A Novel Telomere Structure in a Human Alternative Lengthening of Telomeres Cell Line

Marciniak, Robert A.; Cavazos, David; Montellano, Richard; Chen, Qijun; Guarente, Leonard; Johnson, F. Brad

doi:10.1158/0008-5472.can-04-2888

Cited by 68 publications

(59 citation statements)

References 40 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Moreover, transfer of telomeric DNA between sister chromatids or different chromosomes (Bailey et al, 2004a) should have only a temporary effect on telomere maintenance and survival in C3-cl6 cells given the homogenous and short size of their telomeres. An ALT cell line that lacks APBs but retains other features of ALT has recently been described (Fasching et al, 2005;Marciniak et al, 2005), strengthening our conclusion that the use of the known ALT markers needs to be reassessed. Most relevant, absence of both telomerase and classical ALT has been reported in a high percentage of human osteosarcomas and found associated with improved patient survival, suggesting that lack of telomere maintenance mechanisms may represent a positive prognostic factor (Ulaner et al, 2003).…”

Section: Discussionsupporting

confidence: 72%

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

et al. 2005

View full text Add to dashboard Cite

In human somatic cells proliferation results in telomere shortening due to the end replication problem and the absence of adequate levels of telomerase activity. The progressive loss of telomeric DNA has been associated with replicative senescence. Maintenance of telomere structure and function is, therefore, an essential requisite for cells that proliferate indefinitely. Human cells that have acquired the immortal phenotype mostly rely on telomerase to compensate for telomere shortening with cell division. However, a certain percentage of immortalized cell lines and human tumors maintain their telomeres by Alternative Lengthening of Telomeres (ALT), a mechanism not fully understood but apparently based on homologous recombination. Here, we report the isolation of an immortal human cell line that is derived from an ALT cell line but maintains telomeres in the absence of key features of ALT and of telomerase. The properties of these cells suggest that the identification of ALT cells may not be reliably based on known ALT markers. This finding is of relevance for discriminating between the mortal and immortal phenotype among telomerase-negative cells in vitro and in vivo, particularly in regard to the development of pharmacological approaches for cancer treatment based on telomerase inhibition.

show abstract

Section: Discussionsupporting

confidence: 72%

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

et al. 2005

View full text Add to dashboard Cite

show abstract

“…Type I survivors have telomeres comprising tandem arrays of amplified units of subtelomeric elements and telomere repeats. Recently, an SV40-immortalized human cell line lacking both WRN and telomerase activities was found to maintain telomeres by a mechanism reminiscent of this type I survival pathway (Fasching et al, 2005;Marciniak et al, 2005); this suggests that a subset of human ALT cells could maintain telomeres by establishing tandem arrays. A similar mechanism also appears to operate in telomerase-null mouse ALT cell lines with dysfunctional telomeres (Niida et al, 2000), which suggests that tandem arrays of telomeric sequences can stabilize mammalian termini in the absence of telomerase.…”

Section: Wrnmentioning

confidence: 99%

“…These results indicate that the increased incidence of chromosomal instability and cancer observed in WS patients may be caused by aberrant recombination at telomeres, which promotes the activation of ALT that maintains telomeres through a mechanism analogous to the type I survival pathway observed in sgsl -/-, telomerase-null yeasts. Although not all Wrn -/-, telomerase-null human cells maintain telomeres by this mechanism, the recent discovery of a Wrn -/-, telomerase-null SV40-immortalized ALT cell line that maintains telomeres in a manner reminiscent of the type I survival pathway supports this hypothesis (Fasching et al, 2005;Marciniak et al, 2005). The G5 mTerc -/-Wrn -/-compound knockout mouse thus offers a unique system to discover novel genes involved in ALT activation during tumor formation.…”

