Télomères et Cancer

Publications de l’équipe

Année de publication : 2010

Jing Ye, Christelle Lenain, Serge Bauwens, Angela Rizzo, Adelaïde Saint-Léger, Anaïs Poulet, Delphine Benarroch, Frédérique Magdinier, Julia Morere, Simon Amiard, Els Verhoeyen, Sébastien Britton, Patrick Calsou, Bernard Salles, Anna Bizard, Marc Nadal, Erica Salvati, Laure Sabatier, Yunlin Wu, Annamaria Biroccio, Arturo Londoño-Vallejo, Marie-Josèphe Giraud-Panis, Eric Gilson (2010 Jul 27)

TRF2 and apollo cooperate with topoisomerase 2alpha to protect human telomeres from replicative damage.

Cell : 230-42 : DOI : 10.1016/j.cell.2010.05.032 En savoir plus
Résumé

Human telomeres are protected from DNA damage by a nucleoprotein complex that includes the repeat-binding factor TRF2. Here, we report that TRF2 regulates the 5′ exonuclease activity of its binding partner, Apollo, a member of the metallo-beta-lactamase family that is required for telomere integrity during S phase. TRF2 and Apollo also suppress damage to engineered interstitial telomere repeat tracts that were inserted far away from chromosome ends. Genetic data indicate that DNA topoisomerase 2alpha acts in the same pathway of telomere protection as TRF2 and Apollo. Moreover, TRF2, which binds preferentially to positively supercoiled DNA substrates, together with Apollo, negatively regulates the amount of TOP1, TOP2alpha, and TOP2beta at telomeres. Our data are consistent with a model in which TRF2 and Apollo relieve topological stress during telomere replication. Our work also suggests that cellular senescence may be caused by topological problems that occur during the replication of the inner portion of telomeres.

Replier
Sophie Georgin-Lavialle, Achille Aouba, Luc Mouthon, J Arturo Londono-Vallejo, Yves Lepelletier, Anne-Sophie Gabet, Olivier Hermine (2010 May 4)

The telomere/telomerase system in autoimmune and systemic immune-mediated diseases.

Autoimmunity reviews : 646-51 : DOI : 10.1016/j.autrev.2010.04.004 En savoir plus
Résumé

Telomeres are specialized nucleoproteic structures that cap and protect the ends of chromosomes. They can be elongated by the telomerase enzyme, but in telomerase negative cells, telomeres shorten after each cellular division because of the end replicating problem. This phenomenon leads ultimately to cellular senescence, conferring to the telomeres a role of biological clock. Oxidative stress, inflammation and increased cell renewal are supplementary environmental factors that accelerate age-related telomere shortening. Similar to other types of DNA damage, very short/dysfunctional telomeres activate a DNA response pathway leading to different outcomes: DNA repair, cell senescence or apoptosis. During the last 10 years, studies on the telomere/telomerase system in autoimmune and/or systemic immune-mediated diseases have revealed its involvement in relevant physiopathological processes. Here, we present a literature review of telomere and telomerase homeostasis in systemic inflammatory diseases including systemic lupus erythematosus, rheumatoid arthritis and granulomatous diseases. The available data indicate that both telomerase activity and telomere length are modified in various systemic immune-mediated diseases and appear to be connected with premature immunosenescence. Studies on the telomere/telomerase system open new research avenues for the basic understanding and for therapeutic approaches of these pathologies.

Replier
Johans Fakhoury, Delphine Tamara Marie-Egyptienne, José-Arturo Londoño-Vallejo, Chantal Autexier (2010 Apr 30)

Telomeric function of mammalian telomerases at short telomeres.

Journal of cell science : 1693-704 : DOI : 10.1242/jcs.063636 En savoir plus
Résumé

