Correlations of telomere length, telomerase activity, and telomeric-repeat binding factor 1 expression in colorectal carcinoma

Current and Future Trends of Colorectal Cancer Treatment: Exploring Advances in Immunotherapy

Cancer of the colon and rectum (CRC) has been identified among the three most prevalent types of cancer and cancer-related deaths for both sexes. Even though significant progress in surgical and chemotherapeutic techniques has markedly improved disease-free and overall survival rates in contrast to those three decades ago, recent years have seen a stagnation in these improvements. This underscores the need for new therapies aiming to augment patient outcomes. A number of emerging strategies, such as immune checkpoint inhibitors (ICIs) and adoptive cell therapy (ACT), have exhibited promising outcomes not only in preclinical but also in clinical settings. Additionally, a thorough appreciation of the underlying biology has expanded the scope of research into potential therapeutic interventions. For instance, the pivotal role of altered telomere length in early CRC carcinogenesis, leading to chromosomal instability and telomere dysfunction, presents a promising avenue for future treatments. Thus, this review explores the advancements in CRC immunotherapy and telomere-targeted therapies, examining potential synergies and how these novel treatment modalities intersect to potentially enhance each other's efficacy, paving the way for promising future therapeutic advancements.

GPC1 Is Associated with Poor Prognosis and Treg Infiltration in Colon Adenocarcinoma

Glypican-1 (GPC1) is a glycosylated protein recognized as a promising biomarker for cancer. Nonetheless, there have been few systematic studies on GPC1 in colon adenocarcinoma (COAD). We conducted bioinformatic analysis based on The Cancer Genome Atlas (TCGA) and used clinical samples to verify that GPC1 is overexpressed in colon adenocarcinoma. Kaplan-Meier analysis showed that higher GPC1 expression was associated with poor overall survival (OS). The Cox regression model further showed that GPC1 expression is an independent negative prognostic factor for COAD. Gene set enrichment analysis demonstrated that multiple oncogenic signaling pathways were differentially enriched in GPC1 high- versus low-expressing COAD tumors, including DNA methylation, G2/M damage checkpoint, and telomere dysfunction. We observed a positive correlation between GPC1 expression and immune cell infiltration, such as regulatory T cells (Tregs), macrophages, and mast cells, and immunohistochemistry of 50 COAD tissues revealed that GPC1 expression was positively associated with Treg enrichment. Our results provide a promising candidate gene to predict the prognosis of COAD and new insights into tumor immunity. Further research is required to validate these results.

Relative Telomere Length Change in Colorectal Carcinoma and Its Association with Tumor Characteristics, Gene Expression and Microsatellite Instability

We compared tumor and adjacent normal tissue samples from 165 colorectal carcinoma (CRC) patients to study change in relative telomere length (RTL) and its association with different histological and molecular features. To measure RTL, we used a Luminex-based assay. We observed shorter RTL in the CRC tissue compared to paired normal tissue (RTL 0.722 ± SD 0.277 vs. 0.809 ± SD 0.242, p = 0.00012). This magnitude of RTL shortening (by ~0.08) in tumor tissue is equivalent to RTL shortening seen in human leukocytes over 10 years of aging measured by the same assay. RTL was shorter in cancer tissue, irrespective of age group, gender, tumor pathology, location and microsatellite instability (MSI) status. RTL shortening was more prominent in low-grade CRC and in the presence of microsatellite instability (MSI). In a subset of patients, we also examined differential gene expression of (a) telomere-related genes, (b) genes in selected cancer-related pathways and (c) genes at the genome-wide level in CRC tissues to determine the association between gene expression and RTL changes. RTL shortening in CRC was associated with (a) upregulation of DNA replication genes, cyclin dependent-kinase genes (anti-tumor suppressor) and (b) downregulation of "caspase executor", reducing apoptosis.

Combination of resveratrol and BIBR1532 inhibits proliferation of colon cancer cells by repressing expression of LncRNAs

Colorectal cancer (CRC) is the third most common cancer worldwide. The development of tumor drug resistance is observed in the treatment of CRC. Combinations of anticancer agents are attracting considerable interest in order to overcome drug resistance in CRC. This study aims to investigate the effect of resveratrol and BIBR1532, either alone or in combination, on the cell viability as well as on expression of long non-coding RNAs (LncRNAs) for HT-29 colon adenocarcinoma cells. The cytotoxic effects of resveratrol and BIBR1532 on HT-29 cells were determined using WST-1 test. Flow cytometry was used to determine apoptotic cell death after treatments. Real-Time PCR was used to identify expression of LncRNAs after treatments. LncExpDB and GEPIA2 were used to evaluate expression profiles of LncRNAs, whose expression levels were decreased in HT-29 cells after treatments, in normal tissues and colon adenocarcinoma tumors. IC₅₀ concentrations of BIBR1532 and resveratrol were found to be 50.81 μM at 48 h and 86.23 μM at 72 h, respectively. Combination index value was 1.07617. BIBR1532, resveratrol, or their combination reduced the cell viability of HT-29 cells. CCAT1, CRNDE, HOTAIR, PCAT1, PVT1, SNHG16 were down-regulated after treatments. In silico analysis revealed that LncRNAs whose expression levels were decreased after treatments were associated with CRC. Resveratrol, BIBR1532, or their combination may have anti-proliferative effect on colorectal cancer cells through repressing expression of LncRNAs that are involved in progression of CRC.

Obesity and telomere status in the prognosis of patients with colorectal cancer submitted to curative intention surgical treatment

The risk of colorectal cancer (CRC) development has been associated with telomere dysfunction and obesity. However, clinical relevance of these parameters in CRC prognosis is not clear. Therefore, the aim of the present study was to evaluate the impact of obesity and telomere status in the prognosis of patients affected by CRC and submitted to curative surgical treatment. According to published data, this is the first work in which obesity and telomere status are jointly considered in relation to CRC prognosis. A prospective study including 162 patients with CRC submitted to curative surgical treatment was performed. Subjects were classified according to their BMI. Telomere status was established through telomere length and telomerase activity evaluation. Statistical analyses were performed using the SPSS software package version 22. Telomere shortening was inversely associated with BMI in patients with CRC. Notably, among patients with CRC, subjects with obesity exhibited less shortening of tumor telomeres than non-obese patients (P=0.047). Patients with shorter telomeres, both in the tumor (median telomere length <6.5 kb) and their non-tumor paired tissues (median telomere length <7.1 kb), had the best clinical evolution, regardless of the Dukes' stage of cancers (P=0.025, for tumor samples; P=0.003, for non-tumor samples). Additionally, subjects with a BMI >31.85 kg/m² showed the worse clinical outcomes compared with subjects with other BMI values. Interestingly, the impact of BMI showed sex dependence, since only the group of men displayed significant differences in CRC prognosis in relation to obesity status (P=0.037). From the results of the present study, based on a multivariate prediction model to establish prognosis, it was concluded that telomere length is a useful biomarker to predict prognosis in patients with CRC. Regardless of BMI values, the improved clinical evolution was associated with shorter telomeres. The impact of BMI seems to be associated with other factors, such as sex.

Non-canonical roles of canonical telomere binding proteins in cancers

Reactivation of telomerase is a major hallmark observed in 90% of all cancers. Yet paradoxically, enhanced telomerase activity does not correlate with telomere length and cancers often possess short telomeres; suggestive of supplementary non-canonical roles that telomerase might play in the development of cancer. Moreover, studies have shown that aberrant expression of shelterin proteins coupled with their release from shortening telomeres can further promote cancer by mechanisms independent of their telomeric role. While targeting telomerase activity appears to be an attractive therapeutic option, this approach has failed in clinical trials due to undesirable cytotoxic effects on stem cells. To circumvent this concern, an alternative strategy could be to target the molecules involved in the non-canonical functions of telomeric proteins. In this review, we will focus on emerging evidence that has demonstrated the non-canonical roles of telomeric proteins and their impact on tumorigenesis. Furthermore, we aim to address current knowledge gaps in telomeric protein functions and propose future research approaches that can be undertaken to achieve this.

