Kaposi's sarcoma-associated herpesvirus gene expression in endothelial (spindle) tumor cells

Kaposi's sarcoma herpesvirus-induced endothelial cell reprogramming supports viral persistence and contributes to Kaposi's sarcoma tumorigenesis

Kaposi's sarcoma (KS) is an endothelial tumor causally linked to Kaposi's sarcoma herpesvirus (KSHV) infection. At early stages of KS, inflammation and aberrant neoangiogenesis are predominant, while at late stages the disease is characterized by the proliferation of KSHV-infected spindle cells (SC). Since KSHV infection modifies the endothelial cell (EC) identity, the origin of SCs remains elusive. Yet, pieces of evidence indicate the lymphatic origin. KSHV-infected ECs display increased proliferative, angiogenic and migratory capacities which account for KS oncogenesis. Here we propose a model in which KSHV reprograms the EC identity, induces DNA damage and establishes a dysregulated gene expression program involving interplay of latent and lytic genes allowing continuous reinfection of ECs attracted to the tumor by the secretion of virus-induced cellular factors.

The Kaposi's sarcoma-associated herpesvirus (KSHV) non-structural membrane protein K15 is required for viral lytic replication and may represent a therapeutic target

Kaposi’s sarcoma-associated herpesvirus (KSHV) is the infectious cause of the highly vascularized tumor Kaposi’s sarcoma (KS), which is characterized by proliferating spindle cells of endothelial origin, extensive neo-angiogenesis and inflammatory infiltrates. The KSHV K15 protein contributes to the angiogenic and invasive properties of KSHV-infected endothelial cells. Here, we asked whether K15 could also play a role in KSHV lytic replication. Deletion of the K15 gene from the viral genome or its depletion by siRNA lead to reduced virus reactivation, as evidenced by the decreased expression levels of KSHV lytic proteins RTA, K-bZIP, ORF 45 and K8.1 as well as reduced release of infectious virus. Similar results were found for a K1 deletion virus. Deleting either K15 or K1 from the viral genome also compromised the ability of KSHV to activate PLCγ1, Erk1/2 and Akt1. In infected primary lymphatic endothelial (LEC-rKSHV) cells, which have previously been shown to spontaneously display a viral lytic transcription pattern, transfection of siRNA against K15, but not K1, abolished viral lytic replication as well as KSHV-induced spindle cell formation. Using a newly generated monoclonal antibody to K15, we found an abundant K15 protein expression in KS tumor biopsies obtained from HIV positive patients, emphasizing the physiological relevance of our findings. Finally, we used a dominant negative inhibitor of the K15-PLCγ1 interaction to establish proof of principle that pharmacological intervention with K15-dependent pathways may represent a novel approach to block KSHV reactivation and thereby its pathogenesis.

Both the latent and lytic replication phases of the KSHV life cycle are thought to contribute to its persistence and pathogenesis. The non-structural signaling membrane protein K15 is involved in the angiogenic and invasive properties of KSHV-infected endothelial cells. Here we show that the K15 protein is required for virus replication, early viral gene expression and virus production through its activation of the cellular signaling pathways PLCγ1 and Erk 1/2. K15 is abundantly expressed in KSHV-infected lymphatic endothelial cells (LECs) and contributes to KSHV-induced endothelial spindle cell formation. The abundant K15 protein expression observed in LECs is also observed in KS tumors. We also show that it may be possible to target K15 in order to intervene therapeutically with KSHV lytic replication and pathogenesis.

HIV-associated Kaposi sarcoma and related diseases

: The search for the etiologic agent for Kaposi sarcoma led to the discovery of Kaposi sarcoma-associated herpesvirus (KSHV) in 1994. KSHV, also called human herpesvirus-8, has since been shown to be the etiologic agent for several other tumors and diseases, including primary effusion lymphoma (PEL), an extracavitary variant of PEL, KSHV-associated diffuse large B-cell lymphoma, a form of multicentric Castleman disease, and KSHV inflammatory cytokine syndrome. KSHV encodes several genes that interfere with innate and specific immunity, thwart apoptosis, enhance cell proliferation and cytokine production, and promote angiogenesis, and these play important roles in disease pathogenesis. HIV is an important cofactor in Kaposi sarcoma pathogenesis, and widespread use of antiretroviral therapy has reduced Kaposi sarcoma incidence. However, Kaposi sarcoma remains the second most frequent tumor arising in HIV-infected patients in the United States and is particularly common in sub-Saharan Africa. KSHV prevalence varies substantially in different populations. KSHV is secreted in saliva, and public health measures to reduce its spread may help reduce the incidence of KSHV-associated diseases. Although there have been advances in the treatment of Kaposi sarcoma, KSHV-multicentric Castleman disease, and PEL, improved therapies are needed, especially those that are appropriate for Kaposi sarcoma in resource-poor regions.

Diagnosis and Treatment of Kaposi Sarcoma

Kaposi sarcoma (KS) is the most common neoplasm of people living with HIV today. In Sub-Saharan Africa, KS is among the most common cancers in men, overall. Not only HIV-positive individuals present with KS; any immune compromised person infected with KS-associated herpesvirus (KSHV) or human herpesvirus 8 is at risk: the elderly, children in KSHV-endemic areas, and transplant recipients. KS diagnosis is based on detection of the viral protein latency-associated nuclear antigen (LANA) in the biopsy, but not all cases of KS are the same or will respond to the same therapy. Standard KS therapy has not changed in 20 years, but newer modalities are on the horizon and will be discussed.

Glycolysis, Glutaminolysis, and Fatty Acid Synthesis Are Required for Distinct Stages of Kaposi's Sarcoma-Associated Herpesvirus Lytic Replication

Kaposi's sarcoma-associated herpesvirus (KSHV) is the etiologic agent of Kaposi's sarcoma (KS). KSHV infection induces and requires multiple metabolic pathways, including the glycolysis, glutaminolysis, and fatty acid synthesis (FAS) pathways, for the survival of latently infected endothelial cells. To determine the metabolic requirements for productive KSHV infection, we induced lytic replication in the presence of inhibitors of different metabolic pathways. We found that glycolysis, glutaminolysis, and FAS are all required for maximal KSHV virus production and that these pathways appear to participate in virus production at different stages of the viral life cycle. Glycolysis and glutaminolysis, but not FAS, inhibit viral genome replication and, interestingly, are required for different early steps of lytic gene expression. Glycolysis is necessary for early gene transcription, while glutaminolysis is necessary for early gene translation but not transcription. Inhibition of FAS resulted in decreased production of extracellular virions but did not reduce intracellular genome levels or block intracellular virion production. However, in the presence of FAS inhibitors, the intracellular virions are noninfectious, indicating that FAS is required for virion assembly or maturation. KS tumors support both latent and lytic KSHV replication. Previous work has shown that multiple cellular metabolic pathways are required for latency, and we now show that these metabolic pathways are required for efficient lytic replication, providing novel therapeutic avenues for KS tumors.IMPORTANCE KSHV is the etiologic agent of Kaposi's sarcoma, the most common tumor of AIDS patients. KS spindle cells, the main tumor cells, all contain KSHV, mostly in the latent state, during which there is limited viral gene expression. However, a percentage of spindle cells support lytic replication and production of virus and these cells are thought to contribute to overall tumor formation. Our previous findings showed that latently infected cells are sensitive to inhibitors of cellular metabolic pathways, including glycolysis, glutaminolysis, and fatty acid synthesis. Here we found that these same inhibitors block the production of infectious virus from lytically infected cells, each at a different stage of viral replication. Therefore, inhibition of specific cellular metabolic pathways can both eliminate latently infected cells and block lytic replication, thereby inhibiting infection of new cells. Inhibition of metabolic pathways provides novel therapeutic approaches for KS tumors.

Reactivation and Lytic Replication of Kaposi's Sarcoma-Associated Herpesvirus: An Update

The life cycle of Kaposi’s sarcoma-associated herpesvirus (KSHV) consists of two phases, latent and lytic. The virus establishes latency as a strategy for avoiding host immune surveillance and fusing symbiotically with the host for lifetime persistent infection. However, latency can be disrupted and KSHV is reactivated for entry into the lytic replication. Viral lytic replication is crucial for efficient dissemination from its long-term reservoir to the sites of disease and for the spread of the virus to new hosts. The balance of these two phases in the KSHV life cycle is important for both the virus and the host and control of the switch between these two phases is extremely complex. Various environmental factors such as oxidative stress, hypoxia, and certain chemicals have been shown to switch KSHV from latency to lytic reactivation. Immunosuppression, unbalanced inflammatory cytokines, and other viral co-infections also lead to the reactivation of KSHV. This review article summarizes the current understanding of the initiation and regulation of KSHV reactivation and the mechanisms underlying the process of viral lytic replication. In particular, the central role of an immediate-early gene product RTA in KSHV reactivation has been extensively investigated. These studies revealed multiple layers of regulation in activation of RTA as well as the multifunctional roles of RTA in the lytic replication cascade. Epigenetic regulation is known as a critical layer of control for the switch of KSHV between latency and lytic replication. The viral non-coding RNA, PAN, was demonstrated to play a central role in the epigenetic regulation by serving as a guide RNA that brought chromatin remodeling enzymes to the promoters of RTA and other lytic genes. In addition, a novel dimension of regulation by microPeptides emerged and has been shown to regulate RTA expression at the protein level. Overall, extensive investigation of KSHV reactivation and lytic replication has revealed a sophisticated regulation network that controls the important events in KSHV life cycle.

