Ac34 protein of AcMNPV promoted progeny virus production and induced the apoptosis in host Sf9 cells.
Objectives: To analyze the function of Ac34 in Autographa californica multiple nuclear polyhedrosis virus (AcMNPV) and elucidate the JNK apoptotic signaling pathway activation in host Spodoptera frugiperda 9 (Sf9) cells induced by the recombinant virus AcMNPV-Ac34-EGFP. Results: AcMNPV is an important species of baculoviruses. First, viral propagation assay indicated that overexpression of Ac34 protein promoted replication of AcMNPV. Quantitative RT-PCR analysis showed that Ac34 increased the transcriptional level of late genes 38k and vp39, which suggested that Ac34 promoted the production of progeny virus by upregulating transcription of late genes. Second, AcMNPV-Ac34-EGFP inhibited the proliferation of Sf9 cells. Moreover, Sf9 cells infected with AcMNPV-Ac34-EGFP resulted in abundant expression of SfP53 and its accumulation in the nucleus. c-Jun N-terminal kinase (JNK) activation requires MKK4 and MKK7 mediated phosphorylation at Thr183 and Tyr185. We found increased levels of p-JNK1/2 in Sf9 cells infected by AcMNPV-Ac34-EGFP, with concomitant induction of Sf9 cell death. Furthermore, treatment of infected Sf9 cells with SP600125 (an inhibitor of JNK pathway) downregulated p-JNK1/2 and influenced the expression of virus-induced apoptosis protein SfP53, as well as Cytochrome C and Bax. Conclusion: AcMNPV-Ac34-EGFP virus upregulated the progeny virus production and triggered apoptosis via activation of the JNK pathway in Sf9 cells. In this work, we unveiled an effective virus replication factor-Ac34 and more importantly, developed a recombinant virus that can be used as an improved version of biopesticide.