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At least 127 records · Page 7Linked to original sources
PubMed1986

Monoclonal antibody to the amino-terminal L sequence of murine leukemia virus glycosylated gag polyproteins demonstrates their unusual orientation in the cell membrane.

To analyze cell surface murine leukemia virus gag protein expression, we have prepared monoclonal antibodies against the spontaneous AKR T lymphoma KKT-2. One of these antibodies, 43-13, detects an AKR-specific viral p12 determinant. A second monoclonal antibody, 43-17, detects a novel murine leukemia virus-related antigen found on glycosylated gag polyproteins (gp95gag, gp85gag, and gp55gag) on the surface of cells infected with and producing ecotropic endogenous viruses, but does not detect antigens within these virions. The 43-17 antibody immunoprecipitates the precursor of the cell surface gag protein whether in its glycosylated or unglycosylated state, but does not detect the cytoplasmic precursor of the virion gag proteins (Pr65gag). Based on these findings, we have localized the 43-17 determinant to the unique amino-terminal part of the glycosylated gag polyprotein (the L domain). We have determined that gp95gag contains L-p15-p12-p30-p10 determinants, whereas gp85gag lacks the carboxyterminal p10 determinant, and gp55gag lacks both p30 and p10 carboxy terminal determinants. Analysis of cell surface gag expression with the 43-17 antibody leads us to propose that the L domain plays a crucial role in (i) the insertion and orientation of murine leukemia virus gag polyproteins in the cell membrane and (ii) the relative abundance of expression of AKR leukemia virus versus Moloney murine leukemia virus glycosylated gag polyproteins in infected cells.

Animals↗
PubMed1986

Bovine leukemia virus protease: purification, chemical analysis, and in vitro processing of gag precursor polyproteins.

Bovine leukemia virus protease was purified to homogeneity and assayed by using murine leukemia virus Pr65gag, a polyprotein precursor of the viral core structural proteins, as the substrate. A chemical analysis of the protease, including an amino acid composition and NH2- and COOH-terminal amino acid sequence analysis, revealed that it has an Mr of 14,000 and is encoded by a segment of the viral RNA located between the gag gene and the putative reverse transcriptase gene. As expected from the nucleotide sequence data (Rice et al., Virology 142:357-377, 1985), the reading frame for the protease is different from both the gag and reverse transcriptase reading frames. The 5' end of the protease open reading frame extends 38 codons upstream from the codon for the NH2-terminal residue of the mature viral protease and overlaps the gag open reading frame by 7 codons. The 3' end of the protease open reading frame extends 26 codons beyond the codon for the COOH-terminal residue of the mature protease and overlaps 8 codons of the reverse transcriptase open reading frame. Several lines of evidence, such as protein mapping of the gag polyprotein precursor, the characteristic structure of the mRNA, and promotion of the synthesis of a gag polyprotein precursor by lysine tRNA in vitro, suggest that the protease could be translated by frameshift suppression of the gag termination codon. In vitro synthesized bovine leukemia virus gag-related polyproteins were cleaved by the protease into fragments which were the same size as the known components of bovine leukemia virus, suggesting that the specificity of cleavage catalyzed in vitro by the purified protease is the same as the specificity of cleavage found in the virus.

Amino Acid Sequence↗
PubMed1988

Processing of gag precursor polyprotein of human T-cell leukemia virus type I by virus-encoded protease.

The biological activity encoded in the putative protease gene (pro) of human T-cell leukemia virus type I was investigated by using a vaccinia virus expression vector. The 53-kilodalton gag precursor polyprotein was processed into the mature p19, p24, and p15 gag proteins when the gag and protease-coding sequence was expressed under the control of a vaccinia virus promoter, suggesting that the protease may be synthesized through the mechanism of ribosomal frame shifting. The processing defect of a protease mutant could be complemented by cointroduction of a wild-type construct into the cell, demonstrating that the pro gene encodes the biologically active protease molecules which are capable of processing the gag precursor polyprotein in vivo in trans. A study involving the use of a variety of mutants constructed in vitro revealed that the protease consists of a nonessential carboxy-terminal region and a part essential for its activity, including the putative catalytic residue, aspartic acid. Furthermore, a cluster of adenine residues positioned at the overlapping region between the gag and pro genes was shown to be involved in the ribosomal frameshifting event for the synthesis of protease. To mimic the formation of the 76-kilodalton gag-pro precursor polyprotein formed by ribosomal slipping, the coding frames of the gag and pro gene were adjusted. The processing of the gag-pro precursor polyprotein depended on an intact protease gene, implying that a cis-acting function of human T-cell leukemia virus type I protease may be necessary to trigger the initial cleavage event that leads to the release of protease from the precursor protein.

