MLL Modulates Telomere Length in Mammalian Cells.

Blood ◽  
2006 ◽  
Vol 108 (11) ◽  
pp. 2209-2209
Author(s):  
Corrado Caslini ◽  
Jay L. Hess
Keyword(s):  
Telomere Length ◽  
Cell Lines ◽  
Nuclear Matrix ◽  
Mammalian Cells ◽  
Target Genes ◽  
Histone H3 ◽  
Deletion Mutants ◽  
Multiprotein Complex ◽  
Telomere Shortening ◽  
Chip Analysis

Abstract In mammalian cells, the telomeric complex at the end of chromosomes consists of several thousand copies of the exanucleotide TTAGGG and associated proteins attached to the nuclear matrix. Chromatin modifying enzymes involved in histone H3/lysine 9 and histone H4/lysine 20 trimethylation, and DNA methylation are known to preserve the telomere heterochromatic structure, length and capping function. Loss of these heterochromatic marks leads to telomere lengthening, most likely through the negative regulation of telomerase or alternative lengthening of telomeres (ALT) mechanisms. The MLL protein is a chromatin modifying enzyme with histone H3/lysine 4 methyltransferase activity, which maintains active transcriptional state of target genes in a large multiprotein complex. Analogously, the yeast’s MLL homologous protein Set1 is part of a multiprotein complex required for maintenance of target genes expression. In addition, Set1 deletion mutants show disruption of telomeric silencing along with telomere shortening or lengthening, respectively in budding and fission yeast. This raised the question of whether MLL, like Set1, plays a role in epigenetic maintenance of telomeric heterochromatin. Here, using chromatin immunoprecipitation (ChIP) analysis, we show that MLL associates with the heterochromatic complex at telomeres of primary and transformed human cell lines. ChIP analysis of cell lines conditionally expressing Flag-tagged MLL chimeric proteins and deletion mutants shows the amino terminus of MLL, which confers association to the nuclear matrix, is responsible for targeting to the telomeric complex. MLL associates with the telomeres of telomerase and ALT positive cell lines in amount that is proportional to the telomere length, as revealed by Southern blot terminal restriction fragment analysis. Moreover, immunoprecipitation analysis evidenced the association of MLL with the terminal-repeat binding factor TRF2, a protein known to play a key role in telomere capping, and indirect immunofluorescence analysis showed MLL and TRF2 colocalization at ALT-associated PML nuclear bodies. In search for possible biological functions of MLL at the telomeric complex, we found abnormally longer telomeres in Mll-null mouse embryonic stem (ES) cells and fibroblasts (MEFs) than in wild-type control cells. In Mll-null MEFs, a significant telomere shortening was obtained by stable reexpression of an MLL allele. In addition, we found that in aging human cells the MLL binding to the telomeric complex is abrogated by the progressive telomere shortening due to telomere attrition, suggesting a possible involvement of MLL in signaling for replicative senescence.

The Telomerase Inhibitor RHPS4 Induces Telomere Shortening, DNA-Damage and Cell Death in AML Cells and Chemosensitises Cells to Daunorubicin.

Blood ◽  
2009 ◽  
Vol 114 (22) ◽  
pp. 2760-2760
Author(s):  
Monica Pallis ◽  
Dotun Ojo ◽  
Jaineeta Richardson ◽  
John Ronan ◽  
Malcolm Stevens ◽  
...  
Keyword(s):  
Dna Damage ◽  
Cell Death ◽  
Telomere Length ◽  
Progenitor Cells ◽  
Cell Lines ◽  
Dna Damage Response ◽  
Cell Types ◽  
Telomere Shortening ◽  
Damage Response

