Response to cAMP levels of the Epstein-Barr virus EBNA2-inducible LMP1 oncogene and EBNA2 inhibition of a PP1-like activity.

Fåhræus, Robin; Palmqvist, Lars; Nerdstedt, A; Farzad, Sara Amel; Rymo, Lars; Laı́n, Sonia

doi:10.1002/j.1460-2075.1994.tb06950.x

Cited by 24 publications

(25 citation statements)

References 79 publications

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“…44,45 The promoter-proximal part of the LMP1 promoter contains an ATF/CRE site at position Ϫ41 relative to the transcription initiation site. 29,46 We tested whether the LMP1 promoter constitutes a novel downstream target of PERK/ ATF4 pathway. EBV-negative B cells were electroporated with reporter plasmids containing a wild-type or mutated ATF/CRE site in LMP1's promoter driving chloramphenicol acetyl transferase (CAT) gene expression.…”

Section: Lmp1's Promoter Is a Novel Downstream Target Of The Perk/atfmentioning

confidence: 99%

The LMP1 oncogene of EBV activates PERK and the unfolded protein response to drive its own synthesis

Lee

Sugden

2008

Blood

116

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phorylation of eIF2␣, which upregulates activating transcription factor 4 (ATF4) expression. ATF4, in turn, transactivates LMP1's own promoter. LMP1 activates not only PERK but also inositol requiring kinase 1 (IRE1) and ATF6, 3 pathways of the unfolded protein response (UPR). Increasing expression levels of LMP1 induced a dose-dependent increase in IRE1 activity, as measured by its "splicing" of XBP-1. These infected B cells secrete immunoglobins independent of the levels of LMP1, indicating that only a threshold level of XBP-1 is required for the secretion. These findings indicate that LMP1's activation of the UPR is a normal event in a continuum of LMP1's expression that leads both to stimulatory and inhibitory functions and regulates the physiology of EBV-infected B cells in multiple, unexpected modes. IntroductionOncogenes are dominantly acting regulators of cell proliferation and survival. They can be derived from proto-oncogenes by mutations that alter their enzymatic activity, as in the case of Ha-ras in carcinomas, or their levels of expression, as in the case of Bcl-2 in diffuse, large B-cell lymphomas. 1,2 The latent membrane protein 1 (LMP1) oncogene of Epstein-Barr virus (EBV) stands out among the regulators of cell proliferation because it has opposing activities dependent on its own level of expression. 3 These levels vary naturally in individual cells of clonal populations by more than 100-fold such that in any untreated population, some cells are proliferating while others are not.EBV contributes causally to multiple lymphomas and carcinomas. An important part of its oncogenicity in lymphoid cells lies in its ability to infect, induce, and maintain proliferation in B lymphocytes. This proliferation requires signaling by the LMP1 oncogene. 4-6 LMP1's signaling in B cells is in one way similar to that of the cellular CD40 receptor: both activate nuclear factor-B (NF-B), AP-1, and Stat-1 by associating with molecules such as TRAFs and JAK3. 7-15 LMP1's signaling, however, differs fundamentally from CD40, because LMP1 regulates these signaling pathways without itself being regulated by a ligand, as is CD40. When LMP1 is expressed at intermediate levels, it drives signaling through NF-B, for example, to promote cell proliferation. 6,16 When it is expressed at the high end of physiologic levels, it has been shown to induce the phosphorylation of eukaryotic initiation factor 2␣ (eIF2␣), an inhibition of general protein synthesis and cellular cytostasis. 3,[17][18][19] It is thus essential to elucidate the mechanism by which the levels of LMP1 are regulated to understand its functioning as an oncogene.We examined the path by which LMP1 induces the phosphorylation of eIF2␣ and have found that LMP1 activates the kinase, PERK, which phosphorylates eIF2␣. LMP1's activation of PERK is accompanied by its activation of the inositol requiring kinase 1 (IRE1), and activating transcription factor 6 (ATF6), indicating that LMP1 induces the unfolded protein response (UPR) pathway. LMP1's induction of the UPR is de...

