Map location of the thymidine kinase gene of bovine herpesvirus 1

Expression of the genomic form of the bovine viral diarrhea virus E2 ORF in a bovine herpesvirus-1 vector

Bovine viral diarrhea virus (BVDV) is a ubiquitous pathogen of cattle with a world-wide distribution. Recently, the possibility of using recombinant virus vectors to immunize cattle against selected BVDV genes has gained widespread interest. Among the virus vectors tested, bovine herpesvirus-1 (BHV1) provides many unique advantages. However, results of recent studies have raised the possibility that the codon usage pattern required for optimal expression in a BHV1-infected cell may be incompatible with the codon usage pattern of BVDV. If true, use of BHV1 to express BVDV proteins would require construction of synthetic BVDV genes that have been modified to resemble the codon pattern of BHV1. To explore this possibility, we constructed a BHV1 recombinant containing the genomic form of the BVDV (NADL) E2 ORF and compared expression of the E2 protein with that of the endogenous BHV1 gD protein. We observed that E2 was expressed at a significant rate compared to that of the gD protein. We conclude that codon usage problems are unlikely to constitute a serious problem for expression of BVDV proteins in BHV1 vectors.

A hepadnavirus regulatory element enhances expression of a type 2 bovine viral diarrhea virus E2 protein from a bovine herpesvirus 1 vector

Recently, the possibility of using virus vectors to immunize cattle against selected bovine viral diarrhea virus (BVDV) genes has gained widespread interest. However, when we attempted to express the E2 protein from type 2 (890 strain) BVDV in a bovine herpesvirus 1 (BHV1) vector, we observed that expression was poor. This often happens when genes from a cytoplasmic virus are expressed in the cell nucleus. To counter this effect, we attempted to enhance expression by a strategy employed by viruses. RNAs of retroviruses and hepadnaviruses contain cis-acting elements that facilitate expression of RNAs that otherwise are degraded or retained within the nucleus. In Mason-Pfizer monkey virus, the required RNA sequence element is known as a constitutive transport element (CTE). A related element from woodchuck hepatitis virus is known as the woodchuck posttranscriptional regulatory element (WPRE). We tested the ability of the CTE, the WPRE, and introns to enhance expression of E2. All three elements stimulated expression of E2 from plasmids. The combination of the WPRE and an intron yielded the highest level of E2 expression in plasmids. However, when E2 was expressed from a BHV1 vector, the presence of an intron was inhibitory. In contrast, the WPRE was very efficient at stimulating E2 expression from a BHV1 vector. This result represents the first expression of a type 2 BVDV E2 protein from a mammalian virus vector and raises the possibility that the WPRE may provide a general method of enhancing foreign gene expression from BHV1 and other herpesvirus vectors.

BHV-1: new molecular approaches to control a common and widespread infection

BACKGROUND

Herpesviruses are widespread viruses, causing severe infections in both humans and animals. Eradication of herpesviruses is extremely difficult because of their ability to establish latent and life-long infections. However, latency is only one tool that has evolved in herpesviruses to successfully infect their hosts; such viruses display a wide (and still incompletely known) panoply of genes and proteins that are able to counteract immune responses of their hosts. Envelope glycoproteins and cytokine inhibitors are two examples of such weapons. All of these factors make it difficult to develop diagnostics and vaccines, unless they are based on molecular techniques.

MATERIALS AND METHODS

Animal herpesviruses, because of their striking similarity to human ones, are suitable models to study the molecular biology of herpesviruses and develop strategies aimed at designing neurotropic live vectors for gene therapy as well as engineered attenuated vaccines.

RESULTS

BHV-1 is a neurotropic herpesvirus causing infectious rhinotracheitis (IBR) in cattle. It is a major plague in zootechnics and commercial trade, because of its ability to spread through asymptomatic carrier animals, frozen semen, and embryos. Such portals of infections are also important for human herpesviruses, which mainly cause systemic, eye, and genital tract infections, leading even to the development of cancer.

