Chromosome end maintenance by telomerase

Multifunctional Nanocarriers for Alzheimer's Disease: Befriending the Barriers

Neurodegenerative diseases (NDDs) have been increasing in incidence in recent years and are now widespread worldwide. Neuronal death is defined as the progressive loss of neuronal structure or function which is closely associated with NDDs and represents the intrinsic features of such disorders. Amyotrophic lateral sclerosis, frontotemporal dementia, Alzheimer's, Parkinson's, and Huntington's diseases (AD, PD, and HD, respectively) are considered neurodegenerative diseases that affect a large number of people worldwide. Despite the testing of various drugs, there is currently no available therapy that can remedy or effectively slow the progression of these diseases. Nanomedicine has the potential to revolutionize drug delivery for the management of NDDs. The use of nanoparticles (NPs) has recently been developed to improve drug delivery efficiency and is currently subjected to extensive studies. Nanoengineered particles, known as nanodrugs, can cross the blood-brain barrier while also being less invasive compared to the most treatment strategies in use. Polymeric, magnetic, carbonic, and inorganic NPs are examples of NPs that have been developed to improve drug delivery efficiency. Primary research studies using NPs to cure AD are promising, but thorough research is needed to introduce these approaches to clinical use. In the present review, we discussed the role of metal-based NPs, polymeric nanogels, nanocarrier systems such as liposomes, solid lipid NPs, polymeric NPs, exosomes, quantum dots, dendrimers, polymersomes, carbon nanotubes, and nanofibers and surfactant-based systems for the therapy of neurodegenerative diseases. In addition, we highlighted nanoformulations such as N-butyl cyanoacrylate, poly(butyl cyanoacrylate), D-penicillamine, citrate-coated peptide, magnetic iron oxide, chitosan (CS), lipoprotein, ceria, silica, metallic nanoparticles, cholinesterase inhibitors, an acetylcholinesterase inhibitors, metal chelators, anti-amyloid, protein, and peptide-loaded NPs for the treatment of AD.

Hidradenitis suppurativa associated telomere-methylome dysregulations in blood

BACKGROUND

Hidradenitis suppurativa (HS) is a chronic debilitating disease with a significant burden of both organic and psychological comorbidities. It has been shown that certain telomere-related genes (TRGs) affect a wide range of diseases, including HS and its associated comorbidities, but their exact role in HS pathogenesis is still unknown.

OBJECTIVES

To determine whether TRG methylomes can be used as biomarkers in HS.

METHODS

Using the Illumina HumanMethylation450 BeadChip array, we examined methylation variations associated with TRGs in HS cases and age-, sex- and ethnicity-matched healthy controls. The study utilized integrated bioinformatics statistical methods, such as a false discovery rate (FDR), the area under the receiver operating characteristic curve (AUC) and principal component analysis.

RESULTS

There were a total of 585 different differentially methylated CpG sites identified in 585 TRGs associated with HS (474 hypomethylated and 111 hypermethylated) (FDR p-value < 0.05). A number of these CpGs have been identified as being involved in increased pain sensitivity including EPAS1, AHR, CSNK1D, DNMT1, IKBKAP, NOS3, PLCB1 and PRDM16 genes; GABRB3 as a potential alcohol addiction marker; DDB1, NSMCE2 and HNRNPA2B1 associated with cancers. Pathway analysis identified 67 statistically significant pathways, including DNA repair, telomere maintenance, mismatch repair and cell cycle control (p < 0.001).

CONCLUSION

The disruption of TRGs leads to the shortening of telomeres, which is associated with HS progression, ageing, cellular senescence and an increased risk of various diseases, including cancer and associated comorbidities, such as metabolic syndrome, cardiovascular disease and inflammatory disorders. Further research is necessary to better understand the underlying mechanisms and establish causal links between TRGs and HS. The present study is the first effort to comprehend potential pathomechanisms of sporadic HS cases concentrating on PBMC methylome since ours.

Transposition, duplication, and divergence of the telomerase RNA underlies the evolution of Mimulus telomeres

Telomeres are nucleoprotein complexes with a crucial role of protecting chromosome ends. It consists of simple repeat sequences and dedicated telomere-binding proteins. Because of its vital functions, components of the telomere, for example its sequence, should be under strong evolutionary constraint. But across all plants, telomere sequences display a range of variation and the evolutionary mechanism driving this diversification is largely unknown. Here, we discovered in Monkeyflower (Mimulus) the telomere sequence is even variable between species. We investigated the basis of Mimulus telomere sequence evolution by studying the long noncoding telomerase RNA (TR), which is a core component of the telomere maintenance complex and determines the telomere sequence. We conducted total RNA-based de novo transcriptomics from 16 Mimulus species and analyzed reference genomes from 6 species, and discovered Mimulus species have evolved at least three different telomere sequences: (AAACCCT)n, (AAACCCG)n, and (AAACCG)n. Unexpectedly, we discovered several species with TR duplications and the paralogs had functional consequences that could influence telomere evolution. For instance, M. lewisii had two sequence-divergent TR paralogs and synthesized a telomere with sequence heterogeneity, consisting of AAACCG and AAACCCG repeats. Evolutionary analysis of the M. lewisii TR paralogs indicated it had arisen from a transposition-mediate duplication process. Further analysis of the TR from multiple Mimulus species showed the gene had frequently transposed and inserted into new chromosomal positions during Mimulus evolution. From our results, we propose the TR transposition, duplication, and divergence model to explain the evolutionary sequence turnovers in Mimulus and potentially all plant telomeres.

Reduced intestinal lipid absorption improves glucose metabolism in aged G2-Terc knockout mice

BACKGROUND

Biological aging is an important factor leading to the development of pathologies associated with metabolic dysregulation, including type 2 diabetes, cancer, cardiovascular and neurodegenerative diseases. Telomere length, a central feature of aging, has additionally been identified as inversely associated with glucose tolerance and the development of type 2 diabetes. However, the effects of shortened telomeres on body weight and metabolism remain incompletely understood. Here, we studied the metabolic consequences of moderate telomere shortening using second generation loss of telomerase activity in mice.

RESULTS

Aged male and female G2 Terc-/- mice and controls were characterized with respect to body weight and composition, glucose homeostasis, insulin sensitivity and metabolic activity. This was complemented with molecular and histological analysis of adipose tissue, liver and the intestine as well as microbiota analysis. We show that moderate telomere shortening leads to improved insulin sensitivity and glucose tolerance in aged male and female G2 Terc-/- mice. This is accompanied by reduced fat and lean mass in both sexes. Mechanistically, the metabolic improvement results from reduced dietary lipid uptake in the intestine, characterized by reduced gene expression of fatty acid transporters in enterocytes of the small intestine. Furthermore, G2-Terc-/- mice showed significant alterations in the composition of gut microbiota, potentially contributing to the improved glucose metabolism.

CONCLUSIONS

Our study shows that moderate telomere shortening reduces intestinal lipid absorption, resulting in reduced adiposity and improved glucose metabolism in aged mice. These findings will guide future murine and human aging studies and provide important insights into the age associated development of type 2 diabetes and metabolic syndrome.

Challenges and advances for glioma therapy based on inorganic nanoparticles

Glioma is one of the most serious central nervous system diseases, with high mortality and poor prognosis. Despite the continuous development of existing treatment methods, the median survival time of glioma patients is still only 15 months. The main treatment difficulties are the invasive growth of glioma and the obstruction of the blood-brain barrier (BBB) to drugs. With rapid advancements in nanotechnology, inorganic nanoparticles (INPs) have shown favourable application prospects in the diagnosis and treatment of glioma. Due to their extraordinary intrinsic features, INPs can be easily fabricated, while doping with other elements and surface modification by biological ligands can be used to enhance BBB penetration, targeted delivery and biocompatibility. Guided glioma theranostics with INPs can improve and enhance the efficacy of traditional methods such as chemotherapy, radiotherapy and gene therapy. New strategies, such as immunotherapy, photothermal and photodynamic therapy, magnetic hyperthermia therapy, and multifunctional inorganic nanoplatforms, have also been facilitated by INPs. This review emphasizes the current state of research and clinical applications of INPs, including glioma targeting and BBB penetration enhancement methods, in vivo and in vitro biocompatibility, and diagnostic and treatment strategies. As such, it provides insights for the development of novel glioma treatment strategies.