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Section: Lmp1's Promoter Is a Novel Downstream Target Of The Perk/atfmentioning

confidence: 99%

The LMP1 oncogene of EBV activates PERK and the unfolded protein response to drive its own synthesis

Lee

Sugden

2008

Blood

116

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“…PKAcs␣ agonists have been reported to have an overall small positive effect on LMP1 expression in LCLs and on EBV Bam W EBNA promoter activity (4,18,35). The LMP1 and Bam W promoters are also positively affected by nearby CREB binding sites in some cell lines (18,35,59). The positive effects of PKA through these sites appear to be mediated by activation of an ATF-1/CREB-1 heterodimer (59).…”

Section: Vol 22 2002 Protein Kinase a Associates With Ha95 2141mentioning

confidence: 99%

“…Instead, HA95 associates with the lamin B receptor, laminaassociated polypeptide, and emerin on the inner aspect of the nuclear membrane and has a role in mitosis-associated nuclear membrane breakdown and chromatin condensation (43). Since HA95 is also highly associated with EBNA-LP, a coactivator of EBNA-2-mediated transcription, and PKA affects EBNA-2-mediated gene regulation (18,59), we have investigated whether HA95 and PKA interact with EBNA-LP and affect EBNA-LP-and EBNA-2-mediated transcriptional coactivation.…”

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confidence: 99%

Protein Kinase A Associates with HA95 and Affects Transcriptional Coactivation by Epstein-Barr Virus Nuclear Proteins

Han

Xue

Harada

et al. 2002

Molecular and Cellular Biology

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HA95, a nuclear protein homologous to AKAP95, has been identified in immune precipitates of the EpsteinBarr virus (EBV) coactivating nuclear protein EBNA-LP from EBV-transformed lymphoblastoid cells (LCLs).We now find that HA95 and EBNA-LP are highly associated in LCLs and in B-lymphoma cells where EBNA-LP is expressed by gene transfer. Binding was also evident in yeast two-hybrid assays. HA95 binds to the EBNA-LP repeat domain that is the principal coactivator of transcription. EBNA-LP localizes with HA95 and causes HA95 to partially relocalize with EBNA-LP in promyelocytic leukemia nuclear bodies. Protein kinase A catalytic subunit ␣ (PKAcs␣) is significantly associated with HA95 in the presence or absence of EBNA-LP. Although EBNA-LP is not a PKA substrate, HA95 or PKAcs␣ expression in B lymphoblasts specifically down-regulates the strong coactivating effects of EBNA-LP. The inhibitory effects of PKAcs␣ are reversed by coexpression of protein kinase inhibitor. PKAcs␣ also inhibits EBNA-LP coactivation with the EBNA-2 acidic domain fused to the Gal4 DNA binding domain. Furthermore, EBNA-LP-and EBNA-2-induced expression of the EBV oncogene, LMP1, is down-regulated by PKAcs␣ or HA95 expression in EBV-infected lymphoblasts. These experiments indicate that HA95 and EBNA-LP localize PKAcs␣ at nuclear sites where it can affect transcription from specific promoters. The role of HA95 as a scaffold for transcriptional regulation is discussed.Epstein-Barr virus (EBV) is a ubiquitous human herpesvirus that latently infects B lymphocytes and causes their efficient proliferation into continuous lymphoblastoid cell lines (LCLs) (28, 51, 52). EBV-infected B lymphoblasts can cause lymphoproliferative diseases in immune-compromised people (53). EBV is also causally associated with Burkitt's lymphoma (BL), nasopharyngeal carcinoma, and Hodgkin's disease (11,16,27,29). Five EBV-encoded nuclear proteins, EBNA-1, -2, -3A, -3C, and -LP, and a latent-infection-associated membrane protein, LMP1, are critical for the conversion of resting B lymphocytes to LCLs (7,22,33,42,54,64). EBNA-LP and EBNA-2 are the first two EBV proteins expressed in latent infection of human B lymphocytes (2). EBNA-2 activates transcription of cellular genes, including CD21, CD23, and c-myc and of viral genes, including the EBNAs, LMP1, and LMP2 (1,2,8,17,32,60,(69)(70)(71). EBNA-2 has the intrinsic ability to self associate and recognizes promoters by binding to RBP-J and PU.1/Spi1, cellular transcription factors that recognize specific DNA sequences (20,25,26,31,58). Once associated with a promoter, the EBNA-2 acidic domain can recruit basal and activated transcription factors p300, CBP, and PCAF histone acetylases and a p100 transcriptional coactivator (25,(65)(66)(67)73). EBNA-LP strongly coactivates transcription mediated by EBNA-2 or by the EBNA-2 acidic domain (24, 47). In coactivating transcription with EBNA-2, EBNA-LP has a central role in the EBV effects on cell growth and survival.The experiments reported here focus on the role of a recently descri...

