Dataset Information

A Genome-Wide RNA Interference Screen Identifies a Role for Wnt/?-Catenin Signaling during Rift Valley Fever Virus Infection.

ABSTRACT:

Unlabelled

Rift Valley fever virus (RVFV) is an arbovirus within the Bunyaviridae family capable of causing serious morbidity and mortality in humans and livestock. To identify host factors involved in bunyavirus replication, we employed genome-wide RNA interference (RNAi) screening and identified 381 genes whose knockdown reduced infection. The Wnt pathway was the most represented pathway when gene hits were functionally clustered. With further investigation, we found that RVFV infection activated Wnt signaling, was enhanced when Wnt signaling was preactivated, was reduced with knockdown of ?-catenin, and was blocked using Wnt signaling inhibitors. Similar results were found using distantly related bunyaviruses La Crosse virus and California encephalitis virus, suggesting a conserved role for Wnt signaling in bunyaviral infection. We propose a model where bunyaviruses activate Wnt-responsive genes to regulate optimal cell cycle conditions needed to promote efficient viral replication. The findings in this study should aid in the design of efficacious host-directed antiviral therapeutics.

Importance

RVFV is a mosquito-borne bunyavirus that is endemic to Africa but has demonstrated a capacity for emergence in new territories (e.g., the Arabian Peninsula). As a zoonotic pathogen that primarily affects livestock, RVFV can also cause lethal hemorrhagic fever and encephalitis in humans. Currently, there are no treatments or fully licensed vaccines for this virus. Using high-throughput RNAi screening, we identified canonical Wnt signaling as an important host pathway regulating RVFV infection. The beneficial role of Wnt signaling was observed for RVFV, along with other disparate bunyaviruses, indicating a conserved bunyaviral replication mechanism involving Wnt signaling. These studies supplement our knowledge of the fundamental mechanisms of bunyavirus infection and provide new avenues for countermeasure development against pathogenic bunyaviruses.

SUBMITTER: Harmon B

PROVIDER: S-EPMC4984662 | biostudies-literature | 2016 Aug

REPOSITORIES: biostudies-literature

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Publications

A Genome-Wide RNA Interference Screen Identifies a Role for Wnt/β-Catenin Signaling during Rift Valley Fever Virus Infection.

Harmon Brooke B Bird Sara W SW Schudel Benjamin R BR Hatch Anson V AV Rasley Amy A Negrete Oscar A OA

Journal of virology 20160727 16

<h4>Unlabelled</h4>Rift Valley fever virus (RVFV) is an arbovirus within the Bunyaviridae family capable of causing serious morbidity and mortality in humans and livestock. To identify host factors involved in bunyavirus replication, we employed genome-wide RNA interference (RNAi) screening and identified 381 genes whose knockdown reduced infection. The Wnt pathway was the most represented pathway when gene hits were functionally clustered. With further investigation, we found that RVFV infectio ...[more]

PMID: 27226375

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Project description:The emerging bunyavirus Rift Valley fever virus (RVFV) is transmitted to humans and livestock by a large number of mosquito species. RNA interference (RNAi) has been characterized as an important innate immune defense mechanism used by mosquitoes to limit replication of positive-sense RNA flaviviruses and togaviruses; however, little is known about its role against negative-strand RNA viruses such as RVFV. We show that virus-specific small RNAs are produced in infected mosquito cells, in Drosophila melanogaster cells, and, most importantly, also in RVFV vector mosquitoes. By addressing the production of small RNAs in adult Aedes sp. and Culex quinquefasciatus mosquitoes, we showed the presence of virus-derived Piwi-interacting RNAs (piRNAs) not only in Aedes sp. but also in C. quinquefasciatus mosquitoes, indicating that antiviral RNA interference in C. quinquefasciatus mosquitoes is similar to the described activities of RNAi in Aedes sp. mosquitoes. We also show that these have antiviral activity, since silencing of RNAi pathway effectors enhances viral replication. Moreover, our data suggest that RVFV does not encode a suppressor of RNAi. These findings point toward a significant role of RNAi in the control of RVFV in mosquitoes. IMPORTANCE Rift Valley fever virus (RVFV; Phlebovirus, Bunyaviridae) is an emerging zoonotic mosquito-borne pathogen of high relevance for human and animal health. Successful strategies of intervention in RVFV transmission by its mosquito vectors and the prevention of human and veterinary disease rely on a better understanding of the mechanisms that govern RVFV-vector interactions. Despite its medical importance, little is known about the factors that govern RVFV replication, dissemination, and transmission in the invertebrate host. Here we studied the role of the antiviral RNA interference immune pathways in the defense against RVFV in natural vector mosquitoes and mosquito cells and draw comparisons to the model insect Drosophila melanogaster. We found that RVFV infection induces both the exogenous small interfering RNA (siRNA) and piRNA pathways, which contribute to the control of viral replication in insects. Furthermore, we demonstrate the production of virus-derived piRNAs in Culex quinquefasciatus mosquitoes. Understanding these pathways and the targets within them offers the potential of the development of novel RVFV control measures in vector-based strategies.

Project description:Rift Valley fever virus (RVFV) is a Phlebovirus (Bunyaviridae family) transmitted by mosquitoes. It infects humans and ruminants, causing dramatic epidemics and epizootics in Africa, Yemen, and Saudi Arabia. While recent studies demonstrated the importance of the nonstructural protein NSs as a major component of virulence in vertebrates, little is known about infection of mosquito vectors. Here we studied RVFV infection in three different mosquito cell lines, Aag2 cells from Aedes aegypti and U4.4 and C6/36 cells from Aedes albopictus. In contrast with mammalian cells, where NSs forms nuclear filaments, U4.4 and Aag2 cells downregulated NSs expression such that NSs filaments were never formed in nuclei of U4.4 cells and disappeared at an early time postinfection in the case of Aag2 cells. On the contrary, in C6/36 cells, NSs nuclear filaments were visible during the entire time course of infection. Analysis of virus-derived small interfering RNAs (viRNAs) by deep sequencing indicated that production of viRNAs was very low in C6/36 cells, which are known to be Dicer-2 deficient but expressed some viRNAs presenting a Piwi signature. In contrast, Aag2 and U4.4 cells produced large amounts of viRNAs predominantly matching the S segment and displaying Dicer-2 and Piwi signatures. Whereas 21-nucleotide (nt) Dicer-2 viRNAs were prominent during early infection, the population of 24- to 27-nt Piwi RNAs (piRNAs) increased progressively and became predominant later during the acute infection and during persistence. In Aag2 and U4.4 cells, the combined actions of the Dicer-2 and Piwi pathways triggered an efficient antiviral response permitting, among other actions, suppression of NSs filament formation and allowing establishment of persistence. In C6/36 cells, Piwi-mediated RNA interference (RNAi) appeared to be sufficient to mount an antiviral response against a secondary infection with a superinfecting virus. This study provides new insights into the role of Dicer and Piwi in mosquito antiviral defense and the development of the antiviral response in mosquitoes.