Tissue invasion and metastasis: Molecular, biological and clinical perspectives.

Cancer is a key health issue across the world, causing substantial patient morbidity and mortality. Patient prognosis is tightly linked with metastatic dissemination of the disease to distant sites, with metastatic diseases accounting for a vast percentage of cancer patient mortality. While advances in this area have been made, the process of cancer metastasis and the factors governing cancer spread and establishment at secondary locations is still poorly understood. The current article summarizes recent progress in this area of research, both in the understanding of the underlying biological processes and in the therapeutic strategies for the management of metastasis. This review lists the disruption of E-cadherin and tight junctions, key signaling pathways, including urokinase type plasminogen activator (uPA), phosphatidylinositol 3-kinase/v-akt murine thymoma viral oncogene (PI3K/AKT), focal adhesion kinase (FAK), ß-catenin/zinc finger E-box binding homeobox 1 (ZEB-1) and transforming growth factor beta (TGF-ß), together with inactivation of activator protein-1 (AP-1) and suppression of matrix metalloproteinase-9 (MMP-9) activity as key targets and the use of phytochemicals, or natural products, such as those from Agaricus blazei, Albatrellus confluens, Cordyceps militaris, Ganoderma lucidum, Poria cocos and Silybum marianum, together with diet derived fatty acids gamma linolenic acid (GLA) and eicosapentanoic acid (EPA) and inhibitory compounds as useful approaches to target tissue invasion and metastasis as well as other hallmark areas of cancer. Together, these strategies could represent new, inexpensive, low toxicity strategies to aid in the management of cancer metastasis as well as having holistic effects against other cancer hallmarks.

Progeroid syndromes: models for stem cell aging?

Stem cells are responsible for tissue repair and maintenance and it is assumed that changes observed in the stem cell compartment with age underlie the concomitant decline in tissue function. Studies in murine models have highlighted the importance of intrinsic changes occurring in stem cells with age. They have also drawn the attention to other factors, such as changes in the local or systemic environment as the primary cause of stem cell dysfunction. Whilst knowledge in murine models has been advancing rapidly there has been little translation of these data to human aging. This is most likely due to the difficulties of testing the regenerative capacity of human stem cells in vivo and to substantial differences in the aging phenotype within humans. Here we summarize evidence to show how progeroid syndromes, integrated with other models, can be valuable tools in addressing questions about the role of stem cell aging in human degenerative diseases of older age and the molecular pathways involved.

A systems biology approach to Down syndrome: identification of Notch/Wnt dysregulation in a model of stem cells aging.

Stem cells are central to the development and maintenance of many tissues. This is due to their capacity for extensive proliferation and differentiation into effector cells. More recently it has been shown that the proliferative and differentiative ability of stem cells decreases with age, suggesting that this may play a role in tissue aging. Down syndrome (DS), is associated with many of the signs of premature tissue aging including T-cell deficiency, increased incidence of early Alzheimer-type, Myelodysplastic-type disease and leukaemia. Previously we have shown that both hematopoietic (HSC) and neural stem cells (NSC) in patients affected by DS showed signs of accelerated aging. In this study we tested the hypothesis that changes in gene expression in HSC and NSC of patients affected by DS reflect changes occurring in stem cells with age. The profiles of genes expressed in HSC and NSC from DS patients highlight pathways associated with cellular aging including a downregulation of DNA repair genes and increases in proapoptotic genes, s-phase cell cycle genes, inflammation and angiogenesis genes. Interestingly, Notch signaling was identified as a potential hub, which when deregulated may drive stem cell aging. These data suggests that DS is a valuable model to study early events in stem cell aging.

High level of telomerase RNA gene expression is associated with chromatin modification, the ALT phenotype and poor prognosis in liposarcoma.

