Quantitative relationship between functionally active telomerase and major telomerase components (hTERT and hTR) in acute leukaemia cells

Telomerase (hTERT) Overexpression Reveals a Promising Prognostic Biomarker and Therapeutical Target in Different Clinical Subtypes of Pediatric Acute Lymphoblastic Leukaemia

Acute Lymphoblastic Leukemia (ALL) is a neoplasm of the hematopoietic system defined as a clonal expansion of an abnormal lymphoid precursor cell. It mostly affects children under five years of age and is the most common tumor to afflict pediatric patients. The expression of the human telomerase gene (hTERT) in patients with ALL has been studied as a biomarker and could become a new therapeutic target. We evaluate the role of hTERT gene expression in ALL pediatric patients, through quantitative real-time PCR technique, and the possible correlation between hTERT expression and clinical variables: gender, age, white blood cells (WBC), gene fusions, and immunophenotyping. The analysis between healthy controls and ALL patients (N = 244) was statistically significant (p < 0.001), demonstrating hTERT overexpression in these patients. In comparison with the usual set of clinical variables, the data were not statistically significant (p > 0.05), indicating that hTERT is equally overexpressed among patients regardless of gender, age, gene fusions, and immunophenotyping. Moreover, patients who presented a higher hTERT expression level had a significant (p < 0.0001) lower overall survival rate. In summary, hTERT expression emerges as an important molecular pathway in leukemogenesis regardless patient's clinical variables, thus, the data here presented pointed it as a valuable biomarker in pediatric acute lymphoblastic leukemia and a promising target for new therapeutic and prognostic measures.

Alternative Splicing of Human Telomerase Reverse Transcriptase (hTERT) and Its Implications in Physiological and Pathological Processes

Alternative splicing (AS) of human telomerase catalytic subunit (hTERT, human telomerase reverse transcriptase) pre-mRNA strongly regulates telomerase activity. Several proteins can regulate AS in a cell type-specific manner and determine the functions of cells. In addition to being involved in telomerase activity regulation, AS provides cells with different splice variants that may have alternative biological activities. The modulation of telomerase activity through the induction of hTERT AS is involved in the development of different cancer types and embryos, and the differentiation of stem cells. Regulatory T cells may suppress the proliferation of target human and murine T and B lymphocytes and NK cells in a contact-independent manner involving activation of TERT AS. This review focuses on the mechanism of regulation of hTERT pre-mRNA AS and the involvement of splice variants in physiological and pathological processes.

Endometriosis Is Associated with a Significant Increase in hTERC and Altered Telomere/Telomerase Associated Genes in the Eutopic Endometrium, an Ex-Vivo and In Silico Study

Telomeres protect chromosomal ends and they are maintained by the specialised enzyme, telomerase. Endometriosis is a common gynaecological disease and high telomerase activity and higher hTERT levels associated with longer endometrial telomere lengths are characteristics of eutopic secretory endometrial aberrations of women with endometriosis. Our ex-vivo study examined the levels of hTERC and DKC1 RNA and dyskerin protein levels in the endometrium from healthy women and those with endometriosis (n = 117). The in silico study examined endometriosis-specific telomere- and telomerase-associated gene (TTAG) transcriptional aberrations of secretory phase eutopic endometrium utilising publicly available microarray datasets. Eutopic secretory endometrial hTERC levels were significantly increased in women with endometriosis compared to healthy endometrium, yet dyskerin mRNA and protein levels were unperturbed. Our in silico study identified 10 TTAGs (CDKN2A, PML, ZNHIT2, UBE3A, MCCC2, HSPC159, FGFR2, PIK3C2A, RALGAPA1, and HNRNPA2B1) to be altered in mid-secretory endometrium of women with endometriosis. High levels of hTERC and the identified other TTAGs might be part of the established alteration in the eutopic endometrial telomerase biology in women with endometriosis in the secretory phase of the endometrium and our data informs future research to unravel the fundamental involvement of telomerase in the pathogenesis of endometriosis.

