EGFR and EphA2 are host factors for hepatitis C virus entry and possible targets for antiviral therapy

Claudin-1 gene variants and susceptibility to hepatitis C infection in HIV-1 infected intravenous drug users (an ANRS case-control study)

Hepatitis C virus (HCV) seroprevalence is highly diverse among human immunodeficiency virus-1 (HIV-1) infected patients, ranging between 10% of HIV-1 infected homo-bisexuel men, to >92% in patients infected with HIV-1 who acquired HIV-1 through intravenous drug use. Thus, being HCV-free while having acquired HIV-1 via intravenous drug use is a rare situation. Claudin-1 is a protein involved in intracellular tight-junctions and has been identified as a major cellular co-receptor for HCV infection. Our objective was to determine whether Claudin-1 gene (CLDN1) mutations might be involved in natural resistance to HCV infection. We conducted a case-control study. All recruited patients acquired HIV-1 infection via intravenous drug use route before 1995. The case study patients remained free from HCV infection (negative anti-HCV antibodies and HCV-RNA). The control study patients was co-infected with HCV (positive anti-HCV antibodies). Direct genomic sequencing of the CLDN1 gene coding region and adjacent intron/exons junctions was performed from peripheral blood mononuclear cells. A total of 138 Caucasian patients were enrolled. Twenty-two patients (cases) were free from HCV infection and 116 (controls) were co-infected with HCV. We found single nucleotide polymorphisms (SNPs) described previously with no significant differences in allele frequencies between cases and controls. In conclusion, despite being a major cellular co-receptor for HCV entry in vitro, we did not identify any specific substitution in CLDN1 gene coding region in our study patients highly exposed but resistant to HCV infection in vivo. Other cellular co-factors involved in HCV infection should be investigated in this highly-exposed intravenous drug users patients.

Identification of HNRNPK as regulator of hepatitis C virus particle production

Hepatitis C virus (HCV) is a major cause of chronic liver disease affecting around 130 million people worldwide. While great progress has been made to define the principle steps of the viral life cycle, detailed knowledge how HCV interacts with its host cells is still limited. To overcome this limitation we conducted a comprehensive whole-virus RNA interference-based screen and identified 40 host dependency and 16 host restriction factors involved in HCV entry/replication or assembly/release. Of these factors, heterogeneous nuclear ribonucleoprotein K (HNRNPK) was found to suppress HCV particle production without affecting viral RNA replication. This suppression of virus production was specific to HCV, independent from assembly competence and genotype, and not found with the related Dengue virus. By using a knock-down rescue approach we identified the domains within HNRNPK required for suppression of HCV particle production. Importantly, HNRNPK was found to interact specifically with HCV RNA and this interaction was impaired by mutations that also reduced the ability to suppress HCV particle production. Finally, we found that in HCV-infected cells, subcellular distribution of HNRNPK was altered; the protein was recruited to sites in close proximity of lipid droplets and colocalized with core protein as well as HCV plus-strand RNA, which was not the case with HNRNPK variants unable to suppress HCV virion formation. These results suggest that HNRNPK might determine efficiency of HCV particle production by limiting the availability of viral RNA for incorporation into virions. This study adds a new function to HNRNPK that acts as central hub in the replication cycle of multiple other viruses.

Statin use is associated with a reduced risk of fibrosis progression in chronic hepatitis C

BACKGROUND & AIMS

Therapies that slow fibrosis progression in chronic liver disease are needed. Animal models have demonstrated that statins prevent the progression of hepatic fibrosis, but human data is lacking so far. We evaluated the association between statins and fibrosis progression in the HALT-C trial cohort.

METHODS

Subjects with chronic hepatitis C (CHC) and advanced hepatic fibrosis underwent serial liver biopsies over 3.5 years. The primary outcome was a ⩾ 2-point increase in the Ishak fibrosis score on at least one of two serial biopsies. We used complementary log-log regression analysis to assess the association between statins and fibrosis progression among subjects without baseline cirrhosis.

RESULTS

Fibrosis progression occurred in 3/29 (10%) statin users and 145/514 (29%) non-users. The unadjusted hazard ratio (HR) for fibrosis progression among statin users compared to non-users was 0.32 (95% CI 0.10-0.99). This association remained significant after adjusting for established predictors of histological outcome, including body mass index, platelets and hepatic steatosis (adjusted HR 0.31; 95% CI 0.10-0.97). The mean change in Ishak fibrosis score over the 3.5 year study period was -0.34 (SE 0.18) for statin users compared to +0.42 (SE 0.07) for non-users (p = 0.006, after adjustment for baseline fibrosis score).

CONCLUSIONS

Statin use is associated with a reduced risk of fibrosis progression in advanced CHC. Our findings suggest a potential role for statins in preventing liver disease progression.

HDL in infectious diseases and sepsis

During infection significant alterations in lipid metabolism and lipoprotein composition occur. Triglyceride and VLDL cholesterol levels increase, while reduced HDL cholesterol (HDL-C) and LDL cholesterol (LDL-C) levels are observed. More importantly, endotoxemia modulates HDL composition and size: phospholipids are reduced as well as apolipoprotein (apo) A-I, while serum amyloid A (SAA) and secretory phospholipase A2 (sPLA2) dramatically increase, and, although the total HDL particle number does not change, a significant decrease in the number of small- and medium-size particles is observed. Low HDL-C levels inversely correlate with the severity of septic disease and associate with an exaggerated systemic inflammatory response. HDL, as well as other plasma lipoproteins, can bind and neutralize Gram-negative bacterial lipopolysaccharide (LPS) and Gram-positive bacterial lipoteichoic acid (LTA), thus favoring the clearance of these products. HDLs are emerging also as a relevant player during parasitic infections, and a specific component of HDL, namely, apoL-1, confers innate immunity against trypanosome by favoring lysosomal swelling which kills the parasite. During virus infections, proteins associated with the modulation of cholesterol bioavailability in the lipid rafts such as ABCA1 and SR-BI have been shown to favor virus entry into the cells. Pharmacological studies support the benefit of recombinant HDL or apoA-I mimetics during bacterial infection, while apoL-1-nanobody complexes were tested for trypanosome infection. Finally, SR-BI antagonism represents a novel and forefront approach interfering with hepatitis C virus entry which is currently tested in clinical studies. From the coming years, we have to expect new and compelling observations further linking HDL to innate immunity and infections.

Curcumin differs from tetrahydrocurcumin for molecular targets, signaling pathways and cellular responses

Curcumin (diferuloylmethane), a golden pigment from turmeric, has been linked with antioxidant, anti-inflammatory, anticancer, antiviral, antibacterial, and antidiabetic properties. Most of the these activities have been assigned to methoxy, hydroxyl, α,β-unsaturated carbonyl moiety or to diketone groups present in curcumin. One of the major metabolites of curcumin is tetrahydrocurcumin (THC), which lacks α,β-unsaturated carbonyl moiety and is white in color. Whether THC is superior to curcumin on a molecular level is unclear and thus is the focus of this review. Various studies suggest that curcumin is a more potent antioxidant than THC; curcumin (but not THC) can bind and inhibit numerous targets including DNA (cytosine-5)-methyltransferase-1, heme oxygenase-1, Nrf2, β-catenin, cyclooxygenase-2, NF-kappaB, inducible nitric oxide synthase, nitric oxide, amyloid plaques, reactive oxygen species, vascular endothelial growth factor, cyclin D1, glutathione, P300/CBP, 5-lipoxygenase, cytosolic phospholipase A2, prostaglandin E2, inhibitor of NF-kappaB kinase-1, -2, P38MAPK, p-Tau, tumor necrosis factor-α, forkhead box O3a, CRAC; curcumin can inhibit tumor cell growth and suppress cellular entry of viruses such as influenza A virus and hepatitis C virus much more effectively than THC; curcumin affects membrane mobility; and curcumin is also more effective than THC in suppressing phorbol-ester-induced tumor promotion. Other studies, however, suggest that THC is superior to curcumin for induction of GSH peroxidase, glutathione-S-transferase, NADPH: quinone reductase, and quenching of free radicals. Most studies have indicated that THC exhibits higher antioxidant activity, but curcumin exhibits both pro-oxidant and antioxidant properties.

