Importance of Akt signaling pathway for apoptosis in SARS-CoV-infected Vero E6 cells

Inhibition of Pim kinases triggers a broad antiviral activity by affecting innate immunity and via the PI3K-Akt-mTOR axis the endolysosomal system

Zoonoses such as ZIKV and SARS-CoV-2 pose a severe risk to global health. There is urgent need for broad antiviral strategies based on host-targets filling gaps between pathogen emergence and availability of therapeutic or preventive strategies. Significant reduction of pathogen titers decreases spread of infections and thereby ensures health systems not being overloaded and public life to continue. Based on previously observed interference with FGFR1/2-signaling dependent impact on interferon stimulated gene (ISG)-expression, we identified Pim kinases as promising druggable cellular target. We therefore focused on analyzing the potential of pan-Pim kinase inhibition to trigger a broad antiviral response. The pan-Pim kinase inhibitor AZD1208 exerted an extraordinarily high antiviral effect against various ZIKV isolates, SARS-CoV-2 and HBV. This was reflected by strong reduction in viral RNA, proteins and released infectious particles. Especially in case of SARS-CoV-2, AZD1208 led to a complete removal of viral traces in cells. Kinome-analysis revealed vast changes in kinase landscape upon AZD1208 treatment, especially for inflammation and the PI3K/Akt-pathway. For ZIKV, a clear correlation between antiviral effect and increase in ISG-expression was observed. Based on a cell culture model with impaired ISG-induction, activation of the PI3K-Akt-mTOR axis, leading to major changes in the endolysosomal equilibrium, was identified as second pillar of the antiviral effect triggered by AZD1208-dependent Pim kinase inhibition, also against HBV. We identified Pim-kinases as cellular target for a broad antiviral activity. The antiviral effect exerted by inhibition of Pim kinases is based on at least two pillars: innate immunity and modulation of the endolysosomal system.

An integrated in-silico Pharmaco-BioInformatics approaches to identify synergistic effects of COVID-19 to HIV patients

BACKGROUND

With high inflammatory states from both COVID-19 and HIV conditions further result in complications. The ongoing confrontation between these two viral infections can be avoided by adopting suitable management measures.

PURPOSE

The aim of this study was to figure out the pharmacological mechanism behind apigenin's role in the synergetic effects of COVID-19 to the progression of HIV patients.

METHOD

We employed computer-aided methods to uncover similar biological targets and signaling pathways associated with COVID-19 and HIV, along with bioinformatics and network pharmacology techniques to assess the synergetic effects of apigenin on COVID-19 to the progression of HIV, as well as pharmacokinetics analysis to examine apigenin's safety in the human body.

RESULT

Stress-responsive, membrane receptor, and induction pathways were mostly involved in gene ontology (GO) pathways, whereas apoptosis and inflammatory pathways were significantly associated in the Kyoto encyclopedia of genes and genomes (KEGG). The top 20 hub genes were detected utilizing the shortest path ranked by degree method and protein-protein interaction (PPI), as well as molecular docking and molecular dynamics simulation were performed, revealing apigenin's strong interaction with hub proteins (MAPK3, RELA, MAPK1, EP300, and AKT1). Moreover, the pharmacokinetic features of apigenin revealed that it is an effective therapeutic agent with minimal adverse effects, for instance, hepatoxicity.

CONCLUSION

Synergetic effects of COVID-19 on the progression of HIV may still be a danger to global public health. Consequently, advanced solutions are required to give valid information regarding apigenin as a suitable therapeutic agent for the management of COVID-19 and HIV synergetic effects. However, the findings have yet to be confirmed in patients, suggesting more in vitro and in vivo studies.

Live and let die: signaling AKTivation and UPRegulation dynamics in SARS-CoVs infection and cancer

The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is the pathogen responsible for the coronavirus disease 2019 (COVID-19) pandemic. Of particular interest for this topic are the signaling cascades that regulate cell survival and death, two opposite cell programs whose control is hijacked by viral infections. The AKT and the Unfolded Protein Response (UPR) pathways, which maintain cell homeostasis by regulating these two programs, have been shown to be deregulated during SARS-CoVs infection as well as in the development of cancer, one of the most important comorbidities in relation to COVID-19. Recent evidence revealed two way crosstalk mechanisms between the AKT and the UPR pathways, suggesting that they might constitute a unified homeostatic control system. Here, we review the role of the AKT and UPR pathways and their interaction in relation to SARS-CoV-2 infection as well as in tumor onset and progression. Feedback regulation between AKT and UPR pathways emerges as a master control mechanism of cell decision making in terms of survival or death and therefore represents a key potential target for developing treatments for both viral infection and cancer. In particular, drug repositioning, the investigation of existing drugs for new therapeutic purposes, could significantly reduce time and costs compared to de novo drug discovery.

Recent Progress in the Development of Opaganib for the Treatment of Covid-19

The Covid-19 pandemic driven by the SARS-CoV-2 virus continues to exert extensive humanitarian and economic stress across the world. Although antivirals active against mild disease have been identified recently, new drugs to treat moderate and severe Covid-19 patients are needed. Sphingolipids regulate key pathologic processes, including viral proliferation and pathologic host inflammation. Opaganib (aka ABC294640) is a first-in-class clinical drug targeting sphingolipid metabolism for the treatment of cancer and inflammatory diseases. Recent work demonstrates that opaganib also has antiviral activity against several viruses including SARS-CoV-2. A recently completed multinational Phase 2/3 clinical trial of opaganib in patients hospitalized with Covid-19 demonstrated that opaganib can be safely administered to these patients, and more importantly, resulted in a 62% decrease in mortality in a large subpopulation of patients with moderately severe Covid-19. Furthermore, acceleration of the clearance of the virus was observed in opaganib-treated patients. Understanding the biochemical mechanism for the anti-SARS-CoV-2 activity of opaganib is essential for optimizing Covid-19 treatment protocols. Opaganib inhibits three key enzymes in sphingolipid metabolism: sphingosine kinase-2 (SK2); dihydroceramide desaturase (DES1); and glucosylceramide synthase (GCS). Herein, we describe a tripartite model by which opaganib suppresses infection and replication of SARS-CoV-2 by inhibiting SK2, DES1 and GCS. The potential impact of modulation of sphingolipid signaling on multi-organ dysfunction in Covid-19 patients is also discussed.

The Promising Mechanisms of Low Molecular Weight Compounds of Panax Ginseng C.A. Meyer in Alleviating COVID-19: A Network Pharmacology Analysis

Panax Ginseng C.A. Meyer (PGCAM) is a well-known phytomedicine, but most of its compounds, such as ginsenoside derivatives, have poor absorption and bioavailability profile due to high molecular weight (≥500 Daltons), which is the major hurdle for their clinical application. Hence, this research explored the efficiency of low molecular weight compounds (LMWCs) (<500 Daltons) screened from PGCAM and their anti-COVID-19 mechanisms through network pharmacology. Molecular compounds from PGCAM were identified using public databases and filtered out by the drug-likeness evaluation. Genes interacted with these filtered compounds, and COVID-19-related genes were extracted from public databases. In addition, overlapping genes between compounds and interactive genes were identified using the Venn diagram. In parallel, the networking between compounds and overlapping genes was analyzed by RStudio. The pathway enrichment analysis of overlapping genes was determined by STRING. Finally, the key bioactive compounds were documented through virtual screening. The bubble chart suggested that the mechanisms of PGCAM against COVID-19 were related to 28 signaling pathways. The key molecular anti-COVID-19 mechanisms might be the anti-inflammation, anti-permeability, and pro-apoptosis by inactivating the PI3K-Akt signaling pathway. The six key genes and the five compounds related to the PI3K-Akt signaling pathway were RELA-paeonol, NFKB1-frutinone A, IL6-nepetin, MCL1-ramalic acid, VEGFA-trifolirhizin, and IL2-trifolirhizin. The docking between these key genes and compounds demonstrated promising binding affinity with a good binding score. Overall, our proposed LMWCs from PGCAM provide a fundamental basis with noteworthy pharmacological evidence to support the therapeutic efficacy of PGCAM in relieving the main symptoms of COVID-19.

