Alterations In Telomere Length Research Articles

Prostate Cancer Cell Telomere Length Variability and Stromal Cell Telomere Length as Prognostic Markers for Metastasis and Death

Current prognostic indicators are imperfect predictors of outcome in men with clinically localized prostate cancer. Thus, tissue-based markers are urgently needed to improve treatment and surveillance decision-making. Given that shortened telomeres enhance chromosomal instability and such instability is a hallmark of metastatic lesions, we hypothesized that alterations in telomere length in the primary cancer would predict risk of progression to metastasis and prostate cancer death. To test this hypothesis, we conducted a prospective cohort study of 596 surgically treated men who participated in the ongoing Health Professionals Follow-up Study. Men who had the combination of more variable telomere length among prostate cancer cells (cell-to-cell) and shorter telomere length in prostate cancer-associated stromal (CAS) cells were substantially more likely to progress to metastasis or die of their prostate cancer. These findings point to the translational potential of this telomere biomarker for prognostication and risk stratification for individualized therapeutic and surveillance strategies. In this prospective study, the combination of more variable telomere length among cancer cells and shorter telomere length in CAS cells was strongly associated with progression to metastasis and prostate cancer death, pointing to the translational potential for prognostication and risk stratifi cation for individualized therapeutic and surveillance strategies.

Telomere length and adrenergic-induced left ventricular dilatation and systolic chamber dysfunction in rats

The mechanisms responsible for telomere shortening in heart failure are uncertain. We evaluated whether left ventricular (LV) dilatation and systolic chamber dysfunction produced by chronic β-adrenergic receptor (β-AR) activation is associated with leukocyte or cardiac telomere shortening. Following 6 months of daily injections of the β-AR agonist, isoproterenol (0.02 mg/kg/day) or the saline vehicle to rats, the extent of LV dilatation and LV systolic chamber dysfunction were determined using echocardiography and isolated perfused heart procedures, and relative telomere length of leukocyte (LTL) and cardiac (CTL) deoxyribonucleic acid were determined using a quantitative real-time polymerase chain reaction assay. β-AR activation resulted in LV dilatation as indexed by increased LV diastolic diameters (9.2 ± 0.6 vs. 8.4 ± 0.9 mm, P = 0.01) and increased diastolic volume intercepts at zero pressure of the LV diastolic pressure-volume relationship (isolated, perfused heart preparation) (0.40 ± 0.06 vs. 0.37 ± 0.08 ml, P = 0.03). Moreover, β-AR activation resulted in LV systolic chamber dysfunction as indexed by reductions in LV endocardial fractional shortening (0.40 ± 0.05 vs. 0.45 ± 0.06, P = 0.01) and the slope of the LV systolic pressure-volume relation (609 ± 176 vs. 901 ± 230, P = 0.01). Although LTL decreased with age in rats receiving either the β-AR agonist or the saline vehicle (P < 0.05), neither CTL (-0.10 ± 0.14 vs. -0.15 ± 0.12, P = 0.3) nor LTL (-0.11 ± 0.19 vs. -0.15 ± 0.18, P = 0.5) were modified by β-AR activation. In conclusion, chronic β-AR activation sufficient to produce LV dilatation and systolic chamber dysfunction is not associated with alterations in leukocyte or cardiac telomere length. Telomere shortening in chronic heart failure is unlikely to be attributed to chronic β-AR activation.

Genotoxicity biomarkers associated with exposure to traffic and near-road atmospheres: a review

Diesel and gasoline emissions, which are the primary components of traffic exhaust, are known or possible human carcinogens, respectively, and working or living near high-traffic roads is associated with various health effects, including cancer. To help understand the mechanistic basis for this observation, the present article reviews 63 studies on genotoxicity biomarkers in traffic-exposed subjects, with office workers being the typical control subjects. The six primary biomarkers used in these studies were the traditional cytogenetic end points, chromosome aberrations (CAs), micronucleus (MN) and sister chromatid exchange, and the standard molecular end points for DNA damage, (32)P-postlabeling, the comet assay and urinary 8-hydroxydeoxyguanosine. These six assays accounted for 74 of the 87 biomarker assessments reported in the studies; all six effectively distinguished traffic-exposed from control populations, giving an average 89% positive results among exposed versus control subjects. In addition, three genomic biomarkers effectively distinguished between the exposed and control populations; these assays measured changes in gene expression, leukocyte telomere length and DNA methylation. Nearly half of all of the studies included exposure assessments involving blood (primarily protein adducts), urine (primarily 1-hydroxypyrene) or air (primarily polycyclic aromatic hydrocarbons); these assays distinguished the exposed from the control subjects for the vast majority of the studies. All but three of the 63 reports were environmental studies that investigated 18 general exposure categories, such as traffic police and automobile/bus mechanics. The studies were performed in 20 countries; however, nearly all of the environmental studies were performed in Europe and Asia, with only one each from Africa, North America and South America. Given that several of the biomarkers are associated with increased cancer risk, including CAs, MNs and altered telomere length, the data reviewed here provide strong mechanistic support for the ability of chronic exposure to traffic exhaust to increase cancer risk.

