Enzyme Telomerase Research Articles

Innovative anti-proliferative effect of the antiviral favipiravir against MCF-7 breast cancer cells using green nanoemulsion and eco-friendly assessment tools.

Telomerase enzyme prevents telomere shortening during division, having human telomerase reverse transcriptase (hTERT) as its catalytic subunit. Favipiravir (FAV), an RNA-dependent RNA polymerases inhibitor, shared structural similarity with hTERT and thus assumed to have cytotoxic effect on cancer cells, in addition to its prophylactic effect to immunocompromised cancer patients. Nanoemulsion (NE) is a potential tumor cells targeting delivery system, thereby enhancing therapeutic efficacy at the intended site, mitigating systemic toxicity, and overcoming multidrug resistance. The objective of this study is to develop a green FAV nanoemulsion (FNE) that is environmentally friendly and safe for patients, while aiming to enhance its cytotoxic effects. The study also highlights the environmental sustainability of the developed RP-HPLC method and assesses its greenness impact. The FNE formulation underwent thermodynamic stability testing and invitro characterization. Greenness was assessed using advanced selected tools like the Analytical Eco-Scale (AES), Analytical Greenness Metric for Sample Preparation (AGREEprep), and green analytical procedure index (GAPI). The cytotoxic potential of FNE was screened against MCF-7 breast cancer and Vero normal cell lines using SRB assay. Stable and ecofriendly FNE was formulated having a particle size (PS) of 25.29 ± 0.57nm and a zeta potential of -6.79 ± 5.52 mV. The cytotoxic effect of FNE on MCF-7 cells was more potent than FAV with lower IC50 while FNE showed non-toxic effect on VERO normal cell line. Therefore, the FAV nanoemulsion formulation showed targeted cytotoxicity on MCF-7 cells while being non-toxic on normal Vero cells.

Benzimidazole-based small molecules as anticancer agents targeting telomeric G-quadruplex and inhibiting telomerase enzyme.

Telomeres, crucial for chromosomal integrity, have been related to aging and cancer formation, mainly through regulating G-quadruplex structures. G-quadruplexes are structural motifs that can arise as secondary structures of nucleic acids, especially in guanine-rich DNA and RNA regions. Targeting these structures by small compounds shows promise in the selective suppression of cell growth, opening up novel possibilities for anticancer treatment. A comprehensive investigation of the many structural forms of G-quadruplex ligands is required to create ground-breaking anticancer drugs. Recent research into using specific benzimidazole molecules in stabilizing telomeric DNA into G-quadruplex structures has highlighted their ability to influence oncogene expression and demonstrate antiproliferative characteristics against cancer cells. This review describes the benzimidazole derivative, designed to enhance the stability of the G-quadruplex structure DNA to suppress the activity of telomerase enzyme, exhibiting promising potential for anticancer therapy.

The Effect of Telomerase Enzyme on Cell Aging and Cancer Formation-Treatment

Research has made the effects of the telomerase enzyme on both cellular ageing and cancer even more important. Measurement of telomerase activity appears to be a unique marker in addition to known methods for cancer diagnosis and treatment. In addition, numerous studies have shown that the reduction of telomeres shortens the life span of living cells. It is a known fact that cells with shortened lifespan age earlier and predispose to many diseases, especially cancer types. The fact that old cells are the basis for many diseases and young cells are resistant to many diseases has revealed the reality of keeping the cells young in order to prevent diseases. Studies aimed at understanding the activation of the telomerase enzyme on telomeres, have shown that this enzyme will have a positive effect on cellular rejuvenation on living cells, prolong the life span of living cells, thus preventing age-related diseases before they occur, and also making it impossible for many types of cancer that may develop due to old age to occur in the first place. Predictions such as preventing and stopping cellular senescence in human cells, providing cellular rejuvenation by reversing cellular senescence and extending human life span as much as desired are also worthy of further emphasis with the studies carried out.

Aging, Cancer, and Inflammation: The Telomerase Connection.

