The infected cell protein 0 encoded by bovine herpesvirus 1 (bICP0) associates with interferon regulatory factor 7 and consequently inhibits beta interferon promoter activity

Stress Can Induce Bovine Alpha-Herpesvirus 1 (BoHV-1) Reactivation from Latency

Bovine alpha-herpesvirus 1 (BoHV-1) is a significant problem for the cattle industry, in part because the virus establishes latency, and stressful stimuli increase the incidence of reactivation from latency. Sensory neurons in trigeminal ganglia and unknown cells in pharyngeal tonsils are importantsites for latency. Reactivation from latency can lead to reproductive problems in pregnant cows, virus transmission to young calves, suppression of immune responses, and bacterial pneumonia. BoHV-1 is also a significant cofactor in bovine respiratory disease (BRD). Stress, as mimicked by the synthetic corticosteroid dexamethasone, reproducibly initiates reactivation from latency. Stress-mediated activation of the glucocorticoid receptor (GR) stimulates viral replication and transactivation of viral promoters that drive the expression of infected cell protein 0 (bICP0) and bICP4. Notably, GR and Krüppel-like factor 15 (KLF15) form a feed-forward transcription loop that cooperatively transactivates immediate early transcription unit 1 (IEtu1 promoter). Two pioneer transcription factors, GR and KLF4, cooperatively transactivate the bICP0 early promoter. Pioneer transcription factors bind silent viral heterochromatin, remodel chromatin, and activate gene expression. Thus, wepredict that these novel transcription factors mediate early stages of BoHV-1 reactivation from latency.

Comparative transcriptome analysis of MDBK cells reveals that BoIFN-γ augmented host immune responses to bovine herpesvirus 1 infection

Bovine herpesvirus 1 (BoHV-1) is an alphaherpesvirus that causes infectious bovine rhinotracheitis and infectious pustular vulvovaginitis in cattle. Ιnterferon-gamma (IFN-γ) is a pleiotropic cytokine with antiviral activity that modulates the innate and adaptive immune responses. In this study, we prepared high-purity bovine interferon gamma (BoIFN-γ) dimer protein using prokaryotic expression system and affinity chromatography. We subsequently investigated the effect of BoIFN-γ on BoHV-1 infection in Madin-Darby bovine kidney (MDBK) cells. The results showed that BoIFN-γ pre-treament not only decreased the production of BoHV-1 but also reduced the cytopathic effect of the virus. Differential gene expression profiles of BoHV-1 infected MDBK cells were then analysed through high-throughput RNA sequencing. The data showed that BoIFN-γ pre-treatment reduced lipid metabolism disorder and DNA damage caused by BoHV-1 infection. Furthermore, BoIFN-γ treatment upregulated the transcription of interferon regulatory transcription factors (IRF1 and GBP5) and interferon-stimulated genes (ISGs) of MDBK cells. Additionally, BoIFN-γ promotes expression of cellular protein involved in complement activation and coagulation cascades response as well as antigen processing and presentation process, while BoHV-1 infection dramatically downregulates transcription of these immune components including C3, C1r, C1s, PLAT, ITGB2, PROCR, BoLA, CD74, B2M, PA28, BoLA-DRA, and TAPBP. Collectively, our findings revealed that BoIFN-γ pre-treatment can improve host resistance to BoHV-1 infection and regulate transcription or expression of host protein associated with cellular metabolism and innate immune response. This provides insights into the development of prophylactic agents for prevention and control of BoHV-1 infection.

β-Catenin-Specific Inhibitor, iCRT14, Promotes BoHV-1 Infection-Induced DNA Damage in Human A549 Lung Adenocarcinoma Cells by Enhancing Viral Protein Expression

Oncolytic bovine herpesvirus type 1 (BoHV-1) infection induces DNA damage in human lung adenocarcinoma cell line A549. However, the underlying mechanisms are not fully understood. We found that BoHV-1 infection decreased the steady-state protein levels of p53-binding protein 1 (53BP1), which plays a central role in dictating DNA damage repair and maintaining genomic stability. Furthermore, BoHV-1 impaired the formation of 53BP1 foci, suggesting that BoHV-1 inhibits 53BP1-mediated DNA damage repair. Interestingly, BoHV-1 infection redistributed intracellular β-catenin, and iCRT14 (5-[[2,5-Dimethyl-1-(3-pyridinyl)-1H-pyrrol-3-yl]methylene]-3-phenyl-2,4-thiazolidinedione), a β-catenin-specific inhibitor, enhanced certain viral protein expression, such as the envelope glycoproteins gC and gD, and enhanced virus infection-induced DNA damage. Therefore, for the first time, we provide evidence showing that BoHV-1 infection disrupts 53BP1-mediated DNA damage repair and suggest β-catenin as a potential host factor restricting both virus replication and DNA damage in A549 cells.

