Kaposi's sarcoma-associated herpesvirus: epidemiology, virology, and molecular biology

GRWD1-WDR5-MLL2 Epigenetic Complex Mediates H3K4me3 Mark and Is Essential for Kaposi's Sarcoma-Associated Herpesvirus-Induced Cellular Transformation

Infection by Kaposi's sarcoma-associated herpesvirus (KSHV) is causally associated with numerous cancers. The mechanism of KSHV-induced oncogenesis remains unclear. By performing a CRISPR-Cas9 screening in a model of KSHV-induced cellular transformation of primary cells, we identified epigenetic regulators that were essential for KSHV-induced cellular transformation. Examination of TCGA data sets of the top 9 genes, including glutamate-rich WD repeat containing 1 (GRWD1), a WD40 family protein upregulated by KSHV, that had positive effects on cell proliferation and survival of KSHV-transformed cells (KMM) but not the matched primary cells (MM), uncovered the predictive values of their expressions for patient survival in numerous types of cancer. We revealed global epigenetic remodeling including H3K4me3 epigenetic active mark in KMM cells compared to MM cells. Knockdown of GRWD1 inhibited cell proliferation, cellular transformation, and tumor formation and caused downregulation of global H3K4me3 mark in KMM cells. GRWD1 interacted with WD repeat domain 5 (WDR5), the core protein of H3K4 methyltransferase complex, and several H3K4me3 methyltransferases, including myeloid leukemia 2 (MLL2). Knockdown of WDR5 and MLL2 phenocopied GRWD1 knockdown, caused global reduction of H3K4me3 mark, and altered the expression of similar sets of genes. Transcriptome sequencing (RNA-seq) and chromatin immunoprecipitation sequencing (ChIP-seq) analyses further identified common and distinct cellular genes and pathways that were regulated by GRWD1, WDR5, and MLL2. These results indicate that KSHV hijacks the GRWD1-WDR5-MLL2 epigenetic complex to regulate H3K4me3 methylation of specific genes, which is essential for KSHV-induced cellular transformation. Our work has identified an epigenetic complex as a novel therapeutic target for KSHV-induced cancers. IMPORTANCE By performing a genome-wide CRISPR-Cas9 screening, we have identified cellular epigenetic regulators that are essential for KSHV-induced cellular transformation. Among them, GRWD1 regulates epigenetic active mark H3K4me3 by interacting with WDR5 and MLL2 and recruiting them to chromatin loci of specific genes in KSHV-transformed cells. Hence, KSHV hijacks the GRWD1-WDR5-MLL2 complex to remodel cellular epigenome and induce cellular transformation. Since the dysregulation of GRWD1 is associated with poor prognosis in several types of cancer, GRWD1 might also be a critical driver in other viral or nonviral cancers.

Tissue Pathogens and Cancers: A Review of Commonly Seen Manifestations in Histo- and Cytopathology

Tissue pathogens are commonly encountered in histopathology and cytology practice, where they can present as either benign mimickers of malignancy or true malignancies. The aim of this review is to provide a timely synthesis of our understanding of these tissue pathogens, with an emphasis on pertinent diagnostic conundrums associated with the benign mimickers of malignancy that can be seen with viral infections and those which manifest as granulomas. The oncogenic pathogens, including viruses, bacteria, and parasites, are then discussed with relationship to their associated malignancies. Although not exhaustive, the epidemiology, clinical manifestations, pathogenesis, and histological findings are included, along with a short review of emerging therapies.

Human Herpesvirus 6 and Malignancy: A Review

In order to determine the role of human herpesvirus 6 (HHV-6) in human disease, several confounding factors, including methods of detection, types of controls, and the ubiquitous nature of the virus, must be considered. This is particularly problematic in the case of cancer, in which rates of detection vary greatly among studies. To determine what part, if any, HHV-6 plays in oncogenesis, a review of the literature was performed. There is evidence that HHV-6 is present in certain types of cancer; however, detection of the virus within tumor cells is insufficient for assigning a direct role of HHV-6 in tumorigenesis. Findings supportive of a causal role for a virus in cancer include presence of the virus in a large proportion of cases, presence of the virus in most tumor cells, and virus-induced in-vitro cell transformation. HHV-6, if not directly oncogenic, may act as a contributory factor that indirectly enhances tumor cell growth, in some cases by cooperation with other viruses. Another possibility is that HHV-6 may merely be an opportunistic virus that thrives in the immunodeficient tumor microenvironment. Although many studies have been carried out, it is still premature to definitively implicate HHV-6 in several human cancers. In some instances, evidence suggests that HHV-6 may cooperate with other viruses, including EBV, HPV, and HHV-8, in the development of cancer, and HHV-6 may have a role in such conditions as nodular sclerosis Hodgkin lymphoma, gastrointestinal cancer, glial tumors, and oral cancers. However, further studies will be required to determine the exact contributions of HHV-6 to tumorigenesis.

Factors affecting progression-free survival in non-HIV-related Kaposi sarcoma

BACKGROUND

Non-HIV related Kaposi sarcoma (NHKS) is a rare indolent neoplasm which is more common around Mediterranean origin. Data concerning factors that influence progression-free survival (PFS) for NHKS are insufficient. The purpose of present retrospective analysis was to distinguish the factors affecting PFS in patients with NHKS.

METHODS

A hundred and twenty-eight consecutive patients with NHKS who were treated or observed between 1997 and 2014 at Istanbul University Institute of Oncology were included into the study. Treatment response and progression definitions were determined according to different treatment modalities administered at first line.

RESULTS

Majority of patients were male (n = 97, 75.8%). Median age of the whole group was 66 years (28-85). Of the patients, 15 patients were immunosuppressant, whereas 113 patients had no disease that caused immunosuppression. Patients were treated with local excision (n = 57, 44.5%), chemotherapy (n = 32, 25.0%) and/or radiotherapy (n = 13, 10.2%) or observed without treatment (n = 26, 20.3%). At a median follow-up of 28 months, 71 (55.5%) patients had progression, while 3 patients (2.3%) died of NHKS. On univariate analysis, patients who had hypertension (HT) had poorer PFS compared with others (19 ± 12 versus 41 ± 22 months; p = 0.03), whereas plaque formation was associated with better outcome (25 ± 9 versus 54 ± 12 months; p = 0.03). In addition, heavy smoking (≥40 pack-years) had a borderline significance regarding better PFS time (23 ± 24 versus 45 ± 38 months, p = 0.06). On multivariate analysis, none of factors evaluated had any impact on PFS.

CONCLUSIONS

HT was correlated with poorer outcome among NHKS patients. Patients with plaque formation and ≥40 pack-years of smoking had better PFS than others.

The conundrum of causality in tumor virology: the cases of KSHV and MCV

Controversy has plagued tumor virology since the first tumor viruses were described over 100 years ago. Methods to establish cancer causation, such as Koch's postulates, work poorly or not at all for these viruses. Kaposi's sarcoma herpesvirus (KSHV/HHV8) and Merkel cell polyomavirus (MCV) were both found using nucleic acid identification methods but they represent opposite poles in the patterns for tumor virus epidemiology. KSHV is uncommon and has specific risk factors that contribute to infection and subsequent cancers. MCV and Merkel cell carcinoma (MCC), in contrast, is an example in which mutations to our normal viral flora contribute to cancer. Given the near-ubiquity of human MCV infection, establishing cancer causality relies on molecular evidence that does not fit comfortably within traditional infectious disease epidemiological models. These two viruses reveal some of the challenges and opportunities for inferring viral cancer causation in the age of molecular biology.