Understanding the complex dynamics of telomere biology is important in the strong link between aging and cancer. Telomeres, the protective caps at the end of chromosomes, are central players in this connection. While their gradual shortening due to replication limits tumors expansion by triggering DNA repair mechanisms, it also promotes oncogenic changes within chromosomes, thus sustaining tumorigenesis. The enzyme telomerase, responsible for maintaining telomere length, emerges as a central player in this context. Its expression in cancer cells facilitates the preservation of telomeres, allowing them to circumvent the growth-limiting effects of short telomeres. Interestingly, the influence of telomerase extends beyond telomere maintenance, as evidenced by its involvement in promoting cell growth through alternative pathways. In this context, inflammation accelerates telomere shortening, resulting in telomere dysfunction, while telomere elements also play a role in modulating the inflammatory response. The recognition of this interplay has promoted the development of novel therapeutic approaches centered around telomerase inhibition. This review provides a comprehensive overview of the field, emphasizing recent progress in knowledge and the implications in understanding of cancer biology.

Development and validation of novel keloid-derived immortalized fibroblast cell lines.

Keloids are a common connective tissue disorder with an ill-understood etiopathogenesis and no effective treatment. This is exacerbated because of the absence of an animal model. Patient-derived primary keloid cells are insufficient as they age through passaging and have a limited supply. Therefore, there is an unmet need for development of a cellular model that can consistently and faithfully represent keloid's pathognomic features. In view of this, we developed keloid-derived immortalized fibroblast (KDIF) cell lines from primary keloid fibroblasts (PKF) by transfecting the human telomerase reverse transcriptase (hTERT) gene. The TERT gene encodes the catalytic subunit of the telomerase enzyme, which is responsible for maintaining the cellular replicative potential (cellular immortalization). Primary fibroblasts from keloid-specific lesional (peripheral, middle, and top) as well as extralesional sites were isolated and evaluated for cell line development and comparative cellular characteristics by employing qRT-PCR and immunofluorescence staining. Moreover, the immortalized behavior of KDIF cell lines was evaluated by comparing with cutaneous fibrosarcoma and dermatofibrosarcoma protuberans cell lines. Stable KDIF cell lines with elevated expression of hTERT exhibited the cellular characteristics of site-specific keloid fibroblasts. Histochemical staining for β-galactosidase revealed a significantly lower number of β-gal-positive cells in all three KDIF cell lines compared with that in PKFs. The cell growth curve pattern was studied over 10 passages for all three KDIF cell lines and was compared with the control groups. The results showed that all three KDIF cell lines grew significantly faster and obtained a fast growing characteristic as compared to primary keloid and normal fibroblasts. Phenotypic behavior in growth potential is an indication of hTERT-mediated immortalized transformation. Cell migration analysis revealed that the top and middle KDIF cell lines exhibited similar migration trend as site-specific PKFs. Notably, peripheral KDIF cell line showed significantly enhanced cell migration in comparison to the primary peripheral fibroblasts. All KDIF cell lines expressed Collagen I protein as a keloid-associated fibrotic marker. Functional testing with triamcinolone inhibited cell migration in KDIF. ATCC short tandem repeat profiling validated the KDIF as keloid representative cell line. In summary, we provide the first novel KDIF cell lines. These cell lines overcome the limitations related to primary cell passaging and tissue supply due to immortalized features and present an accessible and consistent experimental model for keloid research.

Studying the Pathogenic Effect of New Nucleotide Changes in the Promoter Region of the TERT Gene in Patients with Glioblastoma Brain Tumor

Introduction: Brain tumors are considered to be one of the most dangerous types of cancer, despite decades of research and treatment efforts. The activation of the telomerase enzyme is a critical factor in the immortality of these cells. Mutations in the promoter region of the TERT gene, particularly in the promoter hot spots, can influence the binding of activating transcription factors and inhibit the binding of negative regulatory factors of the TERT gene, ultimately regulating the gene's expression. This study aimed to identify and investigate the mutations of the TERT gene promoter region in glioblastoma, a malignant brain tumor, using bioinformatics. Methods: A study was conducted using the case-control method where 35 patients with glioblastoma multiform brain tumor were examined along with 40 people who were examined as control samples. In this research, the Touchdown PCR technique and direct DNA sequencing were used to detect mutations in the promoter region of the TERT gene in patients with glioblastoma. Furthermore, bioinformatic analyses were conducted to investigate the pathogenic effect of nucleotide changes in this gene region. Results: In the core region of the TERT gene promoter, three-point mutations were identified (c.*146C>T، c.*144C>G and c.*143G>C). Two of these mutations were novel and have been observed for the first time in glioblastoma multiform. The remaining mutation was located in the promoter core's hot spot of the gene. This mutation was known as c.*146C>T. Conclusion: In this research, the harmful impact of TERT promoter region mutations as a biomarker for glioblastoma was examined. These findings suggest that mutations in regulatory regions, as well as coding sequences, could be significant contributory factors in the process of carcinogenesis.

