Hepatitis C virus core protein suppresses NF-kappaB activation and cyclooxygenase-2 expression by direct interaction with IkappaB kinase beta

From viruses to cancer: exploring the role of the hepatitis C virus NS3 protein in carcinogenesis

Hepatitis C virus (HCV) chronically infects approximately 170 million people worldwide and is a known etiological agent of hepatocellular carcinoma (HCC). The molecular mechanisms of HCV-mediated carcinogenesis are not fully understood. This review article focuses on the oncogenic potential of NS3, a viral protein with transformative effects on cells, although the precise mechanisms remain elusive. Unlike the more extensively studied Core and NS5A proteins, NS3's roles in cancer development are less defined but critical. Research indicates that NS3 is implicated in several carcinogenic processes such as proliferative signaling, cell death resistance, genomic instability and mutations, invasion and metastasis, tumor-related inflammation, immune evasion, and replicative immortality. Understanding the direct impact of viral proteins such as NS3 on cellular transformation is crucial for elucidating HCV's role in HCC development. Overall, this review sheds light on the molecular mechanisms used by NS3 to contribute to hepatocarcinogenesis, and highlights its significance in the context of HCV-associated HCC, underscoring the need for further investigation into its specific molecular and cellular actions.

Potential roles of core and core+1 proteins during the chronic phase of hepatitis C virus infection

The HCV Core protein is a multifunctional protein that interacts with many viral and cellular proteins. In addition to the encapsidation of the viral genome, it can disturb various cellular pathways and impede antiviral cellular responses such as interferon (IFN) production. The Core protein can also disrupt the functions of immune cells against HCV. The Core protein helps viral infection persistency by interfering with apoptosis. The Core+1 protein plays a significant role in inducing chronic HCV infection through diverse mechanisms. We review some of the mechanisms by which Core and Core+1 proteins facilitate HCV infection to chronic infection. These proteins could be considered for designing more sufficient treatments and effective vaccines against HCV.

The HCV Envelope Glycoprotein Down-Modulates NF-κB Signalling and Associates With Stimulation of the Host Endoplasmic Reticulum Stress Pathway

Following acute HCV infection, the virus establishes a chronic disease in the majority of patients whilst few individuals clear the infection spontaneously. The precise mechanisms that determine chronic HCV infection or spontaneous clearance are not completely understood but are proposed to be driven by host and viral genetic factors as well as HCV encoded immunomodulatory proteins. Using the HIV-1 LTR as a tool to measure NF-κB activity, we identified that the HCV E1E2 glycoproteins and more so the E2 protein down-modulates HIV-1 LTR activation in 293T, TZM-bl and the more physiologically relevant Huh7 liver derived cell line. We demonstrate this effect is specifically mediated through inhibiting NF-κB binding to the LTR and show that this effect was conserved for all HCV genotypes tested. Transcriptomic analysis of 293T cells expressing the HCV glycoproteins identified E1E2 mediated stimulation of the endoplasmic reticulum (ER) stress response pathway and upregulation of stress response genes such as ATF3. Through shRNA mediated inhibition of ATF3, one of the components, we observed that E1E2 mediated inhibitory effects on HIV-1 LTR activity was alleviated. Our in vitro studies demonstrate that HCV Env glycoprotein activates host ER Stress Pathways known to inhibit NF-κB activity. This has potential implications for understanding HCV induced immune activation as well as oncogenesis.

Sero-reactivity to three distinct regions within the hepatitis C virus alternative reading frame protein (ARFP/core+1) in patients with chronic HCV genotype-3 infection

Hepatitis C virus (HCV) infection affects more than 71 million people worldwide. The disease slowly progresses to chronic, long-term liver injury which leads to hepatocellular carcinoma (HCC) in 5 % of infections. The alternative reading frame protein (ARFP/core+1) is encoded by a sequence overlapping the HCV core gene in the +1 reading frame. Its role in hepatitis C pathogenesis and the viral life cycle is unclear, although some observers have related its production to disease progression and the development of HCC. The aim of this study was to determine whether ARFP is immunogenic in patients with chronic HCV genotype 3 infection and to assess whether sero-reactivity is associated with disease progression, particularly to HCC. Immunogenic epitopes within the protein were predicted by a bioinformatics tool, and three -20 aa length-peptides (ARFP-P1, ARFP-P2 and ARFP-P3) were synthesized and used in an avidin-biotin ARFP/core+1 peptide ELISA. Serum samples from 50 patients with chronic HCV genotype 3 infection, 50 genotype-1 patients, 50 HBV patients and 110 healthy controls were tested. Sero-reactivity to the ARFP peptides was also tested and compared in 114 chronic HCV genotype-3 patients subdivided on the basis of disease severity into non-cirrhotic, cirrhotic and HCC groups. Chronic HCV genotype-3 patients showed noticeable rates of reactivity to ARFP and core peptides. Seropositivity rates were 58% for ARFP-P1, 47 % for ARFP-P2, 5.9 % for ARFP-P3 and 100 % for C22 peptides. There was no significant difference between these seroreactivities between HCV genotype-3 patients with HCC, and HCV genotype-3 patients with and without liver cirrhosis. Patients with chronic HCV genotype-3 infection frequently produce antibodies against ARFP/core+1 protein. ARFP peptide reactivity was not associated with disease severity in patients with HCV genotype-3. These results support the conclusion that ARFP/core+1 is produced during HCV infection, but they do not confirm that antibodies to ARFP can indicate HCV disease progression.

Implications of viral infection in cancer development

Since the identification of the first human oncogenic virus in 1964, viruses have been studied for their potential role in aiding the development of cancer. Through the modulation of cellular pathways associated with proliferation, immortalization, and inflammation, viral proteins can mimic the effect of driver mutations and contribute to transformation. Aside from the modulation of signaling pathways, the insertion of viral DNA into the host genome and the deregulation of cellular miRNAs represent two additional mechanisms implicated in viral oncogenesis. In this review, we will discuss the role of twelve different viruses on cancer development and how these viruses utilize the abovementioned mechanisms to influence oncogenesis. The identification of specific mechanisms behind viral transformation of human cells could further elucidate the process behind cancer development.

Hepatitis C virus core protein: Not just a nucleocapsid building block, but an immunity and inflammation modulator

Coevolution occurs between viruses and their hosts. The hosts need to evolve means to eliminate pathogenic virus infections, and the viruses, for their own survival and multiplication, have to develop mechanisms to escape clearance by hosts. Hepatitis C virus (HCV) of Flaviviridae is a pathogen which infects human liver and causes hepatitis, a condition of liver inflammation. Unlike most of the other flaviviruses, HCV has an excellent ability to evade host immunity to establish chronic infection. The persistent liver infection leads to chronic hepatitis, liver cirrhosis, hepatocellular carcinoma (HCC), as well as extrahepatic HCV-related diseases. HCV genomic RNA only expresses 10 proteins, many of which bear functions, in addition to those involved in HCV life cycle, for assisting the virus to develop its persistency. HCV core protein is a structural protein which encapsulates HCV genomic RNA and assembles into nucleocapsids. The core protein is also found to exert functions to affect host inflammation and immune responses by altering a variety of host pathways. This paper reviews the studies regarding the HCV core protein-induced alterations of host immunity and inflammatory responses, as well as the involvements of the HCV core protein in pro- and anti-inflammatory cytokine stimulations, host cellular transcription, lipid metabolism, cell apoptosis, cell proliferations, immune cell differentiations, oxidative stress, and hepatocyte steatosis, which leads to liver fibrosis, cirrhosis, and HCC. Implications of roles played by the HCV core protein in therapeutic resistance are also discussed.

