Telomere Length Stability Research Articles

TERT upregulation promotes cell proliferation via degradation of p21 and increases carcinogenic potential.

Telomerase reverse transcriptase (TERT) gene aberration is detectable in >80% of cases with hepatocellular carcinoma (HCC). TERT reactivation is essential for cellular immortalization because it stabilizes telomere length, although the role of TERT in hepatocarcinogenesis remains unelucidated. To elucidate the significance of aberrant TERT expression in hepatocytes in inflammation-associated hepatocarcinogenesis, we generated Alb-Cre;TertTg mice, which overexpress TERT in the liver and examined their phenotype during chronic inflammation. Based on transcriptome data from the liver tissue of Alb-Cre;TertTg mice, we examined the role of TERT in hepatocarcinogenesis in vitro. We also evaluated the relationship between TERT and cell-cycle-related molecules, including p21, in HCC samples. The liver tumor development rate was increased by TERT overexpression during chronic inflammation, especially in the absence of p53 function. Gene set enrichment analysis of liver tissues revealed that gene sets related to TNF-NFκB signaling, cell cycle, and apoptosis were upregulated in Alb-Cre;TertTg liver. A luciferase reporter assay and immunoprecipitation revealed that TERT interacted with NFκB p65 and enhanced NFκB promoter activity. On the other hand, TERT formed protein complexes with p21, cyclin A2, and cyclin E and promoted ubiquitin-mediated degradation of p21, specifically in the G1 phase. In the clinical HCC samples, TERT was highly expressed but p21 was conversely downregulated, and TERT expression was associated with the upregulation of molecules related to the cell cycle. Taken together, the aberrant upregulation of TERT increased NFκB promoter activity and promoted cell cycle progression via p21 ubiquitination, leading to hepatocarcinogenesis. © 2024 The Author(s). The Journal of Pathology published by John Wiley & Sons Ltd on behalf of The Pathological Society of Great Britain and Ireland.

Telomere dynamics in human pluripotent stem cells

ABSTRACT Pluripotent stem cells (PSCs) are a promising source of stem cells for regenerative therapies. Stem cell function depends on telomere maintenance mechanisms that provide them with the proliferative capacity and genome stability necessary to multiply and regenerate tissues. We show here that established human embryonic stem cells (hESCs) have stable telomere length that is dependent on telomerase but not on alternative mechanisms based on homologous recombination pathways. Here, we show that human-induced pluripotent stem cells (hiPSCs) reprogrammed from somatic cells show progressive telomere lengthening until reaching a length similar to ESCs. hiPSCs also acquire telomeric chromatin marks of ESCs including decreased abundance of tri-methylated histone H3K9 and H4K20 and HP1 heterochromatic marks, as well as of the shelterin component TRF2. These chromatin features are accompanied with increased abundance of telomere transcripts or TERRAs. We also found that telomeres of both hESCs and hiPSCs are well protected from DNA damage during telomere elongation and once full telomere length is achieved, and exhibit stable genomes. Collectively, this study highlights that hiPSCs acquire ESC features during reprogramming and reveals the telomere biology in human pluripotent stem cells (hPSCs).

Under pressure-exploring partner changes, physiological responses and telomere dynamics in northern gannets across varying breeding conditions.

