Kaposi's sarcoma-associated herpesvirus: a new DNA tumor virus

KSHV miRNAs target STING to evade innate immunity and facilitate KSHV lytic reactivation from latency

Kaposi sarcoma-associated herpesvirus (KSHV) employs various strategies to evade host immune surveillance and maintain lifelong latency. The cyclic GMP-AMP synthase (cGAS)/stimulator of interferon genes (STING) DNA sensing pathway is a key innate immunity pathway that detects viral DNA and restricts KSHV lytic replication upon reactivation from latency. Here, we identify three KSHV microRNAs (miRNAs), miR-K12-6-3p, miR-K12-7-3p, and miR-K12-11-3p, that directly bind to STING1 mRNA to repress its translation and inhibit downstream immune signaling. Exogenous delivery of these KSHV miRNAs led to decreased STING expression and attenuated cGAS/STING signaling in response to STING agonist stimulation. Conversely, genetic deletion of these KSHV miRNAs rescued STING and interferon-stimulated gene expression in latent KSHV cell lines, delaying KSHV lytic reactivation and reducing KSHV lytic gene expression. These findings shed light on the immune evasion strategy of KSHV miRNA-mediated STING repression, representing the discovery of viral miRNAs that target STING.

Indicators for Increased Likelihood of Epidemic Kaposi Sarcoma Progression after Antiretroviral Therapy Initiation

Kaposi sarcoma (KS) is a common malignancy for people living with HIV (PLWH), despite antiretroviral therapy (ART). Curiously, even with improved CD4+ T-cell counts and low viral loads following ART, some PLWH with KS may still experience KS progression or even death and require adjuvant chemotherapy to manage their KS. The factors associated with persistent or unresponsive KS after ART initiation remain poorly characterized, and biomarkers to identify patients at risk of KS progression are needed, particularly in resource-limited areas where access to chemotherapy is limited. Here we analyzed baseline KS tumor biopsies from PLWH with KS who required chemotherapy due to unresolved KS after ART initiation and those who did not require chemotherapy after ART initiation. By examining participant metadata and viral copy number for Kaposi sarcoma-associated herpesvirus (KSHV), HIV, cytomegalovirus, and Epstein-Barr virus and KSHV gene expression in the tumor biopsies prior to ART initiation, we identified a model of factors associated with KS progression after ART initiation, including biological sex, age, and the log ratio of KSHV/HIV copy number in the tumor. We believe that the ratio of KSHV/HIV may be linked to the cell types that each virus infects, and future work exploring the relationship between tumor and immune cells in the baseline tumors is planned. Innovation would be necessary to reduce costs and simplify the viral quantification assays, enabling the translation of these findings into routine clinical care, particularly in resource-limited settings.

Advancements in LAMP-Based Diagnostics: Emerging Techniques and Applications in Viral Detection with a Focus on Herpesviruses in Transplant Patient Management

Loop-mediated isothermal amplification (LAMP) is a highly effective molecular diagnostic technique, particularly advantageous for point-of-care (POC) settings. In recent years, LAMP has expanded to include various adaptations such as DARQ-LAMP, QUASR, FLOS-LAMP, displacement probes and molecular beacons. These methods enable multiplex detection of multiple targets in a single reaction, enhancing cost-effectiveness and diagnostic efficiency. Consequently, LAMP has gained significant traction in diagnosing diverse viruses, notably during the COVID-19 pandemic. However, its application for detecting Herpesviridae remains relatively unexplored. This group of viruses is of particular interest due to their latency and potential reactivation, crucial for immunocompromised patients, including organ and hematopoietic stem cell transplant recipients. This review highlights recent advancements in LAMP for virus diagnosis and explores current research trends and future prospects, emphasizing the detection challenges posed by Herpesviridae.

Linear ubiquitination regulates the KSHV replication and transcription activator protein to control infection

Like many other viruses, KSHV has two life cycle modes: the latent phase and the lytic phase. The RTA protein from KSHV is essential for lytic reactivation, but how this protein's activity is regulated is not fully understood. Here, we report that linear ubiquitination regulates the activity of RTA during KSHV lytic reactivation and de novo infection. Overexpressing OTULIN inhibits KSHV lytic reactivation, whereas knocking down OTULIN or overexpressing HOIP enhances it. Intriguingly, we found that RTA is linearly polyubiquitinated by HOIP at K516 and K518, and these modifications control the RTA's nuclear localization. OTULIN removes linear polyubiquitin chains from cytoplasmic RTA, preventing its nuclear import. The RTA orthologs encoded by the EB and MHV68 viruses are also linearly polyubiquitinated and regulated by OTULIN. Our study establishes that linear polyubiquitination plays a critically regulatory role in herpesvirus infection, adding virus infection to the list of biological processes known to be controlled by linear polyubiquitination.

Lytic Replication and Reactivation from B Cells Is Not Required for Establishing or Maintaining Gammaherpesvirus Latency In Vivo

Gammaherpesviruses (GHVs) are lymphotropic tumor viruses with a biphasic infectious cycle. Lytic replication at the primary site of infection is necessary for GHVs to spread throughout the host and establish latency in distal sites. Dissemination is mediated by infected B cells that traffic hematogenously from draining lymph nodes to peripheral lymphoid organs, such as the spleen. B cells serve as the major reservoir for viral latency, and it is hypothesized that periodic reactivation from latently infected B cells contributes to maintaining long-term chronic infection. While fundamentally important to an understanding of GHV biology, aspects of B cell infection in latency establishment and maintenance are incompletely defined, especially roles for lytic replication and reactivation in this cell type. To address this knowledge gap and overcome limitations of replication-defective viruses, we generated a recombinant murine gammaherpesvirus 68 (MHV68) in which ORF50, the gene that encodes the essential immediate-early replication and transcription activator protein (RTA), was flanked by loxP sites to enable conditional ablation of lytic replication by ORF50 deletion in cells that express Cre recombinase. Following infection of mice that encode Cre in B cells with this virus, splenomegaly and viral reactivation from splenocytes were significantly reduced; however, the number of latently infected splenocytes was equivalent to WT MHV68. Despite ORF50 deletion, MHV68 latency was maintained over time in spleens of mice at levels approximating WT, reactivation-competent MHV68. Treatment of infected mice with lipopolysaccharide (LPS), which promotes B cell activation and MHV68 reactivation ex vivo, yielded equivalent increases in the number of latently infected cells for both ORF50-deleted and WT MHV68, even when mice were simultaneously treated with the antiviral drug cidofovir to prevent reactivation. Together, these data demonstrate that productive viral replication in B cells is not required for MHV68 latency establishment and support the hypothesis that B cell proliferation facilitates latency maintenance in vivo in the absence of reactivation. IMPORTANCE Gammaherpesviruses establish lifelong chronic infections in cells of the immune system and place infected hosts at risk for developing lymphomas and other diseases. It is hypothesized that gammaherpesviruses must initiate acute infection in these cells to establish and maintain long-term infection, but this has not been directly tested. We report here the use of a viral genetic system that allows for cell-type-specific deletion of a viral gene that is essential for replication and reactivation. We employ this system in an in vivo model to reveal that viral replication is not required to initiate or maintain infection within B cells.

