[Show abstract][Hide abstract] ABSTRACT: EBV causes B lymphomas and undifferentiated nasopharyngeal carcinoma (NPC). Although the mechanisms by which EBV infects B lymphocytes have been extensively studied, investigation of the mechanisms by which EBV infects nasopharyngeal epithelial cells (NPECs) has only recently been enabled by the successful growth of B lymphoma Mo-MLV insertion region 1 homolog (BMI1)-immortalized NPECs in vitro and the discovery that neuropilin 1 expression positively affects EBV glycoprotein B (gB)-mediated infection and tyrosine kinase activations in enhancing EBV infection of BMI1-immortalized NPECs. We have now found that even though EBV infected NPECs grown as a monolayer at extremely low efficiency (<3%), close to 30% of NPECs grown as sphere-like cells (SLCs) were infected by EBV. We also identified nonmuscle myosin heavy chain IIA (NMHC-IIA) as another NPEC protein important for efficient EBV infection. EBV gH/gL specifically interacted with NMHC-IIA both in vitro and in vivo. NMHC-IIA densely aggregated on the surface of NPEC SLCs and colocalized with EBV. EBV infection of NPEC SLCs was significantly reduced by NMHC-IIA siRNA knock-down. NMHC-IIA antisera also efficiently blocked EBV infection. These data indicate that NMHC-IIA is an important factor for EBV NPEC infection.
Full-text · Article · Sep 2015 · Proceedings of the National Academy of Sciences
[Show abstract][Hide abstract] ABSTRACT: Epstein-Barr virus (EBV) infects germinal center (GC) B cells and establishes persistent infection in memory B cells. EBV-infected B cells can cause B-cell malignancies in humans with T- or natural killer-cell deficiency. We now find that EBV-encoded latent membrane protein 2A (LMP2A) mimics B-cell antigen receptor (BCR) signaling in murine GC B cells, causing altered humoral immune responses and autoimmune diseases. Investigation of the impact of LMP2A on B-cell differentiation in mice that conditionally express LMP2A in GC B cells or all B-lineage cells found LMP2A expression enhanced not only BCR signals but also plasma cell differentiation in vitro and in vivo. Conditional LMP2A expression in GC B cells resulted in preferential selection of low-affinity antibody-producing B cells despite apparently normal GC formation. GC B-cell-specific LMP2A expression led to systemic lupus erythematosus-like autoimmune phenotypes in an age-dependent manner. Epigenetic profiling of LMP2A B cells found increased H3K27ac and H3K4me1 signals at the zinc finger and bric-a-brac, tramtrack domain-containing protein 20 locus. We conclude that LMP2A reduces the stringency of GC B-cell selection and may contribute to persistent EBV infection and pathogenesis by providing GC B cells with excessive prosurvival effects.
Full-text · Article · Aug 2015 · Proceedings of the National Academy of Sciences
[Show abstract][Hide abstract] ABSTRACT: The Epstein-Barr virus (EBV)-encoded oncoprotein latent membrane protein 1 (LMP1) constitutively activates nuclear factor κB (NFκB) from intracellular membranes to promote cell growth and survival. LMP1 associates with CD63 in intracellular membranes and is released via exosomes. Whether tumour necrosis factor (TNF) receptor-associated factors (TRAFs) mediate LMP1 NFκB signalling from endosomes and modulate exosomal sorting is unknown. In this article, we show that LMP1-TRAF2 signalling complexes accumulate at endosomes in a palmitoylation-dependent manner, thereby driving LMP1-dependent oncogenicity. Palmitoylation is a reversible post-translational modification and is considered to function as a membrane anchor for proteins. Mutagenesis studies showed that LMP1-TRAF2 trafficking to endosomes is dependent on one single cysteine residue (C78), a known palmitoylation site of LMP1. Notably, growth assays in soft agar revealed that oncogenic properties of the palmitoylation-deficient LMP1 mutant C78A were diminished compared to wild-type LMP1. Since LMP1 recruitment of TRAF2 and downstream NFκB signalling were not affected by a disturbance in palmitoylation, the specific localization of LMP1 at endosomal membranes appears crucial for its transforming potential. The importance of palmitoylation for trafficking to and signalling from endosomal membranes was not restricted to LMP1, as similar observations were made for the cellular oncoproteins Src and Fyn. Despite abundant LMP1-TRAF2 association at endosomal membranes TRAF2 could not be detected in exosomes by Western blotting or proteomics. Interestingly, point mutations that prevented TRAF binding strongly promoted the sorting and release of LMP1 via exosomes. These observations reveal that LMP1-TRAF2 complexes at endosomes support oncogenic NFκB activation and suggest that LMP1 dissociates from the activated signalling complexes upon sorting into intraluminal vesicles. We propose that "signalling endosomes" in EBV-infected tumour cells can fuse with the plasma membrane, explaining LMP1 release via exosomes.
