The Antiviral RNAi Response in Vector and Non-vector Cells against Orthobunyaviruses

Abstract

BackgroundVector arthropods control arbovirus replication and spread through antiviral innate immune responses including RNA interference (RNAi) pathways. Arbovirus infections have been shown to induce the exogenous small interfering RNA (siRNA) and Piwi-interacting RNA (piRNA) pathways, but direct antiviral activity by these host responses in mosquito cells has only been demonstrated against a limited number of positive-strand RNA arboviruses. For bunyaviruses in general, the relative contribution of small RNA pathways in antiviral defences is unknown.Methodology/Principal FindingsThe genus Orthobunyavirus in the Bunyaviridae family harbours a diverse range of mosquito-, midge- and tick-borne arboviruses. We hypothesized that differences in the antiviral RNAi response in vector versus non-vector cells may exist and that could influence viral host range. Using Aedes aegypti-derived mosquito cells, mosquito-borne orthobunyaviruses and midge-borne orthobunyaviruses we showed that bunyavirus infection commonly induced the production of small RNAs and the effects of the small RNA pathways on individual viruses differ in specific vector-arbovirus interactions.Conclusions/SignificanceThese findings have important implications for our understanding of antiviral RNAi pathways and orthobunyavirus-vector interactions and tropism.

PIWI pathway against viruses in insects

“…The clear Ping‐Pong signature of RVFV‐specific 27‐28‐nt‐long vpiRNAs was confirmed by a more recent study, including the typical 10 nt overlap between the sense/antisense pairs of vpiRNAs (Dietrich, Jansen, et al, ). Infection with BUNV showed that, apart from siRNAs, also virus‐specific piRNAs (24–30 nt) were produced, possessing a clear vpiRNA signature similar to the one described by Leger et al () (Dietrich, Shi, et al, ). Interestingly, variabilities between the three viral genome segments exist, with regard to: a) their representation in the vpiRNAs pool, with M being the predominant vpiRNA source followed by S and with L having low vpiRNA reads, and b) their strand bias, with M‐ and S‐derived vpiRNAs being biased for the (sense) antigenome, and L‐specific ones for the (antisense) genome strand (Dietrich, Jansen, et al, ; Dietrich, Shi, et al, ).…”

“…Regarding Piwi4, an important but not yet specified role in antiviral defense is proposed for it in the Ae. aegypti Aag2 cell line (Dietrich, Shi, et al, ). When infected with the (+) RNA virus Semliki Forest virus (SFV), silencing of piwi4 enhanced not only viral replication but also virion production, while it had no effect on vpiRNA production (Schnettler, Donald, et al, ; Varjak et al, ; Varjak, Donald, et al, ; Varjak, Maringer, et al, ).…”

“…Importantly, ZIKV‐specific piRNA‐like molecules were found to immunoprecipitate with Piwi4, although binding to Ago3 was more prominent (Varjak, Donald, et al, ). Interestingly, the antiviral role of Piwi4 seems to be specific against mosquito‐specific viruses, as infection with two midge‐specific bunyaviruses was not affected by piwi4 silencing (Dietrich, Shi, et al, ).…”

Aedes anphevirus (AeAV): an insect-specific virus distributed worldwide inAedes aegyptimosquitoes that has complex interplays withWolbachiaand dengue virus infection in cells

“…These vpiRNAs had the typical ping-pong signature (U 1 -A 10 ) of secondary piRNAs. This signature has also been found in vpiRNAs produced during alphavirus (76) and bunyavirus (63, 77) infections, but not in vpiRNA-like small RNAs in most flaviviruses, such as DENV (78), ZIKV (79, 80) and an insect-specific flavivirus (81). We found a higher proportion of small RNAs from Aag2- w MelPop-CLA cells that mapped to AeAV are vpiRNAs (about 50%) as compared to less than 10% vsiRNAs.…”

African swine fever virus-like integrated elements in a soft tick genome – an ancient virus vector arms race?

“…Through the identification of ASFLI-specific siRNA and piRNA in the ticks and tick cells, we provide data suggesting that the ASFLI-elements might in fact represent an RNAi-based defence against ASFV infection in Ornithodoros ticks. Both siRNA and piRNA are known as major regulation factors of transcription, transposon suppression and defence against viral pathogens (35)(36)(37)(38). Although, for ticks the known arsenal of antiviral mechanisms includes protection by RNAi (39), the role of EVEs in RNAi and protection against viral pathogens has never been reported.…”