Molecular mimicry of human cytokine and cytokine response pathway genes by KSHV

KSHV infection and the pathogenesis of Kaposi's sarcoma

Kaposi's sarcoma (KS) has long been suspected of having an infectious etiology on the basis of its unusual epidemiology, histopathology, and natural history. Nearly a decade ago, a novel herpesviral genome was discovered in KS biopsies, and since that time strong epidemiologic evidence has accumulated correlating infection with this KS-associated herpesvirus (KSHV, also known as human herpesvirus 8) with the development of the disease. Here we review the evidence linking KSHV infection to KS risk and discuss current notions of how KSHV gene expression promotes the development of this remarkable neoplasm. These studies show that both latent and lytic viral replicative cycles contribute significantly-but differently-to KS development. The studies also highlight mechanistic differences between oncogenesis caused by KSHV and that caused by its distant relative Epstein-Barr virus.

Kaposi sarcoma-associated herpesvirus/human herpesvirus 8 and lymphoproliferative disorders

Kaposi sarcoma-associated herpesvirus (KSHV), also known as human herpesvirus 8 (HHV8), is a recent addition to the list of human viruses that are directly associated with lymphoproliferative disorders. KSHV was first shown to be involved in multicentric Castleman disease and primary effusion lymphoma (PEL). Subsequently, the virus was identified in solid lymphomas, often of extranodal sites, with morphological and immunophenotypic characteristics similar to those of PEL, and in other lymphoproliferative disorders with heterogeneous clinicopathological presentations. The recent advances in our understanding of the histology, immunophenotype and pathogenesis of these KSHV-associated lymphoproliferative disorders are reviewed.

Synergistic activation of interferon-beta gene transcription by the viral FLICE inhibitory protein of Kaposi's sarcoma-associated herpesvirus and type I IFN activators

Expression of Kaposi's sarcoma-associated herpesvirus v-FLIP leads to the spindle-shape morphology of endothelial cells and is essential for the survival of primary effusion lymphoma cells. Activation of the NF-kappaB transcription factor by v-FLIP is responsible for these effects. Considering that the interferon-beta (ifn-beta) gene is regulated partly through NF-kappaB, we sought to determine whether v-FLIP would activate the expression of the ifn-beta gene. Our results indicate that when v-FLIP is expressed by itself it has no effect on ifn-beta gene activation but when it is combined with known IFN-beta inducers, a synergistic activation of the ifn-beta gene occurs. This effect is strictly dependent on NF-kappaB and is mediated through the positive regulatory domain II of the IFN-beta promoter. Furthermore, we report that protection from Fas-induced cell-death by v-FLIP is observed whether or not the type I IFN signaling pathway is activated. Our work therefore contributes to increase our knowledge on v-FLIP, highlighting the complex immunomodulatory properties of this anti-apoptotic viral protein.

Roles of lytic viral infection and IL-6 in early versus late passage lymphoblastoid cell lines and EBV-associated lymphoproliferative disease

Lytically infected EBV-positive lymphoblastoid cells enhance the growth of early-passage, but not late-passage, EBV-immortalized lymphoblastoid cell lines (LCLs) in SCID mice and have enhanced IL-6 secretion. Here, we have examined the importance of IL-6 for the growth of early-passage LCLs (EPL) in SCID mice, identified lytic EBV proteins that activate IL-6 production and compared viral and cellular differences between early versus late passage LCLs (LPL). IL-6 was required for efficient growth of EPL in SCID mice. The EBV immediate-early (IE) proteins, BRLF1 and BZLF1, each induced IL-6 secretion when transfected into 293 and BJAB cells. Interestingly, the combination of BZLF1 and the latent EBV protein, LMP-1, induced much more IL-6 expression in both 293 and BJAB cells than either protein alone. Both BZLF1 and BRLF1 also enhanced IL-10 production in 293 cells. In comparison to the EPL, LPL had much reduced expression of early lytic viral proteins and cellular IL-6. In contrast, expression of cellular IL-10 was similar in EPL versus LPL, while VEGF secretion was increased in late-passage LCLs. These results suggest that both BRLF1 and BZLF1 contribute to IL-6 secretion in lytically infected cells and that lytically infected cells may promote early lymphoproliferative disease in patients through enhanced IL-6 production.

K13 blocks KSHV lytic replication and deregulates vIL6 and hIL6 expression: a model of lytic replication induced clonal selection in viral oncogenesis

BACKGROUND

Accumulating evidence suggests that dysregulated expression of lytic genes plays an important role in KSHV (Kaposi's sarcoma associated herpesvirus) tumorigenesis. However, the molecular events leading to the dysregulation of KSHV lytic gene expression program are incompletely understood.

METHODOLOGY/PRINCIPAL FINDINGS

We have studied the effect of KSHV-encoded latent protein vFLIP K13, a potent activator of the NF-kappaB pathway, on lytic reactivation of the virus. We demonstrate that K13 antagonizes RTA, the KSHV lytic-regulator, and effectively blocks the expression of lytic proteins, production of infectious virions and death of the infected cells. Induction of lytic replication selects for clones with increased K13 expression and NF-kappaB activity, while siRNA-mediated silencing of K13 induces the expression of lytic genes. However, the suppressive effect of K13 on RTA-induced lytic genes is not uniform and it fails to block RTA-induced viral IL6 secretion and cooperates with RTA to enhance cellular IL-6 production, thereby dysregulating the lytic gene expression program.

CONCLUSIONS/SIGNIFICANCE

Our results support a model in which ongoing KSHV lytic replication selects for clones with progressively higher levels of K13 expression and NF-kappaB activity, which in turn drive KSHV tumorigenesis by not only directly stimulating cellular survival and proliferation, but also indirectly by dysregulating the viral lytic gene program and allowing non-lytic production of growth-promoting viral and cellular genes. Lytic Replication-Induced Clonal Selection (LyRICS) may represent a general mechanism in viral oncogenesis.

Chemo-angiogenic profile of bovine urinary bladder tumors distinguishes urothelial carcinomas from hemangiosarcomas

Angiogenesis and inflammation are two processes regulated by numerous common molecular mechanisms. Inflammation can stimulate angiogenesis, and angiogenesis can facilitate inflammation; both mechanisms have been shown to be involved in carcinogenesis. With this study we sought to gain an understanding of the molecular mechanisms involved in tumor angiogenesis and inflammation in urinary bladder tumors. Tumor specimens were collected at slaughter from Friesian cows chronically exposed to bracken fern. Bracken chronic toxicity is characterized by the presence of multiple mixed tumors in the bladder, being reported throughout the world under the designation of bovine enzootic hematuria. We conducted molecular analyses of angiogenic factors and chemokine production by real-time RT-PCR, and also assessed microvessel density (MVD), microvessel pericyte coverage index (MPI) to reveal mature vessels, the extent of tumor-infiltrating leukocytes (TILk) and tumor cell apoptosis and proliferation in both epithelial and endothelial-derived bovine urinary bladder tumors. We defined a profile of chemokines/chemokine receptors (Mip1beta, CCR1) and angiogenesis-related factors (VEGF, VEGFR2) that allow distinguishing between urothelial carcinomas (epithelial origin) and hemangiosarcomas (endothelial origin). Taken together, our data reveals previously unrecognized paracrine and autocrine chemo-angiogenic loops in the context of bovine urinary bladder tumorigenesis.