[Show abstract][Hide abstract] ABSTRACT: Epstein-Barr virus (EBV) is implicated as an aetiological factor in B lymphomas and nasopharyngeal carcinoma. The mechanisms of cell-free EBV infection of nasopharyngeal epithelial cells remain elusive. EBV glycoprotein B (gB) is the critical fusion protein for infection of both B and epithelial cells, and determines EBV susceptibility of non-B cells. Here we show that neuropilin 1 (NRP1) directly interacts with EBV gB(23-431). Either knockdown of NRP1 or pretreatment of EBV with soluble NRP1 suppresses EBV infection. Upregulation of NRP1 by overexpression or EGF treatment enhances EBV infection. However, NRP2, the homologue of NRP1, impairs EBV infection. EBV enters nasopharyngeal epithelial cells through NRP1-facilitated internalization and fusion, and through macropinocytosis and lipid raft-dependent endocytosis. NRP1 partially mediates EBV-activated EGFR/RAS/ERK signalling, and NRP1-dependent receptor tyrosine kinase (RTK) signalling promotes EBV infection. Taken together, NRP1 is identified as an EBV entry factor that cooperatively activates RTK signalling, which subsequently promotes EBV infection in nasopharyngeal epithelial cells.
Full-text · Article · Feb 2015 · Nature Communications
[Show abstract][Hide abstract] ABSTRACT: Super-enhancers are principal determinants of cell transcription, development, phenotype, and oncogenesis, not yet implicated in host-pathogen interactions. We found four Epstein-Barr virus (EBV) oncoproteins and five EBV-activated NF-B subunits co-occupying ~1800 enhancer sites in EBV-transformed lymphoblastoid cells (LCLs). Of these, 187 had markedly higher and broader histone H3K27ac signals characteristic of super-enhancers, and were designated “EBV super-enhancers”. EBV super-enhancer associated genes included MYC and BCL2, which enable LCL proliferation and survival. EBV super-enhancers were enriched for specific B cell transcription factor motifs and had high STAT5 and NFAT co-occupancy. EBV super-enhancer associated genes were more highly expressed than other LCL genes. Disruption of EBV super-enhancers by the bromodomain inhibitor, JQ1, by conditional inactivation of an EBV oncoprotein or NF-B, decreased MYC or BCL2 gene expression and arrested LCL growth. These findings provide novel insights into the mechanisms by which EBV causes lymphoproliferation and identify opportunities for therapeutic intervention.
No preview · Article · Feb 2015 · Cell Host & Microbe
[Show abstract][Hide abstract] ABSTRACT: Latent Epstein-Barr virus (EBV) infection has a substantial role in causing many human disorders. The persistence of these viral genomes in all malignant cells, yet with the expression of limited latent genes, is consistent with the notion that EBV latent genes are important for malignant cell growth. While the EBV-encoded nuclear antigen-1 (EBNA-1) and latent membrane protein-2A (LMP-2A) are critical, the EBNA-leader proteins, EBNA-2, EBNA-3A, EBNA-3C and LMP-1, are individually essential for in vitro transformation of primary B cells to lymphoblastoid cell lines. EBV-encoded RNAs and EBNA-3Bs are dispensable. In this review, the roles of EBV latent genes are summarized.
