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Role of latent membrane protein 2 isoforms in Epstein-Barr virus latency. Trends Microbiol 2008; 16:520-7. [PMID: 18835714 DOI: 10.1016/j.tim.2008.08.007] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/11/2008] [Revised: 08/27/2008] [Accepted: 08/28/2008] [Indexed: 12/12/2022]
Abstract
The oncogenic Epstein-Barr virus (EBV) infects the majority of the human population without doing harm and establishes a latent infection in the memory B-cell compartment. To accomplish this, EBV hijacks B-cell differentiation pathways and uses its own viral genes to interfere with B-cell signalling to achieve life-long persistence. EBV latent membrane protein 2A (LMP2A) provides a surrogate B-cell receptor signal essential for cell survival and is believed to have a crucial role in the maintenance of latency by blocking B-cell activation which would otherwise lead to lytic EBV infection. These two functions demand tight control of LMP2A activity and expression levels. Based on recent insights in the function of LMP2B, an isoform of LMP2A, we propose a model for how LMP2B modulates the activity of LMP2A contributing to maintenance of EBV latency.
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Epstein-Barr virus latent membrane protein 2A exploits Notch1 to alter B-cell identity in vivo. Blood 2008; 113:108-16. [PMID: 18815281 DOI: 10.1182/blood-2008-06-160937] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023] Open
Abstract
Expression of latent membrane protein 2 (LMP2A) during B-cell development leads to global alterations in gene transcription similar to those seen in Hodgkin Reed-Sternberg cells of Hodgkin lymphoma (HL). Along with the consistent detection of LMP2A in Epstein-Barr virus-associated HL, this implicates a role for LMP2A in the pathogenesis of HL. We have shown that LMP2A constitutively activates the Notch1 pathway to autoregulate the LMP2A promoter. To determine whether constitutive activation of the Notch pathway is important for LMP2A-mediated alterations in B-cell development in vivo, TgE-LMP2A-transgenic mice were intercrossed with mice expressing loxP-flanked Notch1 genes and Cre recombinase. B cells from TgE Notch1(lox/lox)-CD19(+/Cre) mice have an increase in immunoglobulin M and CD43 and a decrease in CD5 expression in the bone marrow compared with TgE Notch1(lox/lox) mice, indicating the LMP2A signal for developmental aberrations is impaired in the absence of Notch1. Real-time reverse-transcribed polymerase chain reaction analysis reveals that LMP2A requires the Notch1 pathway to alter levels of B cell-specific transcription factors, E2A and EBF. Interestingly, Notch1 appears to be important for LMP2A-mediated survival in low interleukin-7. We propose that LMP2A and the Notch1 pathway may cooperate to induce the alterations in B-cell identity seen in Hodgkin Reed-Sternberg cells.
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Epstein-Barr virus latent membrane protein 2A preferentially signals through the Src family kinase Lyn. J Virol 2008; 82:8520-8. [PMID: 18579586 DOI: 10.1128/jvi.00843-08] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022] Open
Abstract
Latent membrane protein 2A (LMP2A) is a viral protein expressed during Epstein-Barr virus (EBV) latency in EBV-infected B cells both in cell culture and in vivo. LMP2A has important roles in modulating B-cell receptor signal transduction and provides survival and developmental signals to B cells in vivo. Although Lyn has been shown to be important in mediating LMP2A signaling, it is still unclear if Lyn is used preferentially or if LMP2A associates promiscuously with other Src family kinase (SFK) members. To investigate the role of various SFKs in LMP2A signaling, we crossed LMP2A transgenic mice (TgE) with Lyn(-/-), Fyn(-/-), or Blk(-/-) mice. TgE Lyn(-/-) mice had a larger immunoglobulin M (IgM)-positive B-cell population than TgE mice, suggesting that the absence of Lyn prevents LMP2A from delivering survival and developmental signals to the B cells. Both TgE Fyn(-/-) and TgE Blk(-/-) mice have an IgM-negative population of splenic B cells, similar to the TgE mice. LMP2A was also transiently transfected into the human EBV-negative B-cell line BJAB to determine which SFK members associate with LMP2A. Lyn was detected in LMP2A immunoprecipitates, whereas Fyn was not. Both Lyn and Fyn were able to bind to an LMP2A mutant which contained a sequence shown previously to bind tightly to the SH2 domain of multiple SFK members. From these results, we conclude that LMP2A preferentially associates with and signals through Lyn compared to its association with other SFKs. This preferential association is due in part to the SH2 domain of Lyn associating with LMP2A.
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EBV LMP2A affects LMP1-mediated NF-kappaB signaling and survival of lymphoma cells by regulating TRAF2 expression. Blood 2008; 111:3813-20. [PMID: 18230756 DOI: 10.1182/blood-2007-03-080309] [Citation(s) in RCA: 70] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022] Open
Abstract
A mechanism used by Epstein-Barr virus (EBV) for in vitro transformation of B cells into lymphoblastoid cell lines (LCLs) is activation of the NF-kappaB pathway, which is largely mediated by the EBV latent membrane protein 1 (LMP1). LMP1 is coexpressed with LMP2A in many EBV-associated lymphoid malignancies. Since inhibition of NF-kappaB leads to apoptosis of EBV-infected LCLs and lymphoma cell lines, we sought to determine whether LMP1 alone, or in combination with other viral proteins, is responsible for initiating NF-kappaB activation in these cells, thereby playing a role in cell survival. We found that suppression of LMP1 by RNA interference results in inhibition of basal NF-kappaB and induction of apoptosis. Unexpectedly, knockdown of LMP2A also resulted in comparable decrease of NF-kappaB activity and apoptosis. We report that LMP2A protein controls the expression of TRAF2 mRNA, which in turn is necessary for signaling by LMP1. Our data contrast with previous studies showing that transfected LMP1 can signal in the absence of LMP2A or TRAF2, and demonstrate that both LMP2A and TRAF2 are required for survival in naturally infected lymphoma cells and LCLs. These results also support LMP1, LMP2A, and TRAF2 as potential therapeutic targets in a subset of EBV-associated lymphoid malignancies.
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55
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Kutok JL, Wang F. Spectrum of Epstein-Barr virus-associated diseases. ANNUAL REVIEW OF PATHOLOGY-MECHANISMS OF DISEASE 2007; 1:375-404. [PMID: 18039120 DOI: 10.1146/annurev.pathol.1.110304.100209] [Citation(s) in RCA: 353] [Impact Index Per Article: 20.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
The association between Epstein-Barr virus (EBV) and a large number of benign and malignant diseases is unique among DNA viruses. Within infected tissues, proteins that are expressed during the normal lytic and latent viral life cycle lead to cellular alterations that contribute to these EBV-associated diseases. Although the early events of EBV infection are poorly understood, increasing knowledge of the viral processes that govern viral latency has shed light upon the potential mechanisms by which EBV infection can lead to cellular transformation. Our current understanding of the role of EBV in the development of Burkitt lymphoma, Hodgkin lymphoma, nasopharyngeal carcinoma, and other EBV-associated diseases is discussed.
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Affiliation(s)
- J L Kutok
- Department of Pathology, Brigham and Women's Hospital, Harvard Medical School, Boston, Massachusetts 02115, USA.
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56
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Anderson LJ, Longnecker R. An auto-regulatory loop for EBV LMP2A involves activation of Notch. Virology 2007; 371:257-66. [PMID: 17980397 DOI: 10.1016/j.virol.2007.10.009] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/07/2007] [Revised: 06/25/2007] [Accepted: 10/10/2007] [Indexed: 12/11/2022]
Abstract
LMP2A is consistently detected in Hodgkin's lymphoma, nasopharyngeal carcinoma and has also been detected in Burkitt's lymphoma. Interestingly, LMP2A is detected in the absence of the transcriptional activator EBNA2, suggesting that an alternative mechanism is responsible for LMP2A expression. The intracellular domain of Notch (Notch-IC) and EBNA2 are functional homologs and recent microarray analysis indicates that LMP2A may constitutively activate the Notch pathway in vivo. Coupled with evidence that Notch-IC can bind to and activate the LMP2A promoter, we hypothesized that expression of LMP2A results in the constitutive activation of the Notch pathway to auto-regulate its promoter. Our data indicate that LMP2A constitutively activates the Notch pathway in B cells and epithelial cells. Expression of LMP2A alone is sufficient to activate its own expression and the amino-terminal signaling domain is required as LMP2B is unable to activate the LMP2A promoter. In addition, point mutations in tyrosines 31, 101 and 112 each results in a significant decrease in LMP2A promoter activation. Deletion of the RBP-Jkappa consensus sequences results in a significant decrease in promoter activity. The observation that LMP2A activates its own promoter suggests that LMP2A exploits the Notch pathway in order to control its own expression and may explain EBNA2-independent expression of LMP2A in EBV-associated malignancies.
