The Transition between Telomerase and ALT Mechanisms in Hodgkin Lymphoma and Its Predictive Value in Clinical Outcomes

Genetically predicted telomere length and the risk of 11 hematological diseases: a Mendelian randomization study

OBJECTIVE

Previous studies have demonstrated that various hematologic diseases (HDs) induce alterations in telomere length (TL). The aim of this study is to investigate whether genetically predicted changes in TL have an impact on the risk of developing HDs.

METHODS

GWAS data for TL and 11 HDs were extracted from the database. The R software package "TwoSampleMR" was employed to conduct a two-sample Mendelian randomization (MR) analysis, in order to estimate the influence of TL changes on the risk of developing the 11 HDs.

RESULTS

We examined the effect of TL changes on the risk of developing the 11 HDs. The IVW results revealed a significant causal association between genetically predicted longer TL and the risk of developing acute lymphocytic leukemia (ALL), acute myeloid leukemia (AML), chronic lymphocytic leukemia (CLL), mantle cell lymphoma (MANTLE), and hodgkin lymphoma (HODGKIN). However, there was no significant causal relationship observed between TL changes and the risk of developing chronic myeloid leukemia (CML), diffuse large b-cell lymphoma (DLBCL), marginal zone b-cell lymphoma (MARGINAL), follicular lymphoma (FOLLICULAR), monocytic leukemia (MONOCYTIC), and mature T/NK-cell lymphomas (TNK).

CONCLUSIONS

The MR analysis revealed a positive association between genetically predicted longer TL and an increased risk of developing ALL, AML, CLL, MANTLE, and HODGKIN. This study further supports the notion that cells with longer TL have greater proliferative and mutational potential, leading to an increased risk of certain HDs.

A novel telomere-related genes model for predicting prognosis and treatment responsiveness in diffuse large B-cell lymphoma

Diffuse large B cell lymphoma (DLBCL) is a highly heterogeneous disease with diverse clinical and molecular features. Telomere maintenance is widely present in tumors, but there is a lack of relevant reports on the role of telomere-related genes (TRGs) in DLBCL. In this study, we used consensus clustering based on TRGs expression to identify two molecular clusters with distinct prognoses and immune cell infiltration. We developed a TRGs scoring model using univariate Cox regression and LASSO regression in the GSE10846 training cohort. DLBCL patients in the high-risk group had a worse prognosis than those in the low-risk group, as revealed by Kaplan-Meier curves. The scoring model was validated in the GSE10846 testing cohort and GSE87371 cohort, respectively. The high-risk group was characterized by elevated infiltration of activated DCs, CD56 dim natural killer cells, myeloid-derived suppressor cells, monocytes, and plasmacytoid DCs, along with reduced infiltration of activated CD4 T cells, Type 2 T helper cells, γδ T cells, NK cells, and neutrophils. Overexpression of immune checkpoints, such as PDCD1, CD274, and LAG3, was observed in the high-risk group. Furthermore, high-risk DLBCL patients exhibited increased sensitivity to bortezomib, rapamycin, AZD6244, and BMS.536924, while low-risk DLBCL patients showed sensitivity to cisplatin and ABT.263. Using RT-qPCR, we found that three protective model genes, namely TCEAL7, EPHA4, and ELOVL4, were down-regulated in DLBCL tissues compared with control tissues. In conclusion, our novel TRGs-based model has great predictive value for the prognosis of DLBCL patients and provides a promising direction for treatment optimization.

Multi-omics comparison of malignant and normal uveal melanocytes reveals molecular features of uveal melanoma

Uveal melanoma (UM) is a rare cancer resulting from the transformation of melanocytes in the uveal tract. Integrative analysis has identified four molecular and clinical subsets of UM. To improve our molecular understanding of UM, we performed extensive multi-omics characterization comparing two aggressive UM patient-derived xenograft models with normal choroidal melanocytes, including DNA optical mapping, specific histone modifications, and DNA topology analysis using Hi-C. Our gene expression and cytogenetic analyses suggest that genomic instability is a hallmark of UM. We also identified a recurrent deletion in the BAP1 promoter resulting in loss of expression and associated with high risk of metastases in UM patients. Hi-C revealed chromatin topology changes associated with the upregulation of PRAME, an independent prognostic biomarker in UM, and a potential therapeutic target. Our findings illustrate how multi-omics approaches can improve our understanding of tumorigenesis and reveal two distinct mechanisms of gene expression dysregulation in UM.