Hepatitis C virus life cycle and lipid metabolism

Hepatitis C Virus (HCV) infects over 150 million people worldwide. In most cases HCV infection becomes chronic, causing liver disease ranging from fibrosis to cirrhosis and hepatocellular carcinoma. HCV affects the cholesterol homeostasis and at the molecular level, every step of the virus life cycle is intimately connected to lipid metabolism. In this review, we present an update on the lipids and apolipoproteins that are involved in the HCV infectious cycle steps: entry, replication and assembly. Moreover, the result of the assembly process is a lipoviroparticle, which represents a peculiarity of hepatitis C virion. This review illustrates an example of an intricate virus-host interaction governed by lipid metabolism.

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.

Host genetics predict clinical deterioration in HCV-related cirrhosis

Single nucleotide polymorphisms (SNPs) in the epidermal growth factor (EGF, rs4444903), patatin-like phospholipase domain-containing protein 3 (PNPLA3, rs738409) genes, and near the interleukin-28B (IL28B, rs12979860) gene are linked to treatment response, fibrosis, and hepatocellular carcinoma (HCC) in chronic hepatitis C. Whether these SNPs independently or in combination predict clinical deterioration in hepatitis C virus (HCV)-related cirrhosis is unknown. We genotyped SNPs in EGF, PNPLA3, and IL28B from liver tissue from 169 patients with biopsy-proven HCV cirrhosis. We estimated risk of clinical deterioration, defined as development of ascites, encephalopathy, variceal hemorrhage, HCC, or liver-related death using Cox proportional hazards modeling. During a median follow-up of 6.6 years, 66 of 169 patients experienced clinical deterioration. EGF non-AA, PNPLA3 non-CC, and IL28B non-CC genotypes were each associated with increased risk of clinical deterioration in age, sex, and race-adjusted analysis. Only EGF non-AA genotype was independently associated with increased risk of clinical deterioration (hazard ratio [HR] 2.87; 95% confidence interval [CI] 1.31-6.25) after additionally adjusting for bilirubin, albumin, and platelets. Compared to subjects who had 0-1 unfavorable genotypes, the HR for clinical deterioration was 1.79 (95%CI 0.96-3.35) for 2 unfavorable genotypes and 4.03 (95%CI 2.13-7.62) for unfavorable genotypes for all three loci (Ptrend<0.0001). In conclusion, among HCV cirrhotics, EGF non-AA genotype is independently associated with increased risk for clinical deterioration. Specific PNPLA3 and IL28B genotypes also appear to be associated with clinical deterioration. These SNPs have potential to identify patients with HCV-related cirrhosis who require more intensive monitoring for decompensation or future therapies preventing disease progression.

Functional characterization of nuclear localization and export signals in hepatitis C virus proteins and their role in the membranous web

The hepatitis C virus (HCV) is a positive strand RNA virus of the Flavivirus family that replicates in the cytoplasm of infected hepatocytes. Previously, several nuclear localization signals (NLS) and nuclear export signals (NES) have been identified in HCV proteins, however, there is little evidence that these proteins travel into the nucleus during infection. We have recently shown that nuclear pore complex (NPC) proteins (termed nucleoporins or Nups) are present in the membranous web and are required during HCV infection. In this study, we identify a total of 11 NLS and NES sequences in various HCV proteins. We show direct interactions between HCV proteins and importin α5 (IPOA5/kapα1), importin β3 (IPO5/kap β3), and exportin 1 (XPO1/CRM1) both in-vitro and in cell culture. These interactions can be disrupted using peptides containing the specific NLS or NES sequences of HCV proteins. Moreover, using a synchronized infection system, we show that these peptides inhibit HCV infection during distinct phases of the HCV life cycle. The inhibitory effects of these peptides place them in two groups. The first group binds IPOA5 and inhibits infection during the replication stage of HCV life cycle. The second group binds IPO5 and is active during both early replication and early assembly. This work delineates the entire life cycle of HCV and the active involvement of NLS sequences during HCV replication and assembly. Given the abundance of NLS sequences within HCV proteins, our previous finding that Nups play a role in HCV infection, and the relocation of the NLS double-GFP reporter in HCV infected cells, this work supports our previous hypothesis that NPC-like structures and nuclear transport factors function in the membranous web to create an environment conducive to viral replication.

Hepatitis C virus molecular evolution: Transmission, disease progression and antiviral therapy

Hepatitis C virus (HCV) infection represents an important public health problem worldwide. Reduction of HCV morbidity and mortality is a current challenge owned to several viral and host factors. Virus molecular evolution plays an important role in HCV transmission, disease progression and therapy outcome. The high degree of genetic heterogeneity characteristic of HCV is a key element for the rapid adaptation of the intrahost viral population to different selection pressures (e.g., host immune responses and antiviral therapy). HCV molecular evolution is shaped by different mechanisms including a high mutation rate, genetic bottlenecks, genetic drift, recombination, temporal variations and compartmentalization. These evolutionary processes constantly rearrange the composition of the HCV intrahost population in a staging manner. Remarkable advances in the understanding of the molecular mechanism controlling HCV replication have facilitated the development of a plethora of direct-acting antiviral agents against HCV. As a result, superior sustained viral responses have been attained. The rapidly evolving field of anti-HCV therapy is expected to broad its landscape even further with newer, more potent antivirals, bringing us one step closer to the interferon-free era.

The impact of hepatitis C virus entry on viral tropism

Uptake of hepatitis C virus (HCV) into hepatocytes is an orchestrated process, involving numerous host factors, virion-associated lipoproteins, and a growing number of cell-associated factors. Several of these factors likely contribute to the hepatotropism and limited host range of this virus. Discerning the minimal set of human-specific factors required for viral uptake into nonhuman cells has facilitated the development of small animal models with inheritable HCV susceptibility. This review summarizes current knowledge of host factors required for HCV entry, the molecular mechanisms underlying HCV entry into hepatocytes, and aspects of viral entry contributing to HCV host tropism.

The Humoral Immune Response to HCV: Understanding is Key to Vaccine Development

Hepatitis C virus (HCV) remains a global problem, despite advances in treatment. The low cost and high benefit of vaccines have made them the backbone of modern public health strategies, and the fight against HCV will not be won without an effective vaccine. Achievement of this goal will benefit from a robust understanding of virus-host interactions and protective immunity in HCV infection. In this review, we summarize recent findings on HCV-specific antibody responses associated with chronic and spontaneously resolving human infection. In addition, we discuss specific epitopes within HCV's envelope glycoproteins that are targeted by neutralizing antibodies. Understanding what prompts or prevents a successful immune response leading to viral clearance or persistence is essential to designing a successful vaccine.

Hepatitis C virus-associated cancer

Hepatitis C virus (HCV) is one of the major etiologic agents of liver cancer. HCV is an RNA virus that, unlike hepatitis B virus, is unable to integrate into the host genome. Through complex interactions between viral and host proteins that induce host responses and promote inflammation, fibrosis, and ultimately cirrhosis, HCV infection can result in the development of hepatocellular carcinoma (HCC). The HCV oncogenic process involves genetic and epigenetic alterations and oncogenic effects mediated by viral proteins in the activation of cellular oncogenes, inactivation of tumor-suppressor genes, and dysregulation of multiple signal-transduction pathways. Advances in genetics and gene expression profiling have enhanced our current understanding of the pathways involved in HCV-associated liver cancer development. In this review, we summarize the current understanding of mechanisms of hepatocarcinogenesis induced by HCV infection.

New Methods in Tissue Engineering: Improved Models for Viral Infection

New insights in the study of virus and host biology in the context of viral infection are made possible by the development of model systems that faithfully recapitulate the in vivo viral life cycle. Standard tissue culture models lack critical emergent properties driven by cellular organization and in vivo-like function, whereas animal models suffer from limited susceptibility to relevant human viruses and make it difficult to perform detailed molecular manipulation and analysis. Tissue engineering techniques may enable virologists to create infection models that combine the facile manipulation and readouts of tissue culture with the virus-relevant complexity of animal models. Here, we review the state of the art in tissue engineering and describe how tissue engineering techniques may alleviate some common shortcomings of existing models of viral infection, with a particular emphasis on hepatotropic viruses. We then discuss possible future applications of tissue engineering to virology, including current challenges and potential solutions.

