Sequence and genomic analysis of a Rhesus macaque rhadinovirus with similarity to Kaposi's sarcoma-associated herpesvirus/human herpesvirus 8

Genomic characterization of Japanese macaque rhadinovirus, a novel herpesvirus isolated from a nonhuman primate with a spontaneous inflammatory demyelinating disease

Japanese macaque rhadinovirus (JMRV) is a novel gamma-2 herpesvirus that was isolated from a Japanese macaque (JM) with an inflammatory demyelinating encephalomyelitis referred to as Japanese macaque encephalomyelitis, a disease that possesses clinical and histopathological features resembling multiple sclerosis in humans. Genomic DNA sequence analysis reveals that JMRV is a gammaherpesvirus closely related to rhesus macaque rhadinovirus (RRV) and human herpesvirus 8. We describe here the complete nucleotide sequence and structure of the JMRV genome, as well as the sequence of two plaque isolates of this virus. Analysis of the JMRV genome not only demonstrates that this virus shares a number of genes with RRV that may be involved in pathogenesis but also indicates the presence of unique JMRV genes that could potentially contribute to disease development. The knowledge of the genomic sequence of JMRV, and the ability to easily propagate the virus in vitro, make JMRV infection of JM an attractive model for examining the potential role of an infectious viral agent in the development of demyelinating encephalomyelitis disease in vivo.

Exploitation of Cellular Cytoskeletons and Signaling Pathways for Cell Entry by Kaposi's Sarcoma-Associated Herpesvirus and the Closely Related Rhesus Rhadinovirus

As obligate intracellular pathogens, viruses depend on the host cell machinery to complete their life cycle. Kaposi’s sarcoma-associated herpes virus (KSHV) is an oncogenicvirus causally linked to the development of Kaposi’s sarcoma and several other lymphoproliferative malignancies. KSHV entry into cells is tightly regulated by diverse viral and cellular factors. In particular, KSHV actively engages cellular integrins and ubiquitination pathways for successful infection. Emerging evidence suggests that KSHV hijacks both actin and microtubule cytoskeletons at different phases during entry into cells. Here, we review recent findings on the early events during primary infection of KSHV and its closely related primate homolog rhesus rhadinovirus with highlights on the regulation of cellular cytoskeletons and signaling pathways that are important for this phase of virus life cycle.

Distinct roles for extracellular signal-regulated kinase 1 (ERK1) and ERK2 in the structure and production of a primate gammaherpesvirus

During their progression from intranuclear capsids to mature trilaminar virions, herpesviruses incorporate an extensive array of viral as well as a smaller subset of cellular proteins. Our laboratory previously reported that rhesus monkey rhadinovirus (RRV), a close homolog of the human pathogen Kaposi's sarcoma-associated herpesvirus (KSHV), is comprised of at least 33 different virally encoded proteins. In the current study, we found that RRV infection activated the extracellular signal-regulated kinase (ERK) pathway and nascent virions preferentially incorporated the activated form of ERK2 (pERK2) into the tegument. This was evident even in the face of greatly diminished stores of intracellular ERK2, suggesting a clear bias toward the incorporation of pERK2 into the RRV particle. Similar to earlier findings with KSHV, activation of ERK was essential for the production of lytic viral proteins and virions. Knockdown of intracellular ERK, however, failed to inhibit virus production, likely due to maintenance of residual pools of intracellular pERK2. Paradoxically, selective knockdown of ERK1 enhanced virion production nearly 5-fold and viral titers more than 10-fold. These data are the first to implicate ERK1 as a negative regulator of lytic replication in a herpesvirus and the first to demonstrate the incorporation of an activated signaling molecule within a herpesvirus. Together, the results further our understanding of how herpesviruses interact with host cells during infection and demonstrate how this family of viruses can exploit cellular signal transduction pathways to modulate their own replication.

Viral FLICE inhibitory protein of rhesus monkey rhadinovirus inhibits apoptosis by enhancing autophagosome formation

Rhesus monkey rhadinovirus (RRV) is a gamma-2 herpesvirus closely related to human herpesvirus 8 (HHV8). RRV encodes viral FLICE inhibitory protein (vFLIP), which has death effector domains. Little is known about RRV vFLIP. This study intended to examine its function in apoptosis. Here we found that RRV vFLIP inhibits apoptosis induced by tumor necrosis factor-α (TNF-α) and cycloheximide. In HeLa cells with vFLIP expression, the cleavage of poly [ADP-ribose] polymerase 1 (PARP-1) and activities of caspase 3, 7, and 9 were much lower than those in controls. Cell viability of HeLa cells with vFLIP expression was significantly higher than control cells after apoptosis induction. However, RRV vFLIP appears unable to induce NF-κB signaling when tested in NF-κB reporter assay. RRV vFLIP was able to enhance cell survival under starved conditions or apoptosis induction. At early time points after apoptosis induction, autophagosome formation was enhanced and LC3-II level was elevated in cells with vFLIP and, when autophagy was blocked with chemical inhibitors, these cells underwent apoptosis. Moreover, RRV latent infection of BJAB B-lymphoblastoid cells protects the cells against apoptosis by enhancing autophagy to maintain cell survival. Knockdown of vFLIP expression in the RRV-infected BJAB cells with siRNA abolished the protection against apoptosis. These results indicate that vFLIP protects cells against apoptosis by enhancing autophagosome formation to extend cell survival. The finding of vFLIP’s inhibition of apoptosis via the autophagy pathway provides insights of vFLIP in RRV pathogenesis.

Viral interferon regulatory factors decrease the induction of type I and type II interferon during rhesus macaque rhadinovirus infection

Kaposi's sarcoma-associated herpesvirus and rhesus macaque rhadinovirus (RRV), two closely related gammaherpesviruses, are unique in their expression of viral homologs of cellular interferon regulatory factors (IRFs), termed viral IRFs (vIRFs). To assess the role of vIRFs during de novo infection, we have utilized the bacterial artificial chromosome clone of wild-type RRV(17577) (WT(BAC) RRV) to generate a recombinant virus with all 8 of the vIRFs deleted (vIRF-ko RRV). The infection of primary rhesus fibroblasts and peripheral blood mononuclear cells (PBMCs) with vIRF-ko RRV resulted in earlier and increased induction of type I interferon (IFN) (IFN-α/β) and type II IFN (IFN-γ). Additionally, plasmacytoid dendritic cells maintained higher levels of IFN-α production in PBMC cultures infected with vIRF-ko RRV than in cultures infected with WT(BAC) RRV. Moreover, the nuclear accumulation of phosphorylated IRF-3, which is necessary for the induction of type I IFN, was also inhibited following WT(BAC) RRV infection. These findings demonstrate that during de novo RRV infection, vIRFs are inhibiting the induction of IFN at the transcriptional level, and one potential mechanism for this is the disruption of the activation and localization of IRF-3.