Telomere length is maintained by two known mechanisms, activation of telomerase or alternative lengthening of telomeres (ALT). The ALT pathway is more commonly activated in tumours of mesenchymal origin, although the mechanisms involved in the decision of a cell to activate either telomerase or ALT are unknown at present and no molecular markers exist to define the ALT phenotype. We have previously shown an association between chromatin remodelling, telomerase gene expression and ALT in cell line models. Here, we evaluate these findings and investigate their prognostic significance in a panel of liposarcoma tissue samples to understand the biology underlying the ALT phenotype. Liposarcoma samples were split into three groups: telomerase positive (Tel+); ALT positive; ALT-/Tel-. Differences in telomerase gene expression were evident between the groups with increased expression of hTR in ALT and Tel+ compared to ALT-/Tel- samples and increased hTERT in Tel+ samples only. Investigation of a small panel of chromatin modifications revealed significantly increased binding of acetyl H3 in association with hTR expression. We confirm that the presence of the ALT phenotype is associated with poor prognosis and in addition, for the first time, we show a direct association between hTR expression and poor prognosis in liposarcoma patients.

Telomerase redefined: integrated regulation of hTR and hTERT for telomere maintenance and telomerase activity.

Telomerase activity is dependent on the expression of 2 main core component genes, hTERT, which encodes the catalytic component and hTR (also called TERC), which encodes the RNA component. The correlation between telomerase activity and carcinogenesis has made this molecule of great interest in cancer research, however in order to fully understand the regulation of telomerase the mechanisms controlling both telomerase genes need to be studied. Some of these mechanisms of regulation have begun to emerge, however many more remain to be deciphered. For many years hTERT has been regarded as the limiting component of telomerase and much of the research in this field has focussed on its regulation, however it was clear from an early stage that hTR expression was also tightly regulated in normal cells and disease. More recently evidence from biochemistry, promoter studies and mouse models has been steadily increasing for a role for hTR as a limiting and essential component for telomerase activity and telomere maintenance. Perhaps the time has come to redefine our view of telomerase regulation. Knowledge of the mechanisms controlling both telomerase genes in normal systems and cancer may aid our understanding of the role of telomerase in carcinogenesis or highlight potential areas for therapeutic intervention. Here we review the essential requirement of hTR for telomere maintenance and telomerase activity in normal tissues and disease and focus on recent advances in our understanding of hTR regulation in relation to hTERT.

Hypoxic regulation of telomerase gene expression by transcriptional and post-transcriptional mechanisms.

Basal telomerase activity is dependent on expression of the hTERT and hTR genes and upregulation of telomerase gene expression is associated with tumour development. It is therefore possible that signal transduction pathways involved in tumour development and features of the tumour environment itself may influence telomerase gene regulation. The majority of solid tumours contain regions of hypoxia and it has recently been demonstrated that hypoxia can increase telomerase activity by mechanisms that are still poorly defined. Here, we show that hypoxia induces the transcriptional activity of both hTR and hTERT gene promoters. While endogenous hTR expression is regulated at the transcriptional level, hTERT is subject to regulation by alternative splicing under hypoxic conditions, which involves a switch in the splice pattern in favour of the active variant. Furthermore, analysis of the chromatin landscape of the telomerase promoters reveals dynamic recruitment of a transcriptional complex involving the hypoxia-inducible factor-1 transcription factor, p300, RNA polymerase II and TFIIB, to both promoters during hypoxia, which traffics along and remains associated with the hTERT gene as transcription proceeds. These studies show that hTERT and hTR are subject to similar controls under hypoxia and highlight the rapid and dynamic regulation of the telomerase genes in vivo.

Dysregulated expression of the major telomerase components in leukaemic stem cells.

Telomere loss is rapid during the progression of chronic myeloid leukaemia (CML) and correlates with prognosis. We therefore sought to measure expression of the major telomerase components (hTR and hTERT) in CD34+ cells from CML patients and normal controls, to determine if their altered expression may contribute to telomere attrition in vivo. High-purity (median 94.1%) BCR-ABL+ CD34+ cells from CML (n=16) and non-CML (n=14) patients were used. CML samples had a small increase in telomerase activity (TA) compared to normal samples (approximately 1.5-fold, P=0.004), which was inversely correlated with the percentage of G0 cells (P=0.02) suggesting TA may not be elevated on a cell-to-cell basis in CML. Consistent with this, hTERT mRNA expression was not significantly elevated; however, altered mRNA splicing appeared to play a significant role in determining overall full length, functional hTERT levels. Interestingly, Q-RT-PCR for hTR demonstrated a mean five-fold reduction in levels in the chronic phase (CP) CML samples (P=0.002), raising the possibility that telomere homeostasis is disrupted in CML. In summary, the molecular events regulating telomerase gene expression and telomere maintenance during the CP of CML may influence the disease progression observed in these patients.

