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

Seroprevalence and risk factors for Kaposi's Sarcoma associated herpesvirus among men who have sex with men in Shanghai, China

BACKGROUND

This study aimed to facilitate the understanding of the transmission route and risk factors that might contribute to the infection of Kaposi's sarcoma associated herpesvirus (KSHV) among men who have sex with men (MSM).

METHODS

A cross-sectional study of 520 subjects was conducted in Shanghai, China in 2020. Plasma samples were collected and screened for KSHV, HIV, HBV, HCV, and syphilis. Univariate and multivariate logistic regression analyses were conducted to explore potential correlates of KSHV infection.

RESULTS

The overall seroprevalence of KSHV was 43.8%, with an adjusted value of 29.8% according to the sensitivity and specificity of the KSHV screening assay. Individuals with lower levels of monthly income (Chi-sqaure_trend = 4.11, P = 0.043) and more male sex partners (Chi-sqaure_trend = 6.06, P = 0.014) were more likely to be infected with KSHV. Also, KSHV seropositivity was positively associated with being a student (aOR = 1.96; 95%CI: 1.09-3.61), being coinfected with HCV (aOR = 2.61; 95%CI: 1.05-7.10), and syphilis (aOR = 2.91; 95%CI: 1.30-6.89).

CONCLUSIONS

The prevalence of KSHV in MSM remains high. As a risky sexual behavior, having multiple male sex partners is a key contributor to KSHV infection among this population. Efforts designed to control modifiable risk factors in order to reduce the burden of KSHV infection are indispensable. High KSHV seroprevalence among students MSM deserves more attention.

LL-37 disrupts the Kaposi's sarcoma-associated herpesvirus envelope and inhibits infection in oral epithelial cells

Oral epithelial cells (OECs) represent the first line of defense against viruses that are spread via saliva, including Kaposi's sarcoma-associated herpesvirus (KSHV). Infection of humans by KSHV and viral pathogenesis begins by infecting OECs. One method OECs use to limit viral infections in the oral cavity is the production of antimicrobial peptides (AMPs), or host defense peptides (HDPs). However, no studies have investigated the antiviral activities of any HDP against KSHV. The goal of this study was to determine the antiviral activity of one HDP, LL-37, against KSHV in the context of infecting OECs. Our results show that LL-37 significantly decreased KSHV's ability to infect OECs in both a structure- and dose-dependent manner. However, this activity does not stem from affecting OECs, but instead the virions themselves. We found that LL-37 exerts its antiviral activity against KSHV by disrupting the viral envelope, which can inhibit viral entry into OECs. Our data suggest that LL-37 exhibits a marked antiviral activity against KSHV during infection of oral epithelial cells, which can play an important role in host defense against oral KSHV infection. Thus, we propose that inducing LL-37 expression endogenously in oral epithelial cells, or potentially introducing as a therapy, may help restrict oral KSHV infection and ultimately KSHV-associated diseases.

An Unusual Cause of a Parotid Mass in an Immunocompetent Host: Classic Kaposi's Sarcoma

Kaposi's sarcoma (KS) is a virally driven vascular tumor that usually has a multifocal origin, with multiple vascular nodules in the skin and other organs, particularly the gastrointestinal tract. Four variants of KS have been described: HIV-related, African, iatrogenic and classic. Primary classic KS of the head and neck is rare in any case, but KS arising in intraparotid lymph nodes, especially with no cutaneous involvement, is exceptionally rare. We report the case of an immunocompetent 71-year-old man who presented with a three-month history of a slowly progressive swelling in the right parotid region. After parotidectomy and histopathological diagnosis of lymph node localization of KS, a thorough dermatological examination did not reveal any skin lesions, and chest and abdominal computed tomography scans, esophagogastroduodenoscopy, and fecal occult blood test were all negative for visceral and other lymph node localizations. We here discuss the peculiarity of the presentation, the differential diagnosis, and the management strategy of such a rare disease.

