Identification of an African swine fever virus gene with similarity to a myeloid differentiation primary response gene and a neurovirulence-associated gene of herpes simplex virus

Genome-wide transcriptomic analysis of highly virulent African swine fever virus infection reveals complex and unique virus host interaction

African swine fever virus (ASFV), one of the most devastating emerging swine pathogens in China, causes nearly 100 % mortality in naive herds. Here, whole-transcriptome RNA-seq analysis was conducted in porcine alveolar macrophages (PAMs) infected with Pig/Heilongjiang/2018 (Pig/HLJ/18) ASFV at different time points. Our data suggested that ASFV genes expression demonstrated a time-depended pattern and ASFV early genes were involved in antagonizing host innate immunity. Moreover, viral small RNA (vsRNA) was generated as well. Meanwhile, transcriptome analysis of host genes suggested a strong inhibition host immunity-related genes by ASFV infection in PAMs, while enhanced chemokine-mediated signaling pathways and neutrophil chemotaxis were observed in ASFV infected PAMs. Furthermore, ASFV infection also down-regulated host microRNAs (miRNAs) that putatively targeted viral genes, while also triggering dysregulation of host metabolism that promoted virus replication at transcription level. Most importantly, infection of PAMs with ASFV induced a different transcriptome pattern from that of highly pathogenic porcine reproductive and respiratory syndrome virus (HP-PRRSV), which is known to trigger a host cytokine storm. In conclusion, our transcriptome data implied that ASFV infection in PAMs appeared to be associated with strong inhibition of host immune responses, dysregulation of host chemokine axis and metabolic pathways.

African swine fever: Etiology, epidemiological status in Korea, and perspective on control

African swine fever (ASF), caused by the ASF virus, a member of the Asfarviridae family, is one of the most important diseases in the swine industry due to its clinical and economic impacts. Since the first report of ASF a century ago, ample information has become available, but prevention and treatment measures are still inadequate. Two waves of epizootic outbreaks have occurred worldwide. While the first wave of the epizootic outbreak was controlled in most of the infected areas, the second wave is currently active in the European and Asian continents, causing severe economic losses to the pig industry. There are different patterns of spreading in the outbreaks between those in European and Asian countries. Prevention and control of ASF are very difficult due to the lack of available vaccines and effective therapeutic measures. However, recent outbreaks in South Korea have been successfully controlled on swine farms, although feral pigs are periodically being found to be positive for the ASF virus. Therefore, we would like to share our story regarding the preparation and application of control measures. The success in controlling ASF on farms in South Korea is largely due to the awareness and education of swine farmers and practitioners, the early detection of infected animals, the implementation of strict control policies by the government, and widespread sharing of information among stakeholders. Based on the experience gained from the outbreaks in South Korea, this review describes the current understanding of the ASF virus and its pathogenic mechanisms, epidemiology, and control.

Deletion of virulence associated genes from attenuated African swine fever virus isolate OUR T88/3 decreases its ability to protect against challenge with virulent virus

African swine fever virus (ASFV) causes an acute haemorrhagic disease of domestic pigs against which there is no effective vaccine. The attenuated ASFV strain OUR T88/3 has been shown previously to protect vaccinated pigs against challenge with some virulent strains including OUR T88/1. Two genes, DP71L and DP96R were deleted from the OUR T88/3 genome to create recombinant virus OUR T88/3ΔDP2. Deletion of these genes from virulent viruses has previously been shown to reduce ASFV virulence in domestic pigs. Groups of 6 pigs were immunised with deletion virus OUR T88/3ΔDP2 or parental virus OUR T88/3 and challenged with virulent OUR T88/1 virus. Four pigs (66%) were protected by inoculation with the deletion virus OUR T88/3ΔDP2 compared to 100% protection with the parental virus OUR T88/3. Thus the deletion of the two genes DP71L and DP96R from OUR T88/3 strain reduced its ability to protect pigs against challenge with virulent virus.

