Molecular biology of KSHV lytic reactivation

Association of polymorphisms in NFκB1 promoter and NFκBIA gene with the development of antibodies against HHV-8 in HIV-infected individuals

Human gammaherpesvirus 8 (HHV-8) is the etiologic agent of Kaposi's sarcoma, multicentric Castleman's disease and primary effusion lymphoma. Like other herpesviruses, the HHV-8 may exhibit latent or lytic cycle, both regulated by viral and host factors. Regarding host factors, we analysed the association of polymorphisms in NFkB1 promoter (NFkB1-94 ins/del ATTG) and NFκBIA gene (NFκBIA 3'UTR A→G) with the development of antibodies against latent or lytic antigens from HHV-8. The ins/del [OR 7.9 (95% CI 3.3-19.1), p < 0.001], AG [OR 12.3 (95% CI 4.3-34.9) p < 0.001], GG [OR 9.4 (95% CI 3.2-27.9), p < 0.001], ins/del + AG [OR 94.5 (95% CI 9.6-924.4), <0.0001], ins/del + GG [OR 50.4 (95% CI 5.2-482.2, p < 0.0001] and G allele [OR 3.3 (95% CI 2.0-5.6), p < 0.001] were strongly related with the presence of antibodies to lytic antigens. This is the first association of polymorphisms in NFκB1 promoter and NFκBIA gene with the development of antibodies against HHV-8.

Molecular Biology of KSHV in Relation to HIV/AIDS-Associated Oncogenesis

Discovered in 1994, Kaposi's sarcoma-associated herpesvirus (KSHV) has been associated with four human malignancies including Kaposi's sarcoma, primary effusion lymphoma, a subset of multicentric Castleman's disease, and KSHV inflammatory cytokine syndrome. These malignancies mostly occur in immunocompromised patients including patients with acquired immunodeficiency syndrome and often cause significant mortality because of the lack of effective therapies. Significant progresses have been made to understand the molecular basis of KSHV infection and KSHV-induced oncogenesis in the last two decades. This chapter provides an update on the recent advancements focusing on the molecular events of KSHV primary infection, the mechanisms regulating KSHV life cycle, innate and adaptive immunity, mechanism of KSHV-induced tumorigenesis and inflammation, and metabolic reprogramming in KSHV infection and KSHV-transformed cells.

Silver nanoparticles selectively induce human oncogenic γ-herpesvirus-related cancer cell death through reactivating viral lytic replication

Silver nanoparticle (nAg), which is one of the most common manufactured nanomaterials, has a wide range of biomedical applications. The human oncogenic γ-herpesviruses, Kaposi's sarcoma-associated herpesvirus (KSHV) and Epstein-Barr Virus (EBV), are etiologically linked to many malignancies. Currently, there are no efficient or specific treatments for these types of tumors, and most patients die because of resistance to conventional cytotoxic chemotherapy. Despite nAg having antitumor and antiviral activities, its effects on oncogenic herpesvirus-related cancer cells remain largely unknown. Here, we reveal that nAg presents higher cytotoxicity against KSHV- or EBV-latently infected cells via reactivating viral lytic replication, which relies on the induction of reactive oxygen species (ROS) generation and autophagy. Moreover, nAg blocks KSHV primary infection by directly destroying virion particles, as well as effectively inhibits colony formation and moderately represses the growth of KSHV-associated tumors in xenograft mouse model. Taken together, these results demonstrate the therapeutic potential of nAg for use in the antiviral infection and treatment of oncogenic herpesvirus-related cancers.

Reduction of Kaposi's Sarcoma-Associated Herpesvirus Latency Using CRISPR-Cas9 To Edit the Latency-Associated Nuclear Antigen Gene

Kaposi's sarcoma-associated herpesvirus (KSHV) is the etiologic agent of Kaposi's sarcoma (KS), an AIDS-defining cancer in HIV-1-infected individuals or immune-suppressed transplant patients. The prevalence for both KSHV and KS are highest in sub-Saharan Africa where HIV-1 infection is also epidemic. There is no effective treatment for advanced KS; therefore, the survival rate is low. Similar to other herpesviruses, KSHV's ability to establish latent infection in the host presents a major challenge to KS treatment or prevention. Strategies to reduce KSHV episomal persistence in latently infected cells might lead to approaches to prevent KS development. The CRISPR-Cas9 system is a gene editing technique that has been used to specifically manipulate the HIV-1 genome but also Epstein-Barr virus (EBV) which, similar to KSHV, belongs to the Gammaherpesvirus family. Among KSHV gene products, the latency-associated nuclear antigen (LANA) is absolutely required in the maintenance, replication, and segregation of KSHV episomes during mitosis, which makes LANA an ideal target for CRISPR-Cas9 editing. In this study, we designed a replication-incompetent adenovirus type 5 to deliver a LANA-specific Cas9 system (Ad-CC9-LANA) into various KSHV latent target cells. We showed that KSHV latently infected epithelial and endothelial cells transduced with Ad-CC9-LANA underwent significant reductions in the KSHV episome burden, LANA RNA and protein expression over time, but this effect is less profound in BC3 cells due to the low infection efficiency of adenovirus type 5 for B cells. The use of an adenovirus vector might confer potential in vivo applications of LANA-specific Cas9 against KSHV infection and KS.IMPORTANCE The ability for Kaposi's sarcoma-associated herpesvirus (KSHV), the causative agent of Kaposi's sarcoma (KS), to establish and maintain latency has been a major challenge to clearing infection and preventing KS development. This is the first study to demonstrate the feasibility of using a KSHV LANA-targeted CRISPR-Cas9 and adenoviral delivery system to disrupt KSHV latency in infected epithelial and endothelial cell lines. Our system significantly reduced the KSHV episomal burden over time. Given the safety record of adenovirus as vaccine or delivery vectors, this approach to limit KSHV latency may also represent a viable strategy against other tumorigenic viruses and may have potential benefits in developing countries where the viral cancer burden is high.

N6-Methyladenosine and Viral Infection

N⁶-methyladenosine (m⁶A), as a dynamic posttranscriptional RNA modification, recently gave rise to the field of viral epitranscriptomics. The interaction between virus and host is affected by m⁶A. Multiple m⁶A-modified viral RNAs have been observed. The epitranscriptome of m⁶A in host cells are altered after viral infection. The expression of viral genes, the replication of virus and the generation of progeny virions are influenced by m⁶A modifications in viral RNAs during virus infection. Meanwhile, the decorations of m⁶A in host mRNAs can make viral infections more likely to happen or can enhance the resistance of host to virus infection. However, the mechanism of m⁶A regulation in viral infection and host immune response has not been thoroughly elucidated to date. With the development of sequencing-based biotechnologies, transcriptome-wide mapping of m⁶A in viruses has been achieved, laying the foundation for expanding its functions and corresponding mechanisms. In this report, we summarize the positive and negative effects of m⁶A in distinct viral infection. Given the increasingly important roles of m⁶A in diverse viruses, m⁶A represents a novel potential target for antiviral therapy.

