Identification of transforming genes of subgroup A and C strains of Herpesvirus saimiri

Idiopathic pulmonary fibrosis is strongly associated with productive infection by herpesvirus saimiri

Idiopathic pulmonary fibrosis is a fatal disease without effective therapy or diagnostic test. To investigate a potential role for γ-herpesviruses in this disease, 21 paraffin-embedded lung biopsies from patients diagnosed with idiopathic pulmonary fibrosis and 21 lung biopsies from age-matched controls with pulmonary fibrosis of known etiology were examined for a series of γ-herpesviruses' DNA/RNA and related proteins using in situ hybridization and reverse transcriptase-polymerase chain reaction (RT-PCR)-based methods. We detected four proteins known to be in the genome of several γ-herpesviruses (cyclin D, thymidylate synthase, dihydrofolate reductase, and interleukin-17) that were strongly co-expressed in the regenerating epithelial cells of each of the 21 idiopathic pulmonary fibrosis cases and not in the benign epithelia of the controls. Among the γ-herpesviruses, only herpesvirus saimiri expresses all four of these 'pirated' mammalian proteins. We found herpesvirus saimiri DNA in the regenerating epithelial cells of 21/21 idiopathic pulmonary fibrosis cases using four separate probe sets but not in the 21 controls. RT-PCR showed that the source of the cyclin D RNA in active idiopathic pulmonary fibrosis was herpesvirus saimiri and not human. We cloned and sequenced part of genome corresponding to the DNA polymerase herpesvirus saimiri gene from an idiopathic pulmonary fibrosis sample and it matched 100% with the published viral sequence. These data are consistent with idiopathic pulmonary fibrosis representing herpesvirus saimiri-induced pulmonary fibrosis. Thus, treatment directed against viral proliferation and/or viral-associated proteins may halt disease progression. Further, demonstration of the viral nucleic acids or proteins may help diagnose the disease.

Bioengineered collagens: emerging directions for biomedical materials

Mammalian collagen has been widely used as a biomedical material. Nevertheless, there are still concerns about the variability between preparations, particularly with the possibility that the products may transmit animal-based diseases. Many groups have examined the possible application of bioengineered mammalian collagens. However, translating laboratory studies into large-scale manufacturing has often proved difficult, although certain yeast and plant systems seem effective. Production of full-length mammalian collagens, with the required secondary modification to give proline hydroxylation, has proved difficult in E. coli. However, recently, a new group of collagens, which have the characteristic triple helical structure of collagen, has been identified in bacteria. These proteins are stable without the need for hydroxyproline and are able to be produced and purified from E. coli in high yield. Initial studies indicate that they would be suitable for biomedical applications.

Genome-wide histone acetylation profiling of Herpesvirus saimiri in human T cells upon induction with a histone deacetylase inhibitor

Herpesviruses establish latency in suitable host cells after primary infection and persist in their host organisms for life. Most of the viral genes are silenced during latency, also enabling the virus to escape from an immune response. This study addresses the control of viral gene silencing by epigenetic mechanisms, using Herpesvirus saimiri (HVS) as a model system. Strain C488 of this gamma-2-herpesvirus can transform human T cells to stable growth in vitro, and it persists in the nuclei of those latently infected T cells as a nonintegrating, circular, and histone-associated episome. The whole viral genome was probed for histone acetylation at high resolution by chromatin immunoprecipitation-on-chip (ChIP-on-chip) with a custom tiling microarray. Corresponding to their inactive status in human T cells, the lytic promoters consistently revealed a heterochromatic phenotype. In contrast, the left terminal region of the genome, which encodes the stably expressed oncogenes stpC and tip as well as the herpesvirus U RNAs, was associated with euchromatic histone acetylation marks representing "open" chromatin. Although HVS latency in human T lymphocytes is considered a stable and irreversible state, incubation with the histone deacetylase inhibitor trichostatin A resulted in changes reminiscent of the induction of early lytic replication. However, infectious viral particles were not produced, as the majority of cells went into apoptosis. These data show that epigenetic mechanisms are involved in both rhadinoviral latency and transition into lytic replication.

Rhadinovirus vector-derived human telomerase reverse transcriptase expression in primary T cells

The rhadinovirus herpesvirus saimiri (HVS) as a gene delivery vector allows large DNA insertions and long-termed gene expression. In the case of T-cell transduction, such vectors use the viral transformation-associated genes of HVS C488 for T-cell amplification. In this report, we investigated whether the gene for the catalytic telomerase subunit human telomerase reverse transcriptase (hTERT) can substitute for the transformation-associated genes in rhadinoviral T-cell transduction and amplification. By using virus mutants generated by en passant mutagenesis from bacterial artificial chromosomes, we observed a very early and functional transgene expression even by virus mutants without transformation-associated genes. The markers of T-cell transformation by HVS, namely CD2 hyperreactivity, overexpression of interleukin-26, and of the tyrosine kinase Lyn could neither be induced nor enhanced by ectopic hTERT expression. When the viral transformation-associated genes were replaced by the hTERT gene, it was not sufficient for growth transformation, although hTERT was efficiently transduced and functionally expressed by the rhadinovirus vector. Thus, the transformation-associated proteins StpC and Tip are responsible for the T-cell phenotype after transduction by HVS and, additionally, modulate telomerase activity independently of hTERT expression.

Immune evasion by gammaherpesvirus genome maintenance proteins

Viruses that establish lifelong latent infections must ensure that the viral genome is maintained within the latently infected cell throughout the life of the host, yet at the same time must also be capable of avoiding elimination by the immune surveillance system. Gammaherpesviruses, which include the human viruses Epstein-Barr virus and Kaposi's sarcoma-associated herpesvirus, establish latent infections in lymphocytes. Infection of this dynamic host-cell population requires that the viruses have appropriate strategies for enabling the viral genome to persist while these cells go through rounds of mitosis, but at the same time must avoid detection by host CD8(+) cytotoxic T lymphocytes (CTLs). The majority of gammaherpesviruses studied have been found to encode a specific protein that is critical for maintenance of the viral genome within latently infected cells. This protein is termed the genome maintenance protein (GMP). Due to its vital role in long-term latency, this offers the immune system a crucial target for detection and elimination of virus-infected cells. GMPs from different gammaherpesviruses have evolved related strategies that allow the protein to be present within latently infected cells, but to remain effectively hidden from circulating CD8(+) CTLs. In this review, I will summarize the role of the GMPs and highlight the available data describing the immune-evasion properties of these proteins.

NF-kappaB activation by the viral oncoprotein StpC enhances IFN-gamma production in T cells

Interferon-gamma (IFN-gamma) is an essential regulator of innate and adaptive immune responses and a hallmark of the Th1 T-cell subset. It is produced at high levels by human T lymphocytes upon transformation with Herpesvirus saimiri, which depends on the expression of the viral oncoproteins saimiri transformation-associated protein of subgroup C (StpC) and tyrosine kinase-interacting protein (Tip). Here, we show that IFN-gamma production was induced by Tip in Jurkat T cells. StpC by itself did not affect IFN-gamma expression, but enhanced the effect of Tip. Our results substantiated the findings that StpC induces NF-kappaB activation and demonstrated that other transcription factors, including NFAT, AP-1 and serum response element regulators, were not activated by StpC in unstimulated T cells. Studies using StpC mutants deficient in NF-kappaB activation, dominant negative IkappaBalpha and constitutively active IKK2, established the importance of NF-kappaB in StpC-mediated upregulation of IFN-gamma production. These observations suggest that NF-kappaB induction by StpC contributes to the Th1-like phenotype of virus-transformed human T cells.

