Up-regulation of hepatitis C virus replication and production by inhibition of MEK/ERK signaling

Adaptor protein Abelson interactor 1 in homeostasis and disease

Dysregulation of Abelson interactor 1 (ABI1) is associated with various states of disease including developmental defects, pathogen infections, and cancer. ABI1 is an adaptor protein predominantly known to regulate actin cytoskeleton organization processes such as those involved in cell adhesion, migration, and shape determination. Linked to cytoskeleton via vasodilator-stimulated phosphoprotein (VASP), Wiskott-Aldrich syndrome protein family (WAVE), and neural-Wiskott-Aldrich syndrome protein (N-WASP)-associated protein complexes, ABI1 coordinates regulation of various cytoplasmic protein signaling complexes dysregulated in disease states. The roles of ABI1 beyond actin cytoskeleton regulation are much less understood. This comprehensive, protein-centric review describes molecular roles of ABI1 as an adaptor molecule in the context of its dysregulation and associated disease outcomes to better understand disease state-specific protein signaling and affected interconnected biological processes.

Intrinsic apoptosis and cytokine induction regulated in human tonsillar epithelial cells infected with enterovirus A71

Enterovirus A71 (EV-A71) has emerged as a clinically important neurotropic virus following poliovirus eradication. Recent studies have shown that human tonsillar epithelial cell lines (UT-SCC-60A and UT-SCC-60B) were susceptible to EV-A71, suggesting that human tonsillar crypt epithelium could be important in EV-A71 pathogenesis. However, the mechanism about how EV-A71 infects the upper oro-digestive tract remains largely unclear. In this study, we demonstrated that the human tonsillar epithelial cells infected with EV-A71 underwent apoptotic, in which cytochrome c was released from the mitochondria to the cytosol and caspase-9 was activated, while caspase-2 and -8 were not cleaved or activated during the infection. A selective inhibitor of caspase-9, Z-LEHD-FMK, inhibited the cleavage of the executioner caspase-3 and -7, indicating that only mitochondria-mediated intrinsic apoptotic pathway was activated in EV-A71-infected tonsillar epithelial cells. No evidence of pyroptosis or necroptosis was involved in the cell death. EV-A71 infection induced interferon, pro-inflammatory cytokines and chemokines, including IFN-β, IL-6, CCL5, and TNF-α in tonsillar epithelial cells, which may play a critical role in EV-A71-caused herpangina. Our data indicated that the induction of the cytokines was partially regulated by the mitogen-activated protein kinases (MAPKs) signaling pathway. The findings unveiled the host response to EV-A71 and its regulation mechanism, and will further our understanding the significance about the tonsillar crypt epithelium as the initial and primary portal in viral pathogenesis for EV-A71 infection.

ROS induced by spring viraemia of carp virus activate the inflammatory response via the MAPK/AP-1 and PI3K signaling pathways

Spring viraemia of carp virus (SVCV) can cause a high mortality in common carp (Cyprinus carpio), and its main pathological processes include the inflammatory response. However, the detailed mechanism is still unclear. Reactive oxygen species (ROS) have been shown to play critical roles in the immune response, including inflammation, in different models. Our previous studies have demonstrated that SVCV infection results in the accumulation of ROS, including H₂O₂, in epithelioma papulosum cyprini (EPC) cells. In this study, we aimed to explore the relationship between H₂O₂ accumulation and inflammation during SVCV infection. After EPC cells were infected with SVCV, the expression levels of the inflammatory factors tumor necrosis factor (TNF)-α, cyclooxygenase (COX)-2, and interleukin (IL)-8 were up-regulated, while the expression of the anti-inflammatory factor interleukin (IL)-10 was down-regulated, compared with that in mock-infected EPC cells. The antioxidant N-acetyl-l-cysteine (NAC) could dampen the increased TNF-ɑ and COX-2 expression induced by SVCV and H₂O₂, suggesting a relationship between ROS accumulation and inflammation during SVCV infection. Dual luciferase reporter assays demonstrated that SVCV could not activate the NF-κB pathway. In addition, inhibition of NF-κB by pyrrolidine dithiocarbamate (PDTC) treatment had no effect on the expression of inflammatory factors. Furthermore, inhibition of the ERK, JNK, and p38MAPK signaling pathways by U0126, SP600125, and SB203580, respectively, reduced the expression of TNF-ɑ, COX-2, and IL-8, indicating that these three signaling pathways were all involved in the inflammatory response after SVCV infection. In addition, the PI3K signaling pathway was involved in the expression of the chemokine IL-8 in the SVCV-induced inflammatory response. We also showed that inhibition of the MAPK or PI3K signaling pathway facilitated the expression of SVCV-G as well as increased the SVCV viral titer. Altogether these results reveal the mechanism of the SVCV-mediated inflammatory response. Thus, targeting these signaling pathways may provide novel treatment strategies for SVCV-mediated diseases.