The secrets of telomerase: Retrospective analysis and future prospects

Telomerase plays a significant role to maintain and regulate the telomere length, cellular immortality and senescence by the addition of guanine-rich repetitive sequences. Chronic inflammation or oxidative stress-induced infection downregulates TERT gene modifying telomerase activity thus contributing to the early steps of gastric carcinogenesis process. Furthermore, telomere-telomerase system performs fundamental role in the pathogenesis and progression of diabetes mellitus as well as in its vascular intricacy. The cessation of cell proliferation in cultured cells by inhibiting the telomerase activity of transformed cells renders the rationale for culling of telomerase as a target therapy for the treatment of metabolic disorders and various types of cancers. In this article, we have briefly described the role of immune system and malignant cells in the expression of telomerase with critical analysis on the gaps and potential for future studies. The key findings regarding the secrets of the telomerase summarized in this article will help in future treatment modalities for the prevention of various types of cancers and metabolic disorders notably diabetes mellitus.

Different TERT Expression between Colorectal Adenoma and Serrated Polyp

Background and Objectives: Telomere regulation have an association with colorectal cancer. Previous studies demonstrated its implication in colorectal carcinogenesis. This study aimed to identify the role of telomerase reverse transcriptase (TERT) in colorectal carcinogenesis and determine TERT expression and their associated genes in precancerous lesions. Materials and Methods: TERT expression in 93 colorectal precursor lesions was analyzed. This included 61 tubular adenomas (TAs) and 32 serrated polyps (SPs). Furthermore, KRAS and BRAF gene mutations and microsatellite instability were analyzed. Statistical tests were performed to analyze the relationship between variables. Results: TERT expression in TAs, when compared with those observed in paired adjacent nontumor tissues, was 0.92 ± 0.78. TERT expression levels were significantly lower in SPs (0.38 ± 0.14, p < 0.001). KRAS and BRAF mutations were mutually exclusive in TAs and SPs (p < 0.001). TERT expression tended to be associated with KRAS mutations (46.7% vs. 22.0%, p = 0.098) and low-grade tumors (35.0% vs. 16.0%, p = 0.096), but this difference was insignificant. Conclusions: TERT expression has a pivotal role in progression to TAs in colorectal tissue. Considering the association between TERT expression and KRAS mutation, therapeutic drugs targeting this pathway can be developed for cancer prevention.

Telomere Length Maintenance and Its Transcriptional Regulation in Lynch Syndrome and Sporadic Colorectal Carcinoma

Background: Activation of telomere maintenance mechanisms (TMMs) is a hallmark of most cancers, and is required to prevent genome instability and to establish cellular immortality through reconstitution of capping of chromosome ends. TMM depends on the cancer type. Comparative studies linking tumor biology and TMM have potential impact for evaluating cancer onset and development. Methods: We have studied alterations of telomere length, their sequence composition and transcriptional regulation in mismatch repair deficient colorectal cancers arising in Lynch syndrome (LS-CRC) and microsatellite instable (MSI) sporadic CRC (MSI s-CRC), and for comparison, in microsatellite stable (MSS) s-CRC and in benign colon mucosa. Our study applied bioinformatics analysis of whole genome DNA and RNA sequencing data and a pathway model to study telomere length alterations and the potential effect of the "classical" telomerase (TEL-) and alternative (ALT-) TMM using transcriptomic signatures. Results: We have found progressive decrease of mean telomere length in all cancer subtypes compared with reference systems. Our results support the view that telomere attrition is an early event in tumorigenesis. TMM gets activated in all tumors studied due to concerted overexpression of a large fraction of genes with direct relation to telomere function, where only a very small fraction of them showed recurrent mutations. TEL-related transcriptional state was dominating in all CRC subtypes, showing, however, subtype-specific activation patterns; while contribution of the ALT-TMM was slightly more prominent in the hypermutated MSI s-CRC and LS-CRC. TEL-TMM is mainly activated by over-expression of DKC1 and/or TERT genes and their interaction partners, where DKC1 is more prominent in MSS than in MSI s-CRC and can serve as a transcriptomic marker of TMM activity. Conclusions: Our results suggest that transcriptional patterns are indicative for TMM pathway activation with subtle differences between TEL and ALT mechanisms in a CRC subtype-specific fashion. Sequencing data potentially provide a suited measure to study alterations of telomere length and of underlying transcriptional regulation. Further studies are needed to improve this method.

Relationship of telomere length in colorectal cancer patients with cancer phenotype and patient prognosis

BACKGROUND

Telomeres, repetitive DNA capping ends of eukaryotic chromosomes, are important in the maintenance of genomic integrity. Perturbed telomeres are common features of many human malignancies, including colorectal cancer.

METHODS

Telomere length (TL), measured by a Monochrome Multiplex Real-Time qPCR, was investigated in tumour tissues, adjacent mucosa, and blood from patients with colorectal cancer with different clinicopathological features and its impact on patient survival. TL was also measured in a limited number of liver metastases, non-cancerous liver tissues or corresponding tissues from the same patients.

RESULTS

TL in tumour tissues was shorter than in the adjacent mucosa (P < 0.0001). Shorter TL was observed in tumours with lower stage than in those with advanced stages (P = 0.001). TL was shorter in tumours at the proximal than at the distal sites of the colon (P < 0.0001). Shorter TL was also associated with microsatellite instability (P = 0.001) and mucinous tumour histology (P < 0.0001). Patients with a smaller TL ratio between tumour tissues and the adjacent mucosa were associated with increased overall survival (P = 0.022). Metastasised tumours had shorter telomeres than the adjacent non-cancerous liver tissues (P = 0.0005).

CONCLUSIONS

Overall, the results demonstrate differences in TL between tumours and the adjacent mucosa, between tumours located at different sites and association with patient survival.

Lymphocyte telomere length predicts clinical outcomes of HPV-positive oropharyngeal cancer patients after definitive radiotherapy

Because lymphocyte telomere length (LTL) plays critical roles in the maintenance of genomic stability and integrity, LTL thus may influence the etiology and prognosis of squamous cell carcinoma of the oropharynx (SCCOP). However, given the association between LTL and risk of human papillomavirus (HPV)-associated SCCOP and between LTL and tumor HPV status of SCCOP, we hypothesized that LTL is associated with SCCOP prognosis, particularly in HPV-positive patients after definitive radiotherapy. LTL and tumor HPV type 16 (HPV16) status were determined in 564 incident SCCOP patients before radiotherapy or chemoradiation. Both univariate and multivariable Cox regression analyses were performed to estimate the association between LTL and prognosis. Eighty-five percent patients had HPV16-positive tumors. Patients with shorter telomeres had significantly better overall, disease-specific and disease-free survival than did those with longer telomeres (log-rank P < 0.001). Moreover, patients with shorter telomeres had significantly lower risk of death overall [hazard ratio (HR) = 0.2; 95% confidence interval (CI) = 0.1-0.4], death due to SCCOP (HR = 0.2; 95% CI = 0.1-0.4) and SCCOP recurrence (HR = 0.3; 95% CI = 0.2-0.5) after adjusting for other important prognostic confounders. Finally, we found more pronounced effects of LTL on survival in HPV16-positive SCCOP patients after stratified analysis according to tumor HPV status. These findings indicate that LTL plays a significant role in the survival of patients with SCCOP, especially HPV16-positive patients who undergo definitive radiotherapy. Therefore, pretreatment LTL may be an independent prognostic biomarker for HPV16-positive SCCOP. Prospective studies with larger sample sizes are needed to confirm these findings.

