Interaction of hepatitis C virus F protein with prefoldin 2 perturbs tubulin cytoskeleton organization

Protein Quality Control Systems and ER Stress as Key Players in SARS-CoV-2-Induced Neurodegeneration

The COVID-19 pandemic has brought to the forefront the intricate relationship between SARS-CoV-2 and its impact on neurological complications, including potential links to neurodegenerative processes, characterized by a dysfunction of the protein quality control systems and ER stress. This review article explores the role of protein quality control systems, such as the Unfolded Protein Response (UPR), the Endoplasmic Reticulum-Associated Degradation (ERAD), the Ubiquitin-Proteasome System (UPS), autophagy and the molecular chaperones, in SARS-CoV-2 infection. Our hypothesis suggests that SARS-CoV-2 produces ER stress and exploits the protein quality control systems, leading to a disruption in proteostasis that cannot be solved by the host cell. This disruption culminates in cell death and may represent a link between SARS-CoV-2 and neurodegeneration.

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

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

Comprehensive analysis of the prognostic value and functions of prefoldins in hepatocellular carcinoma

Prefoldins (PFDNs), a group of proteins known to be associated with cytoskeletal rearrangement, are involved in tumor progression in various cancer types. However, little is known about the roles of PFDNs in hepatocellular carcinoma (HCC). Herein, we investigated the transcriptional and survival data of PFDNs from The Cancer Genome Atlas (TCGA) database. Gene Ontology (GO), Gene Set Enrichment Analysis (GSEA), and single-sample gene set enrichment analysis (ssGSEA) were used to evaluate the potential functions of PFDN1/2/3/4. We also detected the expression of PFDN1/2/3/4 via immunohistochemistry (IHC), Western blotting, and real-time PCR in our clinical samples. We found that the PFDN family showed elevated expression in HCC tissues, while only PFDN1/2/3/4 were found to be significantly correlated with poor prognosis of patients with HCC in the TCGA database. Further investigation was associated with PFDN1–4. We found that the expression of PFDN1/2/3/4 was significantly associated with advanced clinicopathologic features. Apart from the TCGA database, IHC, real-time PCR, and immunoblotting identified the overexpression of PFDN1/2/3/4 in HCC tissues and HCC cell lines. Taken together, these results indicated that PFDN1/2/3/4 might be novel prognostic biomarkers and treatment targets for patients with HCC.

Prefoldin Function in Cellular Protein Homeostasis and Human Diseases

Cellular functions are largely performed by proteins. Defects in the production, folding, or removal of proteins from the cell lead to perturbations in cellular functions that can result in pathological conditions for the organism. In cells, molecular chaperones are part of a network of surveillance mechanisms that maintains a functional proteome. Chaperones are involved in the folding of newly synthesized polypeptides and assist in refolding misfolded proteins and guiding proteins for degradation. The present review focuses on the molecular co-chaperone prefoldin. Its canonical function in eukaryotes involves the transfer of newly synthesized polypeptides of cytoskeletal proteins to the tailless complex polypeptide 1 ring complex (TRiC/CCT) chaperonin which assists folding of the polypeptide chain in an energy-dependent manner. The canonical function of prefoldin is well established, but recent research suggests its broader function in the maintenance of protein homeostasis under physiological and pathological conditions. Interestingly, non-canonical functions were identified for the prefoldin complex and also for its individual subunits. We discuss the latest findings on the prefoldin complex and its subunits in the regulation of transcription and proteasome-dependent protein degradation and its role in neurological diseases, cancer, viral infections and rare anomalies.

A comprehensive analysis of prefoldins and their implication in cancer

Prefoldins (PFDNs) are evolutionary conserved co-chaperones, initially discovered in archaea but universally present in eukaryotes. PFDNs are prevalently organized into hetero-hexameric complexes. Although they have been overlooked since their discovery and their functions remain elusive, several reports indicate they act as co-chaperones escorting misfolded or non-native proteins to group II chaperonins. Unlike the eukaryotic PFDNs which interact with cytoskeletal components, the archaeal PFDNs can bind and stabilize a wide range of substrates, possibly due to their great structural diversity. The discovery of the unconventional RPB5 interactor (URI) PFDN-like complex (UPC) suggests that PFDNs have versatile functions and are required for different cellular processes, including an important role in cancer. Here, we summarize their functions across different species. Moreover, a comprehensive analysis of PFDNs genomic alterations across cancer types by using large-scale cancer genomic data indicates that PFDNs are a new class of non-mutated proteins significantly overexpressed in some cancer types.