Immune Reconstitution Inflammatory Syndrome Associated Kaposi Sarcoma

People living with HIV (PLWH) with advanced immunosuppression who initiate antiretroviral therapy (ART) are susceptible to the occurrence of an immune reconstitution inflammatory syndrome (IRIS). Although ART is responsible for AIDS- associated Kaposi sarcoma (KS) improvement and resolution, new onset (unmasking KS-IRIS) or sudden progression of preexisting KS (paradoxical KS-IRIS) can occur after a time delay of between a few days and 6 months after the initiation or resumption of ART, even in patients with a low degree of immunocompromise. KS-IRIS incidence varies from 2.4% to 39%, depending on study design, populations, and geographic regions. Risk factors for developing KS-IRIS include advanced KS tumor stage (T1), pre-treatment HIV viral load >5 log10 copies/mL, detectable pre-treatment plasma-KSHV, and initiation of ART alone without concurrent chemotherapy. Both paradoxical and unmasking KS-IRIS have been associated with significant morbidity and mortality, and thrombocytopenia (<100,000 platelets/mm3 at 12 weeks) has been associated with death. KS-IRIS is not to be considered as ART failure, and an ART regimen must be pursued. Systemic chemotherapy for KS in conjunction with ART is recommended and, in contrast with management of IRIS for other opportunistic infections, glucocorticoids are contra-indicated. Despite our preliminary results, the place of targeted therapies in the prevention or treatment of KS-IRIS needs further assessment.

Kaposi's Sarcoma-Associated Herpesvirus, the Etiological Agent of All Epidemiological Forms of Kaposi's Sarcoma

Simple Summary

Kaposi’s sarcoma-associated herpesvirus (KSHV) is one of the seven oncogenic viruses currently recognized by the International Agency for Research on Cancer. Its presence for Kaposi’s sarcoma development is essential and knowledge on the oncogenic process has increased since its discovery in 1994. However, some uncertainties remain to be clarified, in particular on the exact routes of transmission and disparities in KSHV seroprevalence and the prevalence of Kaposi’s sarcoma worldwide. Here, we summarized the current data on the KSHV viral particle’s structure, its genome, the replication, its seroprevalence, the viral diversity and the lytic and latent oncogenesis proteins involved in Kaposi’s sarcoma. Lastly, we reported the environmental, immunological and viral factors possibly associated with KSHV transmission that could also play a role in the development of Kaposi’s sarcoma.

Abstract

Kaposi’s sarcoma-associated herpesvirus (KSHV), also called human herpesvirus 8 (HHV-8), is an oncogenic virus belonging to the Herpesviridae family. The viral particle is composed of a double-stranded DNA harboring 90 open reading frames, incorporated in an icosahedral capsid and enveloped. The viral cycle is divided in the following two states: a short lytic phase, and a latency phase that leads to a persistent infection in target cells and the expression of a small number of genes, including LANA-1, v-FLIP and v-cyclin. The seroprevalence and risk factors of infection differ around the world, and saliva seems to play a major role in viral transmission. KSHV is found in all epidemiological forms of Kaposi’s sarcoma including classic, endemic, iatrogenic, epidemic and non-epidemic forms. In a Kaposi’s sarcoma lesion, KSHV is mainly in a latent state; however, a small proportion of viral particles (<5%) are in a replicative state and are reported to be potentially involved in the proliferation of neighboring cells, suggesting they have crucial roles in the process of tumorigenesis. KSHV encodes oncogenic proteins (LANA-1, v-FLIP, v-cyclin, v-GPCR, v-IL6, v-CCL, v-MIP, v-IRF, etc.) that can modulate cellular pathways in order to induce the characteristics found in all cancer, including the inhibition of apoptosis, cells’ proliferation stimulation, angiogenesis, inflammation and immune escape, and, therefore, are involved in the development of Kaposi’s sarcoma.

Recent advancements in our understanding of equid gammaherpesvirus infections

Equid gammaherpesviruses are ubiquitous and widespread in the equine population. Despite their frequent detection, their contribution to immune system modulation and the pathogenesis of several diseases remains unclear. Genetic variability and the combination of equid gammaherpesvirus strains a horse is infected with might be clinically significant. Initial gammaherpesvirus infection occurs in foals peripartum with latency then established in peripheral blood mononuclear cells. A novel EHV-5 study suggests that following inhalation equid gammaherpesviruses might obtain direct access to T and B lymphocytes via the tonsillar crypts to establish latency. EHV-5 is associated with equine multinodular pulmonary fibrosis, however, unlike with EHV-2 there is currently minimal evidence for its role in milder cases of respiratory disease and poor performance. Transmission is presumed to be via the upper respiratory tract with periodic reactivation of the latent virus in adult horses. Stress of transport has been identified as a risk factor for reactivation and shedding of equine gammaherpesviruses. There is currently a lack of evidence for the effectiveness of antiviral drugs in the treatment of equine gammaherpesvirus infections.

Inhibition of polo-like kinase 1 (PLK1) facilitates reactivation of gamma-herpesviruses and their elimination

Both Kaposi's sarcoma-associated herpesvirus (KSHV) and Epstein-Barr virus (EBV) establish the persistent, life-long infection primarily at the latent status, and associate with certain types of tumors, such as B cell lymphomas, especially in immuno-compromised individuals including people living with HIV (PLWH). Lytic reactivation of these viruses can be employed to kill tumor cells harboring latently infected viral episomes through the viral cytopathic effects and the subsequent antiviral immune responses. In this study, we identified that polo-like kinase 1 (PLK1) is induced by KSHV de novo infection as well as lytic switch from KSHV latency. We further demonstrated that PLK1 depletion or inhibition facilitates KSHV reactivation and promotes cell death of KSHV-infected lymphoma cells. Mechanistically, PLK1 regulates Myc that is critical to both maintenance of KSHV latency and support of cell survival, and preferentially affects the level of H3K27me3 inactive mark both globally and at certain loci of KSHV viral episomes. Furthremore, we recognized that PLK1 inhibition synergizes with STAT3 inhibition to efficiently induce KSHV reactivation. We also confirmed that PLK1 depletion or inhibition yields the similar effect on EBV lytic reactivation and cell death of EBV-infected lymphoma cells. Lastly, we noticed that PLK1 in B cells is elevated in the context of HIV infection and caused by HIV Nef protein to favor KSHV/EBV latency.

Bone Marrow-Derived SH-SY5Y Neuroblastoma Cells Infected with Kaposi's Sarcoma-Associated Herpesvirus Display Unique Infection Phenotypes and Growth Properties

Kaposi's sarcoma-associated herpesvirus (KSHV) is an important oncogenic virus previously shown to be neurotropic, but studies on neuronal cell infection and pathogenesis are still very limited. Here, we characterized the effects of KSHV infection on neuronal SH-SY5Y cells by the recombinant virus rKSHV.219, which expresses both green fluorescent protein (GFP) and red fluorescent protein (RFP) to reflect the latent and lytic phases of infection. We demonstrated that infected cells have a higher growth rate and that KSHV infection can be sustained. Interestingly, the infected cells can transition spontaneously back and forth between lytic and latent phases of infection, producing progeny viruses but without any adverse effects on cell growth. In addition, transcriptome analysis of viral and cellular genes in latent and lytic cells showed that unlike other infected cell lines, the latently infected cells expressed both latent and most, but not all, of the lytic genes required for infectious virion production. The viral genes uniquely expressed by the lytic cells were mainly involved in the early steps of virus binding. Some of the cellular genes that were deregulated in both latently and lytically infected cells are involved in cell adhesion, cell signal pathways, and tumorigenesis. The downregulated cellular CCDN1, PAX5, and NFASC and upregulated CTGF, BMP4, YAP1, LEF1, and HLA-DRB1 genes were found to be associated with cell adhesion molecules (CAMs), hippo signaling, and cancer. These deregulated genes may be involved in creating an environment that is unique in neuronal cells to sustain cell growth upon KSHV infection and not observed in other infected cell types. IMPORTANCE Our study has provided evidence that neuronal SH-SY5Y cells displayed unique cellular responses upon KSHV infection. Unlike other infected cells, this neuronal cell line displayed a higher growth rate upon infection and can spontaneously transition back and forth between latent and lytic phases of infection. Unlike other latently infected cells, a number of lytic genes were also expressed in the latent phase of infection in addition to the established latent viral genes. They may play a role in deregulating a number of host genes that are involved in cell signaling and tumorigenesis in order to sustain the infection and growth advantages for the cells. Our study has provided novel insights into KSHV infection of neuronal cells and a potential new model for further studies to explore the underlying mechanism in viral and host interactions for neuronal cells and the association of KSHV with neuronal diseases.

