Microplitis bicoloratus bracovirus regulates cyclophilin A-apoptosis-inducing factor interaction to induce cell apoptosis in the insect immunosuppressive process.

Microplitis bicoloratus bracovirus (MbBV) induces apoptosis in hemocytes of the host (Spodoptera litura) via the cyclophilin A (CypA)-mediated signaling pathway. However, the mechanisms underlying CypA-mediated signaling during apoptosis remain largely unknown. Therefore, in this study, we investigated how CypA and apoptosis-inducing factor (AIF) interact during MbBV-mediated apoptosis. Our findings showed that MbBV induces apoptosis through the CypA-AIF axis of insect immune suppression. In MbBV-infected Spli221 cells, both the expression of the cypa gene and the release of AIF from the mitochondria increased the number of apoptotic cells. CypA and AIF underwent concurrent cytoplasm-nuclear translocation. Conversely, blocking of AIF release from mitochondria not only inhibited the CypA-AIF interaction but also inhibited the cytoplasmic-nuclear translocation of AIF and CypA. Importantly, the survival of the apoptotic phenotype was significantly rescued in MbBV-infected Spli221 cells. In addition, we found that the cyclosporine A-mediated inhibition of CypA did not prevent the formation of the CypA and AIF complex; rather, this only suppressed genomic DNA fragmentation. In vitro experiments revealed direct molecular interactions between recombinant CypA and AIF. Taken together, our results demonstrate that the CypA-AIF interaction plays an important role in MbBV-induced innate immune suppression. This study will help to clarify aspects of insect immunological mechanisms and will be relevant to biological pest control.