All-trans-retinoic acid modulates glycolysis via H19 and telomerase: the role of mir-let-7a in estrogen receptor-positive breast cancer cells

BackgroundBreast cancer (BC) is the most commonly diagnosed cancer in women. Treatment approaches that differ between estrogen-positive (ER+) and triple-negative BC cells (TNBCs) and may subsequently affect cancer biomarkers, such as H19 and telomerase, are an emanating delight in BC research. For instance, all-trans-Retinoic acid (ATRA) could represent a potent regulator of these oncogenes, regulating microRNAs, mostly let-7a microRNA (miR-let-7a), which targets the glycolysis pathway, mainly pyruvate kinase M2 (PKM2) and lactate dehydrogenase A (LDHA) enzymes. Here, we investigated the potential role of ATRA in H19, telomerase, miR-let-7a, and glycolytic enzymes modulation in ER + and TNBC cells.MethodsMCF-7 and MDA-MB-231 cells were treated with 5 µM ATRA and/or 100 nM fulvestrant. Then, ATRA-treated or control MCF-7 cells were transfected with either H19 or hTERT siRNA. Afterward, ATRA-treated or untreated MDA-MB-231 cells were transfected with estrogen receptor alpha ER(α) or beta ER(β) expression plasmids. RNA expression was evaluated by RT‒qPCR, and proteins were assessed by Western blot. PKM2 activity was measured using an NADH/LDH coupled enzymatic assay, and telomerase activity was evaluated with a quantitative telomeric repeat amplification protocol assay. Student’s t-test or one-way ANOVA was used to analyze data from replicates.ResultsOur results showed that MCF-7 cells were more responsive to ATRA than MDA-MB-231 cells. In MCF-7 cells, ATRA and/or fulvestrant decreased ER(α), H19, telomerase, PKM2, and LDHA, whereas ER(β) and miR-let-7a increased. H19 or hTERT knockdown with or without ATRA treatment showed similar results to those obtained after ATRA treatment, and a potential interconnection between H19 and hTERT was found. However, in MDA-MB-231 cells, RNA expression of the aforementioned genes was modulated after ATRA and/or fulvestrant, with no significant effect on protein and activity levels. Overexpression of ER(α) or ER(β) in MDA-MB-231 cells induced telomerase activity, PKM2 and LDHA expression, in which ATRA treatment combined with plasmid transfection decreased glycolytic enzyme expression.ConclusionsTo the best of our knowledge, our study is the first to elucidate a new potential interaction between the estrogen receptor and glycolytic enzymes in ER + BC cells through miR-let-7a.

Loss of RAB25 Cooperates with Oncogenes in the Transformation of Human Mammary Epithelial Cells (HMECs) to Give Rise to Claudin-Low Tumors.

The loss of RAB25 expression-RAS superfamily of GTPase characteristic of numerous breast cancers-corresponds with H-RAS point mutations, particularly in triple-negative breast cancers (TNBC), a subtype associated with a poor prognosis. To address the poorly understood factors dictating the progression of TNBC tumors, we examine the cooperative effects that loss of RAB25 expression in human mammary epithelial cell (HMEC) lines with H-RAS mutations confers in tumorigenesis. HMECs were immortalized by transduction with LXSN CDK4 R24C, a mutant form of cyclin-dependent kinase, followed by transduction with hTERT, a catalytic subunit of the telomerase enzyme. We found that with the loss of RAB25 and overexpression of mutant H-RAS61L, immortal HMECs transformed toward anchorage-independent growth and acquired an increased ability to migrate. Furthermore, cells express low CD24, high CD44, and low claudin levels, indicating stem-like properties upon transformation. Besides, loss of RAB25 and overexpression of H-RAS61L resulted in increased expression of transcription factors Snail and Slug that drive these cells to lose E-cadherin and undergo epithelial-mesenchymal transition (EMT). This study confirms that loss of RAB25 and overexpression of mutant H-RAS can drive HMECs toward a mesenchymal stem-like state. Our findings reveal that RAB25 functions as a tumor suppressor gene, and loss of RAB25 could serve as a novel biomarker of the claudin-low type of TNBC.