CONCLUSIONS

This review covers both the genetics and molecular biology of BHV-1 and its related herpesviruses. Epidemiology and diagnostic approaches to herpesvirus infections are presented. The role of herpesviruses in gene therapy and a broad introduction to classic and engineered vaccines against herpesviruses are also provided. http://link.springer-ny. com/link/service/journals/00020/bibs/5n5p261.html

Bovine herpes virus expressing envelope protein (E2) of bovine viral diarrhea virus as a vaccine candidate

The gene encoding the envelope protein (E2) of bovine viral diarrhea virus (BVDV) was expressed under the thymidine kinase (TK) promoter of Korean bovine herpesvirus 1 (BHV-1) isolate. Thymidine kinase negative (TK-) BHV-1 recombinants expressing E2 of BVDV were constructed and the expression of E2 was identified by immunofluorescence and Western blotting. Compared to wild type BHV-1, the recombinant BHV-1 had a delayed cytopathogenic effect in cells. The immunogenicity of the recombinant BHV-1 was examined in guinea pigs and cattle. Although an increase in body temperature was detected for a few days, the inoculated cattle returned to normal temperature with the development of neutralizing antibodies to BVDV.

Sequence, transcriptional analysis, and deletion of the bovine adenovirus type 1 E3 region

The early 3 (E3) transcriptional unit of human adenoviruses (HAV) encodes proteins that modulate host antiviral immune defenses. HAV E3 sequences are highly variable; different HAV groups encode phylogenetically unrelated proteins. The role of the E3 region of many human and animal adenoviruses is unknown because the sequences are unrelated to previously characterized viruses and the functions of proteins encoded by these regions have not been studied. We sequenced a portion of the bovine adenovirus serotype 1 (BAV-1) genome corresponding to the putative E3 region. This sequence was substantially different from other adenoviral E3 sequences, including those of two other bovine adenoviruses. However, two regions of putative sequence conservation were identified. BAV-1 E3 sequences were identified in early and late transcripts, but, unlike HAV, introns were not detected in the E3 region transcripts. Like HAV E3, a majority of the BAV-1 E3 region was not essential for growth in cell culture, as demonstrated by the construction of a recombinant BAV-1 lacking 60% of the putative E3 region.

From essential to beneficial: glycoprotein D loses importance for replication of bovine herpesvirus 1 in cell culture

Glycoprotein D (gD) of bovine herpesvirus 1 (BHV-1) has been shown to be an essential component of virions involved in virus entry. gD expression in infected cells is also required for direct cell-to-cell spread. Therefore, BHV-1 gD functions are identical in these aspects to those of herpes simplex virus 1 (HSV-1) gD. In contrast, the gD homolog of pseudorabies virus (PrV), although essential for penetration, is not necessary for direct cell-to-cell spread. Cocultivation of cells infected with phenotypically gD-complemented gD- mutant BHV-1/80-221 with noncomplementing cells resulted in the isolation of the cell-to-cell-spreading gD-negative mutant ctcs+BHV-1/80-221, which was present in the gD-null BIV-1 stocks. ctcs+BHV-1/80-221 could be propagated only by mixing infected with uninfected cells, and virions released into the culture medium were noninfectious. Marker rescue experiments revealed that a single point mutation in the first position of codon 450 of the glycoprotein H open reading frame, resulting in a glycine-to-tryptophan exchange, enabled complementation of the gD function for cell-to-cell spread. After about 40 continuous passages of ctcs+BHV-1/80-221-infected cells with noninfected cells, the plaque morphology in the cultures started to change from roundish to comet shaped. Cells from such plaques produced infectious gD- virus, named gD-infBHV-1, which entered cells much more slowly than wild-type BHV-1. In contrast, integration of the gD gene into the genomes of gD-infBHV-1 and ctcs+BHV-1/80-221 resulted in recombinants with accelerated penetration in comparison to wild-type virions. In summary, our results demonstrate that under selective conditions, the function of BHV-1 gD for direct cell-to-cell spread and entry into cells can be compensated for by mutations in other viral (glyco)proteins, leading to the hypothesis that gD is involved in formation of penetration-mediating complexes in the viral envelope of which gH is a component. Together with results for PrV, varicella-zoster virus, which lacks a gD homolog, and Marek's disease virus, whose gD homolog is not essential for infectivity, our data may open new insights into the evolution of alphaherpesviruses.

