The hepatitis C virus NS2 protein is an inhibitor of CIDE-B-induced apoptosis

CIDE proteins and their regulatory mechanisms in lipid droplet fusion and growth

The cell death-inducing DFF45-like effector (CIDE) proteins, including Cidea, Cideb, and Cidec/Fsp27, regulate various aspects of lipid homeostasis, including lipid storage, lipolysis, and lipid secretion. This review focuses on the physiological roles of CIDE proteins based on studies on knockout mouse models and human patients bearing CIDE mutations. The primary cellular function of CIDE proteins is to localize to lipid droplets (LDs) and to control LD fusion and growth across different cell types. We propose a four-step process of LD fusion, characterized by (a) the recruitment of CIDE proteins to the LD surface and CIDE movement, (b) the enrichment and condensate formation of CIDE proteins to form LD fusion plates at LD-LD contact sites, (c) lipid transfer through lipid-permeable passageways within the fusion plates, and (d) the completion of LD fusion. Lastly, we outline CIDE-interacting proteins as regulatory factors, as well as their contribution in LD fusion.

Apoptotic Cell Death in an Animal Model of Virus-Induced Acute Liver Failure-Observations during Lagovirus europaeus/GI.2 Infection

Lagovirus europaeus/GI.2 causes severe and highly fatal Rabbit Hemorrhagic Disease (RHD). Because of its characteristics, this infection is used as an animal model for acute liver failure (ALF). Apoptosis is one of the key processes underlying ALF and has been described as one of the mechanisms of RHD pathogenesis. Apoptotic cell death has been quite well characterized in infection with different variants of GI.1 strains, but so far, the GI.2 genotype has not been widely studied. In this study, we performed an evaluation of apoptotic cell death in hepatocytes of rabbits infected with Lagovirus europaeus/GI.2. We analyzed the expression of genes involved in apoptotic cell death by real-time PCR and performed immunohistochemical (IHC) assays. We showed a significant increase in the expression of caspase-3 and the proapoptotic Bax and anti-apoptotic Bcl-2 in infected animals. In addition, we recorded increased Bax/Bcl-2 ratios. IHC analyses showed the presence of morphological signs of apoptosis in the hepatocytes of infected rabbits. Our results indicate that caspase-3 and proteins from the Bcl-2 families play a key role in apoptosis induced by Lagovirus europaeus/GI.2 infection.

Dinotefuran exposure induces autophagy and apoptosis through oxidative stress in Bombyx mori

As a third-generation neonicotinoid insecticide, dinotefuran is extensively used in agriculture, and its residue in the environment has potential effects on nontarget organisms. However, the toxic effects of dinotefuran exposure on nontarget organism remain largely unknown. This study explored the toxic effects of sublethal dose of dinotefuran on Bombyx mori. Dinotefuran upregulated reactive oxygen species (ROS) and malondialdehyde (MDA) levels in the midgut and fat body of B. mori. Transcriptional analysis revealed that the expression levels of many autophagy and apoptosis-associated genes were significantly altered after dinotefuran exposure, consistent with ultrastructural changes. Moreover, the expression levels of autophagy-related proteins (ATG8-PE and ATG6) and apoptosis-related proteins (BmDredd and BmICE) were increased, whereas the expression level of an autophagic key protein (sequestosome 1) was decreased in the dinotefuran-exposed group. These results indicate that dinotefuran exposure leads to oxidative stress, autophagy, and apoptosis in B. mori. In addition, its effect on the fat body was apparently greater than that on the midgut. In contrast, pretreatment with an autophagy inhibitor effectively downregulated the expression levels of ATG6 and BmDredd, but induced the expression of sequestosome 1, suggesting that dinotefuran-induced autophagy may promote apoptosis. This study reveals that ROS generation regulates the impact of dinotefuran on the crosstalk between autophagy and apoptosis, laying the foundation for studying cell death processes such as autophagy and apoptosis induced by pesticides. Furthermore, this study provides a comprehensive insight into the toxicity of dinotefuran on silkworm and contributes to the ecological risk assessment of dinotefuran in nontarget organisms.

Hypermethylation-Mediated Silencing of CIDEA, MAL and PCDH17 Tumour Suppressor Genes in Canine DLBCL: From Multi-Omics Analyses to Mechanistic Studies

Gene expression is controlled by epigenetic deregulation, a hallmark of cancer. The DNA methylome of canine diffuse large B-cell lymphoma (cDLBCL), the most frequent malignancy of B-lymphocytes in dog, has recently been investigated, suggesting that aberrant hypermethylation of CpG loci is associated with gene silencing. Here, we used a multi-omics approach (DNA methylome, transcriptome and copy number variations) combined with functional in vitro assays, to identify putative tumour suppressor genes subjected to DNA methylation in cDLBCL. Using four cDLBCL primary cell cultures and CLBL-1 cells, we found that CiDEA, MAL and PCDH17, which were significantly suppressed in DLBCL samples, were hypermethylated and also responsive (at the DNA, mRNA and protein level) to pharmacological unmasking with hypomethylating drugs and histone deacetylase inhibitors. The regulatory mechanism underneath the methylation-dependent inhibition of those target genes expression was then investigated through luciferase and in vitro methylation assays. In the most responsive CpG-rich regions, an in silico analysis allowed the prediction of putative transcription factor binding sites influenced by DNA methylation. Interestingly, regulatory elements for AP2, MZF1, NF-kB, PAX5 and SP1 were commonly identified in all three genes. This study provides a foundation for characterisation and experimental validation of novel epigenetically-dysregulated pathways in cDLBCL.

To Explore the Potential Targets and Current Structure-based Design Strategies Utilizing Co-crystallized Ligand to Combat HCV

BACKGROUND

Hepatitis C Virus (HCV) belongs to the Hepacivirus family. HCV has been designated as a very dreadful virus as it can attack the liver, causing inflammation and even may lead to cancer in chronic conditions. It was estimated that 71 million people around the world have chronic HCV infection. World Health Organization (WHO) reported that about 399000 people died because of chronic cirrhosis and liver cancer globally. In spite of the abundance of availability of drugs for the treatment of HCV, however, the issue of drug resistance surpasses all the possibilities of therapeutic management of HCV. Therefore, to address this issue of 'drug-resistance', various HCV targets were explored to quest the evaluation of the mechanism of the disease progression.

METHODS

An attempt has been made in the present study to explore the various targets of HCV involved in the mechanism(s) of the disease initiation and progression and to focus on the mode of binding of ligands, which are co-crystallized at the active cavity of different HCV targets.

CONCLUSION

The present study could predict some crucial features of these ligands, which possibly interacted with various amino acid residues responsible for their biological activity and molecular signaling pathway(s). Such binding mode may be considered as a template for the high throughput screening and designing of active congeneric ligands to combat HCV.

