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C W Dawson

Publications and source records attributed to C W Dawson.

At least 19 recordsLinked to original sources
PubMed2001

The Epstein-Barr virus encoded latent membrane protein 2A augments signaling from latent membrane protein 1.

The frequent coexpression of the EBV-encoded latent membrane proteins LMP1 and LMP2A/B in virus-associated tumors suggests that these two proteins may cooperate in the transformation process. While LMP2A is unable to directly activate the NF-kappaB and AP-1 pathways, we found that coexpression of LMP2A with LMP1 resulted in a significant enhancement of LMP1-mediated activation of these pathways. This enhancement was found to be critically dependent on the tyrosine residues present within the ITAM motif (Y74/Y85) and, to a lesser extent, the tyrosine at position 112 (Y112). Subsequent analysis revealed that LMP2A is able to stabilize and modulate the turnover of LMP1 by extending its half-life. This ability does not require a direct physical interaction between the two proteins but rather, results from an indirect effect of LMP2A on the turnover of the LMP1 protein. This study highlights an important role for LMP2A as a modulator of LMP1 activity in epithelial cells.

Blotting, Western↗
PubMed2001

The transmembrane domains of the EBV-encoded latent membrane protein 1 (LMP1) variant CAO regulate enhanced signalling activity.

Sequence variants of the Epstein-Barr virus (EBV)-encoded latent membrane protein-1 (LMP1) have been reported in association with EBV-linked malignancies but little is known about their effects on signalling pathways and phenotype. We have examined the ability of the nasopharyngeal carcinoma (NPC)-derived variant, CAO-LMP1 to activate the transcription factors NF-kappaB and AP-1 in epithelial cells. In this study, transient expression of CAO-LMP1 was found to activate higher levels of NF-kappaB and AP-1 than the prototype B95.8-LMP1 in human embryonic kidney (HEK) 293 cells and SV40-transformed keratinocytes (SVK). In addition, pulse-chase analysis revealed that CAO-LMP1 has a longer half-life than B95.8-LMP1. Chimera studies localised these phenomena to the transmembrane domains of CAO-LMP1, suggesting that this enhanced signalling capacity may be a consequence of its prolonged half-life. The ability of CAO-LMP1 to activate higher levels of NF-kappaB and AP-1 may contribute to its potent transforming properties.

Cell Line↗
PubMed2000

CTL control of EBV in nasopharyngeal carcinoma (NPC): EBV-specific CTL responses in the blood and tumors of NPC patients and the antigen-processing function of the tumor cells.

Undifferentiated nasopharyngeal carcinoma (NPC) is latently infected with EBV and expresses a restricted number of viral proteins. Studies in healthy virus carriers have demonstrated that at least some of these proteins can act as targets for HLA class I-restricted CTLs. Therefore we have explored the possibility of a CTL-based therapy for NPC by characterizing EBV-specific CTL responses in 10 newly diagnosed NPC cases and 21 healthy virus carriers from Southeast Asia. Using the autologous EBV-transformed lymphoblastoid cell line, virus-specific CTL were reactivated in vitro from PBMC, cloned, and screened for cytotoxicity against target cells expressing individual EBV proteins from recombinant vaccinia vectors. EBV-specific CTLs were identified in 6 of 10 patients and 14 of 21 controls and mainly targeted the EBV nuclear Ag 3 (EBNA3) family of viral latent proteins. However, in 3 of 10 patients and 11 of 21 controls, CTLs specific for the NPC-associated protein LMP2 were also detected, albeit at low frequency. EBV-specific CTLs were detected in tumor biopsy material obtained from 3 of 6 of the patients, indicating that functional CTL are present at the tumor site, but none was specific for tumor-associated viral proteins. To assess the Ag-presenting function in NPC we studied two NPC-derived cell lines (C15 and c666.1) and demonstrated that both were capable of processing and presenting endogenously synthesized protein to HLA class I-restricted CTL clones. Overall, our data provide a sound theoretical basis for therapeutic strategies that aim to boost or elicit LMP2-specific CTL responses in NPC patients.

Adult↗
PubMed2000

Identification of functional differences between prototype Epstein-Barr virus-encoded LMP1 and a nasopharyngeal carcinoma-derived LMP1 in human epithelial cells.

