Natural chromosome ends resemble double-stranded DNA breaks, but they do not activate a damage response in healthy cells. Telomeres therefore have evolved to solve the 'end-protection problem' by inhibiting multiple DNA damage–response pathways. During the past decade, the view of telomeres has progressed from simple caps that hide chromosome ends to complex machineries that have an active role in organizing the genome. Here we focus on mammalian telomeres and summarize and interpret recent discoveries in detail, focusing on how repair pathways are inhibited, how resection and replication are controlled and how these mechanisms govern cell fate during senescence, crisis and transformation.
Subscribe to Journal
Get full journal access for 1 year
only $17.42 per issue
All prices are NET prices.
VAT will be added later in the checkout.
Rent or Buy article
Get time limited or full article access on ReadCube.
All prices are NET prices.
de Lange, T. Shelterin: the protein complex that shapes and safeguards human telomeres. Genes Dev. 19, 2100–2110 (2005).
Karlseder, J. p53- and ATM-dependent apoptosis induced by telomeres lacking TRF2. Science 283, 1321–1325 (1999).
Smogorzewska, A., Karlseder, J., Holtgreve-Grez, H., Jauch, A. & de Lange, T. DNA ligase IV-dependent NHEJ of deprotected mammalian telomeres in G1 and G2. Curr. Biol. 12, 1635–1644 (2002).
van Steensel, B., Smogorzewska, A. & de Lange, T. TRF2 protects human telomeres from end-to-end fusions. Cell 92, 401–413 (1998).
Smogorzewska, A. & de Lange, T. Different telomere damage signaling pathways in human and mouse cells. EMBO J. 21, 4338–4348 (2002).
Oh, S., Wang, Y., Zimbric, J. & Hendrickson, E.A. Human LIGIV is synthetically lethal with the loss of Rad54B-dependent recombination and is required for certain chromosome fusion events induced by telomere dysfunction. Nucleic Acids Res. 41, 1734–1749 (2013).
Griffith, J.D. et al. Mammalian telomeres end in a large duplex loop. Cell 97, 503–514 (1999).
Stansel, R.M., de Lange, T. & Griffith, J.D. T-loop assembly in vitro involves binding of TRF2 near the 3′ telomeric overhang. EMBO J. 20, 5532–5540 (2001).
Doksani, Y., Wu, J.Y., de Lange, T. & Zhuang, X. Super-resolution fluorescence imaging of telomeres reveals TRF2-dependent T-loop formation. Cell 155, 345–356 (2013).
Okamoto, K. et al. A two-step mechanism for TRF2-mediated chromosome-end protection. Nature 494, 502–505 (2013). This publication highlights the exact mechanisms of ATM-pathway suppression by TRF2, identifying the iDDR region in TRF2 as being inhibitory downstream of ATM, at the level of RNF168 suppression.
Dimitrova, N., Chen, Y.C., Spector, D.L. & de Lange, T. 53BP1 promotes non-homologous end joining of telomeres by increasing chromatin mobility. Nature 456, 524–528 (2008).
Wang, X. et al. Rapid telomere motions in live human cells analyzed by highly time-resolved microscopy. Epigenetics Chromatin 1, 4 (2008).
Ribes-Zamora, A., Indiviglio, S.M., Mihalek, I., Williams, C.L. & Bertuch, A.A. TRF2 interaction with Ku heterotetramerization interface gives insight into c-NHEJ prevention at human telomeres. Cell Reports 5, 194–206 (2013). This manuscript explains the presence of Ku at protected telomeres and how c-NHEJ is suppressed despite the presence of Ku.
Sfeir, A., Kabir, S., van Overbeek, M., Celli, G.B. & de Lange, T. Loss of Rap1 induces telomere recombination in the absence of NHEJ or a DNA damage signal. Science 327, 1657–1661 (2010).
Kabir, S., Hockemeyer, D. & de Lange, T. TALEN gene knockouts reveal no requirement for the conserved human shelterin protein Rap1 in telomere protection and length regulation. Cell Reports 9, 1273–1280 (2014).
Chen, Y. et al. A conserved motif within RAP1 has diversified roles in telomere protection and regulation in different organisms. Nat. Struct. Mol. Biol. 18, 213–221 (2011).
Sarthy, J., Bae, N.S., Scrafford, J. & Baumann, P. Human RAP1 inhibits non-homologous end joining at telomeres. EMBO J. 28, 3390–3399 (2009).