Current and future targets of antiviral therapy in the hepatitis C virus life cycle

ABSTRACT 

Advances in our understanding of the hepatitis C virus (HCV) life cycle have enabled the development of numerous clinically advanced direct-acting antivirals. Indeed, the recent approval of first-generation direct-acting antivirals that target the viral NS3–4A protease and NS5B RNA-dependent RNA polymerase brings closer the possibility of universally efficacious and well-tolerated antiviral therapies for this insidious infection. However, the complexities of comorbidities, unforeseen side effects or drug–drug interactions, viral diversity, the high mutation rate of HCV RNA replication and the elegant and constantly evolving mechanisms employed by HCV to evade host and therapeutically implemented antiviral strategies remain as significant obstacles to this goal. Here, we review advances in our understanding of the HCV life cycle and associated opportunities for antiviral therapy.

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.

Pathogenesis and prevention of hepatitis C virus-induced hepatocellular carcinoma

Hepatitis C virus (HCV) is one of the major aetiologic agents that causes hepatocellular carcinoma (HCC) by generating an inflammatory, fibrogenic, and carcinogenic tissue microenvironment in the liver. HCV-induced HCC is a rational target for cancer preventive intervention because of the clear-cut high-risk condition, cirrhosis, associated with high cancer incidence (1% to 7% per year). Studies have elucidated direct and indirect carcinogenic effects of HCV, which have in turn led to the identification of candidate HCC chemoprevention targets. Selective molecular targeted agents may enable personalized strategies for HCC chemoprevention. In addition, multiple experimental and epidemiological studies suggest the potential value of generic drugs or dietary supplements targeting inflammation, oxidant stress, or metabolic derangements as possible HCC chemopreventive agents. While the successful use of highly effective direct-acting antiviral agents will make important inroads into reducing long-term HCC risk, there will remain an important role for HCC chemoprevention even after viral cure, given the persistence of HCC risk in persons with advanced HCV fibrosis, as shown in recent studies. The successful development of cancer preventive therapies will be more challenging compared to cancer therapeutics because of the requirement for larger and longer clinical trials and the need for a safer toxicity profile given its use as a preventive agent. Molecular biomarkers to selectively identify high-risk population could help mitigate these challenges. Genome-wide, unbiased molecular characterization, high-throughput drug/gene screening, experimental model-based functional analysis, and systems-level in silico modelling are expected to complement each other to facilitate discovery of new HCC chemoprevention targets and therapies.

Susceptibility to Plasmodium yoelii preerythrocytic infection in BALB/c substrains is determined at the point of hepatocyte invasion

After transmission by Anopheles mosquitoes, Plasmodium sporozoites travel to the liver, infect hepatocytes, and rapidly develop as intrahepatocytic liver stages (LS). Rodent models of malaria exhibit large differences in the magnitude of liver infection, both between parasite species and between strains of mice. This has been mainly attributed to differences in innate immune responses and parasite infectivity. Here, we report that BALB/cByJ mice are more susceptible to Plasmodium yoelii preerythrocytic infection than BALB/cJ mice. This difference occurs at the level of early hepatocyte infection, but expression levels of reported host factors that are involved in infection do not correlate with susceptibility. Interestingly, BALB/cByJ hepatocytes are more frequently polyploid; thus, their susceptibility converges on the previously observed preference of sporozoites to infect polyploid hepatocytes. Gene expression analysis demonstrates hepatocyte-specific differences in mRNA abundance for numerous genes between BALB/cByJ and BALB/cJ mice, some of which encode hepatocyte surface molecules. These data suggest that a yet-unknown receptor for sporozoite infection, present at elevated levels on BALB/cByJ hepatocytes and also polyploid hepatocytes, might facilitate Plasmodium liver infection.

Eph receptors and ephrins: therapeutic opportunities

The erythropoietin-producing hepatocellular carcinoma (Eph) receptor tyrosine kinase family plays important roles in developmental processes, adult tissue homeostasis, and various diseases. Interaction with Eph receptor-interacting protein (ephrin) ligands on the surface of neighboring cells triggers Eph receptor kinase-dependent signaling. The ephrins can also transmit signals, leading to bidirectional cell contact-dependent communication. Moreover, Eph receptors and ephrins can function independently of each other through interplay with other signaling systems. Given their involvement in many pathological conditions ranging from neurological disorders to cancer and viral infections, Eph receptors and ephrins are increasingly recognized as attractive therapeutic targets, and various strategies are being explored to modulate their expression and function. Eph receptor/ephrin upregulation in cancer cells, the angiogenic vasculature, and injured or diseased tissues also offer opportunities for Eph/ephrin-based targeted drug delivery and imaging. Thus, despite the challenges presented by the complex biology of the Eph receptor/ephrin system, exciting possibilities exist for therapies exploiting these molecules.

Recombinant hepatitis C virus envelope glycoprotein vaccine elicits antibodies targeting multiple epitopes on the envelope glycoproteins associated with broad cross-neutralization

Although effective hepatitis C virus (HCV) antivirals are on the horizon, a global prophylactic vaccine for HCV remains elusive. The diversity of the virus is a major concern for vaccine development; there are 7 major genotypes of HCV found globally. Therefore, a successful vaccine will need to protect against HCV infection by all genotypes. Despite the diversity, many monoclonal antibodies (MAbs) with broadly cross-neutralizing activity have been described, suggesting the presence of conserved epitopes that can be targeted to prevent infection. Similarly, a vaccine comprising recombinant envelope glycoproteins (rE1E2) derived from the genotype 1a HCV-1 strain has been shown to be capable of eliciting cross-neutralizing antibodies in guinea pigs, chimpanzees, and healthy human volunteers. In order to investigate the basis for this cross-neutralization, epitope mapping of anti-E1E2 antibodies present within antisera from goats and humans immunized with HCV-1 rE1E2 was conducted through peptide mapping and competition studies with a panel of cross-neutralizing MAbs targeting various epitopes within E1E2. The immunized-goat antiserum was shown to compete with the binding of all MAbs tested (AP33, HC33.4, HC84.26, 1:7, AR3B, AR4A, AR5A, IGH526, and A4). Antisera showed the best competition against HC84.26 and AR3B and the weakest competition against AR4A. Furthermore, antisera from five immunized human vaccinees were shown to compete with five preselected MAbs (AP33, AR3B, AR4A, AR5A, and IGH526). These data show that immunization with HCV-1 rE1E2 elicits antibodies targeting multiple cross-neutralizing epitopes. Our results further support the use of such a vaccine antigen to induce cross-genotype neutralization.

IMPORTANCE

An effective prophylactic vaccine for HCV is needed for optimal control of the disease burden. The high diversity of HCV has posed a challenge for developing vaccines that elicit neutralizing antibodies for protection against infection. Despite this, we have previously shown that a vaccine comprising recombinant envelope glycoproteins derived from a single genotype 1a strain was capable of eliciting a cross-neutralizing antibody response in human volunteers. Here, we have used competition binding assays and peptide binding assays to show that antibodies present in the antisera from vaccinated goats and humans bind epitopes overlapping with those of a variety of well-characterized cross-neutralizing monoclonal antibodies. This provides a mechanism for the cross-neutralizing human antisera: antibodies present in the antisera bind to conserved regions associated with cross-neutralization. Importantly, this work provides further support for a vaccine comprising recombinant envelope glycoproteins, perhaps in a formulation with a vaccine component eliciting strong anti-HCV CD4(+) and CD8(+) T cell responses.