A critical Sp1 element in the rhesus rhadinovirus (RRV) Rta promoter confers high-level activity that correlates with cellular permissivity for viral replication

KSHV establishes characteristic latent infections in vitro, while RRV, a related macaque rhadinovirus, establishes characteristic permissive infections with virus replication. We identified cells that are not permissive for RRV replication and recapitulate the latent KSHV infection and reactivation processes. The RRV replication and transactivator (Rta) promoter was characterized in permissive and non-permissive cells and compared to the KSHV Rta promoter. Both promoters contained a critical Sp1 element, had equivalent activities in different cell types, and were inhibited by LANA. RRV and KSHV infections were non-permissive in cells with low Rta promoter activity. While RRV infections were permissive in cells with high basal promoter activity, KSHV infections remained non-permissive. Our studies suggest that RRV lacks the Rta-inducible LANA promoter that is responsible for LANA inhibition of the KSHV Rta promoter and induction of latency during KSHV infection. Instead, the outcome of RRV infection is determined by host factors, such as Sp1.

Kaposi sarcoma-associated herpes virus and response to antiretroviral therapy: a prospective study of HIV-infected adults

BACKGROUND

The possible impact of coinfection with the Kaposi sarcoma-associated herpes virus (KSHV) on the response to antiretroviral therapy (ART) is unknown. Prospective studies are rare, particularly in Africa.

METHODS

We enrolled a prospective cohort of HIV-infected adults initiating ART in Johannesburg, South Africa. The subjects were defined as seropositive to KSHV if they were reactive to either KSHV lytic K8.1 or latent Orf73 antigen or to both. The subjects were followed from ART initiation until 18 months of treatment. HIV viral load and CD4 counts were tested 6 monthly. Linear generalized estimating and log-binomial regression models were used to estimate the effect of KSHV infection on immunologic recovery and response and HIV viral load suppression within 18 months after ART initiation.

RESULTS

Three hundred eighty-five subjects initiating ART from November 2008 to March 2009 were considered to be eligible including 184 (48%) KSHV+. The KSHV+ group was similar to the KSHV- in terms of age, gender, initiating CD4 count, body mass index, tuberculosis, and hemoglobin levels. The KSHV+ group gained a similar number of cells at 6 [difference of 10 cells per cubic millimeter, 95% confidence interval (CI): -11 to 31], 12 (3 cells per cubic millimeter, 95% CI: -19 to 25), and 18 months (24 cells per cubic millimeter, 95% CI: -13 to 61) compared with that gained by the KSHV- group. Adjusted relative risk of failure to suppress viral load to <400 copies per milliliter (1.03; 95% CI: 0.90 to 1.17) were similar for KSHV+ and KSHV- by 6 months on treatment.

CONCLUSIONS

In a population with a high KSHV prevalence, HIV-positive adults coinfected with KSHV achieved similar immunologic and virologic responses to ART early after treatment initiation compared with those with KSHV-.

Construction and identification of recombinant lentiviral vector containing HIV-1 Tat gene and its expression in 293T cells

Objective

To construct a lentiviral vector expressing HIV-1 Tat and identify its expression in 293T cells.

Methods

The gene fragment of HIV-1 Tat₁₀₁ was subcloned to lentiviral transfer vector pHAGE-CMV-MCS-IZsGreen, which was named pHAGE-Tat. Then the constructed pHAGE-Tat was used to co-transfect the packing 293T cells, together with the packaging plasmids pMD2.G and psPAX2. The packaged viral particles designated LV-Tat were used to infect the 293T cells and the viral titer was calculated. The expression of HIV-1 Tat in 293T cells was confirmed using RT-PCR and western blot.

Results

The recombinant lentiviral vector was successfully constructed and could express HIV-1 Tat in 293T cells. The virus titer was 5.73×10⁶ ifu/ml.

Conclusion

The successfully constructed recombinant lentiviral vector makes a strong foundation for further exploring the possible role of HIV-1 Tat in the development of prostate cancer.

Cutaneous manifestations of gastrointestinal disease: part II

The gastrointestinal (GI) and cutaneous organ systems are closely linked. In part I of this continuing medical education article, the intricacies of this relationship were explored as they pertained to hereditary polyposis disorders, hamartomatous disorders, and paraneoplastic disease. Part II focuses on the cutaneous system's links to inflammatory bowel disease and vascular disorders. An in-depth analysis of inflammatory bowel disease skin findings is provided to aid dermatologists in recognizing and facilitating early consultation and intervention by gastroenterologists. Cutaneous signs of inflammatory bowel disease include fissures and fistulae, erythema nodosum, pyoderma gangrenosum, pyostomatitis vegetans, oral aphthous ulcers, cutaneous polyarteritis nodosa, necrotizing vasculitis, and epidermolysis bullosa acquisita. Additional immune-mediated conditions, such as diverticulitis, bowel-associated dermatosis-arthritis syndrome, Henoch-Schönlein purpura, dermatitis herpetiformis, and Degos disease, in which the skin and GI system are mutually involved, will also be discussed. Genodermatoses common to both the GI tract and the skin include Hermansky-Pudlak syndrome, pseudoxanthoma elasticum, Ehlers-Danlos syndrome, hereditary hemorrhagic telangiectasia, and blue rubber bleb nevus syndrome. Kaposi sarcoma is a neoplastic disease with lesions involving both the skin and the gastrointestinal tract. Acrodermatitis enteropathica, a condition of zinc deficiency, likewise affects both the GI and dermatologic systems. These conditions are reviewed with updates on the genetic basis, diagnostic and screening modalities, and therapeutic options. Finally, GI complications associated with vascular disorders will also be discussed.

Increased risk of cancer after Bell's palsy: a 5-year follow-up study

Reactivation of latent herpes simplex virus (HSV) type I or varicella-zoster virus (VZV) has been recognized as the most common pathomechanism underlying Bell's palsy. There is also increased reactivation of HSV or VZV in patients with immunosuppressed states and in cancer patients. The purpose of this study was to investigate the risk for cancer during a 5-year follow-up period after diagnosis of Bell's palsy by using a population-based dataset in Taiwan. We used data from the "Longitudinal Health Insurance Database". We identified 2,618 patients with Bell's palsy as the study cohort and randomly selected 13,090 patients to be used as a comparison cohort. Cox proportional hazards regression was performed to compare the 5-year risk of subsequent cancer between the study and comparison cohorts. We found that the incidence of cancer was 1.55 (95 % CI 1.35-1.78) per 100 person-years for patients with Bell's palsy and 1.09 (95 % CI 1.02-1.18) per 100 person-years for comparison patients. After censoring cases that died from non-cancer causes during the follow-up period and adjusting for urbanization, monthly income, geographic region, and diabetes, the hazard ratio (HR) for cancer during the 5-year follow-up period for patients with Bell's palsy was 1.43 times that for comparison patients (95 % CI 1.22-1.73). There was a particularly increased risk of oral cancer (HR = 2.49; 95 % CI 1.54-4.03) for patients with Bell's palsy compared with the other patients. We conclude that patients with Bell's palsy were at significant risk of cancer during a 5-year follow-up period after diagnosis.

