Hepatitis C virus and its protein NS4B activate the cancer-related STAT3 pathway via the endoplasmic reticulum overload response

Immunity of two novel hepatitis C virus polyepitope vaccines

Hepatitis C virus (HCV) infection remains a serious public health burden around the world. So far there is no effective vaccine against this virus. Neutralizing antibody (NAb) responses to the epitopes within HCV E1 and E2 proteins are related to the resolution of hepatitis C infection. E. coli heat-labile enterotoxin B subunit (LTB) has been described as potent immunity adjuvants. In this study, we constructed recombinant pET vectors: pET-R9-Bp (B cell polyepitopes) expressing 7 epitopes from HCV E1 and E2 proteins including R9 (E2_384-411aa)-Bp (E1_313-327aa-E2_396-424aa-E2_436-447aa-E2_523-540aa-E2_610-627aa-E2_631-648aa) and pET-LTB-R9-Bp expressing LTB adjuvant in combination with R9-Bp. Recombinant proteins R9-Bp and LTB-R9-Bp were expressed successfully in E. coli and purified by the Ni-NTA column. Both R9-Bp and LTB-R9-Bp in BALB/c mice induced robust humoral immune response in the context of intraperitoneal or intramuscular immunization but not oral immunization. Intraperitoneal administration of LTB-R9-Bp induced a higher antibody titer (peak titer: 1:341000) than that of R9-Bp (peak titer: 1:85000) after the second boost (P = 0.0036 or 0.0002). However, comparable antibody peak titers were elicited for both R9-Bp and LTB-R9-Bp in intramuscular immunization albeit with significant difference (P = 0.0032) a week after the second boost. In addition, both R9-Bp and LTB-R9-Bp induced the secretion of cytokines including IFN-γ and IL-4 at similar levels. anti-sera induced by both R9-Bp and LTB-R9-Bp recognized native HCV E1 and E2 proteins. Moreover, these HCV-specific antisera inhibited significantly the entry of HCV (P < 0.0001). Taken together, these findings showed that E. coli-based both R9-Bp and LTB-R9-Bp could become promising HCV vaccines.

Cellular OCIAD2 protein is a proviral factor for hepatitis C virus replication

Hepatitis C virus (HCV) nonstructural protein NS4B is necessary for HCV replication. Our previous research found that NS4B-associated cellular proteins PREB and Surfeit 4 are involved in HCV replication. However, the molecular mechanism of HCV replication is not fully understood. Here we identified cellular ovarian cancer immunoreactive antigen domain containing 2 (OCIAD2) protein as a novel NS4B-associated HCV host cofactor by screening with small interfering RNA. Knockdown of OCIAD2 reduced significantly the HCV replication in a dose-dependent and genotype-independent manner. Further research showed that OCIAD2 was recruited into the HCV RNA replication complex by the interaction with NS4B. Interestingly, HCV replication induced OCIAD2 expression. In turn, overexpression of wild OCIAD2 also promoted virus replication whereas that of OCIAD2 mutant lacking the ability to bind NS4B exerted no effect on HCV replication. We also examined whether OCIAD2 interacted with other proteins participating in the HCV RNA replication complex including viral proteins NS5A, NS5B, and cellular proteins PREB, Surfeit 4. The results showed that OCIAD2 interacted with PREB and NS5A, but not NS5B or Surfeit 4. Our findings provide new insights into the function of OCIAD2 and HCV replication mechanism.

Activation of the STAT3 Signaling Pathway by the RNA-Dependent RNA Polymerase Protein of Arenavirus

Arenaviruses cause chronic and asymptomatic infections in their natural host, rodents, and several arenaviruses cause severe hemorrhagic fever that has a high mortality in infected humans, seriously threatening public health. There are currently no FDA-licensed drugs available against arenaviruses; therefore, it is important to develop novel antiviral strategies to combat them, which would be facilitated by a detailed understanding of the interactions between the viruses and their hosts. To this end, we performed a transcriptomic analysis on cells infected with arenavirus lymphocytic choriomeningitis virus (LCMV), a neglected human pathogen with clinical significance, and found that the signal transducer and activator of transcription 3 (STAT3) signaling pathway was activated. A further investigation indicated that STAT3 could be activated by the RNA-dependent RNA polymerase L protein (Lp) of LCMV. Our functional analysis found that STAT3 cannot affect LCMV multiplication in A549 cells. We also found that STAT3 was activated by the Lp of Mopeia virus and Junin virus, suggesting that this activation may be conserved across certain arenaviruses. Our study explored the interactions between arenaviruses and STAT3, which may help us to better understand the molecular and cell biology of arenaviruses.