Finding candidate drugs for hepatitis C based on chemical-chemical and chemical-protein interactions

Hepatitis C virus (HCV) is an infectious virus that can cause serious illnesses. Only a few drugs have been reported to effectively treat hepatitis C. To have greater diversity in drug choice and better treatment options, it is necessary to develop more drugs to treat the infection. However, it is time-consuming and expensive to discover candidate drugs using experimental methods, and computational methods may complement experimental approaches as a preliminary filtering process. This type of approach was proposed by using known chemical-chemical interactions to extract interactive compounds with three known drug compounds of HCV, and the probabilities of these drug compounds being able to treat hepatitis C were calculated using chemical-protein interactions between the interactive compounds and HCV target genes. Moreover, the randomization test and expectation-maximization (EM) algorithm were both employed to exclude false discoveries. Analysis of the selected compounds, including acyclovir and ganciclovir, indicated that some of these compounds had potential to treat the HCV. Hopefully, this proposed method could provide new insights into the discovery of candidate drugs for the treatment of HCV and other diseases.

miR-27a suppresses EV71 replication by directly targeting EGFR

Enterovirus 71 (EV71), a major causative agent of hand, foot, and mouth disease, has broken out several times and was accompanied by neurological disease. microRNAs, a class of small non-coding RNAs that are approximately 20 nucleotides long, play important roles in the regulation of various biological processes, including antiviral defense. However, the roles of miRNAs in EV71 replication and pathogenesis are not well understood. In this study, we found that the expression of miR-27a was significantly decreased in EV71-infected cells. Interestingly, the over-expression of miR-27a could inhibit EV71 replication, as measured by virus titration, qPCR, and Western blotting. We identified EGFR mRNA is a bona fide target of miR-27a by computational analysis and luciferase reporter assays. Furthermore, miR-27a could decrease EGFR expression, as measured by qPCR and Western blotting. Moreover, the inhibition of EGFR expression by miR-27a decreased the phosphorylation of Akt and ERK, which facilitate EV71 replication. These results suggest that miR-27a may have antiviral activity against EV71 by inhibiting EGFR.

Mir-194 is a hepatocyte gate keeper hindering HCV entry through targeting CD81 receptor

OBJECTIVE

The tetraspanin CD81 is one of the main receptors involved in hepatitis C virus entry. Herein, we aimed to explore the role of microRNAs in regulating CD81 receptor expression and function.

PATIENTS AND METHODS

Bioinformatics analysis was carried out to select potential mircroRNAs that binds CD81 3'untranslated region. Liver biopsies taken from 28 HCV genotype- 4 patients and 10 healthy donors were screened. Naïve, JFH1 and ED43/JFH1- infected- Huh7 cells were transfected with mimics and inhibitors followed by analyzing CD81 protein and mRNA expression. This was done using flow cytometry and Q-RT PCR, respectively. HCV entry into Huh7 cells was investigated post-transfection. Binding confirmation was done using luciferase reporter vector harboring wild/mutant target sites of microRNA. The impact of Epigallocatechin-gallate on modulating microRNA/CD81 expression was assessed.

RESULTS

Bioinformatics revealed that CD81 is a potential down-stream target for miR-194. A significant inverse correlation was found between miR-194 and CD81 expression in liver biopsies of HCV patients. Forcing the expression of miR-194 showed a down-regulation of CD81 protein, mRNA expression and significantly abrogated the HCV infectivity of Huh7 cells. Stimulation with EGCG enhanced mir-194 expression and down-regulated CD81 expression.

CONCLUSION

This study showed that mir-194 hinders HCV entry through targeting CD81 receptors.

The role of Kupffer cells in hepatitis B and hepatitis C virus infections

Globally, over 500 million people are chronically infected with the hepatitis B virus (HBV) or hepatitis C virus (HCV). These chronic infections cause liver inflammation, and may result in fibrosis/cirrhosis or hepatocellular carcinoma. Albeit that HBV and HCV differ in various aspects, clearance, persistence, and immunopathology of either infection depends on the interplay between the innate and adaptive responses in the liver. Kupffer cells, the liver-resident macrophages, are abundantly present in the sinusoids of the liver. These cells have been shown to be crucial players to maintain homeostasis, but also contribute to pathology. However, it is important to note that especially during pathology, Kupffer cells are difficult to distinguish from infiltrating monocytes/macrophages and other myeloid cells. In this review we discuss our current understanding of Kupffer cells, and assess their role in the regulation of anti-viral immunity and disease pathogenesis during HBV and HCV infection.

Bridging basic science and clinical research: the EASL Monothematic Conference on Translational Research in Viral Hepatitis

The EASL Monothematic Conference on Translational Research in Viral Hepatitis brought together a group of leading scientists and clinicians working on both, basic and clinical aspects of viral hepatitis, thereby building bridges from bench to bedside. This report recapitulates the presentations and discussions at the conference held in Lyon, France on November 29-30, 2013. In recent years, great advances have been made in the field of viral hepatitis, particularly in hepatitis C virus (HCV) infection. The identification of IL28B genetic polymorphisms as a major determinant for spontaneous and treatment-induced HCV clearance was a seminal discovery. Currently, hepatologists are at the doorstep of even greater advances, with the advent of a wealth of directly acting antivirals (DAAs) against HCV. Indeed, promising results have accumulated over the last months and few years, showing sustained virological response (SVR) rates of up to 100% with interferon-free DAA combination therapies. Thus, less than 25 years after its identification, HCV infection may soon be curable in the vast majority of patients, highlighting the great success of HCV research over the last decades. However, viral hepatitis and its clinical complications such as liver cirrhosis and hepatocellular carcinoma (HCC) remain major global challenges. New therapeutic strategies to tackle hepatitis B virus (HBV) and hepatitis D virus (HDV) infection are needed, as current therapies have undeniable limitations. Nucleoside/nucleotide analogues (NUC) can efficiently control HBV replication and reduce or even reverse liver damage. However, these drugs have to be given for indefinite periods in most patients to maintain virological and biochemical responses. Although sustained responses off treatment can be achieved by treatment with (pegylated) interferon-α, only about 10-30% of patients effectively resolve chronic hepatitis B. It was the goal of this conference to review the progress made over the last years in chronic viral hepatitis research and to identify key questions that need to be addressed in order to close the gap between basic and clinical research and to develop novel preventive and treatment approaches for this most common cause of liver cirrhosis and HCC.

A simple method for analyzing actives in random RNAi screens: introducing the "H Score" for hit nomination & gene prioritization

Due to the numerous challenges in hit identification from random RNAi screening, we have examined current practices with a discovery of a variety of methodologies employed and published in many reports; majority of them, unfortunately, do not address the minimum associated criteria for hit nomination, as this could potentially have been the cause or may well be the explanation as to the lack of confirmation and follow up studies, currently facing the RNAi field. Overall, we find that these criteria or parameters are not well defined, in most cases arbitrary in nature, and hence rendering it extremely difficult to judge the quality of and confidence in nominated hits across published studies. For this purpose, we have developed a simple method to score actives independent of assay readout; and provide, for the first time, a homogenous platform enabling cross-comparison of active gene lists resulting from different RNAi screening technologies. Here, we report on our recently developed method dedicated to RNAi data output analysis referred to as the BDA method applicable to both arrayed and pooled RNAi technologies; wherein the concerns pertaining to inconsistent hit nomination and off-target silencing in conjugation with minimal activity criteria to identify a high value target are addressed. In this report, a combined hit rate per gene, called "H score", is introduced and defined. The H score provides a very useful tool for stringent active gene nomination, gene list comparison across multiple studies, prioritization of hits, and evaluation of the quality of the nominated gene hits.

Mycoplasma hyorhinis infection promotes NF-κB-dependent migration of gastric cancer cells

Chronic infection of Mycoplasma hyorhinis (M. hyorhinis) has been postulated to be associated with several types of cancer, but its effect on patients' survival and host factors mediating its infection remain unclear. Herein, we demonstrated that M. hyorhinis p37 protein expression in gastric cancer tissues predicts poor survival and associates with metastasis. M. hyorhinis infects mammalian cells and promotes gastric cancer cell invasiveness via its membrane protein p37. Synthesized peptide corresponding to the N-terminus of p37 prevents M. hyorhinis infection. Host Annexin A2 (ANXA2) interacts with the N-terminus of p37. In addition, EGFR forms a complex with p37 and ANXA2, and is required for M. hyorhinis-induced phosphorylation and membrane recruitment of ANXA2. M. hyorhinis infection is inhibited by siRNA-mediated knockdown of ANXA2 or EGFR, but is enhanced by expression of ectopic ANXA2 or EGFR. Downstream of ANXA2 and EGFR, the NF-κB pathway is activated and mediates M. hyorhinis-driven cell migration. In conclusion, our study unveils the effect of M. hyorhinis infection on gastric cancer survival and uncovers the mechanisms by which M. hyorhinis infects mammalian cells and promotes cancer cell migration.

