Dataset Information

Epstein-Barr Virus encoded LMP1 regulates cyclin D1 promoter activity by nuclear EGFR and STAT3 in CNE1 cells.

ABSTRACT: The principal Epstein-Barr virus (EBV) oncoprotein, latent membrane protein 1 (LMP1) is strongly associated with nasopharyngeal carcinoma (NPC), a prevalent cancer in China. The epidermal growth factor receptor (EGFR) is important in carcinogenesis, as it is a ubiquitously expressed receptor tyrosine kinase. Signal transducer and activator of transcription 3 (STAT3) is a master transcriptional regulator in proliferation and apoptosis. Our previous study demonstrated that the nuclear EGFR could bind to the cyclin D1 promoter directly in the presence of LMP1, and the correlation between EGFR and STAT3 in NPC remains to be further explored. Here, we have shown that the interaction of EGFR and STAT3 increased in the nucleus in the presence of LMP1. LMP1 promoted both EGFR and STAT3 binding to the promoter region of cyclin D1, in turn, enhancing the promoter activity of cyclin D1. Furthermore, we demonstrated that both transcriptional activity and mRNA levels of cyclin D1 were decreased by small molecule interference of EGFR and STAT3 activity. These findings may provide a novel linkage between the EGFR and STAT3 signaling pathways and the activation of cyclin D1 by LMP1 in the carcinogenesis of NPC.

SUBMITTER: Xu Y

PROVIDER: S-EPMC3843577 | biostudies-literature | 2013 Nov

REPOSITORIES: biostudies-literature

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Epstein-Barr Virus encoded LMP1 regulates cyclin D1 promoter activity by nuclear EGFR and STAT3 in CNE1 cells.

Xu Yang Y Shi Ying Y Yuan Qi Q Liu Xuli X Yan Bin B Chen Ling L Tao Yongguang Y Cao Ya Y

Journal of experimental & clinical cancer research : CR 20131113

The principal Epstein-Barr virus (EBV) oncoprotein, latent membrane protein 1 (LMP1) is strongly associated with nasopharyngeal carcinoma (NPC), a prevalent cancer in China. The epidermal growth factor receptor (EGFR) is important in carcinogenesis, as it is a ubiquitously expressed receptor tyrosine kinase. Signal transducer and activator of transcription 3 (STAT3) is a master transcriptional regulator in proliferation and apoptosis. Our previous study demonstrated that the nuclear EGFR could b ...[more]

PMID: 24499623

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Project description:BackgroundEpstein-Barr virus (EBV)-encoded LMP1 protein is commonly expressed in nasopharyngeal carcinoma (NPC). LMP1 is a prime candidate for driving tumourigenesis given its ability to activate multiple signalling pathways and to alter the expression and activity of variety of downstream targets. Resistance to TGFbeta-mediated cytostasis is one of the growth transforming effects of LMP1. Of the downstream targets manipulated by LMP1, the induction of Id1 and inactivation of Foxo3a appear particularly relevant to LMP1-mediated effects. Id1, a HLH protein is implicated in cell transformation and plays a role in cell proliferation, whilst Foxo3a, a transcription factor controls cell integrity and homeostasis by regulating apoptosis. The mechanism(s) by which LMP1 induces these effects have not been fully characterised.ResultsIn this study, we demonstrate that the ability of LMP1 to induce the phosphorylation and inactivation of Foxo3a is linked to the upregulation of Id1. Furthermore, we show that the induction of Id1 is essential for the transforming function of LMP1 as over-expression of Id1 increases cell proliferation, attenuates TGFbeta-SMAD-mediated transcription and renders cells refractory to TGFbeta-mediated cytostasis. Id1 silencing in LMP1-expressing epithelial cells abolishes the inhibitory effect of LMP1 on TGFbeta-mediated cell growth arrest and reduces the ability of LMP1 to attenuate SMAD transcriptional activity. In response to TGFbeta stimulation, LMP1 does not abolish SMAD phosphorylation but inhibits p21 protein expression. In addition, we found the induction of Id1 in LMP1-expressing cells upon stimulation by TGFbeta. We provide evidence that LMP1 suppresses the transcriptional repressor ATF3, possibly leading to the TGFbeta-induced Id1 upregulation.ConclusionThe current data provide novel information regarding the mechanisms by which LMP1 suppresses TGFbeta-induced cytostasis, highlighting the importance of Id1 in LMP1 mediated cell transformation.

Project description:Epstein-Barr virus (EBV) is closely associated with nasopharyngeal carcinoma (NPC), a human malignancy notorious for its highly metastatic nature. Among EBV-encoded genes, latent membrane protein 1 (LMP1) is expressed in most NPC tissues and exerts oncogenicity by engaging multiple signaling pathways in a ligand-independent manner. LMP1 expression also results in actin cytoskeleton reorganization, which modulates cell morphology and cell motility- cellular process regulated by RhoGTPases, such as Cdc42. Despite the prominent association of Cdc42 activation with tumorigenesis, the molecular basis of Cdc42 activation by LMP1 in NPC cells remains to be elucidated. Here using GST-CBD (active Cdc42-binding domain) as bait in GST pull-down assays to precipitate active Cdc42 from cell lysates, we demonstrated that LMP1 acts through its transmembrane domains to preferentially induce Cdc42 activation in various types of epithelial cells, including NPC cells. Using RNA interference combined with re-introduction experiments, we identified FGD4 (FYVE, RhoGEF and PH domain containing 4) as the GEF (guanine nucleotide exchange factor) responsible for the activation of Cdc42 by LMP1. Serial deletion experiments and co-immunoprecipitation assays further revealed that ectopically expressed FGD4 modulated LMP1-mediated Cdc42 activation by interacting with LMP1. Moreover, LMP1, through its transmembrane domains, directly bound FGD4 and enhanced FGD4 activity toward Cdc42, leading to actin cytoskeleton rearrangement and increased motility of NPC cells. Depletion of FGD4 or Cdc42 significantly reduced (?50%) the LMP1-stimulated cell motility, an effect that was partially reversed by expression of a constitutively active mutant of Cdc42. Finally, quantitative RT-PCR and immunohistochemistry analyses showed that FGD4 and LMP1 were expressed in NPC tissues, supporting the potential physiologically relevance of this mechanism in NPC. Collectively, our results not only uncover a novel mechanism underlying LMP1-mediated Cdc42 activation, namely LMP1 interaction with FGD4, but also functionally link FGD4 to NPC tumorigenesis.

Dataset Information

Epstein-Barr Virus encoded LMP1 regulates cyclin D1 promoter activity by nuclear EGFR and STAT3 in CNE1 cells.

Publications

Epstein-Barr Virus encoded LMP1 regulates cyclin D1 promoter activity by nuclear EGFR and STAT3 in CNE1 cells.

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