Life history theory predicts trade-offs between reproduction and survival in species like the northern gannet (Morus bassanus). During breeding, demanding foraging conditions lead them to expand their foraging range and diversify their diet, increasing the risk of reproductive failure. Changing partners may enhance breeding success but lead to more physiological costs. To investigate the physiological costs of reproduction upon partner changes, we measured and compared 21 biomarkers related to telomere dynamics, oxidative stress, inflammation, hematology, nutritional status, and muscle damage. We used a longitudinal approach with gannets (n=38) over three contrasting years (2017, 2018 and 2019). Our results suggest that annual breeding conditions exert a greater influence on physiological changes than partnership status. Individuals that changed partner experienced greater short-term stress than retained partners. This transient increase in stress was marked by short-term increases in oxidative lipid damage, lower antioxidant capacity, signs of inflammation, and greater weight loss than individuals that retained partners. During favorable conditions, individuals that changed mates had stabilized telomere length, decreased antioxidant capacity, glucose concentration, and muscle damage, along with increased oxygen transport capacity. Conversely, unfavorable breeding conditions led to increased telomere attrition, stabilized antioxidant capacity, decreased inflammation susceptibility, diminished oxygen transport capacity, and increased muscle damage. In the cases where partners were retained, distinct physiological changes were observed depending on the year's conditions, yet the telomere dynamics remained consistent across both partnership status categories. During the favorable year, there was an increase in unsaturated fatty acids and oxygen transport capacity in the blood, coupled with a reduction in inflammation potential and protein catabolism. In contrast, during the unfavorable year in the retained mates, we observed an increase in oxidative DNA damage, antioxidant capacity, weight loss, but a decrease in inflammation susceptibility as observed in changed mates. Our study shows that behavioral flexibility such as mate switching can help seabirds cope with the challenges of food scarcity during reproduction, but these coping strategies may have a negative impact on physiological status at the individual level. In addition, the marked reduction in telomere length observed during harsh conditions, coupled with the stabilization of telomere length in favorable conditions, highlights the long-term physiological impact of annual breeding conditions on seabirds. These findings underscore the effect on their potential survival and fitness, emphasizing that the influence of annual breeding conditions is greater than that of partnership status.

Metabolic regulation reduces the oxidative damage of arid lizards in response to moderate heat events.

Climate warming poses a significant threat to species worldwide, particularly those inhabiting arid and semi-arid regions where extreme temperatures are increasingly prevalent. However, empirical studies investigating how moderate heat events affect the physiological processes of arid and semi-arid animals are largely scarce. To address this knowledge gap, we used an arid and semi-arid lizard species (Phrynocephalus przewalskii) as a study system. We manipulated thermal environments to simulate moderate heat events (43.5 ± 0.3°C during the heating period) for lizards and examined physiological and biochemical traits related to survival, metabolism, locomotion, oxidative stress, and telomere length. We found that the body condition and survival of the lizards were not significantly affected by moderate heat events, despite an increase in body temperature and a decrease in locomotion at high test temperatures were detected. Mechanistically, we found that the lizards exhibited down-regulated metabolic rates and enhanced activities of antioxidative enzymes, resulting in reduced oxidative damage and stable telomere length under moderate heat events. Based on these findings, which indicated a beneficial regulation of fitness by physiological and biochemical processes, we inferred that moderate heat events did not have a detrimental effect on the toad-headed agama, P. przewalskii. Overall, our research contributes to understanding the impacts of moderate heat events on arid and semi-arid species and highlights the adaptive responses and resilience exhibited by the toad-headed agama in the face of climate warming.

Polyadenylated Telomeric Noncoding RNA Functions as a Pivotal Therapeutic Target of Anti-Ageing to Stabilize Telomere Length of Chromosomes Via Collaborating With Zscan4c.

Telomeres are closely associated with the development of cell aging. Shortening or erosion of telomeres will cause cell mortality, suggesting that the maintenance of telomere integrity facilitates cell anti-senescence. However, the mechanism of how to keep the telomere length remains fragmentary. Here, we found that polyadenylated telomeric noncoding RNA (TERRA) can promote the self-renewal when overexpressed in mouse embryonic stem cells (mESCs), implying that TERRA with polyadenylation is critical for mESC maintenance. Further studies revealed that TERRA with a polyadenylated tail plays an important role in the sustenance of telomere length. High-throughput sequencing and quantitative real-time PCR show that zinc finger and SCAN domain containing 4C (Zscan4c) may be a potential target of TERRA. Zscan4c is negatively regulated by TERRA and collaborates with TERRA to stabilize the telomere length of chromosomes in mESCs. Our study not only identifies TERRA as a potential novel factor of telomere length regulation and uncovers the new molecular mechanism of cell anti-aging, but also indicates that Zscan4c could be a key therapeutic target candidate for therapy in dysfunctional chromosome diseases. These data will expand our understanding of the cell fate regulatory network and will be beneficial to drug discovery and theragnostics for antiaging and anticancer therapy in the future.