Association of Kaposi’s sarcoma-associated herpesvirus (KSHV) with bladder cancer in Croatian patients

As the seventh most common human malignancy, bladder cancer represents a global health problem. In addition to well-recognized risk factors such as smoking and exposure to chemicals, various infectious agents have been implicated as cofactors in the pathogenesis of urothelial malignancies. The aim of the present study was to assess the possible association of viral infection and bladder cancer in Croatian patients. Biopsy specimens were collected from a total of 55 patients diagnosed with different stages of bladder cancer. Initial screening of DNA extracts for the presence of viruses on Lawrence Livermore Microbial Detection Array revealed Kaposi’s sarcoma-associated herpesvirus (KSHV) in each of three randomly chosen biopsy specimens. The prevalence of infection with KSHV among study population was then examined by KSHV-specific polymerase chain reaction (PCR) and immunoblotting. By nested PCR, KSHV DNA was detected in 55% of patients. KSHV, also known as human herpesvirus 8, is an infectious agent known to cause cancer. Its oncogenic potential is primarily recognized from its role in Kaposi’s sarcoma, but it has also been involved in pathogenesis of two lymphoproliferative disorders. A high prevalence of KSHV infection in our study indicates that KSHV may play a role in tumorigenesis of bladder cancer and warrants further studies.

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.

Professional antigen presenting cells in human herpesvirus 8 infection

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

Infectious agents in human cancers: lessons in immunity and immunomodulation from gammaherpesviruses EBV and KSHV

Members of the herpesvirus family have evolved the ability to persist in their hosts by establishing a reservoir of latently infected cells each carrying the viral genome with reduced levels of viral protein synthesis. In order to spread within and between hosts, in some cells, the quiescent virus will reactivate and enter lytic cycle replication to generate and release new infectious virus particles. To allow the efficient generation of progeny viruses, all herpesviruses have evolved a wide variety of immunomodulatory mechanisms to limit the exposure of cells undergoing lytic cycle replication to the immune system. Here we have focused on the human gammaherpesviruses Epstein-Barr virus (EBV) and Kaposi's sarcoma-associated herpesvirus (KSHV) that, uniquely among the eight human herpesviruses identified to date, have growth transforming potential. Most people infected with these viruses will not develop cancer, viral growth-transforming activity being kept under control by the host's antigen-specific immune responses. Nonetheless, EBV and KSHV are associated with several malignancies in which various viral proteins, either predominantly or exclusively latency-associated, are expressed; at least some of these proteins also have immunomodulatory activities. Of these malignancies, some are the result of a disrupted virus/immune balance through genetic, infectious or iatrogenic immune suppression. Others develop in people that are not overtly immune suppressed and likely modulate the immunological response. This latter aspect of immune modulation by EBV and KSHV forms the basis of this review.

Modulation of interferon regulatory factor 5 activities by the Kaposi sarcoma-associated herpesvirus-encoded viral interferon regulatory factor 3 contributes to immune evasion and lytic induction

Multiple Kaposi's sarcoma-associated herpesvirus (KSHV)-encoded proteins with potential roles in KSHV-associated neoplasms have been identified. KSHV encodes 4 genes with homology to transcription factors of the interferon (IFN) regulatory factor (IRF) family. Viral IRF3 (vIRF3) is expressed in latently KSHV-infected primary effusion lymphoma (PEL) cells and was recently shown to be essential for the survival of PEL cells. The focus of this study was to determine the mechanism(s) of vIRF3 oncogenic activity contributing to KSHV-associated lymphoma. We report that vIRF3 interacts with the amino-terminal DNA binding domain of human IRF5, leading to a complex manipulation of IRF5 function. vIRF3 associated with both exogenous and endogenous IRF5, thereby inhibiting IRF5-mediated IFN promoter activation and the synthesis of biologically active type I IFNs by blocking its binding to endogenous IFNA promoters. The function of this interaction was not limited to the IFN system as IRF5-mediated cell growth regulation was significantly altered by overexpression of vIRF3 in B cells. vIRF3 prevented IRF5-mediated growth inhibition and G2/M cell cycle arrest. Important, IRF5 was upregulated by the protein kinase C agonist 12-O-tetradecanoyl-phorbol-13-acetate in BCBL1 PEL cells and interaction with vIRF3 was observed at the endogenous p21 promoter in response to 12-O-tetradecanoyl-phorbol-13-acetate, suggesting that these 2 proteins cooperate in the regulation of lytic cycle-induced G1 arrest, which is an important early step for the reactivation of KSHV. In conclusion, cellular IRF5 and vIRF3 interact, leading to the functional modulation of IRF5-mediated type I IFN expression and cell cycle regulation. These findings support an important role for vIRF3 in immune evasion and cell proliferation that likely contribute to the survival of PEL cells.

