Nonstructural Protein 3 Protease Research Articles

Analysis of Cleavage Activity of Dengue Virus Protease by Co-transfections.

The genome of the dengue virus codes for a single polypeptide that yields three structural and seven non-structural (NS) proteins upon post-translational modifications. Among them, NS protein-3 (NS3) possesses protease activity, involved in the processing of the self-polypeptide and in the cleavage of host proteins. Identification and analysis of such host proteins as substrates of this protease facilitate the development of specific drugs. In vitro cleavage analysis has been applied, which requires homogeneously purified components. However, the expression and purification of both S3 and erythroid differentiation regulatory factor 1 (EDRF1) are difficult and unsuccessful on many occasions. EDRF1 was identified as an interacting protein of dengue virus protease (NS3). The amino acid sequence analysis indicates the presence of NS3 cleavage sites in this protein. As EDRF1 is a high-molecular-weight (~138 kDa) protein, it is difficult to express and purify the complete protein. In this protocol, we clone the domain of the EDRF1 protein (C-terminal end) containing the cleavage site and the NS3 into two different eukaryotic expression vectors containing different tags. These recombinant vectors are co-transfected into mammalian cells. The cell lysate is subjected to SDS-PAGE followed by western blotting with anti-tag antibodies. Data suggest the disappearance of the EDRF1 band in the lane co-transfected along with NS3 protease but present in the lane transfected with only EDRF1, suggesting EDRF1 as a novel substrate of NS3 protease. This protocol is useful in identifying the substrates of viral-encoded proteases using ex vivo conditions. Further, this protocol can be used to screen anti-protease molecules. Key features • This protocol requires the cloning of protease and substrate into two different eukaryotic expression vectors with different tags. • Involves the transfection and co-transfection of both the above recombinant vectors individually and together. • Involves western blotting of the same PVDF membrane containing total proteins of the cell lysate with two different antibodies. • Does not require purified proteins for the analysis of cleavage of any suspected substrate by the protease.

Lambda-free light chain: A serum marker of dengue disease via NS3 protease-mediated antibody cleavage

ABSTRACT Dengue poses a significant global public health threat, with diverse clinical manifestations due to complex interactions between the host and the pathogen. Recent reports have highlighted elevated serum-free light chain (FLC) levels in viral infectious diseases. Hence, our study aimed to investigate serum FLC levels in dengue patients. The findings revealed elevated serum λ FLCs, which were associated with the severity of dengue. Receiver operating characteristic curve (ROC) analysis demonstrated that λ FLCs may serve as a serum marker for identifying dengue disease (AUC: 0.7825, sensitivity: 80, specificity: 71.43) and classifying severe dengue (AUC: 0.8102, sensitivity: 75, specificity: 79.52). The viral protease, Dengue virus (DENV) nonstructural protein 3 (NS3), acts as a protease that cleaves viral polyproteins as well as host substrates. Therefore, we proposed that antibodies might be potential targets of NS3 protease, leading to an increase in FLCs. LC/MS-MS analysis confirmed that λ FLCs were the predominant products after antibody degradation by NS3 protease. Additionally, purified NS3 protease cleaved both human IgG and DENV2-neutralizing antibodies, resulting in the presence of λ FLCs. Moreover, NS3 protease administration in vitro led to a reduction in the neutralizing efficacy of DENV2-neutralizing antibodies. In summary, the elevated serum λ FLC levels effectively differentiate dengue patients from healthy individuals and identify severe dengue. Furthermore, the elevation of serum λ FLCs is, at least in part, mediated through NS3 protease-mediated antibody cleavage. These findings provide new insights for developing diagnostic tools and understanding the pathogenesis of DENV infection.

An ivermectin – atorvastatin combination impairs nuclear transport inhibiting dengue infection in vitro and in vivo

Dengue virus (DENV) uses cellular nuclear transport machinery to import some proteins into the nucleus. Recently, the non-structural protein 3 (NS3) of DENV was localized in the nucleus of infected cells; however, its nuclear import mechanism is still unknown. In this study, we demonstrate that Ivermectin (IVM) inhibits the nuclear localization of NS3 through the inhibition of the Importin α/β1 pathway. We also report that Atorvastatin (ATV) can modulate the nuclear transport of NS3 protease and NS5 polymerase of DENV-2. On the other hand, we found that IVM and ATV treatments reduce the alteration of nuclear pore complex (NPC) proteins, and an IVM+ATV combination reduced DENV infection both invitro and invivo. Hence, we conclude that ATV transport inhibition is an additional antiviral effect of this drug, suggesting a potential anti-DENV therapy in combination with IVM.

