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Distinct Roles of Cellular ESCRT-I and ESCRT-III Proteins in Efficient Entry and Egress of Budded Virions of Autographa californica Multiple Nucleopolyhedrovirus.

ABSTRACT: The endosomal sorting complex required for transport (ESCRT) machinery is necessary for budding of many enveloped viruses. Recently, it was demonstrated that Vps4, the key regulator for recycling of the ESCRT-III complex, is required for efficient infection by the baculovirus Autographa californica multiple nucleopolyhedrovirus (AcMNPV). However, ESCRT assembly, regulation, and function are complex, and little is known regarding the details of participation of specific ESCRT complexes in AcMNPV infection. In this study, the core components of ESCRT-I (Tsg101 and Vps28) and ESCRT-III (Vps2B, Vps20, Vps24, Snf7, Vps46, and Vps60) were cloned from Spodoptera frugiperda Using a viral complementation system and RNA interference (RNAi) assays, we found that ESCRT-I and ESCRT-III complexes are required for efficient entry of AcMNPV into insect cells. In cells knocking down or overexpressing dominant negative (DN) forms of the components of ESCRT-I and ESCRT-III complexes, entering virions were partially trapped within the cytosol. To examine only egress, cells were transfected with the double-stranded RNA (dsRNA) targeting an individual ESCRT-I or ESCRT-III gene and viral bacmid DNA or viral bacmid DNA that expressed DN forms of ESCRT-I and ESCRT-III components. We found that ESCRT-III components (but not ESCRT-I components) are required for efficient nuclear egress of progeny nucleocapsids. In addition, we found that several baculovirus core or conserved proteins (Ac11, Ac76, Ac78, GP41, Ac93, Ac103, Ac142, and Ac146) interact with Vps4 and components of ESCRT-III. We propose that these viral proteins may form an "egress complex" that is involved in recruiting ESCRT-III components to a virus egress domain on the nuclear membrane.IMPORTANCE The ESCRT system is hijacked by many enveloped viruses to mediate budding and release. Recently, it was found that Vps4, the key regulator of the cellular ESCRT machinery, is necessary for efficient entry and egress of Autographa californica multiple nucleopolyhedrovirus (AcMNPV). However, little is known about the roles of specific ESCRT complexes in AcMNPV infection. In this study, we demonstrated that ESCRT-I and ESCRT-III complexes are required for efficient entry of AcMNPV into insect cells. The components of ESCRT-III (but not ESCRT-I) are also necessary for efficient nuclear egress of progeny nucleocapsids. Several baculovirus core or conserved proteins were found to interact with Vps4 and components of ESCRT-III, and these interactions may suggest the formation of an "egress complex" involved in the nuclear release or transport of viral nucleocapsids.

SUBMITTER: Yue Q

PROVIDER: S-EPMC5730794 | biostudies-literature | 2018 Jan

REPOSITORIES: biostudies-literature

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Distinct Roles of Cellular ESCRT-I and ESCRT-III Proteins in Efficient Entry and Egress of Budded Virions of Autographa californica Multiple Nucleopolyhedrovirus.

Yue Qi Q Yu Qianlong Q Yang Qi Q Xu Ye Y Guo Ya Y Blissard Gary W GW Li Zhaofei Z

Journal of virology 20171214 1

The endosomal sorting complex required for transport (ESCRT) machinery is necessary for budding of many enveloped viruses. Recently, it was demonstrated that Vps4, the key regulator for recycling of the ESCRT-III complex, is required for efficient infection by the baculovirus Autographa californica multiple nucleopolyhedrovirus (AcMNPV). However, ESCRT assembly, regulation, and function are complex, and little is known regarding the details of participation of specific ESCRT complexes in AcMNPV ...[more]

PMID: 29046462

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Project description:In eukaryotic cells, the soluble N-ethylmaleimide-sensitive factor (NSF) attachment protein receptor (SNARE) proteins comprise the minimal machinery that triggers fusion of transport vesicles with their target membranes. Comparative studies revealed that genes encoding the components of the SNARE system are highly conserved in yeast, insect, and human genomes. Upon infection of insect cells by the virus Autographa californica multiple nucleopolyhedrovirus (AcMNPV), the transcript levels of most SNARE genes initially were upregulated. We found that overexpression of dominant-negative (DN) forms of NSF or knockdown of the expression of NSF, the key regulator of the SNARE system, significantly affected infectious AcMNPV production. In cells expressing DN NSF, entering virions were trapped in the cytoplasm or transported to the nucleus with low efficiency. The presence of DN NSF also moderately reduced trafficking of the viral envelope glycoprotein GP64 to the plasma membrane but dramatically inhibited production of infectious budded virions (BV). Transmission electron microscopy analysis of infections in cells expressing DN NSF revealed that progeny nucleocapsids were retained in a perinuclear space surrounded by inner and outer nuclear membranes. Several baculovirus conserved (core) proteins (Ac76, Ac78, GP41, Ac93, and Ac103) that are important for infectious budded virion production were found to associate with NSF, and NSF was detected within the assembled BV. Together, these data indicate that the cellular SNARE system is involved in AcMNPV infection and that NSF is required for efficient entry and nuclear egress of budded virions of AcMNPV.IMPORTANCE Little is known regarding the complex interplay between cellular factors and baculoviruses during viral entry and egress. Here, we examined the cellular SNARE system, which mediates the fusion of vesicles in healthy cells, and its relation to baculovirus infection. Using a DN approach and RNA interference knockdown, we demonstrated that a general disruption of the SNARE machinery significantly inhibited the production of infectious BV of AcMNPV. The presence of a DN NSF protein resulted in low-efficiency entry of BV and the retention of progeny nucleocapsids in the perinuclear space during egress. Combined with these effects, we also found that several conserved (core) baculovirus proteins closely associate with NSF, and these results suggest their involvement in the egress of BV. Our findings are the first to demonstrate that the SNARE system is required for efficient entry of BV and nuclear egress of progeny nucleocapsids of baculoviruses.

