[en] Hyphantria cunea nucleopolyhedrovirus (HycuNPV) infection protected SpIm cells from actinomycin D (ActD)-induced apoptosis as early as 4 h postinfection. Analysis by Southern hybridization revealed that the HycuNPV genome possessed three members of inhibitor of apoptosis genes (iaps) that were designated as hycu-iap1, hycu-iap2, and hycu-iap3 because of their amino acid sequence homology with iaps identified in other baculoviruses. Functional analysis of Hycu-IAPs by transient expression assay in Sf9 cells revealed that Hycu-IAP3 blocked apoptosis induced by actinomycin D and rescued replication of p35 deficient-mutant AcMNPV, while Hycu-IAP1 and Hycu-IAP2 did not show any anti-apoptotic functions. Knockdown of hycu-iap3 expression by RNAi during HycuNPV infection in SpIm cells induced apoptosis. These results indicate that Hycu-IAP3 is essential for blockage of apoptosis during HycuNPV infection of permissive SpIm cells

[en] Despite close genetic relationship, Bombyx mori nucleopolyhedrovirus (BmNPV) and Autographa californica multicapsid NPV (AcMNPV) display a distinct host range property. Here, BmNPV replication was examined in Sf9 and High Five cells that were nonproductive for BmNPV infection but supported high titers of AcMNPV replication. Recombinant BmNPV, vBm/gfp/lac, containing bm-ie1 promoter-driven egfp showed that few Sf9 and High Five cells infected with vBm/gfp/lac expressed EGFP, while large proportion of EGFP-expressing cells was observed when transfected with vBm/gfp/lac DNA. Immunocytochemical analysis showed that BmNPV was not imported into the nucleus of these two cell lines, while recombinant BmNPV, vBmΔ64/ac-gp64 possessing AcMNPV gp64 was imported into the nucleus, yielding progeny virions in High Five cells, but not Sf9 cells. These results indicate that the defective nuclear import of infected virions due to insufficient BmNPV GP64 function is involved in the restricted BmNPV replication in Sf9 and High Five cells

[en] We have previously shown that budded viruses of Bombyx mori nucleopolyhedrovirus (BmNPV) enter the cell cytoplasm but do not migrate into the nuclei of non-permissive Sf9 cells that support a high titer of Autographa californica multicapsid nucleopolyhedrovirus (AcMNPV) multiplication. Here we show, using the syncytium formation assay, that low-pH-triggered membrane fusion of BmNPV GP64 protein (Bm-GP64) is significantly lower than that of AcMNPV GP64 protein (Ac-GP64). Mutational analyses of GP64 proteins revealed that a single amino acid substitution between Ac-GP64 H155 and Bm-GP64 Y153 can have significant positive or negative effects on membrane fusion activity. Studies using bacmid-based GP64 recombinant AcMNPV harboring point-mutated ac-gp64 and bm-gp64 genes showed that Ac-GP64 H155Y and Bm-GP64 Y153H substitutions decreased and increased, respectively, the multiplication and cell-to-cell spread of progeny viruses. These results indicate that Ac-GP64 H155 facilitates the low-pH-triggered membrane fusion reaction between virus envelopes and endosomal membranes.