Construction and characterization of an attenuated bovine herpesvirus type 1 (BHV-1) recombinant virus

A recombinant bovine herpesvirus type 1 (BHV-1) virus (Gal-TK) has been constructed. The Gal-TK virus contains a chimeric reporter/marker gene coding for bacterial beta-galactosidase (beta-gal gene) that was inserted stably within the viral TK gene. This resulted in inactivation of the TK gene. The beta-gal gene is under the regulation of a strong, human cytomegalovirus-immediate early (HCMV-IE) promoter and is expressed as an authentic viral-coded gene. Even though the one-step growth kinetics of the recombinant and parent viruses were similar, the recombinant virus yielded less than the parent virus on Madin-Darby bovine kidney cells. After intranasal inoculation, the engineered virus was virtually avirulent for colostrum-deprived new-born calves. Similar to the parent virus, the recombinant virus replicated in the upper respiratory tract of calves, but the amount of progeny viruses produced was reduced significantly. The progeny viruses recovered from nasal swabs of animals inoculated with the recombinant and the Cooper strains of BHV-1 were easily distinguishable based on the beta-gal marker.

Identification of the bovine herpesvirus 1 circ protein, a myristylated and virion-associated polypeptide which is not essential for virus replication in cell culture

We have recently reported immediate-early (IE) transcription over covalently joined genome ends of bovine herpesvirus 1 (BHV-1). A spliced 1.5-kb IE RNA (IER1.5) is coterminal with an unspliced 1.1-kb late RNA (LR1.1) which is transcribed from the left end of the genome. Sequence analysis reveals an open reading frame common to IER1.5 and LR1.1 predicted to encode the 247-amino-acid circ polypeptide. This paper reports on the identification of circ as a protein. Using a rabbit antiserum raised against a synthetic oligopeptide representing the carboxy terminus of the predicted circ polypeptide for Western blot (immunoblot) analyses and immunofluorescence assays, we identified a 34-kDa virion-associated protein which accumulated in the cytoplasm of infected cells. To confirm that LR1.1 indeed encoded the 34-kDa polypeptide, we inserted a DNA fragment containing circ coding sequences into the Autographa californica baculovirus genome. A group of recombinant polypeptides with sizes of 32, 34, and 35 kDa were identified by their reactivity with the antipeptide serum. Chicken egg yolk antibodies raised against total proteins of insect cells infected with the recombinant baculovirus identified the 34-kDa circ protein specified by BHV-1. The recombinant circ polypeptides and the circ protein specified by BHV-1 were both myristylated, as determined by radiolabeling with [3H]myristic acid. It was noted that the circ gene could be deleted from the BHV-1 genome without impairing virus replication in cell culture.

Immediate-early gene expression and gene mapping comparisons among isolates of bovine herpesvirus 1 and 5

Bovine herpesviruses (BHV) are associated with a variety of clinical syndromes. Bovine herpesvirus 1 isolates were placed into three genome subtypes based on restriction endonuclease analyses, which were loosely associated by clinical manifestation as BHV1.1 (respiratory), BHV1.2 (genital), and BHV1.3 (encephalitic). More recently the encephalitic isolate has been classified BHV5. A comparison of the cytopathic effect (CPE) in fetal bovine lung cell cultures in the presence of cycloheximide showed that BHV1.1 and 1.2 isolates produced elongated, spindle-shaped CPE, whereas BHV5 produced more syncytial-like CPE. Each BHV-1 subtype synthesized four immediate-early transcripts. The sizes in kb were: 1.6, 3.4, 5.8, 7.5 (BHV1.1); 1.8, 3.6, 5.8, 7.5 (BHV1.2); and 1.8, 3.6, 5.8, 8.6 (BHV5). These transcripts were mapped to the inverted repeat region of each isolate by Southern blot hybridization using cDNA prepared from cycloheximide-treated BHV1-infected cellular polyA RNA. A possible unique immediate-early RNA may be produced by the BHV5 encephalitic isolate from an area of the internal repeat region unique to this isolate. Hybridization analysis using BHV1.1 cloned probes of the immediate-early protein gene, thymidine kinase gene, DNA binding/DNA polymerase gene, and glycoprotein III gene provided information for mapping of these genes to the BHV5 encephalitic isolate.

