Kaposi's sarcoma herpesvirus is associated with osteosarcoma in Xinjiang populations

IFI16 recruits HDAC1 and HDAC2 to deacetylate the Kaposi's sarcoma-associated herpesvirus (KSHV) latency-associated nuclear antigen (LANA), facilitating latency

IFI16 (interferon-γ-inducible protein 16) is an innate-immune DNA sensor that detects viral dsDNA in the nucleus. It also functions as an antiviral restriction factor, playing a crucial role in regulating the latency/lytic balance of several herpesviruses, including Kaposi's sarcoma-associated herpesvirus (KSHV). We previously demonstrated that IFI16 achieves this by regulating the deposition of H3K9me3 marks on the KSHV genome. Here, we explored whether IFI16 impacts the KSHV latency/lytic balance through additional mechanisms. Our analysis of the IFI16 interactome revealed that IFI16 binds to the class-I HDACs, HDAC1 and HDAC2, and recruits them to the KSHV major latency protein, latency-associated nuclear antigen (LANA). Previous reports have suggested that LANA undergoes lysine acetylation through unknown mechanisms, which results in the loss of its ability to bind to the KSHV transactivator protein (RTA) promoter. However, how the LANA acetylation-deacetylation cycle is orchestrated and what effect this has on KSHV gene expression remains unknown. Here, we demonstrate that LANA, by default, undergoes post-translational acetylation, and during latency, IFI16 interacts with this acetylated LANA and recruits HDAC1/2 to it. This keeps LANA in a deacetylated form, competent in binding and repressing lytic promoters. However, during lytic reactivation, IFI16 is degraded via the proteasomal pathway, leading to the accumulation of acetylated LANA, which cannot bind to the RTA promoter. This results in the de-repression of the RTA and, subsequently, other lytic promoters, driving reactivation. These findings shed new light on the role of IFI16 in KSHV latency and suggest that KSHV utilizes the cellular IFI16-HDAC1/2 interaction to facilitate its latency.

IMPORTANCE

Kaposi's sarcoma-associated herpesvirus (KSHV) is an oncogenic γ-herpesviruses etiologically associated with several human malignancies, including Kaposi's sarcoma, primary effusion B-cell lymphoma, and multicentric Castleman's disease. Understanding the molecular mechanisms governing the establishment and maintenance of latency in γ-herpesviruses is crucial because latency plays a pivotal role in oncogenesis and disease manifestation post-infection. Here, we have elucidated a new mechanism by which IFI16, a previously discovered antiviral restriction factor, is hijacked by KSHV to recruit class-I HDACs on latency-associated nuclear antigen (LANA), resulting in the latter's deacetylation. The acetylation status of LANA is critical for KSHV latency because it governs LANA's binding to the KSHV replication and transcription activator (RTA) promoter, an immediate-early gene crucial for lytic reactivation. Depletion of IFI16 results in the accumulation of acetylated LANA, which is incapable of maintaining latency. These newly discovered interactions between IFI16 and LANA and between IFI16 and HDAC1/2 enhance our understanding of KSHV latency regulations.

Infection of human induced pluripotent stem cells by an oncogenic herpesvirus

Objective

As one of the major human oncogenic viruses, Kaposi's Sarcoma-associated Herpesvirus (KSHV) is closely related to several cancers such as Kaposi's sarcoma (KS) and primary effusion lymphoma (PEL). KSHV can infect a broad tropism of human primary cells in vitro and in vivo. Embryonic stem cell-like pluripotent stem cells can be generated by the simultaneous introduction of several factors, into somatic cells, yielding induced pluripotent stem (iPS) cells. However, it remains unclear whether human induced pluripotent stem cells (hiPSCs) are permissive to KSHV and how this oncogenic virus infection may affect cellular gene profile.

Methods

In the current study, we examined whether hiPSCs were permissive to KSHV infection. The flow cytometry was used to assess the impacts of KSHV infection on hiPSCs viability and apoptosis. The Illumina RNA-Sequencing was used to determine cellular gene profile changed in KSHV-infected hiPSCs and lytically induced cells.

Results

We report that KSHV successfully establishes latent infection in hiPSCs, which can be completely induced to lytic reactivation and release infectious virions. KSHV de novo infection arrests the growth of hiPSCs through inducing cell apoptosis. Transcriptomic analysis revealed significant changes in global cellular gene expression in KSHV-infected hiPSCs as well as lytically induced cells.

Conclusion

Our findings demonstrate hiPSCs as a powerful tool to explore the potential impacts of KSHV infection on stem cell functions and virus pathogenesis in stem cell differentiated cells.