Telomere Maintenance-Associated PML Is a Potential Specific Therapeutic Target of Human Colorectal Cancer

Telomere length maintenance is essential for cell proliferation, which is particularly prominent in cancer. We validate that the primary colorectal tumors exhibit heterogeneous telomere lengths but mostly (90%) short telomeres relative to normal tissues. Intriguingly, relatively short telomeres are associated with tumor malignancy as indicated by poorly differentiated state, and these tumors contain more cancer stem-like cells (CSLCs) identified by several commonly used markers CD44, EPHB2 or LGR5. Moreover, promyelocytic leukemia (PML) and ALT-associated PML nuclear bodies (APBs) are frequently found in tumors with short telomeres and high proliferation. In contrast, distant normal tissues rarely or only minimally express PML. Inhibition of PML and APBs by an ATR inhibitor decreases proliferation of CSLCs and organoids, suggesting a potential therapeutic target to progressive colorectal tumors. Together, telomere maintenance underling tumor progression is connected with CSLCs.

Relative telomere lengths in tumor and normal mucosa are related to disease progression and chromosome instability profiles in colorectal cancer

Telomeric dysfunction is linked to colorectal cancer (CRC) initiation. However, the relationship of normal tissue and tumor telomere lengths with CRC progression, molecular features and prognosis is unclear. Here, we measured relative telomere length (RTL) by real-time quantitative PCR in 90 adenomas (aRTL), 419 stage I-IV CRCs (cRTL) and adjacent normal mucosa (nRTL). Age-adjusted RTL was analyzed against germline variants in telomere biology genes, chromosome instability (CIN), microsatellite instability (MSI), CpG island methylator phenotype (CIMP), TP53, KRAS, BRAF mutations and clinical outcomes. In 509 adenoma or CRC patients, nRTL decreased with advancing age. Female gender, proximal location and the TERT rs2736100 G allele were independently associated with longer age-adjusted nRTL. Adenomas and carcinomas exhibited telomere shortening in 79% and 67% and lengthening in 7% and 15% of cases. Age-adjusted nRTL and cRTL were independently associated with tumor stage, decreasing from adenoma to stage III and leveling out or increasing from stage III to IV, respectively. Cancer MSI, CIMP, TP53, KRAS and BRAF status were not related to nRTL or cRTL. Near-tetraploid CRCs exhibited significantly longer cRTLs than CIN- and aneuploidy CRCs, while cRTL was significantly shorter in CRCs with larger numbers of chromosome breaks. Age-adjusted nRTL, cRTL or cRTL:nRTL ratios were not associated with disease-free or overall survival in stage II/III CRC. Taken together, our data show that both normal mucosa and tumor RTL are independently associated with CRC progression, and highlight divergent associations of CRC telomere length with tumor CIN profiles.

Measurement of Telomere Length in Colorectal Cancers for Improved Molecular Diagnosis

All tumors have in common to reactivate a telomere maintenance mechanism to allow for unlimited proliferation. On the other hand, genetic instability found in some tumors can result from the loss of telomeres. Here, we measured telomere length in colorectal cancers (CRCs) using TRF (Telomere Restriction Fragment) analysis. Telomeric DNA content was also quantified as the ratio of total telomeric (TTAGGG) sequences over that of the invariable Alu sequences. In most of the 125 CRCs analyzed, there was a significant diminution in telomere length compared with that in control healthy tissue. Only 34 tumors exhibited no telomere erosion and, in some cases, a slight telomere lengthening. Telomere length did not correlate with age, gender, tumor stage, tumor localization or stage of tumor differentiation. In addition, while telomere length did not correlate with the presence of a mutation in BRAF (V-raf murine sarcoma viral oncogene homolog B), PIK3CA (phosphatidylinositol 3-kinase catalytic subunit), or MSI status, it was significantly associated with the occurrence of a mutation in KRAS. Interestingly, we found that the shorter the telomeres in healthy tissue of a patient, the larger an increase in telomere length in the tumor. Our study points to the existence of two types of CRCs based on telomere length and reveals that telomere length in healthy tissue might influence telomere maintenance mechanisms in the tumor.

Meta-analysis of associations between telomere length and colorectal cancer survival from observational studies

BACKGROUND

Telomere length (TL) has been reported to be associated with the risk and survival of several cancers. But it is unclear for the prognostic role of TL in colorectal cancer (CRC).

MATERIALS AND METHODS

Relevant citations were searched and identified using several major online databases through April 2017 which investigated associations between TL and CRC prognosis. We combined summary estimates using hazard ratios (HRs) with 95% confidence interval (CI), which were pooled using a random-effects model. Overall survival (OS) was set as the primary outcome of interest.

RESULTS

There are 8 cohort studies encompassing 1622 patients included in the meta-analysis. Pooled estimate indicated that long TL was not significantly associated with patient OS (HR 1.26, 95% CI, 0.76 to 2.08). When we conducted subgroup analyses based on baseline charcteristics, we found that long TL (versus short TL) was significantly associated with poor OS in studies conducted in Europe (n = 4, HR 2.73, 95% CI, 1.65 to 4.52, I² = 0), using Southern blot to measure TL (n = 3, HR 2.93, 95% CI, 1.69 to 5.10, I² = 0) and patients' age more than 60 years (n = 3, HR 2.65, 95% CI, 1.22 to 5.76, I² = 0). We found no significant associations between TL and patient disease-free, recurrence-free or progression-free survival (HR 1.19, 95% CI, 0.45 to 3.15).

CONCLUSIONS

Current evidence did not provide solid indication that long TL is significantly associated with improved or poor survival for patients with CRC. Further large sample size prospective cohort studies are warranted to determine the true relationship for specific patients.

Telomere length regulation through epidermal growth factor receptor signaling in cancer

Length of the telomere (TL), a structure at the tip of chromosome that protects and ensures stability, is determined by multi-protein complexes such as telosome/shelterin and telomerase. Earlier studies from our laboratory show that longer TL has potential to be positive predictive biomarker of clinical outcome to anti-epidermal growth factor receptor (EGFR) monoclonal antibody therapy in patients with KRAS WT metastatic colorectal cancer. Although there is extensive literature suggesting the role of shelterin and telomerase, not much literature exists that describes the role of EGFR and KRAS pathway in regulating TL. This detailed review focuses on an insight into various components, including proteins, enzymes and transcription factors, interlinking between EGFR pathways and telomerase that regulate TL.

Genetic and epigenetic markers in colorectal cancer screening: recent advances

INTRODUCTION

Colorectal cancer (CRC) is a heterogenous disease which develops from benign intraepithelial lesions known as adenomas to malignant carcinomas. Acquired alterations in Wnt signaling, TGFβ, MAPK pathway genes and clonal propagation of altered cells are responsible for this transformation. Detection of adenomas or early stage cancer in asymptomatic patients and better prognostic and predictive markers is important for improving the clinical management of CRC. Area covered: In this review, the authors have evaluated the potential of genetic and epigenetic alterations as markers for early detection, prognosis and therapeutic predictive potential in the context of CRC. We have discussed molecular heterogeneity present in CRC and its correlation to prognosis and response to therapy. Expert commentary: Molecular marker based CRC screening methods still fail to gain trust of clinicians. Invasive screening methods, molecular heterogeneity, chemoresistance and low quality test samples are some key challenges which need to be addressed in the present context. New sequencing technologies and integrated omics data analysis of individual or population cohort results in GWAS. MPE studies following a GWAS could be future line of research to establish accurate correlations between CRC and its risk factors. This strategy would identify most reliable biomarkers for CRC screening and management.