NLRC5 restricts dengue virus infection by promoting the autophagic degradation of viral NS3 through E3 ligase CUL2 (cullin 2)

ABSTRACT NLRC5 has been reported to be involved in antiviral immunity; however, the underlying mechanism remains poorly understood. Here, we investigated the functional role of NLRC5 in the infection of a flavivirus, dengue virus (DENV). We found that the expression of NLRC5 was strongly induced by virus infection and IFNB or IFNG stimulation in different cell lines. Overexpression of NLRC5 remarkably suppressed DENV infection, whereas knockout of NLRC5 led to a significant increase in DENV infection. Mechanistic study revealed that NLRC5 interacted with the viral nonstructural protein 3 (NS3) protease domain and mediated degradation of NS3 through a ubiquitin-dependent selective macroautophagy/autophagy pathway. We demonstrated that NLRC5 recruited the E3 ubiquitin ligase CUL2 (cullin 2) to catalyze K48-linked poly-ubiquitination of the NS3 protease domain, which subsequently served as a recognition signal for cargo receptor TOLLIP-mediated selective autophagic degradation. Together, we have demonstrated that NLRC5 exerted an antiviral effect by mediating the degradation of a multifunctional protein of DENV, providing a novel antiviral signal axis of NLRC5-CUL2-NS3-TOLLIP. This study expands our understanding of the regulatory network of NLRC5 in the host defense against virus infection.

A positively charged surface patch on the pestivirus NS3 protease module plays an important role in modulating NS3 helicase activity and virus production.

Pestivirus nonstructural protein 3 (NS3) is a multifunctional protein with protease and helicase activities that are essential for virus replication. In this study, we used a combination of biochemical and genetic approaches to investigate the relationship between a positively charged patch on the protease module and NS3 function. The surface patch is composed of four basic residues, R50, K74 and K94 in the NS3 protease domain and H24 in the structurally integrated cofactor NS4APCS. Single-residue or simultaneous four-residue substitutions in the patch to alanine or aspartic acid had little effect on ATPase activity. However, single substitutions of R50, K94 or H24 or a simultaneous four-residue substitution resulted in apparent changes in the helicase activity and RNA-binding ability of NS3. When these mutations were introduced into a classical swine fever virus (CSFV) cDNA clone, a single substitution at K94 or a simultaneous four-residue substitution (Qua_A or Qua_D) impaired the production of infectious virus. Furthermore, the replication efficiency of the CSFV variants was partially correlated with the helicase activity of NS3 in vitro. Our results suggest that the conserved positively charged patch on NS3 plays an important role in modulating the NS3 helicase activity in vitro and CSFV production.

Monoclonal Antibody That Inhibits Cleavage Activity of Japanese Encephalitis Virus NS3.

Flavivirus protease has been deemed a potential target for drug and therapeutics development due to its crucial role in viral replication. In this study we prepared a monoclonal antibody (mAb) against nonstructural protein 3 (NS3) protease portion of Japanese encephalitis virus (JEV), and evaluated its inhibitory effect for NS3 protease activity. First, a JEV NS3 protease-specific mAb (designated 2C2) was generated by the traditional cell fusion technique. Second, the binding specificity of 2C2 for NS3 protease was determined by indirect fluorescent assay and Western blotting. Finally, inhibitory effect of 2C2 for NS3 protease cleaving human stimulator of interferon gene was evaluated. Therefore, mAb 2C2 provides a potential diagnostic tool for differential diagnosis for patients who have been vaccinated with inactivated vaccine or naturally infected, and might be genetically reconstructed and optimized for new therapeutics development.

Potential Dual Role of West Nile Virus NS2B in Orchestrating NS3 Enzymatic Activity in Viral Replication.