Genome-Wide Identification of Direct RTA Targets Reveals Key Host Factors for Kaposi's Sarcoma-Associated Herpesvirus Lytic Reactivation

Kaposi's sarcoma-associated herpesvirus (KSHV) is a human oncogenic virus, which maintains the persistent infection of the host by intermittently reactivating from latently infected cells to produce viral progenies. While it is established that the replication and transcription activator (RTA) viral transcription factor is required for the induction of lytic viral genes for KSHV lytic reactivation, it is still unknown to what extent RTA alters the host transcriptome to promote KSHV lytic cycle and viral pathogenesis. To address this question, we performed a comprehensive time course transcriptome analysis during KSHV reactivation in B-cell lymphoma cells and determined RTA-binding sites on both the viral and host genomes, which resulted in the identification of the core RTA-induced host genes (core RIGs). We found that the majority of RTA-binding sites at core RIGs contained the canonical RBP-Jκ-binding DNA motif. Subsequently, we demonstrated the vital role of the Notch signaling transcription factor RBP-Jκ for RTA-driven rapid host gene induction, which is consistent with RBP-Jκ being essential for KSHV lytic reactivation. Importantly, many of the core RIGs encode plasma membrane proteins and key regulators of signaling pathways and cell death; however, their contribution to the lytic cycle is largely unknown. We show that the cell cycle and chromatin regulator geminin and the plasma membrane protein gamma-glutamyltransferase 6, two of the core RIGs, are required for efficient KSHV reactivation and virus production. Our results indicate that host genes that RTA rapidly and directly induces can be pivotal for driving the KSHV lytic cycle.IMPORTANCE The lytic cycle of KSHV is involved not only in the dissemination of the virus but also viral oncogenesis, in which the effect of RTA on the host transcriptome is still unclear. Using genomics approaches, we identified a core set of host genes which are rapidly and directly induced by RTA in the early phase of KSHV lytic reactivation. We found that RTA does not need viral cofactors but requires its host cofactor RBP-Jκ for inducing many of its core RIGs. Importantly, we show a critical role for two of the core RIGs in efficient lytic reactivation and replication, highlighting their significance in the KSHV lytic cycle. We propose that the unbiased identification of RTA-induced host genes can uncover potential therapeutic targets for inhibiting KSHV replication and viral pathogenesis.

Evolutionary effects of the AID/APOBEC family of mutagenic enzymes on human gamma-herpesviruses

The human gamma-herpesviruses, Epstein-Barr virus and Kaposi's sarcoma-associated herpesvirus, establish lifelong latency in B cells and are associated with multiple malignancies. Virus-host coevolution often drive changes in both host immunity and in the viral genome. We consider one host immune mechanism, the activation-induced deaminase (AID)/APOBEC family of cytidine deaminases, that induces mutations in viral DNA. AID, the ancestral gene in the family has a conserved role in somatic hypermutation, a key step in antibody affinity maturation. The APOBEC3 subfamily, of which there are seven genes in human, have evolved antiviral functions and have diversified in terms of their expression pattern, subcellular localization, and DNA mutation motifs (hotspots). In this study, we investigated how the human gamma-herpesviruses have evolved to avoid the action of the AID/APOBEC enzymes and determine if these enzymes are contributing to the ongoing evolution of the viruses. We used computational methods to evaluate observed versus expected frequency of AID/APOBEC hotspots in viral genomes and found that the viruses have evolved to limit the representation of AID and certain APOBEC3 motifs. At the same time, the remaining hotspots were highly likely to cause amino acid changes, suggesting prolonged evolutionary pressure of the enzymes on the viruses. To study current hypermutation, as opposed to historical mutation processes, we also analyzed putative mutations derived from alignments of published viral genomes and found again that AID and APOBEC3 appear to target the genome most frequently. New protein variants resulting from AID/APOBEC activity may have important consequences in health, including vaccine development (epitope evolution) and host immune evasion.

Human herpesvirus 8 infection DNA positivity is associated with low insulin secretion: A case-control study in a sub-Saharan African population with diabetes

BACKGROUND

Viruses have been considered potential triggers for the development of diabetes. This study assessed insulin secretion and insulin sensitivity in human herpesvirus 8 (HHV8)-infected and uninfected sub-Saharan African people with diabetes.

METHODS

In all, 173 people with non-autoimmune diabetes were enrolled consecutively: 124 with type 2 diabetes mellitus (T2DM) and 49 with ketosis-prone diabetes (KPD) admitted in hyperglycemic crisis. Those with KPD were further subdivided into those with new-onset ketotic-phase KPD (n = 34) or non-ketotic phase KPD (n = 15). All participants were screened for HHV8-specific antibodies and genomic DNA. Blood samples were collected for analysis of fasting glucose, HbA1c, lipid profile, and C-peptide, with insulin resistance and secretion estimated by homeostasis model assessment.

RESULTS

Among the 173 diabetic participants, 88 (50.9%) were positive for HHV8 antibodies (Ac-HHV8+), including 15 (8.7%) positive for HHV8 DNA (DNA-HHV8+). The seroprevalence of HHV8 was similar between T2DM (55.6%) and KPD (61.2%) subjects. Of those with and without ketotic-phase KPD, 35.3% and 46.7% were Ac-HHV8+, respectively. Body mass index was significantly in lower DNA-HHV8+ than DNA-HHV8- subjects. Low-density lipoprotein and total cholesterol were significantly higher, but C-peptide and homeostatic model assessment of β-cell function (HOMA-β) were significantly lower in DNA-HHV8+ than DNA-HHV8- participants. After excluding DNA-HHV8+ participants, triglyceride concentrations were significantly higher in Ac-HHV8+ (n = 73) than Ac-HHV8- (n = 85) subjects. In contrast, HOMA-β was significantly higher among Ac-HHV8+ than Ac-HHV8- participants.

CONCLUSIONS

In the present study, HHV8 DNA positivity was associated with low insulin secretion in this sub-Saharan African diabetes population.

Human Herpesvirus 8 and Lymphoproliferative Disorders

The spectrum of lymphoproliferative disorders linked to human herpesvirus 8 (HHV-8) infection has constantly been increasing since the discovery of its first etiologic association with primary effusion lymphoma (PEL). PEL is a rapidly progressing non-Hodgkin’s B-cell lymphoma that develops in body cavities in an effusional form. With the increase in the overall survival of PEL patients, as well as the introduction of HHV-8 surveillance in immunocompromised patients, the extracavitary, solid counterpart of PEL was later identified. Moreover, virtually all plasmablastic variants of multicentric Castleman’s disease (MCD) developing in HIV-1-infected individuals harbor HHV-8, providing a strong etiologic link between MCD and this oncogenic herpesvirus. Two other pathologic conditions develop in HIV-1-infected persons concomitantly with MCD: MCD with plasmablastic clusters and HHV-8-positive diffuse large B-cell lymphoma not otherwise specified (HHV-8+ DLBCL NOS), the first likely representing an intermediate stage preceding the full neoplastic form. MCD in leukemic phase has also been described, albeit much less commonly. The germinotropic lymphoproliferative disorder (GLPD) may resemble extracavitary PEL, but develops in immune competent HHV8-infected individuals, and, unlike the other disorders, it responds well to conventional therapies. Almost all HHV-8-mediated lymphoproliferative disorders are the result of an interaction between HHV-8 infection and a dysregulated immunological system, leading to the formation of inflammatory niches in which B cells, at different developmental stages, are infected, proliferate and may eventually shift from a polyclonal state to a monoclonal/neoplastic disorder. Herein, we describe the association between HHV-8 and lymphoproliferative disorders and highlight the predominant distinctive features of each disease.

