Changes of telomerase and telomere lengths in paired normal and cancer tissues of breast

Diagnostic performance of peripheral leukocyte telomere G-tail length for detecting breast cancer

The telomere G‐tail (G‐tail) plays an essential role in maintaining chromosome stability. In this study, we assessed the leukocyte G‐tail length of breast cancer (BC) patients and cancer‐free individuals and evaluated the association between the G‐tail length and the presence of BC. A significant shortening of the median G‐tail length was observed in BC patients compared with cancer‐free individuals and was found in the early phase of BC. Our study indicated that the leukocyte G‐tail length might be a potential biomarker for BC detection.

Fundamental mechanisms of telomerase action in yeasts and mammals: understanding telomeres and telomerase in cancer cells

Aberrant activation of telomerase occurs in 85–90% of all cancers and underpins the ability of cancer cells to bypass their proliferative limit, rendering them immortal. The activity of telomerase is tightly controlled at multiple levels, from transcriptional regulation of the telomerase components to holoenzyme biogenesis and recruitment to the telomere, and finally activation and processivity. However, studies using cancer cell lines and other model systems have begun to reveal features of telomeres and telomerase that are unique to cancer. This review summarizes our current knowledge on the mechanisms of telomerase recruitment and activation using insights from studies in mammals and budding and fission yeasts. Finally, we discuss the differences in telomere homeostasis between normal cells and cancer cells, which may provide a foundation for telomere/telomerase targeted cancer treatments.

Cross-Platform Cancer Cell Identification Using Telomerase-Specific Spherical Nucleic Acids

Distinguishing tumor cells from normal cells holds the key to precision diagnosis and effective intervention of cancers. The fundamental difficulties, however, are the heterogeneity of tumor cells and the lack of truly specific and ideally universal cancer biomarkers. Here, we report a concept of tumor cell detection, bypassing the specific genotypic and phenotypic features of different tumor cell types and directly going toward the hallmark of cancer, uncontrollable growth. Combining spherical nucleic acids (SNAs) with exquisitely engineered molecular beacons (SNA beacons, dubbed SNAB technology) is capable of identifying tumor cells from normal cells based on the molecular phenotype of telomerase activity, largely bypassing the heterogeneity problem of cancers. Owing to the cell-entry capability of SNAs, the SNAB probe readily achieves tumor cell detection across multiple platforms, ranging from solution-based assay, to single cell imaging and in vivo solid tumor imaging (unlike PCR that is restricted to cell lysates). We envision the SNAB technology will impact cancer diagnosis, therapeutic response assessment, and image-guided surgery.

Changes in telomerase activity due to alternative splicing of human telomerase reverse transcriptase in colorectal cancer

Human telomerase reverse transcriptase (hTERT) expression level may not always correlate with telomerase activity. The present study analyzed hTERT splicing patterns with respect to hTERT and telomerase activity in colorectal cancer. Telomerase activity was determined by telomeric repeat amplification protocol assay, and spliced variants of hTERT were identified by reverse transcription-polymerase chain reaction in 40 colorectal cancer tissue samples. In the lower range of telomerase activity (0-100 units), the percentage of the β variant decreased with the increment in telomerase activity, whereas in the higher range of telomerase activity (>100 units), total hTERT expression level revealed a trend toward increment. There was a positive correlation between the full-length variant level and β variant level. Conversely, there was a negative correlation between the percentage of the full-length variant and β variant. Tumor-node-metastasis stage was the strongest prognostic factor in multivariate analysis and the percentage of the full-length variant was an independent prognostic factor for survival. Telomerase activity was primarily altered with changes in alternative splicing of the full-length and β variants of hTERT in colorectal cancer.

Comparison of telomere length and insulin-like growth factor-binding protein 7 promoter methylation between breast cancer tissues and adjacent normal tissues in Turkish women

BACKGROUND

Both insulin-like growth factor-binding protein 7 (IGFBP7) and telomere length (TL) are associated with proliferation and senescence of human breast cancer. This study assessed the clinical significance of both TL and IGFBP7 methylation status in breast cancer tissues compared with adjacent normal tissues. We also investigated whether IGFBP7 methylation status could be affecting TL.

