Direct interaction between α-actinin and hepatitis C virus NS5B

Interaction of influenza A virus NS1 and cytoskeleton scaffolding protein α-actinin 4

NS1 (Non-structural protein 1) is a non-structural protein that can highly express when the avian influenza virus infects the host cells. NS1 can interact with various proteins to alter the intracellular distribution of host proteins and regulate the virulence and pathogenicity of the avian influenza virus. To further study the role of NS1 protein in replication and pathogenesis of avian influenza virus, Glutathione S-transferase (GST) Pull-down was used for screening more proteins interacting with NS1 in human lung adenocarcinoma cell line A549. By mass spectrometry, a potential interacted protein is identified as α-actinin 4 and its interaction with NS1 has not been reported yet. The interaction between NS1 and α-actinin 4 in vitro was confirmed by enzyme-linked immunosorbent assay experiments, and the results showed that the absorbance value of OD_450nm in the experimental group was positively correlated with the concentration of NS1-GST protein compared to the negative control group. The co-immunoprecipitation and immunofluorescence results further confirmed the interaction between NS1 and α-actinin 4 at the cellular level. The interaction between NS1 and α-actinin 4 provided a new target for pathogenic mechanism studying and drug screening.

The actin cytoskeleton is important for rotavirus internalization and RNA genome replication

•

Different stages of the rotavirus lifecycle depend on the dynamics of the actin cytoskeleton.

•

Alpha-actinin, Diaph, and the GTPase Cdc42 are important for virus entry.

•

The GTPAse Rac1 is required for maximal viral RNA synthesis.

Numerous host factors are required for the efficient replication of rotavirus, including the activation and inactivation of several cell signaling pathways. One of the cellular structures that are reorganized during rotavirus infection is the actin cytoskeleton. In this work, we report that the dynamics of the actin microfilaments are important at different stages of the virus life cycle, specifically, during virus internalization and viral RNA synthesis at 6 h post-infection. Our results show that the actin-binding proteins alpha-actinin 4 and Diaph, as well as the Rho-family small GTPase Cdc42 are necessary for an efficient virus entry, while GTPase Rac1 is required for maximal viral RNA synthesis.

iTRAQ-Based Proteomics Identification of Serum Biomarkers of Two Chronic Hepatitis B Subtypes Diagnosed by Traditional Chinese Medicine

Background. Chronic infection with hepatitis B virus (HBV) is a leading cause of cirrhosis and hepatocellular carcinoma. By traditional Chinese medicine (TCM) pattern classification, damp heat stasis in the middle-jiao (DHSM) and liver Qi stagnation and spleen deficiency (LSSD) are two most common subtypes of CHB. Results. In this study, we employed iTRAQ proteomics technology to identify potential serum protein biomarkers in 30 LSSD-CHB and 30 DHSM-CHB patients. Of the total 842 detected proteins, 273 and 345 were differentially expressed in LSSD-CHB and DHSM-CHB patients compared to healthy controls, respectively. LSSD-CHB and DHSM-CHB shared 142 upregulated and 84 downregulated proteins, of which several proteins have been reported to be candidate biomarkers, including immunoglobulin (Ig) related proteins, complement components, apolipoproteins, heat shock proteins, insulin-like growth factor binding protein, and alpha-2-macroglobulin. In addition, we identified that proteins might be potential biomarkers to distinguish LSSD-CHB from DHSM-CHB, such as A0A0A0MS51_HUMAN (gelsolin), PON3_HUMAN, Q96K68_HUMAN, and TRPM8_HUMAN that were differentially expressed exclusively in LSSD-CHB patients and A0A087WT59_HUMAN (transthyretin), ITIH1_HUMAN, TSP1_HUMAN, CO5_HUMAN, and ALBU_HUMAN that were differentially expressed specifically in DHSM-CHB patients. Conclusion. This is the first time to report serum proteins in CHB subtype patients. Our findings provide potential biomarkers can be used for LSSD-CHB and DHSM-CHB.

