Ginsenoside Rg3 restores hepatitis C virus-induced aberrant mitochondrial dynamics and inhibits virus propagation.

Hepatitis C virus (HCV) alters mitochondrial dynamics associated with persistent viral infection and suppression of innate immunity. Mitochondrial dysfunction is also a pathologic feature of direct-acting antiviral (DAA) treatment. Despite the high efficacy of DAAs, their use in treating patients with chronic hepatitis C in interferon-sparing regimens occasionally produces undesirable side effects such as fatigue, migraine, and other conditions, which may be linked to mitochondrial dysfunction. Here, we show that clinically prescribed DAAs, including sofosbuvir, affect mitochondrial dynamics. To counter these adverse effects, we examined HCV-induced and DAA-induced aberrant mitochondrial dynamics modulated by ginsenoside, which is known to support healthy mitochondrial physiology and the innate immune system. We screened several ginsenoside compounds showing antiviral activity using a robust HCV cell culture system. We investigated the role of ginsenosides in antiviral efficacy, alteration of mitochondrial transmembrane potential, abnormal mitochondrial fission, its upstream signaling, and mitophagic process caused by HCV infection or DAA treatment. Only one of the compounds, ginsenoside Rg3 (G-Rg3), exhibited notable and promising anti-HCV potential. Treatment of HCV-infected cells with G-Rg3 increased HCV core protein-mediated reduction in the expression level of cytosolic p21, required for increasing cyclin-dependent kinase 1 activity, which catalyzes Ser616 phosphorylation of dynamin-related protein 1. The HCV-induced mitophagy, which follows mitochondrial fission, was also rescued by G-Rg3 treatment. CONCLUSION: G-Rg3 inhibits HCV propagation. Its antiviral mechanism involves restoring the HCV-induced dynamin-related protein 1-mediated aberrant mitochondrial fission process, thereby resulting in suppression of persistent HCV infection. (Hepatology 2017;66:758-771).

Multifaceted therapeutic targeting of ovarian peritoneal carcinomatosis through virus-induced immunomodulation.

Immunosuppression associated with ovarian cancer (OC) and resultant peritoneal carcinomatosis (PC) hampers the efficacy of many promising treatment options, including immunotherapies. It is hypothesized that oncolytic virus-based therapies can simultaneously kill OC and mitigate immunosuppression. Currently, reovirus-based anticancer therapy is undergoing phase I/II clinical trials for the treatment of OC. Hence, this study was focused on characterizing the effects of reovirus therapy on OC and associated immune microenvironment. Our data shows that reovirus efficiently killed OC cells and induced higher expression of the molecules involved in antigen presentation including major histocompatibility complex (MHC) class I, ß2-microglobulin (ß2M), TAP-1, and TAP-2. In addition, in the presence of reovirus, dendritic cells (DCs) overcame the OC-mediated phenotypic suppression and successfully stimulated tumor-specific CD8+ T cells. In animal studies, reovirus targeted local and distal OC, alleviated the severity of PC and significantly prolonged survival. These therapeutic effects were accompanied by decreased frequency of suppressive cells, e.g., Gr1.1+, CD11b+ myeloid derived suppressor cells (MDSCs), and CD4+, CD25+, FOXP3+ Tregs, tumor-infiltration of CD3+ cells and higher expression of Th1 cytokines. Finally, reovirus therapy during early stages of OC also resulted in the postponement of PC development. This report elucidates timely information on a therapeutic approach that can target OC through clinically desired multifaceted mechanisms to better the outcomes.

Structural safety analysis based on seismic service conditions for butterfly valves in a nuclear power plant.

The structural integrity of valves that are used to control cooling waters in the primary coolant loop that prevents boiling within the reactor in a nuclear power plant must be capable of withstanding earthquakes or other dangerous situations. In this study, numerical analyses using a finite element method, that is, static and dynamic analyses according to the rigid or flexible characteristics of the dynamic properties of a 200A butterfly valve, were performed according to the KEPIC MFA. An experimental vibration test was also carried out in order to verify the results from the modal analysis, in which a validated finite element model was obtained via a model-updating method that considers changes in the in situ experimental data. By using a validated finite element model, the equivalent static load under SSE conditions stipulated by the KEPIC MFA gave a stress of 135 MPa that occurred at the connections of the stem and body. A larger stress of 183 MPa was induced when we used a CQC method with a design response spectrum that uses 2% damping ratio. These values were lower than the allowable strength of the materials used for manufacturing the butterfly valve, and, therefore, its structural safety met the KEPIC MFA requirements.