Characterization of Kaposi's Sarcoma-Associated Herpesvirus-Related Lymphomas by DNA Microarray Analysis

Among herpesviruses, γ-herpesviruses are supposed to have typical oncogenic activities. Two human γ-herpesviruses, Epstein-Barr virus (EBV) and Kaposi's sarcoma-associated herpesvirus (KSHV), are putative etiologic agents for Burkitt lymphoma, nasopharyngeal carcinoma, and some cases of gastric cancers, and Kaposi's sarcoma, multicentric Castleman's disease, and primary effusion lymphoma (PEL) especially in AIDS setting for the latter case, respectively. Since such two viruses mentioned above are highly species specific, it has been quite difficult to prove their oncogenic activities in animal models. Nevertheless, the viral oncogenesis is epidemiologically and/or in vitro experimentally evident. This time, we investigated gene expression profiles of KSHV-oriented lymphoma cell lines, EBV-oriented lymphoma cell lines, and T-cell leukemia cell lines. Both KSHV and EBV cause a B-cell-originated lymphoma, but the gene expression profiles were typically classified. Furthermore, KSHV could govern gene expression profiles, although PELs are usually coinfected with KSHV and EBV.

Merkel cell carcinoma: a virus-induced human cancer

Merkel cell polyomavirus (MCV) is the first polyomavirus directly linked to human cancer, and its recent discovery helps to explain many of the enigmatic features of Merkel cell carcinoma (MCC). MCV is clonally integrated into MCC tumor cells, which then require continued MCV oncoprotein expression to survive. The integrated viral genomes have a tumor-specific pattern of tumor antigen gene mutation that incapacitates viral DNA replication. This human cancer virus provides a new model in which a common, mostly harmless member of the human viral flora can initiate cancer if it acquires a precise set of mutations in a host with specific susceptibility factors, such as age and immune suppression. Identification of this tumor virus has led to new opportunities for early diagnosis and targeted treatment of MCC.

Viral oncogenesis and its role in nonmelanoma skin cancer

In recent years, the contribution of viruses to cutaneous oncogenesis has steadily gained recognition. The archetype is human herpesvirus 8, which is well established as the causative agent in Kaposi sarcoma. Other viruses believed to play a role in nonmelanoma skin cancer include human papillomavirus and the recently described Merkel cell polyomavirus. We review the mechanisms by which these three viruses interact with the host cell, ultraviolet radiation and immunosuppression to result in carcinogenesis.

Why do viruses cause cancer? Highlights of the first century of human tumour virology

The year 2011 marks the centenary of Francis Peyton Rous's landmark experiments on an avian cancer virus. Since then, seven human viruses have been found to cause 10-15% of human cancers worldwide. Viruses have been central to modern cancer research and provide profound insights into both infectious and non-infectious cancer causes. This diverse group of viruses reveals unexpected connections between innate immunity, immune sensors and tumour suppressor signalling that control both viral infection and cancer. This Timeline article describes common features of human tumour viruses and discusses how new technologies can be used to identify infectious causes of cancer.

Viruses and human cancer: from detection to causality

The study of cancer is incomplete without taking into consideration of tumorigenic viruses. Initially, searches for human cancer viruses were fruitless despite an expansion of our knowledge in the same period concerning acute-transforming retroviruses in animals. However, over the last 40 years, we have witnessed rapid progress in the tumor virology field. Currently, acknowledged human cancer viruses include Epstein-Barr virus, hepatitis B virus, hepatitis C virus, high-risk human papilloma viruses, human T-cell lymphotropic virus type 1 and Kaposi's sarcoma-associated herpesvirus. Extensive epidemiological and mechanistic studies have led to the development of novel preventive and therapeutic approaches for managing some of these infections and associated cancers. In addition, recent advances in molecular technologies have enabled the discovery of a new potential human tumor virus, Merkel cell polyomavirus, but its association with cancer remains to be validated. It is anticipated that in the next few decades many additional human cancer viruses will be discovered and the mechanisms underlying viral oncogenesis delineated. Thus, it can be expected that better tools for preventing and treating virus-associated cancer will be available in the near future.

Understanding pathogenetic aspects and clinical presentation of primary effusion lymphoma through its derived cell lines

Primary effusion lymphoma (PEL) is a very rare subgroup of B-cell lymphomas presenting as pleural, peritoneal and pericardial neoplastic effusions in the absence of a solid tumor mass or recognizable nodal involvement. There is strong evidence that Kaposi's sarcoma-associated herpesvirus (KSHV) is a causal agent of PEL. PEL tumor cells are latently infected by KSHV with consistent expression of several viral proteins and microRNAs that can affect cellular proliferation, differentiation and survival. The most relevant data on pathogenesis and biology of KSHV have been provided by studies on PEL-derived cell lines. Fourteen continuous cell lines have been established from the malignant effusions of patients with AIDS-associated and non-AIDS-associated PEL. These KSHV+ EBV+/- cell lines are well characterized, authenticated and mostly available from public biological resource centers. The PEL cell lines display unique features and are clearly distinct from other lymphoma cell lines. PEL cell lines represent an indispensable tool for the understanding of KSHV biology and its impact on the clinical manifestation of PEL. Studies on PEL cell lines have shown that a number of viral genes, expressed during latency or lytic life cycle, have effects on cell binding, proliferation, angiogenesis and inflammation. Also, PEL cell lines are important model systems for the study of the disorder of PEL including the lack of invasive or destructive growth patterns and the peculiar propensity of PEL to involve body cavity surfaces.

Differential impact of ageing on cellular and humoral immunity to a persistent murine gamma-herpesvirus

Background

Oncogenic γ-herpesviruses establish life-long infections in their hosts and control of these latent infections is dependent on continual immune surveillance. Immune function declines with age, raising the possibility that immune control of γ-herpesvirus infection becomes compromised with increasing age, allowing viral reactivation and/or increased latent load, both of which are associated with the development of malignancies.

Results

In this study, we use the experimental mouse γ-herpesvirus model, γHV68, to investigate viral immunity in aged mice. We found no evidence of viral recrudescence or increased latent load in aged latently-infected mice, suggesting that effective immune control of γ-herpesvirus infection remains intact with ageing. As both cellular and humoral immunity have been implicated in host control of γHV68 latency, we independently examined the impact of ageing on γHV68-specific CD8 T cell function and antibody responses. Virus-specific CD8 T cell numbers and cytolytic function were not profoundly diminished with age. In contrast, whereas ELISA titers of virus-specific IgG were maintained over time, there was a progressive decline in neutralizing activity. In addition, although aged mice were able to control de novo acute infection with only slightly delayed viral clearance, serum titers of neutralizing antibody were reduced in aged mice as compared to young mice.