Endoplasmic reticulum & mitochondrial calcium homeostasis: The interplay with viruses

Calcium ions (Ca²⁺) act as secondary messengers in a plethora of cellular processes and play crucial role in cellular organelle function and homeostasis. The average resting concentration of Ca²⁺ is nearly 100 nM and in certain cells it can reach up to 1 µM. The high range of Ca²⁺ concentration across the plasma membrane and intracellular Ca²⁺ stores demands a well-coordinated maintenance of free Ca²⁺ via influx, efflux, buffering and storage. Endoplasmic Reticulum (ER) and Mitochondria depend on Ca²⁺ for their function and also serve as major players in intracellular Ca²⁺ homeostasis. The ER-mitochondria interplay helps in orchestrating cellular calcium homeostasis to avoid any detrimental effect resulting from Ca²⁺ overload or depletion. Since Ca²⁺ plays a central role in many biological processes it is an essential component of the virus-host interactions. The large gradient across membranes enable the viruses to easily modulate this buffered environment to meet their needs. Viruses exploit Ca²⁺ signaling to establish productive infection and evade the host immune defense. In this review we will detail the interplay between the viruses and cellular & ER-mitochondrial calcium signaling and the significance of these events on viral life cycle and disease pathogenesis.

p300 promotes cell proliferation through suppressing Kaposi's sarcoma-associated herpesvirus (KSHV) reactivation in the infected B-lymphoma cells

Primary Effusion Lymphoma (PEL) is a B-cell lymphoma associated with Kaposi's sarcoma herpesvirus (KSHV) infection. However, the mechanism of oncogenesis of PEL is still unclear. Studies have shown that the cellular transcriptional coactivator p300 regulates the interaction between host and virus, which plays a vital role in viral replication. In this study, we investigated the role of p300 in BCBL1 cells during the KSHV life cycle. We found that p300 knockout resulted in an overall increase for the early lytic genes and changed the expression of genes associated with tumor development, proliferation, and the immune response in the KSHV infected B cells. However, knockout of p300 significantly inhibited the expression of the immediate-early gene RTA and the late lytic gene K8 after KSHV lytic activation. Additionally, the intracellular KSHV genome copy number and the virion production were reduced. These results demonstrated that p300 plays a crucial role in suppressing KSHV viral replication in BCBL1. Furthermore, we observed that the growth of BCBL1 was inhibited by knockout of p300, which confirmed our findings that p300 promotes cell proliferation. This study further provided evidence that p300 plays an important role in the pathogenesis of BCBL1, which might lead to the oncogenesis of PEL caused by KSHV infection.

Viral interleukin-6 encoded by an oncogenic virus promotes angiogenesis and cellular transformation by enhancing STAT3-mediated epigenetic silencing of caveolin 1

Kaposi's sarcoma (KS) caused by oncogenic Kaposi's sarcoma-associated herpesvirus (KSHV) is a highly angiogenic and invasive vascular tumor and the most common AIDS-associated cancer. KSHV-encoded viral interleukin-6 (vIL-6) is implicated in the development of KSHV-induced malignancies; however, the mechanisms underlying vIL-6-induced angiogenesis and tumorigenesis remain undefined. Here, we show that vIL-6 promotes angiogenesis, cell proliferation, and invasion by downregulating caveolin 1 (CAV1) that plays a pivotal and versatile role in multiple cancer-associated processes. Mechanistically, vIL-6 signaling led to the phosphorylation and acetylation of STAT3 that targeted DNA methyltransferase 1 (DNMT1) in a sequential manner. Specifically, the vIL-6-induced phosphorylated form of STAT3 transcriptionally activated DNMT1 expression. Furthermore, vIL-6-induced acetylated form of STAT3 interacted with DNMT1 to form a transcription factor complex that bound to and methylated the CAV1 promoter, leading to CAV1 expression silencing. In fact, downregulation of CAV1 expression resulted in the activation of AKT signaling, promoting cell invasion, and growth transformation induced by KSHV. Finally, genetic deletion of vIL-6 from the KSHV genome abolished KSHV-induced cellular transformation and impaired angiogenesis. Our results reveal that vIL-6 epigenetically silences CAV1 expression to promote angiogenesis and tumorigenesis by regulating the formation of STAT3-DNMT1 complex. These novel findings define a mechanism by which KSHV inhibits the CAV1 pathway and establish the scientific basis for targeting this pathway to treat KSHV-associated cancers.

Kaposi's sarcoma-associated herpesvirus is cell-intrinsically controlled in latency in microgravity

In the next several decades, humans will explore deep space, including Mars. During long-term space flight, astronauts will be exposed to various physical stressors. Among these stressors, microgravity may compromise the immune system. Consistently, the reactivation of several latent herpesviruses has been reported in astronauts. Although herpesvirus infection status is determined by both cell-intrinsic and -extrinsic factors, it remains unclear which factors play major roles in the virus reactivation in microgravity. Here, using Kaposi's sarcoma-associated herpesvirus (KSHV)-infected cells, we found that KSHV is cell-intrinsically controlled in latency in microgravity. Innate immunity appeared to be unaffected in microgravity, while the expression of some restriction factors against KSHV, such as CTCF and AMPK, was upregulated. Collectively, the infected cells in microgravity can control KSHV in latency, possibly by unimpaired innate immunity and upregulated KSHV restriction factors. This is the first pilot study of the conflicts between cell-intrinsic defense systems and viruses in microgravity and provides fundamental information regarding host-virus interactions in microgravity.

Identification of viral SIM-SUMO2-interaction inhibitors for treating primary effusion lymphoma

Primary effusion lymphoma (PEL) is an aggressive B-cell malignancy without effective treatment, and caused by the infection of Kaposi's sarcoma-associated herpesvirus (KSHV), predominantly in its latent form. Previously we showed that the SUMO2-interacting motif within the viral latency-associated nuclear antigen (LANASIM) is essential for establishment and maintenance of KSHV latency. Here, we developed a luciferase based live-cell reporter system to screen inhibitors selectively targeting the interaction between LANASIM and SUMO2. Cambogin, a bioactive natural product isolated from the Garcinia genus (a traditional herbal medicine used for cancer treatment), was obtained from the reporter system screening to efficiently inhibit the association of SUMO2 with LANASIM, in turn reducing the viral episome DNA copy number for establishment and maintenance of KSHV latent infection at a low concentration (nM). Importantly, Cambogin treatments not only specifically inhibited proliferation of KSHV-latently infected cells in vitro, but also induced regression of PEL tumors in a xenograft mouse model. This study has identified Cambogin as a novel therapeutic agent for treating PEL as well as eliminating persistent infection of oncogenic herpesvirus.

IFI16, a nuclear innate immune DNA sensor, mediates epigenetic silencing of herpesvirus genomes by its association with H3K9 methyltransferases SUV39H1 and GLP

IFI16, an innate immune DNA sensor, recognizes the nuclear episomal herpes viral genomes and induces the inflammasome and interferon-β responses. IFI16 also regulates cellular transcription and act as a DNA virus restriction factor. IFI16 knockdown disrupted the latency of Kaposi’s sarcoma associated herpesvirus (KSHV) and induced lytic transcripts. However, the mechanism of IFI16’s transcription regulation is unknown. Here, we show that IFI16 is in complex with the H3K9 methyltransferase SUV39H1 and GLP and recruits them to the KSHV genome during de novo infection and latency. The resulting depositions of H3K9me2/me3 serve as a docking site for the heterochromatin-inducing HP1α protein leading into the IFI16-dependent epigenetic modifications and silencing of KSHV lytic genes. These studies suggest that IFI16’s interaction with H3K9MTases is one of the potential mechanisms by which IFI16 regulates transcription and establish an important paradigm of an innate immune sensor’s involvement in epigenetic silencing of foreign DNA.