Cortactin Interacts with Hepatitis C Virus Core and NS5A Proteins: Implications for Virion Assembly

Hepatitis C virus (HCV) exploits cellular proteins to facilitate viral propagation. To identify the cellular factors involved in the HCV life cycle, we previously performed protein microarray assays using either HCV nonstructural 5A (NS5A) protein or core protein as a probe. Interestingly, cellular cortactin strongly interacted with both NS5A and core. Cortactin is an actin-binding protein critically involved in tumor progression by regulating the migration and invasion of cancerous cells. Protein interaction between cortactin and NS5A or core was confirmed by coimmunoprecipitation and immunofluorescence assays. We showed that cortactin interacted with NS5A and core via the N-terminal acidic domain of cortactin. Cortactin expression levels were not altered by HCV infection. Small interfering RNA (siRNA)-mediated knockdown of cortactin dramatically decreased HCV protein expression and infectivity levels, whereas overexpression of cortactin increased viral propagation. Ectopic expression of the siRNA-resistant cortactin recovered the viral infectivity, suggesting that cortactin was specifically required for HCV propagation. We further showed that cortactin was involved in the assembly step without affecting viral entry, HCV internal ribosome entry site (IRES)-mediated translation, and the replication steps of the HCV life cycle. Of note, silencing of cortactin markedly reduced both NS5A and core protein levels on the lipid droplets (LDs), and this effect was reversed by the overexpression of cortactin. Importantly, NS5A and core promoted cell migration by activating the phosphorylation of cortactin at tyrosine residues 421 and 466. Taken together, these data suggest that cortactin is not only involved in HCV assembly but also plays an important role in the cell migration.IMPORTANCE Cortactin is a cytoskeletal protein that regulates cell migration in response to a number of extracellular stimuli. The functional involvement of cortactin in the virus life cycle is not yet fully understood. The most significant finding is that cortactin strongly interacted with both hepatitis C virus (HCV) core and NS5A. Cortactin is involved in HCV assembly by tethering core and NS5A on the lipid droplets (LDs) with no effect on LD biogenesis. It was noteworthy that HCV NS5A and core activated cortactin by phosphorylation at tyrosines 421 and 466 to regulate cell migration. Collectively, our study shows that cortactin is a novel host factor involved in viral production and HCV-associated pathogenesis.

The bZIP Proteins of Oncogenic Viruses

Basic leucine zipper (bZIP) transcription factors (TFs) govern diverse cellular processes and cell fate decisions. The hallmark of the leucine zipper domain is the heptad repeat, with leucine residues at every seventh position in the domain. These leucine residues enable homo- and heterodimerization between ZIP domain α-helices, generating coiled-coil structures that stabilize interactions between adjacent DNA-binding domains and target DNA substrates. Several cancer-causing viruses encode viral bZIP TFs, including human T-cell leukemia virus (HTLV), hepatitis C virus (HCV) and the herpesviruses Marek’s disease virus (MDV), Epstein–Barr virus (EBV) and Kaposi’s sarcoma-associated herpesvirus (KSHV). Here, we provide a comprehensive review of these viral bZIP TFs and their impact on viral replication, host cell responses and cell fate.

