Structural analyses of EBER1 and EBER2 ribonucleoprotein particles present in Epstein-Barr virus-infected cells

Screening for Epstein-Barr virus in Hodgkin's lymphoma

A link between chronic inflammation and cancer has been known for well over a century. However, direct evidence detailing the role of inflammation in carcinogenesis has been slow forthcoming. In Hodgkin's lymphoma (HL), a malignancy which has many features reminiscent of chronic inflammation, it is widely believed that Epstein-Barr virus (EBV) plays a role in the pathogenesis of a proportion of the cases. Indeed, this oncogenic virus has been consistently shown to be present in the malignant cells of HL. Furthermore, it is proposed that chronic inflammation, triggered by factors such as EBV, is likely to contribute to tumour cell proliferation, progression and inhibition of apoptosis. A sensitive and reliable method of demonstrating the presence of EBV at the cellular level is, therefore, of particular value when investigating a role for this ubiquitous virus in disease process. In this context, the technique of EBER in situ hybridization described here has become the gold standard for the detection of EBV in histological material.

Comprehensive profiling of Epstein-Barr virus microRNAs in nasopharyngeal carcinoma

Epstein-Barr Virus (EBV) establishes a long-term latent infection and is associated with a number of human malignancies that are thought to arise from deregulation of different stages of the viral life cycle. Recently, a large number of microRNAs (miRNAs) have been described for EBV, and it has been suggested that their expression may vary between the different latency states found in normal and malignant tissue. To date, however, no technique has been utilized to comprehensively and quantitatively test this idea by profiling expression of the EBV miRNAs in primary infected tissues. We describe here a multiplex reverse transcription-PCR assay that allows the profiling of 39 of the 40 known mature EBV miRNAs from as little as 250 ng of RNA. With this approach, we present a comprehensive profile of EBV miRNAs in primary nasopharyngeal carcinoma (NPC) tumors including estimates of miRNA copy number per tumor cell. This is the first comprehensive profiling of EBV miRNAs in any EBV-associated tumor. In contrast to previous suggestions, we show that the BART-derived miRNAs are present in a wide range of copy numbers from < or =10(3) per cell in both primary tumors and the widely used NPC-derived C666-1 cell line. However, we confirm the hypothesis that the BHRF1 miRNAs are not expressed in NPC. Lastly, we demonstrate that EBV miRNA expression in the widely used NPC line C666-1 is, with some caveats, broadly representative of primary NPC tumors.

The properties and functions of virus encoded microRNA, siRNA, and other small noncoding RNAs

microRNAs (miRNAs) represent a class of noncoding RNA species, believed to be regulating gene expression by binding to complementary sites in the 3'UTRs of target mRNAs. They play important regulatory roles in various metabolic pathways in most eukaryotes. The recent discovery of virus encoded miRNAs suggests that viruses may be using them to regulate host and viral gene expression. Another class of closely related small interfering RNAs (siRNAs) also has been found within the HIV-1 genome and shown to be exerting a limited impact on virus reproduction. Additionally, an additional type of viral noncoding RNAs named small noncoding RNAs (sncRNAs) ranging from a few tens to a few hundred nucleotides in length, has also been identified. sncRNAs have a wide phylogenesis and high levels of expression, suggesting they may play an important roles in different species. Here we discuss the genomic organization, expression, conservation as well as potential function of virally encoded miRNA, siRNA, and sncRNAs.

EBER2 RNA-induced transcriptome changes identify cellular processes likely targeted during Epstein Barr Virus infection

BACKGROUND

Little is known about the physiological role of the EBER1 and 2 nuclear RNAs during Epstein Barr viral infection. The EBERs are transcribed by cellular RNA Polymerase III and their strong expression results in 106 to 107 copies per EBV infected cell, making them reliable diagnostic markers for the presence of EBV. Although the functions of most of the proteins targeted by EBER RNAs have been studied, the role of EBERs themselves still remains elusive.

FINDINGS

The cellular transcription response to EBER2 expression using the wild-type and an internal deletion mutant was determined. Significant changes in gene expression patterns were observed. A functional meta-analysis of the regulated genes points to inhibition of stress and immune responses, as well as activation of cellular growth and cytoskeletal reorganization as potential targets for EBER2 RNA. Different functions can be assigned to different parts of the RNA.

CONCLUSION

These results provide new avenues to the understanding of EBER2 and EBV biology, and set the grounds for a more in depth functional analysis of EBER2 using transcriptome activity measurements.

Epstein-Barr virus-encoded small RNA induces IL-10 through RIG-I-mediated IRF-3 signaling

Epstein-Barr virus-encoded small RNA (EBER) is nonpolyadenylated, noncoding RNA, forms stem-loop structure by intermolecular base-pairing giving rise to double-stranded RNA (dsRNA)-like molecule and exists abundantly in EBV-infected cells. EBER induces IL-10 and thus supports the growth of Burkitt's lymphoma (BL) cells. In this study, the mechanism of IL-10 induction by EBER was analysed in the context of dsRNA signaling pathway. Knockdown of retinoic acid-inducible gene I (RIG-I) by small interfering RNA (siRNA), and expression of dominant-negative RIG-I downregulated IL-10 induction in EBER(+) EBV-infected and EBER plasmid-transfected BL cells. Transfection of EBER-expressing plasmid or in vitro synthesized EBER induced IL-10 in RIG-I-expressing cell clones, and activation of IL-10 promoter by EBER was blocked by dominant-negative RIG-I. Blocking of nuclear factor (NF)-kappaB by dominant-negative IkappaB-alpha plasmid did not block IL-10 expression, whereas knockdown of IRF-3 by siRNA resulted in downregulation of IL-10 in EBER(+) BL cells. NF-kappaB is reported to function downstream of RIG-I signaling pathway and is involved in the induction of proinflammatory cytokines. Our results indicate that EBER induces an anti-inflammatory cytokine IL-10 through RIG-I-mediated IRF-3 but not NF-kappaB signaling. These findings suggest a new mechanism of dsRNA signaling pathway that triggers the expression of IL-10, which acts as an autocrine growth factor in BL cells.

Detection of Epstein Barr virus by chromogenic in situ hybridization in cases of extra-hepatic biliary atresia

Introduction

Extra-hepatic biliary atresia (EHBA) is an important cause of neonatal cholestasis. Several infectious agents have been proposed as etiologic factors such as Rotavirus and Reovirus. There is limited data on the role of Epstein Barr virus (EBV) infection in EHBA, so we decided to study the presence of EBV virus in a series of 16 proven EHBA cases by Chromogenic in situ hybridization (CISH) technique.

Methods

In the current study a total of 16 liver wedge biopsies of proven cases of EHBA were selected in a period of 4 years. CISH staining for EBV-encoded RNA (EBER) transcript was performed.

Results

The review of H&E-stained slides of liver biopsies revealed fibrosis and marked ductular proliferation. In CISH-stained slides, EBV trace was observed in hepatocytes in two cases and in biliary epithelium in one case of EHBA.