Quantitative Analysis of the KSHV Transcriptome Following Primary Infection of Blood and Lymphatic Endothelial Cells

The transcriptome of the Kaposi’s sarcoma-associated herpesvirus (KSHV/HHV8) after primary latent infection of human blood (BEC), lymphatic (LEC) and immortalized (TIME) endothelial cells was analyzed using RNAseq, and compared to long-term latency in BCBL-1 lymphoma cells. Naturally expressed transcripts were obtained without artificial induction, and a comprehensive annotation of the KSHV genome was determined. A set of unique coding sequence (UCDS) features and a process to resolve overlapping transcripts were developed to accurately quantitate transcript levels from specific promoters. Similar patterns of KSHV expression were detected in BCBL-1 cells undergoing long-term latent infections and in primary latent infections of both BEC and LEC cultures. High expression levels of poly-adenylated nuclear (PAN) RNA and spliced and unspliced transcripts encoding the K12 Kaposin B/C complex and associated microRNA region were detected, with an elevated expression of a large set of lytic genes in all latently infected cultures. Quantitation of non-overlapping regions of transcripts across the complete KSHV genome enabled for the first time accurate evaluation of the KSHV transcriptome associated with viral latency in different cell types. Hierarchical clustering applied to a gene correlation matrix identified modules of co-regulated genes with similar correlation profiles, which corresponded with biological and functional similarities of the encoded gene products. Gene modules were differentially upregulated during latency in specific cell types indicating a role for cellular factors associated with differentiated and/or proliferative states of the host cell to influence viral gene expression.

Integrated systems biology analysis of KSHV latent infection reveals viral induction and reliance on peroxisome mediated lipid metabolism

Kaposi’s Sarcoma associated Herpesvirus (KSHV), an oncogenic, human gamma-herpesvirus, is the etiological agent of Kaposi’s Sarcoma the most common tumor of AIDS patients world-wide. KSHV is predominantly latent in the main KS tumor cell, the spindle cell, a cell of endothelial origin. KSHV modulates numerous host cell-signaling pathways to activate endothelial cells including major metabolic pathways involved in lipid metabolism. To identify the underlying cellular mechanisms of KSHV alteration of host signaling and endothelial cell activation, we identified changes in the host proteome, phosphoproteome and transcriptome landscape following KSHV infection of endothelial cells. A Steiner forest algorithm was used to integrate the global data sets and, together with transcriptome based predicted transcription factor activity, cellular networks altered by latent KSHV were predicted. Several interesting pathways were identified, including peroxisome biogenesis. To validate the predictions, we showed that KSHV latent infection increases the number of peroxisomes per cell. Additionally, proteins involved in peroxisomal lipid metabolism of very long chain fatty acids, including ABCD3 and ACOX1, are required for the survival of latently infected cells. In summary, novel cellular pathways altered during herpesvirus latency that could not be predicted by a single systems biology platform, were identified by integrated proteomics and transcriptomics data analysis and when correlated with our metabolomics data revealed that peroxisome lipid metabolism is essential for KSHV latent infection of endothelial cells.

Kaposi’s Sarcoma herpesvirus (KSHV) is the etiologic agent of Kaposi’s Sarcoma, the most common tumor of AIDS patients. KSHV modulates host cell signaling and metabolism to maintain a life-long latent infection. To unravel the underlying cellular mechanisms modulated by KSHV, we used multiple global systems biology platforms to identify and integrate changes in both cellular protein expression and transcription following KSHV infection of endothelial cells, the relevant cell type for KS tumors. The analysis identified several interesting pathways including peroxisome biogenesis. Peroxisomes are small cytoplasmic organelles involved in redox reactions and lipid metabolism. KSHV latent infection increases the number of peroxisomes per cell and proteins involved in peroxisomal lipid metabolism are required for the survival of latently infected cells. In summary, through integration of multiple global systems biology analyses we were able to identify novel pathways that could not be predicted by one platform alone and found that lipid metabolism in a small cytoplasmic organelle is necessary for the survival of latent infection with a herpesvirus.

Expression of the Antisense-to-Latency Transcript Long Noncoding RNA in Kaposi's Sarcoma-Associated Herpesvirus

The regulation of latency is central to herpesvirus biology. Recent transcriptome-wide surveys have uncovered evidence for promiscuous transcription across the entirety of the Kaposi's sarcoma-associated herpesvirus (KSHV) genome and postulated the existence of multiple viral long noncoding RNAs (lncRNAs). Next-generation sequencing studies are highly dependent on the specific experimental approach and particular algorithms of analysis and therefore benefit from independent confirmation of the results. The antisense-to-latency transcript (ALT) lncRNA was discovered by genome-tiling microarray (Chandriani et al., J Virol 86:7934-7942, 2010, https://doi.org/10.1128/JVI.00645-10). To characterize ALT in detail, we physically isolated this lncRNA by a strand-specific hybrid capture assay and then employed transcriptome sequencing and novel reverse transcription-PCR (RT-PCR) assays to distinguish all RNA species in the KSHV latency region. These methods confirm that ALT initiates at positions 120739/121012 and encodes a single splice site, which is shared with the 3'-coterminal K14-vGPCR/ORF74 mRNA, terminating at 130873 (GenBank accession number GQ994935), resulting in an ∼10,000-nucleotide transcript. No shorter ALT isoforms were identified. This study also identified a novel intron within the LANA 5' untranslated region using a splice acceptor at 127888. In summary, ALT joins PAN/nut1/T1.1 as a bona fide lncRNA of KSHV with potentially important roles in viral gene regulation and pathogenesis.

IMPORTANCE

Increasing data support the importance of noncoding RNAs (ncRNAs), including microRNAs (miRNAs) and lncRNAs, which have been shown to exert critical regulatory functions without coding for recognizable proteins. Defining the sequences of these ncRNAs is essential for future studies aiming to functionally characterize a specific ncRNA. Most lncRNA studies are highly dependent on high-throughput sequencing and bioinformatic analyses, few studies follow up on the initial predictions, and analyses are at times discordant. The manuscript characterizes one key viral lncRNA, ALT, by physically isolating ALT and by a sequencing-independent assay. It provides for a simple assay to monitor lncRNA expression in experimental and clinical samples. ALT is expressed antisense to the major viral latency transcripts encoding LANA as well as the viral miRNAs and thus has the potential to regulate this key part of the viral life cycle.

Kaposi's Sarcoma-Associated Herpesvirus: Epidemiology and Molecular Biology

Kaposi's sarcoma-associated herpesvirus (KSHV), also known as Human herpesvirus 8 (HHV-8), is a member of the lymphotropic gammaherpesvirus subfamily and a human oncogenic virus. Since its discovery in AIDS-associated KS tissues by Drs. Yuan Chang and Patrick Moore, much progress has been made in the past two decades. There are four types of KS including classic KS, endemic KS, immunosuppressive therapy-related KS, and AIDS-associated KS. In addition to KS, KSHV is also involved in the development of primary effusion lymphoma (PEL) and certain types of multicentric Castleman's disease. KSHV manipulates numerous viral proteins to promote the progression of angiogenesis and tumorigenesis. In this chapter, we review the epidemiology and molecular biology of KSHV and the mechanisms underlying KSHV-induced diseases.

Altering the Anti-inflammatory Lipoxin Microenvironment: a New Insight into Kaposi's Sarcoma-Associated Herpesvirus Pathogenesis

Lipoxins are host anti-inflammatory molecules that play a vital role in restoring tissue homeostasis. The efficacy of lipoxins and their analog epilipoxins in treating inflammation and its associated diseases has been well documented. Kaposi's sarcoma (KS) and primary effusion lymphoma (PEL) are two well-known inflammation related diseases caused by Kaposi's sarcoma-associated herpesvirus (KSHV). Controlling inflammation is one of the strategies adopted to treat KS and PEL, a primary motivation for exploring and evaluating the therapeutic potential of using lipoxins. This study documents how KSHV manipulates and downregulates the secretion of the anti-inflammatory lipoxin A4 in host cells and the viral factors involved in this process using in vitro KS and PEL cells as models. The presence of the lipoxin A4 receptor/formyl peptidyl receptor (ALX/FPR) in KS patient tissue sections and in vitro KS and PEL cell models offers a novel possibility for treating KS and PEL with lipoxins. Treating de novo KSHV-infected endothelial cells with lipoxin and epilipoxin creates an anti-inflammatory environment by decreasing the levels of NF-κB, AKT, ERK1/2, COX-2, and 5-lipoxygenase. Lipoxin treatment on CRISPR/CAS9 technology-mediated ALX/FPR gene deletion revealed the importance of the lipoxin receptor ALX for effective lipoxin signaling. A viral microRNA (miRNA) cluster was identified as the primary factor contributing to the downregulation of lipoxin A4 secretion in host cells. The KSHV miRNA cluster probably targets enzyme 15-lipoxygenase, which is involved in lipoxin A4 synthesis. This study provides a new insight into the potential treatment of KS and PEL using nature's own anti-inflammatory molecule, lipoxin.