Affinity Purification of the Hepatitis C Virus Replicase Identifies Valosin-Containing Protein, a Member of the ATPases Associated with Diverse Cellular Activities Family, as an Active Virus Replication Modulator

Like almost all of the positive-strand RNA viruses, hepatitis C virus (HCV) induces host intracellular membrane modification to form the membrane-bound viral replication complex (RC), within which viral replicases amplify the viral RNA genome. Despite accumulated information about how HCV co-opts host factors for viral replication, our knowledge of the molecular mechanisms by which viral proteins hijack host factors for replicase assembly has only begun to emerge. Purification of the viral replicase and identification of the replicase-associated host factors to dissect their roles in RC biogenesis will shed light on the molecular mechanisms of RC assembly. To purify the viral replicase in the context of genuine viral replication, we developed an HCV subgenomic replicon system in which two different affinity tags were simultaneously inserted in frame into HCV NS5A and NS5B. After solubilizing the replicon cells, we purified the viral replicase by two-step affinity purification and identified the associated host factors by mass spectrometry. We identified valosin-containing protein (VCP), a member of the ATPases associated with diverse cellular activities (AAA+ATPase) family, as an active viral replication modulator whose ATPase activity is required for viral replication. A transient replication assay indicated that VCP is involved mainly in viral genome amplification. VCP associated with viral replicase and colocalized with a viral RC marker. Further, in an HCV replicase formation surrogate system, abolishing VCP function resulted in aberrant distribution of HCV NS5A. We propose that HCV may co-opt a host AAA+ATPase for its replicase assembly.

IMPORTANCE

Almost all of the positive-strand RNA viruses share a replication strategy in which viral proteins modify host membranes to form the membrane-associated viral replicase. Viruses hijack host factors to facilitate this energy-unfavorable process. Understanding of this fundamental process is hampered by the challenges of purifying the replicase because of the technical difficulties involved. In this study, we developed an HCV subgenomic replicon system in which two different affinity tags were simultaneously inserted in frame into two replicase components. Using this dual-affinity-tagged replicon system, we purified the viral replicase and identified valosin-containing protein (VCP) AAA+ATPase as a pivotal viral replicase-associated host factor that is required for viral genome replication. Abolishing VCP function resulted in aberrant viral protein distribution. We propose that HCV hijacks a host AAA+ATPase for its replicase assembly. Understanding the molecular mechanism of VCP regulates viral replicase assembly may lead to novel antiviral strategies targeting the most conserved viral replication step.

Resistance to hepatitis C virus: potential genetic and immunological determinants

Studies of individuals who were highly exposed but seronegative (HESN) for HIV infection led to the discovery that homozygosity for the Δ32 deletion mutation in the CCR5 gene prevents viral entry into target cells, and is associated with resistance to infection. Additionally, evidence for protective immunity has been noted in some HESN groups, such as sex workers in The Gambia. Population studies of individuals at high risk for hepatitis C virus infection suggest that an HESN phenotype exists. The body of evidence, which suggests that protective immunity allows clearance of hepatitis C virus without seroconversion is growing. Furthermore, proof-of-principle evidence from in-vitro studies shows that genetic polymorphisms can confer resistance to establishment of infection. This Review discusses the possibility that genetic mutations confer resistance against hepatitis C virus, and also explores evidence for protective immunity, including via genetically programmed variations in host responses. The data generally strengthens the notion that investigations of naturally arising polymorphisms within the hepatitis C virus interactome, and genetic association studies of well characterised HESN individuals, could identify potential targets for vaccine design and inform novel therapies.

Influenza A viral nucleoprotein interacts with cytoskeleton scaffolding protein α-actinin-4 for viral replication

Influenza A virus (IAV), similar to other viruses, exploits the machinery of human host cells for its survival and replication. We identified α‐actinin‐4, a host cytoskeletal protein, as an interacting partner of IAV nucleoprotein (NP). We confirmed this interaction using co‐immunoprecipitation studies, first in a coupled in vitro transcription‐translation assay and then in cells either transiently co‐expressing the two proteins or infected with whole IAV. Importantly, the NP–actinin‐4 interaction was observed in several IAV subtypes, including the 2009 H1N1 pandemic virus. Moreover, immunofluorescence studies revealed that both NP and actinin‐4 co‐localized largely around the nucleus and also in the cytoplasmic region of virus‐infected A549 cells. Silencing of actinin‐4 expression resulted in not only a significant decrease in NP, M2 and NS1 viral protein expression, but also a reduction of both NP mRNA and viral RNA levels, as well as viral titers, 24 h post‐infection with IAV, suggesting that actinin‐4 was critical for viral replication. Furthermore, actinin‐4 depletion reduced the amount of NP localized in the nucleus. Treatment of infected cells with wortmannin, a known inhibitor of actinin‐4, led to a decrease in NP mRNA levels and also caused the nuclear retention of NP, further strengthening our previous observations. Taken together, the results of the present study indicate that actinin‐4, a novel interacting partner of IAV NP, plays a crucial role in viral replication and this interaction may participate in nuclear localization of NP and/or viral ribonucleoproteins.