Inflammatory Mechanisms of HCC Development

HCC (hepatocellular carcinoma) is the second leading cause of cancer deaths worldwide, with several etiologic causes, mostly inflammation-associated. Different inflammatory responses in the liver can be triggered by different etiological agents. The inflammatory process can be resolved or be persistent, depending on the etiology and multiple other factors. Chronic inflammation, tissue remodeling, genetic alterations, and modifications in cellular signaling are considered to be key processes promoting immunosuppression. The progressive immunosuppression leads to the inactivation of anti-tumor immunity involved in HCC carcinogenesis and progression. Tumor cellular processes including DNA damage, necrosis, and ER (endoplasmic reticulum) stress can affect both immune-surveillance and cancer-promoting inflammation, supporting a mutual interdependence. Here, we review the current understanding of how chronic liver injury and inflammation is triggered and sustained, and how inflammation is linked to HCC. The identification of many hepatic microenvironmental inflammatory processes and their effector molecules, has resulted in extensive translational work and promising clinical trials of new immunomodulatory agents.

Complexity on modulation of NF-κB pathways by hepatitis B and C: A double-edged sword in hepatocarcinogenesis

Nuclear factor-κB (NF-κB), a family of master regulated dimeric transcription factors, signaling transduction pathways are active players in the cell signaling that control vital cellular processes, including cell growth, proliferation, differentiation, apoptosis, morphogenesis, angiogenesis, and immune responses. Nevertheless, aberrant regulation of the NF-κB signaling pathways has been associated with a significant number of human cancers. In fact, NF-κB acts as a double-edged sword in the vital cellular processes and carcinogenesis. This review provides an overview on the modulation of the NF-κB signaling pathways by proteins of hepatitis B and C viruses. One of the major NF-κB events that are modulated by these viruses is the induction of hepatocellular carcinoma. Given the central function of NF-κB in carcinogenesis, it has turned out to be a considerable therapeutic target for cancer therapy.

The hepatitis C virus (HCV) protein, p7, suppresses inflammatory responses to tumor necrosis factor (TNF)-α via signal transducer and activator of transcription (STAT)3 and extracellular signal-regulated kinase (ERK)-mediated induction of suppressor of cytokine signaling (SOCS)3

Viruses use a spectrum of immune evasion strategies that enable infection and replication. The acute phase of hepatitis C virus (HCV) infection is characterized by nonspecific and often mild clinical symptoms, suggesting an immunosuppressive mechanism that, unless symptomatic liver disease presents, allows the virus to remain largely undetected. We previously reported that HCV induced the regulatory protein suppressor of cytokine signaling (SOCS)3, which inhibited TNF-α-mediated inflammatory responses. However, the mechanism by which HCV up-regulates SOCS3 remains unknown. Here we show that the HCV protein, p7, enhances both SOCS3 mRNA and protein expression. A p7 inhibitor reduced SOCS3 induction, indicating that p7's ion channel activity was required for optimal up-regulation of SOCS3. Short hairpin RNA and chemical inhibition revealed that both the Janus kinase-signal transducer and activator of transcription (JAK-STAT) and MAPK pathways were required for p7-mediated induction of SOCS3. HCV-p7 expression suppressed TNF-α-mediated IκB-α degradation and subsequent NF-κB promoter activity, revealing a new and functional, anti-inflammatory effect of p7. Together, these findings identify a molecular mechanism by which HCV-p7 induces SOCS3 through STAT3 and ERK activation and demonstrate that p7 suppresses proinflammatory responses to TNF-α, possibly explaining the lack of inflammatory symptoms observed during early HCV infection.-Convery, O., Gargan, S., Kickham, M., Schroder, M., O'Farrelly, C., Stevenson, N. J. The hepatitis C virus (HCV) protein, p7, suppresses inflammatory responses to tumor necrosis factor (TNF)-α via signal transducer and activator of transcription (STAT)3 and extracellular signal-regulated kinase (ERK)-mediated induction of suppressor of cytokine signaling (SOCS)3.

The Immunogenicity in Mice of HCV Core Delivered as DNA Is Modulated by Its Capacity to Induce Oxidative Stress and Oxidative Stress Response

HCV core is an attractive HCV vaccine target, however, clinical or preclinical trials of core-based vaccines showed little success. We aimed to delineate what restricts its immunogenicity and improve immunogenic performance in mice. We designed plasmids encoding full-length HCV 1b core and its variants truncated after amino acids (aa) 60, 98, 152, 173, or up to aa 36 using virus-derived or synthetic polynucleotides (core191/60/98/152/173/36_191v or core152s DNA, respectively). We assessed their level of expression, route of degradation, ability to trigger the production of reactive oxygen species/ROS, and to activate the components of the Nrf2/ARE antioxidant defense pathway heme oxygenase 1/HO-1 and NAD(P)H: quinone oxidoreductase/Nqo-1. All core variants with the intact N-terminus induced production of ROS, and up-regulated expression of HO-1 and Nqo-1. The capacity of core variants to induce ROS and up-regulate HO-1 and Nqo-1 expression predetermined their immunogenicity in DNA-immunized BALB/c and C57BL/6 mice. The most immunogenic was core 152s, expressed at a modest level and inducing moderate oxidative stress and oxidative stress response. Thus, immunogenicity of HCV core is shaped by its ability to induce ROS and oxidative stress response. These considerations are important in understanding the mechanisms of viral suppression of cellular immune response and in HCV vaccine design.

Hepatitis C virus core protein modulates several signaling pathways involved in hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is the fifth most common cancer, and hepatitis C virus (HCV) infection plays a major role in HCC development. The molecular mechanisms by which HCV infection leads to HCC are varied. HCV core protein is an important risk factor in HCV-associated liver pathogenesis and can modulate several signaling pathways involved in cell cycle regulation, cell growth promotion, cell proliferation, apoptosis, oxidative stress and lipid metabolism. The dysregulation of signaling pathways such as transforming growth factor β (TGF-β), vascular endothelial growth factor (VEGF), Wnt/β-catenin (WNT), cyclooxygenase-2 (COX-2) and peroxisome proliferator-activated receptor α (PPARα) by HCV core protein is implicated in the development of HCC. Therefore, it has been suggested that this protein be considered a favorable target for further studies in the development of HCC. In addition, considering the axial role of these signaling pathways in HCC, they are considered druggable targets for cancer therapy. Therefore, using strategies to limit the dysregulation effects of core protein on these signaling pathways seems necessary to prevent HCV-related HCC.

