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PubMed2004

[Ubiquitin-proteasome pathway and virus infection].

Ubiquitin is highly conserved 76 amino acid protein found in all eukaryotic organisms and ubiquitin-proteasome pathway (UPP) plays a very important role in regulated non-lysosomal ATP dependent protein degradation. This pathway participates in or regulates numerous cellular processes, such as selective protein degradation, cell cycle progression, apoptosis, signal transduction, transcriptional regulation, receptor control by endocytosis, immune response and the processing of antigens. Nevertheless, roles of UPP in virus infection are only beginning to be clarified. Ubiquitin homology has also been found in insect viruses. All viral ubiquitin genes encode an N-terminal ubiquitin sequence and 3-256 amino acids C-terminal peptides. Most of the residues known to be essential for ubiquitin function have been conserved in the viral variant. In Autographa californica nucleopolyhedrovirus (AcMNPV), viral ubiquitin is attached to the inner surface of budded viron membrane by a covalently linked phospholipid and is not essential for viral replication. Currently, insect viruses are the only viruses known to encode ubiquitin. However, ubiquitin also plays a role in the life cycle of other viruses. Host ubiquitin molecules have been found in some plant viruses and other animal viruses. Additionally, Africa swine fever virus (ASFV) encodes a ubiquitin-conjugating enzyme (E2) and a putative causal link between human immunodeficiency virus type 1 (HIV-1) and ubiquitin was established by showing that depletion of the intracellular pool of free ubiquitin inhibits the virus budding. Further analyses indicated that many retroviruses proteins which are required for efficient pinching off the virus bud contain a late domain. The core element of the late domain is a proline-rich motif (PPXY) which mediates the late domain to be ubiquitinated by cellular proteins. Recently, it has been shown that many retroviruses have developed mechanisms to escape the cellular immune response, to facilitate virus replication and to promote virus assembly and budding via host UPP.

African Swine Fever Virus↗
PubMed2000

Phylogenetic position of the Diadromus pulchellus ascovirus DNA polymerase among viruses with large double-stranded DNA genomes.

The ASCOVIRIDAE: is a family of large double-stranded (ds) DNA insect viruses that contains four species, the Spodoptera frugiperda (SfAV1), Trichoplusia ni (TnAV2), Heliothis virescens (HvAV3) and Diadromus pulchellus (DpAV4) ascoviruses. These are unique among insect viruses in that the primary means of transmission among their lepidopteran hosts is generally by being vectored mechanically by hymenopteran parasitoids. Ascoviruses are similar in virion structure, but their relationships with their parasitoid vectors vary from being opportunistic to obligate. Little is known, however, about the relatedness of these viruses to one another or to other large dsDNA viruses. We therefore cloned and sequenced the delta DNA polymerase gene of DpAV4, characterized it and compared it to 59 eukaryotic and viral delta and epsilon DNA polymerases. Phylogenetic analyses based on these genes revealed that the ascoviruses DpAV4 and SfAV1 formed a group of virus species distinct from, but closely related to, species of the family IRIDOVIRIDAE: Detailed analyses of the relatedness of ascovirus species based on conserved delta DNA polymerase motifs showed two groups within the family ASCOVIRIDAE:, one containing DpAV4 and the other containing SfAV1, TnAV2 and HvAV3, which was consistent with their host-vector relationships. Despite significant differences in capsid symmetry between ascoviruses and iridoviruses, these results suggest that these viruses may have originated from a common ancestral virus.

Amino Acid Sequence↗
PubMed1998

Role of virus-induced apoptosis in a host defense mechanism against virus infection.

Many animal viruses are known to induce apoptosis in infected cells. This virus-induced apoptosis has been often described as a mechanism of host defense against virus infection, based on the finding that mutants of an insect virus with the ability to induce extensive apoptosis in some cells cannot grow in the same cells. In animal virus infection, we have shown that (1) viruses can somehow overcome this defense mechanism and that (2) virus multiplication in the apoptotic cells is not as completely suppressed as in the insect virus infection. These results suggest that, in the case of animal viruses, the virus-induced apoptosis does not play the same role in the host defense system as in insect cells. However, by examining the virus infection under the conditions comparable to the infection in vivo, we demonstrated the defensive role of apoptosis in animal virus infection.

Animals↗
PubMed1992

Expression of the nonstructural proteins of Sindbis virus in insect cells by a baculovirus vector.

