence (therapeutic) doses, dose-dependent loss of intercellular hepatic TJ-associated ZO-1 protein expression was evident with progressive clinical signs of liver injury. Temporal, dose-dependent and specific disruption of the TJ-associated ZO-1 and cytoskeletal-F-actin proteins, correlated with modulation of hepatic ultrastructure. Real-time impedance biosensing verified in vitro early, dose-dependent quantitative decreases in TJ and cell-substrate adhesions. Whereas treatment with NAPQI, the reactive metabolite of acetaminophen, or the PKCα-activator and TJ-disruptor phorbol-12-myristate-13-acetate, similarly reduced TJ integrity, which may implicate oxidative stress and the PKC pathway in TJ destabilization. These findings are relevant to the clinical presentation of acetaminophen-hepatotoxicity and may inform future mechanistic studies to identify specific molecular targets and pathways that may be altered in acetaminophen-induced hepatic depolarization.

PI3K/SHIP2/PTEN pathway in cell polarity and hepatitis C virus pathogenesis

Hepatitis C virus (HCV) infects hepatocytes, polarized cells in the liver. Chronic HCV infection often leads to steatosis, fibrosis, cirrhosis and hepatocellular carcinoma, and it has been identified as the leading cause of liver transplantation worldwide. The HCV replication cycle is dependent on lipid metabolism and particularly an accumulation of lipid droplets in host cells. Phosphoinositides (PIs) are minor phospholipids enriched in different membranes and their levels are tightly regulated by specific PI kinases and phosphatases. PIs are implicated in a vast array of cellular responses that are central to morphogenesis, such as cytoskeletal changes, cytokinesis and the recruitment of downstream effectors to govern mechanisms involved in polarization and lumen formation. Important reviews of the literature identified phosphatidylinositol (PtdIns) 4-kinases, and their lipid products PtdIns(4)P, as critical regulators of the HCV life cycle. SH2-containing inositol polyphosphate 5-phosphatase (SHIP2), phosphoinositide 3-kinase (PI3K) and their lipid products PtdIns(3,4)P2 and PtdIns(3,4,5)P3, respectively, play an important role in the cell membrane and are key to the establishment of apicobasal polarity and lumen formation. In this review, we will focus on these new functions of PI3K and SHIP2, and their deregulation by HCV, causing a disruption of apicobasal polarity, actin organization and extracellular matrix assembly. Finally we will highlight the involvement of this pathway in the event of insulin resistance and nonalcoholic fatty liver disease related to HCV infection.

Study of Ethanol-Induced Golgi Disorganization Reveals the Potential Mechanism of Alcohol-Impaired N-Glycosylation

BACKGROUND

It is known that ethanol (EtOH) and its metabolites have a negative effect on protein glycosylation. The fragmentation of the Golgi apparatus induced by alteration of the structure of largest Golgi matrix protein, giantin, is the major consequence of damaging effects of EtOH-metabolism on the Golgi; however, the link between this and abnormal glycosylation remains unknown. Because previously we have shown that Golgi morphology dictates glycosylation, we examined the effect EtOH administration has on function of Golgi residential enzymes involved in N-glycosylation.

METHODS

HepG2 cells transfected with mouse ADH1 (VA-13 cells) were treated with 35 mM EtOH for 72 hours. Male Wistar rats were pair-fed Lieber-DeCarli diets for 5 to 8 weeks. Characterization of Golgi-associated mannosyl (α-1,3-)-glycoprotein beta-1,2-N-acetylglucosaminyltransferase (MGAT1), α-1,2-mannosidase (Man-I), and α-mannosidase II (Man-II) were performed in VA-13 cells and rat hepatocytes followed by three-dimensional structured illumination microscopy (3D SIM).