Crystal structure and structural mechanism of a novel anti-human immunodeficiency virus and D-amino acid-containing chemokine

Chemokines and their receptors play important roles in normal physiological functions and the pathogeneses of a wide range of human diseases, including the entry of human immunodeficiency virus type 1 (HIV-1). However, the use of natural chemokines to probe receptor biology or to develop therapeutic drugs is limited by their lack of selectivity and the poor understanding of mechanisms in ligand-receptor recognition. We addressed these issues by combining chemical and structural biology in research into molecular recognition and inhibitor design. Specifically, the concepts of chemical biology were used to develop synthetically and modularly modified (SMM) chemokines that are unnatural and yet have properties improved over those of natural chemokines in terms of receptor selectivity, affinity, and the ability to explore receptor functions. This was followed by using structural biology to determine the structural basis for synthetically perturbed ligand-receptor selectivity. As a proof-of-principle for this combined chemical and structural-biology approach, we report a novel D-amino acid-containing SMM-chemokine designed based on the natural chemokine called viral macrophage inflammatory protein II (vMIP-II). The incorporation of unnatural D-amino acids enhanced the affinity of this molecule for CXCR4 but significantly diminished that for CCR5 or CCR2, thus yielding much more selective recognition of CXCR4 than wild-type vMIP-II. This D-amino acid-containing chemokine also showed more potent and specific inhibitory activity against HIV-1 entry via CXCR4 than natural chemokines. Furthermore, the high-resolution crystal structure of this D-amino acid-containing chemokine and a molecular-modeling study of its complex with CXCR4 provided the structure-based mechanism for the selective interaction between the ligand and chemokine receptors and the potent anti-HIV activity of D-amino acid-containing chemokines.

Immune evasion by Kaposi's sarcoma-associated herpesvirus

To efficiently establish a persistent infection, Kaposi's sarcoma-associated herpesvirus (KSHV; also known as HHV8) dedicates a large amount of its coding potential to produce proteins that antagonize the immune system of its host. These viral immunomodulators interfere with both the innate and adaptive immune responses and most of them are homologous to cellular proteins, suggesting that they have been pirated from the host during viral evolution. In this Review, I present recent advances in the understanding of immune evasion by KSHV, with a particular focus on the virally encoded modulators of immune responses that are unique to this virus.

Identification of cellular genes targeted by KSHV-encoded microRNAs

MicroRNAs (miRNAs) are 19 to 23 nucleotide–long RNAs that post-transcriptionally regulate gene expression. Human cells express several hundred miRNAs which regulate important biological pathways such as development, proliferation, and apoptosis. Recently, 12 miRNA genes have been identified within the genome of Kaposi sarcoma–associated herpesvirus; however, their functions are still unknown. To identify host cellular genes that may be targeted by these novel viral regulators, we performed gene expression profiling in cells stably expressing KSHV-encoded miRNAs. Data analysis revealed a set of 81 genes whose expression was significantly changed in the presence of miRNAs. While the majority of changes were below 2-fold, eight genes were down-regulated between 4- and 20-fold. We confirmed miRNA-dependent regulation for three of these genes and found that protein levels of thrombospondin 1 (THBS1) were decreased >10-fold. THBS1 has previously been reported to be down-regulated in Kaposi sarcoma lesions and has known activity as a strong tumor suppressor and anti-angiogenic factor, exerting its anti-angiogenic effect in part by activating the latent form of TGF-β. We show that reduced THBS1 expression in the presence of viral miRNAs translates into decreased TGF-β activity. These data suggest that KSHV-encoded miRNAs may contribute directly to pathogenesis by down-regulation of THBS1, a major regulator of cell adhesion, migration, and angiogenesis.

Kaposi sarcoma–associated herpesvirus (KSHV) is a gamma-herpesvirus associated with Kaposi sarcoma, primary effusion lymphoma, and a subset of muticentric Castleman disease. Recently, it was found that KSHV encodes 12 microRNAs (miRNAs) within its latency-associated region. miRNAs are small ∼22 nucleotide-long single-stranded RNA molecules that act to inhibit gene expression by binding to target messenger RNAs (mRNAs). Because miRNAs bind to these targets with limited base pairing, it has been difficult to find targets. The goal of our study was to identify cellular mRNAs targeted by KSHV-encoded miRNAs. Microarray analysis of cells expressing the KSHV miRNAs revealed a set of 81 genes that were changed. Several genes are regulators of important functions such as blood vessel growth, cell proliferation, and cell death. One target, thrombospondin 1, is a potent inhibitor of blood vessel growth and is known to be down-regulated in Kaposi sarcoma tumors. Thrombospondin 1, which is targeted by multiple miRNAs, also showed reduced protein levels in our study. To our knowledge, our data describe the first targets for tumorvirus-encoded miRNAs and suggest that these novel regulators may have roles in pathogenesis.

HHV-8 encoded LANA-1 alters the higher organization of the cell nucleus

The latency-associated nuclear antigen (LANA-1) of Human Herpes Virus 8 (HHV-8), alternatively called Kaposi Sarcoma Herpes Virus (KSHV) is constitutively expressed in all HHV-8 infected cells. LANA-1 accumulates in well-defined foci that co-localize with the viral episomes. We have previously shown that these foci are tightly associated with the borders of heterochromatin [1]. We have also shown that exogenously expressed LANA-1 causes an extensive re-organization of Hoechst 33248 DNA staining patterns of the nuclei in non-HHV-8 infected cells [2]. Here we show that this effect includes the release of the bulk of DNA from heterochromatic areas, in both human and mouse cells, without affecting the overall levels of heterochromatin associated histone H3 lysine 9 tri-methylation (3MK9H3). The release of DNA from the heterochromatic chromocenters in LANA-1 transfected mouse cells co-incides with the dispersion of the chromocenter associated methylcytosin binding protein 2 (MECP2). The localization of 3MK9H3 to the remnants of the chromocenters remains unaltered. Moreover, exogeneously expressed LANA-1 leads to the relocation of the chromocenters to the nuclear periphery, indicating extensive changes in the positioning of the chromosomal domains in the LANA-1 harboring interphase nucleus. Using a series of deletion mutants we have shown that the chromatin rearranging effects of LANA-1 require the presence of a short (57 amino acid) region that is located immediately upstream of the internal acidic repeats. This sequence lies within the previously mapped binding site to histone methyltransferase SUV39H1. We suggest that the highly concentrated LANA-1, anchored to the host genome in the nuclear foci of latently infected cells and replicated through each cell generation, may function as "epigenetic modifier". The induction of histone modification in adjacent host genes may lead to altered gene expression, thereby contributing to the viral oncogenesis.

