Normal telomere length and chromosomal end capping in poly(ADP-ribose) polymerase–deficient mice and primary cells despite increased chromosomal instability
TL;DR: The results presented here indicate that PARp-1 does not play a major role in regulating telomere length or in telomeric end capping, and the chromosomal instability of PARP-1−/− primary cells can be explained by the repair defect associated to PARP -1 deficiency.
Abstract: Poly(ADP-ribose) polymerase (PARP)-1, a detector of single-strand breaks, plays a key role in the cellular response to DNA damage. PARP-1-deficient mice are hypersensitive to genotoxic agents and display genomic instability due to a DNA repair defect in the base excision repair pathway. A previous report suggested that PARP-1-deficient mice also had a severe telomeric dysfunction consisting of telomere shortening and increased end-to-end fusions (d'Adda di Fagagna, F., M.P. Hande, W.-M. Tong, P.M. Lansdorp, Z.-Q. Wang, and S.P. Jackson. 1999. NAT: Genet. 23:76-80). In contrast to that, and using a panoply of techniques, including quantitative telomeric (Q)-FISH, we did not find significant differences in telomere length between wild-type and PARP-1(-/)- littermate mice or PARP-1(-/)- primary cells. Similarly, there were no differences in the length of the G-strand overhang. Q-FISH and spectral karyotyping analyses of primary PARP-1(-/)- cells showed a frequency of 2 end-to-end fusions per 100 metaphases, much lower than that described previously (d'Adda di Fagagna et al., 1999). This low frequency of end-to-end fusions in PARP-1(-/)- primary cells is accordant with the absence of severe proliferative defects in PARP-1(-/)- mice. The results presented here indicate that PARP-1 does not play a major role in regulating telomere length or in telomeric end capping, and the chromosomal instability of PARP-1(-/)- primary cells can be explained by the repair defect associated to PARP-1 deficiency. Finally, no interaction between PARP-1 and the telomerase reverse transcriptase subunit, Tert, was found using the two-hybrid assay.
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TL;DR: Recurrent somatic mutations in POT1 (encoding protection of telomeres 1) are identified in 3.5% of the cases and may facilitate novel approaches for the clinical management of this disease.
Abstract: Carlos Lopez-Otin and colleagues report recurrent mutations in POT1 in chronic lymphocytic leukemia. This is the first member of the telomeric shelterin complex reported to be mutated in human cancer.
254 citations
TL;DR: It is shown that absence of Ku86 prevents the end‐to‐end chromosomal fusions that result from critical telomere shortening in telomerase‐deficient mice, and Ku86 deficiency rescues the male early germ cell apoptosis triggered by short telomeres in these mice.
Abstract: Here we analyze the functional interaction between Ku86 and telomerase at the mammalian telomere by studying mice deficient for both proteins. We show that absence of Ku86 prevents the end-to-end chromosomal fusions that result from critical telomere shortening in telomerase-deficient mice. In addition, Ku86 deficiency rescues the male early germ cell apoptosis triggered by short telomeres in these mice. Together, these findings define a role for Ku86 in mediating chromosomal instability and apoptosis triggered by short telomeres. In addition, we show here that Ku86 deficiency results in telomerase-dependent telomere elongation and in the fusion of random pairs of chromosomes in telomerase-proficient cells, suggesting a model in which Ku86 keeps normal-length telomeres less accessible to telomerase- mediated telomere lengthening and to DNA repair activities.
228 citations
TL;DR: A functional role of PARP-2 activity in the maintenance of telomere integrity is suggested as well as a covalent heteromodification of the dimerization domain of TRF2 and a noncovalent binding of poly(ADP-ribose) to the myb domain ofTRF2.
Abstract: The DNA damage-dependent poly(ADP-ribose) polymerase-2 (PARP-2) is, together with PARP-1, an active player of the base excision repair process, thus defining its key role in genome surveillance and protection. Telomeres are specialized DNA-protein structures that protect chromosome ends from being recognized and processed as DNA strand breaks. In mammals, telomere protection depends on the T2AG3 repeat binding protein TRF2, which has been shown to remodel telomeres into large duplex loops (t-loops). In this work we show that PARP-2 physically binds to TRF2 with high affinity. The association of both proteins requires the N-terminal domain of PARP-2 and the myb domain of TRF2. Both partners colocalize at promyelocytic leukemia bodies in immortalized telomerase-negative cells. In addition, our data show that PARP activity regulates the DNA binding activity of TRF2 via both a covalent heteromodification of the dimerization domain of TRF2 and a noncovalent binding of poly(ADP-ribose) to the myb domain of TRF2. PARP-2/ primary cells show normal telomere length as well as normal telomerase activity compared to wild-type cells but display a spontaneously increased frequency of chromosome and chromatid breaks and of ends lacking detectable T2AG3 repeats. Altogether, these results suggest a functional role of PARP-2 activity in the maintenance of telomere integrity.