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

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

MicroRNA-let-7c suppresses hepatitis C virus replication by targeting Bach1 for induction of haem oxygenase-1 expression

MicroRNAs are small noncoding RNAs that are central factors between hepatitis C virus (HCV) and host cellular factors for viral replication and liver disease progression, including liver fibrosis, cirrhosis and hepatocellular carcinoma. In the present study, we found that overexpressing miR-let-7c markedly reduced HCV replication because it induced haem oxygenase-1 (HO-1) expression by targeting HO-1 transcriptional repressor Bach1, ultimately leading to stimulating an antiviral interferon response and blockade of HCV viral protease activity. In contrast, the antiviral actions of miR-let-7c were attenuated by miR-let-7c inhibitor treatment, exogenously expressing Bach1 or suppressing HO-1 activity and expression. A proposed model indicates a key role for miR-let-7c targeting Bach1 to transactivate HO-1-mediated antiviral actions against HCV. miR-let-7c may serve as an attractive target for antiviral development.

STAT3 roles in viral infection: antiviral or proviral?

Signal transducer and activator of transcription 3 (STAT3) is a transcription factor which can be activated by cytokines, growth factor receptors, and nonreceptor-like tyrosine kinase. An activated STAT3 translocates into the nucleus and combines with DNA to regulate the expression of target genes involved in cell proliferation, differentiation, apoptosis and metastasis. Recent studies have shown that STAT3 plays important roles in viral infection and pathogenesis. STAT3 exhibits a proviral function in several viral infections, including those of HBV, HCV, HSV-1, varicella zoster virus, human CMV and measles virus. However, in some circumstances, STAT3 has an antiviral function in other viral infections, such as enterovirus 71, severe acute respiratory syndrome coronavirus and human metapneumovirus. This review summarizes the roles of STAT3 in viral infection and pathogenesis, and briefly discusses the molecular mechanisms involved in these processes.

Japanese encephalitis virus induces apoptosis by inhibiting Foxo signaling pathway

Japanese encephalitis virus (JEV) infection induces brain tissue disease characterized by neuron death. however, little is known about the underlying mechanism. Using RNA sequencing, we profiled global mRNA expression changes in response to in vitro and in vivo JEV infection. Integration analysis of in vitro and in vivo mRNA transcriptome revealed that JEV infection regulated apoptosis-related Foxo signaling pathway. Foxo expression was reduced by JEV infection in vitro and in vivo. Knockdown of Foxo promoted apoptosis, while its overexpression reduced apoptosis in JEV-infected Neuro-2a cells. JEV infection in Neuro-2a cells decreased the expression of Foxo downstream genes including pro-apoptotic protein Bim, anti-apoptotic protein Bcl-6 and p21. Overexpression of anti-apoptotic proteins Bcl-6 and p21 repressed JEV-induced apoptosis. These findings suggest that Foxo primarily exerts an anti-apoptotic function via Bcl-6 and p21 in JEV-infected Neuro-2a cells. A STAT3 binding site was identified in the promoter region of Foxo by TFBIND software and confirmed by ChIP and reporter assays. JEV infection reduced STAT3 expression as well as its binding at the Foxo promoter compared to mock infection in Neuro-2a cells. Moreover, STAT3 knockdown reduced Foxo promoter activity and Foxo expression. Therefore, JEV reduced Foxo expression, at least in part, by downregulating STAT3. Taken together, we found that JEV induced cell apoptosis by inhibiting STAT3-Foxo-Bcl-6/p21 pathway, which provides a novel insight into JEV-caused encephalitis.

ER homeostasis and autophagy

The endoplasmic reticulum (ER) is a key site for lipid biosynthesis and folding of nascent transmembrane and secretory proteins. These processes are maintained by careful homeostatic control of the environment within the ER lumen. Signalling sensors within the ER detect perturbations within the lumen (ER stress) and employ downstream signalling cascades that engage effector mechanisms to restore homeostasis. The most studied signalling mechanism that the ER employs is the unfolded protein response (UPR), which is known to increase a number of effector mechanisms, including autophagy. In this chapter, we will discuss the emerging role of autophagy as a UPR effector pathway. We will focus on the recently discovered selective autophagy pathway for ER, ER-phagy, with particular emphasis on the structure and function of known mammalian ER-phagy receptors, namely FAM134B, SEC62, RTN3 and CCPG1. Finally, we conclude with our view of where the future of this field can lead our understanding of the involvement of ER-phagy in ER homeostasis.