Molecular Docking Study of Binding of Perylene Di-imide to a Bio Molecular Human Telomeric G-quadruplex

Human telomeres are comprised of d(TTAGGG) repeats involved in the formation of G-quadruplex DNA structures. Ligands stabilizing these G-quadruplex DNA structures are potential inhibitors of the cancer cell-associated enzyme telomerase. In human cells , telomerase adds multiple copies of the 5’-GGTTAG-3’ motif to the end of the G-strand of the telomere and in the majority of tumor cells it results over-expressed. Several structural studies have revealed a diversity of topologies for telomeric quadruplexes, which are sensitive to the nature of the cations present, to the flanking sequences, and probably also to concentration, as confirmed by the different conformations deposited in the Protein Data Bank (PDB). The existence of different polymorphism in the DNA quadruplex and the absence of a uniquely precise binding site give rise to check docking approach . As target we have selected six different experimental models of the human telomeric sequence d[AG3(T2AG3)3] based on three G-tetrads and as ligands the perylene di-imide . We checked out molecular docking simulation of binding of perylene di-imide to a slected G-quadruplex using dock 6.9 to examine whether or not to reproduced the loop binding mode of perylene di-imide. The simulation gave the two highest rank docking pose of perylene di-imide and the binding mode were external stacking on the terminal guanine tetrade and the groove binding.

Telomerase is essential for cardiac differentiation and sustained metabolism of human cardiomyocytes

Telomeres as the protective ends of linear chromosomes, are synthesized by the enzyme telomerase (TERT). Critically short telomeres essentially contribute to aging-related diseases and are associated with a broad spectrum of disorders known as telomeropathies. In cardiomyocytes, telomere length is strongly correlated with cardiomyopathies but it remains ambiguous whether short telomeres are the cause or the result of the disease. In this study, we employed an inducible CRISPRi human induced pluripotent stem cell (hiPSC) line to silence TERT expression enabling the generation of hiPSCs and hiPSC-derived cardiomyocytes with long and short telomeres. Reduced telomerase activity and shorter telomere lengths of hiPSCs induced global transcriptomic changes associated with cardiac developmental pathways. Consequently, the differentiation potential towards cardiomyocytes was strongly impaired and single cell RNA sequencing revealed a shift towards a more smooth muscle cell like identity in the cells with the shortest telomeres. Poor cardiomyocyte function and increased sensitivity to stress directly correlated with the extent of telomere shortening. Collectively our data demonstrates a TERT dependent cardiomyogenic differentiation defect, highlighting the CRISPRi TERT hiPSCs model as a powerful platform to study the mechanisms and consequences of short telomeres in the heart and also in the context of telomeropathies.

In vitro generation of epidermal keratinocytes from human CD34-positive hematopoietic stem cells.

The epidermis is largely composed of keratinocytes (KCs), and the proliferation and differentiation of KCs from the stratum basale to the stratum corneum is the cellular hierarchy present in the epidermis. In this study, we explore the differentiation abilities of human hematopoietic stem cells (HSCs) into KCs. Cultured HSCs positive for CD34, CD45, and CD133 with prominent telomerase activity were induced with keratinocyte differentiation medium (KDM), which is composed of bovine pituitary extract (BPE), epidermal growth factor (EGF), insulin, hydrocortisone, epinephrine, transferrin, calcium chloride (CaCl2), bone morphogenetic protein 4 (BMP4), and retinoic acid (RA). Differentiation was monitored through the expression of cytokeratin markers K5 (keratin 5), K14 (keratin 14), K10 (keratin 10), K1 (keratin 1), transglutaminase 1 (TGM1), involucrin (IVL), and filaggrin (FLG) on day 0 (D0), day 6 (D6), day 11 (D11), day 18 (D18), day 24 (D24), and day 30 (D30) using immunocytochemistry, fluorescence microscopy, flow cytometry, qPCR, and Western blotting. The results revealed the expression of K5 and K14 genes in D6 cells (early keratinocytes), K10 and K1 genes in D11-D18 cells (mature keratinocytes) with active telomerase enzyme, and FLG, IVL, and TGM1 in D18-D24 cells (terminal keratinocytes), and by D30, the KCs were completely enucleated similar to cornified matrix. This method of differentiation of HSCs to KCs explains the cellular order exists in the normal epidermis and opens the possibility of exploring the use of human HSCs in the epidermal differentiation.