Using interferon-alpha to block expression of cellular ribosome subunit S24 variant 2 in human fibroblasts inhibits translation of the poliovirus genome

Studies about the proteins induced by interferon (IFN-)-alpha stimulation have provided some data on their mechanism of antiviral effect. These proteins were confirmed to contribute to antiviral functions. In this study, IFN-alpha stimulation of human fibroblasts was shown to induce the inhibition of S24 variant 2 (a structural component of the ribosomal small subunit) at the mRNA and protein levels, implying a possible antiviral mechanism for IFN-alpha in human fibroblasts. The delay of poliovirus replication by IFN-alpha was partially compensated for by S24 variant 2 expressed in pcDNA vector-transfected cells, and the interference RNA of S24 variant 2 was able to induce mimetically, to some extent, this poliovirus replication delay. These observations revealed that S24 variant 2 could be involved in the antiviral effects of IFN-alpha in human fibroblasts.

In vivo-restricted and reversible malignancy induced by human herpesvirus-8 KSHV: a cell and animal model of virally induced Kaposi's sarcoma

Transfection of a Kaposi's sarcoma (KS) herpesvirus (KSHV) Bacterial Artificial Chromosome (KSHVBac36) into mouse bone marrow endothelial-lineage cells generates a cell (mECK36) that forms KS-like tumors in mice. mECK36 expressed most KSHV genes and were angiogenic, but they didn't form colonies in soft agar. In nude mice, mECK36 formed KSHV-harboring vascularized spindle cell sarcomas that were LANA+/podoplanin+, overexpressed VEGF and Angiopoietin ligands and receptors, and displayed KSHV and host transcriptomes reminiscent of KS. mECK36 that lost the KSHV episome reverted to nontumorigenicity. siRNA suppression of KSHV vGPCR, an angiogenic gene upregulated in mECK36 tumors, inhibited angiogenicity and tumorigenicity. These results show that KSHV malignancy is in vivo growth restricted and reversible, defining mECK36 as a biologically sensitive animal model of KSHV-dependent KS.

Induction of chemokine production by latent Kaposi's sarcoma-associated herpesvirus infection of endothelial cells

Infection with Kaposi's sarcoma (KS)-associated herpesvirus (KSHV) is linked strongly to development of KS, an endothelial neoplasm also characterized by striking neoangiogenesis and infiltration with inflammatory cells. To elucidate the links between endothelial infection and inflammation, primary human umbilical vein endothelial cells (HUVECs) were examined for the production of chemokines following latent KSHV infection. Several chemokines that are produced in the ground state, including MCP-1, NAP 2 and RANTES, are upregulated significantly by KSHV infection. Moreover, the chemokine CXCL16, which is nearly absent in uninfected cells, is induced significantly following infection. This induction is attributable primarily to expression of vFLIP, a known inducer of NF-kappaB. CXCL16 induces the chemotaxis of activated T cells, whose products have been proposed to positively regulate KS tumour-cell survival and growth. Whilst CXCL16 has also been proposed as a direct endothelial chemoattractant and mitogen, neither proliferation nor chemotaxis of HUVECs was observed following CXCL16 exposure. These results suggest that CXCL16 induction by KSHV contributes to the inflammatory phenotype of KS, but plays little role in the recruitment of endothelial spindle cells.

Kaposi sarcoma-associated herpesvirus in non-Hodgkin lymphoma and reactive lymphadenopathy in Uganda

Kaposi sarcoma-associated herpesvirus (KSHV) causes Kaposi sarcoma and is also associated with primary effusion lymphoma, a subset of diffuse large B-cell lymphomas, and multicentric Castleman disease. Because KSHV infection is endemic in sub-Saharan Africa, we sought to identify cases of KSHV-positive non-Hodgkin lymphomas (NHLs) and reactive lymphadenopathy in this region. One hundred forty-four cases (80 NHLs, 64 reactive lymph nodes) from the major pathology laboratory in Uganda were reviewed. One NHL was KSHV-positive, as indicated by staining for the viral latent nuclear antigen. This NHL was a diffuse large B-cell lymphoma in a 5-year-old boy. The tumor was also Epstein-Barr virus-positive. In addition, 2 reactive lymph nodes, both classified histologically as follicular involution, stained KSHV latent nuclear antigen-positive and thus most likely represent multicentric Castleman disease. In all 3 KSHV-positive cases, a minority of cells expressed KSHV viral interleukin 6, a biologically active cytokine homolog. In conclusion, we show that KSHV is rarely associated with lymphoproliferative disorders in sub-Saharan Africa. We describe the first case of a KSHV-positive NHL from this region; this case is also the first reported pediatric lymphoma associated with KSHV infection.

Molecular biology of KSHV in relation to AIDS-associated oncogenesis

KSHV has been established as the causative agent of KS, PEL, and MCD, malignancies occurring more frequently in AIDS patients. The aggressive nature of KSHV in the context of HIV infection suggests that interactions between the two viruses enhance pathogenesis. KSHV latent infection and lytic reactivation are characterized by distinct gene expression profiles, and both latency and lytic reactivation seem to be required for malignant progression. As a sophisticated oncogenic virus, KSHV has evolved to possess a formidable repertoire of potent mechanisms that enable it to target and manipulate host cell pathways, leading to increased cell proliferation, increased cell survival, dysregulated angiogenesis, evasion of immunity, and malignant progression in the immunocompromised host. Worldwide, approximately 40.3 million people are currently living with HIV infection. Of these, a significant number are coinfected with KSHV. The complex interplay between the two viruses dramatically elevates the risk for development of KSHV-induced malignancies, KS, PEL, and MCD. Although HAART significantly reduces HIV viral load, the entire T-cell repertoire and immune function may not be completely restored. In fact, clinically significant immune deficiency is not necessary for the induction of KSHV-related malignancy. Because of variables such as lack of access to therapy noncompliance with prescribed treatment, failure to respond to treatment and the development of drug-resistant strains of HIV, KSHV-induced malignancies will continue to present as major health concerns.

Concurrent CMV and EBV DNAemia is significantly correlated with a delay in the response to HAART in treatment-naive HIV type 1-positive patients

The purpose of this study was to assess the qualitative single and multiple herpes virus DNAemia in the peripheral blood leukocytes (PBLs) of HIV-1-positive patients and its impact on the response to highly active antiretroviral therapy (HAART) and immune reconstitution. All (163) HIV-1-positive patients attending "Syngros AIDS Referral Center" from November 2000 to February 2001 were recruited. CMV, HSV-1, HSV-2, EBV, and HHV-8 DNA were detected in PBLs by polymerase chain reaction (PCR). Patients' follow-up comprised regular measurements of CD4(+) T cell count and HIV-1 viral load (VL) for an average period of 21 months. Immune reconstitution was defined as an increase in the CD4 T cell count by above 200 cells/micro l, while response to HAART was defined as a decrease in HIV-1 VL to undetectable levels. Single and multiple herpetic DNAemia in PBLs was found to be significantly higher in HIV-1-positive patients compared to healthy controls (p < 0.02) for all the viruses detected apart from HSV-2, which was not detected in the PBLs of either population. Concurrent CMV and EBV DNAemia significantly correlates with a delay in the response to HAART (p = 0.033) in treatment-naive patients. Untreated patients with a CD4(+) T cell count <200 cells/micro l, and with either CMV or EBV DNAemia, presented a delayed increase in the CD4 count after initiation of HAART (p = 0.035 and p = 0.037 respectively), while multiple herpetic DNAemia in the above patients was borderline associated with immune reconstitution (p = 0.068). Conclusively, CMV and EBV DNAemia may be poor prognostic factors for the response to HAART in treatment-naive HIV-1 patients.