Histone modification pattern of the T-cellular Herpesvirus saimiri genome in latency

Herpesvirus saimiri (HVS) subgroup C strains are able to growth transform human T lymphocytes in vitro. The stably persisting and nonintegrating HVS episome represents an optimal prerequisite for the investigation of the epigenetic state of latent herpesvirus genomes in vitro. Quantitative chromatin immunoprecipitation experiments using seven different histone acetylation- or methylation-specific antibodies revealed repressive marks at four lytic gene promoters and a variable pattern at the weakly transcribed LANA/orf73 promoter. The constitutive stpC/tip promoter regulating the viral oncoproteins and, more interestingly, the noncoding repetitive H-DNA elements flanking the coding region, showed a permissive chromatin structure. This study provides an appropriate model for the analysis of epigenetic herpesvirus genome modifications and their dynamics in T cells.

Growth transformation of human T cells by herpesvirus saimiri requires multiple Tip-Lck interaction motifs

Lymphoma induction and T-cell transformation by herpesvirus saimiri strain C488 depends on two viral oncoproteins, StpC and Tip. The major interaction partner of Tip is the protein tyrosine kinase Lck, a key regulator of T-cell activation. The Lck binding domain (LBD) of Tip comprises two interaction motifs, a proline-rich SH3 domain-binding sequence (SH3B) and a region with homology to the C terminus of Src family kinase domains (CSKH). In addition, biophysical binding analyses with purified Lck-SH2 domain suggest the phosphorylated tyrosine residue 127 of Tip (pY127) as a potential third Lck interaction site. Here, we addressed the relevance of the individual binding motifs, SH3B, CSKH, and pY127, for Tip-Lck interaction and for human T-cell transformation. Both motifs within the LBD displayed Lck binding activities and cooperated to achieve a highly efficient interaction, while pY127, the major tyrosine phosphorylation site of Tip, did not enhance Lck binding in T cells. Herpesvirus saimiri strain C488 recombinants lacking one or both LBD motifs of Tip lost their transforming potential on human cord blood lymphocytes. Recombinant virus expressing Tip with a mutation at position Y127 was still able to transform human T lymphocytes but, in contrast to wild-type virus, was strictly dependent on exogenous interleukin-2. Thus, the strong Lck binding mediated by cooperation of both LBD motifs was essential for the transformation of human T cells by herpesvirus saimiri C488. The major tyrosine phosphorylation site Y127 of Tip was particularly required for transformation in the absence of exogenous interleukin-2, suggesting its involvement in cytokine signaling pathways.

StpC-based gene therapy targeting latent reservoirs of HIV-1

The ability of HIV-1 to form latent reservoirs presents a major obstacle to eradication. One approach to elimination of the latent reservoir is induction therapy, whereby cells harboring latent virus are activated and therefore initiate virus replication. We have constructed a lentiviral vector encoding Herpesvirus saimiri subgroup C saimiri transformation-associated protein (StpC), which has been shown to modulate HIV-1 replication, under the control of a cytomegalovirus promoter in order to determine the ability of StpC to upregulate latent HIV-1. We have included a suicide gene, herpes simplex virus thymidine kinase (TK), under the control of the HIV-1 long terminal repeat (LTR) promoter. We hypothesized that upon StpC expression in latently infected cells induction of virus replication and subsequent production of viral transactivators of the LTR will activate expression of the tk gene, sensitizing the cells to the nucleoside analogue ganciclovir (GCV). Transduction of the latently infected cell line J1.1 resulted in increased virus replication. In the presence of GCV transduced cells exhibited decreased HIV-1 replication, inhibition of cell proliferation, and increased apoptosis. This prototype vector serves as a proof of concept of the utility of gene-based induction agents and suicide genes as a new method for targeting reservoirs of latent HIV-1.

Regulation of intracellular signalling by the terminal membrane proteins of members of the Gammaherpesvirinae

The human gamma(1)-herpesvirus Epstein-Barr virus (EBV) and the gamma(2)-herpesviruses Kaposi's sarcoma-associated herpesvirus (KSHV), rhesus rhadinovirus (RRV), herpesvirus saimiri (HVS) and herpesvirus ateles (HVA) all contain genes located adjacent to the terminal-repeat region of their genomes, encoding membrane proteins involved in signal transduction. Designated 'terminal membrane proteins' (TMPs) because of their localization in the viral genome, they interact with a variety of cellular signalling molecules, such as non-receptor protein tyrosine kinases, tumour-necrosis factor receptor-associated factors, Ras and Janus kinase (JAK), thereby initiating further downstream signalling cascades, such as the MAPK, PI3K/Akt, NF-kappaB and JAK/STAT pathways. In the case of TMPs expressed during latent persistence of EBV and HVS (LMP1, LMP2A, Stp and Tip), their modulation of intracellular signalling pathways has been linked to the provision of survival signals to latently infected cells and, hence, a contribution to occasional cellular transformation. In contrast, activation of similar pathways by TMPs of KSHV (K1 and K15) and RRV (R1), expressed during lytic replication, may extend the lifespan of virus-producing cells, alter their migration and/or modulate antiviral immune responses. Whether R1 and K1 contribute to the oncogenic properties of KSHV and RRV has not been established satisfactorily, despite their transforming qualities in experimental settings.

Tyrosine phosphorylation of the Tio oncoprotein is essential for transformation of primary human T cells

Human T cells are transformed to antigen-independent permanent growth in vitro upon infection with herpesvirus saimiri subgroup C strains. The viral oncoproteins required for this process, StpC and Tip, could be replaced by Tio, the oncoprotein of herpesvirus ateles. Here we demonstrate that proliferation of lymphocytes transformed with Tio-recombinant herpesvirus saimiri required the activity of Src family kinases. Src kinases had previously been identified as interaction partners of Tio. This interaction was now shown to be independent of any of the four tyrosine residues of Tio but to be dependent on an SH3-binding motif. Mutations within this motif abrogated the transforming capabilities of Tio-recombinant herpesvirus saimiri. Furthermore, kinase interaction resulted in the phosphorylation of Tio on a single tyrosine residue at position 136. Mutation of this residue in the viral context revealed that this phosphorylation site, but none of the other tyrosine residues, was required for T-cell transformation. These data indicate that the interaction of Tio with a Src kinase is essential for both the initiation and the maintenance of T-cell transformation by recombinant herpesvirus saimiri. The requirement for the tyrosine phosphorylation site at position 136 suggests a role for Tio beyond simple deregulation of the kinase.