Structured digital abstract

•http://www.uniprot.org/uniprot/P03466 http://www.ebi.ac.uk/ontology-lookup/?termId=MI:0915 with http://www.uniprot.org/uniprot/O43707 by http://www.ebi.ac.uk/ontology-lookup/?termId=MI:0006 (http://www.ebi.ac.uk/intact/interaction/EBI-9512541, http://www.ebi.ac.uk/intact/interaction/EBI-9512553)•http://www.uniprot.org/uniprot/Q8JR21 and http://www.uniprot.org/uniprot/O43707 http://www.ebi.ac.uk/ontology-lookup/?termId=MI:0403 by http://www.ebi.ac.uk/ontology-lookup/?termId=MI:0416 (http://www.ebi.ac.uk/intact/interaction/EBI-9514040)•http://www.uniprot.org/uniprot/Q91U50 http://www.ebi.ac.uk/ontology-lookup/?termId=MI:0915 with http://www.uniprot.org/uniprot/O43707 by http://www.ebi.ac.uk/ontology-lookup/?termId=MI:0006 (http://www.ebi.ac.uk/intact/interaction/EBI-9514006)•http://www.uniprot.org/uniprot/Q5L4H4 http://www.ebi.ac.uk/ontology-lookup/?termId=MI:0407 to http://www.uniprot.org/uniprot/O43707 by http://www.ebi.ac.uk/ontology-lookup/?termId=MI:0007 (http://www.ebi.ac.uk/intact/interaction/EBI-9512166, http://www.ebi.ac.uk/intact/interaction/EBI-9512219)•http://www.uniprot.org/uniprot/C3W6D7 http://www.ebi.ac.uk/ontology-lookup/?termId=MI:0915 with http://www.uniprot.org/uniprot/O43707 by http://www.ebi.ac.uk/ontology-lookup/?termId=MI:0006 (http://www.ebi.ac.uk/intact/interaction/EBI-9513951)•http://www.uniprot.org/uniprot/Q5L4H4 http://www.ebi.ac.uk/ontology-lookup/?termId=MI:0915 with http://www.uniprot.org/uniprot/O43707 by http://www.ebi.ac.uk/ontology-lookup/?termId=MI:0007 (http://www.ebi.ac.uk/intact/interaction/EBI-9512237)•http://www.uniprot.org/uniprot/Q6DPG0 http://www.ebi.ac.uk/ontology-lookup/?termId=MI:0915 with http://www.uniprot.org/uniprot/O43707 by http://www.ebi.ac.uk/ontology-lookup/?termId=MI:0006 (http://www.ebi.ac.uk/intact/interaction/EBI-9513984) •http://www.uniprot.org/uniprot/B2BU63 http://www.ebi.ac.uk/ontology-lookup/?termId=MI:0915 with http://www.uniprot.org/uniprot/O43707 by http://www.ebi.ac.uk/ontology-lookup/?termId=MI:0006 (http://www.ebi.ac.uk/intact/interaction/EBI-9513930) •http://www.uniprot.org/uniprot/Q5L4H4 http://www.ebi.ac.uk/ontology-lookup/?termId=MI:0915 with http://www.uniprot.org/uniprot/O43707 by http://www.ebi.ac.uk/ontology-lookup/?termId=MI:0018 (http://www.ebi.ac.uk/intact/interaction/EBI-9512145, http://www.ebi.ac.uk/intact/interaction/EBI-9512095) •http://www.uniprot.org/uniprot/C9S3S8 http://www.ebi.ac.uk/ontology-lookup/?termId=MI:0915 with http://www.uniprot.org/uniprot/O43707 by http://www.ebi.ac.uk/ontology-lookup/?termId=MI:0006 (http://www.ebi.ac.uk/intact/interaction/EBI-9513909)

