Conversion of US3-encoded protein kinase gene from pseudorabies virus in a diploid gene located within inverted repeats by genetic recombination between the viral genome isomers

Construction of recombinant pseudorabies viruses by using PRV BACs deficient in IE180 or pac sequences: Application of vBAC90D recombinant virus to production of PRV amplicons

We describe a simple and efficient method to obtain recombinant pseudorabies virus (PRV) in mammalian cells by using the PRV BACs, PBAC80 deficient in pac sequences and PBAC90 deficient in the IE180 gene. These essential viral sequences were used as targets to obtain viable recombinant viruses. PBAC80 was constructed, confirmed to encode a copy of the IE180 gene regulated by the inducible Ptet promoter, and used to obtain recombinant attenuated PRV viruses that express the EGFP protein (PRV-BT80GF virus). PBAC90 was used to obtain the vBAC90D virus, deficient in IE180 and free of replication-competent revertants, and which can be used as a helper in the production of PRV amplicons.

Expression of the immediate early IE180 protein under the control of the hTERT and CEA tumor-specific promoters in recombinant pseudorabies viruses: Effects of IE180 protein on promoter activity and apoptosis induction

Since the pseudorabies virus (PRV) genome encodes for a single immediate-early protein, IE180, we reasoned that this strong transactivating protein could represent a key regulatory switch that could be genetically manipulated in order to alter its tropism towards cancer cells. We therefore initiated studies to test whether the human telomerase reverse transcriptase (hTERT) and carcinoembryonic antigen (CEA) tumor promoters could functionally replace the IE180 promoter. We show that both promoters can functionally substitute the IE180 promoter in plasmid constructs and recombinant viruses, and observed that IE180 differentially auto-regulated each promoter tested, with PRV IE180 negatively regulating the hTERT promoter but positively hyper-activating the CEA promoter. Interestingly, we also observed that the recombinant PRV-TER and PRV-CEA viruses preferentially replicated in diverse cancer cell lines compared to control non-cancer cells, and the PRV-CEA was capable of additionally inducing a profound apoptotic phenotype which we correlated to the overexpression of IE180.

Construction and properties of a recombinant pseudorabies virus with tetracycline-regulated control of immediate-early gene expression

A study was carried out to determine whether altering the control of expression of the IE180 gene of pseudorabies virus (PRV), by replacing the IE180 promoter with the tetracycline-responsive promoter (Ptet), affects virus replication and virulence. This PRV-BT90 mutant virus was constructed by complementation and recombination in Hela Tet-Off cells. The virus yield produced by infection of Hela Tet-Off cells with PRV-BT90 was similar to that of the parental virus vBecker2. Viral replication of PRV-BT90 was reduced in Vero cells as reflected by a reduction of virus yield and plating efficiency compared to vBecker2. PRV-BT90 plaque formation in Hela Tet-Off cells was inhibited in the presence of doxycycline, whereas vBecker2 plaque formation was not affected. Subcutaneous infection of mice with the two viruses revealed a LD(50) higher than 10(6) TCID(50) for the PRV-BT90 mutant virus while the LD(50) was 178 TCID(50) for the vBecker2 parental virus.

Glycoprotein G from pseudorabies virus binds to chemokines with high affinity and inhibits their function

Pseudorabies virus (PRV), also known as suid herpesvirus, is the aetiological agent of Aujeszky's disease in swine. In other animals, except higher-order primates, PRV infection is often fatal. The mechanisms of PRV pathogenesis and immune modulation are largely unknown. PRV codes for 11 glycoproteins. Among them, glycoprotein G (gG) is the most abundant PRV protein found in the supernatant of PRV-infected cell cultures. PRV-gG has low amino acid sequence similarity with gG from other animal alphaherpesviruses and its function is unknown. gG from other animal alphaherpesviruses, with the exception of at least equine herpesvirus 4, binds to chemokines. We show here that PRV-gG binds to the human chemokine CL1 and several CC and CXC human chemokines with high affinity. Chemokine-binding activity can be detected in the supernatants of PRV-infected cell cultures, and insertional inactivation of the gene encoding gG from the PRV genome results in loss of chemokine-binding activity. Binding of PRV-gG to chemokines inhibits chemokine-mediated cell migration, suggesting a role for PRV-gG in immune evasion.