Genomic analysis of highly virulent Georgia 2007/1 isolate of African swine fever virus

African swine fever is widespread in Africa but has occasionally been introduced into other continents. In June 2007, African swine fever was isolated in the Caucasus Region of the Republic of Georgia and subsequently in neighboring countries (Armenia, Azerbaijan, and 9 states of the Russian Federation). Previous data for sequencing of 3 genes indicated that the Georgia 2007/1 isolate is closely related to isolates of genotype II, which has been identified in Mozambique, Madagascar, and Zambia. We report the complete genomic coding sequence of the Georgia 2007/1 isolate and comparison with other isolates. A genome sequence of 189,344 bp encoding 166 open reading frames (ORFs) was obtained. Phylogeny based on concatenated sequences of 125 conserved ORFs showed that this isolate clustered most closely with the Mkuzi 1979 isolate. Some ORFs clustered differently, suggesting that recombination may have occurred. Results provide a baseline for monitoring genomic changes in this virus.

African swine fever virus

African swine fever virus (ASFV) is a large, intracytoplasmically-replicating DNA arbovirus and the sole member of the family Asfarviridae. It is the etiologic agent of a highly lethal hemorrhagic disease of domestic swine and therefore extensively studied to elucidate the structures, genes, and mechanisms affecting viral replication in the host, virus-host interactions, and viral virulence. Increasingly apparent is the complexity with which ASFV replicates and interacts with the host cell during infection. ASFV encodes novel genes involved in host immune response modulation, viral virulence for domestic swine, and in the ability of ASFV to replicate and spread in its tick vector. The unique nature of ASFV has contributed to a broader understanding of DNA virus/host interactions.

Inhibition of a large double-stranded DNA virus by MxA protein

Increasing evidence points to the importance of the interferon (IFN) response in determining the host range and virulence of African swine fever virus (ASFV). Infection with attenuated strains of ASFV leads to the upregulation of genes controlled by IFN pathways, including myxovirus resistance (Mx) genes that are potent effectors of the antiviral state. Mx gene products are known to inhibit the replication of many negative-sense single-stranded RNA viruses, as well as double-stranded RNA viruses, positive-sense single-stranded RNA viruses, and the reverse-transcribing DNA virus hepatitis B virus. Here, we provide data that extend the known range of viruses inhibited by Mx to include the large double-stranded DNA viruses. Stably transfected Vero cells expressing human MxA protein did not support ASFV plaque formation, and virus replication in these cells was reduced 100-fold compared with that in control cells. In contrast, ASFV replication in cells expressing MxB protein or a mutant MxA protein was similar to that in control Vero cells. There was a drastic reduction in ASFV late protein synthesis in MxA-expressing cells, correlating with the results of previous work on the effect of IFN on viral replication. Strikingly, the inhibition of ASFV replication was linked to the recruitment of MxA protein to perinuclear viral assembly sites, where the protein surrounded the virus factories. Interactions between ASFV and MxA were similar to those seen between MxA and different RNA viruses, suggesting a common inhibitory mechanism.

The MyD116 African swine fever virus homologue interacts with the catalytic subunit of protein phosphatase 1 and activates its phosphatase activity

The DP71L protein of African swine fever virus (ASFV) shares sequence similarity with the herpes simplex virus ICP34.5 protein over a C-terminal domain. We showed that the catalytic subunit of protein phosphatase 1 (PP1) interacts specifically with the ASFV DP71L protein in a yeast two-hybrid screen. The chimeric full-length DP71L protein, from ASFV strain Badajoz 71 (BA71V), fused to glutathione S-transferase (DP71L-GST) was expressed in Escherichia coli and shown to bind specifically to the PP1-alpha catalytic subunit expressed as a histidine fusion protein (6xHis-PP1alpha) in E. coli. The functional effects of this interaction were investigated by measuring the levels of PP1 and PP2A in ASFV-infected Vero cells. This showed that infection with wild-type ASFV strain BA71V activated PP1 between two- and threefold over that of mock-infected cells. This activation did not occur in cells infected with the BA71V isolate in which the DP71L gene had been deleted, suggesting that expression of DP71L leads to PP1 activation. In contrast, no effect was observed on the activity of PP2A following ASFV infection. We showed that infection of cells with wild-type BA71V virus resulted in decreased phosphorylation of the alpha subunit of eukaryotic initiation factor 2 (eIF-2alpha). ICP34.5 recruits PP1 to dephosphorylate the alpha subunit of eukaryotic translational initiation factor 2 (also known as eIF-2alpha); possibly the ASFV DP71L protein has a similar function.

