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Latent membrane protein 1 regulates STAT1 through NF-kappaB-dependent interferon secretion in Epstein-Barr virus-immortalized B cells.

ABSTRACT: Constitutive activation of signal transducer and activator of transcription 1 (STAT1) is a distinctive feature of Epstein-Barr virus (EBV)-immortalized B cells (lymphoblastoid cell lines [LCLs]). The expression of STAT1 in these cells is modulated by the latent membrane protein 1 (LMP1), but the mechanism of STAT1 activation has remained unclear. We demonstrate that the tyrosine phosphorylation of STAT1 in LCLs results from an indirect pathway encompassing an NF-kappaB-dependent secretion of interferons (IFNs). The cell culture supernatant of LCLs induced tyrosine phosphorylation of STAT1 in cells with no constitutively activated STAT1. Moreover, removal of supernatant from LCLs was sufficient to decrease the phosphorylation of STAT1. Inhibition of NF-kappaB activity by different pharmacological inhibitors (i.e., parthenolide, MG132 and BAY 11-7082) and by overexpressed mutated IkappaBalpha prevented the activation of STAT1. To identify the factors involved, we performed macroarray cDNA profiling with or without inhibition of NF-kappaB. The expression of several cytokines was NF-kappaB dependent among those alpha and gamma IFNs (IFN-alpha and IFN-gamma), known activators of STAT1. By real-time PCR and enzyme-linked immunosorbent assay we show that IFN-alpha and IFN-gamma are expressed and released by LCLs in an NF-kappaB-dependent manner. Finally, the blocking of the IFN-alpha and IFN-gamma by neutralizing antibodies led to the complete inhibition of tyrosine phosphorylation of STAT1. Taken together, our results clearly show that LMP1-induced tyrosine phosphorylation of STAT1 is almost exclusively due to the NF-kappaB-dependent secretion of IFNs. Whether this response, which is usually considered to be antiviral, is in fact required for the persistence of the virus remains to be elucidated.

SUBMITTER: Najjar I

PROVIDER: S-EPMC1069527 | biostudies-literature | 2005 Apr

REPOSITORIES: biostudies-literature

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Latent membrane protein 1 regulates STAT1 through NF-kappaB-dependent interferon secretion in Epstein-Barr virus-immortalized B cells.

Najjar Imen I Baran-Marszak Fanny F Le Clorennec Christophe C Laguillier Christelle C Schischmanoff Olivier O Youlyouz-Marfak Ibtissam I Schlee Martin M Bornkamm Georg W GW Raphaël Martine M Feuillard Jean J Fagard Remi R

Journal of virology 20050401 8

Constitutive activation of signal transducer and activator of transcription 1 (STAT1) is a distinctive feature of Epstein-Barr virus (EBV)-immortalized B cells (lymphoblastoid cell lines [LCLs]). The expression of STAT1 in these cells is modulated by the latent membrane protein 1 (LMP1), but the mechanism of STAT1 activation has remained unclear. We demonstrate that the tyrosine phosphorylation of STAT1 in LCLs results from an indirect pathway encompassing an NF-kappaB-dependent secretion of int ...[more]

PMID: 15795279

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Project description:Transporter associated with antigen processing 2 (Tap-2) is responsible for ATP-dependent transport of peptides from the cytosol to the endoplasmic reticulum, where peptides bind to newly synthesized human leukocyte antigen (HLA) class I molecules, which are essential for cellular immune responses. Epstein-Barr virus (EBV) latent membrane protein 1 (LMP-1) has been shown to induce the expression of Tap-2. In this study, the induction of endogenous Tap-2 by LMP-1 is shown to be associated with and requires the expression of interferon regulatory factor 7 (IRF-7). In DG75 Burkitt's lymphoma (BL) cells, in which LMP-1 induces the expression of IRF-7, LMP-1 induced endogenous Tap-2, and ectopic expression of IRF-7 could enhance the induction. In Akata BL cells, in which LMP-1 could not induce IRF-7, LMP-1 could not induce Tap-2. Addition of IRF-7, which complements the defect in Akata cells, could stimulate the expression of Tap-2. Furthermore, LMP-1 and IRF-7A but not other IRF-7 splicing variants could activate endogenous Tap-2. A Tap-2 promoter reporter construct could be activated by the overexpression of IRF-7A. The activation could be specifically enhanced by LMP-1 and was dependent on an intact interferon-stimulated response element (ISRE) present in the Tap-2 promoter. Also, IRF-7 can bind to the Tap-2 promoter under physiological conditions in vivo, as shown by formaldehyde cross-linking, as well as to the Tap-2 ISRE in vitro, as shown by gel mobility shift assays. Furthermore, LMP-1 facilitates the phosphorylation and nuclear translocation of IRF-7. These data point to the role of IRF-7 as a secondary mediator of LMP-1-activated signal transduction for Tap-2 as follows: LMP-1 stimulates the expression of IRF-7 and facilitates its phosphorylation and nuclear translocation, and then the activated IRF-7 mediates the activation of the cellular Tap-2 gene. The induction of Tap-2 by IRF-7 and LMP-1 may have an important implication for the immune response to EBV and its persistence in vivo.