Cooperative activation of bovine herpesvirus 1 productive infection and viral regulatory promoters by androgen receptor and Krüppel-like transcription factors 4 and 15

Bovine herpesvirus 1 (BoHV-1), a significant viral pathogen, establishes latency in sensory neurons. The viral genome contains more than 100 consensus glucocorticoid receptor (GR) regulatory elements (GREs): consequently, stress stimulates viral replication and reactivation from latency. The immediate early transcription unit 1 (IEtu1) and bICP0 early promoters are transactivated by GR and synthetic corticosteroid dexamethasone. The androgen receptor (AR), like GR, is a Type 1 nuclear hormone receptor that binds and stimulates certain promoters containing GREs. Consequently, we hypothesized AR and 5α-Dihydrotestosterone (DHT) stimulate productive infection and key viral promoters. New studies demonstrated AR, DHT, and Krüppel like transcription factor 4 (KLF4) cooperatively stimulated productive infection and bICP0 E promoter activity in mouse neuroblastoma cells (Neuro-2A). KLF15 also cooperated with AR and DHT to stimulate IEtu1 promoter activity. We suggest AR and testosterone increase the prevalence of virus in semen by stimulating viral gene expression and replication.

Ubiquitination modification: critical regulation of IRF family stability and activity

Interferon regulatory factors (IRFs) play pivotal and critical roles in innate and adaptive immune responses; thus, precise and stringent regulation of the stability and activation of IRFs in physiological processes is necessary. The stability and activities of IRFs are directly or indirectly targeted by endogenous and exogenous proteins in an ubiquitin-dependent manner. However, few reviews have summarized how host E3 ligases/DUBs or viral proteins regulate IRF stability and activity. Additionally, with recent technological developments, details about the ubiquitination of IRFs have been continuously revealed. As knowledge of how these proteins function and interact with IRFs may facilitate a better understanding of the regulation of IRFs in immune responses or other biological processes, we summarized current studies on the direct ubiquitination of IRFs, with an emphasis on how these proteins interact with IRFs and affect their activities, which may provide exciting targets for drug development by regulating the functions of specific E3 ligases.

BICP0 Negatively Regulates TRAF6-Mediated NF-κB and Interferon Activation by Promoting K48-Linked Polyubiquitination of TRAF6

The infected cell protein 0 (BICP0) is an immediate early protein encoded by BHV-1, and its RING finger domain, which endows BICP0 with intrinsic E3 ubiquitin ligase activity, is common in all ICP0 proteins. Tumor necrosis factor receptor-associated factor 6 (TRAF6) is one of the TRAF family members and is ubiquitously expressed in mammalian tissues. TRAF6 forms the MyD88-TRAF6-IRF7 complex and activates interferon induction in the TLR (Toll-like receptors) and the RLR (RIG-I-like receptor) pathway. Previous studies showed that BICP0 reduced IFN-β promoter activity by interacting with IRF7. In this study, we found that BICP0 promoted the K48-ubiquitination and degradation of TRAF6 through the ubiquitin proteasome system. The interaction between BICP0 and TRAF6 is a prerequisite for ubiquitination modification, and the 346-PAERQY-351 of BICP0 is indispensable. The motif mutation experiments showed that the tyrosine 351 of BICP0 is the key amino acid involved. Further studies demonstrated that BICP0 suppressed the NF-κB pathway via the interference of TRAF6. Moreover, degradation of TRAF6 protein influenced the K63-linked ubiquitination of IRF7 and activation of interferon promoter. Collectively, these findings indicate that the BICP0 protein suppresses the inflammation signaling and IFN production by K48-linked polyubiquitination of TRAF6 and may further clarify the immune evasion function of BICP0.

Equid Herpesvirus 1 Targets the Sensitization and Induction Steps To Inhibit the Type I Interferon Response in Equine Endothelial Cells

Equid herpesvirus 1 (EHV-1) is a viral pathogen of horse populations worldwide spread by the respiratory route and is known for causing outbreaks of neurologic syndromes and abortion storms. Previously, we demonstrated that an EHV-1 strain of the neuropathogenic genotype, T953, downregulates the beta interferon (IFN-β) response in vitro in equine endothelial cells (EECs) at 12 h postinfection (hpi). In the present study, we explored the molecular correlates of this inhibition as clues toward an understanding of the mechanism. Data from our study revealed that EHV-1 infection of EECs significantly reduced both Toll-like receptor 3 (TLR3) and TLR4 mRNA expression at 6 hpi and 12 hpi. While EHV-1 was able to significantly reduce IRF9 mRNA at both 6 hpi and 12 hpi, the virus significantly reduced IFN regulatory factor 7 (IRF7) mRNA only at 12 hpi. EHV-1 did not alter the cellular level of Janus-activated kinase 1 (JAK1) at any time point. However, EHV-1 reduced the cellular level of expression of tyrosine kinase 2 (TYK2) at 12 hpi. Downstream of JAK1-TYK2 signaling, EHV-1 blocked the phosphorylation and activation of signal transducer and activator of transcription 2 (STAT2) when coincubated with exogenous IFN, at 12 hpi, although not at 3 or 6 hpi. Immunofluorescence staining revealed that the virus prevented the nuclear translocation of STAT2 molecules, confirming the virus-mediated inhibition of STAT2 activation. The pattern of suppression of phosphorylation of STAT2 by EHV-1 implicated viral late gene expression. These data help illuminate how EHV-1 strategically inhibits the host innate immune defense by limiting steps required for type I IFN sensitization and induction.IMPORTANCE To date, no commercial vaccine label has a claim to be fully protective against the diseases caused by equid herpesvirus 1 (EHV-1), especially the neurologic form. The interferon (IFN) system, of which type I IFN is of great importance, still remains a viable immunotherapeutic option against EHV-1 infection. The type I IFN system has been exploited successfully to treat other viral infections, such as chronic hepatitis B and C in humans. The current state of research on how EHV-1 interferes with the protective effect of type I IFN has indicated transient induction of type I IFN production followed by a rapid shutdown in vitro in equine endothelial cells (EECs). The significance of our study is the identification of certain steps in the type I IFN signaling pathway targeted for inhibition by EHV-1. Understanding this pathogen-host relationship is essential for the long-term goal of developing effective immunotherapy against EHV-1.