Characterization of extensive genetic alterations in ductal carcinoma in situ by fluorescence in situ hybridization and molecular analysis.

BACKGROUND: The molecular genetic analysis of invasive breast cancer has identified breast cancer as a genetically complex disease. Ductal carcinoma in situ (DCIS) is thought to represent a preinvasive step in breast cancer progression, yet we know little about its biologic behavior or the genetic alterations present. Because of the increasing diagnosis of DCIS by mammography screening and the debate over how DCIS should be managed, there is a clear need to define the molecular events underlying the development of DCIS. PURPOSE: Our purpose was to identify patterns of genetic alterations in DCIS. METHODS: A group of 30 formalin-fixed, paraffin-embedded blocks of tissue collected from 1987 through 1989 from 21 patients with DCIS was studied. Chromosomal imbalances were determined by interphase cytogenetic analysis using the fluorescence in situ hybridization (FISH) technique. DNA probes were used that recognize chromosome-specific repetitive sequence loci at the centromeres of chromosomes 1, 3, 4, 6, 7, 8, 9, 10, 11, 16, 17, and 18. FISH was also used to detect ERBB2 gene amplification in DCIS. To complement the FISH studies, microsatellite analysis of markers near the BRCA1 region of chromosome 17 was done on tissue microdissected from multiple areas of DCIS. Chromosomal imbalances were determined by comparisons of chromosomal indices (total number of hybridization spots per total number of nuclei counted) of normal and DCIS tissue, using the two-sided Mann-Whitney test. RESULTS: Using FISH, we have identified patterns of DNA loss and gain of certain chromosome-specific centromeric markers in DCIS. We observed frequent gains of markers on chromosomes 3, 10, and 17 as well as loss of chromosome 18-specific centromeric sequences. ERBB2 gene amplification was detected in tumors from four of 15 patients studied and was clearly limited to the tumor cells within the ducts. Because of the availability of topologically distinct regions of tumors from individuals, we were able to show that paired tumor specimens from individuals share genetic alterations and also have unique ones, suggesting clonal diversity within tumors. The combination of FISH and microsatellite analyses suggested that alterations in chromosome 17 may be quite complex; three of five patients whose samples were analyzed had allelic imbalance at markers on the long arm of chromosome 17. CONCLUSIONS: FISH and microsatellite analyses are useful in detecting extensive genetic alterations in DCIS. Examinations of DCIS tissue using these techniques have identified chromosomes 1, 3, 10, 16, 17, and 18 as candidate sites worthy of immediate study. IMPLICATIONS: This approach may give direction to future research aimed at precisely mapping loci altered in DCIS and help in understanding the biologic events associated with tumor progression or recurrence.

Response of mouse skin tumors to doxorubicin is dependent on carcinogen exposure.

To investigate the role of carcinogenesis in determining the response of tumors to anticancer drugs, we have used the in vivo model of multistage carcinogenesis of the mouse skin. Mice were initiated with Harvey murine sarcoma virus or single and repeated applications of dimethylbenzanthracene (DMBA). The papillomas which developed as a result of these initiation protocols were monitored quantitatively for their response to the anticancer drug doxorubicin. A single dose of 10 mg/kg doxorubicin is relatively inefficient at reducing the frequency of papillomas arising as a result of either single or repeated applications of the chemical DMBA. However, virally initiated papillomas are sensitive to the single 10-mg/kg dose of doxorubicin and are reduced in frequency by greater than 80%. Repeat treatment with four doses of 5 mg/kg doxorubicin over a 4-week period also reveals differences in the responses of the papillomas to doxorubicin. As with the single dose of doxorubicin, papillomas initiated with multiple applications of DMBA showed only a limited response to four 5-mg/kg doses of doxorubicin. In comparison both the virally initiated and the single DMBA initiated papillomas responded to the four doses of doxorubicin and are reduced in frequency by about 80%. These data show that the response of papillomas to doxorubicin is related to the initiating event. Papillomas derived by viral initiation are most sensitive to doxorubicin while increasing the level of exposure to the chemical carcinogen DMBA increases the proportion of papillomas which do not respond to treatment with doxorubicin. There was no obvious relationship between the method of initiation or the treatment of the mice with doxorubicin and the levels of P-glycoprotein expression observed in the papillomas. All the papillomas expressed detectable levels of P-glycoprotein approaching that of the multidrug resistant cell line, CHRC5.

