Nucleotide sequence specifying the glycoprotein gene, gB, of herpes simplex virus type 1

Antiviral activity of mitoxantrone dihydrochloride against human herpes simplex virus mediated by suppression of the viral immediate early genes

Background

HSV-1 is a common pathogen that infects 50–90% of the human population worldwide. HSV-1 causes numerous infection-related diseases, some of which are severely life-threatening. There are antiviral medications with activity against HSV-1. However, with the emergence of drug-resistant mutant strains of HSV-1, there is an urgent need to develop new effective anti-HSV-1 agents.

Methods

Therefore, we screened a chemical library of approximately 1500 compounds to identify inhibitors of HSV-1-induced toxicity for further drug development. Moreover, we performed several experiments, including western blot analysis, Q-PCR analysis and luciferase activity assay, to explore the antiviral mechanism of the candidates.

Results

Here, we identified a small molecule, mitoxantrone dihydrochloride, with potency against HSV-1-induced toxicity. Furthermore, the viral titers and expression levels of HSV-1 viral proteins were potently reduced by the presence of MD in many cell lines. Using Q-PCR analysis, we found that MD efficiently reduced the transcription of viral genes that are essential for DNA synthesis, namely, UL5, UL9, UL29, UL30, UL42 and UL52. Notably, MD also significantly inhibited the transcription of the immediate early genes ICP0, ICP22, ICP27 and ICP47, all of which are required for the expression of early and late viral gene products. Using immunofluorescence and western blot analysis, we found that the antiviral effect of MD was independent of the activation of the NF-κB and MAPK pathways. Furthermore, we found that the reduction in the transcription of viral immediate early genes was not related to the promoter activities of ICP0.

Conclusions

Therefore, the identification of compound MD as an inhibitor of toxicity induced by HSV-1 highlights its potential use in the development of novel anti-HSV-1 drugs.

Prediction of conserved sites and domains in glycoproteins B, C and D of herpes viruses

Glycoprotein B (gB), C (gC) and D (gD) of herpes simplex virus are implicated in virus adsorption and penetration. The gB, gC and gD are glycoproteins for different processes of virus binding and attachment to the host cells. Moreover, their expression is necessary and sufficient to induce cell fusion in the absence of other glycoproteins. Egress of herpes simplex virus (HSV) and other herpes viruses from cells involves extensive modification of cellular membranes and sequential envelopment, de-envelopment and re-envelopment steps. Viral glycoproteins are important in these processes, and frequently two or more glycoproteins can largely suffice in any step. Hence, we target the 3 important glycoproteins (B, C and D) of eight different herpes viruses of different species. These species include human (HSV1 and 2), bovine (BHV1), equine (EHV1 and 4), chicken (ILT1 and MDV2) and pig (PRV1). By applying different bioinformatics tools, we highlighted the conserved sites in these glycoproteins which might be most significant regarding attachment and infection of the viruses. Moreover the conserved domains in these glycoproteins are also highlighted. From this study, we will able to analyze the role of different viral glycoproteins of different species during herpes virus adsorption and penetration. Moreover, this study will help to construct the antivirals that target the glycoproteins of different herpes viruses.

Misdirection of endosomal trafficking mediated by herpes simplex virus-encoded glycoprotein B

Herpes simplex virus (HSV)-encoded glycoprotein B (gB) is the most abundant protein in the viral envelope and promotes fusion of the virus with the cellular membrane. In the present study, we found that gB impacts on the major histocompatibility complex (MHC)-II pathway of antigen presentation by fostering homotypic fusion of early endosomes and trapping MHC-II molecules in these altered endosomes. By using an overexpression approach, we demonstrated that transient expression of gB induces giant vesicles of early endosomal origin, which contained Rab5, early endosomal antigen 1 (EEA1), and large amounts of MHC-II molecules [human leukocyte antigen (HLA)-DR, and HLA-DM], but no CD63. In HSV-1-infected and stably transfected cell lines that expressed lower amounts of gB, giant endosomes were not observed, but strongly increased amounts of HLA-DR and HLA-DM were found in EEA1⁺ early endosomes. We used these giant vesicles as a model system and revealed that gB interacts with Rab5 and EEA1, and that gB-induced homotypic fusion of early endosomes to giant endosomes requires phosphatidylinositol 3-phosphate, the activity of soluble N-ethylmaleimide-sensitive factor attachment protein receptors, and the cytosolic gB sequence ⁸⁸⁹YTQVPN⁸⁹⁴ We conclude that gB expression alters trafficking of molecules of the HLA-II processing pathway, which leads to increased retention of MHC-II molecules in early endosomal compartments, thereby intercepting antigen presentation.-Niazy, N., Temme, S., Bocuk, D., Giesen, C., König, A., Temme, N., Ziegfeld, A., Gregers, T. F., Bakke, O., Lang, T., Eis-Hübinger, A. M., Koch, N. Misdirection of endosomal trafficking mediated by herpes simplex virus-encoded glycoprotein B.

The membrane-proximal region (MPR) of herpes simplex virus gB regulates association of the fusion loops with lipid membranes

Glycoprotein B (gB), gD, and gH/gL constitute the fusion machinery of herpes simplex virus (HSV). Prior studies indicated that fusion occurs in a stepwise fashion whereby the gD/receptor complex activates the entire process, while gH/gL regulates the fusion reaction carried out by gB. Trimeric gB is a class III fusion protein. Its ectodomain of 773 amino acids contains a membrane-proximal region (MPR) (residues 731 to 773) and two fusion loops (FLs) per protomer. We hypothesized that the highly hydrophobic MPR interacts with the FLs, thereby masking them on virions until fusion begins. To test this hypothesis, we made a series of deletion, truncation, and point mutants of the gB MPR. Although the full-length deletion mutants were expressed in transfected cells, they were not transported to the cell surface, suggesting that removal of even small stretches of the MPR was highly detrimental to gB folding. To circumvent this limitation, we used a baculovirus expression system to generate four soluble proteins, each lacking the transmembrane region and cytoplasmic tail. All retained the FLs and decreasing portions of the MPR [gB(773t) (gB truncated at amino acid 773), gB(759t), gB(749t), and gB(739t)]. Despite the presence of the FLs, all were compromised in their ability to bind liposomes compared to the control, gB(730t), which lacks the MPR. We conclude that residues 731 to 739 are sufficient to mask the FLs, thereby preventing liposome association. Importantly, mutation of two aromatic residues (F732 and F738) to alanine restored the ability of gB(739t) to bind liposomes. Our data suggest that the MPR is important for modulating the association of gB FLs with target membranes.

To successfully cause disease, a virus must infect host cells. Viral infection is a highly regulated, multistep process. For herpesviruses, genetic material transfers from the virus to the target cell through fusion of the viral and host cell lipid membranes. Here, we provide evidence that the ability of the herpes simplex virus (HSV) glycoprotein B (gB) fusion protein to interact with the host membrane is regulated by its membrane-proximal region (MPR), which serves to cover or shield its lipid-associating moieties (fusion loops). This in turn prevents the premature binding of gB with host cells and provides a level of regulation to the fusion process. These findings provide important insight into the complex regulatory steps required for successful herpesvirus infection.

Entry of herpes simplex virus 1 and other alphaherpesviruses via the paired immunoglobulin-like type 2 receptor alpha

Herpes simplex virus 1 (HSV-1) enters cells either via fusion of the virion envelope and host cell plasma membrane or via endocytosis, depending on the cell type. In the study reported here, we investigated a viral entry pathway dependent on the paired immunoglobulin-like type 2 receptor alpha (PILRalpha), a recently identified entry coreceptor for HSV-1 that associates with viral envelope glycoprotein B (gB). Experiments using inhibitors of endocytic pathways and ultrastructural analyses of Chinese hamster ovary (CHO) cells transduced with PILRalpha showed that HSV-1 entry into these cells was via virus-cell fusion at the cell surface. Together with earlier observations that HSV-1 uptake into normal CHO cells and those transduced with a receptor for HSV-1 envelope gD is mediated by endocytosis, these results indicated that expression of PILRalpha produced an alternative HSV-1 entry pathway in CHO cells. We also showed that human and murine PILRalpha were able to mediate entry of pseudorabies virus, a porcine alphaherpesvirus, but not of HSV-2. These results indicated that viral entry via PILRalpha appears to be conserved but that there is a PILRalpha preference among alphaherpesviruses.

