Ubiquitination is required for effective replication of coxsackievirus B3

Deciphering intricate plant-virus interactions: Potyvirids orchestrate protein posttranslational modifications to regulate pathogenicity

In a molecular-arm-race between viruses and their hosts, viruses have evolved to harness their host's post-translational modifications (PTMs) machinery to gain a competitive edge. These modifications are the most reliable target of plant viruses to overcome the host defence for successful infection. Relatively fewer PTMs i.e., phosphorylation, O-GlcNAcylation, Ubiquitination, and SUMOylation have been studied regulating the potyvirus-plant interaction. Therefore, it is worth drawing attention towards the importance and potential of this undermined but key strategy of potyvirids (members of family Potyviridae) to abduct their host defence line, suggesting to review in detail the existing knowledge of these PTMs and highlight the unexplored modifications that might have played their part in establishing successful infection. The current review provides an understanding of how PTMs execute viral replication and infection dynamics during plant-potyvirid interactions. We highlighted that PTMs linked to CP, NIa-pro, NIb, and VPg are important to specify their host, virulence, overcoming host innate immunity, and most importantly disarming the host of RNA silencing tool of nailing any intruder. The limitations and potential improvements in studying undermined PTMs, including acetylation, glycosylation, methylation, and neddylation, as well as challenges and future perspectives of this inevitable process are mechanistically deciphered in the course of plant-virus interactions. This communication opens new avenues for investigating the fundamental mechanisms of virus infection and the development of new antiviral strategies for sustainable disease managements.

TRIM56 restricts Coxsackievirus B infection by mediating the ubiquitination of viral RNA-dependent RNA polymerase 3D

Coxsackievirus B (CVB) is the major causative pathogen for severe diseases such as viral myocarditis, meningitis, and pancreatitis. There is no effective antiviral therapy currently available for CVB infection primarily due to that the pathogenesis of CVB has not been completely understood. Viruses are obligate intracellular pathogens which subvert cellular processes to ensure viral replication. Dysregulation of ubiquitination has been implicated in CVB infection. However, how ubiquitination is involved in CVB infection remains unclear. Here we found that the 3D protein of CVB3, the RNA-dependent RNA polymerase, was modified at K220 by K48-linked polyubiquitination which promoted its degradation through proteasome. Proteomic analysis showed that the E3 ligase TRIM56 was upregulated in CVB3-infected cells, while the majority of TRIMs remained unchanged. Pull-down and immunoprecipitation analyses showed that TRIM56 interacted with CVB3 3D. Immunofluorescence observation showed that viral 3D protein was colocalized with TRIM56. TRIM56 overexpression resulted in enhanced ubiquitination of CVB3 3D and decreased virus yield. Moreover, TRIM56 was cleaved by viral 3C protease in CVB3-infected cells. Taken together, this study demonstrated that TRIM56 mediates the ubiquitination and proteasomal degradation of the CVB3 3D protein. These findings demonstrate that TRIM56 is an intrinsic cellular restriction factor against CVB infection, and enhancing viral protein degradation could be a potential strategy to control CVB infection.

Multiple functions of the nonstructural protein 3D in picornavirus infection

3D polymerase, also known as RNA-dependent RNA polymerase, is encoded by all known picornaviruses, and their structures are highly conserved. In the process of picornavirus replication, 3D polymerase facilitates the assembly of replication complexes and directly catalyzes the synthesis of viral RNA. The nuclear localization signal carried by picornavirus 3D polymerase, combined with its ability to interact with other viral proteins, viral RNA and cellular proteins, indicate that its noncatalytic role is equally important in viral infections. Recent studies have shown that 3D polymerase has multiple effects on host cell biological functions, including inducing cell cycle arrest, regulating host cell translation, inducing autophagy, evading immune responses, and triggering inflammasome formation. Thus, 3D polymerase would be a very valuable target for the development of antiviral therapies. This review summarizes current studies on the structure of 3D polymerase and its regulation of host cell responses, thereby improving the understanding of picornavirus-mediated pathogenesis caused by 3D polymerase.

Crosstalk between ubiquitin ligases and ncRNAs drives cardiovascular disease progression

Cardiovascular diseases (CVDs) are multifactorial chronic diseases and have the highest rates of morbidity and mortality worldwide. The ubiquitin-proteasome system (UPS) plays a crucial role in posttranslational modification and quality control of proteins, maintaining intracellular homeostasis via degradation of misfolded, short-lived, or nonfunctional regulatory proteins. Noncoding RNAs (ncRNAs, such as microRNAs, long noncoding RNAs, circular RNAs and small interfering RNAs) serve as epigenetic factors and directly or indirectly participate in various physiological and pathological processes. NcRNAs that regulate ubiquitination or are regulated by the UPS are involved in the execution of target protein stability. The cross-linked relationship between the UPS, ncRNAs and CVDs has drawn researchers' attention. Herein, we provide an update on recent developments and perspectives on how the crosstalk of the UPS and ncRNAs affects the pathological mechanisms of CVDs, particularly myocardial ischemia/reperfusion injury, myocardial infarction, cardiomyopathy, heart failure, atherosclerosis, hypertension, and ischemic stroke. In addition, we further envision that RNA interference or ncRNA mimics or inhibitors targeting the UPS can potentially be used as therapeutic tools and strategies.

Role of protein Post-translational modifications in enterovirus infection

Enteroviruses (EVs) are the main cause of a number of neurological diseases. Growing evidence has revealed that successful infection with enteroviruses is highly dependent on the host machinery, therefore, host proteins play a pivotal role in viral infections. Both host and viral proteins can undergo post-translational modification (PTM) which can regulate protein activity, stability, solubility and interactions with other proteins; thereby influencing various biological processes, including cell metabolism, metabolic, signaling pathways, cell death, and cancer development. During viral infection, both host and viral proteins regulate the viral life cycle through various PTMs and different mechanisms, including the regulation of host cell entry, viral protein synthesis, genome replication, and the antiviral immune response. Therefore, protein PTMs play important roles in EV infections. Here, we review the role of various host- and virus-associated PTMs during enterovirus infection.

Influenza A virus uses PSMA2 for downregulation of NRF2-mediated oxidative stress response

Influenza A virus (IAV), an obligatory intracellular parasite, uses host cellular molecules to complete its replication cycle and suppress immune responses. Proteasome subunit alpha type 2 (PSMA2) is a cellular protein highly expressed in IAV-infected human lung epithelial A549 cells. PSMA2 is part of the 20S proteasome complex that degrades or recycles defective proteins and involves proteolytic modification of many cellular regulatory proteins. However, the role of PSMA2 in IAV replication is not well understood. In this study, PSMA2 knockdown (KD) in A549 cells caused a significant reduction in extracellular progeny IAV, but intracellular viral protein translation and viral RNA transcription were not affected. This indicates that PSMA2 is a critical host factor for IAV maturation. To better understand the interplay between PSMA2 KD and IAV infection at the proteomic level, we used the SomaScan 1.3K version, which measures 1,307 proteins to analyze alterations induced by these treatments. We found seven cellular signaling pathways, including phospholipase C signaling, Pak signaling, and nuclear factor erythroid 2p45-related factor 2 (NRF2)-mediated oxidative stress response signaling, that were inhibited by IAV infection but significantly activated by PSMA2 KD. Further analysis of NRF2-mediated oxidative stress response signaling indicated IAV inhibits accumulation of reactive oxygen species (ROS), but ROS levels significantly increased during IAV infection in PSMA2 KD cells. However, IAV infection caused significantly higher NFR2 nuclear translocation that was inhibited in PSMA2 KD cells. This indicates that PSMA2 is required for NRF2-mediated ROS neutralization and that IAV uses PSMA2 to escape viral clearance via the NRF2-mediated cellular oxidative response.