The herpes simplex virus (HSV) protein ICP34.5 is a virion component that forms a DNA-binding complex with proliferating cell nuclear antigen and HSV replication proteins

The replicative ability of ICP34.5-null herpes simplex virus (HSV) is cell type and state dependent. In certain cells, ICP34.5 interacts with protein phosphatase 1 to preclude host cell protein synthesis shutoff by dephosphorylation of the eukaryotic initiation factor eIF-2alpha. However, host cell shutoff is not induced by ICP34.5-null HSV in most cells, irrespective of type and state. In general, dividing cells support replication of ICP34.5-null HSV; nondividing cells cannot. Previously the authors showed that ICP34.5 binds to proliferating cell nuclear antigen (PCNA), a protein necessary for cellular DNA replication and repair. Here the authors demonstrate that (1) the interaction between ICP34.5 and PCNA involves two regions of the virus protein; (2) ICP34.5 forms a complex with HSV replication proteins that is DNA binding; (3) at early times in infection, ICP34.5 colocalizes with PCNA and HSV replication proteins in cell nuclei, before accumulating in the cytoplasm; and (4) ICP34.5 is a virion protein. In light of ongoing clinical trials assessing the safety and efficacy of ICP34.5-null HSV, it is vital that the roles of ICP34.5 in HSV replication are understood. The authors propose that in nondividing cells, ICP34.5 is required to switch PCNA from repair to replication mode, a prerequisite for the initiation of HSV replication.

Counteraction of interferon-induced antiviral responses by herpes simplex viruses

The outcome of a viral infection of a host involves the complex interplay of viral determinants of virulence and host resistance factors. Among the first lines of defense for the host in attempts to control viral infection are the interferons (IFNs). A large body of work has now shown that the IFNs are a family of soluble proteins that serve to mediate antiviral effects, to regulate cell growth, and to modulate the activation of immune responses. The innate antiviral activities of IFNs are exceedingly potent and rapid. It is, therefore, not surprising that so many viruses have evolved ways to either preclude the synthesis of IFNs or evade downstream antiviral events. Such evasion allows for the virus to spread before the development of a specific adaptive immune response and likely represents a pivotal determinant of virulence for the invading virus. This review describes some of the research on herpes simplex virus (HSV) that has elucidated genes involved in evasion of the IFN response. In particular, the roles of specific viral genes in resistance to the antiviral effects of PKR and RNaseL are described, along with other HSV genes and loci associated with resistance to IFN for which mechanisms have yet to be described.

Myeloid differentiation (MyD) primary response genes in hematopoiesis

Myeloid Differentiation (MyD) primary response and Growth Arrest DNA-Damage (Gadd) genes comprise a set of overlapping genes, including known (IRF-1, EGR-1, Jun) and novel (MyD88, Gadd45alpha MyD118/Gadd45beta, GADD45gamma, MyD116/Gadd34) genes, that have been cloned by virtue of there being co-ordinately induced upon the onset of terminal myeloid differentiation. This review delineates the role MyD genes play in blood cell development, where they function as positive regulators of terminal differentiation, lineage specific blood cell development and control of blood cell homeostasis, including growth inhibition and apoptosis.

Myeloid differentiation (MyD)/growth arrest DNA damage (GADD) genes in tumor suppression, immunity and inflammation

Myeloid differentiation (MyD) primary response and growth arrest DNA damage (Gadd) genes comprise a set of overlapping genes, including known (IRF-1, EGR-1, Jun) and novel (MyD88, Gadd45alpha, MyD118/Gadd45beta, GADD45gamma, MyD116/ Gadd34) genes, that have been cloned by virtue of being co-ordinately induced upon the onset of terminal myeloid differentiation and following exposure of cells to stress stimuli. In recent years it has become evident that MyD/Gadd play a role in blood cell development, where they function as positive regulators of terminal differentiation, lineage-specific blood cell development and control of blood cell homeostasis, including growth inhibition and apoptosis. MyD/Gadd are also involved in inflammatory responses to invading micro-organisms, and response to environmental stress and physiological stress, such as hypoxia, which results in ischemic tissue damage. An intricate network of interactions among MyD/GADD genes and gene products appears to control their diverse functions. Deregulated growth, increased cell survival, compromised differentiation and deficiencies in DNA repair are hallmarks of malignancy and its progression. Thus, the role MyD/Gadd play in negative growth control, including cell cycle arrest and apoptosis, and in DNA repair, make them attractive molecular targets for tumor suppression. The role MyD/Gadd play in innate immunity and host response to hypoxia also make these genes and gene products attractive molecular targets to treat immunity and inflammation disorders, such as septic shock and ischemic tissue damage.