RESULTS

First, we detected that EtOH administration results in the loss of sialylated N-glycans on asialoglycoprotein receptor; however, the high-mannose-type N-glycans are increased. Further analysis by 3D SIM revealed that EtOH treatment despite Golgi disorganization does not change cis-Golgi localization for Man-I, but does induce medial-to-cis relocation of MGAT1 and Man-II. Using different approaches, including electron microscopy, we revealed that EtOH treatment results in dysfunction of ADP-ribosylation factor 1 (Arf1) GTPase followed by a deficiency in COPI vesicles at the Golgi. Silencing beta-COP or expression of GDP-bound mutant Arf1(T31N) mimics the EtOH effect on retaining MGAT1 and Man-II at the cis-Golgi, suggesting that (i) EtOH specifically blocks activation of Arf1, and (ii) EtOH alters the proper localization of Golgi enzymes through impairment of COPI. Importantly, the level of MGAT1 was reduced, because likely MGAT1, contrary to Man-I and Man-II, is giantin sensitive.

CONCLUSIONS

Thus, we provide the mechanism by which EtOH-induced Golgi remodeling may significantly modify formation of N-glycans.

Hypoxia-inducible factors as molecular targets for liver diseases

Liver disease is a growing global health problem, as deaths from end-stage liver cirrhosis and cancer are rising across the world. At present, pharmacologic approaches to effectively treat or prevent liver disease are extremely limited. Hypoxia-inducible factor (HIF) is a transcription factor that regulates diverse signaling pathways enabling adaptive cellular responses to perturbations of the tissue microenvironment. HIF activation through hypoxia-dependent and hypoxia-independent signals have been reported in liver disease of diverse etiologies, from ischemia-reperfusion-induced acute liver injury to chronic liver diseases caused by viral infection, excessive alcohol consumption, or metabolic disorders. This review summarizes the evidence for HIF stabilization in liver disease, discusses the mechanistic involvement of HIFs in disease development, and explores the potential of pharmacological HIF modifiers in the treatment of liver disease.

Chimeric antigen receptor (CAR)-engineered T cells redirected against hepatitis C virus (HCV) E2 glycoprotein

OBJECTIVE

The recent availability of novel antiviral drugs has raised new hope for a more effective treatment of hepatitis C virus (HCV) infection and its severe sequelae. However, in the case of non-responding or relapsing patients, alternative strategies are needed. To this end we have used chimeric antigen receptors (CARs), a very promising approach recently used in several clinical trials to redirect primary human T cells against different tumours. In particular, we designed the first CARs against HCV targeting the HCV/E2 glycoprotein (HCV/E2).

DESIGN

Anti-HCV/E2 CARs were composed of single-chain variable fragments (scFvs) obtained from a broadly cross-reactive and cross-neutralising human monoclonal antibody (mAb), e137, fused to the intracellular signalling motif of the costimulatory CD28 molecule and the CD3ζ domain. Activity of CAR-grafted T cells was evaluated in vitro against HCV/E2-transfected cells as well as hepatocytes infected with cell culture-derived HCV (HCVcc).

RESULTS

In this proof-of-concept study, retrovirus-transduced human T cells expressing anti-HCV/E2 CARs were endowed with specific antigen recognition accompanied by degranulation and secretion of proinflammatory and antiviral cytokines, such as interferon γ, interleukin 2 and tumour necrosis factor α. Moreover, CAR-grafted T cells were capable of lysing target cells of both hepatic and non-hepatic origin expressing on their surface the HCV/E2 glycoproteins of the most clinically relevant genotypes, including 1a, 1b, 2a, 3a, 4 and 5. Finally, and more importantly, they were capable of lysing HCVcc-infected hepatocytes.

CONCLUSIONS

Clearance of HCV-infected cells is a major therapeutic goal in chronic HCV infection, and adoptive transfer of anti-HCV/E2 CARs-grafted T cells represents a promising new therapeutic tool.

A New Signaling Pathway for HCV Inhibition by Estrogen: GPR30 Activation Leads to Cleavage of Occludin by MMP-9

