Genomic organization and promoter characterization of the gene encoding the human telomerase reverse transcriptase (hTERT)

The enzyme telomerase plays a crucial role in cellular proliferation and tu morigenesis. By adding hexameric repeats to chromosome ends, it prevents te lomeric loss and, thus, entry into senescence. Recent data suggest that exp ression of the human telomerase reverse transcriptase subunit (hTERT) repre sents the limiting factor for telomerase activity. To gain an insight into the mechanisms regulating hTERT expression, we have determined the complete genomic organization of the hTERT gene and isolated the 5'- and 3'- flanki ng region. The hTERT gene encompasses more than 37 kb and consists of 16 ex ons. We show that all hTERT insertion and deletion variants described so fa r most likely result from the usage of alternative splice consensus sequenc es in intron or exon regions. Furthermore, we identified a new hTERT splice variant. Analysis of the DNA sequence surrounding the putative transcripti onal start region revealed a TATA-less promoter located in a CpG island. A promoter fragment spanning the first 1100 bp upstream of the initiating ATG start codon exhibited high-level activity in HEK-293 cells. Several consen sus binding sites for the transcription factor Sp1 as well as a c-Myc bindi ng site were identified in this promoter region. Altogether, these results provide the basis for more detailed studies on the regulation of telomerase activity in normal and cancer cells, and may lead to the development of ne w cancer therapies. (C) 1999 Elsevier Science B.V. All rights reserved.