Conclusion

Although there is no obvious loss of immune control of latent virus, these data indicate that ageing has differential impacts on anti-viral cellular and humoral immune protection during persistent γHV68 infection. This observation has potential relevance for understanding γ-herpesvirus immune control during disease-associated or therapeutic immunosuppression.

gamma-Herpesvirus-induced protection against bacterial infection is transient

Herpesviruses are widely disseminated in the population and establish lifelong latency, which is associated with a variety of pathological consequences. A recent report showed that mice latently infected with either murine gamma-herpesvirus-68 (gammaHV68) or murine cytomegalovirus (mCMV), mouse pathogens genetically similar to the human herpesviruses, Epstein-Barr virus, Kaposi's sarcoma-associated herpesvirus, and cytomegalovirus, had enhanced resistance to subsequent bacterial infection, suggesting protective as well as deleterious effects of latency. Here we confirm that latent gammaHV68 infection confers protection against subsequent infection with Listeria monocytogenes. However, the effect is transient, lasting only a few months.

Immune evasion in Kaposi's sarcoma-associated herpes virus associated oncogenesis

A hallmark of herpesviruses is a lifelong persistent infection, which often leads to diseases upon immune suppression of infected host. Kaposi's sarcoma-associated herpesvirus (KSHV), also known as human herpesvirus 8 (HHV8), is etiologically linked to the development of Kaposi's sarcoma (KS), primary effusion lymphoma (PEL), and Multicentric Castleman's disease (MCD). In order to establish a persistent infection, KSHV dedicates a large portion of its genomic information to sabotage almost every aspect of host immune system. Thus, understanding the interplay between KSHV and the host immune system is important in not only unraveling the complexities of viral persistence and pathogenesis, but also discovering novel therapeutic targets. This review summarizes current knowledge of host immune evasion strategies of KSHV and their contributions to KSHV-associated diseases.

Risk factors for human Herpesvirus 8 infection and AIDS-associated Kaposi's sarcoma among men who have sex with men in a European multicentre study

We aimed to identify risk factors for Kaposi's sarcoma (KS) among HIV-positive patients and behaviors associated with human Herpesvirus 8 (HHV-8) infection, as well as to assess KS incidence and mortality rates longitudinally. To fulfill the first objective, a European case-control study was designed in the early 1990s (each KS case was matched to 2 controls with another AIDS indicative disease). After the discovery of HHV-8, serology testing enabled us to assess risk factors for KS development among HHV-8 and HIV-1 coinfected men who have sex with men (MSM), as well as risk factors for HHV-8 infection. HHV-8 seroprevalence was determined using a latent immunofluorescence assay. Relevant information was obtained by means of a questionnaire and medical charts review. Assessment of risk factors for KS development and HHV-8 infection was performed using conditional and unconditional logistic regression models, respectively. A low CD4 count was the only significant risk factor for KS. HHV-8 infection was most strongly linked to the number of life-time sex partners, and multiple body fluids such as saliva and semen are quite likely involved in sexual transmission. Longitudinal follow up showed a significant protective role for highly-active antiretroviral therapy (HAART) both on KS development and mortality of KS patients. Although more conclusive data from cohort studies are needed to better define specific transmission mechanisms for HHV-8, our results contribute to explain why KS incidence is higher among MSM, and the decreasing KS incidence trend observed in countries with universal access to HAART.

Intracellular-activated Notch1 can reactivate Kaposi's sarcoma-associated herpesvirus from latency

Kaposi's sarcoma-associated herpesvirus (KSHV) establishes a predominantly latent infection in the infected host. Importantly, during latency, only a small number of viral encoded genes are expressed. This viral gene expression pattern contributes to the establishment of long-term infection as well as the ability of the virus to evade the immune system. Previous studies have been shown that the replication and transcription activator (RTA) encoded by ORF50 activates it downstream genes and initiates viral lytic reactivation through functional interaction with RBP-Jkappa, the major downstream effector of the Notch signaling pathway. This indicates that RTA can usurp the conserved Notch signaling pathway and mimic the activities of intracellular Notch1 to modulate gene expression. In this report, we show that the activated intracellular domain of Notch1 (ICN) is aberrantly accumulated in KSHV latently infected pleural effusion lymphoma (PEL) cells. ICN activated the RTA promoter in a dose-dependent manner, and forced expression of ICN in latently infected KSHV-positive cells initiated full blown lytic replication with the production of infectious viral progeny. However, latency-associated nuclear antigen (LANA) which is predominantly expressed during latency can specifically down-modulate ICN-mediated transactivation of RTA and so control KSHV for lytic reactivation. These results demonstrate that LANA can inhibit viral lytic replication by antagonizing ICN function and suggest that LANA is a critical component of the regulatory control mechanism for switching between viral latent and lytic replication by directly interacting with effectors of the conserved cellular Notch1 pathway.

Kaposi's sarcoma-associated herpesvirus: clinical, diagnostic, and epidemiological aspects

Kaposi's sarcoma-associated herpesvirus (KSHI) is one of the few viruses proven to be associated with tumorigenesis in humans. Its causal association with all clinical and epidemiological variants of Kaposi's sarcoma (KS) is well established. KSHV is also involved in the pathogenesis of primary effusion lymphoma (PEL) and a subset of multicentric Castleman's disease (MCD). Possible associations of KSHV with other clinical settings have been extensively examined. The findings from several of these studies are contradictory and are yet to be resolved. Concentrated effort over the last decade, since the initial discovery of KSHV, led to the development of several experimental systems that resulted in a better comprehension of the biological characteristics of KSHV and set the stage for the understanding of mechainisms by which diseases are induced by the virus. The development of molecular, histological, and serological tools for KSHV diagnosis allowed researchers to track the transmission and to study the epidemiology of KSHV. These assays have been applied, in particular in ambiguous cases, in order to confirm clinically and pathologically based diagnoses. Here, we review the advances in the clinical, experimental, diagnostic, and epidemiological research of KSHV.

Induction of Kaposi's sarcoma-associated herpesvirus latency-associated nuclear antigen by the lytic transactivator RTA: a novel mechanism for establishment of latency

Kaposi's sarcoma-associated herpesvirus (KSHV) is the etiological agent contributing to development of Kaposi's sarcoma, primary effusion lymphoma, and multicentric Castleman desease. Following primary infection, latency is typically established. However, the mechanism by which KSHV establishes latency is not understood. We have reported that the latency-associated nuclear antigen (LANA) can repress RTA (for replication and transcription activator) expression by down-regulating its promoter. In this study, we show that RTA is associated with the virion particle. We also show that RTA can activate the LANA promoter and induce LANA expression in transient reporter assays. Additionally, the transcription of RTA correlates with LANA expression in the early stages of de novo infection of KSHV, and induction of LANA transcription is responsive to induction of RTA with an inducible system. This induction in LANA transcription was dependent on recombination signal sequence binding protein Jkappa (RBP-Jkappa), as a RBP-Jkappa-deficient cell line was significantly delayed and inefficient in LANA transcription with expression of RTA. These studies suggest that RTA contributes to establishment of KSHV latency by activating LANA expression in the early stages of infection by utilizing the major effector of the Notch signaling pathway RBP-Jkappa. This describes a feedback mechanism by which LANA and RTA can regulate each other and is likely to be a key event in the establishment of KSHV latency.