New pharmacological strategies to fight enveloped viruses

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Many emerging or known, chronic viral diseases are caused by enveloped viruses.

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The review discusses research driven development of antivirals that became recently available or are in clinical evaluation.

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The main focus is on antiviral strategies with a broader therapeutic range, and on novel immune based therapeutics.

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Broad-spectrum antivirals will help to react faster to newly emerging viral diseases.

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Targeting immune cells against infected cells can restore immune responses in chronic infections.

Enveloped viruses pose an important health threat because most of the persistent and many emerging viruses are enveloped. In particular, newly emerging viruses create a need to develop broad-spectrum antivirals, which usually are obtained by targeting host cell factors. Persistent viruses have developed efficient strategies to escape host immune control, and treatment options are limited. Targeting host cell factors essential for virus persistence, or immune-based therapies provide alternative approaches. In this review, we therefore focus on recent developments to generate antivirals targeting host cell factors or immune-based therapeutic approaches to fight infections with enveloped viruses.

Alternative endocytosis pathway for productive entry of hepatitis C virus

Previous studies have shown that hepatitis C virus (HCV) enters human hepatic cells through interaction with a series of cellular receptors, followed by clathrin-mediated, pH-dependent endocytosis. Here, we investigated the mechanisms of HCV entry into multiple HCV-permissive human hepatocyte-derived cells using trans-complemented HCV particles (HCVtcp). Knockdown of CD81 and claudin-1, or treatment with bafilomycin A1, reduced infection in Huh-7 and Huh7.5.1 cells, suggesting that HCV entered both cell types via receptor-mediated, pH-dependent endocytosis. Interestingly, knockdown of the clathrin heavy chain or dynamin-2 (Dyn2), as well as expression of the dominant-negative form of Dyn2, reduced infection of Huh-7 cells with HCVtcp, whereas infectious entry of HCVtcp into Huh7.5.1 cells was not impaired. Infection of Huh7.5.1 cells with culture-derived HCV (HCVcc) via a clathrin-independent pathway was also observed. Knockdown of caveolin-1, ADP-ribosylation factor 6 (Arf6), flotillin, p21-activated kinase 1 (PAK1) and the PAK1 effector C-terminal binding protein 1 of E1A had no inhibitory effects on HCVtcp infection into Huh7.5.1 cells, thus suggesting that the infectious entry pathway of HCV into Huh7.5.1 cells was not caveolae-mediated, or Arf6- and flotillin-mediated endocytosis and macropinocytosis, but rather may have occurred via an undefined endocytic pathway. Further analysis revealed that HCV entry was clathrin- and dynamin-dependent in ORL8c and HepCD81/miR122 cells, but productive entry of HCV was clathrin- and dynamin-independent in Hep3B/miR122 cells. Collectively, these data indicated that HCV entered different target cells through different entry routes.

Exploration of genetically determined resistance against hepatitis C infection in high-risk injecting drug users

Genetic resistance to specific infections is well recognized. In hepatitis C virus (HCV) infection, genetic polymorphisms in IL-28B and the killer cell immunoglobulin-like receptors (KIR) and their HLA class I ligands have been shown to affect clearance of the virus following infection. There are limited data regarding resistance to established HCV infection. Reliable quantification of repeated exposure in high-risk populations, such as injecting drug users (IDU), is a key limitation of previous studies of resistance. Behavioural data and DNA from IDU (n = 210) in the Hepatitis C Incidence and Transmission Study in prisons (HITS-p) cohort were genotyped for polymorphisms in: IL-28B, peptidyl-prolyl isomerase A (PPIA), HLA-C and KIR2. To quantify risk, a composite risk index based on factors predictive of incident HCV infection was derived. Logistic regression analysis revealed the risk index was strongly associated with incident HCV infection (P < 0.0001). The upper tertile of the uninfected individuals had risk indices comparable to the incident cases, but remained uninfected. There were no significant differences in the frequencies of IL-28B or PPIA polymorphisms between these exposed-uninfected cases, or in the frequencies of KIR2-DL3, HLA-C1, or their combination. A framework for the investigation of genetic determinants of resistance to HCV infection has been developed. Several candidate gene associations were investigated and excluded. Further investigation of genetic determinants of resistance to HCV infection is warranted.

Endocytosis, signaling, and beyond

The endocytic network comprises a vast and intricate system of membrane-delimited cell entry and cargo sorting routes running between biochemically and functionally distinct intracellular compartments. The endocytic network caters to the organization and redistribution of diverse subcellular components, and mediates appropriate shuttling and processing of materials acquired from neighboring cells or the extracellular milieu. Such trafficking logistics, despite their importance, represent only one facet of endocytic function. The endocytic network also plays a key role in organizing, mediating, and regulating cellular signal transduction events. Conversely, cellular signaling processes tightly control the endocytic pathway at different steps. The present article provides a perspective on the intimate relationships that exist between particular endocytic and cellular signaling processes in mammalian cells, within the context of understanding the impact of this nexus on integrated physiology.

Structure-activity studies of (-)-epigallocatechin gallate derivatives as HCV entry inhibitors

Preventing viral entry into cells is a recognized approach for HIV therapy and has attracted attention for use against the hepatitis C virus (HCV). Recent reports described the activity of (-)-epigallocatechin gallate (EGCG) as an inhibitor of HCV entry with modest potency. EGCG is a polyphenolic natural product with a wide range of biological activity and unfavorable pharmaceutical properties. In an attempt to identify more drug-like EGCG derivatives with improved efficacy as HCV entry inhibitors, we initiated structure-activity investigations using semi-synthetic and synthetic EGCG analogs. The data show that there are multiple regions in the EGCG structure that contribute to activity. The gallate ester portion of the molecule appears to be of particular importance as a 3,4-difluoro analog of EGCG enhanced potency. This derivative and other active compounds were shown not to be cytotoxic in Huh-7 cell culture. These data suggest that more potent, non-cytotoxic EGCG analogs can be prepared in an attempt to identify more drug-like candidates to treat HCV infection by this mechanism.

The HCV life cycle: in vitro tissue culture systems and therapeutic targets

Hepatitis C virus (HCV) is a highly variable plus-strand RNA virus of the family Flaviviridae. Viral strains are grouped into six epidemiologically relevant genotypes that differ from each other by more than 30% at the nucleotide level. The variability of HCV allows immune evasion and facilitates persistence. It is also a substantial challenge for the development of specific antiviral therapies effective across all HCV genotypes and for prevention of drug resistance. Novel HCV cell culture models were instrumental for identification and profiling of therapeutic strategies. Concurrently, these models revealed numerous host factors critical for HCV propagation, some of which have emerged as targets for antiviral therapy. It is generally assumed that the use of host factors is conserved among HCV isolates and genotypes. Additionally, the barrier to viral resistance is thought to be high when interfering with host factors. Therefore, current drug development includes both targeting of viral factors but also of host factors essential for virus replication. In fact, some of these host-targeting agents, for instance inhibitors of cyclophilin A, have advanced to late stage clinical trials. Here, we highlight currently available cell culture systems for HCV, review the most prominent host-targeting strategies against hepatitis C and critically discuss opportunities and risks associated with host-targeting antiviral strategies.

Benzhydrylpiperazine compounds inhibit cholesterol-dependent cellular entry of hepatitis C virus

Hepatitis C virus (HCV) remains a serious global health problem that lacks an effective cure. Although the introduction of protease inhibitors to the current standard-of-care interferon/ribavirin therapy for HCV infection has improved sustained virological response of genotype 1-infected patients, these inhibitors exacerbate already problematic side effects. Thus, new HCV antivirals are urgently needed. Using a cell-protection screen previously developed in our laboratory, we evaluated 30,426 compounds for inhibitors of potentially any stage of the HCV life cycle and identified 49 new HCV inhibitors. The two most potent hits, hydroxyzine and chlorcyclizine, belong to the family of benzhydrylpiperazines and were found to inhibit the entry of cell culture-produced HCV with IC50 values of 19 and 2.3 nM, respectively, and therapeutic indices of >500 and >6500. Both compounds block HCV entry at a late stage of entry prior to viral fusion and their inhibitory activities are highly dependent on the host's cholesterol content. Both compounds are currently used in the clinic for treating allergy-related disorders and the reported peak plasma level (160 nM) and estimated liver concentration (1.7 μM) of hydroxyzine in humans are much higher than the molecule's anti-HCV IC90 in cell culture (64 nM). Further studies are therefore justified to evaluate the use of these molecules in an anti-HCV therapeutic regimen.