IMPORTANCE

KSHV infection has been shown to upregulate several host proinflammatory factors, which aid in its survival and pathogenesis. The influence of KSHV infection on anti-inflammatory molecules is not well studied. Since current treatment methods for KS and PEL are fraught with unwanted side effects and low efficiency, the search for new therapeutics is therefore imperative. The use of nature's own molecule lipoxin as a drug is promising. This study opens up new domains in KSHV research focusing on how the virus modulates lipoxin secretion and warrants further investigation of the therapeutic potential of lipoxin using in vitro cell models for KS and PEL.

Fine-Tuning of the Kaposi's Sarcoma-Associated Herpesvirus Life Cycle in Neighboring Cells through the RTA-JAG1-Notch Pathway

Kaposi’s sarcoma (KS)-associated herpesvirus (KSHV) is an oncogenic pathogen that displays latent and lytic life cycles. In KS lesions, infiltrated immune cells, secreted viral and/or cellular cytokines, and hypoxia orchestrate a chronic pro-lytic microenvironment that can promote KSHV reactivation. However, only a small subset of viruses spontaneously undergoes lytic replication in this pro-lytic microenvironment while the majority remains in latency. Here, we show that the expression of the Notch ligand JAG1 is induced by KSHV-encoded replication and transcription activator (RTA) during reactivation. JAG1 up-regulation activates Notch signaling in neighboring cells and prevents viral lytic replication. The suppression of JAG1 and Notch1 with inhibitors or small interfering RNA promotes lytic replication in the presence of RTA induction or under conditions of hypoxia. The underlying mechanism involves the Notch downstream effector hairy and enhancer of split 1 (Hes1), which directly binds lytic gene promoters and attenuates viral lytic gene expression. RTA interacts with lymphoid enhancer-binding factor 1 (LEF1), disrupts LEF1/Groucho/TLE suppressive complexes and releases LEF1 to activate JAG1 expression. Taken together, our results suggest that cells with viral lytic replication can inhibit KSHV reactivation in neighboring cells through an RTA-JAG1-Notch pathway. These data provide insight into the mechanism by which the virus maintains the balance between lytic and latent infection in the pro-lytic tumor microenvironment.

KSHV infected cells display significant heterogeneity in viral lytic replication within the universal pro-lytic inflammatory milieu, suggesting that the balance between latency and reactivation is carefully regulated. This fine-tuned regulatory mechanism is essential for KSHV to persist in the host and drive cells to malignancy. In the present study, we show that KSHV can usurp the Notch signaling pathway to inhibit the viral lytic life cycle in neighboring cells. Notch signaling in surrounding cells can be activated through an RTA-JAG1-Notch pathway initiated by cells in which KSHV is reactivated. Activated Notch inhibits KSHV reactivation through its downstream effector Hes1. These findings suggest that the ability of Notch to determine the fate of adjacent cells is hijacked by KSHV to maintain its life cycle, providing a mechanistic explanation for the phenomenon by which only a small fraction of viruses enters lytic replication in the common pro-lytic microenvironment.

Conceptual Emergence of Human Herpesvirus 8 (Kaposi’s Sarcoma-associated Herpesvirus) as an Oral Herpesvirus

Recognition of the various clinico-epidemiologic forms of Kaposi’s sarcoma, a disease putatively caused by an infectious agent, did not provide ready clues as to how that agent might be transmitted, although fecal and sexual routes were implicated. Application of serologic and genome-detection assays, and cell-culture studies following the identification of human herpesvirus 8 as the causative agent now implicate that virus as one that is orally shed. While oral transmission of the virus might account for the viral endemicity in Africa and Mediterranean countries, why it is particularly prevalent among male homosexuals in the West remains more difficult to explain. Such explanation may be sought from behavioral studies into the role saliva plays in sexual interactions.

Kaposi's sarcoma-associated herpesvirus: the role of lytic replication in targeted therapy

PURPOSE OF REVIEW

To discuss the role of Kaposi's sarcoma-associated herpesvirus (KSHV) lytic replication in viral-associated diseases and assess the progress on targeting KSHV lytic replication as a strategy to prevent KSHV-related malignancies.

RECENT FINDINGS

New inhibitors of viral lytic replication are being developed as well as novel modalities are being investigated to target cellular processes that the virus hijacks during its life cycle. Research has also focused on reactivating viral lytic replication in latently infected tumour cells (lytic induction therapy) to promote death of tumour cells.

SUMMARY

KSHV is linked to three malignancies: Kaposi sarcoma, primary effusion lymphoma, and multicentric Castleman disease. Despite significant progress in understanding KSHV pathobiology, no therapeutic guidelines for the management of KSHV-related diseases exist, and current treatments are suboptimal and associated with toxicity. Antiherpesvirus drugs have shown inconsistent results in KSHV-associated malignancies that harbour the virus in a latent state. However, lytic replication plays a crucial role in the process of tumorigenesis. Therefore, not only antiviral agents directed against the virus replicative cycle but also agents that target cellular processes that are activated by the virus are being investigated. Antivirals may also be used in combination with inducers of the viral lytic stage.

Modulation of gene expression in Kaposi’s sarcoma-associated herpesvirus-infected lymphoid and epithelial cells

Aim: To evaluate the gene expression changes that occur soon after the active infection of two susceptible cell types with human herpesvirus 8 (HHV-8). Materials & methods: The expression profile of 282 human genes involved in the inflammatory process was investigated in HHV-8 A1 or C3 subtype-infected and mock-infected human epithelial cells and lymphoid cells. Results: The HHV-8-induced transcriptional profiles in the epithelial and lymphoid cells were very different. A robust increase in the expression was found in genes belonging to different categories, especially the categories of inflammation response and signal transduction. Conclusion: These results indicate that during early infection, HHV-8 induces a variety of cell type-specific processes, thus providing infection signatures useful as potential targets for therapeutic intervention.

Viral Evasion and Manipulation of Host RNA Quality Control Pathways

Viruses have evolved diverse strategies to maximize the functional and coding capacities of their genetic material. Individual viral RNAs are often used as substrates for both replication and translation and can contain multiple, sometimes overlapping open reading frames. Further, viral RNAs engage in a wide variety of interactions with both host and viral proteins to modify the activities of important cellular factors and direct their own trafficking, packaging, localization, stability, and translation. However, adaptations increasing the information density of small viral genomes can have unintended consequences. In particular, viral RNAs have developed features that mark them as potential targets of host RNA quality control pathways. This minireview focuses on ways in which viral RNAs run afoul of the cellular mRNA quality control and decay machinery, as well as on strategies developed by viruses to circumvent or exploit cellular mRNA surveillance.

OX40 and 4-1BB downregulate Kaposi’s sarcoma-associated herpesvirus replication in lymphatic endothelial cells, but 4-1BB and not OX40 inhibits viral replication in B-cells

Kaposi’s sarcoma-associated herpesvirus (KSHV) belongs to the human gammaherpesvirus subfamily and is associated with malignancies of endothelial origin (Kaposi’s sarcoma, KS) and B-cell origin [primary effusion lymphoma (PEL) and multicentric Castleman’s disease (MCD)]. Viral lytic replication is known to be required for KS and MCD. As KSHV-related tumours mostly develop in human subjects when the immune system is compromised by immunosuppressive regimen, human immunodeficiency virus infection or some genetic deficiencies, KSHV-specific immune responses are believed to be important in the control of KSHV replication. However, analysis of the roles of immune cells in viral pathogenesis has been difficult due to the lack of an adequate animal model. Recently, congenital OX40 deficiency, as determined by genome-wide exome sequencing, was shown to be associated with aggressive childhood KS in a patient, suggesting that disrupted OX40–OX40L interactions might be implicated in disease development. Here, we report that interaction of recombinant OX40 protein with OX40L expressed on endothelial cells severely impaired KSHV lytic replication. Furthermore, 4-1BB–4-1BBL interactions were also capable of efficiently inhibiting viral replication in B-cells and endothelial cells. To the best of our knowledge, this is the first direct evidence that ligation of tumour necrosis factor superfamily members and their cognate receptors is important for the control of viral lytic replication. These data are likely to pave the way for the development of KSHV-specific therapies for KS and MCD, in which viral lytic replication is a disease-determining factor.