Discussion

Considering the association of hepatitis with the Epstein-Barr virus in later life, it is likely that EBV hepatitis and its complications occur in the neonatal/perinatal period. Since EHBA is a relatively rare disease, a similar study on wedge biopsies of this number of proven cases of EHBA has not been performed to date. Current observation proposes the need for a study of larger series and employing other methods for confirming the etiologic role of EBV in EHBA cases.

Viral dsRNA inhibitors prevent self-association and autophosphorylation of PKR

Host response to viral RNA genomes and replication products represents an effective strategy to combat viral invasion. PKR is a Ser/Thr protein kinase that binds to double-stranded (ds)RNA, autophosphorylates its kinase domain, and subsequently phosphorylates eukaryotic initiation factor 2alpha (eIF2alpha). This results in attenuation of protein translation, preventing synthesis of necessary viral proteins. In certain DNA viruses, PKR function can be evaded by transcription of highly structured virus-encoded dsRNA inhibitors that bind to and inactivate PKR. We probe here the mechanism of PKR inhibition by two viral inhibitor RNAs, EBER(I) (from Epstein-Barr) and VA(I) (from human adenovirus). Native gel shift mobility assays and isothermal titration calorimetry experiments confirmed that the RNA-binding domains of PKR are sufficient and necessary for the interaction with dsRNA inhibitors. Both EBER(I) and VA(I) are effective inhibitors of PKR activation by preventing trans-autophosphorylation between two PKR molecules. The RNA inhibitors prevent self-association of PKR molecules, providing a mechanistic basis for kinase inhibition. A variety of approaches indicated that dsRNA inhibitors remain associated with PKR under activating conditions, as opposed to activator dsRNA molecules that dissociate due to reduced affinity for the phosphorylated form of PKR. Finally, we show using a HeLa cell extract system that inhibitors of PKR result in translational recovery by the protein synthesis machinery. These data indicate that inhibitory dsRNAs bind preferentially to the latent, dephosphorylated form of PKR and prevent dimerization that is required for trans-autophosphorylation.

Epstein-Barr virus (EBV)-encoded RNA 2 (EBER2) but not EBER1 plays a critical role in EBV-induced B-cell growth transformation

Epstein-Barr virus (EBV)-encoded RNA 1 (EBER1) and EBER2 are untranslated RNAs and the most abundant viral transcripts in latently EBV-infected cells. We previously reported that EBERs play a critical role in efficient EBV-induced growth transformation of primary B cells. To investigate whether EBER1 and EBER2 have distinct roles in B-cell growth transformation, recombinant EBVs carrying either EBER1 or EBER2 were generated. The transforming ability of recombinant EBVs expressing EBER2 was as high as that of EBVs expressing both EBER1 and EBER2. In contrast, the transforming ability of recombinant EBVs carrying EBER1 was impaired and was similar to that of EBV lacking both EBER1 and EBER2. Lymphoblastoid cell lines (LCLs) established with EBVs carrying EBER2 proliferated at low cell densities, while LCLs established with EBVs carrying EBER1 did not. Interleukin 6 (IL-6) production in LCLs expressing EBER2 was more abundant than in those lacking EBER2. The growth of LCLs lacking EBER2 was enhanced by the addition of recombinant IL-6 to the cell culture, while the growth of EBER2-expressing LCLs was inhibited by a neutralizing anti-IL-6 antibody. These results demonstrate that EBER2, but not EBER1, contributes to efficient B-cell growth transformation. We conclude that EBER1 and EBER2, despite their structural similarity, have different functions in latently infected lymphoblastoid cells.

A phylogenetically conserved RNA structure in the poliovirus open reading frame inhibits the antiviral endoribonuclease RNase L

RNase L is an antiviral endoribonuclease that cleaves viral mRNAs after single-stranded UA and UU dinucleotides. Poliovirus (PV) mRNA is surprisingly resistant to cleavage by RNase L due to an RNA structure in the 3C(Pro) open reading frame (ORF). The RNA structure associated with the inhibition of RNase L is phylogenetically conserved in group C enteroviruses, including PV type 1 (PV1), PV2, PV3, coxsackie A virus 11 (CAV11), CAV13, CAV17, CAV20, CAV21, and CAV24. The RNA structure is not present in other human enteroviruses (group A, B, or D enteroviruses). Coxsackievirus B3 mRNA and hepatitis C virus mRNA were fully sensitive to cleavage by RNase L. HeLa cells expressing either wild-type RNase L or a dominant-negative mutant RNase L were used to examine the effects of RNase L on PV replication. PV replication was not inhibited by RNase L activity, but rRNA cleavage characteristic of RNase L activity was detected late during the course of PV infection, after assembly of intracellular virus. Rather than inhibiting PV replication, RNase L activity was associated with larger plaques and better cell-to-cell spread. Mutations in the RNA structure associated with the inhibition of RNase L did not affect the magnitude of PV replication in HeLa cells expressing RNase L, consistent with the absence of observed RNase L activity until after virus assembly. Thus, PV carries an RNA structure in the 3C protease ORF that potently inhibits the endonuclease activity of RNase L, but this RNA structure does not prevent RNase L activity late during the course of infection, as virus assembly nears completion.

Epstein-Barr virus in patients with chronic lymphocytic leukemia: a pilot study

The objective of this study was to assess the incidence and the clinical significance of Epstein-Barr virus (EBV) in patients with chronic lymphocytic leukemia (CLL)/small lymphocytic lymphoma (SLL). Patients with CLL/SLL who presented at The University of Texas M. D. Anderson Cancer Center over a 2-year period and had available marrow paraffin blocks were studied for evidence of EBV infection using a highly specific in-situ hybridization assay for detection of EBV encoded RNA (EBERs). Results were analysed in relation to other presenting characteristics and outcome. Thirty-two patients were examined. EBERs were detected in the bone marrow of 12 of 32 (38%) CLL/SLL marrows vs 0 of 20 normal marrows (p = 0.002). EBERs were observed in sporadic granulocytes alone or in addition to its presence in lymphocytes in nine of the 12 EBV-positive patients. EBERs were detected less frequently in patients with Rai stage 0 - 1 disease (20%) compared with Rai stage 2 - 4 (66%; p = 0.008). EBER-positive patients tended to have higher lactate dehydrogenase levels (p = 0.053). The 10-year survival rate was 22% vs 58% for patients with and without discernible EBERs (log-rank, p = 0.08). Evidence of EBV infection was found in 38% of patients with CLL/SLL. Despite the small number of patients tested, discernable EBERs were significantly more common in individuals with more advanced Rai stage and there was a trend toward shorter survival in patients in whom EBV EBERs were discerned. Larger studies are needed to determine the prognostic value and role of EBV infection in patients with CLL/SLL.