Down-Regulation of CIDEA Promoted Tumor Growth and Contributed to Cisplatin Resistance by Regulating the JNK-p21/Bad Signaling Pathways in Esophageal Squamous Cell Carcinoma

Esophageal squamous cell carcinoma (ESCC) is one of the most common malignancies with poor prognosis and lack of effective targeted therapies. In this study, we investigated the tumor suppressive role of the cell death inducing DFF like effector A (CIDEA) in ESCC. Firstly, public datasets and ESCC tissue microarray analysis showed that CIDEA was frequently down-regulated at both the mRNA and protein level. This was significantly associated with low differentiation and TNM stage in ESCC, and indicated poor prognosis for ESCC patients. Bisulfite genomic sequencing (BGS) and methylation-specific PCR (MSP) analysis revealed that the down-regulation of CIDEA was associated with hypermethylation of its promoter, which was also correlated with the poor prognosis in ESCC patients. In vitro and in vivo functional studies demonstrated that CIDEA decreased cell growth, foci formation, DNA replication, and tumorigenesis in nude mice. Further study revealed that, during starvation or cisplatin induced DNA damage, CIDEA facilitated the G1-phase arrest or caspase-dependent mitochondrial apoptosis through the JNK-p21/Bad pathway. Therefore, CIDEA is a novel tumor suppressor gene that plays an important role in the development and progression of ESCC, and may provide a potential therapeutic target for patients with ESCC.

TCDD promotes liver fibrosis through disordering systemic and hepatic iron homeostasis

2, 3, 7, 8-Tetrachlorodibenzo-p-dioxin (TCDD) is a toxic environmental pollutant which can cause severe health problems, such as fibrosis. However, the toxic effects and related mechanism of TCDD on the liver remain largely unknown. In this study, we established a liver fibrosis mouse model upon exposure of TCDD, as evidenced by increased collagen I, tumor growth factor β1 (TGFβ1), α-smooth muscle actin (α-SMA), and Masson staining. Meanwhile, there was also a significant increase of inflammatory factors and TUNEL-positive hepatocytes in liver, indicating that liver inflammation and hepatic cell apoptosis occurred. In addition, increased serum and liver iron were concomitant with liver injury induced by TCDD. We further investigated the mechanism underlying TCDD-induced hepatocyte apoptosis through apoptosis polymerase chain reaction array, and found that a crucial apoptosis-related gene, cell death-inducing DFF45-like effector b (Cideb), was significantly increased in primary hepatocytes from TCDD-exposed mice, and accompanied by liver iron deposition in hepcidin knockout mice. Therefore, Cideb depletion could effectively attenuated TCDD or iron induced cell death related genes expression. In conclusion, our results showed that iron-induced Cideb expression played a critical role in promoting TCDD-induced hepatocyte apoptosis and liver fibrosis, which provide a novel mechanism for understanding TCDD-induced liver injury.

The journey of Zika to the developing brain

Zika virus is a mosquito-borne Flavivirus originally isolated from humans in 1952. Following its re-emergence in Brazil in 2015, an increase in the number of babies born with microcephaly to infected mothers was observed. Microcephaly is a neurodevelopmental disorder, characterised phenotypically by a smaller than average head size, and is usually developed in utero. The 2015 outbreak in the Americas led to the World Health Organisation declaring Zika a Public Health Emergency of International Concern. Since then, much research into the effects of Zika has been carried out. Studies have investigated the structure of the virus, its effects on and evasion of the immune response, cellular entry including target receptors, its transmission from infected mother to foetus and its cellular targets. This review discusses current knowledge and novel research into these areas, in hope of developing a further understanding of how exposure of pregnant women to the Zika virus can lead to impaired brain development of their foetus. Although no longer considered an epidemic in the Americas, the mechanism by which Zika acts is still not comprehensively and wholly understood, and this understanding will be crucial in developing effective vaccines and treatments.

Hepatitis C Virus NS2 Protein Suppresses RNA Interference in Cells

RNAi interference (RNAi) is an evolutionarily conserved post-transcriptional gene silencing mechanism and has been well recognized as an important antiviral immunity in eukaryotes. Numerous viruses have been shown to encode viral suppressors of RNAi (VSRs) to antagonize antiviral RNAi. Hepatitis C virus (HCV) is a medically important human pathogen that causes acute and chronic hepatitis. In this study, we screened all the nonstructural proteins of HCV and found that HCV NS2 could suppress RNAi induced either by small hairpin RNAs (shRNAs) or small interfering RNAs (siRNAs) in mammalian cells. Moreover, we demonstrated that NS2 could suppress RNAi via its direct interaction with double-stranded RNAs (dsRNAs) and siRNAs, and further identified that the cysteine 184 of NS2 is required for the RNAi suppression activity through a serial of point mutation analyses. Together, our findings uncovered that HCV NS2 can act as a VSR in vitro, thereby providing novel insights into the life cycle and virus-host interactions of HCV.

CIDE Proteins in Human Health and Disease

Cell death-Inducing DNA Fragmentation Factor Alpha (DFFA)-like Effector (CIDE) proteins have emerged as lipid droplet-associated proteins that regulate fat metabolism. There are three members in the CIDE protein family—CIDEA, CIDEB, and CIDEC (also known as fat-specific protein 27 (FSP27)). CIDEA and FSP27 are primarily expressed in adipose tissue, while CIDEB is expressed in the liver. Originally, based upon their homology with DNA fragmentation factors, these proteins were identified as apoptotic proteins. However, recent studies have changed the perception of these proteins, redefining them as regulators of lipid droplet dynamics and fat metabolism, which contribute to a healthy metabolic phenotype in humans. Despite various studies in humans and gene-targeting studies in mice, the physiological roles of CIDE proteins remains elusive. This review will summarize the known physiological role and metabolic pathways regulated by the CIDE proteins in human health and disease.

Evolution of efficacious pangenotypic hepatitis C virus therapies

Hepatitis C compromises the quality of life of more than 350 million individuals worldwide. Over the last decade, therapeutic regimens for treating hepatitis C virus (HCV) infections have undergone rapid advancements. Initially, structure-based drug design was used to develop molecules that inhibit viral enzymes. Subsequently, establishment of cell-based replicon systems enabled investigations into various stages of HCV life cycle including its entry, replication, translation, and assembly, as well as role of host proteins. Collectively, these approaches have facilitated identification of important molecules that are deemed essential for HCV life cycle. The expanded set of putative virus and host-encoded targets has brought us one step closer to developing robust strategies for efficacious, pangenotypic, and well-tolerated medicines against HCV. Herein, we provide an overview of the development of various classes of virus and host-directed therapies that are currently in use along with others that are undergoing clinical evaluation.

HCV non-structural NS4A protein of genotype 3a induces mitochondria mediated death by activating Bax and the caspase cascade

Currently almost 170 million of the world population is suffering with Hepatitis C virus (HCV) that is the major cause of liver diseases, which leads to liver fibrosis, cirrhosis and hepatocellular carcinoma. Approximately 6% of the Pakistani population is chronically infected with HCV, with genotype 3a being the most prominent strain in Pakistan. Complex of HCV non-structural proteins NS3-4A plays an important role in the viral replication machinery that together has serine protease and helicase activity. Genetic heterogeneity within HCV genotypes makes it pertinent to assess the apoptotic pathway within different HCV genotypes. Findings of present study reveal that HCV genotype 3a NS4A and NS3-NS4A induce cell death in Huh-7 cells. Moreover, our results demonstrated that NS3-4A and NS4A proteins were not only localized on ER but also on the mitochondria. Bax a pro-apoptotic protein was found translocated to the mitochondria in the transfected cells, while up-regulated expression of Bax and down-regulated expression of anti-apoptotic Bcl-xL protein was also observed in the presence of NS4A and NS3-4A proteins. High level of mitochondrial superoxide generation was observed in the transfected cells and NS3-4A and NS4A triggered a cascade of activation starting from caspase-9, then caspase-7 and caspase-3 that ultimately led to the cleavage of poly (ADP-ribose) polymerase PARP. Collectively findings of the present study suggest that NS4A and co-expression of NS3-4A and NS4A of genotype 3a has similar capacity to induce apoptosis through a Bax-triggered, mitochondrial-mediated, caspase cascade.