Castleman Disease

Castleman disease (CD) is divided clinically into unicentric or multicentric type. Pathologically, CD is divided into hyaline-vascular and plasma cell variants. Unicentric CD is most common, about 75% of these cases are hyaline-vascular variant, and surgical excision is often curative. In contrast, there are a number of types of multicentric CD including HHV8-associated, idiopathic, and a subset of cases that arise in association with POEMS syndrome. Therapy is required for most patients with multicentric CD, but there is no consensus approach currently. As is evidence, the designation Castleman disease encompasses a heterogeneous group of diseases of varied pathogenesis and which require different therapies.

Latent infection with Kaposi's sarcoma-associated herpesvirus enhances retrotransposition of long interspersed element-1

Kaposi's sarcoma (KS)-associated herpesvirus (KSHV), a gamma-2 herpesvirus, is the causative agent of KS, primary effusion lymphoma (PEL), and a plasma cell variant of multicentric Castleman's disease. Although KSHV latency is detected in KS-related tumors, oncogenic pathways activated by KSHV latent infection are not fully understood. Here, we found that retrotransposition of long interspersed element-1 (L1), a retrotransposon in the human genome, was enhanced in PEL cells. Among the KSHV latent genes, viral FLICE-inhibitory protein (vFLIP) enhanced L1 retrotransposition in an NF-κB-dependent manner. Intracellular cell adhesion molecule-1 (ICAM-1), an NF-κB target, regulated the vFLIP-mediated enhancement of L1 retrotransposition. Furthermore, ICAM-1 downregulated the expression of Moloney leukemia virus 10 (MOV10), an L1 restriction factor. Knockdown of ICAM-1 or overexpression of MOV10 relieved the vFLIP-mediated enhancement of L1 retrotransposition. Collectively, during KSHV latency, vFLIP upregulates ICAM-1 in an NF-κB-dependent manner, which, in turn, downregulates MOV10 expression and thereby enhances L1 retrotransposition. Because active L1 retrotransposition can lead to genomic instability, which is commonly found in KS and PEL, activation of L1 retrotransposition during KSHV latency may accelerate oncogenic processes through enhancing genomic instability. Our results suggest that L1 retrotransposition may be a novel target for impeding tumor development in KSHV-infected patients.

Omega-3 decreases IL-6 levels in HIV and human herpesvirus-8 coinfected patients in Uganda

OBJECTIVE

Kaposi sarcoma is a HIV-associated malignancy caused by human herpesvirus-8 (HHV-8) that occurs at highest incidence in sub-Saharan Africa. Kaposi sarcoma patients often present with inflammatory symptoms associated with higher mortality.

DESIGN

We conducted a double-blind, randomized, placebo-controlled study in Uganda to test whether omega-3 supplementation could reduce inflammation in HIV and HHV-8 coinfected adults. Patients with acute illness, AIDS, or advanced Kaposi sarcoma were ineligible, as were pregnant women. Participant IDs were pre-randomized, blocked by Kaposi sarcoma status, to either the omega-3 or placebo arm.

METHODS

Omega-3 participants received a 3-g pill dose daily for 12 weeks (1.8-g eicosapentaenoic acid, 1.2-mg docosapentaenoic acid); placebo participants received 44.8 mg of high oleic safflower oil that appeared indistinguishable from the active supplement. Intervention effects were evaluated as the baseline-adjusted mean difference after 12 weeks between omega-3 and placebo participants in concentrations of fatty acids, inflammatory cytokines, and immune cells.

RESULTS

The final study population included 56 Kaposi sarcoma patients and 11 Kaposi sarcoma-negative, HIV and HHV-8-positive participants randomized to receive either omega-3 (N = 33) or placebo (N = 34). Inflammatory cytokine IL-6 concentrations decreased in omega-3 participants (-0.78 pg/ml) but increased in placebo participants (+3.2 pg/ml; P = 0.04). We observed a trend toward decreased IL-6 after omega-3 supplementation specific to Kaposi sarcoma patients (P = 0.08). CD8 T-cell counts tended to increase in the omega-3 arm Kaposi sarcoma patients (+60 cells/μl), in contrast to decreases (-47 cells/μl) among placebo (P = 0.11).

CONCLUSION

Omega-3 supplementation decreased IL-6 concentrations among HIV and HHV-8 coinfected Ugandans, which may have clinical benefit for Kaposi sarcoma patients.

IL-10 promoter transactivation by the viral K-RTA protein involves the host-cell transcription factors, specificity proteins 1 and 3

Kaposi's sarcoma-associated herpesvirus (KSHV)/human herpesvirus-8 (HHV-8) causes a persistent infection, presenting latent and lytic replication phases during its life cycle. KSHV-related diseases are associated with deregulated expression of inflammatory cytokines, including IL-6 and IL-10, but the mechanisms underlying this dysregulation are unclear. Herein, we report a molecular mechanism for KSHV-induced IL-10 gene expression. KSHV replication and transcription activator (K-RTA) is a molecular switch for the initiation of expression of viral lytic genes, and we describe, for the first time, that K-RTA significantly activates the promoter of the human IL-10 gene. Of note, mutations involving a basic region of K-RTA reduced the association of K-RTA with the IL-10 promoter. Moreover, the host-cell transcription factors, specificity proteins (SP) 1 and 3, play a pivotal cooperative role in K-RTA-mediated transactivation of the IL-10 promoter. K-RTA can interact with SP1 and SP3 directly in vitro, and electrophoresis mobility shift assays (EMSAs) revealed co-operative interaction involving K-RTA, SP1, and SP3 in binding to the IL-10 promoter. As DNase I footprinting assays indicated that K-RTA did not affect SP3 binding to the IL-10 promoter, SP3 can function to recruit K-RTA to the IL-10 promoter. These findings indicate that K-RTA can directly contribute to IL-10 up-regulation via a functional interplay with the cellular transcription factors SP1 and SP3.

Epigenetic Landscape of Kaposi's Sarcoma-Associated Herpesvirus Genome in Classic Kaposi's Sarcoma Tissues

Kaposi's sarcoma-associated herpesvirus (KSHV) is etiologically related to Kaposi's sarcoma (KS), primary effusion lymphoma (PEL) and multicentric Castleman's disease (MCD). It typically displays two different phases in its life cycle, the default latency and occasional lytic replication. The epigenetic modifications are thought to determine the fate of KSHV infection. Previous studies elegantly depicted epigenetic landscape of latent viral genome in in vitro cell culture systems. However, the physiologically relevant scenario in clinical KS tissue samples is unclear. In the present study, we established a protocol of ChIP-Seq for clinical KS tissue samples and mapped out the epigenetic landscape of KSHV genome in classic KS tissues. We examined AcH3 and H3K27me3 histone modifications on KSHV genome, as well as the genome-wide binding sites of latency associated nuclear antigen (LANA). Our results demonstrated that the enriched AcH3 was mainly restricted at latent locus while H3K27me3 was widespread on KSHV genome in classic KS tissues. The epigenetic landscape at the region of vIRF3 gene confirmed its silenced state in KS tissues. Meanwhile, the abundant enrichment of LANA at the terminal repeat (TR) region was also validated in the classic KS tissues, however, different LANA binding sites were observed on the host genome. Furthermore, we verified the histone modifications by ChIP-qPCR and found the dominant repressive H3K27me3 at the promoter region of replication and transcription activator (RTA) in classic KS tissues. Intriguingly, we found that the TR region in classic KS tissues was lacking in AcH3 histone modifications. These data now established the epigenetic landscape of KSHV genome in classic KS tissues, which provides new insights for understanding KSHV epigenetics and pathogenesis.