Consecutive Inhibition of Telomerase and Alternative Lengthening Pathway Promotes Hodgkin's Lymphoma Cell Death

Telomere maintenance is key during cancer development. Malignant cells can either use telomerase or an alternative lengthening of telomere (ALT) pathway to maintain their telomere length. In Hodgkin's Lymphoma (HL), the presence of telomerase activation is established. The activation of ALT has been reported recently. Our data confirm this notion describing co-localization of the phosphorylated form of telomeric repeat-binding factor 1 (pT371-TRF1) with ALT-associated promyelocytic leukemia bodies. Surprisingly, to our knowledge, there are no published studies targeting both telomere maintenance pathways in HL. Consequently, we investigated, for the first time, the effects of both telomerase and ALT inhibition on HL cell viability: We inhibited telomerase and/or ALT, given either individually, simultaneously, or consecutively. We report that the inhibition of telomerase using BIBR1532 followed by ALT inhibition, using trabectedin, caused a decrease of greater than 90% in cell viability in three patient-derived HL cell lines. Our results suggest that HL cells are most vulnerable to the consecutive inhibition of telomerase followed by ALT inhibition.

Patient-Derived iPSCs Reveal Evidence of Telomere Instability and DNA Repair Deficiency in Coats Plus Syndrome

Coats plus (CP) syndrome is an inherited autosomal recessive condition that results from mutations in the conserved telomere maintenance component 1 gene (CTC1). The CTC1 protein functions as a part of the CST protein complex, a protein heterotrimer consisting of CTC1-STN1-TEN1 which promotes telomere DNA synthesis and inhibits telomerase-mediated telomere elongation. However, it is unclear how CTC1 mutations may have an effect on telomere structure and function. For that purpose, we established the very first induced pluripotent stem cell lines (iPSCs) from a compound heterozygous patient with CP carrying deleterious mutations in both alleles of CTC1. Telomere dysfunction and chromosomal instability were assessed in both circulating lymphocytes and iPSCs from the patient and from healthy controls of similar age. The circulating lymphocytes and iPSCs from the CP patient were characterized by their higher telomere length heterogeneity and telomere aberrations compared to those in control cells from healthy donors. Moreover, in contrast to iPSCs from healthy controls, the high levels of telomerase were associated with activation of the alternative lengthening of telomere (ALT) pathway in CP-iPSCs. This was accompanied by inappropriate activation of the DNA repair proteins γH2AX, 53BP1, and ATM, as well as with accumulation of DNA damage, micronuclei, and anaphase bridges. CP-iPSCs presented features of cellular senescence and increased radiation sensitivity. Clonal dicentric chromosomes were identified only in CP-iPSCs after exposure to radiation, thus mirroring the role of telomere dysfunction in their formation. These data demonstrate that iPSCs derived from CP patients can be used as a model system for molecular studies of the CP syndrome and underscores the complexity of telomere dysfunction associated with the defect of DNA repair machinery in the CP syndrome.