[Show abstract][Hide abstract] ABSTRACT: Epstein-Barr Virus (EBV) conversion of B-lymphocytes to Lymphoblastoid Cell Lines (LCLs) requires four EBV nuclear antigen (EBNA) oncoproteins: EBNA2, EBNALP, EBNA3A, and EBNA3C. EBNA2 and EBNALP associate with EBV and cell enhancers, up-regulate the EBNA promoter, MYC, and EBV Latent infection Membrane Proteins (LMPs), which up-regulate BCL2 to protect EBV-infected B-cells from MYC proliferation-induced cell death. LCL proliferation induces p16(INK4A) and p14(ARF)-mediated cell senescence. EBNA3A and EBNA3C jointly suppress p16(INK4A) and p14(ARF), enabling continuous cell proliferation. Analyses of the EBNA3A human genome-wide ChIP-seq landscape revealed 37% of 10,000 EBNA3A sites to be at strong enhancers; 28% to be at weak enhancers; 4.4% to be at active promoters; and 6.9% to be at weak and poised promoters. EBNA3A colocalized with BATF-IRF4, ETS-IRF4, RUNX3, and other B-cell Transcription Factors (TFs). EBNA3A sites clustered into seven unique groups, with differing B-cell TFs and epigenetic marks. EBNA3A coincidence with BATF-IRF4 or RUNX3 was associated with stronger EBNA3A ChIP-Seq signals. EBNA3A was at MYC, CDKN2A/B, CCND2, CXCL9/10, and BCL2, together with RUNX3, BATF, IRF4, and SPI1. ChIP-re-ChIP revealed complexes of EBNA3A on DNA with BATF. These data strongly support a model in which EBNA3A is tethered to DNA through a BATF-containing protein complexes to enable continuous cell proliferation.
Full-text · Article · Dec 2014 · Proceedings of the National Academy of Sciences
[Show abstract][Hide abstract] ABSTRACT: The nuclear factor κB (NF-κΒ) subunits RelA, RelB, cRel, p50, and p52 are each critical for B cell development and function. To systematically characterize their responses to canonical and noncanonical NF-κB pathway activity, we performed chromatin immunoprecipitation followed by high-throughput DNA sequencing (ChIP-seq) analysis in lymphoblastoid B cell lines (LCLs). We found a complex NF-κB-binding landscape, which did not readily reflect the two NF-κB pathway paradigms. Instead, 10 subunit-binding patterns were observed at promoters and 11 at enhancers. Nearly one-third of NF-κB-binding sites lacked κB motifs and were instead enriched for alternative motifs. The oncogenic forkhead box protein FOXM1 co-occupied nearly half of NF-κB-binding sites and was identified in protein complexes with NF-κB on DNA. FOXM1 knockdown decreased NF-κB target gene expression and ultimately induced apoptosis, highlighting FOXM1 as a synthetic lethal target in B cell malignancy. These studies provide a resource for understanding mechanisms that underlie NF-κB nuclear activity and highlight opportunities for selective NF-κB blockade.
[Show abstract][Hide abstract] ABSTRACT: TRAFs constitute a family of proteins that have been implicated in signal transduction by immunomodulatory cellular receptors and viral proteins. TRAF2 and TRAF6 have an E3-ubiquitin ligase activity, which is dependent on the integrity of their RING finger domain and it has been associated with their ability to activate the NF-κB and AP1 signaling pathways. A yeast two-hybrid screen with TRAF2 as bait, identified the regulatory subunit PP4R1 of protein phosphatase PP4 as a TRAF2-interacting protein. The interaction of TRAF2 with PP4R1 depended on the integrity of the RING finger domain of TRAF2. PP4R1 could interact also with the TRAF2-related factor TRAF6 in a RING domain-dependent manner. Exogenous expression of PP4R1 inhibited NF-κB activation by TRAF2, TRAF6, TNF and the Epstein-Barr virus oncoprotein LMP1. In addition, expression of PP4R1 downregulated IL8 induction by LMP1, whereas downregulation of PP4R1 by RNA interference enhanced the induction of IL8 by LMP1 and TNF. PP4R1 could mediate the dephosphorylation of TRAF2 Ser11, which has been previously implicated in TRAF2-mediated activation of NF-κB. Finally, PP4R1 could inhibit TRAF6 polyubiquitination, indicating an interference with the E3 ubiquitin ligase activity of TRAF6. Taken together, our data identify a novel mechanism of NF-κB pathway inhibition which is mediated by PP4R1-dependent targeting of specific TRAF molecules.