Chromosome-specific telomere lengths and the minimal functional telomere revealed by nanopore sequencing.

We developed a method to tag telomeres and measure telomere length by nanopore sequencing in the yeast S. cerevisiae. Nanopore allows long-read sequencing through the telomere, through the subtelomere, and into unique chromosomal sequence, enabling assignment of telomere length to a specific chromosome end. We observed chromosome end–specific telomere lengths that were stable over 120 cell divisions. These stable chromosome-specific telomere lengths may be explained by slow clonal variation or may represent a new biological mechanism that maintains equilibrium unique to each chromosome end. We examined the role of RIF1 and TEL1 in telomere length regulation and found that TEL1 is epistatic to RIF1 at most telomeres, consistent with the literature. However, at telomeres that lack subtelomeric Y′ sequences, tel1Δ rif1Δ double mutants had a very small, but significant, increase in telomere length compared with the tel1Δ single mutant, suggesting an influence of Y′ elements on telomere length regulation. We sequenced telomeres in a telomerase-null mutant (est2Δ) and found the minimal telomere length to be ∼75 bp. In these est2Δ mutants, there were apparent telomere recombination events at individual telomeres before the generation of survivors, and these events were significantly reduced in est2Δ rad52Δ double mutants. The rate of telomere shortening in the absence of telomerase was similar across all chromosome ends at ∼5 bp per generation. This new method gives quantitative, high-resolution telomere length measurement at each individual chromosome end and suggests possible new biological mechanisms regulating telomere length.

An Intermediate Concentration of Calcium with Antioxidant Supplement in Culture Medium Enhances Proliferation and Decreases the Aging of Bone Marrow Mesenchymal Stem Cells.

Human bone marrow stem cells (HBMSCs) are isolated from the bone marrow. Stem cells can self-renew and differentiate into various types of cells. They are able to regenerate kinds of tissue that are potentially used for tissue engineering. To maintain and expand these cells under culture conditions is difficult—they are easily triggered for differentiation or death. In this study, we describe a new culture formula to culture isolated HBMSCs. This new formula was modified from NCDB 153, a medium with low calcium, supplied with 5% FBS, extra growth factor added to it, and supplemented with N-acetyl-L-cysteine and L-ascorbic acid-2-phosphate to maintain the cells in a steady stage. The cells retain these characteristics as primarily isolated HBMSCs. Moreover, our new formula keeps HBMSCs with high proliferation rate and multiple linage differentiation ability, such as osteoblastogenesis, chondrogenesis, and adipogenesis. It also retains HBMSCs with stable chromosome, DNA, telomere length, and telomerase activity, even after long-term culture. Senescence can be minimized under this new formulation and carcinogenesis of stem cells can also be prevented. These modifications greatly enhance the survival rate, growth rate, and basal characteristics of isolated HBMSCs, which will be very helpful in stem cell research.

Newborn telomere length predicts later life telomere length: Tracking telomere length from birth to child- and adulthood.

BackgroundTelomere length (TL) is considered a biological marker of aging and may indicate age-related disease susceptibility. Adults and children show a fixed ranking and tracking of TL over time. However, the contribution of an individual's initial birth TL to their later life TL is unknown. We evaluated change and tracking of TL from birth to child- and adulthood.MethodsTelomere length at birth was measured using qPCR in two independent prospective birth cohorts. After a median follow-up period of 4 years in ENVIRONAGE (n = 273) we assessed leukocyte telomere length (LTL) and after 23 years in EFPTS (n = 164) buccal TL was assessed. Correlations and multivariable regression models were applied to study telomere tracking and determinants of TL change from birth onwards.FindingsIn children, LTL at the age of 4 correlates with TL at the start of life both in cord blood (r = 0.71, P < 0.0001;) and placenta (r = 0.60, P < 0.0001) and was –11.2% and –33.1% shorter, respectively. In adulthood, buccal TL at the age of 23 correlates with placental TL (r = 0.46, P < 0.0001) and was –35.9% shorter. TL attrition was higher in individuals with longer birth TL. However, based on TL ranking, individuals do not tend to change dramatically from TL rank after 4 or 23 years of follow-up. Finally, longer maternal TL associates with lower telomere attrition in the next generation.InterpretationThe high prediction of newborn TL for later life TL, and stable TL ranking from birth onwards underscores the importance of understanding the initial setting of newborn TL and its significance for later life.FundingEuropean Research Council (ERC-StG310898) and Flemish Scientific Fund (12X9620N).