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Affiliation(s)
- Leah J Anderson
- Department of Microbiology and Immunology, Northwestern University, Chicago, Illinois 60611, USA
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57
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Tomaszewski-Flick MJ, Rowe DT. Minimal protein domain requirements for the intracellular localization and self-aggregation of Epstein-Barr Virus Latent Membrane Protein 2. Virus Genes 2007; 35:225-34. [PMID: 17564822 DOI: 10.1007/s11262-007-0118-8] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/17/2007] [Accepted: 05/14/2007] [Indexed: 12/11/2022]
Abstract
The EBV Latent Membrane Protein 2 (LMP2) may have a role in the establishment and maintenance of in vivo latency. The gene is transcribed into two mRNAs that produce two LMP2 protein isoforms. The LMP2a protein isoform has 12 transmembrane segments (TMs) and an amino terminal cytoplasmic signaling domain (CSD) while the LMP2b isoform is identical but lacks the CSD. There has not been a consensus on the cellular membrane localization being sometimes ascribed to either a plasma membrane or an intracellular location [M. Rovedo, R. Longnecker, J. Virol. 81:89-94, 2007; D. Lynch, J. Zimmerman, D.T. Rowe, J. Gen. Virol. 83:1025-1035, 2002; C. Dawson, J. George, S. Blake, R. Longnecker, L.S. Young, Virology 289:192-207, 2001]. Fluorescent marker and epitope tagged LMP2b truncation mutants progressively removing TMs from the N and C termini were used to assess the localization and aggregation properties of LMP2b. wtLMP2b had an exclusively intracellular perinuclear localization, while all truncations of the protein resulted in localization to the cell surface. By epitope loop-tagging, all the truncated LMP2b proteins were verified to be in the predicted membrane orientation. In co-transfection experiments, the C-terminal region was implicated in the self-aggregation properties of LMP2b. Thus, an intact 12 TM domain was required for intracellular localization and protein-protein interaction while a C-terminal region was responsible for auto-aggregative properties.
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Affiliation(s)
- Monica Jo Tomaszewski-Flick
- Department of Infectious Diseases and Microbiology, Graduate School of Public Health, University of Pittsburgh, 130 DeSoto St, Pittsburgh, PA 15213, USA
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58
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Grande SM, Bannish G, Fuentes-Panana EM, Katz E, Monroe JG. Tonic B-cell and viral ITAM signaling: context is everything. Immunol Rev 2007; 218:214-34. [PMID: 17624955 DOI: 10.1111/j.1600-065x.2007.00535.x] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Abstract
The presence of an immunoreceptor tyrosine-based activation motif (ITAM) makes immunoreceptors different from other signaling receptors, like integrins, G-coupled protein receptors, chemokine receptors, and growth factor receptors. This unique motif has the canonical sequence D/Ex(0-2)YxxL/Ix(6-8)YxxL/I, where x represents any amino acid and is present at least once in all immunoreceptor complexes. Immunoreceptors can promote survival, activation, and differentiation by transducing signals through these highly conserved motifs. Traditionally, ITAM signaling is thought to occur in response to ligand-induced aggregation, although evidence indicates that ligand-independent tonic signaling also provides functionally relevant signals. The majority of proteins containing ITAMs are transmembrane proteins that exist as part of immunoreceptor complexes. However, oncogenic viruses also have ITAM-containing proteins. In this review, we discuss what is known about tonic signaling by both cellular and viral ITAM-containing proteins and speculate what we might learn from each context.
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Affiliation(s)
- Shannon M Grande
- Department of Pathology and Laboratory Medicine, University of Pennsylvania, Philadelphia, PA, USA
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59
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Rechsteiner MP, Berger C, Weber M, Sigrist JA, Nadal D, Bernasconi M. Silencing of latent membrane protein 2B reduces susceptibility to activation of lytic Epstein-Barr virus in Burkitt's lymphoma Akata cells. J Gen Virol 2007; 88:1454-1459. [PMID: 17412973 DOI: 10.1099/vir.0.82790-0] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023] Open
Abstract
Epstein-Barr virus (EBV) latent membrane protein 2A (LMP2A) blocks B-cell receptor (BCR) signalling after BCR cross-linking to inhibit activation of lytic EBV, and ectopically expressed LMP2B negatively regulates LMP2A. Here, it is demonstrated that silencing of LMP2B in EBV-harbouring Burkitt's lymphoma Akata cells results in reduced expression of EBV immediate-early lytic BZLF1 gene mRNA and late lytic gp350/220 protein upon BCR cross-linking. Similarly, reduction of lytic EBV activation was observed in Akata cells overexpressing LMP2A. In contrast, silencing of LMP2A expression resulted in higher lytic EBV mRNA and protein expression in BCR cross-linked Akata cells. These observations indicate a role for LMP2B distinct from that of LMP2A in regulation of lytic EBV activation in the host cell and support the hypothesis that LMP2B exhibits a negative-regulatory effect on the ability of LMP2A to maintain EBV latency by preventing the switch to lytic replication.
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Affiliation(s)
- Markus P Rechsteiner
- Experimental Infectious Diseases and Cancer Research, University Children's Hospital of Zurich, Zurich, Switzerland
| | - Christoph Berger
- Experimental Infectious Diseases and Cancer Research, University Children's Hospital of Zurich, Zurich, Switzerland
| | - Matthias Weber
- Experimental Infectious Diseases and Cancer Research, University Children's Hospital of Zurich, Zurich, Switzerland
| | - Jürg A Sigrist
- Experimental Infectious Diseases and Cancer Research, University Children's Hospital of Zurich, Zurich, Switzerland
| | - David Nadal
- Experimental Infectious Diseases and Cancer Research, University Children's Hospital of Zurich, Zurich, Switzerland
| | - Michele Bernasconi
- Experimental Infectious Diseases and Cancer Research, University Children's Hospital of Zurich, Zurich, Switzerland
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60
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Swanson-Mungerson M, Longnecker R. Epstein–Barr virus latent membrane protein 2A and autoimmunity. Trends Immunol 2007; 28:213-8. [PMID: 17398159 DOI: 10.1016/j.it.2007.03.002] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/29/2007] [Revised: 02/26/2007] [Accepted: 03/16/2007] [Indexed: 11/18/2022]
Abstract
Epstein-Barr virus (EBV) has been associated with autoimmune diseases for over 40 years. However, the mechanisms by which EBV might promote autoimmune development remain elusive. Many of the hypotheses for the means by which EBV might achieve this incorporate the idea that autoimmune responses are initially immune responses against EBV proteins that crossreact with endogenous human proteins. However, recent evidence using transgenic mouse models suggests that B cells expressing the EBV-encoded protein latent membrane protein 2A (LMP2A) bypasses normal tolerance checkpoints and enhances the development of autoimmune diseases. Evidence from transgenic mouse models supports a paradigm in which LMP2A could promote autoimmune development. This novel model provides a framework to test potential mechanisms by which EBV could promote the development of autoimmune responses and might enable the identification of strategies to treat EBV-associated autoimmune diseases.
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Affiliation(s)
- Michelle Swanson-Mungerson
- Department of Microbiology and Immunology, Feinberg School of Medicine, Northwestern University, Chicago, IL 60611, USA
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61
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Matskova LV, Helmstetter C, Ingham RJ, Gish G, Lindholm CK, Ernberg I, Pawson T, Winberg G. The Shb signalling scaffold binds to and regulates constitutive signals from the Epstein–Barr virus LMP2A membrane protein. Oncogene 2007; 26:4908-17. [PMID: 17311000 DOI: 10.1038/sj.onc.1210298] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
The Epstein-Barr virus latency-associated membrane protein LMP2A has been shown to activate the survival kinase Akt in epithelial and B cells in a phosphoinositide 3-kinase-dependent fashion. In this study, we demonstrate that the signalling scaffold Shb associates through SH2 and PTB domain interactions with phosphorylated tyrosine motifs in the LMP2A N-terminal tail. Additionally, we show that mutation of tyrosines in these motifs as well as shRNA-mediated downregulation of Shb leads to a loss of constitutive Akt-activation in LMP2A-expressing cells. Furthermore, utilization by Shb of the LMP2A ITAM motif regulates stability of the Syk tyrosine kinase in LMP2A-expressing cells. Our data set the precedent for viral utilization of the Shb signalling scaffold and implicate Shb as a regulator of LMP2A-dependent Akt activation.
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Affiliation(s)
- L V Matskova
- Microbiology and Tumor Biology Center, Karolinska Institutet, Stockholm, Sweden.
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62
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Wang S, Wang S, Maeng H, Young DP, Prakash O, Fayad LE, Younes A, Samaniego F. K1 protein of human herpesvirus 8 suppresses lymphoma cell Fas-mediated apoptosis. Blood 2006; 109:2174-82. [PMID: 17090655 PMCID: PMC1801039 DOI: 10.1182/blood-2006-02-003178] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022] Open
Abstract
Expression of the K1 gene of human herpesvirus 8 activates nuclear factor-kappaB and induces lymph node hyperplasia and lymphomas in transgenic mice. To further delineate its role in cell survival, we determined whether K1 altered apoptosis of lymphoma cells. K1 protein is expressed in Kaposi sarcoma and primary effusion lymphoma. We retrovirally transfected BJAB lymphoma, THP-1, U937, and Kaposi sarcoma SLK cells to express K1 and a K1 mutant with the deleted immunoreceptor tyrosine-based activation motif (K1m). We challenged cells with an agonistic anti-Fas antibody, Fas ligand, irradiation, and tumor necrosis factor-related apoptosis-inducing ligand. K1 transfectants but not K1m transfectants exhibited reduced levels of apoptosis induced by the anti-Fas antibody but not apoptosis induced by the tumor necrosis factor-related apoptosis-inducing ligand or irradiation. K1 expression resulted in reduced apoptosis rates as shown in several assays. K1 induced a modest reduction in levels of Fas-associated death domain protein, and procaspase 8 recruited to the death-inducing signaling complex. Finally, K1 transfectants cleaved procaspase 8 at significantly lower rates than did K1m transfectants. K1-transfected mice, compared with vector-transfected mice, showed lower death rates after challenge with anti-Fas antibody. K1 may contribute to lymphoma development by stimulating cell survival by selectively blocking Fas-mediated apoptosis.