Abstract Abstract 2760 Poster Board II-736 The quadruplex ligand RHPS4 is the lead compound in a drug discovery program at the University of Nottingham. It has been shown to bind to telomeres and inhibit telomerase, and subsequently induces growth arrest in progenitor cells from cancer cell lines whilst sparing normal haematopoietic progenitor cells. We explored its in vitro effects in AML cells, which are reported generally to have considerably shorter telomeres than normal CD34+ cells. AML cell lines were grown for 21 days in suspension culture. Primary samples were cultured for 14 days in semi-solid medium. Telomere length was measured by Southern blotting. γH2A.X was used to identify a DNA damage response, and cell viability was measured flow cytometrically with 7-amino actinomycin D. As reported in other tumour cell types, sensitivity to RHPS4 was found to be greatest in those AML cells with the shortest telomeres. In the OCI-AML3 cell line 0.3 μM RHPS4 inhibited cell growth by 50% in a 21 day clonogenic assay, accompanied by shortening of telomeres from 2.6 Kb to <1 Kb. Molm 13 cells (initial telomere length 3.2kB) also underwent telomere shortening in the presence of 0.3 μM RHPS4 (2.8Kb), whereas TF1a and U937 (both with initial telomere lengths approximately 6.5 kB) were insensitive at that concentration. After 6 days at 0.3 μM, RHPS4 was cytostatic, but at higher concentrations (1 μM) the drug was found to induce a substantial DNA damage response and loss of viability to OCI-AML3 cells. Moreover 0.3 μM RHPS4 enhanced the γH2A.X expression and cell death induced by the chemotherapy drug daunorubicin in these cells. Using 14 day clonogenic assays in primary AML samples (n=6), we found that the IC50 for RHPS4 alone was 0.7 μM. However, in the presence of 0.3 μM RHPS4, the median IC50 to daunorubicin was reduced from 19 nM to 5.5 nM. In conclusion we have determined that RHPS4 has telomere-shortening, cytostatic, cytotoxic and chemosensitising properties in AML cells. Disclosures: Stevens: Pharminox Ltd: director and shareholder of Pharminox Ltd which has a financial interest in RHPS4.

Telomerase Inhibitor BIBR1532 Induces Telomere Shortening and Growth Inhibition in Extra-Germinal Center (GC)-Derived Lymphoid Cell Lines.

Blood ◽  
2004 ◽  
Vol 104 (11) ◽  
pp. 3389-3389 ◽  
Author(s):  
Marco Ladetto ◽  
Irene Ricca ◽  
Mara Compagno ◽  
Dario Ferrero ◽  
Alberto Rocci ◽  
...  
Keyword(s):  
Growth Inhibition ◽  
Telomere Length ◽  
Cell Lines ◽  
Lymphoid Cell ◽  
G1 Arrest ◽  
Telomere Shortening ◽  
Extensive Evaluation ◽  
Hematological Cancers ◽  
Lymphoid Cell Lines ◽  
Telomere Erosion

Abstract Background and aim of the study. Telomerase inhibition is a novel promising anticancer strategy which has been pursued using antisense oligonucleotides and more recently pharmacological inhibitors. BIBR-1532 is a mixed-type non-competitive inhibitor of the catalytic subunit of telomerase (h-TERT). In solid tumor cell lines, BIBR-1532 successfully induced telomere shortening and growth inhibition (Damm K et al, The Embo J, 2001). The activity of BIBR-1532 has not been so far evaluated in hematological cancers. Aim of this study is to evaluate the activity of this compound in cell lines derived from B-cell lymphoid tumors. These neoplasms are an interesting model to investigate BIBR1532 since they show marked differences in their telomere lenght according to GC origin (i.e. GC-derived have long telomeres and extra GC-derived have short telomeres)(Ladetto et al Blood 2004). Methods. We employed two extra-GC derived cell lines (the multiple myeloma KMS-11 and the chronic lymphocytic leukemia JVM-2 provided respectively by M. Massaia MD and C Carlo Stella MD) and two GC-derived cell lines (the Burkitt’s Lymphoma CA46 and the follicular lymphoma cell line DHL16 provided by J.G. Gribben MD). All the four cell lines were h-TERT positive. BIBR-1532 (kindly provided by Klaus Damm MD and Jacques van Meel, PhD, Boehringer Ingelheim Pharma, Germany) was administrated thrice a week to the standard concentration of 10μM. Cells were cultured for at least 80 mitotic divisions both in presence and absence of the agent. Cell growth was assessed three times a week. Aliquots of cultured cells were taken approximately every 20 days for telomere length evaluation. Cells were also assessed using the propidium iodide assay to verify whether growth inhibition was due to apotosis or prolipherative arrest. Results. As expected based on their GC-status, the four cell lines had different baseline telomere length (CA46: 6500bp DHL 16: 7000bp KMS11 3200bp, JVM-2 3500). When cells were cultured without BIBR 1532 no significant telomere shortening occurred over the whole culture period. In the presence of BIBR-1532, cell lines approximately lost 32bp at each mitotic division. After 20 mitoses KMS-11 and JVM-2 underwent marked and progressive growth inhibition with a clear plateau effect after 50 to 55 mitoses. In contrast no growth inhibition was noticed in GC-derived cell lines despite a similar degree telomere erosion. Growth inhibition in cell lines responsive to BIBR-1532 was mostly associated with G1 arrest. Conclusions: These results are the first reported experience on the use of BIBR1532 on B-lymphoid cell lines and indicate that: a) BIBR1532 effectively induces telomere shortening in lymphoid tumors; b) in extra-GC telomere erosion quickly lead to pharmacologically-induced senescence with marked growth inhibition; c) GC-derived lymphoid cell lines are effectively protected from pharmacological senescence induced by BIBR 1532 due to their long telomeres. These results indicate that telomerase inhibitors require extensive evaluation as anti-cancer agents in extra-GC-derived lymphoid tumors.