Cytoskeletal proteins: shaping progression of hepatitis C virus-induced liver disease

Hepatitis C virus (HCV) infection, which results in chronic hepatitis C (CHC) in most patients (70-85%), is a major cause of liver disease and remains a major therapeutic challenge. The mechanisms determining liver damage and the key factors that lead to a high rate of CHC remain imperfectly understood. The precise role of cytoskeletal (CS) proteins in HCV infection remains to be determined. Some studies including our recent study have demonstrated that changes occur in the expression of CS proteins in HCV-infected hepatocytes. A variety of host proteins interact with HCV proteins. Association between CS and HCV proteins may have implications in future design of CS protein-targeted therapy for the treatment for HCV infection. This chapter will focus on the interaction between host CS and viral proteins to signify the importance of this event in HCV entry, replication and transportation.

Evaluation of antiviral activities of four local Malaysian Phyllanthus species against herpes simplex viruses and possible antiviral target

Nucleoside analogues such as acyclovir are effective antiviral drugs against herpes simplex virus infections since its introduction. However, with the emergence of acyclovir-resistant HSV strains particularly in immunocompromised patients, there is a need to develop an alternative antiherpetic drug and plants could be the potential lead. In this study, the antiviral activity of the aqueous extract of four Phyllanthus species were evaluated against herpes simplex virus type-1 (HSV-1) and HSV-2 in Vero cells by quantitative PCR. The protein expressions of untreated and treated infected Vero cells were studied by 2D-gel electrophoresis and Western blot. This is the first study that reported the antiviral activity of P. watsonii. P. urinaria was shown to demonstrate the strongest antiviral activity against HSV-1 and HSV-2, with SI >33.6. Time-of-addition studies suggested that the extract may act against the early infection stage and the replication stage. Protein expression studies indicated that cellular proteins that are involved in maintaining cytoskeletal structure could be potential target for development of antiviral drugs. Preliminary findings indicated that P. urinaria demonstrated potent inhibitory activity against HSV. Hence, further studies such as in vivo evaluation are required for the development of effective antiherpetic drug.

Anti-α actinin antibodies as new predictors of response to treatment in autoimmune hepatitis type 1

BACKGROUND

We reported that combined presence of autoantibodies (Abs) against filamentous-actin (AFA) and α-actinin are specific for autoimmune hepatitis type 1 (AIH-1) diagnosis.

AIM

To explore our data and assess whether anti-α-actinin and AFA Abs could be used as indicators of response to treatment and predictors of AIH-1 flares in a large cohort of AIH-1 patients.

METHODS

Seven hundred and sixty-four serial serum samples of 86 consecutive AIH-1 patients, 509 pathological and 110 normal controls were tested for the presence of anti-α-actinin and AFA Abs by an in-house IgG-specific ELISA and a standardised commercially available ELISA respectively. Patients sera were divided into baseline group (active disease before treatment initiation, n = 86) and then according to treatment response into group A-responders (n = 40 patients), group B-relapsers/incomplete responders (n = 37 patients) and group C-not-treated (n = 9 patients).

RESULTS

Anti-α-actinin and AFA levels were significantly higher at baseline. Double reactivity against α-actinin and AFA was associated with disease activity (OR 4.9; 95% CI: 2.7-9). Anti-α-actinin optical densities (ODs) before treatment decreased significantly at first remission (P < 0.05). Treatment response was associated with anti-α-actinin Abs negativity before treatment (OR 3.4; 95% CI: 1.3-8.9) and absence of double positivity for anti-α-actinin and AFA Abs before treatment (OR 3.8; 95% CI: 1.4-10.4). Responders had lower baseline levels of anti-α-actinin than relapsers and/or incomplete responders (P = 0.002). Binary logistic regression revealed lower levels of anti-α-actinin as the only independent predictors of response (P = 0.05).

CONCLUSIONS

Anti-α-actinin Abs at baseline appear to predict treatment response and therefore they might be used for monitoring treatment outcome in AIH-1.