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Affiliation(s)
- Suizhao Wang
- Department of Lymphoma and Myeloma, The University of Texas M. D. Anderson Cancer Center, Houston, TX 77030, USA
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63
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Ross SR, Schmidt JW, Katz E, Cappelli L, Hultine S, Gimotty P, Monroe JG. An immunoreceptor tyrosine activation motif in the mouse mammary tumor virus envelope protein plays a role in virus-induced mammary tumors. J Virol 2006; 80:9000-8. [PMID: 16940512 PMCID: PMC1563925 DOI: 10.1128/jvi.00788-06] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Mouse mammary tumor virus (MMTV) induces breast cancer with almost 100% efficiency in susceptible strains through insertional activation of protooncogenes, such as members of the wnt and fibroblast growth factor (fgf) families. We previously showed that expression of the MMTV envelope protein (Env) in normal immortalized mammary epithelial cells grown in three-dimensional cultures caused their morphological transformation, and that this phenotype depended on an immunoreceptor tyrosine-based activation motif (ITAM) present in Env and signaling through the Syk tyrosine kinase (E. Katz, M. H. Lareef, J. C. Rassa, S. M. Grande, L. B. King, J. Russo, S. R. Ross, and J. G. Monroe, J. Exp. Med. 201:431-439, 2005). Here, we examined the role of the Env protein in virus-induced mammary tumorigenesis in vivo. Similar to the effect seen in vitro, Env expression in the mammary glands of transgenic mice bearing either full-length wild-type provirus or only Env transgenes showed increased lobuloalveolar budding. Introduction of the ITAM mutation into the env of an infectious, replication-competent MMTV or into MMTV/murine leukemia virus pseudotypes had no effect on incorporation of Env into virus particles or on in vitro infectivity. Moreover, replication-competent MMTV bearing the ITAM mutation in Env infected lymphoid and mammary tissue at the same level as wild-type MMTV and was transmitted through milk. However, mammary tumor induction was greatly attenuated, and the pattern of oncogene activation was altered. Taken together, these studies indicate that the MMTV Env protein participates in mammary epithelial cell transformation in vivo and that this requires a functional ITAM in the envelope protein.
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Affiliation(s)
- Susan R Ross
- University of Pennsylvania, 313BRBII/III, 421 Curie Blvd., Philadelphia, PA 19104, USA.
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64
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Abstract
Studies carried out over the past few years provide strong support for the idea that Ig alpha-Ig beta-containing complexes such as the pre-B-cell receptor and the B-cell receptor can signal independently of ligand engagement, and this has been termed tonic signalling. In this Review, I discuss recent literature that is relevant to the potential mechanisms by which tonic signals are initiated and regulated, and discuss views on how tonic and ligand-dependent (aggregation-mediated) signalling differ. These mechanisms are relevant to the possibility that tonic signals generated through immunoreceptor tyrosine-based activation motif (ITAM)-containing proteins that are expressed by oncogenic viruses induce transformation in non-haematopoietic cells.
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Affiliation(s)
- John G Monroe
- Department of Pathology and Laboratory Medicine, University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania 19104, USA.
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65
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Brinkmann MM, Schulz TF. Regulation of intracellular signalling by the terminal membrane proteins of members of the Gammaherpesvirinae. J Gen Virol 2006; 87:1047-1074. [PMID: 16603506 DOI: 10.1099/vir.0.81598-0] [Citation(s) in RCA: 83] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022] Open
Abstract
The human gamma(1)-herpesvirus Epstein-Barr virus (EBV) and the gamma(2)-herpesviruses Kaposi's sarcoma-associated herpesvirus (KSHV), rhesus rhadinovirus (RRV), herpesvirus saimiri (HVS) and herpesvirus ateles (HVA) all contain genes located adjacent to the terminal-repeat region of their genomes, encoding membrane proteins involved in signal transduction. Designated 'terminal membrane proteins' (TMPs) because of their localization in the viral genome, they interact with a variety of cellular signalling molecules, such as non-receptor protein tyrosine kinases, tumour-necrosis factor receptor-associated factors, Ras and Janus kinase (JAK), thereby initiating further downstream signalling cascades, such as the MAPK, PI3K/Akt, NF-kappaB and JAK/STAT pathways. In the case of TMPs expressed during latent persistence of EBV and HVS (LMP1, LMP2A, Stp and Tip), their modulation of intracellular signalling pathways has been linked to the provision of survival signals to latently infected cells and, hence, a contribution to occasional cellular transformation. In contrast, activation of similar pathways by TMPs of KSHV (K1 and K15) and RRV (R1), expressed during lytic replication, may extend the lifespan of virus-producing cells, alter their migration and/or modulate antiviral immune responses. Whether R1 and K1 contribute to the oncogenic properties of KSHV and RRV has not been established satisfactorily, despite their transforming qualities in experimental settings.
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Affiliation(s)
- Melanie M Brinkmann
- Institut für Virologie, Medizinische Hochschule Hannover, Carl-Neuberg Str. 1, D-30625 Hannover, Germany
| | - Thomas F Schulz
- Institut für Virologie, Medizinische Hochschule Hannover, Carl-Neuberg Str. 1, D-30625 Hannover, Germany
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66
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Humphrey MB, Lanier LL, Nakamura MC. Role of ITAM-containing adapter proteins and their receptors in the immune system and bone. Immunol Rev 2005; 208:50-65. [PMID: 16313340 DOI: 10.1111/j.0105-2896.2005.00325.x] [Citation(s) in RCA: 171] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/16/2023]
Abstract
The immunoreceptor tyrosine-based activation motif (ITAM) is a highly conserved region in the cytoplasmic domain of signaling chains and receptors and is a critical mediator of intracellular signals. ITAM-mediated signals depend on the Syk or zeta-associated protein of 70 kDa tyrosine kinases, and ITAM signaling is required for the differentiation and function of B and T cells in adaptive immunity. ITAM-dependent receptors also regulate the function of innate immune cells, including natural killer cells, and myeloid-derived cells such as macrophages, neutrophils, dendritic cells, and mast cells. Myeloid lineage cells also include osteoclasts (OCLs), the cells required for bone resorption, and recent studies show a critical role for the ITAM-containing adapter proteins DAP12 and the FcRgamma chain (Fcepsilon receptor I gamma chain) in OCL differentiation. Mice deficient in both the DAP12 and FcRgamma ITAM-bearing adapters are significantly osteopetrotic with a severe defect in OCL differentiation, demonstrating the requirement for ITAM signals in bone and further implicating this pathway in the development of highly specialized cell functions in hematopoietic cells. Regulation of osteoclastogenesis by ITAM-dependent receptors suggests that OCLs, similar to related myeloid cells, are tightly controlled by arrays of receptors that allow them to sense and respond to their local microenvironment like other innate immune cells.
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Affiliation(s)
- Mary Beth Humphrey
- Department of Medicine, University of California, San Francisco, CA 94121, USA
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67
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Abstract
In Hodgkin's lymphoma (HL), the B cell origin of the tumour cells, the Hodgkin and Reed-Sternberg (HRS) cells, has been disclosed by molecular single cell analysis about 10 yr ago. This finding formed the basis for various studies aimed to better understand the pathogenesis of this peculiar malignancy and the pathophysiology of the HRS cells. Work of our groups in this regard was focussed recently on two main topics, namely the study of differential gene expression in HRS cells and the pathogenesis of composite lymphomas. Composite lymphomas are combinations of HL and B cell non-Hodgkin lymphomas, that turned out to be often clonally related. By molecular analysis of several composite lymphomas for potential transforming events, we identified examples of both shared as well as distinct transforming events. Comparing gene expression profiles of HL-derived cell lines with the corresponding profiles from other B cell lymphomas and normal B cell subsets revealed a global down-regulation of the B cell-specific gene expression signature in HRS cells. Moreover, we identifed aberrant expression and activity of multiple receptor tyrosine kinases in HRS cells of classical and to a lesser extend lymphocyte predominant HL, which appears to be a unique feature of HL, and may offer novel strategies for treatment.
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Affiliation(s)
- Ralf Küppers
- Institute for Cell Biology (Tumour Research), University of Duisburg-Essen, Medical School, Essen, Germany.