Chromatin Regulation by HP1γ Contributes to Survival of 5-Azacytidine-Resistant Cells

Recent investigations of the treatment for hematologic neoplasms have focused on targeting epigenetic regulators. The DNA methyltransferase inhibitor 5-azacytidine (AZA) has produced good results in the treatment of patients with myelodysplastic syndromes. The mechanism underlying its pharmacological activity involves many cellular processes including histone modifications, but chromatin regulation in AZA-resistant cells is still largely unknown. Therefore, we compared human leukemia cells with AZA resistance and their AZA-sensitive counterparts with regard to the response of histone modifications and their readers to AZA treatment to identify novel molecular target(s) in hematologic neoplasms with AZA resistance. We observed an a decrease of HP1γ, a methylated lysine 9 of histone H3-specific reader protein, in AZA-sensitive cells after treatment, whereas AZA treatment did not affect HP1 family proteins in AZA-resistant cells. The expression of shRNA targeting HP1γ reduced viability and induced apoptosis specifically in AZA-resistant cells, which accompanied with down-regulation of ATM/BRCA1 signaling, indicating that chromatin regulation by HP1γ plays a key role in the survival of AZA-resistant cells. In addition, the amount of HP1γ protein in AZA-sensitive and AZA-resistant cells was decreased after treatment with the bromodomain inhibitor I-BET151 at a dose that inhibited the growth of AZA-resistant cells more strongly than that of AZA-sensitive cells. Our findings demonstrate that treatment with AZA, which affects an epigenetic reader protein and targets HP1γ, or a bromodomain inhibitor is a novel strategy that can be used to treat patients with hematopoietic neoplasms with AZA resistance.

Expression analysis of the MCPH1/BRIT1 and BRCA1 tumor suppressor genes and telomerase splice variants in epithelial ovarian cancer

AIMS

The aim of this study was to explore the correlation of hTERT splice variant expression with MCPH1/BRIT1 and BRCA1 expression in epithelial ovarian cancer (EOC) samples.

BACKGROUND

Telomerase activation can contribute to the progression of tumors and the development of cancer. However, the regulation of telomerase activity remains unclear. MCPH1 (also known as BRIT1, BRCT-repeat inhibitor of hTERT expression) and BRCA1 are tumor suppressor genes that have been linked to telomerase expression.

METHODS

qPCR was used to investigate telomerase splice variants, MCPH1/BRIT1 and BRCA1 expression in EOC tissue and primary cultures.

RESULTS

The wild type α+/β+ hTERT variant was the most common splice variant in the EOC samples, followed by α+/β- hTERT, a dominant negative regulator of telomerase activity. EOC samples expressing high total hTERT demonstrated significantly lower MCPH1/BRIT1 expression in both tissue (p = 0.05) and primary cultures (p = 0.03). We identified a negative correlation between MCPH1/BRIT1 and α+/β+ hTERT (p = 0.04), and a strong positive association between MCPH1/BRIT1 and both α-/β+ hTERT and α-/β- hTERT (both p = 0.02). A positive association was observed between BRCA1 and α-/β+ hTERT and α-/β- hTERT expression (p = 0.003 and p = 0.04, respectively).

CONCLUSIONS

These findings support a regulatory effect of MCPH1/BRIT1 and BRCA1 on telomerase activity, particularly the negative association between MCPH1/BRIT1 and the functional form of hTERT (α+/β+).

Simultaneous Quantification of Multiple Alternatively Spliced mRNA Transcripts Using Droplet Digital PCR

Currently there is no sensitive, precise, and reproducible method to quantitate alternative splicing of mRNA transcripts. Droplet digital™ PCR (ddPCR™) analysis allows for accurate digital counting for quantification of gene expression. Human telomerase reverse transcriptase (hTERT) is one of the essential components required for telomerase activity and for the maintenance of telomeres. Several alternatively spliced forms of hTERT mRNA in human primary and tumor cells have been reported in the literature. Using one pair of primers and two probes for hTERT, four alternatively spliced forms of hTERT (α-/β+, α+/β- single deletions, α-/β- double deletion, and nondeletion α+/β+) were accurately quantified through a novel analysis method via data collected from a single ddPCR reaction. In this chapter, we describe this ddPCR method that enables direct quantitative comparison of four alternatively spliced forms of the hTERT messenger RNA without the need for internal standards or multiple pairs of primers specific for each variant, eliminating the technical variation due to differential PCR amplification efficiency for different amplicons and the challenges of quantification using standard curves. This simple and straightforward method should have general utility for quantifying alternatively spliced gene transcripts.