Epigenetic modifications are thought to determine the fate of KSHV infection. The epigenetic landscape of KSHV genome in in vitro cell culture systems was well studied previously. However, the physiologically relevant scenario in clinical KS tissues is unclear. In this study, we performed ChIP-Seq experiments in classic KS tissues and mapped out the AcH3 and H3K27me3 histone modifications on KSHV genome, as well as the genome-wide LANA binding sites. The results revealed a similar H3K27me3 landscape but distinct AcH3 patterns on the KSHV genome compared to the results from in vitro cultured PEL and KSHV infected SLK cells. Intriguingly, there were different LANA binding sites seen on the host genome and a reduced number of AcH3 histone modifications at the TR region of KSHV genome were found. The established epigenetic landscape of KSHV genome in classic KS tissues provides new insights towards our understanding of KSHV epigenetics, which is important for future studies on the mechanism of KSHV infection and pathogenesis.

Chloroquine inhibits lytic replication of Kaposi's sarcoma-associated herpesvirus by disrupting mTOR and p38-MAPK activation

Lytic infection is essential for the persistent infection and pathogenesis of Kaposi's sarcoma-associated herpesvirus (KSHV), and inhibiting KSHV lytic replication may effectively prevent the occurrence of KSHV-related diseases. Chloroquine (CQ), a well-known antimalarial drug and autophagy inhibitor, exerts broad-spectrum antiviral effects and shows anti-cancer therapeutic potential. However, the ability of CQ and its derivatives to control infection of oncogenic γ-herpesvirus remains undefined. Here we reveal that CQ suppresses KSHV lytic gene expression and virion production, and shows cytotoxicity toward KSHV lytically infected B cells at clinically acceptable doses. CQ suppresses mTOR and p38-MAPK pathway activation during KSHV lytic replication but not latent infection. Furthermore, CQ blocks Epstein-Barr virus (EBV) lytic replication via a distinct mechanism that is invoked to block virion production but does not affect viral gene expression. These results suggest that CQ is an effective antiviral drug against KSHV lytic infection. Our findings indicate that CQ treatment should be considered for controlling KSHV-related diseases, particularly for primary use in co-infection of KSHV with malaria.

Suppression of KSHV-induced angiopoietin-2 inhibits angiogenesis, infiltration of inflammatory cells, and tumor growth

Kaposi's sarcoma (KS) is a highly angiogenic and inflammatory neoplasia. The angiogenic and inflammatory cytokine angiopoietin-2 (Ang-2) is strongly expressed in KS due to Kaposi's sarcoma-associated herpesvirus (KSHV) infection. In the present study, we determined how Ang-2 contributes to development of KS by using telomerase-immortalized human umbilical vein endothelial cells (TIVE) as a model, which become malignantly transformed and express increased levels of Ang-2 following KSHV infection. Ang-2 released from TIVE-KSHV cells induces tyrosine phosphorylation of Tie-2 receptor from both human and mouse endothelial cells and promotes angiogenesis in nude mice. Functional inhibition or expressional "knock-down" of Ang-2 in these cells blocks angiogenesis and inhibits tumor growth. Ang-2 suppression also reduces the numbers of infiltrating monocytes/macrophages in tumors. In transwell-based cell migration assays, Ang-2 indeed enhances migration of human monocytes in a dose-dependent manner. These results underscore a pivotal role of KSHV-induced Ang-2 in KS tumor development by promoting both angiogenesis and inflammation. Our data also suggest that selective drug targeting of Ang-2 may be used for treatment of KS.

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.

The Role of Gammaherpesviruses in Cancer Pathogenesis

Worldwide, one fifth of cancers in the population are associated with viral infections. Among them, gammaherpesvirus, specifically HHV4 (EBV) and HHV8 (KSHV), are two oncogenic viral agents associated with a large number of human malignancies. In this review, we summarize the current understanding of the molecular mechanisms related to EBV and KSHV infection and their ability to induce cellular transformation. We describe their strategies for manipulating major cellular systems through the utilization of cell cycle, apoptosis, immune modulation, epigenetic modification, and altered signal transduction pathways, including NF-kB, Notch, Wnt, MAPK, TLR, etc. We also discuss the important EBV latent antigens, namely EBNA1, EBNA2, EBNA3’s and LMP’s, which are important for targeting these major cellular pathways. KSHV infection progresses through the engagement of the activities of the major latent proteins LANA, v-FLIP and v-Cyclin, and the lytic replication and transcription activator (RTA). This review is a current, comprehensive approach that describes an in-depth understanding of gammaherpes viral encoded gene manipulation of the host system through targeting important biological processes in viral-associated cancers.

Triptolide decreases expression of latency-associated nuclear antigen 1 and reduces viral titers in Kaposi's sarcoma-associated and herpesvirus-related primary effusion lymphoma cells

Kaposi's sarcoma-associated herpesvirus (KSHV) can establish a life-long persistence in the host after primary infection and is associated with certain malignancies, which are resistant to conventional chemotherapeutic agents with a poor prognosis. Latency-associated nuclear antigen 1 (LANA1) encoded by KSHV is essential for segregation, replication and maintenance of viral genome. In addition, LANA1 upregulates the transcriptional activity of signal transducer and activator of transcription 3 (STAT3), which plays an important role in promoting survival of KSHV-associated primary effusion lymphoma (PEL) cells. Furthermore, LANA1 mediates transcriptional modulation of KSHV and host genome in host cells. In the present study, the antitumor effect of triptolide was assessed. CCK-8 assays were performed to demonstrate that the proliferations of PEL cells were efficiently inhibited by triptolide in a dose- and time-dependent manner. Flow cytometric results indicated that triptolide induced cell cycle arrest and apoptosis. Western blot results suggested that triptolide downregulated LANA1 expression and reduced half-life of LANA1 in the KSHV-infected malignant cells. Viral titer experiments indicated that triptolide treatment impaired the number of viral DNA copies and the production of virions in BCBL-1 cells. Triptolide also suppressed STAT3 activity and inhibited secretion of IL-6 in PEL cells. In a mouse xenograft model of primary effusion lymphoma by BCBL-1 cells, triptolide treatment significantly inhibited ascites formation and diffused organ infiltration. These results indicate that triptolide impairs the expression of LANA1 and shows antitumor activity against PEL in vitro and in vivo. Triptolide may be a potential agent for treatment of PEL.

The role of Kaposi's sarcoma-associated herpesvirus infection in the proliferation of human bladder cancer cells

Existing evidence suggests a possible role of viruses in human bladder cancer development. Recently, Kaposi's sarcoma-associated herpesvirus (KSHV) was reported to be the most frequently detected virus in bladder cancer tissue from Croatian patients on screening with the Lawrence Livermore Microbial Detection Array. In the current study, to investigate the functional roles of KSHV in bladder cancer, five bladder cancer cell lines were infected with KSHV and their tumour progression-associated changes investigated. Four KSHV-infected bladder cancer cell lines were established; two invasive bladder cancer cell lines showed higher proliferation rates than uninfected cells. Additionally, these KSHV-infected invasive bladder cancer cells showed a greater number of colonies, which were also significantly larger than those of uninfected cells, in a soft agar colony formation assay. cDNA microarray analysis showed that various genes associated with cell proliferation and cancer development were upregulated in these KSHV-infected bladder cancer cells. Taken together, we suggest that KSHV infection affects the proliferation of a subset of invasive bladder cancer cells and may therefore play a role in their oncogenic progression. Further studies are required to elucidate the exact mechanism used by KSHV to promote bladder cancer progression.