Novel swine virulence determinant in the left variable region of the African swine fever virus genome

Previously we have shown that the African swine fever virus (ASFV) NL gene deletion mutant E70DeltaNL is attenuated in pigs. Our recent observations that NL gene deletion mutants of two additional pathogenic ASFV isolates, Malawi Lil-20/1 and Pr4, remained highly virulent in swine (100% mortality) suggested that these isolates encoded an additional virulence determinant(s) that was absent from E70. To map this putative virulence determinant, in vivo marker rescue experiments were performed by inoculating swine with infection-transfection lysates containing E70 NL deletion mutant virus (E70DeltaNL) and cosmid DNA clones from the Malawi NL gene deletion mutant (MalDeltaNL). A cosmid clone representing the left-hand 38-kb region (map units 0.05 to 0.26) of the MalDeltaNL genome was capable of restoring full virulence to E70DeltaNL. Southern blot analysis of recovered virulent viruses confirmed that they were recombinant E70DeltaNL genomes containing a 23- to 28-kb DNA fragment of the Malawi genome. These recombinants exhibited an unaltered MalDeltaNL disease and virulence phenotype when inoculated into swine. Additional in vivo marker rescue experiments identified a 20-kb fragment, encoding members of multigene families (MGF) 360 and 530, as being capable of fully restoring virulence to E70DeltaNL. Comparative nucleotide sequence analysis of the left variable region of the E70DeltaNL and Malawi Lil-20/1 genomes identified an 8-kb deletion in the E70DeltaNL isolate which resulted in the deletion and/or truncation of three MGF 360 genes and four MGF 530 genes. A recombinant MalDeltaNL deletion mutant lacking three members of each MGF gene family was constructed and evaluated for virulence in swine. The mutant virus replicated normally in macrophage cell culture but was avirulent in swine. Together, these results indicate that a region within the left variable region of the ASFV genome containing the MGF 360 and 530 genes represents a previously unrecognized virulence determinant for domestic swine.

Val193 and Phe195 of the gamma 1 34.5 protein of herpes simplex virus 1 are required for viral resistance to interferon-alpha/beta

Herpes simplex viruses (HSV) are resistant to the antiviral action of interferon. However, the underlying mechanisms are not well understood. In this report, we show that unlike that of wild-type HSV-1, replication of the gamma 1 34.5 null mutants was significantly inhibited by exogenous interferon-alpha in cells devoid of interferon-alpha/beta genes. Using a series of gamma 1 34.5 deletion mutants, the domain required for interferon resistance was mapped to the region containing amino acids 146 to 263 in the gamma 1 34.5 protein. Interestingly, Val193 Glu and Phe195 Leu substitutions in the protein phosphatase 1 interacting motif of the gamma 1 34.5 protein rendered HSV-1 sensitive to interferon-alpha. Furthermore, gamma 1 34.5 null mutants were sensitive to interferon-alpha/beta in PKR+/+ but not in PKR-/- mouse embryo fibroblasts. These findings provide evidence that the gamma 1 34.5 protein contributes to HSV-1 resistance to interferon-alpha/beta by inhibiting PKR function.