Bovine herpesvirus 1 as a live virus vector for expression of foreign genes

DNA sequence analysis and 5'-end mapping of mRNA were used to identify and clone DNA fragments which contain the presumptive promoter (Pgl) and poly(A) site (An) of the bovine herpesvirus 1 (BHV1) gl glycoprotein. To confirm the presence of these regulatory regions in the above fragments, they were cloned together with a chloramphenicol acetyltransferase (CAT) reporter gene into pUC19. The recombinant plasmid formed, pEC3, was capable of inducing CAT activity when transfected into bovine cells demonstrating that the Pgl-CAT-An sequence constituted a functional CAT expression cassette. The cassette was excised from pEC3, transferred to a plasmid insertion vector (pIV3A) and subsequently inserted into the thymidine kinase (tk) gene of BHV1. Insertion in either orientation, relative to the tk gene, gave rise to BHV1 recombinants which expressed CAT activity in infected cells. Analysis of RNA from infected cells indicated that CAT transcripts were present in multiple species of RNA. This unexpected result was found to reflect temporal shifts in promoter and poly(A) site usage during infection. Although the poly(A) site which forms part of the expression cassette was used extensively early in infection, most CAT transcripts synthesized at late times read through this promoter-proximal site and terminated at the distal site normally used for tk mRNA synthesis.

Sequence and transcript analysis of the bovine herpesvirus 1 thymidine kinase locus

A detailed sequence and transcript analysis of the thymidine kinase (tk) gene of bovine herpesvirus 1 (BHV1, Cooper strain) was carried out. A tk open reading frame (ORF) of 1077 bp was identified and compared with tk ORFs previously published for other strains of BHV1. The Cooper sequence was in good agreement with that of strain Q3932 but differed significantly from strains 6660 and LA. Reanalysis of the LA tk sequence, however, failed to confirm this difference. Except for five single base substitutions, our results indicate that the Cooper, Q3932, and LA strains share the same tk sequence. The size of the tk mRNA was determined by Northern blot analysis. In contrast to the size of other herpesvirus tk mRNAs (approximately 1.5 kb), the BHV1 tk transcript was 4.3 kb. Northern blot analysis indicated that the tk transcript was 3' coterminal with the downstream 3.1-kb transcript which encodes a BHV1 homologue of the HSV1 H glycoprotein (gH). The 5' ends of the tk and gH mRNAs were mapped by S1 analysis to positions 135 and 91 bp upstream of their respective translation start sites. The 5' end of the tk transcript was found to overlap a 5.2-kb transcript with opposite polarity to the tk mRNA.

Relationship of bovine herpesvirus 1 immediate-early, early, and late gene expression to host cellular gene transcription

Bovine herpesvirus 1 (BHV-1) gene expression was examined by RNA blot hybridization using clones representing immediate-early, early, and late genes. An immediate-early protein gene probe hybridized with two transcripts, 3.4 and 5.8 kb, expressed by infected cells in the presence of cycloheximide (CH). During infection of cells without metabolic inhibitors these transcripts were detected as early as 2 hr postinfection (p.i.) and accumulated to 8 hr p.i. The early gene probe, thymidine kinase, hybridized with a 4.3-kb RNA that was detected in the presence of phosphonoacetic acid (PAA), but not in the presence of CH. The late gene probe, glycoprotein III, (gIII) hybridized with a 1.6-kb transcript that was not expressed by infected cells treated with CH and only in very reduced amounts by infected cells treated with PAA. The gIII RNA was not detected until 4 hr p.i. in total cell RNA. Transcripts for the bovine actin and beta-galactosyltransferase genes did not decrease in BHV-1-infected cells until 6 hr p.i., coincident with the increase of BHV-1 DNA and RNA synthesis. Consequently, shutoff of host cell transcription by BHV-1 may be different than what has been described for herpes simplex virus.