Quantitative and qualitative aspects of topoisomerase I and II alpha and beta in untreated and platinum/cyclophosphamide treated malignant ovarian tumors.

Quantitative and qualitative aspects of topoisomerase (Topo) I and II were studied in 17 malignant ovarian tumors [eight untreated and nine after platinum/cyclophosphamide (Pt/Cy) chemotherapy]. Median Topo II catalytic activity was lower (P < 0.05) in tumors after Pt/Cy chemotherapy in comparison to untreated tumors, while no differences were found for Topo I catalytic activity in tumors before and after chemotherapy, as was also found in a previous study (Van der Zee et al. Cancer Res., 51: 5915-5920, 1991). Teniposide (VM-26)-induced cleavable complex formation correlated (r = 0.60; P < 0.05) with Topo II activity, while Topo II decatenation activity was equally but incompletely inhibited by VM-26 in all tumors. No differences were found in Topo II cleavage site patterns in plasmid BR322 DNA for all tumors using an indirect end-labeling procedure. Cleavable complex formation of Topo I by camptothecin (Cpt) did not correlate with Topo I catalytic activity, while Topo I catalytic activity could equally and completely be inhibited by Cpt. By Western blotting, Topo II alpha protein expression was detected in four of eight untreated tumors and three of nine tumors after Pt/Cy chemotherapy, whereas in all tumors a M(r) 150,000 degradation product of Topo II beta was detected. Topo I protein was detected in all tumors at varying levels, but the protein levels did not correlate with Topo I catalytic activity or cleavable complex formation by Cpt. Our study shows that Topo I and II, isolated from human malignant tumors, can be stimulated by Cpt and VM-26, respectively, to induce DNA cleavage, which suggests that topoisomerases are real targets for chemotherapy in patients with ovarian cancer. From in vitro data from the literature it appears that the cleavable complex assay reflects both quantitative and qualitative changes as well as changes in the phosphorylation state of Topo I and II. In combination with the feasibility of the cleavable complex assay for Topo I and II in human malignant tumors, which was found in the present study, it appears that at present the determination of cleavable complex formation by tumors seems to be the most promising parameter of Topo I or II expression in human tumors to be related to response to Topo I- or II-targeted chemotherapy.

Lack of telomerase RNA gene hTERC expression in alternative lengthening of telomeres cells is associated with methylation of the hTERC promoter.

The immortal phenotype of most human cancers is attributable to telomerase expression. However, a number of immortal cell lines and tumors achieve telomere maintenance in the absence of telomerase via alternative mechanisms known as ALT (alternative lengthening of telomeres). Here we show that the promoter of the telomerase RNA gene (hTERC) is methylated in three of five ALT cell lines and is associated with a total absence of hTERC expression in the three lines. Treatment with 5-azacytidine in combination with trichostatin A resulted in partial demethylation of the hTERC promoter and expression of the gene. Partial methylation was detected in tumors (5%) and in immortal cell lines (27%). Cell lines with partial methylation express hTERC. Only in ALT cell lines does there appear to be a strong correlation between hTERC promoter hypermethylation and lack of hTERC expression.

Quantitative estimation of epidermal growth factor receptor and c-erbB-2 in human breast cancer.

Epidermal growth factor receptor (EGFR) expression by human breast cancer has been shown to predict poor patient outcome, as has amplification of the c-erbB-2 proto-oncogene. We have developed a quantitative immunohistochemical method for measuring protein levels of both receptors and have applied this to a series of 123 breast primaries. We find EGFR expression is substantially lower than normal in nearly all breast cancers (97%). Quantification of p185erbB-2 indicates overexpression in 91% of the tumors. Two separate tumor populations are apparent with levels of c-erbB-2 expression ranging from 0.33 to 19 and 45 to 480 times normal, respectively. Within the lower population, p185erbB-2 expression is inversely related to EGFR expression (rank correlation, P < 0.0005). Using fluorescent in situ hybridization we show that tumors in the latter population have c-erbB-2 amplification and that amplification is restricted to this group. Our findings indicate that significant overexpression of p185erbB-2 occurs in the absence of amplification; these lower levels of expression may have functional significance. Fifty-three patients underwent in vivo bromodeoxyuridine labeling, allowing flow cytometric analysis of tumor cell cycle kinetics. EGFR expression correlates directly to the labeling index (P = 0.011) and indirectly to potential doubling time (P = 0.010), but not to the duration of the S-phase (P = 0.502). Conversely, p185erbB-2 expression does not relate to indices of proliferation. Our results have important implications for the use of both receptor types as therapeutic targets.