Cytokine-Modulated Natural Killer Cells Differentially Regulate the Activity of the Hepatitis C Virus

HCV genotype 2a strain JFH-1 replicates and produces viral particles efficiently in human hepatocellular carcinoma (huh) 7.5 cells, which provide a stable in vitro cell infection system for the hepatitis C virus (HCVcc system). Natural killer (NK) cells are large lymphoid cells that recognize and kill virus-infected cells. In this study, we investigated the interaction between NK cells and the HCVcc system. IL-10 is a typical immune regulatory cytokine that is produced mostly by NK cells and macrophages. IL-21 is one of the main cytokines that stimulate the activation of NK cells. First, we used anti-IL-10 to neutralize IL-10 in a coculture of NK cells and HCVcc. Anti-IL-10 treatment increased the maturation of NK cells by enhancing the frequency of the CD56^+dim population in NK-92 cells. However, with anti-IL-10 treatment of NK cells in coculture with J6/JFH-1-huh 7.5 cells, there was a significant decrease in the expression of STAT1 and STAT5 proteins in NK-92 cells and an increase in the HCV Core and NS3 proteins. In addition, rIL-21 treatment increased the frequency of the CD56^+dim population in NK-92 cells, Also, there was a dramatic increase in the expression of STAT1 and STAT5 proteins in rIL-21 pre-stimulated NK cells and a decrease in the expression of HCV Core protein in coculture with J6/JFH-1-huh 7.5 cells. In summary, we found that the functional activation of NK cells can be modulated by anti-IL-10 or rIL-21, which controls the expression of HCV proteins as well as HCV RNA replication.

IL-15 and IFN-γ signal through the ERK pathway to inhibit HCV replication, independent of type I IFN signaling

Despite effective new treatments for Hepatitis C virus (HCV) infection, development of drug resistance, safety concerns and cost are remaining challenges. More importantly, there is no vaccine available against hepatitis C infection. Recent data suggest that there is a strong correlation between spontaneous HCV clearance and human NK cell function, particularly IFN-γ production. Further, IL-15 has innate antiviral activity and is also one of the main factors that activates NK cells to produce IFN-γ. To examine whether IL-15 and IFN-γ have direct antiviral activity against HCV, Huh7.5 cells were treated with either IFN-γ or IL-15 prior to HCV infection. Our data demonstrate that IFN-γ and IL-15 block HCV replication in vitro. Additionally, we show that IL-15 and IFN-γ do not induce anti-HCV effects through the type I interferon signaling pathway or nitric oxide (NO) production. Instead, IL-15 and IFN-γ provide protection against HCV via the ERK pathway. Treatment of Huh7.5 cells with a MEK/ERK inhibitor abrogated the anti-HCV effects of IL-15 and IFN-γ and overexpression of ERK1 prevented HCV replication compared to control transfection. Our in vitro data support the hypothesis that early production of IL-15 and activation of NK cells in the liver lead to control of HCV replication.