Amino Acid Sequence↗
PubMed1989

Polyprotein processing of Theiler's murine encephalomyelitis virus.

To investigate polyprotein processing of Theiler's murine encephalomyelitis viruses, we analyzed in vitro translation reactions programmed by in vitro-derived transcripts from an infectious full-length cDNA clone of the DA strain of Theiler's virus. To help identify the proteinases that carried out the processing, we modified the DA cDNA clone transcription template by linearization with different restriction endonucleases that generate templates of different lengths or by constructing linker insertion or deletion mutations or both in putative proteinase-coding regions. Protein 3C carried out most of the cleavages of the polyprotein, as is true for the other picornaviruses that have been studied. A second proteinase also appeared active at the LP12A-2B junction. A protein of slightly faster mobility than the leader protein was seen with translation of transcripts derived from DA cDNA but not GDVII cDNA. This protein may be synthesized from an alternative initiation site in the DA leader-coding region out of phase with the polyprotein reading frame. Our findings are relevant to ongoing investigations of the abnormal virus expression seen in DA virus late demyelinating disease, since polyprotein processing is critical in regulating picornaviral gene expression.

Animals↗
PubMed1995

Complex formation between the NS3 serine-type proteinase of the hepatitis C virus and NS4A and its importance for polyprotein maturation.

Processing of the hepatitis C virus polyprotein is mediated by host cell signalases and at least two virally encoded proteinases. Of these, the serine-type proteinase encompassing the amino-terminal one-third of NS3 is responsible for cleavage at the four sites carboxy terminal of NS3. The activity of this proteinase is modulated by NS4A, a 54-amino-acid polyprotein cleavage product essential for processing at the NS3/4A, NS4A/4B, and NS4B/5A sites and enhancing cleavage efficiency between NS5A and NS5B. Using the vaccinia virus-T7 hybrid system to express hepatitis C virus polypeptides in BHK-21 cells, we studied the role of NS4A in proteinase activation. We found that the NS3 proteinase and NS4A form a stable complex when expressed as a single polyprotein or as separate molecules. Results from deletion mapping show that the minimal NS4A domain required for proteinase activation is located in the center of NS4A between amino acids 1675 and 1686 of the polyprotein. Amino acid substitutions within this domain destabilizing the NS3-NS4A complex also impair trans cleavage at the NS4A-dependent sites. Similarly, deletion of amino-terminal NS3 sequences impairs complex formation as well as cleavage at the NS4B/5A site but not at the NS4A-independent NS5A/5B site. These results suggest that a stable NS3-NS4A interaction is important for cleavage at the NS4A-dependent sites and that amino-terminal NS3 sequences and the central NS4A domain are directly involved in complex formation.

Algorithms↗
PubMed1996

The human foamy virus pol gene is expressed as a Pro-Pol polyprotein and not as a Gag-Pol fusion protein.