Bovine Herpesvirus 1 Counteracts Immune Responses and Immune-Surveillance to Enhance Pathogenesis and Virus Transmission

Infection of cattle by bovine herpesvirus 1 (BoHV-1) can culminate in upper respiratory tract disorders, conjunctivitis, or genital disorders. Infection also consistently leads to transient immune-suppression. BoHV-1 is the number one infectious agent in cattle that is associated with abortions in cattle. BoHV-1, as other α-herpesvirinae subfamily members, establishes latency in sensory neurons. Stressful stimuli, mimicked by the synthetic corticosteroid dexamethasone, consistently induce reactivation from latency in latently infected calves and rabbits. Increased corticosteroid levels due to stress have a two-pronged effect on reactivation from latency by: (1) directly stimulating viral gene expression and replication, and (2) impairing antiviral immune responses, thus enhancing virus spread and transmission. BoHV-1 encodes several proteins, bICP0, bICP27, gG, UL49.5, and VP8, which interfere with key antiviral innate immune responses in the absence of other viral genes. Furthermore, the ability of BoHV-1 to infect lymphocytes and induce apoptosis, in particular CD4+ T cells, has negative impacts on immune responses during acute infection. BoHV-1 induced immune-suppression can initiate the poly-microbial disorder known as bovine respiratory disease complex, which costs the US cattle industry more than one billion dollars annually. Furthermore, interfering with antiviral responses may promote viral spread to ovaries and the developing fetus, thus enhancing reproductive issues associated with BoHV-1 infection of cows or pregnant cows. The focus of this review is to describe the known mechanisms, direct and indirect, by which BoHV-1 interferes with antiviral immune responses during the course of infection.

Synergistic Activation of Bovine Herpesvirus 1 Productive Infection and Viral Regulatory Promoters by the Progesterone Receptor and Krüppel-Like Transcription Factor 15

Bovine herpesvirus 1 (BoHV-1), including modified live vaccines, readily infects the fetus and ovaries, which can lead to reproductive failure. The BoHV-1 latency reactivation cycle in sensory neurons may further complicate reproductive failure in pregnant cows. The immediate early transcription unit 1 (IEtu1) promoter drives expression of important viral transcriptional regulators (bICP0 and bICP4). This promoter contains two functional glucocorticoid receptor (GR) response elements (GREs) that have the potential to stimulate productive infection following stressful stimuli. Since progesterone and the progesterone receptor (PR) can activate many GREs, we hypothesized that the PR and/or progesterone regulates productive infection and viral transcription. New studies demonstrated that progesterone stimulated productive infection. Additional studies revealed the PR and Krüppel-like transcription factor 15 (KLF15) cooperated to stimulate productive infection and IEtu1 promoter activity. IEtu1 promoter activation required both GREs, which correlated with the ability of the PR to interact with wild-type (wt) GREs but not mutant GREs. KLF15 also cooperated with the PR to transactivate the bICP0 early promoter, a promoter that maintains bICP0 protein expression during productive infection. Intergenic viral DNA fragments (less than 400 bp) containing two GREs and putative KLF binding sites present within genes encoding unique long 52 (UL-52; component of DNA primase/helicase complex), Circ, bICP4, and IEtu2 were stimulated by KLF15 and the PR more than 10-fold, suggesting that additional viral promoters are activated by these transcription factors. Collectively, these studies suggest progesterone and the PR promote BoHV-1 spread to reproductive tissues, thus increasing the incidence of reproductive failure.IMPORTANCE Bovine herpesvirus 1 (BoHV-1) is the most frequently diagnosed cause of abortions in pregnant cows and can cause "abortion storms" in susceptible herds. Virulent field strains and even commercially available modified live vaccines can induce abortion, in part because BoHV-1 replicates efficiently in the ovary and corpus luteum. We now demonstrate that progesterone and the progesterone receptor (PR) stimulate productive infection. The BoHV-1 genome contains approximately 100 glucocorticoid receptor (GR) response elements (GREs). Interestingly, the PR can bind and activate many promoters that contain GREs. The PR and Krüppel-like transcription factor 15 (KLF15), which regulate key steps during embryo implantation, cooperate to stimulate productive infection and two viral promoters that drive expression of key viral transcriptional regulators. These studies suggest that the ability of progesterone and the PR to stimulate productive infection has the potential to promote virus spread in reproductive tissue and induce reproductive failure.