Comparative proteomics reveals that YK51, a 4-Hydroxypandurantin-A analogue, downregulates the expression of proteins associated with dengue virus infection

Dengue is endemic throughout tropical and subtropical regions of the world. Currently, there is no clinically approved therapeutic drug available for this acute viral infection. Although the first dengue vaccine Dengvaxia has been approved for use in certain countries, it is limited to those without a previous dengue infection while the safety and efficacy of the vaccine in those elderly and younger children still need to be identified. Therefore, it is becoming increasingly important to develop therapeutics/drugs to combat dengue virus (DENV) infection. YK51 is a synthetic analogue of 4-Hydroxypandurantin A (a compound found in the crude extract of the rhizomes of Boesenbergia rotunda) that has been extensively studied by our research group. It has been shown to possess outstanding antiviral activity due to its inhibitory activity against NS2B/NS3 DENV2 protease. However, it is not known how YK51 affects the proteome of DENV infected cells. Therefore, we performed a comparative proteomics analysis to identify changes in protein expression in DENV infected HepG2 cells treated with YK51. Classical two-dimensional gel electrophoresis followed by protein identification using tandem mass spectrometry was employed in this study. Thirty proteins were found to be down-regulated with YK51 treatment. In silico analysis predicted that the down-regulation of eight of these proteins may inhibit viral infection. Our results suggested that apart from inhibiting the NS2B/NS3 DENV2 protease, YK51 may also be causing the down-regulation of a number of proteins that may be responsible in, and/or essential to virus infection. However, functional characterization of these proteins will be necessary before we can conclusively determine their roles in DENV infection.

Establishment and Application of a High Throughput Screening System Targeting the Interaction between HCV Internal Ribosome Entry Site and Human Eukaryotic Translation Initiation Factor 3

Viruses are intracellular obligate parasites and the host cellular machinery is usually recruited for their replication. Human eukaryotic translation initiation factor 3 (eIF3) could be directly recruited by the hepatitis C virus (HCV) internal ribosome entry site (IRES) to promote the translation of viral proteins. In this study, we establish a fluorescence polarization (FP) based high throughput screening (HTS) system targeting the interaction between HCV IRES and eIF3. By screening a total of 894 compounds with this HTS system, two compounds (Mucl39526 and NP39) are found to disturb the interaction between HCV IRES and eIF3. And these two compounds are further demonstrated to inhibit the HCV IRES-dependent translation in vitro. Thus, this HTS system is functional to screen the potential HCV replication inhibitors targeting human eIF3, which is helpful to overcome the problem of viral resistance. Surprisingly, one compound HP-3, a kind of oxytocin antagonist, is discovered to significantly enhance the interaction between HCV IRES and eIF3 by this HTS system. HP-3 is demonstrated to directly interact with HCV IRES and promote the HCV IRES-dependent translation both in vitro and in vivo, which strongly suggests that HP-3 has potentials to promote HCV replication. Therefore, this HTS system is also useful to screen the potential HCV replication enhancers, which is meaningful for understanding the viral replication and screening novel antiviral drugs. To our knowledge, this is the first HTS system targeting the interaction between eIF3 and HCV IRES, which could be applied to screen both potential HCV replication inhibitors and enhancers.

Hepatitis C Virus Nonstructural 5A Protein Interacts with Abelson Interactor 1 and Modulates Epidermal Growth Factor-mediated MEK/ERK Signaling Pathway

The propagation of hepatitis C virus (HCV) is highly dependent on host cellular factors. To identify the cellular factors involved in HCV propagation, we have previously performed protein microarray assays using the HCV nonstructural 5A (NS5A) protein as a probe. Of ∼9,000 host proteins immobilized in a microarray, ∼90 cellular proteins were identified as HCV NS5A interacting partners. Of these candidates, we selected Abelson interactor 1 (Abi1) for further characterization. Binding of HCV NS5A to Abi1 was verified by both in vitro pulldown and coimmunoprecipitation assays. HCV NS5A interacted with Abi1 through regions I + II of Abi1 and domain I of NS5A. We further demonstrated that Abi1 colocalized with the HCV NS5A protein in the cytoplasm. We showed that NS5A inhibited epidermal growth factor-mediated ERK and Egr1 activations and this inhibitory activity of NS5A was nullified in Abi1-knockdown cells. Moreover, silencing of Abi1 expression impaired HCV replication, whereas overexpression of Abi1 promoted HCV propagation. Collectively, these data indicate that HCV exploits host Abi1 protein via NS5A to modulate MEK/ERK signaling pathway for its own propagation.

