PAX5 activates the transcription of the human telomerase reverse transcriptase gene in B cells.
Telomerase is an RNA-dependent DNA polymerase that synthesizes telomeric DNA. Its activity is not detectable in most somatic cells but it is reactivated during tumorigenesis. In most cancers, the combination of hTERT hypermethylation and hypomethylation of a short promoter region is permissive for low-level hTERT transcription. Activated and malignant lymphocytes express high telomerase activity, through a mechanism that seems methylation-independent. The aim of this study was to determine which mechanism is involved in the enhanced expression of hTERT in lymphoid cells. Our data confirm that in B cells, some T cell lymphomas and non-neoplastic lymph nodes, the hTERT promoter is unmethylated. Binding sites for the B cell-specific transcription factor PAX5 were identified downstream of the ATG translational start site through EMSA and ChIP experiments. ChIP assays indicated that the transcriptional activation of hTERT by PAX5 does not involve repression of CTCF binding. In a B cell lymphoma cell line, siRNA-induced knockdown of PAX5 expression repressed hTERT transcription. Moreover, ectopic expression of PAX5 in a telomerase-negative normal fibroblast cell line was found to be sufficient to activate hTERT expression. These data show that activation of hTERT in telomerase-positive B cells is due to a methylation-independent mechanism in which PAX5 plays an important role.
Bougel
Stéphanie
S
Institute of Pathology, Centre Hospitalier Universitaire Vaudois and University of Lausanne, CH-1011 Lausanne, Switzerland.
Renaud
Stéphanie
S
Braunschweig
Richard
R
Loukinov
Dmitri
D
Morse
Herbert C
HC
Bosman
Fred T
FT
Lobanenkov
Victor
V
Benhattar
Jean
J
D001402:B-Lymphocytes / Q000201:enzymology*; D001483:Base Sequence; D001665:Binding Sites; D001667:Binding, Competitive; D000076246:CCCTC-Binding Factor; D018899:CpG Islands / Q000235:genetics; D019175:DNA Methylation; D004273:DNA, Neoplasm / Q000235:genetics; D015972:Gene Expression Regulation, Neoplastic; D006801:Humans; D008223:Lymphoma / Q000235:genetics / Q000378:metabolism; D008969:Molecular Sequence Data; D009363:Neoplasm Proteins / Q000235:genetics / Q000378:metabolism; D051757:PAX5 Transcription Factor / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D011401:Promoter Regions, Genetic; D012333:RNA, Messenger / Q000235:genetics; D012334:RNA, Neoplasm / Q000235:genetics; D034741:RNA, Small Interfering / Q000235:genetics; D012097:Repressor Proteins / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction / Q000379:methods; D019098:Telomerase / Q000235:genetics* / Q000378:metabolism; D015533:Transcriptional Activation / Q000235:genetics*; D014407:Tumor Cells, Cultured
D000076246:CCCTC-Binding Factor; C000619697:CTCF protein, human; D004273:DNA, Neoplasm; D009363:Neoplasm Proteins; D051757:PAX5 Transcription Factor; C497281:PAX5 protein, human; D012333:RNA, Messenger; D012334:RNA, Neoplasm; D034741:RNA, Small Interfering; D012097:Repressor Proteins; C509186:TERT protein, human; D019098:Telomerase