Reovirus variants with mutations in genome segments S1 and L2 exhibit enhanced virion infectivity and superior oncolysis.

Reovirus preferentially replicates in transformed cells and is being explored as a cancer therapy. Immunological and physical barriers to virotherapy inspired a quest for reovirus variants with enhanced oncolytic potency. Using a classical genetics approach, we isolated two reovirus variants (T3v1 and T3v2) with superior replication relative to wild-type reovirus serotype 3 Dearing (T3wt) on various human and mouse tumorigenic cell lines. Unique mutations in reovirus λ2 vertex protein and σ1 cell attachment protein were associated with the large plaque-forming phenotype of T3v1 and T3v2, respectively. Both T3v1 and T3v2 exhibited higher infectivity (i.e., a higher PFU-to-particle ratio) than T3wt. A detailed analysis of virus replication revealed that virus cell binding and uncoating were equivalent for variant and wild-type reoviruses. However, T3v1 and T3v2 were significantly more efficient than T3wt in initiating productive infection. Thus, when cells were infected with equivalent input virus particles, T3v1 and T3v2 produced significantly higher levels of early viral RNAs relative to T3wt. Subsequent steps of virus replication (viral RNA and protein synthesis, virus assembly, and cell death) were equivalent for all three viruses. In a syngeneic mouse model of melanoma, both T3v1 and T3v2 prolonged mouse survival compared to wild-type reovirus. Our studies reveal that oncolytic potency of reovirus can be improved through distinct mutations that increase the infectivity of reovirus particles.

Current Status of Epidemiology, Diagnosis, Therapeutics, and Vaccines for the Re-Emerging Human Monkeypox Virus.

Monkeypox (Mpox) virus, a member of the Poxviridae family, causes a severe illness similar to smallpox, which is characterized by symptoms such as high fever, rash, and pustules. Human-to-human transmission cases have been reported but remained low since the first recorded case of human infection occurred in the Congo in 1970. Recently, Mpox has re-emerged, leading to an alarming surge in infections worldwide since 2022, originating in the United Kingdom. Consequently, the World Health Organization (WHO) officially declared the '2022-23 Mpox outbreak'. Currently, no specific therapy or vaccine is available for Mpox. Therefore, patients infected with Mpox are treated using conventional therapies developed for smallpox. However, the vaccines developed for smallpox have demonstrated only partial efficacy against Mpox, allowing viral transmission among humans. In this review, we discuss the current epidemiology of the ongoing Mpox outbreak and provide an update on the progress made in diagnosis, treatment, and development of vaccines for Mpox.

Biochemical characterization of a recombinant SARS coronavirus nsp12 RNA-dependent RNA polymerase capable of copying viral RNA templates.

The severe acute respiratory syndrome coronavirus (SARS-CoV) RNA genome is replicated by a virus-encoded RNA replicase, the key component of which is the nonstructural protein 12 (nsp12). In this report, we describe the biochemical properties of a full-length recombinant SARS-CoV nsp12 RNA-dependent RNA polymerase (RdRp) capable of copying viral RNA templates. The purified SARS-CoV nsp12 showed both primer-dependent and primer-independent RNA synthesis activities using homopolymeric RNA templates. The RdRp activity was strictly dependent on Mn(2+). The nsp12 preferentially copied homopolymeric pyrimidine RNA templates in the absence of an added oligonucleotide primer. It was also able to initiate de novo RNA synthesis from the 3'-ends of both the plus- and minus-strand genome of SARS-CoV, using the 3'-terminal 36- and 37-nt RNA, respectively. The in vitro RdRp assay system established with a full-length nsp12 will be useful for understanding the mechanisms of coronavirus replication and for the development of anti-SARS-CoV agents.

Distinct Molecular Mechanisms Characterizing Pathogenesis of SARS-CoV-2.

