BmCH25H,a vertebrate interferon-stimulated gene(ISG)homolog,inhibits BmNPV infection dependent on its hydroxylase activity in Bombyx mori

Cholesterol-25-hydroxylase(CH25H)has been identified as an interferon-stimulated gene(ISG)in mammals that exerts its antiviral effects by catalyzing the conversion of cholesterol to 25-hydroxycholesterol(25HC).However,invertebrates lack an antiviral system homologous to vertebrate interferons(IFNs)because the genomes of invertebrates do not encode IFN-like cytokines.Nevertheless,CH25H is present in insect genomes and it therefore deserves further study of whether and by which mechanism it could exert an antiviral effect in invertebrates.In this study,the Bombyx mori CH25H(BmCH25H)gene,of which the encoded protein has high homology with other lepidopteran species,was identified and located on chromosome 9.Interestingly,we found that the expression of BmCH25H was significantly upregulated in B.mori nucleopolyhedrovirus(BmNPV)-infected BmN cells and silkworm(B.mori)larvae at the early infection stage.The inhibitory effect of BmCH25H on BmNPV replication was further demonstrated to depend on its catalytic residues to convert cholesterol to 25HC.More importantly,we demonstrated that during BmNPV infection,BmCH25H expression was increased through the Janus kinase–signal transducer and activator of transcription(JAK–STAT)pathway,similar to the induction of ISGs following virus infection in vertebrates.This is the first report that CH25H has antiviral effects in insects;the study also elucidates the regulation of its expression and its mechanism of action.

The piRNA pathway is required for nucleopolyhedrovirus replication in Lepidoptera

The Piwi-interacting RNA(piRNA)pathway has been shown to be involved in the antiviral defense against RNA viruses,especially in mosquitoes,but its universality has been questioned.Here,we used the Bombyx mori nucleopolyhedrovirus(BmNPV)-infected silkworm as a model to explore the effects of the key factors of piRNA pathway,BmAgo3 and Siwi,on replication of a large DNA virus(belonging to the family of Baculoviridae).We demonstrated that BmAgo3 and Siwi could promote the replication of BmNPV through both overexpression and knockdown experiments in BmN cell lines and silkworm larvae.In addition,we also studied the effect of PIWI-class genes on Autographa californica nucleopolyhedrovirus(AcMNPV)replication in the Spodoptera frugiperda cell line Sf9.By knocking down the expression of PIWI-class genes in Sf9,we found that Piwi-like-1 and Piwi-like-2-3 could inhibit AcMNPV replication,while Piwi-like-4-5 promoted virus replication.Our study provides compelling evidence that the piRNA pathway affects host infection by exogenous viruses in Lepidoptera.Also,our results reflect the diversity of the roles of PIWI-class genes in virus infection of the host across species.This study is the first to explore the interaction of PIWI-class proteins with DNA viruses,providing new insights into the functional roles of the piRNA pathway.

Bombyx mori nucleopolyhedrovirus induces BmFABP1 downregulation to promote viral proliferation

Fatty acid binding proteins (FABPs) play an important role as endogenous cytoprotectants. However, studies on FABPs in invertebrates are scarce. Previously, we discovered Bombyx mori fatty acid binding protein 1 (BmFABP1) through co-immunoprecipitation. Here, we cloned and identified BmFABP1 from BmN cells. The results of immunofluorescence indicated that BmFABP1 was localized in the cytoplasm. The tissue expression profile of silkworms showed that BmFABP1 was expressed in all tissues except hemocytes. The expression level of BmFABP1 gradually decreases in BmN cells and B. mori larvae after infection with B. mori nucleopolyhedrovirus (BmNPV). Upregulation of BmFABP1 expression through overexpression or WY14643 treatment significantly inhibited the replication of BmNPV, while downregulation of BmFABP1 expression by RNA interference promoted the replication of BmNPV. The same results were obtained in experiments on silkworm larvae. These results suggest that BmNPV induces BmFABP1 downregulation to promote its proliferation and that BmFABP1 has a potential anti-BmNPV role. This is the first report on the antiviral effect of BmFABP1 in silkworms and provides new insights into the study of the FABP protein family. Also, it is important to study BmNPV resistance in silkworms to breed transgenic silkworms with BmNPV resistance.