The West Nile Virus Capsid Protein Blocks Apoptosis through a Phosphatidylinositol 3-Kinase-Dependent Mechanism

Urbanowski, Matt D.; Hobman, Tom C.

doi:10.1128/jvi.02030-12

Cited by 61 publications

(57 citation statements)

References 55 publications

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“…It was recently found that WNV capsid induces PI3 kinase-dependent activation of Akt by phosphorylation at S473 and that Akt activation was found to delay WNVinduced caspase-3-dependent apoptosis (36). We evaluated the role of S473 phosphorylation on Akt by mTOR in our rictor knockout studies.…”

Section: Discussionmentioning

confidence: 99%

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West Nile Virus-Induced Activation of Mammalian Target of Rapamycin Complex 1 Supports Viral Growth and Viral Protein Expression

Shives

Beatman

Chamanian

et al. 2014

J Virol

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Since its introduction in New York City, NY, in 1999, West Nile virus (WNV) has spread to all 48 contiguous states of the United States and is now the leading cause of epidemic encephalitis in North America. As a member of the family Flaviviridae, WNV is part of a group of clinically important human pathogens, including dengue virus and Japanese encephalitis virus. The members of this family of positive-sense, single-stranded RNA viruses have limited coding capacity and are therefore obligated to co-opt a significant amount of cellular factors to translate their genomes effectively. Our previous work has shown that WNV growth was independent of macroautophagy activation, but the role of the evolutionarily conserved mammalian target of rapamycin (mTOR) pathway during WNV infection was not well understood. mTOR is a serine/threonine kinase that acts as a central cellular censor of nutrient status and exercises control of vital anabolic and catabolic cellular responses such as protein synthesis and autophagy, respectively. We now show that WNV activates mTOR and cognate downstream activators of cap-dependent protein synthesis at early time points postinfection and that pharmacologic inhibition of mTOR (KU0063794) significantly reduced WNV growth. We used an inducible Raptor and Rictor knockout mouse embryonic fibroblast (MEF) system to further define the role of mTOR complexes 1 and 2 in WNV growth and viral protein synthesis. Following inducible genetic knockout of the major mTOR cofactors raptor (TOR complex 1 [TORC1]) and rictor (TORC2), we now show that TORC1 supports flavivirus protein synthesis via cap-dependent protein synthesis pathways and supports subsequent WNV growth. IMPORTANCE Since its introduction in New York West Nile virus (WNV) is an enveloped, single-stranded, positive-sense RNA virus in the genus Flavivirus, which includes multiple clinically important viral species such as dengue virus, yellow fever virus, and Japanese encephalitis virus. Since the first North American outbreak in New York City, NY, in 1999 (1), WNV has spread across the continent to become the leading cause of epidemic encephalitis (2). To date, there have been more than 37,000 confirmed cases of WNV disease, 16,000 cases of neuroinvasive disease, and 1,500 fatalities (www.cdc.gov/westnile). Currently, there is no licensed human vaccine or pharmacologic therapy for WNV. Owing to difficulties in predicting the location and timing of WNV outbreaks, insufficient enrollment of WNV-infected patients has complicated human clinical trial design for candidate vaccines and therapeutic interventions. A better understanding of the molecular pathogenesis of flaviviruses and the mechanisms behind how they successfully compete with host messages for access to translational components may reveal broad-spectrum antiflaviviral targets that can be evaluated and licensed for treatment of acute flaviviral infections.Due to the high mutation rates of RNA viral genomes and their subsequent ability to rapidly generate escape mutations, we ...

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Section: Discussionmentioning

confidence: 99%

“…Flavivirus endocytosis transiently activates Akt through a PI3K-dependent mechanism that can be detected as early as 1 h postinfection (33)(34)(35)(36) and therefore may be important in activating p70S6K in support of viral gene expression. To determine the significance of WNV-induced mTOR- (UV-WNV).…”

Section: Wnv Activates Mtormentioning

confidence: 99%

West Nile Virus-Induced Activation of Mammalian Target of Rapamycin Complex 1 Supports Viral Growth and Viral Protein Expression

Shives

Beatman

Chamanian

et al. 2014

J Virol

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“…Production of polyclonal antibodies to the amino-terminal 20 amino acid residues of DENV-2 capsid protein in guinea pigs was contracted to Pocono Rabbit Farm and Laboratory (Canadensis, PA). Guinea pig and rabbit polyclonal antibodies to WNV capsid protein and goat anti-p32 were generated in our laboratory (2,12,13). Rabbit polyclonal antibodies to the tripeptide Ser-Lys-Leu (SKL) were produced as described previously (14).…”

Section: Methodsmentioning

confidence: 99%

“…Bound immune complexes were washed several times with NP-40 lysis buffer before elution by boiling in protein sample buffer. Proteins were separated by SDS-PAGE and transferred to polyvinylidene difluoride (PVDF) membranes for immunoblotting, as described previously (2). Confocal and superresolution microscopy.…”

