Telomeres, telomerase, and telomerase inhibition: clinical implications for cancer

Encapsulation of cycloastragenol in phospholipid vesicles enhances transport and delivery across the skin barrier

Cycloastragenol (CA) is a plant saponin that functions as a telomerase activator, and it has been made as an oral anti-aging supplement and use as active ingredient in topical cosmetic products. The anti-aging performance in cosmetic products have only been evaluated by description of skin appearance, while direct topical penetration of CA across the skin barrier still needs to be confirmed. The objective of this work was to design encapsulation vehicles to deliver CA across the skin barrier using commercially available ingredients through scalable processes, and to prove its topical penetration. Phospholipid vesicles including liposomes, ethosomes, and transethosomes were prepared using soy and sunflower phospholipids and different penetration enhancers, including ethanol and surfactants. The loading capacity of CA was analyzed using high performance liquid chromatography, and the topical penetration of CA was evaluated using Franz diffusion cells with pig skin. Transethosomes using Tween 80, Span 40, or dicetylphosphate as the penetration enhancer showed better CA delivery across the skin barrier than ethosomes or emulsifier α-gels. Results of this work provide evidence that CA encapsulated in phospholipid vesicles can be transported across the skin barrier. These encapsulation systems could be used for the design of CA-containing anti-aging cosmetic products.

Poly(ADP-ribose) polymerase enzymes and the maintenance of genome integrity

DNA damage response (DDR) relies on swift and accurate signaling to rapidly identify DNA lesions and initiate repair. A critical DDR signaling and regulatory molecule is the posttranslational modification poly(ADP-ribose) (PAR). PAR is synthesized by a family of structurally and functionally diverse proteins called poly(ADP-ribose) polymerases (PARPs). Although PARPs share a conserved catalytic domain, unique regulatory domains of individual family members endow PARPs with unique properties and cellular functions. Family members PARP-1, PARP-2, and PARP-3 (DDR-PARPs) are catalytically activated in the presence of damaged DNA and act as damage sensors. Family members tankyrase-1 and closely related tankyrase-2 possess SAM and ankyrin repeat domains that regulate their diverse cellular functions. Recent studies have shown that the tankyrases share some overlapping functions with the DDR-PARPs, and even perform novel functions that help preserve genomic integrity. In this review, we briefly touch on DDR-PARP functions, and focus on the emerging roles of tankyrases in genome maintenance. Preservation of genomic integrity thus appears to be a common function of several PARP family members, depicting PAR as a multifaceted guardian of the genome.

Cyclic Naphthalene Diimide Dimer with a Strengthened Ability to Stabilize Dimeric G-Quadruplex

A new type of dimeric cyclic naphthalene diimide derivatives (cNDI-dimers) carrying varied linker length were designed and synthesized to recognize dimeric G-quadruplex structures. All of the cNDI-dimers exhibited a high preference for recognizing G-quadruplex structures, and significantly enhanced the thermal stability of the dimeric G-quadruplex structure over the cNDI monomer by increasing the melting temperature by more than 23 °C, which indicated the strengthened ability of cNDI dimers for stabilizing dimeric G-quadruplex. cNDI dimers also showed a stronger ability to inhibit telomerase activity and stop telomere DNA elongation than cNDI monomer, which showed an improved anticancer potentiality for further therapeutic application.

G4IPDB: A database for G-quadruplex structure forming nucleic acid interacting proteins

Nucleic acid G-quadruplex structure (G4) Interacting Proteins DataBase (G4IPDB) is an important database that contains detailed information about proteins interacting with nucleic acids that forms G-quadruplex structures. G4IPDB is the first database that provides comprehensive information about this interaction at a single platform. This database contains more than 200 entries with details of interaction such as interacting protein name and their synonyms, their UniProt-ID, source organism, target name and its sequences, ∆T_m, binding/dissociation constants, protein gene name, protein FASTA sequence, interacting residue in protein, related PDB entries, interaction ID, graphical view, PMID, author's name and techniques that were used to detect their interactions. G4IPDB also provides an efficient web-based "G-quadruplex predictor tool" that searches putative G-quadruplex forming sequences simultaneously in both sense and anti-sense strands of the query nucleotide sequence and provides the predicted G score. Studying the interaction between proteins and nucleic acids forming G-quadruplex structures could be of therapeutic significance for various diseases including cancer and neurological disease, therefore, having detail information about their interactions on a single platform would be helpful for the discovery and development of novel therapeutics. G4IPDB can be routinely updated (twice in year) and freely available on http://bsbe.iiti.ac.in/bsbe/ipdb/index.php.