The genome of Sindbis virus encodes the polypeptides that are required for the replication and transcription of the virus RNA in infected cells. These polypeptides are translated as a polyprotein that is co- and post-translationally cleaved by an autoproteinase to give rise to four polypeptides designated nsP1, nsP2, nsP3 and nsP4. We have initiated a study of the functions of these proteins by expressing them in the Autographa californica baculovirus polyhedrin expression system. Spodoptera frugiperda cells infected with the recombinant baculovirus synthesized the four Sindbis polypeptides. We used a complementation assay which measures chloramphenicol acetyltransferase (CAT) activity to demonstrate that these proteins were biologically active. The infected cells were transfected with a Sindbis defective RNA that contains the CAT gene downstream of the promoter for the synthesis of the viral subgenomic RNA. CAT activity was found only in cells that had been infected with the recombinant baculovirus, not with wild type baculovirus, indicating that the required Sindbis nsP activities were present. Sindbis virions grew poorly in S. frugiperda cells and self-replicating Sindbis RNAs produced only very low levels of biological activity. Our results suggest that these cells are defective in their ability to replicate Sindbis RNAs and that the block is partially overcome when the Sindbis nsP mRNA is expressed under the control of the baculovirus DNA.

Animals↗
PubMed1994

Insect iridescent virus type 6 encodes a polypeptide related to the largest subunit of eukaryotic RNA polymerase II.

Cytoplasmic DNA viruses encode a DNA-dependent RNA polymerase (DdRP) that is essential for transcription of viral genes. The amino acid sequences of known large subunits of DdRPs contain highly conserved regions. Oligonucleotide primers, deduced from two conserved domains [RQP(T/S)LH and NADFDGDE] were used in PCR experiments for the detection of the corresponding gene of the genome of insect iridescent virus type 6, also known as Chilo iridescent virus (CIV). A specific DNA product of about 150 bp could be amplified and was used as a hybridization probe against the CIV gene library to identify the corresponding gene. The gene encoding the DdRP was identified within the EcoRI fragments M (7099 bp) and L (7400 bp) of CIV DNA, between map units 0.310 and 0.347 (7990 bp). The DNA nucleotide sequence (3153 bp) of the gene encoding the largest subunit of DdRP (RPO1) was determined. Northern blot hybridization revealed the presence of a 3.4 kb RNA transcript in CIV-infected cells that hybridized to the CIV DdRP gene. This predicted viral protein consists of 1051 amino acid residues (120K) and showed considerably higher similarity to the largest subunit of eukaryotic RNA polymerase II than to the homologous proteins of vaccinia virus and African swine fever virus. Phylogenetic analysis suggested that the putative RPO1 of CIV could have evolved from RNA polymerase II after the divergence of the three types of eukaryotic RNA polymerases. The putative RPO1 of CIV lacked the C-terminal domain that is conserved in eukaryotic, eubacterial and other viral RNA polymerases and in this respect was analogous to the RNA polymerases of Archaea. It is hypothesized that the equivalent of the C-terminal domain may reside in another subunit of CIV DdRP encoded by an unidentified viral gene.

Amino Acid Sequence↗
PubMed2003

A single-tube multiplex reverse transcription-polymerase chain reaction for detection and differentiation of vesicular stomatitis Indiana 1 and New Jersey viruses in insects.

A multiplex single-tube reverse transcription-polymerase chain reaction (RT-PCR) has been developed for the detection and differentiation of vesicular stomatitis viruses (VSV), Indiana 1 and New Jersey, from insect samples. Using this assay, detection of either or both viruses in as little as 20 fg of total RNA from tissue culture was achieved, along with detection of vesicular stomatitis (VS) RNA from macerates containing 2 infected mosquitoes in pools of 10-30 noninfected mosquitoes. Vesicular stomatitis virus was detected by RT-PCR in all culture-positive samples, and detection as low as 4 plaque forming units per milliliter was achieved. Comparison between RT-PCR and tissue culture revealed that RT-PCR was able to detect VSV in a volume of insect macerate averaging almost 100 times less than that required for detection by tissue culture. The reported RT-PCR is a potential valuable tool for rapid and sensitive detection and differentiation of VS in insects because intense work associated with viral isolation, the cytotoxicity of insect extracts, and separate virus identification steps can be avoided. Potential application to detection and differentiation of VSV serotypes from vertebrate hosts is addressed.