Kaposi's Sarcoma-Associated Herpesvirus Deregulates Host Cellular Replication during Lytic Reactivation by Disrupting the MCM Complex through ORF59

Minichromosome maintenance proteins (MCMs) play an important role in DNA replication by binding to the origins as helicase and recruiting polymerases for DNA synthesis. During the S phase, MCM complex is loaded to limit DNA replication once per cell cycle. We identified MCMs as ORF59 binding partners in our protein pulldown assays, which led us to hypothesize that this interaction influences DNA replication. ORF59's interactions with MCMs were confirmed in both endogenous and overexpression systems, which showed its association with MCM3, MCM4, MCM5, and MCM6. Interestingly, MCM6 interacted with both the N- and C-terminal domains of ORF59, and its depletion in BCBL-1 and BC3 cells led to an increase in viral genome copies, viral late gene transcripts, and virion production compared to the control cells following reactivation. MCMs perform their function by loading onto the replication competent DNA, and one means of regulating chromatin loading/unloading, in addition to enzymatic activity of the MCM complex, is by posttranslational modifications, including phosphorylation of these factors. Interestingly, a hypophosphorylated form of MCM3, which is associated with reduced loading onto the chromatin, was detected during lytic reactivation and correlated with its inability to associate with histones in reactivated cells. Additionally, chromatin immunoprecipitation showed lower levels of MCM3 and MCM4 association at cellular origins of replication and decreased levels of cellular DNA synthesis in cells undergoing reactivation. Taken together, these findings suggest a mechanism in which KSHV ORF59 disrupts the assembly and functions of MCM complex to stall cellular DNA replication and promote viral replication.IMPORTANCE KSHV is the causative agent of various lethal malignancies affecting immunocompromised individuals. Both lytic and latent phases of the viral life cycle contribute to the progression of these cancers. A better understanding of how viral proteins disrupt functions of a normal healthy cell to cause oncogenesis is warranted. One crucial lytic protein produced early during lytic reactivation is the multifunctional ORF59. In this report, we elucidated an important role of ORF59 in manipulating the cellular environment conducive for viral DNA replication by deregulating the normal functions of the host MCM proteins. ORF59 binds to specific MCMs and sequesters them away from replication origins in order to sabotage cellular DNA replication. Blocking cellular DNA replication ensures that cellular resources are utilized for transcription and replication of viral DNA.

Multi-targeted therapy of everolimus in Kaposi's sarcoma associated herpes virus infected primary effusion lymphoma

Kaposi's sarcoma associated herpes virus (KSHV) infected primary effusion lymphoma (PEL) is a rare aggressive form of non-Hodgkin's lymphoma of B cells. KSHV latent and lytic antigens modulate several host cellular signalling pathways especially mammalian target of rapamycin (mTOR), STAT-3 and nuclear factor-kappa B (NF-κB) for rapid tumor progression and immune evasion. Current chemotherapeutic strategies are becoming ineffective as they kill only dividing cells and inefficient to target molecular pathways crucial for active virus replication and its survival. In this study, we evaluated the efficacy of everolimus, an mTOR inhibitor in inducing apoptosis of PEL cells. Dose-dependent treatment of everolimus triggered mitochondria-mediated caspase-dependent apoptosis in PEL cells. Everolimus downregulated KSHV latent antigen expression with concurrent blocking of lytic reactivation for active virus replication. Everolimus also inhibited latent antigen mediated constitutively active STAT-3 and NF-κB signalling. We co-cultured everolimus treated PEL cells with immature dendritic cells and found activation of dendritic cells with increase in surface expression of CD86 and HLA-DR. As everolimus targets and disrupts KSHV antigens as well as antigen facilitated multiple signalling pathways necessary for KSHV survival and maintenance of infection with synchronised boosting of immune system against viral infection, it can be a better therapeutic approach towards treatment of PEL.

Sensitivity of the C-Terminal Nuclease Domain of Kaposi's Sarcoma-Associated Herpesvirus ORF29 to Two Classes of Active-Site Ligands

Kaposi's sarcoma-associated herpesvirus (KSHV), the etiological agent of Kaposi's sarcoma, belongs to the Herpesviridae family, whose members employ a multicomponent terminase to resolve nonparametric viral DNA into genome-length units prior to their packaging. Homology modeling of the ORF29 C-terminal nuclease domain (pORF29C) and bacteriophage Sf6 gp2 have suggested an active site clustered with four acidic residues, D476, E550, D661, and D662, that collectively sequester the catalytic divalent metal (Mn2+) and also provided important insight into a potential inhibitor binding mode. Using this model, we have expressed, purified, and characterized the wild-type pORF29C and variants with substitutions at the proposed active-site residues. Differential scanning calorimetry demonstrated divalent metal-induced stabilization of wild-type (WT) and D661A pORF29C, consistent with which these two enzymes exhibited Mn2+-dependent nuclease activity, although the latter mutant was significantly impaired. Thermal stability of WT and D661A pORF29C was also enhanced by binding of an α-hydroxytropolone (α-HT) inhibitor shown to replace divalent metal at the active site. For the remaining mutants, thermal stability was unaffected by divalent metal or α-HT binding, supporting their role in catalysis. pORF29C nuclease activity was also inhibited by two classes of small molecules reported to inhibit HIV RNase H and integrase, both of which belong to the superfamily of nucleotidyltransferases. Finally, α-HT inhibition of KSHV replication suggests ORF29 nuclease function as an antiviral target that could be combined with latency-activating compounds as a shock-and-kill antiviral strategy.

FUS Negatively Regulates Kaposi's Sarcoma-Associated Herpesvirus Gene Expression

Kaposi’s sarcoma-associated herpesvirus (KSHV) is a human gammaherpesvirus and the etiological agent of Kaposi’s sarcoma. KSHV is also causally associated with the development of lymphoproliferative diseases, including primary effusion lymphoma (PEL). KSHV reactivation from latency plays an integral role in the progression to KSHV-associated disease as several lytic proteins have angiogenic and anti-apoptotic functions essential to the tumor microenvironment. Thus, restriction of KSHV reactivation represents an attractive therapeutic target. Here, we demonstrate that the cellular protein Fused-in-sarcoma (FUS) restricts KSHV lytic reactivation in PEL and in an epithelial cell-based model. Depletion of FUS significantly enhances viral mRNA and protein expression, resulting in increased viral replication and production of infectious virions. Chromatin immunoprecipitation analyses demonstrate that FUS is present at several KSHV lytic cycle genes during the latent stage of infection. We further demonstrate that FUS interacts with RNA polymerase II and negatively affects Serine-2 phosphorylation of its C-terminal domain at the KSHV RTA gene, decreasing nascent RNA synthesis. Knockdown of FUS increases transcription of RTA, thus driving enhanced expression of KSHV lytic genes. Collectively, these data reveal a novel role for FUS in regulating viral gene expression and are the first to demonstrate its role as a viral restriction factor.

Cellular and viral oncogenes: the key to unlocking unknowns of Kaposi's sarcoma-associated herpesvirus pathogenesis

Oncogenic viruses carry an extensive arsenal of oncogenes for hijacking cellular pathways. Notably, variations in oncogenes among tumor-producing viruses give rise to different mechanisms for cellular transformation. Specifically, Kaposi's sarcoma-associated herpesvirus (KSHV) is an oncogenic virus able to infect and transform a variety of cell types. The oncogenicity of KSHV disseminates from the virus' ability to induce and encode a wide variety of both cellular and viral oncogenes. Such an array of cellular and viral oncogenes enables KSHV to induce the malignant phenotype of a KSHV-associated cancer. Evolutionarily, KSHV has acquired many oncogenic homologues capable of inducing cell proliferation, cell differentiation, cell survival, and immune evasion. Integration between inducing and encoding oncogenes plays a vital role in KSHV pathogenicity. KSHV is alleged to harbor the highest number of potential oncogenes by which a virus promotes cellular transformation and malignancy. Many KSHV inducing/encoding oncogenes are mainly expressed during the latent phase of KSHV infection, a period required for virus establishment of malignant cellular transformation. Elucidation of the exact mechanism(s) by which oncogenes promote KSHV pathogenicity would not only give rise to potential novel therapeutic targets/drugs but would also add to our understanding of cancer biology. The scope of this review is to examine the roles of the most important cellular and viral oncogenes involved in KSHV pathogenicity.