Structure-function analysis of herpes simplex virus glycoprotein B with fusion-from-without activity

Fusion-from-without (FFWO) is the rapid induction of cell fusion by virions in the absence of viral protein synthesis. The combination of two amino acid mutations in envelope glycoprotein B (gB), one in the ectodomain and one in the cytoplasmic tail, can confer FFWO activity to wild type herpes simplex virus (HSV). In this report, we analyzed the entry and cell fusion phenotypes of HSV that contains FFWO gB, with emphasis on the cellular receptors for HSV, nectin-1, nectin-2 and HVEM. The ability of an HSV strain with FFWO gB to efficiently mediate FFWO via a specific gD-receptor correlated with its ability to mediate viral entry by that receptor. A FFWO form of gB was not sufficient to switch the entry of HSV from a pH-dependent, endocytic pathway to a direct fusion, pH-independent pathway. The conformation of gB with FFWO activity was not globally altered relative to wild type. However, distinct monoclonal antibodies had reduced reactivity with FFWO gB, suggesting an altered antigenic structure relative to wild type. FFWO was blocked by preincubation of virions with neutralizing antibodies to gB or gD. Together with previous studies, the results indicate that the roles of gB in FFWO and in virus-cell fusion during entry are related but not identical. This study also suggests that the FFWO function of gB is not a specific determinant for the selection of HSV entry pathway and that antigenic differences in FFWO gB may reflect its enhanced fusion activity.

Herpes simplex virus type-1(HSV-1) oncolytic and highly fusogenic mutants carrying the NV1020 genomic deletion effectively inhibit primary and metastatic tumors in mice

Background

The NV1020 oncolytic herpes simplex virus type-1 has shown significant promise for the treatment of many different types of tumors in experimental animal models and human trials. Previously, we described the construction and use of the NV1020-like virus OncSyn to treat human breast tumors implanted in nude mice. The syncytial mutation gKsyn1 (Ala-to-Val at position 40) was introduced into the OncSyn viral genome cloned into a bacterial artificial chromosome using double-red mutagenesis in E. coli to produce the OncdSyn virus carrying syncytial mutations in both gB(syn3) and gK(syn1).

Results

The OncdSyn virus caused extensive virus-induced cell fusion in cell culture. The oncolytic potential of the OncSyn and OncdSyn viruses was tested in the highly metastatic syngeneic mouse model system, which utilizes 4T1 murine mammary cancer cells implanted within the interscapular region of Balb/c mice. Mice were given three consecutive intratumor injections of OncSyn, OncdSyn, or phosphate buffered saline four days apart. Both OncSyn and OncdSyn virus injections resulted in significant reduction of tumor sizes (p < 0.05) compared to control tumors. Virus treated mice but not controls showed a marked reduction of metastatic foci in lungs and internal organs. Mouse weights were not significantly impacted by any treatment during the course of the entire study (p = 0.296).

Conclusion

These results show that the attenuated, but highly fusogenic OncSyn and OncdSyn viruses can effectively reduce primary and metastatic breast tumors in immuncompetent mice. The available bac-cloned OncSyn and OncdSyn viral genomes can be rapidly modified to express a number of different anti-tumor and immunomodulatory genes that can further enhance their anti-tumor potency.

Understanding HSV-1 entry glycoproteins

Herpes Simplex Virus‐1 is a common infectious agent, but the precise detail of entry and infection of cells has only now begun to be clarified. Four viral surface glycoproteins (gB, gD, gH and gL) are required. This review summarises the known structure and function of each of these essential viral envelope glycoproteins, and explores what is known about their close cooperation with each other in mediating cellular membrane fusion. It is suggested that, following gD binding to one of its entry receptors, membrane fusion is mediated by gB and the heterodimer gH/gL. Significantly, these four entry glycoproteins also play a key role in the interaction between HSV and the host immune system. The glycoproteins serve an important role as targets of adaptive immunity. However, recent studies have demonstrated that the same proteins also play a key role in initiating the early innate immune response to HSV. Understanding the complex functions of these HSV proteins may be essential for successful development of vaccines for HSV. Copyright © 2007 John Wiley & Sons, Ltd.

Effective treatment of human breast tumor in a mouse xenograft model with herpes simplex virus type 1 specifying the NV1020 genomic deletion and the gBsyn3 syncytial mutation enabling high viral replication and spread in breast cancer cells

A new oncolytic and fusogenic herpes simplex virus type 1 (HSV-1) was constructed on the basis of the wildtype HSV-1(F) strain. To provide for safety and tumor selectivity, the virus carried a large deletion including one of the two alpha4, gamma(1)34.5, alpha0 genes and the latency-associated transcript region. The gamma(1)34.5 gene, a major neurovirulence factor, was replaced by a gene cassette constitutively expressing the red fluorescent protein gene. Homologous recombination was used to transfer the fusogenic gBsyn3 mutation to the viral genome to produce the OncSyn virus. OncSyn causes extensive virus-induced cell fusion (syncytia) and replicates to higher titers than the parental Onc and HSV-1(F) strains in breast cancer cells. Biochemical analysis revealed that the OncSyn virus retains a stable genome and expresses all major viral glycoproteins. A xenograft mouse model system using MDA-MB-435S-luc (MM4L) human breast cancer cells constitutively expressing the luciferase gene implanted within the interscapular region of animals was used to test the ability of the virus to inactivate breast tumor cells in vivo. Seventy-two mice bearing MM4L breast cancer xenografts were randomly divided into three groups and given two rounds of three consecutive intratumoral injections of OncSyn, inactivated OncSyn, or phosphate-buffered saline 3 days apart. A single round of virus injections resulted in a drastic reduction of tumor sizes (p <or= 0.0001) and diminution of chemiluminescence emitted by the cancer cells (p <or= 0.0002). This effect was enhanced by a second round of virus injections into the tumors 3 days after the first round (p <or= 0.0001). Systematic necropsy and pathological evaluation of the primary tumors revealed that the single round of injections resulted in extensive necrosis of tumor cells (p <or= 0.0001), which was enhanced by the second round of injections (p <or= 0.0002). Internal organs were not affected by virus inoculation. Mouse weights were not significantly impacted by any treatment during the course of the entire study (p = 0.46). These results show that the attenuated, fusogenic, and oncolytic HSV-1(F) virus strain OncSyn may effectively treat human breast tumors in vivo.

Construction and characterization of a herpes simplex virus type I recombinant expressing green fluorescent protein: acute phase replication and reactivation in mice

A recombinant HSV-1 virus expressing EGFP from the HCMV major immediate early promoter (KOS-CMVGFP) was constructed to monitor viral replication and spread in vitro and in mice. KOS-CMVGFP replicated as efficiently as wild-type virus, strain KOS, in single cycle growth experiments in Vero cells indicating that the recombinant virus has no significant growth defects in vitro. Following ocular inoculation of mice, KOS-CMVGFP exhibited slight but statistically significant reductions in mouse tear film titers relative to wild-type virus. Progression of virus infection of the eyes, periocular tissue, and snout was readily followed by fluorescence microscopy. Insertion of the EGFP expression cassette into the KOS genome had no effect on the efficiency of establishment of latency as determined by quantitative competitive PCR of viral genomes in latently infected TG. KOS-CMVGFP reactivated with wild-type kinetics and efficiency by explant cocultivation, but exhibited a significant delay in the kinetics and a modest reduction in the efficiency of reactivation compared to KOS in the more sensitive TG cell culture model. Notably, EGFP expression preceded the detection of infectious virus by greater than 24 h in both ex vivo models and thus is a useful marker of the early stages in the induction of reactivation.

Identification of the authentic varicella-zoster virus gB (gene 31) initiating methionine overlapping the 3' end of gene 30

The varicella-zoster virus (VZV) gB sequence was re-examined in light of recent knowledge about unusually long gB signal peptides in other herpesviral gB homologs. Through mutational analysis, the discovery was made that the authentic initiating methionine for VZV gB is a codon beginning at genome nucleotide 56,819. The total length for the VZV gB primary translation product was 931 amino acids (aa) with a 71-aa signal sequence. Considering the likely signal sequence cleavage site to be located between Ser 71 and Val 72, the length of the mature VZV gB polypeptide would then be 860 amino acids prior to further internal endoproteolytic cleavage between amino acids Arg 494 and Ser 495. In this report, we also produced a full-length gB and demonstrated its association with VZV gE, suggesting a possible gE-gB interaction during gB trafficking before its cleavage in the Golgi.