Signal transduction targets in Kaposi's sarcoma

PURPOSE OF REVIEW

AIDS-related Kaposi's sarcoma results from co-infection with HIV and Kaposi's sarcoma herpesvirus/human herpesvirus-8, which leads to the development of an angiogenic-inflammatory state that is critical in the pathogenesis of the condition. Recent discoveries regarding Kaposi's sarcoma herpesvirus/human herpesvirus-8 infection and its activation of signal transduction have led to a greater understanding into Kaposi's sarcoma pathogenesis and have identified potential targets for therapy.

RECENT FINDINGS

Kaposi's sarcoma is driven by Kaposi's sarcoma herpesvirus/human herpesvirus-8-specific pathways, which include viral G protein-coupled receptor, viral IL-6, and viral chemokine homologues. In addition, cellular growth/angiogenic pathways such as vascular endothelial growth factor, insulin growth factor, platelet-derived growth factor, angiopoietin and matrix metalloproteinases are 'pirated' by Kaposi's sarcoma herpesvirus/human herpesvirus-8. Recent findings show Kaposi's sarcoma herpesvirus/human herpesvirus-8 specific signaling pathways and pirated pathways to be important therapeutic targets.

SUMMARY

Numerous advances have been made recently that expand the understanding of Kaposi's sarcoma pathogenesis. These findings and recent clinical trials of targeted therapy for treatment are a prelude to a shift in the paradigm of how AIDS-related Kaposi's sarcoma is managed.

Persistent activation of STAT3 by latent Kaposi's sarcoma-associated herpesvirus infection of endothelial cells

Kaposi's sarcoma-associated herpesvirus (KSHV) is the infectious cause of Kaposi's sarcoma, primary effusion lymphoma, and plasmablastic multicentric Castleman's disease. STAT3 has been shown to be important for the maintenance of primary effusion lymphoma cells in culture and is chronically activated in many tumor cell lines. However, little is known about the role of KSHV in the activation of STAT3 or the role of STAT3 in KS tumors. We demonstrate that STAT3 is activated by KSHV infection of endothelial cells, the KS tumor cell type, in a biphasic fashion. Viral binding and entry activate STAT3 in the first 2 h after infection, but this activation dissipates by 4 h postinfection. By 12 h after KSHV infection, concomitant with the expression of latent genes, STAT3 is once again activated, and this activation persists for as long as latent infection is maintained. Activated STAT3 translocates to the nucleus, where it can bind to STAT3-specific DNA elements and can activate STAT3-dependent promoter activity. Conditioned medium from KSHV-infected endothelial cells is able to transiently activate STAT3, indicating the involvement of a secreted factor and that a latency-associated factor in KSHV-infected cells is necessary for sustained activation. KSHV upregulates gp130 receptor expression, and both gp130 and JAK2 are required for the activation of STAT3. However, neither human nor viral interleukin-6 is required for STAT3 activation. Persistent activation of the oncogenic signal transducer, STAT3, by KSHV may play a critical role in the viral pathogenesis of Kaposi's sarcoma, as well as in primary effusion lymphomas.

Intracellular Tat of human immunodeficiency virus type 1 activates lytic cycle replication of Kaposi's sarcoma-associated herpesvirus: role of JAK/STAT signaling

Human immunodeficiency virus type 1 (HIV-1) infection significantly increases the risk of Kaposi's sarcoma (KS) occurrence in individuals infected with Kaposi's sarcoma-associated herpesvirus (KSHV). KSHV infection appears to be necessary but not sufficient for KS development without other cofactors. However, factors that facilitate KSHV to cause KS have not been well defined. Previously, we determined that human herpesvirus 6 was one of the cofactors that activated lytic cycle replication of KSHV. Here, we demonstrate that the Tat protein of HIV-1 is a potentially important factor in the pathogenesis of KS, as determined by production of lytic phase mRNA transcripts and viral proteins in BCBL-1 cells. Mechanistic studies showed ectopic expression of Tat induced the production of human interleukin-6 (huIL-6) and its receptor (huIL-6Ra) and activated STAT3 signaling. Neutralization of huIL-6 or huIL-6R or inhibition of STAT3 signaling enhanced the replication. In addition, IL-4/STAT6 signaling also partially contributed to Tat-induced KSHV replication. These findings suggest that Tat may participate in KS pathogenesis by inducing KSHV replication and increasing KSHV viral load. These data also suggest that JAK/STAT signaling may be of therapeutic value in AIDS-related KS patients.

An update on Behçet's disease

Behçet's disease (Adamantiades-Behçet's disease, ABD) is a multisystemic inflammatory disease, the pathogenesis of which is still a mystery. Many questions are still to be answered and the available diverse data need to be brought together to be compared and analysed. There is at least consensus on the effect of possible, but currently unknown, environmental triggering factor(s) against a background of genetic susceptibility. The possible aetiological factors form a broad spectrum, with infectious agents being the most probable ones. Whatever the stimulus is, the target tissue seems to be the small blood vessels, with various consequences of either vasculitis and/or thrombosis in many organ systems. The endothelium seems to be the primary target in this disease; however, it may just be the subject of the bizarre behaviour of the immune system. The diverse existing data could be interpreted in favour of either explanation. A similar confusion exists about the thrombotic tendency in Adamantiades-Behçet's disease, in terms of whether a primary hypercoagulability is present or whether it is secondary to inflammation. Recent interesting immunological data promise a way out of the existing dilemma. These findings will be outlined within the context of possible hypotheses and attention will be paid to further investigations that are needed.

The KSHV viral interleukin-6 is not essential for latency or lytic replication in BJAB cells

Kaposi's Sarcoma-associated herpesvirus encodes a homolog of the human cellular interleukin-6 that may play a formative role in many KSHV-related diseases. While the viral IL-6 can signal similarly to its human counterpart little is known about the role of vIL-6 during KSHV infection. Using homologous recombination and selection in eukaryotic cells, a KSHV isolate was purified that does not express vIL-6 as was a control recombinant that left vIL-6 intact. The two viruses establish and maintain latency to similar levels in BJAB B-cells, reactivate to similar levels in B-cells and Monkey kidney cells and have very similar KSHV gene expression patterns. BJAB cells expressing KSHV survive better than the parental BJAB cells in low serum and the vIL-6 deletion does not abrogate this growth advantage. Thus vIL-6 is not essential for establishment, maintenance, or reactivation from latency in cell culture and is not involved in the survival of infected BJAB B-cells in low serum.

