Regulation of interleukin-1beta transcription by Epstein-Barr virus involves a number of latent proteins via their interaction with RBP

Epstein-Barr virus-encoded BART9 and BART15 miRNAs are elevated in exosomes of cerebrospinal fluid from relapsing-remitting multiple sclerosis patients

Epstein-Barr virus (EBV) infection is approved as the main environmental trigger of multiple sclerosis (MS). In this path, we quantified ebv-miR-BART9-3p and ebv-miR-BART15 in exosomes of cerebrospinal fluid (CSF) of untreated relapsing-remitting MS (RRMS) patients in comparison with the control group. Interestingly, patients displayed significant upregulation of ebv-miR-BART9-3p (18.4-fold) and ebv-miR-BART15 (3.1-fold) expression in CSF exosomes. Moreover, the expression levels of hsa-miR-21-5p and hsa-miR-146a-5p were found to be significantly elevated in the CSF samples obtained from the patient group compared to those obtained from the HC group. The levels of Interferon-gamma (IFN-γ), interleukin-1β (IL-1β), interleukin-6 (IL-6), interleukin-17 (IL-17), interleukin-23 (IL-23), transforming growth factor beta (TGF-β), and tumor necrosis factor-alpha (TNF-α) were observed to be significantly elevated in the serum and CSF exosomes of the patients. The highest increase was observed in TGF-β (8.5-fold), followed by IL-23 (3.9-fold) in CSF exosomes. These findings are in agreement with the association between EBV infection and inflammatory cytokines induction. Furthermore, the ratios of TGF-β: TNF-α and TGF-β: IFN-γ attained values of 4 to 16.4 and 1.3 to 3.6, respectively, in the CSF exosomes of the patients, in comparison to those of the control group. These findings show EBV activity in RRMS patients is different from that of healthy ones. Elevation of ebv-miR-BART9-3p, ebv-miR-BART15, and inflammatory cytokines expression in CSF exosomes in RRMS patients provides a substantial link between EBV activity and the onset of the disease, as well as the transition from EBV infection to MS.

Epstein-Barr virus nuclear antigen 3A protein regulates CDKN2B transcription via interaction with MIZ-1

The Epstein-Barr virus (EBV) nuclear antigen 3 family of protein is critical for the EBV-induced primary B-cell growth transformation process. Using a yeast two-hybrid screen we identified 22 novel cellular partners of the EBNA3s. Most importantly, among the newly identified partners, five are known to play direct and important roles in transcriptional regulation. Of these, the Myc-interacting zinc finger protein-1 (MIZ-1) is a transcription factor initially characterized as a binding partner of MYC. MIZ-1 activates the transcription of a number of target genes including the cell cycle inhibitor CDKN2B. Focusing on the EBNA3A/MIZ-1 interaction we demonstrate that binding occurs in EBV-infected cells expressing both proteins at endogenous physiological levels and that in the presence of EBNA3A, a significant fraction of MIZ-1 translocates from the cytoplasm to the nucleus. Moreover, we show that a trimeric complex composed of a MIZ-1 recognition DNA element, MIZ-1 and EBNA3A can be formed, and that interaction of MIZ-1 with nucleophosmin (NPM), one of its coactivator, is prevented by EBNA3A. Finally, we show that, in the presence of EBNA3A, expression of the MIZ-1 target gene, CDKN2B, is downregulated and repressive H3K27 marks are established on its promoter region suggesting that EBNA3A directly counteracts the growth inhibitory action of MIZ-1.

Cutting edge: miR-223 and EBV miR-BART15 regulate the NLRP3 inflammasome and IL-1β production

Although microRNA (miRNA) regulation of TLR signaling is well established, this has not yet been observed for NLR proteins or the inflammasomes they form. We have now validated a highly conserved miR-223 target site in the NLRP3 3'-untranslated region. miR-223 expression decreases as monocytes differentiate into macrophages, whereas NLRP3 protein increases during this time. However, overexpression of miR-223 prevents accumulation of NLRP3 protein and inhibits IL-1β production from the inflammasome. Virus inhibition of the inflammasome is an emerging theme, and we have also identified an EBV miRNA that can target the miR-223 binding site in the NLRP3 3'-untranslated region. Furthermore, this virus miRNA can be secreted from infected B cells via exosomes to inhibit the NLRP3 inflammasome in noninfected cells. Therefore, we have identified both the first endogenous miRNA that limits NLRP3 inflammatory capacity during myeloid cell development and also a viral miRNA that takes advantage of this, limiting inflammation for its own purposes.