No preview · Article · Aug 2014 · Cellular Signalling
[Show abstract][Hide abstract] ABSTRACT: The replication and persistence of extra chromosomal Epstein-Barr virus (EBV) episome in latently infected cells are primarily dependent on the binding of EBV-encoded nuclear antigen 1 (EBNA1) to the cognate EBV oriP element. In continuation of the previous study, herein we characterized EBNA1 small molecule inhibitors (H20, H31) and their underlying inhibitory mechanisms. In silico docking analyses predicted that H20 fits into a pocket in the EBNA1 DNA binding domain (DBD). However, H20 did not significantly affect EBNA1 binding to its cognate sequence. A limited structure-relationship study of H20 identified a hydrophobic compound H31, as an EBNA1 inhibitor. An in vitro EBNA1 EMSA and in vivo EGFP-EBNA1 confocal microscopy analysis showed that H31 inhibited EBNA1-dependent oriP sequence-specific DNA binding activity, but not sequence-nonspecific chromosomal association. Consistent with this, H31 repressed the EBNA1-dependent transcription, replication, and persistence of an EBV oriP plasmid. Furthermore, H31 induced progressive loss of EBV episome. In addition, H31 selectively retarded the growth of EBV-infected LCL or Burkitt's lymphoma cells. These data indicate that H31 inhibition of EBNA1-dependent DNA binding decreases transcription from and persistence of EBV episome in EBV-infected cells. These new compounds might be useful probes for dissecting EBNA1 functions in vitro and in vivo.
No preview · Article · Jan 2014 · Antiviral research
[Show abstract][Hide abstract] ABSTRACT: Epstein-Barr virus nuclear antigen 3C (EBNA3C) repression of CDKN2A p14(ARF) and p16(INK4A) is essential for immortal human B-lymphoblastoid cell line (LCL) growth. EBNA3C ChIP-sequencing identified >13,000 EBNA3C sites in LCL DNA. Most EBNA3C sites were associated with active transcription; 64% were strong H3K4me1- and H3K27ac-marked enhancers and 16% were active promoters marked by H3K4me3 and H3K9ac. Using ENCODE LCL transcription factor ChIP-sequencing data, EBNA3C sites coincided (±250 bp) with RUNX3 (64%), BATF (55%), ATF2 (51%), IRF4 (41%), MEF2A (35%), PAX5 (34%), SPI1 (29%), BCL11a (28%), SP1 (26%), TCF12 (23%), NF-κB (23%), POU2F2 (23%), and RBPJ (16%). EBNA3C sites separated into five distinct clusters: (i) Sin3A, (ii) EBNA2/RBPJ, (iii) SPI1, and (iv) strong or (v) weak BATF/IRF4. EBNA3C signals were positively affected by RUNX3, BATF/IRF4 (AICE) and SPI1/IRF4 (EICE) cooccupancy. Gene set enrichment analyses correlated EBNA3C/Sin3A promoter sites with transcription down-regulation (P < 1.6 × 10(-4)). EBNA3C signals were strongest at BATF/IRF4 and SPI1/IRF4 composite sites. EBNA3C bound strongly to the p14(ARF) promoter through SPI1/IRF4/BATF/RUNX3, establishing RBPJ-, Sin3A-, and REST-mediated repression. EBNA3C immune precipitated with Sin3A and conditional EBNA3C inactivation significantly decreased Sin3A binding at the p14(ARF) promoter (P < 0.05). These data support a model in which EBNA3C binds strongly to BATF/IRF4/SPI1/RUNX3 sites to enhance transcription and recruits RBPJ/Sin3A- and REST/NRSF-repressive complexes to repress p14(ARF) and p16(INK4A) expression.
Full-text · Article · Dec 2013 · Proceedings of the National Academy of Sciences
[Show abstract][Hide abstract] ABSTRACT: Epstein-Barr virus (EBV) nuclear antigen 1 (EBNA1) is essential for EBV episome maintenance, replication, and transcription. These effects are mediated by EBNA1 binding to cognate oriP DNA, which comprise 20 imperfect copies of a 30-bp dyad symmetry enhancer and an origin for DNA replication. To identify cell proteins essential for these EBNA1 functions, EBNA1 associated cell proteins were immune precipitated and analyzed by liquid chromatography-tandem mass spectrometry. Nucleolin (NCL) was identified to be EBNA1 associated. EBNA1's N-terminal 100 aa and NCL's RNA-binding domains were critical for EBNA1/NCL interaction. Lentivirus shRNA-mediated NCL depletion substantially reduced EBNA1 recruitment to oriP DNA, EBNA1-dependent transcription of an EBV oriP luciferase reporter, and EBV genome maintenance in lymphoblastoid cell lines. NCL RNA-binding domain K429 was critical for ATP and EBNA1 binding. NCL overexpression increased EBNA1 binding to oriP and transcription, whereas NCL K429A was deficient. Moreover, NCL silencing impaired lymphoblastoid cell line growth. These experiments reveal a surprisingly critical role for NCL K429 in EBNA1 episome maintenance and transcription, which may be a target for therapeutic intervention.