Teriflunomide restores 5-azacytidine sensitivity via activation of pyrimidine salvage in 5-azacytidine-resistant leukemia cells

Previous studies showed that downregulation of pyrimidine salvage underlies resistance against 5-azacytidine (AZA), indicating an important role for de novo pyrimidine synthesis in AZA resistance. Because de novo pyrimidine synthesis is inhibited by the immunomodulator teriflunomide and its pro-drug leflunomide, we examined the effect of combined treatment with AZA and teriflunomide on AZA resistance to develop a novel strategy to cancel and prevent AZA resistance. Teriflunomide markedly inhibited the growth of AZA-resistant human leukemia cell lines (R-U937 and R-HL-60) in comparison with their AZA-sensitive counterparts (U937 and HL-60). In the presence of a non-toxic concentration of teriflunomide (1 μM), AZA induced apoptosis in AZA-resistant cells and leukemia cells from AZA-resistant patients. AZA acted as a DNA methyltransferase 3A inhibitor in AZA-resistant cells in the presence of 1 μM teriflunomide. Although AZA-sensitive cells acquired AZA resistance after continuous treatment with AZA for 42 days, the growth of AZA-sensitive cells continuously treated with the combination of AZA and teriflunomide was significantly inhibited in the presence of AZA, demonstrating that the combined treatment prevented AZA resistance. These results suggest that combined treatment with AZA and teriflunomide can be a novel strategy to overcome AZA resistance.

Alternative splicing of hTERT: a further mechanism for the control of active hTERT in acute myeloid leukemia

hTERT component is the key regulator of telomerase. Alternatively spliced variants of hTERT generate different telomerase activity. The goal of the study was to determine the role of different hTERT isoforms in the regulation of telomerase expression in AML patients. Among the 97 studied patients, 45 had a complex karyotype and 52 a normal karyotype. hTERT isoforms expression was determined in bone marrow samples by q-RT-PCR, using SYBR Green I. hTERT expression was lower in AML patients than controls (median 2.5 vs. 10.1, p = .003), though no difference was observed between the complex and normal karyotype (median 3.2 vs. 2.3, p = .37). High trans-dominant negative isoform expression increased the response rate by two. High expression of inactive product (-α - β) was shown to increase the risk of relapse by about three times. In conclusion, our data suggest an intriguing link between the control of hTERT isoforms expression and AML outcome.

Effective control of acute myeloid leukaemia and acute lymphoblastic leukaemia progression by telomerase specific adoptive T-cell therapy

Telomerase (TERT) is a ribonucleoprotein enzyme that preserves the molecular organization at the ends of eukaryotic chromosomes. Since TERT deregulation is a common step in leukaemia, treatments targeting telomerase might be useful for the therapy of hematologic malignancies. Despite a large spectrum of potential drugs, their bench-to-bedside translation is quite limited, with only a therapeutic vaccine in the clinic and a telomerase inhibitor at late stage of preclinical validation. We recently demonstrated that the adoptive transfer of T cell transduced with an HLA-A2-restricted T-cell receptor (TCR), which recognize human TERT with high avidity, controls human B-cell chronic lymphocytic leukaemia (B-CLL) progression without severe side-effects in humanized mice. In the present report, we show the ability of our approach to limit the progression of more aggressive leukemic pathologies, such as acute myeloid leukaemia (AML) and B-cell acute lymphoblastic leukaemia (B-ALL). Together, our findings demonstrate that TERT-based adoptive cell therapy is a concrete platform of T cell-mediated immunotherapy for leukaemia treatment.

Human telomerase reverse transcriptase regulation by DNA methylation, transcription factor binding and alternative splicing (Review)

The catalytic subunit of telomerase, human telomerase reverse transcriptase (hTERT), plays an essential role in telomere maintenance to oppose cellular senescence and, is highly regulated in normal and cancerous cells. Regulation of hTERT occurs through multiple avenues, including a unique pattern of CpG promoter methylation and alternative splicing. Promoter methylation affects the binding of transcription factors, resulting in changes in expression of the gene. In addition to expression level changes, changes in promoter binding can affect alternative splicing in a cotranscriptional manner. The alternative splicing of hTERT results in either the full length transcript which can form the active telomerase complex with hTR, or numerous inactive isoforms. Both regulation strategies are exploited in cancer to activate telomerase, however, the exact mechanism is unknown. Therefore, unraveling the link between promoter methylation status and alternative splicing for hTERT could expose yet another level of hTERT regulation. In an attempt to provide insight into the cellular control of active telomerase in cancer, this review will discuss our current perspective on CpG methylation of the hTERT promoter region, summarize the different forms of alternatively spliced variants, and examine examples of transcription factor binding that affects splicing.