Differential gene regulation by Epstein-Barr virus type 1 and type 2 EBNA2

A transfection assay with a lymphoblastoid cell line infected with Epstein-Barr virus was used to compare the abilities of type 1 and type 2 EBNA2 to sustain cell proliferation. The reduced proliferation in cells expressing type 2 EBNA2 correlated with loss of expression of some cell genes that are known to be targets of type 1 EBNA2. Microarray analysis of EBNA2 target genes identified a small number of genes that are more strongly induced by type 1 than by type 2 EBNA2, and one of these genes (CXCR7) was shown to be required for proliferation of lymphoblastoid cell lines. The Epstein-Barr virus LMP1 gene was also more strongly induced by type 1 EBNA2 than by type 2, but this effect was transient. Type 1 and type 2 EBNA2 were equally effective at arresting cell proliferation of Burkitt's lymphoma cell lines lacking Epstein-Barr virus and were also shown to cause apoptosis in these cells. The results indicate that differential gene regulation by Epstein-Barr virus type 1 and type 2 EBNA2 may be the basis for the much weaker B-cell transformation activity of type 2 Epstein-Barr virus strains compared to type 1 strains.

Epstein-Barr virus nuclear antigen 3A contains six nuclear-localization signals

The Epstein-Barr nuclear antigen 3A (EBNA3A) is one of only six viral proteins essential for Epstein-Barr virus-induced transformation of primary human B cells in vitro. Viral proteins such as EBNA3A are able to interact with cellular proteins, manipulating various biochemical and signalling pathways to initiate and maintain the transformed state of infected cells. EBNA3A has been reported to have one nuclear-localization signal and is targeted to the nucleus during transformation, where it associates with components of the nuclear matrix. By using enhanced green fluorescent protein-tagged deletion mutants of EBNA3A in combination with site-directed mutagenesis, an additional five functional nuclear-localization signals have been identified in the EBNA3A protein. Two of these (aa 63-66 and 375-381) were computer-predicted, whilst the remaining three (aa 394-398, 573-578 and 598-603) were defined functionally in this study.

DNA repair Ku proteins in gastric cancer cells and pancreatic acinar cells

The DNA repair protein Ku acts as a heterodimer of Ku70 and Ku80 that binds to the DNA ends, nicks, or single-to-double-strand transition. It has a crucial role for DNA double-strand-break repair. Either Ku70 or Ku80 itself may have a unique function that is independent of the other Ku subunit. In this review, the role of Ku on cell proliferation and apoptosis will be discussed. Ku acts as a regulator of transcription by interacting with the recombination signal binding protein Jkappa and the NF-kappaB p50 homodimer to up-regulate p50 expression, which may regulate the proliferation of gastric cancer cells. Both Ku70 and Ku80 expressions are mediated by constitutively activated NF-kappaB and constitutively expressed cyclooxygenase-2 in gastric cancer cells, which may be related to gastric cell proliferation and carcinogenesis. In addition, nuclear loss of Ku may underlie the mechanism of apoptosis in pancreatic acinar cells after oxidative stress.

Nuclear localization of the Epstein-Barr virus EBNA3B protein

The Epstein-Barr virus nuclear antigen (EBNA) 3B is a hydrophilic, proline-rich, charged protein that is thought to be involved in transcriptional regulation and is targeted exclusively to the cell nucleus, where it localizes to discrete subnuclear granules. Co-localization studies utilizing a fusion protein between enhanced green fluorescent protein (EGFP) and EBNA3B with FLAG-tagged EBNA3A and EBNA3C proteins demonstrated that EBNA3B co-localized with both EBNA3A and EBNA3C in the nuclei of cells when overexpressed. Computer analyses identified four potential nuclear-localization signals (NLSs) in the EBNA3B amino acid sequence. By utilizing fusion proteins with EGFP, deletion constructs of EBNA3B and site-directed mutagenesis, three of the four NLSs (aa 160-166, 430-434 and 867-873) were shown to be functional in truncated forms of EBNA3B, whilst an additional NLS (aa 243-246) was identified within the N-terminal region of EBNA3B. Only two of the NLSs were found to be functional in the context of the full-length EBNA3B protein.