Repurposing Cytarabine for Treating Primary Effusion Lymphoma by Targeting Kaposi's Sarcoma-Associated Herpesvirus Latent and Lytic Replications

Oncogenic Kaposi's sarcoma-associated herpesvirus (KSHV) is etiologically linked to primary effusion lymphoma (PEL), an aggressive and nontreatable malignancy commonly found in AIDS patients. In this study, we performed a high-throughput screening of 3,731 characterized compounds and identified cytarabine, approved by the FDA for treating numerous types of cancer, as a potent inhibitor of KSHV-induced PEL. We showed the high efficacy of cytarabine in the growth inhibition of various PEL cells by inducing cell cycle arrest and apoptosis. Cytarabine inhibited host DNA and RNA syntheses and therefore induced cellular cytotoxicity. Furthermore, cytarabine inhibited viral DNA and RNA syntheses and induced the rapid degradation of KSHV major latent protein LANA (latency-associated nuclear antigen), leading to the suppression of KSHV latent replication. Importantly, cytarabine effectively inhibited active KSHV replication and virion production in PEL cells. Finally, cytarabine treatments not only effectively inhibited the initiation and progression of PEL tumors but also induced regression of grown PEL tumors in a xenograft mouse model. Altogether, our study has identified cytarabine as a novel therapeutic agent for treating PEL as well as eliminating KSHV persistent infection.IMPORTANCE Primary effusion lymphoma is an aggressive malignancy caused by Kaposi's sarcoma-associated herpesvirus. The outcome of primary effusion lymphoma is dismal without specific treatment. Through a high-throughput screening of characterized compounds, we identified an FDA-approved compound, cytarabine, as a potent inhibitor of primary effusion lymphoma. We showed that cytarabine induced regression of PEL tumors in a xenograft mouse model. Cytarabine inhibited host and viral DNA and RNA syntheses, resulting in the induction of cytotoxicity. Of interest, cytarabine induced the degradation of KSHV major latent protein LANA, hence suppressing KSHV latent replication, which is required for PEL cell survival. Furthermore, cytarabine inhibited KSHV lytic replication program, preventing virion production. Our findings identified cytarabine as a novel therapeutic agent for treating PEL as well as for eliminating KSHV persistent infection. Since cytarabine is already approved by the FDA, it might be an ideal candidate for repurposing for PEL therapy and for further evaluation in advanced clinical trials.

Quantifying Symmetrically Methylated H4R3 on the Kaposi's Sarcoma-associated Herpesvirus (KSHV) Genome by ChIP-Seq

Post-translational modifications to histone tails contribute to the three-dimensional structure of chromatin and play an important role in detegrmining the relative expression of nearby genes. One such modification is symmetric di-methylation of arginine residues, which may exhibit different effects on gene expression including blocking the binding of transcriptional activators, or recruiting repressive effector molecules. Recent ChIP-Seq studies have demonstrated the importance of cross-talk between different histone modifications in gene regulation. Thus, to acquire a comprehensive understanding of the combined efforts of these epigenetic marks, ChIP-Seq must be utilized for identifying specific enrichment on the chromatin. Tumorigenic herpesvirus KSHV, employs epigenetic mechanisms for gene regulation, and by evaluating relative abundance of multiple histone modifications in a thorough, unbiased way, using ChIP-Seq, we can get a superior insight concerning the complex mechanisms of viral replication and pathogenesis.

Nucleolar stress enhances lytic reactivation of the Kaposi's sarcoma-associated herpesvirus

Kaposi's sarcoma-associated herpesvirus (KSHV) is a human tumorigenic virus exhibiting two forms of infection, latent and lytic. Latent infection is abortive and allows the virus to establish lifelong infection, while lytic infection is productive, and is needed for virus dissemination within the host and between hosts. Latent infection may reactivate and switch towards the lytic cycle. This switch is a critical step in the maintenance of long-term infection and for the development of KSHV-related neoplasms. In this study, we examined the effect of nucleolar stress, manifested by failure in ribosome biogenesis or function and often coupled with p53 activation, on lytic reactivation of KSHV. To this end, we induced nucleolar stress by treatment with Actinomycin D, CX-5461 or BMH-21. Treatment with these compounds alone did not induce the lytic cycle. However, enhancement of the lytic cycle by these compounds was evident when combined with expression of the viral protein K-Rta. Further experiments employing combined treatments with Nutlin-3, knock-down of p53 and isogenic p53+/+ and p53-/- cells indicated that the enhancement of lytic reactivation by nucleolar stress does not depend on p53. Thus, our study identifies nucleolar stress as a novel regulator of KSHV infection, which synergizes with K-Rta expression to increase lytic reactivation. This suggests that certain therapeutic interventions, which induce nucleolar stress, may affect the outcome of KSHV infection.

Oxidant species are involved in T/B-mediated ERK1/2 phosphorylation that activates p53-p21 axis to promote KSHV lytic cycle in PEL cells

KSHV is a gammaherpesvirus strongly associated to human cancers such as Primary Effusion Lymphoma (PEL) and Kaposi's Sarcoma. The naturally virus-infected tumor cells usually display latent infection since a minority of cells undergoes spontaneous viral replication. The lytic cycle can be induced in vitro upon appropriate stimuli such as TPA (T), alone or in combination with butyrate (B), (T/B). In previous studies, Protein Kinase C (PKC) δ, Extracellular Signal-regulated Kinase1/2 (ERK1/2) and p53-p21 axis have been separately reported to play a role in KSHV reactivation from latency. Here, we found that these pathways were interconnected to induce KSHV lytic cycle in PEL cells treated with T/B. T/B also increased H₂O₂ that played an important role in the activation of these pathways. Oxidant specie production correlated with PKC δ activation, as the PKC δ inhibitor rottlerin reduced both H₂O₂ and KSHV lytic antigen expression. H₂O₂ contributed to T/B-mediated ERK1/2 activation that mediated p53 phosphorylation at serine 15 (Ser15) and increased p21 expression. Oxidant specie inhibition by quercetin indeed strongly reduced the activation of these pathways, lytic antigen expression and interestingly it also increased T/B-induced cell death. The use of ERK inhibitor PD98059 or p53 silencing demonstrated the importance of p53Ser15 phosphorylation and of p53-p21 axis in KSHV lytic cycle activation. Understanding the role of oxidant species and the molecular mechanisms involved in KSHV lytic cycle induction is particularly important since oxidant species represent the most physiological stimulus for viral reactivation in vivo and it is known that viral production contributes to the maintenance/progression of KSHV associated malignancies.

KSHV inhibits stress granule formation by viral ORF57 blocking PKR activation

TIA-1 positive stress granules (SG) represent the storage sites of stalled mRNAs and are often associated with the cellular antiviral response. In this report, we provide evidence that Kaposi's sarcoma-associated herpesvirus (KSHV) overcomes the host antiviral response by inhibition of SG formation via a viral lytic protein ORF57. By immunofluorescence analysis, we found that B lymphocytes with KSHV lytic infection are refractory to SG induction. KSHV ORF57, an essential post-transcriptional regulator of viral gene expression and the production of new viral progeny, inhibits SG formation induced experimentally by arsenite and poly I:C, but not by heat stress. KSHV ORF37 (vSOX) bearing intrinsic endoribonuclease activity also inhibits arsenite-induced SG formation, but KSHV RTA, vIRF-2, ORF45, ORF59 and LANA exert no such function. ORF57 binds both PKR-activating protein (PACT) and protein kinase R (PKR) through their RNA-binding motifs and prevents PACT-PKR interaction in the PKR pathway which inhibits KSHV production. Consistently, knocking down PKR expression significantly promotes KSHV virion production. ORF57 interacts with PKR to inhibit PKR binding dsRNA and its autophosphorylation, leading to inhibition of eIF2α phosphorylation and SG formation. Homologous protein HSV-1 ICP27, but not EBV EB2, resembles KSHV ORF57 in the ability to block the PKR/eIF2α/SG pathway. In addition, KSHV ORF57 inhibits poly I:C-induced TLR3 phosphorylation. Altogether, our data provide the first evidence that KSHV ORF57 plays a role in modulating PKR/eIF2α/SG axis and enhances virus production during virus lytic infection.