Hepatitis C virus NS4B protein induces epithelial-mesenchymal transition by upregulation of Snail

Background

Chronic hepatitis C virus (HCV) infection is an important cause of hepatocellular carcinoma (HCC). Epithelial to mesenchymal transition (EMT) is a key process associated with tumor metastasis and poor prognosis. HCV infection, HCV core and NS5A protein could induce EMT process, but the role of NS4B on EMT remains poorly understood.

Methods

We overexpressed HCV NS4B protein in HepG2 cells or Huh7.5.1 cells infected by HCVcc, the E-cadherin expression, N-cadherin expression and the EMT-associated transcriptional factor Snail were determined. The migration and invasion capabilities of the transfected cells were evaluated using wound-healing assay. Additionally, we used Snail siRNA interference to confirm the relation of HCV NS4B and Snail on EMT promotion.

Results

HCV NS4B increased the expression of EMT related markers and promoted cell migration and invasion. Snail knock-down almost completely eliminated the function of NS4B protein in EMT changes and reversed cell migration capacity to lower level. HCV NS4B protein could reduce the expression of Scribble and Hippo signal pathway were subsequently inactivated, resulting in the activation of PI3K/AKT pathway, which may be the reason for the up-regulation of Snail.

Conclusions

This study demonstrates that HCV NS4B protein induces EMT progression via the upregulation of Snail in HCC, which may be a novel underlying mechanism for HCV-associated HCC development, invasion and metastasis.

GRIM-19 Restricts HCV Replication by Attenuating Intracellular Lipid Accumulation

Gene-associated with retinoid-interferon-induced mortality 19 (GRIM-19) targets multiple signaling pathways involved in cell death and growth. However, the role of GRIM-19 in the pathogenesis of hepatitis virus infections remains unexplored. Here, we investigated the restrictive effects of GRIM-19 on the replication of hepatitis C virus (HCV). We found that GRIM-19 protein levels were reduced in HCV-infected Huh7 cells and Huh7 cells harboring HCV replicons. Moreover, ectopically expressed GRIM-19 caused a reduction in both intracellular viral RNA levels and secreted viruses in HCVcc-infected cell cultures. The restrictive effect on HCV replication was restored by treatment with siRNA against GRIM-19. Interestingly, GRIM-19 overexpression did not alter the level of phosphorylated STAT3 or its subcellular distribution. Strikingly, forced expression of GRIM-19 attenuated an increase in intracellular lipid droplets after oleic acid (OA) treatment or HCVcc infection. GRIM-19 overexpression abrogated fatty acid-induced upregulation of sterol regulatory element-binding transcription factor-1 (SREBP-1c), resulting in attenuated expression of its target genes such as fatty acid synthase (FAS) and acetyl CoA carboxylase (ACC). Treatment with OA or overexpression of SREBP-1c in GRIM-19-expressing, HCVcc-infected cells restored HCV replication. Our results suggest that GRIM-19 interferes with HCV replication by attenuating intracellular lipid accumulation and therefore is an anti-viral host factor that could be a promising target for HCV treatment.

Non-metabolic functions of glycolytic enzymes in tumorigenesis

Cancer cells reprogram their metabolism to meet the requirement for survival and rapid growth. One hallmark of cancer metabolism is elevated aerobic glycolysis and reduced oxidative phosphorylation. Emerging evidence showed that most glycolytic enzymes are deregulated in cancer cells and play important roles in tumorigenesis. Recent studies revealed that all essential glycolytic enzymes can be translocated into nucleus where they participate in tumor progression independent of their canonical metabolic roles. These noncanonical functions include anti-apoptosis, regulation of epigenetic modifications, modulation of transcription factors and co-factors, extracellular cytokine, protein kinase activity and mTORC1 signaling pathway, suggesting that these multifaceted glycolytic enzymes not only function in canonical metabolism but also directly link metabolism to epigenetic and transcription programs implicated in tumorigenesis. These findings underscore our understanding about how tumor cells adapt to nutrient and fuel availability in the environment and most importantly, provide insights into development of cancer therapy.