Latency and reactivation of a thymidine kinase-negative bovine herpesvirus 1 deletion mutant

A bovine herpesvirus 1 (BHV 1) mutant variant with a deletion in the thymidine kinase (TK) gene was assessed for its ability to establish latency and be reactivated in cattle. After treatment with dexamethasone, reactivated TK- BHV 1 was isolated from one of four cattle that received virus by intravenous inoculation only, and from four of four cattle that received virus by intranasal, intravaginal, and intravenous inoculation. Results prove that TK- BHV 1 will establish latency and can be reactivated in the natural host.

Virus reactivation in pigs latently infected with a thymidine kinase negative vaccine strain of pseudorabies virus

Attenuated, gene-deletion mutants of pseudorabies virus (PRV) were tested for their ability to establish a reactivatable latent infection in pigs. The viruses (designated A, B, and C) were from each of three vaccines commercially available in the United States. Viruses A and C were similar in that they had genetically engineered gene deletions for thymidine kinase (TK) and glycoprotein X (gX); however, they had been prepared from genetically different parental strains. Virus B was TK positive, but had a naturally occurring gene deletion for glycoprotein I (gI). Four pigs were exposed oronasally to each of the viruses, and 10 weeks later they were treated with dexamethasone in an attempt to induce virus reactivation. All of the viruses replicated after initial exposure as evidenced by virus isolation from nasal swabs and the pigs' immune responses. Virus reactivation was subsequently induced by dexamethasone treatment in two of four pigs exposed to virus A. Notably, both pigs remained free of serum antibody for gX. Restriction endonuclease analysis and tests for TK activity and the presence of gX indicated that reactivated virus was similar, if not identical, to virus A used to establish latent infection. Virus shedding after dexamethasone treatment was not identified for either of the other pigs exposed to virus A nor for any of the pigs exposed to viruses B or C. The results indicated that attenuated, TK-negative PRV can establish a reactivatable, latent infection in pigs.

Transcriptional analysis of the bovine herpesvirus 1 Cooper isolate. Temporal analysis and characterization of immediate-early, early, and late RNA

Blot hybridization analysis of infected bovine herpesvirus 1 (BHV-1) cellular RNA isolated at various times post infection and after treatment with specific metabolic inhibitors was used to characterize transcription of the BHV-1 Cooper isolate. Synthesis of BHV-1 RNA was detected as early as 3 h post infection and reached a maximum at six to eight hours post infection. The most transcriptionally active area of the genome was between map units 0.110 to 0.195, within the HindIII I fragment. From the entire genome a total of 59 transcripts ranging in size from approximately 0.6 to 10 kilobases were characterized as belonging to one of three distinct classes. Using the protein synthesis inhibitor cycloheximide, three immediate-early transcripts were identified as originating from the internal inverted repeat region between map units 0.734 and 0.842, corresponding to the HindIII D fragment. Using phosphonoacetic acid to prevent virus DNA synthesis by inhibition of the BHV-1 DNA polymerase, 28 early transcripts were recognized. The remaining 28 transcripts, classified as late RNA, were detected without the use of metabolic inhibitors at 6 to 8 h post infection. Transcription of early and late RNA was not restricted to any specific area of the genome. Eighty percent of the transcripts from both the HindIII A fragment, between map units 0.381 to 0.537 within the unique long segment, and the HindIII K fragment, between map units 0.840 to 0.907 of the unique short segment, were designated as belonging to the early class.

The three major immediate-early transcripts of bovine herpesvirus 1 arise from two divergent and spliced transcription units