Section: Methodsmentioning

confidence: 99%

“…As such, from a temporal perspective, capsid proteins are well positioned to modulate the host cell environment during the infection cycle. For example, we have shown that the WNV capsid protein inhibits apoptosis via a mechanism requiring phosphatidylinositol 3-kinase activity (2). The capsid protein of the most intensely studied flavivirus, hepatitis C virus (HCV), has been shown to interact with at least 28 different human proteins, many with known roles in apoptotic pathways (reviewed in reference 3).…”

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confidence: 99%

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Flavivirus Infection Impairs Peroxisome Biogenesis and Early Antiviral Signaling

You

Hou

Malik-Soni

et al. 2015

J Virol

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Flaviviruses are significant human pathogens that have an enormous impact on the global health burden. Currently, there are very few vaccines against or therapeutic treatments for flaviviruses, and our understanding of how these viruses cause disease is limited. Evidence suggests that the capsid proteins of flaviviruses play critical nonstructural roles during infection, and therefore, elucidating how these viral proteins affect cellular signaling pathways could lead to novel targets for antiviral therapy. We used affinity purification to identify host cell proteins that interact with the capsid proteins of West Nile and dengue viruses. One of the cellular proteins that formed a stable complex with flavivirus capsid proteins is the peroxisome biogenesis factor Pex19. Intriguingly, flavivirus infection resulted in a significant loss of peroxisomes, an effect that may be due in part to capsid expression. We posited that capsid protein-mediated sequestration and/or degradation of Pex19 results in loss of peroxisomes, a situation that could result in reduced early antiviral signaling. In support of this hypothesis, we observed that induction of the lambda interferon mRNA in response to a viral RNA mimic was reduced by more than 80%. Together, our findings indicate that inhibition of peroxisome biogenesis may be a novel mechanism by which flaviviruses evade the innate immune system during early stages of infection. IMPORTANCERNA viruses infect hundreds of millions of people each year, causing significant morbidity and mortality. Chief among these pathogens are the flaviviruses, which include dengue virus and West Nile virus. Despite their medical importance, there are very few prophylactic or therapeutic treatments for these viruses. Moreover, the manner in which they subvert the innate immune response in order to establish infection in mammalian cells is not well understood. Recently, peroxisomes were reported to function in early antiviral signaling, but very little is known regarding if or how pathogenic viruses affect these organelles. We report for the first time that flavivirus infection results in significant loss of peroxisomes in mammalian cells, which may indicate that targeting of peroxisomes is a key strategy used by viruses to subvert early antiviral defenses. Flaviviruses are arthropod-transmitted pathogens that infect hundreds of millions of people each year. Dengue virus (DENV) is the etiological agent of the most common mosquitoborne disease in the world, dengue fever (reviewed in reference 1). The related flavivirus West Nile virus (WNV) is the most important vector-transmitted pathogen in North America. Despite their medical significance, there are no DENV/WNV-specific vaccines or antiviral therapies that are approved for use in humans. Understanding how these viruses take advantage of and manipulate host cells may provide the foundation for therapies that target virushost interactions.Recent studies identified flavivirus capsid proteins as critical components of the virus-host interface. T...

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A Brief Review of West Nile Virus Biology

Londoño-Rentería

Colpitts

2016

Methods in Molecular Biology

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West Nile virus (WNV) is an arbovirus with increased global incidence in the last decade. It is also a major cause of human encephalitis in the USA. WNV is an arthropod-transmitted virus that mainly affects birds but humans become infected as incidental dead-end hosts which can cause outbreaks in naïve populations. The main vectors of WNV are mosquitoes of the genus Culex, which preferentially feed on birds. As in many other arboviruses, the characteristics that allow Flaviviruses like WNV to replicate and transmit to different hosts are encrypted in their genome, which also contains information for the production of structural and nonstructural proteins needed for host cell infection. WNV and other Flaviviruses have developed different strategies to establish infection, replication, and successful transmission. Most of these strategies include the diversion of the host's immune responses away from the virus. In this review, we describe the molecular structure and protein function of WNV with emphasis on protein involvement in the modulation of antiviral immune responses.

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The West Nile Virus Capsid Protein Blocks Apoptosis through a Phosphatidylinositol 3-Kinase-Dependent Mechanism

Cited by 61 publications

References 55 publications

West Nile Virus-Induced Activation of Mammalian Target of Rapamycin Complex 1 Supports Viral Growth and Viral Protein Expression

West Nile Virus-Induced Activation of Mammalian Target of Rapamycin Complex 1 Supports Viral Growth and Viral Protein Expression

Flavivirus Infection Impairs Peroxisome Biogenesis and Early Antiviral Signaling

A Brief Review of West Nile Virus Biology

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