Upregulation of Id1 by Epstein-Barr Virus-encoded LMP1 confers resistance to TGF[beta]-mediated growth inhibition

Background Epstein-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....

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Bibliographic Details
Published in:Molecular cancer 2010-06, Vol.9, p.155
Main Authors: Lo, Angela KF, Dawson, Christopher W, Lo, Kwok W, Yu, Yanxing, Young, Lawrence S
Format: Article
Language:English
Subjects:
Epstein-Barr virus
Genetic aspects
Growth
Health aspects
Membrane proteins
Nasopharyngeal cancer
Risk factors
Transforming growth factors
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Summary:Background Epstein-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 TGF[beta]-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. Results In 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 TGF[beta]-SMAD-mediated transcription and renders cells refractory to TGF[beta]-mediated cytostasis. Id1 silencing in LMP1-expressing epithelial cells abolishes the inhibitory effect of LMP1 on TGF[beta]-mediated cell growth arrest and reduces the ability of LMP1 to attenuate SMAD transcriptional activity. In response to TGF[beta] 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 TGF[beta]. We provide evidence that LMP1 suppresses the transcriptional repressor ATF3, possibly leading to the TGF[beta]-induced Id1 upregulation. Conclusion The current data provide novel information regarding the mechanisms by which LMP1 suppresses TGF[beta]-induced cytostasis, highlighting the importance of Id1 in LMP1 mediated cell transformation
ISSN:1476-4598
1476-4598
DOI:10.1186/1476-4598-9-155