Prefoldin subunits (PFDN1-6) serve as poor prognostic markers in gastric cancer

Prefoldin subunits (PFDN), primarily known for co-chaperone function associated with cytoskeletal rearrangement, have been found involved in epithelial–mesenchymal transition (EMT) and cancer progression. However, studies focusing on the roles of PFDN in gastric cancer (GC) remain limited. The present study aims to evaluate the prognostic values of PFDN in GC. Prognostic roles of PFDNs were analyzed via the Kaplan–Meier platform, followed by subset analysis within various clinical parameters. High mRNA expression of PFDN2, PFDN3 and PFDN4 displayed poor overall survival (OS) while PFDN5 displayed favorable OS. In HER2+ subset, PFDN2, PFDN3, PFDN4 and PFDN6 displayed poor OS. In human epidermal growth factor receptor 2 (HER2−) subset, PFDN2, PFDN3 and PFDN4 displayed poor OS. In intestinal type subset, PFDN1 and PFDN2 displayed poor OS. In diffuse-type subset, PFDN2 and PFDN6 displayed poor OS. In moderate differentiation type subset, PFDN1 displayed poor OS. In poor differentiation type subset, PFDN2 and PFDN6 displayed poor OS. In metastasis negative subset, PFDN1, PFDN2 and PFDN6 displayed poor OS. In lymph node (LN) positive subset, PFDN2 and PFDN5 displayed poor OS. The present study provided insightful clues into the poor prognostic values of PFDNs in GC patients.

Variant in NHLRC2 leads to increased hnRNP C2 in developing neurons and the hippocampus of a mouse model of FINCA disease

Background

FINCA disease is a pediatric cerebropulmonary disease caused by variants in the NHL repeat-containing 2 (NHLRC2) gene. Neurological symptoms are among the first manifestations of FINCA disease, but the consequences of NHLRC2 deficiency in the central nervous system are currently unexplored.

Methods

The orthologous mouse gene is essential for development, and its complete loss leads to early embryonic lethality. In the current study, we used CRISPR/Cas9 to generate an Nhlrc2 knockin (KI) mouse line, harboring the FINCA patient missense mutation (c.442G > T, p.Asp148Tyr). A FINCA mouse model, resembling the compound heterozygote genotype of FINCA patients, was obtained by crossing the KI and Nhlrc2 knockout mouse lines. To reveal NHLRC2-interacting proteins in developing neurons, we compared cortical neuronal precursor cells of E13.5 FINCA and wild-type mouse embryos by two-dimensional difference gel electrophoresis.

Results

Despite the significant decrease in NHLRC2, the mice did not develop severe early onset multiorgan disease in either sex. We discovered 19 altered proteins in FINCA neuronal precursor cells; several of which are involved in vesicular transport pathways and actin dynamics which have been previously reported in other cell types including human to have an association with dysfunctional NHLRC2. Interestingly, isoform C2 of hnRNP C1/C2 was significantly increased in both developing neurons and the hippocampus of adult female FINCA mice, connecting NHLRC2 dysfunction with accumulation of RNA binding protein.

Conclusions

We describe here the first NHLRC2-deficient mouse model to overcome embryonic lethality, enabling further studies on predisposing and causative mechanisms behind FINCA disease. Our novel findings suggest that disrupted RNA metabolism may contribute to the neurodegeneration observed in FINCA patients.

Hepatitis C virus alternative reading frame protein (ARFP): Production, features, and pathogenesis

Earlier observation suggests that hepatitis C virus (HCV) is a single-stranded RNA virus which encodes at least 10 viral proteins. F protein is a novel protein which has been discovered recently. These studies suggest three mechanisms for the production of this protein concerning ribosomal frameshift at codon 10, initial translation at codons 26 and 85 or 87. In this study, the association between protein F and chronicity of hepatocellular carcinoma (HCC) has been reviewed. Evidence suggests that humoral immune system can recognize this protein and produce antibodies against it. By detecting antibodies in infected people, investigators found that F protein might have a role in HCV infection causing chronic cirrhosis and HCC as higher prevalence was found in patients with mentioned complications. The increment of CD4+, CD25+, and FoxP3+ T cells, along with CD8+ T cells with low expression of granzyme B, also leads to weaker responses of the immune system which helps the infection to become chronic. Moreover, it contributes to the survival of the virus in the body through affecting the production of interferon. F protein also might play roles in the disease development, resulting in HCC. The existence of F protein affects cellular pathways through upregulating p53, c-myc, cyclin D1, and phosphorylating Rb. This review will summarize these effects on immune system and related mechanisms in cellular pathways.