Rho GDP-dissociation inhibitor α is a potential prognostic biomarker and controls telomere regulation in colorectal cancer

Rho GDP‐dissociation inhibitor α (RhoGDIα) is an essential regulator for Rho GTPases. Although RhoGDIα may serve as an oncogene in colorectal cancer (CRC), the underlying mechanism is still unclear. We investigated the function, mechanism, and clinical significance of RhoGDIα in CRC progression. We founded that downregulation of RhoGDIα repressed CRC cell proliferation, motility, and invasion. Overexpression of RhoGDIα increased DNA damage response signals at telomeres, and led to telomere shortening in CRC cells, also being validated in 26 pairs of CRC tissues. Mechanistic studies revealed that RhoGDIα could promote telomeric repeat factor 1 (TRF1) expression through the phosphatidylinositol 3‐kinase–protein kinase B signal pathway. Moreover, RhoGDIα protein levels were strongly correlated with TRF1 in CRC tissues. A cohort of 297 CRC samples validated the positive relationship between RhoGDIα and TRF1, and revealed that RhoGDIα and TRF1 levels were negatively associated with CRC patients' survival. Taken together, our results suggest that RhoGDIα regulate TRF1 and telomere length and may be novel prognostic biomarkers in colorectal cancer.

Prognostic role of telomere length in malignancies: A meta-analysis and meta-regression

Telomere length (TL) has been associated with several health conditions including cancer. To quantify the effect of TL on outcomes in malignancies and explore the role of type of TL measurement we conducted a librarian-led systematic search of electronic databases identified publications exploring the prognostic role of TL on cancer outcomes. Overall survival (OS) was the primary outcome measure while other time-to-event endpoints were secondary outcomes. Data from studies reporting a hazard ratio (HR) with 95% confidence interval (CI) and/or p-value were pooled in a meta-analysis. HRs were weighted by generic inverse variance and computed by random effects modeling. All statistical tests were two-sided. Sixty-one studies comprising a total of 14,720 patients were included of which 41 (67%) reported OS outcomes. Overall, the pooled HR for OS was 0.88 (95%CI=0.69-1.11, p=0.28). Long (versus short) telomeres were associated with improved outcomes in chronic lymphatic leukemia (CLL) and urothelial cancer (HR=0.45, 95%CI=0.29-0.71 and HR=0.68, 95%CI=0.46-1.00, respectively), conversely worse OS was seen with hepatocellular carcinoma (HR=1.90, 95%CI=1.51-2.38). Pooled HRs (95% CI) for progression-free survival, relapse/disease-free survival, cancer-specific survival, and treatment-free survival were 0.56 (0.41-0.76), 0.76 (0.53-1.10), 0.72 (0.48-1.10), and 0.48 (0.39-0.60), respectively. There was substantial heterogeneity of tissues and methods used for TL measurement and no clear association between TL and outcome was identified in subgroups. In conclusion, there is inconsistent effect of TL on cancer outcomes possibly due to variable methods of measurement. Standardization of measurement and reporting of TL is warranted before the prognostic value of TL can be accurately assessed.

Association between telomere length and the risk of colorectal cancer: a meta-analysis of observational studies

BACKGROUND

Human chromosomes are capped and stabilized by telomeres. Telomere length regulates a 'cellular mitotic clock' that defines the number of cell divisions and hence, cellular life span. This study aimed to synthesize the evidence on the association between peripheral blood leucocytes (PBL) telomere length and the risk of colorectal cancer (CRC).

METHODS

We searched relevant studies in electronic databases. When two or more observational studies reported the same outcome measures, we performed pooled analysis. All the analyses were performed on PBL using PCR. The odds ratio (OR) and its 95% confidence interval (CI) were used to assess the strength of association.

RESULTS

Seven studies (with 8 datasets) were included in this meta-analysis; 3 prospective studies, 3 retrospective studies and 1 study with a separate prospective and retrospective designs. The pooled analysis of 4 prospective studies (summary OR 1.01, 95% CI: 0.77-1.34, I ²:30%) and 4 retrospective studies (summary OR 1.65, 95% CI: 0.96-2.83, I ²:96%) showed no relationship between PBL telomere length and the CRC risk. A subgroup analysis of 2 prospective studies exclusively on females also showed no association between PBL telomere length and the CRC risk (summary OR, 1.17, 95% CI:0.72-1.91, I ²:57%).

CONCLUSION

The current analysis is insufficient to provide evidence on the relationship between PBL telomere length and the risk of CRC. Findings suggest that there may be a complex relationship between PBL telomere length and the CRC risk or discrepancy between genetics, age of patients and clinical studies. Future well powered, large prospective studies on the relationship between telomere length and the risk of CRC, and the investigations of the biologic mechanisms are recommended.

Association between telomere length and survival in cancer patients: a meta-analysis and review of literature

The relationship between telomere length and cancer survival has been widely studied. To gain a deeper insight, we reviewed the published studies. A total of 29 studies evaluated telomere length in the peripheral blood; 22 studies evaluated telomere length in the tumor tissue. First, in the peripheral blood studies, for solid tumor patients with shortened telomere length, the combined hazard ratios (HRs) for mortality and tumor progression were 1.21 (95%CI, 1.10-1.32) and 1.71 (95%CI, 1.37-2.13), respectively. Meanwhile, in hematology malignancy, the combined HRs for mortality and tumor progression were 2.83 (95%CI, 2.14-3.74) and 2.65 (95%CI, 2.18-3.22), respectively. Second, in the studies that use tumor tissue, for patients with shortened telomeres, the combined HRs for mortality and tumor progression were 1.26 (95%CI, 0.95-1.66) and 1.65 (95%CI, 1.26-2.15), respectively. In the studies that calculate the telomere length ratios of tumor tissue to adjacent normal mucosa, for patients with lower telomere length ratios, the combined HRs were 0.66 (95%CI, 0.53-0.83) and 0.74 (95%CI, 0.41-1.32) for mortality and tumor progression, respectively. In conclusion, shortened telomere in peripheral blood and tumor tissue might indicate poor survival for cancer patients. However, by calculating the telomere length ratios of tumor tissue to adjacent normal mucosa, the lower ratio might indicate better survival.

Crystal structure of a tankyrase 1-telomere repeat factor 1 complex

Telomere repeat factor 1 (TRF1) is a subunit of shelterin (also known as the telosome) and plays a critical role in inhibiting telomere elongation by telomerase. Tankyrase 1 (TNKS1) is a poly(ADP-ribose) polymerase that regulates the activity of TRF1 through poly(ADP-ribosyl)ation (PARylation). PARylation of TRF1 by TNKS1 leads to the release of TRF1 from telomeres and allows telomerase to access telomeres. The interaction between TRF1 and TNKS1 is thus important for telomere stability and the mitotic cell cycle. Here, the crystal structure of a complex between the N-terminal acidic domain of TRF1 (residues 1-55) and a fragment of TNKS1 covering the second and third ankyrin-repeat clusters (ARC2-3) is presented at 2.2 Å resolution. The TNKS1-TRF1 complex crystals were optimized using an `oriented rescreening' strategy, in which the initial crystallization condition was used as a guide for a second round of large-scale sparse-matrix screening. This crystallographic and biochemical analysis provides a better understanding of the TRF1-TNKS1 interaction and the three-dimensional structure of the ankyrin-repeat domain of TNKS.

The Relationship between Telomerase Activity and Clinicopathological Parameters in Colorectal Cancer: A Meta-Analysis

BACKGROUND

Recently, accumulated research has found that the expression of telomerase activity (TA) was associated with colorectal cancer (CRC) advancement, whereas the TA prognostic effect in CRC patients is still controversial.

AIMS

To investigate relationships between TA and CRC clinicopathological parameters.

STUDY DESIGN

Meta-analysis study.

METHODS

We searched published studies in databases, such as EMBASE, the Cochrane Library, PubMed, and Ovid databases (last search updated to October 2014) by meeting specified search criteria. The quality of the included studies was usually evaluated and a meta-analysis was implemented by Stata 12.0 software. We used an odds ratio (OR) with a 95% confidence interval (CI) to evaluate relationship strengths between TA and CRC clinicopathological parameters.