Poor outcome in response to hepatitis C virus, including higher viral load, hepatocellular carcinoma and cirrhosis, is more associated with men and postmenopausal women than with premenopausal women and women receiving hormone replacement therapy, suggesting that β-estradiol plays an innate role in preventing viral infection and liver disease. Consequently, most research in the field has concluded that estrogen affects HCV replication through viral interactions with estrogen receptor-α. Previously, estrogen-like antagonists, including Tamoxifen, were shown to reduce HCV RNA production and prevent viral entry, although the authors did not identify host factors involved. Estrogen can act alternatively through the membrane-bound G-protein-coupled estrogen receptor, GPR30. Here, human hepatoma Huh7.5 cells were infected with HCV J6/JFH-1 and treated with estrogen or Tamoxifen, resulting in a marked decrease in detectable virus. The effect was mimicked by G1, a GPR30-specific agonist, and was reversed by the GPR30-specific antagonist, G15. While previous studies have demonstrated that estrogen down-regulated occludin in cervical cancer cells, its action on liver cells was unknown. Occludin is a tight junction protein and HCV receptor and here we report that activation and cellular export of MMP-9 led to the cleavage of occludin upon estrogen treatment of liver cells. This is the first report of the cleavage of an HCV receptor in response to estrogen. We also identify the occludin cleavage site in extracellular Domain D; the motif required for HCV entry and spread. This pathway gives new insight into a novel innate antiviral pathway and the suboptimal environment that estrogen provides for the proliferation of the virus. It may also explain the disparate host-virus responses to HCV demonstrated by the two sexes. Moreover, these data suggest that hormone replacement therapy may have beneficial antiviral enhancement properties for HCV-infected postmenopausal women and show promise for new antiviral treatments for both men and women.

Claudin-6 and Occludin Natural Variants Found in a Patient Highly Exposed but Not Infected with Hepatitis C Virus (HCV) Do Not Confer HCV Resistance In Vitro

The clinical course of Hepatitis C Virus (HCV) infection is highly variable between infected individual hosts: up to 80% of acutely HCV infected patients develop a chronic infection while 20% clear infection spontaneously. Spontaneous clearance of HCV infection can be predicted by several factors, including symptomatic acute infection, favorable IFNL3 polymorphisms and gender. In our study, we explored the possibility that variants in HCV cell entry factors might be involved in resistance to HCV infection. In a same case patient highly exposed but not infected by HCV, we previously identified one mutation in claudin-6 (CLDN6) and a rare variant in occludin (OCLN), two tight junction proteins involved in HCV entry into hepatocytes. Here, we conducted an extensive functional study to characterize the ability of these two natural variants to prevent HCV entry. We used lentiviral vectors to express Wildtype or mutated CLDN6 and OCLN in different cell lines and primary human hepatocytes. HCV infection was then investigated using cell culture produced HCV particles (HCVcc) as well as HCV pseudoparticles (HCVpp) expressing envelope proteins from different genotypes. Our results show that variants of CLDN6 and OCLN expressed separately or in combination did not affect HCV infection nor cell-to-cell transmission. Hence, our study highlights the complexity of HCV resistance mechanisms supporting the fact that this process probably not primarily involves HCV entry factors and that other unknown host factors may be implicated.

Roles of lipoprotein receptors in the entry of hepatitis C virus

Infection by hepatitis C virus (HCV), a plus-stranded RNA virus that can cause cirrhosis and hepatocellular carcinoma, is one of the major health problems in the world. HCV infection is considered as a multi-step complex process and correlated with abnormal metabolism of lipoprotein. In addition, virus attacks hepatocytes by the initial attaching viral envelop glycoprotein E1/E2 to receptors of lipoproteins on host cells. With the development of HCV model system, mechanisms of HCV cell entry through lipoprotein uptake and its receptor have been extensively studied in detail. Here we summarize recent knowledge about the role of lipoprotein receptors, scavenger receptor class B type I and low-density lipoprotein receptor in the entry of HCV, providing a foundation of novel targeting therapeutic tools against HCV infection.