Accessory proteins 8b and 8ab of severe acute respiratory syndrome coronavirus suppress the interferon signaling pathway by mediating ubiquitin-dependent rapid degradation of interferon regulatory factor 3

Severe acute respiratory syndrome coronavirus (SARS-CoV) is an inefficient inducer of interferon (IFN) response. It expresses various proteins that effectively circumvent IFN production at different levels via distinct mechanisms. Through the construction of recombinant IBV expressing proteins 8a, 8b and 8ab encoded by SARS-CoV ORF8, we demonstrate that expression of 8b and 8ab enables the corresponding recombinant viruses to partially overcome the inhibitory actions of IFN activation to achieve higher replication efficiencies in cells. We also found that proteins 8b and 8ab could physically interact with IRF3. Overexpression of 8b and 8ab resulted in the reduction of poly (I:C)-induced IRF3 dimerization and inhibition of the IFN-β signaling pathway. This counteracting effect was partially mediated by protein 8b/8ab-induced degradation of IRF3 in a ubiquitin-proteasome-dependent manner. Taken together, we propose that SARS-CoV may exploit the unique functions of proteins 8b and 8ab as novel mechanisms to overcome the effect of IFN response during virus infection.

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Recombinant IBV expressing SARS-CoV protein 8b or 8ab replicates better than wild type in cells pre-treated with poly(I:C).

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8b interacts with the IAD domain of IRF3.

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Overexpression of 8b or 8ab reduces poly(I:C)-induced IRF3 dimerization and interferon induction.

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8b and 8ab induce degradation of IRF3 in a ubiquitin-proteasome-dependent manner.

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8b and 8ab suppress interferon response induced by constitutively active IRF3.

Complete genome sequence of Ostreid herpesvirus type 1 µVar isolated during mortality events in the Pacific oyster Crassostrea gigas in France and Ireland

Infections with Ostreid herpesvirus 1 (OsHV-1) microvariants in young Pacific oysters are associated with massive mortality events and significant economic losses. Previous studies, focusing on few regions of the genome, have revealed the genomic diversity of these genotypes with respect to the reference type. We used a NGS process to sequence the whole genome of the OsHV-1 µVar in infected individuals, collected during mortality events in France and Ireland. The final genome length of OsHV-1 µVar was approximately 205kbp, shorter than the reference genotype and the overall genome organisation resembled herpes simplex viruses. 94.4% similarity was observed with the OsHV-1 reference genotype. Large indels, including five deletions and three insertions were found to induce the loss and the addition of several ORFs, summed with codon substitutions in 64% of genes shared with the reference type. This diversity raises the question of the exact origin and evolution of OsHV-1 µVar.

Protein Composition of the Bovine Herpesvirus 1.1 Virion

Bovine herpesvirus (BoHV) type 1 is an important agricultural pathogen that infects cattle and other ruminants worldwide. Acute infection of the oro-respiratory tract leads to immune suppression and allows commensal bacteria to infect an otherwise healthy lower respiratory tract. This condition is known as the Bovine Respiratory Disease (BRD). BoHV-1 latently infects the host for life and periodical stress events re-initiate BRD, translating into high morbidity and large economic losses. To gain a better understanding of the biology of BoHV-1 and the disease it causes, we elucidated the protein composition of extracellular virions using liquid chromatography-mass spectrometry analysis. We detected 33 viral proteins, including the expected proteins of the nucleocapsid and envelope as well as other regulatory proteins present in the viral tegument. In addition to viral proteins, we have also identified packaged proteins of host origin. This constitutes the first proteomic characterization of the BoHV virion.

Impairment of infectious laryngotracheitis virus replication by deletion of the UL[-1] gene

Infectious laryngotracheitis virus (ILTV) encodes several unique genes, including a pair of unique nuclear proteins UL0 and UL[-1] that are expressed during replication in cell culture. Although the UL0 gene has been shown to be dispensable for replication, the role of UL[-1] has not been elucidated. In this study a deletion mutant of ILTV lacking the UL[-1] gene was constructed using homologous recombination. The coding sequences of the gene were replaced with the gene for enhanced green fluorescent protein and the cytomegalovirus major immediate early promoter element. The progeny virus carrying the reporter gene was readily identified using fluorescent microscopy, but was unable to propagate in the permissive cells in the absence of wild type ILTV. Even after plaque purification and fluorescent associated cell sorting the recombinant virus deficient in UL[-1] gene could not be successfully isolated. Our findings suggest that the UL[-1] gene has an important role in ILTV replication.