Telomere Dysfunction Is Associated with Altered DNA Organization in Trichoplein/Tchp/Mitostatin (TpMs) Depleted Cells

Recently, we highlighted a novel role for the protein Trichoplein/TCHP/Mitostatin (TpMs), both as mitotic checkpoint regulator and guardian of chromosomal stability. TpMs-depleted cells show numerical and structural chromosome alterations that lead to genomic instability. This condition is a major driving force in malignant transformation as it allows for the cells acquiring new functional capabilities to proliferate and disseminate. Here, the effect of TpMs depletion was investigated in different TpMs-depleted cell lines by means of 3D imaging and 3D Structured illumination Microscopy. We show that TpMs depletion causes alterations in the 3D architecture of telomeres in colon cancer HCT116 cells. These findings are consistent with chromosome alterations that lead to genomic instability. Furthermore, TpMs depletion changes the spatial arrangement of chromosomes and other nuclear components. Modified nuclear architecture and organization potentially induce variations that precede the onset of genomic instability and are considered as markers of malignant transformation. Our present observations connect the tumor suppression ability of TpMs with its novel functions in maintaining the proper chromosomal segregation as well as the proper telomere and nuclear architecture. Further investigations will investigate the connection between alterations in telomeres and nuclear architecture with the progression of human tumors with the aim of developing personalized therapeutic interventions.

TGS1 mediates 2,2,7-trimethyl guanosine capping of the human telomerase RNA to direct telomerase dependent telomere maintenance

Pathways that direct the selection of the telomerase-dependent or recombination-based, alternative lengthening of telomere (ALT) maintenance pathway in cancer cells are poorly understood. Using human lung cancer cells and tumor organoids we show that formation of the 2,2,7-trimethylguanosine (TMG) cap structure at the human telomerase RNA 5′ end by the Trimethylguanosine Synthase 1 (TGS1) is central for recruiting telomerase to telomeres and engaging Cajal bodies in telomere maintenance. TGS1 depletion or inhibition by the natural nucleoside sinefungin impairs telomerase recruitment to telomeres leading to Exonuclease 1 mediated generation of telomere 3′ end protrusions that engage in RAD51-dependent, homology directed recombination and the activation of key features of the ALT pathway. This indicates a critical role for 2,2,7-TMG capping of the RNA component of human telomerase (hTR) in enforcing telomerase-dependent telomere maintenance to restrict the formation of telomeric substrates conductive to ALT. Our work introduces a targetable pathway of telomere maintenance that holds relevance for telomere-related diseases such as cancer and aging.

Telomerase protects chromosome ends in stem cells and cancer cells. Here the authors show that Trimethylguaonsine Synthase 1 (TGS-1) – dependent trimethylguanosine capping of the RNA component of the human telomerase complex has an important role in directing telomere dependent telomere maintenance and suppressing the ALT pathway in cancer cells.

A Role for Human DNA Polymerase λ in Alternative Lengthening of Telomeres

Telomerase negative cancer cell types use the Alternative Lengthening of Telomeres (ALT) pathway to elongate telomeres ends. Here, we show that silencing human DNA polymerase (Pol λ) in ALT cells represses ALT activity and induces telomeric stress. In addition, replication stress in the absence of Pol λ, strongly affects the survival of ALT cells. In vitro, Pol λ can promote annealing of even a single G-rich telomeric repeat to its complementary strand and use it to prime DNA synthesis. The noncoding telomeric repeat containing RNA TERRA and replication protein A negatively regulate this activity, while the Protection of Telomeres protein 1 (POT1)/TPP1 heterodimer stimulates Pol λ. Pol λ associates with telomeres and colocalizes with TPP1 in cells. In summary, our data suggest a role of Pol λ in the maintenance of telomeres by the ALT mechanism.

Clinical Relevance of Alternative Lengthening of Telomeres in Cancer

The alternative lengthening of telomere (ALT) is a pathway responsible for cell immortalization in some kinds of tumors. Since the first description of ALT is relatively recent in the oncology field, its mechanism remains elusive, but recent works address ALT-related proteins or cellular structures as potential druggable targets for more specific and efficient antitumor therapies. Moreover, some new generation compounds for antitelomerase therapy in cancer were able to provoke acquisition of ALT phenotype in treated tumors, enhancing the importance of studies on this alternative lengthening of the telomere. However, ALT has been implicated in different - sometimes opposite - outcomes, according to the tumor type studied. Then, in order to design and develop new drugs for ALT+ cancer in an effective way, it is crucial to understand its clinical implications. In this review, we gathered works published in the last two decades to highlight the clinical relevance of ALT on oncology.