Advances in experimental systems to study hepatitis C virus in vitro and in vivo

Hepatitis C virus (HCV) represents a global health concern affecting over 185 million people worldwide. Chronic HCV infection causes liver fibrosis and cirrhosis and is the leading indication for liver transplantation. Recent advances in the field of direct-acting antiviral drugs (DAAs) promise a cure for HCV in over 90% of cases that will get access to these expensive treatments. Nevertheless, the lack of a protective vaccine and likely emergence of drug-resistant viral variants call for further studies of HCV biology. With chimpanzees being for a long time the only non-human in vivo model of HCV infection, strong efforts were put into establishing in vitro experimental systems. The initial models only enabled to study specific aspects of the HCV life cycle, such as viral replication with the subgenomic replicon and entry using HCV pseudotyped particles (HCVpp). Subsequent development of protocols to grow infectious HCV particles in cell-culture (HCVcc) ignited investigations on the full cycle of HCV infection and the virus-host interactions required for virus propagation. More recently, small animal models permissive to HCV were generated that allowed in vivo testing of novel antiviral therapies as well as vaccine candidates. This review provides an overview of the currently available in vitro and in vivo experimental systems to study HCV biology. Particular emphasis is given to how these model systems furthered our understanding of virus-host interactions, viral pathogenesis and immunological responses to HCV infection, as well as drug and vaccine development.

The missing pieces of the HCV entry puzzle

The past decade has witnessed steady and rapid progress in HCV research, which has led to the recent breakthrough in therapies against this significant human pathogen. Yet a deeper understanding of the life cycle of the virus is required to develop more affordable treatments and to advance vaccine design. HCV entry presents both a challenge for scientific research and an opportunity for alternative intervention approaches, owning to its highly complex nature and the myriad of players involved. More than half a dozen cellular proteins are implicated in HCV entry; and a more definitive picture regarding the structures of the glycoproteins is emerging. A role of apolipoproteins in HCV entry has also been established. Still, major questions remain, and the answers to these, which we summarize in this review, will hopefully close the gaps in our understanding and complete the puzzle that is HCV entry.

The mechanism of HCV entry into host cells

Hepatitis C virus (HCV) is an enveloped, positive strand RNA virus classified within the Flaviviridae family and is a major cause of liver disease worldwide. HCV life cycle and propagation are tightly linked to several aspects of lipid metabolism. HCV propagation depends on and also shapes several aspects of lipid metabolism such as cholesterol uptake and efflux through different lipoprotein receptors during its entry into cells, lipid metabolism modulating HCV genome replication, lipid droplets acting as a platform for recruitment of viral components, and very low density lipoprotein assembly pathway resulting in incorporation of neutral lipids and apolipoproteins into viral particles. During the first steps of infection, HCV enters hepatocytes through a multistep and slow process. The initial capture of HCV particles by glycosaminoglycans and/or lipoprotein receptors is followed by coordinated interactions with the scavenger receptor class B type I, a major receptor of high-density lipoprotein, the CD81 tetraspanin, and the tight junction proteins Claudin-1 and Occludin. This tight concert of receptor interactions ultimately leads to uptake and cellular internalization of HCV through a process of clathrin-dependent endocytosis. Over the years, the identification of the HCV entry receptors and cofactors has led to a better understanding of HCV entry and of the narrow tropism of HCV for the liver. Yet, the role of the two HCV envelope glycoproteins, E1 and E2, remains ill-defined, particularly concerning their involvement in the membrane fusion process. Here, we review the current knowledge and advances addressing the mechanism of HCV cell entry within hepatocytes and we highlight the challenges that remain to be addressed.

[Claudin 1 as a target for anti-hepatitis C virus strategy]

Chronic hepatitis C virus (HCV) infection is a global public health issue because ～30% of HCV-carriers develop severe liver diseases including hepatic steatosis, cirrhosis, and hepatocellular carcinoma. Not only viral factors but also host/viral interactions are promising targets for antiviral preventive and therapeutic strategies. Recent studies showed that a tight junction protein claudin 1 is involved in HCV entry into host cells. Consistent with these studies, we isolated the several hepatic Huh7-derived cell clones defective in claudin 1 as HCV-resistant mutants, and cellular permissiveness to HCV was restored by expression of claudin 1 into these cell mutants. These results strongly suggest that claudin 1 is a promising target for antiviral therapy. We thus tried to isolate antibodies against extracellular domain of human claudin 1. Finally we established four mouse anti-claudin 1 monoclonal antibodies by using DNA immunization method and hybridoma screening with the above claudin 1-defective mutant. In the cell culture-infection system using Huh7.5.1 cells and HCV-JFH1 strain, these four antibodies efficiently inhibited infection by HCV in a dose-dependent manner, but do not affect tight junction localization of claudin 1 and cellular barrier function. These monoclonal antibodies targeting claudin 1 might be useful for preventing HCV infection, such as after liver transplantation, and also blocking viral spread in HCV-infected patients.