Telomere dynamics and oxidative stress in Arabidopsis grown in lunar regolith simulant.

NASA envisions a future where humans establish a thriving colony on the Moon by 2050. Plants will be essential for this endeavor, but little is known about their adaptation to extraterrestrial bodies. The capacity to grow plants in lunar regolith would represent a major step towards this goal by minimizing the reliance on resources transported from Earth. Recent studies reveal that Arabidopsis thaliana can germinate and grow on genuine lunar regolith as well as on lunar regolith simulant. However, plants arrest in vegetative development and activate a variety of stress response pathways, most notably the oxidative stress response. Telomeres are hotspots for oxidative damage in the genome and a marker of fitness in many organisms. Here we examine A. thaliana growth on a lunar regolith simulant and the impact of this resource on plant physiology and on telomere dynamics, telomerase enzyme activity and genome oxidation. We report that plants successfully set seed and generate a viable second plant generation if the lunar regolith simulant is pre-washed with an antioxidant cocktail. However, plants sustain a higher degree of genome oxidation and decreased biomass relative to conventional Earth soil cultivation. Moreover, telomerase activity substantially declines and telomeres shorten in plants grown in lunar regolith simulant, implying that genome integrity may not be sustainable over the long-term. Overcoming these challenges will be an important goal in ensuring success on the lunar frontier.

Unzipped genome assemblies of polyploid root-knot nematodes reveal unusual and clade-specific telomeric repeats

Using long-read sequencing, we assembled and unzipped the polyploid genomes of Meloidogyne incognita, M. javanica and M. arenaria, three of the most devastating plant-parasitic nematodes. We found the canonical nematode telomeric repeat to be missing in these and other Meloidogyne genomes. In addition, we find no evidence for the enzyme telomerase or for orthologs of C. elegans telomere-associated proteins, suggesting alternative lengthening of telomeres. Instead, analyzing our assembled genomes, we identify species-specific composite repeats enriched mostly at one extremity of contigs. These repeats are G-rich, oriented, and transcribed, similarly to canonical telomeric repeats. We confirm them as telomeric using fluorescent in situ hybridization. These repeats are mostly found at one single end of chromosomes in these species. The discovery of unusual and specific complex telomeric repeats opens a plethora of perspectives and highlights the evolutionary diversity of telomeres despite their central roles in senescence, aging, and chromosome integrity.

Mechanisms of telomere maintenance and associated therapeutic vulnerabilities in malignant gliomas.

A majority of cancers (~85%) activate the enzyme telomerase to maintain telomere length over multiple rounds of cellular division. Telomerase-negative cancers activate a distinct, telomerase-independent mechanism of telomere maintenance termed alternative lengthening of telomeres (ALT). ALT uses homologous recombination to maintain telomere length and exhibits features of break-induced DNA replication. In malignant gliomas, the activation of either telomerase or ALT is nearly ubiquitous in pediatric and adult tumors, and the frequency with which these distinct telomere maintenance mechanisms (TMMs) is activated varies according to genetically defined glioma subtypes. In this review, we summarize the current state of the field of TMMs and their relevance to glioma biology and therapy. We review the genetic alterations and molecular mechanisms leading to telomerase activation or ALT induction in pediatric and adult gliomas. With this background, we review emerging evidence on strategies for targeting TMMs for glioma therapy. Finally, we comment on critical gaps and issues for moving the field forward to translate our improved understanding of glioma telomere maintenance into better therapeutic strategies for patients.