Novel therapeutic strategies targeting telomere maintenance mechanisms in high-risk neuroblastoma

The majority of high-risk neuroblastomas can be divided into three distinct molecular subgroups defined by the presence of MYCN amplification, upstream TERT rearrangements or alternative lengthening of telomeres (ALT). The common defining feature of all three subgroups is altered telomere maintenance; MYCN amplification and upstream TERT rearrangements drive high levels of telomerase expression whereas ALT is a telomerase independent telomere maintenance mechanism. As all three telomere maintenance mechanisms are independently associated with poor outcomes, the development of strategies to selectively target either telomerase expressing or ALT cells holds great promise as a therapeutic approach that is applicable to the majority of children with aggressive disease.Here we summarise the biology of telomere maintenance and the molecular drivers of aggressive neuroblastoma before describing the most promising therapeutic strategies to target both telomerase expressing and ALT cancers. For telomerase-expressing neuroblastoma the most promising targeted agent to date is 6-thio-2'-deoxyguanosine, however clinical development of this agent is required. In osteosarcoma cell lines with ALT, selective sensitivity to ATR inhibition has been reported. However, we present data showing that in fact ALT neuroblastoma cells are more resistant to the clinical ATR inhibitor AZD6738 compared to other neuroblastoma subtypes. More recently a number of additional candidate compounds have been shown to show selectivity for ALT cancers, such as Tetra-Pt (bpy), a compound targeting the telomeric G-quadruplex and pifithrin-α, a putative p53 inhibitor. Further pre-clinical evaluation of these compounds in neuroblastoma models is warranted.In summary, telomere maintenance targeting strategies offer a significant opportunity to develop effective new therapies, applicable to a large proportion of children with high-risk neuroblastoma. In parallel to clinical development, more pre-clinical research specifically for neuroblastoma is urgently needed, if we are to improve survival for this common poor outcome tumour of childhood.

The Use of Natural Agents to Counteract Telomere Shortening: Effects of a Multi-Component Extract of Astragalus mongholicus Bunge and Danazol

A link between telomere shortening and oxidative stress was found in aging people and patients with cancer or inflammatory diseases. Extracts of Astragalus spp. are known to stimulate telomerase activity, thereby compensating telomere shortening. We characterized a multi-component hydroethanolic root extract (HRE) of Astragalus mongholicus Bunge and assessed its effects on telomeres compared to those of danazol. Astragalosides I to IV, flavonoids, amino acids and sugars were detected in the HRE. Samples of peripheral blood lymphocytes with short telomeres from 18 healthy donors (mean age 63.5 years; range 32–86 years) were exposed to a single dose of 1 µg/mL HRE or danazol for three days. Telomere length and telomerase expression were then measured. Significant elongation of telomeres associated to a less toxicity was observed in lymphocytes from 13/18 donors following HRE treatment (0.54 kb (0.15–2.06 kb)) and in those from 9/18 donors after danazol treatment (0.95 kb (0.06–2.06 kb)). The rate of cells with short telomeres (<3 kb) decreased in lymphocytes from all donors after exposure to either HRE or danazol, telomere elongation being telomerase-dependent. These findings suggest that the HRE could be used for the management of age-related diseases.

Telomere dynamics in adult hematological malignancies

Telomeres are repetitive DNA sequences protecting physical ends of linear chromosomes against degradation and end-to-end chromosomal fusion. Telomeres shorten with each cell division, which regulates the cellular lifespan in somatic cells and limits their renewal capacity. Cancer cells are often able to overcome this physiological barrier and become immortal with unlimited replicative capacity. In this review, we present current knowledge on the role of telomeres in human aging with a focus on their behavior in hematological malignancies of adults. Associations of telomere length to age-related diseases and to the prevention of telomere shortening are also discussed.