Hypoxia inducible factors in liver disease and hepatocellular carcinoma: current understanding and future directions

Hypoxia inducible transcription factors (HIFs) activate diverse pathways that regulate cellular metabolism, angiogenesis, proliferation, and migration, enabling a cell to respond to a low oxygen or hypoxic environment. HIFs are regulated by oxygen-dependent and independent signals including: mitochondrial dysfunction, reactive oxygen species, endoplasmic reticular stress, and viral infection. HIFs have been reported to play a role in the pathogenesis of liver disease of diverse aetiologies. This review explores the impact of HIFs on hepatocellular biology and inflammatory responses, highlighting the therapeutic potential of targeting HIFs for an array of liver pathologies.

Virology and cell biology of the hepatitis C virus life cycle: an update

Hepatitis C virus (HCV) is an important human pathogen that causes hepatitis, liver cirrhosis and hepatocellular carcinoma. It imposes a serious problem to public health in the world as the population of chronically infected HCV patients who are at risk of progressive liver disease is projected to increase significantly in the next decades. However, the arrival of new antiviral molecules is progressively changing the landscape of hepatitis C treatment. The search for new anti-HCV therapies has also been a driving force to better understand how HCV interacts with its host, and major progresses have been made on the various steps of the HCV life cycle. Here, we review the most recent advances in the fast growing knowledge on HCV life cycle and interaction with host factors and pathways.

Design of novel rho kinase inhibitors using energy based pharmacophore modeling, shape-based screening, in silico virtual screening, and biological evaluation

Rho-associated protein kinase (ROCK) plays a key role in regulating a variety of cellular processes, and dysregulation of ROCK signaling or expression is implicated in numerous diseases and infections. ROCK proteins have therefore emerged as validated targets for therapeutic intervention in various pathophysiological conditions such as diabetes-related complications or hepatitis C-associated pathogenesis. In this study, we report on the design and identification of novel ROCK inhibitors utilizing energy based pharmacophores and shape-based approaches. The most potent compound 8 exhibited an IC50 value of 1.5 μM against ROCK kinase activity and inhibited methymercury-induced neurotoxicity of IMR-32 cells at GI50 value of 0.27 μM. Notably, differential scanning fluorometric analysis revealed that ROCK protein complexed with compound 8 with enhanced stability relative to Fasudil, a validated nanomolar range ROCK inhibitor. Furthermore, all compounds exhibited ≥96 μM CC50 (50% cytotoxicity) in Huh7 hepatoma cells, while 6 compounds displayed anti-HCV activity in HCV replicon cells. The identified lead thus constitutes a prototypical molecule for further optimization and development as anti-ROCK inhibitor.

In vitro infection of primary human hepatocytes by HCV-positive sera: insights on a highly relevant model

OBJECTIVE

Adult primary human hepatocytes (PHHs) support the complete infection cycle of natural HCV from patients' sera. The molecular details underlying sera infectivity towards these cells remain largely unknown. Therefore, we sought to gain a deeper comprehension of these features in the most physiologically relevant culture system.

DESIGN

Using kinetic experiments, we defined the optimal conditions to infect PHH and explored the link between cell organisation and permissivity. Based on their infectivity, about 120 sera were classified in three groups. Concentration of 52 analytes was measured in 79 selected sera using multiplexed immunobead-based analyte profiling.

RESULTS

PHH permissivity towards HCV infection negatively correlated with cell polarisation and formation of functional bile canaliculi. PHH supported HCV replication for at least 2 weeks with de novo virus production. Depending on their reactivity, sera could be classified in three groups of high, intermediate or low infectivity toward PHH. Infectivity could not be predicted based on the donors' clinical characteristics, viral load or genotype. Interestingly, highly infectious sera displayed a specific cytokine profile with low levels of most of the 52 tested analytes. Among them, 24 cytokines/growth factors could impact hepatocyte biology and infection efficiency.