Epstein-Barr virus and rheumatoid arthritis: is there a link?

Rheumatoid arthritis is a systemic autoimmune disease characterized by chronic, destructive, debilitating arthritis. Its etiology is unknown; it is presumed that environmental factors trigger development in the genetically predisposed. Epstein–Barr virus, a nearly ubiquitous virus in the human population, has generated great interest as a potential trigger. This virus stimulates polyclonal lymphocyte expansion and persists within B lymphocytes for the host's life, inhibited from reactivating by the immune response. In latent and replicating forms, it has immunomodulating actions that could play a role in the development of this autoimmune disease. The evidence linking Epstein–Barr virus and rheumatoid arthritis is reviewed.

The Epstein–Barr virus nuclear antigen-6 protein co-localizes with EBNA-3 and survival of motor neurons protein

The Epstein-Barr virus nuclear antigen (EBNA)-6 protein is essential for Epstein-Barr virus (EBV)-induced immortalization of primary human B-lymphocytes in vitro. In this study, fusion proteins of EBNA-6 with green fluorescent protein (GFP) have been used to characterize its nuclear localization and organization within the nucleus. EBNA-6 associates with nuclear structures and in immunofluorescence demonstrate a punctate staining pattern. Herein, we show that the association of EBNA-6 with these nuclear structures was maintained throughout the cell cycle and with the use of GFP-E6 deletion mutants, that the region amino acids 733-808 of EBNA-6 contains a domain that can influence the association of EBNA-6 with these nuclear structures. Co-immunofluorescence and confocal analyses demonstrated that EBNA-6 and EBNA-3 co-localize in the nucleus of cells. Expression of EBNA-6, but not EBNA-3, caused a redistribution of nuclear survival of motor neurons protein (SMN) to the EBNA-6 containing nuclear structures resulting in co-localization of SMN with EBNA-6.

Identification of the nuclear localization signals within the Epstein–Barr virus EBNA-6 protein

Epstein-Barr virus nuclear antigen (EBNA)-6 is essential for EBV-induced immortalization of primary human B-lymphocytes in vitro. Previous studies have shown that EBNA-6 acts as a transcriptional regulator of viral and cellular genes; however at present, few functional domains of the 140 kDa EBNA-6 protein have been completely characterized. There are five computer-predicted nuclear localization signals (NLS), four monopartite and one bipartite, present in the EBNA-6 amino acid sequence. To identify which of these NLS are functional, fusion proteins between green fluorescent protein and deletion constructs of EBNA-6 were expressed in HeLa cells. Each of the constructs containing at least one of the NLS was targeted to the nucleus of cells whereas a construct lacking all of the NLS was cytoplasmic. Site-directed mutation of these NLS demonstrated that only three of the NLS were functional, one at the N-terminal end (aa 72-80), one in the middle (aa 412-418) and one at the C-terminal end (aa 939-945) of the EBNA-6 protein.

The Ku antigen-recombination signal-binding protein Jkappa complex binds to the nuclear factor-kappaB p50 promoter and acts as a positive regulator of p50 expression in human gastric cancer cells