Identification of PML-RARa Target Genes Using Microarray and ChIP-on-Chip Analysis.

Blood ◽  
2005 ◽  
Vol 106 (11) ◽  
pp. 2994-2994
Author(s):  
Wenlin Yuan ◽  
Nicole R. Grieselhuber ◽  
Roland D. Green ◽  
Timothy J. Ley
Keyword(s):  
Vector Control ◽  
Cell Lines ◽  
Neutrophil Elastase ◽  
Target Genes ◽  
Experimental System ◽  
Myeloid Cell ◽  
U937 Cells ◽  
Cancer Pathogenesis ◽  
On Chip ◽  
Chip Analysis

Abstract PML-RARa is very toxic to early myeloid cell lines that express neutrophil elastase. As a consequence, myeloid cell lines that stably express PML-RARa must undergo significant adaptations to avoid toxicity (eg. loss of expression of neutrophil elastase (Lane and Ley, MCB, 2005). To identify the direct target genes of PML-RARa, we decided to bypass the issue of adaptation by profiling naive U937 cells that transiently expressed PML-RARa. To define “immediate-early” expression changes caused by PML-RARa, we harvested U937 cells electroporated with expression vectors containing eGFP-PML-RARa (known to possess all the measurable functional properties of PML-RARa) vs. eGFP alone, at the earliest time point when adequate numbers of eGFP positive cells could be collected via high speed cell sorting (6 hours). RNA obtained from these cells was subjected to linear amplification and hybridized with Affymetrix U133 Plus 2.0 arrays. Probesets that demonstrated the largest differences in expression between cells transfected with eGFP vs. eGFP-PML-RARa were PML and RARa themselves (15-fold increase for PML, 9-fold for RARa), providing an important validation for the experimental system. Differentially expressed genes were selected by three filters for further study: (i) ANOVA statistic (P &lt; 0.05); (ii) “present” call and &gt;150 average expression units in at least one sample; and (iii) Reproducible (n=2) &gt;2-fold differences between eGFP-PML-RARa vs. eGFP vector transfected cells. Only 280 probesets (out of 54,613 total) met all of these criteria. Among them, 37 genes were involved in signal transduction, 15 in cell proliferation and differentiation, 7 in apoptosis, 14 in cell cycle, 15 in transport, 27 in protein metabolism and modification, 13 in oncogenesis, and 13 in immunity and defense (Panther classification system). 15/15 genes selected from a variety of categories were further validated with Q-PCR in duplicate using replicate samples, and all differences were statistically significant (p&lt;0.05). Q-PCR validated genes that were up-regulated at 6 hours by eGFP-PML-RARa included CD36 (196% increase over eGFP vector control), LATS2 (204%), Sox4 (395%), COPEB (325%), HoxA5 (294%), IFITM3 (139%), AIF1 (197%), and PLD1 (315%). Q-PCR validated genes that were down-regulated by eGFP-PML-RARa at 6 hours included BTG2 (60% the level of eGFP vector control), KLF7(52%), CDKN1A (p21)(39%), Pim1 (58%), SLC23A2 (36%), HoxA13 (51%), and PDCD1LG1 (42%). Among these genes, Sox4, Pim1, BTG2, and PDCD1LG1 have previously been implicated in cancer pathogenesis by retroviral insertional mutagenesis (http://RTCGD.ncifcrf.gov). To identify promoters that were directly in contact with the eGFP-PML-RARa fusion protein, we performed “ChIP-on-chip” analysis using chromatin immunoprecipitation coupled with a NimbleGen promoter tiling array containing 15 50-mer probes (~100 bp spacing) between positions −1500 and +500 of the transcription initiation sites of a curated subset of 24,275 known human genes (HG17, Build 35). By subtracting non-specific hybridization signals from the eGFP control chip, we identified and validated several promoter regions as direct binding targets of eGFP-PML-RARa, including HoxA13 and CDKN1A (p21). This experimental system provides a new approach for the identification of the direct transcriptional targets of PML-RARa, which may lead to new insights into APL pathogenesis and treatment.