Abstract 5810: Fyn kinase negatively regulates telomere length in stem cells and cancer cells

Abstract Telomere maintenance is on the critical biological process in stem cell, aging, and cancer. Cells maintain telomere either by Telomerase (TERT) dependent pathway or by alternative lengthening of telomere (ALT) pathway. Here we report a link between Fyn kinase expression and telomere length. Fyn deficient mouse and mouse embryonic stem cells (mESC) maintain a stable telomere length through activation of ALT pathway. Fyn deficient mice are also resistant to the aging process as compared to wild type mice. We uncover a novel molecular mechanism of telomere maintenance. Menin, an essential component of an MLL/SET1 histone methyltransferase (HMT) complex that specifically methylates 'Lys-4' of histone H3 (H3K4), is a potential phosphorylation target of Fyn. Phosphorylation of Menin facilitates SUMOylation and binding to Telomerase RNA Component (TERC). The telomere dysfunction is one pivotal reason for many genetic disorders, including telomere related diseases like dyskeratosis congenita (DC). Currently, there are no curative therapies for these diseases of telomere dysfunction. We knockout Fyn gene from DC mice model and also used 4-Amino-5-(4-chlorophenyl)-7-(dimethyl ethyl) pyrazolo[3,4-d]pyrimidine (PP2), a selective inhibitor of Fyn kinase. Our results demonstrate that Fyn could be a therapeutic target in telomere related diseases. Knockout of Fyn or inhibition of Fyn by using inhibitor improves DC phenotype in mice like bone marrow failure. Human iPSC generated from DC patient's skin fibroblast shows higher expression of p-Menin and maintains a stable telomere length when we inhibited Fyn. Citation Format: Souren Paul, Thi My Le Le, Joohyun Ryu, Ki Beom Bae, Ann M. Bode, Zigang Dong. Fyn kinase negatively regulates telomere length in stem cells and cancer cells [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 5810.

Telomerase reverse transcriptase gene amplification in hematological malignancies

BackgroundTelomere is a complex DNA–protein structure located at the end of all eukaryotic chromosomes. The major role of human telomerase is to catalyze the addition of telomeric repeat sequences TTAGGG onto chromosome ends for stabilization of telomere length in attaining cellular immortality and may therefore be a critical step in carcinogenesis. Expression of significant levels of telomerase can dramatically increase proliferative life span and promote cellular immortality, thereby contributing to the malignant phenotype. The purpose of this study is to investigate telomerase reverse transcriptase (TERT) gene amplification in hematological neoplasms, e.g., multiple myeloma (MM), B-non-Hodgkin lymphoma (B-NHL), and acute myeloid leukemia (AML), using FISH technique and to evaluate its potential use as a prognostic marker.ResultsTERT amplification was detected in all groups of the participant patients (15 MM, 15 B-NHL, and 15 AML patients), with higher incidence in AML patients (53.3%). A significant association between the pattern of presentation and telomerase amplification was detected in 88.9% of the relapsed patients who demonstrated amplification of TERT. TERT amplification shows a significant association with p53 deletion and a highly significant association with poor prognosis.ConclusionsTERT gene amplification is significantly associated with hematological malignancies and may play a critical role in carcinogenesis; thus, elucidation of their regulatory mechanism is highly demanding. Higher amplification was found in relapsed cases than de novo cases which highlight its potential implication in clinical analysis and disease monitoring. Moreover, our results suggest the future use of TERT gene as a potential prognostic marker that may aid in treatment decision and chemotherapy.