Expression and Subcellular Localization of the Kaposi's Sarcoma-Associated Herpesvirus K15P Protein during Latency and Lytic Reactivation in Primary Effusion Lymphoma Cells

The K15P membrane protein of Kaposi's sarcoma-associated herpesvirus (KSHV) interacts with multiple cellular signaling pathways and is thought to play key roles in KSHV-associated endothelial cell angiogenesis, regulation of B-cell receptor (BCR) signaling, and the survival, activation, and proliferation of BCR-negative primary effusion lymphoma (PEL) cells. Although full-length K15P is ∼45 kDa, numerous lower-molecular-weight forms of the protein exist as a result of differential splicing and poorly characterized posttranslational processing. K15P has been reported to localize to numerous subcellular organelles in heterologous expression studies, but there are limited data concerning the sorting of K15P in KSHV-infected cells. The relationships between the various molecular weight forms of K15P, their subcellular distribution, and how these may differ in latent and lytic KSHV infections are poorly understood. Here we report that a cDNA encoding a full-length, ∼45-kDa K15P reporter protein is expressed as an ∼23- to 24-kDa species that colocalizes with the trans-Golgi network (TGN) marker TGN46 in KSHV-infected PEL cells. Following lytic reactivation by sodium butyrate, the levels of the ∼23- to 24-kDa protein diminish, and the full-length, ∼45-kDa K15P protein accumulates. This is accompanied by apparent fragmentation of the TGN and redistribution of K15P to a dispersed peripheral location. Similar results were seen when lytic reactivation was stimulated by the KSHV protein replication and transcription activator (RTA) and during spontaneous reactivation. We speculate that expression of different molecular weight forms of K15P in distinct cellular locations reflects the alternative demands placed upon the protein in the latent and lytic phases.IMPORTANCE The K15P protein of Kaposi's sarcoma-associated herpesvirus (KSHV) is thought to play key roles in disease, including KSHV-associated angiogenesis and the survival and growth of primary effusion lymphoma (PEL) cells. The protein exists in multiple molecular weight forms, and its intracellular trafficking is poorly understood. Here we demonstrate that the molecular weight form of a reporter K15P molecule and its intracellular distribution change when KSHV switches from its latent (quiescent) phase to the lytic, infectious state. We speculate that expression of different molecular weight forms of K15P in distinct cellular locations reflects the alternative demands placed upon the protein in the viral latent and lytic stages.

De Novo Human Herpesvirus 8 Tumors Induced by Rituximab in Autoimmune or Inflammatory Systemic Diseases

OBJECTIVE

Human herpesvirus 8 (HHV-8), also known as Kaposi's sarcoma (KS)-associated herpesvirus, is involved in KS and other tumors, including multicentric Castleman's disease and primary effusion lymphoma. Rituximab (RTX) is currently used for the treatment of several autoimmune or inflammatory diseases and humoral organ transplant rejection. De novo HHV-8 tumors induced by RTX used for these indications have not been reported previously. This study was undertaken to evaluate de novo HHV-8 tumors induced by RTX.

METHODS

In this retrospective study, we investigated the clinical, virologic, and pathologic features of 5 HIV-negative male patients with HHV-8 tumors induced by RTX therapy.

RESULTS

Patients were all immunocompromised by previous treatments, which consisted of steroids and/or immunosuppressive agents, and received RTX for insufficient response, disease progression, or transplant rejection. They developed HHV-8 tumors a median of 4 months after beginning treatment with RTX (range 3-13 months). Four patients had at least 1 risk factor for HHV-8, including a high Fitzpatrick skin phototype (of >3) (n = 3) and homosexuality (n = 1). Four patients developed KS (all 4 had skin lesions and 2 had visceral involvement), and 1 patient developed a solid primary effusion lymphoma. RTX was discontinued in all patients, and immunosuppressants were reduced when feasible. After a median follow-up of 20 months, 2 patients died. Remission of KS was complete in 1 patient and partial in 1 patient, and 1 patient had progression.

CONCLUSION

Our findings indicate that patients who have a high skin phototype and are at risk of HHV-8 should be carefully screened for HHV-8 before RTX therapy. The safety of RTX, especially in nonlymphomatous disorders, should be carefully evaluated in patients at risk of HHV-8 tumors.

Bortezomib promotes KHSV and EBV lytic cycle by activating JNK and autophagy

KSHV and EBV are gammaherpesviruses strictly linked to human cancers. Even if the majority of cancer cells harbor a latent infection, the few cells that undergo viral replication may contribute to the pathogenesis and maintenance of the virus-associated malignancies. Cytotoxic drugs used for the therapies of cancers harboring virus-infection often have, as side effect, the activation of viral lytic cycle. Therefore it is important to investigate whether they affect viral reactivation and understand the underlying mechanisms involved. In this study, we found that proteasome inhibitor bortezomib, a cytotoxic drug that efficiently target gammaherpesvirus-associated B cell lymphomas, triggered KSHV or EBV viral lytic cycle by activating JNK, in the course of ER stress, and inducing autophagy. These results suggest that the manipulation of these pathways could limit viral spread and improve the outcome of bortezomib treatment in patients affected by gammaherpesvirus-associated lymphomas.

1, 25(OH)2 D3 Induces Reactivation and Death of Kaposi's Sarcoma-Associated Herpesvirus of Primary Effusion Lymphoma cells

Kaposi's sarcoma associated herpesvirus (KSHV) a gammaherpesvirus establishes perennial latency in the host with periodic reactivation. Occasionally change in the physiological condition like hypoxia, host cell differentiation can trigger the lytic switch and reactivation of the virus. The biologically active form of 1, 25(OH)2 D3 plays a critical role in the regulation of various physiological processes (e.g. regulation of mineral homeostasis and control of bone metabolism). Apart from its role in host physiology, 1, 25(OH)2 D3 has been implicated as a potential agent for the prevention and/or treatment of many a tumors. Here we show that 1, 25(OH)2 D3 induces both death of Kaposi sarcoma associated herpesvirus infected PEL cells and KSHV replication. 1, 25(OH)2 D3 mediated inhibition of proliferation was associated with apoptosis of the PEL cells, and virus reactivation. In addition, p38 signalling is required for KSHV reactivation. Furthermore, treatment of PEL cells with p38 inhibitor abrogated the expression of ORF57, thus blocking lytic switch. Furthermore, silencing of VDR resulted in reduced ORF57 expression compared to the control cells, signifying the potential role of 1, 25(OH)2 D3 in KSHV reactivation. Thus, our studies have revealed a novel role of 1, 25(OH)2 D3 in the regulation of KSHV reactivation and PEL cell death.

Metformin triggers apoptosis in PEL cells and alters bortezomib-induced Unfolded Protein Response increasing its cytotoxicity and inhibiting KSHV lytic cycle activation

Metformin, the most used drug for the treatment of diabetes type 2 patients, has been shown to have anti-cancer properties. In this study, we found that metformin induced apoptosis in Primary Effusion Lymphoma (PEL) cells, an aggressive B cell lymphoma associated with KSHV against which the conventional therapies usually fail. The cytotoxic effect of metformin correlated with intracellular reactive oxygen species reduction, activation of AMPK, the inhibition of pro-survival pathways such as mTOR and STAT3 and the down-regulation of v-FLIP, a latent viral antigen that also plays a pivotal role in PEL cell survival. Interestingly, we found that metformin could be used to potentiate the bortezomib-mediated cytotoxicity against PEL cells and to inhibit the activation of KSHV lytic cycle, a side effect of this treatment that resulted in a block of autophagy in these cells. Mechanistically, metformin altered UPR activated by bortezomib, leading to a reduced expression of BiP, up-regulation of CHOP and down-regulation of Bcl-2. In summary, this study suggests that metformin could represent a promising strategy for the treatment of PEL alone or in combination with bortezomib. In the latter case, besides exerting a stronger cytotoxic effect, it might be used to restrain bortezomib-induced viral replication that is involved in the maintenance and progression of KSHV-associated malignancies.