Mechanism of the Elevated UPR in CN Patients but Not in CyN Patients Carrying Same ELANE Mutations

Blood ◽  
2011 ◽  
Vol 118 (21) ◽  
pp. 14-14
Author(s):  
Rainer Nustede ◽  
Inna Kuznetsova ◽  
Karl Welte ◽  
Julia Skokowa
Keyword(s):  
Cell Lines ◽  
Mammalian Cells ◽  
Target Genes ◽  
Conflicts Of Interest ◽  
Myeloid Cells ◽  
Myeloid Cell ◽  
Severe Congenital Neutropenia ◽  
Healthy Individuals ◽  
Congenital Neutropenia ◽  
Cyclic Neutropenia

Abstract Abstract 14 Several studies found that in patients with severe congenital neutropenia (CN) harboring mutations in the ELANE gene mutated NE protein induced unfolded protein response (UPR) leading to elevated apoptosis and diminished differentiation of myeloid cells. However, it is unclear, why UPR was not detected in patients with cyclic neutropenia (CyN) carrying the same ELANE mutations, which have been found in CN patients. Several UPR components have been identified in mammalian cells, which include three transducers (IRE1, PERK, and activating transcription factor 6 (ATF-6) as well as one master regulator (BiP/GRP78). BiP is known to be regulated by ATF6. The activation of ATF6 and its target genes (GADD34, CHOP and BiP) in CN patients has not been studied yet. We were able to detect significantly elevated levels of ATF6 and BiP in myeloid cells of CN patients with ELANE mutations, in comparison to CyN patients and to healthy individuals. Therefore, we investigated the mechanism of UPR and activation of ATF6 and ATF6 target genes in CN patients in comparison to CyN patients. We transduced the myeloid cell lines HL60 and NB4 with lentiviral constructs contained either wild type (WT) ELANE cDNA, or mutated (MUT) ELANE cDNA and measured mRNA and protein expression of ATF6 as well as mRNA expression of ATF6 target genes. We compared the effects of three ELANE mutations: C42R, V145-C152del (both mutations presented in CN patients, but not in CyN patients) and S97L (typical for CN and CyN patients) with WT ELANE. We found that in both cell lines only C42R ELANE MUT, but not V145-C152del ELANE MUT or S97L ELANE MUT induced expression of ATF6, GADD34, CHOP and BiP, as compared to control transduced cells. Furthermore, we hypothesize that degradation of mutated NE protein by Secretory Leukocyte Protease Inhibitor (SLPI) might be involved in UPR induction. However, we detected only very low levels of SLPI mRNA in CD33+ myeloid cells and in PMNs of patients with severe congenital neutropenia (CN), as compared to patients with cyclic neutropenia (CyN) and to healthy individuals. The lack of the NE inhibitor, SLPI in CN patients may further contribute to elevated UPR triggered by ELANE MUT and normal levels of SLPI in CyN patients might protect from ELANE MUT-induced UPR. Indeed, inhibition of SLPI using SLPI-specific shRNA led to a significantly elevated expression levels of ATF6, GADD34 and BIP, as compared to ctrl shRNA transduced cells. More importantly, co-transduction of NB4 cells with SLPI shRNA in combination with ELANE S97L MUT (which is common for both CN and CyN patients), but not with WT ELANE led to elevated levels of ATF6, GADD34 and BIP. In summary, different ELANE mutations have different effects on UPR as judged by ATF6 activation and the level of ELANE-triggered UPR is regulated by SLPI. Disclosures: No relevant conflicts of interest to declare.

MHC Class-II Expression Reveals Differential Regulation of BLIMP-1 Target Genes.