The Role of Prefoldin and Its Subunits in Tumors and Their Application Prospects in Nanomedicine

Prefoldin (PFDN) is a hexameric chaperone complex that is widely found in eukaryotes and archaea and consists of six different subunits (PFDN1-6). Its main function is to transfer actin and tubulin monomers to the eukaryotic cell cytoplasmic chaperone protein (c-CPN) specific binding during the assembly of the cytoskeleton, to stabilize the newly synthesized peptides so that they can be folded correctly. The current study found that each subunit of PFDN has different functions, which are closely related to the occurrence, development and prognosis of tumors. However, the best characteristics of each subunit have not been fully affirmed. The connection between research and tumors can change the understanding of PFDN and further extend its potential prognostic role and structural function to cancer research and clinical practice. This article mainly reviews the role of canonical PFDN and its subunits in tumors and other diseases, and discusses the potential prospects of the unique structure and function of PFDN in nanomedicine.

Genotypic Regulation of Type I Interferon Induction Pathways by Frameshift (F) Proteins of Hepatitis C Virus

Hepatitis C virus (HCV) has evolved mechanisms to evade innate immunity that are leading to chronic infections. The immunological function of the HCV frameshift (F) protein, which is a frameshift product of core coding sequences, has not been well characterized. The HCV F protein is produced during natural HCV infections and is found most commonly in genotype 1 HCV. In this study, we investigated whether the F protein plays a role in type I interferon (IFN) induction pathways. We engineered F expression constructs from core coding sequences of 4 genotypes (1a, 2a, 3a, and 4a) of HCV as well as the sequences which would only be able to produce core proteins. The peptide lengths and amino acids sequences of F proteins are highly variable. We hypothesized that F proteins from different genotypes might control the type I IFN production and response differently. We found that both IFN-beta (IFN-β) promoter activities are significantly higher in genotype 1a F protein (F1a)-expressing cells. Conversely, the IFN-β promoter activities are lower in genotype 2a F (F2a) protein-expressing cells. We also used real-time PCR to confirm IFN-β mRNA expression levels. By generating chimera F proteins, we discovered that the effects of F proteins were determined by the amino acid sequence 40 to 57 of genotype 1a. The regulation of type I IFN induction pathway is related but not limited to the activity of F1a to interact with proteasome subunits and to disturb the proteasome activity. Further molecular mechanisms of how F proteins from different genotypes of HCV control these pathways differently remain to be investigated.IMPORTANCE Although naturally present in HCV infection patient serum, the virological or immunological functions of the HCV F protein, which is a frameshift product of core coding sequences, remain unclear. Here, we report the effects of the HCV F protein between genotypes and discuss a potential explanation for the differential responses to type I IFN-based therapy among patients infected with different genotypes of HCV. Our study provides one step forward to understanding the host response during HCV infection and new insights for the prediction of the outcome of IFN-based therapy in HCV patients.

Chaperone client proteins evolve slower than non-client proteins

Chaperones are important molecular machinery that assists proteins to attain their native three-dimensional structure crucial for function. Earlier studies using experimental evolution showed that chaperones impose a relaxation of sequence constraints on their "client" proteins, which may lead to the fixation of slightly deleterious mutations on the latter. However, we hypothesized that such a phenomenon might be harmful to the organism in a natural physiological condition. In this study, we investigated the evolutionary rates of chaperone client and non-client proteins in five model organisms from both prokaryotic and eukaryotic lineages. Our study reveals a slower evolutionary rate of chaperone client proteins in all five organisms. Additionally, the slower folding rate and lower aggregation propensity of chaperone client proteins reveal that the chaperone may play an essential role in rescuing the slightly disadvantageous effects due to random mutations and subsequent protein misfolding. However, the fixation of such mutations is less likely to be selected in the natural population.

Proteostasis in Viral Infection: Unfolding the Complex Virus-Chaperone Interplay

Viruses are obligate intracellular parasites that rely on their hosts for protein synthesis, genome replication, and viral particle production. As such, they have evolved mechanisms to divert host resources, including molecular chaperones, facilitate folding and assembly of viral proteins, stabilize complex structures under constant mutational pressure, and modulate signaling pathways to dampen antiviral responses and prevent premature host death. Biogenesis of viral proteins often presents unique challenges to the proteostasis network, as it requires the rapid and orchestrated production of high levels of a limited number of multifunctional, multidomain, and aggregation-prone proteins. To overcome such challenges, viruses interact with the folding machinery not only as clients but also as regulators of chaperone expression, function, and subcellular localization. In this review, we summarize the main types of interactions between viral proteins and chaperones during infection, examine evolutionary aspects of this relationship, and discuss the potential of using chaperone inhibitors as broad-spectrum antivirals.