An alpha-helical domain within the carboxyl terminus of herpes simplex virus type 1 (HSV-1) glycoprotein B (gB) is associated with cell fusion and resistance to heparin inhibition of cell fusion

Previous studies from our laboratory indicated that a 28-amino-acid carboxyl-terminal truncation of gB caused extensive virus-induced cell fusion (Baghian et al., 1993, J Virol 67, 2396-2401). We tested the ability of additional truncations and mutations within gB to cause cell fusion in the recently established virus-free cell fusion assay (Turner et al., 1998, J. Virol. 72, 873-875). Deletion of the carboxyl-terminal 28 amino acids of gB (gBDelta28), which removed part of the predicted alpha-helical structure H17b, caused extensive cell fusion. A gB truncation specified by gBDelta36, which removed the entire H17b domain, caused as much cell fusion as the gBDelta28 truncation. Similarly, gB(A874P) containing a substitution of an Ala with Pro within H17b caused cell fusion. Heparin, a gB-specific inhibitor of virus-induced cell fusion, inhibited both wild-type gB and gB(syn3)-mediated cell fusion. In contrast, fusion of cells transfected with gB(Delta28), gB(Delta36), or gB(A874P) was resistant to heparin inhibition of cell fusion. We concluded the following: (1) The predicted alpha-helical structure of H17b within the carboxyl terminus of gB is involved in both virus-induced and virus-free cell fusion. (2) Heparin is a specific inhibitor of gB-mediated fusion in both systems. (3) Resistance to heparin inhibition of gB-mediated cell fusion is associated with the predicted alpha-helical structure H17b within the carboxyl terminus of gB.

Herpes simplex virus 1 (HSV-1) strain HSZP glycoprotein B gene: comparison of mutations among strains differing in virulence

The nonpathogenic HSZP strain of HSV-1 induces large polykaryocytes due to a syn3 mutation (His for Arg at residue 858) in the C-terminal endodomain of glycoprotein B (gB) (40). We determined the nucleotide (nt) sequence of the UL27 gene specifying the gB polypeptide of HSZP (gBHSZP) and found 3 mutations in its ectodomain at aminoacids (aa) 59, 79 and 108. The ANGpath virus, which also has a syn3 mutation in the C-terminal endodomain of gB (Val for Ala at residue 855) is pathogenic for adult mice (39), but can be made nonpathogenic by replacing the gBANGpath gene by the corresponding gBKOS sequence (21). The gBANGpath had three ectodomain mutations (at aa 62, 77 and 285), while gBKOS had at least four ectomain mutations (aa 59, 79, 313, and 553). Two mutations (aa 59 and 79) in the latter, located in the variable antigenic site IV/D1 were common for gBKOS and gBHSZP. These together with the gBANGpath mutations at aa 62 and 77 create a cluster of 4 mutations in diverse region of the N-terminal part of gB (between aa 59-79), in which the gBs of pathogenic ANGpath and 17 viruses differ from the gBs of nonpathogenic HSZP and KOS viruses. The lower pathogenicity of KOS as related to gBKOS, is furthermore associated with the change of Ser to Thr at aa 313 (locus III/D2). The possibility is discussed that mutations in both above mentioned antigenic loci could result in higher immunogenicity of the corresponding antigenic epitopes, which, in turn, would contribute to the decreased virulence of HSZP and KOS viruses.

Detection of human serum antibodies against type-specifically reactive peptides from the N-terminus of glycoprotein B of herpes simplex virus type 1 and type 2 by surface plasmon resonance

A single-step surface plasmon resonance protocol for the detection of antibodies against herpes simplex virus type 1 and type 2 (HSV-1, HSV-2) in human sera was established using the BIAcore system. Two peptides from corresponding segments of the N-terminus of HSV-1 and HSV-2 glycoprotein B (gB), i.e. peptide gB-1 (60-73) (GAAPTGDPKPKKNK) and peptide gB-2 (55-68) (SPATTKARKRKTKK), were identified as immunogenic. Employing both peptides as diagnostic antigens in the surface plasmon resonance assay, a sensitivity for the detection of HSV-1 and HSV-2 type-specific antibodies of 83 and 86%, respectively, was achieved as compared with immunoblotting as a reference method. Peptide gB-1 (60-73) allowed the discrimination between HSV-1 and HSV-2 type-specific antibodies with a specificity of 67%, whereas peptide gB-2 (55-68) reacted in a strictly HSV-2 type-specific manner. It is concluded that peptides from the N-terminus of gB-1 and gB-2 are recognized predominantly by human sera in an HSV-specific manner. Peptide gB-2 (55-68) can be employed successfully for the determination of type-specific antibodies against HSV-2.

Detection of varicella-zoster virus and herpes simplex virus by the polymerase chain reaction with degenerate primers

Varicella-zoster virus (VZV) and herpes simplex virus (HSV) are human pathogens of significance involved in multiple diseases with either typical or atypical clinical features. In neonates and immunocompromised patients these alphaherpesviruses may cause life-threatening diseases such as encephalitis. Detection of VZV by virus culture is difficult. Polymerase chain reaction (PCR) is quicker and more sensitive and applicable in most clinical microbiological laboratories. Using degenerate primers, glycoprotein B (gB) DNA was amplified from all alphaherpesvirus field strains present in clinical samples. The amplification of gB allowed virus typing of VZV, HSV-1 and HSV-2 using restriction enzyme digestion of the PCR products. Degenerate primers can replace conventional primers in diagnostic PCR without loss of sensitivity and specificity.

Mutations in the conserved carboxy-terminal hydrophobic region of glycoprotein gB affect infectivity of herpes simplex virus

Glycoprotein gB is the most highly conserved glycoprotein in the herpesvirus family and plays a critical role in virus entry and fusion. Glycoprotein gB of herpes simplex virus type 1 contains a hydrophobic stretch of 69 aa near the carboxy terminus that is essential for its biological activity. To determine the role(s) of specific amino acids in the carboxy-terminal hydrophobic region, a number of amino acids were mutagenized that are highly conserved in this region within the gB homologues of the family HERPESVIRIDAE: Three conserved residues in the membrane anchor domain, namely A786, A790 and A791, as well as amino acids G743, G746, G766, G770 and P774, that are non-variant in Herpesviridae, were mutagenized. The ability of the mutant proteins to rescue the infectivity of the gB-null virus, K082, in trans was measured by a complementation assay. All of the mutant proteins formed dimers and were incorporated in virion particles produced in the complementation assay. Mutants G746N, G766N, F770S and P774L showed negligible complementation of K082, whereas mutant G743R showed a reduced activity. Virion particles containing these four mutant glycoproteins also showed a markedly reduced rate of entry compared to the wild-type. The results suggest that non-variant residues in the carboxy-terminal hydrophobic region of the gB protein may be important in virus infectivity.

Characterization of pseudorabies virus glycoprotein B expressed by canine herpesvirus

A recombinant canine herpesvirus (CHV) which expressed glycoprotein B (gB) of pseudorabies virus (PrV) was constructed. The antigenicity of the PrV gB expressed by the recombinant CHV is similar to that of the native PrV. The expressed PrV gB was shown to be transported to the surface of infected cells as judged by an indirected immunofluorescence test. Antibodies raised in mice immunized with the recombinant CHV neutralized the infectivity of PrV in vitro. It is known that the authentic PrV gB exists as a glycoprotein complex, which consists of gBa, gBb and gBc. In MDCK cells, PrV gB expressed by the recombinant CHV was processed like authentic PrV gB, suggesting that the cleavage mechanism of PrV gB depends on a functional cleavage domain from PrV gB gene and protease from infected cells.

Role of the membrane anchoring and cytoplasmic domains in intracellular transport and localization of viral glycoproteins

Nuclear factor-κB (NF-κB) binds to nucleotide sequences between -80 and -70 bp upstream of the transcriptional start site in the interleukin-8 (IL-8) promoter and is crucial for transcription of the IL-8 gene. We showed that exogenous nitric oxide in the form of a nitric oxide donor significantly reduced IL-8 mRNA in cytokine-activated ECV304. Similarly, nitric oxide significantly reduced migration of polymorphonuclear neutrophils through cytokine-activated ECV304 monolayers, an IL-8-dependent process. Using a luciferase reporter construct containing the NF-κB site of the IL-8 gene, we showed that exposing cytokine-activated ECV304 to exogenous nitric oxide resulted in significant reduction of NF-κB binding. Follow-up studies using a luciferase reporter construct possessing a mutated NF-κB site confirmed that the luciferase activity observed in the NF-κB reporter resulted from NF-κB binding. These studies demonstrate that nitric oxide, supplied exogenously into reactions containing activated endothelium, down-regulates pro-inflammatory activity, such as the secretion of chemokines, and functional activity, such as transendothelial migration of neutrophils. Key words: interleukin-8, nuclear factor κ B, transendothelial migration, nitric oxide.