Knockdown of hTERT alters biophysical properties of K562 cells resulting in decreased migration rate in vitro

It has been shown that 90% of tumors, including hematological malignant tumors and leukemia, have much higher levels of telomerase expression than normal cells. To investigate the effect of telomerase on leukemia cells, we transfected K562, a human erythroleukemia cell line with an antisense-hTERT (human telomerase reverse transcriptase) cDNA vector, and examined the biological and biophysical properties of the stably transfected cells (referred to as KAT). Un-transfected cells (K562) and cells transfected with the empty vector (referred to as KC) were used as controls. Cell growth curve and (3)H-TdR test showed that the growth rate and DNA synthesis of KAT decreased compared with those of K562 and KC cells. Apoptosis and cell cycle distribution in KAT cells under normal culture condition were similar to those of K562 and KC cells, but changed after serum deprivation. KAT cells had significantly different biophysical characteristics from K562 and KC in terms of cell electrophoresis, membrane fluidity, membrane fluidity, and viscoelasticity. Furthermore, the transendothelial migration rate of KAT was much lower than those of K562 and KC cells. Confocal microscopy showed that KAT cells had higher F-actin content, suggesting the reorganization of cytoskeleton. Flow cytometry analysis revealed a lowered intracellular calcium concentration and CD71 expression, explaining the high F-actin content in KAT cells. In conclusion, we found that the knockdown of hTERT in K562 cells changed their cytoskeleton and biophysical features, and reduced the cell migration.

Steep your genes in health: drink tea

Tea, one of the most commonly consumed beverages in the world, has many health benefits. Tea polyphenols support health by promoting antioxidant enzymes, promoting apoptosis, preventing angiogenesis, and modulating epigenetic change. Considerable basic science and epidemiologic evidence supports the regular consumption of this tasty, inexpensive beverage.

Antiproliferative effects of cucurbitacin B in breast cancer cells: down-regulation of the c-Myc/hTERT/telomerase pathway and obstruction of the cell cycle

Naturally occurring cucurbitacins have been shown to have anticancer, antimicrobial and anti-inflammatory activities. In this study, we determined the effects of cucurbitacin B extracted from the Thai herb Trichosanthes cucumerina L. on telomerase regulation in three human breast cancer cell lines (T47D, SKBR-3, and MCF-7) and a mammary epithelium cell line (HBL-100). Cell viability after treatment with cucurbitacin B, which is an active ingredient of this herb, was assessed. Telomeric Repeat Amplification Protocol (TRAP) assays and RT-PCR (qualitative and realtime) were performed to investigate activity of telomerase as well as expression of human telomerase reverse transcriptase (hTERT) and c-Myc. The c-Myc protein level was also determined in SKBR-3 and HBL-100 cells. Our results show that the cucurbitacin B inhibits growth and telomerase activity in the three breast cancer cell lines and exerts an obvious inhibitory effect in the estrogen receptor (ER)-negative breast cancer SKBR-3 cells. The expression of hTERT and c-Myc were also inhibited by cucurbitacin B, In addition, a clear reduction of c-Myc protein was observed after treatment in SKBR-3 cells even with a concentration of cucurbitacin B that was ten-times lower compared to the concentration used for HBL-100. Our findings imply that cucurbitacin B exerts an anticancer effect by inhibiting telomerase via down regulating both the hTERT and c-Myc expression in breast cancer cells.

