Mapping of the gene for the human telomerase reverse transcriptase, hTERT,to chromosome 5p15.33 by fluorescence in situ hybridization

Telomerase, the enzyme that maintains the ends of chromosomes, is absent fr om the majority of somatic cells but is present and active in most tumours. The gene for the reverse transcriptase component of telomerase (hTERT) has recently been identified. A cDNA clone of this gene was used as a probe to identify three genomic bacterial artificial chromosome (BAC) clones, one o f which was used as a probe to map hTERT by fluorescence in situ hybridizat ion (FISH) to chromosome 5p15.33. This BAC probe was further used to look a t copy number of the hTERT region in immortal cell lines. We found that 10/ 15 immortal cell lines had a modal copy number of 3 or more per cell, with one cell line (CaSki) having a modal copy number of 11. This suggests that increases in copy number of the hTERT gene region do occur, and may well be one route to upregulating telomerase levels in tumour cells. 5p15 gains an d amplifications have been documented for various tumour types, including n on-small cell lung carcinoma, squamous cell carcinoma of head and neck, and uterine cervix cancer, making hTERT a potential target.