Dengue virus NS2 and NS4: Minor proteins, mammoth roles

Despite the ever-increasing global incidence of dengue fever, there are no specific chemotherapy regimens for its treatment. Structural studies on dengue virus (DENV) proteins have revealed potential drug targets. Major DENV proteins such as the envelope protein and non-structural (NS) proteins 3 and 5 have been extensively investigated in antiviral studies, but with limited success in vitro. However, the minor NS proteins NS2 and NS4 have remained relatively underreported. Emerging evidence indicating their indispensable roles in virus propagation and host immunomodulation should encourage us to target these proteins for drug discovery. This review covers current knowledge on DENV NS2 and NS4 proteins from structural and functional perspectives and assesses their potential as targets for antiviral design. Antiviral targets in NS2A include surface-exposed transmembrane regions involved in pathogenesis, while those in NS2B include protease-binding sites in a conserved hydrophilic domain. Ideal drug targets in NS4A include helix α4 and the PEPEKQR sequence, which are essential for NS4A-2K cleavage and NS4A-NS4B association, respectively. In NS4B, the cytoplasmic loop connecting helices α5 and α7 is an attractive target for antiviral design owing to its role in dimerization and NS4B-NS3 interaction. Findings implicating NS2A, NS2B, and NS4A in membrane-modulation and viroporin-like activities indicate an opportunity to target these proteins by disrupting their association with membrane lipids. Despite the lack of 3D structural data, recent topological findings and progress in structure-prediction methods should be sufficient impetus for targeting NS2 and NS4 for drug design.

Interactions between the Hepatitis C Virus Nonstructural 2 Protein and Host Adaptor Proteins 1 and 4 Orchestrate Virus Release

Hepatitis C virus (HCV) spreads via secreted cell-free particles or direct cell-to-cell transmission. Yet, virus-host determinants governing differential intracellular trafficking of cell-free- and cell-to-cell-transmitted virus remain unknown. The host adaptor proteins (APs) AP-1A, AP-1B, and AP-4 traffic in post-Golgi compartments, and the latter two are implicated in basolateral sorting. We reported that AP-1A mediates HCV trafficking during release, whereas the endocytic adaptor AP-2 mediates entry and assembly. We demonstrated that the host kinases AAK1 and GAK regulate HCV infection by controlling these clathrin-associated APs. Here, we sought to define the roles of AP-4, a clathrin-independent adaptor; AP-1A; and AP-1B in HCV infection. We screened for interactions between HCV proteins and the μ subunits of AP-1A, AP-1B, and AP-4 by mammalian cell-based protein fragment complementation assays. The nonstructural 2 (NS2) protein emerged as an interactor of these adaptors in this screening and by coimmunoprecipitations in HCV-infected cells. Two previously unrecognized dileucine-based motifs in the NS2 C terminus mediated AP binding and HCV release. Infectivity and coculture assays demonstrated that while all three adaptors mediate HCV release and cell-free spread, AP-1B and AP-4, but not AP-1A, mediate cell-to-cell spread. Live-cell imaging revealed HCV cotrafficking with AP-1A, AP-1B, and AP-4 and that AP-4 mediates HCV trafficking in a post-Golgi compartment. Lastly, HCV cell-to-cell spread was regulated by AAK1 and GAK and thus susceptible to treatment with AAK1 and GAK inhibitors. These data provide a mechanistic understanding of HCV trafficking in distinct release pathways and reveal a requirement for APs in cell-to-cell viral spread.

HCV spreads via cell-free infection or cell-to-cell contact that shields it from antibody neutralization, thereby facilitating viral persistence. Yet, factors governing this differential sorting remain unknown. By integrating proteomic, RNA interference, genetic, live-cell imaging, and pharmacological approaches, we uncover differential coopting of host adaptor proteins (APs) to mediate HCV traffic at distinct late steps of the viral life cycle. We reported that AP-1A and AP-2 mediate HCV trafficking during release and assembly, respectively. Here, we demonstrate that dileucine motifs in the NS2 protein mediate AP-1A, AP-1B, and AP-4 binding and cell-free virus release. Moreover, we reveal that AP-4, an adaptor not previously implicated in viral infections, mediates cell-to-cell spread and HCV trafficking. Lastly, we demonstrate cell-to-cell spread regulation by AAK1 and GAK, host kinases controlling APs, and susceptibility to their inhibitors. This study provides mechanistic insights into virus-host determinants that facilitate HCV trafficking, with potential implications for pathogenesis and antiviral agent design.

Innate Immune Evasion Mediated by Flaviviridae Non-Structural Proteins

Flaviviridae-caused diseases are a critical, emerging public health problem worldwide. Flaviviridae infections usually cause severe, acute or chronic diseases, such as liver damage and liver cancer resulting from a hepatitis C virus (HCV) infection and high fever and shock caused by yellow fever. Many researchers worldwide are investigating the mechanisms by which Flaviviridae cause severe diseases. Flaviviridae can interfere with the host’s innate immunity to achieve their purpose of proliferation. For instance, dengue virus (DENV) NS2A, NS2B3, NS4A, NS4B and NS5; HCV NS2, NS3, NS3/4A, NS4B and NS5A; and West Nile virus (WNV) NS1 and NS4B proteins are involved in immune evasion. This review discusses the interplay between viral non-structural Flaviviridae proteins and relevant host proteins, which leads to the suppression of the host’s innate antiviral immunity.

Cell-death-inducing DFFA-like Effector B Contributes to the Assembly of Hepatitis C Virus (HCV) Particles and Interacts with HCV NS5A

Hepatitis C virus (HCV) uses components of the very-low-density lipoprotein (VLDL) pathway for assembly/release. We previously reported that hepatocyte nuclear factor 4α (HNF4α) participates in HCV assembly/release through downstream factors those participate in VLDL assembly/secretion. Cell-death-inducing DFFA-like effector B (CIDEB) is an important regulator of the VLDL pathway. CIDEB is required for entry of HCV particles from cell culture (HCVcc), but the effects of CIDEB on the post-entry steps of the HCV lifecycle are unclear. In the present study, we determined that CIDEB is required for HCV assembly in addition to HCVcc entry. Furthermore, CIDEB interacts with the HCV NS5A protein, and the N terminus of CIDEB and the domain I of NS5A are involved in this interaction. Moreover, CIDEB silencing impairs the association of apolipoprotein E (ApoE) with HCV particles. Interestingly, CIDEB is also required for the post-entry stages of the dengue virus (DENV) life cycle. Collectively, these results indicate that CIDEB is a new host factor that is involved in HCV assembly, presumably by interacting with viral protein, providing new insight into the exploitation of the VLDL regulator CIDEB by HCV.