The contribution of Epstein-Barr virus (EBV) strain variation to the pathogenesis of virus-associated tumours remains unknown. Given the central role of LMP1 in EBV-induced transformation, much interest has focused on the influence of LMP1 sequence variation on the signaling pathways and multiple downstream phenotypic consequences of LMP1 expression. The identification of LMP1 variants with a common 10-amino-acid deletion and additional point mutations (typified by the CAO-LMP1 isolate) in EBV strains associated with nasopharyngeal carcinoma prompted us to examine the effect of stable prototype B95.8-LMP1 and CAO-LMP1 expression on the phenotype and differentiation of SCC12F human epithelial cells. Both forms of LMP1 were able to induce expression of the antiapoptotic A20 protein and provide protection from tumour necrosis factor-alpha-induced cytotoxicity. Although B95.8-LMP1 induced growth inhibition, expression of certain cell surface molecules (CD40, CD44, and CD54), and secretion of interleukin-6 and -8 in SCC12F cells, stable CAO-LMP1 expression failed to elicit these effects. Furthermore, B95. 8-LMP1, but not CAO-LMP1, induced alterations in cell morphology and blocked epithelial cell differentiation. Both B95.8-LMP1 and CAO-LMP1 induced similar levels of nuclear factor-kappaB activation, but the ability of CAO-LMP1 to activate the AP-1 pathway was relatively impaired. These data highlight significant functional differences between the prototype B95.8-LMP1 and the CAO-LMP1 variant when stably expressed in human epithelial cells and suggest that continued analysis of LMP1 variants will help to further dissect the signaling pathways activated by LMP1 as well as provide insights into the contribution of LMP1 sequence variation to the pathogenesis of EBV-associated tumours.

Antigens, CD↗
PubMed2000

The expression and function of Epstein-Barr virus encoded latent genes.

The association of Epstein-Barr virus (EBV) with various malignancies is well established but the pattern of EBV latent gene expression in these different tumours is variable, reflecting distinct aspects of the virus-cell interaction. These different forms of EBV latency are associated with phenotypic variation and highlight the influence of EBV latent proteins on cell growth and survival. The EBV latent proteins have distinct functions associated with the maintenance of EBV infection and the control of various signalling and transcriptional pathways that facilitate the proliferation and survival of infected cells. Understanding the function of these EBV latent proteins will not only provide insight into the mechanisms governing fundamental cell processes but will also identify targets for novel treatment.

Cell Communication↗
PubMed2000

Inductive learning approaches to rainfall-runoff modelling.

Trying to model the rainfall-runoff process is a complex activity as it is influenced by a number of implicit and explicit factors--for example, precipitation distribution, evaporation, transpiration, abstraction, watershed topography, and soil types. However, this kind of forecasting is particularly important as it is used to predict serious flooding, estimate erosion and identify problems associated with low flow. Inductive learning approaches (e.g. decision trees and artificial neural networks) are particularly well suited to problems of this nature as they can often interpret underlying factors (such as seasonal variations) which cannot be modelled by other techniques. In addition, these approaches can easily be trained on the explicit factors (e.g. rainfall) and the inexplicit factors (e.g. abstraction) that affect river flow. Inductive learning approaches can also be extended to account for new factors that emerge over a period of time. This paper evaluates the application of decision trees and two artificial neural network models (the multilayer perceptron and the radial basis function network) to river flow forecasting in two flood prone UK catchments using real hydrometric data. Comparisons are made between the performance of these approaches and conventional flood forecasting systems.

Algorithms↗
PubMed1999

Activation of the p38 mitogen-activated protein kinase pathway by Epstein-Barr virus-encoded latent membrane protein 1 coregulates interleukin-6 and interleukin-8 production.

The Epstein-Barr virus-encoded latent membrane protein 1 (LMP1) is a pleiotropic protein the activities of which include effects on gene expression and cell transformation, growth, and death. LMP1 has been shown to induce nuclear factor (NF)-kappaB and c-Jun NH2-terminal kinase/AP-1 activities in target cells, and in this study we demonstrate that LMP1 also engages the p38 mitogen-activated protein kinase cascade, leading to activation of the transcription factor ATF2. Mutational analysis of the LMP1 cytoplasmic COOH terminus revealed that p38 activation occurs from both the tumor necrosis factor receptor-associated factor (TRAF)-interacting, membrane-proximal COOH-terminal activating region (CTAR)1 domain (amino acids 186-231) and the extreme tumor necrosis factor receptor-associated death domain (TRADD) binding CTAR2 region (amino acids 351-386). Because LMP1 also engages signaling on the NF-kappaB axis through CTAR1 and CTAR2, we have examined whether these two pathways are overlapping or independent. We have found that inhibition of p38 by the highly specific inhibitor SB203580 did not affect NF-kappaB binding activity. Conversely, although the metabolic inhibitor D609 blocked NF-kappaB activation, it did not impair the ability of LMP1 to signal on the p38 axis, suggesting that these two LMP1-mediated pathways are primarily independent. Divergence of signals must, however, occur downstream of TRAF2 as a dominant negative TRAF2 mutant that blocks LMP1-induced NF-kappaB activation also inhibited p38 signaling. In addition, we have found that p38 inhibition significantly impaired LMP1-mediated interleukin-6 and -8 expression. Thus, p38 may play a significant cooperative role in regulating at least some of the pleiotropic activities of LMP1.

