Activation of Telomerase RNA Gene Promoter Activity by NF-Y, Sp1, and the Retinoblastoma Protein and Repression by Sp3

Abstract

Expression of the human telomerase RNA component gene, hTERC is essential for telomerase activity. The hTERC gene is expressed during embryogenesis and then downregulated during normal development, leaving most adult somatic cells devoid of hTERC expression. During oncogenesis, however, hTERC is re-expressed consequently contributing to the unrestricted proliferative capacity of many human cancers. Thus the identification of the molecular basis for the regulation of the telomerase RNA component gene in normal cells and its deregulation in cancer cells is of immediate interest. We have previously cloned the hTERC promoter and in this study have identified several transcription factors that modulate the expression of hTERC. We demonstrate that NF-Y binding to the CCAAT region of the hTERC promoter is essential for promoter activity. Sp1 and the retinoblastoma protein (pRb) are activators of the hTERC promoter and Sp3 is a potent repressor. These factors appear to act in a species-specific manner. Whereas Sp1 and Sp3 act on the human, bovine, and mouse TERC promoters, pRb activates only the human and bovine promoter, and NF-Y is only essential for the human TERC gene.

High level of telomerase RNA gene expression is associated with chromatin modification, the ALT phenotype and poor prognosis in liposarcoma

“…The activity of the ribonucleoprotein complex telomerase is reliant on the expression of both hTR and hTERT genes, the regulation of which is tightly coordinated on multiple levels by transcriptional, post-transcriptional (Zhao et al, 2000(Zhao et al, , 2005Cong et al, 2002;Anderson et al, 2006;Bilsland et al, 2006) and epigenetic mechanisms (Atkinson et al, 2005;Serakinci et al, 2006). In most normal somatic cells, telomerase is inactivated following development so that telomeres shorten after each round of replication until they reach a critical length, signalling senescence or cell death.…”

Telomerase-specific suicide gene therapy vectors expressing bacterial nitroreductase sensitize human cancer cells to the pro-drug CB1954

“…The recent accumulation of detailed knowledge on telomerase gene regulation suggests that both the human telomerase reverse transcriptase gene (hTERT) and the telomerase RNA gene (hTR) are controlled at least in part at the transcriptional level (Abdul-Ghani et al, 2000;Gu et al, 2000;Gunes et al, 2000;Hoare et al, 2001;Koga et al, 2000;Majumdar et al, 2001;Yi et al, 1999;Zhao et al, 2000). Studies from our group and others suggest that the hTR gene is expressed at high levels in cancer cells, yet can also be detected at low levels in some normal tissues (Heine et al, 1998;Hiyama et al, 1999;Maitra et al, 1999;Park et al, 1999;Sarvesvaran et al, 1999;Soder et al, 1998;Stanta et al, 1999;Weng et al, 1997;Wisman et al, 2000;Yashima et al, 1998).…”

“…In order to assess transgene expression from the hTERT and hTR promoters in various cells, plasmid vectors expressing the luciferase reporter gene driven by a 536 bp hTERT promoter fragment (nucleotide position 2834 ± 3369 in GenBank Accession number AB016767) (Takakura et al, 1999), or an 867 bp hTR promoter fragment described previously, (nucleotide position 1 ± 867 in GenBank Accession number AF047386), were used (Zhao et al, 1998(Zhao et al, , 2000.…”

“…Cells were treated with varying concentrations of CB1954 and Figure 1c,d shows representative dose response curves for the C33a and GLC4 cell lines containing the telomerase gene therapy vectors. The concentration of CB1954 required to give a 50% reduction in growth, (IC 50 ) was Figure 1 Activities of the (a) hTERT and (b) hTR promoters in cancer, ALT and mortal cell lines quanti®ed by luciferase assay, (Zhao et al, 1998(Zhao et al, , 2000. Cell lines were transfected in 6-well plates using Qiagen superfect transfection reagent and 3 mg of the luciferase reporter constructs pLh2023 (hTR promoter) or pLhTERT19 (hTERT promoter).…”

Tiptoeing to chromosome tips: facts, promises and perils of today's human telomere biology

“…NF-Y binding to the CCAAT region of the hTR promoter is essential for promoter activity whereas Sp1 and the retinoblastoma protein (pRb) are activators of the promoter and Sp3 is a potent repressor. These factors appear to act in a species-speci c manner (Zhao et al 2000). In cell lines exhibiting ALT and total absence of hTR expression, the promoter of the hTR gene is methylated, and treatment with 5-azacytidine in combination with trichostatin A resulted in partial demethylation of the promoter and expression of the gene (Hoare et al 2001).…”