It has been reported recently that the human foamy virus (HFV) Pol polyprotein of 120 kDa is synthesized in the absence of the active HFV aspartic protease. To gain more information on how the 120-kDa Pro-Pol protein is synthesized, mutant HFV genomes were constructed and the resulting proviruses were analyzed with respect to HFV pol expression and infectivity. HFV proviruses that contain termination codons in the nucleocapsid domain of gag and thus lack a gag-pol overlap region assumed to be required for translational frameshifting, nevertheless expressed the 120-kDa Pro-Pol precursor, the 80-kDa reverse transcriptase/RNase H, and a 40-kDa integrase in amounts similar to those observed for wild-type genomes. Since a Gag-independent expression of authentic Pol proteins was detectable in cells transfected with eukaryotic HFV pol expression plasmids, the data indicate that the HFV Pol precursor of 120 kDa is expressed independently of Gag by a mechanism that does not rely on ribosomal frameshifting, since the postulated HFV Gag-Pol protein of 190 kDa was not detectable under the conditions used. Furthermore, replacement of the Met residue by Thr at position 9 in pol within the gag-pol overlap region resulted in strongly reduced HFV Pol polyprotein expression and infectivity of the resulting proviruses. This Met residue of pol conserved in foamy virus sequences is the likely candidate for translational initiation of the 120-kDa Pro-Pol polyprotein. trans complementation of the HFV mutant with the Met-to-Thr substitution in the pol gene by a eukaryotic plasmid that expressed the HFV Pro-Pol protein resulted in partial recovery of infectivity. When HFV pol was fused in frame to gag, an engineered 190-kDa Gag-Pol fusion protein was formed and the enzymatic activity of the HFV protease was partially retained. The results imply that HFV is the first retrovirus that expresses a Pol polyprotein without formation of a Gag-Pol fusion protein.

Amino Acid Sequence↗
PubMed1997

Proteolytic processing of the coronavirus infectious bronchitis virus 1a polyprotein: identification of a 10-kilodalton polypeptide and determination of its cleavage sites.

Proteolytic processing of the polyprotein encoded by mRNA 1 is an essential step in coronavirus RNA replication and gene expression. We have previously reported that an open reading frame (ORF) 1a-specific proteinase of the picornavirus 3C proteinase group is involved in processing of the coronavirus infectious bronchitis virus (IBV) 1a/1b polyprotein, leading to the formation of a mature viral protein of 100 kDa. We report here the identification of a novel 10-kDa polypeptide and the involvement of the 3C-like proteinase in processing of the ORF 1a polyprotein to produce the 10-kDa protein species. By using a region-specific antiserum, V47, raised against a bacterial-viral fusion protein containing IBV sequence encoded between nucleotides 11488 and 12600, the 10-kDa polypeptide was detected in lysates from both IBV-infected and plasmid DNA-transfected Vero cells. Coexpression, deletion, and mutagenesis studies showed that this novel polypeptide was encoded by ORF 1a from nucleotide 11545 to 11878 and was cleaved from the 1a polyprotein by the 3C-like proteinase domain. Evidence presented suggested that a previously predicted Q-S (Q3783 S3784) dipeptide bond encoded by ORF 1a between nucleotides 11875 and 11880 was responsible for the release of the C terminus of the 10-kDa polypeptide and that a novel Q-N (Q3672 N3673) dipeptide bond encoded between nucleotides 11542 and 11547 was responsible for the release of the N terminus of the 10-kDa polypeptide.

Animals↗
PubMed1998

Characterization of replication-competent hepatitis A virus constructs containing insertions at the N terminus of the polyprotein.

To determine whether hepatitis A virus (HAV) could tolerate the insertion of exogenous sequences, we constructed full-length HAV cDNAs containing in-frame insertions at the N terminus of the polyprotein and transfected the derived T7 RNA polymerase in vitro transcripts into FRhK-4 cells. Replication of HAVvec1, a construct containing an insertion of 60 nucleotides coding for a polylinker, a 2B/2C cleavage site for HAV protease 3Cpro, and two initiation codons that restored the sequence of the N terminus of the polyprotein, was detected 2 weeks after transfection by indirect immunofluorescence analysis using anti-HAV monoclonal antibodies. Western blot analysis of HAVvec1-infected cells using anti-VP2 and anti-VP4 antibodies failed to detect the expression of the inserted sequences. Insertion of a 24-mer oligonucleotide coding for a FLAG epitope into HAVvec1 resulted in its HAV-mediated expression which was retained upon deletion of a Gln residue from the inserted 2B/2C cleavage site. Western blot analysis using anti-FLAG and anti-VP2 antibodies showed that the FLAG epitope accumulated in infected cells fused to VP0. Replacement of the FLAG epitope with an epitope of the circumsporozoite protein (CSP) of Plasmodium falciparum resulted in its stable HAV-mediated expression for at least six serial passages in FRhK-4 cells. Sedimentation analysis in sucrose density gradients showed that the CSP epitope accumulated in infected cells fused to VP0, forming 80S empty capsids which also contained native VP0. Our data suggest that the HAV internal ribosome entry site can efficiently direct dual initiation of translation of the polyprotein from AUG codons separated by 66 to 78 nucleotides and show that HAV can tolerate insertions at the N terminus of the polyprotein.