Kaposi's sarcoma-associated herpesvirus reactivation is regulated by interaction of latency-associated nuclear antigen with recombination signal sequence-binding protein Jkappa, the major downstream effector of the Notch signaling pathway

Kaposi's sarcoma-associated herpesvirus (KSHV) is the major biological cofactor contributing to development of Kaposi's sarcoma. KSHV establishes a latent infection in human B cells expressing the latency-associated nuclear antigen (LANA), a critical factor in the regulation of viral latency. LANA controls KSHV latent infection through repression of RTA, an activator of many lytic promoters. RTA activates the expression of several lytic viral genes by interacting with recombination signal sequence-binding protein Jkappa (RBP-Jkappa), a transcriptional repressor and the target of the Notch signaling pathway. The recognition that a number of KSHV lytic gene promoters, including RTA, contain RBP-Jkappa binding sites raised the possibility that RBP-Jkappa-mediated repression may be central to the establishment of latency. Here, we tested this hypothesis by examining the regulation of RTA by LANA through binding to RBP-Jkappa. This study demonstrates that LANA physically associates with RBP-Jkappa in vitro and in KSHV-infected cells, with the complex formed capable of binding to RBP-Jkappa cognate sequences. RBP-Jkappa binding sites within the RTA promoter have been found to be critical for LANA-mediated repression. Our study describes a novel mechanism through which LANA maintains KSHV latency by targeting a major downstream effector of the Notch signaling pathway.

Inhibiting primary effusion lymphoma by lentiviral vectors encoding short hairpin RNA

We use lentiviral-delivered RNA interference (RNAi) to inhibit the growth of a model of primary effusion lymphoma (PEL) in vitro and in vivo. RNAi is a phenomenon allowing the sequence-specific targeting and silencing of exogenous and endogenous gene expression and is being applied to inhibit viral replication both in vitro and in vivo. We show that silencing of genes believed to be essential for the Kaposi sarcoma-associated herpesvirus (KSHV) latent life cycle (the oncogenic cluster) has a varied effect in PEL cell lines cultured in vitro, however, concomitant silencing of the viral cyclin (vcyclin) and viral FLICE (Fas-associating protein with death domain-like interleukin-1β-converting enzyme) inhibitory protein (vFLIP) caused efficient apoptosis in all PEL lines tested. We demonstrate that in a murine model of PEL, lentiviral-mediated RNA interference both inhibits development of ascites and can act as a treatment for established ascites. We also show that the administered lentiviral vectors are essentially limited to the peritoneal cavity, which has advantages for safety and dosage in a therapeutic setting. This shows the use of lentiviral-mediated RNA interference in vivo as a potential therapeutic against a virally driven human cancer.

Evidence for both lytic replication and tightly regulated human herpesvirus 8 latency in circulating mononuclear cells, with virus loads frequently below common thresholds of detection

To address whether human herpesvirus 8 (HHV-8) DNA in peripheral blood mononuclear cells (PBMCs) might be the product of latent or lytic infection and to shed light on sporadic detection of HHV-8 DNA in individuals seropositive for the virus, we studied the frequency of infected cells, total virus load, and virus load per infected cell in PBMCs from men coinfected with HHV-8 and human immunodeficiency virus (HIV), some of whom had Kaposi's sarcoma. The low frequencies of infected cells detected (fewer than one per million cells in some individuals) suggest that the prevalence of the virus in circulating leukocytes was underestimated in previous studies that employed more conventional sampling methods (single, small-volume specimens). Mean virus loads ranged from 3 to 330 copies per infected PBMC; these numbers can represent much higher loads in individual lytically infected cells (>10(3) genomes/cell) in mixtures that consist predominantly of latently (relatively few genomes) infected cells. The presence in some subjects of high HHV-8 mean genome copy numbers per infected cell, together with viral DNA being found in plasma only from subjects with positive PBMCs, supports earlier suggestions that the virus can actively replicate in PBMCs. In some individuals, mean virus loads were less than 10 genomes per infected cell, suggesting a tightly controlled purely latent state. HHV-8 genome copy numbers are substantially higher in latently infected cells derived from primary effusion lymphomas; thus, it appears that HHV-8 is able to adopt more than one latency program, perhaps analogous to the several types of Epstein-Barr virus latency.

Role of protein kinase C delta in reactivation of Kaposi's sarcoma-associated herpesvirus

TPA (12-O-tetradecanoylphorbol-13-acetate), a well-known activator of protein kinase C (PKC), can experimentally induce reactivation of Kaposi's sarcoma-associated herpesvirus (KSHV) in certain latently infected cells. We selectively blocked the activity of PKC isoforms by using GF 109203X or rottlerin and demonstrated that this inhibition largely decreased lytic KSHV reactivation by TPA. Translocation of the PKCdelta isoform was evident shortly after TPA stimulation. Overexpression of the dominant-negative PKCdelta mutant supported an essential role for the PKCdelta isoform in virus reactivation, yet overexpression of PKCdelta alone was not sufficient to induce lytic reactivation of KSHV, suggesting that additional signaling molecules participate in this pathway.

Poly(ADP-ribose) polymerase 1 binds to Kaposi's sarcoma-associated herpesvirus (KSHV) terminal repeat sequence and modulates KSHV replication in latency

During latency, Kaposi's sarcoma-associated herpesvirus (KSHV) is thought to replicate once and to be partitioned in synchrony with the cell cycle of the host. In this replication cycle, the KSHV terminal repeat (TR) sequence functions as a replication origin, assisted by the latency-associated nuclear antigen (LANA). Thus, TR seems to function as a cis element for the replication and partitioning of the KSHV genome. Viral replication and partitioning are also likely to require cellular factors that interact with TR in either a LANA-dependent or -independent manner. Here, we sought to identify factors that associate with TR by using a TR DNA column and found that poly(ADP-ribose) polymerase 1 (PARP1) and known replication factors, including ORC2, CDC6, and Mcm7, bound to TR. PARP1 bound directly to a specific region within TR independent of LANA, and LANA was poly(ADP-ribosyl)ated by PARP1. Drugs such as hydroxyurea and niacinamide, which raise or lower PARP activity, respectively, affected the virus copy number in infected cells. Thus, the poly(ADP-ribosyl)ation status of LANA appears to affect the replication and/or maintenance of the viral genome. Drugs that specifically up-regulate PARP activity may lead to the disappearance of latent KSHV.

Repeated measures study of human herpesvirus 8 (HHV-8) DNA and antibodies in men seropositive for both HHV-8 and HIV

OBJECTIVE

To study the natural history and pathogenesis of human herpesvirus 8 (HHV-8) infection in HHV-8-seropositive, immunosuppressed men.

DESIGN

Longitudinal study of 87 HHV-8- and HIV-seropositive men [42 with Kaposi's sarcoma (KS)] during four visits over a 2 month period.

METHODS

: Patients provided oral fluid and blood. HHV-8 antibody titers were measured with peptide-based enzyme-linked immunosorbent assays (ELISA) for ORF65 and K8.1; HHV-8 DNA was detected with polymerase chain reaction ELISA.

RESULTS

HHV-8 DNA was present in oral fluid or peripheral blood mononuclear cells (PBMC) at one or more of the four visits in 71% of men with KS and 56% of men without KS. The strongest correlate of HHV-8 DNA in PBMC was the presence of KS [odds ratio (OR), 8.7; 95% confidence interval (CI), 3.4-22]. Detection of HHV-8 DNA in oral fluid or PBMC was often intermittent, but individuals who shed virus at one time point were more likely to shed at other times. Some men had incomplete epitope recognition in their anti-HHV-8 antibody response. High antibody titers were associated with the absence of circulating HHV-8, particularly for the ORF65 seroassay (OR, 0.16; 95% CI, 0.05-0.51).