Human Herpesvirus 8 Infects and Replicates in Langerhans Cells and Interstitial Dermal Dendritic Cells and Impairs Their Function

The predominant types of dendritic cells (DC) in the skin and mucosa are Langerhans cells (LC) and interstitial dermal DC (iDDC). LC and iDDC process cutaneous antigens and migrate out of the skin and mucosa to the draining lymph nodes to present antigens to T and B cells. Because of the strategic location of LC and iDDC and the ability of these cells to capture and process pathogens, we hypothesized that they could be infected with human herpesvirus 8 (HHV-8) (Kaposi's sarcoma [KS]-associated herpesvirus) and have an important role in the development of KS. We have previously shown that HHV-8 enters monocyte-derived dendritic cells (MDDC) through DC-SIGN, resulting in nonproductive infection. Here we show that LC and iDDC generated from pluripotent cord blood CD34⁺ cell precursors support productive infection with HHV-8. Anti-DC-SIGN monoclonal antibody (MAb) inhibited HHV-8 infection of iDDC, as shown by low expression levels of viral proteins and DNA. In contrast, blocking of both langerin and the receptor protein tyrosine kinase ephrin A2 was required to inhibit HHV-8 infection of LC. Infection with HHV-8 did not alter the cell surface expression of langerin on LC but downregulated the expression of DC-SIGN on iDDC, as we previously reported for MDDC. HHV-8-infected LC and iDDC had a reduced ability to stimulate allogeneic CD4⁺ T cells in the mixed-lymphocyte reaction. These results indicate that HHV-8 can target both LC and iDDC for productive infection via different receptors and alter their function, supporting their potential role in HHV-8 pathogenesis and KS.

IMPORTANCE Here we show that HHV-8, a DNA tumor virus that causes Kaposi's sarcoma, infects three types of dendritic cells: monocyte-derived dendritic cells, Langerhans cells, and interstitial dermal dendritic cells. We show that different receptors are used by this virus to infect these cells. DC-SIGN is a major receptor for infection of both monocyte-derived dendritic cells and interstitial dermal dendritic cells, yet the virus fully replicates only in the latter. HHV-8 uses langerin and the ephrin A2 receptor to infect Langerhans cells, which support full HHV-8 lytic replication. This infection of Langerhans cells and interstitial dermal dendritic cells results in an impaired ability to stimulate CD4⁺ helper T cell responses. Taken together, our data show that HHV-8 utilizes alternate receptors to differentially infect and replicate in these tissue-resident DC and support the hypothesis that these cells play an important role in HHV-8 infection and pathogenesis.

Experience with Kaposi Sarcoma Herpesvirus Inflammatory Cytokine Syndrome in a Large Urban HIV Clinic in the United States: Case Series and Literature Review

In 2010, a new entity, characterized by the classical signs and symptoms of Kaposi sarcoma herpesvirus–associated multicentric Castleman’s disease (KSHV-MCD) in the absence of pathologic evidence of MCD, was described in individuals living with HIV. This syndrome was named KSHV inflammatory cytokine syndrome (KICS). It carries mortality rates of up to 60%. To date, there are no standard therapies. Treatment regimens studied in clinical trials for MCD disease are used in cases of KICS.

Effects of the NEDD8-Activating Enzyme Inhibitor MLN4924 on Lytic Reactivation of Kaposi's Sarcoma-Associated Herpesvirus

The switch of Kaposi's sarcoma-associated herpesvirus (KSHV) from latency to lytic replication is a key event for viral dissemination and pathogenesis. MLN4924, a novel neddylation inhibitor, reportedly causes the onset of KSHV reactivation but impairs later phases of the viral lytic program in infected cells. Thus far, the molecular mechanism involved in the modulation of the KSHV lytic cycle by MLN4924 is not yet fully understood. Here, we confirmed that treatment of different KSHV-infected primary effusion lymphoma (PEL) cell lines with MLN4924 substantially induces viral lytic protein expression. Due to the key role of the virally encoded ORF50 protein in the latent-to-lytic switch, we investigated its transcriptional regulation by MLN4924. We found that MLN4924 activates the ORF50 promoter (ORF50p) in KSHV-positive cells (but not in KSHV-negative cells), and the RBP-Jκ-binding elements within the promoter are critically required for MLN4924 responsiveness. In KSHV-negative cells, reactivation of the ORF50 promoter by MLN4924 requires the presence of the latency-associated nuclear antigen (LANA). Under such a condition, LANA acts as a repressor to block the ORF50p activity, whereas MLN4924 treatment relieves LANA-mediated repression. Importantly, we showed that LANA is a neddylated protein and can be deneddylated by MLN4924. On the other hand, we revealed that MLN4924 exhibits concentration-dependent biphasic effects on 12-O-tetradecanoylphorbol-13-acetate (TPA)- or sodium butyrate (SB)-induced viral reactivation in PEL cell lines. In other words, low concentrations of MLN4924 promote activation of TPA- or SB-mediated viral reactivation, whereas high concentrations of MLN4924, conversely, inhibit the progression of TPA- or SB-mediated viral lytic program.IMPORTANCE MLN4924 is a neddylation (NEDD8 modification) inhibitor, which currently acts as an anti-cancer drug in clinical trials. Although MLN4924 has been reported to trigger KSHV reactivation, many aspects regarding the action of MLN4924 in regulating the KSHV lytic cycle are not fully understood. Since the KSHV ORF50 protein is the key regulator of viral lytic reactivation, we focus on its transcriptional regulation by MLN4924. We here show that activation of the ORF50 gene by MLN4924 involves the relief of LANA-mediated transcriptional repression. Importantly, we find that LANA is a neddylated protein. To our knowledge, this is the first report showing that neddylation occurs in viral proteins. Additionally, we provide evidence that different concentrations of MLN4924 have opposite effects on TPA-mediated or SB-mediated KSHV lytic cycle activation. Therefore, in clinical application, we propose that MLN4924 needs to be used with caution in combination therapy to treat KSHV-positive subjects.

Kaposi's Sarcoma-Associated Herpesvirus Infection of Neurons in HIV-Positive Patients

Background

Kaposi's sarcoma-associated herpesvirus (KSHV) is the causative agent of Kaposi sarcoma (KS), one of the leading cancers in human immunodeficiency virus (HIV)-infected patients in Zambia. KSHV was detected in the human central nervous system (CNS) by polymerase chain reaction (PCR) analysis, but tissue location and cell tropism for KSHV infection has not been established. Given the neurotropism exhibited by other herpesviruses and the frequent coinfection of HIV-positive individuals by KSHV, we sought to determine whether the central nervous system (CNS) can be infected by KSHV in HIV-positive Zambian individuals.

Methods

Postmortem brain tissue specimens were collected from individuals coinfected with KSHV and HIV. PCR and Southern blots were performed on DNA extracted from the brain tissue specimens to verify KSHV infection. Immunohistochemical analysis and immunofluorescent microscopy were used to localize and identify KSHV-infected cells. Tropism was further established by in vitro infection of primary human neurons with rKSHV.219.

Results

KSHV DNA was detected in the CNS from 4 of 11 HIV-positive individuals. Immunohistochemical analysis and immunofluorescent microscopy demonstrated that KSHV infected neurons and oligodendrocytes in parenchymal brain tissues. KSHV infection of neurons was confirmed by in vitro infection of primary human neurons with rKSHV.219.

Conclusion

Our study showed that KSHV infects human CNS-resident cells, primarily neurons, in HIV-positive Zambian individuals.