Identification of Secreted Proteins Involved in Nonspecific dsRNA-Mediated Lutzomyia longipalpis LL5 Cell Antiviral Response

Hematophagous insects transmit infectious diseases. Sand flies are vectors of leishmaniasis, but can also transmit viruses. We have been studying immune responses of Lutzomyia longipalpis, the main vector of visceral leishmaniasis in the Americas. We identified a non-specific antiviral response in L. longipalpis LL5 embryonic cells when treated with non-specific double-stranded RNAs (dsRNAs). This response is reminiscent of interferon response in mammals. We are investigating putative effectors for this antiviral response. Secreted molecules have been implicated in immune responses, including interferon-related responses. We conducted a mass spectrometry analysis of conditioned medium from LL5 cells 24 and 48 h after dsRNA or mock treatment. We identified 304 proteins. At 24 h, 19 proteins had an abundance equal or greater than 2-fold change, while the levels of 17 proteins were reduced when compared to control cells. At the 48 h time point, these numbers were 33 and 71, respectively. The two most abundant secreted peptides at 24 h in the dsRNA-transfected group were phospholipid scramblase, an interferon-inducible protein that mediates antiviral activity, and forskolin-binding protein (FKBP), a member of the immunophilin family, which mediates the effect of immunosuppressive drugs. The transcription profile of most candidates did not follow the pattern of secreted protein abundance.

Hepatitis C Virus Frameshift/Alternate Reading Frame Protein Suppresses Interferon Responses Mediated by Pattern Recognition Receptor Retinoic-Acid-Inducible Gene-I

Hepatitis C virus (HCV) actively evades host interferon (IFN) responses but the mechanisms of how it does so are not completely understood. In this study, we present evidence for an HCV factor that contributes to the suppression of retinoic-acid-inducible gene-I (RIG-I)-mediated IFN induction. Expression of frameshift/alternate reading frame protein (F/ARFP) from HCV -2/+1 frame in Huh7 hepatoma cells suppressed type I IFN responses stimulated by HCV RNA pathogen-associated molecular pattern (PAMP) and poly(IC). The suppression occurred independently of other HCV factors; and activation of interferon stimulated genes, TNFα, IFN-λ1, and IFN-λ2/3 was likewise suppressed by HCV F/ARFP. Point mutations in the full-length HCV sequence (JFH1 genotype 2a strain) were made to introduce premature termination codons in the -2/+1 reading frame coding for F/ARFP while preserving the original reading frame, which enhanced IFNα and IFNβ induction by HCV. The potentiation of IFN response by the F/ARFP mutations was diminished in Huh7.5 cells, which already have a defective RIG-I, and by decreasing RIG-I expression in Huh7 cells. Furthermore, adding F/ARFP back via trans-complementation suppressed IFN induction in the F/ARFP mutant. The F/ARFP mutants, on the other hand, were not resistant to exogenous IFNα. Finally, HCV-infected human liver samples showed significant F/ARFP antibody reactivity, compared to HCV-uninfected control livers. Therefore, HCV F/ARFP likely cooperates with other viral factors to suppress type I and III IFN induction occurring through the RIG-I signaling pathway. This study identifies a novel mechanism of pattern recognition receptor modulation by HCV and suggests a biological function of the HCV alternate reading frame in the modulation of host innate immunity.

Chaperones in hepatitis C virus infection

The hepatitis C virus (HCV) infects approximately 3% of the world population or more than 185 million people worldwide. Each year, an estimated 350000-500000 deaths occur worldwide due to HCV-associated diseases including cirrhosis and hepatocellular carcinoma. HCV is the most common indication for liver transplantation in patients with cirrhosis worldwide. HCV is an enveloped RNA virus classified in the genus Hepacivirus in the Flaviviridae family. The HCV viral life cycle in a cell can be divided into six phases: (1) binding and internalization; (2) cytoplasmic release and uncoating; (3) viral polyprotein translation and processing; (4) RNA genome replication; (5) encapsidation (packaging) and assembly; and (6) virus morphogenesis (maturation) and secretion. Many host factors are involved in the HCV life cycle. Chaperones are an important group of host cytoprotective molecules that coordinate numerous cellular processes including protein folding, multimeric protein assembly, protein trafficking, and protein degradation. All phases of the viral life cycle require chaperone activity and the interaction of viral proteins with chaperones. This review will present our current knowledge and understanding of the role of chaperones in the HCV life cycle. Analysis of chaperones in HCV infection will provide further insights into viral/host interactions and potential therapeutic targets for both HCV and other viruses.