A comparison of enhanced green fluorescent protein expression induced by immediate-early cytomegalovirus (IE-CMV) and gG pseudorabies virus (gG-PRV) promoters, using pseudorabies virus amplicons as vectors

This study compares the expression efficiencies of the IE-CMV and gG-PRV promoters following their transfection into cultured human and monkey cells, using pseudorabies virus amplicons as vectors and enhanced green fluorescence protein (EGFP) as an expression marker. EGFP expression was similarly strong with both promoters. Pseudorabies virus amplicons appear to be useful vectors in gene expression studies due to their replication in the presence of helpers and their wide range of cellular hosts.

Recombination in alphaherpesviruses

Within the Herpesviridae family, Alphaherpesvirinae is an extensive subfamily which contains numerous mammalian and avian viruses. Given the low rate of herpesvirus nucleotide substitution, recombination can be seen as an essential evolutionary driving force although it is likely underestimated. Recombination in alphaherpesviruses is intimately linked to DNA replication. Both viral and cellular proteins participate in this recombination-dependent replication. The presence of inverted repeats in the alphaherpesvirus genomes allows segment inversion as a consequence of specific recombination between repeated sequences during DNA replication. High molecular weight intermediates of replication, called concatemers, are the site of early recombination events. The analysis of concatemers from cells coinfected by two distinguishable alphaherpesviruses provides an efficient tool to study recombination without the bias introduced by invisible or non-viable recombinants, and by dominance of a virus over recombinants. Intraspecific recombination frequently occurs between strains of the same alphaherpesvirus species. Interspecific recombination depends on enough sequence similarity to enable recombination between distinct alphaherpesvirus species. The most important prerequisite for successful recombination is coinfection of the individual host by different virus strains or species. Consequently the following factors affecting the distribution of different viruses to shared target cells need to be considered: dose of inoculated virus, time interval between inoculation of the first and the second virus, distance between the marker mutations, genetic homology, virulence and latency. Recombination, by exchanging genomic segments, may modify the virulence of alphaherpesviruses. It must be carefully assessed for the biosafety of antiviral therapy, alphaherpesvirus-based vectors and live attenuated vaccines.

Negative regulation of herpes simplex virus type 1 ICP4 promoter by IE180 protein of pseudorabies virus

Recombinant pseudorabies viruses (PRVs) gIS8 and N1aHTK were constructed by the insertion of a chimeric gene (alpha4-TK) from herpes simplex virus type 1 (HSV-1) into wild-type PRV. HSV-1 TK expression by these recombinant viruses resulted in enhanced sensitivity to ganciclovir, compared to that of the wild-type PRV, and was similar to the sensitivity shown by HSV-1. Infection with gIS8 or N1aHTK recombinant viruses led to expression of HSV-1 TK mRNA as an immediate-early (IE) gene, observed by downregulation of the HSV-1 alpha4 promoter. This negative regulation was due to a PRV IE protein, IE180. IE180, however, does not have all the regulatory functions of the infected-cell protein ICP4, as it does not restore the growth of ICP4-deficient HSV-1 mutants.

Development of new expression vector based on Pseudorabies virus amplicons: application to human insulin expression

Pseudorabies virus (PrV), a herpesvirus from the Alphaherpesvirinae subfamily, is suitable for amplicon vector replication and packaging into virions, with helper virus for trans replication and cleavage-packaging functions. PrV amplicon vectors were developed in a bacterial plasmid construction using PrV ori(s) and pac signals as the required cis elements. Human insulin cDNA was then cloned in the amplicon vector for human proinsulin expression. In the same construction, green fluorescent protein was used as a marker. PrV amplicons may have several advantages over herpes simplex virus type 1 (HSV1) amplicons in human gene therapy because it can infect human cells in vitro and in vivo, it is not pathogenic for primates and there is no pre-existing immunity and risk of recombination with latent PrV as occurs with HSV1.