Abstract
EBV-encoded LMP-1 is absolutely required for EBV transformation of cells. Previous studies showed that LMP-1 is responsible for mediating resistance to the anti-proliferative effects of TGF-beta that characterizes EBV-transformed cells. To clarify the mechanisms of resistance to TGF-beta by LMP-1, we examined the effect of expression of LMP-1 on the activity of TGF-beta-responsive promoters. Interestingly, LMP-1 inhibited TGF-beta-responsive promoters activity despite lack of direct interaction of LMP-1 and Smad proteins, intracellular signaling molecules in the TGF-beta signal transduction pathway. Although TGF-beta treatment increased the expression of p15, TGF-beta-induced gene, this effect was counteracted by expression of LMP-1. The repressive effect was mapped to the NF-kappaB activation domains in the cytoplasmic carboxyl terminus of LMP-1. Furthermore, LMP-1-mediated inhibition of TGF-beta-responsive promoter was markedly restored after inhibition of NF-kappaB activity. LMP-1 failed to affect receptor-dependent formation of heteromers containing Smad proteins as well as the DNA-binding activity of Smad proteins. Overexpression of the transcriptional coactivator CBP and p300 abrogated the inhibitory effect of LMP-1 on the TGF-beta-responsive promoter. Our results suggest that LMP-1 represses the TGF-beta signaling through the NF-kappaB signaling pathway at transcriptional level by competing for a limited pool of transcriptional coactivators. These results enhance our understanding of the molecular mechanisms of viral pathogenesis in EBV-associated malignancies.
Copyright 2003 Wiley-Liss, Inc.
MeSH terms
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Animals
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Binding, Competitive
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Carcinoma, Hepatocellular / pathology
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Cell Cycle Proteins / biosynthesis
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Cell Line
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Cell Transformation, Viral / physiology*
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Cyclin-Dependent Kinase Inhibitor p15
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Cyclin-Dependent Kinase Inhibitor p16 / biosynthesis
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DNA-Binding Proteins / physiology*
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Gene Expression Regulation, Viral*
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Genes, Reporter
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Genes, p16
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Herpesvirus 4, Human / genetics
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Herpesvirus 4, Human / physiology*
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Humans
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I-kappa B Proteins / genetics
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I-kappa B Proteins / physiology
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Liver Neoplasms / pathology
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Lung
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Mink
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Models, Genetic
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NF-KappaB Inhibitor alpha
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NF-kappa B / metabolism*
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Nuclear Proteins / biosynthesis
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Nuclear Proteins / genetics
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Nuclear Proteins / physiology
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Promoter Regions, Genetic
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Protein Serine-Threonine Kinases
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Receptor, Transforming Growth Factor-beta Type II
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Receptors, Transforming Growth Factor beta / physiology
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Recombinant Fusion Proteins / physiology
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Signal Transduction
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Smad2 Protein
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Smad3 Protein
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Smad4 Protein
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Trans-Activators / biosynthesis
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Trans-Activators / genetics
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Trans-Activators / physiology*
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Transcription, Genetic*
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Transfection
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Transforming Growth Factor beta / antagonists & inhibitors*
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Tumor Suppressor Proteins*
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Viral Matrix Proteins / physiology*
Substances
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CDKN2B protein, human
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Cell Cycle Proteins
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Cyclin-Dependent Kinase Inhibitor p15
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Cyclin-Dependent Kinase Inhibitor p16
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DNA-Binding Proteins
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EBV-associated membrane antigen, Epstein-Barr virus
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I kappa B beta protein
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I-kappa B Proteins
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NF-kappa B
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NFKBIA protein, human
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Nuclear Proteins
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Receptors, Transforming Growth Factor beta
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Recombinant Fusion Proteins
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SMAD2 protein, human
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SMAD3 protein, human
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SMAD4 protein, human
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Smad2 Protein
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Smad3 Protein
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Smad4 Protein
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Trans-Activators
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Transforming Growth Factor beta
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Tumor Suppressor Proteins
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Viral Matrix Proteins
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NF-KappaB Inhibitor alpha
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Protein Serine-Threonine Kinases
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Receptor, Transforming Growth Factor-beta Type II