CONCLUSIONS

Among HHV-8 seropositive men, circulating virus is common even in the absence of disease. The link between KS and HHV-8 DNA in PBMC suggests that anti-herpes drugs may impede KS development or progression. Seroassays should target multiple epitopes to achieve maximal sensitivity. HHV-8 replication may be limited by high antibody titers or other immune function for which antibodies are a marker.

Functional co-operation between the Kaposi's sarcoma-associated herpesvirus ORF57 and ORF50 regulatory proteins

Kaposi's sarcoma (KS)-associated herpesvirus (KSHV) proteins ORF57 (also known as MTA) and ORF50 (also known as RTA) act post-transcriptionally and transcriptionally to regulate viral lytic gene expression and synergistically activate certain early and late KSHV promoters. When ORF57 and ORF50 were co-expressed, they co-operatively stimulated expression from the promoter of the immediate-early ORF50 gene itself. Co-immunoprecipitations with extracts of KSHV-infected cells showed that ORF57 and ORF50 proteins were present in the same complex. Using the pull-down assay with extracts of KSHV-infected cells, ORF50 protein was shown to interact with a glutathione S-transferase-ORF57 fusion protein. A chromatin immunoprecipitation assay showed that ORF50 promoter sequences were preferentially associated with immunoprecipitated chromatin using both anti-ORF50 and anti-ORF57 antibodies consistent with both an in vivo physical association between ORF57 and ORF50 and a potential role for ORF57 at the transcriptional level. This is the first demonstration of an interaction between these two lytic regulatory proteins in a gammaherpesvirus. Expression of ORF50 protein is sufficient to induce lytic replication in latently infected cells and may determine viral host range, spread and KS pathogenesis in vivo. A new insight into the co-ordinated activities of these two key regulatory proteins is provided in which upregulation of the ORF50 promoter with augmentation of ORF50 activity by ORF57 protein, and vice versa, would facilitate the cascade of lytic viral gene expression, thereby breaking latency. A functional and physical interaction between these two gammaherpesvirus regulatory protein counterparts could be a general feature of the herpesviruses.

A requirement for NF-κB induction in the production of replication-competent HHV-8 virions

The gammaherpesvirus human herpesvirus 8 (HHV-8) infects endothelial and B-lymphoid cells and is responsible for the development of Kaposi's sarcoma and primary effusion lymphoma (PEL). In the present study, we demonstrate that the activation of the NF-kappaB pathway during HHV-8 lytic replication is required for the generation of replication-competent virions capable of initiating a de novo infection of endothelial cells. In the HHV-8-positive PEL cell line BCBL-1, tetradecanoyl phorbol acetate (TPA) induction of the lytic cycle activates the NF-kappaB pathway, and this activation requires the induction of the IKKbeta component of the classical IkappaB kinase (IKK) complex. To further investigate the role of NF-kappaB activation in HHV-8 lytic replication, the NF-kappaB super-repressor IkappaBalpha-2NDelta4 was introduced into BCBL-1 cells by retroviral transduction. Expression of IkappaBalpha-2NDelta4 completely abolished NF-kappaB activity, as demonstrated by the loss of NF-kappaB DNA-binding activity and the absence of expression of the endogenous, NF-kappaB-regulated IkappaBalpha gene. NF-kappaB blockade dramatically impaired the ability of HHV-8 to produce infectious particles capable of initiating an effective de novo infection of endothelial EA.hy926 cells, as demonstrated by the lack of viral protein production in the target cells. Diminished infectivity did not appear to be caused by a reduction in virus titer, as demonstrated by equivalent viral DNA content in the supernatant of TPA-stimulated BCBL-1 and BCBL-1/2N4 cells. Although the viral and/or cellular products affected by NF-kappaB inactivation remain to be fully characterized, these data demonstrate an unexpected role for NF-kappaB induction during lytic reactivation in the production of replication-competent HHV-8 virions.

The Evolutionarily Conserved Kaposi's Sarcoma-associated Herpesvirus ORF57 Protein Interacts with REF Protein and Acts as an RNA Export Factor

ORF57 (MTA) one of the earliest Kaposi's sarcoma-associated herpesvirus (KSHV) regulatory proteins to be expressed is essential for virus lytic replication. A counterpart is present in every herpesvirus sequenced, indicating the importance of this signature viral protein and those examined act post-transcriptionally, affecting RNA splicing and transport. In KSHV-infected cells, ORF57 protein was present in a complex with REF (Aly) and TAP (NXF1), factors involved in cellular mRNA export. The ORF57 N-terminal region interacts with REF, whereas both N- and C-terminal domains of REF interact with ORF57. The ORF57-REF interaction was direct, whereas TAP appeared to be recruited via REF. In somatic cells, ectopically expressed ORF57 protein was shown to function as a CRM1-independent nuclear mRNA export factor, promoting export of mRNAs that are poor substrates for splicing. The gamma-herpesvirus ORF57 protein, and its alpha-1 herpesvirus ICP27 counterpart both export RNA through pathways involving REF and TAP proteins, although divergence of these herpesvirus subfamilies occurred some 180-210 million years ago. The TAP-mediated cellular mRNA export pathway is CRM1-independent. However, human immunodeficiency virus type 1 Rev protein-mediated RNA export, which is CRM1-dependent, was considerably inhibited by ORF57, suggesting that Rev and ORF57 compete for a common export component. These data strengthen arguments that TAP and CRM1 pathways converge in accessing similar components of the nuclear pore complex. We propose that ORF57-mediated RNA export may use different export factors to accommodate the KSHV-infected host cell environments, for example, in B-cells or endothelial cells and during the different phases of lytic virus replication.

Kaposi's sarcoma-associated herpesvirus-encoded latency-associated nuclear antigen inhibits lytic replication by targeting Rta: a potential mechanism for virus-mediated control of latency

Like other herpesviruses, Kaposi's sarcoma-associated herpesvirus (KSHV, also designated human herpesvirus 8) can establish a latent infection in the infected host. During latency a small number of genes are expressed. One of those genes encodes latency-associated nuclear antigen (LANA), which is constitutively expressed in cells during latent as well as lytic infection. LANA has previously been shown to be important for the establishment of latent episome maintenance through tethering of the viral genome to the host chromosomes. Under specific conditions, KSHV can undergo lytic replication, with the production of viral progeny. The immediate-early Rta, encoded by open reading frame 50 of KSHV, has been shown to play a critical role in switching from viral latent replication to lytic replication. Overexpression of Rta from a heterologous promoter is sufficient for driving KSHV lytic replication and the production of viral progeny. In the present study, we show that LANA down-modulates Rta's promoter activity in transient reporter assays, thus repressing Rta-mediated transactivation. This results in a decrease in the production of KSHV progeny virions. We also found that LANA interacts physically with Rta both in vivo and in vitro. Taken together, our results demonstrate that LANA can inhibit viral lytic replication by inhibiting expression as well as antagonizing the function of Rta. This suggests that LANA may play a critical role in maintaining latency by controlling the switch between viral latency and lytic replication.