Human herpesvirus-8 glycoprotein B interacts with Epstein-Barr virus (EBV) glycoprotein 110 but fails to complement the infectivity of EBV mutants

To characterize human herpesvirus 8 (HHV-8) gB, the open reading frame was PCR amplified from the HHV-8-infected cell line BCBL-1 and cloned into an expression vector. To facilitate detection of expressed HHV-8 gB, the cytoplasmic tail of the glycoprotein was tagged with the influenza hemagglutinin (HA) epitope. Expression of tagged HHV-8 gB (gB-HA), as well as the untagged form, was readily detected in CHO-K1 cells and several lymphoblastoid cell lines (LCLs). HHV-8 gB-HA was sensitive to endoglycosidase H treatment, and immunofluorescence revealed that HHV-8 gB-HA was detectable in the perinuclear region of CHO-K1 cells. These observations suggest that HHV-8 gB is not processed in the Golgi and localizes to the endoplasmic reticulum or nuclear membrane. Because both HHV-8 and EBV are gamma-herpesviruses, the ability of HHV-8 gB to interact with and functionally complement EBV gp110 was examined. HHV-8 gB-HA and EBV gp110 co-immunoprecipitated, indicating formation of hetero-oligomers. However, HHV-8 gB-HA and HHV-8 gB failed to restore the infectivity of gp110-negative EBV mutants. These findings indicate that although HHV-8 gB and EBV gp110 have similar patterns of intracellular localization and can interact, there is not sufficient functional homology to allow efficient complementation.

Expression of the enhanced green fluorescent protein by herpes simplex virus type 1 (HSV-1) as an in vitro or in vivo marker for virus entry and replication

Glycoprotein K (gK) is involved in membrane fusion phenomena during infectious virus production and egress and is an important determinant for neurovirulence. To assess better the in vitro and in vivo roles of gK in virus replication, a recombinant virus was constructed expressing an engineered enhanced green fluorescent protein (EGFP) under the control of the human cytomegalovirus immediate early gene promoter (HCMV-IEP) inserted in place of the gK gene. The EGFP gene insertion was confirmed by diagnostic polymerase chain reaction (PCR), and the presence of the EGFP protein was detected by western immunoblot analysis using anti-GFP monoclonal antibody. Fluorescence microscopy revealed that virus infected cells emitted bright fluorescence when examined using filters for fluorescein. Fluorescence emission was detected as early as 4 h post-infection. Fluorescence intensity increased over time and was stable at late times after infection at which point viral plaques continued to emit bright green fluorescence. The amount of fluorescence emitted by virus infected Vero cells was monitored by fluorescence cytometry using a FACS cytometer. At an MOI of 3, all infected cells emitted strong green fluorescence as quantified by cytometry at 48 h post-infection. The deltagK-EGFP expressing recombinant virus will enable the determination of the role of gK in virus entry and egress as well as the role of gK in the molecular pathogenesis of herpes simplex virus type 1 (HSV-1).

UL27.5 is a novel gamma2 gene antisense to the herpes simplex virus 1 gene encoding glycoprotein B

An antibody made against the herpes simplex virus 1 US5 gene predicted to encode glycoprotein J was found to react strongly with two proteins, one with an apparent Mr of 23,000 and mapping in the S component and one with a herpes simplex virus protein with an apparent Mr of 43,000. The antibody also reacted with herpes simplex virus type 2 proteins forming several bands with apparent Mrs ranging from 43,000 to 50,000. Mapping studies based on intertypic recombinants, analyses of deletion mutants, and ultimately, reaction of the antibody with a chimeric protein expressed by in-frame fusion of the glutathione S-transferase gene to an open reading frame antisense to the gene encoding glycoprotein B led to the definitive identification of the new open reading frame, designated UL27.5. Sequence analyses indicate the conservation of a short amino acid sequence common to US5 and UL27.5. The coding sequence of the herpes simplex virus UL27.5 open reading frame is strongly homologous to the sequence encoding the carboxyl terminus of the herpes simplex virus 2 UL27.5 sequence. However, both open reading frames could encode proteins predicted to be significantly larger than the mature UL27.5 proteins accumulating in the infected cells, indicating that these are either processed posttranslationally or synthesized from alternate, nonmethionine-initiating codons. The UL27.5 gene expression is blocked by phosphonoacetate, indicating that it is a gamma2 gene. The product accumulated predominantly in the cytoplasm. UL27.5 is the third open reading frame found to map totally antisense to another gene and suggests that additional genes mapping antisense to known genes may exist.

Herpes simplex virus type 1 glycoprotein B requires a cysteine residue at position 633 for folding, processing, and incorporation into mature infectious virus particles

Herpes simplex virus type 1 (HSV-1) glycoprotein B (gB) resides in the virus envelope in an oligomeric form and plays an essential role in virus entry into susceptible host cells. The oligomerizing domain is a movable element consisting of amino acids 626 to 653 in the gB external domain. This domain contains a single cysteine residue at position 633 (Cys-633) that is predicted to form an intramolecular disulfide bridge with Cys-596. In this study, we examined gB oligomerization, processing, and incorporation into mature virus during infection by two mutant viruses in which either the gB Cys-633 [KgB(C633S)] or both Cys-633 and Cys-596 [KgB(C596S/C633S)] residues were mutated to serine. The result of immunofluorescence studies and analyses of released virus particles showed that the mutant gB molecules were not transported to the cell surface or incorporated into mature virus envelopes and thus infectious virus was not produced. Immunoprecipitation studies revealed that the mutant gB molecules were in an oligomeric configuration and that these mutants produced hetero-oligomers with a truncated form of gB consisting of residues 1 to 43 and 595 to 904, the latter containing the oligomerization domain. Pulse-chase experiments in combination with endoglycosidase H treatment determined that the mutant molecules were improperly processed, having been retained in the endoplasmic reticulum (ER). Coimmunoprecipitation experiments revealed that the cysteine mutations resulted in gB misfolding and retention by the molecular chaperones calnexin, calreticulin, and Grp78 in the ER. The altered conformation of the gB mutant glycoproteins was directly detected by a reduction in monoclonal antibody recognition of two previously defined distinct antigenic sites located within residues 381 to 441 and 595 to 737. The misfolded molecules were not transported to the cell surface as hetero-oligomers with wild-type gB, suggesting that the conformational change could not be corrected by intermolecular interactions with the wild-type molecule. Together, these experiments confirmed that a disulfide bridge involving Cys-633 and Cys-596 is not essential for oligomerization but rather is required for proper folding and maintenance of a gB domain essential to complete posttranslational modification, transport, and incorporation into mature virus particles.

Use of a neural network secondary structure prediction to define targets for mutagenesis of herpes simplex virus glycoprotein B

Herpes simplex virus glycoprotein B (HSV gB) is essential for penetration of virus into cells, for cell-to-cell spread of virus, and for cell-cell fusion. Every member of the family Herpesviridae has a gB homolog, underlining its importance. The antigenic structure of gB has been studied extensively, but little is known about which regions of the protein are important for its roles in virus entry and spread. In contrast to successes with other HSV glycoproteins, attempts to map functional domains of gB by insertion mutagenesis have been largely frustrated by the misfolding of most mutants. The present study shows that this problem can be overcome by targeting mutations to the loop regions that connect alpha-helices and beta-strands, avoiding the helices and strands themselves. The positions of loops in the primary sequence were predicted by the PHD neural network procedure, using a multiple sequence alignment of 19 alphaherpesvirus gB sequences as input. Comparison of the prediction with a panel of insertion mutants showed that all mutants with insertions in predicted alpha-helices or beta-strands failed to fold correctly and consequently had no activity in virus entry; in contrast, half the mutants with insertions in predicted loops were able to fold correctly. There are 27 predicted loops of four or more residues in gB; targeting of mutations to these regions will minimize the number of misfolded mutants and maximize the likelihood of identifying functional domains of the protein.

Influence of membrane anchoring and cytoplasmic domains on the fusogenic activity of vesicular stomatitis virus glycoprotein G

Chimeric proteins in which the transmembrane anchoring sequence (TM) or both the TM and the cytoplasmic tail (CT) of vesicular stomatitis virus glycoprotein G were replaced with corresponding domains of viral or cellular integral membrane proteins were used to examine the influence of these domains on acidic-pH-induced membrane fusion by G protein. The TM and CT of G were also replaced with the lipid anchor glycosylphosphatidylinositol. Hybrids containing foreign TM or TM and CT sequences were fusogenic at acidic pH but glycosylphosphatidylinositol-anchored G was nonfusogenic at acidic pH. The results suggest that the fusogenic activity of G protein requires membrane anchoring by a hydrophobic peptide sequence and the specific amino acid sequence of the TM has no influence on fusogenic activity.