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68
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Morrison JA, Raab-Traub N. Roles of the ITAM and PY motifs of Epstein-Barr virus latent membrane protein 2A in the inhibition of epithelial cell differentiation and activation of {beta}-catenin signaling. J Virol 2005; 79:2375-82. [PMID: 15681438 PMCID: PMC546559 DOI: 10.1128/jvi.79.4.2375-2382.2005] [Citation(s) in RCA: 75] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022] Open
Abstract
Epstein-Barr virus (EBV) latent membrane protein 2A (LMP2A) is important for maintenance of latency in infected B lymphocytes. Through its immunoreceptor tyrosine-based activation motif (ITAM) and PY motifs, LMP2A is able to block B-cell receptor (BCR) signaling, bind BCR-associated kinases, and manipulate the turnover of itself and these kinases via a PY-mediated interaction with the Nedd4 family of ubiquitin ligases. In epithelial cells, LMP2A has been shown to activate the phosphatidylinositol 3'-OH kinase/Akt and beta-catenin signaling pathways. In the present study, the biological consequences of LMP2A expression in the normal human foreskin keratinocyte (HFK) cell line were investigated and the importance of the ITAM and PY motifs for LMP2A signaling effects in HFK cells was ascertained. The ITAM was essential for the activation of Akt by LMP2A in HFK cells, while both the ITAM and PY motifs contributed to LMP2A-mediated accumulation and nuclear translocation of the oncoprotein beta-catenin. LMP2A inhibited induction of differentiation in an assay conducted with semisolid methylcellulose medium, and the PY motifs were critical for this inhibition. LMP2A is expressed in the EBV-associated epithelial malignancies nasopharyngeal carcinoma and gastric carcinoma, and these data indicate that LMP2A affects cellular processes that likely contribute to carcinogenesis.
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Affiliation(s)
- Jennifer A Morrison
- Department of Microbiology and Immunology, University of North Carolina-Chapel Hill, Mason Farm Rd., Chapel Hill, NC 27599, USA
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69
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Abstract
Chromosomal translocations involving the immunoglobulin loci are a hallmark of many types of B-cell lymphoma. Other factors, however, also have important roles in the pathogenesis of B-cell malignancies. Most B-cell lymphomas depend on the expression of a B-cell receptor (BCR) for survival, and in several B-cell malignancies antigen activation of lymphoma cells through BCR signalling seems to be an important factor for lymphoma pathogenesis. Recent insights into the lymphomagenic role of factors supplied by the microenvironment also offer new therapeutic strategies.
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Affiliation(s)
- Ralf Küppers
- Institute for Cell Biology (Tumor Research), University of Duisburg-Essen, Medical School, Germany.
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70
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Bordin L, Ion-Popa F, Brunati AM, Clari G, Low PS. Effector-induced Syk-mediated phosphorylation in human erythrocytes. BIOCHIMICA ET BIOPHYSICA ACTA-MOLECULAR CELL RESEARCH 2005; 1745:20-8. [PMID: 16085052 DOI: 10.1016/j.bbamcr.2004.12.010] [Citation(s) in RCA: 37] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Subscribe] [Scholar Register] [Received: 07/28/2004] [Revised: 12/09/2004] [Accepted: 12/28/2004] [Indexed: 11/21/2022]
Abstract
Band 3 (AE1), the most prominent polypeptide of the human erythrocyte membrane, becomes heavily tyrosine phosphorylated following treatment of intact cells with protein tyrosine phosphatase inhibitors such as diamide, pervanadate, vanadate, or N-ethylmaleimide (NEM). The mechanism underlying this tyrosine phosphorylation is thought to involve the sequential action of two protein tyrosine kinases, Syk (p72syk) and Lyn (p53/56lyn). While Lyn catalysed phosphorylation appears to be strictly dependent on prior phosphorylation of Tyr8 and 21 of band 3 by Syk, little is known about the mechanism of induction of Syk phosphorylation. Data presented here show that both the fraction of Syk that associates with the membrane and the extent of phosphorylation of band 3 differ in response to the above inhibitors. While diamide and NEM stimulate syk translocation to the membrane during their induction of band 3 tyrosine phosphorylation, pervanadate and vanadate induce no change in kinase distribution. Moreover, diamide and NEM-induced Syk recruitment to the membrane are phosphotyrosine independent and involve their preferential association with Triton X-100-insoluble membrane skeletons. Together these data reveal a complex process controlling the association and catalytic activity of protein tyrosine kinases syk and lyn with the human erythrocyte membrane.
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Affiliation(s)
- Luciana Bordin
- Department of Biological Chemistry, University of Padua, Viale G. Colombo 3, 35121 Padua, Italy
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71
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Portis T, Longnecker R. Epstein-Barr virus (EBV) LMP2A mediates B-lymphocyte survival through constitutive activation of the Ras/PI3K/Akt pathway. Oncogene 2004; 23:8619-28. [PMID: 15361852 DOI: 10.1038/sj.onc.1207905] [Citation(s) in RCA: 155] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
Abstract
Epstein-Barr virus (EBV) establishes a lifelong latent infection in host B cells and is associated with the development of a variety of malignancies. The viral LMP2A protein mediates viral latency by mimicking a constitutively activated B-cell receptor (BCR). In vivo LMP2A provides developmental and survival signals to BCR-negative B cells, allowing them to survive in peripheral lymphoid organs. In this study, we have demonstrated that Ras is constitutively active in peripheral, BCR-negative B cells from LMP2A transgenic mice. Furthermore, increased expression of activated Ras correlated with elevated levels of Bcl-xL expression and a slower migrating, band-shifted form of Bcl-2. B cells from LMP2A transgenic mice were sensitive to apoptosis induction in the presence of specific inhibitors of Ras, phosphatidylinositol 3-kinase (PI3K), and Akt, indicating that LMP2A activates the Ras/PI3K/Akt pathway to mediate B-cell survival. Increased B-cell apoptosis correlated with reduced expression of Bcl-xL, suggesting that this Bcl-2 family member may be involved in apoptosis inhibition mediated by LMP2A. The ability of LMP2A to activate constitutively the Ras pathway, a common event during tumorigenesis, suggests that this viral protein plays an active role in the development of EBV-associated malignancies.
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Affiliation(s)
- Toni Portis
- Department of Microbiology and Immunology, Feinberg School of Medicine, Northwestern University, Chicago, IL 60611, USA
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72
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Katzman RB, Longnecker R. LMP2A does not require palmitoylation to localize to buoyant complexes or for function. J Virol 2004; 78:10878-87. [PMID: 15452208 PMCID: PMC521828 DOI: 10.1128/jvi.78.20.10878-10887.2004] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Epstein-Barr virus (EBV) latent membrane protein 2A (LMP2A) is expressed constitutively in lipid rafts in latently infected B lymphocytes. Lipid rafts are membrane microdomains enriched in cholesterol and sphingolipids selective for specific protein association. Lipid rafts have been shown to be necessary for B-cell receptor (BCR) signal transduction. LMP2A prevents BCR recruitment to lipid rafts, thereby abrogating BCR function. As LMP2A is palmitoylated, whether this fatty acid modification is necessary for LMP2A to localize to lipid rafts and for protein function was investigated. LMP2A palmitoylation was confirmed in latently infected B cells. LMP2A was found to be palmitoylated on multiple cysteines only by S acylation. An LMP2A mutant that was not palmitoylated was identified and functioned similar to wild-type LMP2A; unmodified LMP2A localized to lipid rafts, was tyrosine phosphorylated, was associated with LMP2A-associated proteins, was ubiquitinated, and was able to block calcium mobilization following BCR cross-linking. Therefore, palmitoylation of LMP2A is not required for LMP2A targeting to buoyant complexes or for function.
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Affiliation(s)
- Rebecca B Katzman
- Department of Microbiology-Immunology, Northwestern University Medical School, Chicago, IL 60611, USA
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73
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Ikeda A, Merchant M, Lev L, Longnecker R, Ikeda M. Latent membrane protein 2A, a viral B cell receptor homologue, induces CD5+ B-1 cell development. THE JOURNAL OF IMMUNOLOGY 2004; 172:5329-37. [PMID: 15100272 DOI: 10.4049/jimmunol.172.9.5329] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Subscribe] [Scholar Register] [Indexed: 01/09/2023]
Abstract
The latent membrane protein 2A (LMP2A) of EBV plays a key role in regulating viral latency and EBV pathogenesis by functionally mimicking a constitutively active B cell Ag receptor. When expressed as a B cell-specific transgene in mice, LMP2A drives B cell development, resulting in the bypass of normal developmental checkpoints. In this study, we have demonstrated that expression of LMP2A in transgenic mice results in B cell development that exclusively favors B-1 cells. This switch to B-1 cell development occurs at the pre-B-cell stage of normal B cell development in the bone marrow, a B cell stage much earlier than appreciated for B-1 commitment. This finding indicates that all pre-B cells have the capacity to assume a B-1 cell phenotype if they encounter the appropriate signal during normal development. Furthermore, these studies offer insight into EBV latency and pathogenesis in the human host.