CONCLUSIONS

We identified critical factors leading to efficient PHH infection by HCV sera in vitro. Overall, we showed that this cellular model provides a useful tool for studying the mechanism of HCV infection in its natural host cell, selecting highly infectious isolates, and determining the potency of drugs towards various HCV strains.

How viruses use the immune system to promote infection of polarized cells

ABSTRACT: 

To establish infection and access bodily compartments including the gut, lung, liver and brain, viruses must traverse polarized epithelial and endothelial cell sheets. Many viruses use components of the immune system to successfully infect epithelial cells and gain access to underlying tissue. Recently, several reports have highlighted new and surprising ways by which viruses can hijack the immune system to invade polarized cells. This review will summarize recent advances in our understanding of how viruses interact with the immune system, and with polarized cells, for successful infection. These studies raise important questions about the design and screening of therapeutics and vaccines that activate the immune system, which may need to consider the role of immune cells and the inflammatory microenvironment.

The role of epithelial tight junctions involved in pathogen infections

Tight junctions (TJs) are sealing complexes between adjacent epithelial cells, functioning by controlling paracellular passage and maintaining cell polarity. These functions of TJs are primarily based on structural integrity as well as dynamic regulatory balance, indicating plasticity of TJ in response to external stimuli. An indispensable role of TJs involved in pathogen infection has been widely demonstrated since disruption of TJs leads to a distinct increase in paracellular permeability and polarity defects which facilitate viral or bacterial entry and spread. In addition to pathological changes in TJ integrity, TJ proteins such as occludin and claudins can either function as receptors for pathogen entry or interact with viral/bacterial effector molecules as an essential step for characterizing an infective stage. This suggests a more complicated role for TJ itself and especially specific TJ components. Thus, this review surveys the role of the epithelial TJs involved in various pathogen infections, and extends TJ targeted therapeutic and pharmacological application prospects.

Scalable spheroid model of human hepatocytes for hepatitis C infection and replication

Developing effective new drugs against hepatitis C (HCV) virus has been challenging due to the lack of appropriate small animal and in vitro models recapitulating the entire life cycle of the virus. Current in vitro models fail to recapitulate the complexity of human liver physiology. Here we present a method to study HCV infection and replication on spheroid cultures of Huh 7.5 cells and primary human hepatocytes. Spheroid cultures are constructed using a galactosylated cellulosic sponge with homogeneous macroporosity, enabling the formation and maintenance of uniformly sized spheroids. This facilitates easy handling of the tissue-engineered constructs and overcomes limitations inherent of traditional spheroid cultures. Spheroids formed in the galactosylated cellulosic sponge show enhanced hepatic functions in Huh 7.5 cells and maintain liver-specific functions of primary human hepatocytes for 2 weeks in culture. Establishment of apical and basolateral polarity along with the expression and localization of all HCV specific entry proteins allow for a 9-fold increase in viral entry in spheroid cultures over conventional monolayer cultures. Huh 7.5 cells cultured in the galactosylated cellulosic sponge also support replication of the HCV clone, JFH (Japanese fulminant hepatitis)-1 at higher levels than in monolayer cultures. The advantages of our system in maintaining liver-specific functions and allowing HCV infection together with its ease of handling make it suitable for the study of HCV biology in basic research and pharmaceutical R&D.

Viruses and tetraspanins: lessons from single molecule approaches

Tetraspanins are four-span membrane proteins that are widely distributed in multi-cellular organisms and involved in several infectious diseases. They have the unique property to form a network of protein-protein interaction within the plasma membrane, due to the lateral associations with one another and with other membrane proteins. Tracking tetraspanins at the single molecule level using fluorescence microscopy has revealed the membrane behavior of the tetraspanins CD9 and CD81 in epithelial cell lines, providing a first dynamic view of this network. Single molecule tracking highlighted that these 2 proteins can freely diffuse within the plasma membrane but can also be trapped, permanently or transiently, in tetraspanin-enriched areas. More recently, a similar strategy has been used to investigate tetraspanin membrane behavior in the context of human immunodeficiency virus type 1 (HIV-1) and hepatitis C virus (HCV) infection. In this review we summarize the main results emphasizing the relationship in terms of membrane partitioning between tetraspanins, some of their partners such as Claudin-1 and EWI-2, and viral proteins during infection. These results will be analyzed in the context of other membrane microdomains, stressing the difference between raft and tetraspanin-enriched microdomains, but also in comparison with virus diffusion at the cell surface. New advanced single molecule techniques that could help to further explore tetraspanin assemblies will be also discussed.