3C Viral Proteases↗
PubMed1998

Cleavage of human immunodeficiency virus type 1 proteinase from the N-terminally adjacent p6* protein is essential for efficient Gag polyprotein processing and viral infectivity.

Maturation of infectious human immunodeficiency virus (HIV) particles requires proteolytic cleavage of the structural polyproteins by the viral proteinase (PR), which is itself encoded as part of the Gag-Pol polyprotein. Expression of truncated PR-containing sequences in heterologous systems has mostly led to the autocatalytic release of an 11-kDa species of PR which is capable of processing all known cleavage sites on the viral precursor proteins. Relatively little is known about cleavages within the nascent virus particle, on the other hand, and controversial results concerning the active PR species inside the virion and the relative activities of extended PR species have been reported. Here, we report that HIV type 1 (HIV-1) particles of four different strains obtained from different cell lines contain an 11-kDa PR, with no extended PR proteins detectable. Furthermore, mutation of the N-terminal PR cleavage site leading to production of an N-terminally extended 17-kDa PR species caused a severe defect in Gag polyprotein processing and a complete loss of viral infectivity. We conclude that N-terminal release of PR from the HIV-1 polyprotein is essential for viral replication and suggest that extended versions of PR may have a transient function in the proteolytic cascade.

Animals↗
PubMed2002

Repression of African swine fever virus polyprotein pp220-encoding gene leads to the assembly of icosahedral core-less particles.

African swine fever virus (ASFV) polyprotein pp220, encoded by the CP2475L gene, is an N-myristoylated precursor polypeptide that, after proteolytic processing, gives rise to the major structural proteins p150, p37, p34, and p14. These proteins localize at the core shell, a matrix-like virus domain placed between the DNA-containing nucleoid and the inner envelope. In this study, we have examined the role of polyprotein pp220 in virus morphogenesis by means of an ASFV recombinant, v220i, containing an inducible copy of the CP2475L gene regulated by the Escherichia coli repressor-operator system. Under conditions that repress pp220 expression, the virus yield of v220i was about 2.6 log units lower than that of the parental virus or of the recombinant grown under permissive conditions. Electron microscopy revealed that pp220 repression leads to the assembly of icosahedral particles virtually devoid of the core structure. Analysis of recombinant v220i by immunoelectron microscopy, immunoblotting, and DNA hybridization showed that mutant particles essentially lack, besides the pp220-derived products, a number of major core proteins as well as the viral DNA. On the other hand, transient expression of the CP2475L gene in COS cells showed that polyprotein pp220 assembles into electron-dense membrane-bound coats, whereas a mutant nonmyristoylated version of pp220 does not associate with cellular membranes but forms large cytoplasmic aggregates. Together, these findings indicate that polyprotein pp220 is essential for the core assembly and suggest that its myristoyl moiety may function as a membrane-anchoring signal to bind the developing core shell to the inner viral envelope.

African Swine Fever Virus↗
PubMed2005

Involvement of PKR and RNase L in translational control and induction of apoptosis after Hepatitis C polyprotein expression from a vaccinia virus recombinant.