EB virus-encoded RNAs are recognized by RIG-I and activate signaling to induce type I IFN

Epstein-Barr virus (EBV)-encoded small RNAs (EBERs) are nonpolyadenylated, untranslated RNAs, exist most abundantly in latently EBV-infected cells, and are expected to show secondary structures with many short stem-loops. Retinoic acid-inducible gene I (RIG-I) is a cytosolic protein that detects viral double-stranded RNA (dsRNA) inside the cell and initiates signaling pathways leading to the induction of protective cellular genes, including type I interferons (IFNs). We investigated whether EBERs were recognized by RIG-I as dsRNA. Transfection of RIG-I plasmid induced IFNs and IFN-stimulated genes (ISGs) in EBV-positive Burkitt's lymphoma (BL) cells, but not in their EBV-negative counterparts or EBER-knockout EBV-infected BL cells. Transfection of EBER plasmid or in vitro-synthesized EBERs induced expression of type I IFNs and ISGs in RIG-I-expressing, EBV-negative BL cells, but not in RIG-I-minus counterparts. EBERs activated RIG-I's substrates, NF-kappaB and IFN regulatory factor 3, which were necessary for type I IFN activation. It was also shown that EBERs co-precipitated with RIG-I. These results indicate that EBERs are recognized by RIG-I and activate signaling to induce type I IFN in EBV-infected cells.

Detection of Epstein-Barr virus in lower gastrointestinal tract lymphomas: a study in Malaysian patients

BACKGROUND

Many studies in the literature have shown that Epstein-Barr virus (EBV) is associated with several human lymphoid and epithelial malignancies. However, the prevalence of EBV in non-Hodgkin lymphoma (NHL) of the lower gastrointestinal (GI) tract has not been fully elucidated.

AIM

The aim of this study was to determine the presence and distribution of EBV in formalin-fixed paraffin-embedded tissue samples obtained from 18 Malaysian patients diagnosed with NHL of the lower GI tract.

METHODS

The GI tract lymphoma tissue samples analyzed for the presence of EBV were divided into the following groups: NHL of the small intestine (seven cases); NHL of the ileocecum (ten cases); and NHL of the rectum (one case). The presence of EBV-encoded RNA (EBER) in all of the above tissue samples was tested for using conventional in situ hybridization technology.

RESULTS

Two of 18 cases (11.1%) of NHL of the lower GI tract demonstrated positive signals for EBV/EBER. In the first positive case, EBV/EBER signals were located in lymphoma cells in the serosa layer of the small intestine. In the second EBV/EBER-positive case, EBV/EBER signals were detected in diffuse B-cell lymphoma of the ileocecum.

CONCLUSION

These findings demonstrate a rare association between EBV and lower GI tract lymphomas in this group of Malaysian patients.

Inhibition of PKR by RNA and DNA viruses

Interferons were the first of the anti-viral innate immune modulators to be characterized, initially characterized solely as anti-viral proteins [reviewed in Le Page, C., Genin, P., Baines, M.G., Hiscott, J., 2000. Inteferon activation and innate immunity. Rev. Immunogenet. 2, 374-386]. As we have progressed in our understanding of the interferons they have taken a more central role in our understanding of innate immunity and its interplay with the adaptive immune response. One of the key players in function of interferon is the interferon-inducible enzyme, protein kinase (PKR, activatable by RNA). The key role played by PKR in the innate response to virus infection is emphasized by the large number of viruses, DNA viruses as well as RNA viruses, whose hosts range from insects to humans, that code for PKR inhibitors. In this review we will first describe activation of PKR and then describe the myriad of ways that viruses inhibit function of PKR.

Multiple domains of EBER 1, an Epstein-Barr virus noncoding RNA, recruit human ribosomal protein L22

EBER 1, a small noncoding viral RNA abundantly expressed in all cells transformed by Epstein-Barr virus (EBV), has been shown to associate with the human ribosomal protein L22. Here we present in vitro binding studies using purified RNAs and recombinant proteins. Electrophoretic mobility-shift assays (EMSAs) show that recombinant L22 (rL22) and maltose-binding protein (MBP)-tagged L22 protein bind EBER 1 in vitro, both forming three specific protein-dependent mobility shifts. Use of a mixture of rL22 and MBP-L22 indicates that these three shifts contain one, two, or three L22 proteins per EBER 1 molecule. EMSAs performed with EBER 1 deletion constructs and EBER 1 stem-loops inserted into a nonbinding RNA, HSUR 3, identify stem-loops I, III, and IV as L22 binding sites. The existence of multiple L22 binding sites on EBER 1 inside cells is demonstrated by in vivo UV cross-linking. Our results are discussed with respect to the function of EBER 1 in EBV-infected human B cells.

The effect of Epstein-Barr virus status on clinical outcome in Hodgkin's lymphoma

The association of Epstein-Barr virus (EBV) with Hodgkin's lymphoma (HL) has been investigated over the last few years. The impact of EBV on clinical outcome is still controversial, however. In this study, we investigated the effect of EBV status on clinical outcome of HL patients. Between January 1986 and September 2004, fifty-six patients, diagnosed as having HL, were included in the analysis. Clinical data were reviewed retrospectively from the patients' records. Tissues from 56 patients were analyzed for the presence of EBV using the in situ hybridization (ISH) for EBV-encoded RNA (EBER) and immunohistochemistry for latent membrane protein (LMP)1. EBV infection was identified in 41.1% of cases by EBER ISH, 26.8% by LMP1 expression, and 26.8% by LMP1 and EBER ISH. EBER-positive HL were significantly more frequent in mixed cellularity (MC) subtype (P=0.014) and advanced stage (P=0.034). There was a trend toward shorter overall survival in EBER-positive patients without statistical significance (P=0.238). LMP1 expression also correlated with MC subtype (P=0.006) and advanced stage (P=0.007), although it did not significantly influence the survival outcome. In subgroup analysis, both EBER and LMP1 positivities were associated with longer progression-free survival in patients with age <25 years old (P=0.045). Reverse trends were shown in patients > or =25 years old. In this study, we demonstrated that the impact of tumor EBV status on prognosis may be age dependent and young patients with latent EBV infection have favorable prognosis.

Protection from interferon-induced apoptosis by Epstein-Barr virus small RNAs is not mediated by inhibition of PKR

The Epstein-Barr virus (EBV) EBER transcripts are small, highly structured RNAs able to bind to and inhibit activation of the double-stranded RNA-dependent protein kinase PKR in cell-free systems, and within latently infected B-cell lines they inhibit alpha interferon-induced apoptosis that is believed to be mediated through PKR. Here, we address the consequences of EBER expression for PKR activation in vivo in response to alpha interferon. In agreement with published findings, either EBV infection or the EBERs alone protected Burkitt lymphoma cells from alpha-interferon-induced apoptosis. However, utilizing multiple phosphorylation state-specific antibodies to monitor PKR activation within cells in response to interferon, we demonstrate that the EBERs are unable to inhibit phosphorylation of either cytoplasmic or nuclear PKR. Concordantly, a direct substrate of PKR, the alpha subunit of eukaryotic initiation factor 2 (eIF-2alpha), was equally phosphorylated in EBV-positive and EBV-negative cells following interferon treatment. Therefore, EBER inhibition of alpha-interferon-induced apoptosis, and potentially other PKR-mediated events, is unlikely to be mediated through direct inhibition of PKR, as previously thought.