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

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-specific 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 confined 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 significant differences 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. Differentiated tissues within ovarian germ cell tumours and in testicular teratomas lacked detectable hTR expression. These studies show that different 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.

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

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 amplified 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 amplification. These results are the first report of genetic alterations involving a known component of telomerase in human cancer. Indeed, it is also the first report of the amplification of a specific locus within the chromosome 3q region frequently subject to copy number gains in human tumours. In addition, we also show for the first time the histological distribution of the RNA component of telomerase in human tumours.

Telomerase-specific suicide gene therapy vectors expressing bacterial nitroreductase sensitize human cancer cells to the pro-drug CB1954.

Telomerase activation is considered to be a critical step in cancer progression due to its role in cellular immortalization. The prevalence of telomerase expression in human cancers makes it an attractive candidate for new mechanism-based targets for cancer therapy. The selective killing of cancer cells can be achieved by gene-directed enzyme pro-drug therapy (GDEPT). In this study we have tested the feasibility of using the transcriptional regulatory sequences from the hTERT and hTR genes to regulate expression of the bacterial nitroreductase enzyme in combination with the pro-drug CB1954 in a suicide gene therapy strategy. hTERT and hTR promoter activity was compared in a panel of 10 cell lines and showed a wide distribution in activity; low activity was observed in normal cells and telomerase-negative immortal ALT cell lines, with up to 300-fold higher activity observed in telomerase positive cancer lines. Placing the nitroreductase gene under the control of the telomerase gene promoters sensitized cancer cells in tissue culture to the pro-drug CB1954 and promoter activity was predictive of sensitization to the pro-drug (2-20-fold sensitization), with cell death restricted to lines exhibiting high levels of promoter activity. The in vivo relevance of these data was tested using two xenograft models (C33a and GLC4 cells). Significant tumour reduction was seen with both telomerase promoters and the promoter-specific patterns of sensitization observed in tissue culture were retained in xenograft models. Thus, telomerase-specific suicide gene therapy vectors expressing bacterial nitroreductase sensitize human cancer cells to the pro-drug CB1954.

Expression in UVW glioma cells of the noradrenaline transporter gene, driven by the telomerase RNA promoter, induces active uptake of [131I]MIBG and clonogenic cell kill.

One of the most effective ways to kill cancer cells is by treatment of tumours with radiation. However, the administered dose of radiation to the tumour is limited by normal tissue toxicity. Strategies which decrease normal tissue exposure relative to tumour dose are urgently sought. One such promising scheme involves gene transfer, leading to the introduction of transporters specific for pharmaceuticals which can be labelled with radionuclides. We have previously demonstrated in vitro, that transfer of the noradrenaline transporter (NAT) gene, under viral promoter control, induces in host cells the active accumulation of the radiopharmaceutical [131I]meta-iodobenzylguanidine ([131I]MIBG) which results in kill of clonogens. We now report 17-fold enhancement of [131I]MIBG uptake by UVW glioma cells transfected with the NAT gene whose expression is driven by the human telomerase RNA (hTR) promoter (70% the uptake achieved by the strong viral promoter). Multicellular spheroids composed of hTR-NAT-transfected UVW cells exhibited dose-dependent susceptibility to treatment with [131I]MIBG. This was demonstrated by decreased survival of clonogens and complete sterilization of clonogens derived from spheroids and also failure of spheroids to regrow after administration of 7 MBq/ml [131I]MIBG. These data suggest hTR regulated expression of NAT may be an effective gene therapy strategy.