The cell cycle and how it is steered by Kaposi's sarcoma-associated herpesvirus cyclin

A timely coordination of cellular DNA synthesis and division cycles is governed by the temporal and spatial activation of cyclin-dependent kinases (Cdks). The primary regulation of Cdk activation is through binding to partner cyclin proteins. Several gammaherpesviruses encode a viral homologue of cellular cyclin D, which may function to deregulate host cell cycle progression. One of these is encoded by Kaposi's sarcoma-associated herpesvirus (KSHV) and is called K cyclin or viral cyclin (v-cyclin). v-Cyclin is expressed in most of the malignant cells that are associated with KSHV infection in humans, labelling v-cyclin as a putative viral oncogene. Here are described some of the major structural and functional properties of mammalian cyclin/Cdk complexes, some of which are phenocopied by v-cyclin. In addition, the molecular events leading to orderly progression through the G1/S and G/M cell cycle phases are reviewed. This molecular picture serves as a platform on which to explain v-cyclin-specific functional properties. Interesting but largely speculative issues concern the interplay between v-cyclin-mediated cell cycle deregulation and molecular progression of KSHV-associated neoplasms.

Kaposi sarcoma-associated herpesvirus (KSHV) induces heme oxygenase-1 expression and activity in KSHV-infected endothelial cells

Kaposi sarcoma (KS) is the most common AIDS-associated malignancy and is characterized by angiogenesis and the presence of spindle cells. Kaposi sarcoma-associated herpesvirus (KSHV) is consistently associated with all clinical forms of KS, and in vitro infection of dermal microvascular endothelial cells (DMVECs) with KSHV recapitulates many of the features of KS, including transformation, spindle cell proliferation, and angiogenesis. To study the molecular mechanisms of KSHV pathogenesis, we compared the protein expression profiles of KSHV-infected and uninfected DMVECs. This comparison revealed that heme oxygenase-1 (HO-1), the inducible enzyme responsible for the rate-limiting step in heme catabolism, was up-regulated in infected endothelial cells. Recent evidence suggests that the products of heme catabolism have important roles in endothelial cell biology, including apoptosis and angiogenesis. Here we show that HO-1 mRNA and protein are up-regulated in KSHV-infected cultures. Comparison of oral and cutaneous AIDS-KS tissues with normal tissues revealed that HO-1 mRNA and protein were also up-regulated in vivo. Increased HO-1 enzymatic activity in vitro enhanced proliferation of KSHV-infected DMVECs in the presence of free heme. Treatment with the HO-1 inhibitor chromium mesoporphyrin IX abolished heme-induced proliferation. These data suggest that HO-1 is a potential therapeutic target for KS that warrants further study.

Epidemiology of classic Kaposi's sarcoma in the Israeli Jewish population between 1960 and 1998

Trends in the incidence of classic Kaposi's sarcoma in the Jewish population in Israel for the period between 1960 and 1998 were analysed. World standardised incidence rates of 20.7 and 7.5 per million among men and women, respectively, were calculated. The highest incidence rates were displayed by men originated from Africa and by Asian-born women.

The latency protein LANA2 from Kaposi's sarcoma-associated herpesvirus inhibits apoptosis induced by dsRNA-activated protein kinase but not RNase L activation

Kaposi's sarcoma-associated herpesvirus (KSHV) uses several strategies to counteract the interferon (IFN) system. In this study, the relationship of the protein LANA2 from KSHV to the IFN-activated protein kinase (PKR) and 2-5A system was analysed. It was found that LANA2 could not abrogate apoptosis or RNA degradation mediated by the 2-5A system. However, expression of LANA2 inhibited apoptosis triggered by PKR. LANA2 also counteracted the PKR-mediated inhibition of protein synthesis and partially blocked PKR-induced phosphorylation of eIF-2alpha. Analysis of PKR-induced activation of caspases 3 and 9 revealed that LANA2 abrogated activation of caspase 3 but not of caspase 9. These findings show that LANA2 is able to interfere with downstream events triggered by PKR. Hence, LANA2 should be considered as a KSHV defence protein against IFN.

Expression and purification of recombinant Kaposi's sarcoma-associated herpesvirus DNA polymerase using a Baculovirus vector system

The DNA polymerase (POL) of Kaposi's sarcoma-associated herpesvirus (KSHV) is essential for viral DNA replication and, thus, may be considered as a viable target for anti-KSHV therapeutics. To produce large quantities of homogeneous and pure POL required for high-throughput screening (HTS) for inhibitors, we generated a recombinant baculovirus vector encoding a hexahistidine (His6)-tagged POL and infected Spodoptera frugiperda Sf-9 insect cells. High expression of recombinant POL (rPOL) was achieved for up to 72h post-infection. The rPOL was solubilized in lysis buffer containing 0.3% Cymal-5 detergent, purified by metal-chelating and dsDNA-cellulose affinity chromatography, and analyzed by anti-His antibody Western blot and mass spectrometry. The functionality of rPOL was confirmed by its DNA synthesis activity in vitro, which was effectively blocked by the anti-herpetic DNA polymerase inhibitors, foscarnet and cidofovir diphosphate, in a dose-dependent manner. The POL expressed and purified from the recombinant baculovirus-infected insect cells may be useful toward the development of HTS of large chemical libraries to identify novel KSHV DNA polymerase inhibitors.

Differential gamma-herpesvirus distribution in distinct anatomical locations and cell subsets during persistent infection in mice

Murine gamma-herpesvirus 68 (MHV-68) provides an important experimental model for analyzing gamma-herpesvirus latent infection. After intranasal infection with MHV-68, we analyzed the distribution of the virus in different anatomical locations and purified populations of cells. Our data show that long-term latency is maintained in a variety of anatomical locations and cell populations with different frequencies. Importantly, we demonstrate that although latency in the lung is established in a variety of cell subsets, long-term latency in the lung is only maintained in B cells. In contrast, splenic latency is maintained in macrophages and dendritic cells, as well as in B cells. In blood, isotype-switched B cells constitute the major viral reservoir. These results show that the cell subsets in which latency is established vary within different anatomical sites. Finally, we demonstrate that long-term latency is accompanied by a low level of infectious virus in lung and spleen. These data have important implications for understanding the establishment and maintenance of latency by gamma(2)-herpesviruses.

Risk factors for Kaposi's sarcoma in men seropositive for both human herpesvirus 8 and human immunodeficiency virus

OBJECTIVE

To identify risk factors for Kaposi's sarcoma (KS) among men seropositive for both human herpesvirus 8 (HHV-8) and HIV.

DESIGN

Cross-sectional study of 91 HHV-8 seropositive, HIV seropositive men who have sex with men (57 with KS), and 70 controls at lower risk for KS.

METHODS

Patients received clinical evaluations. Blood, oral fluids, semen, rectal brush, rectal swab, and urine were collected, and tests for HHV-8 were performed.

RESULTS

Men with KS were more likely to have HHV-8 DNA in peripheral blood mononuclear cells (PBMC) than men without KS [35.1 versus 5.9%, odds ratio (OR), 8.6, 95% confidence interval (CI), 1.9-39.9]. The prevalence of HHV-8 DNA in oral fluids was similar for the two groups (37.0 versus 32.4%; OR, 1.2; 95% CI, 0.5-3.0). HHV-8 DNA was rarely detected in specimens of other types from these men, or in any specimens from the 70 controls. Among men with KS, HHV-8 DNA in PBMC was associated with new KS lesions (OR, 4.5; 95% CI, 1.4-14.5), and HHV-8 DNA in oral fluids was associated with oropharyngeal KS lesions (OR, 3.1; 95% CI, 1.0-10.1). Men with high HHV-8 antibody titers were more likely to have KS (OR, 9.6; 95% CI, 1.2-78.2), but were less likely to have new KS lesions (OR, 0.2; 95% CI, 0.0-1.1) or HHV-8 DNA in PBMC (OR, 0.2; 95% CI, 0.0-1.6) or oral fluids (OR, undefined; = 0.001).