RESULTS

In total, 11 studies (715 patients) were included to assess the relation between TA and metastasis-related parameters in CRC patients. The results indicate that a senior TA expression was connected with the existence of lymph node metastasis (180 patients; OR=2.85, 95% CI=1.40-5.81, p=0.004), and tumor site (522 patients; OR=2.93, 95% CI=1.29-6.67, p=0.010). However, a senior TA expression was not connected with tumor size (137 patients; OR=1.57, 95% CI=0.71-3.47, p=0.267), histological differentiation (570 patients; OR=1.28, 95% CI=0.78-2.09, p=0.332), depth of invasion (57 patients; OR=3.76, 95% CI=0.61-23.04, p=0.152), distant metastasis (123 patients; OR=1.76, 95% CI=0.54-5.74, p=0.346), and clinical stage of the cancer (543 patients; OR=1.59, 95% CI=0.74-3.38, p=0.232).

CONCLUSION

This meta-analysis suggests that a positive TA was correlated with lymph node metastasis progression and tumor site of the CRC but did not correlate with other important clinicopathological parameters. TA can play a useful part in the prognosis and treatment of CRC patients, but further studies are required to confirm this.

Clinical Relevance of Telomere Status and Telomerase Activity in Colorectal Cancer

The role of telomeres and telomerase in colorectal cancer (CRC) is well established as the major driving force in generating chromosomal instability. However, their potential as prognostic markers remains unclear. We investigated the outcome implications of telomeres and telomerase in this tumour type. We considered telomere length (TL), ratio of telomere length in cancer to non-cancer tissue (T/N ratio), telomerase activity and TERT levels; their relation with clinical variables and their role as prognostic markers. We analyzed 132 CRCs and paired non-cancer tissues. Kaplan-Meier curves for disease-free survival were calculated for TL, T/N ratio, telomerase activity and TERT levels. Overall, tumours had shorter telomeres than non-tumour tissues (P < 0.001) and more than 80% of CRCs displayed telomerase activity. Telomere lengths of non-tumour tissues and CRCs were positively correlated (P < 0.001). Considering telomere status and clinical variables, the lowest degree of telomere shortening was shown by tumours located in the rectum (P = 0.021). Regarding prognosis studies, patients with tumours showing a mean TL < 6.35 Kb experienced a significantly better clinical evolution (P < 0.001) and none of them with the highest degree of tumour telomere shortening relapsed during the follow-up period (P = 0.043). The mean TL in CRCs emerged as an independent prognostic factor in the Cox analysis (P = 0.017). Telomerase-positive activity was identified as a marker that confers a trend toward a poor prognosis. In CRC, our results support the use of telomere status as an independent prognostic factor. Telomere status may contribute to explaining the different molecular identities of this tumour type.

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.

The Association between Telomere Length and Cancer Prognosis: Evidence from a Meta-Analysis

BACKGROUND

Telomeres are essential for chromosomal integrity and stability. Shortened telomere length (TL) has been associated with risk of cancers and aging-related diseases. Several studies have explored associations between TL and cancer prognosis, but the results are conflicting.

METHODS

Prospective studies on the relationship between TL and cancer survival were identified by a search of PubMed up to May 25, 2015. There were no restrictions on the cancer type or DNA source. The quality of the included studies was assessed using the Newcastle-Ottawa Scale. Meta-analysis approaches were conducted to determine pooled relative risks and 95% confidence intervals.

RESULTS

Thirty-three articles containing forty-five independent studies were ultimately involved in our meta-analysis, of which twenty-seven were about overall cancer survival and eighteen were about cancer progression. Short TL was associated with increased cancer mortality risk (RR = 1.30, 95%CI: 1.06-1.59) and poor cancer progression (RR = 1.44, 95%CI: 1.10-1.88), both with high levels of heterogeneity (I2 = 83.5%, P = 0.012for overall survival and I2 = 75.4%, P = 0.008 for progression). TL was an independent predictor of overall cancer survival and progression in chronic lymphocytic leukemia. Besides, short telomeres were also associated with increased colorectal cancer mortality and decreased overall survival of esophageal cancer, but not in other cancers. Cancer progression was associated with TL in Asian and America populations and short TL predicted poor cancer survival in older populations. Compared with tumor tissue cells, TL in blood lymphocyte cells was better for prediction. In addition, the associations remained significant when restricted to studies with adjustments for age, with larger sample sizes, measuring TL using southern blotting or estimating risk effects by hazard ratios.

CONCLUSION

Short TL demonstrated a significant association with poor cancer survival, suggesting the potential prognostic significance of TL. Additional large well-designed studies are needed to confirm our findings.

The relationship between telomere length and clinicopathologic characteristics in colorectal cancers among Tunisian patients

Alterations in telomere dynamics have emerged as having a causative role in carcinogenesis. Both the telomere attrition contribute to tumor initiation via increasing chromosomal instability and that the telomere elongation induces cell immortalization and leads to tumor progression. The objectives of this study are to investigate the dynamics of telomere length in colorectal cancer (CRC) and the clinicopathological parameters implicated. We measured the relative telomere length (RTL) in cancerous tissues and in corresponding peripheral blood leukocytes (PBL) using quantitative PCR (Q-PCR) from 94 patients with CRC. Telomere length correlated significantly in cancer tissues and corresponding PBL (r = 0.705). Overall, cancer tissue had shorter telomeres than PBL (p = 0.033). In both cancer tissue and PBL, the RTL was significantly correlated with age groups (p = 0.008 and p = 0.012, respectively). The RTL in cancer tissue was significantly longer in rectal tumors (p = 0.04) and in the late stage of tumors (p = 0.01). In PBL, the RTL was significantly correlated with the macroscopic aspect of tumors (p = 0.02). In addition, the telomere-length ratio of cancer to corresponding PBL increased significantly with late-stage groups. Shortening of the telomere was detected in 44.7%, elongation in 36.2%, and telomeres were unchanged in 19.1% of 94 tumors. Telomere shortening occurred more frequently in the early stage of tumors (p = 0.01). This study suggests that the telomere length in PBL is affected by the macroscopic aspect of tumors and that telomere length in cancer tissues is a marker for progression of CRC and depends on tumor-origin site.

In colon cancer, normal colon tissue and blood cells have altered telomere lengths

BACKGROUND

Telomere length (TL) shortened occurs in colorectal carcinogenetic process. Our objective is to determine if it is only a local fact or there are alterations in normal colon cells and in other body cells.

METHODS

TL of tumoral and normal mucosa and leukocytes of 40 patients operated of colorectal cancer (CRC) and 40 control patients with normal colonoscopy were measured by Southern-blot. Groups were matched by the same localization as tumors, sex, and age.

RESULTS

In CRC patients, TRFL (Telomere Repeat Factor Length) leukocytes mean was 8.84 kpb, normal colonic mucosa 7.97 kpb, and tumoral mucosa 7.33 kpb (P < 0.001). In the 40 normal control patients, mean TRFL of colonic mucosa was 7.76 kpb, while in blood cells was 7.01 kpb (P < 0.001). We observed an inverse correlation between leukocytes TRFL and age (r(2)  = 0.17, P = 0.008). Mucosa TRFL correlates significantly with patient's age (r(2)  = 0.138, P = 0.018). TRFL of controls colonic mucosa correlates with TRFL of their blood cells (r(2)  = 0.354, P < 0.001).

CONCLUSIONS

Normal colonic mucosa and leukocytes in CCR patients presents telomere altered in respect to normal patients. Telomere length in normal leukocytes could be an initial marker for colorectal cancer.