IMPORTANCE Influenza A virus (IAV) remains one of the most significant infectious agents, responsible for 3 million to 5 million illnesses each year and more than 50 million deaths during the 20th century. The cellular processes that promote and inhibit IAV infection and pathogenesis remain only partially understood. PSMA2 is a critical component of the 20S proteasome and ubiquitin-proteasome system, which is important in the replication of numerous viruses. This study examined host protein responses to IAV infection alone, PSMA2 knockdown alone, and IAV infection in the presence of PSMA2 knockdown and determined that interfering with PSMA2 function affected IAV maturation. These results help us better understand the importance of PSMA2 in IAV replication and may pave the way for designing additional IAV antivirals targeting PSMA2 or the host proteasome for the treatment of seasonal flu.

Monocyte Chemotactic Protein-Induced Protein 1 (MCPIP-1): A Key Player of Host Defense and Immune Regulation

Inflammatory response is a host-protective mechanism against tissue injury or infections, but also has the potential to cause extensive immunopathology and tissue damage, as seen in many diseases, such as cardiovascular diseases, neurodegenerative diseases, metabolic syndrome and many other infectious diseases with public health concerns, such as Coronavirus Disease 2019 (COVID-19), if failure to resolve in a timely manner. Recent studies have uncovered a superfamily of endogenous chemical molecules that tend to resolve inflammatory responses and re-establish homeostasis without causing excessive damage to healthy cells and tissues. Among these, the monocyte chemoattractant protein-induced protein (MCPIP) family consisting of four members (MCPIP-1, -2, -3, and -4) has emerged as a group of evolutionarily conserved molecules participating in the resolution of inflammation. The focus of this review highlights the biological functions of MCPIP-1 (also known as Regnase-1), the best-studied member of this family, in the resolution of inflammatory response. As outlined in this review, MCPIP-1 acts on specific signaling pathways, in particular NFκB, to blunt production of inflammatory mediators, while also acts as an endonuclease controlling the stability of mRNA and microRNA (miRNA), leading to the resolution of inflammation, clearance of virus and dead cells, and promotion of tissue regeneration via its pleiotropic effects. Evidence from transgenic and knock-out mouse models revealed an involvement of MCPIP-1 expression in immune functions and in the physiology of the cardiovascular system, indicating that MCPIP-1 is a key endogenous molecule that governs normal resolution of acute inflammation and infection. In this review, we also discuss the current evidence underlying the roles of other members of the MCPIP family in the regulation of inflammatory processes. Further understanding of the proteins from this family will provide new insights into the identification of novel targets for both host effectors and microbial factors and will lead to new therapeutic treatments for infections and other inflammatory diseases.

Antiviral strategies targeting host factors and mechanisms obliging +ssRNA viral pathogens

The ongoing COVID-19 pandemic, periodic recurrence of viral infections, and the emergence of challenging variants has created an urgent need of alternative therapeutic approaches to combat the spread of viral infections, failing to which may pose a greater risk to mankind in future. Resilience against antiviral drugs or fast evolutionary rate of viruses is stressing the scientific community to identify new therapeutic approaches for timely control of disease. Host metabolic pathways are exquisite reservoir of energy to viruses and contribute a diverse array of functions for successful replication and pathogenesis of virus. Targeting the host factors rather than viral enzymes to cease viral infection, has emerged as an alternative antiviral strategy. This approach offers advantage in terms of increased threshold to viral resistance and can provide broad-spectrum antiviral action against different viruses. The article here provides substantial review of literature illuminating the host factors and molecular mechanisms involved in innate/adaptive responses to viral infection, hijacking of signalling pathways by viruses and the intracellular metabolic pathways required for viral replication. Host-targeted drugs acting on the pathways usurped by viruses are also addressed in this study. Host-directed antiviral therapeutics might prove to be a rewarding approach in controlling the unprecedented spread of viral infection, however the probability of cellular side effects or cytotoxicity on host cell should not be ignored at the time of clinical investigations.

Coxsackievirus B3 Exploits the Ubiquitin-Proteasome System to Facilitate Viral Replication

Infection by RNA viruses causes extensive cellular reorganization, including hijacking of membranes to create membranous structures termed replication organelles, which support viral RNA synthesis and virion assembly. In this study, we show that infection with coxsackievirus B3 entails a profound impairment of the protein homeostasis at virus-utilized membranes, reflected by an accumulation of ubiquitinylated proteins, including K48-linked polyubiquitin conjugates, known to direct proteins to proteasomal degradation. The enrichment of membrane-bound ubiquitin conjugates is attributed to the presence of the non-structural viral proteins 2B and 3A, which are known to perturb membrane integrity and can cause an extensive rearrangement of cellular membranes. The locally increased abundance of ubiquitinylated proteins occurs without an increase of oxidatively damaged proteins. During the exponential phase of replication, the oxidative damage of membrane proteins is even diminished, an effect we attribute to the recruitment of glutathione, which is known to be required for the formation of infectious virus particles. Furthermore, we show that the proteasome contributes to the processing of viral precursor proteins. Taken together, we demonstrate how an infection with coxsackievirus B3 affects the cellular protein and redox homeostasis locally at the site of viral replication and virus assembly.

TRIM7 inhibits enterovirus replication and promotes emergence of a viral variant with increased pathogenicity

To control viral infection, vertebrates rely on both inducible interferon responses and less well-characterized cell-intrinsic responses composed of "at the ready" antiviral effector proteins. Here, we show that E3 ubiquitin ligase TRIM7 is a cell-intrinsic antiviral effector that restricts multiple human enteroviruses by targeting viral 2BC, a membrane remodeling protein, for ubiquitination and proteasome-dependent degradation. Selective pressure exerted by TRIM7 results in emergence of a TRIM7-resistant coxsackievirus with a single point mutation in the viral 2C ATPase/helicase. In cultured cells, the mutation helps the virus evade TRIM7 but impairs optimal viral replication, and this correlates with a hyperactive and structurally plastic 2C ATPase. Unexpectedly, the TRIM7-resistant virus has a replication advantage in mice and causes lethal pancreatitis. These findings reveal a unique mechanism for targeting enterovirus replication and provide molecular insight into the benefits and trade-offs of viral evolution imposed by a host restriction factor.

IKKε isoform switching governs the immune response against EV71 infection

The reciprocal interactions between pathogens and hosts are complicated and profound. A comprehensive understanding of these interactions is essential for developing effective therapies against infectious diseases. Interferon responses induced upon virus infection are critical for establishing host antiviral innate immunity. Here, we provide a molecular mechanism wherein isoform switching of the host IKKε gene, an interferon-associated molecule, leads to alterations in IFN production during EV71 infection. We found that IKKε isoform 2 (IKKε v2) is upregulated while IKKε v1 is downregulated in EV71 infection. IKKε v2 interacts with IRF7 and promotes IRF7 activation through phosphorylation and translocation of IRF7 in the presence of ubiquitin, by which the expression of IFNβ and ISGs is elicited and virus propagation is attenuated. We also identified that IKKε v2 is activated via K63-linked ubiquitination. Our results suggest that host cells induce IKKε isoform switching and result in IFN production against EV71 infection. This finding highlights a gene regulatory mechanism in pathogen-host interactions and provides a potential strategy for establishing host first-line defense against pathogens.

Design and synthesis of new 4-(2-nitrophenoxy)benzamide derivatives as potential antiviral agents: molecular modeling and in vitro antiviral screening

Novel benzamide derivatives as anti adenovirus, HSV-1, coxsackievirus, and SARS-CoV-2: in vitro and in silico study.

The ubiquitin proteasome system is necessary for efficient proliferation of porcine reproductive and respiratory syndrome virus

The ubiquitin-proteasome system (UPS) plays a vital role in cellular protein homeostasis by ensuring protein quality control and maintaining a critical level of important regulatory proteins. Thus, it is not surprising that the functional UPS is manipulated by viruses to assist in viral propagation. Porcine reproductive and respiratory syndrome virus (PRRSV) is an economically significant swine disease that has been devastating the swine industry worldwide. However, the role of UPS in PRRSV infection is unknown. In this study, we found that treatment with the proteasome inhibitor MG132 significantly inhibited PRRSV proliferation in a dose-dependent manner. The anti-PRRSV effect of MG132 was most significant in the middle stage of the PRRSV lifecycle, which is achieved via inhibition of viral attachment and replication. Interestingly, the expression of poly-ubiquitin was drastically decreased and the accumulation of free-ubiquitin was obviously elevated in the middle stage of PRRSV infection. Furthermore, the ectopic expression of ubiquitin in MG132-treated cells partially reversed the inhibitory effect of MG132 on PRRSV proliferation. Taken together, these results suggest that PRRSV manipulates UPS to promote self-proliferation by cheating or taking advantage of the host proteasome, degrading intracellular poly-ubiquitin and increasing the accumulation of free ubiquitin.

