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

Abstract

Maintenance of telomere structure by the ribonucleoprotein enzyme telomerase is considered central to the development of most human cancers. However, regulatory mechanisms governing telomerase expression during oncogenesis are largely unknown. We address potential tumour-speci®c regulation of telomerase RNA gene expression by RNA in situ hybridization to over 300 tumour samples of germ cell and epithelial origin. Twenty-six per cent of non-small cell lung cancers (NSCLC), expressed detectable levels of the telomerase RNA gene (hTR), and interestingly expression was almost con®ned to squamous carcinomas (41%), being rare in pulmonary adenocarcinomas and large-cell anaplastic carcinomas (P=0.006). Low frequency hTR expression was also associated with adenocarcinoma of the breast (13%), and ovary (17%). In comparison, hTR expression was detected in 43% of cervical cancers with no signi®cant di erences in frequency between squamous-cell carcinoma and adenocarcinoma or in transitions between intraepithelial neoplasia and invasive carcinoma. In contrast to the common epithelial cancers, the malignant cells in 73% of testicular germ-cell tumours (seminomas and teratomas), expressed hTR consistent with hTR expression in normal testicular germ cells. Di erentiated tissues within ovarian germ cell tumours and in testicular teratomas lacked detectable hTR expression. These studies show that di erent tumour types have distinct patterns of hTR expression, which has implications for our understanding of mechanisms regulating telomerase activity and for targeting the telomerase RNA component as an anti-cancer therapy.

Cloning and characterization of human and mouse telomerase RNA gene promoter sequences

“…In addition, we have recently shown tumourspeci®c patterns of hTR gene expression with clear di erentials in expression between cancerous and adjacent normal tissue (Soder et al, 1997a,b). Therefore, the hTR gene promoter may be of considerable use in genetic therapies requiring selective expression of therapeutic genes in cancer cells expressing high levels of hTR (Connors, 1995;Miller and Whelan, 1997;Soder et al, 1997a). The constructs described in the present study will be ideal for more focused gene therapy studies and the development of transcription based therapeutics.…”

“…The levels of telomerase RNA gene expression vary during normal development and between normal and cancerous cells and tissues (Avilion et al, 1996;Bestilny et al, 1996;Blasco et al, 1995Blasco et al, , 1996Bodnar et al, 1996;Broccoli et al, 1996;Feng et al, 1995;Kuniyasu et al, 1997;Soder et al, 1997a). Knowledge of telomerase RNA gene expression should therefore aid our understanding of the signal transduction pathways linking telomere attrition to proliferation, cellular senescence, di erentiation and oncogenesis.…”

“…The genes for the human, (hTR), and mouse, (terc), RNA components have recently been cloned, as has the human protein component; (hTRT) (Blasco et al, 1995;Feng et al, 1995;Nakamura et al, 1997;Soder et al, 1997b,c). Whilst telomerase expression is detectable in normal embryonic tissues and germline stem cells, telomerase expression is repressed in most normal postnatal somatic cells (Blasco et al, 1995;Feng et al, 1995;Prowse and Greider, 1995;Soder et al, 1997a;Wright et al, 1996). The lack of telomerase expression may be the major reason for the progressive loss of telomeric sequences in somatic cells, which is considered to be one regulatory mechanism which monitors the number of times a cell divides before entering replicative senescence (Campisi, 1997).…”

“…However, at present there are few studies which directly address the mechanisms regulating telomerase expression in normal and cancer cells (Bodnar et al, 1996;Broccoli et al, 1997;Li et al, 1997;Mandal and Kumar, 1997;Morin, 1997;Nakamura et al, 1997;Soder et al, 1997a). To identify elements important for the regulation of telomerase RNA genes, we have cloned genomic DNA sequences encompassing both the human and mouse telomerase RNA genes, including 5'-¯anking regions.…”

Dysregulated expression of the major telomerase components in leukaemic stem cells

“…11 Additional studies have shown it to be upregulated in solid tumours. 12,13 To determine if hTR levels may be limiting for telomere maintenance in CP CML, we performed Q-RT-PCR for hTR in CML vs normal CD34 þ selected cells (Figure 7). Interestingly, the mean hTR level in CML CD34 þ cells was some five-fold lower than that for normal.…”