Schizophrenia: a pathogenetic autoimmune disease caused by viruses and pathogens and dependent on genes

Many genes have been implicated in schizophrenia as have viral prenatal or adult infections and toxoplasmosis or Lyme disease. Several autoantigens also target key pathology-related proteins. These factors are interrelated. Susceptibility genes encode for proteins homologous to those of the pathogens while the autoantigens are homologous to pathogens' proteins, suggesting that the risk-promoting effects of genes and risk factors are conditional upon each other, and dependent upon protein matching between pathogen and susceptibility gene products. Pathogens' proteins may act as dummy ligands, decoy receptors, or via interactome interference. Many such proteins are immunogenic suggesting that antibody mediated knockdown of multiple schizophrenia gene products could contribute to the disease, explaining the immune activation in the brain and lymphocytes in schizophrenia, and the preponderance of immune-related gene variants in the schizophrenia genome. Schizophrenia may thus be a “pathogenetic” autoimmune disorder, caused by pathogens, genes, and the immune system acting together, and perhaps preventable by pathogen elimination, or curable by the removal of culpable antibodies and antigens.

Alpha-actinin: a multidisciplinary protein with important role in B-cell driven autoimmunity

Alpha-actinin (α-actinin) is a ubiquitous cytoskeletal protein, which belongs to the superfamily of filamentous actin (F-actin) crosslinking proteins. It is present in multiple subcellular regions of both muscle and non-muscle cells, including cell-cell and cell-matrix contact sites, cellular protrusions and stress fiber dense regions and thus, it seems to bear multiple important roles in the cell by linking the cytoskeleton to many different transmembrane proteins in a variety of junctions. Four isoforms of human α-actinin have already been identified namely, the "muscles" α-actinin-2 and α-actinin-3 and the "non-muscles" α-actinin-1 and α-actinin-4. The precise functions of α-actinin isoforms as well as the precise role and significance of their binding to F-actin particularly in-vivo, have been elusive. They are generally believed to represent key structural components of large-scale F-actin cohesion in cells required for cell shape and motility. α-Actinin-2 has been implicated in myopathies such as nemalin body myopathy, hypertrophic and dilated cardiomyopathy and it may have at least an indirect pathogenetic role in diseases of the central nervous system (CNS) like schizophrenia, epilepsy, ischemic brain damage, CNS lupus and neurodegenerative disorders. The role of "non-muscle" α-actinins in the kidney seems to be crucial as an essential component of the glomerular filtration barrier. Therefore, they have been implicated in the pathogenesis of familial focal segmental glomerulosclerosis, nephrotic syndrome, IgA nephropathy, focal segmental glomerulosclerosis and minimal change disease. α-Actinin is also expressed on the membrane and cytosol of parenchymal and ductal cells of the liver and it seems that it interacts with hepatitis C virus in an essential way for the replication of the virus. Finally α-actinin, especially α-actinin-4, has been implicated in cancer cell progression and metastasis, as well as the migration of several cell types participating in the immune response. Based on these functions, the accumulating reported evidence of the importance of α-actinin as a target autoantigen in the pathogenesis of autoimmune diseases, particularly systemic lupus erythematosus and autoimmune hepatitis, is also discussed along with the possible perspectives that are potentially emerging from the study of this peculiar molecule in health and disease.

Isoform-specific interaction of pyruvate kinase with hepatitis C virus NS5B

Hepatitis C virus (HCV) replication and pathogenesis involve both virus-encoded proteins and cellular factors. In our study, we showed that NS5B, the HCV RNA-dependent RNA polymerase, interacted with M2 type pyruvate kinase (M2PK) but not L type pyruvate kinase. We confirmed the interaction by GST pull down, coimmunoprecipitation and confocal immunofluorescence analysis in cells with transient expression of NS5B and M2PK as well as in a HCV replicon-bearing cell line. Furthermore shRNA which specifically down-regulated M2PK expression could inhibit the replication of HCV in HCV replicon 9B cells.

Desflurane preconditioning inhibits endothelial nuclear factor-kappa-B activation by targeting the proximal end of tumor necrosis factor-alpha signaling

BACKGROUND

Volatile anesthetics interfere with inflammatory cytokine production and expression of adhesion molecules which are critical for ischemia reperfusion induced injury. Nuclear factor (NF)-kappaB has been reported to be suppressed in this process, but the detailed molecular mechanism is still unclear.