Kaposi sarcoma-associated herpesvirus and other viruses in human lymphomagenesis

Kaposi sarcoma-associated herpesvirus (KSHV), also called human herpesvirus 8 (HHV-8), is associated with a specific subset of lymphoproliferative disorders. These include two main categories. The first is primary effusion lymphomas and related solid variants. The second is multicentric Castleman disease, from which KSHV-positive plasmablastic lymphomas can arise. KSHV contributes to lymphomagenesis by subverting the host cell molecular signaling machinery to deregulate cell growth and survival. KSHV expresses a selected set of genes in the lymphoma cells, encoding viral proteins that play important roles in KSHV lymphomagenesis. Deregulation of the NF-kappaB pathway is an important strategy used by KSHV to promote lymphoma cell survival, and the viral protein vFLIP is essential for this process. Two other viruses that are well documented to be causally associated with lymphoid neoplasia in humans are Epstein-Barr virus (EBV/HHV-4) and human T-cell lymphotropic virus (HTLV-1). Both of these are similar to KSHV in their use of viral proteins to promote cell survival by deregulating the NF-kappaB pathway. Here we review the basic information and recent developments that have contributed to our knowledge of lymphomas caused by KSHV and other viruses. The understanding of the mechanisms of viral lymphomagenesis should lead to the identification of novel therapeutic targets and to the development of rationally designed therapies.

Regulation of KSHV lytic gene expression

The life cycle of KSHV, latency versus lytic replication, is mainly determined at the transcriptional regulation level. A viral immediate-early gene product, replication and transcription activator (RTA), has been identified as the molecular switch for initiation of the lytic gene expression program from latency. Here we review progress on two key questions: how RTA gene expression is controlled by viral proteins and cellular signals and how RTA regulates the expression of downstream viral genes. We summarize the interactions of RTA with cellular and other viral proteins. We also discuss critical issues that must be addressed in the near future.

Structural requirements for gp80 independence of human herpesvirus 8 interleukin-6 (vIL-6) and evidence for gp80 stabilization of gp130 signaling complexes induced by vIL-6

Human herpesvirus 8 interleukin-6 (vIL-6) displays 25% amino acid identity with human IL-6 (hIL-6) and shares an overall four-helix-bundle structure and gp130-mediated STAT/mitogen-activated protein kinase signaling with its cellular counterpart. However, vIL-6 is distinct in that it can signal through gp130 alone, in the absence of the nonsignaling gp80 alpha-subunit of the IL-6 receptor. To investigate the structural requirements for gp80 independence of vIL-6, a series of expression vectors encoding vIL-6/hIL-6 chimeric and site-mutated IL-6 proteins was generated. The replacement of hIL-6 residues with three vIL-6-specific tryptophans implicated in gp80 independence from crystallographic studies or the A and C helices containing these residues did not confer gp80 independence to hIL-6. The N- and C-terminal regions of vIL-6 could be substituted with hIL-6 sequences with the retention of gp80-independent signaling, but substitutions of other regions of vIL-6 (helix A, A/B loop, helix B, helix C, and proximal half of helix D) with equivalent sequences of hIL-6 abolished gp80 independence. Interestingly, the B helix of vIL-6 was absolutely required for gp80 independence, despite the fact that this region contains no receptor-binding residues. Point mutational analysis of helix C, which contains residues involved in physical and functional interactions with gp130 domains 2 and 3 (cytokine-binding homology region), identified a variant, VI120EE, that was able to signal and dimerize gp130 only in the presence of gp80. gp80 was also found to stabilize gp130:g130 dimers induced by a distal D helix variant of vIL-6 that was nonetheless able to signal independently of gp80. Together, our data reveal the crucial importance of overall vIL-6 structure and conformation for gp80-independent signaling and provide functional and physical evidence of the stabilization of vIL-6-induced gp130 signaling complexes by gp80.

Distinct expression of Kaposi's sarcoma-associated herpesvirus-encoded proteins in Kaposi's sarcoma and multicentric Castleman's disease

The expression of Kaposi's sarcoma-associated herpesvirus (KSHV/HHV-8)-encoded proteins is herein demonstrated in Kaposi's sarcoma (KS) and multicentric Castleman's disease (MCD) in a single lymph node derived from a patient with acquired immunodeficiency syndrome. Immunohistochemistry revealed that both lytic and latent KSHV proteins were expressed in cells of the MCD lesion. KSHV-encoded viral interleukin-6 was also detected in follicular dendritic cells of the germinal center. Cytoplasmic localization of open reading frame 59 protein and latency-associated nuclear antigen suggested KSHV activation in the MCD lesion. Moreover, a high copy number of KSHV was detected in the blood. Clinically, pegylated-liposomal doxorubicin induced regression of not only KS, but also lymphadenopathy of the MCD lesion with a decrease in KSHV load and human interleukin-6 in the blood. To the best of the authors' knowledge this is the first case demonstrating differential expression of virus proteins in two KSHV-associated diseases, KS and MCD, in the same section. The case confirms lytic KSHV infection in MCD, and suggests that clinical symptoms of MCD might be closely linked with KSHV activation.

Abrogation of viral interleukin-6 (vIL-6)-induced signaling by intracellular retention and neutralization of vIL-6 with an anti-vIL-6 single-chain antibody selected by phage display

Human herpesvirus 8 (HHV-8) encodes several putative oncogenes, which are homologues to cellular host genes known to function in cell cycle regulation, control of apoptosis, and cytokine signaling. Viral interleukin (vIL-6) is believed to play an important role in the pathogenesis of Kaposi's sarcoma as well as primary effusion lymphoma and multicentric Castleman's disease. Therefore, vIL-6 is a promising target for novel therapies directed against HHV-8-associated diseases. By phage display screening of human synthetic antibody libraries, we have selected a specific recombinant antibody, called monoclonal anti-vIL-6 (MAV), binding to vIL-6. The epitope recognized by MAV was localized on the top of the D helix of the vIL-6 protein, which is a part of receptor binding site III. Consequently, MAV specifically inhibits vIL-6-mediated growth of the primary effusion lymphoma-derived cell line BCBL-1 and blocks STAT3 phosphorylation in the human hepatoma cell line HepG2. Since it was previously found that vIL-6 can also induce signals from within the cell, presumably within the endoplasmic reticulum, we fused the recombinant antibody MAV with the endoplasmic retention sequence KDEL (MAV-KDEL). As a result, COS-7 cells expressing MAV-KDEL and synthesizing vIL-6 ceased to secrete the cytokine. Moreover, we observed that vIL-6 that was bound to MAV-KDEL and retained in the endoplasmic reticulum did not induce STAT3 phosphorylation in HepG2 cells. We conclude that the activity of the intracellularly retained vIL-6 protein is neutralized by MAV-KDEL. Our results might represent a novel therapeutic strategy to neutralize virally encoded growth factors or oncogenes.

Identification of proteins immunologically related to interferon regulatory factor-1 that bind with interferon regulatory factor element

Interferon regulatory factor (IRF)-1 expression was surveyed in nontransformed and oncogene-transformed mouse fibroblasts, using Western immunoblot with an IRF-1-specific antiserum, to examine possible differences resulting from cellular transformation. Ten additional proteins that reacted with the IRF-1 antibody and that underwent specific competition by peptide antigen were observed in extracts of both nontransformed and oncogene-transformed cell lines. Cross-reacting proteins were also observed in mouse macrophage extracts. Protein was captured from fibroblast nuclear extracts, using oligonucleotides representing IRF-binding sequences linked to magnetic beads. Captured proteins were eluted and analyzed by immunoblot with anti-IRF-1. Along with 43-kDa IRF-1, 4 of the 7 nuclearly located cross-reacting proteins (97, 90, 66, and 33 kDa) were found to complex with the IRF binding element. These proteins, with an epitope in common with the IRF-1 C-terminal region and IRF element DNA sequence-binding capability, may represent new members of the IRF family.