A comprehensive map of hotspots of de novo telomere addition in Saccharomyces cerevisiae

Telomere healing occurs when telomerase, normally restricted to chromosome ends, acts upon a double-strand break to create a new, functional telomere. De novo telomere addition (dnTA) on the centromere-proximal side of a break truncates the chromosome but, by blocking resection, may allow the cell to survive an otherwise lethal event. We previously identified several sequences in the baker's yeast, Saccharomyces cerevisiae, that act as hotspots of dnTA [termed Sites of Repair-associated Telomere Addition (SiRTAs)], but the distribution and functional relevance of SiRTAs is unclear. Here, we describe a high-throughput sequencing method to measure the frequency and location of telomere addition within sequences of interest. Combining this methodology with a computational algorithm that identifies SiRTA sequence motifs, we generate the first comprehensive map of telomere-addition hotspots in yeast. Putative SiRTAs are strongly enriched in subtelomeric regions where they may facilitate formation of a new telomere following catastrophic telomere loss. In contrast, outside of subtelomeres, the distribution and orientation of SiRTAs appears random. Since truncating the chromosome at most SiRTAs would be lethal, this observation argues against selection for these sequences as sites of telomere addition per se. We find, however, that sequences predicted to function as SiRTAs are significantly more prevalent across the genome than expected by chance. Sequences identified by the algorithm bind the telomeric protein Cdc13, raising the possibility that association of Cdc13 with single-stranded regions generated during the response to DNA damage may facilitate DNA repair more generally.

A comprehensive map of hotspots of de novo telomere addition in Saccharomyces cerevisiae

Telomere healing occurs when telomerase, normally restricted to chromosome ends, acts upon a double-strand break to create a new, functional telomere. De novo telomere addition on the centromere-proximal side of a break truncates the chromosome but, by blocking resection, may allow the cell to survive an otherwise lethal event. We previously identified several sequences in the baker’s yeast, Saccharomyces cerevisiae , that act as hotspots of de novo telomere addition (termed Sites of Repair-associated Telomere Addition or SiRTAs), but the distribution and functional relevance of SiRTAs is unclear. Here, we describe a high-throughput sequencing method to measure the frequency and location of telomere addition within sequences of interest. Combining this methodology with a computational algorithm that identifies SiRTA sequence motifs, we generate the first comprehensive map of telomere-addition hotspots in yeast. Putative SiRTAs are strongly enriched in subtelomeric regions where they may facilitate formation of a new telomere following catastrophic telomere loss. In contrast, outside of subtelomeres, the distribution and orientation of SiRTAs appears random. Since truncating the chromosome at most SiRTAs would be lethal, this observation argues against selection for these sequences as sites of telomere addition per se. We find, however, that sequences predicted to function as SiRTAs are significantly more prevalent across the genome than expected by chance. Sequences identified by the algorithm bind the telomeric protein Cdc13, raising the possibility that association of Cdc13 with single-stranded regions generated during the response to DNA damage may facilitate DNA repair more generally.

Cumulative Evidence for Relationships Between Multiple Variants in the TERT and CLPTM1L Region and Risk of Cancer and Non-Cancer Disease

Background

Genetic studies previously reported that variants in TERT-CLPTM1L genes were related to susceptibility of cancer and non-cancer diseases. However, conclusions were not always concordant.

Methods

We performed meta-analyses to assess correlations between 23 variants within TERT-CLPTM1L region and susceptibility to 12 cancers and 1 non-cancer disease based on data in 109 papers (involving 139,510 cases and 208,530 controls). Two approaches (false-positive report probability test and Venice criteria) were adopted for assessing the cumulative evidence of significant associations. Current study evaluated the potential role of these variants based on data in Encyclopedia of DNA Elements (ENCODE) Project.

Results

Thirteen variants were statistically associated with susceptibility to 11 cancers and 1 non-cancer disease (p < 0.05). Besides, 12 variants with eight cancers and one non-cancer disease were rated as strong evidence (rs2736098, rs401681, and rs402710 in bladder cancer; rs2736100, rs2853691, and rs401681 in esophageal cancer; rs10069690 in gastric cancer; rs2736100 and rs2853676 in glioma; rs2242652, rs2736098, rs2736100, rs2853677, rs31489, rs401681, rs402710, rs465498, and rs4975616 in lung cancer; rs2736100 in idiopathic pulmonary fibrosis and myeloproliferative neoplasms; and rs401681 in pancreatic and skin cancer). According to data from ENCODE and other public databases, 12 variants with strong evidence might fall within putative functional regions.

Conclusions

This paper demonstrated that common variants of TERT-CLPTM1L genes were related to susceptibility to bladder, esophageal, gastric, lung, pancreatic, and skin cancer, as well as to glioma, myeloproliferative neoplasms, and idiopathic pulmonary fibrosis, and, besides, the crucial function of the TERT-CLPTM1L region in the genetic predisposition to human diseases is elucidated.

A short review on cancer therapeutics

Cancer as a disease has been a remarkable scourge and over the past years, advances have been made in understanding the molecular basis of carcinogenesis and combating this disease. The common traits exhibited by cancer have been individually studied to figure out its mode of action and its mechanism of survival even in the most austere conditions. The various hallmarks noted so far have been effectively studied and different therapies revolving around each hallmark are still being studied in order to find the most appropriate treatment for the different types of cancer in existence. Emerging therapies have been able to elucidate the mechanism of receptor blockage which facilitate the ability of cancer to proliferate as well as evade tumor suppressors, prevent cell death, support replicative immortality, escape immune destruction, stimulate angiogenesis, reduce cellular energetics as well as metabolism and prevent the destruction of the immune system. This life-threatening disease should be tackled aggressively with a combined therapy that involves two or more hallmarks of cancer and adverse effects of each therapy should also be considered.

Telomere and Telomerase-Associated Proteins in Endometrial Carcinogenesis and Cancer-Associated Survival

Risk of relapse of endometrial cancer (EC) after surgical treatment is 13% and recurrent disease carries a poor prognosis. Research into prognostic indicators is essential to improve EC management and outcome. "Immortality" of most cancer cells is dependent on telomerase, but the role of associated proteins in the endometrium is poorly understood. The Cancer Genome Atlas data highlighted telomere/telomerase associated genes (TTAGs) with prognostic relevance in the endometrium, and a recent in silico study identified a group of TTAGs and proteins as key regulators within a network of dysregulated genes in EC. We characterise relevant telomere/telomerase associated proteins (TTAPs) NOP10, NHP2, NOP56, TERF1, TERF2 and TERF2IP in the endometrium using quantitative polymerase chain reaction (qPCR) and immunohistochemistry (IHC). qPCR data demonstrated altered expression of multiple TTAPs; specifically, increased NOP10 (p = 0.03) and reduced NHP2 (p = 0.01), TERF2 (p = 0.01) and TERF2IP (p < 0.003) in EC relative to post-menopausal endometrium. Notably, we report reduced NHP2 in EC compared to post-menopausal endometrium in qPCR and IHC (p = 0.0001) data; with survival analysis indicating high immunoscore is favourable in EC (p = 0.0006). Our findings indicate a potential prognostic role for TTAPs in EC, particularly NHP2. Further evaluation of the prognostic and functional role of the examined TTAPs is warranted to develop novel treatment strategies.