BACKGROUND: Hepatitis C virus (HCV) infection is of growing concern in public health with around 350 million chronically infected individuals worldwide. Although the IFN-alpha/rivabirin is the only approved therapy with 10-30% clinical efficacy, the protective molecular mechanism involved during the treatment is still unknown. To analyze the effect of HCV polyprotein expression on the antiviral response of the host, we developed a novel vaccinia virus (VV)-based delivery system (VT7-HCV7.9) where structural and nonstructural (except part of NS5B) proteins of HCV ORF from genotype 1b are efficiently expressed and produced, and timely regulated in mammalian cell lines. RESULTS: Regulated transcript production and viral polypeptide processing was demonstrated in various cell lines infected with the recombinant VT7-HCV7.9, indicating that the cellular and viral proteolytic machineries are functional within these cells. The inducible expression of the HCV polyprotein by VV inhibits the synthesis of both host and viral proteins over the time and also induces apoptosis in HeLa and HepG2-infected cells. These effects occur accompanying with the phosphorylation of the translation initiation factor eIF-2alpha. In cells co-infected with VT7-HCV7.9 and a recombinant VV expressing the dominant negative eIF-2alpha-S51A mutant in the presence of the inductor isopropyl-thiogalactoside (IPTG), protein synthesis is rescued. The IFN-inducible protein kinase PKR is responsible for the translational block, as demonstrated with PKR-/- and PKR +/+ cell lines. However, apoptosis induced by VT7-HCV7.9 is mediated by the RNase L pathway, in a PKR-independent manner. CONCLUSION: These findings demonstrate the antiviral relevance of the proteins induced by interferon, PKR and RNase L during expression from a VV recombinant of the HCV polyprotein in human cell lines. HCV polyprotein expression caused a severe cytopathological effect in human cells as a result of inhibition of protein synthesis and apoptosis induction, triggered by the activation of the IFN-induced enzymes PKR and RNase L systems. Thus, the virus-cell system described here highlights the relevance of the IFN system as a protective mechanism against HCV infection.

Apoptosis↗
PubMed1999

Sequence-divergent units of the ABA-1 polyprotein array of the nematode Ascaris suum have similar fatty-acid- and retinol-binding properties but different binding-site environments.

Polyproteins comprise long polypeptides that are post-translationally cleaved into proteins of different function, or tandemly repetitive polypeptides which are processed into multiple versions of proteins which are presumed to have the same function. In the latter case the individual units of the polyprotein can differ substantially in sequence. Identity of function between the different units therefore cannot be assumed. Here we have examined the ABA-1 polyprotein allergen of the parasitic nematode Ascaris suum and found it to contain units which show a 50% difference in amino acid sequence. The parasite therefore produces at least two radically different forms of the allergen encoded within the polyprotein array. In fluorescence-based ligand-binding assays, recombinant polypeptides representing the two forms (designated ABA-1A1 and ABA-1B1) showed similar binding affinities for a range of fluorescent active-site probes [retinol, dansylundecanoic acid, dansyl-DL-alpha-amino-octanoic acid, cis-parinaric acid (cPnA)] and for the non-specific hydrophobic surface probe 8-anilinonaphthalene-1-sulphonic acid. However, the molecular environments in the active sites are markedly different, as indicated by disparate fluorescence emission peaks and intensities of bound probes. CD showed that the proteins have similar secondary structures but differ in susceptibility to chemical denaturation/unfolding by guanidinium chloride. Both retain a single conserved tryptophan residue in a characteristic non-polar environment, as revealed by extreme fluorescence blue shift. Thus the gross differences in sequence of the two proteins are not reflected in their ligand-binding specificities but in their binding-site environments.

Allergens↗
PubMed1989

[Nucleotide sequence of the genome and complete amino acid sequence of a polyprotein of the tick-borne encephalitis virus].