Hepatitis C Virus-Induced Degradation of Cell Death-Inducing DFFA-Like Effector B Leads to Hepatic Lipid Dysregulation

Individuals chronically infected with hepatitis C virus (HCV) commonly exhibit hepatic intracellular lipid accumulation, termed steatosis. HCV infection perturbs host lipid metabolism through both cellular and virus-induced mechanisms, with the viral core protein playing an important role in steatosis development. We have recently identified a liver protein, the cell death-inducing DFFA-like effector B (CIDEB), as an HCV entry host dependence factor that is downregulated by HCV infection in a cell culture model. In this study, we investigated the biological significance and molecular mechanism of this downregulation. HCV infection in a mouse model downregulated CIDEB in the liver tissue, and knockout of the CIDEB gene in a hepatoma cell line results in multiple aspects of lipid dysregulation that can contribute to hepatic steatosis, including reduced triglyceride secretion, lower lipidation of very-low-density lipoproteins, and increased lipid droplet (LD) stability. The potential link between CIDEB downregulation and steatosis is further supported by the requirement of the HCV core and its LD localization for CIDEB downregulation, which utilize a proteolytic cleavage event that is independent of the cellular proteasomal degradation of CIDEB.

IMPORTANCE

Our data demonstrate that HCV infection of human hepatocytesin vitroandin vivoresults in CIDEB downregulation via a proteolytic cleavage event. Reduction of CIDEB protein levels by HCV or gene editing, in turn, leads to multiple aspects of lipid dysregulation, including LD stabilization. Consequently, CIDEB downregulation may contribute to HCV-induced hepatic steatosis.

Decreased Expression of Inhibitor of Caspase-Activated DNase (ICAD) in Renal Cell Carcinoma - Tissue Microarray of Human Samples

Although primary localised tumours of renal cell carcinoma (RCC) can be treated relatively successfully with surgery, metastatic RCC has poor prognosis because of late diagnosis and resistance to therapies. In the present study, we were interested in profiling the protein expression of “inhibitor of caspase-activated DNase” (ICAD), an apoptosis inhibitor, in kidney cancer and its paired normal kidney. Immunohistochemistry with automated batch staining and morphometry using digital pathology were used to compare ICAD in 121 RCC specimens with their paired normal kidney tissue. Tissue microarray of formalin-fixed, paraffin-embedded archival tissue was used. Intensity and localisation of ICAD were compared between normal and cancer samples, and against grading within the cancers. The results demonstrated that, in this cohort, ICAD was highly expressed in the proximal tubular epithelium of normal kidney, and significantly decreased in clear cell RCC tissue (p < 0.05) as well as other subtypes of RCC (p < 0.01) compared with normal kidney. There was a tendency towards nuclear localisation of ICAD in clear cell RCC, but not in other subtypes of RCC. No significant association was found between ICAD intensity and grade of RCC. In summary, down-regulation of ICAD occurs in RCC. ICAD normally inhibits DNA fragmentation and apoptosis; thus, its down-regulation was unexpected in a cancer known for its resistance to apoptosis. However, these RCC samples were from primary, not metastatic, RCC sites, and down-regulated ICAD may be part of a progressive pathway that promotes RCC metastasis.

Host restriction factors for hepatitis C virus

Host-hepatitis C virus (HCV) interactions have both informed fundamental concepts of viral replication and pathogenesis and provided novel insights into host cell biology. These findings are illustrated by the recent discovery of host-encoded factors that restrict HCV infection. In this review, we briefly discuss these restriction factors in different steps of HCV infection. In each case, we discuss how these restriction factors were identified, the mechanisms by which they inhibit HCV infection and their potential contribution to viral pathogenesis.

Naringenin and quercetin--potential anti-HCV agents for NS2 protease targets

Nonstructural proteins of hepatitis C virus had drawn much attention for the scientific fraternity in drug discovery due to its important role in the disease. 3D structure of the protein was predicted using molecular modelling protocol. Docking studies of 10 medicinal plant compounds and three drugs available in the market (control) with NS2 protease were employed by using rigid docking approach of AutoDock 4.2. Among the molecules tested for docking study, naringenin and quercetin revealed minimum binding energy of - 7.97 and - 7.95 kcal/mol with NS2 protease. All the ligands were docked deeply within the binding pocket region of the protein. The docking study results showed that these compounds are potential inhibitors of the target; and also all these docked compounds have good inhibition constant, vdW+Hbond+desolv energy with best RMSD value.

A basic cluster in the N terminus of yellow fever virus NS2A contributes to infectious particle production

The flavivirus NS2A protein is involved in the assembly of infectious particles. To further understand its role in this process, a charged-to-alanine scanning analysis was performed on NS2A encoded by an infectious cDNA clone of yellow fever virus (YFV). Fifteen mutants containing single, double, or triple charged-to-alanine changes were tested. Five of them did not produce infectious particles, whereas efficient RNA replication was detectable for two of the five NS2A mutants (R22A-K23A-R24A and R99A-E100A-R101A mutants). Prolonged cultivation of transfected cells resulted in the recovery of pseudorevertants. Besides suppressor mutants in NS2A, a compensating second-site mutation in NS3 (D343G) arose for the NS2A R22A-K23A-R24A mutant. We found this NS3 mutation previously to be suppressive for the NS2Aα cleavage site Q189S mutant, also deficient in virion assembly. In this study, the subsequently suggested interaction between NS2A and NS3 was proven by coimmunoprecipitation analyses. Using selectively permeabilized cells, we could demonstrate that the regions encompassing R22A-K23A-R24A and Q189S in NS2A are localized to the cytoplasm, where NS3 is also known to reside. However, the defect in particle production observed for the NS2A R22A-K23A-R24A and Q189S mutants was not due to a defect in physical interaction between NS2A and NS3, as the NS2A mutations did not interrupt NS3 interaction. In fact, a region just upstream of R22-K23-R24 was mapped to be critical for NS2A-NS3 interaction. Taken together, these data support a complex interplay between YFV NS2A and NS3 in virion assembly and identify a basic cluster in the NS2A N terminus to be critical in this process.

IMPORTANCE

Despite an available vaccine, yellow fever remains endemic in tropical areas of South America and Africa. To control the disease, antiviral drugs are required, and an understanding of the determinants of virion assembly is central to their development. In this study, we identified a basic cluster of amino acids in the N terminus of YFV NS2A which inhibited virion assembly upon mutation. The defect was rescued by a spontaneously occurring mutation in NS3. Our study proves an interaction between NS2A and NS3, which, remarkably, was maintained for the NS2A mutant in the presence and absence of the NS3 mutation. This suggests a role for other viral and/or cellular proteins in virion assembly. Residues important for YFV virion production reported here only partially coincided with those reported for other flaviviruses, suggesting that the determinants for particle production are virus specific. Reconstruction of a YFV encoding tagged NS2A paves the way to identify further NS2A interaction partners.