198 citations
TL;DR: It is reported that the combined expression of adenovirus E1A, Ha-RasV12, and MDM2 is sufficient to convert a normal human cell into a cancer cell and provides evidence that activation of telomere maintenance strategies is not an obligate characteristic of tumorigenic human cells.
160 citations
Cites background from "Normal telomere length and chromoso..."
...Through genetic analyses, we have also identified require- al., 1998; Herrera et al., 1999, 2000; Samper et al., 2001)....
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...These phenotypes can be rescued by telomerase activation (Lee et quires negation of both the Rb and p53 tumor suppressor pathways. Through genetic analyses, we have also identified require- al., 1998; Herrera et al., 1999, 2000; Samper et al., 2001)....
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TL;DR: The protective "cap" that assembles at chromosome ends recruits and controls an intricate network of biochemical activities, each one critical for telomere structure and the maintenance of genomic stability.
149 citations
References
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TL;DR: P16 seems to act in a regulatory feedback circuit with CDK4, D-type cyclins and retinoblastoma protein, and inhibits the catalytic activity of theCDK4/cyclin D enzymes.
Abstract: The division cycle of eukaryotic cells is regulated by a family of protein kinases known as the cyclin-dependent kinases (CDKs). The sequential activation of individual members of this family and their consequent phosphorylation of critical substrates promotes orderly progression through the cell cycle. The complexes formed by CDK4 and the D-type cyclins have been strongly implicated in the control of cell proliferation during the G1 phase. CDK4 exists, in part, as a multi-protein complex with a D-type cyclin, proliferating cell nuclear antigen and a protein, p21 (refs 7-9). CDK4 associates separately with a protein of M(r) 16K, particularly in cells lacking a functional retinoblastoma protein. Here we report the isolation of a human p16 complementary DNA and demonstrate that p16 binds to CDK4 and inhibits the catalytic activity of the CDK4/cyclin D enzymes. p16 seems to act in a regulatory feedback circuit with CDK4, D-type cyclins and retinoblastoma protein.
3,716 citations
"Normal telomere length and chromoso..." refers methods in this paper
...As control for the two-hybrid assay we show interaction between the cell cycle proteins CDK4 and p16 as described previously (Table VI; Serrano et al., 1993)....
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TL;DR: The DNA of telomeres—the terminal DNA-protein complexes of chromosomes—differs notably from other DNA sequences in both structure and function, and has been shown to be essential for telomere maintenance and long-term viability.
Abstract: The DNA of telomeres--the terminal DNA-protein complexes of chromosomes--differs notably from other DNA sequences in both structure and function. Recent work has highlighted its remarkable mode of synthesis by the ribonucleoprotein reverse transcriptase, telomerase, as well as its ability to form unusual structures in vitro. Moreover, telomere synthesis by telomerase has been shown to be essential for telomere maintenance and long-term viability.
3,139 citations
TL;DR: Electron microscopy reported here demonstrated that TRF2 can remodel linear telomeric DNA into large duplex loops (t loops) in vitro, which may provide a general mechanism for the protection and replication of telomeres.
2,413 citations
TL;DR: Results indicate that telomerase is essential for telomere length maintenance but is not required for establishment of cell lines, oncogenic transformation, or tumor formation in mice.
2,066 citations
"Normal telomere length and chromoso..." refers background or methods in this paper
...These Robertsonian fusions are different from those found in late generation telomerase-deficient mice that have critically short telomeres (Blasco et al., 1997)....
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...5 embryos derived from heterozygous crosses as described (Blasco et al., 1997)....
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...Telomeres have an essential role in chromosome stability and are proposed to be biological determinants in the processes of tumorigenesis and aging (for reviews see Blackburn, 1991; Autexier and Greider, 1996; Greider, 1996; Blasco et al., 1997; Lee et al., 1998)....
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...Then the plugs were digested with MboI overnight and run in a pulse field gel electrophoresis as described (Blasco et al., 1997)....
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TL;DR: The history and present situation of Spanish language, culture, literature, cuisine, tourism, and more are explored in more detail in this booklet.
Abstract: TELOMERES DEFINED . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 579 TELOMERE FUNCTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 580 SEQUENCE AND STRUCTURE OF TELOMERES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 581 SOLUTIONS FOR REPLICATION OF DNA TERMINI . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 586 STRUCTURE OF SUBTELOMERIC REGIONS.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 589 FORMA TION OF TELOMERES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ... . . . . . .. 591 PROTEINS THAT INTERACT WITH TELOMERES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 594 ARE TELOMERES REALLY ESSENTIAL? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 597 FUTURE PROSPECTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 598
1,923 citations
"Normal telomere length and chromoso..." refers background in this paper
...Vertebrate telomeres consist of tandem repeats of the sequence TTAGGG (for review see Blackburn, 1991)....
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...Telomeres have an essential role in chromosome stability and are proposed to be biological determinants in the processes of tumorigenesis and aging (for reviews see Blackburn, 1991; Autexier and Greider, 1996; Greider, 1996; Blasco et al., 1997; Lee et al., 1998)....
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