VP8, the Major Tegument Protein of Bovine Herpesvirus 1, Interacts with Cellular STAT1 and Inhibits Interferon Beta Signaling

The UL47 gene product, VP8, is the most abundant tegument protein of bovine herpesvirus 1 (BoHV-1). Previously, we demonstrated that a UL47-deleted BoHV-1 mutant (BoHV1-ΔUL47) exhibits 100-fold-reduced virulence in vitro and is avirulent in vivo In this study, we demonstrated that VP8 expression or BoHV-1 infection inhibits interferon beta (IFN-β) signaling by using an IFN-α/β-responsive plasmid in a luciferase assay. As transducer and activator of transcription (STAT) is an essential component in the IFN-signaling pathways, the effect of VP8 on STAT was investigated. An interaction between VP8 and STAT1 was established by coimmunoprecipitation assays in both VP8-transfected and BoHV-1-infected cells. Two domains of VP8, amino acids 259 to 482 and 632 to 686, were found to be responsible for its interaction with STAT1. The expression of VP8 did not induce STAT1 ubiquitination or degradation. Moreover, VP8 did not reduce STAT1 tyrosine phosphorylation to downregulate IFN-β signaling. However, the expression of VP8 or a version of VP8 (amino acids 219 to 741) that contains the STAT1-interacting domains but not the nuclear localization signal prevented nuclear accumulation of STAT1. Inhibition of nuclear accumulation of STAT1 also occurred during BoHV-1 infection, while nuclear translocation of STAT1 was observed in BoHV1-ΔUL47-infected cells. During BoHV-1 infection, VP8 was detected in the cytoplasm at 2 h postinfection without any de novo protein synthesis, at which time STAT1 was already retained in the cytoplasm. These results suggest that viral VP8 downregulates IFN-β signaling early during infection, thus playing a role in overcoming the antiviral response of BoHV-1-infected cells.

IMPORTANCE

Since VP8 is the most abundant protein in BoHV-1 virions and thus may be released in large amounts into the host cell immediately upon infection, we proposed that it might have a function in the establishment of conditions suitable for viral replication. Indeed, while nonessential in vitro, it is critical for BoHV-1 replication in vivo In this study, we determined that VP8 plays a role in downregulation of the antiviral host response by inhibiting IFN-β signaling. VP8 interacted with and prevented nuclear accumulation of STAT1 at 2 h postinfection in the absence of de novo viral protein synthesis. Two domains of VP8, amino acids 259 to 482 and 632 to 686, were found to be responsible for this interaction. These results provide a new functional role for VP8 in BoHV-1 infection and a potential explanation for the lack of viral replication of the UL47 deletion mutant in cattle.

Bovine herpesvirus 1 productive infection stimulates inflammasome formation and caspase 1 activity

Bovine herpesvirus 1 (BoHV-1), a significant viral pathogen of cattle, causes inflammation in affected tissue during acute infection. Consequently, we tested whether productively infected bovine cells stimulate inflammasome formation. Expression of two components required for inflammasome formation, the DNA sensor IFI16 (gamma-interferon-inducible protein 16) and NLRP3 (NOD-like receptor family, pyrin domain containing 3), were induced in bovine kidney cells by eight hours after infection. IFI16 was detected in punctate granules localized to the cytoplasm and nucleus. During productive infection, more than ten times more cells were caspase 1 positive, which is activated following inflammasome formation. Two caspase 1 inhibitors had no effect on productive infection. Conversely, another caspase 1 inhibitor, glyburide, significantly inhibited virus infection suggesting it had off-target effects on related enzymes or interfered with infection via non-enzymatic mechanisms. Collectively, these studies demonstrated that BoHV-1 infection stimulated inflammasome formation, which we predict is important for clinical symptoms in cattle.

Bovine herpesvirus 1 regulatory proteins bICP0 and VP16 are readily detected in trigeminal ganglionic neurons expressing the glucocorticoid receptor during the early stages of reactivation from latency

Bovine herpesvirus 1 (BHV-1) establishes a lifelong latent infection in sensory neurons following acute infection. Increased corticosteroid levels, due to stress, increases the incidence of reactivation from latency. Within minutes, corticosteroids activate the glucocorticoid receptor and transcription of promoters containing a glucocorticoid receptor element. A single intravenous injection of the synthetic corticosteroid dexamethasone consistently induces reactivation from latency in calves. Lytic cycle viral gene expression is detected within 6 h after dexamethasone treatment of calves latently infected with BHV-1. Cellular transcription factors are induced by dexamethasone in trigeminal ganglionic neurons within 1.5 h after dexamethasone treatment, suggesting they promote viral gene expression during the early phases of reactivation from latency, which we operationally defined as the escape from latency. In this study, immunohistochemistry was utilized to examine viral protein expression during the escape from latency. Within 1.5 h after dexamethasone treatment, bICP0 and a late protein (VP16) were consistently detected in a subset of trigeminal ganglionic neurons. Most neurons expressing bICP0 also expressed VP16. Additional studies revealed that neurons expressing the glucocorticoid receptor also expressed bICP0 or VP16 at 1.5 h after dexamethasone treatment. Two other late proteins, glycoprotein C and D, were not detected until 6 h after dexamethasone treatment and were detected in only a few neurons. These studies provide evidence that VP16 and the promiscuous viral trans-activator (bICP0) are expressed during the escape from latency, suggesting they promote the production of infectious virus in a small subset of latently infected neurons.