Antiviral action of the tumor suppressor ARF

Oncogenic viruses frequently target the pathways controlled by tumor suppressor genes, suggesting an extra function for these proteins as antiviral factors. The control exerted by the tumor suppressor Arf on cellular proliferation is crucial to restrict tumor development; however, a potential contribution of Arf to prevent viral infectivity has remained unexplored. In the present study, we investigated the consequences of loss or increased expression of Arf on viral infection. Our results reveal that ARF expression is induced by interferon and after viral infection. Furthermore, we show that ARF protects against viral infection in a gene dosage-dependent manner, and that this antiviral action is mediated in part by PKR through a mechanism that involves ARF-induced release of PKR from nucleophosmin complexes. Finally, Arf-null mice were hypersensitive to viral infection compared to wild-type mice. Together, our results reveal a novel and unexpected role for the tumor suppressor ARF in viral infection surveillance.

KSHV encoded LANA upregulates Pim-1 and is a substrate for its kinase activity

Pim kinases are proto-oncogenes that are upregulated in a number of B cell cancers, including Epstein-Barr Virus (EBV) associated Burkitt's lymphoma. They have also been shown to be upregulated in Kaposi sarcoma-associated herpes virus (KSHV) infected primary B cells. Most cells in KSHV-associated tumors are latently infected and express only a small subset of viral genes, with KSHV latency associated nuclear antigen (LANA) being constitutively expressed. LANA regulates the transcription of a large number of cellular and viral genes. Here, we show that LANA upregulates transcription from the Pim-1 promoter (pPim-1) and map this activation to a region in the promoter located within the sequence (-681 to +37). We show that LANA expressing cells can proliferate faster and are better protected from drug induced apoptosis. Since transition through cell cycle check points and anti-apoptosis are functions associated with Pim-1, it is likely that higher Pim-1 expression in cells expressing LANA is responsible, at least in part, for this effect. A Pim-1 phosphorylation site was also identified within the amino-terminal domain of LANA. Using in vitro kinase assays, we confirmed that LANA was indeed a Pim-1 substrate, and the failure of Pim-1 to phosphorylate LANA mutated at SS205/6RR identified this site as the specific serine residues phosphorylated by Pim-1. This report provides valuable insight into yet another cellular signaling pathway subverted by KSHV LANA and suggests a contribution to KSHV related oncogenesis.

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.

Functional genomics and the development of pathogenesis-targeted therapies for Kaposi's sarcoma

Kaposi's sarcoma (KS) is a multifocal angioproliferative disorder affecting the skin, mucosa and viscera of individuals infected with human herpesvirus-8 (HHV-8; also Kaposi's sarcoma-associated herpesvirus [KSHV]). KS is the most common neoplasm in AIDS patients; the clinical outcome of AIDS-KS is significantly improved by highly active antiretroviral therapy (HAART). However, in Africa, where the severest manifestations of KS occur, there is limited access to these and other effective but expensive drugs. Here we present a review of current efforts to identify novel therapeutic targets for the treatment of KS using functional genomics, with recommendations regarding the development of economically feasible treatments for use in Africa.

Activity of subcutaneous interleukin-12 in AIDS-related Kaposi sarcoma

Interleukin-12 (IL-12) enhances Th1-type T-cell responses and exerts antiangiogenic effects. We initiated a phase 1 pilot study of IL-12 in 32 patients with acquired immunodeficiency syndrome (AIDS)-related Kaposi sarcoma (KS) whose KS was progressing while on antiretroviral therapy. Fifteen patients had poor prognosis T(1)S(1) disease. IL-12 was administered subcutaneously twice weekly at doses from 100 to 625 ng/kg. The maximum tolerated dose was 500 ng/kg, and the principal toxicities were flulike symptoms, transaminase or bilirubin elevations, neutropenia, hemolytic anemia, and depression. No tumor responses were seen at the lowest dose (100 ng/kg), but 17 of 24 evaluable patients at the higher doses had partial or complete responses (response rate, 71%; 95% confidence interval, 48%-89%). Only 3 of 17 patients had a change in antiretroviral therapy before responding, and there were no significant differences between responders and nonresponders with regard to changes in CD4 counts or viral loads. Patients had increases in their serum IL-12, interferon-gamma, and inducible protein-10 (IP-10) after the first dose, and increases above baseline persisted after week 4. These results provide preliminary evidence that IL-12 has substantial activity against AIDS-related KS with acceptable toxicity and warrants further investigation for this indication.

Inhibition of replication and transcription activator and latency-associated nuclear antigen of Kaposi's sarcoma-associated herpesvirus by morpholino oligomers

Kaposi's sarcoma-associated herpesvirus (KSHV) is associated with Kaposi's sarcoma and primary effusion lymphoma (PEL). The KSHV replication and transcription activator (RTA) and latency-associated nuclear antigen (LANA) play key roles in activating KSHV lytic replication and maintaining KSHV latency, respectively. Phosphorodiamidate morpholino oligomers (PMO) are similar to short single-stranded DNA oligomers, but possess a modified backbone that confers highly specific binding and resistance to nucleases. In this study, RTA and LANA mRNA in PEL cells were targeted by antisense peptide-conjugated PMO (P-PMO) in an effort to suppress KSHV replication. Highly efficient P-PMO uptake by PEL cells was observed. Treatment of PEL cells with a RTA P-PMO (RP1) reduced RTA expression in a dose-dependent and sequence-specific manner, and also caused a significant decrease in several KSHV early and late gene products, including vIL-6, vIRF-1, and ORF-K8.1A. KSHV viral DNA levels were reduced both in cells and culture supernatants of RP1 P-PMO-treated cells, indicating that KSHV lytic replication was suppressed. Treatment of BCBL-1 cells with P-PMO against LANA resulted in a reduction of LANA expression. Cell viability assays detected no cytotoxicity from P-PMO alone, within the concentration range used for the experiments in this study. These results suggest that RP1 P-PMO can specifically block KSHV replication, and further study is warranted.

Interleukin-6 and its receptor: from bench to bedside

Interleukin-6 (IL-6) is an inflammatory cytokine with a well-documented role in inflammation and cancer. The cytokine binds to a membrane bound IL-6 receptor (IL-6R) and this complex associates with two molecules of the signal transducing protein gp130 thereby initiating intracellular signaling. While gp130 is present on most if not all cells of the body, the IL-6R is only present on some cells, mainly hepatocytes and several leukocytes. Cells, which only express gp130 and no IL-6R are refractory to IL-6 signals. We have shown earlier that the IL-6R can exist as a soluble protein generated by limited proteolysis of the membrane bound receptor or by translation from an alternatively spliced mRNA. This soluble IL-6R (sIL-6R) can bind the ligand IL-6 and the soluble complex of sIL-6R and IL-6 can bind to gp130 on cells which lack the membrane bound IL-6R and trigger gp130 signaling. We have named this process 'trans-signaling'. We will review data, which clearly show that IL-6 uses classical signaling via the membrane bound receptor and trans-signaling via the soluble receptor in various physiological and pathophysiological situations. Furthermore, we have developed designer cytokines, which can specifically enhance or inhibit IL-6 trans-signaling. These designer cytokines have been shown to be extremely useful to in therapeutic applications ranging from the long-term culture of stem cells and enhancing liver regeneration up to the blockade of chronic inflammation and cancer.