West Nile virus (WNV) nonstructural protein 3 (NS3) harbors the viral triphosphatase and helicase for viral RNA synthesis and, together with NS2B, constitutes the protease responsible for polyprotein processing. NS3 is a soluble protein, but it is localized to specialized compartments at the rough endoplasmic reticulum (RER), where its enzymatic functions are essential for virus replication. However, the mechanistic details behind the recruitment of NS3 from the cytoplasm to the RER have not yet been fully elucidated. In this study, we employed immunofluorescence and biochemical assays to demonstrate that NS3, when expressed individually and when cleaved from the viral polyprotein, is localized exclusively to the cytoplasm. Furthermore, NS3 appeared to be peripherally recruited to the RER and proteolytically active when NS2B was provided in trans. Thus, we provide evidence for a potential additional role for NS2B in not only serving as the cofactor for the NS3 protease, but also in recruiting NS3 from the cytoplasm to the RER for proper enzymatic activity. Results from our study suggest that targeting the interaction between NS2B and NS3 in disrupting the NS3 ER localization may be an attractive avenue for antiviral drug discovery.

Screening and identification of bioactive compounds from citrus against non-structural protein 3 protease of hepatitis C virus genotype 3a by fluorescence resonance energy transfer assay and mass spectrometry.

BACKGROUNDHepatitis C virus genotype 3a (HCV G3a) is highly prevalent in Pakistan. Due to the elevated cost of available Food and Drug Administration-approved drugs against HCV, medicinal natural products of potent antiviral activity should be screened for the cost-effective treatment of the disease. Furthermore, from natural products, active compounds against vital HCV proteins like non-structural protein 3 (NS3) protease could be identified to prevent viral proliferation in the host.AIMTo develop cost-effective HCV genotype 3a NS3 protease inhibitors from citrus fruit extracts.METHODSFull-length NS3 without co-factor non-structural protein 4A (NS4A) and codon optimized NS3 protease in fusion with NS4A were expressed in Escherichia coli. The expressed protein was purified by metal ion affinity chromatography and gel filtration. Citrus fruit extracts were screened using fluorescence resonance energy transfer (FRET) assay against the protease and polyphenols were identified as potential inhibitors using electrospray ionization-mass spectrometry (MS)/MS technique. Among different polyphenols, highly potent compounds were screened using molecular modeling approaches and consequently the most active compound was further evaluated against HCV NS4A-NS3 protease domain using FRET assay.RESULTSNS4A fused with NS3 protease domain gene was overexpressed and the purified protein yield was high in comparison to the lower yield of the full-length NS3 protein. Furthermore, in enzyme kinetic studies, NS4A fused with NS3 protease proved to be functionally active compared to full-length NS3. So it was concluded that co-factor NS4A fusion is essential for the purification of functionally active protease. FRET assay was developed and validated by the half maximal inhibitory concentration (IC50) values of commercially available inhibitors. Screening of citrus fruit extracts against the native purified fused NS4A-NS3 protease domain showed that the grapefruit mesocarp extract exhibits the highest percentage inhibition 91% of protease activity. Among the compounds identified by LCMS analysis, hesperidin showed strong binding affinity with the protease catalytic triad having S-score value of -10.98.CONCLUSIONFused NS4A-NS3 protease is functionally more active, which is effectively inhibited by hesperidin from the grapefruit mesocarp extract with an IC50 value of 23.32 µmol/L.

Crystal structures of full length DENV4 NS2B-NS3 reveal the dynamic interaction between NS2B and NS3

Flavivirus is a genus of the Flaviviridae family which includes significant emerging and re-emerging human disease-causing arboviruses such as dengue and Zika viruses. Flaviviral non-structural protein 3 (NS3) protease-helicase plays essential roles in viral replication and is an attractive antiviral target. A construct which connects the cytoplasmic cofactor region of NS2B and NS3 protease with an artificial glycine-rich flexible linker has been widely used for structural, biochemical and drug-screening studies. The effect of this linker on the dynamics and enzymatic activity of the protease has been studied by several biochemical and NMR methods but the findings remained inconclusive. Here, we designed and carried out a comparative study of constructs of NS2B cofactor joined to the full length DENV4 NS3 in three different ways, namely bNS2B47NS3 (bivalent), eNS2B47NS3(enzymatically cleavable) and gNS2B47NS3 (glycine-rich linker). We report the crystal structures of linked and unlinked NS2B47-NS3 constructs in their free state and in complex with bovine pancreatic trypsin inhibitor (BPTI). These structures demonstrate that the NS2B cofactor predominantly adopts a closed conformation in complex with full-length NS3. The glycine-rich linker between NS2B and NS3 may promote the open conformation which interferes with protease activity. This negative impact on the enzyme structure and function is restricted to the protease activity as the ATPase activity is not affected in vitro.