KSHV hijacks the antiviral kinase IKKε to initiate lytic replication

IKKε is a traditional antiviral kinase known for positively regulating the production of type I interferon (IFN) and the expression of IFN-stimulated genes (ISGs) during various virus infections. However, through an inhibitor screen targeting cellular kinases, we found that IKKε plays a crucial role in the lytic replication of Kaposi's sarcoma-associated herpesvirus (KSHV). Mechanistically, during KSHV lytic replication, IKKε undergoes significant SUMOylation at both Lys321 and Lys549 by the viral SUMO E3 ligase ORF45. This SUMOylation event leads to the association of IKKε with PML, resulting in the disruption of PML nuclear bodies (PML NBs) and subsequent increase in lytic replication of KSHV. Notably, IKKε does not affect the total expression level of PML but facilitates the translocation of PML from the nucleus to the cytoplasm during KSHV lytic replication. Further experiments utilizing mutations on the SUMOylation sites of IKKε or inhibiting IKKε using BAY-985 showed that these actions no longer impact PML NBs and completely suppress the lytic replication of KSHV. These findings not only emphasize the essential role of IKKε in the life cycle of KSHV but also illustrate how KSHV exploits IKKε through SUMOylation modification to enhance its own replication process.

Association between human herpesvirus 8 and lipid profile in northwest China: A cross-sectional study

Human herpesvirus 8 (HHV-8) infection shows obvious regional and ethnic differences. Although studies have shown that these differences may be associated with lipid metabolism, to date, no large-scale studies have explored this. This study explored the seropositivity rate of HHV-8 among 2516 residents from 10 regions of northwest China and then the correlates of HHV-8 infection with lipid profile. The HHV-8 serological positivity rate was 15.6% among all residents. The HHV-8 seroprevalence ranged 11.2-27.6% among different ethnicities. Across different BMI levels, the positive rates of HHV-8 were 27.6%, 16.9%, and 13.6% for a BMI < 18.5, 18.5-24.9, and ≥25, respectively. HHV-8 seropositivity rate was lower for hypertensive people (12.6%) than for non-hypertensive people (16.7%). Univariate logistic regression analyses revealed that age, hypertension, systolic blood pressure, BMI, total cholesterol, and high-density lipoprotein cholesterol (HDL-C) significantly correlated with HHV-8 seropositivity (p < 0.05). Multivariate logistic regression analysis after adjusting for confounding factors showed that HDL-C (odds ratio [OR]: 0.132, 95% confidence interval [CI], 0.082-0.212; p < 0.001) and BMI (OR: 0.959, 95% CI 0.933-0.986; p = 0.003) were associated with HHV-8 seropositivity. Subgroup analyses concerning ethnicity, sex, or age demonstrated a consistent relationship with HDL-C. The results of HHV-8 seropositivity and BMI were inconsistent in the subgroups. However, Spearman's correlation analysis between HHV-8 serum antibody titer and HDL-C levels showed no linear relationship among HHV-8 seropositive individuals (ρ = -0.080, p = 0.058). HHV-8 serum antibody titers were also not significantly correlated with BMI (ρ = -0.015, p = 0.381). Low HDL-C levels may be an independent risk factor for HHV-8 infection, but there is no significant correlation between HDL-C levels and HHV-8 antibody titers.

Kaposi sarcoma-associated herpesvirus complement control protein (KCP) and glycoprotein K8.1 are not required for viral infection in vitro or in vivo

Kaposi sarcoma-associated herpesvirus (KSHV), also known as human herpesvirus-8, is the causal agent of Kaposi sarcoma, a cancer that appears as tumors on the skin or mucosal surfaces, as well as primary effusion lymphoma and KSHV-associated multicentric Castleman disease, which are B-cell lymphoproliferative disorders. Effective prophylactic and therapeutic strategies against KSHV infection and its associated diseases are needed. To develop these strategies, it is crucial to identify and target viral glycoproteins involved in KSHV infection of host cells. Multiple KSHV glycoproteins expressed on the viral envelope are thought to play a pivotal role in viral infection, but the infection mechanisms involving these glycoproteins remain largely unknown. We investigated the role of two KSHV envelope glycoproteins, KSHV complement control protein (KCP) and K8.1, in viral infection in various cell types in vitro and in vivo. Using our newly generated anti-KCP antibodies, previously characterized anti-K8.1 antibodies, and recombinant mutant KSHV viruses lacking KCP, K8.1, or both, we demonstrated the presence of KCP and K8.1 on the surface of both virions and KSHV-infected cells. We showed that KSHV lacking KCP and/or K8.1 remained infectious in KSHV-susceptible cell lines, including epithelial, endothelial, and fibroblast, when compared to wild-type recombinant KSHV. We also provide the first evidence that KSHV lacking K8.1 or both KCP and K8.1 can infect human B cells in vivo in a humanized mouse model. Thus, these results suggest that neither KCP nor K8.1 is required for KSHV infection of various host cell types and that these glycoproteins do not determine KSHV cell tropism.