E2 ubiquitin-conjugating enzyme UBE2L6 promotes Senecavirus A proliferation by stabilizing the viral RNA polymerase

Senecavirus A (SVA), discovered in 2002, is an emerging pathogen of swine that has since been reported in numerous pork producing countries. To date, the mechanism of SVA replication remains poorly understood. In this study, utilizing iTRAQ analysis we found that UBE2L6, an E2 ubiquitin-conjugating enzyme, is up-regulated in SVA-infected BHK-21 cells, and that its overexpression promotes SVA replication. We determined that UBE2L6 interacts with, and ubiquitinates the RNA-dependent RNA polymerase of SVA, (the 3D protein) and this ubiquitination serves to inhibit the degradation of 3D. UBE2L6-mediated ubiquitination of 3D requires a cystine at residue 86 in UBE2L6, and lysines at residues 169 and 321 in 3D. Virus with mutations in 3D (rK169R and rK321R) exhibited significantly decreased replication compared to wild type SVA and the repaired viruses, rK169R(R) and rK321R(R). These data indicate that UBE2L6, the enzyme, targets the 3D polymerase, the substrate, during SVA infection to facilitate replication.

Senecavirus A (SVA) is a newly emerging pathogen causing swine idiopathic vesicular disease and epidemic transient neonatal losses. Infections have been reported in many pork producing countries, yet the mechanism of SVA replication remains poorly understood. In this study, we found that UBE2L6, an E2 ubiquitin-conjugating enzyme, is up-regulated in SVA-infected BHK-21 cells. The viral RNA dependent RNA polymerase (RdRp) 3D is ubiquitinated by UBE2L6, and the lysines at residues 169 and 321 of 3D are the required ubiquitination sites. The level of replication of recombinant viruses harboring ubiquitination-deficient 3D was significantly decreased compared to parental SVA. Our data demonstrate that UBE2L6 ubiquitinates SVA 3D, thereby facilitating SVA infection. These results may make it possible to identify novel targets for disease treatment.

MG132 Attenuates the Replication of Classical Swine Fever Virus in vitro

The 26S proteasome, in charge of intracellular protein degradation, plays significant roles in the modulation of various cellular activities as well as in the interplay between virus and host. However, studies about the relationship between 26S proteasome and classical swine fever virus (CSFV) is limited up to now. MG132 is a proteasome inhibitor and has been extensively used in studies about replication of many viruses. Herein, we investigated the role of MG132 in CSFV replication and results showed that MG132 significantly decreased virus titers and viral RNA copies in CSFV-infected PK-15 cells. Further studies demonstrated that MG132 upregulated the expression of several interferon-stimulated genes (ISGs), in CSFV-infected cells. Since the activation of ISGs is controlled by the JAK-STAT signal pathway, we next examined the effect of MG132 on the expression and localization of key molecular STAT1 in the infected cells using Western blot and confocal laser scanning microscopy, respectively. Results showed that CSFV infection and viral NS4A protein decreased the protein level of STAT1, and MG132 promoted the accumulation of STAT1 in the nucleus of cells adjacent to the CSFV-infected cells. Besides, MG132 did not affect the expressions of IFN-α, STAT1, Mx1, OAS1, and PKR genes in cells without CSFV. In conclusion, we identify that MG132 significantly inhibits CSFV replication in vitro, in which the activation of the JAK-STAT pathway and the subsequent upregulation of expressions of ISGs might play significant roles, providing a potential preventive method for CSF.

The ubiquitin-proteasome system is necessary for the replication of duck Tembusu virus

Duck Tembusu virus (DTMUV) is a newly emerging pathogenic flavivirus that has caused massive economic losses to the duck industry in China. The cellular factors required for DTMUV replication have been poorly studied. The ubiquitin-proteasome system (UPS), the major intracellular proteolytic pathway, mediates diverse cellular processes, including endocytosis and signal transduction, which may be involved in the entry of virus. In the present study, we explored the interplay between DTMUV replication and the UPS in BHK-21 cells and found that treatment with proteasome inhibitor (MG132 and lactacystin) significantly decreased the DTMUV progency at the early infection stage. We further revealed that inhibition of the UPS mainly occurs on the level of viral protein expression and RNA transcription. In addition, using specific siRNAs targeting ubiquitin reduces the production of viral progeny. In the presence of MG132 the staining for the envelope protein of DTMUV was dramatically reduced in comparison with the untreated control cells. Overall, our observations reveal an important role of the UPS in multiple steps of the DTMUV infection cycle and identify the UPS as a potential drug target to modulate the impact of DTMUV infection.

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Treatment with proteasome inhibitor significantly decreased the DTMUV progency.

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Inhibition of the UPS mainly occurs on the level of viral protein expression and RNA transcription.

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Inhibit the expression of ubiquitin reduces the production of viral progeny.

Ubiquitin-Proteasome System Is Required for Efficient Replication of Singapore Grouper Iridovirus

The ubiquitin-proteasome system (UPS) serves as the major intracellular pathway for protein degradation and plays crucial roles in several cellular processes. However, little is known about the potential actions of the UPS during fish virus infection. In this study, we elucidated the possible roles of UPS in the life cycle of Singapore grouper iridovirus (SGIV); a large DNA virus that usually causes serious systemic diseases with high mortality in groupers. Data from transcriptomic analysis of differentially expressed genes illustrated that expression of 65 genes within the UPS pathway, including ubiquitin encoding, ubiquitination, deubiquitination, and proteasome, were up- or down-regulated during SGIV infection. Using different proteasome inhibitors, inhibition of the proteasome decreased SGIV replication in vitro, accompanied by inhibition of virus assembly site formation, and viral gene transcription and protein transportation. Over-expression of ubiquitin partly rescued the inhibitory effect of ubiquitin inhibitor on SGIV replication, suggesting that UPS was required for fish iridovirus infection in vitro. Viral or host proteins regulated by proteasome inhibition during SGIV infection were investigated with two-dimensional gel electrophoresis and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry. Sixty-two differentially expressed proteins, including 15 viral and 47 host proteins, were identified after SGIV infection. The host proteins were involved in ubiquitin-mediated protein degradation, metabolism, cytoskeleton, macromolecular biosynthesis, and signal transduction. Among them, 11 proteins were negatively regulated upon MG132 treatment during SGIV infection. This is believed to be the first study to provide evidence that UPS was essential for fish virus infection and replication.