A pathway map of signaling events triggered upon SARS-CoV infection

Severe acute respiratory syndrome coronaviruses (SARS-CoVs) caused worldwide epidemics over the past few decades. Extensive studies on various strains of coronaviruses provided a basic understanding of the pathogenesis of the disease. Presently, severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is leading a global pandemic with unprecedented challenges. This is the third coronavirus outbreak of this century. A signaling pathway map of signaling events induced by SARS-CoV infection is not yet available. In this study, we present a literature-annotated signaling pathway map of reactions induced by SARS-CoV infected cells. Multiple signaling modules were found to be orchestrated including PI3K-AKT, Ras-MAPK, JAK-STAT, Type 1 IFN and NFκB. The signaling pathway map of SARS-CoV consists of 110 molecules and 101 reactions mediated by SARS-CoV proteins. The pathway reaction data are available in various community standard data exchange formats including Systems Biology Graphical Notation (SBGN). The pathway map is publicly available through the GitHub repository and data in various formats can be freely downloadable.

α-Ketoglutarate Inhibits Thrombosis and Inflammation by Prolyl Hydroxylase-2 Mediated Inactivation of Phospho-Akt

Background

Phospho-Akt1 (pAkt1) undergoes prolyl hydroxylation at Pro125 and Pro313 by the prolyl hydroxylase-2 (PHD2) in a reaction decarboxylating α-ketoglutarate (αKG). We investigated whether the αKG supplementation could inhibit Akt-mediated activation of platelets and monocytes, in vitro as well as in vivo, by augmenting PHD2 activity.

Methods

We treated platelets or monocytes isolated from healthy individuals with αKG in presence of agonists in vitro and assessed the signalling molecules including pAkt1. We supplemented mice with dietary αKG and estimated the functional responses of platelets and monocytes ex vivo. Further, we investigated the impact of dietary αKG on inflammation and thrombosis in lungs of mice either treated with thrombosis-inducing agent carrageenan or infected with SARS-CoV-2.

Findings

Octyl αKG supplementation to platelets promoted PHD2 activity through elevated intracellular αKG to succinate ratio, and reduced aggregation in vitro by suppressing pAkt1(Thr308). Augmented PHD2 activity was confirmed by increased hydroxylated-proline and enhanced binding of PHD2 to pAkt in αKG-treated platelets. Contrastingly, inhibitors of PHD2 significantly increased pAkt1 in platelets. Octyl-αKG followed similar mechanism in monocytes to inhibit cytokine secretion in vitro. Our data also describe a suppressed pAkt1 and reduced activation of platelets and leukocytes ex vivo from mice supplemented with dietary αKG, unaccompanied by alteration in their number. Dietary αKG significantly reduced clot formation and leukocyte accumulation in various organs including lungs of mice treated with thrombosis-inducing agent carrageenan. Importantly, in SARS-CoV-2 infected hamsters, we observed a significant rescue effect of dietary αKG on inflamed lungs with significantly reduced leukocyte accumulation, clot formation and viral load alongside down-modulation of pAkt in the lung of the infected animals.

Interpretation

Our study suggests that dietary αKG supplementation prevents Akt-driven maladies such as thrombosis and inflammation and rescues pathology of COVID19-infected lungs.

Funding

Study was funded by the Department of Biotechnology (DBT), Govt. of India (grants: BT/PR22881 and BT/PR22985); and the Science and Engineering Research Board, Govt. of India (CRG/000092).

Multifunctional inhibitors of SARS-CoV-2 by MM/PBSA, essential dynamics, and molecular dynamic investigations

The ongoing COVID-19 pandemic demands a novel approach to combat and identify potential therapeutic targets. The SARS-CoV-2 infection causes a hyperimmune response followed by a spectrum of diseases. Limonoids are a class of triterpenoids known to prevent the release of IL-6, IL-15, IL-1α, IL-1β via TNF and are also known to modulate PI3K/Akt/GSK-3β, JNK1/2, MAPKp38, ERK1/2, and PI3K/Akt/mTOR signaling pathways and could help to avoid viral infection, persistence, and pathogenesis. The present study employs a computational approach of virtual screening and molecular dynamic (MD) simulations of such compounds against RNA-dependent RNA polymerase (RdRp), Main protease (Mpro), and Papain-like protease (PLpro) of SARS-CoV-2. MD simulation, Molecular Mechanics Poisson-Boltzmann Surface Area (MM/PBSA), and Essential dynamics revealed that the macromolecule-ligand complexes are stable with very low free energy of binding. Such compounds that could modulate both host responses and inhibit viral machinery could be beneficial in effectively controlling the global pandemic.

Immunoprotective potential of Ayurvedic herb Kalmegh (Andrographis paniculata) against respiratory viral infections - LC-MS/MS and network pharmacology analysis

INTRODUCTION

Immunity boosting has emerged as a global strategy to fight the SARS-CoV-2 pandemic situation. In India, AYUSH systems of medicine have been promoted as an immune-protection strategy. Andrographis paniculata (Burm. F) Nees (AP) mentioned in Ayurveda has been widely used for treating sore throat, flu, and upper respiratory tract infections which may provide possible novel therapeutic approaches, exclusively targeting SARS-CoV-2 and its pathways.

OBJECTIVES

The present work uses liquid chromatography-tandem mass spectrometry (LC-MS/MS) metabolomics and combination synergy analysis based on network pharmacology to mine multimode evidence to understand the possible mechanism of action, diseases association, protein-protein interaction and major pathways involved therein.

MATERIAL AND METHODS

Metabolite profiling was performed by Agilent QTOF LC-MS/MS system. Network pharmacology analysis was performed by using functional annotation analysis based on databases like Binding DB, STRING, DAVID and KEGG for further data mining. Further combination synergy was evaluated using "neighbourhood approach" and networks were constructed through Cytoscape 3.2.1.

RESULTS

The molecules from kalmegh provides immune-protection and anti-viral response via involving different pathways, like toll-like receptor pathway, PI3/AKT pathway and MAP kinase pathways against COVID-19 infection. The KEGG analysis showed that in a vast majority of the most enriched pathways, AP were associated with viral infections and upper respiratory tract infections.

CONCLUSIONS

The results suggest a synergy between andrographolide and other molecules identified as safe and efficacious anti-inflammatory agent having effects on upper respiratory tract infections and can significantly decrease the production of cytokines and pro-inflammatory factors in viral infections.

The Association of Respiratory Viruses with Oxidative Stress and Antioxidants. Implications for the COVID-19 Pandemic

The spread of a new strain of coronavirus, SARS-CoV-2, a pandemic, poses a serious health problem for all humanity. Compared with the previous outbreaks of coronavirus infection in 2002 and 2012, COVID-19 infection has high rates of lethality, contagiousness, and comorbidity. The effective methods of prevention and treatment are extremely limited. Oxidative stress is actively involved in the mechanisms of initiation and maintenance of violations of homeostatic reactions in respiratory viral infections. It is important to stop systemic inflammation aimed at "extinguishing" the cytokine "storm", caused by the production of reactive oxygen species. Antioxidant defense medications, such as vitamin C, N-acetylcysteine, melatonin, quercetin, glutathione, astaxanthin, polyphenols, fat-soluble vitamins, and polyunsaturated fatty acids have proven well in experimental and clinical studies of influenza, pneumonia, and other respiratory disorders. The use of medications with antioxidant activity could be justified and most probably would increase the effectiveness of the fight against new coronavirus.