Triazolyl Dibenzo[a,c]phenazines Stabilize Telomeric G-quadruplex and Inhibit Telomerase

We herein report the synthesis and biophysical evaluation of triazolyl dibenzo[a,c]phenazine derivatives as a novel class of G-quadruplex ligands. The aromatic core facilitates π-π interaction and the flexible, protonatable side chains interact with the phosphate backbone of DNA via electrostatic interactions. Förster resonance energy transfer (FRET) melting assay and isothermal titration calorimetry (ITC) studies suggest that these ligands show binding preference for the hTELO G-quadruplex over G-quadruplexes found in the promoter region of various oncogenes and duplex DNA. The in vitro telomeric repeat amplification protocol (Q-TRAP) assay reveals that these ligands reduce telomerase activity in cancer cells.

Natural variation in plant telomere length is associated with flowering time

Telomeres are highly repetitive DNA sequences found at the ends of chromosomes that protect the chromosomes from deterioration duringcell division. Here, using whole-genome re-sequencing and terminal restriction fragment assays, we found substantial natural intraspecific variation in telomere length in Arabidopsis thaliana, rice (Oryza sativa), and maize (Zea mays). Genome-wide association study (GWAS) mapping in A. thaliana identified 13 regions with GWAS-significant associations underlying telomere length variation, including a region that harbors the telomerase reverse transcriptase (TERT) gene. Population genomic analysis provided evidence for a selective sweep at the TERT region associated with longer telomeres. We found that telomere length is negatively correlated with flowering time variation not only in A. thaliana, but also in maize and rice, indicating a link between life-history traits and chromosome integrity. Our results point to several possible reasons for this correlation, including the possibility that longer telomeres may be more adaptive in plants that have faster developmental rates (and therefore flower earlier). Our work suggests that chromosomal structure itself might be an adaptive trait associated with plant life-history strategies.

When the Ends Justify the Means: Regulation of Telomere Addition at Double-Strand Breaks in Yeast

Telomeres, repetitive sequences located at the ends of most eukaryotic chromosomes, provide a mechanism to replenish terminal sequences lost during DNA replication, limit nucleolytic resection, and protect chromosome ends from engaging in double-strand break (DSB) repair. The ribonucleoprotein telomerase contains an RNA subunit that serves as the template for the synthesis of telomeric DNA. While telomere elongation is typically primed by a 3′ overhang at existing chromosome ends, telomerase can act upon internal non-telomeric sequences. Such de novo telomere addition can be programmed (for example, during chromosome fragmentation in ciliated protozoa) or can occur spontaneously in response to a chromosome break. Telomerase action at a DSB can interfere with conservative mechanisms of DNA repair and results in loss of distal sequences but may prevent additional nucleolytic resection and/or chromosome rearrangement through formation of a functional telomere (termed “chromosome healing”). Here, we review studies of spontaneous and induced DSBs in the yeast Saccharomyces cerevisiae that shed light on mechanisms that negatively regulate de novo telomere addition, in particular how the cell prevents telomerase action at DSBs while facilitating elongation of critically short telomeres. Much of our understanding comes from the use of perfect artificial telomeric tracts to “seed” de novo telomere addition. However, endogenous sequences that are enriched in thymine and guanine nucleotides on one strand (TG-rich) but do not perfectly match the telomere consensus sequence can also stimulate unusually high frequencies of telomere formation following a DSB. These observations suggest that some internal sites may fully or partially escape mechanisms that normally negatively regulate de novo telomere addition.

Telomerase and telomeres in aging theory and chronographic aging theory (Review)

The current review focuses on the connection of telomerase and telomeres with aging. In this review, we describe the changes in telomerase and telomere length (TEL) during development, their role in carcinogenesis processes, and the consequences of reduced telomerase activity. More specifically, the connection of TEL in peripheral blood cells with the development of aging‑associated diseases is discussed. The review provides systematic data on the role of telomerase in mitochondria, the biology of telomeres in stem cells, as well as the consequences of the forced expression of telomerase (telomerization) in human cells. Additionally, it presents the effects of chronic stress exposure on telomerase activity, the effect of TEL on fertility, and the effect of nutraceutical supplements on TEL. Finally, a comparative review of the chronographic theory of aging, presented by Olovnikov is provided based on currently available scientific research on telomere, telomerase activity, and the nature of aging by multicellular organisms.

Interaction of yeast Rad51 and Rad52 relieves Rad52-mediated inhibition of de novo telomere addition

DNA double-strand breaks (DSBs) are toxic forms of DNA damage that must be repaired to maintain genome integrity. Telomerase can act upon a DSB to create a de novo telomere, a process that interferes with normal repair and creates terminal deletions. We previously identified sequences in Saccharomyces cerevisiae (SiRTAs; Sites of Repair-associated Telomere Addition) that undergo unusually high frequencies of de novo telomere addition, even when the original chromosome break is several kilobases distal to the eventual site of telomerase action. Association of the single-stranded telomere binding protein Cdc13 with a SiRTA is required to stimulate de novo telomere addition. Because extensive resection must occur prior to Cdc13 binding, we utilized these sites to monitor the effect of proteins involved in homologous recombination. We find that telomere addition is significantly reduced in the absence of the Rad51 recombinase, while loss of Rad52, required for Rad51 nucleoprotein filament formation, has no effect. Deletion of RAD52 suppresses the defect of the rad51Δ strain, suggesting that Rad52 inhibits de novo telomere addition in the absence of Rad51. The ability of Rad51 to counteract this effect of Rad52 does not require DNA binding by Rad51, but does require interaction between the two proteins, while the inhibitory effect of Rad52 depends on its interaction with Replication Protein A (RPA). Intriguingly, the genetic interactions we report between RAD51 and RAD52 are similar to those previously observed in the context of checkpoint adaptation. Forced recruitment of Cdc13 fully restores telomere addition in the absence of Rad51, suggesting that Rad52, through its interaction with RPA-coated single-stranded DNA, inhibits the ability of Cdc13 to bind and stimulate telomere addition. Loss of the Rad51-Rad52 interaction also stimulates a subset of Rad52-dependent microhomology-mediated repair (MHMR) events, consistent with the known ability of Rad51 to prevent single-strand annealing.

DNA double-strand breaks (DSBs) can lead to chromosome loss and rearrangement associated with cancer and genetic disease, so understanding how the cell coordinates multiple possible repair pathways is of critical importance. Telomerase is a ribonucleoprotein enzyme that uses an intrinsic RNA component as a template for the addition of highly repetitive, protective sequences (called telomeres) at normal chromosome ends. Rarely, telomerase acts upon a DSB to create a new or de novo telomere with resultant loss of sequences distal to the site of telomere addition. Here, we show that interactions between proteins with known roles during DSB repair modulate the probability of telomerase action at hotspots of de novo telomere addition in the yeast genome by influencing the association of Cdc13, a protein required for telomerase recruitment, with sites of telomere addition. Intriguingly, the same interactions that facilitate telomere addition prevent other types of rearrangements in response to chromosome breaks.

Seryl tRNA synthetase cooperates with POT1 to regulate telomere length and cellular senescence

Deregulated telomere length is a causative factor in many physiological and pathological processes, including aging and cancer. Many studies focusing on telomeres have revealed important roles for cooperation between the Shelterin protein complex and telomerase in maintaining telomere length. However, it remains largely unknown whether and how aging-related stresses, such as deregulated protein homeostasis, impact telomere length. Here, we explored the possible roles of aminoacyl tRNA synthetases (AARSs), key enzymes catalyzing the first reactions in protein synthesis, in regulating telomere length and aging. We selected seryl tRNA synthetase (SerRS) since our previous studies discovered expanded functions of SerRS in the nucleus in addition to its canonical cytoplasmic role in protein synthesis. In this study, we revealed that overexpression of SerRS promoted cellular senescence and inhibited the growth of cervical tumor xenografts in mice by triggering the senescence of tumor cells. In the nucleus, SerRS directly bound to telomeric DNA repeats and tethered more POT1 proteins to telomeres through a direct interaction between the UNE-S domain of SerRS and the OB1 domain of POT1. We further demonstrated that SerRS-induced enrichment of POT1 prevented the recruitment of telomerase to telomeres, resulting in progressive telomere shortening. Our data suggested a possible molecular link between protein synthesis and telomere length control, the deregulation of which may be associated with aging and cancer.