T-cell transformation and oncogenesis by gamma2-herpesviruses

gamma2-Herpesviruses, also termed rhadinoviruses, have long been known as animal pathogens causing lymphoproliferative diseases such as malignant catarrhal fever in cattle or T-cell lymphoma in certain Neotropical primates. The rhadinovirus prototype is Herpesvirus saimiri (HVS), a T-lymphotropic agent of squirrel monkeys (Saimiri sciureus); Herpesvirus ateles (HVA) is closely related to HVS. The first human rhadinovirus, human herpesvirus type 8 (HHV-8), was discovered a decade ago in Kaposi's sarcoma (KS) biopsies. It was found to be strongly associated with all forms of KS, as well as with multicentric Castleman's disease and primary effusion lymphoma (PEL). Since DNA of this virus is regularly found in all KS forms, and specifically in the spindle cells of KS, it was also termed KS-associated herpesvirus (KSHV). Several simian rhadinoviruses related to KSHV have been discovered in various Old World primates, though they seem only loosely associated with pathogenicity or tumor induction. In contrast, HVS and HVA cause T-cell lymphoma in numerous non-natural primate hosts; HVS strains of the subgroup C are capable of transforming human and simian T-lymphocytes to continuous growth in cell culture and can provide useful tools for T-cell immunology or gene transfer. Here, we describe their natural history, genome structure, biology, and pathogenesis in T-cell transformation and oncogenesis.

Cell transformation by Herpesvirus saimiri

Herpesvirus saimiri (Saimiriine herpesvirus-2), a gamma2-herpesvirus (rhadinovirus) of non-human primates, causes T-lymphoproliferative diseases in susceptible organisms and transforms human and non-human T lymphocytes to continuous growth in vitro in the absence of stimulation. T cells transformed by H. saimiri retain many characteristics of intact T lymphocytes, such as the sensitivity to interleukin-2 and the ability to recognize the corresponding antigens. As a result, H. saimiri is widely used in immunobiology for immortalization of various difficult-to-obtain and/or -to-maintain T cells in order to obtain useful experimental models. In particular, H. saimiri-transformed human T cells are highly susceptible to infection with HIV-1 and -2. This makes them a convenient tool for propagation of poorly replicating strains of HIV, including primary clinical isolates. Therefore, the mechanisms mediating transformation of T cells by H. saimiri are of considerable interest. A single transformation-associated protein, StpA or StpB, mediates cell transformation by H. saimiri strains of group A or B, respectively. Strains of group C, which exhibit the highest oncogenic potential, have two proteins involved in transformation-StpC and Tip. Both proteins have been shown to dramatically affect signal transduction pathways leading to the activation of crucial transcription factors. This review is focused on the biological effects and molecular mechanisms of action of proteins involved in H. saimiri-dependent transformation.

Autocrine stimulation of rhadinovirus-transformed T cells by the chemokine CCL1/I-309

The rhadinovirus herpesvirus saimiri transforms human T lymphocytes to stable growth in culture. Besides the viral oncogenes stpC and tip, little is understood about the transformation process at the cellular level. To identify cellular factors that might contribute to growth transformation, we compared cellular gene expression in pairs of herpesvirus saimiri-transformed and nontransformed human T-cell clones. Using cDNA arrays and suppressive subtractive hybridization, we were able to identify the chemokine CCL1/I-309 as one of the few cellular genes that are strongly overexpressed in T cells after growth transformation with herpesvirus saimiri. The transformed T cells expressed CCR8, the receptor for CCL1, which rapidly induced intracellular calcium ion levels. Neutralizing antibodies to CCL1 led to reduced secretion of interferon-gamma and tumor necrosis factor-alpha as well as to reduced proliferation rates in transformed T cells. Thus, we propose that growth transformation of human T cells with herpesvirus saimiri gives rise to an autocrine loop where the proliferation of transformed T cells is supported by the endogenous production of the chemokine CCL1.

Characterization of the Herpesvirus saimiri Orf51 protein

Herpesvirus saimiri (HVS) is a gamma(2)-herpesvirus sharing genomic colinearity and a high degree of functional homology with HHV-8. To begin exploring the correlates of HVS infectivity and neutralization, we designed and implemented a new reporter assay. Using this assay, we could demonstrate that HVS neutralizing antibodies are present at high levels in naturally infected squirrel monkeys and are strongly induced after pathogenic, experimental infection of common marmosets. Further, we demonstrated that viral entry is influenced by cellular glycosaminoglycans and that, similar to HHV-8, soluble heparin is capable of blocking infectivity. We next cloned and characterized the positional homologue of HHV-8 K8.1, HVS Orf51. N-glycosidase F treatment indicates that like K8.1, Orf51 is a glycoprotein. Found in the viral particle, it localizes to the endoplasmic reticulum of expressing cells. Like K8.1, Orf51 could bind to agarose-conjugated heparin, implicating this molecule in viral attachment to cells. These studies provide the groundwork for additional experiments into the role that this protein may be playing in viral pathogenicity, persistence, and cell tropism.

Herpesvirus ateles Tio can replace herpesvirus saimiri StpC and Tip oncoproteins in growth transformation of monkey and human T cells

Herpesvirus saimiri group C strains are capable of transforming human and simian T-lymphocyte populations to permanent antigen-independent growth. Two viral oncoproteins, StpC and Tip, that are encoded by a single bicistronic mRNA, act in concert to mediate this phenotype. A closely related New World monkey herpesvirus, herpesvirus ateles, transcribes a single spliced mRNA at an equivalent genome locus. The encoded protein, Tio, has sequence homologies to both StpC and Tip. We inserted the tio sequence of herpesvirus ateles strain 73 into a recombinant herpesvirus saimiri C488 lacking its own stpC/tip oncogene. Simian as well as human T lymphocytes were growth transformed by the chimeric Tio-expressing viruses. Thus, a single herpesvirus protein appears to be responsible for the oncogenic effects of herpesvirus ateles.

Herpesvirus saimiri STP A11 protein interacts with STAT3 and stimulates its transcriptional activity

Herpesvirus saimiri (HVS) is an oncogenic gamma-2 herpesvirus that causes lymphoma in New World primates. HVS can be further divided into subgroups A, B, and C, based on sequence divergence. Saimiri transforming protein (STP) is coded for by the first open reading frame at the left end of the HVS genome and is responsible for its oncogenic potential. Here we show that STP A11 binds to signal transducers and activators of transcription 3 (STAT3), stimulates STAT3 phosphorylation, and activates STAT3-dependent transcription. STP A11 recruited c-Src kinase to phosphorylate STAT3 protein, and co-expression of STP A11 with c-Src dramatically increased STAT3 phosphorylation. We found that the amino terminal domain of STP A11 is required for both STAT3 interaction and activation, and that physical interaction is required for STAT3 activation.