CCR5 interactions with the variable 3 loop of gp120

The G-protein coupled receptor CCR5 functions pathologically as the primary co-receptor for macrophage tropic (R5) strains of HIV-1. The interactions responsible for co-receptor activity are unknown. Molecular-dynamics simulations of the extracellular and adjacent transmembrane domains of CCR5 were performed with explicit solvation utilizing a rhodopsin-based homology model. The functional unit of co-receptor binding was constructed via docking and molecular-dynamics simulation of CCR5 and the variable 3 loop of gp120, which is a dominant determinant of co-receptor utilization. The variable 3 loop was demonstrated to interact primarily with the amino terminus and the second extracellular loop of CCR5, providing novel structural information regarding the co-receptor-binding site. Alanine mutants that alter chemokine binding and co-receptor activity were examined. Molecular-dynamics simulations with and without the variable 3 loop of gp120 were able to rationalize the activities of these mutants successfully, providing support for the proposed model. Based on these results, the global complex of CCR5, gp120 including the V3 loop and CD4, was investigated. The utilization of computational analysis, in combination with molecular biological data, provides a powerful approach for understanding the use of CCR5 as a co-receptor by HIV-1.

Reciprocal transactivation between HIV-1 and other human viruses

A variety of rare clinical syndromes are seen with strikingly increased prevalence in HIV-1-infected individuals, many with underlying viral etiologies. The emergence of these diseases in AIDS reflects a reduction in the ability of the immune system to mount an adequate defense against viruses in general due to the damage inflicted to the immune system by HIV-1 infection. However, in many cases, it has been found that HIV-1 can enhance the level of expression and hence the life cycle of other viruses independently of immunosuppression through specific interactions with the viruses. This can occur either directly by HIV-1 proteins such as Tat enhancing the activity of heterologous viral promoters, and/or indirectly by HIV-1 inducing the expression of cytokines and activation of their downstream signaling that eventually promotes the multiplication of the other virus. In a reciprocal manner, the effects of other viruses can enhance the pathogenicity of HIV-1 infection in individuals with AIDS through stimulation of the HIV-1 promoter activity and genome expression. The purpose of this review is to examine the cross-interactions between these viruses and HIV-1.

Associations of Classic Kaposi Sarcoma with Common Variants in Genes that Modulate Host Immunity

Classic Kaposi sarcoma (CKS) is an inflammatory-mediated neoplasm primarily caused by Kaposi sarcoma-associated herpesvirus (KSHV). Kaposi sarcoma lesions are characterized, in part, by the presence of proinflammatory cytokines and growth factors thought to regulate KSHV replication and CKS pathogenesis. Using genomic DNA extracted from 133 CKS cases and 172 KSHV-latent nuclear antigen-positive, population-based controls in Italy without HIV infection, we examined the risk of CKS associated with 28 common genetic variants in 14 immune-modulating genes. Haplotypes were estimated for IL1A, IL1B, IL4, IL8, IL8RB, IL10, IL12A, IL13, and TNF. Compared with controls, CKS risk was decreased with 1235T/-1010G-containing diplotypes of IL8RB (odds ratio, 0.49; 95% confidence interval, 0.30-0.78; P = 0.003), whereas risk was increased with diplotypes of IL13 containing the promoter region variant 98A (rs20541, alias +130; odds ratio, 1.88; 95% confidence interval, 1.15-3.08; P = 0.01) when considered in multivariate analysis. Risk estimates did not substantially vary by age, sex, incident disease, or disease burden. Our data provide preliminary evidence for variants in immune-modulating genes that could influence the risk of CKS. Among KSHV-seropositive Italians, CKS risk was associated with diplotypes of IL8RB and IL13, supporting laboratory evidence of immune-mediated pathogenesis.

Specific probes for chemokine receptors

Chemokine receptors have attracted a good deal of public attention as important therapeutic targets for many diseases and disorders. In this issue of Chemistry & Biology, Kumar and colleagues propose a new concept of synthetic modular modifications to generate unnatural chemokines, which exhibit high receptor selectivity .

SMM-chemokines: a class of unnatural synthetic molecules as chemical probes of chemokine receptor biology and leads for therapeutic development

Chemokines and their receptors play important roles in numerous physiological and pathological processes. To develop natural chemokines into receptor probes and inhibitors of pathological processes, the lack of chemokine-receptor selectivity must be overcome. Here, we apply chemical synthesis and the concept of modular modifications to generate unnatural synthetically and modularly modified (SMM)-chemokines that have high receptor selectivity and affinity, and reduced toxicity. A proof of the concept was shown by transforming the nonselective viral macrophage inflammatory protein-II into new analogs with enhanced selectivity and potency for CXCR4 or CCR5, two principal coreceptors for human immunodeficiency virus (HIV)-1 entry. These new analogs provided insights into receptor binding and signaling mechanisms and acted as potent HIV-1 inhibitors. These results support the concept of SMM-chemokines for studying and controlling the function of other chemokine receptors.

The pleiotropic effects of Kaposi's sarcoma herpesvirus

Kaposi's sarcoma herpesvirus (KSHV), or human herpesvirus 8 (HHV8), is an essential factor in the pathogenesis of Kaposi's sarcoma (KS), multicentric Castleman's disease (MCD), and primary effusion lymphoma (PEL). Case reports suggest an occasional involvement in bone marrow hypoplasia and haemophagocytic syndrome, but other disease associations are unconfirmed or controversial. KSHV-associated disease is of particular importance in immunosuppressed individuals, in particular in patients with HIV infection and transplant recipients. KSHV establishes a latent infection in the majority of infected cells in KS, MCD, and PEL, but lytic replication occurs in a small fraction of infected cells. Viral proteins expressed during both the latent and the lytic phase of the viral life cycle contribute to the pathogenesis of KSHV-associated diseases.

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.