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.

Monofunctional and polyfunctional CD8+ T cell responses to human herpesvirus 8 lytic and latency proteins

Human herpesvirus 8 (HHV-8) is the etiological agent of Kaposi's sarcoma, primary effusion lymphoma, and multicentric Castleman's disease. It is postulated that CD8(+) T cell responses play an important role in controlling HHV-8 infection and preventing development of disease. In this study, we investigated monofunctional and polyfunctional CD8(+) T cell responses to HHV-8 lytic proteins gB (glycoprotein B) and K8.1 and latency proteins LANA-1 (latency-associated nuclear antigen-1) and K12. On the basis of our previous findings that dendritic cells (DC) reveal major histocompatibility complex (MHC) class I epitopes in gB, we used a DC-based system to identify 2 novel epitopes in gB, 2 in K8.1, 5 in LANA-1, and 1 in K12. These new HHV-8 epitopes activated monofunctional and polyfunctional CD8(+) T cells that produced various combinations of gamma interferon, interleukin 2, tumor necrosis factor alpha, macrophage inhibitory protein 1β, and cytotoxic degranulation marker CD107a in healthy HHV-8-seropositive individuals. We were also able to detect HHV-8-specific CD8(+) T cells in peripheral blood samples using HLA A*0201 pentamer complexes for one gB epitope, one K8.1 epitope, two LANA-1 epitopes, and one K12 epitope. These immunogenic regions of viral lytic and latency proteins could be important in T cell control of HHV-8 infection.

Viral latency and its regulation: lessons from the gamma-herpesviruses

Latency is a state of cryptic viral infection associated with genomic persistence and highly restricted gene expression. Its hallmark is reversibility: under appropriate circumstances, expression of the entire viral genome can be induced, resulting in the production of infectious progeny. Among the small number of virus families capable of authentic latency, the herpesviruses stand out for their ability to produce such infections in every infected individual and for being completely dependent upon latency as a mode of persistence. Here, we review the molecular basis of latency, with special attention to the gamma-herpesviruses, in which the understanding of this process is most advanced.

KSHV and the pathogenesis of Kaposi sarcoma: listening to human biology and medicine

The linkage of Kaposi sarcoma (KS) to infection by a novel human herpesvirus (Kaposi sarcoma-associated herpesvirus [KSHV]) is one of the great successes of contemporary biomedical research and was achieved by using advanced genomic technologies in a manner informed by a nuanced understanding of epidemiology and clinical investigation. Ongoing efforts to understand the molecular mechanisms by which KSHV infection predisposes to KS continue to be powerfully influenced by insights emanating from the clinic. Here, recent developments in KS pathogenesis are reviewed, with particular emphasis on clinical, pathologic, and molecular observations that highlight the many differences between this process and tumorigenesis by other oncogenic viruses.