Human Wharton's Jelly-Derived Mesenchymal Stem Cells Minimally Improve the Growth Kinetics and Cardiomyocyte Differentiation of Aged Murine Cardiac c-kit Cells in In Vitro without Rejuvenating Effect

Cardiac c-kit cells show promise in regenerating an injured heart. While heart disease commonly affects elderly patients, it is unclear if autologous cardiac c-kit cells are functionally competent and applicable to these patients. This study characterised cardiac c-kit cells (CCs) from aged mice and studied the effects of human Wharton’s Jelly-derived mesenchymal stem cells (MSCs) on the growth kinetics and cardiac differentiation of aged CCs in vitro. CCs were isolated from 4-week- and 18-month-old C57/BL6N mice and were directly co-cultured with MSCs or separated by transwell insert. Clonogenically expanded aged CCs showed comparable telomere length to young CCs. However, these cells showed lower Gata4, Nkx2.5, and Sox2 gene expressions, with changes of 2.4, 3767.0, and 4.9 folds, respectively. Direct co-culture of both cells increased aged CC migration, which repopulated 54.6 ± 4.4% of the gap area as compared to aged CCs with MSCs in transwell (42.9 ± 2.6%) and CCs without MSCs (44.7 ± 2.5%). Both direct and transwell co-culture improved proliferation in aged CCs by 15.0% and 16.4%, respectively, as traced using carboxyfluorescein succinimidyl ester (CFSE) for three days. These data suggest that MSCs can improve the growth kinetics of aged CCs. CCs retaining intact telomere are present in old hearts and could be obtained based on their self-renewing capability. Although these aged CCs with reduced growth kinetics are improved by MSCs via cell–cell contact, the effect is minimal.

Chemical Regulation of DNA i-Motifs for Nanobiotechnology and Therapeutics

DNA sequences rich in cytosine have the propensity, under acidic pH, to fold into four-stranded intercalated DNA structures called i-motifs. Recent studies have provided significant breakthroughs that demonstrate how chemists can manipulate these structures for nanobiotechnology and therapeutics. The first section of this Minireview discusses the development of advanced functional nanostructures by synthetic conjugation of i-motifs with organic scaffolds and metal nanoparticles and their role in therapeutics. The second section highlights the therapeutic targeting of i-motifs with chemical scaffolds and their significance in biology. For this, first we shed light on the long-lasting debate regarding the stability of i-motifs under physiological conditions. Next, we present a comparative analysis of recently reported small molecules for specifically targeting i-motifs over other abundant DNA structures and modulating their function in cellular systems. These advances provide new insights into i-motif-targeted regulation of gene expression, telomere maintenance, and therapeutic applications.

Interleukin 8 is a biomarker of telomerase inhibition in cancer cells

Background

Telomerase activity is required for both initiation and maintenance of tumorigenesis and over 90% cancers overexpress telomerase. Therefore, telomerase targeting has emerged as a potential strategy for cancer treatment. In agreement with this, several telomerase inhibitors are being tested for cancer treatment and have shown some promise. However, because of the variability in response between the cancer patients, it is important to identify biomarkers that allow for distinguishing cancers that are responsive to telomerase inhibition from the cancers that are not. Therefore, in this study we performed experiments to identify a biomarker that can be used to predict telomerase inhibition induced tumor growth inhibition.

Methods

In our study, we have performed transcriptome-wide gene expression analysis on multiple ovarian and colon cancer cell lines that were treated with telomerase inhibitor imetelstat and were responsive to telomerase inhibition-induced tumor growth attenuation.

Results

We demonstrate that telomerase inhibition by telomerase inhibitor imetelstat results in decreased expression of interleukin 8 (IL8) in all telomerase responsive cancer cell lines. This phenomenon is of general occurrence because we find that multiple ovarian and colon cell lines show decrease in IL8 mRNA and protein levels after telomerase inhibition. Additionally, we find loss of IL8 phenocopy Telomerase inhibition mediated growth inhibitory effect in cancer cells.

Conclusion

Taken together, our results show that IL8 is a biomarker that predict telomerase inhibition mediated growth attenuation of cancer cells and its loss phenocopy telomerase inhibition. Therefore, IL8 expression can be utilized as a biomarker for telomerase targeted cancer therapies to potentially predict therapeutic response.

Electronic supplementary material

The online version of this article (10.1186/s12885-018-4633-x) contains supplementary material, which is available to authorized users.

MicroRNA-1 and MicroRNA-21 Individually Regulate Cellular Growth of Non-malignant and Malignant Renal Cells

BACKGROUND/AIM

Due to its poor prognosis, it is increasingly necessary to understand the biology of renal cell cancer (RCC). Therefore, we investigated the role of microRNAs miR-1 and miR-21 in the growth of RCC cells compared to that of non-malignant renal cells.

MATERIALS AND METHODS

Four malignant cell lines (Caki-1, 786-O, RCC4, A498) were examined regarding their cell growth, microRNA and telomerase expression, and were compared to non-malignant RC-124 renal cells.

RESULTS

Inconsistencies appeared in the panel of RCC cells regarding antiproliferative and proliferative properties of miR-1 and miR-21, respectively. Notably, and most likely due to immortaliziation, non-malignant RC-124 cells exhibited telomerase expression and activity.

CONCLUSION

miR-1 and miR-21 functionality in cancer progression, particularly in tumor growth, may be more dependent on the individual cellular context and may reflect RCC heterogeneity. Thus, both microRNAs, in combination with other stratifying biomarkers, may be useful in terms of RCC diagnosis, prognosis, or treatment response.

Down regulation of human telomerase reverse transcriptase (hTERT) expression by BIBR1532 in human glioblastoma LN18 cells

Increased telomerase activity can be blocked by targeting the hTERT activity at both RNA and catalytic subunits. Various inhibitors had been used to regulate hTERT activity in glioblastoma cell lines and showed promising results. The present study hypothesized that the telomerase specific inhibitor BIBR1532 can effectively down-regulate the telomerase activity in LN18 glioblastoma cell line. LN18 glioblastoma cell line was treated with various concentrations of BIBR1532 at different time intervals. MTT assay was performed to determine cell viability after BIBR1532 treatment. hTERT mRNA and protein expression were determined by qRT-PCR and western blotting, respectively. Flow cytometry and TRAP assay was performed to detect the rate of apoptosis and telomerase activity in treated and control samples. One-way ANOVA was performed to compare the mean values of variables in control and BIBR1532 treated groups. LN18 cells showed a significant dose dependent cytotoxic effect after treatment with BIBR1532. hTERT mRNA expression in cells treated with 25, 100 and 200 μM BIBR1532 treated groups was decreased ~ 21, ~ 61.2, and ~ 77%, respectively (p < 0.05). We also observed that, BIBR1532 treatment reduced the expression of hTERT protein in LN18 cells in a dose dependent manner. The Flow cytometry data showed that, the drug induced significant increase in the total percentage of apoptotic cells with 200 μM concentration of BIBR1532 at all time points. BIBR1532 exhibited potent inhibition of telomerase activity in a dose-dependent manner in LN18 cells. BIBR1532 could induce apoptosis in LN18 cells through the downregulation of telomerase activity at transcriptional and translational level. We conclude that BIBR1532 may be a therapeutic agent to suppress telomerase activity, however, further efforts are necessary in order to explore this therapeutic strategy.