Unexpected structural features of the hepatitis C virus envelope protein 2 ectodomain

Hepatitis C virus (HCV), a member of the family Flaviviridae, is a leading cause of chronic liver disease and cancer. Recent advances in HCV therapeutics have resulted in improved cure rates, but an HCV vaccine is not available and is urgently needed to control the global pandemic. Vaccine development has been hampered by the lack of high-resolution structural information for the two HCV envelope glycoproteins, E1 and E2. Recently, Kong and coworkers (Science 342:1090-1094, 2013, doi:10.1126/science.1243876) and Khan and coworkers (Nature 509[7500]:381-384, 2014, doi:10.1038/nature13117) independently determined the structure of the HCV E2 ectodomain core with some unexpected and informative results. The HCV E2 ectodomain core features a globular architecture with antiparallel β-sheets forming a central β sandwich. The residues comprising the epitopes of several neutralizing and nonneutralizing human monoclonal antibodies were also determined, which is an essential step toward obtaining a fine map of the human humoral response to HCV. Also clarified were the regions of E2 that directly bind CD81, an important HCV cellular receptor. While it has been widely assumed that HCV E2 is a class II viral fusion protein (VFP), the newly determined structure suggests that the HCV E2 ectodomain shares structural and functional similarities only with domain III of class II VFPs. The new structural determinations suggest that the HCV glycoproteins use a different mechanism than that used by class II fusion proteins for cell fusion.

Identification of conserved residues in hepatitis C virus envelope glycoprotein E2 that modulate virus dependence on CD81 and SRB1 entry factors

In spite of the high variability of its sequence, hepatitis C virus (HCV) envelope glycoprotein E2 contains several conserved regions. In this study, we explored the structural and functional features of the highly conserved E2 segment from amino acid (aa) 502 to 520, which had been proposed as a fusion peptide and shown to strongly overlap a potential conserved neutralizing epitope. For this purpose, we used reverse genetics to introduce point mutations within this region, and we characterized the phenotypes of these mutants in the light of the recently published structure of E2. The functional analyses showed that their phenotypes are in agreement with the positions of the corresponding residues in the E2 crystal structure. In contrast, our data ruled out the involvement of this region in membrane fusion, and they indicate that alternative conformations would be necessary to expose the potential neutralizing epitope present in this segment. Of particular interest, we identified three specific mutations (Y507L, V514A, and V515A) located within this neutralizing epitope which only mildly reduced infectivity and showed no assembly defect. These mutations modulated HCV dependence on the viral receptor SRB1, and/or they also modulated virion sensitivity to neutralizing antibodies. Importantly, their characterization also showed that amino acids Y507, V514, and V515 contribute to E2 interaction with HCV receptor CD81. In conclusion, our data show that the highly conserved E2 segment from aa 502 to 520 plays a key role in cell entry by influencing the association of the viral particle with coreceptors and neutralizing antibodies.

IMPORTANCE

Hepatitis C virus (HCV) envelope proteins E1 and E2 exhibit sequence variability. However, some segments of the envelope proteins are highly conserved, suggesting that these sequences play a key role at some steps of the HCV life cycle. In this work, we characterized the function and structure of a highly conserved E2 region that is targeted by neutralizing antibodies and had been proposed as a fusion peptide. Our data ruled out the involvement of this region in membrane fusion but allowed for the identification of new residues modulating the interaction of the virus with entry factors and its sensitivity to neutralizing antibodies. Moreover, structural data suggest that alternative conformations could exist for E2, which would explain the presence of a partially masked neutralizing epitope in this segment in the currently available E2 structure. Overall, our findings highlight the importance of conserved regions in the sequences of HCV envelope proteins.

Turmeric curcumin inhibits entry of all hepatitis C virus genotypes into human liver cells

OBJECTIVE

Hepatitis C virus (HCV) infection causes severe liver disease and affects more than 160 million individuals worldwide. People undergoing liver organ transplantation face universal re-infection of the graft. Therefore, affordable antiviral strategies targeting the early stages of infection are urgently needed to prevent the recurrence of HCV infection. The aim of the study was to determine the potency of turmeric curcumin as an HCV entry inhibitor.

DESIGN

The antiviral activity of curcumin and its derivatives was evaluated using HCV pseudo-particles (HCVpp) and cell-culture-derived HCV (HCVcc) in hepatoma cell lines and primary human hepatocytes. The mechanism of action was dissected using R18-labelled virions and a membrane fluidity assay.

RESULTS

Curcumin treatment had no effect on HCV RNA replication or viral assembly/release. However, co-incubation of HCV with curcumin potently inhibited entry of all major HCV genotypes. Similar antiviral activities were also exerted by other curcumin derivatives but not by tetrahydrocurcumin, suggesting the importance of α,β-unsaturated ketone groups for the antiviral activity. Expression levels of known HCV receptors were unaltered, while pretreating the virus with the compound reduced viral infectivity without viral lysis. Membrane fluidity experiments indicated that curcumin affected the fluidity of the HCV envelope resulting in impairment of viral binding and fusion. Curcumin has also been found to inhibit cell-to-cell transmission and to be effective in combination with other antiviral agents.

CONCLUSIONS

Turmeric curcumin inhibits HCV entry independently of the genotype and in primary human hepatocytes by affecting membrane fluidity thereby impairing virus binding and fusion.

Protective immunity against hepatitis C: many shades of gray

The majority of individuals who become acutely infected with hepatitis C virus (HCV) develop chronic infection and suffer from progressive liver damage while approximately 25% are able to eliminate the virus spontaneously. Despite the recent introduction of new direct-acting antivirals, there is still no vaccine for HCV. As a result, new infections and reinfections will remain a problem in developing countries and among high risk populations like injection drug users who have limited access to treatment and who continue to be exposed to the virus. The outcome of acute HCV is determined by the interplay between the host genetics, the virus, and the virus-specific immune response. Studies in humans and chimpanzees have demonstrated the essential role of HCV-specific CD4 and CD8 T cell responses in protection against viral persistence. Recent data suggest that antibody responses play a more important role than what was previously thought. Individuals who spontaneously resolve acute HCV infection develop long-lived memory T cells and are less likely to become persistently infected upon reexposure. New studies examining high risk cohorts are identifying correlates of protection during real life exposures and reinfections. In this review, we discuss correlates of protective immunity during acute HCV and upon reexposure. We draw parallels between HCV and the current knowledge about protective memory in other models of chronic viral infections. Finally, we discuss some of the yet unresolved questions about key correlates of protection and their relevance for vaccine development against HCV.