GLTSCR2/PICT-1, a putative tumor suppressor gene product, induces the nucleolar targeting of the Kaposi's sarcoma-associated herpesvirus KS-Bcl-2 protein

KS-Bcl-2, encoded by Kaposi's sarcoma-associated herpesvirus (KSHV), is a structural and functional homologue of the Bcl-2 family of apoptosis regulators. Like several other Bcl-2 family members, KS-Bcl-2 protects cells from apoptosis and autophagy. Using a yeast two-hybrid screen and coimmunoprecipitation assays, we identified a novel KS-Bcl-2-interacting protein, referred to as protein interacting with carboxyl terminus 1 (PICT-1), encoded by a candidate tumor suppressor gene, GLTSCR2. Confocal laser scanning microscopy revealed nucleolar localization of PICT-1, whereas KS-Bcl-2 was located mostly at the mitochondrial membranes with a small fraction in the nucleoli. Ectopic expression of PICT-1 resulted in a large increase in the nucleolar fraction of KS-Bcl-2, and only a minor fraction remained in the cytoplasm. Furthermore, knockdown of endogenous PICT-1 abolished the nucleolar localization of KS-Bcl-2. However, ectopically expressed PICT-1 did not alter the cellular distribution of human Bcl-2. Subsequent analysis mapped the crucial amino acid sequences of both KS-Bcl-2 and PICT-1 required for their interaction and for KS-Bcl-2 targeting to the nucleolus. Functional studies suggest a correlation between nucleolar targeting of KS-Bcl-2 by PICT-1 and reduction of the antiapoptotic activity of KS-Bcl-2. Thus, these studies demonstrate a cellular mechanism to sequester KS-Bcl-2 from the mitochondria and to downregulate its virally encoded antiapoptotic activity. Additional characterization of the interaction of KS-Bcl-2 and PICT-1 is likely to shed light on the functions of both proteins.

SIAH-1 interacts with the Kaposi's sarcoma-associated herpesvirus-encoded ORF45 protein and promotes its ubiquitylation and proteasomal degradation

Kaposi's sarcoma-associated herpesvirus (KSHV), also referred to as human herpesvirus 8, is a potentially tumorigenic virus implicated in the etiology of Kaposi's sarcoma, primary effusion lymphoma, and some forms of multicentric Castleman's disease. The open reading frame 45 (ORF45) protein, encoded by the KSHV genome, is capable of inhibiting virus-dependent interferon induction and appears to be essential for both early and late stages of infection. In the present study, we show, both in yeast two-hybrid assays and in mammalian cells, that the ORF45 protein interacts with the cellular ubiquitin E3 ligase family designated seven in absentia homologue (SIAH). We provide evidence that SIAH-1 promotes the degradation of KSHV ORF45 through a RING domain-dependent mechanism and via the ubiquitin-proteasome system. Furthermore, our data indicate the involvement of SIAH-1 in the regulation of the expression of ORF45 in KSHV-infected cells. Since the availability of KSHV ORF45 is expected to influence the course of KSHV infection, our findings identify a novel biological role for SIAH proteins as modulators of virus infection.

Transcriptional regulation of the open reading frame 35 encoded by Kaposi's sarcoma-associated herpesvirus

Kaposi's sarcoma-associated herpesvirus (KSHV) is a member of the Gammaherpesvirinae and is causally associated with Kaposi's sarcoma, primary effusion lymphoma, and multicentric Castleman's disease. The KSHV genome encodes over 85 genes; the function of some is entirely unknown. We have characterized the transcriptional regulation of a conserved and uncharacterized Gammaherpesvirinae open reading frame, orf35, which lies in a cluster of several overlapping genes, orf34 to orf38. We identified the transcription start site and analyzed upstream sequences. We found that expression of the KSHV lytic replication and transcription activator (RTA) strongly increased the orf35 promoter activity through a 46-nucleotide region which includes a conserved AP-1 binding site. Electrophoretic mobility shift assay demonstrated direct binding of cJUN and cFOS to the predicted AP-1 binding site. Finally, using a mutated promoter lacking the AP-1 site and dominant-negative cFOS, we established that the RTA-mediated orf35 transactivation is AP-1-dependent.