Herpes simplex virus type 1 glycoprotein K is not essential for infectious virus production in actively replicating cells but is required for efficient envelopment and translocation of infectious virions from the cytoplasm to the extracellular space

We characterized the glycoprotein K (gK)-null herpes simplex virus type 1 [HSV-1] (KOS) delta gK and compared it to the gK-null virus HSV-1 F-gKbeta (L. Hutchinson et al., J. Virol. 69:5401-5413, 1995). delta gK and F-gKbeta mutant viruses produced small plaques on Vero cell monolayers at 48 h postinfection. F-gKbeta caused extensive fusion of 143TK cells that was sensitive to melittin, a specific inhibitor of gK-induced cell fusion, while delta gK virus did not fuse 143TK cells. A recombinant plasmid containing the truncated gK gene specified by F-gKbeta failed to rescue the ICP27-null virus KOS (d27-1), while a plasmid with the delta gK deletion rescued the d27-1 virus efficiently. delta gK virus yield was approximately 100,000-fold lower in stationary cells than in actively replicating Vero cells. The plaquing efficiencies of delta gK and F-gKbeta virus stocks on VK302 cells were similar, while the plaquing efficiency of F-gKbeta virus stocks on Vero cells was reduced nearly 10,000-fold in comparison to that of delta gK virus. Mutant delta gK and F-gKbeta infectious virions accumulated within Vero and HEp-2 cells but failed to translocate to extracellular spaces. delta gK capsids accumulated in the nuclei of Vero but not HEp-2 cells. Enveloped delta gK virions were visualized in the cytoplasms of both Vero and HEp-2 cells, and viral capsids were found in the cytoplasm of HEp-2 cells within vesicles. Glycoproteins B, C, D, and H were expressed on the surface of delta gK-infected Vero cells in amounts similar to those for KOS-infected Vero cells. These results indicate that gK is involved in nucleocapsid envelopment, and more importantly in the translocation of infectious virions from the cytoplasm to the extracellular spaces, and that actively replicating cells can partially compensate for the envelopment but not for the cellular egress deficiency of the delta gK virus. Comparison of delta gK and F-gKbeta viruses suggests that the inefficient viral replication and plaquing efficiency of F-gKbeta virus in Vero cells and its syncytial phenotype in 143TK- cells are most likely due to expression of a truncated gK.

Inhibition of generation of authentic genomic termini of herpes simplex virus type 1 DNA in temperature-sensitive mutant BHK-21 cells with a mutated CCG1/TAF(II)250 gene

A temperature-sensitive (ts) mutant from the BHK-21 hamster cell line, tsBN462, has a defect in progression of the G1 phase at the nonpermissive temperature of 39.5 degrees C. The ts mutation in tsBN462 is located in the CCG1 gene, encoding the general transcription factor TAF(II)250. In tsBN462 at 39.5 degrees C, infectious progeny of herpes simplex virus type 1 (HSV-1) was not produced and generation of authentic genomic termini of HSV-1 was inhibited. HSV-1 concatemers containing L components in two possible orientations were produced in tsBN462 at 39.5 degrees C; hence, the generation of authentic genomic termini seemed to be dispensable for inversion of the L component. As production of mRNAs of HSV-1 genes of three kinetic classes in the tsBN462 at 39.5 degrees C was comparable to findings under permissive conditions, the sequential and regulated manner in which HSV-1 gene expression is processed is likely to be maintained in the nonpermissive condition.

Disulfide bonds of herpes simplex virus type 2 glycoprotein gB

Glycoprotein B (gB) is the most highly conserved envelope glycoprotein of herpesviruses. The gB protein is required for virus infectivity and cell penetration. Recombinant forms of gB being used for the development of subunit vaccines are able to induce virus-neutralizing antibodies and protective efficacy in animal models. To gain structural information about the protein, we have determined the location of the disulfide bonds of a 696-amino-acid residue truncated, recombinant form of herpes simplex virus type 2 glycoprotein gB (HSV gB2t) produced by expression in Chinese hamster ovary cells. The purified protein, which contains virtually the entire extracellular domain of herpes simplex virus type 2 gB, was digested with trypsin under nonreducing conditions, and peptides were isolated by reversed-phase high-performance liquid chromatography (HPLC). The peptides were characterized by using mass spectrometry and amino acid sequence analysis. The conditions of cleavage (4 M urea, pH 7) induced partial carbamylation of the N termini of the peptides, and each disulfide peptide was found with two or three different HPLC retention times (peptides with and without carbamylation of either one or both N termini). The 10 cysteines of the molecule were found to be involved in disulfide bridges. These bonds were located between Cys-89 (C1) and Cys-548 (C8), Cys-106 (C2) and Cys-504 (C7), Cys-180 (C3) and Cys-244 (C4), Cys-337 (C5) and Cys-385 (C6), and Cys-571 (C9) and Cys-608 (C10). These disulfide bonds are anticipated to be similar in the corresponding gBs from other herpesviruses because the 10 cysteines listed above are always conserved in the corresponding protein sequences.

Deletion of the carboxy-terminus of herpes simplex virus type 1 (HSV-1) glycoprotein B does not affect oligomerization, heparin-binding activity, or its ability to protect against HSV challenge

A recombinant vaccinia virus designated VgBt which expresses a truncated secreted herpes simplex virus gB (gBt) was constructed and compared to V11gB, a vaccinia recombinant previously studied which expresses gB exclusively on the surface of infected cells. Indirect immunofluorescence assay (IFA) revealed that gBt was strongly associated with the surface of infected cells despite being released slowly into the cell culture medium. Both gB and gBt existed as oligomers, and both membrane bound and secreted forms of gBt exhibited heparin-binding activity. In protection studies VgBt and V11gB conferred equivalent protection against both homologous (HSV-1) and heterologous (HSV-2) challenge with HSV.

Glycoprotein B of herpes simplex virus type 1 oligomerizes through the intermolecular interaction of a 28-amino-acid domain

Herpes simplex virus type 1 glycoprotein B (gB) is an envelope component that plays an essential role in virus infection. The biologically active form of gB is an oligomer that contributes to the process of viral envelope fusion with the cell surface membrane, resulting in viral penetration and initiation of the replication cycle. In previous studies, two discontinuous sites for oligomer formation were identified: a nonessential upstream site located between residues 93 and 282 and an essential downstream site located between residues 596 and 711. In this study, in vitro-transcribed and -translated gB test molecules were used to characterize the more active essential membrane-proximal domain. A series of gB test polypeptides mutated in this downstream oligomerization domain were assayed for their abilities to form oligomers with a mutant gB capture polypeptide containing the analogous wild-type domain. Detection of oligomers was achieved by coimmunoprecipitation of two gB mutant molecules by using a monoclonal antibody specific for a hemagglutinin epitope tag introduced into the coding sequence of the capture polypeptide. Analysis of the immune-precipitated products by sodium dodecyl sulfate-polyacrylamide gel electrophoresis demonstrated that the downstream oligomerization domain resided within residues 626 to 676. This region was further resolved into two segments, residues 626 to 653 and 653 to 675, each of which was independently sufficient to form oligomers. However, residues 626 to 653 provided for a stronger interaction between gB monomers. Moreover, this stretch of 28 amino acids was shown to form oligomers when introduced into the carboxy-terminal region of gB monomers lacking this domain at the normal site, thus indicating that this domain was functionally independent of its natural location within the gB molecule. Further analysis of the sequence within residues 596 to 653 by using mutant test polypeptides altered in individual amino acids revealed that cysteines 9 and 10 located at positions 596 and 633, respectively, were not required for oligomer formation but contributed to dimer formation and/or stabilization. The results of this study suggest that oligomerization of gB monomers is induced by interactions between contiguous residues localized within the ectodomain near the site of molecule insertion into the viral envelope membrane.

Two mutations in gB-1 and gD-1 of herpes simplex virus type 1 are involved in the "fusion from without" phenotype in different cell types

Previous studies have shown that certain strains of herpes simplex viruses type 1 (HSV-1) are able to induce "fusion from without" (FFWO) which means no transcription or translation of the viral genome happens. The main determinants for FFWO in BHK cells are mutations in the C-terminal part of gB-1. But single mutations in this part of the genome are not sufficient to transfer the FFWO phenotype also to Vero cells. Here, we report that FFWO of HSV strains indeed need additional mutations in the N-terminal part of gD in order to produce the FFWO phenotype in BHK and Vero cells. By marker transfer we are able to show that loss of mutations in the N-terminal part of gD influences the ability to induce FFWO in Vero cells but not in BHK cells. We assume that a mutated gD allows the entrance of a multiple number of virus particles into the cell and enhances therefore the fusion activity of the mutated gB. Mutations in gD alone are not sufficient for fusion activity of HSV.