Activation of DNA Damage Response Induced by the Kaposi's Sarcoma-Associated Herpes Virus

The human herpes virus 8 (HHV-8), also known as Kaposi sarcoma-associated herpes virus (KSHV), can infect endothelial cells often leading to cell transformation and to the development of tumors, namely Kaposi’s sarcoma (KS), primary effusion lymphoma (PEL), and the plasmablastic variant of multicentric Castleman’s disease. KSHV is prevalent in areas such as sub-Saharan Africa and the Mediterranean region presenting distinct genotypes, which appear to be associated with differences in disease manifestation, according to geographical areas. In infected cells, KSHV persists in a latent episomal form. However, in a limited number of cells, it undergoes spontaneous lytic reactivation to ensure the production of new virions. During both the latent and the lytic cycle, KSHV is programmed to express genes which selectively modulate the DNA damage response (DDR) through the activation of the ataxia telangiectasia mutated (ATM) pathway and by phosphorylating factors associated with the DDR, including the major tumor suppressor protein p53 tumor suppressor p53. This review will focus on the interplay between the KSHV and the DDR response pathway throughout the viral lifecycle, exploring the putative molecular mechanism/s that may contribute to malignant transformation of host cells.

Hijacking GPCRs by viral pathogens and tumor

G protein-coupled receptors (GPCRs) constitute the largest family of molecules that transduce signals across the plasma membrane. Herpesviruses are successful pathogens that evolved diverse mechanisms to benefit their infection. Several human herpesviruses express GPCRs to exploit cellular signaling cascades during infection. These viral GPCRs demonstrate distinct biochemical and biophysical properties that result in the activation of a broad spectrum of signaling pathways. In immune-deficient individuals, human herpesvirus infection and the expression of their GPCRs are implicated in virus-associated diseases and pathologies. Emerging studies also uncover diverse mutations in components, particularly GPCRs and small G proteins, of GPCR signaling pathways that render the constitutive activation of proliferative and survival signal, which contributes to the oncogenesis of various human cancers. Hijacking GPCR-mediated signaling is a signature shared by diseases associated with constitutively active viral GPCRs and cellular mutations activating GPCR signaling, exposing key molecules that can be targeted for anti-viral and anti-tumor therapy.

KSHV Genome Replication and Maintenance

Kaposi's sarcoma associated herpesvirus (KSHV) or human herpesvirus 8 (HHV8) is a major etiological agent for multiple severe malignancies in immune-compromised patients. KSHV establishes lifetime persistence in the infected individuals and displays two distinct life cycles, generally a prolonged passive latent, and a short productive or lytic cycle. During latent phase, the viral episome is tethered to the host chromosome and replicates once during every cell division. Latency-associated nuclear antigen (LANA) is a predominant multifunctional nuclear protein expressed during latency, which plays a central role in episome tethering, replication and perpetual segregation of the episomes during cell division. LANA binds cooperatively to LANA binding sites (LBS) within the terminal repeat (TR) region of the viral episome as well as to the cellular nucleosomal proteins to tether viral episome to the host chromosome. LANA has been shown to modulate multiple cellular signaling pathways and recruits various cellular proteins such as chromatin modifying enzymes, replication factors, transcription factors, and cellular mitotic framework to maintain a successful latent infection. Although, many other regions within the KSHV genome can initiate replication, KSHV TR is important for latent DNA replication and possible segregation of the replicated episomes. Binding of LANA to LBS favors the recruitment of various replication factors to initiate LANA dependent DNA replication. In this review, we discuss the molecular mechanisms relevant to KSHV genome replication, segregation, and maintenance of latency.

Kaposi's Sarcoma-Associated Herpesvirus Interleukin-6 Modulates Endothelial Cell Movement by Upregulating Cellular Genes Involved in Migration

Kaposi’s sarcoma-associated herpesvirus (KSHV) is the causative agent of human Kaposi’s sarcoma, a tumor that arises from endothelial cells, as well as two B cell lymphoproliferative diseases, primary effusion lymphoma and multicentric Castleman’s disease. KSHV utilizes a variety of mechanisms to evade host immune responses and promote cellular transformation and growth in order to persist for the life of the host. A viral homolog of human interleukin-6 (hIL-6) named viral interleukin-6 (vIL-6) is encoded by KSHV and expressed in KSHV-associated cancers. Similar to hIL-6, vIL-6 is secreted, but the majority of vIL-6 is retained within the endoplasmic reticulum, where it can initiate functional signaling through part of the interleukin-6 receptor complex. We sought to determine how intracellular vIL-6 modulates the host endothelial cell environment by analyzing vIL-6’s impact on the endothelial cell transcriptome. vIL-6 significantly altered the expression of many cellular genes associated with cell migration. In particular, vIL-6 upregulated the host factor carcinoembryonic antigen-related cell adhesion molecule 1 (CEACAM1) at the protein and message levels. CEACAM1 has been implicated in tumor invasion and metastasis and promotes migration and vascular remodeling in endothelial cells. We report that vIL-6 upregulates CEACAM1 by a STAT3-dependent mechanism and that CEACAM1 promotes vIL-6-mediated migration. Furthermore, latent and de novo KSHV infections of endothelial cells also induce CEACAM1 expression. Collectively, our data suggest that vIL-6 modulates endothelial cell migration by upregulating the expression of cellular factors, including CEACAM1.

Kaposi’s sarcoma-associated herpesvirus (KSHV) is linked with the development of three human malignancies, Kaposi’s sarcoma, multicentric Castleman’s disease, and primary effusion lymphoma. KSHV expresses many factors that enable the virus to manipulate the host environment in order to persist and induce disease. The viral interleukin-6 (vIL-6) produced by KSHV is structurally and functionally homologous to the human cytokine interleukin-6, except that vIL-6 is secreted slowly and functions primarily from inside the host cell. To investigate the unique intracellular role of vIL-6, we analyzed the impact of vIL-6 on endothelial cell gene expression. We report that vIL-6 significantly alters the expression of genes associated with cell movement, including that for CEACAM1. The gene for CEACAM1 was upregulated by vIL-6 and by latent and primary KSHV infection and promotes vIL-6-mediated endothelial cell migration. This work advances the field’s understanding of vIL-6 function and its contribution to KSHV pathogenesis.

Inhibiting the Recruitment of PLCγ1 to Kaposi's Sarcoma Herpesvirus K15 Protein Reduces the Invasiveness and Angiogenesis of Infected Endothelial Cells

Kaposi’s sarcoma (KS), caused by Kaposi’s sarcoma herpesvirus (KSHV), is a highly vascularised tumour of endothelial origin. KSHV infected endothelial cells show increased invasiveness and angiogenesis. Here, we report that the KSHV K15 protein, which we showed previously to contribute to KSHV-induced angiogenesis, is also involved in KSHV-mediated invasiveness in a PLCγ1-dependent manner. We identified βPIX, GIT1 and cdc42, downstream effectors of PLCγ1 in cell migration, as K15 interacting partners and as contributors to KSHV-triggered invasiveness. We mapped the interaction between PLCγ1, PLCγ2 and their individual domains with two K15 alleles, P and M. We found that the PLCγ2 cSH2 domain, by binding to K15P, can be used as dominant negative inhibitor of the K15P-PLCγ1 interaction, K15P-dependent PLCγ1 phosphorylation, NFAT-dependent promoter activation and the increased invasiveness and angiogenic properties of KSHV infected endothelial cells. We increased the binding of the PLCγ2 cSH2 domain for K15P by substituting two amino acids, thereby creating an improved dominant negative inhibitor of the K15P-dependent PLCγ1 activation. Taken together, these results demonstrate a necessary role of K15 in the increased invasiveness and angiogenesis of KSHV infected endothelial cells and suggest the K15-PLCγ1 interaction as a possible new target for inhibiting the angiogenic and invasive properties of KSHV.

Kaposi’s Sarcoma (KS), etiologically linked to Kaposi’s sarcoma herpesvirus (KSHV), is a tumour of endothelial origin characterised by angiogenesis and invasiveness. In vitro, KSHV infected endothelial cells display an increased invasiveness and high angiogenicity. Here we report that the KSHV protein K15, which increases the angiogenicity of endothelial cells, contributes to KSHV-mediated invasiveness by the recruitment and activation of the cellular protein PLCγ1 and its downstream effectors βPIX, GIT1 and cdc42. We explored the functional consequences of disrupting the K15-PLCγ1 interaction by using an isolated PLCγ2 cSH2 domain as a dominant negative inhibitor. This protein fragment, by interacting with K15, reduces K15-driven recruitment and activation of PLCγ1 in a dose-dependent manner. Moreover, the PCLγ2 cSH2 domain, when overexpressed in KSHV infected endothelial cells, reduces the angiogenesis and invasiveness induced by the virus. These findings highlight the role of the K15-PLCγ1 interaction in KSHV-mediated invasiveness and identify it as a possible therapeutic target.