Molecular Mechanisms of Hepatocarcinogenesis Following Sustained Virological Response in Patients with Chronic Hepatitis C Virus Infection

Despite the success of direct-acting antiviral (DAA) agents in treating chronic hepatitis C virus (HCV) infection, the number of cases of HCV-related hepatocellular carcinoma (HCC) is expected to increase over the next five years. HCC develops over the span of decades and is closely associated with fibrosis stage. HCV both directly and indirectly establishes a pro-inflammatory environment favorable for viral replication. Repeated cycles of cell death and regeneration lead to genomic instability and loss of cell cycle control. DAA therapy offers >90% sustained virological response (SVR) rates with fewer side effects and restrictions than interferon. While elimination of HCV helps to restore liver function and reverse mild fibrosis, post-SVR patients remain at elevated risk of HCC. A series of studies reporting higher than expected rates of HCC development among DAA-treated patients ignited debate over whether use of DAAs elevates HCC risk compared to interferon. However, recent prospective and retrospective studies based on larger patient cohorts have found no significant difference in risk between DAA and interferon therapy once other factors are taken into account. Although many mechanisms and pathways involved in hepatocarcinogenesis have been elucidated, our understanding of drivers specific to post-SVR hepatocarcinogenesis is still limited, and lack of suitable in vivo and in vitro experimental systems has hampered efforts to examine etiology-specific mechanisms that might serve to answer this question more thoroughly. Further research is needed to identify risk factors and biomarkers for post-SVR HCC and to develop targeted therapies based on more complete understanding of the molecules and pathways implicated in hepatocarcinogenesis.

The hepatitis C virus protein NS3 suppresses TNF-α-stimulated activation of NF-κB by targeting LUBAC

The transcription factor nuclear factor κB (NF-κB) is crucial for innate immune defense against viral infections, and its activation requires the ubiquitylation of upstream proteins, including the adaptor protein NEMO (NF-κB essential modulator). Many infectious pathogens, including hepatitis C virus (HCV), inhibit NF-κB signaling in host cells, which promotes pathogen survival. Frequently, HCV-infected individuals develop a chronic infection, which suggests that HCV can subvert host antiviral responses. We found that HCV infection and replication inhibited the activation of NF-κB by the inflammatory cytokine tumor necrosis factor-α (TNF-α), which was mediated by the viral protein NS3 and, to a lesser extent, NS5B. NS3 directly interacted with linear ubiquitin chain assembly complex (LUBAC), competed with NEMO for binding to LUBAC, and inhibited the LUBAC-mediated linear ubiquitylation of NEMO and the subsequent activation of NF-κB. Together, our results highlight an immune evasion strategy adopted by HCV to modulate host antiviral responses and enhance virus survival and persistence.

Enterovirus 71 2C Protein Inhibits NF-κB Activation by Binding to RelA(p65)

Viruses evolve multiple ways to interfere with NF-κB signaling, a key regulator of innate and adaptive immunity. Enterovirus 71 (EV71) is one of primary pathogens that cause hand-foot-mouth disease. Here, we identify RelA(p65) as a novel binding partner for EV71 2C protein from yeast two-hybrid screen. By interaction with IPT domain of p65, 2C reduces the formation of heterodimer p65/p50, the predominant form of NF-κB. We also show that picornavirus 2C family proteins inhibit NF-κB activation and associate with p65 and IKKβ. Our findings provide a novel mechanism how EV71 antagonizes innate immunity.

Betulinic acid exerts anti-hepatitis C virus activity via the suppression of NF-κB- and MAPK-ERK1/2-mediated COX-2 expression

BACKGROUND AND PURPOSE

This study was designed to evaluate the effect of betulinic acid (BA), extracted from Avicennia marina, on the replication of hepatitis C virus (HCV) and to investigate the mechanism of this BA-mediated anti-HCV activity.

EXPERIMENTAL APPROACH

HCV replicon and infectious systems were used to evaluate the anti-HCV activity of BA. Exogenous COX-2 or knock-down of COX-2 expression was used to investigate the role of COX-2 in the anti-HCV activity of BA. The effects of BA on the phosphorylation of NF-κB and on kinases in the MAPK signalling pathway were determined. The anti-HCV activity of BA in combination with other HCV inhibitors was also determined to assess its use as an anti-HCV supplement.

KEY RESULTS

BA inhibited HCV replication in both Ava5 replicon cells and in a cell culture-derived infectious HCV particle system. Treatment with a combination of BA and IFN-α, the protease inhibitor telaprevir or the NS5B polymerase inhibitor sofosbuvir resulted in the synergistic suppression of HCV RNA replication. Exogenous overexpression of COX-2 gradually attenuated the inhibitory effect of BA on HCV replication, suggesting that BA reduces HCV replication by suppressing the expression of COX-2. In particular, BA down-regulated HCV-induced COX-2 expression by reducing the phosphorylation of NF-κB and ERK1/2 of the MAPK signalling pathway.

CONCLUSIONS AND IMPLICATIONS

BA inhibits HCV replication by suppressing the NF-κB- and ERK1/2-mediated COX-2 pathway and may serve as a promising compound for drug development or as a potential supplement for use in the treatment of HCV-infected patients.

Hepatitis C virus-mediated Aurora B kinase inhibition modulates inflammatory pathway and viral infectivity

BACKGROUND & AIMS

Chronic hepatitis C is a leading cause of chronic liver disease, cirrhosis and hepatocellular carcinoma. DNA methylation and histone covalent modifications constitute crucial mechanisms of genomic instability in human disease, including liver fibrosis and hepatocellular carcinoma. The present work studies the consequences of HCV-induced histone modifications in early stages of infection.

METHODS

Human primary hepatocytes and HuH7.5 cells were transiently transfected with the core protein of hepatitis C virus (HCV) genotypes 1a, 1b, and 2a. Infectious genotype 2a HCV in culture was also used.

RESULTS

We show that HCV and core protein inhibit the phosphorylation of Serine 10 in histone 3. The inhibition is due to the direct interaction between HCV core and Aurora B kinase (AURKB) that results in a decrease of AURKB activity. HCV and core significantly downregulate NF-κB and COX-2 transcription, two proteins with anti-apoptotic and proliferative effects implicated in the control of the inflammatory response. AURKB depletion reduced HCV and core repression of NF-κB and COX-2 gene transcription and AURKB overexpression reversed the viral effect. AURKB abrogation increased HCV specific infectivity which was decreased when AURKB was overexpressed.

CONCLUSIONS

The core-mediated decrease of AURKB activity may play a role in the inflammatory pathway during the initial steps of viral infection, while ensuring HCV infectivity.

Autoimmune reactions in the course of the hepatitis C virus (HCV) infection

The immune response to the presence of the virus, both specific and non-specific, plays a decisive role in the natural history of the infection, and influences the intensity of lesions in the liver. Despite the great progress which we were able to observe over the last several years, many issues still require clarification.

The problem of autoimmune reactions during hepatitis C virus (HCV) infection includes at least two issues. First, the risk of exacerbating reactions against the organism’s own tissues that existed before the treatment. There is also an increased risk of the development of de novo autoimmune reactions, triggered mostly by interferon α. Hepatitis C virus infection predisposes to the development of diseases characterised as being certainly or probably immune-mediated.