Adherence of pilus- Opa+ gonococci to epithelial cells in vitro involves heparan sulfate

Neisseria gonorrhoeae attaches to host epithelial cells via pili and opacity-associated (Opa) outer membrane proteins. Pilus- gonococci (Gc) of strain MS11 adhere to both human and nonhuman cells, but only when particular Opa proteins are expressed; OpaA+ variants adhere best, OpaC+ variants are next best, and the seven other Opa+ variants adhere poorly or not at all. The adherence of OpaA+ Gc to Chinese hamster ovary (CHO) cells is inhibited by heparin or heparan sulfate (HS), but not by chondroitin sulfate. OpaA+ Gc do not adhere to CHO cells devoid of HS proteoglycans; low concentrations of heparin restore OpaA+ Gc adherence to these HS-deficient CHO cells and high concentrations inhibit it. 3H-heparin binding to whole Gc parallels their adherence abilities (OpaA+ > OpaC+ > OpaH+ >> Opas B, D, E, F, G, I = Opa- = 0). Opa proteins separated by SDS-PAGE also bind 3H-heparin. These data suggest that adherence of pilus-, Opa+ Gc involves HS-proteoglycan of eukaryotic cells.

Sequential isolation of proteoglycan synthesis mutants by using herpes simplex virus as a selective agent: evidence for a proteoglycan-independent virus entry pathway

A novel mouse L-cell mutant cell line defective in the biosynthesis of glycosaminoglycans was isolated by selection for cells resistant to herpes simplex virus (HSV) infection. These cells, termed sog9, were derived from mutant parental gro2C cells, which are themselves defective in heparan sulfate biosynthesis and 90% resistant to HSV type 1 (HSV-1) infection compared with control L cells (S. Gruenheid, L. Gatzke, H. Meadows, and F. Tufaro, J. Virol. 67:93-100, 1993). In this report, we show that sog9 cells exhibit a 3-order-of-magnitude reduction in susceptibility to HSV-1 compared with control L cells. In steady-state labeling experiments, sog9 cells accumulated almost no [35S]sulfate-labeled or [6-3H]glucosamine-labeled glycosaminoglycans, suggesting that the initiation of glycosaminoglycan assembly was specifically reduced in these cells. Despite these defects, sog9 cells were fully susceptible to vesicular stomatitis virus (VSV) and permissive for both VSV and HSV replication, assembly, and egress. HSV plaques formed in the sog9 monolayers in proportion to the amount of input virus, suggesting the block to infection was in the virus entry pathway. More importantly, HSV-1 infection of sog9 cells was not significantly reduced by soluble heparan sulfate, indicating that infection was glycosaminoglycan independent. Infection was inhibited by soluble gD-1, however, which suggests that glycoprotein gD plays a role in the infection of this cell line. The block to sog9 cell infection by HSV-1 could be eliminated by adding soluble dextran sulfate to the inoculum, which may act by stabilizing the virus at the sog9 cell surface. Thus, sog9 cells provide direct genetic evidence for a proteoglycan-independent entry pathway for HSV-1, and results with these cells suggest that HSV-1 is a useful reagent for the direct selection of novel animal cell mutants defective in the synthesis of cell surface proteoglycans.

Characterization of murine gammaherpesvirus 68 glycoprotein B (gB) homolog: similarity to Epstein-Barr virus gB (gp110)

Murine gammaherpesvirus 68 (MHV-68) is a natural pathogen of murid rodents and displays similar pathobiological characteristics to those of the human gammaherpesvirus Epstein-Barr virus (EBV). However, in contrast to EBV, MHV-68 will replicate in epithelial cells in vitro. It has therefore been proposed that MHV-68 may be of use as a model for the study of gammaherpesviruses, EBV in particular, both in vitro and in vivo. The EBV homolog of herpes simplex virus glycoprotein B (gB), termed gp110, is somewhat unusual compared with those of many other herpesviruses. We therefore decided to characterize the homolog of gB encoded by MHV-68 (termed MHV gB) to observe the properties of a gammaherpesvirus gB produced in epithelial cells and also to test the relatedness of MHV-68 and EBV. The MHV gB-coding sequence was determined from cloned DNA. The predicted amino acid sequence shared closest homology with gammaherpesvirus gB homologs. Biochemical analysis showed that MHV gB was a glycoprotein with a molecular weight of 105,000. However, the glycans were of the N-linked, high-mannose type, indicating retention in the endoplasmic reticulum. In line with this, MHV gB was localized to the cytoplasm and nuclear margins of infected cells but was not detected on the cell surface or in virions. Additionally, anti-MHV gB antisera were nonneutralizing. Thus, the MHV gB was unlike many other herpesvirus gBs but was extremely similar to the EBV gB. This highlights the close relationship between MHV-68 and EBV and underlines the potential of MHV-68 as a model for EBV in epithelial cells both in vitro and in vivo.

Glycoprotein B of bovine herpesvirus type 4: its phylogenetic relationship to gB equivalents of the herpesviruses

In order to estimate the phylogenetic relationship of BHV-4 among the herpesviruses, we have cloned and sequenced its glycoprotein B (gB). The 2.6 kb open reading frame codes for a 874 amino acid long protein. The comparison of its deduced amino acid sequence with those of its counterparts in 19 distinct herpesviruses groups BHV-4 into the gamma-herpesvirinae. The calculation of an evolutionary tree emphasized that BHV-4 is more closely related to herpesvirus saimiri (HVS) than to Epstein-Barr virus (EBV). However, in contrast to EBV and HVS, the gB of BHV-4 contains a putative protease cleavage site and 20 potential N-glycosylation sites. The alignment of the amino acid sequences revealed that 10 cysteine and 7 proline residues, as well as the motifs SPF and GQLG, were completely conserved among the 20 investigated gBs.

Transformed cells producing the glycoprotein D of HSV-1 are resistant to infection with clinical strains of HSV

The generality of the resistance exhibited by gD producing cells to HSV-1 infection was tested. We tested three different cell lines producing various amounts of gD for resistance against three HSV-1 strains. The strains used were the prototype laboratory F strain and two recently isolated low passage local clinical strains, VG and VD. The results indicate that: (i) the resistance of the cell lines is directly related to the amount of gD they produce, (ii) the cell lines showed greater resistance against the two local clinical HSV-1 strains than against the laboratory strain, and (iii) the resistance is not mediated at the level of virus adsorption to the cell membranes.

The herpes simplex virus type 1 particle: structure and molecular functions. Review article

This review is a summary of our present knowledge with respect to the structure of the virion of herpes simplex virus type 1. The virion consists of a capsid into which the DNA is packaged, a tegument and an external envelope. The protein compositions of the structures outside the genome are described as well as the functions of individual proteins. Seven capsid proteins are identified, and two of them are mainly present in precursors of mature DNA-containing capsids. The protein components of the 150 hexamers and 12 pentamers in the icosahedral capsid are known. These capsomers all have a central channel and are connected by Y-shaped triplexes. In contrast to the capsid, the tegument has a less defined structure in which 11 proteins have been identified so far. Most of them are phosphorylated. Eleven virus-encoded glycoproteins are present in the envelope, and there may be a few more membrane proteins not yet identified. Functions of these glycoproteins include attachment to and penetration of the cellular membrane. The structural proteins, their functions, coding genes and localizations are listed in table form.

Membrane anchoring domain of herpes simplex virus glycoprotein gB is sufficient for nuclear envelope localization

We have used the glycoprotein gB of herpes simplex virus type 1 (gB-1), which buds from the inner nuclear membrane, as a model protein to study localization of membrane proteins in the nuclear envelope. To determine whether specific domains of gB-1 glycoprotein are involved in localization in the nuclear envelope, we have used deletion mutants of gB-1 protein as well as chimeric proteins constructed by replacing the domains of the cell surface glycoprotein G of vesicular stomatitis virus with the corresponding domains of gB. Mutant and chimeric proteins expressed in COS cells were localized by immunoelectron microscopy. A chimeric protein (gB-G) containing the ectodomain of gB and the transmembrane and cytoplasmic domains of G did not localize in the nuclear envelope. When the ectodomain of G was fused to the transmembrane and cytoplasmic domains of gB, however, the resulting chimeric protein (G-gB) was localized in the nuclear envelope. Substitution of the transmembrane domain of G with the 69 hydrophobic amino acids containing the membrane anchoring domain of gB allowed the hybrid protein (G-tmgB) to be localized in the nuclear envelope, suggesting that residues 721 to 795 of gB can promote retention of proteins in the nuclear envelope. Deletion mutations in the hydrophobic region further showed that a transmembrane segment of 21 hydrophobic amino acids, residues 774 to 795 of gB, was sufficient for localization in the nuclear envelope. Since wild-type gB and the mutant and chimeric proteins that were localized in the nuclear envelope were also retained in the endoplasmic reticulum, the membrane spanning segment of gB could also influence retention in the endoplasmic reticulum.