The p50 subunit of NF-kappaB is a transcription factor that regulates the expression of a variety of genes. Previously, we showed that the expression of Ku antigen, a DNA repair protein, is mediated by NF-kappaB in gastric cancer AGS cells (Lim, J. W., Kim, H., and Kim, K. H. (2002) J. Biol. Chem. 277, 46093-46100). In this study, we report that the inhibition of Ku activity reduced both p50 expression and nuclear NF-kappaB activity in AGS cells. A co-immunoprecipitation experiment demonstrated that Ku antigen interacted with recombination signal-binding protein Jkappa (RBP-Jkappa), a DNA-binding protein. Ku antigen, RBP-Jkappa, and p50 were found to bind to the DNA region containing the kappaB element in the p50 promoter. Supershift and competition experiments demonstrated that Ku antigen and RBP-Jkappa bound sequence-specifically to downstream elements of kappaB at GCTTC and TGGGGG. mRNA expression and de novo synthesis of p50 were inhibited in cells transfected with the mutant gene expression constructs for IkappaBalpha, Ku80, and RBP-Jkappa. A reporter assay demonstrated that p50 transcription was positively mediated by NF-kappaB, Ku antigen, and RBP-Jkappa and that the binding elements for these proteins were required for optimal p50 expression. The interaction of Ku antigen with RBP-Jkappa and NF-kappaB p50 may act as a positive regulator of p50 expression in gastric cancer AGS cells.

Fibrates and medroxyprogesterone acetate induce apoptosis of primary Burkitt's lymphoma cells and cell lines: potential for applying old drugs to a new disease

Current therapies for Burkitt's lymphoma (BL) utilise combined cytotoxic chemotherapy, but these treatments are not always available in areas where the disease is endemic and are also markedly less successful in AIDS-related BL. Therefore, additional therapies are urgently required. We demonstrate here that combined fibrates and MPA exert powerful, antiproliferative actions against well-characterised Daudi, Raji and L3055 BL cell lines and primary BL cells. Detailed studies in L3055 demonstrated that this activity was mediated by induced apoptosis and confirmed by observations that overexpression of the antiapoptotic genes bcl-2 or bcl-x(L) conferred significant protection against the drugs. Importantly, since fibrates and MPA are inexpensive and stable with minimal-associated toxicities, we suggest that these drugs should be considered as adjuncts to currently available treatments for BL in endemic and AIDS-related disease.

Epstein-Barr virus encoded nuclear protein EBNA-3 binds a novel human uridine kinase/uracil phosphoribosyltransferase

BACKGROUND

Epstein-Barr virus (EBV) infects resting B-lymphocytes and transforms them into immortal proliferating lymphoblastoid cell lines (LCLs) in vitro. The transformed immunoblasts may grow up as immunoblastic lymphomas in immuno-suppressed hosts.

RESULTS

In order to identify cellular protein targets that may be involved in Epstein-Barr virus mediated B-cell transformation, human LCL cDNA library was screened with one of the transformation associated nuclear antigens, EBNA-3 (also called EBNA-3A), using the yeast two-hybrid system. A clone encoding a fragment of a novel human protein was isolated (clone 538). The interaction was confirmed using in vitro binding assays. A full-length cDNA clone (F538) was isolated. Sequence alignment with known proteins and 3D structure predictions suggest that F538 is a novel human uridine kinase/uracil phosphoribosyltransferase. The GFP-F538 fluorescent fusion protein showed a preferentially cytoplasmic distribution but translocated to the nucleus upon co-expression of EBNA-3. A naturally occurring splice variant of F538, that lacks the C-terminal uracil phosphoribosyltransferase part but maintain uridine kinase domain, did not translocate to the nucleus in the presence of EBNA3. Antibody that was raised against the bacterially produced GST-538 protein showed cytoplasmic staining in EBV negative Burkitt lymphomas but gave a predominantly nuclear staining in EBV positive LCL-s and stable transfected cells expressing EBNA-3.

CONCLUSION

We suggest that EBNA-3 by direct protein-protein interaction induces the nuclear accumulation of a novel enzyme, that is part of the ribonucleotide salvage pathway. Increased intranuclear levels of UK/UPRT may contribute to the metabolic build-up that is needed for blast transformation and rapid proliferation.