We have cloned and sequenced RNA encoding all virion and nonstructural proteins of tick-borne encephalitis virus (TBEV). Its length is 10,477 bases with a single open reading frame (nucleotides 127-10,363) encoding 3412 amino acids. The 5'- and 3'-noncoding regions have stem- and- loop structure. The polyprotein precursor is proteolytically cleaved, apparently, by a mechanism resembling that proposed for the expression of polyproteins of other flaviviruses, such as yellow fever, West Nile and Kunjin viruses. The deduced TBEV gene order is 5'-C-preM (M)-E-NS1-NS2A-NS2B-NS3-NS4A-NS4B-NS5++ +-3'. The genome and the polyprotein of TBEV and other flaviviruses appears to be structurally similar, although these flaviviruses are transmitted to and from their vertebrate hosts by different carriers, such as ticks or mosquitoes. Analysis of sequence homologies of polyproteins of flaviviruses suggests that TBEV is more closely related to yellow fever virus than to other serological subgroups of flaviviruses (West Nile or Dengue viruses). The hydrophobic profiles of the flaviviruses are highly conservative. Nonstructural proteins NS2A, NS2B, NS4A and NS4B are extremely hydrophobic, suggesting that they are likely to be associated with cellular membranes. Proteins E, NS1, NS3 and NS5 are the most conservative and may be involved in general enzymatic activities related to viral replication and virion assembly.

Amino Acid Sequence↗
PubMed1999

Crystal structure of an inhibitor complex of the 3C proteinase from hepatitis A virus (HAV) and implications for the polyprotein processing in HAV.

The proteolytic processing of the viral polyprotein is an essential step during the life cycle of hepatitis A virus (HAV), as it is in all positive-sense, single-stranded RNA viruses of animals. In HAV the 3C proteinase is the only proteolytic activity involved in the polyprotein processing. The specific recognition of the cleavage sites by the 3C proteinase depends on the amino acid sequence of the cleavage site. The structure of the complex of the HAV 3C proteinase and a dipeptide inhibitor has been determined by X-ray crystallography. The double-mutant of HAV 3C (C24S, F82A) was inhibited with the specific inhibitor iodoacetyl-valyl-phenylalanyl-amide. The resulting complex had an acetyl-Val-Phe-amide group covalently attached to the S(gamma) atom of the nucleophilic Cys 172 of the enzyme. Crystals of the complex of HAV 3C (C24S, F82A) acetyl-Val-Phe-amide were found to be monoclinic, space group P2(1), having 4 molecules in the asymmetric unit and diffracting to 1.9-A resolution. The final refined structure consists of 4 molecules of HAV 3C (C24S,F82A) acetyl-Val-Phe-amide, 1 molecule of DMSO, 1 molecule of glycerol, and 514 water molecules. There are considerable conformational differences among the four molecules in the asymmetric unit. The final R-factor is 20.4% for all observed reflections between 15.0- and 1.9-A resolution and the corresponding R(free) is 29.8%. The dipeptide inhibitor is bound to the S(1)(') and S(2)(') specificity subsites of the proteinase. The crystal structure reveals that the HAV 3C proteinase possesses a well-defined S(2)(') specificity pocket and suggests that the P(2)(') residue could be an important determinant for the selection of the primary cleavage site during the polyprotein processing in HAV.

3C Viral Proteases↗
PubMed2000

Rabbit hemorrhagic disease virus: genome organization and polyprotein processing of a calicivirus studied after transient expression of cDNA constructs.

Rabbit hemorrhagic disease virus (RHDV) belongs to the family Caliciviridae. Studies on this virus are hampered by the lack of a convenient cell culture system. To study viral protein expression a cDNA construct containing the entire protein-coding region of the virus was established and used for transient expression studies. After metabolic labeling of transfected cells and immunoprecipitation with a set of RHDV-specific antisera a variety of polypeptides were identified and assigned to defined regions of the viral genome. The consensus sequences of already identified or putative proteolytic cleavage sites in the viral polyprotein were changed by the introduction of mutations into the expression construct. Expression of these mutated constructs and analysis of the protein patterns allowed us to identify novel cleavage sites in the polyprotein and revealed the first details regarding the order of polyprotein processing.

Chromosome Mapping↗
PubMed2001

Further identification and characterization of novel intermediate and mature cleavage products released from the ORF 1b region of the avian coronavirus infectious bronchitis virus 1a/1b polyprotein.