Project description:The endosomal sorting complex required for transport (ESCRT) is a conserved protein machine mediating membrane remodeling and scission. In the context of viral infection, different components of the ESCRT-III complex, which serve as the core machinery to catalyze membrane fission, are involved in diverse viruses' entry, replication, and/or budding. However, the interplay between ESCRT-III and viral factors in the virus life cycle, especially for that of large enveloped DNA viruses, is largely unknown. Recently, the ESCRT-III components Vps2B, Vps20, Vps24, Snf7, Vps46, and Vps60 were determined for entry and/or egress of the baculovirus Autographa californica multiple nucleopolyhedrovirus (AcMNPV). Here, we identified the final three ESCRT-III components Chm7, Ist1, and Vps2A of Spodoptera frugiperda. Overexpression of the dominant-negative forms of these proteins or RNAi downregulation of their transcripts significantly reduced infectious budded viruses (BVs) production of AcMNPV. Quantitative PCR together with confocal and transmission electron microscopy analysis revealed that these proteins were required for internalization and trafficking of BV during entry and egress of nucleocapsids. In infected Sf9 cells, nine ESCRT-III components were distributed on the nuclear envelope and plasma membrane, and except for Chm7, the other components were also localized to the intranuclear ring zone. Y2H and BiFC analysis revealed that 42 out of 64 BV-related proteins including 35 BV structural proteins and 7 non-BV structural proteins interacted with single or multiple ESCRT-III components. By further mapping the interactome of 64 BV-related proteins, we established the interaction networks of ESCRT-III and the viral protein complexes involved in BV entry and egress.IMPORTANCEFrom archaea to eukaryotes, the endosomal sorting complex required for transport (ESCRT)-III complex is hijacked by many enveloped and nonenveloped DNA or RNA viruses for efficient replication. However, the mechanism of ESCRT-III recruitment, especially for that of large enveloped DNA viruses, remains elusive. Recently, we found the ESCRT-III components Vps2B, Vps20, Vps24, Snf7, Vps46, and Vps60 are necessary for the entry and/or egress of budded viruses (BVs) of Autographa californica multiple nucleopolyhedrovirus. Here, we demonstrated that the other three ESCRT-III components Chm7, Ist1, and Vps2A play similar roles in BV infection. By determining the subcellular localization of ESCRT-III components in infected cells and mapping the interaction of nine ESCRT-III components and 64 BV-related proteins, we built the interaction networks of ESCRT-III and the viral protein complexes involved in BV entry and egress. These studies provide a fundamental basis for understanding the mechanism of the ESCRT-mediated membrane remodeling for replication of baculoviruses.

Project description:Baculoviruses encode a variety of auxiliary proteins that are not essential for viral replication but provide them with a selective advantage in nature. P10 is a 10-kDa auxiliary protein produced in the very late phase of gene transcription by Autographa californica multiple nucleopolyhedrovirus (AcMNPV). The P10 protein forms cytoskeleton-like structures in the host cell that associate with microtubules varying from filamentous forms in the cytoplasm to aggregated perinuclear tubules that form a cage-like structure around the nucleus. These P10 structures may have a role in the release of occlusion bodies (OBs) and thus mediate the horizontal transmission of the virus between insect hosts. Here, using mass spectrometric analysis, it is demonstrated that the C terminus of P10 is phosphorylated during virus infection of cells in culture. Analysis of P10 mutants encoded by recombinant baculoviruses in which putative phosphorylation residues were mutated to alanine showed that serine 93 is a site of phosphorylation. Confocal microscopy examination of the serine 93 mutant structures revealed aberrant formation of the perinuclear tubules. Thus, the phosphorylation of serine 93 may induce the aggregation of filaments to form tubules. Together, these data suggest that the phosphorylation of serine 93 affects the structural conformation of P10.IMPORTANCE The baculovirus P10 protein has been researched intensively since it was first observed in 1969, but its role during viral infection remains unclear. It is conserved in the alphabaculoviruses and expressed at high levels during virus infection. Producing large amounts of a protein is wasteful for the virus unless it is advantageous for the survival of its progeny, and therefore, P10 presents an enigma. As P10 polymerizes to form organized cytoskeletal structures that colocalize with host cell microtubules, the structural relationship of the protein with the host cell may present a key to help understand the function and importance of this protein. This study addresses the importance of the structural changes in P10 during infection and how they may be governed by phosphorylation. The P10 structures affected by phosphorylation are closely associated with the viral progeny and thus may potentially be responsible for its dissemination and survival.

Dataset Information

Distinct Roles of Cellular ESCRT-I and ESCRT-III Proteins in Efficient Entry and Egress of Budded Virions of Autographa californica Multiple Nucleopolyhedrovirus.

Publications

Distinct Roles of Cellular ESCRT-I and ESCRT-III Proteins in Efficient Entry and Egress of Budded Virions of Autographa californica Multiple Nucleopolyhedrovirus.

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