Inhibitors of Deubiquitinating Enzymes Block HIV-1 Replication and Augment the Presentation of Gag-Derived MHC-I Epitopes

In recent years it has been well established that two major constituent parts of the ubiquitin proteasome system (UPS)—the proteasome holoenzymes and a number of ubiquitin ligases—play a crucial role, not only in virus replication but also in the regulation of the immunogenicity of human immunodeficiency virus type 1 (HIV-1). However, the role in HIV-1 replication of the third major component, the deubiquitinating enzymes (DUBs), has remained largely unknown. In this study, we show that the DUB-inhibitors (DIs) P22077 and PR-619, specific for the DUBs USP7 and USP47, impair Gag processing and thereby reduce the infectivity of released virions without affecting viral protease activity. Furthermore, the replication capacity of X4- and R5-tropic HIV-1_NL4-3 in human lymphatic tissue is decreased upon treatment with these inhibitors without affecting cell viability. Most strikingly, combinatory treatment with DIs and proteasome inhibitors synergistically blocks virus replication at concentrations where mono-treatment was ineffective, indicating that DIs can boost the therapeutic effect of proteasome inhibitors. In addition, P22077 and PR-619 increase the polyubiquitination of Gag and thus its entry into the UPS and the major histocompatibility complex (MHC)-I pathway. In summary, our data point towards a model in which specific inhibitors of DUBs not only interfere with virus spread but also increase the immune recognition of HIV-1 expressing cells.

iTRAQ-based quantitative proteomics analysis of molecular mechanisms associated with Bombyx mori (Lepidoptera) larval midgut response to BmNPV in susceptible and near-isogenic strains

Bombyx mori nucleopolyhedrovirus (BmNPV) has been identified as a major pathogen responsible for severe economic loss. Most silkworm strains are susceptible to BmNPV, with only a few highly resistant strains thus far identified. Here we investigated the molecular basis of silkworm resistance to BmNPV using susceptible (the recurrent parent P50) and resistant (near-isogenic line BC9) strains and a combination of iTRAQ-based quantitative proteomics, reverse-transcription quantitative PCR and Western blotting. By comparing the proteomes of infected and non-infected P50 and BC9 silkworms, we identified 793 differentially expressed proteins (DEPs). By gene ontology and KEGG enrichment analyses, we found that these DEPs are preferentially involved in metabolism, catalytic activity, amino sugar and nucleotide sugar metabolism and carbon metabolism. 114 (14.38%) DEPs were associated with the cytoskeleton, immune response, apoptosis, ubiquitination, translation, ion transport, endocytosis and endopeptidase activity. After removing the genetic background and individual immune stress response proteins, we identified 84 DEPs were found that are potentially involved in resistance to BmNPV. Further studies showed that a serine protease was down-regulated in P50 and up-regulated in BC9 after BmNPV infection. Taken together, these results provide insights into the molecular mechanism of silkworm response to BmNPV.

BIOLOGICAL SIGNIFICANCE

Bombyx mori nucleopolyhedrovirus (BmNPV) is highly pathogenic, causing serious losses in sericulture every year. However, the molecular mechanisms of BmNPV infection and host defence remain unclear. Here we combined quantitative proteomic, bioinformatics, RT-qPCR and Western blotting analyses and found that BmNPV invasion causes complex protein alterations in the larval midgut, and that these changes are related to cytoskeleton, immune response, apoptosis, ubiquitination, translation, ion transport, endocytosis and endopeptidase activity. Five important differentially expression proteins were validation by independent approaches. These finding will help address the molecular mechanisms of silkworm resistance to BmNPV and provide a molecular target for resisting BmNPV.

MicroRNA-20b suppresses the expression of ZFP-148 in viral myocarditis

Viral myocarditis is a common cardiovascular disease, which seriously endangers the health of people and even leads to sudden unexpected death. MicroRNAs play very important roles in various physical and pathological processes including cardiogenesis and heart diseases. In recent years, miR-20b has been implicated in various diseases such as breast cancer, gastric cancer, hepatocellular carcinoma, cardiovascular diseases. However, the function of miR-20b in the pathological progress of viral myocarditis has not been reported. In this study, we found that miR-20b was up-regulated in mouse heart tissues post Coxsackievirus B3 (CVB3) infection. Bioinformatics analysis identified ZFP-148, a transcription factor that plays essential roles in the regulation of virus replication, is one of the predicted targets of miR-20b. MiR-20b expression was found to be up-regulated and ZFP-148 protein level was markedly repressed during viral myocarditis. Further studies demonstrated that miR-20b directly binds to the 3'-UTR of ZFP-148 and suppresses its translation. Moreover, aberrant expression of miR-20b promoted the expression of anti-apoptosis proteins Bcl-2 and Bcl-xL, suggesting that altered gene expression might promote cardiomyocytes survival in viral myocarditis. Our findings indicated that miR-20b might be a potential therapeutic target for CVB3-induced viral myocarditis and a useful marker for the diagnosis of viral myocarditis.

Efficacy and Safety of Bortezomib in Multiple Myeloma Patients with Hepatitis B: A Multicenter Retrospective Study

Background:

The efficacy and safety evidence of bortezomib in multiple myeloma (MM) patients with hepatitis B is vacant. This study aimed to investigate the efficacy and safety of bortezomib in MM patients with hepatitis B in China.

Methods:

From 2006 to 2011, 739 newly diagnosed MM patients were screened for serum hepatitis B virus (HBV) biomarkers. HBV-infected patients were followed for HBV reactivation by monitoring of serum alanine transaminase (ALT) and HBV DNA load. The pattern of HBV reactivation in relation to bortezomib was evaluated. Seven hundred thirty-nine MM patients were included in this study.

Results:

The prevalence of MM patients infected with HBV was 3.4% (n = 25), of which 17 cases were treated with bortezomib. Bortezomib had no significant influence on liver function (ALT before and after treatment: 36.69 ± 8.90 U/L vs. 11.31 ± 2.74 U/L, P = 0.19) and HBV DNA of MM patients with HBV (detectable HBV DNA percentage: 5.9% vs. 11.8%, P = 0.12).

Conclusions:

Bortezomib can be used safely and effectively in MM patients with hepatitis B. HBV prophylaxis and surveillance are recommended during the MM treatment.

SUMO Modification Stabilizes Enterovirus 71 Polymerase 3D To Facilitate Viral Replication

Accumulating evidence suggests that viruses hijack cellular proteins to circumvent the host immune system. Ubiquitination and SUMOylation are extensively studied posttranslational modifications (PTMs) that play critical roles in diverse biological processes. Cross talk between ubiquitination and SUMOylation of both host and viral proteins has been reported to result in distinct functional consequences. Enterovirus 71 (EV71), an RNA virus belonging to the family Picornaviridae, is a common cause of hand, foot, and mouth disease. Little is known concerning how host PTM systems interact with enteroviruses. Here, we demonstrate that the 3D protein, an RNA-dependent RNA polymerase (RdRp) of EV71, is modified by small ubiquitin-like modifier 1 (SUMO-1) both during infection and in vitro Residues K159 and L150/D151/L152 were responsible for 3D SUMOylation as determined by bioinformatics prediction combined with site-directed mutagenesis. Also, primer-dependent polymerase assays indicated that mutation of SUMOylation sites impaired 3D polymerase activity and virus replication. Moreover, 3D is ubiquitinated in a SUMO-dependent manner, and SUMOylation is crucial for 3D stability, which may be due to the interplay between the two PTMs. Importantly, increasing the level of SUMO-1 in EV71-infected cells augmented the SUMOylation and ubiquitination levels of 3D, leading to enhanced replication of EV71. These results together suggested that SUMO and ubiquitin cooperatively regulated EV71 infection, either by SUMO-ubiquitin hybrid chains or by ubiquitin conjugating to the exposed lysine residue through SUMOylation. Our study provides new insight into how a virus utilizes cellular pathways to facilitate its replication.

IMPORTANCE

Infection with enterovirus 71 (EV71) often causes neurological diseases in children, and EV71 is responsible for the majority of fatalities. Based on a better understanding of interplay between virus and host cell, antiviral drugs against enteroviruses may be developed. As a dynamic cellular process of posttranslational modification, SUMOylation regulates global cellular protein localization, interaction, stability, and enzymatic activity. However, little is known concerning how SUMOylation directly influences virus replication by targeting viral polymerase. Here, we found that EV71 polymerase 3D was SUMOylated during EV71 infection and in vitro Moreover, the SUMOylation sites were determined, and in vitro polymerase assays indicated that mutations at SUMOylation sites could impair polymerase synthesis. Importantly, 3D is ubiquitinated in a SUMOylation-dependent manner that enhances the stability of the viral polymerase. Our findings indicate that the two modifications likely cooperatively enhance virus replication. Our study may offer a new therapeutic strategy against virus replication.