Telomerase inhibition as a novel therapy for pediatric ependymoma

Ependymomas are the third most common pediatric brain tumor with an overall survival of approximately 50%. Recently, we showed that telomerase [human telomerase reverse transcriptase (hTERT)] expression is a predictor of poor outcome in pediatric ependymoma. Thus, we hypothesized that ependymomas with functional telomerase may behave more aggressively and that these patients may benefit from anti-telomerase therapy. To address our hypothesis, we investigated the effect of telomerase inhibition on primary ependymoma cells harvested at the time of surgery, as no animal models or established cell lines are readily available for this tumor. The cells were characterized for glial fibrillary acidic protein (GFAP) and hTERT expression, initial telomere length and telomerase activity. They were then subjected to telomerase inhibition (MST-312, 1 microM) and tested for effects on cell viability (MTT assay), proliferation (MIB-1), apoptosis (cleaved caspase 3) and DNA damage (gammaH2AX). After 72 h of telomerase inhibition, primary ependymoma cells showed a significant decrease in cell number (P < 0.001), accompanied by increased DNA damage (gammaH2AX expression) (P < 0.01) and decreased proliferative index (MIB-1) (P < 0.01). Half showed an increase in apoptosis (cleaved caspase 3). These data suggest that telomerase inhibition may be an effective adjuvant therapy in pediatric ependymoma, potentially inducing tumor growth arrest in the short term, independent of telomere shortening.

The intrabody targeting of hTERT attenuates the immortality of cancer cells

hTERT (human telomerase reverse transcriptase) plays a key role in the process of cell immortalization. Overexpression of hTERT has been implicated in 85% of malignant tumors and offers a specific target for cancer therapy. In this paper, we describe an effective approach using a single-chain variable fragment (scFv) intrabody derived from monoclonal hybridoma directed against hTERT to attenuate the immortalization of human uterine cervix and hepatoma cells. The scFv we constructed had a high affinity to hTERT, and specifically neutralized over 70% of telomere synthesis activity, thereby inhibiting the viability and proliferation of the cancer cells. Our results indicate that this anti-hTERT intrabody is a promising tool to target hTERT and intervene in the immortalization process of cancer cells.

Genistein depletes telomerase activity through cross-talk between genetic and epigenetic mechanisms

Genistein, a natural isoflavone found in soybean products, has been reported to down-regulate telomerase activity and that this prevents cancer and contributes to the apoptosis of cancer cells. However, the precise molecular mechanism by which genistein represses telomerase is not clear. Here, we show that genistein inhibits the transcription of hTERT (human telomerase reverse transcriptase), the catalytic subunit of the human telomerase enzyme, in breast MCF10AT benign cells and MCF-7 cancer cells in a time- and dose-dependent manner. Three major DNA methyltransferases (DNMT1, 3a and 3b) were also decreased in genistein-treated breast cancer cells suggesting that genistein may repress hTERT by impacting epigenetic pathways. Sequential depletion of the hTERT promoter revealed that the hTERT core promoter region is responsible for the genistein-induced repression of hTERT transcription. Using a newly developed technique of chromatin immunoprecipitation (ChIP)-related bifulfite sequencing analysis, we found an increased binding of E2F-1 to the hTERT promoter is due to the site-specific hypomethylation of the E2F-1 recognition site. In addition, we found that genistein can remodel chromatin structures of the hTERT promoter by increasing trimethyl-H3K9 but decreasing dimethyl-H3K4 in the hTERT promoter. The repression of hTERT was enhanced by combination with genistein and the DNMT inhibitor, 5-aza-2'-deoxycytidine (5-aza-dCyd). These findings collectively show that genistein is working, at least in part, through epigenetic mechanisms of telomerase inhibition in breast benign and cancer cells and may facilitate approaches to breast cancer prevention and treatment using an epigenetic modulator combined with genistein.