Targeting Multiple Signal Transduction Pathways of SARS-CoV-2: Approaches to COVID-19 Therapeutic Candidates

Due to the complicated pathogenic pathways of coronavirus disease 2019 (COVID-19), related medicinal therapies have remained a clinical challenge. COVID-19 highlights the urgent need to develop mechanistic pathogenic pathways and effective agents for preventing/treating future epidemics. As a result, the destructive pathways of COVID-19 are in the line with clinical symptoms induced by severe acute coronary syndrome (SARS), including lung failure and pneumonia. Accordingly, revealing the exact signaling pathways, including inflammation, oxidative stress, apoptosis, and autophagy, as well as relative representative mediators such as tumor necrosis factor-α (TNF-α), nuclear factor erythroid 2-related factor 2 (Nrf2), Bax/caspases, and Beclin/LC3, respectively, will pave the road for combating COVID-19. Prevailing host factors and multiple steps of SARS-CoV-2 attachment/entry, replication, and assembly/release would be hopeful strategies against COVID-19. This is a comprehensive review of the destructive signaling pathways and host-pathogen interaction of SARS-CoV-2, as well as related therapeutic targets and treatment strategies, including potential natural products-based candidates.

Risk of severe herpes zoster infection in patients with polycystic kidney disease: A nation-wide cohort study with propensity score matching analysis

BACKGROUND

Polycystic kidney disease (PKD) is suggested to be likely associated with underlying immunological dysregulation. This lymphopenia poses a risk of viral infection. Data to elucidate the herpes virus infection risk in patients with PKD are lacking; therefore, we conducted a national-wide population-based cohort study to investigate the herpes virus risk in PKD patients.

METHODS

From the Taiwan National Health Insurance Research Database (NHIRD), patients who were hospitalised with a diagnosis of polycystic kidney disease were defined as case group of PKD patients; patients without any diagnosis of PKD during the study period were grouped into the non-PKD cohort. The index date was set as the date when the patients were newly diagnosed with PKD. All study patients were followed up until the occurrence of herpes zoster infection, death, withdrawal from the NHIRD for other reasons, or until December 31, 2013.

RESULTS

We included 4366 PKD patients and 4366 non-PKD patients. The incidence rate and the risk of developing herpes zoster infection were estimated using multivariate stratified analyses. PKD patients had a 1.97-fold risk of herpes zoster virus infection (aHR = 1.97, 95% CI 1.17-3.31) compared with the non-PKD cohort. On multilayer stratification, PKD patients without any comorbidities had a significantly increased risk of herpes zoster infection (aHR = 3.10, 95% CI 1.37-7.00).

CONCLUSION

This is the first study to reveal a high risk of severe herpes zoster infection in patients with PKD. High index suspicion of severe herpes zoster infection should be maintained in clinical professionals.

The roles of signaling pathways in SARS-CoV-2 infection; lessons learned from SARS-CoV and MERS-CoV

The number of descriptions of emerging viruses has grown at an unprecedented rate since the beginning of the 21st century. Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), which causes coronavirus disease 2019 (COVID-19), is the third highly pathogenic coronavirus that has introduced itself into the human population in the current era, after SARS-CoV and Middle East respiratory syndrome coronavirus (MERS-CoV). Molecular and cellular studies of the pathogenesis of this novel coronavirus are still in the early stages of research; however, based on similarities of SARS-CoV-2 to other coronaviruses, it can be hypothesized that the NF-κB, cytokine regulation, ERK, and TNF-α signaling pathways are the likely causes of inflammation at the onset of COVID-19. Several drugs have been prescribed and used to alleviate the adverse effects of these inflammatory cellular signaling pathways, and these might be beneficial for developing novel therapeutic modalities against COVID-19. In this review, we briefly summarize alterations of cellular signaling pathways that are associated with coronavirus infection, particularly SARS-CoV and MERS-CoV, and tabulate the therapeutic agents that are currently approved for treating other human diseases.

Exploring active ingredients and function mechanisms of Ephedra-bitter almond for prevention and treatment of Corona virus disease 2019 (COVID-19) based on network pharmacology

BACKGROUND

COVID-19 has caused a global pandemic, and there is no wonder drug for epidemic control at present. However, many clinical practices have shown that traditional Chinese medicine has played an important role in treating the outbreak. Among them, ephedra-bitter almond is a common couplet medicine in anti-COVID-19 prescriptions. This study aims to conduct an exploration of key components and mechanisms of ephedra-bitter almond anti-COVID-19 based on network pharmacology.

MATERIAL AND METHODS

We collected and screened potential active components of ephedra-bitter almond based on the TCMSP Database, and we predicted targets of the components. Meanwhile, we collected relevant targets of COVID-19 through the GeneCards and CTD databases. Then, the potential targets of ephedra-bitter almond against COVID-19 were screened out. The key components, targets, biological processes, and pathways of ephedra-bitter almond anti-COVID-19 were predicted by constructing the relationship network of herb-component-target (H-C-T), protein-protein interaction (PPI), and functional enrichment. Finally, the key components and targets were docked by AutoDock Vina to explore their binding mode.

RESULTS

Ephedra-bitter almond played an overall regulatory role in anti-COVID-19 via the patterns of multi-component-target-pathway. In addition, some key components of ephedra-bitter almond, such as β-sitosterol, estrone, and stigmasterol, had high binding activity to 3CL and ACE2 by molecular docking simulation, which provided new molecular structures for new drug development of COVID-19.

CONCLUSION

Ephedra-bitter almonds were used to prevent and treat COVID-19 through directly inhibiting the virus, regulating immune responses, and promoting body repair. However, this work is a prospective study based on data mining, and the findings need to be interpreted with caution.

COVID-19: oxidative stress and the relevance of antioxidant therapy

The emergence of viral respiratory pathogens with high pandemic potential, such as the SARS-CoV-2, poses a serious public health problem, with a very limited arsenal of effective tools and techniques to prevent and treat a new pandemic infection. The literature on the involvement of reactive oxygen species in the pathogenesis of coronavirus infections and the potential for antioxidant therapy was reviewed. Because of available evidence on the involvement of oxidative stress in the mechanisms of initiation and maintenance of homeostasis disorders in SARS-CoV-2, approaches combining reduction of ROS synthesis, inhibition of virus replication, anti-inflammatory action, reduction of hypoxia, and reduction of the toxic effects of drug therapy may be very effective. The hypothesis of the expediency of treating systemic inflammation aimed at "quenching" the cytokine "storm", caused largely by the production of reactive oxygen species, seems essential. In this connection, it is pathophysiologically justified to use for prophylactic and therapeutic purposes antioxidant drugs, which have proven themselves on the example of other viral respiratory infections. Thus, the high activity of preparations of vitamin C, N-acetylcysteine, melatonin, quercetin, glutathione, astaxanthin, polyphenols, polyunsaturated fatty acids, etc. was noted. In addition, these drugs effectively protect the vascular wall, which has been proven for a number of cardiovascular diseases and that can be effective in developing with COVID-19 vasculitis. There is a more pronounced combined effect of these drugs, which is already used in treatment protocols for patients with SARS-CoV-2. Special attention should also be paid to the use of antioxidant drugs as a means to reduce the toxic manifestations of antiviral therapy. Thus, the use of drugs with antioxidant activity can be justified and will certainly improve the effectiveness of the fight against the pandemic of new coronavirus infection.

Comprehensive analysis of drugs to treat SARS‑CoV‑2 infection: Mechanistic insights into current COVID‑19 therapies (Review)

The major impact produced by the severe acute respiratory syndrome coronavirus 2 (SARS‑CoV‑2) focused many researchers attention to find treatments that can suppress transmission or ameliorate the disease. Despite the very fast and large flow of scientific data on possible treatment solutions, none have yet demonstrated unequivocal clinical utility against coronavirus disease 2019 (COVID‑19). This work represents an exhaustive and critical review of all available data on potential treatments for COVID‑19, highlighting their mechanistic characteristics and the strategy development rationale. Drug repurposing, also known as drug repositioning, and target based methods are the most used strategies to advance therapeutic solutions into clinical practice. Current in silico, in vitro and in vivo evidence regarding proposed treatments are summarized providing strong support for future research efforts.