IMPORTANCE

Kaposi sarcoma-associated herpesvirus (KSHV) is an oncogenic human gamma-herpesvirus associated with the endothelial malignancy Kaposi sarcoma and the lymphoproliferative disorders primary effusion lymphoma and multicentric Castleman disease. Determining how KSHV glycoproteins such as complement control protein (KCP) and K8.1 contribute to the establishment, persistence, and transmission of viral infection will be key for developing effective anti-viral vaccines and therapies to prevent and treat KSHV infection and KSHV-associated diseases. Using newly generated anti-KCP antibodies, previously characterized anti-K8.1 antibodies, and recombinant mutant KSHV viruses lacking KCP and/or K8.1, we show that KCP and K8.1 can be found on the surface of both virions and KSHV-infected cells. Furthermore, we show that KSHV lacking KCP and/or K8.1 remains infectious to diverse cell types susceptible to KSHV in vitro and to human B cells in vivo in a humanized mouse model, thus providing evidence that these viral glycoproteins are not required for KSHV infection.

Exploration in the Mechanism of Ginsenoside Rg5 for the Treatment of Osteosarcoma by Network Pharmacology and Molecular Docking

OBJECTIVE

Osteosarcoma is a primary malignancy originating from mesenchymal tissue characterized by rapid growth, early metastasis and poor prognosis. Ginsenoside Rg5 (G-Rg5) is a minor ginsenoside extracted from Panax ginseng C.A. Meyer which has been discovered to possess anti-tumor properties. The objective of current study was to explore the mechanism of G-Rg5 in the treatment of osteosarcoma by network pharmacology and molecular docking technology.

METHODS

Pharmmapper, SwissTargetPrediction and similarity ensemble approach databases were used to obtain the pharmacological targets of G-Rg5. Related genes of osteosarcoma were searched for in the GeneCards, OMIM and DrugBank databases. The targets of G-Rg5 and the related genes of osteosarcoma were intersected to obtain the potential target genes of G-Rg5 in the treatment of osteosarccoma. The STRING database and Cytoscape 3.8.2 software were used to construct the protein-protein interaction (PPI) network, and the Database for Annotation, Visualization and Integrated Discovery (DAVID) platform was used to perform gene ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analyses. AutoDock vina software was used to perform molecular docking between G-Rg5 and hub targets. The hub genes were imported into the Kaplan-Meier Plotter online database for survival analysis.

RESULTS

A total of 61 overlapping targets were obtained. The related signaling pathways mainly included PI3K-Akt signaling pathway, Proteoglycans in cancer, Lipid and atherosclerosis and Kaposi sarcoma-associated herpesvirus infection. Six hub targets including PIK3CA, SRC, TP53, MAPK1, EGFR, and VEGFA were obtained through PPI network and targets-pathways network analyses. The results of molecular docking showed that the binding energies were all less than -7 kcal/mol. And the results of survival analysis showed TP53 and VEGFA affect the prognosis of sarcoma patients.

CONCLUSION

This study explored the possible mechanism of G-Rg5 in the treatment of osteosarcoma using network pharmacology method, suggesting that G-Rg5 has the characteristics of multi-targets and multi-pathways in the treatment of osteosarcoma, which lays a foundation for the follow-up experimental and clinical researches on the therapeutic effects of G-Rg5 on osteosarcoma.

Comprehensive analysis and immunohistochemistry localization of NRP1 expression in pancancer and normal individual tissues in relation to SARS‑CoV‑2 susceptibility

Neuropilin 1 (NRP1/CD304) is a typical membrane-bound co-receptor for vascular endothelial growth factor, semaphorin family members and viral severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). However, NRP1 expression levels across cancer types and the potential role of SARS-CoV-2 infection in patients with cancer are not clear. Online databases, such as The Cancer Genome Atlas database of Human Protein Atlas, Gene Expression Profiling Interactive Analysis and cBioPortal were used for the expression analysis in this study. Immunohistochemical (IHC) staining for NRP1 was performed in the tissues of patients with non-small cell carcinoma. As a result, it was found that NRP1 mRNA and protein expression levels were highest in the female reproductive tissues and the respiratory system, specifically in the nasopharynx, bronchus and fallopian tube, as well as in adipocytes, hepatic stellate cells, Sertoli cells, endothelial cells and dendritic cells. IHC showed that the NRP1 protein was mainly localized to the cytoplasm and membrane in the tissues of patients with non-small cell carcinoma, demonstrating its role in lung infection by SARS-CoV-2, due to invasion of cell membranes by the virus. Levels of NRP1 mRNA were significantly increased in lymphoid neoplasm diffuse large B-cell lymphoma, esophageal carcinoma, glioblastoma multiforme, head and neck squamous cell carcinoma, kidney renal clear cell carcinoma (KIRC), pancreatic adenocarcinoma, stomach adenocarcinoma and thymoma, and significantly decreased in cervical squamous cell carcinoma and endocervical adenocarcinoma, kidney chromophobe, lung squamous cell carcinoma, ovarian serous cystadenocarcinoma, uterine corpus endometrial carcinoma and uterine carcinosarcoma, compared with corresponding healthy tissues in pancancer, indicating roles for viral invasion in most cancer types. Moreover, low NRP1 expression was significantly associated with long overall survival (OS) time in adrenocortical carcinoma, brain lower grade glioma, stomach adenocarcinoma and uveal melanoma, but with short OS time in KIRC only. The ENST00000374867.6 (NRP1-202) isoform is most highly expressed in most cancer types and thus could be involved in tumorigenesis and SARS-CoV-2 invasion in cancer patients. NRP1 may be involved in SARS-CoV-2 invasion in patients with cancer, including those with lung cancer.