Activating Transcription Factor 2↗
PubMed1998

CD40 and epithelial cells: across the great divide.

The widespread expression of CD40 in normal epithelial cells and carcinoma cells suggests that this receptor has important, additional influences beyond that of regulating immune responses. Here, Lawrence Young and colleagues discuss the effect of CD40 ligation on epithelial cells and consider the role of this pathway in the pathogenesis and treatment of carcinomas.

Animals↗
PubMed1998

Functional differences between BHRF1, the Epstein-Barr virus-encoded Bcl-2 homologue, and Bcl-2 in human epithelial cells.

BHRF1, a component of the restricted early antigen complex of the Epstein-Barr virus lytic cycle, encodes a 17-kDa protein with both sequence and functional homology to the antiapoptotic Bcl-2 oncogene. Recent work has suggested that BHRF1 behaves like Bcl-2 in protecting cells from apoptosis induced by a range of stimuli. In this study, the effect of BHRF1 and Bcl-2 on the growth and differentiation of the SCC12F human epithelial cell line was examined. The levels of stable transfected BHRF1 expression achievable in SCC12F cells was consistently lower than that obtained with Bcl-2. While both BHRF1 and Bcl-2 inhibited epithelial differentiation, the effect of Bcl-2 was more pronounced, resulting in an almost complete blockade of differentiation in organotypic raft cultures. However, BHRF1-expressing SCC12F cells proliferated at a much higher rate than SCC12F cells expressing Bcl-2, and this effect was supported by cell cycle analysis which demonstrated that BHRF1, but not Bcl-2, promotes rapid transit through the cell cycle. These data highlight important differences between BHRF1 and Bcl-2 and suggest that BHRF1 may function to promote the survival and proliferation of lytically infected cells. The proliferative properties of BHRF1 described in this study, together with the demonstration that other oncogenic gamma herpesviruses encode Bcl-2 homologues, suggests that these proteins may serve to increase the susceptibility of virus-infected cells to oncogenic transformation, thereby contributing to the development of virus-associated tumors.

Apoptosis↗
PubMed1997

Immunohistochemical detection of the Epstein-Barr virus-encoded latent membrane protein 2A in Hodgkin's disease and infectious mononucleosis.

We describe two new monoclonal antibodies specific for the Epstein-Barr virus (EBV)-encoded latent membrane protein 2A (LMP2A) that are suitable for the immunohistochemical analysis of routinely processed paraffin sections. These antibodies were applied to the immunohistochemical detection of LMP2A in Hodgkin's disease (HD). LMP2A-specific membrane staining was seen in the Hodgkin and Reed-Sternberg (HRS) cells of 22 of 42 (52%) EBV-positive HD cases, but not in 39 EBV-negative HD cases. In lymphoid tissues from patients with acute infectious mononucleosis (IM), interfollicular immunoblasts were shown to express LMP2A. This is the first demonstration of LMP2A protein expression at the single-cell level in EBV-associated lymphoproliferations in vivo. The detection of LMP2A protein expression in HD and IM is of importance in view of the proposed role of this protein for maintaining latent EBV infection and its possible contribution for EBV-associated transformation. Because LMP2A provides target epitopes for EBV-specific cytotoxic T cells, the expression of this protein in HRS cells has implications for the immunotherapeutic approaches to the treatment of HD.

Animals↗
PubMed1997

Epstein-Barr virus-encoded LMP1 and CD40 mediate IL-6 production in epithelial cells via an NF-kappaB pathway involving TNF receptor-associated factors.

Expression of the Epstein-Barr virus (EBV) transforming LMP1 in B cells activates the transcription factor NF-kappaB and induces phenotypic changes through two distinct domains in the cytoplasmic C-terminus of the protein. The aa 187-231 domain of LMP1, which is important for growth transformation, binds tumour necrosis factor (TNF) receptor associated factor (TRAF) 1 and TRAF3 and this interaction mediates subsequent signalling events. The TRAFs also associate with CD40, a member of the TNFR family, which upon ligation activates NF-kappaB and induces phenotypic changes similar to those mediated by LMP1. This study demonstrates that LMP1 expression in carcinoma cell lines and SV40-transformed keratinocytes results in induction of the pleiotropic cytokine interleukin 6 (IL6), an effect which is also observed upon CD40 ligation. The mechanism by which either LMP1 expression or CD40 ligation induces IL6 production was found to be NF-kappaB-dependent. Mutational analysis identified domains in the C-terminus of LMP1 which are important for NF-kappaB activation and IL6 secretion. LMP1 and CD40 share a common PxQxT core TRAF binding motif and mutations in or adjacent to this sequence impaired the ability of LMP1 or CD40 to induce NF-kappaB activation and IL6 secretion. The importance of TRAF interactions in mediating these effects was confirmed using dominant negative TRAF2 and TRAF3 mutants which also identified differences in the signalling events mediated by the two NF-kappaB activating domains of LMP1. A20, an anti-apoptotic protein which interacts with TRAF2 and blocks CD40-mediated NF-kappaB activity, also blocked NF-kappaB and IL6 secretion in LMP1-transfected epithelial cells. These results suggest that LMP1 regulates IL6 production in epithelial cells in a manner similar to CD40 ligation and implicate TRAFs as common mediators in the transduction of signals generated via the CD40 and LMP1 pathways. As a role for IL6 in regulating epithelial cell growth has previously been suggested, the control of IL6 secretion via the CD40 and LMP1 pathways may have implications for the growth of both normal and transformed epithelial cells.