Currently the situation has changed due to introducing non-interferon therapies for HCV treatment, which eliminate the risk associated with immunotherapy in patients with autoimmune diseases, yet the therapies are not widely available.

Hepatitis C virus-induced hepatocellular carcinoma

Hepatitis C virus (HCV) is a leading etiology of hepatocellular carcinoma (HCC). The interaction of HCV with its human host is complex and multilayered; stemming in part from the fact that HCV is a RNA virus with no ability to integrate in the host's genome. Direct and indirect mechanisms of HCV-induced HCC include activation of multiple host pathways such as liver fibrogenic pathways, cellular and survival pathways, interaction with the immune and metabolic systems. Host factors also play a major role in HCV-induced HCC as evidenced by genomic studies identifying polymorphisms in immune, metabolic, and growth signaling systems associated with increased risk of HCC. Despite highly effective direct-acting antiviral agents, the morbidity and incidence of liver-related complications of HCV, including HCC, is likely to persist in the near future. Clinical markers to selectively identify HCV subjects at higher risk of developing HCC have been reported however they require further validation, especially in subjects who have experienced sustained virological response. Molecular biomarkers allowing further refinement of HCC risk are starting to be implemented in clinical platforms, allowing objective stratification of risk and leading to individualized therapy and surveillance for HCV individuals. Another role for molecular biomarker-based stratification could be enrichment of HCC chemoprevention clinical trials leading to smaller sample size, shorter trial duration, and reduced costs.

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.

Activation of NF-κB by the Kaposi's sarcoma-associated herpesvirus K15 protein involves recruitment of the NF-κB-inducing kinase, IκB kinases, and phosphorylation of p65

Kaposi's sarcoma herpesvirus (KSHV) (or human herpesvirus 8) is the cause of Kaposi's sarcoma, primary effusion lymphoma (PEL), and the plasma cell variant of multicentric Castleman's disease (MCD). The transmembrane K15 protein, encoded by KSHV, has been shown to activate NF-κB and the mitogen-activated protein kinases (MAPKs) c-jun-N-terminal kinase (JNK) and extracellular signal-regulated kinase (Erk) as well as phospholipase C gamma (PLCγ) and to contribute to KSHV-induced angiogenesis. Here we investigate how the K15 protein activates the NF-κB pathway. We show that activation of NF-κB involves the recruitment of NF-κB-inducing kinase (NIK) and IKK α/β to result in the phosphorylation of p65/RelA on Ser536. A K15 mutant devoid in NIK/IKK recruitment fails to activate NF-κB but remains proficient in the stimulation of both NFAT- and AP1-dependent promoters, showing that the structural integrity of the mutant K15 protein has not been altered dramatically. Direct recruitment of NIK represents a novel way for a viral protein to activate and manipulate the NF-κB pathway.

IMPORTANCE

KSHV K15 is a viral protein involved in the activation of proinflammatory and angiogenic pathways. Previous studies reported that K15 can activate the NF-κB pathway. Here we show the molecular mechanism underlying the activation of this signaling pathway by K15, which involves direct recruitment of the NF-κB-inducing kinase NIK to K15 as well as NIK-mediated NF-κB p65 phosphorylation on Ser536. K15 is the first viral protein shown to activate NF-κB through direct recruitment of NIK. These results indicate a new mechanism whereby a viral protein can manipulate the NF-κB pathway.

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.

Pathogenesis of hepatocellular carcinoma according to aetiology

Hepatocellular carcinoma is related to various etiologies including hepatitis B, hepatitis C, high alcohol intake, aflatoxin B1 and metabolic syndrome. Most of the time HCC developed on cirrhosis. Consequently, the mechanisms of carcinogenesis of these different risk factors are difficult to separate from the events leading to cirrhosis. In contrast, aflatoxin B1 and hepatitis B have a clear direct oncogenic role through point mutations in the TP53 tumour suppressor gene and insertional mutagenesis respectively. Finally, next-generation sequencing and transcriptome analysis will refine our knowledge of the relationship between aetiology and the genetic events that draw the mutational landscape of hepatocellular carcinoma.

Hepatitis C virus core and NS3 antigens induced conjunctival inflammation via toll-like receptor-mediated signaling

PURPOSE

Dry eye condition is an extrahepatic manifestation associated with chronic hepatitis C virus (HCV) infection. Since conjunctival inflammation can contribute to the dry eye condition, in the present study we analyzed the conjunctival inflammatory response to HCV core and NS3 proteins.

METHODS

We used primary human conjunctival fibroblasts for our study. Cytokines were measured with enzyme-linked immunosorbent assay (ELISA). Toll-like receptor (TLR) and cell adhesion molecule gene expression patterns were analyzed with semiquantitative reverse transcription (RT)-PCR. Immunofluorescence staining was performed for the MyD88, nuclear factor-kappa B (NF-kB), and inducible nitric oxide synthase (iNOS) proteins. Nitric oxide (NO) was measured with the Griess assay; terminal deoxynucleotidyl transferase-mediated uridine 5'-triphosphate-biotin nick end labeling (TUNEL) and 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assays were performed for apoptosis and cell viability, respectively.

RESULTS

When exposed to the HCV core and NS3 proteins, the conjunctival fibroblasts secreted interleukin-8 (IL-8), IL-6, tumor necrosis factor-alpha (TNF-α), and IL-10 in a dose-dependent manner. Various TLRs were involved in the innate immune response via MyD88 signaling without NF-kB involvement. The gene expression of cell adhesion molecules such as CD44 and ICAM-1 was upregulated, and the cells secreted NO via iNOS. As the sum of these stress responses, the cells underwent apoptosis, which eventually lead to cell death.

CONCLUSIONS

HCV core and NS3 proteins induced conjunctival inflammation that may form the pathogenesis of dry eye condition.

Merkel cell polyomavirus: molecular insights into the most recently discovered human tumour virus

A fifth of worldwide cancer cases have an infectious origin, with viral infection being the foremost. One such cancer is Merkel cell carcinoma (MCC), a rare but aggressive skin malignancy. In 2008, Merkel cell polyomavirus (MCPyV) was discovered as the causative agent of MCC. It is found clonally integrated into the majority of MCC tumours, which require MCPyV oncoproteins to survive. Since its discovery, research has begun to reveal the molecular virology of MCPyV, as well as how it induces tumourigenesis. It is thought to be a common skin commensal, found at low levels in healthy individuals. Upon loss of immunosurveillance, MCPyV reactivates, and a heavy viral load is associated with MCC pathogenesis. Although MCPyV is in many ways similar to classical oncogenic polyomaviruses, such as SV40, subtle differences are beginning to emerge. These unique features highlight the singular position MCPyV has as the only human oncogenic polyomavirus, and open up new avenues for therapies against MCC.

Cellular activation and intracellular HCV load in peripheral blood monocytes isolated from HCV monoinfected and HIV-HCV coinfected patients

Background

During HCV infection, the activation status of peripheral blood monocytes and its impact on HCV replication are poorly understood. We hypothesized that a modified activation of peripheral blood monocytes in HIV-HCV coinfected compared to HCV monoinfected patients may contribute to different monocytes reservoirs of HCV replication.