Oxidative Stress as Key Player in Severe Acute Respiratory Syndrome Coronavirus (SARS-CoV) Infection

The emergence of viral respiratory pathogens with pandemic potential, such as severe acute respiratory syndrome coronavirus (SARS-CoV), the pathogenic agent of Covid-19, represent a serious health problem worldwide. Respiratory viral infections are, in general, associated with cytokine production, inflammation, cell death, and other pathophysiological processes, which could be link with a redox imbalance or oxidative stress. These phenomena are substantially increased during aging. Actually, severity and mortality risk of SARS-CoV-2 infection or Covid-19 disease have been associated with the age. The aim of the present work was to contribute with the understanding of the possible link between oxidative stress and the pathogenesis, severity and mortality risk in patients affected by SARS-CoV infection.

STAT3 roles in viral infection: antiviral or proviral?

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

The SARS-coronavirus membrane protein induces apoptosis via interfering with PDK1-PKB/Akt signalling

A number of viral gene products are capable of inducing apoptosis by interfering with various cellular signalling cascades. We previously reported the pro-apoptotic property of the SARS-CoV (severe acute respiratory syndrome coronavirus) M (membrane)-protein and a down-regulation of the phosphorylation level of the cell-survival protein PKB (protein kinase B)/Akt in cells expressing M-protein. We also showed that overexpression of PDK1 (3-phosphoinositide-dependent protein kinase 1), the immediate upstream kinase of PKB/Akt, suppressed M-induced apoptosis. This illustrates that M-protein perturbs the PDK1 and PKB/Akt cell survival signalling pathway. In the present study, we demonstrated that the C-terminus of M-protein interacts with the PH (pleckstrin homology) domain of PDK1. This interaction disrupted the association between PDK1 and PKB/Akt, and led to down-regulation of PKB/Akt activity. This subsequently reduced the level of the phosphorylated forkhead transcription factor FKHRL1 and ASK (apoptosis signal-regulating kinase), and led to the activation of caspases 8 and 9. Altogether, our data demonstrate that the SARS-CoV M-protein induces apoptosis through disrupting the interaction of PDK1 with PKB/Akt, and this causes the activation of apoptosis. Our work highlights that the SARS-CoV M protein is highly pro-apoptotic and is capable of simultaneously inducing apoptosis via initiating caspases 8 and 9. Preventing the interaction between M-protein and PDK1 is a plausible therapeutic approach to target the pro-apoptotic property of SARS-CoV.

Inhibition of the PI3K/Akt pathway by Ly294002 does not prevent establishment of persistent Junín virus infection in Vero cells

In previous work, we demonstrated that the arenavirus Junín virus (JUNV) is able to activate Akt by means of the phosphatidylinositol-3-kinase (PI3K) survival pathway during virus entry. This work extends our study, emphasizing the relevance of this pathway in the establishment and maintenance of persistent infection in vitro. During the course of infection, JUNV-infected Vero cells showed a typical cytopathic effect that may be ascribed to apoptotic cell death. Treatment of infected cultures with Ly294002, an inhibitor of the PI3K/Akt pathway, produced an apoptotic response similar to that observed for uninfected cells treated with the drug. This result suggests that virus-induced activation of the PI3K/Akt pathway does not deliver a strong enough anti-apoptotic signal to explain the low proportion of apoptotic cells observed during infection. Also, inhibition of the PI3K/Akt pathway during the acute stage of infection did not prevent the establishment of persistence. Furthermore, treatment of persistently JUNV-infected cells with Ly294002 did not alter viral protein expression. These findings indicate that despite the positive modulation of the PI3/Akt pathway during Junín virus entry, this would not play a critical role in the establishment and maintenance of JUNV persistence in Vero cells.

The endoplasmic reticulum stress sensor IRE1α protects cells from apoptosis induced by the coronavirus infectious bronchitis virus

The unfolded-protein response (UPR) is a signal transduction cascade triggered by perturbation of the homeostasis of the endoplasmic reticulum (ER). UPR resolves ER stress by activating a cascade of cellular responses, including the induction of molecular chaperones, translational attenuation, ER-associated degradation, and other mechanisms. Under prolonged and irremediable ER stress, however, the UPR can also trigger apoptosis. Here, we report that in cells infected with the avian coronavirus infectious bronchitis virus (IBV), ER stress was induced and the IRE1α-XBP1 pathway of UPR was activated. Knockdown and overexpression experiments demonstrated that IRE1α protects infected cells from IBV-induced apoptosis, which required both its kinase and RNase activities. Our data also suggest that splicing of XBP1 mRNA by IRE1α appears to convert XBP1 from a proapoptotic XBP1u protein to a prosurvival XBP1s protein. Moreover, IRE1α antagonized IBV-induced apoptosis by modulating the phosphorylation status of the proapoptotic c-Jun N-terminal kinase (JNK) and the prosurvival RAC-alpha serine/threonine-protein kinase (Akt). Taken together, the data indicate that the ER stress sensor IRE1α is activated in IBV-infected cells and serves as a survival factor during coronavirus infection.

IMPORTANCE

Animal coronaviruses are important veterinary viruses, which could cross the species barrier, becoming severe human pathogens. Molecular characterization of the interactions between coronaviruses and host cells is pivotal to understanding the pathogenicity and species specificity of coronavirus infection. It has been well established that the endoplasmic reticulum (ER) is closely associated with coronavirus replication. Here, we report that inositol-requiring protein 1 alpha (IRE1α), a key sensor of ER stress, is activated in cells infected with the avian coronavirus infectious bronchitis virus (IBV). Moreover, IRE1α is shown to protect the infected cells from apoptosis by modulating the unfolded-protein response (UPR) and two kinases related to cell survival. This study demonstrates that UPR activation constitutes a major aspect of coronavirus-host interactions. Manipulations of the coronavirus-induced UPR may provide novel therapeutic targets for the control of coronavirus infection and pathogenesis.

Make yourself at home: viral hijacking of the PI3K/Akt signaling pathway

As viruses do not possess genes encoding for proteins required for translation, energy metabolism or membrane biosynthesis, they are classified as obligatory intracellular parasites that depend on a host cell to replicate. This genome limitation forces them to gain control over cellular processes to ensure their successful propagation. A diverse spectrum of virally encoded proteins tackling a broad spectrum of cellular pathways during most steps of the viral life cycle ranging from the host cell entry to viral protein translation has evolved. Since the host cell PI3K/Akt signaling pathway plays a critical regulatory role in many cellular processes including RNA processing, translation, autophagy and apoptosis, many viruses, in widely varying ways, target it. This review focuses on a number of remarkable examples of viral strategies, which exploit the PI3K/Akt signaling pathway for effective viral replication.

Influenza A virus neuraminidase protein enhances cell survival through interaction with carcinoembryonic antigen-related cell adhesion molecule 6 (CEACAM6) protein

The influenza virus neuraminidase (NA) protein primarily aids in the release of progeny virions from infected cells. Here, we demonstrate a novel role for NA in enhancing host cell survival by activating the Src/Akt signaling axis via an interaction with carcinoembryonic antigen-related cell adhesion molecule 6/cluster of differentiation 66c (C6). NA/C6 interaction leads to increased tyrosyl phosphorylation of Src, FAK, Akt, GSK3β, and Bcl-2, which affects cell survival, proliferation, migration, differentiation, and apoptosis. siRNA-mediated suppression of C6 resulted in a down-regulation of activated Src, FAK, and Akt, increased apoptosis, and reduced expression of viral proteins and viral titers in influenza virus-infected human lung adenocarcinoma epithelial and normal human bronchial epithelial cells. These findings indicate that influenza NA not only aids in the release of progeny virions, but also cell survival during viral replication.