Viral interferon regulatory factors are critical for delay of the host immune response against rhesus macaque rhadinovirus infection

Kaposi's sarcoma-associated herpesvirus (KSHV) and the closely related gamma-2 herpesvirus rhesus macaque (RM) rhadinovirus (RRV) are the only known viruses to encode viral homologues of the cellular interferon (IFN) regulatory factors (IRFs). Recent characterization of a viral IRF (vIRF) deletion clone of RRV (vIRF-knockout RRV [vIRF-ko RRV]) demonstrated that vIRFs inhibit induction of type I and type II IFNs during RRV infection of peripheral blood mononuclear cells. Because the IFN response is a key component to a host's antiviral defenses, this study has investigated the role of vIRFs in viral replication and the development of the immune response during in vivo infection in RMs, the natural host of RRV. Experimental infection of RMs with vIRF-ko RRV resulted in decreased viral loads and diminished B cell hyperplasia, a characteristic pathology during acute RRV infection that often develops into more severe lymphoproliferative disorders in immune-compromised animals, similar to pathologies in KSHV-infected individuals. Moreover, in vivo infection with vIRF-ko RRV resulted in earlier and sustained production of proinflammatory cytokines and earlier induction of an anti-RRV T cell response compared to wild-type RRV infection. These findings reveal the broad impact that vIRFs have on pathogenesis and the immune response in vivo and are the first to validate the importance of vIRFs during de novo infection in the host.

Microtubule- and dynein-dependent nuclear trafficking of rhesus rhadinovirus in rhesus fibroblasts

We investigated the role of microtubules in rhesus rhadinovirus (RRV) nuclear trafficking in rhesus fibroblasts. Intact microtubules and microtubule dynamics are required for RRV trafficking to perinuclear regions. RRV trafficking was reduced by an inhibitor of the dynein motor and overexpression of dynamitin. Furthermore, RRV particles are colocalized with microtubules and dynein proteins. These results highlight the important roles of microtubules and dynein-dynactin complexes in the transport of RRV particles to nuclei during primary infection.

Sequencing of bovine herpesvirus 4 v.test strain reveals important genome features

Background

Bovine herpesvirus 4 (BoHV-4) is a useful model for the human pathogenic gammaherpesviruses Epstein-Barr virus and Kaposi's Sarcoma-associated Herpesvirus. Although genome manipulations of this virus have been greatly facilitated by the cloning of the BoHV-4 V.test strain as a Bacterial Artificial Chromosome (BAC), the lack of a complete genome sequence for this strain limits its experimental use.

Methods

In this study, we have determined the complete sequence of BoHV-4 V.test strain by a pyrosequencing approach.

Results

The long unique coding region (LUR) consists of 108,241 bp encoding at least 79 open reading frames and is flanked by several polyrepetitive DNA units (prDNA). As previously suggested, we showed that the prDNA unit located at the left prDNA-LUR junction (prDNA-G) differs from the other prDNA units (prDNA-inner). Namely, the prDNA-G unit lacks the conserved pac-2 cleavage and packaging signal in its right terminal region. Based on the mechanisms of cleavage and packaging of herpesvirus genomes, this feature implies that only genomes bearing left and right end prDNA units are encapsulated into virions.

Conclusions

In this study, we have determined the complete genome sequence of the BAC-cloned BoHV-4 V.test strain and identified genome organization features that could be important in other herpesviruses.

Viral interleukin-6: role in Kaposi's sarcoma-associated herpesvirus: associated malignancies

Viral interleukin-6 (vIL-6) is a product of Kaposi's sarcoma-associated herpesvirus (KSHV) expressed in latently infected cells and to a higher degree during viral replication. A distinctive feature of vIL-6 is the ability to directly bind and activate gp130 signaling in the absence of other receptor subunits. Secretion of vIL-6 is generally poor, but vIL-6 can activate gp130 from inside the cell. Due to the wide cell distribution of gp130, vIL-6 has the potential to induce a wide range of biological effects. Expression of vIL-6 is variable in KSHV-associated Kaposi's sarcoma (KS), primary effusion lymphoma (PEL), multicentric Castleman's disease (MCD), and in a newly described MCD-like systemic inflammatory syndrome observed in human immunodeficiency virus-positive patients. PEL effusions usually contain vIL-6 at high concentrations; since vIL-6 induces vascular endothelial growth factor, vIL-6 likely contributes to vascular permeability and formation of PEL effusions. Lymph nodes affected with MCD contain vIL-6-positive cells, and vIL-6 levels rise in conjunction with flares of the disease and likely contribute to symptoms of inflammation. The development of vIL-6 inhibitors is a potentially important advance in the treatment of KSHV-associated malignancies where vIL-6 is expressed.

The viral interferon regulatory factors of KSHV: immunosuppressors or oncogenes?

Kaposi’s sarcoma-associated herpesvirus (KSHV) is a large double-stranded DNA gammaherpesvirus, and the etiological agent for three human malignancies: Kaposi’s sarcoma, primary effusion lymphoma, and multicentric Castleman’s disease. To establish and maintain infection, KSHV has evolved unique mechanisms to evade the host immune response. Cellular interferon regulatory factors (IRFs) are a critical part of the host anti-viral immune response. KSHV encodes four homologs of IRFs, vIRF1–4, which inhibit the activity of their cellular counterparts. vIRF1, 2, and 3 have been shown to interact directly with cellular IRFs. Additionally, the vIRFs have other functions such as modulation of Myc, p53, Notch, transforming growth factor-β, and NF-κB signaling. These activities of vIRFs may contribute to KSHV tumorigenesis. KSHV vIRF1 and vIRF3 have been implicated as oncogenes, making the understanding of KSHV vIRF function vital to understanding KSHV pathogenesis.

Rhesus monkey rhadinovirus ORF57 induces gH and gL glycoprotein expression through posttranscriptional accumulation of target mRNAs

Open reading frame 57 (ORF57) of gamma-2 herpesviruses is a key regulator of viral gene expression. It has been reported to enhance the expression of viral genes by transcriptional, posttranscriptional, or translational activation mechanisms. Previously we have shown that the expression of gH and gL of rhesus monkey rhadinovirus (RRV), a close relative of the human Kaposi's sarcoma-associated herpesvirus (KSHV), could be dramatically rescued by codon optimization as well as by ORF57 coexpression (J. P. Bilello, J. S. Morgan, and R. C. Desrosiers, J. Virol. 82:7231-7237, 2008). We show here that ORF57 coexpression and codon optimization had similar effects, except that the rescue of expression by codon optimization was temporally delayed relative to that of ORF57 coexpression. The transfection of gL mRNA directly into cells with or without ORF57 coexpression and with or without codon optimization recapitulated the effects of these modes of induction on transfected DNA. These findings suggested an important role for the enhancement of mRNA stability and/or the translation of mRNA for these very different modes of induced expression. This conclusion was confirmed by several different measures of gH and gL mRNA stability and accumulation with or without ORF57 coexpression and with or without codon optimization. Our results indicate that RRV gH and gL expression is severely limited by the stability of the mRNA and that ORF57 coexpression and codon optimization independently induce gH and gL expression principally by allowing accumulation and translation of these mRNAs.

Longitudinal patterns of viremia and oral shedding of rhesus rhadinovirus and retroperitoneal fibromatosis herpesviruses in age-structured captive breeding populations of rhesus Macaques (Macaca mulatta)

Rhesus rhadinovirus (RRV) and retroperitoneal fibromatosis herpesvirus (RFHV), 2 closely related γ2 herpesviruses, are endemic in breeding populations of rhesus macaques at our institution. We previously reported significantly different prevalence levels, suggesting the transmission dynamics of RRV and RFHV differ with regard to viral shedding and infectivity. We designed a longitudinal study to further examine the previously observed differences between RRV and RFHV prevalence and the potential influence of age, season, and housing location on the same 90 rhesus macaques previously studied. Virus- and host-genome-specific real-time PCR assays were used to determine viral loads for both RRV and RFHV in blood and saliva samples collected at 6 time points over an 18-mo period. Proportions of positive animals and viral load in blood and saliva were compared between and within viruses by age group, location, and season by using 2-part longitudinal modeling with Bayesian inferences. Our results demonstrate that age and season are significant determinants, with age as the most significant factor analyzed, of viremia and oral shedding for both RRV and RFHV, and these pathogens exhibit distinctly different patterns of viremia and oral shedding over time within a single population.