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“…The TATA-proximal cAMP response element (CRE) in the LMP1 promoter appears to be one of the more critical sites in LMP1 transactivation according to numerous studies (28,53). Accordingly, cAMP increases endogenous LMP1 expression (17). The CRE mediates binding of transcriptional factors that are activated by phosphorylation in response to upstream kinases (14).…”

Section: Discussionmentioning

confidence: 99%

“…Both EBNA2-dependent and -independent transactivation of the LMP1 promoter require an intact CRE in the LMP1 regulatory sequence. Mutations in this site lead to a drastic decrease in promoter activity in reporter assays (17,53), and sequence variations in the site correlate with varied LMP1 expression levels in tumors and tumor cell lines (28). CRE binds the heterodimeric transcription factor CREB-ATF1 (53).…”

Section: Epstein-barr Virus (Ebv) Is a Human B-lymphocryptovirusmentioning

confidence: 99%

The p38 Signaling Pathway Upregulates Expression of the Epstein-Barr Virus LMP1 Oncogene

Johansson

Jansson

Rüetschi

et al. 2010

J Virol

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The Epstein-Barr virus (EBV)-encoded LMP1 oncogene has a role in transformation, proliferation, and metastasis of several EBV-associated tumors. Furthermore, LMP1 is critically involved in transformation and growth of EBV-immortalized B cells in vitro. The oncogenic properties of LMP1 are attributed to its ability to upregulate anti-apoptotic proteins and growth signals. The transcriptional regulation of LMP1 is dependent on the context of cellular and viral proteins present in the cell. Here, we investigated the effect of several signaling pathways on the regulation of LMP1 expression. Inhibition of p38 signaling, using p38-specific inhibitors SB203580 and SB202190, downregulated LMP1 in estrogen-induced EREB2.5 cells. Similarly, p38 inhibition decreased trichostatin A-induced LMP1 expression in P3HR1 cells. Exogenous expression of p38 in lymphoblastoid cell lines (LCLs) led to an increase in LMP1 promoter activity in reporter assays, and this activation was mediated by the previously identified CRE site in the promoter. Inhibition of p38 by SB203580 and p38-specific small interfering RNA (siRNA) also led to a modest decrease in endogenous LMP1 expression in LCLs. Chromatin immunoprecipitation indicated decreased binding of CREB-ATF1 to the CRE site in the LMP1 promoter after inhibition of the p38 pathway in EREB2.5 cells. Taken together, our results suggest that an increase in p38 activation upregulates LMP1 expression. Since p38 is activated in response to stimuli such as stress or possibly primary infection, a transient upregulation of LMP1 in response to p38 may allow the cells to escape apoptosis. Since the p38 pathway itself is activated by LMP1, our results also suggest the presence of an autoregulatory loop in LMP1 upregulation. Epstein-Barr virus (EBV) is a human B-lymphocryptovirusthat infects approximately 90% of the world's adult population and is the causative agent of infectious mononucleosis (IM). EBV is associated with several human malignancies such as Burkitt's lymphoma (BL), Hodgkin's lymphoma (HL), nasopharyngeal carcinoma (NPC), nasal T/NK lymphoma (NL), peripheral T-cell lymphoma, gastric carcinoma, and lymphoproliferative diseases in immunocompromised patients (57). EBV establishes latent infection in human B cells and transforms them in culture. The EBV-encoded LMP1 oncogene is critically involved in the EBV immortalization of B cells and their persistence in vitro, and it has the ability to transform rodent fibroblast and human cell lines in culture (4). LMP1 expression is thought to contribute to the genesis and growth of EBV-associated tumors. The oncogenic ability of LMP1 is attributed to its upregulation of anti-apoptotic proteins and growth signaling pathways (55). LMP1 transcription is regulated by both viral and cellular factors. EBV uses different programs of viral gene expression in order to drive naïve B cells into resting memory cells. These patterns of viral gene expression are referred to as latency types I, II, and III. EBV-associated tumors also exhibit similar patterns o...

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Response to cAMP levels of the Epstein-Barr virus EBNA2-inducible LMP1 oncogene and EBNA2 inhibition of a PP1-like activity.

Cited by 24 publications

References 79 publications

The LMP1 oncogene of EBV activates PERK and the unfolded protein response to drive its own synthesis

The LMP1 oncogene of EBV activates PERK and the unfolded protein response to drive its own synthesis

Protein Kinase A Associates with HA95 and Affects Transcriptional Coactivation by Epstein-Barr Virus Nuclear Proteins

The p38 Signaling Pathway Upregulates Expression of the Epstein-Barr Virus LMP1 Oncogene

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