Analysis of Subcellular Prefoldin 1 Redistribution During Rabies Virus Infection

Background:

Rabies virus (RABV) is one of the old deadly zoonotic viruses. It attacks the central nervous system and causes acute encephalitis in humans and animals. Host factors are known to be essential for virus infection and replication in cells. The identification of the key host factors required for RABV infection may provide important information on RABV replication and may provide new potential targets for RABV drug discovery.

Objectives:

This study aimed to investigate the change in the subcellular distribution and expression of the host protein Prefoldin subunit 1 (PFDN1) in RABV-infected cells and the viral expression of plasmids in the transfected cells.

Materials and Methods:

Mouse Neuro-2a (N2a) cells were infected by RABV or transfected with the plasmids of the nucleoprotein (N) and/or phosphoprotein (P) gene of RABV. The subcellular distribution of PFDN1 was analyzed by confocal microscopy, and the transcription levels of PFDN1 in the N and/or P gene of the RABV-transfected or RABV-infected N2a cells were assessed via real-time quantitative polymerase chain reaction.

Results:

Confocal microscopy showed that PFDN1 was colocalized with the N protein of RABV in the infected N2a cells and was mainly recruited to the characteristic Negri-Body-Like (NBL) structures in the cytoplasm, as well as the cotransfection of the N and P genes of RABV. The transcription of PFDN1 in the RABV-infected N2a cells was upregulated, whereas the transfection of the N and/or P genes did not result in the upregulation of PFDN1.

Conclusions:

The results of this work demonstrated that the subcellular distribution of PFDN1 was altered in the RABV-infected N2a cells and colocalized with the N protein of RABV in the NBL structures.

Production and pathogenicity of hepatitis C virus core gene products

Hepatitis C virus (HCV) is a major cause of chronic liver diseases, including steatosis, cirrhosis and hepatocellular carcinoma, and its infection is also associated with insulin resistance and type 2 diabetes mellitus. HCV, belonging to the Flaviviridae family, is a small enveloped virus whose positive-stranded RNA genome encoding a polyprotein. The HCV core protein is cleaved first at residue 191 by the host signal peptidase and further cleaved by the host signal peptide peptidase at about residue 177 to generate the mature core protein (a.a. 1-177) and the cleaved peptide (a.a. 178-191). Core protein could induce insulin resistance, steatosis and even hepatocellular carcinoma through various mechanisms. The peptide (a.a. 178-191) may play a role in the immune response. The polymorphism of this peptide is associated with the cellular lipid drop accumulation, contributing to steatosis development. In addition to the conventional open reading frame (ORF), in the +1 frame, an ORF overlaps with the core protein-coding sequence and encodes the alternative reading frame proteins (ARFP or core+1). ARFP/core+1/F protein could enhance hepatocyte growth and may regulate iron metabolism. In this review, we briefly summarized the current knowledge regarding the production of different core gene products and their roles in viral pathogenesis.

Th1 and Th2 cytokine profiles induced by hepatitis C virus F protein in peripheral blood mononuclear cells from chronic hepatitis C patients

Th1 and Th2 cytokine response has been confirmed to be correlated with the pathogenesis of HCV infection. The aim of the study is to investigate the Th1 and Th2 cytokine profiles induced by HCV alternate reading frame protein (F protein) in chronic hepatitis C patients. We assessed the immune responses specific to HCV F protein in 55 chronic HCV patients. IFN-γ, IL-2, IL-4 and IL-5 secretion by peripheral blood mononuclear cells (PBMC) post F protein stimulation were compared among HCV patients and healthy donors. Finally, the associations between HCV F protein and HLA class II alleles were explored. We found that the seroprevalence of anti-F antibodies in HCV-related hepatocellular carcinoma (HCC) patients was significantly higher than that of patients without HCC, but such a significant difference in humoral immune responses to F protein was not observed in HCV 1b-infected- and non-HCV 1b-infected-patients. Additionally, the PBMC proliferation of HCC patients was significantly lower than that of patients without HCC. Furthermore, F protein stimulation of PBMCs from F-seropositive patients resulted in Th2 biased cytokine responses (significantly decreased IFN-γ and/or IL-2 and significantly increased IL-4 and/or IL-5 levels) that reportedly may contribute to HCC progression and pathogenesis. However, no significant difference in the association between HCV F protein and HLA-DRB1*0201, 0301, 0405, 1001 and HLA-DQB1*0201, 0401, 0502, 0602 was observed in this study. These findings suggest that F protein may contribute to the HCV-associated bias in Th1/Th2 responses of chronic hepatitis C patients including the progress of HCC pathogenesis.