Bub1 in Complex with LANA Recruits PCNA To Regulate Kaposi's Sarcoma-Associated Herpesvirus Latent Replication and DNA Translesion Synthesis

Latent DNA replication of Kaposi's sarcoma-associated herpesvirus (KSHV) initiates at the terminal repeat (TR) element and requires trans-acting elements, both viral and cellular, such as ORCs, MCMs, and latency-associated nuclear antigen (LANA). However, how cellular proteins are recruited to the viral genome is not very clear. Here, we demonstrated that the host cellular protein, Bub1, is involved in KSHV latent DNA replication. We show that Bub1 constitutively interacts with proliferating cell nuclear antigen (PCNA) via a highly conserved PIP box motif within the kinase domain. Furthermore, we demonstrated that Bub1 can form a complex with LANA and PCNA in KSHV-positive cells. This strongly indicated that Bub1 serves as a scaffold or molecular bridge between LANA and PCNA. LANA recruited PCNA to the KSHV genome via Bub1 to initiate viral replication in S phase and interacted with PCNA to promote its monoubiquitination in response to UV-induced damage for translesion DNA synthesis. This resulted in increased survival of KSHV-infected cells.

IMPORTANCE

During latency in KSHV-infected cells, the viral episomal DNA replicates once each cell cycle. KSHV does not express DNA replication proteins during latency. Instead, KSHV LANA recruits the host cell DNA replication machinery to the replication origin. However, the mechanism by which LANA mediates replication is uncertain. Here, we show that LANA is able to form a complex with PCNA, a critical protein for viral DNA replication. Furthermore, our findings suggest that Bub1, a spindle checkpoint protein, serves as a scaffold or molecular bridge between LANA and PCNA. Our data further support a role for Bub1 and LANA in PCNA-mediated cellular DNA replication processes as well as monoubiquitination of PCNA in response to UV damage. These data reveal a therapeutic target for inhibition of KSHV persistence in malignant cells.

Preparation and characterization of polyclonal antibody against Kaposi's sarcoma-associated herpesvirus lytic gene encoding RTA

Replication and transcription activator (RTA) is a critical lytic protein encoded by Kaposi's sarcoma-associated herpesvirus (KSHV). To prepare rabbit polyclonal antibody against RTA, three antigenic polypeptides of KSHV RTA were initially synthesized. The fragment of RTA was cloned into p3FlagBsd to construct the recombinant plasmid, pRTA-Flag. 293 T and EA.hy926 cells were transfected with pRTA-Flag to obtain RTA-Flag fusion protein, which was detected using anti-Flag antibody. Next, New Zealand white rabbits were immunized with keyhole limpet hemocyanin-conjugated peptides to generate polyclonal antibodies against RTA. Enzyme-linked immunosorbent assays were performed to characterize the polyclonal antibodies, and the titers of the polyclonal antibodies against RTA were greater than 1:11,000. Western blotting and immunofluorescence assay revealed that the prepared antibody reacted specifically with the RTA-Flag fusion protein as well as the native viral protein in KSHV-infected primary effusion lymphoma cells. Collectively, our work successfully constructed the recombinant expression vector, pRTA-Flag, and prepared the polyclonal antibody against RTA, which was valuable for investigating the biochemical and biological functions of the critical KSHV lytic gene.

KSHV LANA--the master regulator of KSHV latency

Kaposi's sarcoma associated herpesvirus (KSHV), like other human herpes viruses, establishes a biphasic life cycle referred to as dormant or latent, and productive or lytic phases. The latent phase is characterized by the persistence of viral episomes in a highly ordered chromatin structure and with the expression of a limited number of viral genes. Latency Associated Nuclear Antigen (LANA) is among the most abundantly expressed proteins during latency and is required for various nuclear functions including the recruitment of cellular machineries for viral DNA replication and segregation of the replicated genomes to daughter cells. LANA achieves these functions by recruiting cellular proteins including replication factors, chromatin modifying enzymes and cellular mitotic apparatus assembly. LANA directly binds to the terminal repeat region of the viral genome and associates with nucleosomal proteins to tether to the host chromosome. Binding of LANA to TR recruits the replication machinery, thereby initiating DNA replication within the TR. However, other regions of the viral genome can also initiate replication as determined by Single Molecule Analysis of the Replicated DNA (SMARD) approach. Recent, next generation sequence analysis of the viral transcriptome shows the expression of additional genes during latent phase. Here, we discuss the newly annotated latent genes and the role of major latent proteins in KSHV biology.

Maturation and vesicle-mediated egress of primate gammaherpesvirus rhesus monkey rhadinovirus require inner tegument protein ORF52

The tegument layer of herpesviruses comprises a collection of proteins that is unique to each viral species. In rhesus monkey rhadinovirus (RRV), a close relative of the human oncogenic pathogen Kaposi's sarcoma-associated herpesvirus, ORF52 is a highly abundant tegument protein tightly associated with the capsid. We now report that ORF52 knockdown during RRV infection of rhesus fibroblasts led to a greater than 300-fold reduction in the viral titer by 48 h but had little effect on the number of released particles and caused only modest reductions in the levels of intracellular viral genomic DNA and no appreciable change in viral DNA packaging into capsids. These data suggested that the lack of ORF52 resulted in the production and release of defective particles. In support of this interpretation, transmission electron microscopy (TEM) revealed that without ORF52, capsid-like particles accumulated in the cytoplasm and were unable to enter egress vesicles, where final tegumentation and envelopment normally occur. TEM also demonstrated defective particles in the medium that closely resembled the accumulating intracellular particles, having neither a full tegument nor an envelope. The disruption in tegument formation from ORF52 suppression, therefore, prevented the incorporation of ORF45, restricting its subcellular localization to the nucleus and appearing, by confocal microscopy, to inhibit particle transport toward the periphery. Ectopic expression of small interfering RNA (siRNA)-resistant ORF52 was able to partially rescue all of these phenotypic changes. In sum, our results indicate that efficient egress of maturing virions and, in agreement with studies on murine gammaherpesvirus 68 (MHV-68), complete tegumentation and secondary envelopment are dependent on intact ORF52.

IMPORTANCE

The tegument, or middle layer, of herpesviruses comprises both viral and cellular proteins that play key roles in the viral life cycle. A subset of these proteins is present only within members of one of the three subfamilies (alphaherpesviruses, betaherpesviruses, or gammaherpesviruses) of Herpesviridae. In this report, we show that the gammaherpesvirus-specific tegument protein ORF52 is critical for maturation of RRV, the closest relative of Kaposi's sarcoma-associated herpesvirus (KSHV) (a human cancer-causing pathogen) that has undergone this type of analysis. Without ORF52, the nascent subviral particles are essentially stuck in maturation limbo, unable to acquire the tegument or outer (envelope) layers. This greatly attenuates infectivity. Our data, together with earlier work on a murine homolog, as well as a more distantly related human homolog, provide a more complete understanding of how early protein interactions involving virus-encoded tegument proteins are critical for virus assembly and are also, therefore, potentially attractive therapeutic targets.

Kaposi's sarcoma-associated herpesvirus-encoded LANA interacts with host KAP1 to facilitate establishment of viral latency

Kaposi's sarcoma-associated herpesvirus (KSHV) typically displays two different phases in its life cycle, the default latent phase and the lytic phase. There is a short period of lytic gene expression in the early stage of KSHV primary infection. The factors involved in the shutdown process of lytic gene expression are poorly identified. It has been shown that the latency-associated nuclear antigen (LANA) encoded by KSHV plays an important role in the establishment of viral latency. In screening, we identified a host protein, Krüppel-associated box domain-associated protein 1 (KAP1), that bound to LANA. We validated the interaction between LANA and KAP1 in vivo and in vitro, as well as their colocalization in the nucleus. We mapped out that LANA interacted with both the N- and C-terminal domains of KAP1. Based on the interface of LANA-KAP1 interaction determined, we proved that LANA recruited KAP1 to the RTA promoter region of the KSHV genome. We revealed that KAP1 was involved in transcriptional repression by LANA. We found multiple cooccupation sites of LANA and KAP1 on the whole KSHV genome by chromatin immunoprecipitation for sequencing (ChIP-seq) and demonstrated that LANA-recruited KAP1 played a critical role in the shutdown of lytic gene expression during the early stage of KSHV primary infection. Taken together, our data suggest that LANA interacts with KAP1 and represses lytic gene expression to facilitate the establishment of KSHV latency.