METHODS

In this study, ECV304 (a human umbilical vein endothelial cell line) was preconditioned with 30 min desflurane (1 minimal alveolar concentration), after 15 min washout, 30 min anoxia, and 60 min reoxygenation was performed. ECV304 was finally stimulated with tumor necrosis factor (TNF)-alpha (10 ng/mL). Control groups, which were not preconditioned and/or not stimulated, were also included in the protocol. IkappaB-alpha, phospho-IkappaB-alpha, phospho-IkappaB kinase (IKKalpha)/IKKbeta, and phospho-p38 were detected by Western blotting. The nuclear NF-kappaB p65 subunit was measured by subcellular fractionation and Western blotting. The surface expression of TNF-R1 was measured by flow cytometry. Receptor-associated signaling adaptors, e.g., TNF receptor-associated factor 2 (TRAF2) and IKK-alpha, were evaluated by immunoprecipitation by TNF-R1 antibody and subsequent Western blotting.

RESULTS

Desflurane preconditioning inhibits IkappaB-alpha phosphorylation, degradation, and p65 nuclear localization. Desflurane also affects p38 phosphorylation, which is needed for optimal inflammatory response. The phosphorylation of IKKalpha/IKKbeta was suppressed by preconditioning while the surface abundance of TNF-R1 was not affected. The association of TRAF2 and IKK-alpha with TNF-R1 was compromised by desflurane.

CONCLUSIONS

Our results suggest that the molecular target of desflurane in the NF-kappaB pathway is upstream of IKK activation. The abundance of TNF-R1 on the cell membrane is not affected by anesthetic preconditioning. We suggest that desflurane preconditioning targets the proximal end of TNF-alpha signaling.

Potential role of RNAi in the treatment of HCV infection

Chronic HCV infection is a leading cause of chronic hepatitis and its sequelae, liver cirrhosis and hepatocellular carcinoma. Current therapeutic options are limited, associated with significant adverse effects and costly. Accordingly, there is strong impetus to develop novel therapeutic strategies that act through alternate mechanisms. RNAi has been widely used for the analysis of gene function and represents a potentially promising approach for the treatment of HCV infection. siRNAs are short RNA duplexes approximately 21 nts long. When introduced into mammalian cells, siRNA can silence specific gene expression. Although efficient suppression of HCV replicon RNA in cell culture has been demonstrated with siRNAs, there is much work to be done to improve delivery, limit off-target effects and minimize development of virus resistance. Here, we review the use of RNAi as a tool to inhibit HCV gene expression and discuss the potential advantages and obstacles for this new potential therapeutic approach against HCV infection.

The NS3 helicase and NS5B-to-3'X regions are important for efficient hepatitis C virus strain JFH-1 replication in Huh7 cells

The JFH-1 strain of hepatitis C virus (HCV) is a genotype 2a strain that can replicate autonomously in Huh7 cells. The J6 strain is also a genotype 2a strain, but its full genomic RNA does not replicate in Huh7 cells. However, chimeric J6/JFH-1 RNA that has J6 structural-protein-coding regions and JFH-1 nonstructural-protein-coding regions can replicate autonomously and produce infectious HCV particles. In order to determine the mechanisms underlying JFH-1 RNA replication, we constructed various J6/JFH-1 chimeras and tested their RNA replication and virus particle production abilities in Huh7 cells. Via subgenomic-RNA-replication assays, we found that both the JFH-1 NS5B-to-3'X (N5BX) and the NS3 helicase (N3H) regions are important for the replication of the J6CF replicon. We applied these results to full-length genomic RNA replication and analyzed replication using Northern blotting. We found that a chimeric J6 clone with JFH-1 N3H and N5BX could replicate autonomously but that a chimeric J6 clone with only JFH-1 N5BX had no replication ability. Finally, we tested the virus production abilities of these clones and found that a chimeric J6 clone with JFH-1 N3H and N5BX could produce infectious HCV particles. In conclusion, the JFH-1 NS3 helicase and NS5B-to-3'X regions are important for efficient replication and virus particle formation of HCV genotype 2a strains.