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MESH Headings
- Animals
- Antigens, CD/biosynthesis
- B-Lymphocyte Subsets/cytology
- B-Lymphocyte Subsets/enzymology
- B-Lymphocyte Subsets/immunology
- B-Lymphocyte Subsets/metabolism
- Biomarkers/analysis
- Bone Marrow Cells/cytology
- Bone Marrow Cells/immunology
- Bone Marrow Cells/metabolism
- CD5 Antigens/biosynthesis
- Cell Differentiation/genetics
- Cell Differentiation/immunology
- Cell Division/immunology
- Cell Line
- Enzyme Precursors/physiology
- Hematopoietic Stem Cells/cytology
- Hematopoietic Stem Cells/immunology
- Hematopoietic Stem Cells/metabolism
- Herpesvirus 4, Human/immunology
- Immunoglobulin M/biosynthesis
- Immunoglobulin M/blood
- Intracellular Signaling Peptides and Proteins
- Leukosialin
- Lipopolysaccharides/pharmacology
- Mice
- Mice, Inbred C57BL
- Mice, Transgenic
- Protein-Tyrosine Kinases/physiology
- Receptors, Antigen, B-Cell/chemistry
- Receptors, Antigen, B-Cell/deficiency
- Receptors, IgE/deficiency
- Sialoglycoproteins/biosynthesis
- Structural Homology, Protein
- Syk Kinase
- Tetradecanoylphorbol Acetate/pharmacology
- Viral Matrix Proteins/biosynthesis
- Viral Matrix Proteins/chemistry
- Viral Matrix Proteins/physiology
- Virus Latency/immunology
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Affiliation(s)
- Akiko Ikeda
- Department of Microbiology-Immunology, Northwestern University Feinberg School of Medicine, Chicago, IL 60611, USA
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74
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Sutkowski N, Chen G, Calderon G, Huber BT. Epstein-Barr virus latent membrane protein LMP-2A is sufficient for transactivation of the human endogenous retrovirus HERV-K18 superantigen. J Virol 2004; 78:7852-60. [PMID: 15220463 PMCID: PMC434102 DOI: 10.1128/jvi.78.14.7852-7860.2004] [Citation(s) in RCA: 66] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Superantigens are microbial proteins that strongly stimulate T cells. We described previously that the Epstein-Barr virus (EBV) transactivates a superantigen encoded by the human endogenous retrovirus, HERV-K18. We now report that the transactivation is dependent upon the EBV latent cycle proteins. Moreover, LMP-2A is sufficient for induction of HERV-K18 superantigen activity.
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Affiliation(s)
- Natalie Sutkowski
- Department of Pathology, Tufts University School of Medicine, Boston, MA 02111, USA
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75
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Portis T, Longnecker R. Epstein-Barr virus (EBV) LMP2A alters normal transcriptional regulation following B-cell receptor activation. Virology 2004; 318:524-33. [PMID: 14972521 DOI: 10.1016/j.virol.2003.09.017] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/21/2003] [Revised: 09/12/2003] [Accepted: 09/17/2003] [Indexed: 11/29/2022]
Abstract
The latent membrane protein 2A (LMP2A) of Epstein-Barr virus (EBV) is an important mediator of viral latency in infected B-lymphocytes. LMP2A inhibits B-cell receptor (BCR) signaling in vitro and allows for the survival of BCR-negative B cells in vivo. In this study, we compared gene transcription in BCR-activated B cells from non-transgenic and LMP2A Tg6 transgenic mice. We found that the transcriptional induction and down-regulation of many genes that normally occurs in B cells following BCR activation did not occur in B cells from LMP2A Tg6 transgenic mice. Furthermore, LMP2A induced the expression of various transcription factors and genes associated with DNA/RNA metabolism, which may allow for the altered transcriptional regulation observed in BCR-activated B cells from LMP2A Tg6 mice. These results suggest that LMP2A may inhibit the downstream effects of BCR signaling by directly or indirectly altering gene transcription to ensure EBV persistence in infected B cells.
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Affiliation(s)
- Toni Portis
- Department of Microbiology and Immunology, Feinberg School of Medicine, Northwestern University, Chicago, IL 60611, USA
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76
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Pike KA, Iacampo S, Friedmann JE, Ratcliffe MJH. The Cytoplasmic Domain of Igα Is Necessary and Sufficient to Support Efficient Early B Cell Development. THE JOURNAL OF IMMUNOLOGY 2004; 172:2210-8. [PMID: 14764688 DOI: 10.4049/jimmunol.172.4.2210] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Abstract
The B cell receptor complex (BcR) is essential for normal B lymphocyte function, and surface BcR expression is a crucial checkpoint in B cell development. However, functional requirements for chains of the BcR during development remain controversial. We have used retroviral gene transfer to introduce components of the BcR into chicken B cell precursors during embryonic development. A chimeric heterodimer, in which the cytoplasmic domains of chicken Igalpha and Igbeta are expressed by fusion with the extracellular and transmembrane domains of murine CD8alpha and CD8beta, respectively, targeted the cytoplasmic domains of the BcR to the cell surface in the absence of extracellular BcR domains. Expression of this chimeric heterodimer supported all early stages of embryo B cell development: bursal colonization, clonal expansion, and induction of repertoire diversification by gene conversion. Expression of the cytoplasmic domain of Igalpha, in the absence of the cytoplasmic domain of Igbeta, was not only necessary, but sufficient to support B cell development as efficiently as the endogenous BcR. In contrast, expression of the cytoplasmic domain of Igbeta in the absence of the cytoplasmic domain of Igalpha failed to support B cell development. The ability of the cytoplasmic domain of Igalpha to support early B cell development required a functional Igalpha immunoreceptor tyrosine-based activation motif. These results support a model in which expression of surface IgM following productive V(D)J recombination in developing B cell precursors serves to chaperone the cytoplasmic domain of Igalpha to the B cell surface, thereby initiating subsequent stages of development.
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MESH Headings
- Amino Acid Motifs/genetics
- Amino Acid Motifs/immunology
- Amino Acid Sequence
- Animals
- Antibody Diversity/genetics
- Antigens, CD/genetics
- Antigens, CD/metabolism
- Antigens, CD/physiology
- B-Lymphocyte Subsets/cytology
- B-Lymphocyte Subsets/immunology
- B-Lymphocyte Subsets/metabolism
- Bursa of Fabricius/cytology
- Bursa of Fabricius/immunology
- Bursa of Fabricius/metabolism
- CD79 Antigens
- CD8 Antigens/biosynthesis
- Cell Differentiation/genetics
- Cell Differentiation/immunology
- Cell Line
- Cell Membrane/genetics
- Cell Membrane/immunology
- Cell Membrane/metabolism
- Chick Embryo
- Chickens
- Cytoplasm/genetics
- Cytoplasm/immunology
- Down-Regulation/genetics
- Down-Regulation/immunology
- Gene Rearrangement, B-Lymphocyte/genetics
- Immunoglobulin M/metabolism
- Immunoglobulin Variable Region/genetics
- Immunoglobulin Variable Region/metabolism
- Mice
- Molecular Sequence Data
- Protein Structure, Tertiary/genetics
- Receptors, Antigen, B-Cell/genetics
- Receptors, Antigen, B-Cell/metabolism
- Receptors, Antigen, B-Cell/physiology
- Recombinant Fusion Proteins/physiology
- Signal Transduction/immunology
- Stem Cells/cytology
- Stem Cells/immunology
- Stem Cells/metabolism
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Affiliation(s)
- Kelly A Pike
- Department of Immunology, University of Toronto, Toronto, Ontario, Canada
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77
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Casola S, Otipoby KL, Alimzhanov M, Humme S, Uyttersprot N, Kutok JL, Carroll MC, Rajewsky K. B cell receptor signal strength determines B cell fate. Nat Immunol 2004; 5:317-27. [PMID: 14758357 DOI: 10.1038/ni1036] [Citation(s) in RCA: 432] [Impact Index Per Article: 21.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/11/2003] [Accepted: 12/02/2003] [Indexed: 11/09/2022]
Abstract
B cell receptor (BCR)-mediated antigen recognition is thought to regulate B cell differentiation. BCR signal strength may also influence B cell fate decisions. Here, we used the Epstein-Barr virus protein LMP2A as a constitutively active BCR surrogate to study the contribution of BCR signal strength in B cell differentiation. Mice carrying a targeted replacement of Igh by LMP2A leading to high or low expression of the LMP2A protein developed B-1 or follicular and marginal zone B cells, respectively. These data indicate that BCR signal strength, rather than antigen specificity, determines mature B cell fate. Furthermore, spontaneous germinal centers developed in gut-associated lymphoid tissue of LMP2A mice, indicating that microbial antigens can promote germinal centers independently of BCR-mediated antigen recognition.
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Affiliation(s)
- Stefano Casola
- CBR Institute for Biomedical Research, Harvard Medical School, Boston, MA 02115, USA.
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78
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Izumi KM. Epstein-Barr virus signal transduction and B-lymphocyte growth transformation. PROGRESS IN MOLECULAR AND SUBCELLULAR BIOLOGY 2004; 36:269-88. [PMID: 15171616 DOI: 10.1007/978-3-540-74264-7_13] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/04/2022]
Abstract
Latent EBV growth transformation of resting B-cells into indefinitely proliferating cell lines is a successful viral strategy for survival in its host and the basis of several human malignancies. EBV transforms cell growth through viral proteins that modify cell gene expression at the level of transcription or by appropriating signaling pathways. Analyses of the EBV-transforming protein LMP1 have begun to reveal that this receptor transduces critical signals by appropriating the TNF receptor signal transduction pathway to activate NF-kappaB and MAPK. While this has brought an important aspect into clearer focus, future progress in delineating the underlying mechanism of transformation, which will be essential to devising effective therapies to treat EBV-associated malignancies, will depend on resolving the intricacies of TRAF signal transduction. Since expression of cytokines, receptors, and anti-apoptotic proteins are regulated by TRAF signaling, another critical issue is delineating the genes that are specifically targeted by LMP1 in order to transform B-lymphocyte growth.
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Affiliation(s)
- K M Izumi
- Department of Microbiology and Immunology, University of Texas Health Science Center at San Antonio, 7703 Floyd Curl Drive, San Antonio, Texas 78229-3900, USA.