Hepatitis C virus reactivation in cancer patients in the era of targeted therapies

The purpose of this review is to summarize the evidence of hepatitis C reactivation in cancer patients in the era of targeted therapies. Targeted therapies are novel therapeutics frequently used in cancer patients. During treatment with targeted therapies, viral replication is one of the major problems that can occur. The PubMed database, ASCO, and ASCO Gastrointestinal Cancer Symposium abstracts were searched up until September 15, 2013 using the following search keywords: “targeted therapies, rituximab, alemtuzumab, brentuximab, hepatitis, hepatitis C reactivation, tyrosine kinase inhibitors, imatinib, mammalian target of rapamycin (mTOR) inhibitors, everolimus, anti-HER therapies, trastuzumab, pertuzumab, lapatinib, anti-epidermal growth factor receptor therapies, cetuximab, panitumumab, and ipilimumab”. Papers considered relevant for the aim of this review were selected by the authors. The data about rituximab-induced hepatic flare in hepatitis C virus (HCV) positive patients is controversial. However, there is the possibility of life-threatening hepatic flare that can develop after HCV ribonucleic acid (HCV-RNA) viral load increases. Routine follow-up of liver function tests should be advised. Especially in high-risk patients, such as those with baseline chronic active hepatitis and cirrhosis, and where there are plans to administer rituximab concomitantly with corticosteroids, it is advised to have close follow-up of HCV viral load. The data is insufficient to make accurate statements about the association of alemtuzumab therapy and HCV reactivation. However, alemtuzumab may cause deep immunosuppression. Due to this, it is better to follow up with liver function tests and HCV RNA levels during alemtuzumab therapy. Brentuximab has effects on antibody dependent cellular toxicity and may decrease humoral immunity. Thus, we believe that during brentuximab treatment of HCV infected patients, clinicians may encounter hepatitis C reactivation. There have been no reported cases of hepatitis C reactivation with imatinib therapy. However, there are many reports of hepatitis B reactivation with imatinib treatment. Based on the evidence of hepatitis B reactivation with imatinib and the effects of imatinib on immune system functions, we suggest that imatinib therapy might be a risk factor for HCV reactivation. Anti-human epidermal growth factor receptor 2 therapies are not associated with hepatic flare in HCV infected patients. Post-transplant studies reported that mTOR was safely administered to patients with active hepatitis C without causing hepatic flare. Cetuximab and panitumumab have not been associated with HCV reactivation. Two cases of HCV infected melanoma were safely treated with ipilimumab without any HCV reactivation or hepatic flare. Targeted therapies are a new and emerging area of oncology treatment modalities. While treating HCV infected cancer patients, clinicians should be mindful of the immunosuppressive properties of targeted therapies. Further randomized trials are needed to establish algorithms for this issue.

The expression of the hepatocyte SLAMF3 (CD229) receptor enhances the hepatitis C virus infection

Hepatitis C virus (HCV) is a leading cause of cirrhosis and liver cancer worldwide. We recently characterized for the first time the expression of Signaling Lymphocyte Activating Molecule 3 (SLAMF3) in human hepatocytes and here, we report that SLAMF3 interacts with the HCV viral protein E2 and is implicated in HCV entry process. We found a strong correlation between SLAMF3 expression level and hepatocyte susceptibility to HCV infection. The use of specific siRNAs to down-modulate SLAMF3 expression and SLAMF3-blocking antibodies both decreased the hepatocytes susceptibility to HCV infection. Moreover, SLAMF3 over-expression significantly increased susceptibility to HCV infection. Interestingly, experiments with peptides derived from each SLAMF3 domain showed that the first N-terminal extracellular domain is essential for interaction with HCV particles. Finally, we showed that recombinant HCV envelop protein E2 can bind SLAMF3 and that anti-SLAMF3 antibodies inhibited specifically this interaction. Overall, our results revealed that SLAMF3 plays a role during HCV entry, likely by enhancing entry of viral particle within hepatocytes.

Suppression of hepatitis C virus replication by cyclin-dependent kinase inhibitors

Hepatitis C virus (HCV) is a causative agent of chronic hepatitis. Although the standard therapy for HCV-infected patients consists of pegylated interferon plus ribavirin, this treatment is associated with serious side effects and high costs, and fails in some patients infected with specific HCV genotypes. To address this problem, we are developing small-molecule inhibitors of cyclin-dependent kinases (CDKs) as novel anti-HCV drug candidates. Previous data showed that HCV replication is inhibited by retinoblastoma protein, which is itself inactivated by CDK-mediated phosphorylation. Here, we report that CDK inhibitors suppress HCV replication in vitro and in vivo, and that CDK4 is required for efficient HCV replication. These findings shed light on the development of novel anti-HCV drugs that target host factors.

Viruses exploit the function of epidermal growth factor receptor

Epidermal growth factor receptor (EGFR) is a receptor tyrosine kinase that regulates cellular homeostatic processes. Following ligand binding, EGFR activates different downstream signalling cascades that promote cell survival, proliferation, motility, and angiogenesis and induces F-actin-dependent EGFR endocytosis, which relocalises the activated receptors for degradation or recycling. The responses that are induced by ligand binding to EGFR, including cell signalling activation, protein kinase phosphorylation and cytoskeletal network rearrangement, resemble those induced by virus infection. Increasing evidence demonstrates that many viruses usurp EGFR endocytosis or EGFR-mediated signalling for entry, replication, inflammation, and viral antagonism to the host antiviral system. In addition, viruses have acquired sophisticated mechanisms to regulate EGFR functions by interrupting the EGFR-recycling process and modulating EGFR expression. In this review, we provide an overview of the mechanisms by which viruses alter EGFR signalling in favour of their continued survival.

Integrative functional genomics of hepatitis C virus infection identifies host dependencies in complete viral replication cycle

Recent functional genomics studies including genome-wide small interfering RNA (siRNA) screens demonstrated that hepatitis C virus (HCV) exploits an extensive network of host factors for productive infection and propagation. How these co-opted host functions interact with various steps of HCV replication cycle and exert pro- or antiviral effects on HCV infection remains largely undefined. Here we present an unbiased and systematic strategy to functionally interrogate HCV host dependencies uncovered from our previous infectious HCV (HCVcc) siRNA screen. Applying functional genomics approaches and various in vitro HCV model systems, including HCV pseudoparticles (HCVpp), single-cycle infectious particles (HCVsc), subgenomic replicons, and HCV cell culture systems (HCVcc), we identified and characterized novel host factors or pathways required for each individual step of the HCV replication cycle. Particularly, we uncovered multiple HCV entry factors, including E-cadherin, choline kinase α, NADPH oxidase CYBA, Rho GTPase RAC1 and SMAD family member 6. We also demonstrated that guanine nucleotide binding protein GNB2L1, E2 ubiquitin-conjugating enzyme UBE2J1, and 39 other host factors are required for HCV RNA replication, while the deubiquitinating enzyme USP11 and multiple other cellular genes are specifically involved in HCV IRES-mediated translation. Families of antiviral factors that target HCV replication or translation were also identified. In addition, various virologic assays validated that 66 host factors are involved in HCV assembly or secretion. These genes included insulin-degrading enzyme (IDE), a proviral factor, and N-Myc down regulated Gene 1 (NDRG1), an antiviral factor. Bioinformatics meta-analyses of our results integrated with literature mining of previously published HCV host factors allows the construction of an extensive roadmap of cellular networks and pathways involved in the complete HCV replication cycle. This comprehensive study of HCV host dependencies yields novel insights into viral infection, pathogenesis and potential therapeutic targets.

Hepatitis C virus (HCV) is a positive strand RNA virus that belongs to the Flaviridae family. Chronic HCV infection is a leading cause of end-stage liver disease, which is associated with significant morbidity and mortality in the world. Our recent genome-wide siRNA screen has revealed that HCV depends extensively on host factors for efficient infection and propagation. Here we systematically and functionally catalogued these host dependencies to various stages of the HCV replication cycle. Applying systems virology and functional genomics approaches with various in vitro HCV model systems, we further defined multiple previously unrecognized host factors or pathways that are involved in either HCV entry, IRES-mediated translation, RNA replication, or assembly/secretion. By bioinformatics meta-analyses and literature mining of existing publications and databases, we constructed an extensive roadmap of the cellular networks and pathways requisite for the complete HCV replication cycle. Our study yields novel insights into viral infection, pathogenesis and potential therapeutic targets. Furthermore, this study serves as a valuable reference source for subsequent work on host pathways and virus-host interactions in general.

Autophagy in hepatitis C virus-host interactions: potential roles and therapeutic targets for liver-associated diseases

Autophagy is a lysosome-associated, degradative process that catabolizes cytosolic components to recycle nutrients for further use and maintain cell homeostasis. Hepatitis C virus (HCV) is a major cause of chronic hepatitis, which often leads to end-stage liver-associated diseases and is a significant burden on worldwide public health. Emerging lines of evidence indicate that autophagy plays an important role in promoting the HCV life cycle in host cells. Moreover, the diverse impacts of autophagy on a variety of signaling pathways in HCV-infected cells suggest that the autophagic process is required for balancing HCV-host cell interactions and involved in the pathogenesis of HCV-related liver diseases. However, the detailed molecular mechanism underlying how HCV activates autophagy to benefit viral growth is still enigmatic. Additionally, how the autophagic response contributes to disease progression in HCV-infected cells remains largely unknown. Hence, in this review, we overview the interplay between autophagy and the HCV life cycle and propose possible mechanisms by which autophagy may promote the pathogenesis of HCV-associated chronic liver diseases. Moreover, we outline the related studies on how autophagy interplays with HCV replication and discuss the possible implications of autophagy and viral replication in the progression of HCV-induced liver diseases, e.g., steatosis and hepatocellular carcinoma. Finally, we explore the potential therapeutics that target autophagy to cure HCV infection and its related liver diseases.