Evaluating Drug Resistant Mutations to HCV NS3 Protease Inhibitors in Iranian Naïve Patients

Hepatitis C virus (HCV) is an important causative agent of acute and chronic hepatitis. The non-structural protein 3 (NS3) of HCV retains two enzymatic domains which are essential for the virus life cycle. The serine protease inhibitors have developed to improve the responses of HCV-infected patients that have an effective impact on NS3. Nonetheless, drug-resistant variants are the prominent obstruction toward therapeutic success. Sixty-eight Iranian patients infected with HCV genotypes 1a and 3a and diagnosed with chronic active hepatitis were examined. Plasma viral RNA was used to amplify and sequence the HCV NS3 gene; also, HCV viral load, molecular genotyping, and the ALT test were determined for all samples. The sequencing results were used to be analyzed by several reliable bioinformatics tools to determine the physicochemical properties, B cell epitopes, post-modification changes and secondary/tertiary structures; and evaluate the interactions with four drugs. Our results showed that 45% of patients were 1a genotype, the rest of them belonged to 3a genotype, and 70% of patients had abnormal ALT and AST levels. Several substitutions were observed in codons I52M, S102A, L132I, and S166A in 3a genotype and 40, 153 and 91 in 1a genotype. Interactions between references and sample sequences with available drugs showed that different genotypes or common mutations could not have any striking effect on the energy value of the interaction. This study displayed resistance mutations and genetic polymorphisms of NS3 region that are crucial in determining the efficiency of protease inhibitor class of drugs in Iranian HCV infected patients.

Studi in Silico Lima Senyawa Aktif Sebagai Penghambat Protein Virus Dengue

Dengue infection is an endemic disease in the tropics and subtropics, caused by dengue virus (DENV) infection. Some compounds have been shown to have antiviral effects on some viruses. In silico study is conducted to predict the stability of natural ingredient compounds: artemisinin, catechin, mangiferin, epigallocatechin gallate (EGCG), and quercetin in their interactions with dengue virus proteins at molecular level. This study is carried out using the 2008 version of the Molecular Operating Environment (MOE) software. Ligands are ribavirin as antiviral control whereas artemisinin, mangiferin, EGCG, and quercetin with 3D mole format structures. The downloaded DENV protein with PDB document format is the DENV serotype 2 envelope protein with 1OKE code, non structural protein 3 (NS3) with 2VBC code and NS5 protein with 1L9K code. In silico test generally showed that catechin, mangiferin, EGCG, and quercetin had more stable docking ligands to DENV’s proteins. In particular, mangiferin had stable docking ligand to envelope proteins, NS3 (helicase and protease) and in NS5-methyltransferase compared to ribavirin. Catechin stabled on NS3-protease, EGCG on NS3 (helicase and protease) and quercetin on NS3-protease. Artemisinin had less stabled bonds than ribavirin. The results indicated that catechin, mangiferin, EGCG, and quercetin had potential inhibition to DENV proteins whereas mangiferin was the most potential compound to inhibit dengue virus protein targets.

Intracellular Delivery of HCV NS3p gene using vectored particles

Viral hepatitis caused by the hepatitis C virus (HCV) affects millions of people worldwide. The non-structural protein 3 (NS3), one of the most conserved proteins in HCV, is the target of many therapeutic studies. The NS3 protease domain (NS3p) has a range of cytotoxic T lymphocyte (CTL) epitopes, and synthesizing the protein inside the cells is the most appropriate way to present it to the immune system. We developed a tool to study this kind of presentation, using two vectored particle (VP) systems, one based on the Semliki Forest virus (SFV) and the other on HCV pseudoparticles (HCVpp), both carrying the protease domain of the NS3 gene. In addition to producing the particles, we developed a method to quantify these VPs using qRT-PCR. We produced batches of approximately 2.4 × 104 SFV-NS3p/μL and 4.0 × 102 HCVpp-NS3p/μL. BHK-21 and HuH-7 cells treated with the VPs expressed the NS3 protein, thus showing the functionality of this system.