K-bZIP Mediated SUMO-2/3 Specific Modification on the KSHV Genome Negatively Regulates Lytic Gene Expression and Viral Reactivation

SUMOylation is associated with epigenetic regulation of chromatin structure and transcription. Epigenetic modifications of herpesviral genomes accompany the transcriptional switch of latent and lytic genes during the virus life cycle. Here, we report a genome-wide comparison of SUMO paralog modification on the KSHV genome. Using chromatin immunoprecipitation in conjunction with high-throughput sequencing, our study revealed highly distinct landscape changes of SUMO paralog genomic modifications associated with KSHV reactivation. A rapid and widespread deposition of SUMO-2/3, compared with SUMO-1, modification across the KSHV genome upon reactivation was observed. Interestingly, SUMO-2/3 enrichment was inversely correlated with H3K9me3 mark after reactivation, indicating that SUMO-2/3 may be responsible for regulating the expression of viral genes located in low heterochromatin regions during viral reactivation. RNA-sequencing analysis showed that the SUMO-2/3 enrichment pattern positively correlated with KSHV gene expression profiles. Activation of KSHV lytic genes located in regions with high SUMO-2/3 enrichment was enhanced by SUMO-2/3 knockdown. These findings suggest that SUMO-2/3 viral chromatin modification contributes to the diminution of viral gene expression during reactivation. Our previous study identified a SUMO-2/3-specific viral E3 ligase, K-bZIP, suggesting a potential role of this enzyme in regulating SUMO-2/3 enrichment and viral gene repression. Consistent with this prediction, higher K-bZIP binding on SUMO-2/3 enrichment region during reactivation was observed. Moreover, a K-bZIP SUMO E3 ligase dead mutant, K-bZIP-L75A, in the viral context, showed no SUMO-2/3 enrichment on viral chromatin and higher expression of viral genes located in SUMO-2/3 enriched regions during reactivation. Importantly, virus production significantly increased in both SUMO-2/3 knockdown and KSHV K-bZIP-L75A mutant cells. These results indicate that SUMO-2/3 modification of viral chromatin may function to counteract KSHV reactivation. As induction of herpesvirus reactivation may activate cellular antiviral regimes, our results suggest that development of viral SUMO E3 ligase specific inhibitors may be an avenue for anti-virus therapy.

Efficient lytic induction of Kaposi's sarcoma-associated herpesvirus (KSHV) by the anthracyclines

Lytic induction of latent Kaposi's sarcoma-associated herpesvirus (KSHV) has been considered as a therapeutic option for efficient treatment of several KSHV-associated malignancies. Here, we developed a robust high-throughput screening system that allows an easy and quantitative measurement of lytic induction of latent KSHV and discovered three anthracyclines as potent inducers from screen of FDA-approved drugs. Lytic induction of latent KSHV by three compounds was verified by the significant induction of lytic genes and subsequent production of infectious KSHV. Importantly, lytic induction by three compounds was much more efficient than that by sodium butyrate, a well-characterized inducer of KSHV lytic cycle. Mechanistically, the anthracyclines caused lytic induction of KSHV through apoptosis induced by their DNA intercalation rather than topoisomerase II inhibition. Consequently, our results clearly demonstrated a role of anthracyclines as effective lytic inducers of KSHV and also provided a molecular basis of their use for efficient treatment of diseases associated with KSHV infection.

Recombinant Murine Gamma Herpesvirus 68 Carrying KSHV G Protein-Coupled Receptor Induces Angiogenic Lesions in Mice

Human gamma herpesviruses, including Kaposi’s sarcoma-associated herpesvirus (KSHV) and Epstein-Barr virus (EBV), are capable of inducing tumors, particularly in in immune-compromised individuals. Due to the stringent host tropism, rodents are resistant to infection by human gamma herpesviruses, creating a significant barrier for the in vivo study of viral genes that contribute to tumorigenesis. The closely-related murine gamma herpesvirus 68 (γHV68) efficiently infects laboratory mouse strains and establishes robust persistent infection without causing apparent disease. Here, we report that a recombinant γHV68 carrying the KSHV G protein-coupled receptor (kGPCR) in place of its murine counterpart induces angiogenic tumors in infected mice. Although viral GPCRs are conserved in all gamma herpesviruses, kGPCR potently activated downstream signaling and induced tumor formation in nude mouse, whereas γHV68 GPCR failed to do so. Recombinant γHV68 carrying kGPCR demonstrated more robust lytic replication ex vivo than wild-type γHV68, although both viruses underwent similar acute and latent infection in vivo. Infection of immunosuppressed mice with γHV68 carrying kGPCR, but not wild-type γHV68, induced tumors in mice that exhibited angiogenic and inflammatory features shared with human Kaposi’s sarcoma. Immunohistochemistry staining identified abundant latently-infected cells and a small number of cells supporting lytic replication in tumor tissue. Thus, mouse infection with a recombinant γHV68 carrying kGPCR provides a useful small animal model for tumorigenesis induced by a human gamma herpesvirus gene in the setting of a natural course of infection.

Human gamma herpesviruses, including Epstein-Barr virus (EBV) and Kaposi’s sarcoma-associated herpesvirus (KSHV), are causatively linked to a spectrum of human oncogenic malignancies. Due to the stringent host restriction, rodents are generally not amenable to infection by EBV and KSHV. Murine gamma herpesvirus 68 (γHV68) is closely related to KSHV and EBV, although infection in mouse does not manifest apparent diseases. Here we developed a recombinant γHV68 that carries the KSHV G protein-coupled receptor, an important signaling molecule implicated in KSHV pathogenesis. Intriguingly, laboratory mice infected with this recombinant γHV68 developed angiogenic lesions that resembled human Kaposi’s sarcoma. This mouse infection with recombinant γHV68 carrying KSHV GPCR represents a useful model to investigate viral oncogenesis induced by human gamma herpesvirus in the context of viral infection.

New insights into the expression and functions of the Kaposi's sarcoma-associated herpesvirus long noncoding PAN RNA

The Kaposi's sarcoma-associated herpesvirus (KSHV) is a clinically relevant pathogen associated with several human diseases that primarily affect immunocompromised individuals. KSHV encodes a noncoding polyadenylated nuclear (PAN) RNA that is essential for viral propagation and viral gene expression. PAN RNA is the most abundant viral transcript produced during lytic replication. The accumulation of PAN RNA depends on high levels of transcription driven by the Rta protein, a KSHV transcription factor necessary and sufficient for latent-to-lytic phase transition. In addition, KSHV uses several posttranscriptional mechanisms to stabilize PAN RNA. A cis-acting element, called the ENE, prevents PAN RNA decay by forming a triple helix with its poly(A) tail. The viral ORF57 and the cellular PABPC1 proteins further contribute to PAN RNA stability during lytic phase. PAN RNA functions are only beginning to be uncovered, but PAN RNA has been proposed to control gene expression by several different mechanisms. PAN RNA associates with the KSHV genome and may regulate gene expression by recruiting chromatin-modifying factors. Moreover, PAN RNA binds the viral latency-associated nuclear antigen (LANA) protein and decreases its repressive activity by sequestering it from the viral genome. Surprisingly, PAN RNA was found to associate with translating ribosomes, so this noncoding RNA may be additionally used to produce viral peptides. In this review, I highlight the mechanisms of PAN RNA accumulation and describe recent insights into potential functions of PAN RNA.

Celecoxib Inhibits the Lytic Activation of Kaposi's Sarcoma-Associated Herpesvirus through Down-Regulation of RTA Expression by Inhibiting the Activation of p38 MAPK

Kaposi’s sarcoma associated herpesvirus (KSHV) is the etiologic agent of Kaposi’s sarcoma (KS), primary effusion lymphoma (PEL), and multicentric Castleman’s disease (MCD). KSHV’s lytic replication cycle is critical for the pathogenesis of KSHV-associated diseases. Despite recent progress in the development of treatments for KSHV associated malignancies, these therapies are not completely efficacious and cause side effects. Therefore, more effective therapies with antiviral agents against KSHV are urgently needed. In this study, we identified celecoxib as an antiviral agent against KSHV. Our data suggest that celecoxib inhibits the lytic activation of KSHV through the down-regulation of the expression of the lytic switch protein, replication and transcription activator (RTA), by inhibiting the activation of p38 MAPK. Therefore, celecoxib may provide a candidate inhibitor for the therapeutic research of KSHV-related malignancies.

Modulation of cellular signaling by herpesvirus-encoded G protein-coupled receptors

Human herpesviruses (HHVs) are widespread infectious pathogens that have been associated with proliferative and inflammatory diseases. During viral evolution, HHVs have pirated genes encoding viral G protein-coupled receptors (vGPCRs), which are expressed on infected host cells. These vGPCRs show highest homology to human chemokine receptors, which play a key role in the immune system. Importantly, vGPCRs have acquired unique properties such as constitutive activity and the ability to bind a broad range of human chemokines. This allows vGPCRs to hijack human proteins and modulate cellular signaling for the benefit of the virus, ultimately resulting in immune evasion and viral dissemination to establish a widespread and lifelong infection. Knowledge on the mechanisms by which herpesviruses reprogram cellular signaling might provide insight in the contribution of vGPCRs to viral survival and herpesvirus-associated pathologies.

BH3 Profiling Reveals Selectivity by Herpesviruses for Specific Bcl-2 Proteins To Mediate Survival of Latently Infected Cells

Herpesviruses, including human cytomegalovirus (HCMV), Epstein-Barr virus (EBV), and Kaposi's sarcoma-associated herpesvirus, establish latency by modulating or mimicking antiapoptotic Bcl-2 proteins to promote survival of carrier cells. BH3 profiling, which assesses the contribution of Bcl-2 proteins towards cellular survival, was able to globally determine the level of dependence on individual cellular and viral Bcl-2 proteins within latently infected cells. Moreover, BH3 profiling predicted the sensitivity of infected cells to small-molecule inhibitors of Bcl-2 proteins.