Urothelial cell senescence is not linked with telomere shortening.

The success of regenerative medicine relies in part on the quality of the cells implanted. Cell cultures from cells isolated from bladder washes have been successfully established, but molecular changes and cell characteristics have not been explored in detail. In this work, we analysed the role of telomere shortening in relation to the regenerative potential and senescence of cells isolated from bladder washes and expanded in culture. We also analysed whether bladder washes would be a potential source for attaining stem cells or promoting stem cell proliferation by using two different substrates to support their growth: a feeder layer of growth-arrested murine fibroblasts J2 3T3 cells and a xeno-free human recombinant laminin-coated surface. We found no association between telomere shortening and senescence in urothelial cells in vitro. Urothelial cells had a stable telomere length and expressed mesenchymal stem cells markers but failed to differentiate into bone or adipocytes. Feeder layer showed an advantage to laminin-coated surfaces in respect to proliferative capacity with the expense of risking that feeder layer cells could persist in later passages. This emphasizes the importance of using carefully controlled culture conditions and molecular quality controls before autotransplantation in future clinical settings. In conclusion, urothelial cells isolated by bladder washes show regenerative potential that need further understanding. Senescence in vitro might be due to cellular stress, and if so, further improvements in culture conditions may lead to longer cell life and higher proliferative capacity.

Targeting Telomerase and ATRX/DAXX Inducing Tumor Senescence and Apoptosis in the Malignant Glioma.

Glioblastoma multiforme (GBM) is a type of brain tumor that is notorious for its aggressiveness and invasiveness, and the complete removal of GBM is still not possible, even with advanced diagnostic strategies and extensive therapeutic plans. Its dismal prognosis and short survival time after diagnosis make it a crucial public health issue. Understanding the molecular mechanisms underlying GBM may inspire novel and effective treatments against this type of cancer. At a molecular level, almost all tumor cells exhibit telomerase activity (TA), which is a major means by which they achieve immortalization. Further studies show that promoter mutations are associated with increased TA and stable telomere length. Moreover, some tumors and immortalized cells maintain their telomeres with a telomerase-independent mechanism termed the “alternative lengthening of telomeres” (ALT), which relates to the mutations of the α-thalassemia/mental retardation syndrome X-linked protein (ATRX), the death-domain associated protein (DAXX) and H3.3. By means of the mutations of the telomerase reverse transcriptase (TERT) promoter and ATRX/DAXX, cancers can immortalize and escape cell senescence and apoptosis. In this article, we review the evidence for triggering GBM cell death by targeting telomerase and the ALT pathway, with an extra focus on a plant-derived compound, butylidene phthalide (BP), which may be a promising novel anticancer compound with good potential for clinical applications.

Telomerase abrogates aneuploidy-induced telomere replication stress, senescence and cell depletion.

The causal role of aneuploidy in cancer initiation remains under debate since mutations of euploidy-controlling genes reduce cell fitness but aneuploidy strongly associates with human cancers. Telomerase activation allows immortal growth by stabilizing telomere length, but its role in aneuploidy survival has not been characterized. Here, we analyze the response of primary human cells and murine hematopoietic stem cells (HSCs) to aneuploidy induction and the role of telomeres and the telomerase in this process. The study shows that aneuploidy induces replication stress at telomeres leading to telomeric DNA damage and p53 activation. This results in p53/Rb-dependent, premature senescence of human fibroblast, and in the depletion of hematopoietic cells in telomerase-deficient mice. Endogenous telomerase expression in HSCs and enforced expression of telomerase in human fibroblasts are sufficient to abrogate aneuploidy-induced replication stress at telomeres and the consequent induction of premature senescence and hematopoietic cell depletion. Together, these results identify telomerase as an aneuploidy survival factor in mammalian cells based on its capacity to alleviate telomere replication stress in response to aneuploidy induction.