RNAi and RNA-based regulation of immune system function

Gene regulation by short RNAs is a ubiquitous and important mode of control. MicroRNAs are short, single-strand RNAs that bind with partial complementarity to the 3' untranslated region of several genes to silence their expression. This expanding class of endogenous short RNAs are evolutionarily conserved and participate in control of development and cell-specific gene function. Several of these microRNAs have been cloned uniquely from mammalian lymphocytes suggesting specialized roles in lymphocyte development and function. In addition, several genes linked to RNAi in lower eukaryotes have mammalian homologs with specialized roles in adaptive immunity. For example, in worms, the nonsense-mediated decay (NMD) and RNAi pathways appear to be intricately linked. NMD plays a key role in regulating antigen-receptor expression in lymphocytes and there are mammalian homologs for factors identified in worms that appear to be common in both RNAi and NMD pathways. On the other hand, RNA editing and RNAi have an inverse relationship and RNA editing has an important role in viral immunity. These observations indicate unique roles for dsRNAs in the mammalian immune system.

Ribosomal protein L22 inhibits regulation of cellular activities by the Epstein-Barr virus small RNA EBER-1

Epstein-Barr virus (EBV) is a potent mitogenic and antiapoptotic agent for B lymphocytes and is associated with several different types of human tumour. The abundantly expressed small viral RNA, EBER-1, binds to the growth inhibitory and pro-apoptotic protein kinase R (PKR) and blocks activation of the latter by double-stranded RNA. Recent evidence has suggested that expression of EBER-1 alone in EBV-negative B cells promotes a tumorigenic phenotype and that this may be related to inhibition of the pro-apoptotic effects of PKR. The ribosomal protein L22 binds to EBER-1 in virus-infected cells, but the significance of this has not previously been established. We report here that L22 and PKR compete for a common binding site on EBER-1. As a result of this competition, L22 interferes with the ability of the small RNA to inhibit the activation of PKR by dsRNA. Transient expression of EBER-1 in murine embryonic fibroblasts stimulates reporter gene expression and partially reverses the inhibitory effect of PKR. However, EBER-1 is also stimulatory when transfected into PKR knockout cells, suggesting an additional, PKR-independent, mode of action of the small RNA. Expression of L22 prevents both the PKR-dependent and -independent effects of EBER-1 in vivo. These results suggest that the association of L22 with EBER-1 in EBV-infected cells can attenuate the biological effects of the viral RNA. Such effects include both the inhibition of PKR and additional mechanism(s) by which EBER-1 stimulates gene expression.

Epstein-Barr virus latency in kidney specimens from transplant recipients

BACKGROUND

Epstein-Barr virus (EBV) infection is common in immunosuppressed patients and can lead to life threatening lymphoproliferative diseases. Small numbers of cells infected by EBV have been detected in human tissues, transplanted or non-transplanted. Little is known about EBV latency in the allograft kidneys of patients without post-transplant lymphoproliferative disease (PTLD). The aims of this study were to look for the presence of EBV-encoded small RNAs (EBER) in allograft kidneys and to quantify their expression.

METHODS

We analysed 62 allograft nephrectomies and 20 native kidneys to determine the presence of EBV; we also quantified its expression and calculated its ratios to CD45 and CD20 cells. The techniques used were: tissue microarray, EBER-1- and 2-specific in situ hybridization and immunohistochemistry.

RESULTS

EBER expression was detected in 30.6% of transplanted kidneys and 5% of non-transplanted kidneys. In the positive specimens, a mean of 8.2 cells/1.57 mm(2) expressed the EBERs (range 1-38 cells). The ratios of EBER-positive (+) cells to CD45 or CD20 cells were 1.7 +/- 2.4% (range 0.1-8.1%) and 8.4 +/- 10.9% (range 0.5-34.4%), respectively. No relationship was found between anti-T-cell treatment and EBER expression in the failed allografts.

CONCLUSIONS

In failed kidney allografts, a small number of lymphocytes can express EBV latency. The number of EBER+ cells is smaller than in PTLD. Studies of functioning grafts are necessary to better understand the clinical relevance of this expression.

Geographic variation in Epstein-Barr virus-associated Burkitt's lymphoma in children from Brazil

In developing countries, BL has a strong association with EBV infection during childhood. In South America, the data have shown an EBV association intermediate between that reported in the United States (30%) and that in equatorial Africa (95%). Early age at EBV infection and lower socioeconomic status have been related to increased EBV-associated BL in developing countries. In Brazil, there are not enough data on childhood BL related to EBV infection. Our aim was to evaluate the clinicopathologic features and EBV association of 44 children with NHL from the state of Rio de Janeiro, situated in the southeast of Brazil. EBV was detected using RNA in situ hybridization in 36 biopsy specimens. DNA from fresh tumor samples and from paraffin-embedded tissues of patients were analyzed by PCR, in which the first reaction included primers for an EBNA-2 common region while the nested reaction amplified the region discriminating between EBV types 1 and 2 in separate reactions. EBV was detected in 21 of 29 BLs (72%), and type 1 virus infected the majority of EBV-positive BLs (18/21). There was a trend for younger age in children with EBV-positive BL compared to EBV-negative BL (median age 4 compared to 6 years, respectively; p = 0.056). Our study confirmed that in the southeast of Brazil BL had an intermediate association with EBV. A higher rate of EBV-associated BL was described in the northeast of Brazil. These differences are probably related to regional socioeconomic status. In conclusion, our study suggests that early infection with EBV in the background of a low socioeconomic condition associated with other environmental factors could contribute to BL in Brazil.

Efficient transcription of the EBER2 gene depends on the structural integrity of the RNA

A 3'-truncated EBER2 RNA gene, although containing all previously identified promoter elements, revealed drastically reduced transcription rates in vitro and in vivo when fused to a heterologous terminator sequence. Inactivations were also observed with double point mutations affecting 5'- or 3'-end sequences of the EBER2 gene. However, wild-type activity of these mutants could be restored by compensatory mutations of the opposite strand of the EBER2 RNA sequence. A similar rescue was achieved with the 3'-truncated EBER2 gene, if the heterologous terminator was adapted for complementarity to the initiator element of the construct. Yet, double-strandedness alone of the RNA ends was not sufficient for high transcriptional activity of these gene constructs. Rather, the use of a nonrefoldable spacer, separating the 5'- and 3'-stem-loop structures, demonstrated that spatial proximity of the ends of EBER2 RNA was required. Furthermore, decay kinetics of wild-type and mutant RNA synthesized in vitro indicated that the effects observed could not be explained by altered transcript stability. Finally, single-round transcription confirmed that the reduced expression of mutant genes was not caused by decreased primary initiation reactions. In addition, differential sarcosyl concentrations demonstrated that the rate of reinitiation clearly was affected with the mutant EBER2 genes. Together, these results indicate that the secondary structure of this viral RNA represents a major determinant for efficient transcription of the EBER2 gene by host cell RNA polymerase III.

