Comparison between different conditions for the incorporation of foreign proteins into Autographa californica multiple polyhedrovirus polyhedra for biotechnological purposes.

The occlusion bodies of Autographa californica multiple nucleopolyhedrovirus are proteinaceous formations with significant biotechnological potential owing to their capacity to integrate foreign proteins through fusion with polyhedrin, their primary component. However, the strategy for successful heterologous protein inclusion still requires further refinement. In this study, we conducted a comparative assessment of various conditions to achieve the embedding of recombinant proteins within polyhedra. Two baculoviruses were constructed: AcPHGFP (polh+), with GFP as a fusion to wild type (wt) polyhedrin and AcΔPHGFP (polh+), with GFP fused to a fragment corresponding to amino acids 19 to 110 of polyhedrin. These baculoviruses were evaluated by infecting Sf9 cells and stably transformed Sf9, Sf9POLH, and Sf9POLHE44G cells. The stably transformed cells contributed another copy of wt or a mutant polyhedrin, respectively. Polyhedra of each type were isolated and characterized by classical methods. The fusion PHGFP showed more-efficient incorporation into polyhedra than ΔPHGFP in the three cell lines assayed. However, ΔPHGFP polyhedron yields were higher than those of PHGFP in Sf9 and Sf9POLH cells. Based on an integral analysis of the studied parameters, it can be concluded that, except for the AcΔPHGFP/Sf9POLHE44G combination, deficiencies in one factor can be offset by improved performance by another. The combinations AcPHGFP/Sf9POLHE44G and AcΔPHGFP/Sf9POLH stand out due to their high level of incorporation and the large number of recombinant polyhedra produced, respectively. Consequently, the choice between these approaches becomes dependent on the intended application.

A simplified strategy to package foreign proteins into baculovirus occlusion bodies without engineering the viral genome.

Polyhedron envelope protein (PEP) is the major component of the calyx that surrounds the baculovirus occlusion body (OB). PEP has been associated with the stabilization and resistance of polyhedra in the environment. Due to the abundant levels of PEP in OBs, we decided to use this protein as a fusion partner to redirect foreign proteins to baculovirus polyhedra. In this study we developed a strategy that involves the generation of a monoclonal transformed insect cell line expressing a protein of interest fused to the the Anticarsia gemmatalis multiple nucleopolyhedrovirus (AgMNPV) N-terminus of PEP that enables the packaging of foreign proteins into the OBs without generating a recombinant baculovirus. This proved to be an efficient platform that could be exploited to improve wild type baculovirus for their use as bioinsecticides without facing the concerns of releasing genetically modified DNA to the environment and bypassing the associated regulatory issues. We demonstrated, using immunological, proteomic and microscopy techniques, that the envelope of AgMNPV OBs can effectively trap chimeric proteins in an infected insect cell line expressing AgMNPV PEP fused to the enhanced green fluorescent protein (eGFP). Furthermore, packaging of chimeric PEP also took place with heterologous OBs such as those of Autographa californica multiple nucleopolyhedrovirus (AcMNPV), another group I alphabaculovirus.

The silencing suppressor (NSs) protein of the plant virus Tomato spotted wilt virus enhances heterologous protein expression and baculovirus pathogenicity in cells and lepidopteran insects.

In this work, we showed that cell death induced by a recombinant (vAcNSs) Autographa californica multiple nucleopolyhedrovirus (AcMNPV) expressing the silencing suppressor (NSs) protein of Tomato spotted wilt virus (TSWV) was enhanced on permissive and semipermissive cell lines. The expression of a heterologous gene (firefly luciferase) during co-infection of insect cells with vAcNSs and a second recombinant baculovirus (vAgppolhfluc) was shown to increase when compared to single vAgppolhfluc infections. Furthermore, the vAcNSs mean time-to-death values were significantly lower than those for wild-type AcMNPV on larvae of Spodoptera frugiperda and Anticarsia gemmatalis. These results showed that the TSWV-NSs protein could efficiently increase heterologous protein expression in insect cells as well as baculovirus pathogenicity and virulence, probably by suppressing the gene-silencing machinery in insects.