Full-text · Article · Dec 2013 · Proceedings of the National Academy of Sciences
[Show abstract][Hide abstract] ABSTRACT: We have previously reported that interleukin-1 (IL-1) receptor-associated kinase (IRAK1) is essential for Epstein-Barr virus
(EBV) latent infection membrane protein 1 (LMP1)-induced p65/RelA serine 536 phosphorylation and NF-κB activation but not
for IκB kinase α (IKKα) or IKKβ activation (Y. J. Song, K. Y. Jen, V. Soni, E. Kieff, and E. Cahir-McFarland, Proc. Natl.
Acad. Sci. U. S. A. 103:2689–2694, 2006, doi:10.1073/pnas.0511096103). Since the kinase activity of IRAK1 is not required
for LMP1-induced NF-κB activation, IRAK1 is proposed to function as a scaffold protein to recruit a p65/RelA serine 536 kinase(s)
to enhance NF-κB-dependent transcriptional activity. We now report that Ca2+/calmodulin-dependent protein kinase II (CaMKII) interacts with IRAK1 and is critical for LMP1-induced p65/RelA serine 536
phosphorylation and NF-κB activation. CaMKII bound the death domain of IRAK1 and directly phosphorylated p65/RelA at serine
536 in vitro. Downregulation of CaMKII activity or expression significantly reduced LMP1-induced p65/RelA serine 536 phosphorylation and
NF-κB activation. Furthermore, LMP1-induced CaMKII activation and p65/RelA serine 536 phosphorylation were significantly reduced
in IRAK1 knockout (KO) mouse embryonic fibroblasts (MEFs). Thus, IRAK1 may recruit and activate CaMKII, which phosphorylates
p65/RelA serine 536 to enhance the transactivation potential of NF-κB in LMP1-induced NF-κB activation pathway.
Preview · Article · Nov 2013 · Molecular and Cellular Biology
[Show abstract][Hide abstract] ABSTRACT: Epstein-Barr virus (EBV) nuclear antigens EBNALP (LP) and EBNA2 (E2) are coexpressed in EBV-infected B lymphocytes and are critical for lymphoblastoid cell line outgrowth. LP removes NCOR and RBPJ repressive complexes from promoters, enhancers, and matrix-associated deacetylase bodies, whereas E2 activates transcription from distal enhancers. LP ChIP-seq analyses identified 19,224 LP sites of which ∼50% were ±2 kb of a transcriptional start site. LP sites were enriched for B-cell transcription factors (TFs), YY1, SP1, PAX5, BATF, IRF4, ETS1, RAD21, PU.1, CTCF, RBPJ, ZNF143, SMC3, NFκB, TBLR, and EBF. E2 sites were also highly enriched for LP-associated cell TFs and were more highly occupied by RBPJ and EBF. LP sites were highly marked by H3K4me3, H3K27ac, H2Az, H3K9ac, RNAPII, and P300, indicative of activated transcription. LP sites were 29% colocalized with E2 (LP/E2). LP/E2 sites were more similar to LP than to E2 sites in associated cell TFs, RNAPII, P300, and histone H3K4me3, H3K9ac, H3K27ac, and H2Az occupancy, and were more highly transcribed than LP or E2 sites. Gene affected by CTCF and LP cooccupancy were more highly expressed than genes affected by CTCF alone. LP was at myc enhancers and promoters and of MYC regulated ccnd2, 23 med complex components, and MYC regulated cell survival genes, igf2r and bcl2. These data implicate LP and associated TFs and DNA looping factors CTCF, RAD21, SMC3, and YY1/INO80 chromatin-remodeling complexes in repressor depletion and gene activation necessary for lymphoblastoid cell line growth and survival.