METHODS

Telomere length was measured by quantitative PCR to compare tumors with their adjacent normal tissues. The IGFBP7 promoter methylation status was evaluated by methylation-specific PCR and its expression levels were determined by western blotting.

RESULTS

Telomeres were shorter in tumor tissues compared to controls (P<.0001). The mean TL was higher in breast cancer with invasive ductal carcinoma (IDC; n=72; P=.014) compared with other histological type (n=29), and TL in IDC with HER2 negative (n=53; P=.017) was higher than TL in IDC with HER2 positive (n=19). However, telomeres were shortened in advanced stages and growing tumors. IGFBP7 methylation was observed in 90% of tumor tissues and 59% of controls (P=.0002). Its frequency was significantly higher in IDC compared with invasive mixed carcinoma (IMC; P=.002) and it was not correlated either with protein expression or the other clinicopathological parameters.

CONCLUSION

These results suggest that IGFBP7 promoter methylation and shorter TL in tumor compared with adjacent tissues may be predictive biomarkers for breast cancer. Telomere maintenance may be indicative of IDC and IDC with HER2 (-) of breast cancer. Further studies with larger number of cases are necessary to verify this association.

Aberrant reduction of telomere repetitive sequences in plasma cell-free DNA for early breast cancer detection

Excessive telomere shortening is observed in breast cancer lesions when compared to adjacent non-cancerous tissues, suggesting that telomere length may represent a key biomarker for early cancer detection. Because tumor-derived, cell-free DNA (cfDNA) is often released from cancer cells and circulates in the bloodstream, we hypothesized that breast cancer development is associated with changes in the amount of telomeric cfDNA that can be detected in the plasma. To test this hypothesis, we devised a novel, highly sensitive and specific quantitative PCR (qPCR) assay, termed telomeric cfDNA qPCR, to quantify plasma telomeric cfDNA levels. Indeed, the internal reference primers of our design correctly reflected input cfDNA amount (R² = 0.910, P = 7.82 × 10⁻⁵²), implying accuracy of this assay. We found that plasma telomeric cfDNA levels decreased with age in healthy individuals (n = 42, R² = 0.094, P = 0.048), suggesting that cfDNA is likely derived from somatic cells in which telomere length shortens with increasing age. Our results also showed a significant decrease in telomeric cfDNA level from breast cancer patients with no prior treatment (n = 47), compared to control individuals (n = 42) (P = 4.06 × 10⁻⁸). The sensitivity and specificity for the telomeric cfDNA qPCR assay was 91.49% and 76.19%, respectively. Furthermore, the telomeric cfDNA level distinguished even the Ductal Carcinoma In Situ (DCIS) group (n = 7) from the healthy group (n = 42) (P = 1.51 × 10⁻³). Taken together, decreasing plasma telomeric cfDNA levels could be an informative genetic biomarker for early breast cancer detection.

Telomere length and telomerase activity in non-small cell lung cancer prognosis: clinical usefulness of a specific telomere status

Background

Considering previous data and the need to incorporate new biomarkers for the prognosis of solid tumours into the clinic, our aim in this work consists of evaluating the potential clinical use of telomeres and telomerase in non-small cell lung cancer (NSCLC).

Methods

Telomere status was established by determination of telomere length using the Terminal Restriction Fragment length method, and telomerase activity by the Telomeric Repeat Amplification Protocol in 142 NSCLCs and their corresponding control samples, obtained from patients submitted to surgery. Group-oriented curves for disease-free survival were calculated according to the Kaplan-Meier method considering telomere length, T/N ratio (telomere length in tumour to control tissue) and telomerase activity.

Results

Overall, tumours had significantly shorter telomeres compared with telomeres in control tissues (P = 0.027). More than 80 % of NSCLCs displayed telomerase activity. Regarding prognosis studies, patients whose tumours showed a mean telomere length (MTL) <7.29 Kb or T/N ratio <0.97 showed a significantly poor clinical evolution (P = 0.034 and P = 0.040, respectively). As result of a Cox multivariate analysis including pathologic state and lymph node dissemination, the MTL and T/N ratio emerged as independent significant prognostic factors.

Conclusions

Telomerase activity was identified as a marker of poor prognosis. The novel finding of this study is the independent prognosis role of a specific telomere status in NSCLC patients. According to our results, telomere function may emerge as a useful molecular tool that allow to select groups of NSCLC patients with different clinical evolution, in order to establish personalized therapy protocols.