Establishment and Characterization of a Reliable Xenograft Model of Hodgkin Lymphoma Suitable for the Study of Tumor Origin and the Design of New Therapies

To identify the cells responsible for the initiation and maintenance of Hodgkin lymphoma (HL) cells, we have characterized a subpopulation of HL cells grown in vitro and in vivo with the aim of establishing a reliable and robust animal model for HL. To validate our model, we challenged the tumor cells in vivo by injecting the alkylating histone-deacetylase inhibitor, EDO-S101, a salvage regimen for HL patients, into xenografted mice. Methodology: Blood lymphocytes from 50 HL patients and seven HL cell lines were used. Immunohistochemistry, flow cytometry, and cytogenetics analyses were performed. The in vitro and in vivo effects of EDO-S101 were assessed. Results: We have successfully determined conditions for in vitro amplification and characterization of the HL L428-c subline, containing a higher proportion of CD30−/CD15− cells than the parental L428 cell line. This subline displayed excellent clonogenic potential and reliable reproducibility upon xenografting into immunodeficient NOD-SCID-gamma (−/−)(NSG) mice. Using cell sorting, we demonstrate that CD30−/CD15− subpopulations can gain the phenotype of the L428-c cell line in vitro. Moreover, the human cells recovered from the seventh week after injection of L428-c cells into NSG mice were small cells characterized by a high frequency of CD30−/CD15− cells. Cytogenetic analysis demonstrated that they were diploid and showed high telomere instability and telomerase activity. Accordingly, chromosomal instability emerged, as shown by the formation of dicentric chromosomes, ring chromosomes, and breakage/fusion/bridge cycles. Similarly, high telomerase activity and telomere instability were detected in circulating lymphocytes from HL patients. The beneficial effect of the histone-deacetylase inhibitor EDO-S101 as an anti-tumor drug validated our animal model. Conclusion: Our HL animal model requires only 10³ cells and is characterized by a high survival/toxicity ratio and high reproducibility. Moreover, the cells that engraft in mice are characterized by a high frequency of small CD30−/CD15− cells exhibiting high telomerase activity and telomere dysfunction.

Independent Mechanisms Lead to Genomic Instability in Hodgkin Lymphoma: Microsatellite or Chromosomal Instability †

Background: Microsatellite and chromosomal instability have been investigated in Hodgkin lymphoma (HL). Materials and Methods: We studied seven HL cell lines (five Nodular Sclerosis (NS) and two Mixed Cellularity (MC)) and patient peripheral blood lymphocytes (100 NS-HL and 23 MC-HL). Microsatellite instability (MSI) was assessed by PCR. Chromosomal instability and telomere dysfunction were investigated by FISH. DNA repair mechanisms were studied by transcriptomic and molecular approaches. Results: In the cell lines, we observed high MSI in L428 (4/5), KMH2, and HDLM2 (3/5), low MSI in L540, L591, and SUP-HD1, and none in L1236. NS-HL cell lines showed telomere shortening, associated with alterations of nuclear shape. Small cells were characterized by telomere loss and deletion, leading to chromosomal fusion, large nucleoplasmic bridges, and breakage/fusion/bridge (B/F/B) cycles, leading to chromosomal instability. The MC-HL cell lines showed substantial heterogeneity of telomere length. Intrachromosmal double strand breaks induced dicentric chromosome formation, high levels of micronucleus formation, and small nucleoplasmic bridges. B/F/B cycles induced complex chromosomal rearrangements. We observed a similar pattern in circulating lymphocytes of NS-HL and MC-HL patients. Transcriptome analysis confirmed the differences in the DNA repair pathways between the NS and MC cell lines. In addition, the NS-HL cell lines were radiosensitive and the MC-cell lines resistant to apoptosis after radiation exposure. Conclusions: In mononuclear NS-HL cells, loss of telomere integrity may present the first step in the ongoing process of chromosomal instability. Here, we identified, MSI as an additional mechanism for genomic instability in HL.