Relationship between human herpesvirus 8 loads and disease stage in classic Kaposi sarcoma patients

Human herpesvirus 8 (HHV-8), also known as Kaposi sarcoma (KS)-associated herpesvirus, is causally implicated in all forms of KS, including the classic form. Our objective was to investigate the relationship between HHV-8 load in peripheral blood mononuclear cells (PBMCs) and the stage of the disease in classic KS (CKS) patients. HHV-8 loads were measured in 41 PBMC samples from CKS patients with different Krigel-based classification stages using a quantitative real-time polymerase chain reaction assay. Low HHV-8 DNA loads reaching a maximum of 75.5 copies/10(5) cells were detected in 73.2% of the patients. HHV-8 loads in patients with stages I and II were similarly distributed. An increased detection rate of HHV-8 DNA, although not statistically significant, was evident in patients diagnosed with CKS stages III and IV. We conclude that the measurements of HHV-8 load in PBMCs provide a limited correlation with the clinical stage of KS.

Targeting the PI3K and MAPK pathways to treat Kaposi's-sarcoma-associated herpes virus infection and pathogenesis

Cells require the ability to appropriately respond to signals in their extracellular environment. To initiate, inhibit and control these processes, the cell has developed a complex network of signaling cascades. The phosphatidylinositol 3-kinase (PI3K) and mitogen-activated protein kinase (MAPK) signaling pathways regulate several responses including mitosis, apoptosis, motility, proliferation, differentiation and many others. It is not surprising, therefore, that many viruses target the PI3K and MAPK pathways as a means to manipulate cellular function. Recently, Kaposi's sarcoma-associated herpes virus (KSHV) has been added to the list. KSHV manipulates the PI3K and MAPK pathways to control such divergent processes as cell survival, cellular migration, immune responses, and to control its own reactivation and lytic replication. Manipulation of the PI3K and MAPK pathways also plays a role in malignant transformation. Here, the authors review the potential to target the PI3K and MAPK signaling pathways to inhibit KSHV infection and pathogenesis.

HIV-associated Kaposi's sarcoma

Kaposi's sarcoma (KS) is a multifocal vascular tumor that occurs most commonly in patients who have immunosuppression caused by HIV. KS-associated herpes virus (human herpes virus 8, KSHV) has been identified as the causative agent. There are marked geographic differences in the prevalence of both KS and seropositivity to KSHV. The incidence of the tumor has shown a marked decline in first-world countries with the widespread use of effective antiretroviral therapy. The most effective anthracycline is pegylated liposomal doxorubicin; however, few developing countries, where KS prevalence is highest, can afford to use these agents.

Absence of human herpesvirus 8 DNA sequences in lung biopsies from Israeli patients with pulmonary arterial hypertension

BACKGROUND

Pulmonary hypertension is a severe pulmonary vascular disease leading to rapid deterioration and death. Histological and clinical evidence suggests that smooth muscle proliferation is part of the pathogenesis of the disease. Human herpesvirus 8 (HHV-8) is a gamma-herpesvirus that is implicated in malignancies and in Kaposi's sarcoma. Recently, the association of HHV-8 with idiopathic pulmonary arterial hypertension (PAH) has been found.

OBJECTIVE

The aim of this study was to investigate the presence of HHV-8 in the lung tissue of Israeli patients with PAH.

METHOD

The presence of HHV-8 sequences was investigated by polymerase chain reaction examination in 6 biopsies of patients with pulmonary hypertension. Three patients had idiopathic pulmonary hypertension, 2 patients pulmonary venoocclusive disease, and 1 patient pulmonary hypertension associated with mixed connective tissue disease.

RESULT

We did not find any association between HHV-8 and PAH in these Israeli patients, as all the samples were negative for polymerase chain reaction.

CONCLUSION

Our findings, together with the epidemiological data of HHV-8 prevalence and incidence rates of Kaposi's sarcoma and PAH in Israel, provide further evidence which argues against an association between HHV-8 infection and PAH.