Dynamic regulation of cortical microtubule organization through prefoldin-DELLA interaction

Plant morphogenesis relies on specific patterns of cell division and expansion. It is well established that cortical microtubules influence the direction of cell expansion, but less is known about the molecular mechanisms that regulate microtubule arrangement. Here we show that the phytohormones gibberellins (GAs) regulate microtubule orientation through physical interaction between the nuclear-localized DELLA proteins and the prefoldin complex, a cochaperone required for tubulin folding. In the presence of GA, DELLA proteins are degraded, and the prefoldin complex stays in the cytoplasm and is functional. In the absence of GA, the prefoldin complex is localized to the nucleus, which severely compromises α/β-tubulin heterodimer availability, affecting microtubule organization. The physiological relevance of this molecular mechanism was confirmed by the observation that the daily rhythm of plant growth was accompanied by coordinated oscillation of DELLA accumulation, prefoldin subcellular localization, and cortical microtubule reorientation.

Both core and F proteins of hepatitis C virus could enhance cell proliferation in transgenic mice

The role of the protein encoded by the alternative open reading frame (ARF/F/core+1) of the Hepatitis C virus (HCV) genome in viral pathogenesis remains unknown. The different forms of ARF/F/core+1 protein were labile in cultured cells, a myc-tag fused at the N-terminus of the F protein made it more stable. To determine the role of core and F proteins in HCV pathogenesis, transgenic mice with either protein expression under the control of Albumin promoter were generated. Expression of core protein and F protein with myc tag (myc-F) could be detected by Western blotting analysis in the livers of these mice. The ratio of liver to body weight is increased for both core and myc-F transgenic mice compared to that of wild type mice. Indeed, the proliferating cell nuclear antigen protein, a proliferation marker, was up-regulated in the transgenic mice with core or myc-F protein. Further analyses by microarray and Western blotting suggested that β-catenin signaling pathway was activated by either core or myc-F protein in the transgenic mice. These transgenic mice were further treated with either Diethynitrosamine (a tumor initiator) or Phenobarbital (a tumor promoter). Phenobarbital but not Diethynitrosamine treatment could increase the liver/body weight ratio of these mice. However, no tumor formation was observed in these mice. In conclusion, HCV core and myc-F proteins could induce hepatocyte proliferation in the transgenic mice possibly through β-catenin signaling pathway.

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.

High levels of HCV core+1 antibodies in HCV patients with hepatocellular carcinoma

The core region of the hepatitis C virus (HCV) genome possesses an overlapping ORF that has been shown to encode a protein, known as the alternate reading frame protein (ARFP), F or core+1. The biological role of this protein remains elusive, as it appears to be non-essential for virus replication. However, a number of independent studies have shown that the ARFP/F/core+1 protein elicits humoral and cellular immune responses in HCV-infected individuals and interacts with important cellular proteins. To assess the significance of the core+1 humoral response in HCV-infected patients, we examined the prevalence of anti-core+1 antibodies in sera from patients with hepatocellular carcinoma (HCC) in comparison with chronically HCV-infected individuals without HCC. We produced two HCV core+1 histidine-tagged recombinant proteins for genotypes 1a (aa 11–160) and 1b (aa 11–144), as well as a non-tagged highly purified recombinant core+1/S protein (aa 85–144) of HCV-1b. Using an in-house ELISA, we tested the prevalence of core+1 antibodies in 45 patients with HCC in comparison with 47 chronically HCV-infected patients without HCC and 77 negative-control sera. More than 50 % of the serum samples from HCC patients reacted with all core+1 antigens, whereas <26 % of the sera from the non-HCC HCV-infected individuals tested positive. No core+1-specific reactivity was detected in any of the control samples. In conclusion, the high occurrence of anti-core+1 antibodies in the serum of HCC patients suggests a role for the ARFP/F/core+1 protein in the pathogenesis of HCC.