Subproteomic study of hepatitis C virus replicon reveals Ras-GTPase-activating protein binding protein 1 as potential HCV RC component

Hepatitis C virus (HCV) RNA synthesis takes place on a detergent resistant membrane (DRM) structure. To identify potential cellular proteins related to HCV replication complexes (RC), we purified DRMs from HCV subgenomic replicon cells and its parental Huh7 cells. The proteins of DRM fractions were separated by two-dimensional gel electrophoresis and identified by mass spectrometry. Comparing with parental Huh7 cells, 60 proteins were up-regulated while 14 proteins were down-regulated in HCV replicon cells. Ras-GTPase-activating protein binding protein 1 (G3BP1), one of the elevated proteins, was found to be associated with HCV NS5B and knockdown of G3BP1 by siRNA in HCV replicon cells significantly reduced HCV replication, which may indicate it a potential component of HCV RC. These results suggest that HCV viral gene and proteins may regulate the presence of host cellular proteins in DRM, ensure appropriate concentrations of replication components, and hence control the rates or efficiencies of HCV replication.

Double reactivity against actin and alpha-actinin defines a severe form of autoimmune hepatitis type 1

Anti-filamentous actin antibodies characterize autoimmune hepatitis type 1 (AIH-1). Recently, the binding domain of alpha-actinin on actin was shown to be a predominant epitope. To test this reactivity, an anti-alpha-actinin enzyme-linked immunosorbent assay was developed, and positivity confirmed by Western blot. Anti-alpha-actinin antibody was found in 21/50 (42%) of AIH-1 patients, compared with 52/401 (12.9%) of liver disease control patients, and with 6/200 (6%) of blood donors. Anti-filamentous and anti-alpha-actinin activities were found specifically together in 66% of anti-filamentous-positive AIH-1 patients. This combination of specificities reflected clinical and histological disease activity, short duration and absence of treatment. Finally, using an actin-alpha-actinin complex assay, the binding of anti-filamentous actin to alpha-actinin-binding domain on actin was demonstrated, as well as that of anti-alpha-actinin on the actin-binding domain of alpha-actinin. Thus, the frequent combination of anti-filamentous and anti-alpha-actinin antibodies seems to be the hallmark of activity in AIH-1.

Proteome analysis of human liver carcinoma Huh7 cells harboring hepatitis C virus subgenomic replicon

Chronic infection by hepatitis C virus (HCV) is closely correlated with serious liver diseases. Although considerable progress has been made during recent years, the mechanism of replication and pathogenesis of HCV infection are still elusive. We have applied proteomic techniques in this work to globally analyze the protein expression profiles of a human liver cell lines Huh7 in absence and presence of HCV replication, aiming at elucidating the components of HCV replication and the cellular responses to HCV replication. The protein mixtures of three subcellular fractions from Huh7 and Huh7-HCV were separated by 2-DE under various pH gradients. Differentially expressed spots were identified by MALDI-TOF MS, followed by database searching. A total of 179 comparative proteins were identified unambiguously, including proteins associated with host cytoskeleton, intracellular traffic, oxidative and ER stress, proteasome degradation, translation, apoptosis, proliferation, etc. Host proteins known to interact with HCV proteins, such as HSP27, alpha-actinin, nucleolin and eukaryotic initiation factor 4A-I, were elevated in Huh7-HCV cells. Our study provides the global information of proteomic alteration of Huh7 cells in the presence of HCV replication and the clues for further understanding of the mechanism of HCV replication and pathogenesis.

RNA viruses redirect host factors to better amplify their genome

This chapter provides an updated view of the host factors that are, at present, believed to participate in replication/transcription of RNA viruses. One of the major hurdles faced when attempting to identify host factors specifically involved in viral RNA replication/transcription is how to discriminate these factors from those involved in translation. Several of the host factors shown to affect viral RNA synthesis are factors known to be involved in protein synthesis, for example, translation factors. In addition, some of the factors identified to date appear to influence viral RNA amplification as well as viral protein synthesis, and translation and replication are frequently tightly associated. Several specific host factors actively participating in viral RNA transcription/replication have been identified and the regions of host protein/replicase or host protein/viral RNA interaction have been determined. The chapter centers exclusively on those factors that appear functionally important for viral amplification. It presents a list of the viruses for which a specific host factor associates with the polymerase, affecting viral genome amplification. It also indicates the usually accepted cell function of the factor and the viral polymerase or polymerase subunit to which the host factor binds.