Regulation of TIMP-1 phenotypic expression in Epstein--Barr virus-immortalized B lymphocytes

Normal B lymphocytes as well as malignant B cells extravasate from blood circulation during physiological and pathological processes and require matrix metalloproteinases (MMPs) to facilitate trafficking through the subendothelial basal lamina and the extracellular matrix. We have previously shown that Epstein-Barr virus (EBV)-immortalized B lymphocytes constitutively synthesized low levels of MMP-9 and huge amounts of its preferential inhibitor, tissue inhibitor of matrix metalloproteinase-1 (TIMP-1). In the present study, TIMP-1 phenotypic expression was extensively investigated in response to various mediators including interleukins, chemokines, growth factors and tumor promotor, and was compared to MMP-9 synthesis. Results showed a roughly constitutive TIMP-1 expression opposed to an inducible MMP-9 synthesis. Nevertheless, further analysis of TIMP-1 synthesis showed the existence of regulation mechanisms: modulation of intracellular Ca(2+) concentration as well as cation ionophore monensin were demonstrated to influence TIMP-1 production and secretion. The precise pathways implicated in these regulation mechanisms are currently under survey.

Alterations in NF-kappaB and RBP-Jkappa by arenavirus infection of macrophages in vitro and in vivo

Pichinde virus is an arenavirus that infects guinea pigs and serves as an animal model for human Lassa fever. An attenuated Pichinde virus variant (P2) and a virulent variant (P18) are being used to delineate pathogenic mechanisms that culminate in shock. In guinea pigs, the infection has been shown to begin in peritoneal macrophages following intraperitoneal inoculation and then spreads to the spleen and other reticuloendothelial organs. We show here that infection of the murine monocytic cell line P388D1 with either Pichinde virus variant resulted in the induction of inflammatory cytokines and effectors, including interleukin-6 and tumor necrosis factor alpha. Since these genes are regulated in part by the cellular transcription factors NF-kappaB and RBP-Jkappa, we compared the activities of NF-kappaB and RBP-Jkappa in P388D1 cells following infection with Pichinde virus. The attenuated P2 virus inhibited NF-kappaB activation and caused a shift in the size of the RBP-Jkappa complex. The virulent P18 virus showed less inhibition of NF-kappaB and failed to alter the size of the RBP-Jkappa complex. Peritoneal cells from P2-infected guinea pigs showed induction of NF-kappaB RelA/p50 heterodimer and p50/p50 homodimer and manifested an increase in the size of RBP-Jkappa. By contrast, P18 induced large amounts of the NF-kappaB p50/p50 dimer but failed to induce RelA/p50 or to cause an increase in the RBP-Jkappa size. Taken together, these changes suggest that the attenuated viral strain induces an "activation" of macrophages, while the virulent form of the virus does not.

Amino acids of Epstein-Barr virus nuclear antigen 3A essential for repression of Jkappa-mediated transcription and their evolutionary conservation

Epstein-Barr virus (EBV) nuclear antigen 3A (EBNA-3A) is essential for virus-mediated immortalization of B lymphocytes in vitro and is believed to regulate transcription of cellular and/or viral genes. One known mechanism of regulation is through its interaction with the cellular transcription factor Jkappa. This interaction downregulates transcription mediated by EBNA-2 and Jkappa. To identify the amino acids that play a role in this interaction, we have generated mutant EBNA-3A proteins. A mutant EBNA-3A protein in which alanine residues were substituted for amino acids 199, 200, and 202 no longer downregulated transcription. Surprisingly, this mutant protein remained able to coimmunoprecipitate with Jkappa. Using a reporter gene assay based on the recruitment of Jkappa by various regions spanning EBNA-3A, we have shown that this mutation abolished binding of Jkappa to the N-proximal region (amino acids 125 to 222) and that no other region of EBNA-3A alone was sufficient to mediate an association with Jkappa. To determine the biological significance of the interaction of EBNA-3A with Jkappa, we have studied its conservation in the simian lymphocryptovirus herpesvirus papio (HVP) by cloning HVP-3A, the homolog of EBNA-3A encoded by this virus. This 903-amino-acid protein exhibited 37% identity with its EBV counterpart, mainly within the amino-terminal half. HVP-3A also interacted with Jkappa through a region located between amino acids 127 and 223 and also repressed transcription mediated through EBNA-2 and Jkappa. The evolutionary conservation of this function, in proteins that have otherwise significantly diverged, argues strongly for an important biological role in virus-mediated immortalization of B lymphocytes.