Modulation of Epstein-Barr-Virus (EBV)-Associated Cancers by Co-Infections

The oncogenic and persistent Epstein Barr virus (EBV) is carried by more than 95% of the human adult population. While asymptomatic in most of these, EBV can cause a wide variety of malignancies of lymphoid or epithelial cell origin. Some of these are also associated with co-infections that either increase EBV-induced tumorigenesis or weaken its immune control. The respective pathogens include Kaposi-sarcoma-associated herpesvirus (KSHV), Plasmodium falciparum and human immunodeficiency virus (HIV). In this review, I will discuss the respective tumor entities and possible mechanisms by which co-infections increase the EBV-associated cancer burden. A better understanding of the underlying mechanisms could allow us to identify crucial features of EBV-associated malignancies and defects in their immune control. These could then be explored to develop therapies against the respective cancers by targeting EBV and/or the respective co-infections with pathogen-specific therapies or vaccinations.

Kaposi's sarcoma-associated herpesvirus glycoprotein K8.1 is critical for infection in a cell-specific manner and functions at the attachment step on keratinocytes

IMPORTANCE

Kaposi's sarcoma-associated herpesvirus (KSHV) is the causative agent of several B cell malignancies and Kaposi's sarcoma. We analyzed the function of K8.1, the major antigenic component of the KSHV virion in the infection of different cells. To do this, we deleted K8.1 from the viral genome. It was found that K8.1 is critical for the infection of certain epithelial cells, e.g., a skin model cell line but not for infection of many other cells. K8.1 was found to mediate attachment of the virus to cells where it plays a role in infection. In contrast, we did not find K8.1 or a related protein from a closely related monkey virus to activate fusion of the viral and cellular membranes, at least not under the conditions tested. These findings suggest that K8.1 functions in a highly cell-specific manner during KSHV entry, playing a crucial role in the attachment of KSHV to, e.g., skin epithelial cells.

Globally invariant behavior of oncogenes and random genes at population but not at single cell level

Cancer is widely considered a genetic disease. Notably, recent works have highlighted that every human gene may possibly be associated with cancer. Thus, the distinction between genes that drive oncogenesis and those that are associated to the disease, but do not play a role, requires attention. Here we investigated single cells and bulk (cell-population) datasets of several cancer transcriptomes and proteomes in relation to their healthy counterparts. When analyzed by machine learning and statistical approaches in bulk datasets, both general and cancer-specific oncogenes, as defined by the Cancer Genes Census, show invariant behavior to randomly selected gene sets of the same size for all cancers. However, when protein-protein interaction analyses were performed, the oncogenes-derived networks show higher connectivity than those relative to random genes. Moreover, at single-cell scale, we observe variant behavior in a subset of oncogenes for each considered cancer type. Moving forward, we concur that the role of oncogenes needs to be further scrutinized by adopting protein causality and higher-resolution single-cell analyses.

The Role of RNA Sensors in Regulating Innate Immunity to Gammaherpesviral Infections

Kaposi's sarcoma-associated herpesvirus (KSHV) and the Epstein-Barr virus (EBV) are double-stranded DNA oncogenic gammaherpesviruses. These two viruses are associated with multiple human malignancies, including both B and T cell lymphomas, as well as epithelial- and endothelial-derived cancers. KSHV and EBV establish a life-long latent infection in the human host with intermittent periods of lytic replication. Infection with these viruses induce the expression of both viral and host RNA transcripts and activates several RNA sensors including RIG-I-like receptors (RLRs), Toll-like receptors (TLRs), protein kinase R (PKR) and adenosine deaminases acting on RNA (ADAR1). Activation of these RNA sensors induces the innate immune response to antagonize the virus. To counteract this, KSHV and EBV utilize both viral and cellular proteins to block the innate immune pathways and facilitate their own infection. In this review, we summarize how gammaherpesviral infections activate RNA sensors and induce their downstream signaling cascade, as well as how these viruses evade the antiviral signaling pathways to successfully establish latent infection and undergo lytic reactivation.

A Kaposi's sarcoma-associated herpes virus-encoded microRNA contributes to dilated cardiomyopathy