Inhibition of the ATM/p53 signal transduction pathway by Kaposi's sarcoma-associated herpesvirus interferon regulatory factor 1

Infected cells recognize viral replication as a DNA damage stress and elicit the ataxia telangiectasia-mutated (ATM)/p53-mediated DNA damage response signal transduction pathway as part of the host surveillance mechanisms, which ultimately induces the irreversible cell cycle arrest and apoptosis. Viruses have evolved a variety of mechanisms to counteract this host intracellular innate immunity. Kaposi's sarcoma-associated herpesvirus (KSHV) viral interferon regulatory factor 1 (vIRF1) interacts with the cellular p53 tumor suppressor through its central DNA binding domain, and this interaction inhibits transcriptional activation of p53. Here, we further demonstrate that KSHV vIRF1 downregulates the total p53 protein level by facilitating its proteasome-mediated degradation. Detailed biochemical study showed that vIRF1 interacted with cellular ATM kinase through its carboxyl-terminal transactivation domain and that this interaction blocked the activation of ATM kinase activity induced by DNA damage stress. As a consequence, vIRF1 expression greatly reduced the level of serine 15 phosphorylation of p53, resulting in an increase of p53 ubiquitination and thereby a decrease of its protein stability. These results indicate that KSHV vIRF1 comprehensively compromises an ATM/p53-mediated DNA damage response checkpoint by targeting both upstream ATM kinase and downstream p53 tumor suppressor, which might circumvent host growth surveillance and facilitate viral replication in infected cells.

Ugandan Kaposi's sarcoma-associated herpesvirus phylogeny: evidence for cross-ethnic transmission of viral subtypes

OBJECTIVE

The aim of this study was to test the relationship between Kaposi's sarcoma-associated herpesvirus (KSHV) phylogeny and host ethnicity at the within-country scale.

METHODS

KSHV genomic DNA samples were isolated from 31 patients across eleven Ugandan ethnic groups. Amino acid sequences of the ORF-K1 gene were used to construct a neighbor-joining phylogenetic tree.

RESULTS

A5 and B1 variants predominated with no evidence of distinct ethnic or geographic distribution. A new K1 subtype (F) was identified in a member of the Bantu Gisu tribe and a new subtype B variant (B3) among members of the Bantu Ganda tribe.

CONCLUSIONS

The phylogeny may yet be structured by host ethnicity if members of Ugandan groups have convoluted biological origins, even as they identify with single tribes. An alternative possibility is that KSHV subtype evolution may have preceded major diversification of sub-Saharan Africans into ethnicities as we know them today, with ethnic groups beginning their histories already hosting multiple subtypes. A third alternative is that horizontal transmission of multiple KSHV subtypes may have broken up vertical lineages of the virus passed down within Ugandan populations.

Epstein-Barr virus lytic infection contributes to lymphoproliferative disease in a SCID mouse model

Most Epstein-Barr virus (EBV)-positive tumor cells contain one of the latent forms of viral infection. The role of lytic viral gene expression in EBV-associated malignancies is unknown. Here we show that EBV mutants that cannot undergo lytic viral replication are defective in promoting EBV-mediated lymphoproliferative disease (LPD). Early-passage lymphoblastoid cell lines (LCLs) derived from EBV mutants with a deletion of either viral immediate-early gene grew similarly to wild-type (WT) virus LCLs in vitro but were deficient in producing LPD when inoculated into SCID mice. Restoration of lytic EBV gene expression enhanced growth in SCID mice. Acyclovir, which prevents lytic viral replication but not expression of early lytic viral genes, did not inhibit the growth of WT LCLs in SCID mice. Early-passage LCLs derived from the lytic-defective viruses had substantially decreased expression of the cytokine interleukin-6 (IL-6), and restoration of lytic gene expression reversed this defect. Expression of cellular IL-10 and viral IL-10 was also diminished in lytic-defective LCLs. These results suggest that lytic EBV gene expression contributes to EBV-associated lymphoproliferative disease, potentially through induction of paracrine B-cell growth factors.

On the Role of Interferon Regulatory Factors in HIV-1 Replication

Interferons (IFNs) are pleiotropic cytokines that possess several biological activities and play a central role in basic and applied research as mediators of antiviral and antigrowth responses, modulators of the immune system, and therapeutic agents against viral diseases and cancer. Interferon regulatory factors (IRFs) have been identified together with signal transducers and activators of transcription (STAT) from studies on the type I IFN as well as IFN-stimulated (ISG) gene regulation and signaling. IRFs constitute a family of transcriptional activators and repressors implicated in multiple biological processes including regulation of immune responses and host defence, cytokine signaling, cell growth regulation, and hematopoietic development. All members share a well-conserved DNA binding domain at the NH(2)-terminal region that recognizes similar DNA sequences, termed IRF element (IRF-E)/interferon-stimulated response element (ISRE), present on the promoter of target genes. Recently, a sequence homologous to the ISRE has been identified downstream from the 5' human immunodeficiency virus type 1 (HIV-1) long terminal repeat (LTR). This sequence is a binding site for IRF-1 and IRF-2. Here we briefly summarize the role of IRFs in the regulation of HIV-1 LTR transcriptional activity and virus replication. The overall effect of IRFs on HIV-1 replication will also be discussed in the context of strategies carried out by the virus to counteract the IFN-mediated host defences both in active replication and during the establishment of viral latency.

Transcripts of the human herpesvirus 8 genome in skin lesions and peripheral blood mononuclear cells of a patient with classic Kaposi's sarcoma

We report a 75-year-old Japanese woman with classic Kaposi's sarcoma. PCR amplified human herpesvirus 8 (HHV-8) DNA sequences from her skin lesions and peripheral blood mononuclear cells (PBMC), but not her plasma, saliva or urine. An antibody test against HHV-8 lytic antigens was positive. Immunohistochemical staining detected latent antigen. There was no evidence of HHV-8 infection in her husband, sister or daughter. Genes coding for HHV-8-encoded viral interleukin-6, viral macrophage inflammatory protein I, viral G protein-coupled receptor, viral cyclin D and viral Bcl-2 were expressed to the same degree in both her skin lesion and PBMC. Latency-associated T0.7 mRNA and HHV-8-encoded viral tegument protein genes were expressed in her PBMC at levels lower than in the skin lesions. Based on the gene expression profile, we concluded that lytic HHV-8 infection was present in her skin lesions and PBMC.

NF-kappaB is essential for the progression of KSHV- and EBV-infected lymphomas in vivo

Activated NF-kappaB is a critical mechanism by which lymphoma cells infected by Epstein-Barr virus (EBV/HHV-4) and Kaposi sarcoma herpesvirus (KSHV/HHV-8) are protected from apoptotic stress. Selective pharmacologic inhibition of constitutive NF-kappaB activity induces apoptosis in KSHV- and EBV-infected lymphoma cells. In both tumor types, pharmacologic inhibition of NF-kappaB in vitro induced identical mitochondrially mediated apoptosis cascades. Assessment of gene regulation by microarray analysis revealed that the inhibition of NF-kappaB in tumor cells results in the down-regulation of a distinct group of prosurvival genes, including cIAP-1, cIAP-2, cFLIP, and IL-6. Using EBV- and KSHV-associated lymphomas in a murine system, we demonstrated that Bay 11-7082, a selective pharmacologic inhibitor of NF-kappaB, prevents or delays tumor growth and prolongs disease-free survival. Inhibition of NF-kappaB activity and tumor growth responses were further documented using a traceable reporter KSHV-positive cell line and in vivo imaging. These findings indicate that specific NF-kappaB-regulated survival factors work cooperatively to protect KSHV- and EBV-infected lymphoma cells from apoptosis such that they promote the establishment and progression of KSHV- and EBV-associated lymphomas in mice. They also support the use of selective NF-kappaB inhibitors in the treatment of herpesvirus-associated lymphomas.