From virus entry to release: the diverse functions of PI3K during RNA virus infections

RNA viruses are the causative agents of severe diseases in vertebrates. Upon viral infection, various intracellular signaling pathways are induced within the infected cells. While most of the different cellular signaling responses are initiated as antiviral defense mechanisms to counteract invading pathogens, they may also be exploited by viruses to support their replication. Recently, PI3K has been added to the growing list of signaling factors and pathways that are activated upon viral infections and regulate the replication process. Here, the current knowledge on RNA virus-induced PI3K-regulated signaling processes and how the pathogens take advantage of these activities within the infected cells is summarized.

Equine torovirus (BEV) induces caspase-mediated apoptosis in infected cells

Toroviruses are gastroenteritis causing agents that infect different animal species and humans. To date, very little is known about how toroviruses cause disease. Here, we describe for the first time that the prototype member of this genus, the equine torovirus Berne virus (BEV), induces apoptosis in infected cells at late times postinfection. Observation of BEV infected cells by electron microscopy revealed that by 24 hours postinfection some cells exhibited morphological characteristics of apoptotic cells. Based on this finding, we analyzed several apoptotic markers, and observed protein synthesis inhibition, rRNA and DNA degradation, nuclear fragmentation, caspase-mediated cleavage of PARP and eIF4GI, and PKR and eIF2α phosphorylation, all these processes taking place after peak virus production. We also determined that both cell death receptor and mitochondrial pathways are involved in the apoptosis process induced by BEV. BEV-induced apoptosis at late times postinfection, once viral progeny are produced, could facilitate viral dissemination in vivo and contribute to viral pathogenesis.

Influenza virus and cell signaling pathways

Influenza viruses comprise a major class of human respiratory pathogens, responsible for causing morbidity and mortality worldwide. Influenza A virus, due to its segmented RNA genome, is highly subject to mutation, resulting in rapid formation of variants. During influenza infection, viral proteins interact with host proteins and exploit a variety of cellular pathways for their own benefit. Influenza virus inhibits the synthesis of these cellular proteins and facilitates expression of its own proteins for viral transcription and replication. Infected cell pathways are hijacked by an array of intracellular signaling cascades such as NF-κB signaling, PI3K/Akt pathway, MAPK pathway, PKC/PKR signaling and TLR/RIG-I signaling cascades. This review presents a research update on the subject and discusses the impact of influenza viral infection on these cell signaling pathways.

Blocking eIF4E-eIF4G interaction as a strategy to impair coronavirus replication

Coronaviruses are a family of enveloped single-stranded positive-sense RNA viruses causing respiratory, enteric, and neurologic diseases in mammals and fowl. Human coronaviruses are recognized to cause up to a third of common colds and are suspected to be involved in enteric and neurologic diseases. Coronavirus replication involves the generation of nested subgenomic mRNAs (sgmRNAs) with a common capped 5' leader sequence. The translation of most of the sgmRNAs is thought to be cap dependent and displays a requirement for eukaryotic initiation factor 4F (eIF4F), a heterotrimeric complex needed for the recruitment of 40S ribosomes. We recently reported on an ultrahigh-throughput screen to discover compounds that inhibit eIF4F activity by blocking the interaction of two of its subunits (R. Cencic et al., Proc. Natl. Acad. Sci. U. S. A. 108:1046-1051, 2011). Herein we describe a molecule from this screen that prevents the interaction between eIF4E (the cap-binding protein) and eIF4G (a large scaffolding protein), inhibiting cap-dependent translation. This inhibitor significantly decreased human coronavirus 229E (HCoV-229E) replication, reducing the percentage of infected cells and intra- and extracellular infectious virus titers. Our results support the strategy of targeting the eIF4F complex to block coronavirus infection.

Modulation of Host Cell Death by SARS Coronavirus Proteins

Both types of cell death, namely necrosis and apoptosis, are found in organs of SARS coronavirus (CoV) infected patients. The gastrointestinal tract, however, although also a target for SARS-CoV replication, is obviously not affected by cell death mechanisms. Such differences in cell death induction are paralleled by in-vitro studies. In a colon-derived cell line (Caco-2), proapoptotic proteins were down- and antiapoptotic proteins were upregulated during SARS-CoV infection. By contrast, in SARS-CoV infected Vero E6 cells, apoptosis was induced via the p38 MAPK and caspase dependent pathways. Both apoptotic pathways, although mostly the intrinsic signal transduction, can be targeted by structural as well as accessory proteins of SARS-CoV. The fact that all structural and most of the accessory proteins of SARS-CoV are implicated in apoptotic scenarios indicates the fundamental role of apoptosis in the SARS-CoV life cycle. Interestingly, at least for the nucleocapsid protein of SARS-CoV, a cell-type specific manipulation of apoptosis was confirmed.

The open reading frame 3a protein of severe acute respiratory syndrome-associated coronavirus promotes membrane rearrangement and cell death

The genome of the severe acute respiratory syndrome-associated coronavirus (SARS-CoV) contains eight open reading frames (ORFs) that encode novel proteins. These accessory proteins are dispensable for in vitro and in vivo replication and thus may be important for other aspects of virus-host interactions. We investigated the functions of the largest of the accessory proteins, the ORF 3a protein, using a 3a-deficient strain of SARS-CoV. Cell death of Vero cells after infection with SARS-CoV was reduced upon deletion of ORF 3a. Electron microscopy of infected cells revealed a role for ORF 3a in SARS-CoV induced vesicle formation, a prominent feature of cells from SARS patients. In addition, we report that ORF 3a is both necessary and sufficient for SARS-CoV-induced Golgi fragmentation and that the 3a protein accumulates and localizes to vesicles containing markers for late endosomes. Finally, overexpression of ADP-ribosylation factor 1 (Arf1), a small GTPase essential for the maintenance of the Golgi apparatus, restored Golgi morphology during infection. These results establish an important role for ORF 3a in SARS-CoV-induced cell death, Golgi fragmentation, and the accumulation of intracellular vesicles.

Signaling Pathways of SARS-CoV In Vitro and In Vivo

Severe acute respiratory syndrome (SARS) is a respiratory illness with variable symptoms that was recognized as the first near-pandemic infectious disease of the twenty-first century. A novel human coronavirus, named SARS coronavirus (SARS-CoV), derived from SARS patients was reported as the etiologic agent of SARS. Studying the signaling pathways of SARS-infected cells is key to understanding the molecular mechanism of SARS viral infection. Cell death is observed in cultured Vero E6 cells after SARS-CoV infection. From SARS-CoV infection to cell death, p38 mitogen-activated protein kinase (MAPK) is a key participant in the determination of cell death and survival. Two signaling pathways comprising signal transducer and activator of transcription 3 (STAT3) and p90 ribosomal S6 kinase (p90RSK) are downstream of p38 MAPK. AKT and JNK (Jun NH₂-terminal kinase) signaling pathways are important to establish persistent infection of SARS-CoV in Vero E6 cells. Expression studies of SARS-CoV proteins indicate that the viral proteins are able to activate signaling pathways of host cells. The study of signaling pathways in SARS-CoV patients is difficult to perform compared with in vitro studies due to the effects of the human immune system. This review highlights recent progress in characterizing signal transduction pathways in SARS-CoV-infected cells in vitro and in vivo.

A new player in a deadly game: influenza viruses and the PI3K/Akt signalling pathway

Upon influenza A virus infection of cells, a wide variety of antiviral and virus‐supportive signalling pathways are induced. Phosphatidylinositol‐3‐kinase (PI3K) is a recent addition to the growing list of signalling mediators that are activated by these viruses. Several studies have addressed the role of PI3K and the downstream effector protein kinase Akt in influenza A virus‐infected cells. PI3K/Akt signalling is activated by diverse mechanisms in a biphasic manner and is required for multiple functions during infection. While the kinase supports activation of the interferon regulatory factor‐3 during antiviral interferon induction, it also exhibits virus supportive functions. In fact, PI3K not only regulates a very early step during viral entry but also results in suppression of premature apoptosis at later stages of infection. The latter function is dependent on the expression of the viral non‐structural protein‐1 (A/NS1). It has been shown that PI3K activation occurs by direct interaction of A/NS1 with the p85 regulatory subunit and interaction sites of A/NS1 and p85 have now been mapped in detail. Here, we summarize the current knowledge on influenza virus‐induced PI3K signalling and how this pathway supports viral propagation.