Rhesus rhadinovirus infection of rhesus fibroblasts occurs through clathrin-mediated endocytosis

Rhesus rhadinovirus (RRV) is a gammaherpesvirus closely related to Kaposi's sarcoma-associated herpesvirus (KSHV), an oncogenic virus linked to the development of Kaposi's sarcoma and several other lymphoproliferative diseases, including primary effusion lymphoma and multicentric Castleman's disease. RRV naturally infects rhesus macaques and induces lymphoproliferative diseases under experimental conditions, making it an excellent model for the study of KSHV. Unlike KSHV, which grows poorly in cell culture, RRV replicates efficiently in rhesus fibroblasts (RFs). In this study, we have characterized the entry pathway of RRV in RFs. Using a luciferase-expressing recombinant RRV (RRV-luciferase), we show that the infectivity of RRV is reduced by inhibitors of endosomal acidification. RRV infectivity is also reduced by inhibitors of clathrin-mediated but not caveola-mediated endocytosis, indicating that RRV enters into RFs via clathrin-mediated endocytosis. Using a red fluorescent protein (RFP)-expressing recombinant RRV (RRV-RFP), we show that RRV particles are colocalized with markers of endocytosis (early endosome antigen 1) and clathrin-mediated endocytosis (clathrin heavy chain) during entry into RFs. RRV particles are also colocalized with transferrin, which enters cells by clathrin-mediated endocytosis, but not with cholera toxin B, which enters cells by caveola-mediated endocytosis. Inhibition of clathrin-mediated endocytosis with a dominant-negative construct of EPS15, an essential component of clathrin-coated pits, blocked the entry of RRV into RFs. Together, these results indicate that RRV entry into RFs is mediated by clathrin-mediated endocytosis.

Simian herpesviruses and their risk to humans

A high level of genetic and physiological homology with humans has rendered non-human primates (NHP) an essential animal model for biomedical research. As such NHP offer a unique opportunity to study host-pathogen interactions in a species that closely mimics human biology but can yet be maintained under tight laboratory conditions. Indeed, studies using NHP have been critical to our understanding of pathogenesis as well as the development of vaccines and therapeutics. This further facilitated by the fact that NHPs are susceptible to a variety of pathogens that bear significant homology to human pathogens. Unfortunately, these same viruses pose a potential health issue to humans. In this review we discuss the simian herpesviruses and their potential to cause disease in researchers that come into close contact with them.

Emerging and reemerging infectious diseases of nonhuman primates in the laboratory setting

Despite numerous advances in the diagnosis and control of infectious diseases of nonhuman primates in the laboratory setting, a number of infectious agents continue to plague colonies. Some, such as measles virus and Mycobacterium tuberculosis, cause sporadic outbreaks despite well-established biosecurity protocols, whereas others, such as retroperitoneal fibromatosis-associated herpesvirus, have only recently been discovered, often as a result of immunosuppressive experimental manipulation. Owing to the unique social housing requirements of nonhuman primates, importation of foreign-bred animals, and lack of antemortem diagnostic assays for many new diseases, elimination of these agents is often difficult or impractical. Recognition of these diseases is therefore essential because of their confounding effects on experimental data, impact on colony health, and potential for zoonotic transmission. This review summarizes the relevant pathology and pathogenesis of emerging and reemerging infectious diseases of laboratory nonhuman primates.

Herpesvirus systematics

This paper is about the taxonomy and genomics of herpesviruses. Each theme is presented as a digest of current information flanked by commentaries on past activities and future directions. The International Committee on Taxonomy of Viruses recently instituted a major update of herpesvirus classification. The former family Herpesviridae was elevated to a new order, the Herpesvirales, which now accommodates 3 families, 3 subfamilies, 17 genera and 90 species. Future developments will include revisiting the herpesvirus species definition and the criteria used for taxonomic assignment, particularly in regard to the possibilities of classifying the large number of herpesviruses detected only as DNA sequences by polymerase chain reaction. Nucleotide sequence accessions in primary databases, such as GenBank, consist of the sequences plus annotations of the genetic features. The quality of these accessions is important because they provide a knowledge base that is used widely by the research community. However, updating the accessions to take account of improved knowledge is essentially reserved to the original depositors, and this activity is rarely undertaken. Thus, the primary databases are likely to become antiquated. In contrast, secondary databases are open to curation by experts other than the original depositors, thus increasing the likelihood that they will remain up to date. One of the most promising secondary databases is RefSeq, which aims to furnish the best available annotations for complete genome sequences. Progress in regard to improving the RefSeq herpesvirus accessions is discussed, and insights into particular aspects of herpesvirus genomics arising from this work are reported.

Viral interferon regulatory factors

Upon viral infection, the major defensive strategy employed by the host immune system is the activation of the interferon (IFN)-mediated antiviral pathway, which is overseen by IFN regulatory factors (IRFs). In order to complete their life cycles, viruses must find a way to modulate the host IFN-mediated immune response. Kaposi's sarcoma-associated herpesvirus (KSHV), a human tumor-inducing herpesvirus, has developed a unique mechanism for antagonizing cellular IFN-mediated antiviral activity by incorporating viral homolog of the cellular IRFs, called vIRFs, into its genome. Here, we summarize the novel evasion mechanisms by which KSHV, through its vIRFs, circumvents IFN-mediated innate immune responses and deregulates the cell growth control mechanism.

Glycoprotein gene sequence variation in rhesus monkey rhadinovirus

Gene sequences for seven glycoproteins from 20 independent isolates of rhesus monkey rhadinovirus (RRV) and of the corresponding seven glycoprotein genes from nine strains of the Kaposi's sarcoma-associated herpesvirus (KSHV) were obtained and analyzed. Phylogenetic analysis revealed two discrete groupings of RRV gH sequences, two discrete groupings of RRV gL sequences and two discrete groupings of RRV gB sequences. We called these phylogenetic groupings gH(a), gH(b), gL(a), gL(b), gB(a) and gB(b). gH(a) was always paired with gL(a) and gH(b) was always paired with gL(b) for any individual RRV isolate. Since gH and gL are known to be interacting partners, these results suggest the need of matching sequence types for function of these cooperating proteins. gB phylogenetic grouping was not associated with gH/gL phylogenetic grouping. Our results demonstrate two distinct, distantly-related phylogenetic groupings of gH and gL of RRV despite a remarkable degree of sequence conservation within each individual phylogenetic group.

Viral interleukin-6 encoded by rhesus macaque rhadinovirus is associated with lymphoproliferative disorder (LPD)

BACKGROUND

Rhesus macaques (RM) co-infected with simian immunodeficiency virus (SIV) and rhesus macaque rhadinovirus (RRV) develop abnormal cellular proliferations characterized as extra-nodal lymphoma and retroperitoneal fibromatosis (RF). RRV encodes a viral interleukin-6 (vIL-6), much like Kaposi's sarcoma-associated herpesvirus, and involvement of the viral cytokine was examined in proliferative lesions.

METHODS

Formalin fixed tissue from RM co-infected with SIV and RRV were analyzed for RRV genomes by in situ hybridization and RRV vIL-6 expression by immunofluorescence analysis.