Bovine Herpes Virus 1 (BHV-1) and Herpes Simplex Virus Type 1 (HSV-1) Promote Survival of Latently Infected Sensory Neurons, in Part by Inhibiting Apoptosis

α-Herpesvirinae subfamily members, including herpes simplex virus type 1 (HSV-1) and bovine herpes virus 1 (BHV-1), initiate infection in mucosal surfaces. BHV-1 and HSV-1 enter sensory neurons by cell-cell spread where a burst of viral gene expression occurs. When compared to non-neuronal cells, viral gene expression is quickly extinguished in sensory neurons resulting in neuronal survival and latency. The HSV-1 latency associated transcript (LAT), which is abundantly expressed in latently infected neurons, inhibits apoptosis, viral transcription, and productive infection, and directly or indirectly enhances reactivation from latency in small animal models. Three anti-apoptosis genes can be substituted for LAT, which will restore wild type levels of reactivation from latency to a LAT null mutant virus. Two small non-coding RNAs encoded by LAT possess anti-apoptosis functions in transfected cells. The BHV-1 latency related RNA (LR-RNA), like LAT, is abundantly expressed during latency. The LR-RNA encodes a protein (ORF2) and two microRNAs that are expressed in certain latently infected neurons. Wild-type expression of LR gene products is required for stress-induced reactivation from latency in cattle. ORF2 has anti-apoptosis functions and interacts with certain cellular transcription factors that stimulate viral transcription and productive infection. ORF2 is predicted to promote survival of infected neurons by inhibiting apoptosis and sequestering cellular transcription factors which stimulate productive infection. In addition, the LR encoded microRNAs inhibit viral transcription and apoptosis. In summary, the ability of BHV-1 and HSV-1 to interfere with apoptosis and productive infection in sensory neurons is crucial for the life-long latency-reactivation cycle in their respective hosts.

ICP27 protein encoded by bovine herpesvirus type 1 (bICP27) interferes with promoter activity of the bovine genes encoding beta interferon 1 (IFN-β1) and IFN-β3

Bovine herpes virus 1 (BHV-1) infection leads to upper respiratory tract infections, conjunctivitis, and the infection predisposes cattle to secondary bacterial infections. The infected cell protein 0 (bICP0) encoded by BHV-1 suppresses antiviral innate immune signaling by interfering with expression of interferon beta (IFN-β). In contrast to humans or mice, cattle contain three IFN-β genes that have distinct transcriptional promoters. We previously cloned and characterized all three bovine IFN-β promoters. In this study, we provide evidence that bICP27; a viral early protein that shuttles between the nucleus and cytoplasm inhibits transcriptional activity of two bovine IFN-β gene promoters (IFN-β1 and IFN-β3). Conversely, the BHV-1 infected cell protein 0 (bICP0) early promoter was not inhibited by bICP27. C-terminal mutants lacking the bICP27 zinc RING finger-like motif did not efficiently inhibit IFN-β3 promoter activity but inhibited IFN-β1 promoter activity as efficiently as wild type bICP27. An N-terminal mutant lacking the nuclear localization signal (NLS) and nucleolar localization signal (NoLS) was localized to the cytoplasm and this mutant had no effect on IFN-β promoter activity. In summary, these studies provided evidence that bICP27 inhibited IFN-β1 and IFN-β3 promoter activity in transiently transfected cells.

Regulation of the latency-reactivation cycle by products encoded by the bovine herpesvirus 1 (BHV-1) latency-related gene

Like other α-herpesvirinae subfamily members, the primary site for bovine herpesvirus 1 (BHV-1) latency is ganglionic sensory neurons. Periodically BHV-1 reactivates from latency, virus is shed, and consequently virus transmission occurs. Transcription from the latency-related (LR) gene is readily detected in neurons of trigeminal ganglia (TG) of calves or rabbits latently infected with BHV-1. Two micro-RNAs and a transcript encompassing a small open reading frame (ORF-E) located within the LR promoter can also be detected in TG of latently infected calves. A BHV-1 mutant that contains stop codons near the beginning of the first open reading frame (ORF2) within the major LR transcript (LR mutant virus) has been characterized. The LR mutant virus does not express ORF2, a reading frame that lacks an initiating ATG (reading frame B), and has reduced expression of ORF1 during productive infection. The LR mutant virus does not reactivate from latency following dexamethasone treatment suggesting that LR protein expression regulates the latency-reactivation cycle. Higher levels of apoptosis occur in TG neurons of calves infected with the LR mutant viruses when compared to wild-type BHV-1 indicating that the anti-apoptotic properties of the LR gene is necessary for the latency-reactivation cycle. ORF2 inhibits apoptosis and regulates certain viral promoters, in part, because it interacts with three cellular transcription factors (C/EBP-alpha, Notch1, and Notch3). Although ORF2 is important for the latency-reactivation cycle, we predict that other LR gene products play a supportive role during life-long latency in cattle.

Attenuation of bovine herpesvirus type 1 by deletion of its glycoprotein G and tk genes and protection against virulent viral challenge