Deletion of the major peroxiredoxin Tsa1 alters telomere length homeostasis

Reactive oxygen species (ROS) are proposed to play a major role in telomere length alterations during aging. The mechanisms by which ROS disrupt telomeres remain unclear. In Saccharomyces cerevisiae, telomere DNA consists of TG(1-3) repeats, which are maintained primarily by telomerase. Telomere length maintenance can be modulated by the expression level of telomerase subunits and telomerase activity. Additionally, telomerase-mediated telomere repeat addition is negatively modulated by the levels of telomere-bound Rap1-Rif1-Rif2 protein complex. Using a yeast strain defective in the major peroxiredoxin Tsa1 that is involved in ROS neutralization, we have investigated the effect of defective ROS detoxification on telomere DNA, telomerase, telomere-binding proteins, and telomere length. Surprisingly, the tsa1 mutant does not show significant increase in steady-state levels of oxidative DNA lesions at telomeres. The tsa1 mutant displays abnormal telomere lengthening, and reduction in oxidative exposure alleviates this phenotype. The telomere lengthening in the tsa1 cells was abolished by disruption of Est2, subtelomeric DNA, Rap1 C-terminus, or Rif2, but not by Rif1 deletion. Although telomerase expression and activity are not altered, telomere-bound Est2 is increased, while telomere-bound Rap1 is reduced in the tsa1 mutant. We propose that defective ROS scavenging can interfere with pathways that are critical in controlling telomere length homeostasis.

Anti-Apoptotic Effect of Human Telomerase Reverse Transcriptase on Endothelial Cells under Oxidative Stress, Independent of Telomere Elongation and Telomerase Activity

Increasing age and replicative senescence with critical shortening of telomeres is associated with endothelial dysfunction followed by atherosclerosis. Although human telomerase reverse transcriptase (hTERT) is suggested to play an important role in endothelial cells, the precise effect of hTERT is still uncertain. In this study we investigated telomerase- independent hTERT function against oxidative stress using a primary culture of endothelial cells in which telomerase enzymatic activity was inhibited by addition of 3’-azido-3’-deoxythymidine (AZT). Overexpression of hTERT attenuated H2O2-induced endothelial apoptosis, assessed by cell viability assay and flow cytometry, accompanied by significant reduction of caspase-3 activity. Of importance, it was suggested that this effect was independent of telomerase enzymatic activity because hTERT expression did not alter telomere length under addition of AZT. Also, suppression of human telomerase-associated protein 1 (TEP-1) by introduction of TEP-1-specific small interfering RNA (siRNA) did not affect the anti-apoptotic effect of hTERT, suggesting that hTERT does not cooperate with TEP-1, another component of telomerase. Moreover, the anti-apoptotic effect of hTERT was through attenuation of H2O2-induced upregulation of p53, followed by reduction of Bax and induction of Bcl-xL. Also, overexpression of hTERT resulted in activation of the transcription factor, NFκB, which is an anti-apoptotic factor. Altogether, the present study demonstrated the anti-apoptotic effect of not telomerase but hTERT itself on cultured endothelial cells under oxidative stress, independent of telomere elongation, followed by acquired replicative ability. Also, this function of hTERT did not require another protein component of telomerase. Moreover, the anti-apoptotic effect of hTERT on endothelial cells was mediated by two pathways; reduction of p53/Bax and activation of NFκB. Keywords: Apoptosis, atherosclerosis, AZT, Bax, Bcl-xL, caspase-3, endothelial cell, hTERT, NFκB, oxidative stress, p53, telomerase, telomere length, TEP-1.