Egr-1 regulates RTA transcription through a cooperative involvement of transcriptional regulators

Kaposi's sarcoma associated herpesvirus (KSHV) regulates the host cellular environment to establish life-long persistent infection by manipulating cellular signaling pathways, with approximately 1- 5% of cells undergoing lytic reactivation during the course of infection. Egr-1 (Early Growth Response Factor-1) is one such cellular transcription factor, which gets phosphorylated during the lytic phase of viral life cycle to perpetrate its function. This study demonstrates the mechanism of how Egr-1 mediates transcription of the immediate early gene, RTA (Replication and transcription activator), which is the lytic switch gene of KSHV. Egr-1 depleted KSHV infected cells exhibited reduced expression of RTA. Also, an increase in Egr-1 phosphorylation led to a higher virion production, which was suppressed in the presence of p38 and Raf inhibitors. Reporter assays showed that coexpression of Egr-1 and CBP (CREB-binding protein) enhances RTA promoter activity as compared to the expression of either Egr-1 or CBP alone. Binding of Egr-1 and CBP at RTA promoter was analyzed by chromatin immunoprecipitation assay (ChIP), which showed an enhanced accumulation during viral reactivation. Mutation in Egr-1 binding site of the RTA promoter eliminated Egr-1 response on promoter activation. Furthermore, de novo infection of THP-1 (monocytic) and HUVECs (endothelial) cells showed an upregulation of Egr-1 phosphorylation, whereas depletion of Egr-1 reduced the mRNA levels of RTA during primary infection. Together, these results demonstrate a cooperative role of Egr-1 and CBP in mediating RTA transcription, which significantly improves our understanding of the involvement of cellular factors controlling RTA transcription in KSHV pathogenesis.

Deregulation of KSHV latency conformation by ER-stress and caspase-dependent RAD21-cleavage

Kaposi’s sarcoma (KS)-associated herpesvirus (KSHV) is a human gammaherpesvirus recognized as the principal causative agent of KS and primary effusion lymphoma (PEL). KSHV establishes persistent latent infection in B lymphocytes where viral gene expression is restricted, in part, by a cohesin-dependent chromosome conformation. Here, we show that endoplasmic reticulum (ER) stress induces a rapid, caspase-dependent cleavage of cohesin subunit RAD21. ER stress-induced cleavage of RAD21 correlated with a rapid and strong viral lytic transcriptional activation. This effect was observed in several KSHV positive PEL cells, but not in other B-cells or non-B-cell models of KSHV latency. The cleaved-RAD21 does not dissociate from viral genomes, nor disassemble from other components of the cohesin complex. However, RAD21 cleavage correlated with the disruption of the latency genome conformation as revealed by chromosome conformation capture (3C). Ectopic expression of C-terminal RAD21 cleaved form could partially induce KSHV lytic genes transcription in BCBLI cells, suggesting that ER-stress induced RAD21 cleavage was sufficient to induce KSHV reactivation from latency in PEL cells. Taken together our results reveal a novel aspect for control and maintenance of KSHV genome latency conformation mediated by stress-induced RAD21 cleavage. Our studies also suggest that RAD21 cleavage may be a general regulatory mechanism for rapid alteration of cellular chromosome conformation and cohesin-dependent transcription regulation.

Latent infection with Kasposi’s Sarcoma (KS)-Associated Herpesivirus (KSHV) is linked to malignant transformation of the host cell. KSHV associated pleural effusion lymphomas (PEL) are highly sensitive to endoplasmic reticulum (ER) stress due to underlying defects in ER stress response pathways. We show here that ER stress inducers lead to a rapid activation of KSHV lytic transcripts, and that an underlying mechanism is found in the caspase and calpain-dependent proteolytic cleavage of RAD21. RAD21 is a subunit of the cohesin complex that maintains a chromosome conformation that restricts KSHV lytic cycle transcription. ER stress-induced cleavage of RAD21 alters the KSHV chromosome conformation associated with latency, and a locus-specific increase in RNA polymerase II association and activation. These findings provide new insights into the regulation of KSHV latency and its response to ER stress, and may further the development of selective treatments for KSHV associated PEL and related malignancies.

Nuclease escape elements protect messenger RNA against cleavage by multiple viral endonucleases

During lytic Kaposi’s sarcoma-associated herpesvirus (KSHV) infection, the viral endonu- clease SOX promotes widespread degradation of cytoplasmic messenger RNA (mRNA). However, select mRNAs, including the transcript encoding interleukin-6 (IL-6), escape SOX-induced cleavage. IL-6 escape is mediated through a 3’ UTR RNA regulatory element that overrides the SOX targeting mechanism. Here, we reveal that this protective RNA element functions to broadly restrict cleavage by a range of homologous and non-homologous viral endonucleases. However, it does not impede cleavage by cellular endonucleases. The IL-6 protective sequence may be representative of a larger class of nuclease escape elements, as we identified a similar protective element in the GADD45B mRNA. The IL-6 and GADD45B-derived elements display similarities in their sequence, putative structure, and several associated RNA binding proteins. However, the overall composition of their ribonucleoprotein complexes appears distinct, leading to differences in the breadth of nucleases restricted. These findings highlight how RNA elements can selectively control transcript abundance in the background of widespread virus-induced mRNA degradation.

The ability of viruses to control the host gene expression environment is crucial to promote viral infection. Many viruses express factors that reduce host gene expression through widespread mRNA decay. However, some mRNAs escape this fate, like the transcript encoding the immunoregulatory cytokine IL-6 during KSHV infection. IL-6 escape relies on an RNA regulatory element located in its 3’UTR and involves the recruitment of a protective protein complex. Here, we show that this escape extends beyond KSHV to a variety of related and unrelated viral endonucleases. However, the IL-6 element does not protect against cellular endonucleases, revealing for the first time a virus-specific nuclease escape element. We identified a related escape element in the GADD45B mRNA, which displays several similarities with the IL-6 element. However, these elements assemble a largely distinct complex of proteins, leading to differences in the breadth of their protective capacity. Collectively, these findings reveal how a putative new class of RNA elements function to control RNA fate in the background of widespread mRNA degradation by viral endonucleases.

KSHV and the Role of Notch Receptor Dysregulation in Disease Progression

Kaposi's sarcoma-associated herpesvirus (KSHV) is the causative agent of two human cancers, Kaposi's Sarcoma (KS) and primary effusion lymphoma (PEL), and a lymphoproliferation, Multicentric Castleman's Disease (MCD). Progression to tumor development in KS is dependent upon the reactivation of the virus from its latent state. We, and others, have shown that the Replication and transcriptional activator (Rta) protein is the only viral gene product that is necessary and sufficient for viral reactivation. To induce the reactivation and transcription of viral genes, Rta forms a complex with the cellular DNA binding component of the canonical Notch signaling pathway, recombination signal binding protein for Jk (RBP-Jk). Formation of this Rta:RBP-Jk complex is necessary for viral reactivation to occur. Expression of activated Notch has been shown to be dysregulated in KSHV infected cells and to be necessary for cell growth and disease progression. Studies into the involvement of activated Notch in viral reactivation have yielded varied results. In this paper, we review the current literature regarding Notch dysregulation by KSHV and its role in viral infection and cellular pathogenesis.