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79
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Portis T, Dyck P, Longnecker R. Epstein-Barr Virus (EBV) LMP2A induces alterations in gene transcription similar to those observed in Reed-Sternberg cells of Hodgkin lymphoma. Blood 2003; 102:4166-78. [PMID: 12907455 DOI: 10.1182/blood-2003-04-1018] [Citation(s) in RCA: 107] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Epstein-Barr virus (EBV) is associated with the development of a variety of malignancies, including Hodgkin lymphoma. One of the few viral transcripts expressed in EBV-positive Hodgkin/Reed-Sternberg (HRS) cells of Hodgkin lymphoma is latent membrane protein 2A (LMP2A). This viral protein blocks B-cell receptor (BCR)-signaling in vitro. Furthermore, expression of LMP2A in developing B cells in vivo induces a global down-regulation of genes necessary for proper B-cell development. In this study we have analyzed gene transcription in primary B cells from LMP2A transgenic mice, LMP2A-expressing human B-cell lines, and LMP2A-positive and -negative EBV-infected lymphoblastoid cell lines (LCLs). We demonstrate that LMP2A increases the expression of genes associated with cell cycle induction and inhibition of apoptosis, alters the expression of genes involved in DNA and RNA metabolism, and decreases the expression of B-cell-specific factors and genes associated with immunity. Furthermore, many alterations in gene expression induced by LMP2A are similar to those recently described in HRS cells of Hodgkin lymphoma and activated, proliferating germinal center centroblasts/centrocytes. These correlations suggest that LMP2A expression in EBV-infected B cells may lead to the induction and maintenance of an activated, proliferative state that could ultimately result in the development of Hodgkin lymphoma.
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Affiliation(s)
- Toni Portis
- Department of Microbiology and Immunology, Feinberg School of Medicine, Northwestern University, Ward 6-231, 303 East Chicago Ave, Chicago, IL 60611, USA
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80
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Geimonen E, Fernandez I, Gavrilovskaya IN, Mackow ER. Tyrosine residues direct the ubiquitination and degradation of the NY-1 hantavirus G1 cytoplasmic tail. J Virol 2003; 77:10760-868. [PMID: 14512526 PMCID: PMC224989 DOI: 10.1128/jvi.77.20.10760-10768.2003] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/05/2003] [Accepted: 07/11/2003] [Indexed: 12/20/2022] Open
Abstract
The hantavirus G1 protein contains a long C-terminal cytoplasmic tail of 142 residues. Hantavirus pulmonary syndrome-associated hantaviruses contain conserved tyrosine residues near the C terminus of G1 which form an immunoreceptor tyrosine activation motif (ITAM) and interact with Src and Syk family kinases. During studies of the G1 ITAM we observed that fusion proteins containing the G1 cytoplasmic tail were poorly expressed. Expression of G1 cytoplasmic tail constructs were dramatically enhanced by treating cells with the proteasome inhibitor ALLN, suggesting that the protein is ubiquitinated and degraded via the 26S proteasome. By using a 6-His-tagged ubiquitin, we demonstrated that the G1 cytoplasmic tail is polyubiquitinated and degraded in the absence of proteasome inhibitors. Expression of only the ITAM-containing domain also directed protein ubiquitination and degradation in the absence of upstream residues. Deleting the C-terminal 51 residues of G1, including the ITAM, stabilized G1 and blocked polyubiquitination and degradation of the protein. Site-directed mutagenesis of both ITAM tyrosines (Y619 and Y632) to phenylalanine also blocked polyubiquitination of G1 proteins and dramatically enhanced G1 protein stability. In contrast, the presence of Y627, which is not part of the ITAM motif, had no effect on G1 stability. Mutagenesis of just Y619 enhanced G1 stability, inhibited G1 ubiquitination, and increased the half-life of G1 by threefold. Mutating only Y632 had less of an effect on G1 protein stability, although Y619 and Y632 synergistically contributed to G1 instability. These findings suggest that Y619, which is conserved in all hantaviruses, is the primary signal for directing G1 ubiquitination and degradation. Collectively these findings indicate that specific conserved tyrosines within the G1 cytoplasmic tail direct the polyubiquitination and degradation of expressed G1 proteins and provide a potential means for down-regulating hantavirus G1 surface glycoproteins and cellular proteins that interact with G1.
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Affiliation(s)
- Erika Geimonen
- Department of Medicine, Molecular Cell Biology Program, State University of New York at Stony Brook, Stony Brook, New York 11794, USA
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81
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Brinkmann MM, Glenn M, Rainbow L, Kieser A, Henke-Gendo C, Schulz TF. Activation of mitogen-activated protein kinase and NF-kappaB pathways by a Kaposi's sarcoma-associated herpesvirus K15 membrane protein. J Virol 2003; 77:9346-58. [PMID: 12915550 PMCID: PMC187392 DOI: 10.1128/jvi.77.17.9346-9358.2003] [Citation(s) in RCA: 108] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022] Open
Abstract
The K15 gene of Kaposi's sarcoma-associated herpesvirus (also known as human herpesvirus 8) consists of eight alternatively spliced exons and has been predicted to encode membrane proteins with a variable number of transmembrane regions and a common C-terminal cytoplasmic domain with putative binding sites for SH2 and SH3 domains, as well as for tumor necrosis factor receptor-associated factors. These features are reminiscent of the latent membrane proteins LMP-1 and LMP2A of Epstein-Barr virus and, more distantly, of the STP, Tip, and Tio proteins of the related gamma(2)-herpesviruses herpesvirus saimiri and herpesvirus ateles. These viral membrane proteins can activate a number of intracellular signaling pathways. We have therefore examined the abilities of different K15-encoded proteins to initiate intracellular signaling. We found that a 45-kDa K15 protein derived from all eight K15 exons and containing 12 predicted transmembrane domains in addition to the cytoplasmic domain activated the Ras/mitogen-activated protein kinase (MAPK) and NF-kappaB pathways, as well as (more weakly) the c-Jun N-terminal kinase/SAPK pathway. Activation of the MAPK and NF-kappaB pathways required phosphorylation of tyrosine residue 481 within a putative SH2-binding site (YEEVL). This motif was phosphorylated by the tyrosine kinases Src, Lck, Yes, Hck, and Fyn. The region containing the YEEVL motif interacted with tumor necrosis factor receptor-associated factor 2 (TRAF-2), and a dominant negative TRAF-2 mutant inhibited the K15-mediated activation of the Ras/MAPK pathway, suggesting the involvement of TRAF-2 in the initiation of these signaling routes. In contrast, several smaller K15 protein isoforms activated these pathways only weakly. All of the K15 isoforms tested were, however, localized in lipid rafts, suggesting that incorporation into lipid rafts is not sufficient to initiate signaling. Additional regions of K15, located presumably in exons 2 to 5, may therefore contribute to the activation of these pathways. These findings illustrate that the 45-kDa K15 protein engages pathways similar to LMP1, LMP2A, STP, Tip, and Tio but combines functional features that are separated between LMP1 and LMP2A or STP and Tip.
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Affiliation(s)
- Melanie M Brinkmann
- Institut für Virologie, Medizinische Hochschule Hannover, D-30625 Hannover, Germany
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82
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Salamon D, Takacs M, Schwarzmann F, Wolf H, Minarovits J, Niller HH. High-resolution methylation analysis and in vivo protein-DNA binding at the promoter of the viral oncogene LMP2A in B cell lines carrying latent Epstein-Barr virus genomes. Virus Genes 2003; 27:57-66. [PMID: 12913358 DOI: 10.1023/a:1025124519068] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
Latency protein LMP2A of Epstein-Barr virus (EBV) has been implicated in EBV related tumorigenesis. To understand the host cell dependent expression of the LMP2A gene, it is necessary to analyse the regulatory mechanisms of the LMP2A promoter (LMP2Ap). By transient transfection and in vitro binding analyses two CBF1 sites have previously been shown to be involved in the regulation of LMP2Ap. However, the promoter structure has not been examined at the nucleotide level in vivo. Therefore we undertook a comprehensive analysis of in vivo protein binding and of CpG-methylation patterns at LMP2Ap in a panel of B cell lines carrying latent EBV genomes. The presence of characteristic footprints on two CBF1 and further binding-sites, together with overall hypomethylation of CpG dinucleotides correlated well with promoter activity. In contrast, the absence of several genomic footprints, as well as the presence of patches of highly methylated CpG dinucleotides were characteristic of silent LMP2Aps.
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Affiliation(s)
- Daniel Salamon
- Microbiological Research Group, National Center for Epidemiology, Pihenö ut 1, H-1529 Budapest, Hungary
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83
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Ikeda A, Caldwell RG, Longnecker R, Ikeda M. Itchy, a Nedd4 ubiquitin ligase, downregulates latent membrane protein 2A activity in B-cell signaling. J Virol 2003; 77:5529-34. [PMID: 12692257 PMCID: PMC153961 DOI: 10.1128/jvi.77.9.5529-5534.2003] [Citation(s) in RCA: 44] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Nedd4 family ubiquitin protein ligases (E3s) specifically associate with latent membrane protein 2A (LMP2A) of Epstein-Barr virus. Our previous studies analyzing LMP2A function in vitro have suggested that Nedd4 family E3s regulate LMP2A function. To determine the role of Nedd4 family E3s in LMP2A B-cell signaling, LMP2A transgenic (LMP2A(+)) mice were crossed with mice with the Itch-deficient (Itch(-/-)) background. Itchy, a mouse homologue of human AIP4, is a Nedd4 family E3 and is also the most abundant Nedd4 family E3 found in LMP2A affinity precipitates from B cells. There were significantly fewer B-cell receptor-positive B cells in spleen and bone marrow B cells in LMP2A(+) Itch(-/-) mice than in LMP2A(+) mice. In addition, LMP2A(+) Itch(-/-) bone marrow B cells formed larger colonies in cultures treated with interleukin-7 (IL-7) than control bone marrow B cells did. Finally, there was a dramatic increase in tyrosine phosphorylation of LMP2A and Syk in IL-7-cultured LMP2A(+) Itch(-/-) B cells. These results indicate that Nedd4 family E3s, in particular Itchy, downmodulate LMP2A activity in B-cell signaling.