Modulation of T-cell receptor signal transduction by herpesvirus signaling adaptor protein

Because of its central regulatory role, T-cell receptor (TCR) signal transduction is a common target of viruses. We report here the identification of a small signaling protein, ORF5, of the T-lymphotropic tumor virus herpesvirus saimiri (HVS). ORF5 is predicted to contain 89 to 91 amino acids with an amino-terminal myristoylation site and six SH2 binding motifs, showing structural similarity to cellular LAT (linker for activation of T cells). Sequence analysis showed that, despite extensive sequence variation, the myristoylation site and SH2 binding motifs were completely conserved among 13 different ORF5 isolates. Upon TCR stimulation, ORF5 was efficiently tyrosine phosphorylated and subsequently interacted with cellular SH2-containing signaling proteins Lck, Fyn, SLP-76, and p85 through its tyrosine residues. ORF5 expression resulted in the marked augmentation of TCR signal transduction activity, evidenced by increased cellular tyrosine phosphorylation, intracellular calcium mobilization, CD69 surface expression, interleukin-2 production, and activation of the NF-AT, NF-kappa B, and AP-1 transcription factors. Despite its structural similarity to cellular LAT, however, ORF5 could only partially substitute for LAT function in TCR signal transduction. These results demonstrate that HVS utilizes a novel signaling protein, ORF5, to activate TCR signal transduction. This activation probably facilitates viral gene expression and, thereby, persistent infection.

Tip, an Lck-interacting protein of Herpesvirus saimiri, causes Fas- and Lck-dependent apoptosis of T lymphocytes

Saimiriine herpesvirus-2 (Herpesvirus saimiri) transforms T lymphocytes, including human, to continuous growth in vitro. H. saimiri-induced transformation is becoming an important tool of T-cell biology, including studies of HIV replication. Two proteins of H. saimiri subgroup C, Tip and StpC, are essential for T-cell transformation. In spite of the important role of these proteins, their biological functions and the molecular mechanisms of their action remain insufficiently understood. To further elucidate the effects of Tip on T cells, we transduced T lymphocytes, using an efficient lentiviral gene transfer system, to express Tip in the absence of other H. saimiri proteins. Our results indicate that Tip specifically inhibits IL-2 production by human T lymphocytes. Furthermore, Tip promotes T-cell apoptosis, which appears to be the reason for the observed decrease in IL-2 production. Finally, the apoptotic effect of Tip in T cells is mediated by Fas and requires the presence of active Lck in the cell.

Molecular mechanisms of the effect of herpesvirus saimiri protein StpC on the signaling pathway leading to NF-kappaB activation

Herpesvirus saimiri (Saimiriine herpesvirus-2) causes lethal T lymphoproliferative diseases in the susceptible species and transforms T lymphocytes to continuous growth in vitro. H. saimiri-induced transformation of T cells is becoming an important experimental tool of biomedical research. Two proteins of H. saimiri subgroup C, Tip and StpC, are essential for T cell transformation by this virus. It has been shown previously that StpC transforms fibroblasts, activates NF-kappaB, and binds to tumor necrosis factor (TNF)-receptor-associated factor (TRAF) proteins, but the molecular mechanism of its action remains insufficiently understood. This study further characterized the effect of StpC on NF-kappaB. First, StpC activates NF-kappaB via the consensus pathway involving activation of I-kappaB kinase and subsequent phosphorylation and degradation of I-kappaB in both T lymphoid and epithelial cells. Second, triggering of this pathway by StpC in both T lymphoid and epithelial cells is dependent on the presence of functional NF-kappaB-inducing kinase (NIK). Third, StpC physically interacts with TRAF in epithelial cells, and the effect of StpC on NF-kappaB activity in these cells requires the presence of functional TRAF. Finally the effect of StpC is completely independent of TNF-alpha, a well described stimulus of NF-kappaB activity. Moreover it appears that StpC uncouples stimulation of NF-kappaB activity from TNF-alpha stimulation. Overall these results argue that the effect of StpC on NF-kappaB is similar to the effects of other viral proteins, "usurping" the TRAF/NIK/I-kappaB kinase pathway, and reinforce the notion that the role of StpC in cell transformation by H. saimiri may be mediated by signaling that results in NF-kappaB activation.

Generation and precise modification of a herpesvirus saimiri bacterial artificial chromosome demonstrates that the terminal repeats are required for both virus production and episomal persistence

Herpesvirus saimiri (HVS) is the prototype gamma-2 herpesvirus, and shares considerable homology with the human gammaherpesviruses Kaposi's sarcoma-associated herpesvirus and Epstein–Barr virus. The generation of herpesvirus mutants is a key facet in the study of virus biology. The use of F-factor-based bacterial artificial chromosomes (BACs) to clone and modify the genomes of herpesviruses has enhanced the variety, precision and simplicity of mutant production. Here we describe the cloning of the genome of HVS non-transforming strain A11-S4 into a BAC. The cloning of the BAC elements disrupts open reading frame (ORF) 15 but the HVS-BAC can still replicate at levels similar to wild-type virus, and can persistently infect fibroblasts. The HVS-BAC was modified by RecA-mediated recombination initially to substitute reporter genes and also to delete the terminal repeats (TR). After deletion of the TR, the HVS-BAC fails to enter a productive virus lytic cycle, and cannot establish a persistent episomal infection when transfected into fibroblast cell lines. This shows that while ORF 15 is dispensable for virus function in vitro, the TR is required for both virus latency and lytic virus production. In addition, the HVS-BAC promises to be a valuable tool that can be used for the routine and precise production and analysis of viral mutants to further explore gammaherpesvirus biology.

The genome of herpesvirus saimiri C488 which is capable of transforming human T cells

Herpesvirus saimiri (HVS), the rhadinovirus prototype, is apathogenic in the persistently infected natural host, the squirrel monkey, but causes acute T cell leukemia in other New World primate species. In contrast to subgroups A and B, only strains of HVS subgroup C such as C488 are capable of transforming primary human T cells to stable antigen-independent growth in culture. Here, we report the complete 155-kb genome sequence of the transformation-competent HVS strain C488. The A+T-rich unique L-DNA of 113,027 bp encodes at least 77 open reading frames and 5 URNAs. In addition to the viral oncogenes stp and tip, only a few genes including the transactivator orf50 and the glycoprotein orf51 are highly divergent. In a series of new primary HVS isolates, the subgroup-specific divergence of the orf50/orf51 alleles was studied. In these new isolates, the orf50/orf51 alleles of the respective subgroup segregate with the stp and/or tip oncogene alleles, which are essential for transformation.

The herpesvirus saimiri tip484 and tip488 proteins both stimulate lck tyrosine protein kinase activity in vivo and in vitro

Herpesvirus saimiri (HVS) of subgroup C efficiently induces leukemia in New World primates and transforms human lymphocytes. The viral tyrosine kinase interacting protein (Tip) binds to the tyrosine protein kinase Lck and is essential for transformation. Understanding how Tip modulates Lck activity is important for elucidating the mechanism of herpesvirus saimiri leukemogenesis. However, there are reports suggesting that whereas the Tip protein of HVS strain 484 stimulates the activity of Lck, the Tip protein of HVS strain 488 inhibits Lck. To determine whether these two divergent Tip proteins have opposite effects on Lck activity, we compared them in parallel. We found that both Tip proteins stimulated Lck kinase activity in vivo and in vitro and that both stimulated NF-AT- and STAT3-dependent transcription in T cells. Our data support the model that HVS infection increases the activity of Lck through the action of Tip.