Telomerase synthesizes telomeric sequences and is minimally composed of a reverse transcriptase (RT) known as TERT and an RNA known as TR. We reconstituted heterologous mouse (m) and human (h) TERT-TR complexes and chimeric mTERT-hTERT-hTR complexes in vitro and in immortalized human alternative lengthening of telomere (ALT) cells. Our data suggest that species-specific determinants of activity, processivity and telomere function map not only to the TR but also to the TERT component. The presence of hTERT-hTR, but not heterologous TERT-TR complexes or chimeric mTERT-hTERT-hTR complexes, significantly reduced the percentage of chromosomes without telomeric signals in ALT cells. Moreover, heterologous and chimeric complexes were defective in recruitment to telomeres. Our results suggest a requirement for several hTERT domains and interaction with multiple proteins for proper recruitment of telomerase to the shortest telomeres in human ALT cells. Late-passage mTERT(-/-) mouse embryonic stem (ES) cells ectopically expressing hTERT or mTERT harboured fewer chromosome ends without telomeric signals and end-to-end fusions than typically observed in late-passage mTERT(-/-) ES cells. The ability of hTERT to function at mouse telomeres and the inability of mTERT to function at human telomeres suggest that mechanisms regulating the recruitment and activity of hTERT at mouse telomeres might be less stringent than the mechanisms regulating mTERT at human telomeres.

Replier
Nausica Arnoult, Caroline Schluth-Bolard, Anne Letessier, Irena Drascovic, Rachida Bouarich-Bourimi, Judith Campisi, Sahn-Ho Kim, Amina Boussouar, Alexandre Ottaviani, Frédérique Magdinier, Eric Gilson, Arturo Londoño-Vallejo (2010 Apr 28)

Replication timing of human telomeres is chromosome arm-specific, influenced by subtelomeric structures and connected to nuclear localization.

PLoS genetics : e1000920 : DOI : 10.1371/journal.pgen.1000920 En savoir plus
Résumé

The mechanisms governing telomere replication in humans are still poorly understood. To fill this gap, we investigated the timing of replication of single telomeres in human cells. Using in situ hybridization techniques, we have found that specific telomeres have preferential time windows for replication during the S-phase and that these intervals do not depend upon telomere length and are largely conserved between homologous chromosomes and between individuals, even in the presence of large subtelomeric segmental polymorphisms. Importantly, we show that one copy of the 3.3 kb macrosatellite repeat D4Z4, present in the subtelomeric region of the late replicating 4q35 telomere, is sufficient to confer both a more peripheral localization and a later-replicating property to a de novo formed telomere. Also, the presence of beta-satellite repeats next to a newly created telomere is sufficient to delay its replication timing. Remarkably, several native, non-D4Z4-associated, late-replicating telomeres show a preferential localization toward the nuclear periphery, while several early-replicating telomeres are associated with the inner nuclear volume. We propose that, in humans, chromosome arm-specific subtelomeric sequences may influence both the spatial distribution of telomeres in the nucleus and their replication timing.

Replier

Année de publication : 2009

Nausica Arnoult, Carole Saintome, Isabelle Ourliac-Garnier, Jean-François Riou, Arturo Londoño-Vallejo (2009 Dec 17)

Human POT1 is required for efficient telomere C-rich strand replication in the absence of WRN.

Genes & development : 2915-24 : DOI : 10.1101/gad.544009 En savoir plus
Résumé

Mechanisms of telomere replication remain poorly defined. It has been suggested that G-rich telomeric strand replication by lagging mechanisms requires, in a stochastic way, the WRN protein. Here we show that this requirement is more systematic than previously thought. Our data are compatible with a situation in which, in the absence of WRN, DNA synthesis at replication forks is uncoupled, thus allowing replication to continue on the C strand, while single G strands accumulate. We also show that in cells in which both WRN and POT1 are limiting, both G- and C-rich telomeric strands shorten, suggesting a complete replication block. Under this particular condition, expression of a fragment spanning the two POT1-OB (oligonucleotide-binding) fold domains is able to restore C (but not G) strand replication, suggesting that binding of POT1 to the lagging strand allows DNA synthesis uncoupling in the absence of WRN. Furthermore, in vitro experiments indicate that purified POT1 has a higher affinity for the telomeric G-rich strand than purified RPA. We propose a model in which the relative enrichments of POT1 versus RPA on the telomeric lagging strand allows or does not allow uncoupling of DNA synthesis at the replication fork. Our study reveals an unanticipated role for hPOT1 during telomere replication.

Replier
J Arturo Londoño-Vallejo (2009 Dec 3)

[Hundred-years-old Nobel celebrates telomers and telomerase].

Médecine sciences : M/S : 973-6 : DOI : 10.1051/medsci/20092511973 En savoir plus
Résumé

Replier
Irena Draskovic, Nausica Arnoult, Villier Steiner, Silvia Bacchetti, Patrick Lomonte, Arturo Londoño-Vallejo (2009 Sep 1)

Probing PML body function in ALT cells reveals spatiotemporal requirements for telomere recombination.