Severe acute respiratory syndrome coronavirus triggers apoptosis via protein kinase R but is resistant to its antiviral activity

In this study, infection of 293/ACE2 cells with severe acute respiratory syndrome coronavirus (SARS-CoV) activated several apoptosis-associated events, namely, cleavage of caspase-3, caspase-8, and poly(ADP-ribose) polymerase 1 (PARP), and chromatin condensation and the phosphorylation and hence inactivation of the eukaryotic translation initiation factor 2alpha (eIF2alpha). In addition, two of the three cellular eIF2alpha kinases known to be virus induced, protein kinase R (PKR) and PKR-like endoplasmic reticulum kinase (PERK), were activated by SARS-CoV. The third kinase, general control nonderepressible-2 kinase (GCN2), was not activated, but late in infection the level of GCN2 protein was significantly reduced. Reverse transcription-PCR analyses revealed that the reduction of GCN2 protein was not due to decreased transcription or stability of GCN2 mRNA. The specific reduction of PKR protein expression by antisense peptide-conjugated phosphorodiamidate morpholino oligomers strongly reduced cleavage of PARP in infected cells. Surprisingly, the knockdown of PKR neither enhanced SARS-CoV replication nor abrogated SARS-CoV-induced eIF2alpha phosphorylation. Pretreatment of cells with beta interferon prior to SARS-CoV infection led to a significant decrease in PERK activation, eIF2alpha phosphorylation, and SARS-CoV replication. The various effects of beta interferon treatment were found to function independently on the expression of PKR. Our results show that SARS-CoV infection activates PKR and PERK, leading to sustained eIF2alpha phosphorylation. However, virus replication was not impaired by these events, suggesting that SARS-CoV possesses a mechanism to overcome the inhibitory effects of phosphorylated eIF2alpha on viral mRNA translation. Furthermore, our data suggest that viral activation of PKR can lead to apoptosis via a pathway that is independent of eIF2alpha phosphorylation.

Transcriptional profiling of Vero E6 cells over-expressing SARS-CoV S2 subunit: insights on viral regulation of apoptosis and proliferation

We have previously demonstrated that over-expression of spike protein (S) of severe acute respiratory syndrome coronavirus (SARS-CoV) or its C-terminal subunit (S2) is sufficient to induce apoptosis in vitro. To further investigate the possible roles of S2 in SARS-CoV-induced apoptosis and pathogenesis of SARS, we characterized the host expression profiles induced upon S2 over-expression in Vero E6 cells by oligonucleotide microarray analysis. Possible activation of mitochondrial apoptotic pathway in S2 expressing cells was suggested, as evidenced by the up-regulation of cytochrome c and down-regulation of the Bcl-2 family anti-apoptotic members. Inhibition of Bcl-2-related anti-apoptotic pathway was further supported by the diminution of S2-induced apoptosis in Vero E6 cells over-expressing Bcl-xL. In addition, modulation of CCN E2 and CDKN 1A implied the possible control of cell cycle arrest at G1/S phase. This study is expected to extend our understanding on the pathogenesis of SARS at a molecular level.

Proteomic analysis of up-regulated proteins in human promonocyte cells expressing severe acute respiratory syndrome coronavirus 3C-like protease

The pathogenesis of severe acute respiratory syndrome coronavirus (SARS CoV) is an important issue for treatment and prevention of SARS. Previously, SARS CoV 3C-like protease (3CLpro) has been demonstrated to induce apoptosis via the activation of caspase-3 and caspase-9 (Lin, C. W., Lin, K. H., Hsieh, T. H., Shiu, S. Y. et al., FEMS Immunol. Med. Microbiol. 2006, 46, 375-380). In this study, proteome analysis of the human promonocyte HL-CZ cells expressing SARS CoV 3CLpro was performed using 2-DE and nanoscale capillary LC/ESI quadrupole-TOF MS. Functional classification of identified up-regulated proteins indicated that protein metabolism and modification, particularly in the ubiquitin proteasome pathway, was the main biological process occurring in SARS CoV 3CLpro-expressing cells. Thirty-six percent of identified up-regulated proteins were located in the mitochondria, including apoptosis-inducing factor, ATP synthase beta chain and cytochrome c oxidase. Interestingly, heat shock cognate 71-kDa protein (HSP70), which antagonizes apoptosis-inducing factor was shown to down-regulate and had a 5.29-fold decrease. In addition, confocal image analysis has shown release of mitochondrial apoptogenic apoptosis-inducing factor and cytochrome c into the cytosol. Our results revealed that SARS CoV 3CLpro could be considered to induce mitochondrial-mediated apoptosis. The study provides system-level insights into the interaction of SARS CoV 3CLpro with host cells, which will be helpful in elucidating the molecular basis of SARS CoV pathogenesis.

Signal transduction in SARS-CoV-infected cells

abstract: Severe acute respiratory syndrome (SARS) is a newly found infectious disease that is caused by a novel human coronavirus, SARS coronavirus (SARS‐CoV). Because the mortality rate of SARS patients is very high, understanding the pathological mechanisms of SARS not only in vivo but in vitro is important for the prevention of SARS. Activation of signaling pathways caused by SARS‐CoV infection leads to the phosphorylation and activation of downstream molecules. Two conflicting cellular programs, apoptosis to eliminate virus‐infected cells and survival to delay apoptosis by producing antiviral cytokines, occur in SARS patients. Recent studies regarding SARS and SARS‐CoV have clarified that activation of mitogen‐activated protein kinases (MAPKs) plays important roles in upregulation of cytokine expression and apoptosis both in vitro and in vivo. Both Akt and p38 MAPK are keys for determination of cell survival or death in SARS‐CoV‐infected cells in vitro. Agents being developed to target these signaling cascades may be important for the design of anti‐SARS‐CoV drugs. This review highlights recent progress regarding SARS‐CoV biology, especially signal transduction in SARS‐CoV‐infected cells.

Activation of cell signaling pathways is dependant on the biotype of bovine viral diarrhea viruses type 2

Bovine viral diarrhea virus (BVDV), a pestivirus of the Flaviviridae family, is an economically important cattle pathogen with a worldwide distribution. Besides the segregation into two distinct species (BVDV1/BVDV2) two different biotypes, a cytopathic (cp) and a noncytopathic (ncp) biotype, are distinguished based on their behavior in epithelial cell cultures. One of the most serious forms of BVDV infection affecting immunocompetent animals of all ages is severe acute BVD (sa BVD) which is caused by highly virulent ncp BVDV2 strains. Previous studies revealed that these highly virulent ncp viruses cause cell death in a lymphoid cell line (BL3) which is not clearly associated with typical apoptotic changes (e.g. PARP cleavage) observed after infection with cp BVDV. To further characterize the underlying molecular mechanisms, we first analyzed the role of the mitochondria and caspases as key mediators of apoptosis. Compared to infection with cp BVDV2, infection with highly virulent ncp BVDV2 resulted in a delayed and less pronounced disruption of the mitochondrial transmembrane potential (DeltaPsi(m)) and a weaker activation of the caspase cascade. In contrast, infection with low virulence ncp BVDV2 showed no significant differences from the uninfected control cells. Since different pro- and anti-apoptotic cellular signaling pathways may become activated upon virus infection, we compared the effect of different BVDV2 strains on cellular signaling pathways in BL3 cells. Stress-mediated p38 MAPK phosphorylation was detected only in cells infected with cp BVDV2. Interestingly, infection with highly virulent ncp BVDV2 was found to influence the phosphoinositide 3-kinase (PI3K)-Akt pathway. This indicates that BL3 cells respond differently to infection with BVDV depending on virulence and biotype.