Gamma herpesviruses: pathogenesis of infection and cell signaling

Altered cell signaling is the molecular basis for cell proliferation occurring in association with several gamma herpesvirus infections. Three gamma herpesviruses, namely EBV/HHV-4, KSHV/HHV-8 and the MHV-68 (and/or MHV-72) and their unusual cell-pirated gene products are discussed in this respect. The EBV, KSHV as well as the MHV DNA may persist lifelong in an episomal form in the host carrier cells (mainly in lymphocytes but also in macrophages, in non-hornifying squamous epithelium and/or in blood vessel endothelial cells). Under conditions of extremely limited transcription, the EBV-infected cells express EBNA1 (EB nuclear antigen 1), the KSHV infected cells express LANA1 (latent nuclear antigen 1), while the MHV DNA carrier cells express the latency-associated protein M2. With the full set of latency-associated proteins expressed, EBV carrier cells synthesize additional EBNAs and at least one LMP (latent membrane protein 1). The latent KSHV carrier cells, in addition to LANA1, may express a viral cyclin, a viral Fas-DD-like ICE inhibitor protein (vFLIP) and a virus-specific transformation protein called kaposin (K12). In MHV latency with a wide expression of latency-associated proteins, the carrier cells express a LANA analogue (ORF73), the M3 protein, the K3/IE (immediate early) proteins and M11/bcl-2 homologue proteins. During the period of limited gene expression, the latency-associated proteins serve mainly for the maintenance of the latent episomal DNA (a typical example is EBNA1). In contrast, during latency with a broader spectrum gene expression, the virus-encoded products activate transcription of otherwise silenced cellular genes, which leads to the synthesis of enzymes capable of promoting not only viral but also cellular DNA replication. Thus, the latency-associated proteins block apoptosis and drive host cells towards division and immortalization. Proliferation of hemopoetic cells, which had become gamma herpesvirus DNA carriers, can be initiated and strongly enhanced in the presence of inflammatory cytokines and by virus-encoded analogues of interleukins, chemokines and IFN regulator proteins. At early stages of tumor formation, many proliferating hemopoetic and/or endothelium cells, which had became transcriptionally active under the influence of chemokines and cytokines, may not yet be infected. In contrast, at later stages of oncogenesis, the virus-encoded proteins, inducing false signaling and activating the proliferation pathways, bring the previously infected cells into full transformation burst.

Pathogenic roles for Epstein-Barr virus (EBV) gene products in EBV-associated proliferative disorders

Epstein-Barr virus (EBV) is associated with a still growing spectrum of clinical disorders, ranging from acute and chronic inflammatory diseases to lymphoid and epithelial malignancies. Based on a combination of in vitro and in vivo findings, EBV is thought to contribute in the pathogenesis of these diseases. The different EBV gene expression patterns in the various disorders, suggest different EBV-mediated pathogenic mechanisms. In the following pages, an overview of the biology of EBV-infection is given and functional aspects of EBV-proteins are discussed and their putative role in the various EBV-associated disorders is described. EBV gene expression patterns and possible pathogenic mechanisms are discussed. In addition, expression of the cellular genes upregulated by EBV in vitro is discussed, and a comparison with the in vivo situation is made.

Regulation by RNA

In recent years, noncoding RNAs (ncRNAs) have been shown to constitute key elements implicated in a number of regulatory mechanisms in the cell. They are present in bacteria and eukaryotes. The ncRNAs are involved in regulation of expression at both transcriptional and posttranscriptional levels, by mediating chromatin modifications, modulating transcription factor activity, and influencing mRNA stability, processing, and translation. Noncoding RNAs play a key role in genetic imprinting, dosage compensation of X-chromosome-linked genes, and many processes of differentiation and development.

The binding site of the RNA-dependent protein kinase (PKR) on EBER1 RNA from Epstein-Barr virus

The RNA-dependent protein kinase (PKR) is an interferon-induced, RNA-activated enzyme that phosphorylates the eukaryotic initiation factor 2alpha, rendering the translation machinery inactive. Viruses have developed strategies for preventing the action of PKR, one of which is the production of small RNAs that inhibit the enzyme. Epstein-Barr virus (EBV) encodes EBER1, a 167 nucleotide non-coding RNA that is constitutively expressed by the EBV-infected cells. EBER1 binds PKR in vitro and has been shown to prevent inhibition of translation by PKR in vitro. We used affinity cleavage by the EDTA.Fe-modified double-stranded RNA-binding domain (dsRBD) of PKR to show that stem-loop IV (nucleotides 87-123) of EBER1 makes specific contacts with the dsRBD. To further demonstrate the specificity of this interaction, we generated a deletion mutant of EBER1, comprising only stem-loop IV (mEBER1). Cleavage patterns produced on mEBER1 by the bound dsRBD were remarkably similar to those found on full-length EBER1. Using cleavage data from two different dsRBD mutants, we present a model of the interaction of PKR dsRBD and mEBER1.

In vivo effects of the Epstein-Barr virus small RNA EBER-1 on protein synthesis and cell growth regulation

Recent studies have suggested a role for the Epstein-Barr virus-encoded RNA EBER-1 in malignant transformation. EBER-1 inhibits the activity of the protein kinase PKR, an inhibitor of protein synthesis with tumour suppressor properties. In human 293 cells and murine embryonic fibroblasts, transient expression of EBER-1 promoted total protein synthesis and enhanced the expression of cotransfected reporter genes. However reporter gene expression was stimulated equally well in cells from control and PKR knockout mice. NIH 3T3 cells stably expressing EBER-1 exhibited a greatly increased frequency of colony formation in soft agar, and protein synthesis in these cells was relatively resistant to inhibition by the calcium ionophore A23187. Nevertheless clones containing a high concentration of EBER-1 were not invariably tumourigenic. We conclude that EBER-1 can enhance protein synthesis by a PKR-independent mechanism and that, although this RNA may contribute to the oncogenic potential of Epstein-Barr virus, its expression is not always sufficient for malignant transformation.

The Epstein-Barr virus and post-transplant lymphoproliferative disease: interplay of immunosuppression, EBV, and the immune system in disease pathogenesis

Transplant patients are at particular risk for developing post-transplant lymphoproliferative disease (PTLD) following administration of immunosuppressive therapy. In many cases the PTLD lesions express Epstein-Barr virus (EBV) latent and lytic genes as well as elevated levels of host cytokines. An outline of the potential contributions of EBV, host cytokines and T cells, and the immunosuppressive cyclosporine A, tacrolimus, and anti-CD3 antibody in the mechanism and pathogenesis of this disease is presented and discussed.