Multiple independent variants at the TERT locus are associated with telomere length and risks of breast and ovarian cancer

TERT-locus SNPs and leukocyte telomere measures are reportedly associated with risks of multiple cancers. Using the Illumina custom genotyping array iCOGs, we analyzed ∼480 SNPs at the TERT locus in breast (n = 103,991), ovarian (n = 39,774) and BRCA1 mutation carrier (n = 11,705) cancer cases and controls. Leukocyte telomere measurements were also available for 53,724 participants. Most associations cluster into three independent peaks. The minor allele at the peak 1 SNP rs2736108 associates with longer telomeres (P = 5.8 × 10(-7)), lower risks for estrogen receptor (ER)-negative (P = 1.0 × 10(-8)) and BRCA1 mutation carrier (P = 1.1 × 10(-5)) breast cancers and altered promoter assay signal. The minor allele at the peak 2 SNP rs7705526 associates with longer telomeres (P = 2.3 × 10(-14)), higher risk of low-malignant-potential ovarian cancer (P = 1.3 × 10(-15)) and greater promoter activity. The minor alleles at the peak 3 SNPs rs10069690 and rs2242652 increase ER-negative (P = 1.2 × 10(-12)) and BRCA1 mutation carrier (P = 1.6 × 10(-14)) breast and invasive ovarian (P = 1.3 × 10(-11)) cancer risks but not via altered telomere length. The cancer risk alleles of rs2242652 and rs10069690, respectively, increase silencing and generate a truncated TERT splice variant.

Association of Leukocyte Telomere Length with Colorectal Cancer Risk: Nested Case–Control Findings from the Shanghai Women's Health Study

Telomeres are specialized chromatin structures essential for maintenance of chromosomal integrity and stability. Abnormal alteration of telomere length has been linked to several cancers; however, epidemiologic evidence about the association of telomere length with colorectal cancer risk has been conflicting. We conducted a nested case-control study to evaluate the association between telomere length and colorectal cancer risk using peripheral blood samples collected before cancer diagnosis. The study included 441 women with incident colorectal cancer and 549 matched controls. Monochrome multiplex quantitative PCR was applied to measure relative telomere length. Multiple logistic regressions were used to derive adjusted OR with 95% confidence intervals (CI) as the measure of association between telomere length and subsequent colorectal cancer risk. A U-shaped association was observed between telomere length and colorectal cancer risk (test for nonlinearity P = 0.0112). Women with telomere length in the third quintile (40th-60th percentiles) had the lowest risk of colorectal cancer, and the risks were elevated with a shorter or longer telomere length. This U-shaped association did not statistically differ for colon cancer and rectum cancer. Our prospective study revealed a U-shaped association between telomere length in peripheral blood cells and colorectal cancer risk. Our findings provide strong evidence that both very short and very long telomeres are associated with increased risk of colorectal cancer.

Aging-Associated Alteration of Telomere Length and Subtelomeric Status in Female Patients With Parkinson's Disease

: A telomere is a repetitive DNA structure at chromosomal ends that stabilizes the chromosome structure and prevents harmful end-to-end recombinations. The telomere length of somatic cells becomes shorter with aging because of the “end replication problem.” This telomere shortening is accelerated by pathophysiological conditions including daily mental stress. Living with Parkinson's disease (PD) causes physical and mental stress; therefore, the authors hypothesized that the telomere length of somatic cells was shortened excessively in patients with PD. In order to detect PD-associated somatic telomeric alterations, the telomere length and subtelomeric methylation status of peripheral leukocytes of PD patients were assessed by Southern blotting, using methylation-sensitive and -insensitive isoschizomers. The results demonstrated that the peripheral leukocytes of Japanese female patients with PD bore fewer long telomeres and a proportional increase of hypomethylated subtelomeres in short telomeres in comparison with the healthy controls. This study indicates that with the neurodegeneration associated with PD, telomeric and subtelomeric structural alterations occur. These structural telomere altertions most likely occur secondary to the acceleration of aging-associated telomeric changes and the accelerated loss of cells bearing short telomeres.