Quantum Dots-siRNA Nanoplexes for Gene Silencing in Central Nervous System Tumor Cells

RNA interfering (RNAi) using short interfering RNA (siRNA) is becoming a promising approach for cancer gene therapy. However, owing to the lack of safe and efficient carriers, the application of RNAi for clinical use is still very limited. In this study, we have developed cadmium sulphoselenide/Zinc sulfide quantum dots (CdSSe/ZnS QDs)-based nanocarriers for in vitro gene delivery. These CdSSe/ZnS QDs are functionalized with polyethyleneimine (PEI) to form stable nanoplex (QD-PEI) and subsequently they are used for siRNA loading which specially targets human telomerase reverse transcriptase (TERT). High gene transfection efficiency (>80%) was achieved on two glioblastoma cell lines, U87 and U251. The gene expression level (49.99 ± 10.23% for U87, 43.28 ± 9.66% for U251) and protein expression level (51.58 ± 7.88% for U87, 50.69 ± 7.59% for U251) of TERT is observed to decrease substantially after transfecting the tumor cells for 48 h. More importantly, the silencing of TERT gene expression significantly suppressed the proliferation of glioblastoma cells. No obvious cytotoxicity from these QD-PEI nanoplexes were observed over at 10 times of the transfected doses. Based on these results, we envision that QDs engineered here can be used as a safe and efficient gene nanocarrier for siRNA delivery and a promising tool for future cancer gene therapy applications.

Leukocyte telomere length positively correlates with duration of lithium treatment in bipolar disorder patients

Bipolar disorder (BD) has been suggested to be associated with accelerated aging and premature cell senescence. While findings on shorter telomeres in BD are controversial, a recent study showed that long-term lithium treatment correlates with longer telomeres in BD. In our study, we sought to investigate the correlation between leukocyte telomere length (LTL) and long-term lithium treatment in a sample of 200 BD patients characterized for lithium response. We also compared data from two different methods commonly used to measure telomere length, quantitative PCR (qPCR) and quantitative fluorescence in situ hybridization (Q-FISH). We also measured, for the first time, the effect of lithium in vitro on the expression of the telomerase gene in human-derived neural progenitor cells (NPCs). Our findings showed that LTL correlated negatively with age (p=0.0002) and was independent of sex, diagnosis, age at onset, suicidal behavior, number of mood episodes, response to lithium and use of other psychotropic medications. After correcting for age, LTL was positively correlated with lithium treatment duration in patients treated for more than two years (n=150, R=0.17, p=0.037). There was a significant correlation between data measured with qPCR and Q-FISH (p=0.012, R=0.826). Lithium treatment increased telomerase expression in NPCs, though this effect was not statistically significant. Our data support previous findings showing that long-term lithium treatment associates with longer telomeres in BD, though this effect appeared to be independent from clinical response to the treatment. Moreover, we suggested for the first time that lithium increases the expression of telomerase gene in human neural progenitor cells.

Endogenous Hot Spots of De Novo Telomere Addition in the Yeast Genome Contain Proximal Enhancers That Bind Cdc13

DNA double-strand breaks (DSBs) pose a threat to genome stability and are repaired through multiple mechanisms. Rarely, telomerase, the enzyme that maintains telomeres, acts upon a DSB in a mutagenic process termed telomere healing. The probability of telomere addition is increased at specific genomic sequences termed sites of repair-associated telomere addition (SiRTAs). By monitoring repair of an induced DSB, we show that SiRTAs on chromosomes V and IX share a bipartite structure in which a core sequence (Core) is directly targeted by telomerase, while a proximal sequence (Stim) enhances the probability of de novo telomere formation. The Stim and Core sequences are sufficient to confer a high frequency of telomere addition to an ectopic site. Cdc13, a single-stranded DNA binding protein that recruits telomerase to endogenous telomeres, is known to stimulate de novo telomere addition when artificially recruited to an induced DSB. Here we show that the ability of the Stim sequence to enhance de novo telomere addition correlates with its ability to bind Cdc13, indicating that natural sites at which telomere addition occurs at high frequency require binding by Cdc13 to a sequence 20 to 100 bp internal from the site at which telomerase acts to initiate de novo telomere addition.

miR-512-5p suppresses tumor growth by targeting hTERT in telomerase positive head and neck squamous cell carcinoma in vitro and in vivo

Telomerase activation has very important implications for head and neck squamous cell carcinoma (HNSCC), but the regulatory mechanisms of telomerase in HNSCC remain unclear. In our present study, we found that miR-512-5P was markedly downregulated in telomerase-positive HNSCC cell lines. Both in vitro and in vivo assays revealed that miR-512-5P mimic attenuated HNSCC cell proliferation, and tumor growth in nude mice, which exerts its tumor suppressor function through elevated apoptosis, inhibition of the telomerase activity, decrease of telomere-binding proteins and shortening of telomere length by human telomerase reverse transcriptase (hTERT) downregulation. Furthermore, the dual-luciferase reporter gene assay results demonstrated that hTERT was a direct target of miR-512-5P. We conclude that the frequently miR-512-5P overexpression can regulate hTERT and function as a tumor suppressor in HNSCC. Therefore, miR-512-5P may serve as a potential therapeutic agent for miR-based HNSCC therapy.

Association of CRR9 locus with elevated risk of squamous cell carcinoma and basal cell carcinoma

BACKGROUND

Published studies have generated inconsistent results related to the contribution of CRR9 rs401681 C allele to the risk of developing non-melanoma skin cancer (NMSC), and it is the inconsistency that promoted us to undertake a meta-analysis to identify the degree of impact the C allele has on NMSC.

METHOD

The PubMed, Science Direct, Embase and Cochrane Library were thoroughly searched from the start of November 2013 to the end of April 2014 by using CRR9, polymorphism, skin cancer and their synonyms. Based on a total of 44,036 subjects, we calculated ORs and 95% CIs to measure the influence of the C allele on NMSC predisposition.

RESULTS

Overall, individuals carrying the risk C allele at rs401681 had 1.16 times (OR = 1.16, 95% CI: 1.10-1.21, heterogeneity: P = 0.298 and I2 = 0.166, Figure 2) greater risk of NMSC compared to the common T allele. In the further stratified analyses, we found a significant association between the C allele and BCC, Icelanders, and non-Icelanders.

CONCLUSION

The results of this meta-analysis suggest that the C allele at rs401681 is likely to modify the genetic predisposition to NMSC.

Telomerase reverse transcriptase (TERT) rs2736100 polymorphism contributes to increased risk of glioma: evidence from a meta-analysis

The rs2736100 polymorphism in telomerase reverse transcriptase (TERT) gene has been implicated as a risk factor for glioma in previous epidemiological studies. However, the data from these studies were inconclusive for the precise association of TERT rs2736100 with glioma. Here we employed a meta-analysis aiming to evaluate such association. The PubMed, Embase, and Web of Science were systematically searched for eligible studies. The odds ratio (OR) and 95% confidence interval (95% CI) was estimated to assess the strength of this association in fixed or random effects models. A total of 5 studies in 16 articles including 7337 cases and 12062 controls were eventually collected. Our analyses showed that there was a significant association between TERT rs2736100 polymorphism and glioma in all five genetic models(homozygous model-GG vs. TT: OR=1.64, 95% CI=1.50~1.79, P heterogeneity=0.253, I(2) =17.5%; heterozygous model-GT vs. TT: OR=1.38, 95% CI=1.27~1.49, P heterogeneity=0.235, I(2) =19.1%; dominant model-GG+GT vs. TT: OR=1.46, 95% CI=1.36~1.57, P heterogeneity=0.167, I(2) =25.5%; recessive model-GG vs. GT+TT: OR=1.31, 95% CI=1.22~1.40, P heterogeneity=0.796, I(2) =0.0%; additive model-G allele vs. T allele: OR=1.27, 95% CI=1.21~1.32, P heterogeneity=0.481, I(2) =0.0%). Further subgroup analysis on control source and ethnicity, we found similar association in population-based, hospital-based and Caucasians groups. The result of heterogeneity test were in acceptable range (P<0.05 and I(2) <50%). Egger's tests and Begg's funnel plot did not show any publication bias. Sensitivity analysis confirmed that our results were reliable. Taken together, our meta-analysis suggested that TERT rs2736100 polymorphism may greatly increase glioma risk.