Methods

We performed a case-control analysis involving HCV-infected patients with and without HIV coinfection. In peripheral blood mononuclear cells (PBMCs), peripheral blood lymphocytes (PBLs) and peripheral blood monocytes isolated from HCV monoinfected and HIV-HCV coinfected patients, intracellular HCV load and a marker of cellular activation, nuclear factor-kappaB (NF-κB) activation, were quantified using intracellular detection of HCV-core protein and electrophoretic mobility shift assay, respectively.

Results

Intracellular HCV loads were higher in monocytes isolated from HIV-HCV coinfected patients than in those of monoinfected patients. Among PBMCs isolated from HIV-HCV coinfected patients, intracellular HCV loads were higher in monocytes compared to PBLs. Cellular activation as measured by NF-κB activation was higher in monocytes isolated from HIV-HCV coinfected patients than in those of monoinfected patients.

Conclusions

Our results reveal the peripheral blood monocytes as an important extrahepatic reservoir for HCV in HIV-HCV coinfected patients and indicate a potential association between the activation state of monocytes and the size of the HCV reservoir in HIV-HCV coinfected patients.

Influenza viral manipulation of sphingolipid metabolism and signaling to modulate host defense system

Viruses attempt to create a distinctive cellular environment to favor viral replication and spread. Recent studies uncovered new functions of the sphingolipid signaling/metabolism during pathogenic virus infections. While sphingolipids such as sphingomyelin and ceramide were reported to influence the entry step of several viruses, sphingolipid-metabolizing enzymes could directly alter viral replication processes. Influenza virus was shown to increase the level of sphingosine kinase (SK) 1 to promote virus propagation. The mechanism involves regulation of intracellular signaling pathways, leading to the amplification of influenza viral RNA synthesis and nuclear export of viral ribonucleoprotein (RNP) complex. However, bovine viral diarrhea virus inhibits SK1 to enhance the efficacy of virus replication, demonstrating the presence of virus-specific strategies for modulation of the sphingolipid system. Therefore, investigating the sphingolipid metabolism and signaling in the context of virus replication could help us design innovative therapeutic approaches to improve human health.

Sphingosine kinase 1 regulates measles virus replication

Measles virus (MV) manipulates host factors to facilitate virus replication. Sphingosine kinase (SK) is an enzyme catalyzing the formation of sphingosine 1-phosphate and modulates multiple cellular processes including the host defense system. Here, we determined the role of SK1 in MV replication. Overexpression of SK1 enhanced MV replication. In contrast, inhibition of SK impaired viral protein expression and infectious virus production from cells expressing MV receptor, SLAM or Nectin-4. The inhibition of virus replication was observed when the cells were infected by vaccine strain or wild type MV or V/C gene-deficient MV. Importantly, SK inhibition suppressed MV-induced activation of NF-κB. The inhibitors specific to NF-κB signal pathway repressed the synthesis of MV proteins, revealing the importance of NF-κB activation for efficient MV replication. Therefore, SK inhibition restricts MV replication and modulates the NF-κB signal pathway, demonstrating that SK is a cellular factor critical for MV replication.

Merkel cell polyomavirus small T antigen targets the NEMO adaptor protein to disrupt inflammatory signaling

Merkel cell carcinoma (MCC) is a highly aggressive nonmelanoma skin cancer arising from epidermal mechanoreceptor Merkel cells. In 2008, a novel human polyomavirus, Merkel cell polyomavirus (MCPyV), was identified and is strongly implicated in MCC pathogenesis. Currently, little is known regarding the virus-host cell interactions which support virus replication and virus-induced mechanisms in cellular transformation and metastasis. Here we identify a new function of MCPyV small T antigen (ST) as an inhibitor of NF-κB-mediated transcription. This effect is due to an interaction between MCPyV ST and the NF-κB essential modulator (NEMO) adaptor protein. MCPyV ST expression inhibits IκB kinase α (IKKα)/IKKβ-mediated IκB phosphorylation, which limits translocation of the NF-κB heterodimer to the nucleus. Regulation of this process involves a previously undescribed interaction between MCPyV ST and the cellular phosphatase subunits, protein phosphatase 4C (PP4C) and/or protein phosphatase 2A (PP2A) Aβ, but not PP2A Aα. Together, these results highlight a novel function of MCPyV ST to subvert the innate immune response, allowing establishment of early or persistent infection within the host cell.

Tumour necrosis factor in infectious disease

TNF signals through two distinct receptors, designated TNFR1 and TNFR2, which initiate diverse cellular effects that include cell survival, activation, differentiation, and proliferation and cell death. These cellular responses can promote immunological and inflammatory responses that eradicate infectious agents, but can also lead to local tissue injury at sites of infection and harmful systemic effects. Defining the molecular mechanisms involved in TNF responses, the effects of natural and experimental genetic diversity in TNF signalling and the effects of therapeutic blockade of TNF has increased our understanding of the key role that TNF plays in infectious disease.

Modulation of mitogen-activated protein kinase-activated protein kinase 3 by hepatitis C virus core protein

Hepatitis C virus (HCV) is highly dependent on cellular proteins for its own propagation. In order to identify the cellular factors involved in HCV propagation, we performed protein microarray assays using the HCV core protein as a probe. Of ~9,000 host proteins immobilized in a microarray, approximately 100 cellular proteins were identified as HCV core-interacting partners. Of these candidates, mitogen-activated protein kinase-activated protein kinase 3 (MAPKAPK3) was selected for further characterization. MAPKAPK3 is a serine/threonine protein kinase that is activated by stress and growth inducers. Binding of HCV core to MAPKAPK3 was confirmed by in vitro pulldown assay and further verified by coimmunoprecipitation assay. HCV core protein interacted with MAPKAPK3 through amino acid residues 41 to 75 of core and the N-terminal half of kinase domain of MAPKAPK3. In addition, both RNA and protein levels of MAPKAPK3 were elevated in both HCV subgenomic replicon cells and cell culture-derived HCV (HCVcc)-infected cells. Silencing of MAPKAPK3 expression resulted in decreases in both protein and HCV infectivity levels but not in the intracellular HCV RNA level. We showed that MAPKAPK3 increased HCV IRES-mediated translation and MAPKAPK3-dependent HCV IRES activity was further increased by core protein. These data suggest that HCV core may modulate MAPKAPK3 to facilitate its own propagation.