Blood ◽  
2005 ◽  
Vol 106 (11) ◽  
pp. 1207-1207
Author(s):  
Reuben Tooze ◽  
Sophie Stephenson ◽  
Gina Doody ◽  
Andy Rawstron
Keyword(s):  
Cell Differentiation ◽  
Cell Lines ◽  
Mhc Class Ii ◽  
Plasma Cell ◽  
Target Genes ◽  
Histone H3 ◽  
Class Ii ◽  
Myeloma Cell ◽  
Cell Phenotype ◽  
Promoter Occupancy

Abstract BLIMP-1 initiates plasma cell differentiation by inhibiting the expression of a limited set of transcription factor genes. BLIMP-1 mediates repression of its targets by promoter occupancy and recruitment of the Groucho corepressor, histone deacetylase and the G9a lysine methyltransferase. The relative contribution of these mechanisms to the stable silencing of BLIMP-1 target genes in plasma cells is not known. Epigenetic changes initiated by BLIMP-1 could be maintained by independent factors or alternatively may be dependent on continuous occupancy of the promoter by BLIMP-1. The aim of this study was to investigate the mechanisms operating at two well-defined BLIMP-1 target genes, MHC2TA and PAX-5. Repression of PAX-5 is essential for extinction of the B-cell phenotype, while repression of MHC2TA mediates the loss of MHC class-II expression characteristic of plasma cell differentiation. PAX-5 is silenced in virtually all cases of myeloma, whereas MHC class-II continues to be expressed in a subset of primary myeloma cells and many myeloma cell lines. Using chromatin immunoprecipitation we demonstrate that BLIMP-1 constitutively binds MHC2TA promoter-3 and is present equally in MHC2TA expressing and non-expressing myeloma cell lines. In expressing cells MHC2TA promoter-3 is associated with acetylation of histone H3 lysine-9, a marker of open chromatin, whereas histone H3 lysine-9 is neither acetylated nor methylated in non-expressing cells. In contrast the PAX-5 promoter is associated with trimethylation of histone H3 lysine-9, a marker of repressed heterochromatin, in all the cell lines examined, but constitutive BLIMP-1 occupancy is not detectable. Although BLIMP-1 does not silence MHC2TA expression in the MHC class-II positive U266 cell line, it is mediating transcriptional repression, since siRNA knockdown of BLIMP-1 is associated with elevated MHC2TA mRNA and MHC class-II surface expression. In contrast PAX-5 mRNA and its target CD19 continue to be repressed. MHC class-II re-expression was associated with loss of CD138 and the entry of the majority of cells into apoptosis. Our data demonstrate that MHC class-II expression in myeloma cell lines is associated with defective silencing of MHC2TA despite BLIMP-1 occupancy, and reveal differences in the contribution of epigenetic modifications and promoter occupancy in the maintenance of target gene silencing by BLIMP-1. Loss of BLIMP-1 results in a partial reversion of plasma cell phenotype that is associated with induction of apoptosis. As continual high levels of BLIMP-1 expression appear to be critical for plasma cell survival, suppression of BLIMP-1 represents a potential therapeutic pathway.

Telomerase Inhibition, Telomere Shortening and Apoptotic Cell Death in Multiple Myeloma Cells Following Exposure to a Novel and Potent Telomerase Inhibitor (GRN163L), Targeting RNA component of Telomerase.

Blood ◽  
2004 ◽  
Vol 104 (11) ◽  
pp. 638-638 ◽  
Author(s):  
Masood A. Shammas ◽  
Hemant Koley ◽  
Alexi Protopopov ◽  
Pierfrancesco Tassone ◽  
Paola Neri ◽  
...  
Keyword(s):  
Multiple Myeloma ◽  
Cell Death ◽  
Telomere Length ◽  
Cell Lines ◽  
Apoptotic Cell ◽  
Annexin V ◽  
Telomerase Activity ◽  
Telomere Shortening ◽  
Myeloma Cells ◽  
Telomerase Inhibitor