Inhibition of telomerase activity by NME2: impact on metastasis suppression?

Though anti-metastatic function of non-metastatic 2 (NME2) has been implicated in multiple cancers, mechanisms of metastases control by NME2 are not clearly understood. Recent observations indicating the involvement of telomerase, the ribonucleoprotein required for telomere synthesis, in metastatic outcome are interesting. Notably, though the role of telomerase dysfunction in tumorigenesis is relatively well studied, involvement in metastasis progression is poorly understood. Recent findings demonstrate NME2 presence at telomere ends, association with telomerase, and NME2’s role in inhibition of telomerase activity in cancer cells. These present a novel opportunity to investigate mechanisms underlying NME2-mediated metastasis suppression.

The potential utility of telomere-related markers for cancer diagnosis

The role telomeres and telomerase play in the initiation and progression of human cancers has been extensively evaluated. Telomeres are nucleoprotein complexes comprising the hexanucleotide DNA repeat sequence, TTAGGG and numerous telomere-associated proteins, including the six member Shelterin complex. The main function of the telomere is to stabilize the ends of the chromosomes. However, through multiple mechanisms, telomeres can become dysfunctional, which may drive genomic instability leading to the development of cancer. The majority of human cancers maintain, or actively lengthen, telomeres through up-regulation of the reverse transcriptase telomerase. Because there are significant differences in telomere length and telomerase activity between malignant and non-malignant tissues, many investigations have assessed the potential to utilize these molecular markers for cancer diagnosis. Here, we critically evaluate whether measurements of telomere lengths and telomerase levels may be clinically utilized as diagnostic markers in solid tumours, with emphasis on breast and prostate cancer as representative examples. Future directions focusing on the direct detection of dysfunctional telomeres are explored. New markers for telomere dysfunction may eventually prove clinically useful.

Short telomere length and breast cancer risk: a study in sister sets

Telomeres consist of a tandem repeats of the sequence TTAGGG at the ends of chromosomes and play a key role in the maintenance of chromosomal stability. Previous studies indicated that short telomeres are associated with increased risk for human bladder, head and neck, lung, and renal cell cancer. We investigated the association between white blood cell telomere length and breast cancer risk among 268 family sets (287 breast cancer cases and 350 sister controls). Telomere length was assessed by quantitative PCR. The mean telomere length was shorter in cases (mean, 0.70; range, 0.03-1.95) than in unaffected control sisters (mean, 0.74; range, 0.03-2.29), but no significant difference was observed (P = 0.11). When subjects were categorized according to the median telomere length in controls (0.70), affected sisters had shorter telomeres compared with unaffected sisters after adjusting for age at blood donation and smoking status [odds ratio (OR), 1.3; 95% confidence interval (95% CI), 0.9-1.8], but the association was not statistically significant. The association by quartile of telomere length (Q4 shortest versus Q1 longest) also supported an increase in risk from shorter telomere length, although the association was not statistically significant (OR, 1.6; 95% CI, 0.9-2.7). This association was more pronounced among premenopausal women (OR, 2.1; 95% CI, 0.8-5.5) than postmenopausal women (OR, 1.3; 95% CI, 0.5-3.6 for Q4 versus Q1). If these associations are replicated in larger studies, they provide modest epidemiologic evidence that shortened telomere length may be associated with breast cancer risk.

Telomere shortening occurs early during breast tumorigenesis: a cause of chromosome destabilization underlying malignant transformation?

Chromosomal instability appears early during breast carcinogenesis and is considered a major driving force in malignant transformation. While current evidence suggests that centrosomal and mitotic checkpoint defects may, in large part, account for numerical chromosomal abnormalities, the mechanisms underlying structural chromosomal abnormalities remain largely unknown. Telomeres stabilize and protect chromosomal termini, but shorten due to cell division and oxidative damage. Moderate telomere shortening signals a tumor suppressive growth arrest in normal cells. Critically short telomeres, in the setting of abrogated DNA damage checkpoints, cause chromosomal instability due to end-to-end chromosomal fusions, subsequent breakage, and rearrangement, resulting in an increased cancer incidence in animal models. Recent results from high resolution in situ telomere length assessment in human breast tissues indicate that significant telomere shortening is prevalent in preinvasive breast lesions (DCIS), as well as focal areas of histologically normal epithelium from which breast carcinoma is thought to arise. Telomere shortening is therefore a strong candidate for the cause of structural chromosome defects that contribute to breast cancer development.