The role of Kaposi sarcoma-associated herpesvirus in the pathogenesis of Kaposi sarcoma

Kaposi sarcoma (KS) is an unusual vascular tumour caused by an oncogenic-herpesvirus, Kaposi sarcoma-associated herpesvirus (KSHV), also known as human herpesvirus 8 (HHV 8). KS lesions are characterized by an abundant inflammatory infiltrate, the presence of KSHV-infected endothelial cells that show signs of aberrant differentiation, as well as faulty angiogenesis/ vascularization. Here we discuss the molecular mechanisms that lead to the development of these histological features of KS, with an emphasis on the viral proteins that are responsible for their development.

Chromatinization of the KSHV Genome During the KSHV Life Cycle

Kaposi's sarcoma-associated herpesvirus (KSHV) belongs to the gamma herpesvirus family and is the causative agent of various lymphoproliferative diseases in humans. KSHV, like other herpesviruses, establishes life-long latent infection with the expression of a limited number of viral genes. Expression of these genes is tightly regulated by both the viral and cellular factors. Recent advancements in identifying the expression profiles of viral transcripts, using tilling arrays and next generation sequencing have identified additional coding and non-coding transcripts in the KSHV genome. Determining the functions of these transcripts will provide a better understanding of the mechanisms utilized by KSHV in altering cellular pathways involved in promoting cell growth and tumorigenesis. Replication of the viral genome is critical in maintaining the existing copies of the viral episomes during both latent and lytic phases of the viral life cycle. The replication of the viral episome is facilitated by viral components responsible for recruiting chromatin modifying enzymes and replication factors for altering the chromatin complexity and replication initiation functions, respectively. Importantly, chromatin modification of the viral genome plays a crucial role in determining whether the viral genome will persist as latent episome or undergo lytic reactivation. Additionally, chromatinization of the incoming virion DNA, which lacks chromatin structure, in the target cells during primary infection, helps in establishing latent infection. Here, we discuss the recent advancements on our understating of KSHV genome chromatinization and the consequences of chromatin modifications on viral life cycle.

Kaposi sarcoma-associated herpesvirus-associated malignancies: epidemiology, pathogenesis, and advances in treatment

Kaposi sarcoma associated herpesvirus (KSHV), a γ2-herpesvirus, also known as human herpesvirus-8, is the etiologic agent of three virally associated tumors: Kaposi sarcoma, a plasmablastic form of multicentric Castleman disease (KSHV-MCD), and primary effusion lymphoma. These malignancies are predominantly seen in people with acquired immunodeficiencies, including acquired immunodeficiency syndrome and iatrogenic immunosuppression in the setting of organ transplantation, but can also develop in the elderly. Kaposi sarcoma (KS) is most frequent in regions with high KSHV seroprevalence, such as sub-Saharan Africa and some Mediterranean countries. In the era of combination antiviral therapy, inflammatory manifestations associated with KSHV-infection, including KSHV-MCD, a recently described KSHV-associated inflammatory cytokine syndrome and KS immune reconstitution syndrome also are increasingly appreciated. Our understanding of viral and immune mechanisms of oncogenesis continues to expand and lead to improved molecular diagnostics, as well as novel therapeutic strategies that employ immune modulatory agents, manipulations of the tumor microenvironment, virus-activated cytotoxic therapy, or agents that target interactions between specific virus-host cell signaling pathways. This review focuses on the epidemiology and advances in molecular and clinical research that reflects the current understanding of viral oncogenesis, clinical manifestations, and therapeutics for KSHV-associated tumors.

KSHV-TK is a tyrosine kinase that disrupts focal adhesions and induces Rho-mediated cell contraction

Paradoxically, the thymidine kinase (TK) encoded by Kaposi sarcoma-associated herpesvirus (KSHV) is an extremely inefficient nucleoside kinase, when compared to TKs from related herpesviruses. We now show that KSHV-TK, in contrast to HSV1-TK, associates with the actin cytoskeleton and induces extensive cell contraction followed by membrane blebbing. These dramatic changes in cell morphology depend on the auto-phosphorylation of tyrosines 65, 85 and 120 in the N-terminus of KSHV-TK. Phosphorylation of tyrosines 65/85 and 120 results in an interaction with Crk family proteins and the p85 regulatory subunit of PI3-Kinase, respectively. The interaction of Crk with KSHV-TK leads to tyrosine phoshorylation of this cellular adaptor. Auto-phosphorylation of KSHV-TK also induces a loss of FAK and paxillin from focal adhesions, resulting in activation of RhoA-ROCK signalling to myosin II and cell contraction. In the absence of FAK or paxillin, KSHV-TK has no effect on focal adhesion integrity or cell morphology. Our observations demonstrate that by acting as a tyrosine kinase, KSHV-TK modulates signalling and cell morphology.

Utilising proteomic approaches to understand oncogenic human herpesviruses (Review)

The γ-herpesviruses Epstein-Barr virus and Kaposi's sarcoma-associated herpesvirus are successful pathogens, each infecting a large proportion of the human population. These viruses persist for the life of the host and may each contribute to a number of malignancies, for which there are currently no cures. Large-scale proteomic-based approaches provide an excellent means of increasing the collective understanding of the proteomes of these complex viruses and elucidating their numerous interactions within the infected host cell. These large-scale studies are important for the identification of the intricacies of viral infection and the development of novel therapeutics against these two important pathogens.

Human viruses and cancer

The first human tumor virus was discovered in the middle of the last century by Anthony Epstein, Bert Achong and Yvonne Barr in African pediatric patients with Burkitt's lymphoma. To date, seven viruses -EBV, KSHV, high-risk HPV, MCPV, HBV, HCV and HTLV1- have been consistently linked to different types of human cancer, and infections are estimated to account for up to 20% of all cancer cases worldwide. Viral oncogenic mechanisms generally include: generation of genomic instability, increase in the rate of cell proliferation, resistance to apoptosis, alterations in DNA repair mechanisms and cell polarity changes, which often coexist with evasion mechanisms of the antiviral immune response. Viral agents also indirectly contribute to the development of cancer mainly through immunosuppression or chronic inflammation, but also through chronic antigenic stimulation. There is also evidence that viruses can modulate the malignant properties of an established tumor. In the present work, causation criteria for viruses and cancer will be described, as well as the viral agents that comply with these criteria in human tumors, their epidemiological and biological characteristics, the molecular mechanisms by which they induce cellular transformation and their associated cancers.

Glutamate secretion and metabotropic glutamate receptor 1 expression during Kaposi's sarcoma-associated herpesvirus infection promotes cell proliferation

Kaposi's sarcoma associated herpesvirus (KSHV) is etiologically associated with endothelial Kaposi's sarcoma (KS) and B-cell proliferative primary effusion lymphoma (PEL), common malignancies seen in immunocompromised HIV-1 infected patients. The progression of these cancers occurs by the proliferation of cells latently infected with KSHV, which is highly dependent on autocrine and paracrine factors secreted from the infected cells. Glutamate and glutamate receptors have emerged as key regulators of intracellular signaling pathways and cell proliferation. However, whether they play any role in the pathological changes associated with virus induced oncogenesis is not known. Here, we report the first systematic study of the role of glutamate and its metabotropic glutamate receptor 1 (mGluR1) in KSHV infected cell proliferation. Our studies show increased glutamate secretion and glutaminase expression during de novo KSHV infection of endothelial cells as well as in KSHV latently infected endothelial and B-cells. Increased mGluR1 expression was detected in KSHV infected KS and PEL tissue sections. Increased c-Myc and glutaminase expression in the infected cells was mediated by KSHV latency associated nuclear antigen 1 (LANA-1). In addition, mGluR1 expression regulating host RE-1 silencing transcription factor/neuron restrictive silencer factor (REST/NRSF) was retained in the cytoplasm of infected cells. KSHV latent protein Kaposin A was also involved in the over expression of mGluR1 by interacting with REST in the cytoplasm of infected cells and by regulating the phosphorylation of REST and interaction with β-TRCP for ubiquitination. Colocalization of Kaposin A with REST was also observed in KS and PEL tissue samples. KSHV infected cell proliferation was significantly inhibited by glutamate release inhibitor and mGluR1 antagonists. These studies demonstrated that elevated glutamate secretion and mGluR1 expression play a role in KSHV induced cell proliferation and suggest that targeting glutamate and mGluR1 is an attractive therapeutic strategy to effectively control the KSHV associated malignancies.