Host-Targeting Agents to Prevent and Cure Hepatitis C Virus Infection

Chronic hepatitis C virus (HCV) infection is a major cause of liver cirrhosis and hepatocellular carcinoma (HCC) which are leading indications of liver transplantation (LT). To date, there is no vaccine to prevent HCV infection and LT is invariably followed by infection of the liver graft. Within the past years, direct-acting antivirals (DAAs) have had a major impact on the management of chronic hepatitis C, which has become a curable disease in the majority of DAA-treated patients. In contrast to DAAs that target viral proteins, host-targeting agents (HTAs) interfere with cellular factors involved in the viral life cycle. By acting through a complementary mechanism of action and by exhibiting a generally higher barrier to resistance, HTAs offer a prospective option to prevent and treat viral resistance. Indeed, given their complementary mechanism of action, HTAs and DAAs can act in a synergistic manner to reduce viral loads. This review summarizes the different classes of HTAs against HCV infection that are in preclinical or clinical development and highlights their potential to prevent HCV infection, e.g., following LT, and to tailor combination treatments to cure chronic HCV infection.

Profiling Kinase Activity during Hepatitis C Virus Replication Using a Wortmannin Probe

To complete its life cycle, the hepatitis C virus (HCV) induces changes to numerous aspects of its host cell. As kinases act as regulators of many pathways utilized by HCV, they are likely enzyme targets for virally induced inhibition or activation. Herein, we used activity-based protein profiling (ABPP), which allows for the identification of active enzymes in complex protein samples and the quantification of their activity, to identify kinases that displayed differential activity in HCV-expressing cells. We utilized an ABPP probe, wortmannin-yne, based on the kinase inhibitor wortmannin, which contains a pendant alkyne group for bioconjugation using bioorthogonal chemistry. We observed changes in the activity of kinases involved in the mitogen-activated protein kinase pathway, apoptosis pathways, and cell cycle control. These results establish changes to the active kinome, as reported by wortmannin-yne, in the proteome of human hepatoma cells actively replicating HCV. The observed changes include kinase activity that affect viral entry, replication, assembly, and secretion, implying that HCV is regulating the pathways that it uses for its life cycle through modulation of the active kinome.

Identification of novel human kinases that suppress hepatitis C virus infection

The human kinome includes between 500 and 600 known kinases and open reading frames (ORFs) that play key roles in regulating many cellular processes. Past studies adopting loss-of-function approaches have identified some kinases whose activities are required for hepatitis C virus (HCV) life cycle. Here, by screening a retroviral cDNA library of 192 active human kinases, we found that three of them, namely cyclin-dependent kinases regulatory subunit 1 (CKS1B), mitogen-activated protein kinase kinase 5 (MAP2K5) and protein kinase C and casein kinase substrate in neurons 1 (PACSIN1), potently suppressed HCV infection. The expression of these kinases did not induce the production of type I interferon (IFN) and interferon-stimulated genes (ISGs); instead, they inhibited HCV at postentry stages. Specifically, CKS1B and MAP2K5 significantly inhibited viral RNA replication. PACSIN1, by contrast, inhibited HCV infection by decreasing the level of HCV p7. Altogether, the identification of human protein kinases that exert an anti-HCV activity highlighted the potential of combating HCV infection by activating specific kinase-mediated pathways, offering an alternative strategy of treatment.