To develop a novel vaccine against infectious bovine rhinotracheitis (IBR), a bovine herpesvirus-1 (BoHV-1) mutant was constructed by deleting the genes for glycoprotein G (gG) and thymidine kinase (tk) through homologous recombination. The resulting sequences for both genes were shown to be correct and a gG expression defect was also confirmed. A parallel study of the BoHV-1 gG(-)/tk(-), gE(-)/tk(-) mutants and wild type (wt) in 31 calves was performed at three different doses, 4×10(5)PFU, 4×10(6)PFU and 4×10(7)PFU. Compared to wt BoHV-1, inoculation of BoHV-1 gG(-)/tk(-) and gE(-)/tk(-) produced no clinical signs and the virus was not reactivated by dexamethasone (dex). Inoculation of BoHV-1 gG(-)/tk(-) at the doses of 4×10(6) and 4×10(7)PFU provided full clinical protection for the cattle against wt BoHV-1 challenge at 4×10(7)PFU/calf. Although the mutants were associated with significantly lower levels of serum neutralizing antibody, interferon gamma (IFN-γ) and tumor necrosis factor alpha (TNF-α) than wt BoHV-1 on days 3, 5 and 7 after immunization, stimulation of IFN-β by BoHV-1 gG(-)/tk(-) was significantly higher than that of wt BoHV-1 and gE(-)/tk(-) on days 3 and 5. We conclude that BoHV-1 gG(-)/tk(-) was attenuated adequately and that it maintains the ability to stimulate immune protection. Therefore, it may be a promising candidate for a marker vaccine against IBR.

Cytoplasmic localized infected cell protein 0 (bICP0) encoded by bovine herpesvirus 1 inhibits β interferon promoter activity and reduces IRF3 (interferon response factor 3) protein levels

Bovine herpesvirus 1 (BHV-1), an alpha-herpesvirinae subfamily member, establishes a life-long latent infection in sensory neurons. Periodically, BHV-1 reactivates from latency, infectious virus is spread, and consequently virus transmission occurs. BHV-1 acute infection causes upper respiratory track infections and conjunctivitis in infected cattle. As a result of transient immune-suppression, BHV-1 infections can also lead to life-threatening secondary bacterial pneumonia that is referred to as bovine respiratory disease. The infected cell protein 0 (bICP0) encoded by BHV-1 reduces human β-interferon (IFN-β) promoter activity, in part, by inducing degradation of interferon response factor 3 (IRF3) and interacting with IRF7. In contrast to humans, cattle contain three IFN-β genes. All three bovine IFN-β proteins have anti-viral activity: but each IFN-β gene has a distinct transcriptional promoter. We have recently cloned and characterized the three bovine IFN-β promoters. Relative to the human IFN-β promoter, each of the three IFN-β promoters contain differences in the four positive regulatory domains that are required for virus-induced activity. In this study, we demonstrate that bICP0 effectively inhibits bovine IFN-β promoter activity following transfection of low passage bovine cells with interferon response factor 3 (IRF3) or IRF7. A bICP0 mutant that localizes to the cytoplasm inhibits bovine IFN-β promoter activity as efficiently as wt bICP0. The cytoplasmic localized bICP0 protein also induced IRF3 degradation with similar efficiency as wt bICP0. In summary, these studies suggested that cytoplasmic localized bICP0 plays a role in inhibiting the IFN-β response during productive infection.

Infection of cultured bovine cells with bovine herpesvirus 1 (BHV-1) or Sendai virus induces different beta interferon subtypes

In contrast to mice or humans, cattle contain three beta interferon (IFN-β) genes with distinct transcriptional promoters suggesting IFN-β gene expression is not stimulated the same by different viruses. To test this hypothesis, we compared expression of the three IFN-β subtypes after infection with a RNA virus, Sendai, versus a large DNA virus, bovine herpesvirus 1 (BHV-1). Infection of low passage bovine kidney (BK) or established bovine kidney cells (CRIB) with Sendai virus has consistently led to high levels of IFN-β1 RNA. Conversely, infection of CRIB cells, but not BK cells, with BHV-1 increased IFN-β3 RNA levels and to a lesser extent the other two IFN-β subtypes. Inhibition of de novo protein synthesis with cycloheximide resulted in higher levels of IFN-β1 and IFN-β2 RNA levels after BHV-1 infection. Further studies demonstrated that BHV-1 immediate early and/or early genes were primarily responsible for inhibiting the IFN response in BK cells. The three bovine IFN-β promoters were cloned upstream of a reporter gene construct, and their properties analyzed in transient transfection assays. Only the IFN-β3 promoter was trans-activated by IRF3 (interferon responsive factor 3). IRF7 and double stranded RNA (polyI:C) stimulated IFN-β1 and IFN-β3 promoter activity, but not IFN-β2. Relative to the human IFN-β promoter, the IFN-β3 promoter contained fewer nucleotide differences in the positive regulatory domain III (PRD III), PRD IV, and PRD I compared to the IFN-β1 and IFN-β2 promoter. Collectively, these studies provide evidence that virus infection differentially stimulates expression of the three bovine IFN-β genes.

