Knockdown of piRNA pathway proteins results in enhanced Semliki Forest virus production in mosquito cells

The exogenous siRNA pathway is important in restricting arbovirus infection in mosquitoes. Less is known about the role of the PIWI-interacting RNA pathway, or piRNA pathway, in antiviral responses. Viral piRNA-like molecules have recently been described following infection of mosquitoes and derived cell lines with several arboviruses. The piRNA pathway has thus been suggested to function as an additional small RNA-mediated antiviral response to the known infection-induced siRNA response. Here we show that piRNA-like molecules are produced following infection with the naturally mosquito-borne Semliki Forest virus in mosquito cell lines. We show that knockdown of piRNA pathway proteins enhance the replication of this arbovirus and define the contribution of piRNA pathway effectors, thus characterising the antiviral properties of the piRNA pathway. In conclusion, in mosquito cells arbovirus infection can trigger the piRNA pathway and knockdown of piRNA proteins enhances virus production.