Abstract 5232: The molecular basis for specific recognition of the biologically relevant hybrid-2 type human telomeric G-quadruplex by epiberberine

Abstract G-quadruplex structures have been shown to form in human telomeres, and the formation of G-quadruplexes can inhibit telomerase, which plays a key role in cancers by stabilizing telomere length and integrity thereby granting limitless replicative potential. The human telomeric G-quadruplex is thus considered to be a potential target for cancer therapeutics. In physiologically relevant potassium solution, human telomeric DNA sequences form two equilibrating hybrid-type G-quadruplex structures, with the hybrid-2 structure being the predominant form in extended sequences. We discovered that epiberberine (EPI), a naturally occurring protoberberine alkaloid, can specifically bind the hybrid-2 human telomeric G-quadruplex and can induce the conversion to the hybrid-2 structure. Using nuclear magnetic resonance (NMR) spectroscopy, we determined the solution structure of the 1:1 complex of EPI and hybrid-2 human telomeric G-quadruplex. Our NMR structure shows EPI bound at the 5’ end of the hybrid-2 telomeric quadruplex with an unexpectedly large drug-induced conformational change in the flanking and loop regions, creating a very well-defined drug binding pocket with extensive capping structures. The EPI molecule and 5’ flanking adenine form an induced quasi-triad plane which is intercalated between the external 5’ tetrad and capping structures. Two layers of new capping structures are formed with the 5’ flanking segment and the second TTA lateral loop to cover the “intercalated quasi-triad”. Notably, the well-defined EPI-induced multi-layer binding-site arrangement is only possible in the hybrid-2 folding topology of telomeric DNA. Our results provide important insights into specific targeting of the physiologically relevant hybrid-2 human telomeric G-quadruplex by a small molecule compound; EPI’s asymmetric crescent-shape and the positioning of its dioxolane moiety, as well as the hybrid-2 folding and the loop and flanking bases in the human telomeric DNA sequence, all contribute toward the specific recognition of EPI. In addition, we have conducted polymerase stop assays, which confirmed that EPI can stabilize the human telomeric G-quadruplex to inhibit polymerase activity. Citation Format: Clement Lin, Guanhui Wu, Yong Shao, Danzhou Yang. The molecular basis for specific recognition of the biologically relevant hybrid-2 type human telomeric G-quadruplex by epiberberine [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 5232. doi:10.1158/1538-7445.AM2017-5232

Targeting telomerase and telomeres to enhance ionizing radiation effects in in vitro and in vivo cancer models.

One of the hallmarks of cancer consists in the ability of tumor cells to divide indefinitely, and to maintain stable telomere lengths throughout the activation of specific telomere maintenance mechanisms (TMM). Therefore in the last fifteen years, researchers proposed to target telomerase or telomeric structure in order to block limitless replicative potential of cancer cells providing a fascinating strategy for a broad-spectrum cancer therapy. In the present review, we report in vitro and in vivo evidence regarding the use of chemical agents targeting both telomerase or telomere structure and showing promising antitumor effects when used in combination with ionizing radiation (IR). RNA interference, antisense oligonucleotides (e.g., GRN163L), non-nucleoside inhibitors (e.g., BIBR1532) and nucleoside analogs (e.g., AZT) represent some of the most potent strategies to inhibit telomerase activity used in combination with IR. Furthermore, radiosensitizing effects were demonstrated also for agents acting directly on the telomeric structure such as G4-ligands (e.g., RHPS4 and Telomestatin) or telomeric-oligos (T-oligos). To date, some of these compounds are under clinical evaluation (e.g., GRN163L and KML001). Advantages of Telomere/Telomerase Targeting Compounds (T/TTCs) coupled with radiotherapy may be relevant in the treatment of radioresistant tumors and in the development of new optimized treatment plans with reduced dose adsorbed by patients and consequent attenuation of short- end long-term side effects. Pros and cons of possible future applications in cancer therapy based on the combination of T/TCCs and radiation treatment are discussed.

Treating Cancer by Targeting Telomeres and Telomerase.