Peripheral T-cell lymphoma in herpesvirus saimiri-infected tamarins: tumor cell lines reveal subgroup-specific differences

Efficiency of lymphoma induction by herpesvirus saimiri (HVS) isolates correlates with the genetically defined viral subgroups A, B, and C. To compare subgroup-specific effects, highly susceptible tamarins were infected with HVS strain A-11, B-SMHI, or C-488. All animals developed T-cell lymphomas indistinguishable with respect to clinical, pathological, and virological parameters. Ex vivo T-cell lines were established readily from the HVS C-488 animal, less efficiently in the presence of HVS A-11, and from only a single HVS B-SMHI sample. These cultivated cells revealed strain-specific biochemical characteristics. HVS A-11 strongly induced the expression of tyrosine kinase Lyn. HVS C-488 led to the activation of STAT3, which is most likely linked to the association of virus-encoded Tip with tyrosine kinase Lck. The lack of these activities in HVS B-SMHI-transformed cells may correlate with the reduced oncogenic phenotype of this virus in species other than tamarins.

Downregulation of p56(lck) tyrosine kinase activity in T cells of squirrel monkeys (Saimiri sciureus) correlates with the nontransforming and apathogenic properties of herpesvirus saimiri in its natural host

Herpesvirus saimiri is capable of transforming T lymphocytes of various primate species to stable growth in culture. The interaction of the T-cellular tyrosine kinase p56(lck) with the transformation-associated viral protein Tip has been shown before to activate the kinase and provides one model for the T-cell-specific transformation by herpesvirus saimiri subgroup C strains. In contrast to other primate species, squirrel monkeys (Saimiri sciureus) are naturally infected with the virus without signs of lymphoma or other disease. Although the endogenous virus was regularly recovered from peripheral blood cells from squirrel monkeys, we observed that the T cells lost the virus genomes in culture. Superinfection with virus strain C488 did not induce growth transformation, in contrast to parallel experiments with T cells of other primate species. Surprisingly, p56(lck) was enzymatically inactive in primary T-cell lines derived from different squirrel monkeys, although the T cells reacted appropriately to stimulatory signals. The cDNA sequence revealed minor point mutations only, and transfections in COS-7 cells demonstrated that the S. sciureus lck gene codes for a functional enzyme. In S. sciureus, the tyrosine kinase p56(lck) was not activated after T-cell stimulation and enzymatic activity could not be induced by Tip of herpesvirus saimiri C488. However, the suppression of p56(lck) was partially released after administration of the phosphatase inhibitor pervanadate. This argues for unique species-specific conditions in T cells of S. sciureus which may interfere with the transforming activity and pathogenicity of herpesvirus saimiri subgroup C strains in their natural host.

Subversion and piracy: DNA viruses and immune evasion

During the co-evolution of viruses with their vertebrate hosts, the DNA viruses have acquired an impressive array of immunomodulatory genes to combat host immune responses and their hosts have developed a sophisticated immune system to contain virus infections. In order to replicate, the viruses have evolved mechanisms to inhibit key host anti-virus responses that include apoptosis, interferon production, chemokine production, inflammatory cytokine production, and the activity of cytotoxic T-cells, natural killer cells and antibody. In addition, some of the viruses encode cytokine or chemokine homologues that recruit or expand cell numbers for infection or that subvert the host cellular response from a protective response to a benign one. The specificity of the viral immunomodulatory molecules reflects the life cycle and the pathogenesis of the viruses. Herpesviruses achieve latency in host cells by inducing cell survival and protecting infected cells from immune recognition. This involves interference with cell signal transduction pathways. Many of the viral immunomodulatory proteins are homologues of host proteins that appear to have been pirated from the host and reassorted in the virus genomes. Some of these have unique functions and indicate novel or important aspects of both viral pathogenesis and host immunity to viruses. The specific example of orf virus infection of sheep is described.

Herpesvirus saimiri

Herpesvirus saimiri (saimiriine herpesvirus 2) is the classical prototype of the gamma(2)-herpesviruses or rhadinoviruses, which also contains a human member, the Kaposi's sarcoma-associated herpesvirus. The T-lymphotropic Herpesvirus saimiri establishes specific replicative and persistent conditions in different primate host species. Virtually all squirrel monkeys (Saimiri sciureus) are persistently infected with this virus. In its natural host, the virus does not cause disease, whereas it induces fatal acute T-cell lymphoma in other monkey species after experimental infection. The virus can be isolated by cocultivation of permissive epithelial cells with peripheral blood cells from naturally infected squirrel monkeys and from susceptible New World monkeys during the virus-induced disease. Tumour-derived and in vitro-transformed T-cell lines from New World monkeys release virus particles. Herpesvirus ateles is a closely related virus of spider monkeys (Ateles spp.) and has similar pathogenic properties to Herpesvirus saimiri in other New World primate species. Similar to other rhadinoviruses, the genome of Herpesvirus saimiri harbours a series of virus genes with pronounced homology to cellular counterparts including a D-type cyclin, a G-protein-coupled receptor, an interleukin-17, a superantigen homologue, and several inhibitors of the complement cascade and of different apoptosis pathways. Preserved function has been demonstrated for most of the homologues of cellular proteins. These viral functions are mostly dispensable for the transforming and pathogenic capability of the virus. However, they are considered relevant for the apathogenic persistence of Herpesvirus saimiri in its natural host. A terminal region of the non-repetitive coding part of the virus genome is essential for pathogenicity and T-cell transformation. Based on the pathogenic phenotypes and the different alleles of this variable region, the virus strains have been assigned to three subgroups, termed A, B and C. In the highly oncogenic subgroup C strains, the two virus genes stpC and tip are transcribed from one bicistronic mRNA and are essential for transformation and leukaemia induction. stpC fulfils the typical criteria of an oncogene; its product interacts with Ras and tumour necrosis factor-associated factors and induces mitogen-activated protein kinase and nuclear factor kappa B activation. Tip interacts with the RNA transport factor Tap, with signal transduction and activation of transcription factors, and with the T-cellular tyrosine kinase Lck, which is activated by this interaction and phosphorylates Tip as a substrate. It is of particular interest that certain subgroup C virus strains such as C488 are capable of transforming human T lymphocytes to stable growth in culture. The transformed human T cells harbour multiple copies of the viral genome in the form of stable, non-integrated episomes. The cells express only a few virus genes and do not produce virus particles. The transformed cells maintain the antigen specificity and many other essential functions of their parental T-cell clones. Based on the preserved functional phenotype of the transformed T cells, Herpesvirus saimiri provides useful tools for T-cell immunology, for gene transfer and possibly also for experimental adoptive immunotherapy.