Single-molecule analysis of thymine dimer-containing G-quadruplexes formed from the human telomere sequence

The human telomere plays crucial roles in maintaining genome stability. In the presence of suitable cations, the repetitive 5'-TTAGGG-3' human telomere sequence can fold into G-quadruplexes that adopt the hybrid, basket, or propeller fold. The telomere sequence is hypersensitive to UV-induced thymine dimer (T=T) formation, yet it does not cause telomere shortening. In this work, the potential structural disruption and thermodynamic stability of the T=T-containing natural telomere sequences were studied to understand why this damage is tolerated in telomeres. First, established methods, such as thermal melting measurements, electrophoretic mobility shift assays, and circular dichroism spectroscopy, were utilized to determine the effects of the damage on these structures. Second, a single-molecule ion channel recording technique using α-hemolysin (α-HL) was employed to examine further the structural differences between the damaged sequences. It was observed that the damage caused slightly lower thermal stabilities and subtle changes in the circular dichroism spectra for hybrid and basket folds. The α-HL experiments determined that T=Ts disrupt double-chain reversal loop formation but are tolerated in edgewise and diagonal loops. The largest change was observed for the T=T-containing natural telomere sequence when the propeller fold (all double-chain reversal loops) was studied. On the basis of the α-HL experiments, it was determined that a triplexlike structure exists under conditions that favor a propeller structure. The biological significance of these observations is discussed.

TERT genetic polymorphism rs2736100 was associated with lung cancer: a meta-analysis based on 14,492 subjects

BACKGROUND

Previous studies focused on the association of the telomerase reverse transcriptase (TERT) gene polymorphism rs2736100 with lung cancer did not reach the same conclusion. In the present study, we performed a meta-analysis to systematically summarize the possible association between TERT polymorphism rs2736100 and the risk for lung cancer.

METHOD

We conducted a search of case-control studies on the association of TERT with susceptibility to lung cancer in PubMed, EMBASE, ISI Web of Science, Wanfang database in China, and Chinese National Knowledge Infrastructure (CNKI) databases. Data from eligible studies were extracted for meta-analysis. Lung cancer risk associated with rs2736100 was estimated by pooled odds ratios (ORs) and 95% confidence intervals (95% CIs).

RESULTS

Six independent case-control studies on rs2736100 were included in our meta-analysis. Our results showed that rs2736100 was associated with the risk of lung cancer not only in an additive model (OR=1.19, 95% CI: 1.04-1.35; p=0.01), but also in a dominant model (OR=1.14, 95% CI: 1.01-1.28; p=0.03).

CONCLUSIONS

This meta-analysis suggests that rs2736100 is associated with the risk of lung cancer.

Expression of the genetic suppressor element 24.2 (GSE24.2) decreases DNA damage and oxidative stress in X-linked dyskeratosis congenita cells

The predominant X-linked form of Dyskeratosis congenita results from mutations in DKC1, which encodes dyskerin, a protein required for ribosomal RNA modification that is also a component of the telomerase complex. We have previously found that expression of an internal fragment of dyskerin (GSE24.2) rescues telomerase activity in X-linked dyskeratosis congenita (X-DC) patient cells. Here we have found that an increased basal and induced DNA damage response occurred in X-DC cells in comparison with normal cells. DNA damage that is also localized in telomeres results in increased heterochromatin formation and senescence. Expression of a cDNA coding for GSE24.2 rescues both global and telomeric DNA damage. Furthermore, transfection of bacterial purified or a chemically synthesized GSE24.2 peptide is able to rescue basal DNA damage in X-DC cells. We have also observed an increase in oxidative stress in X-DC cells and expression of GSE24.2 was able to diminish it. Altogether our data indicated that supplying GSE24.2, either from a cDNA vector or as a peptide reduces the pathogenic effects of Dkc1 mutations and suggests a novel therapeutic approach.

If the cap fits, wear it: an overview of telomeric structures over evolution

Genome organization into linear chromosomes likely represents an important evolutionary innovation that has permitted the development of the sexual life cycle; this process has consequently advanced nuclear expansion and increased complexity of eukaryotic genomes. Chromosome linearity, however, poses a major challenge to the internal cellular machinery. The need to efficiently recognize and repair DNA double-strand breaks that occur as a consequence of DNA damage presents a constant threat to native chromosome ends known as telomeres. In this review, we present a comparative survey of various solutions to the end protection problem, maintaining an emphasis on DNA structure. This begins with telomeric structures derived from a subset of prokaryotes, mitochondria, and viruses, and will progress into the typical telomere structure exhibited by higher organisms containing TTAGG-like tandem sequences. We next examine non-canonical telomeres from Drosophila melanogaster, which comprise arrays of retrotransposons. Finally, we discuss telomeric structures in evolution and possible switches between canonical and non-canonical solutions to chromosome end protection.

Multiple tumor suppressor microRNAs regulate telomerase and TCF7, an important transcriptional regulator of the Wnt pathway

The human TERT (hTERT) gene encodes the telomerase catalytic subunit which plays a role in telomerase regulation. Telomerase is activated in more than 90% of all human malignancies and understanding how telomerase is regulated is necessary for implementation of successful anti-cancer therapies. microRNAs (miRNAs) are important regulators of gene expression in eukaryotic cells but evidence of their role in telomerase regulation has not been documented. To determine whether hTERT activity is regulated by multiple miRNAs, eight miRNAs which have putative binding sites in the hTERT 3'UTR together with miR-138-5p were evaluated in luciferase assays with a reporter containing the hTERT 3'UTR. Six miRNAs (let-7g*, miR-133a, miR-138-5p, miR-342-5p, miR-491-5p, and miR-541-3p) specifically inhibited the expression of the reporter luciferase-driven constructs and let-7g*, miR-133a, miR-138-5p, and miR-491-5p also downregulated endogenous telomerase activity in cells. Moreover, all six miRNAs significantly inhibited cell proliferation. miRNAs (miR-133a, miR-138-5p, 342-5p, 491-5p, 541-3p) also have predicted binding sites within the 3'UTR of three genes involved in Wnt signaling (TCF7, MSI1, and PAX5). These miRNAs inhibited the expression of the luciferase reporter constructs containing 3'UTRs of these genes and downregulated protein expression of the TCF7 transcription factor, which mediates the canonical Wnt pathway. Together, these results suggest the existence of a miRNA regulatory network involving the hTERT and Wnt pathway.

Depletion of sirtuin 1 (SIRT1) leads to epigenetic modifications of telomerase (TERT) gene in hepatocellular carcinoma cells

Sirtuin 1 (SIRT1) is a nicotinamide adenine dinucleotide (NAD)-dependent deacetylase that is implicated in plethora of biological processes, including metabolism, aging, stress response, and tumorigenesis. Telomerase (TERT) is essential for telomere maintenance. Activation of TERT is considered a crucial step in tumorigenesis, and therefore it is a potential therapeutic target against cancer. We have recently found that SIRT1 expression is highly elevated in hepatocellular carcinoma, and the depletion of SIRT1 leads to substantial reduction in TERT mRNA and protein expression. However, the underlying molecular mechanism of SIRT1-dependent TERT expression remains uncharacterized. Here, we elucidated if SIRT1 regulates TERT expression via transcriptional, epigenetic and post-transcriptional mechanisms. We report that depletion of SIRT1 does not lead to significant change in transcriptional activity and CpG methylation patterns of the TERT promoter, nor does it affect mRNA stability or 3′-UTR regulation of TERT. Intriguingly, depletion of SIRT1 is associated with substantial induction of acetylated histone H3-K9 and reduction of trimethyl H3-K9 at the TERT gene, which are known to be associated with gene activation. Our data revealed that SIRT1 regulates histone acetylation and methylation at the TERT promoter. We postulated that SIRT1 may regulate TERT expression via long-range interaction, or via yet unidentified histone modifications.