Telomerase downregulation in cancer brain stem cell

Cancer stem cells (CSCs) are a minute sub-population of self-renewing, immortal cells, which can be responsible for chemoresistance observed in the treatment of cancer. CSCs are similar to cancer cells requiring telomerase activity or alternative mechanisms for their proliferation and regeneration. This study explored the correlation between CD133 (stem cell marker) and telomerase expression using CD133+ cells isolated from the glioma GOS-3 cell line with magnetic affinity cell sorting (MACS). GOS-3 CD133+ showed a transcription downregulation of hTERT ( approximately 100-fold decrease) compared with CD133- cells. In order to further substantiate the novel finding, serum deprivation was adopted to enrich CD133 expression in GOS-3 cells. A pronounced upregulation of cd133 and downregulation of telomerase expression were produced as a consequence of decreasing serum supplement levels in GOS-3 cells. These findings showed for the first time that telomerase is downregulated in brain cancer stem cells compared to cancer cells.

Strategies targeting telomerase inhibition

Telomerase plays a pivotal role in cellular immortality and tumorigenesis. Its activity is normally not detectable in most somatic cells while it is reactivated in the vast majority of cancer cells. Therefore, inhibition of telomerase has been viewed as a promising anticancer approach due to its specificity for cancer cells. Studies so far have shown that telomerase inhibition can inhibit the proliferation of cancer cells or cause apoptosis while it has no effect on most normal cells. Strategies currently being applied to induce telomerase inhibition target virtually all of the major components of the ribonucleoprotein holoenzyme and related cell signal pathways that regulate its activity. These strategies include inhibition of telomerase through targeting at the telomerase reverse transcriptase (TERT) catalytic subunit, the telomerase RNA (TR) component, and associated proteins. Other strategies have been developed to target the proteins associated with telomerase at the telomeric ends of chromosomes such as tankyrase. The specific mechanisms that mediate those inhibition effects include small molecules, antisense RNA, and ribozymes. Although the beneficial evidence of telomerase inhibition is obvious, limitations of strategies remain to be resolved to increase the feasibility of clinical application. This analysis will summarize recent developments of strategies in telomerase inhibition.

Telomerase inhibition induces acute ATM-dependent growth arrest in human astrocytomas

The purpose of the study was to examine the degree of hTERT, the catalytic subunit of telomerase, expression in paediatric high-grade astrocytoma and to explore the potential of telomerase inhibition as a therapy for these tumours. hTERT was expressed at high levels in 36 of 44 paediatric astrocytomas. Telomerase inhibition induced acute DNA damage and ATM-pathway-dependent G2/M cell cycle arrest in astrocytomas in vitro, both occurring prior to telomere shortening itself. Our data suggest that telomerase inhibition could be a useful adjuvant therapy for high-grade astrocytomas, potentially inducing tumour growth arrest following short-term treatment.

Methods of telomerase inhibition

Telomerase is central to cellular immortality and is a key component of most cancer cells although this enzyme is rarely expressed to significant levels in normal cells. Therefore, the inhibition of telomerase has garnered considerable attention as a possible anticancer approach. Many of the methods applied to telomerase inhibition focus on either of the two major components of the ribonucleoprotein holoenzyme, that is, the telomerase reverse transcriptase (TERT) catalytic subunit or the telomerase RNA (TR) component. Other protocols have been developed to target the proteins, such as tankyrase, that are associated with telomerase at the ends of chromosomes. This chapter summarizes some of these recent advances in telomerase inhibition.

Epigenetic and genetic mechanisms contribute to telomerase inhibition by EGCG

The ends of human chromosomes are protected from the degradation associated with cell division by 15-20 kb long segments of hexameric repeats of 5'-TTAGGG-3' termed telomeres. In normal cells telomeres lose up to 300 bp of DNA per cell division that ultimately leads to senescence; however, most cancer cells bypass this lifespan restriction through the expression of telomerase. hTERT, the catalytic subunit essential for the proper function of telomerase, has been shown to be expressed in approximately 90% of all cancers. In this study we investigated the hTERT inhibiting effects of (-)-epigallocatechin-3-gallate (EGCG), the major polyphenol found in green tea catechins, in MCF-7 breast cancers cells and HL60 promyelocytic leukemia cells. Exposure to EGCG reduced cellular proliferation and induced apoptosis in both MCF-7 and HL60 cells in vitro, although hTERT mRNA expression was decreased only in MCF-7 cells when treated with EGCG. Furthermore, down-regulation of hTERT gene expression in MCF-7 cells appeared to be largely due to epigenetic alterations. Treatment of MCF-7 cells with EGCG resulted in a time-dependent decrease in hTERT promoter methylation and ablated histone H3 Lys9 acetylation. In conjunction with demethylation, further analysis showed an increase in hTERT repressor E2F-1 binding at the promoter. From these findings, we propose that EGCG is effective in causing cell death in both MCF-7 and HL60 cancer cell lines and may work through different pathways involving both anti-oxidant effects and epigenetic modulation.

