Amplification, increased dosage and in situ expression of the telomerase RNA gene in human cancer

Abstract

Telomere length is maintained by the enzyme, telomerase, which has been linked to cellular immortality and tumour progression. However, the reasons for the high levels of telomerase found in human tumours are unknown. We have mapped the human telomerase RNA gene, (hTR), to chromosome 3q26.3 and show the hTR gene to be ampli®ed in four carcinomas, (2/33 cervix, 1/31 head and neck, 1/9 lung). In addition, increased copy numbers of the hTR locus was also observed in 97% of tumours. By in situ hybridisation, the histological distribution of high levels of hTR expression could be demonstrated in a lung tumour and its metastasis with hTR ampli®cation. These results are the ®rst report of genetic alterations involving a known component of telomerase in human cancer. Indeed, it is also the ®rst report of the ampli®cation of a speci®c locus within the chromosome 3q region frequently subject to copy number gains in human tumours. In addition, we also show for the ®rst time the histological distribution of the RNA component of telomerase in human tumours.

Tumour specific regulation of telomerase RNA gene expression visualized by in situ hybridization

“…Successful development of telomerase inhibitors will require an understanding of hTR expression in all tumour types. Our studies point to examples of clear di erentials in expression between cancerous and adjacent normal tissue which support the possibility of e ective telomerase-based therapy (Soder et al, 1997). Indeed, the presence of high levels of hTR expression in speci®c cancers suggest the hTR promoter may be an interesting focus for genetic therapies designed to target therapeutic genes to tumours, via tumour speci®c gene expression.…”

“…On the other hand, both squamous and glandular carcinomas of the uterine cervix are exposed to the same carcinogenic in¯uences as far as is known, and both can express hTR suggesting that the carcinogenic insult such as papilloma virus may override tissue or di erentiation speci®c regulation of hTR (Klingelhutz et al, 1996). These data will therefore be of value in analysing the relationship between molecular events occurring during oncogenesis and transcriptional activation of the telomerase RNA gene promoter, and in identifying the molecular controls on signal transduction resulting in telomerase activity (Soder et al, 1997;Villeponteau, 1996). For hTR or telomerase to be useful biomarkers for disease or as a therapeutic target, di erential expression is required between normal and cancerous tissue (Breslow et al, 1997).…”

“…However, in both normal and cancerous tissue, admixture of cell types may confound interpretation of many assays. The in situ approach described here is ideally placed to solve this problem (Soder et al, 1997). Indeed, the ease and reproducibility with which patterns of hTR expression can be assessed by in situ, suggests that hTR should be evaluated as a prognostic marker or as a biomarker for response to conventional therapies.…”

“…Information on telomerase activity in tumours almost exclusively derives from the in vitro telomere repeat ampli®cation protocol (TRAP), and these have shown that telomerase activity may be present in greater than 80% of tumour biopsies yet absent or reduced in normal somatic tissue (Breslow et al, 1997;Kim et al, 1994;Raymond et al, 1996;Shay and Wright, 1996). However, it is unlikely that TRAP assay alone will reveal the true complexities of telomerase regulation, and it is generally recognised that a number of molecular approaches will be required to understand telomere length regulation and telomerase activity (Breslow et al, 1997;Holt et al, 1996a;Lundblad and Wright, 1996;Parkinson et al, 1997;Raymond et al, 1996;Soder et al, 1997). Recently, we and others have introduced a number of more direct in situ approaches to study the telomerase RNA gene (hTR) and its expression in tumours (Soder et al, 1997;Yashima et al, 1997).…”

“…However, it is unlikely that TRAP assay alone will reveal the true complexities of telomerase regulation, and it is generally recognised that a number of molecular approaches will be required to understand telomere length regulation and telomerase activity (Breslow et al, 1997;Holt et al, 1996a;Lundblad and Wright, 1996;Parkinson et al, 1997;Raymond et al, 1996;Soder et al, 1997). Recently, we and others have introduced a number of more direct in situ approaches to study the telomerase RNA gene (hTR) and its expression in tumours (Soder et al, 1997;Yashima et al, 1997). Therefore, in order to gain insight into possible levels of telomerase regulation in vivo, we have examined over 300 tumours of epithelial and germ cell origin for hTR expression by in situ hybridization.…”