Amino Acid Sequence↗
PubMed1997

Viruses and apoptosis.

Virus infection and replication are often associated with apoptosis and this effect is likely to be responsible for much of the pathology associated with infectious disease. Many viruses encode proteins which can inhibit apoptosis thereby either prolonging the survival of infected cells such that the production of progeny virus is maximised or facilitating the establishment of virus persistence. These viral proteins target the cellular pathways responsible for regulating apoptosis and have been instrumental in furthering our understanding of the apoptotic process. Many of the viruses associated with oncogenic transformation have adopted strategies for blocking apoptosis highlighting the centrality of this effect in carcinogenesis. Understanding the mechanisms by which viruses regulate apoptosis may lead to the development of novel therapies for both infectious disease and cancer.

Adenovirus E1 Proteins↗
PubMed1996

CD40-induced growth inhibition in epithelial cells is mimicked by Epstein-Barr Virus-encoded LMP1: involvement of TRAF3 as a common mediator.

CD40, a member of the tumour necrosis factor receptor family, is expressed on the surface of B lymphocytes where its ligation provides a potent survival signal. CD40 is also expressed in basal epithelial cells and in a number of different carcinomas where its function remains unknown. We observed that contrary to the studies in normal B cells, CD40 ligation in carcinoma cell lines and in normal primary epithelial cells resulted in growth inhibition and enhanced susceptibility to apoptosis induced by anti-neoplastic drugs, TNF-alpha, Fas and ceramide. This effect was also observed in CD40-transfected Rat-1 fibroblasts. The expression of Bcl-2 did not affect growth inhibition induced by CD40 ligation in epithelial cells but the Epstein - Barr Virus-encoded latent membrane protein 1 (LMP1) blocked the effect. Whilst transient expression of LMP-1 resulted in the inhibition of epithelial cell growth, this effect was not observed with a LMP1 mutant lacking the binding domain for TRAF3, a protein which may mediate signal transduction by interacting with the cytoplasmic domains of both CD40 and LMP1. Transient expression of TRAF3 also inhibited epithelial cell growth, whilst expression of a dominant-negative TRAF3 partially blocked the inhibitory effect of CD40 ligation and of transient LMP1 expression. These results suggest that CD40 regulates epithelial cell growth in a manner mimicked by LMP1 and implicate TRAF3 as a common mediator in the transduction of the growth inhibitory signals generated via the CD40 and LMP1 pathways.

Animals↗
PubMed1995

BHRF1, a viral homologue of the Bcl-2 oncogene, disturbs epithelial cell differentiation.

Epstein-Barr virus (EBV) is associated with tumours of both lymphoid and epithelial origin. Whilst a role for EBV latent genes in the development of these malignancies is accepted, it is also possible that viral proteins involved in EBV replication may influence the oncogenic process. BHRF1 is an immediate early protein which has homology with the Bcl-2 oncogene and can protect B cells from apoptosis. In vivo this protein is most abundantly expressed in the upper layers of oral 'hairy' leukoplakia (HL), a benign hyperparakeratotic tongue lesion which represents a focus EBV replication. We have transfected BHRF1 into the human squamous cell carcinoma line SCC12F which retains several features of normal keratinocytes behaviour in vitro. BHRF1 expression in these epithelial cells is associated with a delay in the commitment of cells to terminal differentiation, increased resistance to the DNA damaging drug, cis-platin and enhanced survival under conditions of serum deprivation. As the differentiation of epithelial cells is an apoptotic process, this data strongly suggests that BHRF1 expression delays the terminal differentiation of epithelial cells through the prevention of apoptosis. This effect of BHRF1, which may normally function to promote productive EBV infection, could contribute to the development of EBV-associated tumours.

Apoptosis↗