Telomere shortening occurs in subsets of normal breast epithelium as well as in situ and invasive carcinoma

In the setting of inactivated DNA damage-sensitive checkpoints, critically shortened telomeres promote chromosomal instability and the types of widespread cytogenetic alterations that characterize most human carcinomas. Using a direct telomere fluorescence in situ hybridization technique, we analyzed 114 invasive breast carcinomas, 29 carcinoma in situ lesions, 10 benign proliferative lesions, and different normal epithelial components of the male and female breast. We found marked telomere shortening in the majority (52.5%) of invasive carcinomas; smaller subsets of invasive carcinoma demonstrated moderate telomere shortening (17.5%) or normal telomere lengths (21%), while a small subgroup (5%) contained elongated telomeres. Strikingly, the majority (78%) of ductal carcinoma in situ demonstrated markedly or moderately shortened telomeres. Surprisingly, unlike all other normal epithelia studied to date, moderate telomere shortening was observed in benign secretory cells in approximately 50% of histologically-normal terminal duct lobular units (from which most breast cancer is thought to arise), while such shortening was not seen in myoepithelial cells or normal large lactiferous ducts of the female breast or male breast ducts (from which breast cancer infrequently arises). We postulate that such shortening is the result of hormonally driven, physiological proliferation, and may delineate a population of epithelial cells at risk for subsequent malignant transformation.

Telomerase activity and genetic alterations in primary breast carcinomas

It has been proposed that the structural and numerical chromosome abnormalities recorded in breast cancer could be the result of telomere dysfunction and that telomerase is activated de novo to provide a survival mechanism curtailing further chromosomal aberrations. However, recent in vivo and in vitro data show that the ectopic expression of telomerase promotes tumorigenesis via a telomere length-independent mechanism. In this study, the relation between telomerase expression and the extent of chromosomal aberrations was investigated in 62 primary breast carcinomas. Telomerase activity was measured using a polymerase chain reaction-based telomeric repeat amplification protocol assay and 92% of the tumors were found to express telomerase with a relative activity ranging from 0 to 3839.6. Genetic alterations were determined by G-banding and comparative genomic hybridization analysis and 97% of the tumors exhibited chromosomal aberrations ranging from 0 to 44 (average: 10.98). In the overall series, the relationship between telomerase activity levels and genetic changes could be best described by a quadratic model, whereas in tumors with below-average genetic alteration numbers, a significant positive association was recorded between the two variables (coefficient=0.374, P=.017). The relationship between telomerase activity levels and the extent of genetic alteration may reflect the complex effect of telomerase activation upon tumor progression in breast carcinomas.

Gene expression for suppressors of telomerase activity (telomeric-repeat binding factors) in breast cancer

Mechanisms regulating telomerase activity and telomere length remain incompletely understood in human breast cancer. We therefore studied gene expression for telomeric-repeat binding factors (TRFs) in relation to telomerase activity, telomere length, and clinicopathologic factors in human breast cancer. Telomerase activity was detected in 65.8% of 38 breast cancers, but none of 16 noncancerous samples. Terminal restriction fragments were longer in noncancerous than in cancerous tissues, but not significantly. Among 8 patients with both cancer and paired noncancerous tissue available for terminal restriction fragments length assay, terminal restriction fragments were shorter in cancers than in paired noncancerous samples in all but one. Significantly more mRNA encoding TRF1 and 2 was detected in noncancerous than in cancer tissues. Additionally, expression of TRF1 and 2 mRNA was significantly higher in cancers without detectable telomerase activity than in cancers showing activity. Expression of these genes tended to show a negative correlation with terminal restriction fragments length, but this was not statistically significant. No correlation was seen between TRF1 or 2 mRNA expression, and clinicopathologic factors except for TRF1 with respect to tumor size and progesterone receptor status. In addition to reactivation of telomerase activity, escape from negative regulation of this activity is needed to maintain telomere length during cell proliferation in breast cancer. Genes encoding telomerase inhibitors might be of value in gene therapy against human breast cancer.