TeloTool: a new tool for telomere length measurement from terminal restriction fragment analysis with improved probe intensity correction

Telomeres comprise the protective caps of natural chromosome ends and function in the suppression of DNA damage signaling and cellular senescence. Therefore, techniques used to determine telomere length are important in a number of studies, ranging from those investigating telomeric structure to effects on human disease. Terminal restriction fragment (TRF) analysis has for a long time shown to be one of the most accurate methods for quantification of absolute telomere length and range from a number of species. As this technique centers on standard Southern blotting, telomeric DNA is observed on resulting autoradiograms as a heterogeneous smear. Methods to accurately determine telomere length from telomeric smears have proven problematic, and no reliable technique has been suggested to obtain mean telomere length values. Here, we present TeloTool, a new program allowing thorough statistical analysis of TRF data. Using this new method, a number of methodical biases are removed from previously stated techniques, including assumptions based on probe intensity corrections. This program provides a standardized mean for quick and reliable extraction of quantitative data from TRF autoradiograms; its wide application will allow accurate comparison between datasets generated in different laboratories.

DNA Methylation Changes during In Vitro Propagation of Human Mesenchymal Stem Cells: Implications for Their Genomic Stability?

Mesenchymal stem cells (MSCs) hold great promise for the treatment of numerous diseases. A major problem for MSC therapeutic use is represented by the very low amount of MSCs which can be isolated from different tissues; thus ex vivo expansion is indispensable. Long-term culture, however, is associated with extensive morphological and functional changes of MSCs. In addition, the concern that they may accumulate stochastic mutations which lead the risk of malignant transformation still remains. Overall, the genome of human MSCs (hMSCs) appears to be apparently stable throughout culture, though transient clonal aneuploidies have been detected. Particular attention should be given to the use of low-oxygen environment in order to increase the proliferative capacity of hMSCs, since data on the effect of hypoxic culture conditions on genomic stability are few and contradictory. Furthermore, specific and reproducible epigenetic changes were acquired by hMSCs during ex vivo expansion, which may be connected and trigger all the biological changes observed. In this review we address current issues on long-term culture of hMSCs with a 360-degree view, starting from the genomic profiles and back, looking for an epigenetic interpretation of their genetic stability.

The TERT MNS16A polymorphism contributes to cancer susceptibility: meta-analysis of the current studies

The MNS16A polymorphism in the telomerase reverse transcriptase (TERT) gene has been implicated in cancer risk in multiple populations and various types of cancers; however, the results of previous studies exploring this association were inconclusive. To more precisely evaluate the relationship between the TERT MNS16A polymorphism and cancer risk, we performed a meta-analysis based on 8 studies described in 7 articles comprising 7864 controls and 4355 cases. The summary odds ratios (ORs) and their corresponding 95% confidence intervals (CIs) were estimated to assess the strength of the association in a fixed-effects model or a random-effects model where appropriate. Heterogeneity among articles and their publication bias were also tested. Overall, the pooled results indicated that the MNS16A polymorphism was significantly associated with increased cancer risk in the homozygote comparison model (SS vs. LL: OR=1.280, 95% CI 1.060-1.547) and the recessive model (SS vs. LL+SL: OR=1.201, 95% CI 1.004-1.436). In the stratified analyses, a statistically significant association was observed among Caucasians and in population-based studies. We also performed the analyses by cancer type, and a significantly increased risk of glioma was found in four genetic models. Our results suggest that the TERT MNS16A polymorphism most likely contributes to an increased risk of cancer. Moreover, the same relationship was found when the studies were stratified by cancer type, ethnicity and source of controls.

The anaphase promoting complex contributes to the degradation of the S. cerevisiae telomerase recruitment subunit Est1p

Telomerase is a multi-subunit enzyme that reverse transcribes telomere repeats onto the ends of linear eukaryotic chromosomes and is therefore critical for genome stability. S. cerevisiae telomerase activity is cell-cycle regulated; telomeres are not elongated during G1 phase. Previous work has shown that Est1 protein levels are low during G1 phase, preventing telomerase complex assembly. However, the pathway targeting Est1p for degradation remained uncharacterized. Here, we show that Est1p stability through the cell cycle mirrors that of Clb2p, a known target of the Anaphase Promoting Complex (APC). Indeed, Est1p is stabilized by mutations in both essential and non-essential components of the APC. Mutations of putative Destruction boxes (D-boxes), regions shown to be important for recognition of known APC substrates, stabilize Est1p, suggesting that Est1p is likely to be targeted for degradation directly by the APC. However, we do not detect degradation or ubiquitination of recombinant Est1p by the APC in vitro, suggesting either that the recombinant protein lacks necessary post-translational modification and/or conformation, or that the APC affects Est1p degradation by an indirect mechanism. Together, these studies shed light on the regulation of yeast telomerase assembly and demonstrate a new connection between telomere maintenance and cell cycle regulation pathways.

Biogenesis of telomerase ribonucleoproteins

Telomerase adds simple-sequence repeats to the ends of linear chromosomes to counteract the loss of end sequence inherent in conventional DNA replication. Catalytic activity for repeat synthesis results from the cooperation of the telomerase reverse transcriptase protein (TERT) and the template-containing telomerase RNA (TER). TERs vary widely in sequence and structure but share a set of motifs required for TERT binding and catalytic activity. Species-specific TER motifs play essential roles in RNP biogenesis, stability, trafficking, and regulation. Remarkably, the biogenesis pathways that generate mature TER differ across eukaryotes. Furthermore, the cellular processes that direct the assembly of a biologically functional telomerase holoenzyme and its engagement with telomeres are evolutionarily varied and regulated. This review highlights the diversity of strategies for telomerase RNP biogenesis, RNP assembly, and telomere recruitment among ciliates, yeasts, and vertebrates and suggests common themes in these pathways and their regulation.

What mechanisms/processes underlie radiation-induced genomic instability?

Radiation-induced genomic instability is a modification of the cell genome found in the progeny of irradiated somatic and germ cells but that is not confined on the initial radiation-induced damage and may occur de novo many generations after irradiation. Genomic instability in the germ line does not follow Mendelian segregation and may have unpredictable outcomes in every succeeding generation. This phenomenon, for which there is extensive experimental data and some evidence in human populations exposed to ionising radiation, is not taken into account in health risk assessments. It poses an unknown morbidity/mortality burden. Based on experimental data derived over the last 20 years (up to January 2012) six mechanistic explanations for the phenomenon have been proposed in the peer-reviewed literature. This article compares these hypotheses with the empirical data to test their fitness to explain the phenomenon. As a conclusion, the most convincing explanation of radiation-induced genomic instability attributes it to an irreversible regulatory change in the dynamic interaction network of the cellular gene products, as a response to non-specific molecular damage, thus entailing the rejection of the machine metaphor for the cell in favour of one appropriate to a complex dissipative dynamic system, such as a whirlpool. It is concluded that in order to evaluate the likely morbidity/mortality associated with radiation-induced genomic instability, it will be necessary to study the damage to processes by radiation rather than damage to molecules.

