Dicer-2-Dependent Activation of Culex Vago Occurs via the TRAF-Rel2 Signaling Pathway

Prasad N Paradkar,Peter J Walker,Rhonda Voysey,Jean-Bernard Duchemin,Ken E Olson

doi:10.1371/journal.pntd.0002823

Abstract

Despite their importance as vectors of human and livestock diseases, relatively little is known about innate antiviral immune pathways in mosquitoes and other insects. Previous work has shown that Culex Vago (CxVago), which is induced and secreted from West Nile virus (WNV)-infected mosquito cells, acts as a functional homolog of interferon, by activating Jak-STAT pathway and limiting virus replication in neighbouring cells. Here we describe the Dicer-2-dependent pathway leading to WNV-induced CxVago activation. Using a luciferase reporter assay, we show that a NF-κB-like binding site in CxVago promoter region is conserved in mosquito species and is responsible for induction of CxVago expression following WNV infection. Using dsRNA-based gene knockdown, we show that the NF-κB ortholog, Rel2, plays significant role in the signaling pathway that activates CxVago in mosquito cells in vitro and in vivo. Using similar approaches, we also show that TRAF, but not TRAF-3, is involved in activation of Rel2 after viral infection. Overall the study shows that a conserved signaling pathway, which is similar to mammalian interferon activation pathway, is responsible for the induction and antiviral activity of CxVago.

Highlights

Hematophagous insects serve as vectors of many important viral diseases of humans and livestock
Dicer2, which has previously been shown to be involved in RNA interference (RNAi) mediated antiviral activity in mosquitoes, contains helicase domain, which leads to activation of antiviral protein, Vago
Vago is functionally similar to mammalian interferon and after secretion activates Jak-STAT pathway in neighboring cells leading to antiviral effect

Summary

Introduction

Hematophagous insects (mosquitoes, sand flies and midges) serve as vectors of many important viral diseases of humans and livestock. It has been estimated that over 25% of all emerging viral diseases globally are vector-borne [3] with factors such as global warming, increased population densities and ease of world travel driving the spread into new geographical areas [4,5] Despite their importance in the transmission of viral disease, knowledge of the processes of infection and immunity in insects (and other invertebrates) is relatively poor. RNA interference (RNAi) has been shown to be a major aspect of the insect antiviral response to a wide range of both RNA viruses and DNA viruses [7,8] This involves the detection and degradation of viral double-stranded (ds) RNA by Dicer-2, generating short interfering (si) RNAs (siRNA). The Jak-STAT pathway was initially found to be important in antiviral signalling in Drosophila [12] and later has been shown to be play significant role in immunity to dengue virus in mosquitoes [14]

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