Animals↗
PubMed1995

Expression and processing of putative nonstructural proteins of hepatitis C virus in insect cells using baculovirus vector.

Processing of the putative nonstructural (NS) proteins, p70(NS3), p4(NS4A), p27(NS4B), p58/56(NS5A), and p66(NS5B), of Japanese type hepatitis C virus (HCV) in insect cells was analyzed by using a baculovirus expression system. Products processed by the HCV serine proteinase (Cpro-2) were essentially identical to those found in mammalian cultured cells transiently producing the NS region of the HCV precursor polyprotein. A series of internal and carboxy (C)-terminal deletion experiments coupled with epitope scanning analysis showed that efficient cleavage at the Cpro-2-dependent processing sites, except at the p4(NS4A)/p27(NS4B) site, is not significantly influenced by those mutations. Efficient cleavage at p4(NS4A)/p27(NS4B) required about 40% of the NS5A N-terminal region. Estimation of the processing sites by determination of the N-terminal amino acid sequences of the processed products revealed that all the Cpro-2-dependent cleavages occurred at essentially identical sites to those reported for another HCV genotype, suggesting that Cpro-2 is a possible target for the development of a strain-independent anti-HCV agent.

Amino Acid Sequence↗
PubMed2005

The players in a mutualistic symbiosis: insects, bacteria, viruses, and virulence genes.

Aphids maintain mutualistic symbioses involving consortia of coinherited organisms. All possess a primary endosymbiont, Buchnera, which compensates for dietary deficiencies; many also contain secondary symbionts, such as Hamiltonella defensa, which confers defense against natural enemies. Genome sequences of uncultivable secondary symbionts have been refractory to analysis due to the difficulties of isolating adequate DNA samples. By amplifying DNA from hemolymph of infected pea aphids, we obtained a set of genomic sequences of H. defensa and an associated bacteriophage. H. defensa harbors two type III secretion systems, related to those that mediate host cell entry by enteric pathogens. The phage, called APSE-2, is a close relative of the previously sequenced APSE-1 but contains intact homologs of the gene encoding cytolethal distending toxin (cdtB), which interrupts the eukaryotic cell cycle and which is known from a variety of mammalian pathogens. The cdtB homolog is highly expressed, and its genomic position corresponds to that of a homolog of stx (encoding Shiga-toxin) within APSE-1. APSE-2 genomes were consistently abundant in infected pea aphids, and related phages were found in all tested isolates of H. defensa, from numerous insect species. Based on their ubiquity and abundance, these phages appear to be an obligate component of the H. defensa life cycle. We propose that, in these mutualistic symbionts, phage-borne toxin genes provide defense to the aphid host and are a basis for the observed protection against eukaryotic parasites.

Amino Acid Sequence↗
PubMed1991

Expression of the X protein of hepatitis B virus in insect cells using recombinant baculoviruses.

The baculovirus system was used to express the X protein of human hepatitis B virus (HBV). The X open reading frames (X ORFs) from cloned viral DNA of the HBV subtypes ayw and adr were introduced into the genome of Autographa californica nuclear polyhedrosis virus (AcNPV). The HBV-DNA of subtype adr derived from a hepatocellular carcinoma contains an X ORF and a 5' extended preX/X ORF, which were both used to construct X recombinant baculoviruses. Infection of Sf9 insect cells with these recombinant viruses yielded large amounts of the respective X proteins. They were identified by a set of mouse monoclonal antibodies directed against different epitopes of the ayw X protein using immunoblotting techniques. A subpopulation of the X protein expressed is modified, thus raising the molecular weight from the expected size of 17 kD to 21 kD. Indirect immunofluorescence and immunoelectron microscopy was performed to characterize the subcellular distribution of the X protein expressed in Sf9 cells. Data are presented that it accumulates as large globular structures within the cytoplasm and the nucleus of the infected cells.

Animals↗
PubMed1996

Expression of the 69K movement protein of turnip yellow mosaic virus in insect cells.