Dilated cardiomyopathy (DCM) is the leading cause of heart transplantation. By microRNA (miRNA) array, a Kaposi's sarcoma-associated herpes virus (KSHV)-encoded miRNA, kshv-miR-K12-1-5p, was detected in patients with DCM. The KSHV DNA load and kshv-miR-K12-1-5p level in plasma from 696 patients with DCM were measured and these patients were followed-up. Increased KSHV seropositivity and quantitative titers were found in the patients with DCM compared with the non-DCM group (22.0% versus 9.1%, p < 0.05; 168 versus 14 copies/mL plasma, p < 0.05). The risk of the individual end point of death from cardiovascular causes or heart transplantation was increased among DCM patients with the KSHV DNA seropositivity during follow-up (adjusted hazard ratio 1.38, 95% confidence interval 1.01-1.90; p < 0.05). In heart tissues, the KSHV DNA load was also increased in the heart from patients with DCM in comparison with healthy donors (1016 versus 29 copies/105 cells, p < 0.05). The KSHV and kshv-miR-K12-1-5p in DCM hearts were detected using immunofluorescence and fluorescence staining in situ hybridization. KSHV itself was exclusively detectable in CD31-positive endothelium, while kshv-miR-K12-1-5p could be detected in both endothelium and cardiomyocytes. Moreover, kshv-miR-K12-1-5p released by KSHV-infected cardiac endothelium could disrupt the type I interferon signaling pathway in cardiomyocytes. Two models of kshv-miR-K12-1-5p overexpression (agomiR and recombinant adeno-associated virus) were used to explore the roles of KSHV-encoded miRNA in vivo. The kshv-miR-K12-1-5p aggravated known cardiotropic viruses-induced cardiac dysfunction and inflammatory infiltration. In conclusion, KSHV infection was a risk factor for DCM, providing developmental insights of DCM involving virus and its miRNA ( https://clinicaltrials.gov . Unique identifier: NCT03461107).

Neuropilin 1 is an entry receptor for KSHV infection of mesenchymal stem cell through TGFBR1/2-mediated macropinocytosis

Kaposi's sarcoma-associated herpesvirus (KSHV) has been implicated in the pathogenesis of Kaposi's sarcoma (KS) and other malignancies. The cellular origin of KS has been suggested to be either mesenchymal stem cells (MSCs) or endothelial cells. However, receptor(s) for KSHV to infect MSCs remains unknown. By combining bioinformatics analysis and shRNA screening, we identify neuropilin 1 (NRP1) as an entry receptor for KSHV infection of MSCs. Functionally, NRP1 knockout and overexpression in MSCs significantly reduce and promote, respectively, KSHV infection. Mechanistically, NRP1 facilitated the binding and internalization of KSHV by interacting with KSHV glycoprotein B (gB), which was blocked by soluble NRP1 protein. Furthermore, NRP1 interacts with TGF-β receptor type 2 (TGFBR2) through their respective cytoplasmic domains and thus activates the TGFBR1/2 complex, which facilitates the macropinocytosis-mediated KSHV internalization via the small GTPases Cdc42 and Rac1. Together, these findings implicate that KSHV has evolved a strategy to invade MSCs by harnessing NRP1 and TGF-beta receptors to stimulate macropinocytosis.

Today's Kaposi sarcoma is not the same as it was 40 years ago, or is it?

This review will provide an overview of the notion that Kaposi sarcoma (KS) is a disease that manifests under diverse and divergent circumstances. We begin with a historical introduction of KS and KS-associated herpesvirus (KSHV), highlight the diversity of clinical presentations of KS, summarize what we know about the cell of origin for this tumor, explore KSHV viral load as a potential biomarker for acute KSHV infections and KS-associated complications, and discuss immune modulators that impact KSHV infection, KSHV persistence, and KS disease.

KSHV Viral Protein Kinase Interacts with USP9X to Modulate the Viral Lifecycle

Kaposi's sarcoma-associated herpesvirus (KSHV) is the etiological agent of Kaposi sarcoma (KS), the plasmablastic form of multicentric Castleman's disease, and primary effusion lymphoma. In sub-Saharan Africa, KS is the most common HIV-related malignancy and one of the most common childhood cancers. Immunosuppressed patients, including HIV-infected patients, are more prone to KSHV-associated disease. KSHV encodes a viral protein kinase (vPK) that is expressed from ORF36. KSHV vPK contributes to the optimal production of infectious viral progeny and upregulation of protein synthesis. To elucidate the interactions of vPK with cellular proteins in KSHV-infected cells, we used a bottom-up proteomics approach and identified host protein ubiquitin-specific peptidase 9X-linked (USP9X) as a potential interactor of vPK. Subsequently, we validated this interaction using a co-immunoprecipitation assay. We report that both the ubiquitin-like and the catalytic domains of USP9X are important for association with vPK. To uncover the biological relevance of the USP9X/vPK interaction, we investigated whether the knockdown of USP9X would modulate viral reactivation. Our data suggest that depletion of USP9X inhibits both viral reactivation and the production of infectious virions. Understanding how USP9X influences the reactivation of KSHV will provide insights into how cellular deubiquitinases regulate viral kinase activity and how viruses co-opt cellular deubiquitinases to propagate infection. Hence, characterizing the roles of USP9X and vPK during KSHV infection constitutes a first step toward identifying a potentially critical interaction that could be targeted by future therapeutics. IMPORTANCE Kaposi's sarcoma-associated herpesvirus (KSHV) is the etiological agent of Kaposi sarcoma (KS), the plasmablastic form of multicentric Castleman's disease, and primary effusion lymphoma. In sub-Saharan Africa, KS is the most common HIV-related malignancy. KSHV encodes a viral protein kinase (vPK) that aids viral replication. To elucidate the interactions of vPK with cellular proteins in KSHV-infected cells, we used an affinity purification approach and identified host protein ubiquitin-specific peptidase 9X-linked (USP9X) as a potential interactor of vPK. Depletion of USP9X inhibits both viral reactivation and the production of infectious virions. Overall, our data suggest a proviral role for USP9X.