A herpesvirus ribosome-associated, RNA-binding protein confers a growth advantage upon mutants deficient in a GADD34-related function

The herpes simplex virus type 1 gamma34.5 gene product and the cellular GADD34 protein both contain similar domains that can regulate the activity of eukaryotic initiation factor 2 (eIF2), a critical translation initiation factor. Viral mutants that lack the GADD34-related function grow poorly on a variety of malignant human cells, as activation of the cellular PKR kinase leads to the accumulation of inactive, phosphorylated eIF2 at late times postinfection. Termination of translation prior to the completion of the viral reproductive cycle leads to impaired growth. Extragenic suppressors that regain the ability to synthesize proteins efficiently in the absence of the viral GADD34-related function have been isolated. These suppressor alleles are dominant in trans and affect the steady-state accumulation of several viral mRNA species. We demonstrate that deregulated expression of Us11, a virus-encoded RNA-binding, ribosome-associated protein is necessary and sufficient to confer a growth advantage upon viral mutants that lack a GADD34-related function. Ectopic expression of Us11 reduces the accumulation of the activated cellular PKR kinase and allows for sustained protein synthesis. Thus, an RNA-binding, ribosome-associated protein (Us11) and a GADD34-related protein (gamma34.5) both function in a signal pathway that regulates translation by modulating eIF2 phosphorylation.

Functionality and cell anchorage dependence of the African swine fever virus gene A179L, a viral bcl-2 homolog, in insect cells

The African swine fever virus gene A179L has been shown to be a functional member of the ced9/bcl-2 family of apoptosis inhibitors in mammalian cell lines. In this work we have expressed the A179L gene product (p21) under the control of the baculovirus polyhedrin promoter using a baculovirus system. Expression of the A179L gene neither altered the baculovirus replication phenotype nor delayed the shutoff of cellular protein synthesis, but it extended the survival of the infected insect cells to very late times postinfection. The increase in cell survival rates correlated with a marked apoptosis reduction after baculovirus infection. Interestingly, prevention of apoptosis was observed when recombinant baculovirus infections were carried out in monolayer cell cultures but not when cells were infected in suspension, suggesting a cell anchorage dependence for p21 function in insect cells. Cell survival was enhanced under optimal conditions of cell attachment and cell-to-cell contact as provided by extracellular matrix components or poly-D-lysine. Since it was observed that cytoskeleton organization varied depending on culture conditions of insect cells (grown in monolayer versus grown in suspension), these results suggested that A179L might regulate apoptosis in insect cells only when the cytoskeletal support of intracellular signaling is maintained upon cell adhesion. Thus, cell shape and cytoskeleton status might allow variations in intracellular transduction of signals related to cell survival in virus-infected cells.

The gamma134.5 protein of herpes simplex virus 1 has the structural and functional attributes of a protein phosphatase 1 regulatory subunit and is present in a high molecular weight complex with the enzyme in infected cells

The carboxyl-terminal domain of the gamma134.5 protein of the herpes simplex virus 1 binds to protein phosphatase 1alpha (PP1) and is required to prevent the shut-off of protein synthesis resulting from phosphorylation of the alpha subunit of eIF-2 by the double-stranded RNA-activated protein kinase. The corresponding domain of the conserved GADD34 protein homologous to gamma134.5 functionally substitutes for gamma134.5. This report shows that gamma134.5 and PP1 form a complex in the infected cells, that fractions containing this complex specifically dephosphorylate eIF-2alpha, and that both gamma134.5 and GADD34 proteins contain the amino acid sequence motif common to subunits of PP1 that is required for binding to the PP1 catalytic subunit. An oligopeptide containing this motif competes with gamma134.5 for binding to PP1. Substitution of Val193 and Phe195 in the PP1-binding motif abolished activity. These results suggest that the carboxyl-terminal domain of gamma134.5 protein has the structural and functional attributes of a subunit of PP1 specific for eIF-2alpha, that it has evolved to preclude shut-off of protein synthesis, and that GADD34 may have a similar function.

A nonessential African swine fever virus gene UK is a significant virulence determinant in domestic swine