No preview · Article · Oct 2013 · Proceedings of the National Academy of Sciences
[Show abstract][Hide abstract] ABSTRACT: Vibrio parahaemolyticus type III secretion system 2 (T3SS2) is essential for the organism's virulence, but the effectors required for intestinal colonization and induction of diarrhea by this pathogen have not been identified. Here, we identify a type III secretion system (T3SS2)-secreted effector, VopZ, that is essential for V. parahaemolyticus pathogenicity. VopZ plays distinct, genetically separable roles in enabling intestinal colonization and diarrheagenesis. Truncation of VopZ prevents V. parahaemolyticus colonization, whereas deletion of VopZ amino acids 38-62 abrogates V. parahaemolyticus-induced diarrhea and intestinal pathology but does not impair colonization. VopZ inhibits activation of the kinase TAK1 and thereby prevents the activation of MAPK and NF-κB signaling pathways, which lie downstream. In contrast, the VopZ internal deletion mutant cannot counter the activation of pathways regulated by TAK1. Collectively, our findings suggest that VopZ's inhibition of TAK1 is critical for V. parahaemolyticus to induce diarrhea and intestinal pathology.
[Show abstract][Hide abstract] ABSTRACT: Epstein-Barr Virus Nuclear Antigen (EBNA) 2 features an Arg-Gly repeat (RG) domain at amino acid positions 335-360, which is a known target for protein arginine methyltransferaser 5 (PRMT5). In this study, we performed protein affinity pull-down assays to demonstrate that endogenous PRMT5 derived from lymphoblastoid cells specifically associated with the protein bait GST-E2 RG. Transfection of a plasmid expressing PRMT5 induced a 2.5- to 3-fold increase in EBNA2-dependent transcription of both the LMP1 promoter in AKATA cells, which contain the EBV genome endogenously, and a Cp-Luc reporter plasmid in BJAB cells, which are EBV negative. Furthermore, we showed that there was a 2-fold enrichment of EBNA2 occupancy in target promoters in the presence of exogenous PRMT5. Taken together, we show that PRMT5 triggers the symmetric dimethylation of EBNA2 RG domain to coordinate with EBNA2-mediated transcription. This modulation suggests that PRMT5 may play a role in latent EBV infection.
Full-text · Article · Dec 2012 · Biochemical and Biophysical Research Communications
[Show abstract][Hide abstract] ABSTRACT: Germinal centers (GCs) are specialized microenvironments in secondary lymphoid organs where high-affinity antibody-producing B cells are selected based on B-cell antigen receptor (BCR) signal strength. BCR signaling required for normal GC selection is uncertain. We have found that protein kinase N1 (PKN1, also known as PRK1) negatively regulates Akt kinase downstream of the BCR and that this regulation is necessary for normal GC development. PKN1 interacted with and inhibited Akt1 kinase and transforming activities. Pkn1(-/-) B cells were hyperresponsive and had increased phosphorylated Akt1 levels upon BCR stimulation. In the absence of immunization or infection, Pkn1(-/-) mice spontaneously formed GCs and developed an autoimmune-like disease with age, which was characterized by autoantibody production and glomerulonephritis. More B cells, with fewer somatic BCR gene V region hypermutations were selected in Pkn1(-/-) GCs. These results indicate that PKN1 down-regulation of BCR-activated Akt activity is critical for normal GC B-cell survival and selection.