Crimean-Congo haemorrhagic fever replication interplays with regulation mechanisms of apoptosis

Pathogenesis of viral haemorrhagic fevers is associated with alteration of vascular barrier function and haemorrhage. To date, the specific mechanism behind this is unknown. Programmed cell death and regulation of apoptosis in response to viral infection is an important factor for host or virus survival but this has not been well-studied in the case of Crimean-Congo hemorrhagic fever virus (CCHFV). In this study, we demonstrated that CCHFV infection suppresses cleavage of poly(ADP-ribose) polymerase (PARP), triggered by staurosporine early post-infection. We also demonstrated that CCHFV infection suppresses activation of caspase-3 and caspase-9. Most interestingly, we found that CCHFV N can suppress induction of apoptosis by Bax and inhibit the release of cytochrome c from the inner membrane of mitochondria to cytosol. However, CCHFV infection induces activation of Bid late post-infection, suggesting activation of extrinsic apoptotic signalling. Consistently, supernatant from cells stimulated late post-infection was found to induce PARP cleavage, most probably through the TNF-α death receptor pathway. In summary, we found that CCHFV has strategies to interplay with apoptosis pathways and thereby regulate caspase cascades. We suggest that CCHFV suppresses caspase activation at early stages of the CCHFV replication cycle, which perhaps benefits the establishment of infection. Furthermore, we suggest that the host cellular response at late stages post-infection induces host cellular pro-apoptotic molecules through the death receptor pathway.

Investigating the antiviral role of cell death-inducing DFF45-like effector B in HCV replication

Cell-death-inducing DFF45-like effector B (CIDEB) is an apoptotic host factor, which was recently found to also regulate hepatic lipid homeostasis. Herein we delineate the relevance of these dual roles of CIDEB in apoptosis and lipid metabolism in the context of hepatitis C virus (HCV) replication. We demonstrate that HCV upregulates CIDEB expression in human serum differentiated hepatoma cells. CIDEB overexpression inhibits HCV replication in HCV replicon expressing Huh7.5 cells, while small interfering RNA knockdown of CIDEB expression in human serum differentiated hepatoma cells promotes HCV replication and secretion of viral proteins. Furthermore, we characterize a CIDEB mutant, KRRA, which is deficient in lipid droplet clustering and fusion and demonstrate that CIDEB-mediated inhibition of HCV is independent of the protein's lipid droplet fusogenic role. Our results suggest that higher levels of CIDEB expression, which favour an apoptotic role for the host factor, inhibit HCV. Collectively, our data demonstrate that CIDEB can act as an anti-HCV host factor and contribute to altered triglyceride homeostasis.

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.

Genetic polymorphisms of the IFNλ genes are associated with biochemical features in Han Chinese with HCV infection from Yunnan Province, China

Hepatitis C virus (HCV) is the pathogenic factor for hepatitis C disease, which could lead to chronic or serious hepatic diseases. Previous studies have identified that the IL28B gene polymorphisms were associated with therapeutic effect and viral clearness of HCV patients. We aimed to test whether genetic polymorphisms of three IFNλ genes (IL28A, IL28B and IL29) are associated with HCV infection in Han Chinese. We collected whole blood of 261 HCV infectious patients without any therapy and 265 matched normal controls from Yunnan Province. Among these subjects, 28.4% (74/261) of HCV patients and 26.8% (71/265) of controls were male. Ten SNPs (rs8099917, rs10853728, rs11883177, rs12980602, rs4803224, rs11671087, rs11665818, rs8108008, rs7248931, and rs30461), which covered the whole region of the IL28A, IL28B, and IL29 genes, were genotyped. Our results showed that there was no association between genotypes and alleles of the IFNλ gene polymorphisms and HCV infection. One haplotype (TGCTGTGGAT), which was consisted of ten SNPs, showed a significantly higher frequency in HCV patients (11/522 = 2.1%) than in controls (1/530 = 0.2%) (P = 0.003). We performed association analyses for biochemical features and genotype of each SNP, and found that HCV patients with certain genotypes of some SNPs had a higher level of the ALT/AST ratio and total blood bilirubin (TBIL) compared to healthy controls. Our results suggested the IFNλ gene polymorphisms might be associated with clinical features of HCV patients from Yunnan Province, China.

Post-translational modifications of hepatitis C viral proteins and their biological significance

Replication of hepatitis C virus (HCV) depends on the interaction of viral proteins with various host cellular proteins and signalling pathways. Similar to cellular proteins, post-translational modifications (PTMs) of HCV proteins are essential for proper protein function and regulation, thus, directly affecting viral life cycle and the generation of infectious virus particles. Cleavage of the HCV polyprotein by cellular and viral proteases into more than 10 proteins represents an early protein modification step after translation of the HCV positive-stranded RNA genome. The key modifications include the regulated intramembranous proteolytic cleavage of core protein, disulfide bond formation of core, glycosylation of HCV envelope proteins E1 and E2, methylation of nonstructural protein 3 (NS3), biotinylation of NS4A, ubiquitination of NS5B and phosphorylation of core and NS5B. Other modifications like ubiquitination of core and palmitoylation of core and NS4B proteins have been reported as well. For some modifications such as phosphorylation of NS3 and NS5A and acetylation of NS3, we have limited understanding of their effects on HCV replication and pathogenesis while the impact of other modifications is far from clear. In this review, we summarize the available information on PTMs of HCV proteins and discuss their relevance to HCV replication and pathogenesis.

A potential cellular host factor homologous to ZNF-136 can interact with truncated nonstructural protein 2 of hepatitis C virus

The cytoplasmic portion of the NS2 protein of hepatitis C virus (HCV) fused with a thioredoxin (TrX)-His tag was expressed in BL21 (DE3) cells and purified using an Ni-NTA His resin. Using a pull-down assay, a specific protein from the cell lysate of HepG2 cell lines was isolated together with immobilized truncated NS2 protein using Ni-NTA resin. Through peptide mass fingerprinting, this specific protein was found to be homologous to a repressor of transcription, ZNF136.

Signal peptidase complex subunit 1 participates in the assembly of hepatitis C virus through an interaction with E2 and NS2

Hepatitis C virus (HCV) nonstructural protein 2 (NS2) is a hydrophobic, transmembrane protein that is required not only for NS2-NS3 cleavage, but also for infectious virus production. To identify cellular factors that interact with NS2 and are important for HCV propagation, we screened a human liver cDNA library by split-ubiquitin membrane yeast two-hybrid assay using full-length NS2 as a bait, and identified signal peptidase complex subunit 1 (SPCS1), which is a component of the microsomal signal peptidase complex. Silencing of endogenous SPCS1 resulted in markedly reduced production of infectious HCV, whereas neither processing of structural proteins, cell entry, RNA replication, nor release of virus from the cells was impaired. Propagation of Japanese encephalitis virus was not affected by knockdown of SPCS1, suggesting that SPCS1 does not widely modulate the viral lifecycles of the Flaviviridae family. SPCS1 was found to interact with both NS2 and E2. A complex of NS2, E2, and SPCS1 was formed in cells as demonstrated by co-immunoprecipitation assays. Knockdown of SPCS1 impaired interaction of NS2 with E2. Our findings suggest that SPCS1 plays a key role in the formation of the membrane-associated NS2-E2 complex via its interaction with NS2 and E2, which leads to a coordinating interaction between the structural and non-structural proteins and facilitates the early step of assembly of infectious particles.

Viruses hijack host cells and utilize host-derived proteins for viral propagation. In the case of hepatitis C virus (HCV), many host factors have been identified that are required for genome replication; however, only a little is known about cellular proteins that interact with HCV proteins and are important for the viral assembly process. The C-terminal half of nonstructural protein 2 (NS2), and the N-terminal third of NS3, form the NS2-3 protease that cleaves the NS2/3 junction. NS2 also plays a key role in the viral assembly process independently of the protease activity. We performed split-ubiquitin yeast two-hybrid screening and identified signal peptidase complex subunit 1 (SPCS1), which is a subunit of the microsomal signal peptidase complex. In this study, we provide evidence that SPCS1 interacts with both NS2 and E2, resulting in E2-SPCS1-NS2 complex formation, and has a critical role in the assembly of infectious HCV particles. To our knowledge, SPCS1 is the first NS2-interacting cellular factor that is involved in regulation of the HCV lifecycle.