Physical activity in midlife and telomere length measured in old age

Physical activity has been associated with alterations in telomere length, a potential indicator of biological aging, but several inconsistencies exist. Our aim was to investigate the associations between physical activity in midlife and leukocyte telomere length (LTL) measured in old age in the Helsinki Businessmen Study, Finland. At entry, in 1974, 782 men (mean age 47) completed a questionnaire about their physical activity and this was collapsed into 3 categories: low (n=148), moderate (n=398) and high physical activity (n=236, 7 of whom had a competitive activity level). After 29-year follow-up in 2003, mean LTL and the proportion of short (<5kB) telomeres were measured from DNA samples of a random subcohort of survivors (n=204, mean age 76) using the Southern blot technique. Adjusted for age, body mass index (BMI), cholesterol and smoking in 1974, the moderate physical activity group had longer mean LTL (8.27kB, SE 0.05) than the low (8.10kB, SE 0.07), or high (8.10kB, SE 0.05) physical activity groups (P=0.03 between groups). Conversely, the proportion of short telomeres was lowest in the moderate physical activity group (11.35%, SE 0.25), and higher in the high (12.39%, SE 0.29), and the low physical activity (12.21%, SE 0.39) groups (P=0.02 between groups). We conclude that the results of this observational cohort study give support to the idea that both low and high physical activity is in the long-term associated with factors shortening LTL.

Alteration of Telomere Length and Subtelomeric Methylation in Human Endothelial Cell Under Different Levels of Hypoxia

Hypoxia-associated changes of telomeric structure in cell cultures have been analyzed mainly in cancer cells, stem cells, or cells transduced with vectors containing the telomerase gene, but not in somatic cells. The stability of telomere structure has been reported to be associated with subtelomeric methylation status. However, there are no reports of epigenetic alterations of telomeric regions of human somatic cells under hypoxia. This study aims at detecting and analyzing the subtelomeric methylation status in human somatic cells cultured under hypoxia. Mean telomere length and telomerase activity of human umbilical vein endothelial cells (HUVECs) cultured in hypoxic conditions were measured. Subtelomeric methylation status of these cells was assessed by genomic Southern blot with telomere DNA probe using methylation-sensitive and -insensitive isoschizomers, MspI and HpaII. The telomerase activity in HUVECs correlated inversely with the oxygen concentration. Mild hypoxia (10 or 15% oxygen) increased the telomere lengths, whereas the telomere lengths did not appear to change when <1% O(2). The subtelomere of the shortest telomere range was methylated the most at 1% O(2). Subtelomeric hypermethylation of short telomeres at 1% O(2) compared to milder hypoxia implied that the subtelomeric hypermethylation may yield telomere stability and favor the cell survival of short telomere-bearing cells.

Natural Polymorphism in BUL2 Links Cellular Amino Acid Availability with Chronological Aging and Telomere Maintenance in Yeast

Aging and longevity are considered to be highly complex genetic traits. In order to gain insight into aging as a polygenic trait, we employed an outbred Saccharomyces cerevisiae model, generated by crossing a vineyard strain RM11 and a laboratory strain S288c, to identify quantitative trait loci that control chronological lifespan. Among the major loci that regulate chronological lifespan in this cross, one genetic linkage was found to be congruent with a previously mapped locus that controls telomere length variation. We found that a single nucleotide polymorphism in BUL2, encoding a component of an ubiquitin ligase complex involved in trafficking of amino acid permeases, controls chronological lifespan and telomere length as well as amino acid uptake. Cellular amino acid availability changes conferred by the BUL2 polymorphism alter telomere length by modulating activity of a transcription factor Gln3. Among the GLN3 transcriptional targets relevant to this phenotype, we identified Wtm1, whose upregulation promotes nuclear retention of ribonucleotide reductase (RNR) components and inhibits the assembly of the RNR enzyme complex during S-phase. Inhibition of RNR is one of the mechanisms by which Gln3 modulates telomere length. Identification of a polymorphism in BUL2 in this outbred yeast population revealed a link among cellular amino acid availability, chronological lifespan, and telomere length control.