Synonymous mutations in the core gene are linked to unusual serological profile in hepatitis C virus infection

The biological role of the protein encoded by the alternative open reading frame (core+1/ARF) of the Hepatitis C virus (HCV) genome remains elusive, as does the significance of the production of corresponding antibodies in HCV infection. We investigated the prevalence of anti-core and anti-core+1/ARFP antibodies in HCV-positive blood donors from Cambodia, using peptide and recombinant protein-based ELISAs. We detected unusual serological profiles in 3 out of 58 HCV positive plasma of genotype 1a. These patients were negative for anti-core antibodies by commercial and peptide-based assays using C-terminal fragments of core but reacted by Western Blot with full-length core protein. All three patients had high levels of anti-core+1/ARFP antibodies. Cloning of the cDNA that corresponds to the core-coding region from these sera resulted in the expression of both core and core+1/ARFP in mammalian cells. The core protein exhibited high amino-acid homology with a consensus HCV1a sequence. However, 10 identical synonymous mutations were found, and 7 were located in the aa(99–124) region of core. All mutations concerned the third base of a codon, and 5/10 represented a T>C mutation. Prediction analyses of the RNA secondary structure revealed conformational changes within the stem-loop region that contains the core+1/ARFP internal AUG initiator at position 85/87. Using the luciferase tagging approach, we showed that core+1/ARFP expression is more efficient from such a sequence than from the prototype HCV1a RNA. We provide additional evidence of the existence of core+1/ARFP in vivo and new data concerning expression of HCV core protein. We show that HCV patients who do not produce normal anti-core antibodies have unusually high levels of antit-core+1/ARFP and harbour several identical synonymous mutations in the core and core+1/ARFP coding region that result in major changes in predicted RNA structure. Such HCV variants may favour core+1/ARFP production during HCV infection.

Internal translation initiation stimulates expression of the ARF/core+1 open reading frame of HCV genotype 1b

The hepatitis C virus possesses an alternative open reading frame overlapping the Core gene, whose products are referred to as Core+1 or alternative reading frame (ARF) or F protein(s). Extensive studies on genotype HCV-1a demonstrated that ribosomal frameshifting supports the synthesis of core+1 protein, when ten consecutive As are present within core codons 9-11 whereas, in the absence of this motif, expression of the core+1 ORF is mediated mainly by internal translation initiation. However, in HCV-1b, no Core+1 isoforms produced by internal translation initiation have been described. Using constructs which contain the Core/Core+1(342-770) region from previously described HCV-1b clinical isolates from liver biopsies, we provide evidence for the synthesis of Core+1 proteins by internal translation initiation in transiently transfected mammalian cells using nuclear or cytoplasmic expression systems. Site directed mutagenesis analyses revealed that (a) the synthesis of Core+1 proteins is independent from the polyprotein expression, as we observed an increase of Core+1 protein expression from constructs lacking the polyprotein translation initiator, (b) the main Core+1 product is expressed from AUG(85), similarly to the Core+1/S protein of HCV-1a, (c) synthesis of Core+1 isoforms is also mediated from GUG(58) or under certain conditions GUG(26) internal codons, albeit at lower efficiency. Finally, comparable to HCV-1a Core+1 proteins, the HCV-1b Core+1 products are negatively regulated by core expression and the proteaosomal pathway. The expression of Core+1 ORF from HCV-1b clinical isolates and the preservation of translation initiation mechanism that stimulates its expression encourage investigating the role of these proteins in HCV pathogenesis.

The HCV ARFP/F/core+1 protein: production and functional analysis of an unconventional viral product

Hepatitis C virus (HCV) is an enveloped positive-strand RNA virus of the Flaviviridae family. It has a genome of about 9,600 nucleotides encoding a large polyprotein (about 3,000 amino acids) that is processed by cellular and viral proteases into at least 10 structural and nonstructural viral proteins. A novel HCV protein has also been identified by our laboratory and others. This protein--known as ARFP (alternative reading frame protein), F (for frameshift) or core+1 (to indicate the position) protein--is synthesized by an open reading frame overlapping the core gene at nucleotide +1 (core+1 ORF). However, almost 10 years after its discovery, we still know little of the biological role of the ARFP/F/core+1 protein. Abolishing core+1 protein production has no affect on HCV replication in cell culture or uPA-SCID mice, suggesting that core+1 protein is probably not important for the HCV reproductive cycle. However, the detection of specific anti-core+1 antibodies and T-cell responses in HCV-infected patients, as reported by many independent laboratories, provides strong evidence that this protein is produced in vivo. Furthermore, analyses of the HCV sequences isolated from patients with hepatocellular carcinoma and in vitro studies have provided strong preliminary evidence to suggest that core+1 protein plays a role in advanced liver disease and liver cancer. The available in vitro data also suggest that certain core function proteins may depend on production of the core+1 protein. We describe here the discovery of the various forms of the core+1 protein and what is currently known about the mechanisms of their production and their biochemical and functional properties. We also provide a detailed summary of the results of patient-based research.