The modulation of apoptosis by oncogenic viruses

Transforming viruses can change a normal cell into a cancer cell during their normal life cycle. Persistent infections with these viruses have been recognized to cause some types of cancer. These viruses have been implicated in the modulation of various biological processes, such as proliferation, differentiation and apoptosis. The study of infections caused by oncogenic viruses had helped in our understanding of several mechanisms that regulate cell growth, as well as the molecular alterations leading to cancer. Therefore, transforming viruses provide models of study that have enabled the advances in cancer research. Viruses with transforming abilities, include different members of the Human Papillomavirus (HPV) family, Hepatitis C virus (HCV), Human T-cell Leukemia virus (HTLV-1), Epstein Barr virus (EBV) and Kaposi’s Sarcoma Herpesvirus (KSHV).

Apoptosis, or programmed cell death, is a tightly regulated process that plays an important role in development and homeostasis. Additionally, it functions as an antiviral defense mechanism. The deregulation of apoptosis has been implicated in the etiology of diverse diseases, including cancer. Oncogenic viruses employ different mechanisms to inhibit the apoptotic process, allowing the propagation of infected and damaged cells. During this process, some viral proteins are able to evade the immune system, while others can directly interact with the caspases involved in apoptotic signaling. In some instances, viral proteins can also promote apoptosis, which may be necessary for an accurate regulation of the initial stages of infection.

Mean protein evolutionary distance: a method for comparative protein evolution and its application

Proteins are under tight evolutionary constraints, so if a protein changes it can only do so in ways that do not compromise its function. In addition, the proteins in an organism evolve at different rates. Leveraging the history of patristic distance methods, a new method for analysing comparative protein evolution, called Mean Protein Evolutionary Distance (MeaPED), measures differential resistance to evolutionary pressure across viral proteomes and is thereby able to point to the proteins’ roles. Different species’ proteomes can also be compared because the results, consistent across virus subtypes, concisely reflect the very different lifestyles of the viruses. The MeaPED method is here applied to influenza A virus, hepatitis C virus, human immunodeficiency virus (HIV), dengue virus, rotavirus A, polyomavirus BK and measles, which span the positive and negative single-stranded, doubled-stranded and reverse transcribing RNA viruses, and double-stranded DNA viruses. From this analysis, host interaction proteins including hemagglutinin (influenza), and viroporins agnoprotein (polyomavirus), p7 (hepatitis C) and VPU (HIV) emerge as evolutionary hot-spots. By contrast, RNA-directed RNA polymerase proteins including L (measles), PB1/PB2 (influenza) and VP1 (rotavirus), and internal serine proteases such as NS3 (dengue and hepatitis C virus) emerge as evolutionary cold-spots. The hot spot influenza hemagglutinin protein is contrasted with the related cold spot H protein from measles. It is proposed that evolutionary cold-spot proteins can become significant targets for second-line anti-viral therapeutics, in cases where front-line vaccines are not available or have become ineffective due to mutations in the hot-spot, generally more antigenically exposed proteins. The MeaPED package is available from www.pam1.bcs.uwa.edu.au/~michaelw/ftp/src/meaped.tar.gz.

Hepatitis C virus-induced mitochondrial dysfunctions

Chronic hepatitis C is characterized by metabolic disorders and a microenvironment in the liver dominated by oxidative stress, inflammation and regeneration processes that lead in the long term to hepatocellular carcinoma. Many lines of evidence suggest that mitochondrial dysfunctions, including modification of metabolic fluxes, generation and elimination of oxidative stress, Ca²⁺ signaling and apoptosis, play a central role in these processes. However, how these dysfunctions are induced by the virus and whether they play a role in disease progression and neoplastic transformation remains to be determined. Most in vitro studies performed so far have shown that several of the hepatitis C virus (HCV) proteins localize to mitochondria, but the consequences of these interactions on mitochondrial functions remain contradictory, probably due to the use of artificial expression and replication systems. In vivo studies are hampered by the fact that innate and adaptive immune responses will overlay mitochondrial dysfunctions induced directly in the hepatocyte by HCV. Thus, the molecular aspects underlying HCV-induced mitochondrial dysfunctions and their roles in viral replication and the associated pathology need yet to be confirmed in the context of productively replicating virus and physiologically relevant in vitro and in vivo model systems.

Hepatitis C virus NS2 protease inhibits host cell antiviral response by inhibiting IKKε and TBK1 functions

Hepatitis C virus (HCV) encodes for several proteins that can interfere with host cell signaling and antiviral response. Previously, serine protease NS3/4A was shown to block host cell interferon (IFN) production by proteolytic cleavage of MAVS and TRIF, the adaptor molecules of the RIG-I and TLR3 signaling pathways, respectively. This study shows that another HCV protease, NS2 can interfere efficiently with cytokine gene expression. NS2 and its proteolytically inactive mutant forms were able to inhibit type I and type III IFN, CCL5 and CXCL10 gene promoters activated by Sendai virus infection. However, the CXCL8 gene promoter was not inhibited by NS2. In addition, constitutively active RIG-I (ΔRIG-I), MAVS, TRIF, IKKε, and TBK1-induced activation of IFN-β promoter was inhibited by NS2. Cotransfection experiments with IKKε or TBK1 together with interferon regulatory factor 3 (IRF3) and HCV expression constructs revealed that NS2 in a dose-dependent manner inhibited IKKε and especially TBK1-induced IRF3 phosphorylation. GST pull-down experiments with GST-NS2 and in vitro-translated and cell-expressed IKKε and TBK1 demonstrated direct physical interactions of the kinases with NS2. Further evidence that the IKKε/TBK1 kinase complex is the target for NS2 was obtained from the observation that the constitutively active form of IRF3 (IRF3-5D) activated readily IFN-β promoter in the presence of NS2. The present study identified HCV NS2 as a potent interferon antagonist, and describes an explanation of how NS2 downregulates the major signaling pathways involved in the development of host innate antiviral responses.

Cleavage of the Junin virus nucleoprotein serves a decoy function to inhibit the induction of apoptosis during infection

The regulation of apoptosis during infection is an important factor for host survival and, in some cases, also for the virus life cycle. At the same time, mechanisms to prevent the induction of apoptosis have been observed in numerous viral pathogens, but until now the role of apoptosis during arenavirus infection has not been investigated. Junin virus (JUNV) belongs to the New World arenavirus serogroup of the Arenaviridae and is the causative agent of Argentine hemorrhagic fever. We have demonstrated that infection with JUNV in cell culture does not induce apoptosis but leads to cleavage of the nucleoprotein (NP) into discrete products resembling caspase cleavage events. Similar specific NP degradation patterns were also observed in NP-transfected cell lines, and a closer examination of the sequence of NP showed several putative caspase cleavage motifs. Point mutations that abolished these cleavage motifs were consistent with the loss of certain cleavage products. Consistent with these data, further studies showed that treatment with a caspase inhibitor also reduced NP cleavage, indicating that the observed cleavage events were occurring as a result of caspase activity with NP as a substrate. Finally, we showed that expression of NP suppresses the cleavage of caspase 3 in cells treated with an apoptosis activator. Based on these findings, we propose that NP functions as a decoy substrate for caspase cleavage in order to inhibit the induction of apoptosis in JUNV-infected cells.