Enhancement of cytotoxicity against Vero E6 cells persistently infected with SARS-CoV by Mycoplasma fermentans

We previously reported that cells with persistent severe acute respiratory syndrome coronavirus (SARS-CoV) infection were established after apoptotic events. In the present study, we investigated the cytopathic effects of dual infection with SARS-CoV and Mycoplasma fermentans on Vero E6 cells. Dual infection completely killed cells and prevented the establishment of persistent SARS-CoV infection. M. fermentans induced inhibition of cell proliferation, but the cells remained alive. Apoptosis was induced easily in M. fermentans-infected cells, indicating that they were primed for apoptosis. These results indicated that M. fermentans enhances apoptosis in surviving cells that have escaped from SARS-CoV-induced apoptosis.

The SARS-Coronavirus Membrane protein induces apoptosis through modulating the Akt survival pathway

A number of viral gene products are capable of triggering apoptotic cell death through interfering with cellular signaling cascades, including the Akt kinase pathway. In this study, the pro-apoptotic role of the SARS-CoV Membrane (M) structural protein is described. We found that the SARS-CoV M protein induced apoptosis in both HEK293T cells and transgenic Drosophila. We further showed that M protein-induced apoptosis involved mitochondrial release of cytochrome c protein, and could be suppressed by caspase inhibitors. Over-expression of M caused a dominant rough-eye phenotype in adult Drosophila. By performing a forward genetic modifier screen, we identified phosphoinositide-dependent kinase-1 (PDK-1) as a dominant suppressor of M-induced apoptotic cell death. Both PDK-1 and Akt kinases play essential roles in the cell survival signaling pathway. Altogether, our data show that SARS-CoV M protein induces apoptosis through the modulation of the cellular Akt pro-survival pathway and mitochondrial cytochrome c release.

Analysis of proteins that interact with nucleocapsid protein of SARS-CoV using 15-mer phage-displayed library

Analysis of proteins that interact with N protein of SARS-CoV using 15-mer phage-displayed library will help to explore the virus pathogenesis and to develop new drugs and vaccines against SARS. In this study, we cloned, expressed and purified N protein of SARS-CoV. This 46-kD N protein was verified by SDS-PAGE and Western-blot. Then, the peptides binding-specific to N protein were identified using 15-mer phage-displayed library. Surprisingly, all of the 89 clones from monoclonal ELISA were positive (S/N>2.1) and the result was further confirmed experimentally once again. Six N protein-binding peptides, designated separately as SNA1, SNA2, SNA4, SNA5, SNA9 and SNG11, were selected for sequencing. Sequence analysis suggested that SNA5 shared approximatively 100% sequence identity to SNA4, SNA2, SNA9 and SNA1. In addition, the binding specificity of the 15-mer peptides with the SARS-CoV N protein was further demonstrated by blocking ELISA using the synthetical 15-mer peptide according to the deduced amino acid sequence of SNA5. Also, the deduced amino sequence of SNA5 was compared with proteins in translated database using the tblastx program, and the results showed that the proteins with the highest homology were Ubiquinol-cytochrome c reductase iron-sulfur subunits (UCRI or UQCR), otherwise known as the Rieske iron-sulfur proteins (RISP). Notablely, in the [2Fe-2S] redox centre of UCRI, there were 6 residues [GGW(Y)F(Y)CP] compatible to the residues (position 2→7, GGWFCP7) of the NH2-terminal of the 15-mer peptide, which indicated higher binding specificity between the N protein of SARS-CoV and the redox centre of UCRI to some extent. Here, the possible molecular mechanisms of SARS-CoV N protein in the pathogenesis of SARS are discussed.

Biochemical aspects of coronavirus replication and virus-host interaction

Infection by different coronaviruses (CoVs) causes alterations in the transcriptional and translational patterns, cell cycle, cytoskeleton, and apoptosis pathways of the host cells. In addition, CoV infection may cause inflammation, alter immune and stress responses, and modify the coagulation pathways. The balance between the up- and downregulated genes could explain the pathogenesis caused by these viruses. We review specific aspects of CoV-host interactions. CoV genome replication takes place in the cytoplasm in a membrane-protected microenvironment and may control the cell machinery by locating some of their proteins in the host cell nucleus. CoVs initiate translation by cap-dependent and cap-independent mechanisms. CoV transcription involves a discontinuous RNA synthesis (template switching) during the extension of a negative copy of the subgenomic mRNAs. The requirement for base-pairing during transcription has been formally demonstrated in arteriviruses and CoVs. CoV N proteins have RNA chaperone activity that may help initiate template switching. Both viral and cellular proteins are required for replication and transcription, and the role of selected proteins is addressed.

Mechanisms of establishment of persistent SARS-CoV-infected cells

Previously, we reported the establishment of cells with persistent SARS-CoV infection after apoptotic events and showed that both JNK and PI3K/Akt signaling pathways are important for persistence by treatment with inhibitors at the early stages of SARS-CoV infection. However, the mechanisms of establishment of persistent infection are still unclear. In this study, we investigated which signaling pathways play important roles in escape from apoptosis in cells infected with SARS-CoV. In persistently infected cells at 50h.p.i., PI3K/Akt, JNK, p38 MAPK and Bcl-2 were phosphorylated and the protein levels of Bcl-2 and Bcl-xL were increased. When surviving cells were treated with the JNK-specific inhibitor, SP600125, at 50h.p.i., all cells died, suggesting that the JNK signaling pathway is necessary for maintenance of persistently infected cells. Among the signaling pathways in persistently infected cells, Akt and JNK were phosphorylated in SARS-CoV-nucleocapsid (N) protein-expressing Vero E6 cells using vaccinia viral vector (DIs), strongly suggesting that N protein-induced phosphorylation of Akt and JNK are necessary to establish persistence. These results indicated that at least four proteins, Akt, JNK, Bcl-2 and Bcl-xL, are necessary for survival of persistently SARS-CoV-infected cells.

Cytokine regulation in SARS coronavirus infection compared to other respiratory virus infections

The pathogenesis of severe acute respiratory syndrome (SARS) is poorly understood and cytokine dysregulation has been suggested as one relevant mechanism to be explored. We compared the cytokine profile in Caco2 cells after infection of SARS coronavirus (SARS‐CoV) with other respiratory viruses including respiratory syncytial virus (RSV), influenza A virus (FluAV), and human parainfluenza virus type 2 (hPIV2). Interferon (IFN) system (production and response) was not suppressed by SARS‐CoV infection. Therefore, SARS‐CoV replication was suppressed by pretreatment with IFN. SARS‐CoV and RSV induced high levels of IL‐6 and RANTES compared with FluAV and hPIV2. Induction level of suppressor of cytokine signaling‐3 (SOCS3) by SARS‐CoV was significantly lower than that by RSV in spite of the significant production of IL‐6. Toll‐like receptors 4 and 9, which correlate with the induction of inflammatory response, were upregulated by SARS‐CoV infection. Collectively, overinduction of inflammatory cytokine and dysregulation of cytokine signaling may contribute to the immunopathology associated with “severe” inflammation in SARS. J. Med. Virol. 78:417–424, 2006. © 2006 Wiley‐Liss, Inc.