Assessment of the prognostic impact of the Epstein-Barr virus-encoded latent membrane protein-1 expression in Hodgkin's disease

We have examined expression of the Epstein-Barr virus (EBV) latent membrane protein-1 (LMP1) in the malignant Hodgkin and Reed-Sternberg (HRS) cells of Hodgkin's disease (HD) and its impact on response to treatment and on survival. Paraffin tissue from 100 adult immunocompetent patients with HD were analysed using immunohistochemistry to identify LMP1 expression. According to the Rye classification, 8% of patients had lymphocyte predominance (LP) subtype, 48% had nodular sclerosis (NS) disease, 37% were of the mixed cellularity (MC) subtype and 7% were of the lymphocyte depletion (LD) subtype. During the five year follow-up period 27 patients died and 74 patients achieved a complete remission. Patients with LD subtype were older (P = 0.03), less frequently achieved complete remission (P = 0.01), had shorter disease-free survival (P = 0.01) and overall survival (P = 0.002) compared with the other subtypes of HD. LMP1 expression was found in the tumour cells of 26% of cases of HD. LMP1 expression was less common in NS disease than in the other subtypes (P = 0.05), whereas an association between MC subtype and LMP1 expression was not found (P = 0.22). Using the log-rank test there were no differences in overall survival or disease-free survival based on EBV status either when all patients were analysed or when LD and LP subtypes were excluded. However, the presence of EBV was associated with significantly longer disease-free survival in the subgroup of patients </= 30 years old (P = 0.02) and in those patients </= 34 years old (P = 0.05). In contrast, there was a trend for shorter disease-free survival for EBV-positive patients in the subgroup > 35 years old, but this difference was not statistically significant (P = 0.11). A similar trend was observed in patients > 50 years old. Analysis of the impact of LMP1 expression in patients who had different stage and B symptoms status showed that expression of EBV was associated with longer disease-free survival (P = 0.019) in early stage (1 + 2) patients without B symptoms. Significant differences in the other subgroups based on EBV status was not found. Factors adversely affecting the likelihood to achieve a complete remission were: absence of LMP1 expression (OR 6.4, 95% Cl 1.07-38.5, P = 0.04), age (OR 1.68, 95%Cl 1.15-2.5, P = 0.007) and subtype of HD (OR 3.32, 95%Cl 1.11-9.94, P = 0.03). Age and subtype of HD had an independent impact on overall survival (P = 0.01). We conclude that expression of LMP1 in HRS cells has a favourable impact on prognosis for HD patients, but that this effect may be restricted to young adult patients and those with early stage disease.

Molecular virology of Epstein-Barr virus

Epstein-Barr virus (EBV) interacts with its host in three distinct ways in a highly regulated fashion: (i) EBV infects human B lymphocytes and induces proliferation of the infected cells, (ii) it enters into a latent phase in vivo that follows the proliferative phase, and (iii) it can be reactivated giving rise to the production of infectious progeny for reinfection of cells of the same type or transmission of the virus to another individual. In healthy people, these processes take place simultaneously in different anatomical and functional compartments and are linked to each other in a highly dynamic steady-state equilibrium. The development of a genetic system has paved the way for the dissection of those processes at a molecular level that can be studied in vitro, i.e. B-cell immortalization and the lytic cycle leading to production of infectious progeny. Polymerase chain reaction analyses coupled to fluorescent-activated cell sorting has on the other hand allowed a descriptive analysis of the virus-host interaction in peripheral blood cells as well as in tonsillar B cells in vivo. This paper is aimed at compiling our present knowledge on the process of B-cell immortalization in vitro as well as in vivo latency, and attempts to integrate this knowledge into the framework of the viral life cycle in vivo.

Straightening of bulged RNA by the double-stranded RNA-binding domain from the protein kinase PKR

The human interferon-induced protein kinase, PKR, is an antiviral agent that is activated by long stretches of double-stranded (ds)RNA. PKR has an N-terminal dsRNA-binding domain that contains two tandem copies of the dsRNA-binding motif and interacts with dsRNA in a nonsequence-specific fashion. Surprisingly, PKR can be regulated by certain viral and cellular RNAs containing non-Watson-Crick features. We found that RNAs containing bulges in the middle of a helix can bind to p20, a C-terminal truncated PKR containing the dsRNA-binding domain. Bulges are known to change the global geometry of RNA by bending the helical axis; therefore, we investigated the conformational changes of bulged RNA caused by PKR binding. A 66-mer DNA-RNA(+/- A(3) bulge)-DNA chimera was constructed and annealed to a complementary RNA strand. This duplex forces the protein to bind in the middle. A 66-mer duplex with a top strand composed of DNA-DNA(+/-A(3) bulge)-RNA was used as a control. Gel mobility-shift changes among the RNA-protein complexes are consistent with straightening of bulged RNA on protein binding. In addition, a van't Hoff analysis of p20 binding to bulged RNA reveals a favorable DeltaDeltaH degrees and an unfavorable DeltaDeltaS degrees relative to binding to straight dsRNA. These thermodynamic parameters are in good agreement with predictions from a nearest-neighbor analysis for RNA straightening and support a model in which the helical junction flanking the bulge stacks on protein binding. The ability of dsRNA-binding motif proteins to recognize and straighten bent RNA has implications for modulating the topology of RNAs in vivo.

Epstein-Barr virus small RNAs potentiate tumorigenicity of Burkitt lymphoma cells independently of an effect on apoptosis

The tumorigenic potential of the Burkitt lymphoma (BL) cell line Akata is dependent on the restricted latency program of Epstein-Barr virus (EBV) that is characteristically maintained in BL tumors. Within these cells, EBV-mediated inhibition of apoptosis correlates with an up-regulation of BCL-2 levels in concert with a down-regulation in c-MYC expression that occurs under growth-limiting conditions. Here we addressed whether EBV's effects on apoptosis and tumorigenicity are mediated by the EBV small RNAs EBER-1 and EBER-2. Stable expression of the EBERs in EBV-negative Akata BL cells, at levels comparable to those in EBV-positive cells, significantly enhanced the tumorigenic potential of EBV-negative BL cells in SCID mice, but did not fully restore tumorigenicity relative to EBV-positive Akata cells. Furthermore, wild-type or greater levels of EBER expression in EBV-negative Akata cells did not promote BL cell survival. These data therefore suggest that EBV can contribute to BL through at least two avenues: an EBER-dependent mechanism that enhances tumorigenic potential independent of a direct effect on apoptosis, and a second mechanism, mediated by an as-yet-unidentified EBV gene(s), that offsets the proapoptotic consequences of deregulated c-MYC in BL.

Cloning of the rhesus lymphocryptovirus viral capsid antigen and Epstein-Barr virus-encoded small RNA homologues and use in diagnosis of acute and persistent infections

Epstein-Barr virus (EBV) is the most common cause of infectious mononucleosis and is associated with the development of several human malignancies. A closely related herpesvirus in the same lymphocryptovirus (LCV) genera as EBV naturally infects rhesus monkeys and provides an important animal model for studying EBV pathogenesis. We cloned the small viral capsid antigen (sVCA) homologue from the rhesus LCV and developed a peptide enzyme-linked immunosorbent assay (ELISA) to determine whether epitopes in the rhesus LCV sVCA are a reliable indicator of rhesus LCV infection. In order to define a "gold standard" for rhesus LCV infection, we also cloned the EBV-encoded small RNA 1 (EBER1) and EBER2 homologues from rhesus LCV and developed a reverse transcription (RT)-PCR assay to detect persistent LCV infection in rhesus monkey peripheral blood lymphocytes. Animals from a conventional and a hand-reared colony were studied to compare the prevalence of rhesus LCV infection in the two groups. There was a 100% correlation between the peptide ELISA and EBER RT-PCR results for rhesus LCV infection. In addition, specificity for LCV infection and exclusion of potential cross-reactivity to the rhesus rhadinovirus sVCA homologue could be demonstrated using sera from experimentally infected animals. These studies establish two novel assays for reliable diagnosis of acute and persistent rhesus LCV infections. The rhesus LCV sVCA peptide ELISA provides a sensitive and reliable assay for routine screening, and these studies of the hand-reared colony confirm the feasibility of raising rhesus LCV-naive animals.