Abstract Telomeres, the specialized nucleoprotein structures at the ends of chromo-somes, shorten at each DNA replication, and if unopposed leads to chromosomal erosion and cell death. Telomere shortening below a critical length is prevented by telomerase. We have previously observed elevated telomerase activity and shortened telomeres in multiple myeloma (MM), making the telomere maintenance mechanism an important target for therapy. Based on success with other non-specific telomerase inhibitors, in this study, we evaluated the effects of a thio-phosphoramidate oligonucleotide specifically targeting the RNA component of telomerase (GRN163L), with modifications to facilitate its delivery into human cells. Nuclear uptake of GRN163L without need for transfection enhancer at 24h was confirmed in >99% MM cells using fluorescein isothiocyanate-tagged GRN163L and confocal microscopy. Next we evaluated the effects of different concentrations and length of exposure of GRN163L on telomerase activity in diff MM cell lines (ARP and INA6). Whereas control oligonucleotide did not significantly affect telomerase activity, ≥ 80% loss of telomerase activity was observed in MM cell lines at day 3 at submicromolar concentrations of GRN163L. This inhibition of telomerase activity was associated with inhibition of myeloma cell growth and survival. Treatment of INA6 cells with GRN163L for three weeks induced 96±4% and 100% cell death at 0.5 and 1 μM concentrations, respectively, while ARP cells with higher telomerase activity and longer telomeres showed 67 ± 4% cell death at 5 weeks with 0.5 μM inhibitor and 82 ± 3% and 100% cell death at 4 and 5 weeks respectively with 2 μM concentration. The cell death was predominantly apoptotic, as determined by 51% annexin V-positive INA6 cells at two weeks and >80 % annexin V positive ARP cells at four weeks. The apoptotic cell death was associated with reduction in telomere length as analyzed using Telomere-FISH. While the control oligo treated ARP cells showed mean Telomere Fluorescence Intensity (TFI) on interphase chromosomes of 17.2 ± 1.5 (range 1.3–146.4), GRN163L treated cells showed reduction of mean TFI to 13.6 ± 0.46 (range 0.74 – 65.7). Although values above 100 were observed on 2 chromosomes in control oligo treated cells, GRN163L-treated cells had no chromosome with a TFI of more than 70.0. A similar reduction in telomere length was observed for INA6 cells. Subsequently, we were also able to increase cytotoxicity of DNA damaging agents in MM cells treated with GRN163L and shortened telomeres; providing a rationale for evaluation of combination therapies. These data demonstrate GRN163L as a potent and specific telomerase inhibitor able to disrupt telomere integrity and inducing apoptotic death of multiple myeloma cells. Evaluation of this agent in a SCIDhu model of myeloma is underway prior to its clinical evaluation.

Highlighting the Correlation Between Telomere Shortening and the Susceptibility to the Novel SARS-CoV-2 Virus (COVID-19)

2020 ◽  
Author(s):  
Aml Ghanem
Keyword(s):  
Telomere Length ◽  
Stress Responses ◽  
Viral Infections ◽  
Deep Understanding ◽  
The Elderly ◽  
The Novel ◽  
Telomere Shortening ◽  
Infection Pathways ◽  
And Gender ◽  
Demographic Distribution

COVID-19 is a global crisis that requires a deep understanding of infection pathways to facilitate the development of effective treatments and vaccines. Telomere, which is regarded as a biomarker for other respiratory viral infections, might influence the demographic distribution of COVID-19 infection and fatality rates. Viral infection can induce many cellular remodeling events and stress responses, including telomere specific alterations, just as telomere shortening. In brief, this letter aims to highlight the connection between telomere shortening and susceptibility to COVID-19 infection, in addition to changes in telomeric length according to the variation of age and gender of confirmed cases with COVID-19 infection. To sum up, the correlation is revealed from the available data that connect telomere length and COVID-19 infection, demonstrated in the fact that the elderly patients and males are more susceptible to COVID-19 due to shortening in their telomere length.

Regulation And Effect Of Telomerase And Telomeric Length In Stem Cells

2020 ◽  
Vol 15 ◽  
Author(s):  
Basak Celtikci ◽  
Gulnihal Kulaksiz Erkmen ◽  
Zeliha Gunnur Dikmen
Keyword(s):  
Telomere Length ◽  
Somatic Cells ◽  
Telomere Maintenance ◽  
The Other ◽  
Telomerase Reverse Transcriptase ◽  
Human Telomerase Reverse Transcriptase ◽  
Telomere Shortening ◽  
Maintenance Mechanism ◽  
Associated Diseases ◽  
Human Telomerase