Dyskerin and TERC expression may condition survival in lung cancer patients

Dyskerin mediates both the modification of uridine on ribosomal and small nuclear RNAs and the stabilization of the telomerase RNA component (TERC). In human tumors dyskerin expression was found to be associated with both rRNA modification and TERC levels. Moreover, dyskerin overexpression has been linked to unfavorable prognosis in a variety of tumor types, however an explanation for the latter association is not available. To clarify this point, we analyzed the connection between dyskerin expression, TERC levels and clinical outcome in two series of primary lung cancers, differing for the presence of TERC gene amplification, a genetic alteration inducing strong TERC overexpression. TERC levels were significantly higher in tumors bearing TERC gene amplification (P = 0.017). In addition, the well-established association between dyskerin expression and TERC levels was observed only in the series without TERC gene amplification (P = 0.003), while it was not present in TERC amplified tumors (P = 0.929). Similarly, the association between dyskerin expression and survival was found in cases not bearing TERC gene amplification (P = 0.009) and was not observed in TERC amplified tumors (P = 0.584). These results indicate that the influence of dyskerin expression on tumor clinical outcome is linked to its role on the maintenance of high levels of TERC.

The role of telomeres and telomerase reverse transcriptase isoforms in pluripotency induction and maintenance

Telomeres are linear guanine-rich DNA structures at the ends of chromosomes. The length of telomeric DNA is actively regulated by a number of mechanisms in highly proliferative cells such as germ cells, cancer cells, and pluripotent stem cells. Telomeric DNA is synthesized by way of the ribonucleoprotein called telomerase containing a reverse transcriptase (TERT) subunit and RNA component (TERC). TERT is highly conserved across species and ubiquitously present in their respective pluripotent cells. Recent studies have uncovered intricate associations between telomeres and the self-renewal and differentiation properties of pluripotent stem cells. Interestingly, the past decade's work indicates that the TERT subunit also has the capacity to modulate mitochondrial function, to remodel chromatin structure, and to participate in key signaling pathways such as the Wnt/β-catenin pathway. Many of these non-canonical functions do not require TERT's catalytic activity, which hints at possible functions for the extensive number of alternatively spliced TERT isoforms that are highly expressed in pluripotent stem cells. In this review, some of the established and potential routes of pluripotency induction and maintenance are highlighted from the perspectives of telomere maintenance, known TERT isoform functions and their complex regulation.

Highly efficient radiosensitization of human glioblastoma and lung cancer cells by a G-quadruplex DNA binding compound

Telomeres are nucleoprotein structures at the end of chromosomes which stabilize and protect them from nucleotidic degradation and end-to-end fusions. The G-rich telomeric single-stranded DNA overhang can adopt a four-stranded G-quadruplex DNA structure (G4). Stabilization of the G4 structure by binding of small molecule ligands enhances radiosensitivity of tumor cells, and this combined treatment represents a novel anticancer approach. We studied the effect of the platinum-derived G4-ligand, Pt-ctpy, in association with radiation on human glioblastoma (SF763 and SF767) and non-small cell lung cancer (A549 and H1299) cells in vitro and in vivo. Treatments with submicromolar concentrations of Pt-ctpy inhibited tumor proliferation in vitro with cell cycle alterations and induction of apoptosis. Non-toxic concentrations of the ligand were then combined with ionizing radiation. Pt-ctpy radiosensitized all cell lines with dose-enhancement factors between 1.32 and 1.77. The combined treatment led to increased DNA breaks. Furthermore, a significant radiosensitizing effect of Pt-ctpy in mice xenografted with glioblastoma SF763 cells was shown by delayed tumor growth and improved survival. Pt-ctpy can act in synergy with radiation for efficient killing of cancer cells at concentrations at which it has no obvious toxicity per se, opening perspectives for future therapeutic applications.

Expression Pattern of Alternative Splicing Variants of Human Telomerase Reverse Transcriptase (hTERT) in Cancer Cell Lines Was not Associated with the Origin of the Cells

Telomerase and systems controlling their activity have been of great attention. There are controversies regarding the role of the alternative splicing forms of the human telomerase reverse transcriptase (hTERT), the catalytic subunit of telomerase. Therefore, the correlation between telomerase enzyme activity, the abundance of alternatively spliced variants of hTERT and doubling time of a series of cancer cell lines originated from hematopoietic, breast, colorectal, neural, ovarian, lung, kidney, bladder, prostate and head and neck cancers were investigated. Expression levels of four different variants of hTERT (the full length, α-deletion, β-deletion and α/β-deletion) were quantitatively measured by real time PCR. Telomerase activity was determined by the telomerase repeat amplification protocol (TRAP) while doubling time of the cells measured by plotting growth curves. Results showed high diversity in the relative proportions of hTERT transcripts while the majority of the cells expressed the full length variant as the main transcript. Telomerase activity could not be detected in all cells. Relative assessment of hTERT expression showed greater expression of the α-deleted variant in the telomerase negative cells (P= 0.04). Those cells possessed the α/β-deleted variant to a smaller extent when compared to the cells with telomerase activity. Greater association between full length spliced variant and β-variant expression was observed in cells presenting telomerase activity (P= 0.0007, r= 0.74). High degrees of variation among the studied cells regarding the pattern of hTERT expression were present. In spite that, the regulatory roles of hTERT on telomerase activity is still a potential to be utilized as targets for cancer therapies.