Section: Wrnmentioning

confidence: 99%

WRN at telomeres: implications for aging and cancer

Multani

Chang

2007

Journal of Cell Science

View full text Add to dashboard Cite

Werner Syndrome (WS) is a fascinating autosomal recessive disorder affecting ~10 per million individuals (Epstein et al., 1966). Patients appear normal until the second decade of life, when they develop pathologies that phenocopy many aspects of normal human aging, including alopecia, ischemic heart disease, osteoporosis, bilateral ocular cataracts, type II diabetes mellitus, and hypogonadism (Thannhauser, 1945). WS patients also experience an increased risk of rare non-epithelial cancers, especially mesenchymal neoplasms such as sarcomas (Goto et al., 1996). Death usually occurs in the fourth decade from cardiovascular compromise or cancer. Fibroblasts isolated from WS patients characteristically senesce prematurely in culture (Faragher et al., 1993) and display increased chromosomal aberrations (Salk et al., 1981;Melcher et al., 2000). Since WS is caused by mutation of a single gene, WRN, these observations suggest that the WRN gene product functions to maintain genome stability.Cloning of WRN ten years ago revealed that it encodes a protein containing a highly conserved 3Ј to 5Ј DNA helicase domain of the RecQ family (reviewed by Martin and Oshima, 2000). RecQ helicase family members are involved in diverse biochemical processes, including DNA recombination, replication and repair, and WRN has been implicated in all of these (reviewed by Hickson, 2003). WRN also possesses several other conserved domains, including a 3Ј to 5Ј exonuclease domain, a nuclear localization sequence, and a multifunctional DNA/protein-binding domain (DPBD) that interacts with both DNA and proteins (reviewed by Orren, 2006). Through these domains WRN interacts with many factors that participate in diverse aspects of DNA metabolism beyond the scope of this commentary. Here, we focus on recent progress that indicates WRN might have a role at telomeres. Discussion of other aspects of WRN biology can be found elsewhere (Hickson, 2003; Comai and Li, 2004;Bohr, 2005;Orren, 2006). Telomere structure and maintenanceTelomeres are nucleoprotein structures that cap the ends of eukaryotic chromosomes and play crucial roles in maintaining genomic stability by providing both end-protection and a mechanism for generating chromosomal ends (LeBel and Wellinger, 2006). In mammals, telomeres consist of TTAGGG repetitive sequences that terminate in a 3Ј single-stranded Grich overhang. Telomeres can fold into a structure termed the t-loop, in which the 3Ј single-stranded overhang invades a duplex region of the telomere to sequester the overhang, forming a single-stranded displacement (D) loop (Griffith et al., 1999;Murti and Prescott, 1999). This telomeric conformation probably protects natural DNA ends from being recognized as double-strand breaks (DSBs) that would otherwise activate DNA damage checkpoint responses or participate in aberrant recombination events (reviewed by d'Adda di Fagagna et al., 2004). However, an extended telomeric conformation must also exist to facilitate replication of telomeres during S phase. Telomeres are maintained by the e...

show abstract

“…C-circles have been observed in both APB-positive and APB-negative ALT cell lines (11). However, the single APB-negative ALT cell line is a lab immortalized cell line with unique features that may not be representative of naturally arising APBnegative ALT (14). Although C-circles seem ideal to serve as templates for rolling circle-based elongation of telomeres, there remains no clear evidence as to the exact role of these circles in ALT.…”

Section: Introductionmentioning

confidence: 99%

Telomerase Suppresses Formation of ALT-Associated Single-Stranded Telomeric C-Circles

Plantinga

Pascarelli

Merkel

et al. 2013

Molecular Cancer Research

View full text Add to dashboard Cite

Telomere maintenance is an essential characteristic of cancer cells, most commonly achieved by activation of telomerase. Telomeres can also be maintained by a recombination-based mechanism, alternative lengthening of telomeres (ALT). Cells using ALT are characterized by the presence of ALT-associated promyelocytic leukemia (PML) bodies (APB), long, heterogeneously sized telomeres, extrachromosomal telomeric circular DNA, and elevated telomeric recombination. Consistent with other reports, we found that liposarcomas containing APBs, but lacking telomerase expression, always contained C-rich circles (C-circles), and these C-circles were never present in the absence of APBs, indicating a tight link between these features in ALT cells. However, a rare subgroup of tumors showing evidence of telomere maintenance by both telomerase and ALT did not contain C-circles. To test the hypothesis that telomerase expression disrupts the tight link between APBs and C-circles, we used ALT cell lines that were engineered to express telomerase. Introduction of telomerase activity in these ALT cells resulted in, on average, shorter telomeres with retention of APBs. However, at high passage, the level of C-circles was significantly reduced, which was paralleled by a switch from C-strand overhangs to G-strand overhangs. We propose that by extending critically short telomeres in these cells, telomerase is disrupting a key step in the ALT pathway necessary for production and/or maintenance of C-circles. Mol Cancer Res; 11(6); 557-67. Ó2013 AACR.

show abstract

A Novel Telomere Structure in a Human Alternative Lengthening of Telomeres Cell Line

Cited by 68 publications

References 40 publications

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

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

WRN at telomeres: implications for aging and cancer

Telomerase Suppresses Formation of ALT-Associated Single-Stranded Telomeric C-Circles

Contact Info

Product

Resources

About