The modulation of hepatitis C virus 1a replication by PKR is dependent on NF-kB mediated interferon beta response in Huh7.5.1 cells

Protein kinase R (PKR), a sensor of double-stranded RNA, plays an important role in the host response to viral infection. Hepatitis C genotype 2a virus (HCV2a) has been shown to induce PKR activation to suppress the translation of antiviral interferon stimulated genes (ISGs), suggesting that PKR inhibitor can be beneficial for treating chronically HCV-infected patients in conjunction with interferon alpha and ribavirin. However, in this study, we found that PKR inhibition using siRNA PKR, shRNA PKR or PKR inhibitor enhanced HCV 1a replication and rendered Huh7.5.1 cells more susceptible to HCV1a infection. Additionally, PKR silencing suppressed NF-kB activation and NF-kB mediated STAT1 phosphorylation in Huh7.5.1 cells and HCV1a persistently infected Huh7.5.1 cells (2HDD4). These effects were accompanied by a reduction of interferon beta response and thereby enhanced HCV1a replication in Huh7.5.1 cells. We conclude that host cells can employ PKR activation to restrict HCV1a replication through regulation of NF-kB expression.

HCV enters the twenty-first century

Almost one-third of Americans infected with human immunodeficiency virus (HIV) and 7 million worldwide are coinfected with hepatitis C virus (HCV). The principal route of HCV spread in the US is injection drug use but there are recent reports of outbreaks of acute HCV infection among HIV-infected men who have sex with men. With increased survival as a result of highly active antiretroviral therapy, HCV-associated liver disease has become a leading cause of death in HIV-infected individuals. Currently, telaprevir and boceprevir, both NS3/NS4A inhibitors that significantly improve sustained response when added to pegylated interferon and ribavirin, are approved only for HCV monoinfection. The optimal combination of agents, therapy durations and the timing of treatment remain major challenges in coinfected patients.

dsRNA-dependent protein kinase PKR and its role in stress, signaling and HCV infection

The double-stranded RNA-dependent protein kinase PKR plays multiple roles in cells, in response to different stress situations. As a member of the interferon (IFN)‑Stimulated Genes, PKR was initially recognized as an actor in the antiviral action of IFN, due to its ability to control translation, through phosphorylation, of the alpha subunit of eukaryotic initiation factor 2 (eIF2α). As such, PKR participates in the generation of stress granules, or autophagy and a number of viruses have designed strategies to inhibit its action. However, PKR deficient mice resist most viral infections, indicating that PKR may play other roles in the cell other than just acting as an antiviral agent. Indeed, PKR regulates several signaling pathways, either as an adapter protein and/or using its kinase activity. Here we review the role of PKR as an eIF2α kinase, its participation in the regulation of the NF-κB, p38MAPK and insulin pathways, and we focus on its role during infection with the hepatitis C virus (HCV). PKR binds the HCV IRES RNA, cooperates with some functions of the HCV core protein and may represent a target for NS5A or E2. Novel data points out for a role of PKR as a pro-HCV agent, both as an adapter protein and as an eIF2α-kinase, and in cooperation with the di-ubiquitin-like protein ISG15. Developing pharmaceutical inhibitors of PKR may help in resolving some viral infections as well as stress-related damages.

Prostaglandin E2 and the suppression of phagocyte innate immune responses in different organs

The local and systemic production of prostaglandin E₂ (PGE₂) and its actions in phagocytes lead to immunosuppressive conditions. PGE₂ is produced at high levels during inflammation, and its suppressive effects are caused by the ligation of the E prostanoid receptors EP₂ and EP₄, which results in the production of cyclic AMP. However, PGE₂ also exhibits immunostimulatory properties due to binding to EP₃, which results in decreased cAMP levels. The various guanine nucleotide-binding proteins (G proteins) that are coupled to the different EP receptors account for the pleiotropic roles of PGE₂ in different disease states. Here, we discuss the production of PGE₂ and the actions of this prostanoid in phagocytes from different tissues, the relative contribution of PGE₂ to the modulation of innate immune responses, and the novel therapeutic opportunities that can be used to control inflammatory responses.

Hepatitis C virus infection enhances TNFα-induced cell death via suppression of NF-κB

Hepatitis C virus (HCV) infection results in liver injury and long-term complications, such as liver cirrhosis and hepatocellular carcinoma. Liver injury in HCV infection is believed to be caused by host immune responses, not by viral cytopathic effects. Tumor necrosis factor-alpha (TNF-α) plays a pivotal role in the inflammatory processes of hepatitis C. TNF-α induces cell death that can be ameliorated by nuclear factor kappaB (NF-κB) activation. We investigated the regulation of TNF-α signal transduction in HCV-infected cells and identified HCV proteins responsible for sensitization to TNF-α-induced cell death. We studied the effect of HCV infection on TNF-α signal transduction using an in vitro HCV infection model (JFH-1, genotype 2a) with Huh-7 and Huh-7.5 cells. We found that TNF-α-induced cell death significantly increased in HCV-infected cells. HCV infection diminished TNF-α-induced phosphorylation of IκB kinase (IKK) and inhibitor of NF-κB (IκB), which are upstream regulators of NF-κB activation. HCV infection also inhibited nuclear translocation of NF-κB and expression of NF-κB-dependent anti-apoptotic proteins, such as B-cell lymphoma--extra large (Bcl-xL), X-linked inhibitor of apoptosis protein (XIAP), and the long form of cellular-FLICE inhibitory protein (c-FLIP). Decreased levels of Bcl-xL, XIAP, and c-FLIP messenger RNA and protein were also observed in livers with chronic hepatitis C. Transfection with plasmids encoding each HCV protein revealed that core, nonstructural protein (NS)4B, and NS5B attenuated TNF-α-induced NF-κB activation and enhanced TNF-α-induced cell death.

CONCLUSION

HCV infection enhances TNF-α-induced cell death by suppressing NF-κB activation through the action of core, NS4B, and NS5B. This mechanism may contribute to immune-mediated liver injury in HCV infection.

Role of nuclear factor-κB in oxidative stress associated with rabies virus infection of adult rat dorsal root ganglion neurons

Recent studies in an experimental model of rabies showed major structural changes in the brain involving neuronal processes that are associated with severe clinical disease. Cultured adult rat dorsal root ganglion (DRG) neurons infected with the challenge virus standard-11 strain of rabies virus (CVS) showed axonal swellings and immunostaining for 4-hydroxy-2-nonenal (4-HNE), indicating evidence of lipid peroxidation associated with oxidative stress and reduced axonal growth compared to that of mock-infected DRG neurons. We have evaluated whether nuclear factor (NF)-κB might act as a critical bridge linking CVS infection and oxidative stress. On Western immunoblotting, CVS infection induced expression of the NF-κB p50 subunit compared to that of mock infection. Ciliary neurotrophic factor, a potent activator of NF-κB, had no effect on mock-infected rat DRG neurons and reduced the number of 4-HNE-labeled puncta. SN50, a peptide inhibitor of NF-κB, and CVS infection had an additive effect in producing axonal swellings, indicating that NF-κB is neuroprotective. The fluorescent signal for subunit p50 was quantitatively evaluated in the nucleus and cytoplasm of mock- and CVS-infected rat DRG neurons. At 24 h postinfection (p.i.), there was a significant increase in the nucleus/cytoplasm ratio, indicating increased transcriptional activity of NF-κB, perhaps as a response to stress. At both 48 and 72 h p.i., there was significantly reduced nuclear localization of NF-κB. CVS infection may induce oxidative stress by inhibiting nuclear activation of NF-κB. A rabies virus protein may directly inhibit NF-κB activity. Further investigations are needed to gain a better understanding of the basic mechanisms involved in the oxidative damage associated with rabies virus infection.