Project description:Epstein-Barr Virus (EBV) Latent Membrane Protein 1 (LMP1) transforms rodent fibroblasts and is expressed in most EBV-associated malignancies. LMP1 Transformation Effector Site 2 (TES2)/C-Terminal Activation Region 2 (CTAR2) activates NF-kappaB, p38, JNK, ERK and IRF7 pathways. We have investigated LMP1 TES2 genome-wide RNA effects at 4 time points after LMP1 TES2 expression in HEK 293 cells. Using a False Discovery Rate (FDR) of < 0.001 after correction for multiple hypotheses, LMP1 TES2 caused > 2-fold changes in 1916 mRNAs; 1479 RNAs were up-regulated and 437 down-regulated. In contrast to TNFalpha stimulation, which transiently up-regulates many target genes, LMP1 TES2 maintained most RNA effects through the time course, despite robust and sustained induction of negative feedback regulators, such as IkappaBalpha and A20. LMP1 TES2 regulated RNAs encode many NF-kappaB signaling proteins and secondary interacting proteins. Consequently, many LMP1 TES2-regulated RNAs encode proteins that form an extensive interactome. Gene Set Enrichment Analyses found LMP1 TES2 up-regulated genes to be significantly enriched for Pathways in Cancer, B-and T-cell receptor signaling, and Toll-like receptor signaling. Surprisingly, LMP1 TES2 and IkappaBalpha super-repressor co-expression decreased LMP1 TES2 RNA effects to only 5 RNAs with FDR<0.001 and >2 fold change. Thus, canonical NF-kappaB activation is critical for almost all LMP1 TES2 RNA effects in HEK-293 cells and a more significant therapeutic target than previously appreciated. An LMP1 double point mutant (P204A, Q206A) was used to construct a HEK-293 TET-On LMP1 TES2 cell line. Stable cell clones were selected that carry an inducible system for LMP1 TES2 expression. The Tet-system is composed of three parts: 1) the LMP1 TES2 cDNA cloned into the tetracycline-regulated pJEF vector; 2) a tetracycline suppressor (tTS) that binds Tet-operator sites in the absence of tetracyclines and silences expression; 3) a reverse-tetracycline transactivator fused to the 4-hydroxy tamoxifen (4HT) ligand binding domain (rTTA M2). LMP1 expression was induced by addition of doxycycline (1 ug/ml) and 4HT (100 nM). For simultaneous inducible expression of LMP1 TES2 and an IkBa super-repressor, a stable cell line was derived. A pJEF vector encoding IkBa residues 37-317 was introduced into the inducible LMP1 TES2 cell line. Cell lines were cultured with DMEM (GIBCO) supplemented with 10% tetracycline-free serum (Clontech). LMP1 expression was induced by addition of tetracycline (1 ug/ml). RNA samples were collected from triplicate samples using RNABee (Qiagen) according to the manufacturer’s instructions from 293 cells induced for LMP1 TES2 (and IkBa super-repressor, where indicated) expression at 0, 6, 9, 12 and 24 hours of induction. Cells were in the log-phase of growth. Gene expression profiles were assayed using the Affymetrix HU-133 plus2 GeneChip according to the manufacturer's instructions. Real-time RT-PCR was performed with the Power SYBR Green RNA-to-CT™ 1-Step Kit (Applied Biosystems, Foster City, CA). Fold changes were determined using delta delta Ct method and normalized by GAPDH expression levels. RNA expression data were normalized using RMA and array quality assessed by NUSE and RLE scores. The data was collected according to methods that fall under the MIAME standards.

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Latent membrane protein 1 regulates STAT1 through NF-kappaB-dependent interferon secretion in Epstein-Barr virus-immortalized B cells.

Publications

Latent membrane protein 1 regulates STAT1 through NF-kappaB-dependent interferon secretion in Epstein-Barr virus-immortalized B cells.

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