The human telomerase catalytic subunit hTERT: organization of the gene and characterization of the promoter

Abstract

Telomerase, the enzyme that synthesizes telomeric DNA, is not expressed in most human somatic cells but is activated with in vitro immortalization and during tumorigenesis, and repressed by cell differentiation. Of the two components of the core enzyme, the catalytic protein hTERT is limiting for activity. To investigate mechanisms of hTERT gene regulation, we have cloned genomic sequences encompassing the complete hTERT transcription unit. The hTERT gene consists of 16 exons and 15 introns spanning approximately 35 kb. Transient transfections of immortal human cells with potential regulatory 5' sequences linked to a reporter, combined with deletion analysis of these sequences, indicated that elements responsible for promoter activity are contained within a region extending from 330 bp upstream of the ATG to the second exon of the gene. Assays in different cell types have shown that the hTERT promoter is inactive in normal and in transformed pre-immortal cells, but, like telomerase, it is activated with cell immortalization. Sequence analysis revealed that the hTERT promoter is GC-rich, lacks TATA and CAAT boxes but contains binding sites for several transcription factors that may be involved in its regulation. The abundance of these sites suggests the possibility that hTERT expression may be subject to multiple levels of control and be regulated by different factors in different cellular contexts.

Infectivity enhanced, hTERT promoter-based conditionally replicative adenoviruses are useful for SCLC treatment

“…The mechanisms by which the hTERT core promoter works so differentially in tumors and normal cells are still unclear. However, it has been reported that c-Myc, 29,[53][54][55][56][57] Sp1 57 and estrogen 58,59 activated hTERT promoter, but p53, 60 WT-1 61 and Mad1 62 were important factors for the Figure 10 Ad5/3hTERTE1 suppressed tumor growth in vivo. Intact SBC5 cells (1 Â 10 7 ) were injected s.c. into nude mice.…”

TAK1 represses transcription of the human telomerase reverse transcriptase gene

“…TAK1 represses hTERT transcription T Fujiki et al in this repression are located in the first 164 bp of the hTERT promoter, which has been identified as the core promoter region essential for the transcriptional activation of the hTERT gene and contains several potential transcription factor-binding elements such as the GCbox and E-box (Figure 1b) (Cong et al, 1999;Horikawa et al, 1999;Takakura et al, 1999;Won et al, 2002).…”

“…The oncoprotein c-Myc was reported to activate the hTERT core promoter by binding to the E-boxes located at the promoter site (Cong et al, 1999;Horikawa et al, 1999). Further, the identified cis-elements also include the Sp1-binding sites (GC-boxes) at the core promoter that are crucial for the transactivation of the hTERT gene (Horikawa et al, 1999;Takakura et al, 1999).…”

Herpes simplex virus type-1 infection upregulates cellular promoters and telomerase activity in both tumor and nontumor human cells

“…Plasmid pLacZ contains the cytomegalovirus (CMV) promoter-regulated LacZ gene 78 Plasmid pTLuc was generated by subcloning a 342 bp fragment of the hTERT promoter (À344 to À2 relative to the hTERT ATG) from plasmid P-344 79 upstream of the luciferase reporter gene in the pGL2-Basic vector (pGL2, Promega, Madison, WI, USA). Plasmid Tyrosinase-2, containing the tyrosinase promoter-regulated luciferase gene, 7 was kindly provided by Dr. David L. Bartlett (National Cancer Institute, Frederick, MD, USA).…”