The nonstructural 69-kilodalton (K) protein of turnip yellow mosaic virus is necessary for systemic spread of the virus within the plant. To examine the behavior of the 69K protein in vivo, antibodies were raised against the carboxy-terminal region of this protein. The full-length 69K protein was also expressed in insect cells using a recombinant baculovirus. Studies on the posttranslational modifications of the 69K protein in insect cells revealed that the protein is phosphorylated but not glycosylated. Further experiments of subcellular fractionation and indirect immunolocalization in insect cells showed that the 69K protein is localized in the cytoplasm and/or in the plasma membrane.

Animals↗
PubMed1993

Flock house virus: down-regulation of subgenomic RNA3 synthesis does not involve coat protein and is targeted to synthesis of its positive strand.

Flock house virus is a small insect virus with a bipartite RNA genome consisting of RNA1 and RNA2. RNA3 is a subgenomic element encoded by RNA1, the genomic segment required for viral RNA synthesis (T. M. Gallagher, P. D. Friesen, and R. R. Rueckert, J. Virol. 46:481-489, 1983). Synthesis of RNA3 is strongly inhibited by RNA2, the gene for viral coat protein. Evidence that coat protein is not the regulatory element was obtained by using a defective interfering RNA2 which was messenger inactive. It was also found that RNA2 selectively down-regulated synthesis of positive-strand RNA3 but not of its complementary negative strand. cDNA-generated RNA2 transcripts, carrying four extra nonviral bases at the 3' end, failed to repress synthesis of RNA3 but recovered this activity after a single passage in Drosophila cells in the presence of RNA1, suggesting that down-regulation of RNA3 synthesis is controlled by competition with RNA2 for viral replicase.

Animals↗
PubMed2004

Characterization of particles formed by the precursor protein VPX of infectious bursal disease virus in insect Hi-5 cells: implication on its proteolytic processing.

The precursor (VPX) of host immunogen VP2 protein for infectious bursal disease virus (IBDV) was expressed in insect Sf9 and Hi-5 cells, and the types of particles generated as well as the immunogenicity induced by these particles were examined. Recombinant VPXH (rVPXH) protein, expressed in Hi-5 cells at an expression level 4x higher than in Sf9 cells, was efficiently processed by proteases to yield VP2-like proteins with corresponding molecular weight, a phenomenon not observed previously. At least three structures of particles were observed for VPXH and VP2-like proteins purified by immobilized metal-ion affinity chromatography (MAC). In addition to the two previously identified twisted tubular and isometric particle structures, there was a new one: icosahedral particles of approximately 25 nm in diameter. The purified particles were further separated by gel-filtration chromatography (GFC) linking with HPLC, which was able to resolve the isometric from icosahedral particles better than ultracentrifugation. Chromatographic results indicate that rVPXH protein mainly involved in the formation of the isometric particle structure and occasionally twisted tubular structure, and the icosahedral particles were formed by the degraded products of rVPXH (VP2-like proteins). Thus, by combining IMAC and GFC, it was shown that VPX was processed efficiently to yield VP2-like protein that could form small virus-like particles in Hi-5 cells. Finally, we demonstrated that virus-neutralizing antibodies were induced when susceptible chickens were vaccinated with the IMAC-purified rVPXH protein (40 microg per bird). This indicates that these particles are highly immunogenic and might serve as an alternative vaccine candidate for the development of IBDV subunit vaccine.

Animals↗
PubMed1984

DNA analysis of insect iridescent virus 6: evidence for circular permutation and terminal redundancy.

DNA analysis of small insect iridovirus 6 was performed. Combined exonuclease-restriction endonuclease digestions revealed that all resulting fragments were degraded without preference for any one DNA fragment. Upon denaturation and reannealing of native linear Chilo iridescent virus DNA (158 x 10(6) daltons), duplex DNA circles of a smaller size (140 x 10(6) daltons) with protruding tails were formed.

Journal Article↗
PubMedDate not supplied

Insect defenses against virus infection: the role of apoptosis.

Insects, with their lack of an adaptive immune response, provide a unique animal model to examine the effects of apoptosis on viral infection. Several members of the baculovirus family of insect viruses have been shown to induce apoptosis during infection of cultured insect cells, and depending on the virus-host combination this apoptotic response can severely limit viral replication. In response to this evolutionary pressure, all baculoviruses studied to date carry antiapoptotic genes, including members of the p35 and IAP (inhibitor of apoptosis) gene families. Recent work has characterized the apoptotic response during infection of the host insect, and the results directly demonstrate the power of apoptosis as an antiviral response.

Animals↗