The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) pandemic has continued for over 2 years, following the outbreak of coronavirus-19 (COVID-19) in 2019. It has resulted in enormous casualties and severe economic crises. The rapid development of vaccines and therapeutics against SARS-CoV-2 has helped slow the spread. In the meantime, various mutations in the SARS-CoV-2 have emerged to evade current vaccines and therapeutics. A better understanding of SARS-CoV-2 pathogenesis is a prerequisite for developing efficient, advanced vaccines and therapeutics. Since the outbreak of COVID-19, a tremendous amount of research has been conducted to unveil SARSCoV-2 pathogenesis, from clinical observations to biochemical analysis at the molecular level upon viral infection. In this review, we discuss the molecular mechanisms of SARS-CoV-2 propagation and pathogenesis, with an update on recent advances.

Escape and Over-Activation of Innate Immune Responses by SARS-CoV-2: Two Faces of a Coin.

In the past 20 years, coronaviruses (CoVs), including SARS-CoV-1, MERS-CoV, and SARS-CoV-2, have rapidly evolved and emerged in the human population. The innate immune system is the first line of defense against invading pathogens. Multiple host cellular receptors can trigger the innate immune system to eliminate invading pathogens. However, these CoVs have acquired strategies to evade innate immune responses by avoiding recognition by host sensors, leading to impaired interferon (IFN) production and antagonizing of the IFN signaling pathways. In contrast, the dysregulated induction of inflammasomes, leading to uncontrolled production of IL-1 family cytokines (IL-1ß and IL-18) and pyroptosis, has been associated with COVID-19 pathogenesis. This review summarizes innate immune evasion strategies employed by SARS-CoV-1 and MERS-CoV in brief and SARS-CoV-2 in more detail. In addition, we outline potential mechanisms of inflammasome activation and evasion and their impact on disease prognosis.

Immunological and Pathological Peculiarity of Severe Acute Respiratory Syndrome Coronavirus 2 Beta Variant.

Diverse severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) variants have emerged since the beginning of the COVID-19 pandemic. We investigated the immunological and pathological peculiarity of the SARS-CoV-2 beta variant of concern (VoC) compared to the ancestral strain. Comparative analysis of phenotype and pathology revealed that the beta VoC induces slower disease progression and a prolonged presymptomatic period in the early stages of SARS-CoV-2 infection but ultimately causes sudden death in the late stages of infection in the K18-hACE2 mouse model. The beta VoC induced enhanced activation of CXCL1/2-CXCR2-NLRP3-IL-1ß signal cascade accelerating neutrophil recruitment and lung pathology in beta variant-infected mice, as evidenced by multiple analyses of SARS-CoV-2-induced inflammatory cytokines and transcriptomes. CCL2 was one of the most highly secreted cytokines in the early stages of infection. Its blockade reduced virus-induced weight loss and delayed mortality. Our study provides a better understanding of the variant characteristics and need for treatment. IMPORTANCE Since the outbreak of COVID-19, diverse SARS-CoV-2 variants have been identified. These variants have different infectivity and transmissibility from the ancestral strains. However, underlying molecular mechanisms have not yet been fully elucidated. In our study, the beta variant showed distinct pathological conditions and cytokine release kinetics from an ancestral strain in a mouse model. It was associated with higher neutrophil recruitment by increased levels of CXCL1/2, CXCR2, and interleukin 1ß (IL-1ß) at a later stage of viral infection. Our study will provide a better understanding of SARS-CoV-2 pathogenesis.

Ocular tropism of SARS-CoV-2 in animal models with retinal inflammation via neuronal invasion following intranasal inoculation.

Although ocular manifestations are reported in patients with COVID-19, consensus on ocular tropism of SARS-CoV-2 is lacking. Here, we infect K18-hACE2 transgenic mice with SARS-CoV-2 using various routes. We observe ocular manifestation and retinal inflammation with production of pro-inflammatory cytokines in the eyes of intranasally (IN)-infected mice. Intratracheal (IT) infection results in dissemination of the virus from the lungs to the brain and eyes via trigeminal and optic nerves. Ocular and neuronal invasions are confirmed using intracerebral (IC) infection. Notably, the eye-dropped (ED) virus does not cause lung infection and becomes undetectable with time. Ocular and neurotropic distribution of the virus in vivo is evident in fluorescence imaging with an infectious clone of SARS-CoV-2-mCherry. The ocular tropic and neuroinvasive characteristics of SARS-CoV-2 are confirmed in wild-type Syrian hamsters. Our data can improve the understanding regarding viral transmission and clinical characteristics of SARS-CoV-2 and help in improving COVID-19 control procedures.

A screening study of high affinity peptide as molecular binder for AXL, tyrosine kinase receptor involving in Zika virus entry.