Telomere Length in Neoplastic and Nonneoplastic Tissues of Patients with Familial and Sporadic Papillary Thyroid Cancer

Many studies have found an association between altered telomere length (TL), both attrition or elongation, and cancer phenotype. Recently, we have reported that patients with the familial form of papillary thyroid cancer (FPTC) have short telomeres in blood leucocytes. To evaluate relative TL (RTL) at somatic level in neoplastic and nonneoplastic tissues of patients with FPTC (n = 30) and sporadic PTC (n = 46). RTL was measured by quantitative PCR in neoplastic thyroid tissues, in the corresponding nontumor thyroid tissues (normal contralateral thyroid), and in other extrathyroidal tissues (lymph nodes, muscles, or buccal mucosa). RTL was also measured in adenomas and hyperplastic nodules. In a subset of samples, telomerase expression was measured by quantitative PCR. Mean ± SD RTL of FPTC patients was short in neoplastic thyroid tissues (0.87 ± 0.2) with no difference from the normal contralateral thyroid tissues (0.85 ± 0.11) and extrathyroidal tissues (0.85 ± 0.31). On the contrary, in patients with sporadic PTC, the mean ± SD RTL in the neoplastic tissues (1.73 ± 0.63) was significantly shorter than that found in normal contralateral tissues (2.58 ± 0.89) and extrathyroidal tissues (2.5 ± 0.86). For all tissue samples (cancer, normal thyroid, and nonthyroidal tissues) the mean ± SD RTL of familial cases was shorter (P < 0.0001) than that found in tissues from sporadic PTC. RTL of FPTC was also lower (P < 0.0001) than that of 23 follicular adenomas (1.6 ± 0.7) and 24 hyperplastic nodules (2.2 ± 0.9). Our results demonstrate that short telomeres are a consistent feature of PTC, which in familial cases, is not restricted to the tumor tissue. This finding suggests that FPTC has a distinct, heritable, genetic background.

Rif1 Supports the Function of the CST Complex in Yeast Telomere Capping

Telomere integrity in budding yeast depends on the CST (Cdc13-Stn1-Ten1) and shelterin-like (Rap1-Rif1-Rif2) complexes, which are thought to act independently from each other. Here we show that a specific functional interaction indeed exists among components of the two complexes. In particular, unlike RIF2 deletion, the lack of Rif1 is lethal for stn1ΔC cells and causes a dramatic reduction in viability of cdc13-1 and cdc13-5 mutants. This synthetic interaction between Rif1 and the CST complex occurs independently of rif1Δ-induced alterations in telomere length. Both cdc13-1 rif1Δ and cdc13-5 rif1Δ cells display very high amounts of telomeric single-stranded DNA and DNA damage checkpoint activation, indicating that severe defects in telomere integrity cause their loss of viability. In agreement with this hypothesis, both DNA damage checkpoint activation and lethality in cdc13 rif1Δ cells are partially counteracted by the lack of the Exo1 nuclease, which is involved in telomeric single-stranded DNA generation. The functional interaction between Rif1 and the CST complex is specific, because RIF1 deletion does not enhance checkpoint activation in case of CST-independent telomere capping deficiencies, such as those caused by the absence of Yku or telomerase. Thus, these data highlight a novel role for Rif1 in assisting the essential telomere protection function of the CST complex.

Longer leukocyte telomere length predicts increased risk of hepatitis b virus‐related hepatocellular carcinoma

Convincing evidence has indicated that an alteration in telomere length is involved in tumorigenesis. In epidemiologic studies, a strong correlation also has been observed consistently between relative telomere length (RTL) in peripheral blood leukocytes (PBLs) and susceptibility of many cancers. However, whether leukocyte RTL can be used as a predictor of risk for hepatocellular carcinoma (HCC) remains to be determined. The RTL in PBLs was determined by measuring the telomere repeat copy number to single-copy gene number ratio in each sample compared with a reference DNA sample using a polymerase chain reaction-based method in this case-control study. The study participants included 240 patients with HCC (cases), a group of 240 healthy individuals (controls), and 120 noncancer controls with chronic liver disease (CLD). HCC cases exhibited a significantly longer RTL (median, 0.57; range, 0.21-3.3) than CLD controls (median, 0.46; range, 0.15-1.99; P < .001) and healthy controls (median, 0.39; range, 0.13-2.69; P < .001). Compared with individuals who had short RTL, individuals who had long RTL had a significantly increased risk of HCC when either healthy controls (adjusted odds ratio [OR], 7.28; 95% confidence interval, 4.46-11.88) or CLD controls (adjusted OR, 2.86; 95% confidence interval, 1.74-4.70) were used as the reference group. A significant dose-response relation was observed between HCC risk and long RTL (P(trend) < .001 for both control groups). In addition, there was a significantly positive RTL correlation between PBLs and normal liver tissues (r = 0.78; P < .001) or cirrhotic liver tissues (r = 0.67; P = .001). Furthermore, a significant joint effect on the risk of HCC was noted between RTL and smoking status or alcohol use. The current study produced the first epidemiologic evidence linking long RTL in PBLs to an increased risk of HCC. The authors concluded that these findings warrant further investigation in other populations.

