Kaposi's Sarcoma-associated Herpesvirus Activation Research Articles

Hypoxia and hypoxia-inducible factors in Kaposi sarcoma-associated herpesvirus infection and disease pathogenesis.

Kaposi sarcoma-associated herpesvirus (KSHV) is the causative agent of Kaposi sarcoma and several other tumors and hyperproliferative diseases seen predominantly in human immunodeficiency virus-infected and other immunocompromised persons. There is an increasing body of evidence showing that hypoxia and hypoxia-inducible factors (HIFs) play important roles in the biology of KSHV and in the pathogenesis of KSHV-induced diseases. Hypoxia and HIFs can induce lytic activation of KSHV and KSHV can in turn lead to a hypoxic-like state in infected cells. In this review, we describe the complex interactions between KSHV biology, the cellular responses to hypoxia, and the pathogenesis of KSHV-induced diseases. We also describe how interference with HIFs can lead to decreased tumor growth and/or death of infected cells and KSHV-induced tumors. Finally, we show how these observations may lead to novel strategies for the treatment of KSHV-induced diseases.

Abstract 1394: Gene expression profile in BCBL-1 cell line following activation of KSHV

Abstract Patients with HIV/AIDS are at a 3,400 times higher risk of developing Kaposi's sarcoma when compared to healthy populations. Our hypothesis is that the upregulation of viral associated proteins is causing an increase in DNA damage, allowing for the higher incidence rate of Kaposi's sarcoma in infected populations. The direct mechanisms leading to this increased risk is unknown, but the viral infection with Kaposi's sarcoma-associated herpesvirus (KSHV) is an apparent cause of this risk. The cell is under attack of endogenous threats including oxidative stress, causing DNA damage and leading to mutations, but the viral proteins may interfere with the repair mechanisms. In previous experiments we looked at DNA repair dynamics following X-ray exposure in the two different stages and determined there is an inefficiency in the DNA repair process in the cells during active production of viral particles. This project aimed to compare the transcriptomes of the BCBL-1 cell line during latent and acute phases of KSHV production. Our results are showing that genes involved in genome stability are differently expressed during the lytic stage. Comparison of these two transcriptomes allows for identification of which proteins are being upregulated during active viral production. This may be of importance for the HIV/AIDS cancer patients because it shows the mechanisms behind genome stability in KSHV-infected cells. 1) Research reported in this publication was supported by the National Institute Of General Medical Sciences of the National Institutes of Health under Award Numbers UL1GM118991, TL4GM118992, or RL5GM118990. The content is solely the responsibility of the authors and does not necessarily represent the official views of the National Institutes of Health. 2) NASA EPSCoR, NNH15ZHA003C Citation Format: Samantha L. Haines, Sabrina R. Bishop, Viktorija Podlutskaya, Andrej Podlutsky. Gene expression profile in BCBL-1 cell line following activation of KSHV [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 1394.

Kaposi sarcoma-associated herpesvirus miRNAs suppress CASTOR1-mediated mTORC1 inhibition to promote tumorigenesis.

Cytosolic arginine sensor for mTORC1 subunits 1 and 2 (CASTOR1 and CASTOR2) inhibit the mammalian target of rapamycin complex 1 (mTORC1) upon arginine deprivation. mTORC1 regulates cell proliferation, survival, and metabolism and is often dysregulated in cancers, indicating that cancer cells may regulate CASTOR1 and CASTOR2 to control mTORC1 signaling and promote tumorigenesis. mTORC1 is the most effective therapeutic target of Kaposi sarcoma, which is caused by infection with the Kaposi sarcoma-associated herpesvirus (KSHV). Hence, KSHV-induced cellular transformation is a suitable model for investigating mTORC1 regulation in cancer cells. Currently, the mechanism of KSHV activation of mTORC1 in KSHV-induced cancers remains unclear. We showed that KSHV suppressed CASTOR1 and CASTOR2 expression to activate the mTORC1 pathway. CASTOR1 or CASTOR2 overexpression and mTOR inhibitors abolished cell proliferation and colony formation in soft agar of KSHV-transformed cells by attenuating mTORC1 activation. Furthermore, the KSHV-encoded miRNA miR-K4-5p, and probably miR-K1-5p, directly targeted CASTOR1 to inhibit its expression. Knockdown of miR-K1-5p and -K4-5p restored CASTOR1 expression and thereby attenuated mTORC1 activation. Overexpression of CASTOR1 or CASTOR2 and mTOR inhibitors abolished the activation of mTORC1 and growth transformation induced by pre-miR-K1 and -K4. Our results define the mechanism of KSHV activation of the mTORC1 pathway and establish the scientific basis for targeting this pathway to treat KSHV-associated cancers.