THE DOSE-DEPENDENT EFFECTS OF CAFFEINE AND BETAINE ON TELOMERASE ENZYME ACTIVITY IN MICE

The telomerase enzyme, which extends the Deoxyribonucleic Acid (DNA) regions called telomeres at the ends of the chromosomes, has an important place in aging, cancer and stem cell studies. In this study, the effects of betaine and caffeine on telomerase enzyme activity in mice were investigated. Telomerase activity was measured by a Polymerase Chain Reaction-Enzyme Linked Immunosorbent Assay (PCR-ELISA) based method. The activity of Superoxide Dismutase (SOD) and Catalase enzymes in the liver and kidney and the amount of Malondialdehyde (MDA) were also investigated. The results show that betaine has a slightly inhibitory effect (not significant) on telomerase activity, especially at high doses. Caffeine may act as an inhibitor in high doses but may have an activator effect at low doses. Also, it was observed that SOD and Catalase enzyme activities were parallel to the increase/decrease in telomerase enzyme activity in the liver.

Current Progress in Targeting Telomere and Telomerase Enzymes for the Treatment of Cancer

Abstract: Telomere is the repetitive sequence of non-coding DNA that protects chromosomes from damage. However, with cell division, the length of the telomere gets shortened ultimately leading to cell senescence. Telomere shortening is compensated by the addition of telomeric sequence by telomerase enzyme and thus preventing senescence which may lead to abnormal cell growth and ultimately result in cancer. There might not be a direct effect of telomerase on carcinogenesis, however, the role of telomerase in maintaining the length of telomere and thus tumor growth progression is quite evident. Various studies have reported the significance of telomerase activity in tumor cells. Therefore, targeting the telomerase enzyme can be an effective approach for the management of cancer, and drugs targeting telomerase inhibition are possible therapeutic candidates to be used clinically for the treatment of cancer in the future. Thus, in the current paper, we aim to review various telomerase inhibitors against cancer, challenges in proposing telomerase inhibitors for the treatment of cancer, and future perspectives on developing telomerase inhibitors for the management of cancer.

Telomerase activity and hTERT gene expression in patients with acute coronary syndrome and stable coronary artery disease.

In this study, we aimed to examine the telomerase activity and hTERT gene expression in patients with acute coronary syndrome (ACS) and those with stable coronary artery disease (SCAD) and compare the results to controls. Additionally, we compared overall mortality rates relative to the telomerase activity. Atotal of 211 patients (78 ACS and 71 SCAD patients) were included in the study. The telomerase concentration was measured by ELISA and used to determine telomerase activity. The hTERT gene expression was determined by real-time PCR. The serum telomerase enzyme concentration was lower in ACS (36.61 ± 1.54) and SCAD (36.79 ± 1.57) when compared to the control group (37.03 ± 2.25). However, this difference did not reach statistical significance (p = 0.890). The hTERT gene expression acting in telomerase enzyme synthesis was 2.7-fold lower in ACS group (p = 0.070) and 2.2-fold lower in the SCAD group (p = 0.101) compared to the control group. Patients were followed for amedian of 32 months (minimum: 0.1, maximum: 46.8). The serum telomerase concentrations in patients who died and those survived in the SCAD group (35.98 ± 2.02 vs 36.86 ± 1.52 ng/ml, respectively; p= 0.529) were similar to those in the ACS group (36.39 ± 1.08 vs 36.63 ± 1.60 ng/ml, respectively p= 0.993). In the current study, telomerase activity or hTERT expression was similar in patients with ACS, SCAD, and controls. Moreover, telomerase activity was not associated with all- cause mortality during the 32-month follow-up (Tab. 3, Fig. 1, Ref. 29).