Coxsackievirus B3 Induces Autophagic Response in Cardiac Myocytes in vivo

Viral myocarditis is a common disease that contributes to dilated cardiomyopathy or heart failure. Coxsackievirus B (CVB) is one of the major causative pathogens of viral myocarditis. Previous studies have shown that autophagy is exploited to promote CVB replication in cell lines. To study whether cardiac myocytes respond to CVB infection in a similar way, viral myocarditis was established by the inoculation of 3-week-old BALB/c mice with CVB3. Electron microscopic observation showed that autophagosome-like vesicles were induced in the cardiac myocytes of mice infected by CVB3 at 3, 5, and 7 days after viral infection. The lipidated microtubule-associated protein 1 light chain 3 (LC3), LC3-II, was also significantly increased in both myocardium and the cardiac myocytes extracted from the ventricles of mice infected with CVB3. The increased LC3-II coincided with high level of viral RNA and proteins in both myocardium and isolated cardiac myocytes. Moreover, viral protein synthesis was significantly decreased in primary cardiac myocytes by the treatment with 3-methyladenine, an inhibitor of autophagy. The expression and the phosphorylation of extracellular signal regulated kinase (ERK) were also increased in both myocardium and in the isolated cardiac myocytes of the virus-infected mice, while the interplay of ERK with autophagic response remains to be studied. This study demonstrated that cardiac myocytes respond to CVB3 infection by increased formation of autophagosomes in vivo, which might be exploited for viral replication.

Myocarditis

Viral myocarditis remains a prominent infectious-inflammatory disease for patients throughout the lifespan. The condition presents several challenges including varied modes of clinical presentation, a range of timepoints when patients come to attention, a diversity of approaches to diagnosis, a spectrum of clinical courses, and unsettled perspectives on therapeutics in different patient settings and in the face of different viral pathogens. In this review, we examine current knowledge about viral heart disease and especially provide information on evolving understanding of mechanisms of disease and efforts by investigators to identify and evaluate potential therapeutic avenues for intervention.

A novel mosquito ubiquitin targets viral envelope protein for degradation and reduces virion production during dengue virus infection

Background

Dengue virus (DENV) is a mosquito-borne flavivirus that causes significant human disease and mortality in the tropics and subtropics. By examining the effects of virus infection on gene expression, and interactions between virus and vector, new targets for prevention of infection and novel treatments may be identified in mosquitoes. We previously performed a microarray analysis of the Aedes aegypti transcriptome during infection with DENV and found that mosquito ubiquitin protein Ub3881 (AAEL003881) was specifically and highly down-regulated. Ubiquitin proteins have multiple functions in insects, including marking proteins for proteasomal degradation, regulating apoptosis and mediating innate immune signaling.

Methods

We used qRT-PCR to quantify gene expression and infection, and RNAi to reduce Ub3881 expression. Mosquitoes were infected with DENV through blood feeding. We transfected DENV protein expression constructs to examine the effect of Ub3881 on protein degradation. We used site-directed mutagenesis and transfection to determine what amino acids are involved in Ub3881-mediated protein degradation. Immunofluorescence, Co-immunoprecipitation and Western blotting were used to examine protein interactions and co-localization.

Results

The overexpression of Ub3881, but not related ubiquitin proteins, decreased DENV infection in mosquito cells and live Ae. aegypti. The Ub3881 protein was demonstrated to be involved in DENV envelope protein degradation and reduce the number of infectious virions released.

Conclusions

We conclude that Ub3881 has several antiviral functions in the mosquito, including specific viral protein degradation.

General significance

Our data highlights Ub3881 as a target for future DENV prevention strategies in the mosquito transmission vector.

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A novel mosquito ubiquitin, Ub3881, is identified in Aedes aegypti.

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Ub3881 is shown to have antiviral functions during dengue virus infection of the mosquito.

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Ub3881 targets a dengue viral protein for degradation during infection.

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Future dengue virus prevention strategies could incorporate Ub3881 as a target to prevent mosquito infection.

Interplay between the virus and the ubiquitin-proteasome system: molecular mechanism of viral pathogenesis

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Many viruses have evolved to utilize the host UPS for their own benefit.

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Viruses subvert the UPS to maintain optimal level/function of viral proteins.

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Viruses exploit the UPS to degrade host proteins which impede viral growth.

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The UPS serves as an important host anti-viral defense mechanism.

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The UPS is inhibited by some viruses to prevent viral clearance.

The ubiquitin–proteasome system (UPS) plays a central role in a wide range of fundamental cellular functions by ensuring protein quality control and through maintaining a critical level of important regulatory proteins. Viruses subvert or manipulate this cellular machinery to favor viral propagation and to evade host immune response. The UPS serves as a double-edged sword in viral pathogenesis: on the one hand, the UPS is utilized by many viruses to maintain proper function and level of viral proteins; while on the other hand, the UPS constitutes a host defense mechanism to eliminate viral components. To combat this host anti-viral machinery, viruses have evolved to employ the UPS to degrade or inactivate cellular proteins that limit viral growth. This review will highlight our current knowledge pertaining to the different roles for the UPS in viral pathogenesis.

Coxsackievirus B3 replication and pathogenesis

ABSTRACT 

Viruses such as coxsackievirus B3 (CVB3) are entirely host cell-dependent parasites. Indeed, they must cleverly exploit various compartments of host cells to complete their life cycle, and consequently launch disease. Evolution has equipped this pico-rna-virus, CVB3, to use different strategies, including CVB3-induced direct damage to host cells followed by a host inflammatory response to CVB3 infection, and cell death to super-additively promote target organ tissue injury, and dysfunction. In this update, the patho-stratagems of CVB3 are explored from molecular, and systems-level approaches. In summarizing recent developments in this field, we focus particularly on mechanisms by which CVB3 can harness different host cell processes including kinases, host cell-killing and cell-eating machineries, matrix metalloproteinases and miRNAs to promote disease.

Characterization of the polyproline region of the hepatitis E virus in immunocompromised patients

Little is known about virus adaptation in immunocompromised patients with chronic genotype 3 hepatitis E virus (HEV3) infections. Virus-host recombinant strains have been isolated recently from chronically infected patients. The nature and incidence of such recombinant events occurring during infections of solid-organ transplant (SOT) recipients are essentially unknown. The polyproline region (PPR) of strains isolated from SOT patients was sequenced during the acute-infection phase (n = 59) and during follow-up of patients whose infections became chronic (n = 27). These 27 HEV strains included 3 (11%) that showed recombinant events 12, 34, 48, or 88 months after infection. In one strain, parts of the PPR and the RNA-dependent RNA polymerase were concomitantly inserted. In the second, a fragment of a human tyrosine aminotransferase (TAT) gene was inserted first, followed by a fragment of PPR. A fragment of the human inter-α-trypsin inhibitor (ITI) gene was inserted in the third. All the inserted sequences were rich in aliphatic and basic amino acids. In vitro growth experiments suggest that the ITI insertion promoted more vigorous virus growth. In silico studies showed that the inserted sequences could provide potential acetylation, ubiquitination, and phosphorylation sites. We found that recombinant events had occurred in the HEV PPR in approximately 11% of the strains isolated from chronically infected transplant patients followed up in Toulouse University Hospital. These inserted fragments came from the HEV genome or a human gene and could enhance virus replication. Importance: Hepatitis E virus (HEV) can cause chronic infections in immunocompromised patients, including solid-organ transplant (SOT) recipients. Two strains that had undergone recombination with human ribosomal genes were described recently. The strains with inserted sequences replicated better in vitro. Little is known about the frequency of such recombinant events or how such an insertion enhances replication. We therefore investigated 59 SOT patients infected with HEV and found 3 strains with 4 recombinant events in 27 of these patients whose infection became chronic. The 4 inserted sequences were of different origins (human gene or HEV genome), but all were enriched in aliphatic and basic amino acids and provided potential regulation sites. Our data indicate that recombinant events occur in approximately 11% of strains isolated from chronically infected patients. The structures of the inserted sequences provide new clues as to how the inserted sequences could foster virus replication.