Kaposi's sarcoma-associated herpes virus complement control protein: KCP--complement inhibition and more

The complement system is an important part of innate immunity providing immediate protection against pathogens without a need for previous exposure, as well as priming the adaptive immune response through opsonisation, leukocyte recruitment and enhancing humoral immune responses. Its importance is not only shown through recurring fulminant infections in individuals with complement component deficiencies, but also through the many complement evasion strategies discovered for a wide range of infectious microbes (including acquisition of endogenous host complement inhibitors and expression of own homologues). Knowledge of these mechanisms at a molecular level may aid development of vaccines and novel therapeutic strategies. Here, we review the structure-function studies of the membrane-bound complement inhibitor KCP that is expressed on the surface of Kaposi's sarcoma-associated herpesvirus (KSHV) virions and infected cells. KCP accelerates the decay of classical C3 convertase and induces the degradation of activated complement factors C4b and C3b by a serine proteinase, factor I. Molecular modeling and site-directed mutagenesis have identified sites on the surface of KCP required for complement inhibition and support the hypothesis that KCP has evolved to mimic the structure and function of endogenous human inhibitors. KCP additionally enhances virion binding to permissive cells through a heparin/heparan sulfate-binding site located at the N-terminus of the protein.

Kaposi's sarcoma-associated herpesvirus immune modulation: an overview

Kaposi's sarcoma-associated herpesvirus (KSHV) is the most recently discovered human herpesvirus. It is the aetiological agent of Kaposi's sarcoma (KS), a tumour frequently affecting AIDS patients not receiving treatment. KSHV is also a likely cause of two lymphoproliferative diseases: multicentric Castleman's disease and primary effusion lymphoma. The study of KSHV offers exciting challenges for understanding the mechanisms of virus pathogenesis, including those involved in establishing infection and dissemination in the host. To facilitate these processes, approximately one-quarter of KSHV genes encode cellular homologues or unique proteins that have immunomodulatory roles in cytokine production, apoptosis, cell signalling and the immunological synapse. The activities of these molecules are considered in the present review and the positions of their genes are mapped from a complete KSHV genome sequence derived from a KS biopsy. The understanding gained enables the significance of different components of the immune response in protection against KSHV infection to be evaluated. It also helps to unravel the complexities of cellular and immunological pathways and offers the potential for exploiting viral immunomodulators and derivatives in disease therapy.

An essential role of ERK signalling in TPA-induced reactivation of Kaposi's sarcoma-associated herpesvirus

Kaposi's sarcoma-associated herpesvirus (KSHV) is implicated causally in the development of several human malignancies, including primary effusion lymphoma (PEL). PEL cells serve as tools for KSHV research, as most of them are latently infected and allow lytic virus replication in response to various stimuli. 12-O-Tetradecanoyl-phorbol-13-acetate (TPA) is the most potent inducer of lytic KSHV reactivation; nevertheless, the exact mechanism by which it induces reactivation remains unknown. It has previously been reported by our group that the protein kinase C (PKC) delta isoform plays a crucial role in TPA-mediated KSHV reactivation. Here, the activation pathway was dissected and it was demonstrated that TPA induces KSHV reactivation via stimulation of the mitogen-activated protein kinase (MAPK)/extracellular signal-regulated kinase (ERK) pathway. Western blot analysis revealed a rapid phosphorylation of ERK1/2. Cells treated with MAPK/ERK inhibitors before TPA addition demonstrated repression of ERK1/2 phosphorylation, which was associated with a block of KSHV lytic-gene expression. This inhibition prevented c-Fos accumulation, yet increased c-Jun phosphorylation. Similar results were obtained in response to rottlerin, a selective PKCdelta inhibitor. Notably, the PKC inhibitor GF 109203X reduced ERK1/2 phosphorylation, c-Fos accumulation, c-Jun phosphorylation and KSHV reactivation. It is proposed that TPA induces KSHV reactivation through at least two arms. The first involves PKCdelta, ERK phosphorylation and c-Fos accumulation, whilst the second requires another PKC isoform that induces the phosphorylation of c-Jun. c-Fos and c-Jun jointly form an active AP-1 complex, which functions to activate the lytic cascade of KSHV.