IMPORTANCE

Our study revealed the mechanism of transcriptional repression by LANA during KSHV primary infection, providing new insights into the process of KSHV latency establishment.

Preparation and application of polyclonal antibodiesagainst KSHV v-cyclin

We prepared rabbit polyclonal antibodies against Kaposi's sarcoma-associated herpesvirus (KSHV)-encoded v-cyclin (ORF 72) and detected the natural viral protein using these polyclonal antibodies. Three antigenic polypeptides of v-cyclin were designed and synthesized. A fragment of the v-cyclin gene was cloned into a eukaryotic expression vector pEF-MCS-Flag-IRES/Puro to construct a recombinant vector, pEF v-cyclin. Then, pEF v-cyclin was transfected into 293T and EA.hy926 cells to obtain v-cyclin-Flag fusion proteins. Six New Zealand white rabbits were immunized with KLH-conjugated peptides to generate polyclonal antibodies against v-cyclin. The polyclonal antibodies were then characterized by ELISA and Western blotting assays. Finally, the polyclonal antibodies against v-cyclin were used to detect natural viral protein expressed in BCBL-1, BC-3, and JSC-1 cells. The results showed that using the Flag antibody, v-cyclin-Flag fusion protein was detected in 293T and EA.hy926 cells transfected with pEF-v-cyclin. Furthermore, ELISA showed that the titer of the induced polyclonal rabbit anti-v-cyclin antibodies was higher than 1:8,000. In Western blotting assays, the antibodies reacted specifically with the v-cyclin-Flag fusion protein as well as the natural viral protein. The recombinant expression vector pEF-v-cyclin was constructed successfully, and the polyclonal antibodies prepared can be used for various biological tests including ELISA and Western blotting assays.

Professional antigen presenting cells in human herpesvirus 8 infection

Professional antigen presenting cells (APC), i.e., dendritic cells (DC), monocytes/macrophages, and B lymphocytes, are critically important in the recognition of an invading pathogen and presentation of antigens to the T cell-mediated arm of immunity. Human herpesvirus 8 (HHV-8) is one of the few human viruses that primarily targets these APC for infection, altering their cytokine profiles, manipulating their surface expression of MHC molecules, and altering their ability to activate HHV-8-specific T cells. This could be why T cell responses to HHV-8 antigens are not very robust. Of these APC, only B cells support complete, lytic HHV-8 infection. However, both complete and abortive virus replication cycles in APC could directly affect viral pathogenesis and progression to Kaposi's sarcoma (KS) and HHV-8-associated B cell cancers. In this review, we discuss the effects of HHV-8 infection on professional APC and their relationship to the development of KS and B cell lymphomas.

Immunosuppressive properties of mesenchymal stem cells

Mesenchymal stem cells (MSC) can be isolated from different adult tissues including bone marrow, adipose tissue, cord blood and placenta. MSCs modulate the immune function of the major immune cell populations involved in alloantigen recognition and elimination, including antigen presenting cells, T cells, B cells and natural killer cells. Many clinical trials are currently underway that employ MSCs to treat human immunological diseases. However, the molecular mechanism that mediates the immunosuppressive effect of MSCs is still unclear and the safety of using MSC in patient needs further confirmation. Here, we review the cytokines that activate MSCs and the soluble factors produced by MSCs, which allow them to exert their immunosuppressive effects. We review the mechanism responsible, at least in part, for the immune suppressive effects of MSCs and highlight areas of research required for a better understanding of MSC immune modulation.

Cisplatin disrupts the latency of human herpesvirus 8 and induces apoptosis in primary effusion lymphoma cells

Human herpesvirus 8 (HHV8) is the etiologic agent for primary effusion lymphoma (PEL). The aim of this study is to investigate the effects of cisplatin on the PEL cells. Cisplatin treatment induced apoptosis and inhibited the growth of PEL cells, and the effect was more profound in the HHV8-positive lymphoma cells compared with the EBV-positive lymphoma cells. Cisplatin treatment decreased the expression of HHV8 latent genes and activated p53 at serine 15 in PEL cells. Our results indicate that cisplatin can disrupt HHV8 latency and induce reactivation of p53 and highly selective treatment modality for this virally induced lymphoma.

Transmission of human herpesvirus type 8 infection within families in american indigenous populations from the Brazilian Amazon

BACKGROUND

The intrafamilial dynamics of endemic infection with human herpesvirus type 8 (HHV-8) in Amerindian populations is unknown.

METHODS

Serum samples were obtained from 517 Amerindians and tested for HHV-8 anti-latent nuclear antigen (anti-LANA) and antilytic antibodies by immunofluorescence assays. Logistic regression and mixed logistic models were used to estimate the odds of being HHV-8 seropositive among intrafamilial pairs.

RESULTS

HHV-8 seroprevalence by either assay was 75.4% (95% confidence interval [CI]: 71.5%-79.1%), and it was age-dependent (P(trend) < .001). Familial dependence in HHV-8 seroprevalence by either assay was found between mother-offspring (odds ratio [OR], 5.44; 95% CI: 1.62-18.28) and siblings aged ≥10 years (OR 4.42, 95% CI: 1.70-11.45) or siblings in close age range (<5 years difference) (OR 3.37, 95% CI: 1.21-9.40), or in families with large (>4) number of siblings (OR, 3.20, 95% CI: 1.33-7.67). In separate analyses by serological assay, there was strong dependence in mother-offspring (OR 8.94, 95% CI: 2.94-27.23) and sibling pairs aged ≥10 years (OR, 11.91, 95% CI: 2.23-63.64) measured by LANA but not lytic antibodies.

CONCLUSIONS

This pattern of familial dependence suggests that, in this endemic population, HHV-8 transmission mainly occurs from mother to offspring and between close siblings during early childhood, probably via saliva. The mother to offspring dependence was derived chiefly from anti-LANA antibodies.

Leucine zipper domain is required for Kaposi sarcoma-associated herpesvirus (KSHV) K-bZIP protein to interact with histone deacetylase and is important for KSHV replication

The Kaposi sarcoma-associated herpesvirus (KSHV; or human herpesvirus-8)-encoded protein called K-bZIP (also named K8) was found to be multifunctional. In this study, we discovered that K-bZIP interacts with histone deacetylase (HDAC) 1/2 in 12-O-tetradecanoylphorbol-13-acetate-stimulated BCBL-1 lymphocyte cells. K-bZIP appears to repress HDAC activity through this interaction, which we determined to be independent of K-bZIP SUMOylation. We dissected the domains of K-bZIP and found that the leucine zipper (LZ) domain is essential for the interaction of K-bZIP and HDAC. In addition, we constructed a KSHV bacterial artificial chromosome (BAC) with LZ domain-deleted K-bZIP (KSHVdLZ) and transfected this mutated KSHV BAC DNA into HEK 293T cells. As a result, it was consistently found that K-bZIP without its LZ domain failed to interact with HDAC2. We also showed that the interaction between K-bZIP and HDAC is necessary for the inhibition of the lytic gene promoters (ORF50 and OriLyt) of KSHV by K-bZIP. Furthermore, we found that the LZ domain is also important for the interaction of K-bZIP with the promoters of ORF50 and OriLyt. Most interestingly, although it was found to have suppressive effects on the promoters of ORF50 and OriLyt, KSHVdLZ replicates at a significantly lower level than its BAC-derived revertant (KSHVdLZRev) or KSHVWT (BAC36) in HEK 293T cells. The defectiveness of KSHVdLZ replication can be partially rescued by siRNA against HDAC2. Our results suggest that the function of K-bZIP interaction with HDAC is two-layered. 1) K-bZIP inhibits HDAC activity generally so that KSHVdLZ replicates at a lower level than does KSHVWT. 2) K-bZIP can recruit HDAC to the promoters of OriLyt and ORF50 through interaction with HDAC for K-bZIP to have a temporary repressive effect on the two promoters.