Proceedings of the National Academy of Sciences of the United States of America : 15726-31 : DOI : 10.1073/pnas.0907689106 En savoir plus
Résumé

Promyelocytic leukemia (PML) bodies (also called ND10) are dynamic nuclear structures implicated in a wide variety of cellular processes. ALT-associated PML bodies (APBs) are specialized PML bodies found exclusively in telomerase-negative tumors in which telomeres are maintained by recombination-based alternative (ALT) mechanisms. Although it has been suggested that APBs are directly implicated in telomere metabolism of ALT cells, their precise role and structure have remained elusive. Here we show that PML bodies in ALT cells associate with chromosome ends forming small, spatially well-defined clusters, containing on average 2-5 telomeres. Using an innovative approach that gently enlarges PML bodies in living cells while retaining their overall organization, we show that this physical enlargement of APBs spatially resolves the single telomeres in the cluster, but does not perturb the potential of the APB to recruit chromosome extremities. We show that telomere clustering in PML bodies is cell-cycle regulated and that unique telomeres within a cluster associate with recombination proteins. Enlargement of APBs induced the accumulation of telomere-telomere recombination intermediates visible on metaphase spreads and connecting heterologous chromosomes. The strand composition of these recombination intermediates indicated that this recombination is constrained to a narrow time window in the cell cycle following replication. These data provide strong evidence that PML bodies are not only a marker for ALT cells but play a direct role in telomere recombination, both by bringing together chromosome ends and by promoting telomere-telomere interactions between heterologous chromosomes.

Replier
G Tilman, A Loriot, A Van Beneden, N Arnoult, J A Londoño-Vallejo, C De Smet, A Decottignies (2009 Mar 3)

Subtelomeric DNA hypomethylation is not required for telomeric sister chromatid exchanges in ALT cells.

Oncogene : 1682-93 : DOI : 10.1038/onc.2009.23 En savoir plus
Résumé

Most human tumor cells acquire immortality by activating the expression of telomerase, a ribonucleoprotein that maintains stable telomere lengths at chromosome ends throughout cell divisions. Other tumors use an alternative mechanism of telomere lengthening (ALT), characterized by high frequencies of telomeric sister chromatid exchanges (T-SCEs). Mechanisms of ALT activation are still poorly understood, but recent studies suggest that DNA hypomethylation of chromosome ends might contribute to the process by facilitating T-SCEs. Here, we show that ALT/T-SCE(high) tumor cells display low DNA-methylation levels at the D4Z4 and DNF92 subtelomeric sequences. Surprisingly, however, the same sequences retained high methylation levels in ALT/T-SCE(high) SV40-immortalized fibroblasts. Moreover, T-SCE rates were efficiently reduced by ectopic expression of active telomerase in ALT tumor cells, even though subtelomeric sequences remained hypomethylated. We also show that hypomethylation of subtelomeric sequences in ALT tumor cells is correlated with genome-wide hypomethylation of Alu repeats and pericentromeric Sat2 DNA sequences. Overall, this study suggests that, although subtelomeric DNA hypomethylation is often coincident with the ALT process in human tumor cells, it is not required for T-SCE.

Replier
N Arnoult, K Shin-Ya, J A Londoño-Vallejo (2009 Feb 4)

Studying telomere replication by Q-CO-FISH: the effect of telomestatin, a potent G-quadruplex ligand.

Cytogenetic and genome research : 229-36 : DOI : 10.1159/000167808 En savoir plus
Résumé

Telomere replication is a critical process for preserving genome integrity. The telomere replication fork proceeds unidirectionally from the last subtelomeric origin towards the end of the chromosome, replicating the 5′-3′ G-rich strand by lagging mechanisms and the complementary C-rich strand by leading mechanisms. It has been proposed that the G-rich nature of telomeres may favor the formation of secondary structures such as G-quadruplexes during replication and that specific mechanisms must prevent this to allow the fork to progress unimpeded. The potential of G-quadruplex formation by telomeric sequences has been clearly demonstrated in vitro but it is not known whether these structures form in vivo. We tested the effect of a potent and specific G-quadruplex ligand, telomestatin (TMS), on telomere replication using a novel quantitative approach applied to CO-FISH. We show that TMS, although it penetrates and persists within cells, does not affect telomere replication after short or long-term treatments of mouse embryonic fibroblasts. It does however affect the hybridization efficiency of FISH telomeric probes that recognize the G-rich strand. Our work illustrates the use of a novel technique to measure telomere replication efficiency and suggests that G-quadruplex ligands do not affect telomere replication in a non tumoral context.