Hepatitis C virus cell-cell transmission and resistance to direct-acting antiviral agents

Hepatitis C virus (HCV) is transmitted between hepatocytes via classical cell entry but also uses direct cell-cell transfer to infect neighboring hepatocytes. Viral cell-cell transmission has been shown to play an important role in viral persistence allowing evasion from neutralizing antibodies. In contrast, the role of HCV cell-cell transmission for antiviral resistance is unknown. Aiming to address this question we investigated the phenotype of HCV strains exhibiting resistance to direct-acting antivirals (DAAs) in state-of-the-art model systems for cell-cell transmission and spread. Using HCV genotype 2 as a model virus, we show that cell-cell transmission is the main route of viral spread of DAA-resistant HCV. Cell-cell transmission of DAA-resistant viruses results in viral persistence and thus hampers viral eradication. We also show that blocking cell-cell transmission using host-targeting entry inhibitors (HTEIs) was highly effective in inhibiting viral dissemination of resistant genotype 2 viruses. Combining HTEIs with DAAs prevented antiviral resistance and led to rapid elimination of the virus in cell culture model. In conclusion, our work provides evidence that cell-cell transmission plays an important role in dissemination and maintenance of resistant variants in cell culture models. Blocking virus cell-cell transmission prevents emergence of drug resistance in persistent viral infection including resistance to HCV DAAs.

In spite of the rapid development of antiviral agents, antiviral resistance remains a challenge for the treatment of viral infections including hepatitis B and C virus (HBV, HCV), human immunodeficiency virus (HIV) and influenza. Virus spreads from infected cells to surrounding uninfected host cells to develop infection through cell-free and cell-cell transmission routes. Understanding the spread of resistant virus is important for the development of novel antiviral strategies to prevent and treat antiviral resistance. Here, we characterize the spread of resistant viruses and its impact for emergence and prevention of resistance using HCV as a model system. Our results show that cell-cell transmission is the main transmission route for antiviral resistant HCV strains and is crucial for the maintenance of infection. Monoclonal antibodies or small molecules targeting HCV entry factors are effective in inhibiting the spread of resistant HCV in cell culture models and thus should be evaluated clinically for prevention and treatment of HCV resistance. Combination of inhibitors targeting viral entry and clinically used direct-acting antivirals (DAAs) prevents antiviral resistance and leads to viral eradication in cell culture models. Collectively, the investigation provides a new strategy for prevention of viral resistance to antiviral agents.

Cell death-inducing DFFA-like effector b is required for hepatitis C virus entry into hepatocytes

The molecular mechanism of the hepatic tropism of hepatitis C virus (HCV) remains incompletely defined. In vitro hepatic differentiation of pluripotent stem cells produces hepatocyte-like cells (HLCs) permissive for HCV infection, providing an opportunity for studying liver development and host determinants of HCV susceptibility. We previously identified the transition stage of HCV permissiveness and now investigate whether a host protein whose expression is induced during this transition stage is important for HCV infection. We suppressed the expression of a liver-specific protein, cell death-inducing DFFA-like effector b (CIDEB), and performed hepatocyte function and HCV infection assays. We also used a variety of cell-based assays to dissect the specific step of the HCV life cycle that potentially requires CIDEB function. We found CIDEB to be an essential cofactor for HCV entry into hepatocytes. Genetic interference with CIDEB in stem cells followed by hepatic differentiation leads to HLCs that are refractory to HCV infection, and infection time course experiments revealed that CIDEB functions in a late step of HCV entry, possibly to facilitate membrane fusion. The role of CIDEB in mediating HCV entry is distinct from those of the well-established receptors, as it is not required for HCV pseudoparticle entry. Finally, HCV infection effectively downregulates CIDEB protein through a posttranscriptional mechanism.

IMPORTANCE

This study identifies a hepatitis C virus (HCV) entry cofactor that is required for HCV infection of hepatocytes and potentially facilitates membrane fusion between viral and host membranes. CIDEB and its interaction with HCV may open up new avenues of investigation of lipid droplets and viral entry.

Current status in the therapy of liver diseases

Hepatic diseases, like viral hepatitis, autoimmune hepatitis, hereditary hemochromatosis, non-alcoholic fatty liver disease (NAFLD) and Wilson’s disease, play an important role in the development of liver cirrhosis and, hence, hepatocellular carcinoma. In this review, the current treatment options and the molecular mechanisms of action of the drugs are summarized. Unfortunately, the treatment options for most of these hepatic diseases are limited. Since hepatitis B (HBV) and C (HCV) infections are the most common causes of liver cirrhosis and hepatocellular carcinoma, they are the focus of the development of new drugs. The current treatment of choice for HBV/HCV infection is an interferon-based combination therapy with oral antiviral drugs, like nucleos(t)ide analogues, which is associated with improving the therapeutic success and also preventing the development of resistances. Currently, two new protease inhibitors for HCV treatment are expected (deleobuvir, faldaprevir) and together with the promising drug, daclatasvir (NS5A-inhibitor, currently in clinical trials), adequate therapy is to be expected in due course (circumventing the requirement of interferon with its side-effects), while in contrast, efficient HBV therapeutics are still lacking. In this respect, entry inhibitors, like Myrcludex B, the lead substance of the first entry inhibitor for HBV/HDV (hepatitis D) infection, provide immense potential. The pharmacokinetics and the mechanism of action of Myrcludex B are described in detail.

Nuclear receptor 4 group A member 1 determines hepatitis C virus entry efficiency through the regulation of cellular receptor and apolipoprotein E expression

Orphan nuclear receptor subfamily 4 group A member 1 (NR4A1) is a transcription factor stimulated by many factors and plays pivotal roles in metabolism, proliferation and apoptosis. In this study, the expression of NR4A1 in Huh7.5.1 cells was significantly upregulated by hepatitis C virus (HCV) infection. The silencing of NR4A1 inhibited the entry of HCV and reduced the specific infectivity of secreted HCV particles but had only minor or no effect on the genome replication and translation, virion assembly and virus release steps of the virus life cycle. Further experiments demonstrated that the silencing of NR4A1 affected virus entry through pan-downregulation of the expression of HCV receptors scavenger receptor BI, occludin, claudin-1 and epidermal growth factor receptor but not CD81. The reduced specific infectivity of HCV in the knockdown cells was due to decreased apolipoprotein E (ApoE) expression. These results explain the delayed spread of HCV in NR4A1 knockdown Huh7.5.1 cells. Thus, NR4A1 plays a role in HCV replication through regulating the expression of HCV receptors and ApoE, and facilitates HCV entry and spread.

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.

Immunologic, metabolic and genetic factors in hepatitis C virus infection

The mechanisms that regulate disease progression during hepatitis C virus (HCV) infection and the response to treatment are not clearly identified. Numerous studies have demonstrated that a strong host immune response against HCV favors HCV clearance. In addition, genetic factors and metabolic machinery, particularly cholesterol modulation, are involved in HCV infection. It is likely that the interplay between all of these factors contributes to the outcome of HCV infection. In recent years, the world has experienced its largest epidemic of obesity. Mexico and the United States are the leading sufferers from this epidemic at the global level. Obesity is associated with the development of numerous pathologies including hypercholesterolemia which is one of the eight most important risk factors for mortality in Mexico. This may be related to the course of HCV infection in this population. Here, we focus on the urgent need to study the progression of HCV infection in relation to ethnic characteristics. Discoveries are discussed that hold promise in identifying immune, metabolic and genetic factors that, in conjunction, could be therapeutic targets or predictors of the progression of HCV infection.