Differential hTERT mRNA processing between young and older glioma patients

The amplification of hTERT was detected in glioma tissues, although telomerase activity was not always found within these specimens. The aim of this study was to correlate the level of hTERT transcription with telomerase activity in two glioma age groups. hTERT was significantly transcribed at similar copy numbers in both age groups. However, these mRNAs translated to telomerase in 100% of the young compared to only 25% of the older patients. While hTERT transcription correlated directly to telomerase protein level and activity, as well as longer telomeres in the young group, such correlations were missing in the older group.

Accuracy of telomerase in cervical lesions: a systematic review

The detection of telomerase activity in cervix may provide information on cervical carcinogenesis and may be a marker to monitor cervical intraepithelial neoplasia transition. A quantitative systematic review was performed to estimate the accuracy of telomerase assay in cervical lesions. Studies that evaluated the telomerase test (telomerase repeated amplification protocol) for the diagnosis of cervix lesions and compared it to paraffin-embedded sections as the diagnostic standard were included. Ten studies were analyzed, which included 1069 women. The diagnostic odds ratio (DOR) for a positive telomerase test for low-grade squamous intraepithelial lesions (Lo-SIL) vs normal or benign lesions was 3.2 (95% CI, 1.9-5.6). The DOR for a positive telomerase test for high-grade squamous intraepithelial lesions (Hi-SIL) vs Lo-SIL, normal or benign lesions was 5.8 (95% CI, 3.1-10). For cervix cancer vs Hi-SIL, the DOR for a positive telomerase test was 8.1 (95% CI, 3.2-20.3) and for cervix cancer vs Lo-SIL, normal or benign lesions, it was 40.9 (95% CI, 18.2-91). Our data support the current hypothesis that telomerase may activate an early event in cervical carcinogenesis that could be associated with the initiation and progression of cervical lesions.

Study of the telomerase hTERT fraction, PCNA and CD34 expression on pituitary adenomas. Association with clinical and demographic characteristics

To determine the frequency of human telomerase reverse transcriptase (hTERT) catalytic fraction expression and its association with clinical and demographic characteristics of the patient, as well as with the expression of CD34 and proliferating cell nuclear antigen (PCNA) indexes on adenohypophyseal hormone tissues. A transverse study was realized with 49 cases of hypophyseal adenoma with analysis type cases and controls. The different adenohypophyseal hormones [prolactin (PRL), growth hormone (GH), follicle stimulating hormone, luteinizing hormone, thyroid gland stimulant hormone, adrenocorticotropic hormone (ACTH)], the catalytic fraction of the telomerase hTERT, the PCNA index and the CD34 density were determined by means of immunohistochemical techniques. The clinical, demographic and histopathological characteristics of the patients with and without hTERT expression were compared by means of Pearson's Chi-squared, Fisher's exact test and Mann-Whitney's U. Twenty-eight point six percent of the adenomas had positive expression for hTERT. The variables significantly correlated with hTERT's expression were younger age of presentation, diagnostic of adenoma producer, higher PCNA index, higher CD34 density, increased GH on serum and the expression on PRL tissue, GH and ACTH. Tobacco history had a negative association with hTERT's expression. The telomerase could be a marker of cellular proliferation associated with angiogenesis and hormonal activity. Evaluation of these variables could provide information about their biological behavior.