Prognostic value of telomere function in gastric cancers with and without microsatellite instability

OBJECTIVE

To identify molecular markers that may be useful in the selection of gastric cancer patients with different prognoses, we investigated telomere function in gastric cancers with and without microsatellite instability (MSI).

MATERIALS AND METHODS

We analyzed 83 gastric cancers and its paired-normal tissues to investigate MSI and telomere function. MSI was established using five polymorphic human repeat DNA markers. Telomere function was evaluated by determining telomerase activity, telomere length, and telomere-repeat factors 1 and 2 (TRF1 and TRF2) expression.

RESULTS

Patients with high microsatellite instability (MSI-H) gastric cancers showed a significantly better prognosis than those affected by microsatellite stable or low microsatellite instability (MSS/MSI-L) tumors (P = 0.03). The lowest expression levels of TRF1 and TRF2 were associated with MSI-H gastric cancers (P = 0.008 and 0.006, respectively). Moreover, a clear trend toward a worse prognosis was found in the group of patients who had tumors with the shortest telomeres (P = 0.01). Cox multivariate analysis showed that MSI emerged as a protective prognostic factor; MSS/MSI-L tumors conferred a significantly poor prognosis in patients (relative risk = 4.862-fold greater than the MSI-H group) (P = 0.033). Telomere length of gastric tumors less than 2.86 kbp was a factor that led to a poor prognosis (relative risk = 4.420, with respect to tumors showing telomere length ≥ 2.86 kbp) (P = 0.002).

CONCLUSION

We propose telomere status as a potential molecular marker with usefulness in the establishment of the prognosis of gastric cancers both for the mutator phenotype and for the suppressor pathway.

miR-155 drives telomere fragility in human breast cancer by targeting TRF1

Telomeres consist of DNA tandem repeats that recruit the multiprotein complex shelterin to build a chromatin structure that protects chromosome ends. Although cancer formation is linked to alterations in telomere homeostasis, there is little understanding of how shelterin function is limited in cancer cells. Using a small-scale screening approach, we identified miR-155 as a key regulator in breast cancer cell expression of the shelterin component TERF1 (TRF1). miR-155 targeted a conserved sequence motif in the 3'UTR of TRF1, resulting in its translational repression. miR-155 was upregulated commonly in breast cancer specimens, as associated with reduced TRF1 protein expression, metastasis-free survival, and relapse-free survival in estrogen receptor-positive cases. Modulating miR-155 expression in cells altered TRF1 levels and TRF1 abundance at telomeres. Compromising TRF1 expression by elevating miR-155 increased telomere fragility and altered the structure of metaphase chromosomes. In contrast, reducing miR-155 levels improved telomere function and genomic stability. These results implied that miR-155 upregulation antagonizes telomere integrity in breast cancer cells, increasing genomic instability linked to poor clinical outcome in estrogen receptor-positive disease. Our work argued that miRNA-dependent regulation of shelterin function has a clinically significant impact on telomere function, suggesting the existence of "telo-miRNAs" that have an impact on cancer and aging.

Telomeres, telomerase and colorectal cancer

Colorectal cancer (CRC) is the third most common cancer worldwide and, despite improved treatments, is still an important cause of cancer-related deaths. CRC encompasses a complex of diseases arising from a multi-step process of genetic and epigenetic events. Besides heterogeneity in the molecular and biological features of CRC, chromosomal instability is a hallmark of cancer and cancer cells may also circumvent replicative senescence and acquire the ability to sustain unlimited proliferation. Telomere/telomerase interplay is an important mechanism involved in both genomic stability and cellular replicative potential, and its dysfunction plays a key role in the oncogenetic process. The erosion of telomeres, mainly because of cell proliferation, may be accelerated by specific alterations in the genes involved in CRC, such as APC and MSH2. Although there is general agreement that the shortening of telomeres plays a role in the early steps of CRC carcinogenesis by promoting chromosomal instability, the prognostic role of telomere length in CRC is still under debate. The activation of telomerase reverse transcriptase (TERT), the catalytic component of the telomerase complex, allows cancer cells to grow indefinitely by maintaining the length of the telomeres, thus favouring tumour formation/progression. Several studies indicate that TERT increases with disease progression, and most studies suggest that telomerase is a useful prognostic factor. Plasma TERT mRNA may also be a promising marker for the minimally invasive monitoring of disease progression and response to therapy.

Poly (ADP-ribose) polymerase 3 (PARP3), a potential repressor of telomerase activity

BACKGROUND

Considering previous result in Non-Small Cell Lung Cancer (NSCLC), we investigated in human cancer cells the role of PARP3 in the regulation of telomerase activity.

METHODS

We selected A549 (lung adenocarcinoma cell line) and Saos-2 (osteosarcoma cell line), with high and low telomerase activity levels, respectively. The first one was transfected using a plasmid construction containing a PARP3 sequence, whereas the Saos-2 cells were submitted to shRNA transfection to get PARP3 depletion. PARP3 expression on both cell systems was evaluated by real-time quantitative PCR and PARP3 protein levels, by Western-blot. Telomerase activity was determined by TRAP assay.

RESULTS

In A549 cells, after PARP3 transient transfection, data obtained indicated that twenty-four hours after transfection, up to 100-fold increased gene expression levels were found in the transfected cells with pcDNA/GW-53/PARP3 in comparison to transfected cells with the empty vector. Moreover, 48 hours post-transfection, telomerase activity decreased around 33%, and around 27%, 96 hours post-transfection. Telomerase activity average ratio was 0.67 ± 0.05, and 0.73 ± 0.06, respectively, with significant differences. In Saos-2 cells, after shRNA-mediated PARP3 silencing, a 2.3-fold increase in telomerase activity was detected in relation to the control.

CONCLUSION

Our data indicated that, at least in some cancer cells, repression of PARP3 could be responsible for an increased telomerase activity, this fact contributing to telomere maintenance and, therefore, avoiding genome instability.

Telomeres and telomere dynamics: relevance to cancers of the GI tract

Aberrations in telomere length and telomere maintenance contribute to cancer development. In this article, we review the basic principles of telomere length in normal and tumor tissue and the presence of the two main telomere maintenance pathways as they pertain to gastrointestinal tract cancer. Peripheral blood telomeres are shorter in patients with many types of gastrointestinal tract cancers. Telomere length in tumor DNA also appears to shorten early in cancer development. Tumor telomere shortening is often accompanied by telomerase activation to protect genetically damaged DNA from normal cell senescence or apoptosis, allowing immortalized but damaged DNA to persist. Alternative lengthening of telomeres is another mechanism used by cancer to maintain telomere length in cancer cells. Telomerase and alternative lengthening of telomeres activators and inhibitors may become important chemopreventive or chemotherapeutic agents as our understanding of telomere biology, specific telomere-related phenotypes and its relationship to carcinogenesis increases.

Immune senescence and cancer in elderly patients: results from an exploratory study

BACKGROUND

The challenge of immune senescence has never been addressed in elderly cancer patients. This study compares the thymic output and peripheral blood telomere length in ≥70year old cancer patients.

PATIENTS AND METHODS

Fifty-two elderly cancer patients and 39 age-matched controls without personal history of cancer were enrolled. All patients underwent a Comprehensive Geriatric Assessment (CGA), from which a multidimensional prognostic index (MPI) score was calculated. Peripheral blood samples were studied for naïve and recent thymic emigrant (RTE) CD4(+) and CD8(+) cells by flow cytometry. T-cell receptor rearrangement excision circle (TREC) levels, telomere length and telomerase activity in peripheral blood cells were quantified by real-time PCR.