CONCLUSIONS

In HHV-8- and HIV-seropositive men, HHV-8 DNA is associated with KS. Among men without KS, HHV-8 DNA is most commonly found in oral fluids. High HHV-8 antibody titers may protect against circulating HHV-8 and new KS lesions.

Complement regulation by Kaposi's sarcoma-associated herpesvirus ORF4 protein

Kaposi's sarcoma-associated herpesvirus (KSHV) is associated with three types of human tumor: Kaposi's sarcoma, multicentric Castleman's disease, and primary effusion lymphoma. The virus encodes a number of proteins that participate in disrupting the immune response, one of which was predicted by sequence analysis to be encoded by open reading frame 4 (ORF4). The predicted ORF4 protein shares homology with cellular proteins referred to as regulators of complement activation. In the present study, the transcription profile of the ORF4 gene was characterized, revealing that it encodes at least three transcripts, by alternative splicing mechanisms, and three protein isoforms. Functional studies revealed that each ORF4 protein isoform inhibits complement and retains a C-terminal transmembrane domain. Consistent with the complement-regulating activity, we propose to name the proteins encoded by the ORF4 gene collectively as KSHV complement control protein (KCP). KSHV ORF4 is the most complex alternatively spliced gene encoding a viral complement regulator described to date. KCP inhibits the complement component of the innate immune response, thereby possibly contributing to the in vivo persistence and pathogenesis of this virus.

Kaposi's sarcoma-associated herpesvirus immunoevasion and tumorigenesis: two sides of the same coin?

Kaposi's sarcoma-associated herpesvirus (KSHV) [or human herpesvirus 8 (HHV-8)] is the most frequent cause of malignancy among AIDS patients. KSHV and related herpesviruses have extensively pirated cellular cDNAs from the host genome, providing a unique opportunity to examine the range of viral mechanisms for controlling cell proliferation. Many of the viral regulatory homologs encode proteins that directly inhibit host adaptive and innate immunity. Other viral proteins target retinoblastoma protein and p53 control of tumor suppressor pathways, which also play key effector roles in intracellular immune responses. The immune evasion strategies employed by KSHV, by targeting tumor suppressor pathways activated during immune system signaling, may lead to inadvertent cell proliferation and tumorigenesis in susceptible hosts.

Immune evasion by a novel family of viral PHD/LAP-finger proteins of gamma-2 herpesviruses and poxviruses

Many viruses have developed mechanisms to escape the cellular immune response by inhibiting antigen presentation from major histocompatibility complex (MHC) molecules. Most of these immune escape mechanisms are highly host adapted and specific to a given virus species or family. Recent observations however, suggest that a conserved family of viral proteins is used by both gamma-2 herpesviruses and by poxviruses to downregulate MHC class I. In addition, other cell surface molecules involved in immune recognition by T cells and NK cells are also downregulated. Two open reading frames (ORFs), K3 and K5, of Kaposi's sarcoma associated virus (KSHV) and one ORFs, K3, of murine gamma herpesvirus 68 (MHV 68) inhibit surface expression of MHC I molecules. In cells transfected with KSHV-K3 and KSHV-K5, MHC I is rapidly endocytosed and degraded in lysosomes whereas in MHV 68-K3 transfected cells, MHC I is targeted for proteasomal degradation. The K3 and K5 genes display a characteristic conserved domain structure of an amino-terminal plant homeo domain/leukemia associated protein-zinc finger domain followed by two carboxyterminal transmembrane domains. Related proteins are not only found in other gamma-2 herpesviruses, but also in several poxviruses. Moreover, recent data suggest that the K3-related protein of myxoma virus also downregulates MHC I. The presence of similar genes in eukaryotic genomes further indicates that the viral ORFs were originally derived from host genes of as yet unknown function. The molecular mechanism of MHC I downregulation by this novel gene family is only poorly understood at present. However, several lines of evidence suggest that they might function as ubiquitin ligases that regulate the intracellular transport of transmembrane proteins through ubiquitination.

Laboratory diagnosis of human herpesvirus 8 infection in humans

Human herpesvirus 8 (HHV-8) is causally associated with Kaposi's sarcoma, primary effusion lymphoma and multicentric Castleman's disease. Serological and molecular biology assays are used to investigate the biology of this virus in different populations and diseases. Serological assays are mainly used to study the prevalence of the viral infection and to predict the diagnosis of Kaposi's sarcoma and other HHV-8-associated cancers. The appearance of antibodies against lytic antigens precedes the appearance of antibodies against latent antigens, probably explaining the lower sensitivity of assays based on latent HHV-8 antigens. The lack of international reference serum panels is presently the major bottleneck for further progress in the field of HHV-8 serology. Molecular biological assays are an absolute requirement for both the diagnosis and the follow-up of HHV-8 infection. Qualitative methods have been particularly useful to elucidate the mode of transmission and the causal association between HHV-8 and HHV-8-associated diseases. Quantitative methods have become an essential tool to monitor the progression of the infection and the effects of antiviral therapies. This review analyzes the performance of the different serological and molecular biological assays available at present. The main conclusion is that more research is needed to define the most useful laboratory tests for the diagnosis of HHV-8 infection and to establish the clinical role of such tests.

Kaposi's sarcoma-associated herpesvirus (human herpesvirus 8) replication and transcription factor activates the K9 (vIRF) gene through two distinct cis elements by a non-DNA-binding mechanism

The replication and transcription activator (RTA) of Kaposi's sarcoma-associated herpesvirus (KSHV), or human herpesvirus 8, a homologue of Epstein-Barr virus BRLF1 or Rta, is a strong transactivator and inducer of lytic replication. RTA acting alone can induce lytic replication of KSHV in infected cell lines that originated from primary effusion lymphomas, leading to virus production. During the lytic replication process, RTA activates many kinds of genes, including polyadenylated nuclear RNA, K8, K9 (vIRF), ORF57, and so on. We focused here on the mechanism of how RTA upregulates the K9 (vIRF) promoter and identified two independent cis-acting elements in the K9 (vIRF) promoter that responded to RTA. These elements were finally confined to the sequence 5'-TCTGGGACAGTC-3' in responsive element (RE) I-2B and the sequence 5'-GTACTTAAAATA-3' in RE IIC-2, both of which did not share sequence homology. Multiple factors bound specifically with these elements, and their binding was correlated with the RTA-responsive activity. Electrophoretic mobility shift assay with nuclear extract from infected cells and the N-terminal part of RTA expressed in Escherichia coli, however, did not show that RTA interacted directly with these elements, in contrast to the RTA responsive elements in the PAN/K12 promoter region, the ORF57/K8 promoter region. Thus, it was likely that RTA could transactivate several kinds of unique cis elements without directly binding to the responsive elements, probably through cooperation with other DNA-binding factors.