Inhibition of cell proliferation by SARS-CoV infection in Vero E6 cells

Severe acute respiratory syndrome (SARS) is caused by SARS‐coronavirus (SARS‐CoV). Infection of Vero E6 cells with SARS‐CoV inhibits cell proliferation. Our previous study indicated that Akt, which is poorly phosphorylated in confluent cultures of Vero E6 cells, is phosphorylated and then dephosphorylated upon infection by SARS‐CoV. In the present study, we showed that a serine residue of Akt was phosphorylated in Vero E6 cells in subconfluent culture and that Akt was dephosphorylated rapidly after SARS‐CoV infection without up‐regulation of its phosphorylation. Phosphorylation of glycogen synthase kinase‐3β, which is one of the downstream targets of Akt, was prevented in SARS‐CoV‐infected cells. However, treatment with glycogen synthase kinase‐3β small interfering RNA indicated that the glycogen synthase kinase‐3β signaling pathway was not related to inhibition of cell proliferation. Treatment of Vero E6 cells with the phosphatidylinositol 3′‐kinase/Akt inhibitor, LY294002, which induces dephosphorylation of Akt, inhibited cell proliferation. As shown in our previous studies, apoptosis occurred in virus‐infected cells within 18 h postinfection. Cellular mRNA transcription, which was reported to be up‐regulated in SARS‐CoV‐infected Caco‐2 cells, was not up‐regulated in virus‐infected Vero E6 cells, partially as a result of apoptosis. These results suggested that inhibition of cell proliferation is regulated by both the phosphatidylinositol 3′‐kinase/Akt signaling pathway and by apoptosis in SARS‐CoV‐infected Vero E6 cells. This is the first study to analyze SARS‐CoV‐induced cell growth inhibition.

Severe acute respiratory syndrome coronavirus 3C-like protease-induced apoptosis

The pathogenesis of severe acute respiratory syndrome-associated coronavirus (SARS-CoV) is an important issue for the treatment and prevention of severe acute respiratory syndrome. Recently, SARS-CoV has been demonstrated to induce cell apoptosis in Vero-E6 cells. The possible role of SARS-CoV 3C-like protease (3CLpro) in virus-induced apoptosis is characterized in this study. Growth arrest and apoptosis via caspase-3 and caspase-9 activities were demonstrated in SARS-CoV 3CLpro -expressing human promonocyte cells. The fluorescence intensity of dihydrorhodamine 123 staining indicated that cellular reactive oxygen species were markedly increased in SARS-CoV 3CLpro -expressing cells. Moreover, in vivo signalling pathway assay indicated that 3CLpro increased the activation of the nuclear factor-kappa B-dependent reporter, but inhibited activator protein-1-dependent transcription. This finding is likely to be responsible for virus-induced apoptotic signalling.

Bcl-xL inhibits T-cell apoptosis induced by expression of SARS coronavirus E protein in the absence of growth factors

One of the hallmark findings in patients suffering from SARS (severe acute respiratory syndrome) is lymphopenia, which is the result of massive lymphocyte death. SARS-CoV (SARS coronavirus), a novel coronavirus that has been etiologically associated with SARS cases, is homologous with MHV (murine hepatitis coronavirus), and MHV small envelope E protein is capable of inducing apoptosis. We hypothesized that SARS-CoV encodes a small envelope E protein that is homologous with MHV E protein, thus inducing T-cell apoptosis. To test this hypothesis, a cDNA encoding SARS-CoV E protein was created using whole gene synthesis. Our results showed that SARS-CoV E protein induced apoptosis in the transfected Jurkat T-cells, which was amplified to higher apoptosis rates in the absence of growth factors. However, apoptosis was inhibited by overexpressed antiapoptotic protein Bcl-xL. Moreover, we found that SARS-CoV E protein interacted with Bcl-xL in vitro and endogenous Bcl-xL in vivo and that Bcl-xL interaction with SARS-CoV E protein was mediated by BH3 (Bcl-2 homology domain 3) of Bcl-xL. Finally, we identified a novel BH3-like region located in the C-terminal cytosolic domain of SARS-CoV E protein, which mediates its binding to Bcl-xL. These results demonstrate, for the first time, a novel molecular mechanism of T-cell apoptosis that contributes to the SARS-CoV-induced lymphopenia observed in most SARS patients.

Regulation of p90RSK phosphorylation by SARS-CoV infection in Vero E6 cells

The 90 kDa ribosomal S6 kinases (p90RSKs) are a family of broadly expressed serine/threonine kinases with two kinase domains activated by extracellular signal‐regulated protein kinase in response to many growth factors. Our recent study demonstrated that severe acute respiratory syndrome (SARS)‐coronavirus (CoV) infection of monkey kidney Vero E6 cells induces phosphorylation and dephosphorylation of signaling pathways, resulting in apoptosis. In the present study, we investigated the phosphorylation status of p90RSK, which is a well‐known substrate of these signaling pathways, in SARS‐CoV‐infected cells. Vero E6 mainly expressed p90RSK1 and showed weak expression of p90RSK2. In the absence of viral infection, Ser221 in the N‐terminal kinase domain was phosphorylated constitutively, whereas both Thr573 in the C‐terminal kinase domain and Ser380 between the two kinase domains were not phosphorylated in confluent cells. Ser380, which has been reported to be involved in autophosphorylation by activation of the C‐terminal kinase domain, was phosphorylated in confluent SARS‐CoV‐infected cells, and this phosphorylation was inhibited by http://SB203580, which is an inhibitor of p38 mitogen‐activated protein kinases (MAPK). Phosphorylation of Thr573 was not upregulated in SARS‐CoV‐infected cells. Thus, in virus‐infected cells, phosphorylation of Thr573 was not necessary to induce phosphorylation of Ser380. On the other hand, Both Thr573 and Ser380 were phosphorylated by treatment with epidermal growth factor (EGF) in the absence of p38 MAPK activation. Ser220 was constitutively phosphorylated despite infection. These results indicated that phosphorylation status of p90RSK by SARS‐CoV infection is different from that by stimulation of EGF. This is the first detailed report regarding regulation of p90RSK phosphorylation by virus infection.

Functional gene analysis of individual response to challenge of SIVmac239 in M. mulatta PBMC culture

It has previously been shown in macaques that individual animals exhibit varying responses to challenge with the same strain of SIV. We attempted to elucidate these differences using functional genomics and correlate them to biological response. Unfractionated PBMC from three rhesus macaques were isolated, activated, and infected with SIVmac239. Interestingly, one of the three animals used for these experiments exhibited a completely unique response to infection relative to the other two. After repeated attempts to infect the PBMC from this animal, little or no infectivity was seen across the time points considered, and corresponding to this apparent lack of infection, few genes were seen to be differentially expressed when compared to mock-infected cells. For the remaining two animals, gene expression analysis showed that while they exhibited responses for the same groups of pathways, these responses included differences specific to the individual animal at the gene level. In instances where the patterns of differential gene expression differed between these animals, the genes being differentially expressed were associated with the same categories of biological process, mainly immune response and cell signaling. At the pathway level, these animals again exhibited similar responses that could be predicted based on the experimental conditions. Even in these expected results, the degree of response and the specific genes being regulated differed greatly from animal to animal. The differences in gene expression on an individual level have the potential to be used as markers in identification of animals suitable for lentiviral infection experiments. Our results highlight the importance of individual variation in response to viral challenge.

In vivo functional characterization of the SARS-Coronavirus 3a protein in Drosophila

The Severe Acute Respiratory Syndrome-Coronavirus (SARS-CoV) 3a locus encodes a 274 a.a. novel protein, and its expression has been confirmed in SARS patients. To study functional roles of 3a, we established a transgenic fly model for the SARS-CoV 3a gene. Misexpression of 3a in Drosophila caused a dominant rough eye phenotype. Using a specific monoclonal antibody, we demonstrated that the 3a protein displayed a punctate cytoplasmic localization in Drosophila as in SARS-CoV-infected cells. We provide genetic evidence to support that 3a is functionally related to clathrin-mediated endocytosis. We further found that 3a misexpression induces apoptosis, which could be modulated by cellular cytochrome c levels and caspase activity. From a forward genetic screen, 78 dominant 3a modifying loci were recovered and the identity of these modifiers revealed that the severity of the 3a-induced rough eye phenotype depends on multiple cellular processes including gene transcriptional regulation.