Very-low-density lipoprotein (VLDL)-producing and hepatitis C virus-replicating HepG2 cells secrete no more lipoviroparticles than VLDL-deficient Huh7.5 cells

In the plasma samples of hepatitis C virus (HCV)-infected patients, lipoviroparticles (LVPs), defined as (very-) low-density viral particles immunoprecipitated with anti-β-lipoproteins antibodies are observed. This HCV-lipoprotein association has major implications with respect to our understanding of HCV assembly, secretion, and entry. However, cell culture-grown HCV (HCVcc) virions produced in Huh7 cells, which are deficient for very-low-density lipoprotein (VLDL) secretion, are only associated with and dependent on apolipoprotein E (apoE), not apolipoprotein B (apoB), for assembly and infectivity. In contrast to Huh7, HepG2 cells can be stimulated to produce VLDL by both oleic acid treatment and inhibition of the MEK/extracellular signal-regulated kinase (ERK) pathway but are not permissive for persistent HCV replication. Here, we developed a new HCV cell culture model to study the interaction between HCV and lipoproteins, based on engineered HepG2 cells stably replicating a blasticidin-tagged HCV JFH1 strain (JB). Control Huh7.5-JB as well as HepG2-JB cell lines persistently replicated viral RNA and expressed viral proteins with a subcellular colocalization of double-stranded RNA (dsRNA), core, gpE2, and NS5A compatible with virion assembly. The intracellular RNA replication level was increased in HepG2-JB cells upon dimethyl sulfoxide (DMSO) treatment, MEK/ERK inhibition, and NS5A overexpression to a level similar to that observed in Huh7.5-JB cells. Both cell culture systems produced infectious virions, which were surprisingly biophysically and biochemically similar. They floated at similar densities on gradients, contained mainly apoE but not apoB, and were not neutralized by anti-apoB antibodies. This suggests that there is no correlation between the ability of cells to simultaneously replicate HCV as well as secrete VLDL and their capacity to produce LVPs.

Regulation of hepatitis C virus replication and gene expression by the MAPK-ERK pathway

The mitogen activated protein kinases-extracellular signal regulated kinases (MAPK-ERK) pathway is involved in regulation of multiple cellular processes including the cell cycle. In the present study using a Huh7 cell line Con1 with an HCV replicon, we have shown that the MAPK-ERK pathway plays a significant role in the modulation of HCV replication and protein expression and might influence IFN-α signalling. Epithelial growth factor (EGF) was able to stimulate ERK activation and decreased HCV RNA load while a MAPK-ERK pathway inhibitor U0126 led to an elevated HCV RNA load and higher NS5A protein amounts in Con1 cells. It could be further demonstrated that the inhibition of the MAPK-ERK pathway facilitated the translation directed by the HCV internal ribosome entry site. Consistently, a U0126 treatment enhanced activity of the HCV reporter replicon in transient transfection assays. Thus, the MAPK-ERK pathway plays an important role in the regulation of HCV gene expression and replication. In addition, cyclin-dependent kinases (CDKs) downstream of ERK may also be involved in the modulation of HCV replication since roscovitine, an inhibitor of CDKs had a similar effect to that of U0126. Modulation of the cell cycle progression by cell cycle inhibitor or RNAi resulted consistently in changes of HCV RNA levels. Further, the replication of HCV replicon in Con1 cells was inhibited by IFN-α. The inhibitory effect of IFN-α could be partly reversed by pre-incubation of Con-1 cells with inhibitors of the MAPK-ERK pathway and CDKs. It could be shown that the MAPK-ERK inhibitors are able to partially modulate the expression of interferon-stimulated genes.

Curcumin inhibits HCV replication by induction of heme oxygenase-1 and suppression of AKT