The recent extensive spread of Zika virus has led to increased interest in the development of early diagnostic tests. To the best of our knowledge, this is the first study to demonstrate the successful use of phage display to identify affinity peptides for quantitative analysis of AXL, a tyrosine kinase receptor involved in Zika virus entry. Biopanning of M13 phage library successfully identified a high affinity peptide, with the sequence AHNHTPIKQKYL. To study the feasibility of using free peptides for molecular recognition, we synthesized a series of amino acid-substituted peptides and examined their binding affinity for AXL using electrochemical impedance spectroscopy and square wave voltammetry. Most synthetic peptides had non-identical random coil structures based on circular dichroism spectroscopy. Of the peptides tested, AXL BP1 exhibited nanomolar binding affinity for AXL. To verify whether AXL BP1 could be used as a peptide inhibitor at the cellular level, two functional tests were carried out: a WST assay for cell viability and qRT-PCR for quantification of RNA levels in Zika virus-infected Huh7 cells. The results showed that AXL BP1 had low cytotoxicity and could block Zika virus entry. These results indicate that newly identified affinity peptides could potentially be used for the development of Zika virus entry inhibitors.

Structure-Based Virtual Screening: Identification of a Novel NS2B-NS3 Protease Inhibitor with Potent Antiviral Activity against Zika and Dengue Viruses.

Zika virus (ZIKV), which is associated with severe diseases in humans, has spread rapidly and globally since its emergence. ZIKV and dengue virus (DENV) are closely related, and antibody-dependent enhancement (ADE) of infection between cocirculating ZIKV and DENV may exacerbate disease. Despite these serious threats, there are currently no approved antiviral drugs against ZIKV and DENV. The NS2B-NS3 viral protease is an attractive antiviral target because it plays a pivotal role in polyprotein cleavage, which is required for viral replication. Thus, we sought to identify novel inhibitors of the NS2B-NS3 protease. To that aim, we performed structure-based virtual screening using 467,000 structurally diverse chemical compounds. Then, a fluorescence-based protease inhibition assay was used to test whether the selected candidates inhibited ZIKV protease activity. Among the 123 candidate inhibitors selected from virtual screening, compound 1 significantly inhibited ZIKV NS2B-NS3 protease activity in vitro. In addition, compound 1 effectively inhibited ZIKV and DENV infection of human cells. Molecular docking analysis suggested that compound 1 binds to the NS2B-NS3 protease of ZIKV and DENV. Thus, compound 1 could be used as a new therapeutic option for the development of more potent antiviral drugs against both ZIKV and DENV, reducing the risks of ADE.

In Vitro Replication Inhibitory Activity of Xanthorrhizol against Severe Acute Respiratory Syndrome Coronavirus 2.

In spite of the large number of repositioned drugs and direct-acting antivirals in clinical trials for the management of the ongoing COVID-19 pandemic, there are few cost-effective therapeutic options for severe acute respiratory syndrome (SARS) coronavirus 2 (SCoV2) infection. In this paper, we show that xanthorrhizol (XNT), a bisabolane-type sesquiterpenoid compound isolated from the Curcuma xanthorrhizza Roxb., a ginger-line plant of the family Zingiberaceae, displays a potent antiviral efficacy in vitro against SCoV2 and other related coronaviruses, including SARS-CoV-1 (SCoV1) and a common cold-causing human coronavirus. XNT reduced infectious SCoV2 titer by ~3-log10 at 20 µM and interfered with the replication of the SCoV1 subgenomic replicon, while it had no significant antiviral effects against hepatitis C virus and noroviruses. Further, XNT exerted similar antiviral functions against SCoV2 variants, such as a GH clade strain and a delta strain currently predominant worldwide. Neither SCoV2 entry into cells nor the enzymatic activity of viral RNA polymerase (Nsp12), RNA helicase (Nsp13), or the 3CL main protease (Nsp5) was inhibited by XNT. While its CoV replication inhibitory mechanism remains elusive, our results demonstrate that the traditional folk medicine XNT could be a promising antiviral candidate that inhibits a broad range of SCoV2 variants of concern and other related CoVs.

Comparison of Plaque Size, Thermal Stability, and Replication Rate among SARS-CoV-2 Variants of Concern.