Proteolytic cleavage of bovine herpesvirus 1 (BHV-1) glycoprotein gB is not necessary for its function in BHV-1 or pseudorabies virus

Glycoprotein B homologs represent the most highly conserved group of herpesvirus glycoproteins. They exist in oligomeric forms based on a dimeric structure. Despite the high degree of sequence and structural conservation, differences in posttranslational processing are observed. Whereas gB of herpes simplex virus is not proteolytically processed after oligomerization, most other gB homologs are cleaved by a cellular protease into subunits that remain linked via disulfide bonds. Proteolytic cleavage is common for activation of viral fusion proteins, and it has been shown that herpesvirus gB homologs are essential for membrane fusion events during infection, e.g., virus penetration and direct viral cell-to-cell spread. To analyze the importance of proteolytic cleavage for the function of gB homologs, we isolated a mutant bovine herpesvirus 1 (BHV-1) expressing a BHV-1 gB that is no longer proteolytically processed because of a deletion of the proteolytic cleavage site and analyzed its phenotype in cell culture. We showed previously that BHV-1 gB can functionally substitute for the homologous glycoprotein in pseudorabies virus (PrV), based on the isolation of a PrV gB-negative PrV recombinant that expresses BHV-1 gB (A. Kopp and T. C. Mettenleiter, J. Virol, 66:2754-2762, 1992). Therefore, we also isolated a mutant PrV lacking PrV gB but expressing a noncleavable BHV-1 gB. Our results show that cleavage of BHV-1 gB is not essential for its function in either a BHV-1 or a PrV background. Compared with the PrV recombinant expressing cleavable BHV-1 gB, deletion of the cleavage site in the recombinant PrV did not detectably alter the viral phenotype, as analyzed by plaque assays, one-step growth kinetics, and penetration kinetics. In the BHV-1 mutant, the uncleaved BHV-1 gB was functionally equivalent to the wild-type protein with regard to penetration and showed only slightly delayed one-step growth kinetics compared with parental wild-type BHV-1. However, the resulting plaques were significantly smaller, indicating a role for proteolytic cleavage of BHV-1 gB in cell-to-cell spread of BHV-1.

Evidence for a multistep mechanism for cell-cell fusion by herpes simplex virus with mutations in the syn 3 locus using heparin derivatives during fusion from within

Addition of heparin-Na+ as well as related substances of high and intermediate MW (Arteparon and polyanion SP54) 3 h after infection inhibit fusion from within (FFWI) induced by HSV strains with mutations in the syn 3 locus only. The concentration of heparin-Na+ required to inhibit FFWI is 10-fold higher (1 mg/ml) than that needed to inhibit adsorption. Instead of fusion, cell rounding is observed. The effect is readily reversible. A low MW heparin disaccharide is ineffective. Neomycin, at a concentration of 8 mM, inhibits FFWI induced by all HSV-1 but not HSV-2 strains, whereas adsorption is inhibited at 3 mM. We conclude from our observations that cell-cell fusion (FFWI) induced by syn 3 locus mutants of HSV-1 depends on a multistep mechanism. One may be constituted by pre-existing cell-cell connections or microfusions leading to cell rounding, whereas another may be active using newly appearing cell bridges during FFWI; also the three-dimensional structure of the cell membrane may be of importance. Moreover, the molecular mechanisms of FFWI induced by mutations in the syn 3 locus compared to the other 5 syn loci should be different.

Herpes simplex virus glycoproteins E and I facilitate cell-to-cell spread in vivo and across junctions of cultured cells

Herpes simplex virus (HSV) glycoproteins E and I (gE and gI) can act as a receptor for the Fc domain of immunoglobulin G (IgG). To examine the role of HSV IgG Fc receptor in viral pathogenesis, rabbits and mice were infected by the corneal route with HSV gE- or gI- mutants. Wild-type HSV-1 produced large dendritic lesions in the corneal epithelium and subsequent stromal disease leading to viral encephalitis, whereas gE- and gI- mutant viruses produced microscopic punctate or small dendritic lesions in the epithelium and no corneal disease or encephalitis. These differences were not related to the ability of the gE-gI oligomer to bind IgG because the differences were observed before the appearance of anti-HSV IgG and in mice, in which IgG binds to the Fc receptor poorly or not at all. Mutant viruses produced small plaques on monolayers of normal human fibroblasts and epithelial cells. Replication of gE- and gI- mutant viruses in human fibroblasts were normal, and the rates of entry of mutant and wild-type viruses into fibroblasts were similar; however, spread of gE- and gI- mutant viruses from cell to cell was significantly slower than that of wild-type HSV-1. In experiments in which fibroblast monolayers were infected with low multiplicities of virus and multiple rounds of infection occurred, the presence of neutralizing antibodies in the culture medium caused the yields of mutant viruses to drop dramatically, whereas there was a lesser effect on the production of wild-type HSV. It appears that cell-to-cell transmission of wild-type HSV-1 occurs by at least two mechanisms: (i) release of virus from cells and entry of extracellular virus into a neighboring cell and (ii) transfer of virus across cell junctions in a manner resistant to neutralizing antibodies. Our results suggest that gE- and gI- mutants are defective in the latter mechanism of spread, suggesting the possibility that the gE-gI complex facilitates virus transfer across cell junctions, a mode of spread which may predominate in some tissues. It is ironic that the gE-gI complex, usually considered an IgG Fc receptor, may, through its ability to mediate cell-to-cell spread, actually protect HSV from IgG in a manner different than previously thought.

Herpes simplex type 2 in a patient with Mollaret's meningitis: demonstration by polymerase chain reaction

We describe a patient with recurrent self-limited aseptic meningitis meeting the criteria for Mollaret's syndrome, in whom extensive serological investigation and cerebrospinal fluid analysis failed to reveal a specific cause. Using polymerase chain reaction techniques to amplify herpes simplex viral DNA, we were able to identify the presence of herpes simplex virus type 2 in the cerebrospinal fluid. The duration of clinical illness may have been shortened by treatment with intravenous acyclovir. We suggest that herpes simplex virus may be a more common cause of aseptic meningitis than has been demonstrated by current commonly available serological and culture techniques.

Cyclosporin A resistance of herpes simplex virus-induced "fusion from within" as a phenotypical marker of mutations in the Syn 3 locus of the glycoprotein B gene

We here report research in which nine strains of Herpes simplex virus (HSV) with fusing activity were investigated in order to establish precise phenotypical markers of mutations in the carboxy terminus of glycoprotein B (gB). The gene region encoding the carboxy terminus of gB was isolated, then cloned, and finally sequenced. Our investigation showed that seven strains have different mutations in the syn 3 locus. We observed no base difference in the gB gene region encoding the carboxy terminus of gB of two other strains. Strains with a mutation in the carboxy terminus of gB induced fusion from within (FFWI) in the presence of Cyclosporin A (CyA) at a concentration up to 150 microM. There are two clusters of mutations correlated with the syn 3 locus and selected in the presence of CyA: One group comprised of amino acid substitutions at position 816, the other of changes at positions 853, 854, and 857. In contrast, the fusion induced by strains with mutations in other syn loci is CyA sensitive. CyA inhibits the FFWI at concentrations of 20-60 microM. The results demonstrate the CyA resistance of HSV-induced FFWI should serve as a phenotypical marker of mutations in the carboxy terminus of gB. Moreover, our investigations revealed that fusion from without (FFWO) does not always serve as a phenotypical marker of mutations in the syn 3 locus. On the one hand, all FFWO-positive strains possess a syn 3 locus mutation, whilst, on the other hand, five strains with mutations in the carboxy terminus of gB are FFWO negative.(ABSTRACT TRUNCATED AT 250 WORDS)

Glycoprotein B is a specific determinant of herpes simplex virus type 1 neuroinvasiveness

Herpes simplex virus type 1 strains ANG and KOS lack neuroinvasiveness when inoculated on the footpads of mice, and because the strains are able to complement each other, the genes associated with this phenotype differ. In this study, we used marker rescue techniques to show that at least two genes cloned from ANG are required to restore neuroinvasiveness to KOS. One of the two fragments required is the 6.3-kb BamHI-A/EcoRI-D fragment (0.15 to 0.19 map units). The second has been identified as the sequence encoding glycoprotein B (gB) (UL27). Analysis of ANG and KOS DNA sequences in the relevant region of the gB gene revealed two nucleotide differences which result in amino acid differences in the gB protein. One appears to be unique to the strain of KOS used in our laboratory. The second, at codon 523 of the mature gB protein, encodes a valine in KOS and an alanine in ANG. Recombinant KOS viruses which contained ANG sequences in this region were constructed, and two independently selected recombinants demonstrated increased neuroinvasiveness in mice. From these results, we conclude that gB significantly influences neuroinvasiveness. Mechanisms by which this might occur are discussed.