Internal initiation stimulates production of p8 minicore, a member of a newly discovered family of hepatitis C virus core protein isoforms

The hepatitis C virus (HCV) core gene is more conserved at the nucleic acid level than is necessary to preserve the sequence of the core protein, suggesting that it contains information for additional functions. We used a battery of anticore antibodies to test the hypothesis that the core gene directs the synthesis of core protein isoforms. Infectious viruses, replicons, and RNA transcripts expressed a p8 minicore containing the C-terminal portion of the p21 core protein and lacking the N-terminal portion. An interferon resistance mutation, U271A, which creates an AUG at codon 91, upregulated p8 expression in Con1 replicons, suggesting that p8 is produced by an internal initiation event and that 91-AUG is the preferred, but not the required, initiation codon. Synthesis of p8 was independent of p21, as shown by the abundant production of p8 from transcripts containing an UAG stop codon that blocked p21 production. Three infectious viruses, JFH-1 (2a core), J6/JFH (2a core), and H77/JFH (1a core), and a bicistronic construct, Bi-H77/JFH, all expressed both p8 and larger isoforms. The family of minicores ranges in size from 8 to 14 kDa. All lack the N-terminal portion of the p21 core. In conclusion, the core gene contains an internal signal that stimulates the initiation of protein synthesis at or near codon 91, leading to the production of p8. Infectious viruses of both genotype 1 and 2 HCV express a family of larger isoforms, in addition to p8. Minicores lack significant portions of the RNA binding domain of p21 core. Studies are under way to determine their functions.

Differential reactivity of putative genotype 2 hepatitis C virus F protein between chronic and recovered infections

To date, all studies regarding hepatitis C virus (HCV) F protein have been based on expression in vitro/in vivo of recombinant protein or monoclonal antibodies derived from genotype 1a or 1b sequences, but not from other genotypes. The objective of this study was to prepare a putative genotype 2 recombinant F protein and evaluate its reactivity in plasma from individuals with chronic HCV infection or who had recovered from infection. One genotype 2 strain was selected for F protein (F-2) and core expression in bacterial culture. An ELISA was developed and applied to samples from patients with chronic infection or recovered infection of various genotypes. The anti-F-2 response in 117 samples showed a significantly higher reactivity in chronic than in recovered HCV-infected blood donors (P<0.001), but no difference was found among genotypes. However, the correlation between anti-F and anti-core was more significant in genotypes 1 and 2 than in genotype 3. Anti-F-2 titres were also significantly higher in chronic than in recovered individuals (P<0.0001). Antibody titres to recombinant genotype 2 core protein or to genotype 1 multiple proteins used in commercial anti-HCV assays paralleled the anti-F-2 end-point antibody titre. This study thus demonstrated the antigenicity of genotype 2 HCV F protein, although the exact location of the natural frameshift position remains unknown. The difference in anti-F-2 response between chronic and recovered infection, the cross-reactivity irrespective of genotype and the correlation of antibody response with structural and non-structural antigens suggest that the immune response to F protein is an integral part of the natural HCV infection.

Distinct hepatitis C virus core and F protein quasispecies in tumoral and nontumoral hepatocytes isolated via microdissection

Hepatitis C virus (HCV) genetic variability may be involved in liver carcinogenesis. We investigated HCV core and corresponding putative F protein genetic variability in hepatocellular carcinoma (HCC) and cirrhotic nodules. Hepatocyte clusters from 7 patients with HCC and HCV1b-related cirrhosis were isolated via microdissection of HCC tissues and 2 nontumoral cirrhotic nodules. The HCV core complementary DNA was cloned and sequenced from each liver compartment and from the serum of 2 patients. Nucleotide diversity and synonymous and nonsynonymous substitutions were analyzed within and between compartments via phylogenetic analysis and Mantel's test. Liver HCV RNA accumulation was lower in HCC. Increased quasispecies diversity and complexity was observed with HCC in 6 of 7 patients. Mantel's test demonstrated marked compartmentalization of quasispecies between HCC and cirrhotic nodules in all 7 patients and also between the 2 nontumoral nodules in 5 of them. Synonymous-nonsynonymous substitution analysis indicated low selection against tumoral core quasispecies in all patients and a more selective pressure against F protein quasispecies in all compartments. In the 2 subjects analyzed, HCC and nontumoral hepatocyte quasispecies were only minor or undetected in serum.

CONCLUSION

In tumoral hepatocytes, low-replicating hepatitis C quasispecies are compartmentalized and more diversified and are subjected to low selective pressure. Our study supports the importance of core genetic variability in hepatocellular carcinogenesis.