RESULTS

In situ hybridization analysis indicated that RRV is present in both types of lesions. Immunofluorescence analysis of different lymphomas and RF revealed positive staining for vIL-6. Similarly to KS, RF lesion is positive for vimentin, CD117 (c-kit), and smooth muscle actin (SMA) and contains T cell, B cell and monocytes/macrophage infiltrates.

CONCLUSIONS

Our data support the idea that vIL-6 may be critical to the development and progression of lymphoproliferative disorder in RRV/SIV-infected RM.

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.

Autoexcision of bacterial artificial chromosome facilitated by terminal repeat-mediated homologous recombination: a novel approach for generating traceless genetic mutants of herpesviruses

Infectious bacterial artificial chromosomes (BACs) of herpesviruses are powerful tools for genetic manipulation. However, the presence of BAC vector sequence in the viral genomes often causes genetic and phenotypic alterations. While the excision of the BAC vector cassette can be achieved by homologous recombination between extra duplicate viral sequences or loxP site-mediated recombination, these methods either are inefficient or leave a loxP site mark in the viral genome. Here we describe the use of viral intrinsic repeat sequences, which are commonly present in herpesviral genomes, to excise the BAC vector cassette. Using a newly developed in vitro transposon-based cloning approach, we obtained an infectious BAC of rhesus rhadinovirus (RRV) strain RRV26-95 with the BAC vector cassette inserted in the terminal repeat (TR) region. We showed that the BAC vector cassette was rapidly excised upon reconstitution in cells predominantly through TR-mediated homologous recombination. Genetic and phenotypic analysis showed that the BAC-excised virus was reversed to wild-type RRV. Using this autoexcisable BAC clone, we successfully generated an RRV mutant with a deletion of Orf50, which encodes a replication and transcription activator (RTA) protein. Together, these results illustrate the usefulness of TR for genetic manipulation of herpesviruses when combined with the novel transposon-based cloning approach.

Characterization of cytoplasmic motifs important in rhesus rhadinovirus gB processing and trafficking

Rhesus monkey rhadinovirus (RRV) is highly related to Kaposi's sarcoma-associated herpesvirus (KSHV), a human gamma-herpesvirus etiologically-linked with several cancers. Glycoprotein B (gB) homologues are encoded by all herpesviruses and play a role in virus attachment, entry, and in egress. We have found that RRV gB, like KSHV gB, is cleaved at a consensus furin cleavage site and is modified by both N-linked and O-linked glycosylation. Mutagenesis of three tyrosine- based trafficking motifs, a diacidic tyrosine motif, and a di-lucine motif in the cytoplasmic region revealed a role for these sequences in both ER export and endocytosis from the plasma membrane. These experiments provide a basis for further experiments looking at gB incorporation and role in gamma-herpesvirus assembly and egress.

The ORF59 DNA polymerase processivity factor homologs of Old World primate RV2 rhadinoviruses are highly conserved nuclear antigens expressed in differentiated epithelium in infected macaques

Background

ORF59 DNA polymerase processivity factor of the human rhadinovirus, Kaposi's sarcoma-associated herpesvirus (KSHV), is required for efficient copying of the genome during virus replication. KSHV ORF59 is antigenic in the infected host and is used as a marker for virus activation and replication.

Results

We cloned, sequenced and expressed the genes encoding related ORF59 proteins from the RV1 rhadinovirus homologs of KSHV from chimpanzee (PtrRV1) and three species of macaques (RFHVMm, RFHVMn and RFHVMf), and have compared them with ORF59 proteins obtained from members of the more distantly-related RV2 rhadinovirus lineage infecting the same non-human primate species (PtrRV2, RRV, MneRV2, and MfaRV2, respectively). We found that ORF59 homologs of the RV1 and RV2 Old World primate rhadinoviruses are highly conserved with distinct phylogenetic clustering of the two rhadinovirus lineages. RV1 and RV2 ORF59 C-terminal domains exhibit a strong lineage-specific conservation. Rabbit antiserum was developed against a C-terminal polypeptide that is highly conserved between the macaque RV2 ORF59 sequences. This anti-serum showed strong reactivity towards ORF59 encoded by the macaque RV2 rhadinoviruses, RRV (rhesus) and MneRV2 (pig-tail), with no cross reaction to human or macaque RV1 ORF59 proteins. Using this antiserum and RT-qPCR, we determined that RRV ORF59 is expressed early after permissive infection of both rhesus primary fetal fibroblasts and African green monkey kidney epithelial cells (Vero) in vitro. RRV- and MneRV2-infected foci showed strong nuclear expression of ORF59 that correlated with production of infectious progeny virus. Immunohistochemical studies of an MneRV2-infected macaque revealed strong nuclear expression of ORF59 in infected cells within the differentiating layer of epidermis corroborating previous observations that differentiated epithelial cells are permissive for replication of KSHV-like rhadinoviruses.

Conclusion

The ORF59 DNA polymerase processivity factor homologs of the Old World primate RV1 and RV2 rhadinovirus lineages are phylogenetically distinct yet demonstrate similar expression and localization characteristics that correlate with their use as lineage-specific markers for permissive infection and virus replication. These studies will aid in the characterization of virus activation from latency to the replicative state, an important step for understanding the biology and transmission of rhadinoviruses, such as KSHV.

Genetic diversity and molecular evolution of human and non-human primate Gammaherpesvirinae

The Gammaherpesvirinae sub-family is divided into two genera: Lymphocryptovirus and Rhadinovirus. Until the middle of the 1990s, the Rhadinovirus genus was only represented by Herpesvirus saimiri and Herpesvirus ateles, which infect New World monkey species. Until the year 2000, Epstein-Barr virus (EBV), the human prototype of the Lymphocryptovirus, and simian homologues had only been detected in humans and Old World non-human primates. It was thought, therefore, that the separation of the continents had resulted in drastic changes in Gammaherpesvirinae evolution. The discovery of Kaposi's sarcoma-associated herpesvirus in humans, belonging to the Rhadinovirus, followed by the identification of CalHV3 (Callitrichine herpesvirus 3), a lymphocryptovirus of the marmoset, challenged this paradigm. The description of numerous viruses belonging to this sub-family from various Old and New World primate species enabled a cospeciation hypothesis for these viruses and their hosts to be developed. This review focuses on the current knowledge of primate Gammaherpesvirinae genetic diversity and molecular evolution. We discuss the various theories based on current genetic data regarding evolutionary relationships between lymphocryptoviruses of Old World primates, the use of these data as a tool to study evolutionary relationships between New World monkey species, and the possible existence of a ninth human herpesvirus belonging to the Rhadinovirus genus.

Non-human primate model of Kaposi's sarcoma-associated herpesvirus infection

Since Kaposi's sarcoma-associated herpesvirus (KSHV or human herpesvirus 8) was first identified in Kaposi's sarcoma (KS) lesions of HIV-infected individuals with AIDS, the basic biological understanding of KSHV has progressed remarkably. However, the absence of a proper animal model for KSHV continues to impede direct in vivo studies of viral replication, persistence, and pathogenesis. In response to this need for an animal model of KSHV infection, we have explored whether common marmosets can be experimentally infected with human KSHV. Here, we report the successful zoonotic transmission of KSHV into common marmosets (Callithrix jacchus, Cj), a New World primate. Marmosets infected with recombinant KSHV rapidly seroconverted and maintained a vigorous anti-KSHV antibody response. KSHV DNA and latent nuclear antigen (LANA) were readily detected in the peripheral blood mononuclear cells (PBMCs) and various tissues of infected marmosets. Remarkably, one orally infected marmoset developed a KS-like skin lesion with the characteristic infiltration of leukocytes by spindle cells positive for KSHV DNA and proteins. These results demonstrate that human KSHV infects common marmosets, establishes an efficient persistent infection, and occasionally leads to a KS-like skin lesion. This is the first animal model to significantly elaborate the important aspects of KSHV infection in humans and will aid in the future design of vaccines against KSHV and anti-viral therapies targeting KSHV coinfected tumor cells.

