Abstract
Bombyx mori nucleopolyhedrovirus (BmNPV) is closely related to Autographa californica multiple nucleopolyhedrovirus (AcMNPV) with over ~93% amino acid sequence identity. However, their host ranges are essentially nonoverlapping. The mechanism of BmNPV entry into host cells is completely different from that of AcMNPV, and whether the entry mechanism difference relates to the host range remains unclear. BmNPV produces an abortive infection in nonhost cells due to virion nuclear transportation failure. Here, we performed a detailed study by increasing BmNPV infection in Sf21 cells with the aid of methyl-beta-cyclodextrin (MβCD). We found that low-concentration MβCD incubation efficiently activates membrane ruffling in Sf21 cells, which mediates the increase in BmNPV infection. Interestingly, MβCD incubation after virion internalization also increases the infection, which suggests that macropinocytosis is involved in BmNPV infection in Sf21 cells after virion internalization. Further study revealed that clathrin-mediated endocytosis (CME) is employed by BmNPV to facilitate entry into Sf21 cells, and chlorpromazine application abolishes BmNPV infection in cells incubated both with and without MβCD. Based on these studies, we show that BmNPV enters Sf21 cells via CME and that parallel induction of macropinocytosis facilitates BmNPV infection in Sf21 cells. This study reveals the mechanism of BmNPV entry into Sf21 cells and provides clues for improving BmNPV infections in nonpermissive cells.
Highlights
Baculoviruses, which have important applications in the areas of insect pesticides, protein expression, and gene therapy, are pathogens that infect insects from the orders Lepidoptera, Diptera, and Hymenoptera [1]
Occlusion bodies were observed in the late stage of infection in MβCD-treated cells (Figure 1A, red arrow), indicating that MβCD efficiently facilitates Bombyx mori nucleopolyhedrovirus (BmNPV) infection in Sf21 cells
Our results suggest that BmNPV enters into Sf21 cells mainly via clathrin-mediated endocytosis (CME), but parallel macropinocytosis enhances the ability of BmNPV to infect the cells once the virus gets in via CME
Summary
Baculoviruses, which have important applications in the areas of insect pesticides, protein expression, and gene therapy, are pathogens that infect insects from the orders Lepidoptera, Diptera, and Hymenoptera [1]. Each baculovirus exhibits a unique host specificity [2] where a virus can only infect a specific insect or a limited number of insects in the same order. AcMNPV replicates in Spodoptera frugiperda (Sf) cells, but not in Bombyx mori (BmN) cells; BmNPV replicates in BmN cells, but not Sf cells, and almost all of the BmNPV gene expression in Sf9 cells is greatly. Several genes such as dna helicase [6,7,8,9] and gp64 [1,4,10] have been suggested as determinants of the BmNPV and AcMNPV host range, but the mechanism is still unclear [1]
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