Although hepatitis C virus (HCV) affects approximately 130–170 million people worldwide, no vaccines are available. HCV is an important cause of chronic hepatitis, cirrhosis and hepatocellular carcinoma, leading to the need for liver transplantation. In this study, curcumin, a constituent used in traditional Chinese medicine, has been evaluated for its anti-HCV activity and mechanism, using a human hepatoma cell line containing the HCV genotype 1b subgenomic replicon. Below the concentration of 20% cytotoxicity, curcumin dose-dependently inhibited HCV replication by luciferase reporter gene assay, HCV RNA detection and HCV protein analysis. Under the same conditions, curcumin also dose-dependently induced heme oxygenase-1 with the highest induction at 24 h. Hemin, a heme oxygenase-1 inducer, also inhibited HCV protein expression in a dose-dependent manner. The knockdown of heme oxygenase-1 partially reversed the curcumin-inhibited HCV protein expression. In addition to the heme oxygenase-1 induction, signaling molecule activities of AKT, extracellular signal-regulated kinases (ERK) and nuclear factor-κB (NF-κB) were inhibited by curcumin. Using specific inhibitors of PI3K-AKT, MEK-ERK and NF-κB, the results suggested that only PI3K-AKT inhibition is positively involved in curcumin-inhibited HCV replication. Inhibition of ERK and NF-κB was likely to promote HCV protein expression. In summary, curcumin inhibited HCV replication by heme oxygenase-1 induction and AKT pathway inhibition. Although curcumin also inhibits ERK and NF-κB activities, it slightly increased the HCV protein expression. This result may provide information when curcumin is used as an adjuvant in anti-HCV therapy.

Hepatitis C virus sensitizes host cells to TRAIL-induced apoptosis by up-regulating DR4 and DR5 via a MEK1-dependent pathway

Background

Hepatitis C virus (HCV) is the leading cause of liver fibrosis, cirrhosis and hepatocellular carcinoma. It is believed that continuous liver cell apoptosis contributes to HCV pathogenesis. Recent studies have shown that HCV infection can sensitize host cells to TNF-related apoptosis-inducing ligand (TRAIL) induced apoptosis, but the mechanism by which HCV regulates the TRAIL pathway remains unclear.

Methods and Results

Using a sub-genomic replicon and full length virus, JFH-1, we demonstrate that HCV can sensitize host cells to TRAIL-induced apoptosis by up-regulating two TRAIL receptors, death receptor 4 (DR4) and death receptor 5 (DR5). Furthermore, the HCV replicon enhanced transcription of DR5 via Sp1, and the HCV-mediated up-regulation of DR4 and DR5 required MEK1 activity. HCV infection also stimulated the activity of MEK1, and the inhibition of MEK1 activity or the knockdown of MEK1 increased the replication of HCV.

Conclusions

Our studies demonstrate that HCV replication sensitizes host cells to TRAIL-induced apoptosis by up-regulating DR4 and DR5 via a MEK1 dependent pathway. These findings may help to further understand the pathogenesis of HCV infection and provide a therapeutic target.

Involvement of the mitogen-activated protein kinase pathway in soft-shelled turtle iridovirus-induced apoptosis

Iridoviruses are large DNA viruses that infect invertebrates and poikilothermic vertebrates, and result in significant economic losses in aquaculture production, and drastic declines in amphibian populations. Soft-shelled turtle iridovirus (STIV) is the causative agent of severe systemic diseases in farm-raised soft-shelled turtles (Trionyx sinensis). In the present study, the mechanisms of STIV-induced cell death and the roles of the mitogen-activated protein kinase (MAPK) signaling pathway were investigated. STIV infection evoked typical apoptosis in fish cells, as demonstrated by the formation of apoptotic bodies, positive terminal deoxynucleotidyl transferase-mediated nicked-end labeling, and caspase-3 activation. The translocation of cytochrome c from mitochondria to cytoplasm, and caspase-9 activation suggested that a mitochondria-mediated pathway was involved in STIV-induced apoptosis. Moreover, MAPK pathways, including extracellular signal-regulated kinase (ERK), c-Jun N-terminal kinase (JNK) and p38 MAPK signaling were activated during STIV infection. Using specific inhibitors, we found that MAPK signaling molecules, including ERK, JNK and p38 MAPK, were important for virus release, whereas, only ERK and p38 MAPK were involved in STIV-induced apoptosis by modulating caspase-3 activity. Taken together, our findings shed light on the roles of the MAPK signaling pathway in iridovirus-induced apoptosis and virus replication, which provides new insights into understanding iridovirus-host interaction.