Dissecting the regions of virion-associated Kaposi's sarcoma-associated herpesvirus complement control protein required for complement regulation and cell binding

Complement, which bridges innate and adaptive immune responses as well as humoral and cell-mediated immunity, is antiviral. Kaposi's sarcoma-associated herpesvirus (KSHV) encodes a lytic cycle protein called KSHV complement control protein (KCP) that inhibits activation of the complement cascade. It does so by regulating C3 convertases, accelerating their decay, and acting as a cofactor for factor I degradation of C4b and C3b, two components of the C3 and C5 convertases. These complement regulatory activities require the short consensus repeat (SCR) motifs, of which KCP has four (SCRs 1 to 4). We found that in addition to KCP being expressed on the surfaces of experimentally infected endothelial cells, it is associated with the envelope of purified KSHV virions, potentially protecting them from complement-mediated immunity. Furthermore, recombinant KCP binds heparin, an analogue of the known KSHV cell attachment receptor heparan sulfate, facilitating infection. Treating virus with an anti-KCP monoclonal antibody (MAb), BSF8, inhibited KSHV infection of cells by 35%. Epitope mapping of MAb BSF8 revealed that it binds within SCR domains 1 and 2, also the region of the protein involved in heparin binding. This MAb strongly inhibited classical C3 convertase decay acceleration by KCP and cofactor activity for C4b cleavage but not C3b cleavage. Our data suggest similar topological requirements for cell binding by KSHV, heparin binding, and regulation of C4b-containing C3 convertases but not for factor I-mediated cleavage of C3b. Importantly, they suggest KCP confers at least two functions on the virion: cell binding with concomitant infection and immune evasion.

Classic Kaposi sarcoma. Which KSHV-seropositive individuals are at risk?

BACKGROUND

Classic Kaposi sarcoma (CKS) is a relatively rare vascular disease primarily affecting human immunodeficiency virus (HIV)-uninfected elderly men. The infection with Kaposi sarcoma-associated herpesvirus (KSHV) is necessary for the establishment of Kaposi sarcoma (KS), although it is not sufficient. Thus, only a small fraction of KSHV-infected individuals develops KS. The cofactors that influence risk of KS among HIV-uninfected individuals are yet to be determined. The objective of the current study was to assess potential risk factors for CKS in the KSHV-infected Jewish population in Israel.

METHODS

A case-control study involved 35 CKS cases and 48 matched KSHV-infected controls. Lifestyle and medical history data from case patients and controls were compared by logistic regression analysis.

RESULTS

In a multivariate analysis, the authors identified an age-related small increased risk for CKS in subjects originating from Asia and Africa. The risk for CKS increased, although not significantly statistically, in subjects who reported alcohol consumption, diabetes mellitus, herpes simplex, and asthma. No relation was found with cigarette smoking, family size, number of lifetime sexual partners, or sexually transmitted disease.

CONCLUSIONS

A borderline increase in CKS risk among elderly subjects originating from Africa or Asia was identified. These results need to be further evaluated by larger studies. The authors believe that genetic and immunologic parameters may alter risk for CKS and, therefore, should also be investigated.

Inhibition of interferon signaling by the Kaposi's sarcoma-associated herpesvirus full-length viral interferon regulatory factor 2 protein

Interferon (IFN) signal transduction involves interferon regulatory factors (IRF). Kaposi's sarcoma-associated herpesvirus (KSHV) encodes four IRF homologues: viral IRF 1 (vIRF-1) to vIRF-4. Previous functional studies revealed that the first exon of vIRF-2 inhibited alpha/beta interferon (IFN-alpha/beta) signaling. We now show that full-length vIRF-2 protein, translated from two spliced exons, inhibited both IFN-alpha- and IFN-lambda-driven transactivation of a reporter promoter containing the interferon stimulated response element (ISRE). Transactivation of the ISRE promoter by IRF-1 was negatively regulated by vIRF-2 protein as well. Transactivation of a full-length IFN-beta reporter promoter by either IRF-3 or IRF-1, but not IRF-7, was also inhibited by vIRF-2 protein. Thus, vIRF-2 protein is an interferon induction antagonist that acts pleiotropically, presumably facilitating KSHV infection and dissemination in vivo.