No preview · Article · Dec 2012 · Proceedings of the National Academy of Sciences
[Show abstract][Hide abstract] ABSTRACT: Epstein-Barr Virus (EBV) is an oncogenic γ-herpesvirus that capably establishes both latent and lytic modes of infection in host cells and causes malignant diseases in humans. Nuclear antigen 2 (EBNA2)-mediated transcription of both cellular and viral genes is essential for the establishment and maintenance of the EBV latency program in B lymphocytes. Here, we employed a protein affinity pull-down and LC-MS/MS analysis to identify nucleophosmin (NPM1) as one of the cellular proteins bound to EBNA2. Additionally, the specific domains that are responsible for protein-protein interactions were characterized as EBNA2 residues 300 to 360 and the oligomerization domain (OD) of NPM1. As in c-MYC, dramatic NPM1 expression was induced in EBV positively infected B cells after three days of viral infection, and both EBNA2 and EBNALP were implicated in the transactivation of the NPM1 promoter. Depletion of NPM1 with the lentivirus-expressed short-hairpin RNAs (shRNAs) effectively abrogated EBNA2-dependent transcription and transformation outgrowth of lymphoblastoid cells. Notably, the ATP-bound state of NPM1 was required to induce assembly of a protein complex containing EBNA2, RBP-Jκ, and NPM1 by stabilizing the interaction of EBNA2 with RBP-Jκ. In a NPM1-knockdown cell line, we demonstrated that an EBNA2-mediated transcription defect was fully restored by the ectopic expression of NPM1. Our findings highlight the essential role of NPM1 in chaperoning EBNA2 onto the latency-associated membrane protein 1 (LMP1) promoters, which is coordinated with the subsequent activation of transcriptional cascades through RBP-Jκ during EBV infection. These data advance our understanding of EBV pathology and further imply that NPM1 can be exploited as a therapeutic target for EBV-associated diseases.
[Show abstract][Hide abstract] ABSTRACT: Genotypic differences greatly influence susceptibility and resistance to disease. Understanding genotype-phenotype relationships requires that phenotypes be viewed as manifestations of network properties, rather than simply as the result of individual genomic variations. Genome sequencing efforts have identified numerous germline mutations, and large numbers of somatic genomic alterations, associated with a predisposition to cancer. However, it remains difficult to distinguish background, or 'passenger', cancer mutations from causal, or 'driver', mutations in these data sets. Human viruses intrinsically depend on their host cell during the course of infection and can elicit pathological phenotypes similar to those arising from mutations. Here we test the hypothesis that genomic variations and tumour viruses may cause cancer through related mechanisms, by systematically examining host interactome and transcriptome network perturbations caused by DNA tumour virus proteins. The resulting integrated viral perturbation data reflects rewiring of the host cell networks, and highlights pathways, such as Notch signalling and apoptosis, that go awry in cancer. We show that systematic analyses of host targets of viral proteins can identify cancer genes with a success rate on a par with their identification through functional genomics and large-scale cataloguing of tumour mutations. Together, these complementary approaches increase the specificity of cancer gene identification. Combining systems-level studies of pathogen-encoded gene products with genomic approaches will facilitate the prioritization of cancer-causing driver genes to advance the understanding of the genetic basis of human cancer.
[Show abstract][Hide abstract] ABSTRACT: Latent Epstein-Barr virus (EBV) infection is associated with human B cell lymphomas and certain carcinomas. EBV episome persistence, replication, and gene expression are dependent on EBV-encoded nuclear antigen 1 (EBNA1)'s DNA binding domain (DBD)/dimerization domain (DD)-mediated sequence-specific DNA binding activity. Homodimerization of EBNA1 is essential for EBNA1 DNA binding and transactivation. In this study, we characterized a novel small molecule EBNA1 inhibitor EiK1, screened from the previous high throughput screening (HTS). The EiK1 compound specifically inhibited the EBNA1-dependent, OriP-enhanced transcription, but not EBNA1-independent transcription. A Surface Plasmon Resonance Biacore assay revealed that EiK1 associates with EBNA1 amino acid 459-607 DBD/DD. Consistent with the SPR data, in vitro gel shift assays showed that EiK1 suppressed the activity of EBNA1 binding to the cognate familial repeats (FR) sequence, but not control RBP-Jκ binding to the Jκ site. Subsequently, a cross-linker-mediated in vitro multimerization assay and EBNA1 homodimerization-dependent yeast two-hybrid assay showed that EiK1 significantly inhibited EBNA1 dimerization. In an attempt to identify more highly specific peptide inhibitors, small peptides encompassing the EBNA1 DBD/DD were screened for inhibition of EBNA1 DBD-mediated DNA binding function. The small peptide P85, covering EBNA1 a.a. 560-574, significantly blocked EBNA1 DNA binding activity in vitro, prevented dimerization in vitro and in vivo, associated with EBNA1 in vitro, and repressed EBNA1-dependent transcription in vivo. Collectively, this study describes two novel inhibitors of EBNA1 dimerization. This study demonstrates that EBNA1 homodimerization can be effectively targeted by a small molecule or peptide.
Full-text · Article · Jun 2012 · Biochemical and Biophysical Research Communications