TY - JOUR
T1 - Latent membrane protein 1 of Epstein-Barr virus activates the hTERT promoter and enhances telomerase activity in B lymphocytes
AU - Terrin, Liliana
AU - Dal Col, Jessica
AU - Rampazzo, Enrica
AU - Zancai, Paola
AU - Pedrotti, Moreno
AU - Ammirabile, Grazia
AU - Bergamin, Stefano
AU - Rizzo, Silvana
AU - Dolcetti, Riccardo
AU - De Rossi, Anita
PY - 2008/10
Y1 - 2008/10
N2 - Transformation of primary B lymphocytes by Epstein-Barr virus requires the establishment of a strictly latent infection, the expression of several latent viral proteins, and sustained telomerase activity. Our previous findings indicated that induction of hTERT, the rate-limiting catalytic unit of the telomerase complex, was associated with the expression of the viral latent membrane protein 1 (LMP1). In the present study, we demonstrate that ectopic expression of LMP1 in BJAB and Ramos B cells resulted in an increase of hTERT transcripts, thus suggesting that LMP1 acts at the transcriptional level. This was confirmed by transient expression of a luciferase reporter plasmid containing the hTERT promoter cotransfected with an LMP1-expressing vector or transfected into B cells in which LMP1 expression was inducible. Consistently, silencing of LMP1 by small interfering RNA resulted in a reduction of hTERT transcripts. We also provide evidence indicating that LMP1-induced hTERT activation is independently mediated by NF-κB and by mitogen-activated protein kinase and extracellular signal-regulated kinase 1/2 pathways, whereas CD40, Akt, and mTOR signaling has no involvement. Moreover, our results do not support a role for c-Myc in mediating these effects on hTERT, since ectopic expression of LMP1 did not upregulate c-Myc and silencing of this oncogene or E box mutagenesis failed to inhibit LMP1-induced hTERT activation. These findings indicate that LMP1 simultaneously modulates multiple signal transduction pathways in B cells to transactivate the hTERT promoter and enhance telomerase activity, thus confirming the pleiotropic nature of this viral oncoprotein.
AB - Transformation of primary B lymphocytes by Epstein-Barr virus requires the establishment of a strictly latent infection, the expression of several latent viral proteins, and sustained telomerase activity. Our previous findings indicated that induction of hTERT, the rate-limiting catalytic unit of the telomerase complex, was associated with the expression of the viral latent membrane protein 1 (LMP1). In the present study, we demonstrate that ectopic expression of LMP1 in BJAB and Ramos B cells resulted in an increase of hTERT transcripts, thus suggesting that LMP1 acts at the transcriptional level. This was confirmed by transient expression of a luciferase reporter plasmid containing the hTERT promoter cotransfected with an LMP1-expressing vector or transfected into B cells in which LMP1 expression was inducible. Consistently, silencing of LMP1 by small interfering RNA resulted in a reduction of hTERT transcripts. We also provide evidence indicating that LMP1-induced hTERT activation is independently mediated by NF-κB and by mitogen-activated protein kinase and extracellular signal-regulated kinase 1/2 pathways, whereas CD40, Akt, and mTOR signaling has no involvement. Moreover, our results do not support a role for c-Myc in mediating these effects on hTERT, since ectopic expression of LMP1 did not upregulate c-Myc and silencing of this oncogene or E box mutagenesis failed to inhibit LMP1-induced hTERT activation. These findings indicate that LMP1 simultaneously modulates multiple signal transduction pathways in B cells to transactivate the hTERT promoter and enhance telomerase activity, thus confirming the pleiotropic nature of this viral oncoprotein.
UR - http://www.scopus.com/inward/record.url?scp=53749088898&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=53749088898&partnerID=8YFLogxK
U2 - 10.1128/JVI.00321-08
DO - 10.1128/JVI.00321-08
M3 - Article
C2 - 18684838
AN - SCOPUS:53749088898
VL - 82
SP - 10175
EP - 10187
JO - Journal of Virology
JF - Journal of Virology
SN - 0022-538X
IS - 20
ER -