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Affiliation(s)
- Akiko Ikeda
- Department of Microbiology-Immunology, Northwestern University Medical School, Chicago, Illinois 60611, USA
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84
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Abstract
Infectious agents and their hosts interact in a complex manner, involving not only superficially apparent mechanisms, but also the signaling machinery that governs host cells responses. Thus, signaling events, surface molecule expression, and transcriptional control may be affected in various cell types, with profound consequences for the function of individual cells and organ systems. Studies of the biochemistry of cell signaling and cell invasion by infectious agents have begun to detail the interplay between elements of infectious organisms and the host at the molecular level. Consequently, the resulting interferences with lymphocyte signaling may disturb the function of the immune system. In B cells, alterations of immune receptor signaling has implications for human diseases. By affecting the mechanisms of the host's immune defense, this may not only lead to inadequate elimination of an infectious agent, but also to autoimmunity or neoplasia.
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Affiliation(s)
- P Hasler
- Rheumatologische Universitätsklinik, Felix Platter-Spital, Basel, Switzerland
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85
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Geimonen E, LaMonica R, Springer K, Farooqui Y, Gavrilovskaya IN, Mackow ER. Hantavirus pulmonary syndrome-associated hantaviruses contain conserved and functional ITAM signaling elements. J Virol 2003; 77:1638-43. [PMID: 12502882 PMCID: PMC140783 DOI: 10.1128/jvi.77.2.1638-1643.2003] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/10/2002] [Accepted: 10/10/2002] [Indexed: 01/16/2023] Open
Abstract
Hantaviruses infect human endothelial and immune cells, causing two human diseases, hemorrhagic fever with renal syndrome (HFRS) and hantavirus pulmonary syndrome (HPS). We have identified key signaling elements termed immunoreceptor tyrosine-based activation motifs (ITAMs) within the G1 cytoplasmic tail of all HPS-causing hantaviruses. ITAMs direct receptor signaling within immune and endothelial cells and the presence of ITAMs in all HPS-causing hantaviruses provides a means for altering normal cellular responses which maintain vascular integrity. The NY-1 G1 ITAM was shown to coprecipitate a complex of phosphoproteins from cells, and the G1 ITAM is a substrate for the Src family kinase Fyn. The hantavirus ITAM coprecipitated Lyn, Syk, and ZAP-70 kinases from T or B cells, while mutagenesis of the ITAM abolished these interactions. In addition, G1 ITAM tyrosines directed intracellular interactions with Syk by mammalian two-hybrid analysis. These findings demonstrate that G1 ITAMs bind key cellular kinases that regulate immune and endothelial cell functions. There is currently no means for establishing the role of the G1 ITAM in hantavirus pathogenesis. However, the conservation of G1 ITAMs in all HPS-causing hantaviruses and the role of these signaling elements in immune and endothelial cells suggest that functional G1 ITAMs are likely to dysregulate normal immune and endothelial cell responses and contribute to hantavirus pathogenesis.
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Affiliation(s)
- Erika Geimonen
- Department of Medicine, SUNY at Stony Brook, New York 11794, USA
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86
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Portis T, Longnecker R. Epstein-Barr virus LMP2A interferes with global transcription factor regulation when expressed during B-lymphocyte development. J Virol 2003; 77:105-14. [PMID: 12477815 PMCID: PMC140618 DOI: 10.1128/jvi.77.1.105-114.2003] [Citation(s) in RCA: 67] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023] Open
Abstract
Epstein-Barr virus (EBV) is associated with the development of malignant lymphomas and lymphoproliferative disorders in immunocompromised individuals. The LMP2A protein of EBV is thought to play a central role in this process by allowing the virus to persist in latently infected B lymphocytes. We have demonstrated that LMP2A, when expressed in B cells of transgenic mice, allows normal B-cell developmental checkpoints to be bypassed. To identify cellular genes targeted by LMP2A that are involved in this process, we have utilized DNA microarrays to compare gene transcription in B cells from wild-type versus LMP2A transgenic mice. In B cells from LMP2A transgenic mice, we observed decreased expression of many genes associated with normal B-cell development as well as reduced levels of the transcription factors that regulate their expression. In particular, expression of the transcription factor E2A was down-regulated in bone marrow and splenic B cells. Furthermore, E2A activity was inhibited in these cells as determined by decreased DNA binding and reduced expression of its target genes, including the transcription factors early B-cell factor and Pax-5. Expression of two E2A inhibitors, Id2 and SCL, was up-regulated in splenic B cells expressing LMP2A, suggesting a possible mechanism for E2A inhibition. These results indicate that LMP2A deregulates transcription factor expression and activity in developing B cells, and this likely allows for a bypass of normal signaling events required for proper B-cell development. The ability of LMP2A to interfere with B-cell transcription factor regulation has important implications regarding its role in EBV latency.
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Affiliation(s)
- Toni Portis
- Department of Microbiology and Immunology, Northwestern University, Chicago, Illinois 60611, USA
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87
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Abstract
Hodgkin's lymphoma (HL) is unusual among human malignancies in that the epidemiology suggests an infectious aetiology. The Epstein-Barr virus (EBV) is associated with a proportion of cases and this association is believed to be causal. In these cases the Hodgkin and Reed-Sternberg (HRS) cells express the EBV-encoded proteins LMP1 and LMP2, which can mimic CD40 and the B cell receptor, respectively, and therefore may play a critical role in facilitating the survival of HRS cells. EBV-associated and non-EBV-associated HL cases have different epidemiological features and recent data suggest that delayed exposure to EBV is a risk factor for the development of EBV-associated HL in young adults. We suggest that HL can be divided into four entities on the basis of EBV status and age at presentation, with three groups of EBV-associated cases and a single group of EBV-negative cases. The aetiology of the latter cases is obscure although involvement of an infectious agent(s) is suspected.
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Affiliation(s)
- R F Jarrett
- LRF Virus Centre, Institute of Comparative Medicine, Faculty of Veterinary Medicine, University of Glasgow, UK.
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88
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Dehghani H, Brown CR, Plishka R, Buckler-White A, Hirsch VM. The ITAM in Nef influences acute pathogenesis of AIDS-inducing simian immunodeficiency viruses SIVsm and SIVagm without altering kinetics or extent of viremia. J Virol 2002; 76:4379-89. [PMID: 11932405 PMCID: PMC155068 DOI: 10.1128/jvi.76.9.4379-4389.2002] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The role of the immunoreceptor tyrosine-based activation motif (ITAM) that is unique to the Nef protein of the acutely pathogenic simian immunodeficiency virus SIVsmPBj was studied in the context of two AIDS-inducing simian immunodeficiency virus molecular clones. NefY(+) variants of SIVagm9063-2 and SIVsmE543-3 replicated in and induced proliferation of unstimulated pig-tailed macaque PBMC. The pathogenesis of the NefY(+) and NefY(-) clones of SIVagm9063-2, SIVsmE543-3, and PBj6.6 were evaluated by intravenous inoculation of pig-tailed macaques (Macaca nemestrina). Introduction of the ITAM did not increase plasma viral RNA levels nor alter the kinetics of viremia compared with the NefY(-) versions of each clone. Clinical symptoms were not observed in animals inoculated with the NefY(-) variants. In contrast, characteristic PBj symptoms were observed in animals inoculated with any of the three NefY(+) clones. Blunting and fusion of intestinal villi and multifocal infiltration of mononuclear cells were observed in the gastrointestinal tracts of macaques inoculated with the NefY(+) versions. Lesions were associated with active viral replication, as demonstrated by simian immunodeficiency virus-specific in situ hybridization. However, only the macaque inoculated with wild-type NefY(+) SIVsmPBj developed fatal disease; lesions were more widespread and severe in this animal. A switch to macrophages as a viral reservoir and the presence of interleukin-6 in plasma was unique to the macaque infected with PBj6.6. Overall, these data suggest that the ITAM in SIV Nef alters the pathogenesis of simian immunodeficiency virus regardless of the viral background. The change in pathogenesis occurs without enhancement of viral replication. However, NefY(+) variants of SIVagm and SIVsm did not fully recapitulate the virulence of SIVsmPBj, implicating additional viral factors in this unique virus pathogenesis.