: Telomeres are the protective end caps of eukaryotic chromosomes and they decide the proliferative lifespan of somatic cells, as the guardians of the cell replication. Telomere length in leucocytes reflects telomere length in other somatic cells. Leucocyte telomere length can be a biomarker of human ageing. The risk of diseases, which are associated with reduced cell proliferation and tissue degeneration, including aging or aging-associated diseases, such as dyskeratosis congenita, cardiovascular diseases, pulmonary fibrosis and aplastic anemia, are correlated with an increase in short telomeres. On the other hand, the risk of diseases, which are associated with increased proliferative growth, including major cancers, is correlated with long telomeres. In most of the cancers, a telomere maintenance mechanism during DNA replication is essential. The reactivation of the functional ribonucleoprotein holoenzyme complex [telomerase] starts the cascade from normal and premalignant somatic cells to advanced malignant cells. Telomerase is overexpressed during the development of cancer and embryonic stem cells, through controlling genome integrity, cancer formation and stemness. Cancer cells have mechanisms to maintain telomeres to avoid initiation of cellular senescence or apoptosis, and halting cell division by critically short telomeres. Modulation of the human telomerase reverse transcriptase is the ratelimiting step for the production of functional telomerase and the telomere maintenance. Human telomerase reverse transcriptase promoter promotes its gene expression only in tumor cells, but not in normal cells. Some cancers activate an alternative lengthening of telomeres maintenance mechanism via DNA recombination to unshorten their telomeres. Not only heritability but also oxidative stress, inflammation, environmental factors, and therapeutic interventions have an effect on telomere shortening, explaining the variability in telomere length across individuals. There have been a large number of publications, which correlate human diseases with progressive telomere shortening. Telomere length of an individual at birth is also important to follow up telomere shortening, and it can be used as biomarkers for healthy aging. On the other hand, understanding of cellular stress factors, which affect stem cell behavior, will be useful in regeneration or treatment in cancer and age-associated diseases. In this review, we will understand the connection between stem cell and telomere biology, cancer, and aging-associated diseases. This connection may be useful for discovering novel drug targets and improve outcomes for patients having cancer and aging-associated diseases.

scholarly journals Evaluation of AXIN1 and AXIN2 as targets of tankyrase inhibition in hepatocellular carcinoma cell lines

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Wenhui Wang ◽  
Pengyu Liu ◽  
Marla Lavrijsen ◽  
Shan Li ◽  
Ruyi Zhang ◽  
...  
Keyword(s):  
Cell Lines ◽  
Target Genes ◽  
Therapeutic Option ◽  
Carcinoma Cell Lines ◽  
Hepatocellular Carcinomas ◽  
Enhanced Expression ◽  
Mutant Lines ◽  
Substantial Interest ◽  
Support Tumor Growth ◽  
Made In

AbstractAXIN1 mutations are observed in 8–10% of hepatocellular carcinomas (HCCs) and originally were considered to support tumor growth by aberrantly enhancing β-catenin signaling. This view has however been challenged by reports showing neither a clear nuclear β-catenin accumulation nor clearly enhanced expression of β-catenin target genes. Here, using nine HCC lines, we show that AXIN1 mutation or siRNA mediated knockdown contributes to enhanced β-catenin signaling in all AXIN1-mutant and non-mutant lines, also confirmed by reduced signaling in AXIN1-repaired SNU449 cells. Both AXIN1 and AXIN2 work synergistically to control β-catenin signaling. While in the AXIN1-mutant lines, AXIN2 is solely responsible for keeping signaling in check, in the non-mutant lines both AXIN proteins contribute to β-catenin regulation to varying levels. The AXIN proteins have gained substantial interest in cancer research for a second reason. Their activity in the β-catenin destruction complex can be increased by tankyrase inhibitors, which thus may serve as a therapeutic option to reduce the growth of β-catenin-dependent cancers. At concentrations that inhibit tankyrase activity, some lines (e.g. HepG2, SNU398) were clearly affected in colony formation, but in most cases apparently independent from effects on β-catenin signaling. Overall, our analyses show that AXIN1 inactivation leads to enhanced β-catenin signaling in HCC cell lines, questioning the strong statements that have been made in this regard. Enhancing AXIN activity by tankyrase monotherapy provides however no effective treatment to affect their growth exclusively through reducing β-catenin signaling.

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