Regulation of promyelocytic leukemia (PML) protein levels and cell morphology by bovine herpesvirus 1 infected cell protein 0 (bICP0) and mutant bICP0 proteins that do not localize to the nucleus

BHV-1 is an important pathogen of cattle. The infected cell protein 0 (bICP0) encoded by BHV-1 is an important regulatory protein because it is constitutively expressed and can activate all viral promoters. The mechanism by which bICP0 activates viral promoters is not well understood because bICP0 does not appear to be a sequence specific binding protein. A C(3)HC(4) zinc RING (really interesting novel gene) motif at the N-terminus of bICP0 has E3 ubiquitin ligase activity, which is important for activating viral gene expression and inhibiting interferon dependent transcription. Like other alpha-herpesvirinae ICP0 homologues, bICP0 is associated with promyelocytic leukemia (PML) protein-containing nuclear domains. During productive infection of cultured cells, BHV-1 induces degradation of the PML protein, which correlates with efficient productive infection. In this study, we demonstrated that a plasmid expressing bICP0 reduces steady state levels of the PML protein, and the C(3)HC(4) zinc RING finger is important for PML degradation. Surprisingly, bICP0 mutants with an intact C(3)HC(4) zinc RING finger that lack a nuclear localization signal also reduces steady PML protein levels. In addition, mutant bICP0 proteins that primarily localize to the cytoplasm induced morphological changes in transfected cells. During productive infection, bICP0 was detected in the cytoplasm of low-passage bovine kidney, but not established bovine kidney cells. These studies demonstrated that bICP0, even when not able to efficiently localize to the nucleus, was able to induce degradation of the PML protein and alter the morphology of transfected cells.

Bovine herpesvirus type 1 (BHV-1) is an important cofactor in the bovine respiratory disease complex

BHV-1 is an important pathogen of cattle. Because of its ability to induce immune suppression, BHV-1 is an important agent in the multifactorial disorder, bovine respiratory disease complex (BRDC). BHV-1 encodes several proteins that inhibit various arms of the immune system suggesting that these proteins are important in the development of BRDC.

Epstein-Barr virus BRLF1 inhibits transcription of IRF3 and IRF7 and suppresses induction of interferon-beta

Activation of interferon regulatory factors (IRFs) 3 and 7 is essential for the induction of Type I interferons (IFN) and innate antiviral responses, and herpesviruses have evolved mechanisms to evade such responses. We previously reported that Epstein-Barr virus BZLF1, an immediate-early (IE) protein, inhibits the function of IRF7, but the role of BRLF1, the other IE transactivator, in IRF regulation has not been examined. We now show that BRLF1 expression decreased induction of IFN-beta, and reduced expression of IRF3 and IRF7; effects were dependent on N- and C-terminal regions of BRLF1 and its nuclear localization signal. Endogenous IRF3 and IRF7 RNA and protein levels were also decreased during cytolytic EBV infection. Finally, production of IFN-beta was decreased during lytic EBV infection and was associated with increased susceptibility to superinfection with Sendai virus. These data suggest a new role for BRLF1 with the ability to evade host innate immune responses.

Comparison of the biological and biochemical activities of several members of the alphaherpesvirus ICP0 family of proteins

Immediate-early protein ICP0 of herpes simplex virus type 1 (HSV-1) is an E3 ubiquitin ligase of the RING finger class that is required for efficient lytic infection and reactivation from latency. Other alphaherpesviruses also express ICP0-related RING finger proteins, but these have limited homology outside the core RING domain. Existing evidence indicates that ICP0 family members have similar properties, but there has been no systematic comparison of the biochemical activities and biological functions of these proteins. Here, we describe an inducible cell line system that allows expression of the ICP0-related proteins of bovine herpes virus type 1 (BHV-1), equine herpesvirus type 1 (EHV-1), pseudorabies virus (PRV), and varicella-zoster virus (VZV) and their subsequent functional analysis. We report that the RING domains of all the proteins have E3 ubiquitin ligase activity in vitro. The BHV-1, EHV-1, and PRV proteins complement ICP0-null mutant HSV-1 plaque formation and induce derepression of quiescent HSV-1 genomes to levels similar to those achieved by ICP0 itself. VICP0, the ICP0 expressed by VZV, was found to be extremely unstable, which limited its analysis in this system. We compared the abilities of the ICP0-related proteins to disrupt ND10, to induce degradation of PML and Sp100, to affect key components of the interferon signaling pathway, and to interfere with induction of interferon-stimulated genes. We found that the property that correlated most closely with their biological activities was the ability to preclude the recruitment of cellular ND10 proteins to sites closely associated with incoming HSV-1 genomes and early replication compartments.

Regulation of Innate Immune Responses by Bovine Herpesvirus 1 and Infected Cell Protein 0 (bICP0)

Bovine herpesvirus 1 (BoHV-1) infected cell protein 0 (bICP0) is an important transcriptional regulatory protein that stimulates productive infection. In transient transfection assays, bICP0 also inhibits interferon dependent transcription. bICP0 can induce degradation of interferon stimulatory factor 3 (IRF3), a cellular transcription factor that is crucial for activating beta interferon (IFN-β) promoter activity. Recent studies also concluded that interactions between bICP0 and IRF7 inhibit trans-activation of IFN-β promoter activity. The C3HC4 zinc RING (really important new gene) finger located near the amino terminus of bICP0 is important for all known functions of bICP0. A recombinant virus that contains a single amino acid change in a well conserved cysteine residue of the C3HC4 zinc RING finger of bICP0 grows poorly in cultured cells, and does not reactivate from latency in cattle confirming that the C3HC4 zinc RING finger is crucial for viral growth and pathogenesis. A bICP0 deletion mutant does not induce plaques in permissive cells, but induces autophagy in a cell type dependent manner. In summary, the ability of bICP0 to stimulate productive infection, and repress IFN dependent transcription plays a crucial role in the BoHV-1 infection cycle.