title: Mosquito and Drosophila entomobirnaviruses suppress dsRNA- and siRNA-induced RNAi.
abstract: RNA interference (RNAi) is a crucial antiviral defense mechanism in insects, including the major mosquito species that transmit important human viruses. To counteract the potent antiviral RNAi pathway, insect viruses encode RNAi suppressors. However, whether mosquito-specific viruses suppress RNAi remains unclear. We therefore set out to study RNAi suppression by Culex Y virus (CYV), a mosquito-specific virus of the Birnaviridae family that was recently isolated from Culex pipiens mosquitoes. We found that the Culex RNAi machinery processes CYV double-stranded RNA (dsRNA) into viral small interfering RNAs (vsiRNAs). Furthermore, we show that RNAi is suppressed in CYV-infected cells and that the viral VP3 protein is responsible for RNAi antagonism. We demonstrate that VP3 can functionally replace B2, the well-characterized RNAi suppressor of Flock House virus. VP3 was found to bind long dsRNA as well as siRNAs and interfered with Dicer-2-mediated cleavage of long dsRNA into siRNAs. Slicing of target RNAs by pre-assembled RNA-induced silencing complexes was not affected by VP3. Finally, we show that the RNAi-suppressive activity of VP3 is conserved in Drosophila X virus, a birnavirus that persistently infects Drosophila cell cultures. Together, our data indicate that mosquito-specific viruses may encode RNAi antagonists to suppress antiviral RNAi.
authors.affiliation: Department of Medical Microbiology, Radboud University Nijmegen Medical Centre, Radboud Institute for Molecular Life Sciences, P.O. Box 9101, 6500 HB Nijmegen, The Netherlands.
authors.forename: Koen W R
authors.initials: KW
authors.lastname: van Cleef
authors.affiliation: Department of Medical Microbiology, Radboud University Nijmegen Medical Centre, Radboud Institute for Molecular Life Sciences, P.O. Box 9101, 6500 HB Nijmegen, The Netherlands.
authors.forename: Joël T
authors.initials: JT
authors.lastname: van Mierlo
authors.affiliation: Department of Medical Microbiology, Radboud University Nijmegen Medical Centre, Radboud Institute for Molecular Life Sciences, P.O. Box 9101, 6500 HB Nijmegen, The Netherlands.
authors.forename: Pascal
authors.initials: P
authors.lastname: Miesen
authors.affiliation: Department of Medical Microbiology, Radboud University Nijmegen Medical Centre, Radboud Institute for Molecular Life Sciences, P.O. Box 9101, 6500 HB Nijmegen, The Netherlands.
authors.forename: Gijs J
authors.initials: GJ
authors.lastname: Overheul
authors.affiliation: Laboratory of Virology, Wageningen University, Droevendaalsesteeg 1, 6708 PB Wageningen, The Netherlands.
authors.forename: Jelke J
authors.initials: JJ
authors.lastname: Fros
authors.affiliation: Department of Medical Microbiology, Radboud University Nijmegen Medical Centre, Radboud Institute for Molecular Life Sciences, P.O. Box 9101, 6500 HB Nijmegen, The Netherlands.
authors.forename: Susan
authors.initials: S
authors.lastname: Schuster
authors.affiliation: Institute of Virology, University of Bonn Medical Centre, Sigmund Freud Str. 25, 53127 Bonn, Germany.
authors.forename: Marco
authors.initials: M
authors.lastname: Marklewitz
authors.affiliation: Laboratory of Virology, Wageningen University, Droevendaalsesteeg 1, 6708 PB Wageningen, The Netherlands.
authors.forename: Gorben P
authors.initials: GP
authors.lastname: Pijlman
authors.affiliation: Institute of Virology, University of Bonn Medical Centre, Sigmund Freud Str. 25, 53127 Bonn, Germany.
authors.forename: Sandra
authors.initials: S
authors.lastname: Junglen
authors.affiliation: Department of Medical Microbiology, Radboud University Nijmegen Medical Centre, Radboud Institute for Molecular Life Sciences, P.O. Box 9101, 6500 HB Nijmegen, The Netherlands r.vanrij@ncmls.ru.nl.
authors.forename: Ronald P
authors.initials: RP
authors.lastname: van Rij
mesh_terms: D000818:Animals; D002478:Cells, Cultured; D003465:Culex / Q000235:genetics* / Q000821:virology; D004331:Drosophila melanogaster / Q000235:genetics* / Q000821:virology; D019203:Entomobirnavirus / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D034622:RNA Interference; D012330:RNA, Double-Stranded / Q000378:metabolism*; D034741:RNA, Small Interfering / Q000378:metabolism*; D014764:Viral Proteins / Q000378:metabolism
chemical_list: D012330:RNA, Double-Stranded; D034741:RNA, Small Interfering; D014764:Viral Proteins