STAT6 degradation and ubiquitylated TRIML2 are essential for activation of human oncogenic herpesvirus.

Aberrations in STAT6-mediated signaling are linked to the development of multiple cancer types. Increasing evidence has shown that activation of human oncogenic herpesvirus lytic replication is crucial for viral tumorigenesis. However, the role of STAT6 in herpesvirus lytic replication remains elusive. Here, by using Kaposi’s sarcoma-associated herpesvirus (KSHV) as a model, we revealed that RTA, the master regulator of lytic replication, interacts with STAT6 and promotes lysine 48 (K48) and K63-linked ubiquitylation of STAT6 for degradation via the proteasome and lysosome systems. Moreover, degradation of STAT6 is dramatically associated with the increased ubiquitylated form of tripartite motif family like 2 (TRIML2, a tumor suppressor) for prolonged cell survival and virion production, which is also commonly observed in lytic activation of Epstein-Barr virus, herpes simplex virus 1 and cytomegalovirus. These results suggest that degradation of STAT6 is important for the lytic activation of KSHV and as such, may be an attractive therapeutic target.

AMC-053: Pilot Study of an Oncolytic Viral Strategy Using Bortezomib with ICE +/- Rituximab for Relapsed/Refractory HIV+ Lymphomas

Introduction:Both HIV+ Hodgkin and non-Hodgkin lymphomas have higher rates of latent infection by the gamma-herpesviruses (GHVs), Epstein-Barr virus (EBV) and Kaposi sarcoma-associated herpes virus (KSHV), than corresponding lymphomas in the HIV-seronegative population. Bortezomib, a proteasome inhibitor, induces lytic activation of both EBV and KSHV. Lytic activation of GHVs latently infecting lymphoma cells is hypothesized to beneficial both for direct tumor cell lysis as well as increased cytotoxic immune response due to viral lytic gene products. Furthermore, preclinical studies found proteasome inhibition impairs HIV infectivity via preservation of human anti-retroviral APOBEC3G, suggesting a novel therapeutic strategy to control HIV. Given that therapy of relapsed or refractory HIV-associated lymphoma (R/R-HAL) results in modest rates of remission, we sought to capitalize on the high viral association within HAL using an oncolytic strategy with bortezomib.Objectives:The primary objective of this study was to evaluate safety and overall response rate (ORR) of R/R-HAL to bortezomib combined with ifosfamide, carboplatin, etoposide +/- rituximab (ICE/R).The secondary objectives of this study were to estimate the impact of bortezomib on lytic activation of EBV and KSHV, using peripheral blood mononuclear cell (PBMC) viral loads, and on HIV using single copy plasma viral loads; to report overall survival at 1 year (1yr-OS); and to correlate EBV and KSHV viral load changes with lymphoma response.Methods:A 3+3 dose escalation design with a 7-day lead-in period of bortezomib alone prior to bortezomib + ICE/R allowed for assessment of early effects of bortezomib on viral loads. Bortezomib was given intravenously on day 1 and 8 of each cycle at one of 4 dose levels: 0.7, 1, 1.3 or 1.5 mg/m2. Standard dose ICE +/- R began day 8 of cycle 1 (28-day cycle); ICE +/- R began day 1 of all subsequent cycles (21-day cycle). Rituximab was included in the regimen only for CD20+ lymphoma.Binomial proportions were used to estimate ORR. The product-limit (Kaplan-Meier) method was used to estimate 1yr-OS. The Wilcoxon signed rank test was used to evaluate changes in viral loads.Results:Twenty-three subjects were enrolled from 7 sites within the AIDS Malignancy Consortium (AMC). More than 90% of enrolled subjects were men and half were minorities; at baseline, 20/23 were on antiretroviral therapy, median CD4 count was315/µL and median HIV viral load was undetectable. Mean age was 50 years. Over half of subjects had stage IV HAL; the majority had diffuse large B-cell lymphoma (DLBCL) (n=15), 2 had primary effusion (PEL), 3 had plasmablastic and 2 had Hodgkin lymphoma.Figure 1 summarizes grade 3-4 toxicities of the 22 subjects evaluable for adverse events during the dose-limiting toxicity period (cycles 1+2). The maximum tolerated dose was not reached at the highest dose cohort studied (bortezomib 1.5mg/m2).Responses occurred in 14/22 subjects initiating protocol therapy: 5 complete and 9 partial responses (PR). Of the 20 subjects who completed 2 or more cycles, the ORR was 80%. Nine of the responders underwent auto-hematopoietic stem cell transplant after protocol therapy. 1yr-OS was 55%.After bortezomib alone, median values of EBV PBMC viral load measured on day 8 were 2x greater than baseline. However, paired analysis did not confirm significant change in this small sample (n=16 evaluable), and there was no correlation found between change in EBV viral load and response. The 2 subjects with known KSHV+ lymphoma (PEL) each had more than a 1-log increase in day 8 KSHV viral load compared with baseline. Both of these subjects attained a PR from protocol therapy.Conclusions:Addition of bortezomib to ICE/R in R/R HAL is feasible with ORR (80%) and 1yr-OS (55%) comparing very favorably with a prior AMC retrospective report of ICE/R in R/R HAL (n=31, ORR 32%, 1yr-OS 38%, Bayraktar 2012). Evaluation of data collected from individual subjects suggests GHV lytic activation may occur with bortezomib alone. However, the lower bortezomib dose levels used to treat the bulk of study subjects and the limited study sample size limit our power to confirm this conclusion. We plan to further explore the effects of proteasome inhibition on GHVs. Evaluation of the impact of bortezomib on HIV replication is pending and will be presented at the meeting. [Display omitted] DisclosuresReid:Millennium: Research Funding. Sparano:Takeda: Research Funding.