How hepatitis C virus invades hepatocytes: The mystery of viral entry

Hepatitis C virus (HCV) infection is a global health problem, with an estimated 170 million people being chronically infected. HCV cell entry is a complex multi-step process, involving several cellular factors that trigger virus uptake into the hepatocytes. The high- density lipoprotein receptor scavenger receptor class B type I, tetraspanin CD81, tight junction protein claudin-1, and occludin are the main receptors that mediate the initial step of HCV infection. In addition, the virus uses cell receptor tyrosine kinases as entry regulators, such as epidermal growth factor receptor and ephrin receptor A2. This review summarizes the current understanding about how cell surface molecules are involved in HCV attachment, internalization, and membrane fusion, and how host cell kinases regulate virus entry. The advances of the potential antiviral agents targeting this process are introduced.

Activated macrophages promote hepatitis C virus entry in a tumor necrosis factor-dependent manner

Macrophages are critical components of the innate immune response in the liver. Chronic hepatitis C is associated with immune infiltration and the infected liver shows a significant increase in total macrophage numbers; however, their role in the viral life cycle is poorly understood. Activation of blood-derived and intrahepatic macrophages with a panel of Toll-like receptor agonists induce soluble mediators that promote hepatitis C virus (HCV) entry into polarized hepatoma cells. We identified tumor necrosis factor α (TNF-α) as the major cytokine involved in this process. Importantly, this effect was not limited to HCV; TNF-α increased the permissivity of hepatoma cells to infection by Lassa, measles and vesicular stomatitis pseudoviruses. TNF-α induced a relocalization of tight junction protein occludin and increased the lateral diffusion speed of HCV receptor tetraspanin CD81 in polarized HepG2 cells, providing a mechanism for their increased permissivity to support HCV entry. High concentrations of HCV particles could stimulate macrophages to express TNF-α, providing a direct mechanism for the virus to promote infection.

CONCLUSION

This study shows a new role for TNF-α to increase virus entry and highlights the potential for HCV to exploit existing innate immune responses in the liver to promote de novo infection events.

CD81-receptor associations--impact for hepatitis C virus entry and antiviral therapies

Tetraspanins are integral transmembrane proteins organized in microdomains displaying specific and direct interactions with other tetraspanins and molecular partners. Among them, CD81 has been implicated in a variety of physiological and pathological processes. CD81 also plays a crucial role in pathogen entry into host cells, including hepatitis C virus (HCV) entry into hepatocytes. HCV is a major cause of liver cirrhosis and hepatocellular carcinoma. HCV entry into hepatocytes is a complex process that requires the coordinated interaction of viral and host factors for the initiation of infection, including CD81, scavenger receptor BI, claudin-1, occludin, membrane-bound host cell kinases, Niemann-Pick C1 Like 1, Harvey rat sarcoma viral oncogene homolog (HRas), CD63 and transferrin receptor 1. Furthermore, recent data in HCV model systems have demonstrated that targeting critical components of tetraspanins and associated cell membrane proteins open new avenues to prevent and treat viral infection.

CD81 and hepatitis C virus (HCV) infection

Hepatitis C Virus (HCV) infection is a global public health problem affecting over 160 million individuals worldwide. Its symptoms include chronic hepatitis, liver cirrhosis and hepatocellular carcinoma. HCV is an enveloped RNA virus mainly targeting liver cells and for which the initiation of infection occurs through a complex multistep process involving a series of specific cellular entry factors. This process is likely mediated through the formation of a tightly orchestrated complex of HCV entry factors at the plasma membrane. Among HCV entry factors, the tetraspanin CD81 is one of the best characterized and it is undoubtedly a key player in the HCV lifecycle. In this review, we detail the current knowledge on the involvement of CD81 in the HCV lifecycle, as well as in the immune response to HCV infection.