Simultaneous quantification of alternatively spliced transcripts in a single droplet digital PCR reaction

Human telomerase reverse transcriptase (hTERT) is an essential component required for telomerase activity and telomere maintenance. Several alternatively spliced forms of hTERT mRNA have been reported in human primary and tumor cells. Currently, however, there is no sensitive and accurate method for the simultaneous quantification of multiple alternatively spliced RNA transcripts, such as in the case of hTERT. Here we show droplet digital PCR (ddPCR) provides sensitive, simultaneous digital quantification in a single reaction of two alternatively spliced single deletion hTERT transcripts (α-/β+ and α+/β-) as well as the opportunity to manually quantify non-deletion (α+/β+) and double deletion (α-/β-) transcripts. Our ddPCR method enables direct comparison among four alternatively spliced mRNAs without the need for internal standards or multiple primer pairs specific for each variant as real-time PCR (qPCR) requires, thus eliminating potential variation due to differences in PCR amplification efficiency.

Telomere targeting with a new G4 ligand enhances radiation-induced killing of human glioblastoma cells

The aim of this study was to test in vitro the efficacy of TAC, an original G-quadruplex ligand, as a potential radiosensitizing agent for glioblastoma multiforme (GBM). Two human radioresistant telomerase-positive GBM cell lines (SF763 and SF767) were analyzed, with and without TAC treatment, for telomere length, cell proliferation, apoptosis, cell-cycle distribution, gene expression, cytogenetic aberrations, clonogenic survival assay, 53BP1 immunofluorescence staining, and γH2AX phosphorylation. We found that low concentrations of TAC (0.5 and 1 μmol/L) inhibited the proliferation of GBM cells in a concentration-dependent manner after only 1 week of treatment, with minimal effects on cell cycle and apoptosis. TAC treatment had no visible effect on average telomere length but modified expression levels of telomere-related genes (hTERT, TRF1, and TRF2) and induced concentration-dependent DNA damage response and dicentric chromosomes. Survival curves analysis showed that exposure to nontoxic, subapoptotic concentrations of TAC enhanced radiation-induced killing of GBM cells. Analysis of DNA repair after irradiation revealed delayed repair kinetics in GBM cells treated with TAC. Furthermore, the combined treatment (TAC and radiation) significantly increased the frequency of chromosomal aberrations as compared with radiation alone. These findings provide the first evidence that exposure to a G4 ligand radiosensitizes human glioblastoma cells and suggest the prospect of future therapeutic applications.

Telomerase activity and telomerase reverse transcriptase catalytic subunit expression in canine lymphoma: correlation with Ki67 immunoreactivity

Increased telomerase activity (TA) has been found in human and canine solid tumours, stem cells and somatic tissues with enhanced proliferative potential. The relationship between TA in normal and malignant lymphoid tissues remains unclear. The TA and the expression of canine telomerase reverse transcriptase catalytic subunit (dogTERT) messenger RNA (mRNA) were analyzed in malignant lymph nodes from 30 dogs with lymphoma, from two dogs with non-neoplastic illness and from two clinically normal dogs, demonstrating a statistically significant difference between TA in lymphoma lymph nodes (n = 30) and normal nodes (n = 4) but no significant difference in dogTERT mRNA expression. In addition, the expression of telomerase reverse transcriptase catalytic subunit (TERT) protein and Ki67 was analyzed in malignant lymph nodes from 10 dogs with lymphoma and from two clinically normal dogs by immunohistochemistry. TERT expression was associated with Ki67 in all lymphoma nodes (n = 10), and differences were illustrated between TERT and Ki67 expression between lymphoma (n = 10) and non-lymphoma (n = 2) nodes. This data support further investigation of telomerase in canine haematopoietic neoplasia through large-scale prospective studies.

Effect of ellagic acid on the expression of human telomerase reverse transcriptase (hTERT) alpha+beta+ transcript in estrogen receptor-positive MCF-7 breast cancer cells

OBJECTIVES

To evaluate the potential of ellagic acid to inhibit the expression of human telomerase reverse transcriptase (hTERT) alpha+beta+ splice variant in MCF-7 breast cancer cells.