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

Variation in telomerase activity is correlated with cellular senescence and tumour progression. However, although the enzymatic activity of telomerase has been well studied, very little is known about how expression of telomerase genes is regulated in mammalian cells. We have therefore cloned the promoter regions of the human (hTR), and mouse, (terc), telomerase RNA genes in order to identify the regulatory elements controlling telomerase RNA gene transcription. 1.76 kb encompassing the hTR gene promoter region was sequenced, as was 4 kb encompassing the terc promoter. No significant sequence similarity could be detected in comparisons between human and mouse 5'-regions, flanking the transcribed sequences. However, both the human and mouse telomerase RNA genes are within CpG islands and may therefore be under the regulation of DNA methylation. Transient expression of hTR-reporter gene constructs in HeLa and GM847 cells identified the elements responsible for promoter activity are contained in a 231 bp region upstream of the transcriptional start site. Transient expression of terc-reporter gene constructs in Swiss3T3 and A9 cells identified the elements responsible for promoter activity are contained in a 73 bp region upstream of the transcriptional start site. These studies have implications for novel transcription targeted cancer therapies.

Increased dosage and amplification of the focal adhesion kinase gene in human cancer cells.

Focal adhesion kinase (pp125FAK) is present at sites of cell/extracellular matrix adhesion and has been implicated in the control of cell behaviour. In particular, as a key component of integrin-stimulated signal transduction pathways, pp125FAK is involved in cellular processes such as spreading, motility, growth and survival. In addition, a number of reports have indicated that pp125FAK may be up-regulated in human tumour cells of diverse origin, and consequently, a role has been proposed for pp125FAK in the development of invasive cancers. However, to date the mechanisms that lead to elevated pp125FAK expression in tumour cells have not been determined. Here we used in situ hybridization to confirm chromosome 8q as the genomic location of the human fak gene and report that elevation of pp125FAK protein in cell lines derived from invasive squamous cell carcinomas is accompanied by gains in copy number of the fak gene in all cases examined. In addition, we observed increased fak copy number in frozen sections of squamous cell carcinomas. Furthermore, increased dosage of the fak gene was also observed in many cell lines derived from human tumours of lung, breast and colon, including two cell lines Calu3 and HT29, in which fak was amplified. In addition, in an in vitro model for human colon cancer progression there was a copy number gain of the fak gene during conversion from adenoma to carcinoma, which was associated with increased pp125FAK protein expression. Thus, we show for the first time that many cell lines derived from invasive epithelial tumours have increased dosage of the fak gene, which may contribute to the elevated protein expression commonly observed. Although other genes near the fak locus are co-amplified or increased in copy number, including the proto-oncogene c-myc, the biological properties of pp125FAK in controlling the growth, survival and invasiveness of tumour cells, suggest that it may contribute to the selection pressure for maintaining increased dosage of the region of chromosome 8q that encodes these genes.

Activation of telomerase rna gene promoter activity by NF-Y, Sp1, and the retinoblastoma protein and repression by Sp3.

Expression of the human telomerase RNA component gene, hTERC is essential for telomerase activity. The hTERC gene is expressed during embryogenesis and then downregulated during normal development, leaving most adult somatic cells devoid of hTERC expression. During oncogenesis, however, hTERC is re-expressed consequently contributing to the unrestricted proliferative capacity of many human cancers. Thus the identification of the molecular basis for the regulation of the telomerase RNA component gene in normal cells and its deregulation in cancer cells is of immediate interest. We have previously cloned the hTERC promoter and in this study have identified several transcription factors that modulate the expression of hTERC. We demonstrate that NF-Y binding to the CCAAT region of the hTERC promoter is essential for promoter activity. Sp1 and the retinoblastoma protein (pRb) are activators of the hTERC promoter and Sp3 is a potent repressor. These factors appear to act in a species-specific manner. Whereas Sp1 and Sp3 act on the human, bovine, and mouse TERC promoters, pRb activates only the human and bovine promoter, and NF-Y is only essential for the human TERC gene.

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 from 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 of which was used as a probe to map hTERT by fluorescence in situ hybridization (FISH) to chromosome 5p15.33. This BAC probe was further used to look at 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 and amplifications have been documented for various tumour types, including non-small cell lung carcinoma, squamous cell carcinoma of head and neck, and uterine cervix cancer, making hTERT a potential target.