Early growth response protein-1 promoter-mediated synergistic antitumor effect of hTERTC27 gene therapy and 5-Flurorouracil on nasopharyngeal carcinoma

hTERTC27 is a newly constructed polypeptide that can induce telomere dysfunction. To study the synergistic antitumor effects of the hTERTC27 polypeptide driven by the early growth response protein-1 (Egr-1) promoter and chemotherapeutic 5-flurorouracil (5-FU) on nasopharyngeal carcinoma, a series of in vitro and in vivo experiments were performed. The results showed that hTERTC27 expression was significantly increased up to 7.21-folds by the 5-FU-activated Egr-1 promoter in C666-1 cells. Overexpressed hTERTC27 made the cells more sensitive to 5-FU, and additionally, inhibited cell proliferation about 20.41%. Combinational therapy of overexpressed hTERTC27 driven by the 5-FU-activated Egr-1 promoter and 5-FU synergistically inhibited cell proliferation and promoted apoptosis of C666-1 cells for about 4.75-fold and 1.76-fold in comparison with a sole therapy of hTERTC27 or 5-FU in vitro. In vivo experiments showed that overexpressed hTERTC27 driven by 5-FU-activated Egr-1 promoter and 5-FU synergistically reduced tumor volume, tumor weight, and local infiltration, which may be relative to tumor cell apoptosis. These results suggest that combinational therapy of overexpressed hTERTC27, which is driven by the 5-FU-activated Egr-1 promoter, and 5-FU may provide a novel approach to treat nasopharyngeal cancer.

Alternatively spliced telomerase reverse transcriptase variants lacking telomerase activity stimulate cell proliferation

Eight human and six chicken novel alternatively spliced (AS) variants of telomerase reverse transcriptase (TERT) were identified, including a human variant (Δ4-13) containing an in-frame deletion which removed exons 4 through 13, encoding the catalytic domain of telomerase. This variant was expressed in telomerase-negative normal cells and tissues as well as in transformed telomerase-positive cell lines and cells which employ an alternative method to maintain telomere length. The overexpression of the Δ4-13 variant significantly elevated the proliferation rates of several cell types without enhancing telomerase activity, while decreasing the endogenous expression of this variant by use of small interfering RNA (siRNA) technology reduced cell proliferation. The expression of the Δ4-13 variant stimulated Wnt signaling. In chicken cells, AS TERT variants containing internal deletions or insertions that eliminated or reduced telomerase activity also enhanced cell proliferation. This is the first report that naturally occurring AS TERT variants which lack telomerase activity stimulate cell proliferation.

Defects in mTR stability and telomerase activity produced by the Dkc1 A353V mutation in dyskeratosis congenita are rescued by a peptide from the dyskerin TruB domain

BACKGROUND

The predominant X-linked form of dyskeratosis congenita results from mutations in dyskerin, a protein required for ribosomal RNA modification that is also a component of the telomerase complex. We have previously found that expression of an internal fragment of dyskerin (GSE24.2) rescues telomerase activity in X-linked dyskeratosis congenita (X-DC) patient cells.

MATERIALS AND METHODS

Here, we have generated F9 mouse cell lines expressing the most frequent mutation found in X-DC patients, A353V and study the effect of expressing the GSE24.2 cDNA or GSE24.2 peptide on telomerase activity by TRAP assay, and mTERT and mTR expression by Q-PCR. Point mutation in GSE24.2 residues were generated by site-directed mutagenesis.

RESULTS

Expression of GSE24.2 increases mTR and to a lesser extent mTERT RNA levels, and leads to recovery of telomerase activity. Point mutations in GSE24.2 residues known to be highly conserved and crucial for the pseudouridine-synthase activity of dyskerin abolished the effect of the peptide. Recovery of telomerase activity and increase in mTERT levels were found when the GSE24.2 peptide purified from bacteria was introduced into the cells. Moreover, mTR stability was also rescued by transfection of the peptide GSE24.2.

DISCUSSION

These data indicate that supplying GSE24.2, either from a cDNA vector, or as a peptide, can reduces the pathogenic effects of Dkc1 mutations and could form the basis of a novel therapeutic approach.

Investigation of Telomerase/Telomeres system in Bone Marrow Mesenchymal Stem Cells derived from IPF and RA-UIP

OBJECTIVE

Idiopathic Pulmonary Fibrosis and Rheumatoid Arthritis associated usual interstitial pneumonia seem to have the same poor outcome as there is not an effective treatment. The aim of the study is to explore the reparative ability of bone marrow mesenchymal stem cells by evaluating the system telomerase/telomeres and propose a novel therapeutic approach.

METHODS

BM-MSCs were studied in 6 IPF patients, 7 patients with RA-UIP and 6 healthy controls. We evaluated the telomere length as well as the mRNA expression of both components of telomerase (human telomerase reverse transcriptase, h-TERT and RNA template complementary to the telomeric loss DNA, h-TERC).

RESULTS

We found that BM-MSCs from IPF, RA-UIP cases do not present smaller telomere length than the controls (p = 0.170). There was no significant difference regarding the expression of both h-TERT and h-TERC genes between patients and healthy controls (p = 0.107 and p = 0.634 respectively).

CONCLUSIONS

We demonstrated same telomere length and telomerase expression in BM-MSCs of both IPF and RA-UIP which could explain similarities in pathogenesis and prognosis. Maintenance of telomere length in these cells could have future implication in cell replacement treatment with stem cells of these devastating lung disorders.

Telomeres and telomerase dance to the rhythm of the cell cycle

The stability of the ends of linear eukaryotic chromosomes is ensured by functional telomeres, which are composed of short, species-specific direct repeat sequences. The maintenance of telomeres depends on a specialized ribonucleoprotein (RNP) called telomerase. Both telomeres and telomerase are dynamic entities with different physical behaviors and, given their substrate-enzyme relation, they must establish a productive interaction. Regulatory mechanisms controlling this interaction are key missing elements in our understanding of telomere functions. Here, we review the dynamic properties of telomeres and the maturing telomerase RNPs, and summarize how tracking the timing of their dance during the cell cycle will yield insights into chromosome stability mechanisms. Cancer cells often display loss of genome integrity; therefore, these issues are of particular interest for our understanding of cancer initiation or progression.

Functional diversification of yeast telomere associated protein, Rif1, in higher eukaryotes

Background

Telomeres are nucleoprotein complexes at the end of linear eukaryotic chromosomes which maintain the genome integrity by regulating telomere length, preventing recombination and end to end fusion events. Multiple proteins associate with telomeres and function in concert to carry out these functions. Rap1 interacting factor 1 (Rif1), was identified as a protein involved in telomere length regulation in yeast. Rif1 is conserved upto mammals but its function has diversified from telomere length regulation to maintenance of genome integrity.

Results

We have carried out detailed bioinformatic analyses and identified Rif1 homologues in 92 organisms from yeast to human. We identified Rif1 homologues in Drosophila melanogaster, even though fly telomeres are maintained by a telomerase independent pathway. Our analysis shows that Drosophila Rif1 (dRif1) sequence is phylogenetically closer to the one of vertebrates than yeast and has identified a few Rif1 specific motifs conserved through evolution. This includes a Rif1 family specific conserved region within the HEAT repeat domain and a motif involved in protein phosphatase1 docking. We show that dRif1 is nuclear localized with a prominent heterochromatin association and unlike human Rif1, it does not respond to DNA damage by localizing to damaged sites. To test the evolutionary conservation of dRif1 function, we expressed the dRif1 protein in yeast and HeLa cells. In yeast, dRif1 did not perturb yeast Rif1 (yRif1) functions; and in HeLa cells it did not colocalize with DNA damage foci.

Conclusions

Telomeres are maintained by retrotransposons in all Drosophila species and consequently, telomerase and many of the telomere associated protein homologues are absent, including Rap1, which is the binding partner of Rif1. We found that a homologue of yRif1 protein is present in fly and dRif1 has evolutionarily conserved motifs. Functional studies show that dRif1 responds differently to DNA damage, implying that dRif1 may have a different function and this may be conserved in other organisms as well.