DESIGN AND METHODS

MCF-7 cells were incubated with ellagic acid (10(-)(9) M-10(-5) M) in the absence and in the presence of 17beta-estradiol (10(-8) M), a known inducer of hTERT transcription, and hTERT alpha+beta+ mRNA expression was quantified by real-time RT-PCR. 17beta-estradiol and ICI182780, a known estrogen antagonist, served as positive and negative controls respectively.

RESULTS

Ellagic acid, when alone, increased hTERT alpha+beta+ mRNA while its coexistence with 17beta-estradiol reduced significantly the 17beta-estradiol-induced increase in hTERT alpha+beta+ mRNA, implicating thus both its estrogenic and anti-estrogenic effects in breast cancer cells.

CONCLUSIONS

The potential of ellagic acid to down-regulate the 17beta-estradiol-induced hTERT alpha+beta+ mRNA expression may be a mechanism via which ellagic acid exerts, at least in part, its chemopreventive effects in breast cancer.

The oral iron chelator deferasirox represses signaling through the mTOR in myeloid leukemia cells by enhancing expression of REDD1

To evaluate the effect of deferasirox in human myeloid leukemia cells, and to identify the molecular pathways responsible for antiproliferative effects on leukemia cells during chelation therapy, we performed gene expression profiling to focus on the pathway involved in the anticancer effect of deferasirox. The inhibitory concentration (IC50) of deferasirox was 17-50 microM in three human myeloid cell lines (K562, U937, and HL60), while those in fresh leukemia cells obtained from four patients it varied from 88 to 172 microM. Gene expression profiling using Affymerix GeneChips (U133 Plus 2.0) revealed up-regulation of cyclin-dependent kinase inhibitor 1A (CDKN1A) encoding p21CIP, genes regulating interferon (i.e. IFIT1). Pathways related to iron metabolism and hypoxia such as growth differentiation factor 15 (GDF-15) and Regulated in development and DNA damage response (REDD1) were also prominent. Based on the results obtained from gene expression profiling, we particularly focused on the REDD1/mTOR (mammalian target of rapamycin) pathway in deferasirox-treated K562 cells, and found an enhanced expression of REDD1 and its down-stream protein, tuberin (TSC2). Notably, S6 ribosomal protein as well as phosphorylated S6, which is known to be a target of mTOR, was significantly repressed in deferasirox-treated K562 cells, and REDD1 small interfering RNA restored phosphorylation of S6. Although iron chelation may affect multiple signaling pathways related to cell survival, our data support the conclusion that REDD1 functions up-stream of tuberin to down-regulate the mTOR pathway in response to deferasirox. Deferasirox might not only have benefit for iron chelation but also may be an antiproliferative agent in some myeloid leukemias, especially patients who need both iron chelation and reduction of leukemia cells.

Study of oncogenic transformation in ex vivo expanded mesenchymal cells, from paediatric bone marrow

OBJECTIVES

Mesenchymal stromal cells (MSCs) have attracted considerable interest in both the scientific and clinical fields. In order to obtain a sufficient cell number for application, their in vitro expansion is necessary, but during this process their characteristics may be altered and cells may acquire oncogenic properties. We have investigated properties of MSC that may be related to oncogenesis, a critical parameter that has to be evaluated prior to MSC clinical use.

MATERIALS AND METHODS

We studied the expression of p53, p16, RB, H-RAS and human telomerase reverse transcriptase (hTERT) in MSCs from bone marrow of children diagnosed with idiopathic thrombocytopenic purpura (ITP) and autoimmune neutropenia. The same cells were seeded in soft agar to confirm their anchorage dependence and were karyotypically analysed. Finally, MSCs were subcutaneously transplanted into SCID mice and their ectopic osteogenic as well as tumorigenic potential was evaluated.

RESULTS

We have shown that MSCs derived from bone marrow of children with ITP and autoimmune neutropenia do not undergo transformation, the cells expressed normal levels of p53, p16, RB and H-RAS. Expression of hTERT was undetectable, chromosome content remained stable, and their anchorage dependence was confirmed. In an in vivo model, when MSCs were subcutaneously transplanted into SCID mice, no tumorigenesis was observed.

CONCLUSIONS

These findings suggest that MSCs from bone marrow of children do not have oncogenic properties and, therefore, represent validate candidates for applications in regenerative medicine.