Sustained Specific and Cross-Reactive T Cell Responses to Zika and Dengue Virus NS3 in West Africa.

Recent studies on the role of T cells in Zika virus (ZIKV) infection have shown that T cell responses to Asian ZIKV infection are important for protection, and that previous dengue virus (DENV) exposure amplifies the protective T cell response to Asian ZIKV. Human T cell responses to African ZIKV infection, however, remain unexplored. Here, we utilized the modified anthrax toxin delivery system to develop a flavivirus enzyme-linked immunosorbent spot (ELISPOT) assay. Using human ZIKV and DENV samples from Senegal, West Africa, our results demonstrate specific and cross-reactive T cell responses to nonstructural protein 3 (NS3). Specifically, we found that T cell responses to NS3 protease are ZIKV and DENV specific, but responses to NS3 helicase are cross-reactive. Sequential sample analyses revealed immune responses sustained many years after infection. These results have important implications for African ZIKV/DENV vaccine development, as well as for potential flavivirus diagnostics based on T cell responses.IMPORTANCE The recent Zika virus (ZIKV) epidemic in Latin America and the associated congenital microcephaly and Guillain-Barré syndrome have raised questions as to why we have not recognized these distinct clinical diseases in Africa. The human immunologic response to ZIKV and related flaviviruses in Africa represents a research gap that may shed light on the mechanisms contributing to protection. The goal of our study was to develop an inexpensive assay to detect and characterize the T cell response to African ZIKV and DENV. Our data show long-term specific and cross-reactive human immune responses against African ZIKV and DENV, suggesting the usefulness of a diagnostic based on the T cell response. Additionally, we show that prior flavivirus exposure influences the magnitude of the T cell response. The identification of immune responses to African ZIKV and DENV is of relevance to vaccine development.

Phylogenetic analysis, structure modeling and docking study of HCV NS3 protease for the identification of potent inhibitors

The nonstructural protein 3 (NS3) helicase of HCV is believed to be a plausible target for the identification and designing of potent antiviral drugs. NS3 protein is involved in a positive sense single-stranded viral replication as well as it also cleaves viral poly protein into diverse mature proteins at different time spans. Structural exploration of NS3 revealed that HCV helicase could also act as translocase. In order to identify potential inhibitors for HCV-3a, the current study has been designed. Serum samples from the Pakistani HCV positive patients were collected, sequenced and after purification included in the present study. Phylogenetic analysis on the samples clustered around it in the same group with those from India. Using homology modeling technique, we determined 3D structure of NS3 gene of HCV-3a and employed further in docking studies to discover potent inhibitor against it. As a result of docking Compound 1, with IC50 value of 0.015 and −14.4 kcal/mol energy, ranked as a most pungent inhibitor among all the studied inhibitors. Compound 1 also exhibited good hydrogen bond interactions with the modeled protein. The finding of present study could be used as a lead in future to design an effective dual inhibitor against HCV-3a.

FRET studies examining the interaction of hepatitis C NS3 helicase and human DExD/H box helicases