Kaposi's sarcoma-associated herpesvirus (KSHV or human herpesvirus 8), the most recently identified human tumor-inducing virus, has been linked to Kaposi's sarcoma, pleural effusion lymphomas and multicentric Castleman's disease. In fact, KSHV accounts for a large proportion of the cancer deaths in Africa. Further, the incidence of KSHV in the US and Europe has greatly increased due to the AIDS pandemic. Despite these pressing human health problems, studies of KSHV infection are greatly hampered by the lack of cell culture and animal models. To address this serious need, we set out to develop an animal model for KSHV infection. In this manuscript, we report the successful zoonotic transmission of KSHV into common marmosets (Callithrix jacchus, Cj), a New World primate. Our study demonstrates that experimental KSHV infection of the common marmoset is highly analogous to its infection of humans, including the means of infection, sustained serological responses, latent infection of PBMCs, virus persistence, and KS-like skin lesion development, although the latter was infrequent in experimental KSHV infections. This model thus provides a unique opportunity to dissect the molecular mechanisms of KSHV infection, persistence, and pathogenesis directly in primates.

Prevalence of viremia and oral shedding of rhesus rhadinovirus and retroperitoneal fibromatosis herpesvirus in large age-structured breeding groups of rhesus macaques (Macaca mulatta)

We performed a cross-sectional study to estimate the prevalence of 2 gamma-2-herpesviruses, rhesus rhadinovirus (RRV) and retroperitoneal fibromatosis herpesvirus (RFHV), in breeding colonies of rhesus macaques. Of 90 animals selected for sampling, 73 (81%) were positive for RRV, which was detected only in blood in 22 (24%), only in saliva in 15 (16%), and in both blood and saliva in 36 (40%). Detection of RRV DNA in blood and saliva was significantly higher in animals younger than 2 y. In comparison, RFHV was detected in 40 (44%) of the 90 animals: only in blood in 5 (6%), only in saliva in 26 (29%), and in both blood and saliva in 9 (10%). Dual infection was detected in 38 (42%) animals; RFHV was only detected in coinfections. The mean RRV genome copy number in blood was significantly higher than that for RFHV. Age was a significant predictor of RRV copy number in blood and RFHV copy number in saliva. Of the 90 animals, 88 (98%) were positive for rhadinoviral antibodies on an immunofluorescent assay. Both RRV and RFHV are highly endemic in socially housed breeding colonies of rhesus macaques, and their patterns of infection are similar to that for the betaherpesvirus rhesus cytomegalovirus.

Disruption of LANA in rhesus rhadinovirus generates a highly lytic recombinant virus

Rhesus monkey rhadinovirus (RRV) is a gammaherpesvirus that is closely related to human Kaposi's sarcoma-associated herpesvirus (KSHV/HHV-8). RRV is the closest relative to KSHV that has a fully sequenced genome and serves as an in vitro and an in vivo model system for KSHV. The latency-associated nuclear antigen (LANA) protein of both KSHV and RRV plays key roles in the establishment and maintenance of these herpesviruses. We have constructed a RRV recombinant virus (RRVDeltaLANA/GFP) in which the RRV LANA open reading frame has been disrupted with a green fluorescent protein (GFP) expression cassette generated by homologous recombination. The integrity of the recombinant virus was confirmed by diagnostic PCR, restriction digestion, Southern blot analysis, and whole-genome sequencing. We compared the single-step and multistep replication kinetics of RRVDeltaLANA/GFP, RRV-GFP, wild-type (WT) RRV H26-95, and a revertant virus using traditional plaque assays, as well as real-time quantitative PCR-based genome quantification assays. The RRVDeltaLANA/GFP recombinant virus exhibited significantly higher lytic replicative properties compared to RRV-GFP, WT RRV, or the revertant virus. This was observed upon de novo infection and in the absence of chemical inducers such as phorbol esters. In addition, by using a quantitative real-time PCR-based viral array, we are the first to report differences in global viral gene expression between WT and recombinant viruses. The RRVDeltaLANA/GFP virus displayed increased lytic gene transcription at all time points postinfection compared to RRV-GFP. Moreover, we also examined several cellular genes that are known to be repressed by KSHV LANA and report that these genes are derepressed during de novo lytic infection with the RRVDeltaLANA/GFP virus compared to RRV-GFP. Finally, we also demonstrate that the RRVDeltaLANA/GFP virus fails to establish latency in B cells, as measured by the loss of GFP-positive cells and intracellular viral genomes.

Identification of caspase-mediated decay of interferon regulatory factor-3, exploited by a Kaposi sarcoma-associated herpesvirus immunoregulatory protein

Upon virus infection, the cell mounts an innate type I interferon (IFN) response to limit the spread. This response is orchestrated by the constitutively expressed IFN regulatory factor (IRF)-3 protein, which becomes post-translationally activated. Although the activation events are understood in detail, the negative regulation of this innate response is less well understood. Many viruses, including Kaposi sarcoma-associated herpesvirus (KSHV), have evolved defense strategies against this IFN response. Thus, KSHV encodes a viral IRF (vIRF)-2 protein, sharing homology with cellular IRFs and is a known inhibitor of the innate IFN response. Here, we show that vIRF-2 mediates IRF-3 inactivation by a mechanism involving caspase-3, although vIRF-2 itself is not pro-apoptotic. Importantly, we also show that caspase-3 participates in normal IRF-3 turnover in the absence of vIRF-2, during the antiviral response induced by poly(I:C) transfection. These data provide unprecedented insight into negative regulation of IRF-3 following activation of the type I IFN antiviral response and the mechanism by which KSHV vIRF-2 inhibits this innate response.

Identification and functional characterization of a spliced rhesus rhadinovirus gene with homology to the K15 gene of Kaposi's sarcoma-associated herpesvirus

Rhesus monkey rhadinovirus (RRV) is a gamma-2 herpesvirus related to the human Kaposi's sarcoma-associated herpesvirus (KSHV or human herpesvirus 8). This study identified an alternatively spliced gene at the right side of the RRV genome (strain 17577) between open reading frame 75 and the terminal repeat region. Of its eight exons, the first seven encoded up to 12 transmembrane domains, whilst the eighth exon encoded a predicted C-terminal cytoplasmic domain. Structurally and positionally, this RRV gene therefore resembles the K15 gene of KSHV; it was provisionally named RK15 to avoid confusion with other RRV17577 genes. In ectopic expression studies, the 55 kDa RK15 protein isoform activated the JNK and NF-kappaB pathways, like the 45 kDa KSHV K15-encoded protein isoform. In contrast to K15, which activates angiogenic and inflammatory cytokines such as interleukin (IL)-8, IL-6 and CCL20, the range of cellular transcripts activated by the RRV K15 homologue was much more restricted, but included IL-6, IL-8 and FGF21. These data suggest functional differences between terminal membrane proteins at the right end of the genomes of Old World primate gamma-2 herpesviruses.