Integrated nanosensors to determine levels and functional activity of human telomerase

Telomerase is a key oncogenic enzyme, and a number of novel telomerase inhibitors are currently under development. Because inhibition can be achieved either at the protein or at the enzymatic activity level, independent measurements of these parameters are important in the development of effective therapeutic agents. In the current study, we have developed a set of functional magnetic nanosensors capable of measuring the concentration of telomerase, as well as its enzymatic activity in parallel. The method is based on a magnetic relaxation switch assay, which can be performed in crude tissue samples and is fast and extremely sensitive. Using this method, we were able to detect different amounts of telomerase protein and activity in various cancer and normal cell lines. Furthermore, we were able to study the effect of phosphorylation on telomerase activity. This system not only could provide a rapid assay for the evaluation of antitelomerase therapies but could also be implemented to the study of other cancer markers.

Quantification of hTERT splice variants in melanoma by SYBR green real-time polymerase chain reaction indicates a negative regulatory role for the beta deletion variant

Telomerase activity is primarily determined by transcriptional regulation of the catalytic subunit, human telomerase reverse transcriptase (hTERT). Several mRNA splice variants for hTERT have been identified, but it is not clear if telomerase activity is determined by the absolute or relative levels of full-length (functional) and variant hTERT transcripts. We have developed an SYBR green-based reverse transcription-quantitative polymerase chain reaction assay for the enumeration of the four common hTERT mRNA variants and correlated these with telomerase activity and telomere length in 24 human melanoma cell lines. All except five of the lines expressed four hTERT transcripts, with an overall significant level of co-occurrence between absolute mRNA levels of full-length alpha+/beta+ hTERT and the three splice variants alpha-/beta+, alpha+/beta-, and alpha-/beta-. On average, alpha+/beta+ made up the majority (48.1%) of transcripts, followed by alpha+/beta- (44.6%), alpha-/beta- (4.4%), and alpha-/beta+ (2.9%). Telomerase activity ranged from 1 to 247 relative telomerase activity and correlated most strongly with the absolute amount of alpha+/beta+ (R = 0.791, P = .000004) and the relative amount of alpha+/beta- (R = -0.465, P = .022). This study shows that telomerase activity in melanoma cells is best determined by the absolute expression of full-length hTERT mRNA and indicates a role for the hTERT beta deletion variant in the negative regulation of enzyme activity.

Real-Time RT-PCR Quantification of Human Telomerase Reverse Transcriptase Splice Variants in Tumor Cell Lines and Non–Small Cell Lung Cancer

Background: We developed and validated a real-time reverse transcription (RT)–PCR for the quantification of 4 individual human telomerase reverse transcriptase (TERT) splice variants (α+β+, α−β+, α+β−, α−β−) in tumor cell lines and non–small cell lung cancer (NSCLC).

Methods: We used in silico designed primers and a common TaqMan probe for highly specific amplification of each TERT splice variant, PCR transcript–specific DNA external standards as calibrators, and the MCF-7 cell line for the development and validation of the method. We then quantified TERT splice variants in 6 tumor cell lines and telomerase activity and TERT splice variant expression in cancerous and paired noncancerous tissue samples from 28 NSCLC patients.

Results: In most tumor cell lines, we observed little variation in the proportion of TERT splice variants. The α+β− splice variant showed the highest expression and α−β+ and α−β− the lowest. Quantification of the 4 TERT splice variants in NSCLC and surrounding nonneoplastic tissues showed the highest expression percentage for the α+β− variant in both NSCLC and adjacent nonneoplastic tissue samples, followed by α+β+, with the α−β+ and α−β− splice variants having the lowest expression. In the NSCLC tumors, the α+β+ variant had higher expression than other splice variants, and its expression correlated with telomerase activity, overall survival, and disease-free survival.

Conclusions: Real-time RT-PCR quantification is a specific, sensitive, and rapid method that can elucidate the biological role of TERT splice variants in tumor development and progression. Our results suggest that the expression of the TERT α+β+ splice variant may be an independent negative prognostic factor for NSCLC patients.

In situ detection of hTERT variants in anaplastic large cell lymphoma

The expression of hTERT and its isoforms is difficult to assess in lymphoma tissues with the commonly used reverse transcription-polymerase chain reaction (RT-PCR) methods, because non-neoplastic lymphocytes expressing hTERT are always present in the lymphomatous infiltrates. The present study aimed to investigate hTERT mRNA variants in anaplastic large cell lymphoma (ALCL) (n = 38) with in situ hybridization (ISH), along with the immunodetection of hTERT protein. Probes for the identification of mRNAs containing (Bplus) and lacking (Bdel) exons 7 and 8 of the hTERT mRNA were used. Normal lymphocyte populations equally expressed both Bplus and Bdel mRNAs. Although all ALCL examined were found positive for hTERT expression with RT-PCR, hTERT mRNAs were identified in 68% of these tumors with ISH, with a higher incidence in the group bearing ALK translocations (10 out of 11; 90.9%) compared to the ALK negative group (17 out of 27; 59.3%) (PPearson's = 0.002). The same results were obtained with immunohistochemistry for hTERT. In approximately 50% of cases, only Bplus positive cells were identified, again with a higher incidence in the ALK positive compared to the ALK negative group (PPearson's = 0.016). In conclusion, ISH for hTERT mRNAs appears to be a valuable tool for the investigation of hTERT expression in lymphomas. Aberrations in hTERT variant profiles and a decline in the expression of the B deleted isoform may be associated with the pathogenesis of ALCL, especially with respect to ALK positive tumors.