Cancers associated with human gammaherpesviruses

Epstein-Barr virus (EBV; human herpesvirus 4; HHV-4) and Kaposi sarcoma-associated herpesvirus (KSHV; human herpesvirus 8; HHV-8) are human gammaherpesviruses that have oncogenic properties. EBV is a lymphocryptovirus, whereas HHV-8/KSHV is a rhadinovirus. As lymphotropic viruses, EBV and KSHV are associated with several lymphoproliferative diseases or plasmacytic/plasmablastic neoplasms. Interestingly, these viruses can also infect epithelial cells causing carcinomas and, in the case of KSHV, endothelial cells, causing sarcoma. EBV is associated with Burkitt lymphoma, classic Hodgkin lymphoma, nasopharyngeal carcinoma, plasmablastic lymphoma, lymphomatoid granulomatosis, leiomyosarcoma, and subsets of diffuse large B-cell lymphoma, post-transplant lymphoproliferative disorder, and gastric carcinoma. KSHV is implicated in Kaposi sarcoma, primary effusion lymphoma, multicentric Castleman disease, and KSHV-positive diffuse large B-cell lymphoma. Pathogenesis by these two herpesviruses is intrinsically linked to viral proteins expressed during the lytic and latent lifecycles. This comprehensive review intends to provide an overview of the EBV and KSHV viral cycles, viral proteins that contribute to oncogenesis, and the current understanding of the pathogenesis and clinicopathology of their related neoplastic entities.

KSHV (HHV8) vaccine: promises and potential pitfalls for a new anti-cancer vaccine

Seven viruses cause at least 15% of the total cancer burden. Viral cancers have been described as the "low-hanging fruit" that can be potentially prevented or treated by new vaccines that would alter the course of global human cancer. Kaposi sarcoma herpesvirus (KSHV or HHV8) is the sole cause of Kaposi sarcoma, which primarily afflicts resource-poor and socially marginalized populations. This review summarizes a recent NIH-sponsored workshop's findings on the epidemiology and biology of KSHV as an overlooked but potentially vaccine-preventable infection. The unique epidemiology of this virus provides opportunities to prevent its cancers if an effective, inexpensive, and well-tolerated vaccine can be developed and delivered.

Canine and murine models of osteosarcoma

Osteosarcoma (OS) is the most common malignant bone tumor in children. Despite efforts to develop and implement new therapies, patient outcomes have not measurably improved since the 1980s. Metastasis continues to be the main source of patient mortality, with 30% of cases developing metastatic disease within 5 years of diagnosis. Research models are critical in the advancement of cancer research and include a variety of species. For example, xenograft and patient-derived xenograft (PDX) mouse models provide opportunities to study human tumor cells in vivo while transgenic models have offered significant insight into the molecular mechanisms underlying OS development. A growing recognition of naturally occurring cancers in companion species has led to new insights into how veterinary patients can contribute to studies of cancer biology and drug development. The study of canine cases, including the use of diagnostic tissue archives and clinical trials, offers a potential mechanism to further canine and human cancer research. Advancement in the field of OS research requires continued development and appropriate use of animal models. In this review, animal models of OS are described with a focus on the mouse and tumor-bearing pet dog as parallel and complementary models of human OS.

Molecular Mechanisms of Kaposi Sarcoma Development

Simple Summary

There are at least four forms of Kaposi’s sarcoma (KS) with the ‘HIV’-related form being the most aggressive and can involve mucosae or visceral organs. Kaposi’s sarcoma-associated herpes virus (KSHV) is the underlying cause of this disease. It can infect endothelial and/or mesenchymal cells and establish a latent phase in host cells in which latency proteins and various non-coding RNAs (ncRNAs) play a complex role in proliferation and angiogenesis. It also undergoes periods of sporadic lytic reactivation that are key for KS progression. Complex interactions with the microenvironment with production of inflammatory cytokines and paracrine signaling is a standout feature of KS development and maintenance. KSHV impairs the immune response by various mechanisms such as the degradation of a variety of proteins involved in immune response or binding to cellular chemokines. Treatment options include classical chemotherapy, but other novel therapies are being investigated.

Abstract

Kaposi’s sarcoma (KS) is a heterogeneous angioproliferative tumor that generally arises in the skin. At least four forms of this disease have been described, with the ‘HIV’-related form being the most aggressive and can involve mucosae or visceral organs. Three quarters of KS cases occur in sub-Saharan Africa (SSA) as geographic variation is explained by the disparate prevalence of KS-associated herpes virus (KSHV), which is the underlying cause of this disease. It can infect endothelial and/or mesenchymal cells that consequently transdifferentiate to an intermediate state. KSHV establishes a latent phase in host cells in which latency proteins and various non-coding RNAs (ncRNAs) play a complex role in proliferation and angiogenesis. It also undergoes periods of sporadic lytic reactivation triggered by various biological signals in which lytic stage proteins modulate host cell signaling pathways and are key in KS progression. Complex interactions with the microenvironment with production of inflammatory cytokines with paracrine signaling is a standout feature of KS development and maintenance. KSHV impairs the immune response by various mechanisms such as the degradation of a variety of proteins involved in immune response or binding to cellular chemokines. Treatment options include classical chemotherapy, but other novel therapies are being investigated.