Simian homologues of human herpesvirus 8

Gamma-herpesviruses can be found in most primates including Old World an New World monkeys. The gamma-herpesvirinae are grouped into two classes: lymphocryptoviruses (gamma1) and rhadinoviruses (gamma2). The lymphocryptoviruses include Epstein-Barr virus, lymphocryptovirus of rhesus monkeys, and Herpesvirus papio of baboons. Rhadinoviruses that infect New World monkeys include Herpesvirus saimiri, whose natural host is the squirrel monkey, and Herpesvirus ateles, which infects spider monkeys. Rhadinoviruses that infect hominoids and Old World monkeys include Kaposi's sarcoma-associated herpesvirus, also known as HHV-8, and rhesus monkey rhadinovirus.

Molecular evolution of the gamma-Herpesvirinae

Genomic sequences available for members of the gamma-Herpesvirinae allow analysis of many aspects of the group's evolution. This paper examines four topics: (i) the phylogeny of the group; (ii) the histories of gamma-herpesvirus-specific genes; (iii) genomic variation of human herpesvirus 8 (HHV-8); and (iv) the relationship between Epstein-Barr virus types 1 and 2 (EBV-1 and EBV-2). A phylogenetic tree based on eight conserved genes has been constructed for eight gamma-herpesviruses and extended to 14 species with smaller gene sets. This gave a generally robust assignment of evolutionary relationships, with the exception of murine herpesvirus 4 (MHV-4), which could not be placed unambiguously on the tree and which has evidently experienced an unusually high rate of genomic change. The gamma-herpesviruses possess a variable complement of genes with cellular homologues. In the clearest cases these virus genes were shown to have originated from host genome lineages in the distant past. HHV-8 possesses at its left genomic terminus a highly diverse gene (K1) and at its right terminus a gene (K15) having two diverged alleles. It was proposed that the high diversity of K1 results from a positive selection on K1 and a hitchhiking effect that reduces diversity elsewhere in the genome. EBV-1 and EBV-2 differ in their alleles of the EBNA-2, EBNA-3A, EBNA-3B and EBNA-3C genes. It was suggested that EBV-1 and EBV-2 may recombine in mixed infections so that their sequences outside these genes remain homogeneous. Models for genesis of the types, by recombination between diverged parents or by local divergence from a single lineage, both present difficulties.

Herpesvirus saimiri Tip gene causes T-cell lymphomas in transgenic mice

New World primates develop T-cell lymphomas on infection with Herpesvirus saimiri. To investigate the oncogenic potential of the Tip gene of Herpesvirus saimiri strain C488, we tried to establish transgenic mice that should express Tip under control of a constitutive promoter. Although transgene-positive embryos were found, lines could not be established. However, using a system in which the transgene has to be activated by a Cre recombinase-mediated deletion, we were able to obtain several Tip transgenic lines. At high expression levels, the mice developed T-cell lymphomas. Thus, Tip can induce lymphomas and is therefore very likely responsible for the oncogenicity of Herpesvirus saimiri.

Herpesvirus saimiri protein StpB associates with cellular Src

Subgroup B isolates of Herpesvirus saimiri are less efficient in T lymphocyte transformation when compared with subgroups A or C. Here it is shown that subgroup B strain SMHI encodes a protein, StpB, at a position equivalent to those of the ORFs for the saimiri transforming proteins (Stp) of subgroups A and C. StpB shares little similarity with StpA or StpC, but interacts with the SH2 domain of cellular Src, as does StpA. Thus, factors other than c-Src binding determine the efficiency of primary T cell transformation by Herpesvirus saimiri.

Herpesvirus saimiri oncoproteins Tip and StpC synergistically stimulate NF-kappaB activity and interleukin-2 gene expression

Saimiriine herpesvirus 2 (Herpesvirus saimiri) is capable of inducing lethal T-cell lymphoproliferative diseases in primates and of immortalizing human T lymphocytes in vitro. Two viral oncoproteins, Tip and StpC, are essential for T-cell transformation by Herpesvirus saimiri strains of the subgroup C, which exhibits a higher transformation potential than other subgroups of this virus. Despite the importance of these proteins, the molecular basis of their effects on T cells is poorly understood. It remains unclear how Tip and StpC affect gene expression and what is the molecular basis of their cooperation. To address these issues, we expressed Tip and StpC in T lymphoblastoid cells and assessed both their effects on and transcription factors involved in IL-2 gene expression. Our study shows that Tip and StpC cooperate to upregulate IL-2 gene expression, that their effect is mediated primarily by NF-kappaB and NF-AT, which is partially dependent on tyrosine phosphorylation.

Herpesvirus saimiri pathogenicity enhanced by thymidine kinase of herpes simplex virus

Herpesvirus saimiri can be used as an efficient gene expression vector for human T lymphocytes and thus may allow applications in experimental leukemia therapy. We constructed recombinant viruses for the functional expression of the thymidine kinase (TK) of herpes simplex virus type 1 (HSV) as a suicide gene. These viruses reliably allowed the targeted elimination of transduced nonpermissive human T cells in vitro after the administration of ganciclovir. To test the reliability of this function under the most stringent permissive conditions, in this study we analyzed the influence of the prodrugs ganciclovir and acyclovir in common marmosets on the acute leukemogenesis induced by either wild-type herpesvirus saimiri C488 or by a recombinant derivative expressing TK of HSV. Antiviral drug treatment did not influence the rapid development of acute disease. In contrast, the presence of the HSV tk gene resulted in a faster disease progression. In addition, HSV TK-expressing viruses showed faster replication than wild-type virus in culture at low serum concentrations. Thus, HSV TK accelerates the replication of herpesvirus saimiri and enhances its pathogenicity. This should be generally considered when HSV TK is applied as a transgene in replication-competent DNA virus vectors for gene therapy.

Herpesvirus saimiri vFLIP provides an antiapoptotic function but is not essential for viral replication, transformation, or pathogenicity

Apoptosis of infected cells is an important host defense mechanism, and many viruses have exploited antiapoptotic proteins that interfere with crucial cellular pathways. Viral FLICE inhibitory proteins (vFLIPs) are encoded by rhadinoviruses like herpesvirus saimiri, the related Kaposi's sarcoma-associated herpesvirus-human herpesvirus 8 (KSHV/HHV8), and the poxvirus responsible for molluscum contagiosum. The vFLIPs can block the interaction of the death receptor-adapter complex with the cellular effector FLICE (caspase-8), and this prevents the initiation of the downstream caspase cascade. KSHV/HHV8 vFLIP overexpression can confer resistance to T-cell-mediated apoptosis and acts as a tumor progression factor in a murine B-cell lymphoma model. To analyze the function of herpesvirus vFLIPs in the genetic background of the virus and in a model for viral pathogenesis, we deleted the vFLIP gene (open reading frame 71) from the genome of herpesvirus saimiri strain C488. The viral deletion mutant was viable and replicated like the wild-type virus. An antiapoptotic effect could be attributed to the vFLIP gene, but we also show that the vFLIP gene of herpesvirus saimiri is dispensable for viral transformation of T cells in vitro and for pathogenicity in cottontop tamarins in vivo.