Arat, N.Ö. & Griffith, J.D. Human Rap1 interacts directly with telomeric DNA and regulates TRF2 localization at the telomere. J. Biol. Chem. 287, 41583–41594 (2012).
Janoušková, E. et al. Human Rap1 modulates TRF2 attraction to telomeric DNA. Nucleic Acids Res. 43, 2691–2700 (2015).
Denchi, E.L. & de Lange, T. Protection of telomeres through independent control of ATM and ATR by TRF2 and POT1. Nature 448, 1068–1071 (2007).
Hockemeyer, D., Palm, W., Wang, R.C., Couto, S.S. & de Lange, T. Engineered telomere degradation models dyskeratosis congenita. Genes Dev. 22, 1773–1785 (2008).
Takai, K.K., Kibe, T., Donigian, J.R., Frescas, D. & de Lange, T. Telomere protection by TPP1/POT1 requires tethering to TIN2. Mol. Cell 44, 647–659 (2011).
Gong, Y. & de Lange, T.A. Shld1-controlled POT1a provides support for repression of ATR signaling at telomeres through RPA exclusion. Mol. Cell 40, 377–387 (2010).
Sfeir, A. et al. Mammalian telomeres resemble fragile sites and require TRF1 for efficient replication. Cell 138, 90–103 (2009).
Zimmermann, M., Kibe, T., Kabir, S. & de Lange, T. TRF1 negotiates TTAGGG repeat-associated replication problems by recruiting the BLM helicase and the TPP1/POT1 repressor of ATR signaling. Genes Dev. 28, 2477–2491 (2014).
Arnoult, N., Saintome, C., Ourliac-Garnier, I., Riou, J.F. & Londono-Vallejo, A. Human POT1 is required for efficient telomere C-rich strand replication in the absence of WRN. Genes Dev. 23, 2915–2924 (2009).
Wang, M. et al. PARP-1 and Ku compete for repair of DNA double strand breaks by distinct NHEJ pathways. Nucleic Acids Res. 34, 6170–6182 (2006).
Oh, S. et al. DNA ligase III and DNA ligase IV carry out genetically distinct forms of end joining in human somatic cells. DNA Repair (Amst.) 21, 97–110 (2014).
Mateos-Gomez, P.A. et al. Mammalian polymerase θ promotes alternative NHEJ and suppresses recombination. Nature 518, 254–257 (2015).
Ceccaldi, R. et al. Homologous-recombination-deficient tumours are dependent on Poltheta-mediated repair. Nature 518, 258–262 (2015).
Kent, T., Chandramouly, G., McDevitt, S.M., Ozdemir, A.Y. & Pomerantz, R.T. Mechanism of microhomology-mediated end-joining promoted by human DNA polymerase θ. Nat. Struct. Mol. Biol. 22, 230–237 (2015).
Yousefzadeh, M.J. et al. Mechanism of suppression of chromosomal instability by DNA polymerase POLQ. PLoS Genet. 10, e1004654 (2014).
Rai, R. et al. The function of classical and alternative non-homologous end-joining pathways in the fusion of dysfunctional telomeres. EMBO J. 29, 2598–2610 (2010).
Frit, P., Barboule, N., Yuan, Y., Gomez, D. & Calsou, P. Alternative end-joining pathway(s): bricolage at DNA breaks. DNA Repair (Amst.) 17, 81–97 (2014).
Sfeir, A. & de Lange, T. Removal of shelterin reveals the telomere end-protection problem. Science 336, 593–597 (2012). This publication reports the complete removal of shelterin from telomeres, thereby establishing that the chromosome end-protection problem is specified by six DNA-damage and DNA-repair pathways.
Celli, G.B., Denchi, E.L. & de Lange, T. Ku70 stimulates fusion of dysfunctional telomeres yet protects chromosome ends from homologous recombination. Nat. Cell Biol. 8, 885–890 (2006).
Rai, R. et al. The E3 ubiquitin ligase Rnf8 stabilizes Tpp1 to promote telomere end protection. Nat. Struct. Mol. Biol. 18, 1400–1407 (2011).
Palm, W., Hockemeyer, D., Kibe, T. & de Lange, T. Functional dissection of human and mouse POT1 proteins. Mol. Cell. Biol. 29, 471–482 (2009).
Oganesian, L. & Karlseder, J. 5′ C-rich telomeric overhangs are an outcome of rapid telomere truncation events. DNA Repair (Amst.) 12, 238–245 (2013).
