A human cell line that maintains telomeres in the absence of telomerase and of key markers of ALT

Cerone, Maria Antonietta; Autexier, Chantal; Londoño-Vallejo, J. Arturo; Bacchetti, Silvia

doi:10.1038/sj.onc.1208934

Cited by 66 publications

(58 citation statements)

References 55 publications

(74 reference statements)

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“…2C), suggesting that elongation of the shortest telomeres by telomerase may affect the recruitment of chromosome extremities to APBs. In an atypical ALT cell line derived from VA13 cells (VA13-C3-cl6), in which APBs are virtually absent (20), telomere clusters were rarely detected ( Fig. 2 A and C), as expected.…”

Section: Telomeres Are Not Randomly Distributed But Cluster Around Pmlsupporting

confidence: 83%

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

Drašković

Arnoult

Steiner

et al. 2009

Proc. Natl. Acad. Sci. U.S.A.

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142

125

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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.ALT-associated PML bodies (APBs) ͉ alternative lengthening of telomeres (ALT) ͉ Herpes simplex virus ICP0 ͉ telomere clusters P ML (promyelocytic leukemia) nuclear bodies, which are present in most cells, have been extensively studied and a wealth of information concerning their composition, structure, dynamics and function is available (1). The PML protein is essential for the formation of PML bodies and provides the structural scaffold to which other proteins bind. Over 60 additional proteins have been localized to PML bodies spatially or temporally [see the information on PML bodies from the Nuclear Protein Database, (2)], and as a consequence, PML bodies have been implicated in the regulation of virtually every biological function including DNA damage responses.In immortal cells that maintain telomeres by recombinationbased alternative lengthening mechanisms (ALT), a special variety of PML bodies is found that, in addition to the proteins normally associated with PML bodies, contain telomeric DNA, telomerespecific proteins, and DNA recombination and repair proteins (3). The structure and the role of these ALT-associated PML bodies (APBs) are unknown. There is, however, a clear association between the presence of APBs and the utilization of ALT for telomere maintenance. However, in those studies disruptions of APBs have often been achiev...

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Section: Telomeres Are Not Randomly Distributed But Cluster Around Pmlsupporting

confidence: 83%

“…VA13 cells that stably express hTERT and hTR (VA13ϩtelomerase) maintain telomeres by both mechanisms, ALT and telomerase. VA13-C3-cl6 is a clonal cell line derived from VA13 that maintains telomeres by an atypical ALT pathway in the absence of APBs (20). HT1080 is a telomerasepositive human lung sarcoma cell line.…”

Section: Methodsmentioning

confidence: 99%

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

Drašković

Arnoult

Steiner

et al. 2009

Proc. Natl. Acad. Sci. U.S.A.

Self Cite

142

125

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“…One possible explanation could be that telomerase did not completely revert the ALT pathway and/or the associated telomeric heterochromatinization, as suggested earlier (Perrem et al, 2001;Cerone et al, 2005). However, the telomeric repeat addition at short chromosome ends that we observed upon telomerase expression suggests that telomerase T-SCE does not require subtelomeric DNA hypomethylation G Tilman et al acted at the telomeres of these ALT cells.…”

Section: Discussionmentioning

confidence: 47%

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

et al. 2009

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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 DNAmethylation 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.

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“…cerevisiae strains deficient for telomerase can survive with long and heterogeneous telomeres composed of amplified telomere repeats (type II survivors) (7,8). Analogous to type II survivors, long and heterogeneous telomeres occur in almost all in vitro immortalized cell lines and tumor-derived cells lines that are telomerase-negative (9)(10)(11). Furthermore, extensive analysis of telomerase activity and telomere length from primary human tumor samples has revealed that certain telomerase-negative tumors possess long and heterogeneous telomeres, defined as alternative lengthening of telomeres (ALT) tumors (9).…”

Section: Protection Of Telomeres-2 | Telomere Maintenancementioning

confidence: 99%

Caenorhabditis elegans POT-2 telomere protein represses a mode of alternative lengthening of telomeres with normal telomere lengths

Cheng¹,

Shtessel

Brady

et al. 2012

Proc. Natl. Acad. Sci. U.S.A.

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Canonical telomere repeats at chromosome termini can be maintained by a telomerase-independent pathway termed alternative lengthening of telomeres (ALT). Human cancers that survive via ALT can exhibit long and heterogeneous telomeres, although many telomerase-negative tumors possess telomeres of normal length. Here, we report that Caenorhabditis elegans telomerase mutants that survived via ALT possessed either long or normal telomere lengths. Most ALT strains displayed end-to-end chromosome fusions, suggesting that critical telomere shortening occurred before or concomitant with ALT. ALT required the 9-1-1 DNA damage response complex and its clamp loader, HPR-17. Deficiency for the POT-2 telomere binding protein promoted ALT in telomerase mutants, overcame the requirement for the 9-1-1 complex in ALT, and promoted ALT with normal telomere lengths. We propose that telomerase-deficient human tumors with normal telomere lengths could represent a mode of ALT that is facilitated by telomere capping protein dysfunction. PROTECTION OF TELOMERES-2 | telomere maintenanceT elomeres are tandem repeat tracts that cap the ends of linear chromosomes and erode with each cell cycle because of the inability of canonical DNA polymerases to completely replicate chromosome termini (1). However, the ribonucleoprotein telomerase combats this erosion by adding de novo telomeric repeats via reverse transcription (2). Progressive telomere shortening during proliferation of human somatic cells can trigger senescence, which serves as a major tumor suppression mechanism (3). Bypass of senescence and further cell proliferation leads to critical telomere shortening and crisis, resulting in high levels of cell death due to chromosome instability (4). Many tumors overcome this proliferation barrier by activating expression of the telomerase reverse transcriptase. The remaining 10-15% of human tumors do not possess telomerase activity (5, 6).S. cerevisiae strains deficient for telomerase can survive with long and heterogeneous telomeres composed of amplified telomere repeats (type II survivors) (7,8). Analogous to type II survivors, long and heterogeneous telomeres occur in almost all in vitro immortalized cell lines and tumor-derived cells lines that are telomerase-negative (9-11). Furthermore, extensive analysis of telomerase activity and telomere length from primary human tumor samples has revealed that certain telomerase-negative tumors possess long and heterogeneous telomeres, defined as alternative lengthening of telomeres (ALT) tumors (9). However, the majority (81/108) of primary tumors lacking telomerase activity have telomeres of normal lengths (9,(12)(13)(14)(15). This subset of telomerase-negative tumors may have become neoplastic before exhausting their telomere repeat reserves (9, 16). Alternatively, these tumors could have evolved via the same telomeredriven crisis events that give rise to ALT tumors, followed by activation of a distinct form of ALT that maintains telomeres of apparently normal lengths (9).Homologous recombinatio...

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A human cell line that maintains telomeres in the absence of telomerase and of key markers of ALT

Cited by 66 publications

References 55 publications

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

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

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

Caenorhabditis elegans POT-2 telomere protein represses a mode of alternative lengthening of telomeres with normal telomere lengths

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