Immune evasion in Kaposi's sarcoma-associated herpes virus associated oncogenesis

A hallmark of herpesviruses is a lifelong persistent infection, which often leads to diseases upon immune suppression of infected host. Kaposi's sarcoma-associated herpesvirus (KSHV), also known as human herpesvirus 8 (HHV8), is etiologically linked to the development of Kaposi's sarcoma (KS), primary effusion lymphoma (PEL), and Multicentric Castleman's disease (MCD). In order to establish a persistent infection, KSHV dedicates a large portion of its genomic information to sabotage almost every aspect of host immune system. Thus, understanding the interplay between KSHV and the host immune system is important in not only unraveling the complexities of viral persistence and pathogenesis, but also discovering novel therapeutic targets. This review summarizes current knowledge of host immune evasion strategies of KSHV and their contributions to KSHV-associated diseases.

Rhesus macaque rhadinovirus-associated non-Hodgkin lymphoma: animal model for KSHV-associated malignancies

Rhesus macaque rhadinovirus (RRV) is closely related to Kaposi sarcoma-associated herpesvirus (KSHV) and is associated with the development of B-cell hyperplasia and persistent lymphadenopathy resembling multicentric Castleman disease in rhesus macaques (RMs) coinfected with simian immunodeficiency virus (SIV). Here we investigated whether RMs experimentally infected with SIV and RRV can develop other disease manifestations observed in HIV- and KSHV-infected patients. As reported earlier, inoculation of SIV-infected RMs with RRV results in persistent RRV infection, whereas immunocompetent animals infected with RRV exhibit viremia 2 weeks after infection, followed by a period of no virus detection until they are subsequently made immunodeficient by SIV infection. A subset of animals developed abnormal cellular proliferations characterized as extranodal lymphoma and a proliferative mesenchymal lesion. In situ hybridization and immunohistochemistry analysis indicate RRV is present in both malignancies, and DNA microarray analysis detected viral interleukin-6 (vIL-6) and viral FLICE-like inhibitory protein (vFLIP) transcripts. Reverse-transcriptase polymerase chain reaction analysis confirmed vIL-6 and vFLIP expression, and that of RRV open reading frames 72 and 73, homologs of KSHV open reading frames shown to be expressed in primary effusion lymphoma. These data support the utility of the RRV-/SIV-infected RM as an excellent animal model to investigate KSHV-like pathogenesis.

Comparative pathobiology of Kaposi sarcoma-associated herpesvirus and related primate rhadinoviruses

With the emergence of the AIDS epidemic over the last 2 decades and the more recent identification of Kaposi sarcoma-associated herpesvirus (KSHV, Human herpesvirus 8), the genera of rhadinoviruses have gained importance as a family of viruses with oncogenic potential. First recognized in New World primates more than 30 y ago, the rhadinoviruses Saimiriine herpesvirus 2 and Ateline herpesvirus 2 have well-described transforming capabilities. Recently several new species-specific rhadinoviruses of Old World primates have been described, including retroperitoneal fibromatosis herpesvirus and rhesus rhadinovirus (Cercopithecine herpesvirus 17). Molecular analysis of these viruses has elucidated several functionally conserved genes and properties shared with KSHV involved in cellular proliferation, transformation, and immune evasion that facilitate the oncogenic potential of these viruses. This review examines the comparative pathobiology of KSHV, discusses the role of macaque rhadinoviruses as models of human disease, and outlines the derivation of specific pathogen-free animals.

Integrin alphaVbeta3 Binds to the RGD motif of glycoprotein B of Kaposi's sarcoma-associated herpesvirus and functions as an RGD-dependent entry receptor

Kaposi's sarcoma-associated herpesvirus (KSHV) envelope-associated glycoprotein B (gB) is involved in the initial steps of binding to host cells during KSHV infection. gB contains an RGD motif reported to bind the integrin alpha(3)beta(1) during virus entry. Although the ligand specificity of alpha(3)beta(1) has been controversial, current literature indicates that alpha(3)beta(1) ligand recognition is independent of RGD. We compared alpha(3)beta(1) to the RGD-binding integrin, alpha(V)beta(3), for binding to envelope-associated gB and a gB(RGD) peptide. Adhesion assays demonstrated that beta(3)-CHO cells overexpressing alpha(V)beta(3) specifically bound gB(RGD), whereas alpha(3)-CHO cells overexpressing alpha(3)beta(1) did not. Function-blocking antibodies to alpha(V)beta(3) inhibited the adhesion of HT1080 fibrosarcoma cells to gB(RGD), while antibodies to alpha(3)beta(1) did not. Using affinity-purified integrins and confocal microscopy, alpha(V)beta(3) bound to gB(RGD) and KSHV virions, demonstrating direct receptor-ligand interactions. Specific alpha(V)beta(3) antagonists, including cyclic and dicyclic RGD peptides and alpha(V)beta(3) function-blocking antibodies, inhibited KSHV infection by 70 to 80%. Keratinocytes from alpha(3)-null mice lacking alpha(3)beta(1) were fully competent for infection by KSHV, and reconstitution of alpha(3)beta(1) function by transfection with alpha(3) cDNA reduced KSHV infectivity from 74% to 55%. Additional inhibitory effects of alpha(3)beta(1) on the cell surface expression of alpha(V)beta(3) and on alpha(V)beta(3)-mediated adhesion of alpha(3)-CHO cells overexpressing alpha(3)beta(1) were detected, consistent with previous reports of transdominant inhibition of alpha(V)beta(3) function by alpha(3)beta(1). These observations may explain previous reports of an inhibition of KSHV infection by soluble alpha(3)beta(1). Our studies demonstrate that alpha(V)beta(3) is a cellular receptor mediating both the cell adhesion and entry of KSHV into target cells through binding the virion-associated gB(RGD).

Murine gammaherpesvirus 68 ORF52 encodes a tegument protein required for virion morphogenesis in the cytoplasm

The tegument, a semiordered matrix of proteins overlying the nucleocapsid and underlying the virion envelope, in viruses in the gamma subfamily of Herpesviridae is poorly understood. Murine gammaherpesvirus 68 (MHV-68) is a robust model for studying gammaherpesvirus virion structure, assembly, and composition, as MHV-68 efficiently completes the lytic phase and productively infects cultured cells. We have found that MHV-68 ORF52 encodes an abundant tegument protein conserved among gammaherpesviruses. Detergent sensitivity experiments revealed that the MHV-68 ORF52 protein is more tightly bound to the virion nucleocapsid than the ORF45 tegument protein but could be dissociated from particles that retained the ORF65 small capsomer protein. ORF52, tagged with enhanced green fluorescent protein or FLAG epitope, localized to the cytoplasm. A recombinant MHV-68 bacterial artificial chromosome mutant with a nonsense mutation incorporated into ORF52 exhibited viral DNA replication, expression of late lytic genes, and capsid assembly and packaging at levels near those of the wild type. However, the MHV-68 ORF52-null virus was deficient in the assembly and release of infectious virion particles. Instead, partially tegumented capsids produced by the ORF52-null mutant accumulated in the cytoplasm, containing conserved capsid proteins, the ORF64 and ORF67 tegument proteins, but virtually no ORF45 tegument protein. Thus, ORF52 is essential for the tegumentation and egress of infectious MHV-68 particles in the cytoplasm, suggesting an important conserved function in gammaherpesvirus virion morphogenesis.

