Latent membrane protein 1 of Epstein-Barr virus activates the hTERT promoter and enhances telomerase activity in B lymphocytes.
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-kappaB 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.
Terrin
Liliana
L
Cancer Bioimmunotherapy Unit, Centro di Riferimento Oncologico-IRCCS, National Cancer Institute, Via Franco Gallini 2, 33081 Aviano (PN), Italy.
Dal Col
Jessica
J
Rampazzo
Enrica
E
Zancai
Paola
P
Pedrotti
Moreno
M
Ammirabile
Grazia
G
Bergamin
Stefano
S
Rizzo
Silvana
S
Dolcetti
Riccardo
R
De Rossi
Anita
A
D000818:Animals; D001402:B-Lymphocytes / Q000201:enzymology* / Q000502:physiology / Q000821:virology*; D019013:CD40 Antigens / Q000378:metabolism; D002460:Cell Line; D004847:Epithelial Cells / Q000166:cytology / Q000502:physiology; D020031:Epstein-Barr Virus Infections; D005786:Gene Expression Regulation; D004854:Herpesvirus 4, Human / Q000235:genetics / Q000378:metabolism; D006801:Humans; D019950:Mitogen-Activated Protein Kinase 1 / Q000235:genetics / Q000378:metabolism; D048052:Mitogen-Activated Protein Kinase 3 / Q000235:genetics / Q000378:metabolism; D011401:Promoter Regions, Genetic; D011494:Protein Kinases / Q000235:genetics / Q000378:metabolism; D051057:Proto-Oncogene Proteins c-akt / Q000235:genetics / Q000378:metabolism; D034741:RNA, Small Interfering / Q000235:genetics / Q000378:metabolism; D015398:Signal Transduction / Q000502:physiology; D058570:TOR Serine-Threonine Kinases; D019098:Telomerase / Q000235:genetics / Q000378:metabolism; D051996:Transcription Factor RelA / Q000235:genetics / Q000378:metabolism; D014158:Transcription, Genetic; D014763:Viral Matrix Proteins / Q000235:genetics / Q000378:metabolism*
D019013:CD40 Antigens; C037662:EBV-associated membrane antigen, Epstein-Barr virus; D034741:RNA, Small Interfering; D051996:Transcription Factor RelA; D014763:Viral Matrix Proteins; D011494:Protein Kinases; C546842:MTOR protein, human; D051057:Proto-Oncogene Proteins c-akt; D058570:TOR Serine-Threonine Kinases; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; D019098:Telomerase