Modulation of DNA methyltransferases (DNMTs) in Spodoptera frugiperda (Sf9) cells following AcMNPV infection, and its effects on the virus-cell interaction.

Abstract

Baculoviruses have been used to control different insect pests, but further research is needed to understand the mechanisms of their interactions with insect hosts. In this study, the importance of DNA methyltransferases (DNMTs) was investigated in Spodoptera frugiperda Sf9 cells following baculovirus infection. To do this, Sf9 cells were infected with Autographa californica nucleopolyhedrovirus (AcMNPV) and the transcript levels of DNMT1 and DNMT2 were quantified. The expression levels of both DNMTs were upregulated during AcMNPV infection, suggesting induction of the pathway during infection. To determine whether these genes function during virus infection, we treated Sf9 cells with the inhibitor of DNMTs, 5-azacytidine (5-AZA), and 24 h later, the cells were infected with AcMNPV. Quantitative PCR results showed that the viral DNA replication was significantly reduced in the treated cells compared with the control untreated cells. We also showed that 5-AZA modulates antiviral pathways in Sf9 cells. The expression levels of Toll and immune-deficiency (IMD) pathways genes (i.e., Relish and Dorsal) were increased at 24 h post AcMNPV infection, while the expression levels of Gloverin and Defensin antimicrobial peptides (AMPs) were downregulated. In the 5-AZA treated cells, however, the expression levels of both AMPs were elevated during AcMNPV infection. We also assessed the effect of 5-AZA on short interfering RNA and microRNA pathways and found that Dicer 2 expression level was increased in the 5-AZA treated cells, while the transcript levels of other key genes of the two pathways remained unchanged. Together, our results highlight the contribution of DNA methyltransferase activity in the immunity of Sf9 cells against AcMNPV infection through modulation of antiviral immune responses and shed more light on the molecular mechanisms underlying baculovirus-insect cell interactions.