Wang, R.C., Smogorzewska, A. & de Lange, T. Homologous recombination generates T-loop-sized deletions at human telomeres. Cell 119, 355–368 (2004).
Wang, Y., Ghosh, G. & Hendrickson, E.A. Ku86 represses lethal telomere deletion events in human somatic cells. Proc. Natl. Acad. Sci. USA 106, 12430–12435 (2009).
Verdun, R.E. & Karlseder, J. The DNA damage machinery and homologous recombination pathway act consecutively to protect human telomeres. Cell 127, 709–720 (2006).
Pickett, H.A., Cesare, A.J., Johnston, R.L., Neumann, A.A. & Reddel, R.R. Control of telomere length by a trimming mechanism that involves generation of t-circles. EMBO J. 28, 799–809 (2009).
Vannier, J.-B., Pavicic-Kaltenbrunner, V., Petalcorin, M.I.R., Ding, H. & Boulton, S.J. RTEL1 dismantles T loops and counteracts telomeric G4-DNA to maintain telomere integrity. Cell 149, 795–806 (2012).
Sarek, G., Vannier, J.B., Panier, S., Petrini, J.H. & Boulton, S.J. TRF2 recruits RTEL1 to telomeres in S phase to promote t-loop unwinding. Mol. Cell 57, 622–635 (2015). This publication elaborates on how RTEL1 is recruited to telomeres by TRF2 in a cell cycle–specific manner, explaining how catastrophic t-loop processing is avoided in S phase.
Wilson, J.S. et al. Localization-dependent and -independent roles of SLX4 in regulating telomeres. Cell Reports 4, 853–860 (2013).
Wan, B. et al. SLX4 assembles a telomere maintenance toolkit by bridging multiple endonucleases with telomeres. Cell Reports 4, 861–869 (2013).
Sarkar, J. et al. SLX4 contributes to telomere preservation and regulated processing of telomeric joint molecule intermediates. Nucleic Acids Res. 43, 5912–5923 (2015).
Saint-Léger, A. et al. The basic N-terminal domain of TRF2 limits recombination endonuclease action at human telomeres. Cell Cycle 13, 2469–2474 (2014).
Bower, B.D. & Griffith, J.D. TRF1 and TRF2 differentially modulate Rad51-mediated telomeric and nontelomeric displacement loop formation in vitro. Biochemistry 53, 5485–5495 (2014).
Badie, S. et al. BRCA2 acts as a RAD51 loader to facilitate telomere replication and capping. Nat. Struct. Mol. Biol. 17, 1461–1469 (2010).
Wu, P., van Overbeek, M., Rooney, S. & de Lange, T. Apollo contributes to G overhang maintenance and protects leading-end telomeres. Mol. Cell 39, 606–617 (2010).
Chow, T.T., Zhao, Y., Mak, S.S., Shay, J.W. & Wright, W.E. Early and late steps in telomere overhang processing in normal human cells: the position of the final RNA primer drives telomere shortening. Genes Dev. 26, 1167–1178 (2012).
Lam, Y.C. et al. SNMIB/Apollo protects leading-strand telomeres against NHEJ-mediated repair. EMBO J. 29, 2230–2241 (2010).
Wu, P., Takai, H. & de Lange, T. Telomeric 3′ overhangs derive from resection by Exo1 and Apollo and fill-in by POT1b-associated CST. Cell 150, 39–52 (2012).This publication analyzes the steps of overhang generation after telomere replication, elaborating on the balance between resection and polymerization of the lagging-strand product.
Touzot, F. et al. Function of Apollo (SNM1B) at telomere highlighted by a splice variant identified in a patient with Hoyeraal-Hreidarsson syndrome. Proc. Natl. Acad. Sci. USA 107, 10097–10102 (2010).
Dai, X. et al. Molecular steps of G-overhang generation at human telomeres and its function in chromosome end protection. EMBO J. 29, 2788–2801 (2010).
Chapman, J.R., Taylor, M.R. & Boulton, S.J. Playing the end game: DNA double-strand break repair pathway choice. Mol. Cell 47, 497–510 (2012).
Zimmermann, M., Lottersberger, F., Buonomo, S.B., Sfeir, A. & de Lange, T. 53BP1 regulates DSB repair using Rif1 to control 5′ end resection. Science 339, 700–704 (2013).
Chapman, J.R. et al. RIF1 is essential for 53BP1-dependent nonhomologous end joining and suppression of DNA double-strand break resection. Mol. Cell 49, 858–871 (2013).