Curcumin inhibits the replication of enterovirus 71 in vitro

Human enterovirus 71 (EV71) is the main causative pathogen of hand, foot, and mouth disease (HFMD) in children. The epidemic of HFMD has been a public health problem in Asia-Pacific region for decades, and no vaccine and effective antiviral medicine are available. Curcumin has been used as a traditional medicine for centuries to treat a diversity of disorders including viral infections. In this study, we demonstrated that curcumin showed potent antiviral effect again EV71. In Vero cells infected with EV71, the addition of curcumin significantly suppressed the synthesis of viral RNA, the expression of viral protein, and the overall production of viral progeny. Similar with the previous reports, curcumin reduced the production of ROS induced by viral infection. However, the antioxidant property of curcumin did not contribute to its antiviral activity, since N-acetyl-l-cysteine, the potent antioxidant failed to suppress viral replication. This study also showed that extracellular signal-regulated kinase (ERK) was activated by either viral infection or curcumin treatment, but the activated ERK did not interfere with the antiviral effect of curcumin, indicating ERK is not involved in the antiviral mechanism of curcumin. Unlike the previous reports that curcumin inhibited protein degradation through ubiquitin–proteasome system (UPS), we found that curcumin had no impact on UPS in control cells. However, curcumin did reduce the activity of proteasomes which was increased by viral infection. In addition, the accumulation of the short-lived proteins, p53 and p21, was increased by the treatment of curcumin in EV71-infected cells. We further probed the antiviral mechanism of curcumin by examining the expression of GBF1 and PI4KB, both of which are required for the formation of viral replication complex. We found that curcumin significantly reduced the level of both proteins. Moreover, the decreased expression of either GBF1 or PI4KB by the application of siRNAs was sufficient to suppress viral replication. We also demonstrated that curcumin showed anti-apoptotic activity at the early stage of viral infection. The results of this study provide solid evidence that curcumin has potent anti-EV71 activity. Whether or not the down-regulated GBF1 and PI4KB by curcumin contribute to its antiviral effect needs further studies.

The ubiquitin-conjugating system: multiple roles in viral replication and infection

Through the combined action of ubiquitinating and deubiquitinating enzymes, conjugation of ubiquitin to a target protein acts as a reversible post-translational modification functionally similar to phosphorylation. Indeed, ubiquitination is more and more recognized as a central process for the fine regulation of many cellular pathways. Due to their nature as obligate intracellular parasites, viruses rely on the most conserved host cell machineries for their own replication. Thus, it is not surprising that members from almost every viral family are challenged by ubiquitin mediated mechanisms in different steps of their life cycle and have evolved in order to by-pass or exploit the cellular ubiquitin conjugating system to maximize their chance to establish a successful infection. In this review we will present several examples of the complex interplay that links viruses and the ubiquitin conjugation machinery, with a special focus on the mechanisms evolved by the human immunodeficiency virus to escape from cellular restriction factors and to exit from infected cells.

Dominant-negative function of the C-terminal fragments of NBR1 and SQSTM1 generated during enteroviral infection

Coxsackievirus infection induces an abnormal accumulation of ubiquitin aggregates that are generally believed to be noxious to the cells and have a key role in viral pathogenesis. Selective autophagy mediated by autophagy adaptor proteins, including sequestosome 1 (SQSTM1/p62) and neighbor of BRCA1 gene 1 protein (NBR1), are an important pathway for disposing of misfolded/ubiquitin conjugates. We have recently demonstrated that SQSTM1 is cleaved after coxsackievirus infection, resulting in the disruption of SQSTM1 function in selective autophagy. NBR1 is a functional homolog of SQSTM1. In this study, we propose to test whether NBR1 can compensate for the compromise of SQSTM1 after viral infection. Of interest, we found that NBR1 was also cleaved after coxsackievirus infection. This cleavage took place at two sites mediated by virus-encoded protease 2A(pro) and 3C(pro), respectively. In addition to the loss-of-function, we further investigated whether cleavage of SQSTM1/NBR1 leads to the generation of toxic gain-of-function mutants. We showed that the C-terminal fragments of SQSTM1 and NBR1 exhibited a dominant-negative effect against native SQSTM1/NBR1, probably by competing for LC3 and ubiquitin chain binding. Finally, we demonstrated a positive, mutual regulatory relationship between SQSTM1 and NBR1 during viral infection. We showed that knockdown of SQSTM1 resulted in reduced expression of NBR1, whereas overexpression of SQSTM1 led to increased level of NBR1, and vice versa, further excluding the possible compensation of NBR1 for the loss of SQSTM1. Taken together, the findings in this study suggest a novel mechanism through which coxsackievirus infection induces increased accumulation of ubiquitin conjugates and subsequent viral damage.

The ubiquitin-proteasome system is required for the early stages of porcine circovirus type 2 replication

Porcine circovirus type 2 (PCV2) is the primary causative agent of porcine circovirus-associated diseases (PCVAD). It has been shown that the ubiquitin-proteasome system (UPS) is correlated with viral infection, but its role in PCV2 replication remains unknown. In the present study, we explored the interplay between PCV2 replication and the UPS in PK15 cells and found that treatment with a proteasome inhibitor (MG132 and lactacystin) significantly decreased the PCV2 titer at the early infection stage. We further revealed that inhibition of the UPS did not affect virus entry but decreased viral protein expression and RNA transcription potentially in a cell cycle-dependent manner. PCV2 infection has little effect on the chymotrypsin-like activity, and the gene-silencing of ubiquitin reduced the PCV2 titer, which indicates that the effective replication of PCV2 may be related to protein ubiquitination. Taken together, our data suggested that PCV2 replication requires the UPS machinery, which may represent a potential antiviral target against PCV2.

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UPS inhibition reduced PCV2 titer via depression viral translation and transcription.

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Proteasome inhibitors impair cell cycle progression by prolonging G2/M phase.

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siRNA of ubiquitin decreased the PCV2 titer. The effective replication of PCV2 may be related to protein ubiquitination.

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Proteasome inhibition may represent a potential antiviral target against PCV2.

Cleavage of sequestosome 1/p62 by an enteroviral protease results in disrupted selective autophagy and impaired NFKB signaling

The adaptor protein, sequestosome 1 (SQSTM1)/p62, plays an essential role in mediating selective autophagy. It serves as an autophagy receptor targeting ubiquitinated proteins to autophagosomes for degradation. In addition, it functions as a scaffold protein to regulate signaling pathways. Here we explored the interplay between coxsackievirus B3 (CVB3) and SQSTM1-mediated selective autophagy. We reported that SQSTM1 was cleaved at glycine 241 following CVB3 infection through the activity of viral protease 2A(pro). The resulting cleavage fragments of SQSTM1 were no longer the substrates of autophagy, and their ability to form protein aggregates was greatly decreased. Although the C-terminal truncation sustained the binding activity of SQSTM1 to microtubule-associated protein 1 light chain (LC3), it failed to interact with ubiquitinated proteins. It was also found that colocalization between the C-terminal fragment of SQSTM1 (SQSTM1-C) and LC3 and ubiquitin within the punctate structures was markedly disrupted. Moreover, we observed that SQSTM1-C retained the ability of SQSTM1 to stabilize antioxidant transcription factor NFE2L2 [nuclear factor (erythroid-derived 2)-like 2]; however, both the N-terminal fragment of SQSTM1 (SQSTM1-N) and SQSTM1-C lost the function of SQSTM1 in activating NFKB (the nuclear factor of kappa light polypeptide gene enhancer in B-cells) pathway. Collectively, our results suggest a novel model by which cleavage of SQSTM1 as a result of CVB3 infection impairs the function of SQSTM1 in selective autophagy and host defense signaling.