Alternative lengthening of telomeres—An enhanced chromosomal instability in aggressive non‐MYCN amplified and telomere elongated neuroblastomas

Telomere length alterations are known to cause genomic instability and influence clinical course in several tumor types, but have been little investigated in neuroblastoma (NB), one of the most common childhood tumors. In the present study, telomere-dependent chromosomal instability and telomere length were determined in six NB cell lines and fifty tumor biopsies. The alternative lengthening of telomeres (ALT) pathway was assayed by scoring ALT-associated promyelocytic leukemia (PML) bodies (APBs). We found a reduced probability of overall survival for tumors with increased telomere length compared to cases with reduced or unchanged telomere length. In non-MYCN amplified tumors, a reduced or unchanged telomere length was associated with 100% overall survival. Tumor cells with increased telomere length had an elevated frequency of APBs, consistent with activation of the ALT pathway. The vast majority of tumor biopsies and cell lines exhibited an elevated rate of anaphase bridges, suggesting telomere-dependent chromosomal instability. This was more pronounced in tumors with increased telomere length. In cell lines, there was a close correlation between lack of telomere-protective TTAGGG-repeats, anaphase bridging, and remodeling of oncogene sequences. Thus, telomere-dependent chromosomal instability is highly prevalent in NB, and may contribute to the complexity of genomic alterations as well as therapy resistance in the absence of MYCN amplification and in this tumor type.

Telomere length maintenance: a factor to be considered in personalized medicine?

telomerase is required to sustain their growth. The fact that cancer cells have shorter telomeres than normal cells, together with the fact that cancer growth appears to depend on telomerase reactivation, indicates that therapeutic strategies that are aimed at inhibiting telomerase will preferentially kill the tumor cells and have no toxicity on normal cells [3]. Since telomerase and telomere maintenance play a key role in the development of malignancies, several approaches targeting either the telomerase enzyme or the telomeres have been developed. However, while many efforts have been carried out to discover new anti-telomere/telomerase drugs, to date, very few compounds are exploitable for clinical use owing to low effectiveness or toxicity in vivo and also because of our partial knowledge on telomere and telomerase regulation and its functions [4]. There is growing evidence that telomere length carries information that may be of clinical importance for cancer patients. It is well established that telomere length is important for senescence in normal cells and there appears to be a connection between telomere shortening, genetic aberrations and the risk of cell transformation. Interests in investigating telomere length as a potential clinical biomarker in cancer has grown considerably in recent years. For hematogical malignancies, published data demon strate that short telomeres indicate progressive disease and a poor outcome [5]. For solid tumors the data are more heterogeneous. Thus, in colorectal cancer (CRC) telomere reduction appears to occur in parallel in noncancerous mucosa and colon cancer, with a correlation between both. Functional studies have implicated human TRF1 in telomere length Telomeres form specialized structures at the ends of eukaryotic chromosomes, preventing them from being wrongly recognized as damaged DNA. In normal cells, the DNA replication machinery is unable to completely duplicate telomeric DNA; thus, telomeres are shortened after every cell division. When telomeres become critically shortened and compromise genomic stability, chromosome ends activate DNA damage response pathways that can induce apoptosis. In cancer, these mechanisms are often inactivated, and telomeres can become dysfunctional via several mechanisms, such as loss or alteration of telomere-binding proteins involved in telomere maintenance. These proteins are critical for the functions of telomeres as they prevent unwanted DNA repair activity [1]. Tumor cells acquire the hallmark properties of cancer during the carcinogenic selection process. Cell immortality is one of the principal features acquired, which involves the stabilization of telomere length. It is achieved mainly by telomerase activation. Thus, the discovery of telo meres and telomerase allowed an understanding of the mechanisms by which cells can become immortalized [2]. Generally tumors have shorter telomeres than the surrounding normal tissue, owing to the fact that they have had a longer proliferative history in the absence of telomerase activity. Telomere shortening can eventually lead to increased cell death and loss of cell viability within the tumor. However, telomerase is reactivated in more than 90% of all types of human tumor, thereby rescuing and perpetuating cells with short telomeres and high chromosomal instability. Similarly, most metastases also contain telomerase-positive cells, which indicate that