SARS-CoV-2, like other RNA viruses, has a propensity for genetic evolution owing to the low fidelity of its viral polymerase. Several recent reports have described a series of novel SARS-CoV-2 variants. Some of these have been identified as variants of concern (VOCs), including alpha (B.1.1.7, Clade GRY), beta (B.1.351, Clade GH), gamma (P.1, Clade GR), and delta (B.1.617.2, Clade G). VOCs are likely to have some effect on transmissibility, antibody evasion, and changes in therapeutic or vaccine effectiveness. However, the physiological and virological understanding of these variants remains poor. We demonstrated that these four VOCs exhibited differences in plaque size, thermal stability at physiological temperature, and replication rates. The mean plaque size of beta was the largest, followed by those of gamma, delta, and alpha. Thermal stability, evaluated by measuring infectivity and half-life after prolonged incubation at physiological temperature, was correlated with plaque size in all variants except alpha. However, despite its relatively high thermal stability, alpha's small plaque size resulted in lower replication rates and fewer progeny viruses. Our findings may inform further virological studies of SARS-CoV-2 variant characteristics, VOCs, and variants of interest. These studies are important for the effective management of the COVID-19 pandemic.

A Novel Frameshifting Inhibitor Having Antiviral Activity against Zoonotic Coronaviruses.

Recent outbreaks of zoonotic coronaviruses, such as Middle East respiratory syndrome coronavirus (MERS-CoV) and severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), have caused tremendous casualties and great economic shock. Although some repurposed drugs have shown potential therapeutic efficacy in clinical trials, specific therapeutic agents targeting coronaviruses have not yet been developed. During coronavirus replication, a replicase gene cluster, including RNA-dependent RNA polymerase (RdRp), is alternatively translated via a process called -1 programmed ribosomal frameshift (-1 PRF) by an RNA pseudoknot structure encoded in viral RNAs. The coronavirus frameshifting has been identified previously as a target for antiviral therapy. In this study, the frameshifting efficiencies of MERS-CoV, SARS-CoV and SARS-CoV-2 were determined using an in vitro -1 PRF assay system. Our group has searched approximately 9689 small molecules to identify potential -1 PRF inhibitors. Herein, we found that a novel compound, 2-(5-acetylthiophen-2yl)furo[2,3-b]quinoline (KCB261770), inhibits the frameshifting of MERS-CoV and effectively suppresses viral propagation in MERS-CoV-infected cells. The inhibitory effects of 87 derivatives of furo[2,3-b]quinolines were also examined showing less prominent inhibitory effect when compared to compound KCB261770. We demonstrated that KCB261770 inhibits the frameshifting without suppressing cap-dependent translation. Furthermore, this compound was able to inhibit the frameshifting, to some extent, of SARS-CoV and SARS-CoV-2. Therefore, the novel compound 2-(5-acetylthiophen-2yl)furo[2,3-b]quinoline may serve as a promising drug candidate to interfere with pan-coronavirus frameshifting.

Receptor-binding domain of SARS-CoV-2 spike protein efficiently inhibits SARS-CoV-2 infection and attachment to mouse lung.

COVID-19, caused by a novel coronavirus, SARS-CoV-2, poses a serious global threat. It was first reported in 2019 in China and has now dramatically spread across the world. It is crucial to develop therapeutics to mitigate severe disease and viral spread. The receptor-binding domains (RBDs) in the spike protein of SARS-CoV and MERS-CoV have shown anti-viral activity in previous reports suggesting that this domain has high potential for development as therapeutics. To evaluate the potential antiviral activity of recombinant SARS-CoV-2 RBD proteins, we determined the RBD residues of SARS-CoV-2 using a homology search with RBD of SARS-CoV. For efficient expression and purification, the signal peptide of spike protein was identified and used to generate constructs expressing recombinant RBD proteins. Highly purified RBD protein fused with the Fc domain of human IgG showed potent anti-viral efficacy, which was better than that of a protein fused with a histidine tag. Intranasally pre-administrated RBD protein also inhibited the attachment of SARS-COV-2 to mouse lungs. These findings indicate that RBD protein could be used for the prevention and treatment of SARS-CoV-2 infection.

Robust and persistent SARS-CoV-2 infection in the human intestinal brush border expressing cells.