Evolutionary aspects of oncogenic herpesviruses

Several of the gamma-herpesviruses are known to have cellular transforming and oncogenic properties. The genomes of eight distinct gamma-herpesviruses have been sequenced, and the resulting database of information has enabled the identification of genetic similarities and differences between evolutionarily closely related and distant viruses of the subfamily and between the gamma-herpesviruses and other members of the herpesvirus family. The recognition of coincident loci of genetic divergence between individual gamma-herpesviruses and the identification of novel genes and cellular gene homologues in these genomic regions has delineated a subset of genes that are likely to contribute to the unique biological properties of these viruses. These genes, together with gamma-herpesvirus conserved genes not found in viruses outside the family, might be responsible for virus specific pathogenicity and pathogenic effects, such as viral associated neoplasia, characteristic of the subfamily. The presence of the gamma-herpesvirus major divergent genomic loci and the apparent increased mutational frequencies of homologous genes (where they occur) within these regions, indicates that these loci possess particular features that drive genetic divergence. Whatever the mechanisms underlying this phenomenon, it potentially provides the basis for the relatively rapid adaptation and evolution of gamma-herpesviruses and the diversity of biological and pathogenic properties.

The collagen repeat sequence is a determinant of the degree of herpesvirus saimiri STP transforming activity

Herpesvirus saimiri (HVS) is divided into three subgroups, A, B, and C, based on sequence divergence at the left end of genomic DNA in which the saimiri transforming protein (STP) resides. Subgroup A and C strains transform primary common marmoset lymphocytes to interleukin-2-independent growth, whereas subgroup B strains do not. To investigate the nononcogenic phenotype of the subgroup B viruses, STP genes from seven subgroup B virus isolates were cloned and sequenced. Consistent with the lack of oncogenic activity of HVS subgroup B viruses, STP-B was deficient for transforming activity in rodent fibroblast cells. Sequence comparison reveals that STP-B lacks the signal-transducing modules found in STP proteins of the other subgroups, collagen repeats and an authentic SH2 binding motif. Substitution mutations demonstrated that the lack of collagen repeats but not an SH2 binding motif contributed to the nontransforming phenotype of STP-B. Introduction of the collagen repeat sequence induced oligomerization of STP-B, resulting in activation of NF-kappaB activity and deregulation of cell growth control. These results demonstrate that the collagen repeat sequence is a determinant of the degree of HVS STP transforming activity.

Analysis of gene expression in a human cell line stably transduced with herpesvirus saimiri

Herpesvirus saimiri (HVS) is the prototype gamma-2 herpesvirus; it has significant homology to the human gammaherpesviruses Kaposi's sarcoma-associated virus and Epstein-Barr virus and the murine gammaherpesvirus murine herpesvirus 68. HVS causes a persistent asymptomatic infection in its natural host, the squirrel monkey. Both subgroups A and C possess the ability to immortalize common marmoset T lymphocytes to interleukin-2-independent proliferation. However, only subgroup C is capable of transforming human, rabbit, and rhesus monkey lymphocytes in vitro. In addition, HVS can stably transduce a variety of human cell lines where the virus persists as a nonintegrating circular episome. In this study, we have developed a system in which the HVS DNA is stably maintained as a nonintegrated circular episome in the human lung carcinoma cell line A549. Virus production can be reactivated using chemical inducing agents, including tetradecanoyl phorbol acetate and n-butyrate, suggesting that the infection in human A549 cells is latent. To analyze virus gene expression in these stably transduced cells, Northern blot analysis was performed using a series of probes produced from restriction fragments spanning the entire coding region of the HVS genome. This demonstrated that an adjacent set of genes containing open reading frames (ORFs) 71 to 73 are expressed in this stably transduced cell line. Moreover, these genes are transcribed as a polycistronic mRNA species produced from a common promoter upstream of ORF 73. This model may serve as a useful tool in the further analysis of the role of ORFs 71 to 73 in gamma-2 herpesvirus latency.

Lck protein tyrosine kinase is a key regulator of T-cell activation and a target for signal intervention by Herpesvirus saimiri and other viral gene products

Protein tyrosine kinases (PTKs) are critically involved in signaling pathways that regulate cell growth, differentiation, activation, and transformation. It is not surprising, therefore, that viruses acquire effector molecules targeting these kinases to ensure their own replication and/or persistence. This review summarizes our current knowledge on Lck, a member of the Src family of PTK, and its viral interaction partners. Lck plays a key role in T lymphocyte activation and differentiation. It is associated with a variety of cell surface receptors and is critical for signal transduction from the T-cell antigen receptor (TCR). Consequently, Lck is targeted by regulatory proteins of T-lymphotropic viruses, especially by the Herpesvirus saimiri (HVS) tyrosine kinase interacting protein (Tip). This oncoprotein physically interacts with Lck in HVS transformed T cells and has an impact on its catalytic activity. However, while Tip inhibits Lck activity in stably expressing cell lines, opposite effects were observed in several in vitro systems. At least in part, this complex situation may be related to the bipartite nature of the interaction surface of the two proteins. Studies on the interrelationships between Lck and its viral partners contribute to the understanding of the mechanisms of T-cell growth regulation, in general, and of viral pathogenicity in particular. In addition, understanding the regulation of Lck activity by viral proteins may serve as a basis for the development of new drugs capable of modifying Lck activity in different pathological situations.

Functional long-term thymidine kinase suicide gene expression in human T cells using a herpesvirus saimiri vector

Herpesvirus saimiri transforms human T lymphocytes to stable growth and persists episomally without genomic integration and without virus production. The transformed T cells retain essential features of their parental cells including the MHC-restricted antigen specificity which may be useful for applications in adoptive immunotherapy. In order to improve the biological safety of such vectors, the prodrug activating gene thymidine kinase of herpes simplex virus was inserted into the genome of herpesvirus saimiri by homologous recombination. After infection with wild-type or cloned recombinant viruses, T cells from tamarin monkeys and from humans were transformed to stable growth. Thymidine kinase-expressing transformed T cells were efficiently eliminated in the presence of low concentrations of ganciclovir. This elimination mechanism remained fully functional over an observation period of 12 months. The potentially immunogenic neomycin resistance gene expression cassette was deleted from the genome of established mutant viruses by using the prokaryotic Cre/LoxP recombination system. At any time during the course of a therapeutic application, thymidine kinase-expressing transformed human T cells might be eliminated after administration of ganciclovir. In principle, this function could be useful for the T cell-dependent immunotherapy of resistant blood cancer while avoiding the risk of uncontrolled graft-versus-host disease.

Distinct transcriptional and functional properties of the R transactivator gene orf50 of the transforming herpesvirus saimiri strain C488

The transformation-associated region of herpesvirus saimiri strains is variable, whereas other parts of the virus genome are highly conserved. However, we observed considerable interstrain sequence divergence of the early viral regulatory orf50 gene, which encodes the R transactivator, a homolog of Epstein-Barr virus BRLF1. The orf50 gene of strain C488 was transcribed at low abundance during lytic infection, whereas antisense transcripts were simultaneously expressed at high levels. A spliced variant, orf50a, was detectable by RT-PCR and RNase protection assays in stimulated C488-transformed, nonpermissive human T cells. In contrast to strain A11, the short, unspliced orf50b form of C488 displayed complete transactivation capability on the orf6 and orf57 promoters. In summary, there are unexpected structural and functional differences between the orf50 genes of herpesvirus saimiri strains, which differ in their capability to transform human T lymphocytes.