Human herpesvirus 8-associated solid lymphomas that occur in AIDS patients take anaplastic large cell morphology

Human herpesvirus type 8 (HHV-8; Kaposi's sarcoma-associated herpesvirus) is a recently isolated human herpesvirus frequently identified in Kaposi's sarcoma, primary effusion lymphoma, and multicentric Castleman's disease. Here we report three cases of HHV-8-bearing solid lymphomas that occurred in AIDS patients (Cases 1-3). All three patients were homosexual men presenting extranodal masses in the lungs (Case 1) or skin (Cases 2 and 3), together with the presence of Kaposi's sarcoma (Case 1), primary effusion lymphoma (Case 2), or multicentric Castleman's disease (Case 3). These solid lymphomas exhibited anaplastic large cell morphology and expressed CD30, corresponding to the recent diagnostic criteria of anaplastic large cell lymphoma (ALCL). The chromosomal translocation t(2;5)-associated chimeric protein p80NPM/ALK was not observed in any of these cases. HHV-8 was detected in all of these cases by polymerase chain reaction, immunohistochemistry of HHV-8-encoded ORF73 protein, and in situ hybridization of T1.1. Epstein-Barr virus was detected only in Cases 2 and 3 by in situ hybridization. It is interesting that inoculation of a cell line obtained from a primary effusion lymphoma cell in Case 2 to severe combined immunodeficiency mice produced HHV-8-positive and Epstein-Barr virus-negative tumors in inoculated sites. These tumor cells exhibited phenotypes of ALCL that were identical to the subcutaneous tumor cells of this particular patient. These findings clearly show that HHV-8 can associate with solid lymphomas and that it can take anaplastic large cell morphology. Those lymphomas should be distinguished from the classical ALCL as were defined by the revised European-American classification of lymphoid neoplasms even though morphology and a part of immunophenotype mimic that of classical ALCL.

Absence of Epstein-Barr virus (EBV) in intrahepatic cholangiocarcinoma confirmed by lack of EBV-coded nuclear RNA and latent membrane protein-1

AIMS

Studies are disclosing that Epstein-Barr virus (EBV) is involved in the aetiology of various neoplasms including undifferentiated carcinomas of the aerodigestive tract. The aetiology of intrahepatic cholangiocarcinoma (ICC), a malignant neoplasm arising from intrahepatic biliary epithelia, has yet to be fully evaluated. To date, two cases of EBV-related ICC have been reported, and they presented foci of lymphoepitheliomatous undifferentiated carcinoma components.

METHODS AND RESULTS

To determine whether EBV is commonly involved in the developments of ICC, we performed in-situ hybridization and immunohistochemistry for EBV in 215 cases of ICC in Japan, using a probe against EBV-coded nuclear RNA (EBER) and a specific antibody against latent membrane protein-1 (LMP-1), respectively. We did not detect EBV-infected carcinoma cells in any of the ICC cases examined. No lymphoepitheliomatous undifferentiated carcinoma components were found either.

CONCLUSION

The results suggest that EBV infection is unlikely to be involved in the pathogenesis of ICC.

Epstein-Barr virus-induced posttransplant lymphoproliferative disorders. ASTS/ASTP EBV-PTLD Task Force and The Mayo Clinic Organized International Consensus Development Meeting

Epstein-Barr virus-induced posttransplant lymphoproliferative disease (EBV-PTLD) continues to be a major complication after solid organ transplantation in high-risk patients. Despite the identification of risk factors that predispose patients to develop EBV-PTLD, limitations in our knowledge of its pathogenesis, variable criteria for establishing the diagnosis, and lack of randomized studies addressing the prevention and treatment of EBV-PTLD hamper the optimal management of this transplant complication. This review summarizes the current knowledge of EBV-PTLD and, as a result of two separate international meetings on this topic, and provides recommendations for future areas of study.

Detection of Epstein-Barr virus in esophageal squamous cell carcinoma in Taiwan

OBJECTIVE

Recently, an association between viral infection and the development of esophageal carcinoma has been reported, particularly the human papilloma virus (HPV) and Esptein-Bar virus (EBV). However, geographic variation in carcinogenesis is realized. In this study, we investigate the viral carcinogenesis and the biologic effect of viral infection on esophageal squamous cell carcinoma (ESCC) in Taiwan.

METHODS

To determine the association of viral infection (EBV and HPV) with ESCC, we applied polymerase chain reaction (PCR), immunohistochemistry, and in situ hybridization (ISH) to examine 119 surgical specimens from different sites of esophagus in 31 ESCC patients. Additionally, an immunoperoxidase method was used to detect EBV latent membrane protein-1 (LMP-1), p53, CD45RO (UCHL-1), Fas ligand (Fas L), and RNA ISH with oligonucleotide sequences was used to detected interleukin-6 (IL-6) mRNA.

RESULTS

By PCR, EBV DNA was detected in 11 cases (35.5%). Expression of EBERs in ESCC was further confirmed with ISH. Nonetheless, no LMP-1 expression was detected. On the other hand, human papillomavirus (HPV) was identified in only one case (3.2%) of ESCC. Furthermore, HPV was located by ISH in the distant normal region rather than in tumor cells. In EBV-positive cases, accumulation of p53 protein was detected in 10 lesions (91%); CD45RO+ lymphocytes together with expressions of FasL and IL-6 were respectively identified in 100%, 63.6%, and 54.5% of 11 EBV-positive lesions. Interestingly, in the EBV-negative cases (n = 20), p53 protein was detected in 40% of lesions; CD45RO 30%; FasL 50%, and IL-6 10%.

CONCLUSIONS

In this study, no correlation was found between the presence of EBV in ESCC and the patients' age, sex, as well as survival. Although our results indicate that EBV could be associated with ESCC, the clinical role of EBV in ESCC remains to be determined.

Epstein-Barr virus infection and P53 expression in HIV-related oral large B cell lymphoma

BACKGROUND

Head and neck non-Hodgkin's lymphomas in HIV positive patients are highly related with Epstein-Barr virus (EBV) infection. In general, viral agents can alter p53 protein levels by enhancing degradation of cellular p53 or by increasing its half-life by viral protein-p53 interaction. Moreover, it has been reported that modifications of p53 gene can modulate tumor cells' response to radio- and chemotherapy.

METHODS

To assess a possible role of EBV infection, p53 protein deregulation, and p53 gene alterations in exons 5 to 8, we have studied six cases of HIV-related primary oral large B-cell lymphoma. We used in situ hybridization (ISH) for EBV-DNA and EBV-encoded nuclear RNA-1 (EBER-1), immunohistochemistry (IHC) for EBV latent membrane protein -1 (LMP-1) and p53 proteins expression, and single strand conformational polymorphism (SSCP) analysis to screen p53 gene mutations in exons 5 to 8.