hTERT knockdown in human embryonic kidney cells using double-stranded RNA

The method of RNA interference (RNAi) is an easy means of knocking down a gene without having to generate knockout mutants, which may prove to be difficult and time consuming. RNAi is a naturally occurring process that involves targeting the mRNA of a gene by introducing RNAs that are complementary to the target mRNA. The foreign RNAs activate an endogenous enzyme, DICER, which degrades the target mRNA. There are many ways of eliciting the RNAi response in a cell. In this chapter, we describe the use of double-stranded RNA (dsRNA) to knockdown human telomerase reverse transcriptase (hTERT), the gene that codes for the catalytic subunit of the human telomerase enzyme. dsRNA can be used to generate the RNAi response in cells of embryonic origin, such as human embryonic kidney (HEK) cells. The RNAi effect is transient because the dsRNA eventually gets degraded in the cells, and it is useful to study the short-term effects of a gene knockdown.

Glioma: What is the role of c-Myc, hsp90 and telomerase?

The continuous advancements in cancer research have contributed to the overwhelming evidence of the presence of telomerase in primary and secondary tumours together with hsp90 and c-Myc. This review will discuss the important role of telomerase together with hsp90 and c-Myc within the initiation and progression of gliomas. Also it will review the differential expression of these genes in the different grades of gliomas and the possibility of new treatments targeting these specific genes.

Reproduce and die! Why aging? Part II

Whilst in part I of this diptych on aging the question why aging exists at all is discussed; this part deals with the question which mechanisms underly aging and, ultimately, dying. It appears that aging is not just an active process as such--although all kinds of internal (e.g., oxigen-free radicals) and external (e.g., UV radiation; disease) actively damage the organism--but more a passive one: it is mainly the result of a diminishing capacity to resist damaging internal and external influences, notably the capacity to repair the ensuing damage of DNA, until, indeed, the genome is entirely beyond repair and all kinds of vital functions detoriate with as a result that, in the end, the body collapses due to some final internal (e.g., a neoplasm or a CVA) or external (e.g., some infection, accident or attack) push. The time-course with which the capacity to repair DNA diminishes, however, is genetically fixed, and is associated with (even determined by) the reproductive strategy of the species in question: once the phase of reproduction is over, the reins are loosened and all kinds of genetic and physiological errors accumulate, giving rise to a large variety of pathology which ultimately carries the pertinent individual to the grave.

New Trends in Biomedical Aging Research

BACKGROUND

The increasing demand for health care services, the extraordinary results obtained by applying innovative biotechnology, and the intense debate aroused by the possibility that postponement of aging may be in sight should promote public enthusiasm and funding for biomedical aging research aimed at enhancing a healthy life span by healthy productive life.

OBJECTIVE

New trends in biomedical aging research arise from the advancement of knowledge on the basic molecular mechanisms of aging and the availability of advanced biotechnology.

RESULTS

The emerging scenario is that, in opposition to the highly publicized, yet unwarranted claims of existing so-called anti-aging treatments, innovative and promising therapies for the treatment and prevention of age-related diseases and intriguing strategies aimed at the postponement of aging are currently in the process of development.

CONCLUSIONS

Although many problems will remain unsolved for long, it seems that a common consensus has been raised towards the possible serious impact of these strategies on the development of knowledge around the mechanisms of aging.

Telomerase, telomerase inhibition, and cancer

Telomeres, located at the ends of eukaryotic chromosomes, are synthesized by the enzyme telomerase and are responsible for maintaining chromosome length. The absence of telomerase in most somatic cells has been associated with telomere shortening and aging of these cells. In contrast, high levels of telomerase activity are observed in over 90% of human cancer cells. The absence of telomerase in normal and aging cells is considered a natural defense against development of cancer. However, we do not know what triggers the reappearance of telomerase in cancer cells. Telomerase activity is directly correlated with the expression of its active catalytic component, the human telomerase reverse transcriptase (hTERT), which is believed to be controlled primarily at the level of transcription. Elucidation of the control of telomerase in aging and in cancer as an age-related disease has considerable potential in leading to novel approaches in anti-aging medicine.