Di Virgilio, M. et al. Rif1 prevents resection of DNA breaks and promotes immunoglobulin class switching. Science 339, 711–715 (2013).
Boersma, V. et al. MAD2L2 controls DNA repair at telomeres and DNA breaks by inhibiting 5′ end resection. Nature 521, 537–540 (2015).
Xu, G. et al. REV7 counteracts DNA double-strand break resection and affects PARP inhibition. Nature 521, 541–544 (2015).
Clouaire, T. & Legube, G. DNA double strand break repair pathway choice: a chromatin based decision? Nucleus 6, 107–113 (2015).
Bartocci, C. et al. Isolation of chromatin from dysfunctional telomeres reveals an important role for Ring1b in NHEJ-mediated chromosome fusions. Cell Reports 7, 1320–1332 (2014).
Deng, Z., Norseen, J., Wiedmer, A., Riethman, H. & Lieberman, P.M. TERRA RNA binding to TRF2 facilitates heterochromatin formation and ORC recruitment at telomeres. Mol. Cell 35, 403–413 (2009).
Arnoult, N., Van Beneden, A. & Decottignies, A. Telomere length regulates TERRA levels through increased trimethylation of telomeric H3K9 and HP1α. Nat. Struct. Mol. Biol. 19, 948–956 (2012).
Porro, A. et al. Functional characterization of the TERRA transcriptome at damaged telomeres. Nat. Commun. 5, 5379 (2014).
Porro, A., Feuerhahn, S. & Lingner, J. TERRA-reinforced association of LSD1 with MRE11 promotes processing of uncapped telomeres. Cell Reports 6, 765–776 (2014).
Orthwein, A. et al. Mitosis inhibits DNA double-strand break repair to guard against telomere fusions. Science 344, 189–193 (2014).This publication highlights the importance of excluding 53BP1 and RNF8 from chromatin during mitosis, because tethering of these factors to DNA causes telomere fusions.
Ramsay, A.J. et al. POT1 mutations cause telomere dysfunction in chronic lymphocytic leukemia. Nat. Genet. 45, 526–530 (2013).
Bainbridge, M.N. et al. Germline mutations in shelterin complex genes are associated with familial glioma. J. Natl. Cancer Inst. 107, 384 (2015).
Robles-Espinoza, C.D. et al. POT1 loss-of-function variants predispose to familial melanoma. Nat. Genet. 46, 478–481 (2014).
Shi, J. et al. Rare missense variants in POT1 predispose to familial cutaneous malignant melanoma. Nat. Genet. 46, 482–486 (2014).
Baird, D.M., Rowson, J., Wynford-Thomas, D. & Kipling, D. Extensive allelic variation and ultrashort telomeres in senescent human cells. Nat. Genet. 33, 203–207 (2003).
Cesare, A.J. et al. Spontaneous occurrence of telomeric DNA damage response in the absence of chromosome fusions. Nat. Struct. Mol. Biol. 16, 1244–1251 (2009).
Kaul, Z., Cesare, A.J., Huschtscha, L.I., Neumann, A.A. & Reddel, R.R. Five dysfunctional telomeres predict onset of senescence in human cells. EMBO Rep. 13, 52–59 (2012).
Cesare, A.J., Hayashi, M.T., Crabbe, L. & Karlseder, J. The telomere deprotection response is functionally distinct from the genomic DNA damage response. Mol. Cell 51, 141–155 (2013). Here the authors demonstrate that partially deprotected telomeres do not activate the G2 DDR, explaining why senescent cells arrest in G1 with a diploid genome.
Cesare, A.J. & Karlseder, J. A three-state model of telomere control over human proliferative boundaries. Curr. Opin. Cell Biol. 24, 731–738 (2012).
Opresko, P.L., Fan, J., Danzy, S., Wilson, D.M. III & Bohr, V.A. Oxidative damage in telomeric DNA disrupts recognition by TRF1 and TRF2. Nucleic Acids Res. 33, 1230–1239 (2005).
Hewitt, G. et al. Telomeres are favoured targets of a persistent DNA damage response in ageing and stress-induced senescence. Nat. Commun. 3, 708 (2012).
Artandi, S.E. et al. Telomere dysfunction promotes non-reciprocal translocations and epithelial cancers in mice. Nature 406, 641–645 (2000).
Lin, T.T. et al. Telomere dysfunction and fusion during the progression of chronic lymphocytic leukemia: evidence for a telomere crisis. Blood 116, 1899–1907 (2010).