Spectroscopy and calorimetry evidence of binding-induced thermal stabilization of human telomeric G-quadruplex DNA by 1,5-disubstituted morpholino-amido anthraquinone: Molecular basis of anticancer action

We report interaction of 1,5-Bis (3-morpholinopropionamido) anthracene-9,10-dione with Human Telomeric G4 DNA sequences, wHTel26 and HTel22 in presence of K+ and Na+ ions, respectively. Surface Plasmon Resonance yields association constant Kb = 1.0–3.8x105 M−1 with HTel22 in K+-rich solution. Significant hypochromism (46–79 %) and fluorescence quenching (83–92 %), no change in absorption and emission maxima, unaltered fluorescence lifetime of ligand, change in conformation of G4 DNA with no overall disruption of G-quartets and absence of induced Circular Dichroism band, suggest external groove binding of ligand. Molecular docking shows short contacts of 9O, 15N, 18O, 11NH, 12CO atoms of ligand with A3, G4, G22, G23 and A1, G3, G14 bases of 3 + 1 hybrid-2 and 2 + 2 anti-parallel conformers, respectively without making any contact with loops, to an energetically more favourable conformation. Ligand-influenced thermal stabilization, up to ΔTm = 37/48 °C, may disrupt access of telomerase enzyme to telomere and promote apoptosis in malignant tissues.

Telomere maintenance and the DNA damage response: a paradoxical alliance.

Telomeres are the protective caps at the ends of linear chromosomes of eukaryotic organisms. Telomere binding proteins, including the six components of the complex known as shelterin, mediate the protective function of telomeres. They do this by suppressing many arms of the canonical DNA damage response, thereby preventing inappropriate fusion, resection and recombination of telomeres. One way this is achieved is by facilitation of DNA replication through telomeres, thus protecting against a "replication stress" response and activation of the master kinase ATR. On the other hand, DNA damage responses, including replication stress and ATR, serve a positive role at telomeres, acting as a trigger for recruitment of the telomere-elongating enzyme telomerase to counteract telomere loss. We postulate that repression of telomeric replication stress is a shared mechanism of control of telomerase recruitment and telomere length, common to several core telomere binding proteins including TRF1, POT1 and CTC1. The mechanisms by which replication stress and ATR cause recruitment of telomerase are not fully elucidated, but involve formation of nuclear actin filaments that serve as anchors for stressed telomeres. Perturbed control of telomeric replication stress by mutations in core telomere binding proteins can therefore cause the deregulation of telomere length control characteristic of diseases such as cancer and telomere biology disorders.

Recognition of human telomeric G-quadruplex DNA by 1,5-disubstituted diethyl-amido anthraquinone derivative in different ion environments causing thermal stabilization and apoptosis

Ligand binding to G-quadruplex (G4) structures at human telomeric DNA ends promotes thermal stabilization, disrupting the interaction of the telomerase enzyme, which is found active in 80–85% of cancers and serves as a molecular marker. Anthraquinone compounds are well-known G-quadruplex (G4) binders that inhibit telomerase and induce apoptosis in cancer cells. Our current investigation is based on 1,5-bis[3-(diethylamino)propionamido]anthracene-9,10-dione, a derivative of anthraquinone and its binding characterization with two different human telomeric DNA structures, wHTel26 and HTel22, in the effect of K+ and Na+ by using an array of biophysical, calorimetry, molecular docking and cell viability assay techniques. Binding constants (K b) in the range of ∼105–107 M−1 and stoichiometries of 1:1, 2:1 & 4:1 were obtained from the absorbance, fluorescence, and circular dichroism study. Remarkable hypochromism (55, 97%) and ∼17 nm shift in absorbance, fluorescence quenching (95, 97%), the unaltered value of fluorescence lifetime, restoration of Circular Dichroism bands, absence of ICD band, indicated the external groove binding/binding somewhere at loops. This is also evident in molecular docking results, the ligand binds to groove forming base (G4, G5, G24, T25) and in the vicinity to TTA loop (G14, G15, T17) bases of wHTel26 and HTel22, respectively. Thermal stabilization induced by ligand was found greater in Na+ ion (27.5 °C) than (19.1 °C) in K+ ion. Ligand caused cell toxicity in MCF-7 cancer cell lines with an IC50 value of ∼8.4 µM. The above findings suggest the ligand, 1,5-bis[3-(diethylamino)propionamido]anthracene-9,10-dione could be a potent anticancer drug candidate and has great therapeutic implications. Binding of disubstituted amido anthraquinone derivative, 1,5-bis[3-(diethylamino)propionamido]anthracene-9,10-dione to human telomere HTel22 antiparallel conformation induced thermal stabilization. Communicated by Ramaswamy H. Sarma