Lipocalin 2: novel component of proinflammatory signaling in Alzheimer's disease

Alzheimer's disease (AD) is associated with an altered immune response, resulting in chronic increased inflammatory cytokine production with a prominent role of TNF-α. TNF-α signals are mediated by two receptors: TNF receptor 1 (TNFR1) and TNF receptor 2 (TNFR2). Signaling through TNFR2 is associated with neuroprotection, whereas signaling through TNFR1 is generally proinflammatory and proapoptotic. Here, we have identified a TNF-α-induced proinflammatory agent, lipocalin 2 (Lcn2) via gene array in murine primary cortical neurons. Further investigation showed that Lcn2 protein production and secretion were activated solely upon TNFR1 stimulation when primary murine neurons, astrocytes, and microglia were treated with TNFR1 and TNFR2 agonistic antibodies. Lcn2 was found to be significantly decreased in CSF of human patients with mild cognitive impairment and AD and increased in brain regions associated with AD pathology in human postmortem brain tissue. Mechanistic studies in cultures of primary cortical neurons showed that Lcn2 sensitizes nerve cells to β-amyloid toxicity. Moreover, Lcn2 silences a TNFR2-mediated protective neuronal signaling cascade in neurons, pivotal for TNF-α-mediated neuroprotection. The present study introduces Lcn2 as a molecular actor in neuroinflammation in early clinical stages of AD.

ent-kaur-16-en-19-oic Acid, isolated from the roots of Aralia continentalis, induces activation of Nrf2

ETHNOPHARMACOLOGICAL RELEVANCE

Excessive inflammation can lead to tissue damage and dysfunction of vital organs. Hence, regulating inflammatory response is a viable therapeutic approach. In Asian countries, various inflammatory diseases have often effectively been treated with herbal remedies including the root extract of Aralia continentalis Kitagawa (Araliaceae). Here, we investigated the effect of kaurenoic acid (ent-kaur-16-en-19-oic acid: KA), a diterpenoid that is extracted from Aralia continentalis Kitagawa root, on inflammation.

MATERIALS, METHODS, AND RESULTS

Western blot and RT-PCR analyses show that KA induced the nuclear localization of Nrf2 as low as 1 nM in concentration and that KA treatment induced the expression of Nrf2 dependent genes such as GCLC and HO-1. On the other hand, KA did not affect the degradation of cytoplasmic IκB-α, the nuclear localization of RelA (p65), and NF-κB transcriptional activity in RAW264.7 cells treated with endotoxin. Consistent with these data, KA treatment failed to suppress gene expression of representative pro-inflammatory mediators including COX-2, nitric oxide, IL-1β, TNF-α, and IL-12, indicating that KA did not have an important impact on NF-κB activation.

CONCLUSION

Together, these results show that KA was an effective activator of Nrf2, and suggest that the beneficial effects of Aralia continentalis Kitagawa root extract are, at least in part, mediated by activating Nrf2.

Porcine reproductive and respiratory syndrome virus nucleocapsid protein modulates interferon-β production by inhibiting IRF3 activation in immortalized porcine alveolar macrophages

Porcine reproductive and respiratory syndrome virus (PRRSV) infection appears to elicit a weak innate immune response suppressing type 1 interferon (IFN) production. Recent studies have revealed that several nonstructural proteins encoded by the PRRSV genome independently antagonize the type 1 IFN system. The present study sought to identify the structural proteins that possess the immune evasion properties in immortalized porcine alveolar macrophages (PAM). Each structural protein gene was stably expressed in a porcine monocyte-derived macrophage cell line, PAM-pCD163, and tested for its potential to inhibit IFN-β induction. We then focused on the nucleocapsid (N) protein, which has a strong inhibitory effect on dsRNA-induced IFN-β production. Upon dsRNA stimulation, IFN-β production was shown to decrease proportionally with increasing levels of N expression. Furthermore, the PRRSV N protein was found to down-regulate IFN-dependent gene production by dsRNA. Taken together, these results indicate the ability of N to modulate the dsRNA-mediated IFN induction pathways. In addition, the N protein significantly interfered with dsRNA-induced phosphorylation and nuclear translocation of IRF3. Our data suggest that the PRRSV N protein is a responsible component, independent of other nonstructural elements, for evading the IFN response by antagonizing IRF3 activation.

Hepatitis B and C virus hepatocarcinogenesis: lessons learned and future challenges

Worldwide, hepatocellular carcinoma (HCC) is one of the most common cancers. It is thought that 80% of hepatocellular carcinomas are linked to chronic infections with the hepatitis B (HBV) or hepatitis C (HCV) viruses. Chronic HBV and HCV infections can alter hepatocyte physiology in similar ways and may utilize similar mechanisms to influence the development of HCC. There has been significant progress towards understanding the molecular biology of HBV and HCV and identifying the cellular signal transduction pathways that are altered by HBV and HCV infections. Although the precise molecular mechanisms that link HBV and HCV infections to the development of HCC are not entirely understood, there is considerable evidence that both inflammatory responses to infections with these viruses, and associated destruction and regeneration of hepatocytes, as well as activities of HBV- or HCV-encoded proteins, contribute to hepatocyte transformation. In this review, we summarize progress in defining mechanisms that may link HBV and HCV infections to the development of HCC, discuss the challenges of directly defining the processes that underlie HBV- and HCV-associated HCC, and describe areas that remain to be explored.

Hepatitis C virus core protein activates Wnt/β-catenin signaling through multiple regulation of upstream molecules in the SMMC-7721 cell line

The core protein of hepatitis C virus (HCV) has been implicated in HCV-induced liver pathogenesis. Previous data have shown that the HCV core protein has pleiotropic functions, including transcriptional regulation of a number of cellular genes, although the mechanism of gene regulation remains unclear. Wnt/β-catenin signaling is also involved in hepatocellular carcinoma (HCC) tumorigenesis. To elucidate the molecular mechanism of HCV pathogenesis, we examined whether HCV core protein activates Wnt/β-catenin signaling in the hepatoma cell line SMMC-7721. The effects of core protein on Wnt/β-catenin signaling cascades were investigated by luciferase reporter gene assay, immunofluorescence, western blot and RT-PCR analysis. Here, we demonstrate that HCV core protein plays an essential role in activating β-catenin/Tcf-4-dependent transcriptional activity and increases active β-catenin expression and nuclear accumulation in SMMC-7721 cells. An RT-PCR assay indicated that core protein upregulates gene expression of canonical Wnt ligands, such as Wnt2, Wnt3, Wnt3a, Wnt8b, Wnt10a, Wnt10b, frizzled receptors Fzd1, 2, 5, 6, 7, 9, and LRP5/6 co-receptors. However, Wnt antagonists SFRP3, 5 and Dkk1 were moderately repressed. Furthermore, ectopic expression of core protein markedly promoted cell proliferation. The soluble Fzd molecule FrzB or the β-catenin inhibitor siBC efficiently blocked cell growth stimulation by the core gene. Our present findings demonstrate that the HCV core protein activates canonical Wnt signaling through tight regulation of several important molecules upstream of β-catenin and presumably results in promotion of cell proliferation in the SMMC-7721 cell line. Taken together, these data suggested that the core protein may be directly involved in Wnt/β-catenin-mediated liver pathogenesis.