Replier

Année de publication : 2008

Delphine T Marie-Egyptienne, Marie Eve Brault, Graeme A M Nimmo, J Arturo Londoño-Vallejo, Chantal Autexier (2008 Dec 6)

Growth defects in mouse telomerase RNA-deficient cells expressing a template-mutated mouse telomerase RNA.

Cancer letters : 266-76 : DOI : 10.1016/j.canlet.2008.10.027 En savoir plus
Résumé

Cellular viability requires telomere maintenance, which, in mammals, is mainly mediated by the reverse transcriptase telomerase. Telomerase core components are a catalytic subunit TERT and an RNA subunit TR (hTR in humans, mTR in mouse) that carries the template to generate telomeres de novo. Telomere dysfunction can lead to senescence or apoptosis and impairs the continued growth of immortal cancerous cell lines. The introduction of a template-mutated hTR in telomerase-positive and telomerase-negative human cell lines results in dramatic growth defects. No study has addressed the consequences of expressing a template-mutated mTR in mouse immortal cell lines. Therefore, we analyzed the effects of long-term expression of a template-mutated mTR in the telomerase-positive and telomerase-negative murine cell lines CB17 and DKO301, respectively. Whereas the CB17 clones expressing the template-mutated mTR did not demonstrate any growth impairment, many of the DKO301 clones expressing the template-mutated mTR underwent growth and cell cycle defects and eventual cell death. These results suggest that in the absence of wild-type telomerase, the expression of the template-mutated mTR likely perturbs telomere function, leading to decreased cellular viability. Furthermore, whereas the expression of template-mutated hTR in telomerase-negative human cell lines leads to immediate cellular toxicity, the expression of the template-mutated mTR in the telomerase-negative mouse cell line did not.

Replier
J Arturo Londono-Vallejo (2008 Jul 9)

[Cancer as a microevolutionary process affecting telomere structure and dynamics: the contribution of telomeres to cancer].

Ai zheng = Aizheng = Chinese journal of cancer : 775-83 En savoir plus
Résumé

Telomeres play fundamental roles in genome stability, nuclear architecture and chromosome pairing during meiosis. They shorten at every cell division and may be re-elongated or not depending on the presence of the dedicated enzyme, telomerase. Since in most human somatic cells telomerase is not expressed, shortening of telomeres during development and aging is the rule. Short telomeres being, under physiological conditions, incompatible with extended cell proliferation, telomere length defines the proliferation potential of a cell and operates as a mechanism to prevent uncontrolled cell growth. Conversely, in cells in which proliferation checkpoints have been abolished, shortening of telomeres causes chromosomes to fuse and to initiate cycles of breakage-fusion-bridge thus becoming a strong driving force for genome instability. In vitro, transformed cells with highly unstable genomes because of severe telomere shortening accumulate deleterious genetic changes and die (crisis). At the same time, random genetic or epigenetic changes may allow cells to acquire a telomere maintenance mechanism (as well as other tumor phenotypes) and to become immortal. Although telomere shortening and other types of telomere dysfunction probably contribute to the genome instability detected in early tumors in vivo, the direct contributions of dysfunctional telomeres to the acquisition of tumor phenotypes in humans remain largely unspecified.

Replier
Arturo Londoño-Vallejo, Christelle Lenain, Eric Gilson (2008 Apr 15)

[Targeting telomeres to enforce cancer cells to senesce].

Médecine sciences : M/S : 383-9 : DOI : 10.1051/medsci/2008244383 En savoir plus
Résumé

The telomeres protect the end of chromosomes from being recognized and processed as an accidental double stranded break. In human somatic cells, telomeres shorten progressively with every round of DNA replication, leading to dysfunctional telomeres that trigger cellular senescence or apoptosis depending on the cell type. This telomere erosion appears to play a role in cell renewal, ageing and cancer. Two recent studies demonstrated in mouse that eroded telomeres in cancer cells blocked for apoptosis limit cancer formation by triggering senescence. These results suggest that provoking senescence may provide a way to cure cancer and point to new therapeutical strategies targeting specific telomeric functions. Nevertheless, an important question remains unanswered: does replicative senescence limit tumor formation in human?