Zinc ionophores pyrithione inhibits herpes simplex virus replication through interfering with proteasome function and NF-κB activation

Pyrithione (PT), known as a zinc ionophore, is effective against several pathogens from the Streptococcus and Staphylococcus genera. The antiviral activity of PT was also reported against a number of RNA viruses. In this paper, we showed that PT could effectively inhibit herpes simplex virus types 1 and 2 (HSV-1 and HSV-2). PT inhibited HSV late gene (Glycoprotein D, gD) expression and the production of viral progeny, and this action was dependent on Zn(2+). Further studies showed that PT suppressed the expression of HSV immediate early (IE) gene, the infected cell polypeptide 4 (ICP4), but had less effect on another regulatory IE protein, ICP0. It was found that PT treatment could interfere with cellular ubiquitin-proteasome system (UPS), leading to the inhibition of HSV-2-induced IκB-α degradation to inhibit NF-κB activation and enhanced promyelocytic leukemia protein (PML) stability in nucleus. However, PT did not show direct inhibition of 26S proteasome activity. Instead, it induced Zn(2+) influx, which facilitated the dysregulation of UPS and the accumulation of intracellular ubiquitin-conjugates. UPS inhibition by PT caused disruption of IκB-α degradation and NF-κB activation thus leading to marked reduction of viral titer.

How can plant virus satellite RNAs alter the effects of plant virus infection? A study of the changes in the Nicotiana benthamiana proteome after infection by peanut stunt virus in the presence or absence of its satellite RNA

Peanut stunt virus (PSV), which belongs to the Cucumovirus genus, is a pathogen of legumes. Certain PSV strains associated with a satellite RNA (satRNA) modify the symptoms of infected plants and interfere with plant metabolism. We used PSV-P genomic transcripts (GTs) with and without PSV-P satRNA and a comparative proteomic 2D-DIGE/MS study to assess their effects on Nicotiana benthamiana infection. When the proteomes of the PSV-P genomic transcripts-infected (no satRNA present) and mock-inoculated plants were compared 29 differentially regulated proteins were found. When comparisons were made for plants infected with PSV-P-GT in the presence or absence of satRNA, and for mock-infected plants and those infected with the satRNA-associated PSV-P-GT, 40 and 60 such proteins, respectively, were found. The presence of satRNA mostly decreased the amounts of the affected host proteins. Proteins involved in photosynthesis and carbohydrate metabolism, for example ferredoxin-NADP-reductase and malate dehydrogenase, are among the identified affected proteins in all comparisons. Proteins involved in protein synthesis and degradation were also affected. Such proteins include chaperonin 60β--whose abundance of the proteins changed for all comparisons--and aminopeptidase that is a satRNA- or PSV-P-GT/satRNA-responsive protein. Additionally, the levels of the stress-related proteins superoxide dismutase and acidic endochitinase Q increased in the PSV-P-GT- and PSV-P-GT/satRNA-infected plants. This study appears to be the first report on plant proteome changes in response to a satRNA presence during viral infection and, as such, may provide a reference for future studies concerning the influence of satRNAs during viral infections.

Pyrrolidine dithiocarbamate inhibits herpes simplex virus 1 and 2 replication, and its activity may be mediated through dysregulation of the ubiquitin-proteasome system

Pyrrolidine dithiocarbamate (PDTC) is widely used as an antioxidant or an NF-κB inhibitor. It has been reported to inhibit the replication of human rhinoviruses, poliovirus, coxsackievirus, and influenza virus. In this paper, we report that PDTC could inhibit the replication of herpes simplex virus 1 and 2 (HSV-1 and HSV-2). PDTC suppressed the expression of HSV-1 and HSV-2 viral immediate early (IE) and late (membrane protein gD) genes and the production of viral progeny. This antiviral property was mediated by the dithiocarbamate moiety of PDTC and required the presence of Zn(2+). Although PDTC could potently block reactive oxygen species (ROS) generation, it was found that this property did not contribute to its anti-HSV activity. PDTC showed no activity in disrupting the mitogen-activated protein kinase (MAPK) pathway activation induced by viral infection that was vital for the virus's propagation. We found that PDTC modulated cellular ubiquitination and, furthermore, influenced HSV-2-induced IκB-α degradation to inhibit NF-κB activation and enhanced PML stability in the nucleus, resulting in the inhibition of viral gene expression. These results suggested that the antiviral activity of PDTC might be mediated by its dysregulation of the cellular ubiquitin-proteasome system (UPS).

Enterovirus 71 protease 2Apro targets MAVS to inhibit anti-viral type I interferon responses

Enterovirus 71 (EV71) is the major causative pathogen of hand, foot, and mouth disease (HFMD). Its pathogenicity is not fully understood, but innate immune evasion is likely a key factor. Strategies to circumvent the initiation and effector phases of anti-viral innate immunity are well known; less well known is whether EV71 evades the signal transduction phase regulated by a sophisticated interplay of cellular and viral proteins. Here, we show that EV71 inhibits anti-viral type I interferon (IFN) responses by targeting the mitochondrial anti-viral signaling (MAVS) protein--a unique adaptor molecule activated upon retinoic acid induced gene-I (RIG-I) and melanoma differentiation associated gene (MDA-5) viral recognition receptor signaling--upstream of type I interferon production. MAVS was cleaved and released from mitochondria during EV71 infection. An in vitro cleavage assay demonstrated that the viral 2A protease (2A(pro)), but not the mutant 2A(pro) (2A(pro)-110) containing an inactivated catalytic site, cleaved MAVS. The Protease-Glo assay revealed that MAVS was cleaved at 3 residues between the proline-rich and transmembrane domains, and the resulting fragmentation effectively inactivated downstream signaling. In addition to MAVS cleavage, we found that EV71 infection also induced morphologic and functional changes to the mitochondria. The EV71 structural protein VP1 was detected on purified mitochondria, suggesting not only a novel role for mitochondria in the EV71 replication cycle but also an explanation of how EV71-derived 2A(pro) could approach MAVS. Taken together, our findings reveal a novel strategy employed by EV71 to escape host anti-viral innate immunity that complements the known EV71-mediated immune-evasion mechanisms.

MCPIP1 ribonuclease exhibits broad-spectrum antiviral effects through viral RNA binding and degradation

Monocyte chemoattractant protein 1-induced protein 1 (MCPIP1), belonging to the MCPIP family with highly conserved CCCH-type zinc finger and Nedd4-BP1, YacP Nuclease domains, has been implicated in negative regulation of the cellular inflammatory responses. In this report, we demonstrate for the first time that this RNA-binding nuclease also targets viral RNA and possesses potent antiviral activities. Overexpression of the human MCPIP1, but not MCPIP2, MCPIP3 or MCPIP4, inhibited Japanese encephalitis virus (JEV) and dengue virus (DEN) replication. The functional analysis of MCPIP1 revealed that the activities of RNase, RNA binding and oligomerization, but not deubiqutinase, are required for its antiviral potential. Furthermore, infection of other positive-sense RNA viruses, such as sindbis virus and encephalomyocarditis virus, and negative-sense RNA virus, such as influenza virus, as well as DNA virus, such as adenovirus, can also be blocked by MCPIP1. Moreover, the endogenous MCPIP1 gene expression was induced by JEV and DEN infection, and knockdown of MCPIP1 expression enhanced the replication of JEV and DEN in human cells. Thus, MCPIP1 can act as a host innate defense via RNase activity for targeting and degrading viral RNA.

MicroRNA-203 enhances coxsackievirus B3 replication through targeting zinc finger protein-148

Coxsackievirus B3 (CVB3) is the primary causal agent of viral myocarditis. During infection, it hijacks host genes to favour its own replication. However, the underlying mechanism is still unclear. Although the viral receptor is an important factor for viral infectivity, other factors such as microRNAs (miRNA) may also play an essential role in its replication after host cell entry. miRNAs are post-transcriptional gene regulators involved in various fundamental biological processes as well as in diseases. To identify miRNAs involved in CVB3 pathogenesis, we performed microarray analysis of miRNAs using CVB3-infected murine hearts and identified miR-203 as one of the most upregulated candidates. We found that miR-203 upregulation is through the activation of protein kinase C/transcription factor AP-1 pathway. We further identified zinc finger protein-148 (ZFP-148), a transcription factor, as a novel target of miR-203. Ectopic expression of miR-203 downregulated ZFP-148 translation, increased cell viability and subsequently enhanced CVB3 replication. Silencing of ZFP-148 by siRNA showed similar effects on CVB3 replication. Finally, analyses of the signalling cascade downstream of ZFP-148 revealed that miR-203-induced suppression of ZFP-148 differentially regulated the expression of prosurvival and proapoptotic genes of the Bcl-2 family proteins as well as the cell cycle regulators. This altered gene expression promoted cell survival and growth, which provided a favourable environment for CVB3 replication, contributing to the further damage of the infected cells. Taken together, this study identified a novel target of miR-203 and revealed, for the first time, the molecular link between miR-203/ZFP-148 and the pathogenesis of CVB3.