Modulation of NF-κB signalling by microbial pathogens

The nuclear factor-κB (NF-κB) family of transcription factors plays a central part in the host response to infection by microbial pathogens, by orchestrating the innate and acquired host immune responses. The NF-κB proteins are activated by diverse signalling pathways that originate from many different cellular receptors and sensors. Many successful pathogens have acquired sophisticated mechanisms to regulate the NF-κB signalling pathways by deploying subversive proteins or hijacking the host signalling molecules. Here, we describe the mechanisms by which viruses and bacteria micromanage the host NF-κB signalling circuitry to favour the continued survival of the pathogen.

Amino acid substitutions of hepatitis C virus core protein are not associated with intracellular antiviral response to interferon-α in vitro

BACKGROUND

Studies on patients with hepatitis C virus (HCV) of genotype 1b have suggested that amino acids (aa) 70 and/or 91 of the HCV core protein affect the outcome of interferon (IFN)-α and ribavirin (RBV) therapy, although there are no clear supporting data in vitro.

AIMS

This study was designed to determine the differences among the antiviral activities of HCV core proteins with various substitutions at aa70 and/or aa91.

METHODS

The retroviral vectors expressing the HCV core proteins with substitutions of arginine/leucine, arginine/methionine, glutamine/leucine or glutamine/methionine at aa70/aa91 were transiently transfected or stably transducted into an immortalized hepatocyte line (PH5CH8), hepatoma cell lines and an HCV-RNA replicating cell line (sOR) to evaluate antiviral responses to IFN-α or IFN-α/RBV. Sequence analysis was performed using genome-length HCV-RNA replicating cells (OR6 and AH1) to evaluate HCV core mutations during IFN-α treatment.

RESULTS

The promoter activity levels of IFN-stimulated genes in the transiently transfected cells or the mRNA levels of 2'-5'-oligoadenylate synthetase in the stably transducted PH5CH8 cells were not associated with the HCV core aa70 and/or aa91 substitutions during IFN-α treatment. Antiviral responses to IFN-α or IFN-α/RBV treatment were enhanced in sOR cells stably transducted with the HCV core, although there were no differences in antiviral responses among the cells expressing different core types. Sequence analysis showed no aa mutations after IFN-α treatment.

CONCLUSIONS

Antiviral activities were enhanced by HCV core transduction, but they were not associated with the HCV core aa70 and/or aa91 substitutions by in vitro analysis.

Herpes simplex virus immediate-early ICP0 protein inhibits Toll-like receptor 2-dependent inflammatory responses and NF-kappaB signaling

The discovery of the Toll-like receptors (TLRs) and their importance in the regulation of host responses to infection raised attention to the complex interplay between viral gene products and the host innate immune responses in determining the outcome of virus infection. Robust inflammatory cytokine responses are observed in herpes simplex virus (HSV)-infected animals and cells. Our studies have demonstrated that Toll-like receptor 2 (TLR2) activation by HSV results in NF-κB activation with concomitant inflammatory cytokine production and that TLR2 activation plays a critical role in HSV-induced pathology and mortality. Here we demonstrate that the HSV-1 immediate-early ICP0 protein reduces the TLR2-mediated inflammatory response to HSV 1 (HSV-1) infection. Expression of ICP0 alone is sufficient to block TLR2-driven responses to both viral and nonviral ligands at or downstream of the MyD88 adaptor and upstream of p65. ICP0 alone can also reduce the levels of MyD88 and Mal (TIRAP). In HSV-infected cells, the E3 ligase function of ICP0 and cellular proteasomal activity are required for the inhibitory activity. Our results argue for a model in which ICP0 promotes the degradation of TLR adaptor molecules and inhibition of the inflammatory response, much as it inhibits the interferon response by sequestration and degradation of interferon regulatory factor 3 (IRF-3).

Functional characterization of core genes from patients with acute hepatitis C virus infection

BACKGROUND

The hepatitis C virus (HCV) core protein is implicated in diverse aspects of HCV-induced pathogenesis. There is a paucity of information on core in acute hepatitis C infection.

METHODS

We analyzed core gene sequences and protein functions from 13 patients acutely infected with HCV genotype 1.

RESULTS

Although core isolates differed slightly between patients, core quasispecies were relatively homogeneous within each patient. In 2 of 4 patients studied temporally, core quasispecies did not change over time. Comparison with more than 2700 published core isolates indicated that amino acid changes from a prototype reference strain found in acute core isolates were present in chronically infected persons at low frequency (6.4%; range, 0%-32%). Core isolates associated with lipid droplets to similar degrees in Huh7 cells. Core diffusion in cells was not affected by nonconservative changes F130L and G161S in the lipid targeting domain of core. Core isolates inhibited interferon-stimulated response element- and nuclear factor kappaB-dependent transcription and tumor necrosis factor alpha-induced nuclear translocation of nuclear factor kappaB and were also secreted from Huh7 cells.

CONCLUSIONS

The data suggest that upon transmission, core quasispecies undergo genetic homogenization associated with amino acid changes that are rarely found in chronic infection and that, despite genetic variation, acute core isolates retain similar functions in vitro.

Role of nuclear factor kappaB in liver health and disease

NF-kappaB (nuclear factor kappaB) is a heterodimeric transcription factor that is constitutively expressed in all cell types and has a central role as a transcriptional regulator in response to cellular stress. In the present review, we discuss the role of NF-kappaB signalling in the maintenance of liver homoeostasis as well as in the pathogenesis of a wide variety of conditions affecting the liver, including viral hepatitis, steatohepatitis, cirrhosis and hepatocellular carcinoma. Much of the current knowledge of NF-kappaB signalling in the liver relates to the canonical pathway, the IKK [IkappaB (inhibitor of kappaB) kinase] complex and the RelA subunit. We explore the weaknesses of the experimental approaches to date and suggest that further work is needed to investigate in detail the discreet functions of each of the Rel subunits in liver physiology and disease.

Hepatitis C virus-induced hepatocarcinogenesis

Although there is strong evidence that hepatitis C virus (HCV) is one of the leading causes of hepatocellular carcinoma (HCC), there is still much to understand regarding the mechanism of HCV-induced transformation. While liver fibrosis resulting from long-lasting chronic inflammation and liver regeneration resulting from immune-mediated cell death are likely factors that contribute to the development of HCC, the direct role of HCV proteins remains to be determined. In vitro studies have shown that HCV expression may interfere with cellular functions that are important for cell differentiation and cell growth. However, most studies were performed in artificial models which can only give clues for potential mechanisms that need to be confirmed in more relevant models. Furthermore, the difficulty to identify HCV proteins and infected liver cells in patients, contributes to the complexity of our current understanding. For these reasons, there is currently very little experimental evidence for a direct oncogenic role of HCV. Further studies are warranted to clarify these issues.