The innate immune response to viral infection is the intracellular first line of defense against invading pathogens. One strategy that viruses, such as hepatitis C virus (HCV), use to establish a chronic infection is to short circuit this innate immune response. HCV encodes a multi‐functional non‐structural protein 3 (NS3), which is a protease covalently tethered to a C‐terminal helicase. One role of the NS3 protease in innate immune response evasion is to cleave mitochondrial anti‐viral signaling protein (MAVS). The function of the NS3 helicase is essential for replication but it is unclear why it is covalently linked to the protease.We propose that HCV NS3 helicase works to evade the innate immune response by binding to pathogen associated molecular patterns (PAMPs) in the HCV genome and interacting with the RIG‐I like receptor LGP2, to localize the NS3 protease near MAVs for cleavage.In order to study the interaction between human and viral helicases we used a process called Förster resonant energy transfer (FRET) where an excited fluorescent molecule (donor) transfers its energy to a nearby fluorescent molecule of a different type (acceptor) which in turn emits a red shifted fluorescent light. This process occurs in distances smaller than 10 nm between the donor and acceptor which indicates obvious interaction.We generated two sets of plasmids encoding donor (mCFP) and acceptor (mYFP) fused to viral and human helicases respectively. The donor plasmid set encodes recombinant proteins in which all or part of HCV NS3 and its cofactor NS4A were fused to a mCFP fluorescent protein. The first expresses only the NS3 helicase domain (mCFP‐NS3h) fused to mCFP. In the second, mCFP was fused with full‐length NS3 (mCFP‐NS3). In the third, mCFP was fused to NS3 and only the NS3 cofactor domain of NS4A (lacking the membrane anchor and C‐terminus, i.e. mCFP‐NS3‐4Acd), and in the fourth, mCFP was fused to NS3 and full length NS4A (mCFP‐NS3‐NS4A). The acceptor plasmid set encodes recombinant mYFP fused to DDX1, DDX3, DDX5, and DHX 58 (LGP2). HEK293T cells were co‐transfected with each donor plasmid and acceptor plasmid. The live cells were imaged using an optical micro‐spectroscope (OptiMis) which consists of a two photon excitation scanning optical microscope with high spectral resolution. In a separate set of experiments each of the donor plasmids were co‐transfected with a plasmid expressing RFP fused to MAVs and a nuclear localization signal.The fluorescently labeled recombinant NS3 proteins were visualized in real‐time in HEK293T cells. The RFP MAVs re‐localized to the nucleus only when it was co‐transfected with plasmids that encoded NS4A, in addition to the NS3 protease. FRET was observed between all recombinant HCV NS3 proteins and LGP2, but not between any recombinant HCV NS3 proteins and closely related DDX 1, DDX3, and DDX5. Our data indicates that the NS3 fusion proteins are biologically active and that NS3 interacts with LGP2 via its helicase domain.

Recombinant Dengue 2 Virus NS3 Helicase Protein Enhances Antibody and T-Cell Response of Purified Inactivated Vaccine.

Dengue virus purified inactivated vaccines (PIV) are highly immunogenic and protective over the short term, but may be poor at inducing cell-mediated immune responses and long-term protection. The dengue nonstructural protein 3 (NS3) is considered the main target for T-cell responses during viral infection. The amino (N)-terminal protease and the carboxy (C)-terminal helicase domains of DENV-2 NS3 were expressed in E. coli and analyzed for their immune-potentiating capacity. Mice were immunized with DENV-2 PIV with and without recombinant NS3 protease or NS3 helicase proteins, and NS3 proteins alone on days 0, 14 and 28. The NS3 helicase but not the NS3 protease was effective in inducing T-cell responses quantified by IFN-γ ELISPOT. In addition, markedly increased total IgG antibody titer against virus antigen was seen in mice immunized with the PIV/NS3 helicase combination in the ELISA, as well as increased neutralizing antibody titer measured by the plaque reduction neutralization test. These results indicate the potential immunogenic properties of the NS3 helicase protein and its use in a dengue vaccine formulation.

Selection of suitable detergents for obtaining an active dengue protease in its natural form from E. coli

Dengue protease is a two-component enzyme and is an important drug target against dengue virus. The protease activity and protein stability of dengue nonstructural protein 3 (NS3) require a co-factor region from a four-span membrane protein NS2B. A natural form of dengue protease containing full-length NS2B and NS3 protease domain NS2BFL-NS3pro will be useful for dengue drug discovery. In current study, detergents that can be used for protease purification were tested. Using a water soluble protease construct, 39 detergents were selected for both NS2B and NS2BFL-NS3pro purification. The results showed that 18 detergents were able to sustain the activity of the natural dengue protease and 11 detergents could be used for NS2B purification. The results obtained in this study will be useful for biochemical and biophysical studies on dengue protease.

Activation of Type I and III Interferon Response by Mitochondrial and Peroxisomal MAVS and Inhibition by Hepatitis C Virus.