The death domain superfamily in intracellular signaling of apoptosis and inflammation

The death domain (DD) superfamily comprising the death domain (DD) subfamily, the death effector domain (DED) subfamily, the caspase recruitment domain (CARD) subfamily, and the pyrin domain (PYD) subfamily is one of the largest domain superfamilies. By mediating homotypic interactions within each domain subfamily, these proteins play important roles in the assembly and activation of apoptotic and inflammatory complexes. In this chapter, we review the molecular complexes assembled by these proteins, the structural and biochemical features of these domains, and the molecular interactions mediated by them. By analyzing the potential molecular basis for the function of these domains, we hope to provide a comprehensive understanding of the function, structure, interaction, and evolution of this important family of domains.

Molecular characterization of the rhesus rhadinovirus (RRV) ORF4 gene and the RRV complement control protein it encodes

The diversity of viral strategies to modulate complement activation indicates that this component of the immune system has significant antiviral potential. One example is the Kaposi's sarcoma-associated herpesvirus (KSHV) complement control protein (KCP), which inhibits progression of the complement cascade. Rhesus rhadinovirus (RRV), like KSHV, is a member of the subfamily Gammaherpesvirinae and currently provides the only in vivo model of KSHV pathobiology in primates. In the present study, we characterized the KCP homologue encoded by RRV, RRV complement control protein (RCP). Two strains of RRV have been sequenced to date (H26-95 and 17577), and the RCPs they encode differ substantially in structure: RCP from strain H26-95 has four complement control protein (CCP) domains, whereas RCP from strain 17577 has eight CCP domains. Transcriptional analyses of the RCP gene (ORF4, referred to herein as RCP) in infected rhesus macaque fibroblasts mapped the ends of the transcripts of both strains. They revealed that H26-95 encodes a full-length, unspliced RCP transcript, while 17577 RCP generates a full-length unspliced mRNA and two alternatively spliced transcripts. Western blotting confirmed that infected cells express RCP, and immune electron microscopy disclosed this protein on the surface of RRV virions. Functional studies of RCP encoded by both RRV strains revealed their ability to suppress complement activation by the classical (antibody-mediated) pathway. These data provide the foundation for studies into the biological significance of gammaherpesvirus complement regulatory proteins in a tractable, non-human primate model.

Construction of an infectious rhesus rhadinovirus bacterial artificial chromosome for the analysis of Kaposi's sarcoma-associated herpesvirus-related disease development

Rhesus rhadinovirus (RRV) is closely related to Kaposi's sarcoma-associated herpesvirus (KSHV)/human herpesvirus 8 (HHV-8) and causes KSHV-like diseases in immunocompromised rhesus macaques (RM) that resemble KSHV-associated diseases including multicentric Castleman's disease and non-Hodgkin's lymphoma. RRV retains a majority of open reading frames (ORFs) postulated to be involved in the pathogenesis of KSHV and is the closest available animal model to KSHV infection in humans. Here we describe the generation of a recombinant clone of RRV strain 17577 (RRV(17577)) utilizing bacterial artificial chromosome (BAC) technology. Characterization of the RRV BAC demonstrated that it is a pathogenic molecular clone of RRV(17577), producing virus that behaves like wild-type RRV both in vitro and in vivo. Specifically, BAC-derived RRV displays wild-type growth properties in vitro and readily infects simian immunodeficiency virus-infected RM, inducing B cell hyperplasia, persistent lymphadenopathy, and persistent infection in these animals. This RRV BAC will allow for rapid genetic manipulation of the RRV genome, facilitating the creation of recombinant versions of RRV that harbor specific alterations and/or deletions of viral ORFs. This system will provide insights into the roles of specific RRV genes in various aspects of the viral life cycle and the RRV-associated pathogenesis in vivo in an RM model of infection. Furthermore, the generation of chimeric versions of RRV containing KSHV genes will allow analysis of the function and contributions of KSHV genes to viral pathogenesis by using a relevant primate model system.

Molecular biology of KSHV in relation to AIDS-associated oncogenesis

KSHV has been established as the causative agent of KS, PEL, and MCD, malignancies occurring more frequently in AIDS patients. The aggressive nature of KSHV in the context of HIV infection suggests that interactions between the two viruses enhance pathogenesis. KSHV latent infection and lytic reactivation are characterized by distinct gene expression profiles, and both latency and lytic reactivation seem to be required for malignant progression. As a sophisticated oncogenic virus, KSHV has evolved to possess a formidable repertoire of potent mechanisms that enable it to target and manipulate host cell pathways, leading to increased cell proliferation, increased cell survival, dysregulated angiogenesis, evasion of immunity, and malignant progression in the immunocompromised host. Worldwide, approximately 40.3 million people are currently living with HIV infection. Of these, a significant number are coinfected with KSHV. The complex interplay between the two viruses dramatically elevates the risk for development of KSHV-induced malignancies, KS, PEL, and MCD. Although HAART significantly reduces HIV viral load, the entire T-cell repertoire and immune function may not be completely restored. In fact, clinically significant immune deficiency is not necessary for the induction of KSHV-related malignancy. Because of variables such as lack of access to therapy noncompliance with prescribed treatment, failure to respond to treatment and the development of drug-resistant strains of HIV, KSHV-induced malignancies will continue to present as major health concerns.

High levels of retroperitoneal fibromatosis (RF)-associated herpesvirus in RF lesions in macaques are associated with ORF73 LANA expression in spindleoid tumour cells

Two distinct lineages of rhadinoviruses related to Kaposi's sarcoma (KS)-associated herpesvirus (KSHV; Human herpesvirus 8), the causative agent of KS, have been identified. In macaques, the RV1 lineage is represented by retroperitoneal fibromatosis (RF) herpesvirus (RFHV), the homologue of KSHV, whilst the RV2 lineage is represented by rhesus rhadinovirus (RRV), a more distantly related virus. Real-time quantitative PCR was used to estimate the loads of RV1 and RV2 rhadinoviruses in simian acquired immunodeficiency syndrome-associated RF (SAIDS-RF), a neoplasm of macaques with similarities to AIDS-associated KS. Both RV1 and RV2 rhadinoviruses were detected in macaques with RF. The RV1 loads were 220- to 4300-fold higher in RF tumours than in spleen, showing a strong tumour association (mean loads of 1 800 000 vs 2900 copies per 10(6) cells in tumours and spleen, respectively). In contrast, RV2 loads in the RF tumours were 100-fold lower than RV1 loads and showed similar levels in tumours and spleen (mean loads of 16 000 vs 24 000 copies per 10(6) cells, respectively). Immunostaining with antibodies reactive against RFHV ORF73 latency-associated nuclear antigen (LANA) showed intense nuclear staining of the spindleoid RF tumour cells. Correlation of viral load and the number of LANA-positive cells indicated that RF tumour cells contained multiple copies of the RFHV genome per cell. This pattern of infectivity is similar to that seen in KS tumours latently infected with KSHV. Our study demonstrates similarities in the biology of KSHV and RFHV and supports a role for RFHV in the aetiology of SAIDS-RF.