Kaposi's Sarcoma-Associated Herpesvirus Utilizes and Manipulates RNA N6-Adenosine Methylation To Promote Lytic Replication

N⁶-adenosine methylation (m⁶A) is the most common posttranscriptional RNA modification in mammalian cells. We found that most transcripts encoded by the Kaposi's sarcoma-associated herpesvirus (KSHV) genome undergo m⁶A modification. The levels of m⁶A-modified mRNAs increased substantially upon stimulation for lytic replication. The blockage of m⁶A inhibited splicing of the pre-mRNA encoding the replication transcription activator (RTA), a key KSHV lytic switch protein, and halted viral lytic replication. We identified several m⁶A sites in RTA pre-mRNA crucial for splicing through interactions with YTH domain containing 1 (YTHDC1), an m⁶A nuclear reader protein, in conjunction with serine/arginine-rich splicing factor 3 (SRSF3) and SRSF10. Interestingly, RTA induced m⁶A and enhanced its own pre-mRNA splicing. Our results not only demonstrate an essential role of m⁶A in regulating RTA pre-mRNA splicing but also suggest that KSHV has evolved a mechanism to manipulate the host m⁶A machinery to its advantage in promoting lytic replication.IMPORTANCE KSHV productive lytic replication plays a pivotal role in the initiation and progression of Kaposi's sarcoma tumors. Previous studies suggested that the KSHV switch from latency to lytic replication is primarily controlled at the chromatin level through histone and DNA modifications. The present work reports for the first time that KSHV genome-encoded mRNAs undergo m⁶A modification, which represents a new mechanism at the posttranscriptional level in the control of viral replication.

KSHV encoded ORF59 modulates histone arginine methylation of the viral genome to promote viral reactivation

Kaposi's sarcoma associated herpesvirus (KSHV) persists in a highly-ordered chromatin structure inside latently infected cells with the majority of the viral genome having repressive marks. However, upon reactivation the viral chromatin landscape changes into 'open' chromatin through the involvement of lysine demethylases and methyltransferases. Besides methylation of lysine residues of histone H3, arginine methylation of histone H4 plays an important role in controlling the compactness of the chromatin. Symmetric methylation of histone H4 at arginine 3 (H4R3me2s) negatively affects the methylation of histone H3 at lysine 4 (H3K4me3), an active epigenetic mark deposited on the viral chromatin during reactivation. We identified a novel binding partner to KSHV viral DNA processivity factor, ORF59-a protein arginine methyl transferase 5 (PRMT5). PRMT5 is an arginine methyltransferase that dimethylates arginine 3 (R3) of histone H4 in a symmetric manner, one hallmark of condensed chromatin. Our ChIP-seq data of symmetrically methylated H4 arginine 3 showed a significant decrease in H4R3me2s on the viral genome of reactivated cells as compared to the latent cells. Reduction in arginine methylation correlated with the binding of ORF59 on the viral chromatin and disruption of PRMT5 from its adapter protein, COPR5 (cooperator of PRMT5). Binding of PRMT5 through COPR5 is important for symmetric methylation of H4R3 and the expression of ORF59 competitively reduces the association of PRMT5 with COPR5, leading to a reduction in PRMT5 mediated arginine methylation. This ultimately resulted in a reduced level of symmetrically methylated H4R3 and increased levels of H3K4me3 marks, contributing to the formation of an open chromatin for transcription and DNA replication. Depletion of PRMT5 levels led to a decrease in symmetric methylation and increase in viral gene transcription confirming the role of PRMT5 in viral reactivation. In conclusion, ORF59 modulates histone-modifying enzymes to alter the chromatin structure during lytic reactivation.

Modulation of global SUMOylation by Kaposi's sarcoma-associated herpesvirus and its effects on viral gene expression

Some viruses have evolved to exploit the host SUMOylation system to regulate their own replication. Kaposi's sarcoma-associated herpesvirus (KSHV) encodes K-bZIP, a SUMO E3 ligase catalyzing the SUMOylation of viral and host proteins. KSHV also encodes replication and transcriptional activator (RTA), a SUMO-targeted ubiquitin ligase catalyzing the ubiquitination of SUMOylated proteins and targeting them for degradation. Using chronic KSHV-infected TRE × BCBL-1 RTA cells, the expression kinetics of K-bZIP and RTA, and the global SUMOylation level were detected. The endogenous K-bZIP protein increased dramatically after the induction of the RTA gene that is tetracycline responsive, but then decreased rapidly after peaking at 8 h post tetracycline treatment. Consistently, the global SUMO-conjugated proteins increased and remained at high levels until 8 h, and decreased afterward, correlating with the expression kinetics of RTA and K-bZIP. In luciferase reporter assays, transfection of 293T cells with SUMO2 expression plasmid reduced the RTA transactivations of immediate-early genes k8, orf45, and orf50, but enhanced the RTA transactivations of other viral genes including orf57, pan, k2, orf8, and orf73. These results indicated that KSHV might regulate gene expression and viral replication schedule through modulation of the global SUMOylation level, probably via RTA, and RTA-regulated K-bZIP.

Infection of KSHV and Interaction with HIV: The Bad Romance

Kaposi's sarcoma-associated herpesvirus (KSHV), namely, human herpesvirus 8 (HHV-8), is considered as the pathogen of Kaposi's sarcoma (KS), the most frequent cancer in untreated HIV-infected individuals. Patients infected with HIV have a much higher possibility developing KS than average individual. Researchers have found that HIV, which functions as a cofactor of KS, contributes a lot to the development of KS. In this article, we will give a brief introduction of KS and KSHV and how the interaction between KSHV and HIV contributes to the development of KS. Also we will take a glance at the development of treatment in KS, especially AIDS-KS.

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.

The Kaposi's-sarcoma-associated herpesvirus orf35 gene product is required for efficient lytic virus reactivation

Kaposi's sarcoma-associated herpesvirus (KSHV) is implicated in the etiology of several human malignancies. KSHV open reading frame (orf) 35 encodes a conserved gammaherpesvirus protein with an, as yet, unknown function. Employing the bacterial artificial chromosome (BAC) system, we generated a recombinant viral clone that fails to express ORF35 (BAC16-ORF35-stop) but preserves intact adjacent and overlapping reading frames. Using this construct, we studied the role of this previously uncharacterized gene product during lytic reactivation of KSHV. Upon lytic reactivation, the ORF35-stop recombinant virus displayed significantly reduced lytic viral gene expression, viral DNA replication, and progeny virus production as compared to control wild-type virus. Exogenous expression of ORF35-Flag reversed the effects of ORF35 deficiency. These results demonstrate that ORF35 is important for efficient lytic virus reactivation.

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.

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.

Co-infections and Pathogenesis of KSHV-Associated Malignancies

Kaposi’s sarcoma-associated herpesvirus (KSHV), also known as human herpes virus 8 (HHV-8) is one of the several carcinogenic viruses that infect humans. KSHV infection has been implicated in the development of Kaposi’s sarcoma (KS), primary effusion lymphoma, and multicentric Castleman’s Disease. While KSHV infection is necessary for the development of KSHV associated malignancies, it is not sufficient to induce tumorigenesis. Evidently, other co-factors are essential for the progression of KSHV induced malignancies. One of the most important co-factors, necessary for the progression of KSHV induced tumors, is immune suppression that frequently arises during co-infection with HIV and also by other immune suppressants. In this mini-review, we discuss the roles of co-infection with HIV and other pathogens on KSHV infection and pathogenesis.

Kaposi's sarcoma-associated herpesvirus-encoded LANA associates with glucocorticoid receptor and enhances its transcriptional activities

Kaposi's sarcoma-associated herpesvirus (KSHV)-encoded latency-associated nuclear antigen (LANA), which interacts with cellular proteins, plays a central role in modification of viral and/or cellular gene expression. Here, we show that LANA associates with glucocorticoid receptor (GR), and that LANA enhances the transcriptional activity of GR. Co-immunoprecipitation revealed a physical interaction between LANA and GR in transiently transfected 293T and HeLa cells. In human B-lymphoma cells, LANA overexpression enhanced GR activity and cell growth suppression following glucocorticoid stimulation. Furthermore, confocal microscopy showed that activated GR was bound to LANA and accumulated in the nucleus, leading to an increase in binding of activated GR to the glucocorticoid response element of target genes. Taken together, KSHV-derived LANA acts as a transcriptional co-activator of GR. Our results might suggest a careful use of glucocorticoids in the treatment of patients with KSHV-related malignancies such as Kaposi's sarcoma, primary effusion lymphoma, and multicentric Castleman disease.