Antibodies Targeting KSHV gH/gL Reveal Distinct Neutralization Mechanisms

Kaposi’s sarcoma herpesvirus (KSHV) is associated with a significant disease burden, in particular in Sub-Sahara Africa. A KSHV vaccine would be highly desirable, but the mechanisms underlying neutralizing antibody responses against KSHV remain largely unexplored. The complex made of glycoproteins H and L (gH/gL) activates gB for the fusion of viral and cellular membranes in all herpesviruses. KSHV gH/gL also interacts with cellular Eph family receptors. To identify optimal antigens for vaccination and to elucidate neutralization mechanisms, we primed mice with recombinantly expressed, soluble gH/gL (gHecto/gL) that was either wildtype (WT), lacking defined glycosylation sites or bearing modified glycosylation, followed by boosts with WT gHecto/gL. We also immunized with a gL-gHecto fusion protein or a gHecto-ferritin/gL nanoparticle. Immune sera neutralized KSHV and inhibited EphA2 receptor binding. None of the regimens was superior to immunization with WT gHecto/gL with regard to neutralizing activity and EphA2 blocking activity, the gL-gHecto fusion protein was equally effective, and the ferritin construct was inferior. gH/gL-targeting sera inhibited gB-mediated membrane fusion and inhibited infection also independently from receptor binding and gL, as demonstrated by neutralization of a novel KSHV mutant that does not or only marginally incorporate gL into the gH/gL complex and infects through an Eph-independent route.

Kaposi’s sarcoma-associated herpesvirus vFLIP promotes MEndT to generate hybrid M/E state for tumorigenesis

Kaposi’s sarcoma (KS) is an angioproliferative and invasive tumor caused by Kaposi’s sarcoma-associated herpesvirus (KSHV). The cellular origin of KS tumor cells remains contentious. Recently, evidence has accrued indicating that KS may arise from KSHV-infected mesenchymal stem cells (MSCs) through mesenchymal-to-endothelial transition (MEndT), but the transformation process has been largely unknown. In this study, we investigated the KSHV-mediated MEndT process and found that KSHV infection rendered MSCs incomplete endothelial lineage differentiation and formed hybrid mesenchymal/endothelial (M/E) state cells characterized by simultaneous expression of mesenchymal markers Nestin/PDGFRA/α-SAM and endothelial markers CD31/PDPN/VEGFR2. The hybrid M/E cells have acquired tumorigenic phenotypes in vitro and the potential to form KS-like lesions after being transplanted in mice under renal capsules. These results suggest a homology of KSHV-infected MSCs with Kaposi’s sarcoma where proliferating KS spindle-shaped cells and the cells that line KS-specific aberrant vessels were also found to exhibit the hybrid M/E state. Furthermore, the genetic analysis identified KSHV-encoded FLICE inhibitory protein (vFLIP) as a crucial regulator controlling KSHV-induced MEndT and generating hybrid M/E state cells for tumorigenesis. Overall, KSHV-mediated MEndT that transforms MSCs to tumorigenic hybrid M/E state cells driven by vFLIP is an essential event in Kaposi’s sarcomagenesis.

Kaposi’s sarcoma manifests as multifocal lesions with spindle cell proliferation, intense angiogenesis, and erythrocyte extravasation. Although the origin and malignant nature of KS remain contentious, it is established that KSHV infection with concomitant viral oncogene expression in normal cell progenitors causes KS. The mechanism of KSHV oncogenesis could be revealed through a reproduction of KS by infection of normal cells. This study reports that the KSHV infection of mesenchymal stem cells initiates mesenchymal-to-endothelial transition (MEndT) that generates mesenchymal/endothelial (M/E) hybrid state cells. The hybrid M/E cells acquired tumorigenic phenotypes, including tumor initiation, angiogenesis, migration, and the potential to form KS-like lesions after transplanted in mice. This finding faithfully recapitulates Kaposi’s sarcoma where proliferating KS spindle cells and the cells that line KS-specific aberrant vessels are also found to exhibit the hybrid M/E phenotype. We also found that KSHV-encoded viral FLICE inhibitory protein (vFLIP) plays a crucial role in promoting MEndT and the generation of M/E state cells. These results provide a new layer of evidence for KSHV-infected MSCs being the cell source of KS spindle cells and reveal novel insight into KS pathogenesis and viral tumorigenesis.