Enhanced apoptosis in post-liver transplant hepatitis C: Effects of virus and immunosuppressants

Hepatitis C (HCV)-infected patients have a poorer survival post-liver transplantation compared to patients transplanted for other indications, since HCV recurrence post-transplant is universal and commonly follows an aggressive course. There is increasing evidence that in the non-transplant setting, induction of hepatocyte apoptosis is one of the main mechanisms by which HCV drives liver inflammation and fibrosis, and that HCV proteins directly promote apoptosis. Recent studies have shown that post-liver transplant, there is a link between high levels of HCV replication, enhanced hepatocyte apoptosis and the subsequent development of rapidly progressive liver fibrosis. Although the responsible mechanisms remain unclear, it is likely that immunosuppressive drugs play an important role. It is well known that immunosuppressants impair immune control of HCV, thereby allowing increased viral replication. However there is also evidence that immunosuppressants may directly induce apoptosis and this may be facilitated by the presence of high levels of HCV replication. Thus HCV and immunosuppressants may synergistically interact to further enhance apoptosis and drive more rapid fibrosis. These findings suggest that modulation of apoptosis within the liver either by changing immunosuppressive therapy or the use of apoptosis inhibitors may help prevent fibrosis progression in patients with post-transplant HCV disease.

HCV NS4B induces apoptosis through the mitochondrial death pathway

The hepatitis C virus (HCV) NS4B protein is known to induce the formation of a membranous web that is thought to be the site of viral RNA replication. However, the exact functions of NS4B remain poorly characterized. In this study, we found that NS4B induced apoptosis in 293T cells and Huh7 cells, as confirmed by Hoechst staining, DNA fragmentation, and annexin V/PI assays. Furthermore, protein immunoblot analysis demonstrated that NS4B triggered the cleavage of caspase 3, caspase 7, and poly(ADP-ribose) polymerase (PARP). Further studies revealed that NS4B induced the activation of caspase 9, the reduction of mitochondrial membrane potential and the release of cytochrome c from the mitochondria. However, NS4B expression did not trigger XBP1 mRNA splicing and increase the expression of binding immunoglobulin protein (BiP, or GRP78) and C/EBP homologous protein (CHOP), which serves as the indicators of ER stress. Taken together, our results suggest that HCV NS4B induces apoptosis through the mitochondrial death pathway.

External Qi of Yan Xin Qigong induces cell death and gene expression alterations promoting apoptosis and inhibiting proliferation, migration and glucose metabolism in small-cell lung cancer cells

Small-cell lung cancer (SCLC) is a highly malignant carcinoma with poor long-term survival. Effective treatment remains highly demanded. In the present study, we demonstrated that External Qi of Yan Xin Qigong (YXQ-EQ) exerted potent cytotoxic effect towards SCLC cell line NCI-H82 via induction of apoptosis. Global gene expression profiling identified 39 genes whose expression was altered by YXQ-EQ in NCI-82 cells. Among them, semi-quantitative RT-PCR and real-time qPCR analyses confirmed that the gene expression levels of apoptotic proteins death-associated protein kinase 2 and cell death-inducing DFFA-like effector b were upregulated, whereas that of oncoproteins DEK and MYCL1, cell migration-promoting proteins CD24 and integrin-alpha 9, and glycolytic enzyme aldolase A were downregulated. These findings suggest that YXQ-EQ may exert anticancer effect through modulating gene expression in a way that facilitates cancer cell apoptosis while represses proliferation, metastasis, and glucose metabolism.

Cell death-inducing DFF45-like effector b (Cideb) is present in pancreatic beta-cells and involved in palmitate induced beta-cell apoptosis

BACKGROUND

Excessive accumulation of long-chain fatty acids in the pancreatic islets is associated with beta cell dysfunction and ultimately contributes to the pathogenesis of type 2 diabetes. It has been well proved that the cell death-inducing DFF45-like effector b (Cideb) is involved in cell apoptosis and lipid metabolism. However, the expression and function of Cideb in endocrine pancreas remain to be investigated.

METHODS

By using reverse transcript polymerase chain reaction, immunohistochemistry and Western blot, we observed the expression of Cideb in pancreas tissues and clonal beta-cell lines. The physiological role of Cideb was examined under the free fatty acid (FFA) administration and Cideb ribonucleic acid interference, and further analysis on apoptosis was measured by terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick end labelling assay and caspase-3 activity. Nile red staining and quantitative evaluation of triglyceride were used to detect the lipid accumulation. The changes in esterification of FFA were traced by radiolabelled palmitate.

RESULTS

Cideb was abundantly expressed in pancreas and mainly localized in beta cells. FFAs, especially palmitate, induced an obvious increase of Cideb expression in beta cell lines. Adenoviral-mediated overexpression of Cideb increased the apoptosis, whereas ribonucleic acid interference-based Cideb depletion in beta-TC3 cells had no effect on apoptosis in normal condition. Palmitate supplementation led to beta cell lipoapoptosis, and Cideb silencing exacerbated the apoptosis induced by palmitate, reduced intracellular triglyceride content and aggravated FFA overload in beta cells.

CONCLUSIONS

The present results suggest that increased Cideb expression upon palmitate exposure may be involved in beta cell lipoapoptosis through its influence on conversion of FFAs to lipid esters in lipid droplets.

Human cell-death-inducing DFF45-like effector C induces apoptosis via caspase-8

Human cell-death-inducing DNA-fragmentation-factor (DFF45)-like effector C (CIDEC) is a potent apoptotic inducer. Previous studies have indicated that the Fat-specific protein 27 (Fsp27), a mouse homolog of CIDEC, induces apoptosis via caspase-3, -7, and -9 and triggers the release of cytochrome c from mitochondria, which implies that the mitochondrial pathway is involved in Fsp27-induced apoptosis. In the current study, we found that CIDEC-induced apoptosis was mediated by caspase-8. The caspase inhibitor assay showed that CIDEC-induced apoptosis was dramatically reduced in the presence of the general caspase inhibitor, the caspase-3 inhibitor, and the caspase-8 inhibitor, whereas the caspase-9 inhibitor only weakly inhibited CIDEC-induced apoptosis. These results confirmed that the activation of caspase-3 and caspase-8 were involved in CIDEC-induced apoptosis. Moreover, in caspase-3- or caspase-8-deficient cells, CIDEC-induced apoptosis were dramatically decreased, which demonstrated that CIDEC-induced apoptosis might require the activation of caspase-3 and caspase-8. Because caspase-8 in general is a key effecter of death-receptor pathway and activated by Fas-Associated protein with Death Domain (FADD), we examined whether FADD was involved in CIDEC-induced apoptosis. Our results demonstrated that CIDEC-induced apoptosis was independent of FADD, suggesting that CIDEC-induced apoptosis might be in a death-receptor-independent, caspase-8-dependent manner. It was also found that the region of amino acid 168-200 in carboxyl domain of CIDEC was critical for its crucial pro-apoptotic function.

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.