Sensing viruses by pattern recognition receptors (PRR) triggers the innate immune system of the host cell and activates immune signaling cascades such as the RIG-I/IRF3 pathway. Mitochondrial antiviral-signaling protein (MAVS, also known as IPS-1, Cardif, and VISA) is the crucial adaptor protein of this pathway localized on mitochondria, peroxisomes and mitochondria-associated membranes of the endoplasmic reticulum. Activation of MAVS leads to the production of type I and type III interferons (IFN) as well as IFN stimulated genes (ISGs). To refine the role of MAVS subcellular localization for the induction of type I and III IFN responses in hepatocytes and its counteraction by the hepatitis C virus (HCV), we generated various functional and genetic knock-out cell systems that were reconstituted to express mitochondrial (mito) or peroxisomal (pex) MAVS, exclusively. Upon infection with diverse RNA viruses we found that cells exclusively expressing pexMAVS mounted sustained expression of type I and III IFNs to levels comparable to cells exclusively expressing mitoMAVS. To determine whether viral counteraction of MAVS is affected by its subcellular localization we employed infection of cells with HCV, a major causative agent of chronic liver disease with a high propensity to establish persistence. This virus efficiently cleaves MAVS via a viral protease residing in its nonstructural protein 3 (NS3) and this strategy is thought to contribute to the high persistence of this virus. We found that both mito- and pexMAVS were efficiently cleaved by NS3 and this cleavage was required to suppress activation of the IFN response. Taken together, our findings indicate comparable activation of the IFN response by pex- and mitoMAVS in hepatocytes and efficient counteraction of both MAVS species by the HCV NS3 protease.

ID: 105: Activation of type I and III interferon response by mitochondrial and peroxisomal MAVS and inhibition by hepatitis C virus

Sensing viruses by pattern recognition receptors (PRR) triggers the innate immune system of the host cell and activates immune signaling cascades like the RIG-I/IRF3 pathway. Mitochondrial antiviral-signaling protein (MAVS) is the crucial adaptor protein of this pathway localized on mitochondria, peroxisomes and mitochondria associated membranes (MAMs). Activation of MAVS leads to the production of type I and type III interferon (IFN) as well as interferon stimulated genes (ISGs). To refine the role of MAVS subcellular localization for the induction of type I and III IFN responses in hepatocytes, we generated cell lines with organelle-targeted MAVS and characterized innate immune response after viral infection. We established various functional and genetic knock-out cell systems reconstituted to express exclusively mitochondrial or peroxisomal MAVS. Infection with diverse RNA viruses mounted comparable levels of type I and III IFN expression irrespective of MAVS subcellular localization. To determine whether viral counteraction of MAVS is affected in these systems we employed infection of cells with the hepatitis C virus (HCV), a major causative agent of chronic liver diseases with a high propensity to establish persistence. This virus efficiently cleaves MAVS via a viral protease residing in nonstructural protein 3 (NS3). We found that both mitochondrial and peroxisomal MAVS were efficiently cleaved by NS3 and this cleavage was required to suppress activation of the IFN response. Taken together, our findings indicate comparable activation of the IFN response by peroxisomal and mitochondrial MAVS in hepatocytes and efficient counteraction of both MAVS species by the HCV NS3 protease.

Simultaneously Targeting the NS3 Protease and Helicase Activities for More Effective Hepatitis C Virus Therapy.

This study examines the specificity and mechanism of action of a recently reported hepatitis C virus (HCV) nonstructural protein 3 (NS3) helicase-protease inhibitor (HPI), and the interaction of HPI with the NS3 protease inhibitors telaprevir, boceprevir, danoprevir, and grazoprevir. HPI most effectively reduced cellular levels of subgenomic genotype 4a replicons, followed by genotypes 3a and 1b replicons. HPI had no effect on HCV genotype 2a or dengue virus replicon levels. Resistance evolved more slowly to HPI than telaprevir, and HPI inhibited telaprevir-resistant replicons. Molecular modeling and analysis of the ability of HPI to inhibit peptide hydrolysis catalyzed by a variety of wildtype and mutant NS3 proteins suggested that HPI forms a bridge between the NS3 RNA-binding cleft and an allosteric site previously shown to bind other protease inhibitors. In most combinations, the antiviral effect of HPI was additive with telaprevir and boceprevir, minor synergy was observed with danoprevir, and modest synergy was observed with grazoprevir.