Activation of lymphocyte signaling by the R1 protein of rhesus monkey rhadinovirus

Rhesus monkey rhadinovirus (RRV) is a gamma-2 herpesvirus that exhibits a considerable degree of similarity to the human Kaposi's sarcoma-associated herpesvirus (KSHV). The R1 protein of RRV is distantly related to the K1 protein of KSHV, and R1, like K1, can contribute to cell growth transformation. In this study we analyzed the ability of the cytoplasmic tail of R1 to function as a signal transducer. The cytoplasmic domain of the R1 protein contains several tyrosine residues whose phosphorylation is induced in cells expressing Syk kinase. Expression of a CD8 chimera protein containing the extracellular and transmembrane domains of CD8 fused to the cytoplasmic domain of R1 mobilized intracellular calcium and induced cellular tyrosine phosphorylation in B cells upon stimulation with anti-CD8 antibody. None of the CD8-R1 cytoplasmic deletion mutants tested were able to mobilize intracellular calcium or to induce tyrosine phosphorylation to a significant extent upon addition of anti-CD8 antibody. Expression of wild-type R1 protein activated nuclear factor of activated T lymphocytes (NFAT) eightfold in B cells in the absence of antibody stimulation; expression of the CD8-R1C chimera strongly induced NFAT activity (60-fold) but only upon the addition of anti-CD8 antibody. We conclude that the cytoplasmic domain of R1 is capable of transducing signals that elicit B-lymphocyte activation events. The signal-inducing properties of R1 appear to be similar to those of K1 but differ in that the required sequences are distributed over a much longer stretch of the cytoplasmic domain (>150 amino acids). In addition, the induction of calcium mobilization was considerably longer in duration and stronger with R1 than with K1.

Primary structure of the Herpesvirus ateles genome

Herpesvirus ateles is an agent indigenous to spider monkeys (Ateles spp.) and causes fulminant lymphomas in various New World primates. Structural and genetic relatedness led to the classification of this virus as a member of the genus Rhadinovirus. It is most closely related to Herpesvirus saimiri. The 108,409-bp light DNA segment of the herpesvirus ateles strain 73 genome has two genes for U-RNA-like transcripts and 73 open reading frames, of which at least 6 show significant homologies to cellular genes (encoding complement control proteins, apoptosis-regulatory proteins, D-type cyclins, interleukin-8 receptors, and enzymes involved in nucleotide metabolism). The left terminal region of the light DNA segment bears the putative rhadinovirus oncogene tio.

Altered replication of human immunodeficiency virus type 1 (HIV-1) in T cell lines retrovirally transduced to express Herpesvirus saimiri proteins StpC and/or Tip

Human peripheral blood T lymphocytes are transformed in vitro to continuous proliferation by Herpesvirus saimiri subgroup C strains. It has been previously shown that H. saimiri-transformed human T cell lines are a permissive system for HIV-1 and 2 replication and are highly susceptible to infection by HIV-1 and 2. Two open reading frames of H. saimiri, StpC and Tip, are required for T cell transformation and are unique to this herpesvirus. The successful transduction of human T cells with retroviral vectors expressing H. saimiri proteins StpC and Tip has allowed us to extend the previously mentioned observations and investigate the role of StpC and Tip in replication of HIV-1 T-tropic strains (IIIB, MN, and RF) in human T cell lines. StpC expression in Molt4 dramatically enhanced HIV-1 replication as measured by Tat protein expression, syncytia formation, and accumulation of reverse transcriptase activity. In contrast, Tip expression in Molt4 cells inhibited HIV-1 replication and cytopathic effects relative to Molt4 cells transduced with the empty vector alone. The StpC-induced phenotype dominated in Molt4 cells transduced to express both StpC and Tip, suggesting that StpC is responsible for facilitating HIV-1 replication in H. saimiri-transformed T cells. Colony-forming ability of Tip-expressing Molt4 cells following HIV-1 infection was greatly enhanced over Molt4 cells expressing either StpC or no H. saimiri proteins at all. HIV-1 proviral DNA could be detected by PCR in surviving Molt4 cells expressing StpC or Tip, indicating that a persistent infection was established. A better understanding of the effects of Tip and StpC proteins on the biology of human hemopoietic stem cells may lead to novel therapeutic interventions for the treatment of AIDS.

Activation of cJUN N-terminal kinase by herpes simplex virus type 1 enhances viral replication

Signal transduction pathways convey signals generated at the cell surface into the cell nucleus in order to initiate a program of gene expression that is characteristic for particular stimuli. Here we present evidence that infection by herpes simplex virus type 1 activated the two terminal kinases, cJUN N-terminal kinase (JNK) and p38, of stress-activated signal transduction kinase cascades. By using a solid-phase kinase assay, a phospho-specific antibody, and extracts prepared from a variety of infected cell types, we determined that activation of both kinases began 3 to 4 h postinfection (p.i.) and remained elevated out to 14 h p.i. Through the use of UV-irradiated or antibody-neutralized wild-type virus and the temperature-sensitive mutant tsB7, the high level of JNK activation was shown to be dependent on viral gene expression. Activation of JNK following infection by vi13, an ICP4 mutant virus that does not express early or late genes, suggested that only virus entry and immediate-early gene expression were necessary for JNK activation. The activation of JNK and p38 correlated with increased chloramphenicol acetyltransferase (CAT) activity in reporter assays dependent upon the activity of cJUN and ATF2 trans-activation domains. Increased CAT activity dependent on TRE and CRE promoter sites was also observed in response to herpes simplex virus infection. The activities of ERK and ERK-dependent transcription factors were unchanged or depressed following infection, showing that activation of JNK and p38 was a specific event. Finally, the activation of JNK was important for the efficiency of viral replication. The yield of virus in NIH 3T3 cells stably expressing JIP-1, an inhibitor of JNK translocation to the nucleus, was reduced 70% compared to that of control cells, in single-step growth experiments.

Induction of apoptosis in Herpesvirus saimiri-immortalized T lymphocytes by blocking interaction of CD28 with CD80/CD86

We have previously shown that Herpesvirus saimiri (HVS) immortalizes primary macaque monkey T lymphocytes. In this study, we examined the characteristics of the immortalized T cells. The cells showed the phenotype of activated T lymphoblasts (CD3(+) CD25(+) CD69(+) MHC-IIDR(+)) and produced no infectious virus while viral DNA was detected in the Hirt DNA. Interestingly, both a major costimulatory molecule, CD28, and its ligands, CD80/CD86, were coexpressed on the immortalized T cells. The treatment of the cells with a neutralizing monoclonal antibody against CD28, which blocks interaction of CD28 with CD80/CD86, resulted in retarded cell growth and in induction of apoptosis. The effect of the antibody treatment was not overcome by exogenous interleukin-2 treatment. These findings demonstrate the requirement of interaction of CD28 with CD80/CD86 for the optimal growth of HVS-immortalized T cells.