Animal models in the study of hepatitis C virus-associated liver pathologies

It is estimated that more than 170 million individuals worldwide are chronically infected with hepatitis C virus (HCV), with approximately 20% of the cases developing cirrhosis. Each year, between 1 and 4% of patients exhibiting cirrhosis develop hepatocellular carcinoma. Chronic HCV infection is also linked with the development of several metabolic disorders, including hepatic steatosis and insulin resistance. Research into HCV-related pathologies is hampered by a relative paucity of small animal models. As a result, little is known about the molecular mechanisms involved, and much of our current knowledge is drawn by inference from in vitro studies using overexpressed proteins. In this article, we will review the currently available animal models for the study of HCV pathogenesis, with an emphasis on murine models. Then, we will provide an overview of how these models have contributed to the deciphering of the molecular mechanisms underlying dysregulated lipid metabolism and hepatocellular carcinoma during HCV infection.

The Rubella virus capsid is an anti-apoptotic protein that attenuates the pore-forming ability of Bax

Apoptosis is an important mechanism by which virus-infected cells are eliminated from the host. Accordingly, many viruses have evolved strategies to prevent or delay apoptosis in order to provide a window of opportunity in which virus replication, assembly and egress can take place. Interfering with apoptosis may also be important for establishment and/or maintenance of persistent infections. Whereas large DNA viruses have the luxury of encoding accessory proteins whose primary function is to undermine programmed cell death pathways, it is generally thought that most RNA viruses do not encode these types of proteins. Here we report that the multifunctional capsid protein of Rubella virus is a potent inhibitor of apoptosis. The main mechanism of action was specific for Bax as capsid bound Bax and prevented Bax-induced apoptosis but did not bind Bak nor inhibit Bak-induced apoptosis. Intriguingly, interaction with capsid protein resulted in activation of Bax in the absence of apoptotic stimuli, however, release of cytochrome c from mitochondria and concomitant activation of caspase 3 did not occur. Accordingly, we propose that binding of capsid to Bax induces the formation of hetero-oligomers that are incompetent for pore formation. Importantly, data from reverse genetic studies are consistent with a scenario in which the anti-apoptotic activity of capsid protein is important for virus replication. If so, this would be among the first demonstrations showing that blocking apoptosis is important for replication of an RNA virus. Finally, it is tempting to speculate that other slowly replicating RNA viruses employ similar mechanisms to avoid killing infected cells.

Among the variety of defense systems employed by mammalian cells to combat virus infection, apoptosis or programmed cell death is the most drastic response. Some large DNA viruses encode proteins whose sole function is to block apoptosis. Conversely, very little is known about whether RNA viruses encode analogous proteins. In many cases, RNA viruses are able to replicate before cell death occurs, which may be one reason why so little thought has been given to this topic. However, a number of RNA viruses, some of which are important human pathogens, have slow replication cycles and it stands to reason that they must block apoptosis during this time period. Here we show that the multifunctional capsid protein of Rubella virus is a potent inhibitor of apoptosis. Data from reverse genetic experiments suggest that the anti-apoptotic function of a virus-encoded protein is important for replication of an RNA virus. We anticipate that other slowly replicating RNA viruses may employ similar mechanisms and, as such, these studies have implications for development of novel anti-virals and vaccines.

Virus-specific mechanisms of carcinogenesis in hepatitis C virus associated liver cancer

The development of hepatocellular carcinoma (HCC) in persons who are persistently infected with hepatitis C virus (HCV) is a growing problem worldwide. Current antiviral therapies are not effective in many patients with chronic hepatitis C, and a greater understanding of the factors leading to progression of HCC will be necessary to design novel approaches to prevention of HCV-associated HCC. The lack of a small animal model of chronic HCV infection has hampered understanding of these factors. As HCV is an RNA virus with little potential for integration of its genetic material into the host genome, the mechanisms underlying HCV promotion of cancer are likely to differ from other models of viral carcinogenesis. In patients persistently infected with HCV, chronic inflammation resulting from immune responses against infected hepatocytes is associated with progressive fibrosis and cirrhosis. Cirrhosis is an important risk factor for HCC independent of HCV infection, and a majority of HCV-associated HCC arises in the setting of cirrhosis. However, a significant minority arises in the absence of cirrhosis, indicating that cirrhosis is not a prerequisite for cancer. Other lines of evidence suggest that direct, virus-specific mechanisms may be involved. Transgenic mice expressing HCV proteins develop cancer in the absence of inflammation or immune recognition of the transgene. In vitro studies have revealed multiple interactions of HCV-encoded proteins with cell cycle regulators and tumor suppressor proteins, raising the possibility that HCV can disrupt control of cellular proliferation, or impair the cell's response to DNA damage. A combination of virus-specific, host genetic, environmental and immune-related factors are likely to determine the progression to HCC in patients who are chronically infected with HCV. Here, we summarize current knowledge of the virus-specific mechanisms that may contribute to HCV-associated HCC.

Advances in research of interaction between hepatitis C virus nonstructural proteins and host proteins

Hepatitis C virus (HCV) is another common cause of chronic hepatitis, liver cirrhosis, and hepatocellular carcinoma after hepatitis B virus (HBV). Up to now, the mechanisms by which HCV promotes persistent infection and cancer remain unclear, and there are neither effective drugs nor vaccines against HCV available. Interaction between virus proteins and host proteins is a hot topic in research of the pathogenesis of viral hepatitis. Recent research shows that interaction between HCV nonstructural proteins and host proteins has an important impact on viral replication, carcinogenesis, interferon resistance, and disorders of glycometabolism and lipid metabolism. This paper summarizes the recent advances in research of interaction between HCV nonstructural proteins and host proteins.

Structural and functional studies of nonstructural protein 2 of the hepatitis C virus reveal its key role as organizer of virion assembly

Non-structural protein 2 (NS2) plays an important role in hepatitis C virus (HCV) assembly, but neither the exact contribution of this protein to the assembly process nor its complete structure are known. In this study we used a combination of genetic, biochemical and structural methods to decipher the role of NS2 in infectious virus particle formation. A large panel of NS2 mutations targeting the N-terminal membrane binding region was generated. They were selected based on a membrane topology model that we established by determining the NMR structures of N-terminal NS2 transmembrane segments. Mutants affected in virion assembly, but not RNA replication, were selected for pseudoreversion in cell culture. Rescue mutations restoring virus assembly to various degrees emerged in E2, p7, NS3 and NS2 itself arguing for an interaction between these proteins. To confirm this assumption we developed a fully functional JFH1 genome expressing an N-terminally tagged NS2 demonstrating efficient pull-down of NS2 with p7, E2 and NS3 and, to a lower extent, NS5A. Several of the mutations blocking virus assembly disrupted some of these interactions that were restored to various degrees by those pseudoreversions that also restored assembly. Immunofluorescence analyses revealed a time-dependent NS2 colocalization with E2 at sites close to lipid droplets (LDs) together with NS3 and NS5A. Importantly, NS2 of a mutant defective in assembly abrogates NS2 colocalization around LDs with E2 and NS3, which is restored by a pseudoreversion in p7, whereas NS5A is recruited to LDs in an NS2-independent manner. In conclusion, our results suggest that NS2 orchestrates HCV particle formation by participation in multiple protein-protein interactions required for their recruitment to assembly sites in close proximity of LDs.