RESULTS

The EBV-DNA was present in all specimens, according to conventional DNA-ISH. No evidence for EBER-1 was found by ISH. The presence of EBV-DNA was correlated with the LMP-1 expression in all but one case. Moreover, p53 protein expression was negative in three cases and strongly positive in the others. However, mutational analysis of p53 gene in exons 5-8 showed no alteration.

CONCLUSIONS

Our data may suggest that both EBV infection and LMP-1 expression may cause p53 loss of function even in the absence of p53 gene mutations, as assessed by SSCP. We speculate that the presence of EBV-infection and p53 protein deregulation may be responsible for radio- and chemotherapy resistance, by influencing apoptosis of cancer cells.

Activation of the interferon-inducible (2'-5') oligoadenylate synthetase by the Epstein-Barr virus RNA, EBER-1

The 2'-5' oligoadenylate synthetases and the protein kinase PKR are both interferon-induced, double-stranded RNA-dependent proteins that play important roles in the antiviral effects of the interferons and in cellular growth control. Both enzymes are activated by natural or synthetic dsRNAs and by single-stranded RNAs that possess extensive secondary structure. This report describes the effects of the small Epstein-Barr virus-encoded RNA EBER-1 on the regulation of 2-5(A) synthetase activity. We demonstrate that EBER-1 RNA binds to and activates the human 40-kDa 2-5(A) synthetase in a dose-dependent manner. The efficiency of EBER-1 as an activator of 2-5(A) synthetase is approximately 25% of that of the synthetic double-stranded RNA poly(I)/poly(C), and poly(I)/poly(C) further stimulates enzyme activity even in the presence of a high concentration of EBER-1. Conversely, EBER-1 neither stimulates nor inhibits 2-5(A) synthetase that has been activated by a high concentration of poly(I)/poly(C). Competitive binding assays suggest that the relative affinity of the enzyme for poly(I)/poly(C) is considerably higher than that for EBER-1. Our data indicate that EBER-1, like VAI RNA of adenovirus, TAR RNA of HIV-1, and Rex-RE RNA of HTLV-1, is able to activate the 2-5(A) synthetases. The significance of why several viruses may activate the 2-5(A) synthetase/RNase L-mediated RNA degradation pathway is discussed.

Subversion of cytokine networks by viruses

Viruses and the immune system have been competitors throughout their co-evolution. It is therefore not surprising that the viruses in circulation today possess a variety of strategies to counteract those aspects of the immune system that are involved in virus clearance. Examination of these virus encoded functions provides an important view of immune function and an appreciation of the complexity of the virus-host interaction. It is clear that viruses, seeking to subvert the immune system, have become adept in blocking the communication channels of the immune system. There are numerous examples of viral proteins that target the cytokine networks, disrupting the processes by which the delicately balanced immune system is regulated. This review focuses on the gene products of poxviruses, adenoviruses and herpesviruses that function primarily as immune-modulators.

Primary central nervous system lymphomas in immunocompetent individuals: histology, Epstein-Barr virus genome, Ki-67 proliferation index, p53 and bcl-2 gene expression

Epstein-Barr virus (EBV) has been detected in the large majority of HIV-related primary central nervous system lymphomas (PCNSL) suggesting a pathogenetic role of the virus. Unlike HIV-related PCNSL, conflicting data exist with regard to the presence of EBV in non immunodeficiency-related (sporadic) PCNSL. For this reason, a population based material of 41 sporadic PCNSL was analysed for the presence of EBV genome (EBER, BHLF) using RNA in situ hybridisation (RISH). Furthermore, the expression of the gene products of the bcl-2 oncogene and the p53 tumor suppressor gene and the tumor growth fraction reactive with the monoclonal antibody Ki-67 have been evaluated. All cases but two were EBV genome negative. In the two positive cases less than 5% of tumor cells showed EBER positivity. In contrast, more than 75% of cells morphologically belonging to the tumor-cell population stained positively for EBER in two cases of HIV related PCNSL. Immunostaining for the bcl-2 oncoprotein was positive in 28 (72%) of 39 cases examined. In most cases more than 75% of tumor cells showed cytoplasmic expression. Of 37 cases investigated for p53 expression, 21 (57%) stained positively. However, in the large majority of positive cases less than 10% of the neoplastic cells stained. The percentage of Ki-67 positive cells ranged between 10% and 80% with a mean of 50%. The expression of the p53 and bcl-2 oncoproteins and the growth fraction did not have any prognostic impact. We conclude that the EBV genome is rarely detected in sporadic PCNSL, indicating that a pathogenetic role of EBV is unlikely. Like extracerebral B-cell lymphomas a large fraction of PCNSL expresses the p53 and bcl-2 oncoproteins, a feature, however, which does not seem to have prognostic implications.

Site-specific localization of Epstein-Barr virus in pharyngeal carcinomas

In this study, the correlations of factors with Epstein-Barr virus (EBV)-association were investigated in 50 patients with nasopharyngeal carcinoma (NPC), 61 with oropharyngeal carcinoma (OPC), and 55 with hypopharyngeal carcinoma (HPC) in Okinawa and Osaka prefectures in Japan. The incidence of pharyngeal carcinoma in Okinawa was previously found to be higher than that in Osaka; the incidence of OPC was approximately 6 times higher and that of HPC was two times higher. The EBV genome was detected in the tumor cells of the present patients; 83% of the Okinawa and 92% of the Osaka NPC patients. The EBV genome was not detected in OPC or HPC. A univariate analysis showed that sex, the location of the tumor, histology, and the degree of lymphocytic infiltration correlated with the EBV-positive rate. A multivariate analysis revealed that only the location of the tumor was independently correlated with the EBV-positive rate. Histology and tumor size were factors affecting the prognosis of the patients with NPC. The NPC of poorly differentiated type frequently showed the EBV genome, and NPC with lymphocytic infiltration showed a more favorable prognosis compared to the other NPC types. These findings suggest that latent genes of EBV expressed in cancer cells might trigger a cytotoxic T cell reaction against the cancer.

Detection of EBV RNA (EBER-1 and EBER-2) in malaria lymph nodes by in situ hybridization

Acute Plasmodium falciparum malaria in African children allows expansion of latent Epstein-Barr virus infection, leading to colonization of lymph nodes by virus-infected lymphoblasts in 60% of cases as demonstrated by in situ hybridization for the detection of EBER-1 and EBER-2 RNA. This probably arises against a background of malaria-induced immunosuppression to EBV and concurrent lymphoid activation. The relevance of the results to the pathogenesis of African endemic Burkitt's lymphoma is discussed.

Epstein-Barr virus lymphoproliferative disorders after liver transplantation

Post-transplant lymphoproliferative disorders (PTLD) represent a spectrum of histological and immunological abnormalities, ranging from benign polyclonal B-cell hyperplasia to monoclonal malignant lymphoma. The important role of Epstein-Barr virus (EBV) in PTLD in liver transplant patients, particularly in pediatric recipients, is reviewed. Understanding the risks of EBV infection, the clinical presentations and diagnosis of PTLD, and its pathophysiology are crucial to the management of these disorders. Current treatment methods have resulted in better outcomes of these disorders, which in the past were uniformly fatal.