The ubiquitin-proteasome system in positive-strand RNA virus infection

Positive-stranded RNA viruses, like many other viruses, have evolved to exploit the host cellular machinery to their own advantage. In eukaryotic cells, the ubiquitin-proteasome system (UPS) that serves as the major intracellular pathway for protein degradation and modification plays a crucial role in the regulation of many fundamental cellular functions. A growing amount of evidence has suggested that the UPS can be utilized by positive-sense RNA viruses. The UPS eliminates excess viral proteins that prevent viral replication and modulates the function of viral proteins through post-translational modification mediated by ubiquitin or ubiquitin-like proteins. This review will discuss the current understanding of how positive RNA viruses have evolved various mechanisms to usurp the host UPS to modulate the function and stability of viral proteins. In addition to the pro-viral function, UPS-mediated viral protein degradation may also constitute a host defense process against some positive-stranded RNA viral infections. This issue will also be discussed in the current review.

Pharmacological and biological antiviral therapeutics for cardiac coxsackievirus infections

Subtype B coxsackieviruses (CVB) represent the most commonly identified infectious agents associated with acute and chronic myocarditis, with CVB3 being the most common variant. Damage to the heart is induced both directly by virally mediated cell destruction and indirectly due to the immune and autoimmune processes reacting to virus infection. This review addresses antiviral therapeutics for cardiac coxsackievirus infections discovered over the last 25 years. One group represents pharmacologically active low molecular weight substances that inhibit virus uptake by binding to the virus capsid (e.g., pleconaril) or inactivate viral proteins (e.g., NO-metoprolol and ribavirin) or inhibit cellular proteins which are essential for viral replication (e.g., ubiquitination inhibitors). A second important group of substances are interferons. They have antiviral but also immunomodulating activities. The third and most recently discovered group includes biological and cellular therapeutics. Soluble receptor analogues (e.g., sCAR-Fc) bind to the virus capsid and block virus uptake. Small interfering RNAs, short hairpin RNAs and antisense oligonucleotides bind to and led to degradation of the viral RNA genome or cellular RNAs, thereby preventing their translation and viral replication. Most recently mesenchymal stem cell transplantation has been shown to possess antiviral activity in CVB3 infections. Taken together, a number of antiviral therapeutics has been developed for the treatment of myocardial CVB infection in recent years. In addition to low molecular weight inhibitors, biological therapeutics have become promising anti-viral agents.

Viral myocarditis: potential defense mechanisms within the cardiomyocyte against virus infection

Virus infection can inflict significant damage on cardiomyocytes through direct injury and secondary immune reactions, leading to myocarditis and dilated cardiomyopathy. While viral myocarditis or cardiomyopathy is a complication of systemic infection of cardiotropic viruses, most individuals infected with the viruses do not develop significant cardiac disease. However, some individuals proceed to develop severe virus-mediated heart disease. Recent studies have shown that viral infection of cardiomyocytes is required for the development of myocarditis and subsequent cardiomyopathy. This suggests that viral infection of cardiomyocytes can be an important step that determines the pathogenesis of viral myocarditis during systemic infection. Accordingly, this article focuses on potential defense mechanisms within the cardiomyocyte against virus infection. Understanding of the cardiomyocyte defense against invading viruses may give us novel insights into the pathophysiology of viral myocarditis, and enable us to develop innovative strategies of diagnosis and treatment for this challenging clinical entity.

Systematic identification of novel, essential host genes affecting bromovirus RNA replication

Positive-strand RNA virus replication involves viral proteins and cellular proteins at nearly every replication step. Brome mosaic virus (BMV) is a well-established model for dissecting virus-host interactions and is one of very few viruses whose RNA replication, gene expression and encapsidation have been reproduced in the yeast Saccharomyces cerevisiae. Previously, our laboratory identified ∼100 non-essential host genes whose loss inhibited or enhanced BMV replication at least 3-fold. However, our isolation of additional BMV-modulating host genes by classical genetics and other results underscore that genes essential for cell growth also contribute to BMV RNA replication at a frequency that may be greater than that of non-essential genes. To systematically identify novel, essential host genes affecting BMV RNA replication, we tested a collection of ∼900 yeast strains, each with a single essential gene promoter replaced by a doxycycline-repressible promoter, allowing repression of gene expression by adding doxycycline to the growth medium. Using this strain array of ∼81% of essential yeast genes, we identified 24 essential host genes whose depleted expression reproducibly inhibited or enhanced BMV RNA replication. Relevant host genes are involved in ribosome biosynthesis, cell cycle regulation and protein homeostasis, among other cellular processes. BMV 2a^Pol levels were significantly increased in strains depleted for a heat shock protein (HSF1) or proteasome components (PRE1 and RPT6), suggesting these genes may affect BMV RNA replication by directly or indirectly modulating 2a^Pol localization, post-translational modification or interacting partners. Investigating the diverse functions of these newly identified essential host genes should advance our understanding of BMV-host interactions and normal cellular pathways, and suggest new modes of virus control.

Assessing ubiquitination of viral proteins: Lessons from flavivirus NS5

Ubiquitin (Ub) conjugation to a substrate protein is a widely used cellular mechanism for control of protein stability and function, modulation of signal transduction pathways and antiviral responses. Identification and characterization of ubiquitinated viral proteins is an important step in understanding novel mechanisms of viral protein regulation as well as elucidating cellular antiviral strategies. Here we describe a protocol to easily detect and characterize the ubiquitination status of a viral substrate protein expressed either during infection or ectopically expressed as a fusion with a biotinylatable epitope tag. This tag provides advantages over current immunoprecipitation techniques by making use of the extremely tight biotin-streptavidin interaction. We provide an example of this protocol using the nonstructural protein 5 (NS5) from Langat virus (LGTV), a member of the tick-borne encephalitis virus (TBEV) serocomplex within the Flavivirus genus. Using the protocols outlined here, we describe some of the pitfalls inherent in determination of Ub linkage and demonstrate that NS5 is modified by at least two distinct ubiquitination types, multiubiquitination and K48-linked polyubiquitin chains.

Identification of amino acids in auxiliary replicase protein p27 critical for its RNA-binding activity and the assembly of the replicase complex in Red clover necrotic mosaic virus

The specific recognition of genomic RNAs by viral replicase proteins is a key regulatory step during the early replication process in positive-strand RNA viruses. In this study, we characterized the RNA-binding activity of the auxiliary replicase protein p27 of Red clover necrotic mosaic virus (RCNMV), which has a bipartite genome consisting of RNA1 and RNA2. Aptamer pull-down assays identified the amino acid residues of p27 involved in its specific interaction with RNA2. The RNA-binding activity of p27 correlated with its activity in recruiting RNA2 to membranes. We also identified the amino acids required for the formation of the 480-kDa replicase complex, a key player of RCNMV RNA replication. These amino acids are not involved in the functions of p27 that bind viral RNA or replicase proteins, suggesting an additional role for p27 in the assembly of the replicase complex. Our results demonstrate that p27 has multiple functions in RCNMV replication.

Tripeptidyl peptidase II serves as an alternative to impaired proteasome to maintain viral growth in the host cells

The ubiquitin-proteasome system is known to be utilized by coxsackievirus to facilitate its propagation within the host cells. The present study explores the role of tripeptidyl peptidase II (TPPII), a serine peptidase contributing to protein turnover by acting downstream of the proteasome, in regulating coxsackievirus infection. Inhibition of TPPII does not affect virus replication in cells with functional proteasome. However, when the proteasome is impaired, TPPII appears to serve as an alternative to maintain low levels of virus infection. Our results suggest an important function of TPPII in the maintenance of viral growth and may have implications for anti-viral therapy.