Abstract 3212: Development of a chemiluminescence-based single telomere length analysis (STELA) method

Abstract Carcinogenesis is a multistep process characterized by the accumulation of genetic alterations that drive the transformation of normal cells to malignant cells. Telomeres are specialized nucleoprotein structures that function to protect and stabilize the ends of eukaryotic chromosomes by preventing chromosome fusions, masking double strand DNA break damage signals and preventing exonucleolytic chromosomal degradation. It is well established that telomere shortening is present in precursor and invasive stages of many carcinomas. Additionally, numerous investigations have demonstrated that altered telomere length predisposes cells to possess the properties necessary for metastasis formation, and therefore represents a predictor of clinical outcome. However, most of these studies have used assays that measure the average telomere length of all the cells in a particular population. To circumvent this problem, Baird et al. (Nature Genetics, 2003) previously described a PCR-based single telomere length analysis (STELA) method that could accurately measure the full spectrum of telomere lengths from a specific chromosomal arm. Although this method represents a substantial improvement over existing methods, the assay requires the use of radioactive material. Here, we describe a modification of the STELA assay which uses chemiluminescence instead of radioisotopes for product visualization, while maintaining the overall sensitivity of the detection of a wide range of telomere lengths. This new methodology has tremendous potential to illuminate the mechanisms that support the initiation of cancer and may provide an avenue for investigators to address the full extent and significance of telomere shortening in the tumorigenic process at the single chromosome level. The modified assay described here will allow for more widespread use of this technique among cancer researchers. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 3212.

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 50-100bp 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.

Deletion of Ogg1 DNA glycosylase results in telomere base damage and length alteration in yeast

Telomeres consist of short guanine-rich repeats. Guanine can be oxidized to 8-oxo-7,8-dihydroguanine (8-oxoG) and 2,6-diamino-4-hydroxy-5-formamidopyrimidine (FapyG). 8-oxoguanine DNA glycosylase (Ogg1) repairs these oxidative guanine lesions through the base excision repair (BER) pathway. Here we show that in Saccharomyces cerevisiae ablation of Ogg1p leads to an increase in oxidized guanine level in telomeric DNA. The ogg1 deletion (ogg1Delta) strain shows telomere lengthening that is dependent on telomerase and/or Rad52p-mediated homologous recombination. 8-oxoG in telomeric repeats attenuates the binding of the telomere binding protein, Rap1p, to telomeric DNA in vitro. Moreover, the amount of telomere-bound Rap1p and Rif2p is reduced in ogg1Delta strain. These results suggest that oxidized guanines may perturb telomere length equilibrium by attenuating telomere protein complex to function in telomeres, which in turn impedes their regulation of pathways engaged in telomere length maintenance. We propose that Ogg1p is critical in maintaining telomere length homoeostasis through telomere guanine damage repair, and that interfering with telomere length homoeostasis may be one of the mechanism(s) by which oxidative DNA damage inflicts the genome.

Telomere attrition and telomerase activity are associated with GSTM1 polymorphism in oral cancer

Telomere attrition is an important event during tumorigenesis regulated by factors including oxidative stress, mitochondrial function, DNA adducts etc. Critically short telomeres act as signal for telomerase activity in the cancer cells. To determine whether null genotype of GSTM1 gene has any association with telomere length shortening and telomerase activity, we analyzed telomere length, telomerase activity and GSTM1 polymorphism in oral tissues. We observed that malignant tissues exhibited shorter telomere length. Telomerase activity was observed in about 75% malignant tissues. 40% of the oral cancer patients exhibited GSTM1 polymorphism. Further, shorter telomere lengths were observed in patients having GSTM1 polymorphism. Also, the GSTM1 genotype showed negative correlation with telomerase activity and telomere length. Our study proposes role of GSTM1 polymorphism in telomere attrition and subsequent telomerase activity in the cancer cells. The results are suggestive of possible link between absence of GSTM1 gene and telomere length alterations.