Association between malaria exposure and Kaposi's sarcoma-associated herpes virus seropositivity in Uganda.

ObjectiveUnlike other herpes viruses, Kaposi's sarcoma-associated herpes virus (KSHV) is not ubiquitous worldwide and is most prevalent in sub-Saharan Africa. The reasons for this are unclear. As part of a wider investigation of factors that facilitate transmission in Uganda, a high prevalence country, we examined the association between antimalaria antibodies and seropositivity against KSHV.MethodsAntibodies against P. falciparum merozoite surface protein (PfMSP)-1, P. falciparum apical membrane antigen (PfAMA)-1 and KSHV antigens (ORF73 and K8.1) were measured in samples from 1164 mothers and 1227 children.ResultsKaposi's sarcoma-associated herpes virus seroprevalence was 69% among mothers and 15% children. Among mothers, KSHV seroprevalence increased with malaria antibody titres: from 60% to 82% and from 54% to 77%, comparing those with the lowest and highest titres for PfMSP-1 and PfAMA-1, respectively (P < 0.0001). Among children, only antibodies to PfAMA-1 were significantly associated with KSHV seropositivity, (P < 0.0001). In both mothers and children, anti-ORF73 antibodies were more strongly associated with malaria antibodies than anti-K8.1 antibodies.ConclusionThe association between malaria exposure and KSHV seropositivity suggests that malaria is a cofactor for KSHV infection or reactivation.

Herpes Simplex Virus Type 2 Triggers Reactivation of Kaposi's Sarcoma-Associated Herpesvirus from Latency and Collaborates with HIV-1 Tat

Kaposi's sarcoma-associated herpesvirus (KSHV) infection was necessary but not sufficient for Kaposi's sarcoma (KS) development without other cofactors. Previously, we identified that both human immunodeficiency type 1 (HIV-1) Tat and herpes simplex virus 1 (HSV-1) were important cofactors reactivating KSHV from latency. Here, we further investigated the potential of herpes simplex virus 2 (HSV-2) to influence KSHV replication and examined the role of Tat in this procedure. We demonstrated that HSV-2 was a potentially important factor in the pathogenesis of KS, as determined by production of lytic phase mRNA transcripts, viral proteins and infectious viral particles in BCBL-1 cells. These results were further confirmed by an RNA interference experiment using small interfering RNA targeting KSHV Rta and a luciferase reporter assay testing Rta promoter-driven luciferase activity. Mechanistic studies showed that HSV-2 infection activated nuclear factor-kappa B (NF-κB) signaling pathway. Inhibition of NF-κB pathway enhanced HSV-2-mediated KSHV activation, whereas activation of NF-κB pathway suppressed KSHV replication in HSV-2-infected BCBL-1 cells. Additionally, ectopic expression of Tat enhanced HSV-2-induced KSHV replication. These novel findings suggest a role of HSV-2 in the pathogenesis of KS and provide the first laboratory evidence that Tat may participate HSV-2-mediated KSHV activation, implying the complicated pathogenesis of acquired immunodeficiency syndrome (AIDS)-related KS (AIDS-KS) patients.