Epstein-Barr virus encoded nuclear protein EBNA-3 binds XAP-2, a protein associated with Hepatitis B virus X antigen

EBNA-3 (also called EBNA-3A) is one of the EBV encoded nuclear antigens that are necessary for B-cell transformation. EBNA-3 is known to target RBPs, nuclear proteins that also interacts with EBNA-2, EBNA-4 and EBNA-6. In order to identify additional EBNA-3 targets, an EBV-transformed human lymphocyte cDNA library was screened in the yeast two-hybrid system with N-terminus truncated EBNA-3 that cannot interact with RBP-Jkappa. A clone, encoding Xap-2 protein, a cellular partner of Hepatitis B virus X-antigen was isolated. This protein is also known as the p38 subunit of the aryl hydrocarbon receptor complex (ARA9). The specific binding to EBNA-3 was confirmed by showing that the GST-Xap-2 precipitated EBNA-3 from CV1 cells that were infected with recombinant vaccinia virus expressing EBNA-3. Deletion of the C-terminus of Xap-2 eliminated the binding. Fusion with green fluorescent protein showed that Xap-2 is preferentially cytoplasmic but translocates to the nucleus upon expression of EBNA-3.

A role for SKIP in EBNA2 activation of CBF1-repressed promoters

EBNA2 is essential for Epstein-Barr virus (EBV) immortalization of B lymphocytes. EBNA2 functions as a transcriptional activator and targets responsive promoters through interaction with the cellular DNA binding protein CBF1. We have examined the mechanism whereby EBNA2 overcomes CBF1-mediated transcriptional repression. A yeast two-hybrid screen performed using CBF1 as the bait identified a protein, SKIP, which had not previously been recognized as a CBF1-associated protein. Protein-protein interaction assays demonstrated contacts between SKIP and the SMRT, CIR, Sin3A, and HDAC2 proteins of the CBF1 corepressor complex. Interestingly, EBNA2 also interacted with SKIP in glutathione S-transferase affinity and mammalian two-hybrid assays and colocalized with SKIP in immunofluorescence assays. Interaction with SKIP was not affected by mutation of EBNA2 conserved region 6, the CBF1 interaction region, but was abolished by mutation of conserved region 5. Mutation of conserved region 5 also severely impaired EBNA2 activation of a reporter containing CBF1 binding sites. Thus, interaction with both CBF1 and SKIP is necessary for efficient promoter activation by EBNA2. A model is presented in which EBNA2 competes with the SMRT-corepressor complex for contacts on SKIP and CBF1.

Characterization of the transcriptional repressor RBP in Epstein-Barr virus-transformed B cells

RBP, a transcriptional repressor, is intricately involved in Epstein-Barr virus (EBV) transformation of human B cells. The EBV nuclear proteins EBNA-2, -3, -4 and -6 all utilize RBP to regulate the transcription of both cellular and viral genes. This study investigates the isoforms of the RBP protein in Burkitt's lymphoma (BL) cells and in EBV-transformed lymphoblastoid cell lines (LCLs). Two-dimensional gel electrophoresis showed the presence of two different cellular isoforms of RBP; the molecular masses and isoelectric points of these two isoforms corresponded to RBP-Jkappa and RBP-2N. Fractionation studies and green fluorescent protein (GFP)-tagged expression studies demonstrated that both RBP isoforms were located predominantly in the cell nucleus. Interestingly, GFP-tagged RBP-Jkappa showed diffuse, uniform nuclear staining, whereas GFP-tagged RBP-2N showed a discrete nuclear pattern, demonstrating differences between the two isoforms. Within the nuclear fraction of EBV-negative BL cells, RBP existed both in a free form and bound to chromatin, whereas in LCLs the intranuclear RBP was predominantly chromatin-bound. Expression of the EBV latent proteins was found to lead to the sequestering of RBP from the cytoplasm into the cell nucleus and to an increase in the chromatin-bound forms of RBP.