Roger, L. et al. Extensive telomere erosion in the initiation of colorectal adenomas and its association with chromosomal instability. J. Natl. Cancer Inst. 105, 1202–1211 (2013).
Capper, R. et al. The nature of telomere fusion and a definition of the critical telomere length in human cells. Genes Dev. 21, 2495–2508 (2007).
Letsolo, B.T., Rowson, J. & Baird, D.M. Fusion of short telomeres in human cells is characterized by extensive deletion and microhomology, and can result in complex rearrangements. Nucleic Acids Res. 38, 1841–1852 (2010).
Jones, R.E. et al. Escape from telomere-driven crisis is DNA ligase III dependent. Cell Reports 8, 1063–1076 (2014). In this publication, the authors analyze the requirements for escape from telomere-driven crisis and find that suppression of ligase III, but not of ligase IV, is necessary.
Maser, R.S. et al. DNA-dependent protein kinase catalytic subunit is not required for dysfunctional telomere fusion and checkpoint response in the telomerase-deficient mouse. Mol. Cell. Biol. 27, 2253–2265 (2007).
Hayashi, M.T., Cesare, A.J., Fitzpatrick, J.A., Lazzerini-Denchi, E. & Karlseder, J. A telomere-dependent DNA damage checkpoint induced by prolonged mitotic arrest. Nat. Struct. Mol. Biol. 19, 387–394 (2012).
Hayashi, M.T., Cesare, A.J., Rivera, T. & Karlseder, J. Cell death during crisis is mediated by mitotic telomere deprotection. Nature 522, 492–496 (2015). In this publication, the authors discover that few telomere fusions in precrisis cells lead to mitotic arrest. During mitotic arrest, telomere dysfunction is amplified, thus causing cell death in crisis.
Davoli, T. & de Lange, T. Telomere-driven tetraploidization occurs in human cells undergoing crisis and promotes transformation of mouse cells. Cancer Cell 21, 765–776 (2012).
Davoli, T., Denchi, E.L. & de Lange, T. Persistent telomere damage induces bypass of mitosis and tetraploidy. Cell 141, 81–93 (2010).
Simpson, K. et al. Telomere fusion threshold identifies a poor prognostic subset of breast cancer patients. Mol. Oncol. 9, 1186–1193 (2015).
Vannier, J.B. et al. RTEL1 is a replisome-associated helicase that promotes telomere and genome-wide replication. Science 342, 239–242 (2013).
Ye, J. et al. TRF2 and apollo cooperate with topoisomerase 2alpha to protect human telomeres from replicative damage. Cell 142, 230–242 (2010).
Broccoli, D., Smogorzewska, A., Chong, L. & de Lange, T. Human telomeres contain two distinct Myb-related proteins, TRF1 and TRF2. Nat. Genet. 17, 231–235 (1997).
Bilaud, T. et al. Telomeric localization of TRF2, a novel human telobox protein. Nat. Genet. 17, 236–239 (1997).
Chen, Y. et al. A shared docking motif in TRF1 and TRF2 used for differential recruitment of telomeric proteins. Science 319, 1092–1096 (2008).
Lenain, C. et al. The Apollo 5′ exonuclease functions together with TRF2 to protect telomeres from DNA repair. Curr. Biol. 16, 1303–1310 (2006).
van Overbeek, M. & de Lange, T. Apollo, an Artemis-related nuclease, interacts with TRF2 and protects human telomeres in S phase. Curr. Biol. 16, 1295–1302 (2006).
N.A. is supported by the Human Frontier Science Program (LT000284/2013). J.K. is supported by a Salk Institute Cancer Center Core Grant (P30CA014195), the US National Institutes of Health (R01GM087476 and R01CA174942), the Donald and Darlene Shiley Chair, the Highland Street Foundation, the Fritz B. Burns Foundation, the Emerald Foundation and the Glenn Center for Research on Aging.
The authors declare no competing financial interests.
About this article
Cite this article
Arnoult, N., Karlseder, J. Complex interactions between the DNA-damage response and mammalian telomeres. Nat Struct Mol Biol 22, 859–866 (2015). https://doi.org/10.1038/nsmb.3092
Genes & Development (2021)
Association of telomere length and telomerase methylation with n-3 fatty acids in preschool children with obesity
BMC Pediatrics (2021)
Experimental Gerontology (2021)
Pan-cancer analyses reveal regulation and clinical outcome association of the shelterin complex in cancer
Briefings in Bioinformatics (2021)
Current Genetics (2021)