Telomerase is expressed in more than 85% of cancer cells. Tumor cells with metastatic potential may have a high telomerase activity, allowing cells to escape from the inhibition of cell proliferation due to shortened telomeres. Human telomerase primarily consists of two main components: hTERT, a catalytic subunit, and hTR, an RNA template whose sequence is complimentary to the telomeric 5′-dTTAGGG-3′ repeat. In humans, telomerase activity is typically restricted to renewing tissues, such as germ cells and stem cells, and is generally absent in normal cells. While hTR is constitutively expressed in most tissue types, hTERT expression levels are low enough that telomere length cannot be maintained, which sets a proliferative lifespan on normal cells. However, in the majority of cancers, telomerase maintains stable telomere length, thereby conferring cell immortality. Levels of hTERT mRNA are directly related to telomerase activity, thereby making it a more suitable therapeutic target than hTR. Recent data suggests that stabilization of telomeric G-quadruplexes may act to indirectly inhibit telomerase action by blocking hTR binding. Telomeric DNA has the propensity to spontaneously form intramolecular G-quadruplexes, four-stranded DNA secondary structures that are stabilized by the stacking of guanine residues in a planar arrangement. The functional roles of telomeric G-quadruplexes are not completely understood, but recent evidence suggests that they can stall the replication fork during DNA synthesis and inhibit telomere replication by preventing telomerase and related proteins from binding to the telomere. Long-term treatment with G-quadruplex stabilizers induces a gradual reduction in the length of the G-rich 3’ end of the telomere without a reduction of the total telomere length, suggesting that telomerase activity is inhibited. However, inhibition of telomerase, either directly or indirectly, has shown only moderate success in cancer patients. Another promising approach of targeting the telomere is the use of guanine-rich oligonucleotides (GROs) homologous to the 3’ telomere overhang sequence (T-oligos). T-oligos, particularly a specific 11-base oligonucleotide (5’-dGTTAGGGTTAG-3’) called T11, have been shown to induce DNA damage responses (DDRs) such as senescence, apoptosis, and cell cycle arrest in numerous cancer cell types with minimal or no cytostatic effects in normal, non-transformed cells. As a result, T-oligos and other GROs are being investigated as prospective anticancer therapeutics. Interestingly, the DDRs induced by T-oligos in cancer cells are similar to the effects seen after progressive telomere degradation in normal cells. The loss of telomeres is an important tumor suppressor mechanism that is commonly absent in transformed malignant cells, and hence, T-oligos have garnered significant interest as a novel strategy to combat cancer. However, little is known about their mechanism of action. In this review, we discuss the current understanding of how T-oligos exert their antiproliferative effects in cancer cells and their role in inhibition of telomerase. We also discuss the current understanding of telomerase in cancer and various therapeutic targets related to the telomeres and telomerase.

Telomere protein RAP1 levels are affected by cellular aging and oxidative stress.

Telomeres are important for maintaining the integrity of the genome through the action of the shelterin complex. Previous studies indicted that the length of the telomere did not have an effect on the amount of the shelterin subunits; however, those experiments were performed using immortalized cells with stable telomere lengths. The interest of the present study was to observe how decreasing telomere lengths over successive generations would affect the shelterin subunits. As neonatal human dermal fibroblasts aged and their telomeres became shorter, the levels of the telomere-binding protein telomeric repeat factor 2 (TRF2) decreased significantly. By contrast, the levels of one of its binding partners, repressor/activator protein 1 (RAP1), decreased to a lesser extent than would be expected from the decrease in TRF2. Other subunits, TERF1-interacting nuclear factor 2 and protection of telomeres protein 1, remained stable. The decrease in RAP1 in the older cells occurred in the nuclear and cytoplasmic fractions. Hydrogen peroxide (H2O2) stress was used as an artificial means of aging in the cells, and this resulted in RAP1 levels decreasing, but the effect was only observed in the nuclear portion. Similar results were obtained using U251 glioblastoma cells treated with H2O2 or grown in serum-depleted medium. The present findings indicate that TRF2 and RAP1 levels decrease as fibroblasts naturally age. RAP1 remains more stable compared to TRF2. RAP1 also responds to oxidative stress, but the response is different to that observed in aging.