Replier

Année de publication : 2007

Dennis Kappei, J Arturo Londoño-Vallejo (2007 Dec 7)

Telomere length inheritance and aging.

Mechanisms of ageing and development : 17-26 En savoir plus
Résumé

Telomere shortening accompanies human aging, and premature aging syndromes are often associated with short telomeres. These two observations are central to the hypothesis that telomere length directly influences longevity. If true, genetically determined mechanisms of telomere length homeostasis should significantly contribute to variations of longevity in the human population. On the other hand, telomere shortening is also observed in the course of many aging-associated disorders but determining whether it is a cause or a consequence is not an easy task. Here, we review the most relevant experimental and descriptive data relating telomere length, as a quantitative trait, to aging and longevity.

Replier
Natalia S Zhdanova, Julia M Minina, Tatjana V Karamisheva, Irena Draskovic, Nikolai B Rubtsov, Jose-Arturo Londoño-Vallejo (2007 Sep 28)

The very long telomeres in Sorex granarius (Soricidae, Eulipothyphla) contain ribosomal DNA.

Chromosome research : an international journal on the molecular, supramolecular and evolutionary aspects of chromosome biology : 881-90 En savoir plus
Résumé

Two closely related shrew species, Sorex granarius and Sorex araneus, in which Robertsonian rearrangements have played a primary role in karyotype evolution, present very distinct telomere length patterns. S. granarius displays hyperlong telomeres specifically associated with the short arms of acrocentrics, whereas telomere lengths in S. araneus are rather short and homogenous. Using a combined approach of chromosome and fibre FISH, modified Q-FISH, 3D-FISH, Ag-NOR staining and TRF analysis, we carried out a comparative analysis of telomeric repeats and rDNA distribution on chromosome ends of Sorex granarius. Our results show that rDNA sequences forming active nuclear organizing regions are interspersed with the long telomere tracts of all short arms of acrocentrics. These observations suggest that the major rearrangements that gave rise to today’s karyotype in S. granarius were accompanied by a profound reorganization of chromosome ends, which comprised extensive amplification of telomeric and rDNA repeats on the short arms of acrocentrics and finally contributed to the stabilization of telomeres. This is the first time that such telomeric structures have been observed in any mammalian species.

Replier
Anne-Sophie Gabet, Rosita Accardi, Angelica Bellopede, Susanne Popp, Petra Boukamp, Bakary S Sylla, J Arturo Londoño-Vallejo, Massimo Tommasino (2007 Sep 28)

Impairment of the telomere/telomerase system and genomic instability are associated with keratinocyte immortalization induced by the skin human papillomavirus type 38.

FASEB journal : official publication of the Federation of American Societies for Experimental Biology : 622-32 En savoir plus
Résumé

The skin human papillomavirus (HPV) types belonging to the genus beta of the HPV phylogenetic tree appear to be associated with nonmelanoma skin cancer. We previously showed that the beta HPV type 38 E6 and E7 oncoproteins are able to inactivate the tumor suppressors p53 and retinoblastoma. Here, both viral proteins were expressed in primary human skin keratinocytes in order to study their effects on the telomere/telomerase system. We show that immortalization of skin keratinocytes induced by HPV38 E6/E7 is associated with hTERT gene overexpression. This event is, in part, explained by the accumulation of the p53-related protein, DeltaNp73. Despite elevated levels of hTERT mRNA, the telomerase activity detected in HPV38 E6/E7 keratinocytes was lower than that observed in HPV16 E6/E7 keratinocytes. The low telomerase activation in highly proliferative HPV38 E6/E7 keratinocytes resulted in the presence of extremely short and unstable telomeres. In addition, we observed anaphase bridges, mitotic multipolarity, and dramatic genomic aberrations. Interestingly, the ectopic expression of hTERT prevents both telomere erosion and genomic instability. Thus, we showed that in HPV38 E6/E7 keratinocytes characterized by unscheduled proliferation, suboptimal activation of telomerase and subsequent extensive telomere shortening result in genomic instability facilitating cellular immortalization.

Replier