Sequence analysis of the right variable genomic region of the pathogenic African swine fever virus (ASFV) isolate E70 revealed a novel gene, UK, that is immediately upstream from the previously described ASFV virulence-associated gene NL-S (L. Zsak, Z. Lu, G. F. Kutish, J. G. Neilan, and D. L. Rock, J. Virol. 70:8865-8871, 1996). UK, transcriptionally oriented toward the right end of the genome, predicts a protein of 96 amino acids with a molecular mass of 10.7 kDa. Searches of genetic databases did not find significant similarity between UK and other known genes. Sequence analysis of the UK genes from several pathogenic ASFVs from Europe, the Caribbean, and Africa demonstrated that this gene was highly conserved among diverse pathogenic isolates, including those from both tick and pig sources. Polyclonal antibodies raised against the UK protein specifically precipitated a 15-kDa protein from ASFV-infected macrophage cell cultures as early as 2 h postinfection. A recombinant UK gene deletion mutant, deltaUK, and its revertant, UK-R, were constructed from the E70 isolate to study gene function. Although deletion of UK did not affect the growth characteristics of the virus in macrophage cell cultures, deltaUK exhibited reduced virulence in infected pigs. While mortality among parental E70- or UK-R-infected animals was 100%, all deltaUK-infected pigs survived infection. Fever responses were comparable in E70-, UK-R-, and deltaUK-infected groups; however, deltaUK-infected animals exhibited significant, 100- to 1,000-fold, reductions in viremia titers. These data indicate that the highly conserved UK gene of ASFV, while being nonessential for growth in macrophages in vitro, is an important viral virulence determinant for domestic pigs.

An African swine fever virus virulence-associated gene NL-S with similarity to the herpes simplex virus ICP34.5 gene

We described previously an African swine fever virus (ASFV) open reading frame, 23-NL, in the African isolate Malawi Lil 20/1 whose product shared significant similarity in a carboxyl-terminal domain with those of a mouse myeloid differentiation primary response gene, MyD116, and the herpes simplex virus neurovirulence-associated gene, ICP34.5 (M. D. Sussman, Z. Lu, G. Kutish, C. L. Afonso, P. Roberts, and D. L. Rock, J. Virol. 66:5586-5589, 1992). The similarity of 23-NL to these genes suggested that this gene may function in some aspect of ASFV virulence and/or host range. Sequence analysis of additional pathogenic viral isolates demonstrates that this gene is highly conserved among diverse ASFV isolates and that the gene product exists in either a long (184 amino acids as in 23-NL) or a short form (70 to 72 amino acids in other examined ASFV isolates). The short form of the gene, NL-S, encodes the complete highly conserved, hydrophilic, carboxyl-terminal domain of 56 amino acids common to 23-NL, MyD116, and ICP34.5. Recombinant NL-S gene deletion mutants and their revertants were constructed from the pathogenic ASFV isolate E70 and an E70 monkey cell culture-adapted virus, MS44, to study gene function. Although deletion of NL-S did not affect viral growth in primary swine macrophages or Vero cell cultures in vitro, the null mutant, E70/43, exhibited a marked reduction in pig virulence. In contrast to revertant or parental E70 where mortality was 100%, all E70/43-infected animals survived infection. With the exception of a transient fever response, E70/43-infected animals remained clinically normal and exhibited a 1,000-fold reduction in both mean and maximum viremia titers. All convalescent E70/43-infected animals survived infection when challenged with parental E70 at 30 days postinfection. These data indicate that the highly conserved NL-S gene of ASFV, while nonessential for growth in swine macrophages in vitro, is a significant viral virulence factor and may function as a host range gene.

A herpesvirus genetic element which affects translation in the absence of the viral GADD34 function

Novel suppressor variants of conditionally lethal HSV-1 gamma34.5 deletion mutants have been isolated which exhibit restored ability to grow on neoplastic neuronal cells. Deletion of the viral gamma34.5 genes, whose products share functional similarity with the cellular GADD34 gene, renders the virus non-neurovirulent and imposes a block to viral replication in neuronal cells. Protein synthesis ceases at late times post-infection and the translation initiation factor eIF2alpha is phosphorylated by the cellular PKR kinase [Chou et al. (1990) Science, 252, 1262-1266; (1995) Proc. Natl Acad. Sci. USA, 92, 10516-10520]. The suppressor mutants have overcome the translational block imposed by PKR. Multiple, independent isolates all contain rearrangements within a 595 bp element in the HSV-1 genome where the unique short component joins the terminal repeats. This alteration, which affects the production of the viral mRNA and protein from the Us11 and Us12 genes, is both necessary and sufficient to confer the suppressor phenotype on gamma34.5 mutant viruses. HSV-1 thus encodes a specific element which inhibits ongoing protein synthesis in the absence of the viral GADD34-like function. Since this inhibition involves the accumulation of phosphorylated eIF2alpha, the element identified by the suppressor mutations may be a discrete PKR activator. Activation of the PKR kinase thus does not proceed through a general, cellular 'antiviral' sensing mechanism. Instead, the virus deliberately activates PKR and encodes a separate function which selectively prevents the phosphorylation of at least one PKR target, eIF2alpha. The nature of this potential activator element, and how analogous cellular elements could affect PKR pathways which affect growth arrest and differentiation are discussed.