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Affiliation(s)
- Houman Dehghani
- Laboratory of Molecular Microbiology, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Rockville, Maryland 20852, USA
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89
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Leo A, Wienands J, Baier G, Horejsi V, Schraven B. Adapters in lymphocyte signaling. J Clin Invest 2002; 109:301-9. [PMID: 11827988 PMCID: PMC150865 DOI: 10.1172/jci14942] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022] Open
Affiliation(s)
- Albrecht Leo
- Institute for Immunology, Ruprecht-Karls-University Heidelberg, Heidelberg, Germany
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90
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Leo A, Wienands J, Baier G, Horejsi V, Schraven B. Adapters in lymphocyte signaling. J Clin Invest 2002. [DOI: 10.1172/jci0214942] [Citation(s) in RCA: 51] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022] Open
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91
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Billadeau DD, Leibson PJ. ITAMs versus ITIMs: striking a balance during cell regulation. J Clin Invest 2002. [DOI: 10.1172/jci0214843] [Citation(s) in RCA: 133] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022] Open
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92
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Billadeau DD, Leibson PJ. ITAMs versus ITIMs: striking a balance during cell regulation. J Clin Invest 2002; 109:161-8. [PMID: 11805126 PMCID: PMC150845 DOI: 10.1172/jci14843] [Citation(s) in RCA: 68] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022] Open
Affiliation(s)
- Daniel D Billadeau
- Division of Developmental Oncology Research, Mayo Graduate and Medical Schools, Mayo Clinic, Rochester, Minnesota 55905, USA
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93
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Merchant M, Longnecker R. LMP2A survival and developmental signals are transmitted through Btk-dependent and Btk-independent pathways. Virology 2001; 291:46-54. [PMID: 11878875 DOI: 10.1006/viro.2001.1187] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The latent membrane protein 2A (LMP2A) of Epstein--Barr virus (EBV) has been implicated in controlling viral latency due to the ability of LMP2A to block B cell antigen receptor (BCR) signaling in vitro and to alter B cell development and enhance B cell survival in vivo. These LMP2A functions require interactions with the protein tyrosine kinases Syk and Lyn. However, a role for the Bruton's tyrosine kinase (Btk) has not been investigated for these LMP2A functions. To investigate whether Btk is important for LMP2A developmental and survival signals in vivo, LMP2A transgenic animals were mated to Btk deficient (Btk(-/-)) mice. Unlike LMP2A(+), Btk(+/+) transgenic littermate controls, LMP2A(+), Btk(-/-) animals do not generate immunoglobulin (Ig) receptorless B cells in the periphery and instead produce Ig(+) B cells similar to those in the Btk(-/-) mice. Interestingly, however, LMP2A(+), Btk(-/-) animals produce B cells at a vastly reduced level compared to Btk(-/-) littermates, indicating that LMP2A affects B cell development in the absence of Btk. In the RAG-1(-/-), Btk(-/-) double knockout background, LMP2A is still capable of enhancing the survival of Ig-receptorless B cells. Use of Btk phosphopeptide-specific antibodies reveals that Btk is constitutively phosphorylated in LMP2A-expressing cell lines. These data indicate that LMP2A initiates both Btk-dependent and Btk-independent pathways, resulting in altered B cell development and enhanced B cell survival.
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Affiliation(s)
- M Merchant
- Department of Microbiology-Immunology, Northwestern University Medical School, Chicago, Illinois 60611, USA
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94
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Fleming HE, Paige CJ. Pre-B cell receptor signaling mediates selective response to IL-7 at the pro-B to pre-B cell transition via an ERK/MAP kinase-dependent pathway. Immunity 2001; 15:521-31. [PMID: 11672535 DOI: 10.1016/s1074-7613(01)00216-3] [Citation(s) in RCA: 137] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/20/2023]
Abstract
B lymphocyte development is regulated at multiple checkpoints, mediated by signals originating both inside and outside the cell. Two signaling pathways known to be essential in this process are interleukin-7 (IL-7) and the pre-B cell receptor (pBCR). We have shown previously that these signaling pathways intersect functionally. Specifically, response to low concentrations of IL-7 requires pBCR expression. In this report, we identify the ERK/MAP kinase pathway as a key regulatory component of this response. We propose a molecular mechanism for the selective expansion of pBCR(+) precursors and for the culling of inappropriately rearranged pro-B cells.
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Affiliation(s)
- H E Fleming
- Ontario Cancer Institute, Princess Margaret Hospital, University Health Network, Departments of Immunology and Medical Biophysics, University of Toronto, Toronto, Ontario, Canada
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95
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Engels N, Merchant M, Pappu R, Chan AC, Longnecker R, Wienands J. Epstein-Barr virus latent membrane protein 2A (LMP2A) employs the SLP-65 signaling module. J Exp Med 2001; 194:255-64. [PMID: 11489945 PMCID: PMC2193464 DOI: 10.1084/jem.194.3.255] [Citation(s) in RCA: 48] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022] Open
Abstract
In latently infected B lymphocytes, the Epstein-Barr virus (EBV) suppresses signal transduction from the antigen receptor through expression of the integral latent membrane protein 2A (LMP2A). At the same time, LMP2A triggers B cell survival by a yet uncharacterized maintenance signal that is normally provided by the antigen receptor. The molecular mechanisms are unknown as LMP2A-regulated signaling cascades have not been described so far. Using a novel mouse model we have identified the intracellular adaptor protein Src homology 2 (SH2) domain-containing leukocyte protein (SLP)-65 as a critical downstream effector of LMP2A in vivo. Biochemical analysis of the underlying signaling pathways revealed that EBV infection causes constitutive tyrosine phosphorylation of one of the two SLP-65 isoforms and complex formation between SLP-65 and the protooncoprotein CrkL (CT10 regulator of kinase like). This leads to antigen receptor-independent phosphorylation of Cbl (Casitas B lineage lymphoma) and C3G. In contrast, phospholipase C-gamma2 (PLC-gamma2) activation is completely blocked. Our data show that in order to establish a latent EBV infection, LMP2A selectively activates or represses SLP-65-regulated signaling pathways.
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Affiliation(s)
- Niklas Engels
- Department of Biochemistry I, University of Bielefeld, Bielefeld D-33615, Germany
| | - Mark Merchant
- Department of Microbiology and Immunology, Northwestern University Medical School, Chicago, IL 60611
| | - Rajita Pappu
- Center for Immunology, Howard Hughes Medical Institute, Washington University School of Medicine, St. Louis, MO 63110
| | - Andrew C. Chan
- Center for Immunology, Howard Hughes Medical Institute, Washington University School of Medicine, St. Louis, MO 63110
| | - Richard Longnecker
- Department of Microbiology and Immunology, Northwestern University Medical School, Chicago, IL 60611
| | - Jürgen Wienands
- Department of Biochemistry I, University of Bielefeld, Bielefeld D-33615, Germany
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96
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Higuchi M, Izumi KM, Kieff E. Epstein-Barr virus latent-infection membrane proteins are palmitoylated and raft-associated: protein 1 binds to the cytoskeleton through TNF receptor cytoplasmic factors. Proc Natl Acad Sci U S A 2001; 98:4675-80. [PMID: 11296297 PMCID: PMC31893 DOI: 10.1073/pnas.081075298] [Citation(s) in RCA: 106] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Epstein-Barr virus encodes integral membrane proteins LMP1 and LMP2A in transformed lymphoblastoid cell lines. We now find that LMP1 associates with the cell cytoskeleton through a tumor necrosis factor receptor-associated factor-interacting domain, most likely mediated by tumor necrosis factor receptor-associated factor 3. LMP1 is palmitoylated, and the transmembrane domains associate with lipid rafts. Mutation of LMP1 cysteine-78 abrogates palmitoylation but does not affect raft association or NF-kappaB or c-Jun N-terminal kinase activation. LMP2A also associates with rafts and is palmitoylated but does not associate with the cell cytoskeleton. The associations of LMP1 and LMP2A with rafts and of LMP1 with the cell cytoskeleton are likely to effect interactions with cell proteins involved in shape, motility, signal transduction, growth, and survival.
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Affiliation(s)
- M Higuchi
- Department of Medicine, Brigham and Women's Hospital, Channing Laboratory, Harvard Medical School, Boston, MA 02115-5804, USA
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97
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Merchant M, Swart R, Katzman RB, Ikeda M, Ikeda A, Longnecker R, Dykstra ML, Pierce SK. The effects of the Epstein-Barr virus latent membrane protein 2A on B cell function. Int Rev Immunol 2001; 20:805-35. [PMID: 11913951 DOI: 10.3109/08830180109045591] [Citation(s) in RCA: 37] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
Epstein-Barr Virus (EBV) infects B-lymphocytes circulating through the oral epithelium and establishes a lifelong latent infection in a subset of mature-memory B cells. In these latently infected B cells, EBV exhibits limited gene expression with the latent membrane protein 2A (LMP2A) being the most consistently detected transcript. This persistent expression, coupled with many studies ofthe function of LMP2A in vitro and invivo, indicates that LMP2A is functioning to control some aspect of viral latency. Establishment and maintenance of viral latency requires exquisite manipulation of normal B cell signaling and function. LMP2A is capable of blocking normal B cell signal transduction in vitro, suggesting that LMP2A may act to regulate lytic activation from latency in vivo. Furthermore, LMP2A is capable of providing B cells with survival signals in the absence of normal BCR signaling. These data show that LMP2A may help EBV-infected cells to persist in vivo. This review discusses the advances that have been made in our understanding of LMP2A and the effects it has on B cell development, activation, and viral latency.
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Affiliation(s)
- M Merchant
- Department of Microbiology-Immunology, Northwestern University Medical School, Chicago, Illinois 60611, USA
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