RESULTS

The percentages of CD8(+) naïve and CD8(+) RTE cells and TREC levels were significantly lower in cancer patients than in controls (p=0.003, p=0.004, p=0.031, respectively). Telomere lengths in peripheral blood cells were significantly shorter in cancer patients than in controls (p=0.046) and did not correlate with age in patients, whereas it did in controls (r=-0.354, p=0.031). Short telomere (≤median)/low TREC (≤median) profile was associated with higher risk of cancer (OR=3.68 [95% CI 1.22-11.11]; p=0.021). Neither unfitness on CGA nor MPI score were significantly related to thymic output or telomere length in either group.

CONCLUSIONS

Immune senescence is significantly worse in elderly cancer patients than in age-matched controls. The low thymic output and the shorter telomeres in peripheral blood cells of cancer patients may reflect a pre-existing condition which facilitates the onset of malignancies in elderly people.

Extensive telomere erosion in the initiation of colorectal adenomas and its association with chromosomal instability

BACKGROUND

Telomere shortening, dysfunction, and fusion may facilitate the acquisition of large-scale genomic rearrangements, driving clonal evolution and tumor progression. The relative contribution that telomere dysfunction and/or APC mutation play in the chromosome instability that occurs during colorectal tumorigenesis is not clear.

METHODS

We used high-resolution telomere length and fusion analysis to analyze 85 adenomatous colorectal polyps obtained from 10 patients with familial adenomatous polyposis and a panel of 50 colorectal carcinomas with patient-matched normal colonic mucosa. Telomerase activity was determined using the telomeric repeat amplification protocol. Array-CGH was used to detect large-scale genomic rearrangements. Pearson correlation and Student t test were used, and all statistical tests were two-sided.

RESULTS

Despite the presence of telomerase activity, we observed apparent telomere shortening in colorectal polyps that correlated with large-scale genomic rearrangements (P < .0001) but was independent of polyp size and indistinguishable from that observed in colorectal carcinomas (P = .82). We also observed apparent lengthening of telomeres in both polyps and carcinomas. The extensive differences in mean telomere length of up to 4.6kb between patient-matched normal mucosa and polyps were too large to be accounted for by replicative telomere erosion alone. Telomere fusion events were detected in both polyps and carcinomas; the mutational spectrum accompanying fusion was consistent with alternative nonhomologous end joining.

CONCLUSIONS

Telomere length distributions observed in colorectal polyps reflect the telomere length composition of the normal originating cells from which clonal growth was initiated. Originating cells containing both short telomeres and APC mutations may give rise to polyps that exhibit short telomeres and are prone to telomere dysfunction, driving genomic instability and progression to malignancy. J Natl Cancer Inst;2013;105:1202-1211.

Telomere length modulation in human astroglial brain tumors

Background

Telomeres alteration during carcinogenesis and tumor progression has been described in several cancer types. Telomeres length is stabilized by telomerase (h-TERT) and controlled by several proteins that protect telomere integrity, such as the Telomere Repeat-binding Factor (TRF) 1 and 2 and the tankyrase-poli-ADP-ribose polymerase (TANKs-PARP) complex.

Objective

To investigate telomere dysfunction in astroglial brain tumors we analyzed telomeres length, telomerase activity and the expression of a panel of genes controlling the length and structure of telomeres in tissue samples obtained in vivo from astroglial brain tumors with different grade of malignancy.

Materials and Methods

Eight Low Grade Astrocytomas (LGA), 11 Anaplastic Astrocytomas (AA) and 11 Glioblastoma Multiforme (GBM) samples were analyzed. Three samples of normal brain tissue (NBT) were used as controls. Telomeres length was assessed through Southern Blotting. Telomerase activity was evaluated by a telomere repeat amplification protocol (TRAP) assay. The expression levels of TRF1, TRF2, h-TERT and TANKs-PARP complex were determined through Immunoblotting and RT-PCR.

Results

LGA were featured by an up-regulation of TRF1 and 2 and by shorter telomeres. Conversely, AA and GBM were featured by a down-regulation of TRF1 and 2 and an up-regulation of both telomerase and TANKs-PARP complex.

Conclusions

In human astroglial brain tumours, up-regulation of TRF1 and TRF2 occurs in the early stages of carcinogenesis determining telomeres shortening and genomic instability. In a later stage, up-regulation of PARP-TANKs and telomerase activation may occur together with an ADP-ribosylation of TRF1, causing a reduced ability to bind telomeric DNA, telomeres elongation and tumor malignant progression.

Telomerase activity in human brain tumors: astrocytoma and meningioma

Somatic cells do not have telomerase activity but immortalized cell lines and more than 85 % of the cancer cells show telomerase activation to prevent the telomere from progressive shortening. The activation of this enzyme has been found in a variety of human tumors and tumor-derived cell lines, but only few studies on telomerase activity in human brain tumors have been reported. Here, we evaluated telomerase activity in different grades of human astrocytoma and meningioma brain tumors. In this study, assay for telomerase activity performed on 50 eligible cases consisted of 26 meningioma, 24 astrocytoma according to the standard protocols. In the brain tissues, telomerase activity was positive in 39 (65 %) of 50 patients. One sample t test showed that the telomerase activity in meningioma and astrocytoma tumors was significantly positive entirely (P < 0.001). Also, grade I of meningioma and low grades of astrocytoma (grades I and II) significantly showed telomerase activity. According to our results, we suggest that activation of telomerase is an event that starts mostly at low grades of brain including meningioma and astrocytoma tumors.

Telomerase is an independent prognostic marker of overall survival in patients with colorectal cancer

Background:

Colorectal cancer (CRC) is an important cause of cancer-related death. Prediction of recurrence is an important issue in the treatment of disease, particularly for stage II patients. The level of telomere-specific reverse transcriptase (hTERT), the catalytic component of the telomerase complex, increases along with CRC progression, but its prognostic value is still unclear.

Methods:

One hundred and thirty-seven CRC patients were studied for hTERT expression in tumour cells by real-time PCR. hTERT level was evaluated as a prognostic factor of overall survival (OS) in all patients and of disease recurrence in a subgroup of 50 stage II patients.

Results:

The median hTERT level was 93.8 copies (interquartile range 48–254). Patients with high hTERT levels (above the median) showed a significantly worse survival than those with low hTERT levels (below the median; log-rank test P<0.0001; hazard ratio (HR)=3.30 (95% confidence interval (CI) 1.98–5.52); P<0.0001). The negative prognostic value of high hTERT level is independent of the pathological stage and microsatellite instability (HR=2.09 (95% CI 1.20–3.64), P=0.009). Moreover, in stage II CRC, high hTERT levels identified patients with a higher risk of disease recurrence (HR=3.06 (95% CI 1.03–9.04), P=0.043) and death (HR=3.24 (95% CI 1.37–7.71), P=0.008).

Conclusion:

hTERT level is an independent prognostic marker of OS in CRC patients. In addition, assessment of hTERT level could improve stratification of stage II CRC patients for the risk of disease recurrence.

Shelterin complex and digestive system tumor

The Shelterin complex is the crucial components of telomere binding proteins. The regulation of this complex, together with telomerase and the alterative lengthening of telomeres (ALT mechanism), plays a critical role in maintaining telomere functions. Telomeres are DNA-protein complexes that contain short repeat sequences added on to the ends of chromosome by the telomerase for protecting the ends of chromosome and preventing chromosome fusion. The loss of protective function of telomeres is closely related to genome instability, and this is the molecular basis for tumor development. Thus, telomeres play key roles in the process of malignant tumor development. Many studies have shown that telomere binding proteins are associated with gastric, colorectal and liver cancers, and other digestive system tumors. This review will focus on the role of the shelterin complex in digestive system neoplasms to provide an insight into prevention and targeted therapy of these malignancies.

Reduced telomere length in colorectal carcinomas

PURPOSE

Telomeres play a key role in the maintenance of chromosome integrity and stability, and telomere shortening is involved in initiation and progression of malignancies. The aim of this study was to determine whether telomere length is associated with the colorectal carcinoma.