Kaposi's Sarcoma-Associated Herpesvirus Genome Replication, Partitioning, and Maintenance in Latency

Kaposi's sarcoma-associated herpesvirus (KSHV) is thought to be an oncogenic member of the γ-herpesvirus subfamily. The virus usually establishes latency upon infection as a default infection pattern. The viral genome replicates according to the host cell cycle by recruiting the host cellular replication machinery. Among the latently expressing viral factors, LANA plays pivotal roles in viral genome replication, partitioning, and maintenance. LANA binds with two LANA-binding sites (LBS1/2) within a terminal repeat (TR) sequence and is indispensable for viral genome replication in latency. The nuclear matrix region seems to be important as a replication site, since LANA as well as cellular replication factors accumulate there and recruit the viral replication origin in latency (ori-P) by its binding activity to LBS. KSHV ori-P consists of LBS followed by a 32-bp GC-rich segment (32GC). Although it has been reported that LANA recruits cellular pre-replication complexes (pre-RC) such as origin recognition complexes (ORCs) to the ori-P through its interaction with ORCs, this mechanism does not account completely for the requirement of the 32GC. On the other hand, there are few reports about the partitioning and maintenance of the viral genome. LANA interacts with many kinds of chromosomal proteins, including Brd2/RING3, core histones, such as H2A/H2B and histone H1, and so on. The detailed molecular mechanisms by which LANA enables KSHV genome partitioning and maintenance still remain obscure. By integrating the findings reported thus far on KSHV genome replication, partitioning, and maintenance in latency, we will summarize what we know now, discuss what questions remain to be answered, and determine what needs to be done next to understand the mechanisms underlying viral replication, partitioning, and maintenance strategy.

An interaction between KSHV ORF57 and UIF provides mRNA-adaptor redundancy in herpesvirus intronless mRNA export

The hTREX complex mediates cellular bulk mRNA nuclear export by recruiting the nuclear export factor, TAP, via a direct interaction with the export adaptor, Aly. Intriguingly however, depletion of Aly only leads to a modest reduction in cellular mRNA nuclear export, suggesting the existence of additional mRNA nuclear export adaptor proteins. In order to efficiently export Kaposi's sarcoma-associated herpesvirus (KSHV) intronless mRNAs from the nucleus, the KSHV ORF57 protein recruits hTREX onto viral intronless mRNAs allowing access to the TAP-mediated export pathway. Similarly however, depletion of Aly only leads to a modest reduction in the nuclear export of KSHV intronless mRNAs. Herein, we identify a novel interaction between ORF57 and the cellular protein, UIF. We provide the first evidence that the ORF57-UIF interaction enables the recruitment of hTREX and TAP to KSHV intronless mRNAs in Aly-depleted cells. Strikingly, depletion of both Aly and UIF inhibits the formation of an ORF57-mediated nuclear export competent ribonucleoprotein particle and consequently prevents ORF57-mediated mRNA nuclear export and KSHV protein production. Importantly, these findings highlight that redundancy exists in the eukaryotic system for certain hTREX components involved in the mRNA nuclear export of intronless KSHV mRNAs.

Mechanisms of Kaposi's Sarcoma-Associated Herpesvirus Latency and Reactivation

The life cycle of Kaposi's sarcoma-associated herpesvirus (KSHV) consists of latent and lytic replication phases. During latent infection, only a limited number of KSHV genes are expressed. However, this phase of replication is essential for persistent infection, evasion of host immune response, and induction of KSHV-related malignancies. KSHV reactivation from latency produces a wide range of viral products and infectious virions. The resulting de novo infection and viral lytic products modulate diverse cellular pathways and stromal microenvironment, which promote the development of Kaposi's sarcoma (KS). The mechanisms controlling KSHV latency and reactivation are complex, involving both viral and host factors, and are modulated by diverse environmental factors. Here, we review the cellular and molecular basis of KSHV latency and reactivation with a focus on the most recent advancements in the field.

Human herpesvirus 8 viral FLICE-inhibitory protein retards cell proliferation via downregulation of Id2 and Id3 expression

Death receptor-mediated apoptosis is potently inhibited by viral FLIP (FLICE/caspase 8 inhibitory protein) through reduced activation of procaspase 8. In this study, we show that the human herpesvirus 8-encoded vFLIP retards cell proliferation. Overexpression of vFLIP caused cell cycle arrest, with an apparent decrease of cells in the S phase. The Id (inhibitor of DNA binding) proteins are considered as dominant negative regulators of differentiation pathways, but positive regulators of cellular proliferation. The mechanisms by which Id proteins promote the cell cycle are diverse, but appear to involve affecting the expression of cell cycle regulators. RT-PCR results demonstrated that the expression of vFLIP decreased the expression levels of Id2 and Id3 as well as cyclin E and cyclin A compared with the vFLIP-null cells. These indicate that vFLIP affects cell proliferation by decreasing the expression levels of cell cycle regulatory proteins.

Functional availability of gamma-herpesvirus K-cyclin is regulated by cellular CDK6 and p16INK4a

Viral K-cyclin derived from Kaposi's sarcoma-associated herpesvirus is homologous with mammalian D-type cyclins. Here, we demonstrated the regulatory mechanisms for K-cyclin function and degradation in human embryonic kidney HEK293 and primary effusion lymphoma JSC-1 cell lines. Proteasome inhibitor MG132 treatment induced an accumulation of ubiquitinated K-cyclin in these cells, and co-expression of CDK6 prevented K-cyclin ubiquitination. Also K-cyclin mutants incompetent for CDK6-binding were destabilized by proteasome pathway. Furthermore, silencing of p16INK4a promoted K-cyclin-CDK6 complex formation and hence induced K-cyclin-associated kinase activity in HEK293 cells. These observations indicate that CDK6-bound K-cyclin is functionally stable but monomeric K-cyclin is targeted to ubiquitin-dependent degradation pathway in these cells. Our data suggest that the balance between CDK6 and p16INK4a regulates the availability of functional K-cyclin in human cells.

Molecular biology of Kaposi's sarcoma-associated herpesvirus and related oncogenesis

Kaposi's Sarcoma-associated Herpesvirus (KSHV), also known as human herpesvirus 8 (HHV-8), is the most recently identified human tumor virus,and is associated with the pathogenesis of Kaposi's sarcoma and two lymphoproliferative disorders known to occur frequently in AIDS patients-primary effusion lymphoma and multicentric Castleman disease. In the 15 years since its discovery, intense studies have demonstrated an etiologic role for KSHV in the development of these malignancies. Here, we review the recent advances linked to understanding KSHV latent and lytic life cycle and the molecular mechanisms of KSHV-mediated oncogenesis in terms of transformation, cell signaling, cell growth and survival, angiogenesis, immune invasion and response to microenvironmental stress, and highlight the potential therapeutic targets for blocking KSHV tumorigenesis.

Functional genomics as a tool in virus research

Genomics is the study of an organism’s entire genome. It started out as a great scientific endeavor in the 1990s which aimed to sequence the complete genomes of certain biological species. However viruses are not new to this field as complete viral genomes have routinely been sequenced since the past thirty years. The ‘genomic era’ has been said to have revolutionized biology. This knowledge of full genomes has created the field of functional genomics in today’s post-genomic era, which, is in most part concerned with the studies on the expression of the organism’s genome under different conditions. This article is an attempt to introduce its readers to the application of functional genomics to address and answer several complex biological issues in virus research.