Kaposi sarcoma-associated herpesvirus (KSHV) induces a functional tumor-associated phenotype for oral fibroblasts

The Kaposi sarcoma-associated herpesvirus (KSHV) is the causative agent of Kaposi sarcoma (KS), the most common HIV/AIDS-associated tumor worldwide. Involvement of the oral cavity portends a poor prognosis for patients with KS, but mechanisms for KSHV regulation of the oral tumor microenvironment are largely unknown. Infiltrating fibroblasts are found with KS lesions, and KSHV establishes latent infection within human primary fibroblasts in vitro, but contributions for KSHV-infected fibroblasts to the KS microenvironment have not been previously characterized. Secretion of pro-migratory factors and intratumoral invasion are characteristics of tumor-associated fibroblasts (TAF) found in the microenvironment of non-viral malignancies. In the present study, we show that latent KSHV infection of primary human fibroblasts isolated from the oral cavity enhances their secretion of KS-promoting cytokines and intrinsic invasiveness through VEGF-dependent mechanisms. Moreover, we find that KSHV induces these effects through Sp1- and Egr2-dependent transcriptional activation of the Extracellular Matrix MetalloPRoteinase INducer (emmprin). These data implicate KSHV activation of emmprin in the induction of a “TAF-like” phenotype for oral fibroblasts in the KS microenvironment and support the potential utility of targeting TAFs and/or emmprin in the treatment of oral KS.

KSHV activation of VEGF secretion and invasion for endothelial cells is mediated through viral upregulation of emmprin‐induced signal transduction

Kaposi's sarcoma-associated herpesvirus (KSHV) is the etiologic agent of Kaposi's sarcoma (KS)-one of the most common tumors arising in the setting of immune suppression. Hallmarks of KS lesions include KSHV-infected cells of endothelial lineage and neoangiogenesis. Promigratory factors secreted in the tumor microenvironment by KSHV-infected cells promote endothelial cell (EC) migration and angiogenesis but existing therapies targeting these pathways are not widely utilized. This underscores the need for additional characterization of KSHV-host interactions relevant to EC pathogenesis to identify new therapeutic targets. We recently demonstrated that de novo infection by KSHV promotes EC invasion through upregulation of extracellular matrix metalloproteinase inducer (emmprin)-a multifunctional glycoprotein previously shown to induce tumor cell invasion and regional angiogenesis through upregulation of signal transduction and promotion of tumor-stroma interactions. This study was undertaken to determine whether EC invasion for KSHV-infected cells is induced through activation of specific signal transduction pathways and proangiogenic factors by emmprin. We found that KSHV activation of emmprin induces PI3K/Akt- and mitogen-activated protein kinase (MAPK)-dependent secretion of vascular endothelial growth factor (VEGF). Functionally, EC invasion following de novo infection is induced by emmprin-dependent PI3K/Akt and MAPK activation of VEGF. These findings support the potential utility of targeting emmprin for reducing VEGF secretion and EC migration in the KS microenvironment.

An interleukin-6-related systemic inflammatory syndrome in patients co-infected with Kaposi sarcoma-associated herpesvirus and HIV but without Multicentric Castleman disease.

Kaposi sarcoma-associated herpesvirus (KSHV) is the causal agent for Kaposi sarcoma (KS) and multicentric Castleman disease (MCD) in human immunodeficiency virus (HIV)-infected patients. Patients with KSHV-MCD develop fevers, wasting, hypoalbuminemia, cytopenias, and hyponatremia that are related to overproduction of KSHV-encoded viral interleukin (IL)-6 (vIL-6) and human IL-6 (hIL-6). We identified 6 HIV-infected patients with KS or serological evidence of KSHV infection who had severe inflammatory MCD-like symptoms but in whom we could not diagnose MCD, and we hypothesized that these symptoms resulted from vIL-6 overproduction. Serum vIL-6 levels were assessed in these 6 patients and compared with levels in 8 control patients with symptomatic KSHV-MCD and 32 control patients with KS. KSHV viral load, serum hIL-6 level, and human IL-10 level were also evaluated. Patients with inflammatory MCD-like symptoms but without MCD had elevated vIL-6 levels, comparable with levels in patients with symptomatic KSHV-MCD, and had levels that were significantly greater than those in control patients with KS (P = .003). Elevated hIL-6, IL-10, and KSHV viral loads were also comparable to patients with symptomatic KSHV-MCD and significantly greater than those with KS. A subset of patients with HIV and KSHV co-infection, but without MCD, can develop severe systemic inflammatory symptoms associated with elevated levels of KSHV vIL-6, IL-6, and KSHV viral loads. Excess lytic activation of KSHV, production of the lytic gene product vIL6, and associated immunologic dysregulation may underlie the pathophysiology of these symptoms. This IL-6-related inflammatory syndrome is important to consider in critically ill patients with HIV and KSHV co-infection.