Interferon-Induced Transmembrane Proteins Inhibit Infection by the Kaposi's Sarcoma-Associated Herpesvirus and the Related Rhesus Monkey Rhadinovirus in a Cell-Specific Manner

The interferon-induced transmembrane proteins (IFITMs) are broad-spectrum antiviral proteins that inhibit the entry of enveloped viruses. We analyzed the effect of IFITMs on the gamma-2 herpesviruses Kaposi's sarcoma-associated herpesvirus (KSHV) and the closely related rhesus monkey rhadinovirus (RRV). We used CRISPR/Cas9-mediated gene knockout to generate A549 cells, human foreskin fibroblasts (HFF), and human umbilical vein endothelial cells (HUVEC) with combined IFITM1/2/3 knockout and identified IFITMs as cell-dependent inhibitors of KSHV and RRV infection in A549 cells and HFF but not HUVEC. IFITM overexpression revealed IFITM1 as the relevant IFITM that inhibits KSHV and RRV infection. Fluorescent KSHV particles did not pronouncedly colocalize with IFITM-positive compartments. However, we found that KSHV and RRV glycoprotein-mediated cell-cell fusion is enhanced upon IFITM1/2/3 knockout. Taken together, we identified IFITM1 as a cell-dependent restriction factor of KSHV and RRV that acts at the level of membrane fusion. Of note, our results indicate that recombinant IFITM overexpression may lead to results that are not representative for the situation at endogenous levels. Strikingly, we observed that the endotheliotropic KSHV circumvents IFITM-mediated restriction in HUVEC despite high IFITM expression, while influenza A virus (IAV) glycoprotein-driven entry into HUVEC is potently restricted by IFITMs even in the absence of interferon. Mechanistically, we found that KSHV colocalizes less with IFITM1 and IFITM2 in HUVEC than in A549 cells immediately after attachment, potentially contributing to the observed difference in restriction. IMPORTANCE IFITM proteins are the first line of defense against infection by many pathogens and may also have therapeutic importance, as they, among other effectors, mediate the antiviral effect of interferons. Neither their function against herpesviruses nor their mechanism of action is well understood. We report here that in some cells but not in, for example, primary umbilical vein endothelial cells, IFITM1 restricts KSHV and RRV and that, mechanistically, this is likely effected by reducing the fusogenicity of the cell membrane. Further, we demonstrate potent inhibition of IAV glycoprotein-driven infection of cells of extrapulmonary origin by high constitutive IFITM expression.

Kaposi's sarcoma-associated herpesvirus promotes mesenchymal-to-endothelial transition by resolving the bivalent chromatin of PROX1 gene

Increasing evidence suggests that Kaposi’s sarcoma (KS) arises from Kaposi’s sarcoma-associated herpesvirus (KSHV)-infected mesenchymal stem cells (MSCs) through mesenchymal-to-endothelial transition (MEndT). KSHV infection promotes MSC differentiation of endothelial lineage and acquisition of tumorigeneic phenotypes. To understand how KSHV induces MEndT and transforms MSCs to KS cells, we investigated the mechanism underlying KSHV-mediated MSC endothelial lineage differentiation. Like embryonic stem cells, MSC differentiation and fate determination are under epigenetic control. Prospero homeobox 1 (PROX1) is a master regulator that controls lymphatic vessel development and endothelial differentiation. We found that the PROX1 gene in MSCs harbors a distinctive bivalent epigenetic signature consisting of both active marker H3K4me3 and repressive marker H3K27me3, which poises expression of the genes, allowing timely activation upon differentiation signals or environmental stimuli. KSHV infection effectively resolves the bivalent chromatin by decreasing H3K27me3 and increasing H3K4me3 to activate the PROX1 gene. vIL-6 signaling leads to the recruitment of MLL2 and SET1 complexes to the PROX1 promoter to increase H3K4me3, and the vGPCR-VEGF-A axis is responsible for removing PRC2 from the promoter to reduce H3K27me3. Therefore, through a dual signaling process, KSHV activates PROX1 gene expression and initiates MEndT, which renders MSC tumorigenic features including angiogenesis, invasion and migration.

Numerous parallelisms between development and cancer led to the concept that cancer is a development problem over the past 50 years. As our knowledge of epigenetic regulation is advancing, the similarities between development and cancer are becoming more apparent, providing further support to the theory. KSHV infection of mesenchymal stem cells (MSCs) may result in Kaposi’s sarcoma (KS) through mesenchymal-to-endothelial transition (MEndT), a process resembling endothelial differentiation during development. KSHV initiates MEndT by activating the homeobox gene PROX1, a master regulator of the lymphatic endothelial cell differentiation, at the epigenetic level. Here we found that the PROX1 gene resides in bivalent domain chromatin in MSCs and KSHV infection resolves it through a dual signaling process to activates the PROX1 gene, which initiates MEndT and confers MSC KS-like phenotypes. The significance of this study is two-fold. First, the study elucidated the mechanism underlying KSHV-mediated MEndT and KS development at the transcription level. Second, KSHV uses two independent pathways to elevate activating histone modification and decrease repressive marker, respectively, to resolved bivalent chromatin, revealing a two-factor-authentication mechanism in the epigenetic regulation, which may grant a more efficient and accurate response to activate a gene in bivalent chromatin.