Rhesus monkey rhadinovirus: a model for the study of KSHV

Rhesus monkey rhadinovirus (RRV) is one of the closest phylogenetic relatives to the human pathogen Kaposi sarcoma-associated herpesvirus (KSHV)-a gamma-2 herpesvirus and the etiologic agent of three malignancies associated with immunosuppression. In contrast to KSHV, RRV displays robust lytic-phase growth in culture, replicating to high titer, and therefore holds promise as an effective model for studying primate gammaherpesvirus lytic gene transcription as well as virion structure, assembly, and proteomics. More recently, investigators have devised complementary latent systems of RRV infection, thereby also enabling the characterization of the more restricted latent transcriptional program. Another benefit of working with RRV as a primate gammaherpesvirus model is that its efficient lytic growth makes genetic manipulation easier than that in its human counterpart. Exploiting this quality, laboratories have already begun to generate mutant RRV, setting the stage for future work investigating the function of individual viral genes. Finally, rhesus macaques support experimental infection with RRV, providing a natural in vivo model of infection, while similar nonhuman systems have remained resistant to prolonged KSHV infection. Recently, dual infection with RRV and a strain of simian immunodeficiency virus (SIV) has led to a lymphoproliferative disorder (LPD) reminiscent of multicentric Castleman disease (MCD)--a clinical manifestation of KSHV infection in a subset of immunosuppressed patients. RRV, in short, shows a high degree of homology with KSHV yet is more amenable to experimental manipulation both in vitro and in vivo. Taken together, these qualities ensure its current position as one of the most relevant viral models of KSHV biology and infection.

Modern evolutionary history of the human KSHV genome

The genomes of several human herpesviruses, including Kaposi sarcoma (KS) herpesvirus (KSHV), display surprisingly high levels of both genetic diversity and clustered subtyping at certain loci. We have been interested in understanding this phenomenon with the hope that it might be a useful diagnostic tool for viral epidemiology, and that it might provide some insights about how these large viral genomes evolve over a relatively short timescale. To do so, we have carried out extensive PCR DNA sequence analysis across the genomes of 200 distinct KSHV samples collected from KS patients around the world. Here we review and summarize current understanding of the origins of KSHV variability, the spread of KSHV and its human hosts out of Africa, the existence of chimeric genomes, and the concept that different segments of the genome have had different evolutionary histories.

Structure and function of latency-associated nuclear antigen

Latency-associated nuclear antigen (LANA) encoded by open reading frame 73 (ORF73) is the major latent protein expressed in all forms of KSHV-associated malignancies. LANA is a large (222-234 kDa) nuclear protein that interacts with various cellular as well as viral proteins. LANA has been classified as an oncogenic protein as it dysregulates various cellular pathways including tumor suppressor pathways associated with pRb and p53 and can transform primary rat embryo fibroblasts in cooperation with the cellular oncogene Hras. It associates with GSK-3beta, an important modulator of Wnt signaling pathway leading to the accumulation of cytoplasmic beta-catenin, which upregulates Tcf/Lef regulated genes after entering into the nucleus. LANA also blocks the expression of RTA, the reactivation transcriptional activator, which is critical for the latency to lytic switch, and thus helps in maintaining viral latency. LANA tethers the viral episomal DNA to the host chromosomes by directly binding to its cognate binding sequence within the TR region of the genome through its C terminus and to the nucleosomes through the N terminus of the molecule. Tethering to the host chromosomes helps in efficient partitioning of the viral episomes in the dividing cells. Disruptions of LANA expression led to reduction in the episomal copies of the viral DNA, supporting its role in persistence of the viral DNA. The functions known so far suggest that LANA is a key player in KSHV-mediated pathogenesis.

Kaposi sarcoma herpesvirus-encoded interferon regulator factors

The Kaposi sarcoma herpesvirus (KSHV) encodes multiple proteins that disrupt host antiviral responses, including four viral proteins that have homology to the interferon regulatory factor (IRF) family of transcription factors. At least three of the KSHV vIRFs (vIRFs 1-3) alter responses to cellular IRFs and to interferons (IFNs), whereas functional changes resulting from the fourth vIRF (vIRF-4) have not been reported. The vIRFs also affect other important regulatory proteins in the cell, including responses to transforming growth factor beta (TGF-beta) and the tumor suppressor protein p53. This review examines the expression of the vIRFs during the life cycle of KSHV and the functional consequences of their expression.

RFHVMn ORF73 is structurally related to the KSHV ORF73 latency-associated nuclear antigen (LANA) and is expressed in retroperitoneal fibromatosis (RF) tumor cells

Retroperitoneal fibromatosis herpesvirus (RFHV), the macaque homolog of the human rhadinovirus, Kaposi's sarcoma-associated herpesvirus (KSHV), was first identified in retroperitoneal fibromatosis (RF) tumor lesions of macaques with simian AIDS. We cloned and sequenced the ORF73 latency-associated nuclear antigen (LANA) of RFHVMn from the pig-tailed macaque. RFHVMn LANA is structurally analogous to KSHV ORF73 LANA and contains an N-terminal serine-proline-rich region, a large internal glutamic acidic-rich repeat region and a conserved C-terminal domain. RFHVMn LANA reacts with monoclonal antibodies specific for a glutamic acid-proline dipeptide motif and a glutamic acid-glutamine-rich motif in the KSHV LANA repeat region. Immunohistochemical and immunofluorescence analysis revealed that RFHVMn LANA is a nuclear antigen which is highly expressed in RF spindloid tumor cells. These data suggest that RFHV LANA is an ortholog of KSHV LANA and will function similarly to maintain viral latency and play a role in tumorigenicity in macaques.

Kaposi's sarcoma-associated herpes virus complement control protein: KCP--complement inhibition and more

The complement system is an important part of innate immunity providing immediate protection against pathogens without a need for previous exposure, as well as priming the adaptive immune response through opsonisation, leukocyte recruitment and enhancing humoral immune responses. Its importance is not only shown through recurring fulminant infections in individuals with complement component deficiencies, but also through the many complement evasion strategies discovered for a wide range of infectious microbes (including acquisition of endogenous host complement inhibitors and expression of own homologues). Knowledge of these mechanisms at a molecular level may aid development of vaccines and novel therapeutic strategies. Here, we review the structure-function studies of the membrane-bound complement inhibitor KCP that is expressed on the surface of Kaposi's sarcoma-associated herpesvirus (KSHV) virions and infected cells. KCP accelerates the decay of classical C3 convertase and induces the degradation of activated complement factors C4b and C3b by a serine proteinase, factor I. Molecular modeling and site-directed mutagenesis have identified sites on the surface of KCP required for complement inhibition and support the hypothesis that KCP has evolved to mimic the structure and function of endogenous human inhibitors. KCP additionally enhances virion binding to permissive cells through a heparin/heparan sulfate-binding site located at the N-terminus of the protein.

Kaposi's sarcoma-associated herpesvirus immune modulation: an overview

Kaposi's sarcoma-associated herpesvirus (KSHV) is the most recently discovered human herpesvirus. It is the aetiological agent of Kaposi's sarcoma (KS), a tumour frequently affecting AIDS patients not receiving treatment. KSHV is also a likely cause of two lymphoproliferative diseases: multicentric Castleman's disease and primary effusion lymphoma. The study of KSHV offers exciting challenges for understanding the mechanisms of virus pathogenesis, including those involved in establishing infection and dissemination in the host. To facilitate these processes, approximately one-quarter of KSHV genes encode cellular homologues or unique proteins that have immunomodulatory roles in cytokine production, apoptosis, cell signalling and the immunological synapse. The activities of these molecules are considered in the present review and the positions of their genes are mapped from a complete KSHV genome sequence derived from a KS biopsy. The understanding gained enables the significance of different components of the immune response in protection against KSHV infection to be evaluated. It also helps to unravel the complexities of cellular and immunological pathways and offers the potential for exploiting viral immunomodulators and derivatives in disease therapy.