Direct Activation of Emmprin and Associated Pathogenesis by an Oncogenic Herpesvirus

Emmprin (extracellular matrix metalloproteinase inducer) is a multifunctional glycoprotein expressed by cancer cells and stromal cells in the tumor microenvironment. Through both direct effects within tumor cells and promotion of tumor-stroma interactions, emmprin induces tumor cell invasiveness and regional angiogenesis. The Kaposi's sarcoma-associated herpesvirus (KSHV) is a common etiology for cancers arising in the setting of immune suppression, including Kaposi's sarcoma and primary effusion lymphoma. However, whether emmprin expression and function are regulated by KSHV or other oncogenic viruses in the tumor microenvironment to promote viral cancer pathogenesis remains unknown. Fibroblasts and endothelial cells support latent KSHV infection and represent cellular components of Kaposi's sarcoma lesions. Therefore, we used primary human fibroblasts and endothelial cells to determine whether KSHV itself regulates emmprin expression, and whether KSHV-emmprin interactions mediate cell invasiveness. We found that KSHV promotes fibroblast and endothelial cell invasiveness following de novo infection through the upregulation of emmprin, and that this effect is mediated by the KSHV-encoded latency-associated nuclear antigen. We also found that emmprin promotes invasiveness, as well as colony formation, by primary effusion lymphoma cells derived from human tumors. Collectively, these data implicate KSHV activation of emmprin as an important mechanism for cancer progression and support the potential utility of targeting emmprin as a novel therapeutic approach for KSHV-associated tumors.

The interaction between KSHV RTA and cellular RBP-Jκ and their subsequent DNA binding are not sufficient for activation of RBP-Jκ

Kaposi's sarcoma-associated herpesvirus (KSHV) replication and transcription activator (RTA) is necessary and sufficient for the switch from KSHV latency to lytic replication. RTA activates promoters by several mechanisms. RTA can bind to sequences in viral promoters and activate transcription. In addition, RTA interacts with the cellular recombination signal sequence-binding protein-J kappa (RBP-Jκ), a transcriptional repressor, converts the repressor into an activator and activates viral promoters via RBP-Jκ. Because RBP-Jκ is required for RTA to activate lytic replication, it is important to understand how RTA cooperates with RBP-Jκ protein to activate KSHV lytic replication program. Previously, we identified an RTA mutant, RTA-K152E, which has a defect in its direct DNA-binding activity. In this report, the effect of the mutant RTA on KSHV activation via RBP-Jκ protein is examined. We demonstrate that RTA-K152E interacts with RBP-Jκ physically and the mutant RTA and RBP-Jκ complex binds to target DNA properly in vivo and in vitro. However, the complex of RTA-K152E and RBP-Jκ does not activate transcription. Furthermore, the RTA mutant (RTA-K12E) inhibits cellular Notch-mediated RBP-Jκ activation. These data collectively suggest that the complex between KSHV RTA and cellular RBP-Jκ and the subsequent DNA binding by the complex are not sufficient for the activation of RBP-Jκ protein. Other factor(s) whether additional cofactor(s) in the complex or the intrinsic conformation of RTA, are predicted to be required for the activation of RBP-Jκ protein by RTA.

Kaposi's Sarcoma-Associated Herpesvirus Induction of AP-1 and Interleukin 6 during Primary Infection Mediated by Multiple Mitogen-Activated Protein Kinase Pathways

Kaposi's sarcoma is an angioproliferative disseminated tumor of endothelial cells linked to infection with Kaposi's sarcoma-associated herpesvirus (KSHV). AP-1 transcription factors are involved in diverse biological processes, including infection and replication of viruses, cell growth, oncogenesis, angiogenesis, and invasion of cancer cells. Here we show that KSHV activates AP-1 during primary infection. The activation of AP-1 at the early stage of KSHV infection is mainly mediated by virus entry events. Concurrently, KSHV infection strongly activates MEK, JNK, and to a lesser extent, p38 mitogen-activated protein kinase (MAPK) pathways. Specific inhibitors or dominant negative constructs of MEK and JNK completely abolish AP-1 activation by KSHV, while those of p38 reduce it by half. Furthermore, individual MAPK pathways differentially regulate KSHV activation of AP-1 components. KSHV activation of AP-1 leads to the transcriptional induction of interleukin 6 (IL-6), which is inhibited by inhibitors or dominant negative constructs of MAPK pathways. Together, these results demonstrate that KSHV induces AP-1 and IL-6 during primary infection by modulating multiple MAPK pathways. Because of the diverse roles of IL-6, AP-1, and MAPK pathways in viral infection and tumor induction and promotion, these results have important implications in the pathogenesis of KSHV-induced malignancies.