Critically short telomeres in acute myeloid leukemia with loss or gain of parts of chromosomes

Telomeres, nucleoprotein complexes at chromosome ends, protect chromosomes against end-to-end fusion. Previous in vitro studies in human fibroblast models indicated that telomere dysfunction results in chromosome instability. Loss of telomere function can result either from critical shortening of telomeric DNA or from loss of distinct telomere-capping proteins. It is less clear whether telomere dysfunction has an important role in human cancer development in vivo. Acute myeloid leukemia (AML) is a good model to study mechanisms that generate chromosome instability in human cancer development because distinct groups of AML are characterized either by aberrations that theoretically could result from telomere dysfunction (terminal deletions, gains/losses of chromosome parts, nonreciprocal translocations), or aberrations that are unlikely to result from telomere dysfunction (e.g., reciprocal translocations or inversions). Here we demonstrate that AML with multiple chromosome aberrations that theoretically could result from telomere dysfunction is invariably characterized by critically short telomeres. Short telomeres in this group are not associated with low telomerase activity or decreased expression of essential telomeric capping proteins TRF2 and POT1. In contrast, telomerase activity levels are significantly higher in AML with short telomeres. Notably, short telomeres in the presence of high telomerase may relate to significantly higher expression of TRF1, a negative regulator of telomere length. Our observations suggest that, consistent with previous in vitro fibroblast models, age-related critical telomere shortening may have a role in generating chromosome instability in human AML development.

Transcriptional profiling of Epstein-Barr virus (EBV) genes and host cellular genes in nasal NK/T-cell lymphoma and chronic active EBV infection

Nasal NK/T-cell lymphoma is an aggressive subtype of non-Hodgkin lymphoma (NHL) that is closely associated with Epstein–Barr virus (EBV). The clonal expansion of EBV-infected NK or T cells is also seen in patients with chronic active EBV (CAEBV) infection, suggesting that two diseases might share a partially similar mechanism by which EBV affects host cellular gene expression. To understand the pathogenesis of EBV-associated NK/T-cell lymphoproliferative disorders (LPD) and design new therapies, we employed a novel EBV DNA microarray to compare patterns of EBV expression in six cell lines established from EBV-associated NK/T-cell LPD. We found that expression of BZLF1, which encodes the immediate-early gene product Zta, was expressed in SNK/T cells and the expression levels were preferentially high in cell lines from CAEBV infection. We also analyzsd the gene expression patterns of host cellular genes using a human oligonucleotide DNA microarray. We identified a subset of pathogenically and clinically relevant host cellular genes, including TNFRSF10D, CDK2, HSPCA, IL12A as a common molecular biological properties of EBV-associated NK/T-cell LPD and a subset of genes, such as PDCD4 as a putative contributor for disease progression. This study describes a novel approach from the aspects of viral and host gene expression, which could identify novel therapeutic targets in EBV-associated NK/T-cell LPD.

Estimating immunoregulatory gene networks in human herpesvirus type 6-infected T cells

The immune response to viral infection involves complex network of dynamic gene and protein interactions. We present here the dynamic gene network of the host immune response during human herpesvirus type 6 (HHV-6) infection in an adult T-cell leukemia cell line. Using a pathway-focused oligonucleotide DNA microarray, we found a possible association between chemokine genes regulating Th1/Th2 balance and genes regulating T-cell proliferation during HHV-6B infection. Gene network analysis using an integrated comprehensive workbench, VoyaGene, revealed that a gene encoding a TEC-family kinase, ITK, might be a putative modulator in the host immune response against HHV-6B infection. We conclude that Th2-dominated inflammatory reaction in host cells may play an important role in HHV-6B-infected T cells, thereby suggesting the possibility that ITK might be a therapeutic target in diseases related to dysregulation of Th1/Th2 balance. This study describes a novel approach to find genes related with the complex host-virus interaction using microarray data employing the Bayesian statistical framework.