Kaposi's sarcoma associated herpesvirus (KSHV), prevalent in immunosuppressed HIV infected individuals and transplant recipients, is etiologically associated with cancers such as endothelial Kaposi's sarcoma (KS) and B-cell primary effusion lymphoma (PEL). Both KS and PEL develop from the unlimited proliferation of KSHV infected cells. Increased secretion of various host cytokines and growth factors, and the activation of their corresponding receptors, are shown to be contributing to the proliferation of KSHV latently infected cells. Glutamate, a neurotransmitter, is also involved in several cellular events including cell proliferation. In the present study, we report that KSHV-infected latent cells induce the secretion of glutamate and activation of metabotropic glutamate receptor 1 (mGluR1), and KSHV latency associated LANA-1 and Kaposin A proteins are involved in glutaminase and mGluR1 expression. Our functional analysis showed that elevated secretion of glutamate and mGluR1 activation is linked to increased proliferation of KSHV infected cells and glutamate release inhibitor and glutamate receptor antagonists blocked the proliferation of KSHV infected cells. These studies show that proliferation of cancer cells latently infected with KSHV in part depends upon glutamate and glutamate receptor and therefore could potentially be used as therapeutic targets for the control and elimination of KSHV associated cancers.

SUMO and KSHV Replication

Small Ubiquitin-related MOdifier (SUMO) modification was initially identified as a reversible post-translational modification that affects the regulation of diverse cellular processes, including signal transduction, protein trafficking, chromosome segregation, and DNA repair. Increasing evidence suggests that the SUMO system also plays an important role in regulating chromatin organization and transcription. It is thus not surprising that double-stranded DNA viruses, such as Kaposi's sarcoma-associated herpesvirus (KSHV), have exploited SUMO modification as a means of modulating viral chromatin remodeling during the latent-lytic switch. In addition, SUMO regulation allows the disassembly and assembly of promyelocytic leukemia protein-nuclear bodies (PML-NBs), an intrinsic antiviral host defense, during the viral replication cycle. Overcoming PML-NB-mediated cellular intrinsic immunity is essential to allow the initial transcription and replication of the herpesvirus genome after de novo infection. As a consequence, KSHV has evolved a way as to produce multiple SUMO regulatory viral proteins to modulate the cellular SUMO environment in a dynamic way during its life cycle. Remarkably, KSHV encodes one gene product (K-bZIP) with SUMO-ligase activities and one gene product (K-Rta) that exhibits SUMO-targeting ubiquitin ligase (STUbL) activity. In addition, at least two viral products are sumoylated that have functional importance. Furthermore, sumoylation can be modulated by other viral gene products, such as the viral protein kinase Orf36. Interference with the sumoylation of specific viral targets represents a potential therapeutic strategy when treating KSHV, as well as other oncogenic herpesviruses. Here, we summarize the different ways KSHV exploits and manipulates the cellular SUMO system and explore the multi-faceted functions of SUMO during KSHV's life cycle and pathogenesis.

Human herpesvirus 8 induces polyfunctional B lymphocytes that drive Kaposi's sarcoma

Kaposi’s sarcoma (KS) is an unusual neoplasia wherein the tumor consists primarily of endothelial cells infected with human herpesvirus 8 (HHV-8; Kaposi’s sarcoma-associated herpesvirus) that are not fully transformed but are instead driven to excess proliferation by inflammatory and angiogenic factors. This oncogenic process has been postulated but unproven to depend on a paracrine effect of an abnormal excess of host cytokines and chemokines produced by HHV-8-infected B lymphocytes. Using newly developed measures for intracellular detection of lytic cycle proteins and expression of cytokines and chemokines, we show that HHV-8 targets a range of naive B cell, IgM memory B cell, and plasma cell-like populations for infection and induction of interleukin-6, tumor necrosis factor alpha, macrophage inhibitory protein 1α, macrophage inhibitory protein 1β, and interleukin-8 in vitro and in the blood of HHV-8/HIV-1-coinfected subjects with KS. These B cell lineage subsets that support HHV-8 infection are highly polyfunctional, producing combinations of 2 to 5 of these cytokines and chemokines, with greater numbers in the blood of subjects with KS than in those without KS. Our study provides a new paradigm of B cell polyfunctionality and supports a key role for B cell-derived cytokines and chemokines produced during HHV-8 infection in the development of KS.

Kaposi’s sarcoma (KS) is the most common cancer in HIV-1-infected persons and is caused by one of only 7 human cancer viruses, i.e., human herpesvirus 8 (HHV-8). It is unclear how this virus causes neoplastic transformation. Development and outgrowth of endothelial cell lesions characteristic of KS are hypothesized to be dependent on virus replication and multiple immune mediators produced by the KS cells and inflammatory cells, yet the roles of these viral and cell factors have not been defined. The present study advances our understanding of KS in that it supports a central role for HHV-8 infection of B cells inducing multiple cytokines and chemokines that can drive development of the cancer. Notably, HIV-1-infected individuals who developed KS had greater numbers of such HHV-8-infected, polyfunctional B cells across a range of B cell phenotypic lineages than did HHV-8-infected persons without KS. This intriguing production of polyfunctional immune mediators by B cells serves as a new paradigm for B cell function and classification.

KSHV: pathways to tumorigenesis and persistent infection

Kaposi's sarcoma-associated herpesvirus (KSHV; also known as human herpesvirus 8) is the etiologic agent of Kaposi's sarcoma, primary effusion lymphoma, and multicentric Castleman's disease. These cancers often occur in the context of immunosuppression, which has made KSHV-associated malignancies an increasing global health concern with the persistence of the AIDS epidemic. KSHV has also been linked to several acute inflammatory diseases. KSHV exists between a lytic and latent lifecycle, which allows the virus to transition between active replication and quiescent infection. KSHV encodes a number of proteins and small RNAs that are thought to inadvertently transform host cells while performing their functions of helping the virus persist in the infected host. KSHV also has an arsenal of components that aid the virus in evading the host immune response, which help the virus establish a successful lifelong infection. In this comprehensive chapter, we will discuss the diseases associated with KSHV infection, the biology of latent and lytic infection, and individual proteins and microRNAs that are known to contribute to host cell transformation and immune evasion.

HIV: An Epidemiologic study on Head and Neck Involvement in 50 Patients

INTRODUCTION

Acquired immunodeficiency syndrome (AIDS) is a worldwide infection. Because of the vast array of manifestations of AIDS and its many atypical presentations, it is becoming increasingly challenging for clinicians to accurately diagnose new lesions.

MATERIALS AND METHODS

In a descriptive cross-sectional study conducted from 2007 to 2010, 50 patients with a proven human immunodeficiency virus (HIV) infection were evaluated. Based on the findings of a physical examination and paraclinic tests, HIV signs and symptoms were recorded.

RESULTS

The mean (range) age of the patients was 35.45 ±5.24 (5-55) years. Forty-two (84%) cases were male and eight were female. The mean duration of carrying the virus was 4.51 ±1.03 years. Oral manifestations were the most common (94%), followed by rhinologic (88%), otologic (66%), and finally neck (44%) manifestations.

CONCLUSION

Head and neck presentations are very common in HIV patients; therefore otolaryngologists, as the first physicians who may encounter such patients, should be aware of this condition.

Is murine gammaherpesvirus-68 (MHV-68) a suitable immunotoxicological model for examining immunomodulatory drug-associated viral recrudescence?

Immunosuppressive agents are used for treatment of a variety of autoimmune diseases including rheumatoid arthritis (RA), systemic lupus erythematosis (SLE), and psoriasis, as well as for prevention of tissue rejection after organ transplantation. Recrudescence of herpesvirus infections, and increased risk of carcinogenesis from herpesvirus-associated tumors are related with immunosuppressive therapy in humans. Post-transplant lymphoproliferative disorder (PTLD), a condition characterized by development of Epstein Barr Virus (EBV)-associated B-lymphocyte lymphoma, and Kaposi's Sarcoma (KS), a dermal tumor associated with Kaposi Sarcoma-associated virus (KSHV), may develop in solid organ transplant patients. KS also occurs in immunosuppressed Acquired Immunodeficiency (AIDS) patients. Kaposi Sarcoma-associated virus (KSHV) is a herpes virus genetically related to EBV. Murine gammaherpes-virus-68 (MHV-68) is proposed as a mouse model of gammaherpesvirus infection and recrudescence and may potentially have relevance for herpesvirus-associated neoplasia. The pathogenesis of MHV-68 infection in mice mimics EBV/KSHV infection in humans with acute lytic viral replication followed by dissemination and establishment of persistent latency. MHV-68-infected mice may develop lymphoproliferative disease that is accelerated by disruption of the immune system. This manuscript first presents an overview of gammaherpesvirus pathogenesis and immunology as well as factors involved in viral recrudescence. A description of different types of immunodeficiency then follows, with particular focus on viral association with lymphomagenesis after immunosuppression. Finally, this review discusses different gammaherpesvirus animal models and describes a proposed MHV-68 model to further examine the interplay of immunomodulatory agents and gammaherpesvirus-associated neoplasia.