AcMNPV core gene ac109 is required for budded virion transport to the nucleus and for occlusion of viral progeny.

The Autographa californica multiple nucleopolyhedrovirus (AcMNPV) ac109 core gene has been previously characterized as an essential late gene. Our results showed that budded virions could be detected in supernatants of infected Sf-9 cells, even when ac109 knockout viruses displayed a single-cell infection phenotype. Moreover, confocal microscopy analysis revealed that budded virions can enter the cytoplasm but are unable to enter the cell nucleus. This defect could be repaired by complementing ac109 in trans. In addition, polyhedra of normal size could be detected in Sf-9 nuclei infected with ac109 knockout viruses. However, electron microscopy demonstrated that these occlusion bodies were empty. Altogether, these results indicate that ac109 is required for infectivity of both phenotypes of virus.

Synergism between the nucleopolyhedroviruses of Autographa californica and Trichoplusia ni.

Previous observations on high virulence of Autographa californica multiple nucleopolyhedrovirus (AcMNPV) and Trichoplusia ni single nucleopolyhedrovirus (TnSNPV) acting together led us to test possible synergism between these two nucleopolyhedroviruses (NPVs) on cabbage looper larvae. Because synergism between AcMNPV and the Trichoplusia ni granulovirus (TnGV) has been well established before, these two viruses were included in this study as a positive control. Each virus was assayed separately on first-instar cabbage looper and their LC50s were estimated at 2.33, 0.39 and 462 OB/mm2 diet for AcMNPV, TnSNPV and TnGV, respectively. LC50s of AcMNPV mixed with sub-lethal concentrations of TnSNPV and TnGV increased 8 and 10.7 times, respectively. Synergism between the viruses was analyzed by the ANOVA test for the LC50s, the Plackett and Hewlett's joint-action rate test, and the Tammes-Bakuniak graphic method. All three analyses corroborated the synergism between the viruses. The presence of a putative enhancin in the TnSNPV was analyzed by Southern blot hybridization, using a 1.5 kbp KpnI fragment from the TnGV vef gene as a probe. No hybridization was observed. The occurrence of a new putative synergistic factor in TnSNPV is discussed.

Production of viral progeny in insect cells undergoing apoptosis induced by a mutant Anticarsia gemmatalis nucleopolyhedrovirus.

The Anticarsia gemmatalis nucleopolyhedrovirus (AgMNPV) is the most successful viral biopesticide in use worldwide. We have demonstrated that despite widespread apoptosis and no protein synthesis at 48 h p.i., UFL-AG-286 cells infected with a mutant of AgMNPV (vApAg), produced significant amounts of budded virus (BVs) and viral DNA late in infection. However, a different susceptible cell line (BTI-Tn5B 1-4) showed no signs of apoptosis and produced 3.5 times more budded virus when infected with vApAg. A comparison of DNA from AgMNPV and vApAg digested with the same restriction enzymes showed differences in the restriction pattern, indicating that the vApAg phenotype might be due to a mutation in a gene or genes responsible for directly or indirectly inhibiting apoptosis in UFL-AG-286 cells.

Presentation of antigenic sites from foot-and-mouth disease virus on the surface of baculovirus and in the membrane of infected cells.

We describe the construction of recombinant baculoviruses displaying on their surface and in the membrane of infected cells the small, immunodominant antigenic site (site A) or the large polyprotein (P1) coding for the four structural proteins of foot-and-mouth disease virus (FMDV). The coding sequences were inserted in the amino-terminus of gp64, the major glycoprotein of the baculovirus Autographa californica nuclear polyhedrosis virus (AcNPV). Following infection of insect cells with the recombinant baculoviruses, the cellular localization of the chimaeric proteins as well as their presence in the surface of extracellular viruses was assessed by immunofluorescence microscopy and Western blot. The antigenicity of the recombinant viruses was studied by competitive ELISAs, which showed that although both recombinant viruses were able to compete with FMDV-specific monoclonal antibodies (MAbs), their patterns of reactivity were different. The results suggest that this eukaryotic display system could be an alternative method of presentation of foreign antigens in a multimeric form as a new approach to biosynthetic vaccines.