Studies on patients with the coronavirus disease-2019 (COVID-19) have implicated that the gastrointestinal (GI) tract is a major site of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection. We established a human GI tract cell line model highly permissive to SARS-CoV-2. These cells, C2BBe1 intestinal cells with a brush border having high levels of transmembrane serine protease 2 (TMPRSS2), showed robust viral propagation, and could be persistently infected with SARS-CoV-2, supporting the clinical observations of persistent GI infection in COVID-19 patients. Ectopic expression of viral receptors revealed that the levels of angiotensin-converting enzyme 2 (ACE2) expression confer permissiveness to SARS-CoV-2 infection, and TMPRSS2 greatly facilitates ACE2-mediated SARS-CoV-2 dissemination. Interestingly, ACE2 but not TMPRSS2 expression was significantly promoted by enterocytic differentiation, suggesting that the state of enterocytic differentiation may serve as a determining factor for viral propagation. Thus, our study sheds light on the pathogenesis of SARS-CoV-2 in the GI tract.

Antiviral efficacy of orally delivered neoagarohexaose, a nonconventional TLR4 agonist, against norovirus infection in mice.

The neoagarohexaose (NA6) is an oligosaccharide that is derived from agarose, the major component of red algae cell walls, by enzymatic hydrolysis. Here we show that NA6 is a noncanonical Toll-like receptor 4 (TLR4) agonist with antiviral activity against norovirus. Its TLR4 activation was dependent on myeloid differentiation factor 2 (MD2) and cluster of differentiation 14 (CD14), leading to interferon-ß (IFN-ß) and tumor necrosis factor-α (TNF-α) production. This effect was abolished by TLR4 knockdown or knockout in murine macrophages. NA6 inhibited murine norovirus (MNV) replication with an EC50 of 1.5 µM in RAW264.7 cells. It also lowered viral RNA titer in a human hepatocellular carcinoma Huh7-derived cell line harboring a human norovirus subgenomic replicon. The antiviral activity of NA6 was mainly attributed to IFN-ß produced through the TLR4-TRIF signaling pathway. NA6-induced TNF-α, which had little effect on norovirus replication per se, primed macrophages to mount greater antiviral innate immune responses when IFN signaling was activated. NA6 boosted the induction of IFN-ß in MNV-infected RAW264.7 cells and upregulated IFN-regulatory factor-1, an IFN-stimulated gene. NA6 induced IFN-ß expression in the distal ileum with Peyer's patches and oral administration of NA6 reduced MNV loads through activation of TLR4 signaling, highlighting its potential contribution to protective antiviral innate immunity against norovirus.

Current Status of Epidemiology, Diagnosis, Therapeutics, and Vaccines for Novel Coronavirus Disease 2019 (COVID-19).

Coronavirus disease 2019 (COVID-19), which causes serious respiratory illness such as pneumonia and lung failure, was first reported in Wuhan, the capital of Hubei, China. The etiological agent of COVID-19 has been confirmed as a novel coronavirus, now known as severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), which is most likely originated from zoonotic coronaviruses, like SARS-CoV, which emerged in 2002. Within a few months of the first report, SARS-CoV-2 had spread across China and worldwide, reaching a pandemic level. As COVID-19 has triggered enormous human casualties and serious economic loss posing global threat, an understanding of the ongoing situation and the development of strategies to contain the virus's spread are urgently needed. Currently, various diagnostic kits to test for COVID-19 are available and several repurposing therapeutics for COVID-19 have shown to be clinically effective. In addition, global institutions and companies have begun to develop vaccines for the prevention of COVID-19. Here, we review the current status of epidemiology, diagnosis, treatment, and vaccine development for COVID-19.

Regulation of hepatitis C virus replication by the core protein through its interaction with viral RNA polymerase.

The hepatitis C virus (HCV) core protein is a structural component of the nucleocapsid and has been shown to modulate cellular signaling pathways by interaction with various cellular proteins. In the present study, we investigated the role of HCV core protein in viral RNA replication. Immunoprecipitation experiments demonstrated that the core protein binds to the amino-terminal region of RNA-dependent RNA polymerase (RdRp), which encompasses the finger and palm domains. Direct interaction between HCV RdRp and core protein led to inhibition of RdRp RNA synthesis activity of in vitro. Furthermore, over-expression of core protein, but not its derivatives lacking the RdRp-interacting domain, suppressed HCV replication in a hepatoma cell line harboring an HCV subgenomic replicon RNA. Collectively, our results suggest that the core protein, through binding to RdRp and inhibiting its RNA synthesis activity, is a viral regulator of HCV RNA replication.