Structural proteins of Kaposi's sarcoma-associated herpesvirus antagonize p53-mediated apoptosis

The tumor suppressor p53 is a central regulatory molecule of apoptosis and is commonly mutated in tumors. Kaposi's sarcoma-associated herpesvirus (KSHV)-related malignancies express wild-type p53. Accordingly, KSHV encodes proteins that counteract the cell death-inducing effects of p53. Here, the effects of all KSHV genes on the p53 signaling pathway were systematically analyzed using the reversely transfected cell microarray technology. With this approach we detected eight KSHV-encoded genes with potent p53 inhibiting activity in addition to the previously described inhibitory effects of KSHV genes ORF50, K10 and K10.5. Interestingly, the three most potent newly identified inhibitors were KSHV structural proteins, namely ORF22 (glycoprotein H), ORF25 (major capsid protein) and ORF64 (tegument protein). Validation of these results with a classical transfection approach showed that these proteins inhibited p53 signaling in a dose-dependent manner and that this effect could be reversed by small interfering RNA-mediated knockdown of the respective viral gene. All three genes inhibited p53-mediated apoptosis in response to Nutlin-3 treatment in non-infected and KSHV-infected cells. Addressing putative mechanisms, we could show that these proteins could also inhibit the transactivation of the promoters of apoptotic mediators of p53 such as BAX and PIG3. Altogether, we demonstrate for the first time that structural proteins of KSHV can counteract p53-induced apoptosis. These proteins are expressed in the late lytic phase of the viral life cycle and are incorporated into the KSHV virion. Accordingly, these genes may inhibit cell death in the productive and in the early entrance phase of KSHV infection.

Kaposi's sarcoma associated herpesvirus tegument protein ORF75 is essential for viral lytic replication and plays a critical role in the antagonization of ND10-instituted intrinsic immunity

Nuclear domain 10 (ND10) components are restriction factors that inhibit herpesviral replication. Effector proteins of different herpesviruses can antagonize this restriction by a variety of strategies, including degradation or relocalization of ND10 proteins. We investigated the interplay of Kaposi's Sarcoma-Associated Herpesvirus (KSHV) infection and cellular defense by nuclear domain 10 (ND10) components. Knock-down experiments in primary human cells show that KSHV-infection is restricted by the ND10 components PML and Sp100, but not by ATRX. After KSHV infection, ATRX is efficiently depleted and Daxx is dispersed from ND10, indicating that these two ND10 components can be antagonized by KSHV. We then identified the ORF75 tegument protein of KSHV as the viral factor that induces the disappearance of ATRX and relocalization of Daxx. ORF75 belongs to a viral protein family (viral FGARATs) that has homologous proteins in all gamma-herpesviruses. Isolated expression of ORF75 in primary cells induces a relocalization of PML and dispersal of Sp100, indicating that this viral effector protein is able to influence multiple ND10 components. Moreover, by constructing a KSHV mutant harboring a stop codon at the beginning of ORF75, we could demonstrate that ORF75 is absolutely essential for viral replication and the initiation of viral immediate-early gene expression. Using recombinant viruses either carrying Flag- or YFP-tagged variants of ORF75, we could further corroborate the role of ORF75 in the antagonization of ND10-mediated intrinsic immunity, and show that it is independent of the PML antagonist vIRF3. Members of the viral FGARAT family target different ND10 components, suggesting that the ND10 targets of viral FGARAT proteins have diversified during evolution. We assume that overcoming ND10 intrinsic defense constitutes a critical event in the replication of all herpesviruses; on the other hand, restriction of herpesviral replication by ND10 components may also promote latency as the default outcome of infection.

Molecular biology of human herpesvirus 8: novel functions and virus-host interactions implicated in viral pathogenesis and replication

Human herpesvirus 8 (HHV-8), also known as Kaposi's sarcoma-associated herpesvirus (KSHV), is the second identified human gammaherpesvirus. Like its relative Epstein-Barr virus, HHV-8 is linked to B-cell tumors, specifically primary effusion lymphoma and multicentric Castleman's disease, in addition to endothelial-derived KS. HHV-8 is unusual in its possession of a plethora of "accessory" genes and encoded proteins in addition to the core, conserved herpesvirus and gammaherpesvirus genes that are necessary for basic biological functions of these viruses. The HHV-8 accessory proteins specify not only activities deducible from their cellular protein homologies but also novel, unsuspected activities that have revealed new mechanisms of virus-host interaction that serve virus replication or latency and may contribute to the development and progression of virus-associated neoplasia. These proteins include viral interleukin-6 (vIL-6), viral chemokines (vCCLs), viral G protein-coupled receptor (vGPCR), viral interferon regulatory factors (vIRFs), and viral antiapoptotic proteins homologous to FLICE (FADD-like IL-1β converting enzyme)-inhibitory protein (FLIP) and survivin. Other HHV-8 proteins, such as signaling membrane receptors encoded by open reading frames K1 and K15, also interact with host mechanisms in unique ways and have been implicated in viral pathogenesis. Additionally, a set of micro-RNAs encoded by HHV-8 appear to modulate expression of multiple host proteins to provide conditions conducive to virus persistence within the host and could also contribute to HHV-8-induced neoplasia. Here, we review the molecular biology underlying these novel virus-host interactions and their potential roles in both virus biology and virus-associated disease.

The Kaposi's sarcoma-associated herpesvirus (KSHV)-induced 5-lipoxygenase-leukotriene B4 cascade plays key roles in KSHV latency, monocyte recruitment, and lipogenesis

Kaposi's sarcoma-associated herpesvirus (KSHV) is etiologically associated with Kaposi's sarcoma (KS) and primary effusion lymphoma (PEL). KS lesions are characterized by endothelial cells with multiple copies of the latent KSHV episomal genome, lytic replication in a low percentage of infiltrating monocytes, and inflammatory cytokines plus growth factors. We demonstrated that KSHV utilizes inflammatory cyclooxygenase 2/prostaglandin E2 to establish and maintain latency (Sharma-Walia, N., A. G. Paul, V. Bottero, S. Sadagopan, M. V. Veettil, N. Kerur, and B. Chandran, PLoS Pathog 6:e1000777, 2010 [doi:10.1371/journal.ppat.1000777]). Here, we evaluated the role of 5-lipoxygenase (5LO) and its chemotactic metabolite leukotriene B4 (LTB4) in KSHV biology. Abundant staining of 5LO was detected in human KS tissue sections. We observed elevated levels of 5LO and high levels of secretion of LTB4 during primary KSHV infection of endothelial cells and in PEL B cells (BCBL-1 and BC-3 cells). Blocking the 5LO/LTB4 cascade inhibited viral latent ORF73, immunomodulatory K5, viral macrophage inflammatory protein 1 (MIP-1), and viral MIP-2 gene expression, without much effect on lytic switch ORF50, immediate early lytic K8, and viral interferon-regulatory factor 2 gene expression. 5LO inhibition significantly downregulated latent viral Cyclin and latency-associated nuclear antigen 2 levels in PEL cells. 5LO/LTB4 inhibition downregulated TH2-related cytokine secretion, elevated TH1-related cytokine secretion, and reduced human monocyte recruitment, adhesion, and transendothelial migration. 5LO/LTB4 inhibition reduced fatty acid synthase (FASN) promoter activity and its expression. Since FASN, a key enzyme required in lipogenesis, is important in KSHV latency, these findings collectively suggest that 5LO/LTB4 play important roles in KSHV biology and that effective inhibition of the 5LO/LTB4 pathway could potentially be used in treatment to control KS/PEL.

Antiviral activity of (+)-rutamarin against Kaposi's sarcoma-associated herpesvirus by inhibition of the catalytic activity of human topoisomerase II

Kaposi's sarcoma-associated herpesvirus (KSHV) is an etiological agent of several AIDS-associated malignancies, including Kaposi's sarcoma (KS), primary effusion lymphoma (PEL), and multicentric Castleman's disease (MCD). Its lytic replication cycle has been proven to be critical for the pathogenesis of KSHV-associated diseases. In KS lesions, lytic viral replication, production of virion particles, and reinfection of endothelial cells are essential to sustain the population of infected cells that otherwise would be quickly lost as spindle cells divide. Thus, antivirals that block KSHV replication could be a strategy in the treatment of KSHV-associated diseases. However, there is no effective anti-KSHV drug currently available. Our previous work showed that human topoisomerase II (Topo II) is indispensable for KSHV lytic replication and is suggested to be an effective target for antiviral drugs. Here, we report the discovery and characterization of a novel catalytic inhibitor of human Topo IIα, namely, (+)-rutamarin. The binding mode of (+)-rutamarin to the ATPase domain of human Topo IIα was established by docking and validated by molecular dynamics (MD) simulations. More importantly, (+)-rutamarin efficiently inhibits KSHV lytic DNA replication in BCBL-1 cells with a half-maximal inhibitory concentration (IC50) of 1.12 μM and blocks virion production with a half-maximal antiviral effective concentration (EC50) of 1.62 μM. It possesses low cytotoxicity, as indicated by the selectivity index (SI) of 84.14. This study demonstrated great potential for (+)-rutamarin to become an effective drug for treatment of human diseases associated with KSHV infection.

Soft tissue sarcomas--new approaches to diagnosis and classification

The study of sarcoma pathology is a rapidly evolving field. The continued refinement of classic diagnostic techniques in conjunction with the molecular diagnostics has resulted in an abundance of data regarding this diverse and rare group of tumors. We anticipate that cutting edge technology including next generation sequencing will continue to further our understanding of saromagenesis and enable more precise classification and diagnosis of sarcomas in the future.