Role of Telomeres and Telomerase in Aging and Cancer.

Telomeres progressively shorten throughout life. A hallmark of advanced malignancies is the ability for continuous cell divisions that almost universally correlates with the stabilization of telomere length by the reactivation of telomerase. The repression of telomerase and shorter telomeres in humans may have evolved, in part, as an anticancer protection mechanism. Although there is still much we do not understand about the regulation of telomerase, it remains a very attractive and novel target for cancer therapeutics. This review focuses on the current state of advances in the telomerase area, identifies outstanding questions, and addresses areas and methods that need refinement. Despite many recent advances, telomerase remains a challenging target for cancer therapy. There are few telomerase-directed therapies, and many of the assays used to measure telomeres and telomerase have serious limitations. This review provides an overview of the current state of the field and how recent advances could affect future research and treatment approaches. Cancer Discov; 6(6); 584-93. ©2016 AACR.

Baseline biopsychosocial determinants of telomere length and 6-year attrition rate

BackgroundShort leukocyte telomere length (TL) and accelerated telomere attrition have been associated with various deleterious health outcomes, although their determinants have not been explored collectively in a large-scale study. Material and methodsLeukocyte TL was measured (baseline N=2936; 6-year follow-up N=1860) in participants (18–65 years) from the NESDA study. Baseline determinants of TL included sociodemographics, lifestyle, chronic diseases, psychosocial stressors, and metabolic and physiological stress markers. Multivariate linear regression models were used to examine the associations between these determinants and (1) baseline TL, and (2) 6-year TL change. Multinomial logistic regression analyses were used to examine the predictors of telomere attrition and lengthening, as compared to stable TL. ResultsShort baseline TL was associated with older age, male sex, non-European ethnicity, cigarette smoking, recent life events, and higher triglycerides, glucose and pre-ejection period (R2=11.3%). The 6-year telomere attrition was inversely associated with baseline TL (R2=51.6%); also older age, long sleep, not having a partner, high childhood trauma index, and gastrointestinal disease were associated with 6-year TL attrition (additional R2=3.7%). Telomere attrition seemed to have slightly more predictors than lengthening. ConclusionsSociodemographic, lifestyle, psychosocial stress and metabolic and physiological stress factors are cross-sectionally linked with TL. Telomere attrition over six years was strongly associated with baseline TL, suggesting an internal homeostatic influence. Modulation of the identified determinants may become target of future studies to promote telomere maintenance and healthy aging.

Telomere Length as a Prognostic Factor for Overall Survival in Colorectal Cancer Patients

Background/Aims: The stabilization of telomere length has important roles in the carcinogenesis of colorectal cancer. A systemic review and meta-analysis of published studies was performed to assess the prognostic role of telomere length in colorectal cancer. Methods: Pubmed and Embase were searched for eligible studies on the association between telomere length and overall survival in colorectal cancer patients. The pooled hazard ratio (HR) and corresponding 95% confidence intervals (95%CI) was calculated using fixed-effects or random-effects model according to the magnitude of between-study heterogeneity. Results: Seven individual studies with a total of 956 colorectal cancer patients were included. Long telomere length in cancer tissues was marginally associated with poorer overall survival (Random-effects HR = 1.85, 95% 0.90 to 3.83, P = 0.09). When using studies with adjusted estimates, long telomere length in cancer tissues was independently and significantly associated with poorer overall survival (Fixed-effects HR = 2.70, 95% 1.51 to 4.84, P = 0.001). However, short telomere length in peripheral blood leukocytes was independently and significantly associated with poorer overall survival (Fixed-effects HR = 2.01, 95% 1.46 to 2.77, P < 0.001). Conclusions: There is some evidence for telomere length as a prognostic factor for overall survival in colorectal cancer patients. More studies with large number of participants are needed to further assess the prognostic significance of telomere length in colorectal cancer patients.