Effects of deletions in the carboxy-terminal hydrophobic region of herpes simplex virus glycoprotein gB on intracellular transport and membrane anchoring

The gB glycoprotein of herpes simplex virus type 1 is involved in viral entry and fusion and contains a predicted membrane-anchoring sequence of 69 hydrophobic amino acids, which can span the membrane three times, near the carboxy terminus. To define the membrane-anchoring sequence and the role of this hydrophobic stretch, we have constructed deletion mutants of gB-1, lacking one, two, or three predicted membrane-spanning segments within the 69 amino acids. Expression of the wild-type and mutant glycoproteins in COS-1 cells show that mutant glycoproteins lacking segment 3 (amino acids 774 to 795 of the gB-1 protein) were secreted from the cells. Protease digestion and alkaline extraction of microsomes containing labeled mutant proteins further showed that segment 3 was sufficient for stable membrane anchoring of the glycoproteins, indicating that this segment may specify the transmembrane domain of the gB glycoprotein. Also, the mutant glycoproteins containing segment 3 were localized in the nuclear envelop, which is the site of virus budding. Deletion of any of the hydrophobic segments, however, affected the intracellular transport and processing of the mutant glycoproteins. The mutant glycoproteins, although localized in the nuclear envelope, failed to complement the gB-null virus (K082). These results suggest that the carboxy-terminal hydrophobic region contains essential structural determinants of the functional gB glycoprotein.

Cross-hybridization of equid herpesvirus-2 (EHV-2) and herpes simplex virus-1 (HSV-1) genes to equid herpesvirus-1 (EHV-1)

In contrast to previous findings, the Ab4 isolate of equid herpesvirus-1 (EHV-1) was shown to share homology with the G9 isolate of equid herpesvirus-2 (EHV-2). Using Southern blotting and stringent hybridization conditions, a significant proportion of this cross-hybridization was identified by the immediate-early gene-3 (IE-3) probe from herpes simplex virus-1 (HSV-1). The HSV-1 UL48 gene probe (encoding the IE gene transactivating protein VmW65, which is also known as alpha-TIF or VP16) was used to identify and isolate its counterpart in EHV-1. The relevance of shared homology to transactivation is being investigated.

Syncytium-inducing mutations localize to two discrete regions within the cytoplasmic domain of herpes simplex virus type 1 glycoprotein B

Herpes simplex virus type 1 glycoprotein B (gB) is essential for virus entry, an event involving fusion of the virus envelope with the cell surface membrane, and virus-induced cell-cell fusion, resulting in polykaryocyte, or syncytium, formation. The experiments described in this report employed a random mutagenesis strategy to develop a more complete genetic map of mutations resulting in the syn mutant phenotype. The results indicate that syn mutations occur within two essential and highly conserved hydrophilic, alpha-helical regions of the gB cytoplasmic domain. Region I is immediately proximal to the transmembrane domain and includes residues R796 to E816/817. Region II is localized centrally in the cytoplasmic domain and includes residues A855 and R858. Positively charged residues were particularly affected in both regions, suggesting that charge interactions may be required to suppress the syn mutant phenotype. No syn mutations were identified within the transmembrane domain. A virus containing a rate of entry (roe) mutation at residue A851, either within or immediately proximal to syn region II, was isolated. Since roe mutations have also been discovered in the external domain of gB, it appears likely that the external and cytoplasmic domains cooperate in virus penetration. Moreover, the observation that both roe and syn mutations occur in the cytoplasmic domain further suggests that gB functions in an analogous manner in both membrane fusion events. It might be predicted from these observations that membrane fusion involves transduction of a fusion signal along the gB molecule through the transmembrane domain. Communication between the external and cytoplasmic domain may thus be required for gB-mediated membrane fusion events.

A mutant herpes simplex virus type 1 unable to express glycoprotein L cannot enter cells, and its particles lack glycoprotein H

Herpes simplex virus type 1 (HSV-1) glycoprotein H (gH) is essential for virus entry into cells and forms a hetero-oligomer with a newly described viral glycoprotein, gL. Normal folding, posttranslational processing, and intracellular transport of both gH and gL depend upon the coexpression of gH and gL in cells infected with vaccinia virus vectors (L. Hutchinson, H. Browne, V. Wargent, N. Davis-Poynter, S. Primorac, K. Goldsmith, A. C. Minson, and D. C. Johnson, J. Virol. 66:2240-2250, 1992). Homologs of gH and gL have been found in herpesviruses of all subgroups, and thus it appears likely that the gH-gL complex serves a highly conserved function during herpesvirus penetration into cells. To examine the role of gL in the infectious cycle of HSV-1, a mutant HSV-1 unable to express gL was constructed by inserting a lacZ gene cassette into the coding sequences of the UL1 (gL) gene. Because gL was found to be essential for virus replication, cell lines capable of expressing gL were constructed to complement the virus mutant. In the absence of gL, virus particles were produced, and these particles reached the cell surface; however, gL-negative particles purified from infected cells were also deficient in gH. Mutant virions lacking gH and gL were able to adsorb onto cells but were unable to enter cells and initiate an infection. Further, the role of gL in fusion of infected cells was reexamined. A mutation in HSV-1 (804) which produces the syncytial phenotype had previously been mapped to a region of the HSV-1 genome which includes the UL1 gene and no other open reading frame. However, in contrast to this previous report, we found that the syncytial mutation in 804 affects the UL53 gene, which encodes gK, a gene commonly mutated in syncytial viruses.

Truncation of the carboxy-terminal 28 amino acids of glycoprotein B specified by herpes simplex virus type 1 mutant amb1511-7 causes extensive cell fusion

Three amber mutations were introduced proximal to the syn3 locus of the herpes simplex virus type 1 glycoprotein B (gB) gene specifying gB derivatives lacking the carboxy-terminal 28, 49, or 64 amino acids. A complementation system that utilized gBs expressed in COS cells to complement gB-null virus K delta T was established. The 49- or 64-amino-acid-truncated gBs failed to complement gB-null virus K delta T, while the 28-amino-acid-truncated gB complemented K delta T efficiently. Mutant herpes simplex virus type 1 KOS (amb1511-7) specifying the 28-amino-acid-truncated gB fused Vero cells extensively.

Sequence analysis of herpes simplex virus gB gene homologs of two platyrrhine monkey alpha-herpesviruses

Homologs of the herpes simplex virus gB gene were identified in two alpha-herpesviruses of platyrrhine monkeys, Herpesvirus saimiri 1 (HVS 1) and H. ateles 1 (HVA 1). These genes were cloned and sequenced in their entirety. Analysis of the predicted amino acid sequences indicated that the gB glycoproteins of these two viruses are of similar size, have 10 Cys residues and 5 potential N-linked glycosylation sites which align exactly with those in other primate alpha-herpesvirus gB polypeptides, and have a similar distribution of predicted secondary structural features, all of which indicate a conserved structure of the gB polypeptide. Alignment of these two gB sequences with those of four other primate alpha-herpesviruses (SA 8, B virus, HSV 1 and HSV 2) revealed localized regions of extensive sequence divergence as well as highly conserved regions. On comparison of the six primate virus gB sequences, the gBs of the two platyrrhine monkey viruses form a subgroup separate from that of the four catarrhine virus gBs. The degree of relatedness of the HVA 1 and HVS 1 gB sequences to each other was equivalent to the degree of relatedness between the human and the cercopithecine monkey virus gB sequences.

The UL16 gene of human cytomegalovirus encodes a glycoprotein that is dispensable for growth in vitro

The UL16 gene of human cytomegalovirus (HCMV) encodes a predicted translation product with features characteristic of glycoproteins (signal and anchor sequences and eight potential N-linked glycosylation sites). Antisera were raised against the UL16 gene product expressed in Escherichia coli as a beta-galactosidase fusion protein. The antisera detected a 50-kDa glycoprotein in HCMV-infected cells that was absent from purified virions. The UL16 glycoprotein was synthesized at early times after infection and accumulated to the highest levels at late times after infection. A recombinant HCMV in which UL16 coding sequences were interrupted by a lacZ expression cassette was constructed by insertional mutagenesis. Analysis of the phenotype of the recombinant virus indicated that the UL16 gene product is nonessential for virus infectivity and growth in tissue culture.