Herpes simplex virus 1 gamma(1)34.5 gene function, which blocks the host response to infection, maps in the homologous domain of the genes expressed during growth arrest and DNA damage

The gamma(1)34.5 gene of herpes simplex virus is dispensable in some cell lines (e.g., Vero). In others (e.g., human neuroblastoma cell line SK-N-SH), the gamma(1)34.5- deletion mutant triggers a premature total shutoff of all protein synthesis, thereby rendering the cell nonviable and reducing drastically viral yields. The inability to prevent the cellular stress response that causes the infected cell to die may be responsible for the inability of the deletion mutant to multiply and cause pathology in the central nervous system of mice. The gamma(1)34.5 gene consists of an amino-terminal domain, a variable linker sequence consisting of 3 amino acids repeated 5-10 times, and a carboxyl-terminal domain homologous to the corresponding domain of MyD116, a gene expressed in myeloid leukemia cells induced to differentiate by interleukin 6, and growth arrest and DNA damage gene 34 (GADD34), a gene induced by growth arrest and DNA damage. We have constructed several viral mutants from which various domains of the gamma(1)34.5 gene had been deleted or rendered mute by the insertion of a stop codon. Studies on those mutants show that the domain of the gamma(1)34.5 gene necessary to preclude the total shutoff of protein synthesis corresponds to the carboxyl-terminal domain of the gamma(1)34.5 gene homologous to the corresponding coding domain of the MyD116 and GADD34 genes.

ICP34.5 mutants of herpes simplex virus type 1 strain 17syn+ are attenuated for neurovirulence in mice and for replication in confluent primary mouse embryo cell cultures

In a recent report, the neurovirulence of herpes simplex virus type 1 (HSV-1) was mapped to the ICP34.5 gene (J. Chou, E. R. Kern, R. J. Whitley, and B. Roizman, Science 250:1262-1266, 1990). In this report, specific mutations within ICP34.5 were constructed in HSV-1 strain 17syn+ to determine the effects of these mutations in a fully neurovirulent isolate. It was found that termination of the ICP34.5 gene after the N-terminal 30 amino acids resulted in a mutant, 17termA, which was 25- to 90-fold reduced in neurovirulence. This reduction of neurovirulence was associated with restricted replication of the mutant virus in mouse brain. The reduced replication phenotype was also evident in the trigeminal and dorsal root ganglia following inoculation at the periphery. 17termA was capable of replicating with wild-type kinetics in mouse footpads, and therefore the restriction seen in neural tissues was not due to a generalized replication defect in mouse cells. Significantly, replication of the mutant was also restricted in the mouse cornea in vivo and in confluent primary mouse embryo cells and mouse 10T1/2 cells in vitro. However, 17termA replicated with much greater efficiency in subconfluent mouse embryo cells, suggesting that the physiological state of the cell may be an important factor for productive replication of this mutant. Restoration of the ICP34.5 gene to the mutant resulted in a virus which displayed wild-type neurovirulence and replication kinetics in all cells and tissues tested.

Long-term persistent infection of swine monocytes/macrophages with African swine fever virus

Long-term persistent infection was established in 100% of pigs (n = 19) experimentally infected with African swine fever virus (ASFV). Viral DNA was detected in peripheral blood mononuclear leukocytes (PBML) at greater than 500 days postinfection by a PCR assay. Infectious virus was not, however, isolated from the same PBML samples. In cell fractionation studies of PBML, monocytes/macrophages were found to harbor viral DNA during the persistent phase of infection. This result indicates that monocytes/macrophages are persistently infected with ASFV and that ASFV-swine monocyte/macrophage interactions can result in either lytic or persistent infection.