Among 54 transcripts expressed in a temporal cascade during lytic infection with bovine herpesvirus 1, we have previously identified three major immediate-early (IE) RNAs, IER4.2 (4.2 kb), IER2.9 (2.9 kb), and IER1.7 (1.6 to 1.8 kb depending on the virus strain) transcribed from the HindIII C genome region (U. V. Wirth, K. Gunkel, M. Engels, and M. Schwyzer, J. Virol. 63:4882-4889, 1989). Northern (RNA) blot, S1 nuclease protection, and primer extension analysis used in the present study demonstrated that all three IE transcripts were spliced and originated from two divergent transcription units with start sites located in the inverted repeat. Transcription unit 1 encoded two alternative spliced transcripts, IER4.2 and IER2.9, with a common exon 1 located at 0.797 to 0.795 map units (m.u.) and an exon 2 for IER4.2 (0.792 to 0.762 m.u.) in the inverted repeat; exon 2 for IER2.9 (0.754 to 0.738 m.u.) was located in the unique long sequence and transcribed in antisense orientation to latency-related RNA. Transcription unit 2 (0.818 to 0.836 m.u.), further characterized by cDNA cloning, encoded the spliced IER1.7 with three exons in the inverted repeat. Additional minor IE transcripts were interpreted as unspliced precursors and splicing variants. With regard to the number and layout of IE genes, bovine herpesvirus 1 occupies an intermediate position between pseudorabies virus and equine herpesvirus 1 on the one hand and varicella-zoster virus and herpes simplex virus type 1 on the other.

Gene mapping of infectious bovine rhinotracheitis viral DNA genome

A bovine herpesvirus I (BHV-I) HindIII genomic bank spanning 89% of the entire genome was constructed and individual fragments analyzed for their capacity to select specific mRNAs which were then expressed by in vitro translation assays. This procedure allowed the mapping of more than 20 viral polypeptides to discrete regions of the DNA genome. Some polypeptides map in neighboring HindIII fragments while most seem encoded in single fragments. In particular, the coding sequences for an abundant 94 kDa polypeptide, which is the potential unglycosylated precursor of gII glycoprotein, have been assigned to the small 3.6 kbp HindIII genomic fragment M. The localization of structural and non-structural gene-coding sequences will help to characterize viral polypeptides and eventually, a better understanding of BHV-I infection will be gained.

Spatial and temporal distribution of bovine herpesvirus 1 transcripts

Northern (RNA) blot analysis was used to determine the spatial and temporal distribution of bovine herpesvirus 1 (BHV-1) transcripts. Total RNA was isolated from Madin-Darby bovine kidney cells which had been infected with BHV-1.2b strain K22 or BHV-1.1 strain Jura in the presence or absence of metabolic inhibitors. Cloned restriction fragments representing the entire genome of strain K22 were labeled with 32P and hybridized to immobilized RNA. A total of 54 BHV-1 transcripts were found, ranging in size from 0.4 to larger than 8 kilobases (kb). The inverted repeat regions and an adjacent segment of the unique large part of the BHV-1 genome encoded three major immediate-early (IE) transcripts and one minor IE transcript enriched after cycloheximide treatment of infected cells. Late transcripts were identified by drastically reduced abundance after cytosine arabinoside (araC) treatment. Twelve late transcripts were encoded mainly by the unique long genome region, with a cluster of four transcripts located on HindIII fragment K (map units 0.677 to 0.733). The 21 transcripts unaffected by araC treatment were defined as early; they showed dispersed locations over the whole genome, with a cluster on the unique short sequence. The 17 remaining transcripts could not be classified unambiguously as early or late by these techniques. The IE transcript with a size of 4.2 kb exhibited homology with the single IE gene of pseudorabies virus, and the IE transcript with a size of 2.9 kb was encoded in part by the genome region known to be transcriptionally active during latency.

Evolution of the herpes thymidine kinase: identification and comparison of the equine herpesvirus 1 thymidine kinase gene reveals similarity to a cell-encoded thymidylate kinase

We have identified the equine herpesvirus 1 (EHV-1) thymidine kinase gene (TK) by DNA-mediated transformation and by DNA sequencing. Alignment of the amino acid sequence of the EHV-1 TK with the TKs from 3 other herpesviruses revealed regions of homology, some of which correspond to the previously identified substrate binding sites, while others have as yet, no assigned function. In particular, the strict conservation of an aspartate within the proposed nucleoside binding site suggests a role in ATP binding for this residue. Comparison of 5 herpes TKs with the thymidylate kinase of yeast revealed significant similarity which was strongest in those regions important to catalytic activity of the herpes TKs, and, therefore we propose that the herpes TK may be derived from a cellular thymidylate kinase. The implications for the evolution of enzyme activities within a pathway of nucleotide metabolism are discussed.