PATIENTS AND METHODS

A total of 148 colorectal cancer (CRC) samples and corresponding adjacent non-cancerous tissues were evaluated for telomere length, P53 mutation, and cyclooxygenase-2 (COX-2) mutation detected by fluorescent immunohistochemistry. Telomere length was estimated by real-time PCR. Samples with a T/S>1.0 have an average telomere length greater than that of the standard DNA; samples with a T/S<1.0 have an average telomere length shorter than that of the standard DNA.

RESULTS

Telomeres were shorter in CRCs than in adjacent tissues, regardless of tumor stage and grade, site, or genetic alterations (P=0.004). Telomere length in CRCs also had differences with COX-2 status (P=0.004), but did not differ with P53 status (P=0.101), tumor progression (P=0.244), gender (P=0.542), and metastasis (0.488). There was no clear trend between T/S optimal cut-off values (<1 or > 1) and colorectal tumor progression, metastasis, gender, P53 and COX-2 status.

CONCLUSION

These findings suggesting that telomere shortening is associated with colorectal carcinogenesis but does not differ with tumor progression, gender, and metastasis.

PinX1: a sought-after major tumor suppressor at human chromosome 8p23

Human chromosome 8p23 is a region that has the most frequent heterozygosity in common human adult epithelial malignancies, but its major tumor suppressor gene(s) remain to be identified. Telomerase is activated in most human cancers and is critical for cancer cell growth. However, little is known about the significance of telomerase activation in chromosome instability and cancer initiation. The gene encoding the potent and highly conserved endogenous telomerase inhibitor PinX1 is located at human chromosome 8p23. However, the role of PinX1 in telomerase regulation and cancer development is not clear. Recent works from our group indicate that PinX1 is critical for maintaining telomere length at the optimal length. Furthermore, PinX1 is reduced in a large subset of human breast cancer tissues and cells. Significantly, PinX1 inhibition activates telomerase, and elongates telomeres, eventually leading to chromosome instability, all of which are abrogated by telomerase knockdown or knockout. Moreover, PinX1 allele loss causes majority of mice to develop a variety of epithelial cancers, which display chromosome instability and recapitulate to 8p23 allele loss in humans. These results indicate that PinX1 is a sought-after major tumor suppressor at human chromosome 8p23 that is essential for regulating telomerase activity and maintaining chromosome stability. These results suggest that inhibition of telomerase using PinX1 especially its telomerase inhibitory fragment or other methods might be used to treat cancers that have telomerase activation.

Differential expression of senescence and cell death factors in non-small cell lung and colorectal tumors showing telomere attrition

OBJECTIVE

The main aim of this work is to investigate the expression of factors related to senescence and cell death pathways in non-small cell lung cancers (NSCLCs) and colorectal cancers (CRCs) in relation to telomere status.

METHODS

We analyzed 158 tissue samples, 36 NSCLCs, 43 CRCs, and their corresponding control tissues obtained from patients submitted to surgery. Telomere function was evaluated by determining telomerase activity and telomere length. Expression of factors related to senescence, cell death pathways, transformation and tumorigenesis was investigated using arrays. Results were validated by real-time quantitative PCR.

RESULTS

Considering tumors with telomere shortening, expression for BNIP3, DAPK1, NDRG1, EGFR, and CDKN2A was significantly higher in NSCLC than in CRC, whereas TP53 was overexpressed in CRC with respect to NSCLC. Moreover, compared to nontumor samples, DAPK1, GADD45A, SHC1, and TP53 were downregulated in the group of NSCLCs with telomere shortening, and no significant differences were found in CRC.

CONCLUSIONS

In NSCLC, the failure of pathways which involve factors such as DAPK1, GADD45A, SHC1, and TP53, in response to short telomeres, could promote tumor progression. In CRC, the viability of these pathways in response to short telomeres could contribute to limiting tumorigenesis.

Telomere length is a prognostic factor for overall survival in colorectal cancer

AIM

The aim of this study was to determine whether telomere length is an independent prognostic factor for the prevention and survival of colorectal cancer.

METHOD

Terminal restriction fragment (TRF) length was determined by Southern blot in tumours and paired normal tissue samples from 147 patients with sporadic colorectal cancer who had undergone surgery. The TRF length ratio (TRFLR) was determined as the ratio between the length of the patient's tumour and normal tissue.The classification and regression tree technique was used to determine optimal cut-off values (≤ 1 or > 1).

RESULTS

Mean TRF length was 6.79 Kbp (1.19-13.99) in tumour tissue and 7.81 Kbp (3.63-15.70) in normal mucosa (P < 0.001). Mean TRFLR was 0.88. Telomere length and telomere length ratio were not correlated with any clinicopathological factors. In univariate analysis, overall survival was related to N stage (lymph node +/-; P = 0.002), TNM classification (P = 0.019) and TRFLR (≤ 1 or > 1; P = 0.014). In multivariate analysis, overall survival was significantly associated with TRFLR and N stage. Colorectal cancer patients with TRFLR ≤ 1 and negative lymph node involvement had a higher overall survival rate.

CONCLUSION

Telomere length ratio is an independent prognostic factor for survival in colorectal cancer patients, and the telomere lengths in the normal and tumour mucosa of the same patient present with parallel behaviour.

The prognostic value of hTERT expression levels in advanced-stage colorectal cancer patients: a comparison between tissue and serum expression

AIM

Telomeres are regions of highly repetitive, non-coding DNA located at the termini of chromosomes whose principal function is to maintain the structural stability of these ends. In 90% of human tumours, telomere length is maintained by the expression and activation of telomerase reverse transcriptase. Various studies have demonstrated an increase in telomerase activity in tumour tissue, which suggests its possible prognostic value. The main objective of our study was to study the prognostic value of the expression level of telomerase catalytic component (hTERT) in patients with colorectal cancer (CRC).

METHODS

We analysed the prognostic value of the ratio of telomerase expression in tumour tissue to telomerase expression in the adjacent healthy mucosa and the prognostic value of the expression level of hTERT in the serum of patients diagnosed with CRC. As secondary objectives of the study, we (1) analysed the correlation between telomerase expression in the serum and that in the tumour tissue and (2) analysed the relationship between telomerase expression and different clinical parameters.

RESULTS

Peripheral blood and tissue samples taken from 48 patients with CRC were analysed. No significant differences were observed in disease-free survival (DFS) or overall survival time (OST) between the groups of patients categorised based on the ratio of telomerase expression between tumour tissue and healthy tissue. The correlation index (Pearson's coefficient) between telomerase levels in the serum and those in tissue was 0.32. Our study of the relationship between telomerase levels in the serum and different clinical variables, such as tumour size, ganglion affectation, preoperative carcinoembryonic antigen levels and stage, revealed a higher telomerase expression level in patients with stage IV CRC. There was no significant association between telomerase expression in tumour tissue and the clinical parameters analysed.

CONCLUSIONS

The results obtained in our study do not allow us to propose that the level of telomerase expression be used as a prognostic factor in colorectal cancer. Thus, we cannot consider telomerase expression in the serum as a surrogate marker of its expression in tumour tissue.

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.

Alterations of telomere length in human brain tumors

Telomeres at the ends of human chromosomes consist of tandem hexametric (TTAGGG)n repeats, which protect them from degradation. At each cycle of cell division, most normal somatic cells lose approximately 50-100 bp of the terminal telomeric repeat DNA. Precise prediction of growth and estimation of the malignant potential of brain tumors require additional markers. DNA extraction was performed from the 51 frozen tissues, and a non-radioactive chemiluminescent assay was used for Southern blotting. One sample t-test shows highly significant difference in telomere length in meningioma and astrocytoma with normal range. According to our results, higher grades of meningioma and astrocytoma tumors show more heterogeneity in telomere length, and also it seems shortening process of telomeres is an early event in brain tumors.