The coronavirus 3C-like proteinase is one of the viral proteinases responsible for processing of the 1a and 1a/1b polyproteins to multiple mature products. In cells infected with avian coronavirus infectious bronchitis virus (IBV), three proteins of 100, 39, and 35 kDa, respectively, were previously identified as mature cleavage products released from the 1b region of the 1a/1b polyprotein by the 3C-like proteinase. In this report, we show the identification of two more cleavage products of 68 and 58 kDa released from the same region of the polyprotein. In addition, two stable intermediate cleavage products with molecular masses of 160 and 132 kDa, respectively, were identified in IBV-infected cells. The 160-kDa protein was shown to be an intermediate cleavage product covering the 100- and 68-kDa proteins, and the 132-kDa protein to be an intermediate cleavage product covering the 58-, 39-, and 35-kDa proteins. Immunofluorescent staining of IBV-infected cells and cells expressing individual cleavage products showed that the 100-, 68-, and 58-kDa proteins were associated with the membranes of the endoplasmic reticulum, and the 39- and 35-kDa proteins displayed diffuse distribution patterns.

Animals↗
PubMed2006

Oral DNA vaccination with the polyprotein gene of infectious bursal disease virus (IBDV) delivered by the attenuated Salmonella elicits protective immune responses in chickens.

Our previous study showed that vaccination with plasmid DNA containing infectious bursal disease virus (IBDV) gene which encodes complete polyprotein (VP2/4/3) induced protective immune responses. In this study, we examined the efficacy of an oral DNA vaccine carrying the IBDV polyprotein antigen delivered by attenuated Salmonella enterica sv. Typhimurium (S. typhimurium). The recombinant plasmid pCI-VP2/4/3 was transformed by electroporation into an attenuated S.typhimurium Strain (Dam Phop) (designated hereafter as SV/pCI-VP2/4/3). The IBDV polyprotein gene was expressed in chicken embryo fibroblast (CEF) cells infected with strain SV/pCI-VP2/4/3, as shown by gene-specific RT-PCR and Western blot. Oral immunization of 7-day-old specific-pathogen-free (SPF) chickens with SV/pCI-VP2/4/3 elicited specific humoral responses as measured by ELISA. Vaccination with the strain SV/pCI-VP2/4/3 at 10(9) CFU per chicken offered 11/15 (73%) protection of the chickens against virulent IBDV challenge. Our results have implications in the development of DNA vaccines against avian viral diseases by bacteria-vectored oral delivery system.

Administration, Oral↗
PubMed2006

Hepatic iron overload induces hepatocellular carcinoma in transgenic mice expressing the hepatitis C virus polyprotein.

BACKGROUND & AIMS: Despite the evidence of hepatic iron overload in patients with chronic hepatitis C, it remains unknown if iron overload is related to hepatocarcinogenesis in this condition. The aim of this study was to determine whether iron overload contributes to development of hepatocellular carcinoma (HCC) in transgenic mice expressing the hepatitis C virus (HCV) polyprotein. METHODS: Male C57BL/6 transgenic mice expressing the HCV polyprotein and nontransgenic littermates were fed an excess-iron diet or control diet. Mice in each group were assessed for altered liver morphology and function and the development of liver tumors. RESULTS: Hepatic iron concentrations in mice fed the excess-iron diet were comparable to those of patients with chronic hepatitis C. There was no inflammation in transgenic and nontransgenic livers. Compared with mice in 3 other groups, transgenic mice fed the excess-iron diet showed marked hepatic steatosis including the centrilobular microvesicular type, ultrastructural alterations of the mitochondria and decreased degradation activity of fatty acid at 6 months, and greater hepatic content of lipid peroxidation products and 8-hydroxy-2'-deoxyguanosine at 12 months after initiation of feeding. The number of proliferating hepatocytes was significantly increased in mice fed the excess-iron diet but was not different between transgenic and nontransgenic mice. Hepatic tumors including HCC developed in 5 of 11 (45%) transgenic mice fed the excess-iron diet but not in mice in other groups at 12 months after initiation of feeding. CONCLUSIONS: Iron overload induces mitochondrial injury and increases the risk of HCC development in transgenic mice expressing the HCV polyprotein.

Animals↗