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Impact of telomerase ablation on organismal viability, aging, and tumorigenesis in mice lacking the DNA repair proteins PARP-1, Ku86, or DNA-PKcs.

Espejel S, Klatt P, Ménissier-de Murcia J, Martín-Caballero J, Flores JM, Taccioli G, de Murcia G, Blasco MA - J. Cell Biol. (2004)

Bottom Line: First, we show that abrogation of PARP-1 in the absence of telomerase does not affect the rate of telomere shortening, telomere capping, or organismal viability compared with single telomerase-deficient controls.In contrast, mice doubly deficient for telomerase and either Ku86 or DNA-PKcs manifest accelerated loss of organismal viability compared with single telomerase-deficient mice.These results support the notion that absence of telomerase and short telomeres in combination with DNA repair deficiencies accelerate the aging process without impacting on tumorigenesis.

View Article: PubMed Central - PubMed

Affiliation: Molecular Oncology Program, Spanish National Cancer Center (CNIO), E-28029 Madrid, Spain.

ABSTRACT
The DNA repair proteins poly(ADP-ribose) polymerase-1 (PARP-1), Ku86, and catalytic subunit of DNA-PK (DNA-PKcs) have been involved in telomere metabolism. To genetically dissect the impact of these activities on telomere function, as well as organismal cancer and aging, we have generated mice doubly deficient for both telomerase and any of the mentioned DNA repair proteins, PARP-1, Ku86, or DNA-PKcs. First, we show that abrogation of PARP-1 in the absence of telomerase does not affect the rate of telomere shortening, telomere capping, or organismal viability compared with single telomerase-deficient controls. Thus, PARP-1 does not have a major role in telomere metabolism, not even in the context of telomerase deficiency. In contrast, mice doubly deficient for telomerase and either Ku86 or DNA-PKcs manifest accelerated loss of organismal viability compared with single telomerase-deficient mice. Interestingly, this loss of organismal viability correlates with proliferative defects and age-related pathologies, but not with increased incidence of cancer. These results support the notion that absence of telomerase and short telomeres in combination with DNA repair deficiencies accelerate the aging process without impacting on tumorigenesis.

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Telomere length in MEFs derived from successive generations of telomerase-deficient mice lacking PARP-1. Telomere length distribution in primary MEFs from littermate mice of the indicated genotypes. One telomere fluorescence unit (TFU) corresponds to 1 kb of TTAGGG repeats (Zijlmans et al., 1997). The respective genotype, average telomere length, and SD are indicated. Note that SD and not SEM is shown. In addition, the total number of telomeres analyzed and the number of signal-free ends, i.e., telomeres that do not contain any detectable TTAGGG signal as determined by the Q-FISH technique (detection limit is 150 bp), are given. The vertical dashed line is shown to facilitate comparisons between genotypes.
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fig1: Telomere length in MEFs derived from successive generations of telomerase-deficient mice lacking PARP-1. Telomere length distribution in primary MEFs from littermate mice of the indicated genotypes. One telomere fluorescence unit (TFU) corresponds to 1 kb of TTAGGG repeats (Zijlmans et al., 1997). The respective genotype, average telomere length, and SD are indicated. Note that SD and not SEM is shown. In addition, the total number of telomeres analyzed and the number of signal-free ends, i.e., telomeres that do not contain any detectable TTAGGG signal as determined by the Q-FISH technique (detection limit is 150 bp), are given. The vertical dashed line is shown to facilitate comparisons between genotypes.

Mentions: As outlined above, functional interactions between telomerase and the DNA-PK complex (Ku86 and DNA-PKcs) in telomere length maintenance have been already established (Espejel et al., 2002a,b). However, the role of PARP-1 in telomere maintenance remains controversial (d'Adda di Fagagna et al., 1999; Samper et al., 2001; Bailey and Goodwin, 2004). In particular, the question of whether PARP-1 impacts on telomere erosion and chromosomal instability in telomerase-deficient cells in vivo has not been clarified. To this end, we generated successive generations (G1–G4) of mice doubly deficient for PARP-1 and telomerase, Terc−/−/PARP-1−/− mice, and compared telomere length in mouse embryonic fibroblasts (MEFs) derived from these mice to that of the corresponding Terc−/− controls. Comparisons were always made between littermate mice. As shown in Fig. 1, PARP-1 deficiency did not significantly accelerate telomere shortening in increasing Terc−/− generations. Total telomere length reduction along four successive generations of Terc deficiency was 18.2 and 17.9 kb in the presence or absence of PARP-1, respectively. Consistent with this fact, the percentage of critically short telomeres, i.e., chromosomes without detectable TTAGGG repeats, in MEFs from late generation (G4) Terc−/− mice was comparable in the absence (17.8%) or presence (14.7%) of PARP-1 (Fig. 1). Such signal-free ends provoke end-to-end fusions between chromosomes, chromosome breaks, as well as aneuploidies. Specifically, we did not observe significant differences between G4 Terc−/−/PARP-1+/+ and G4 Terc−/−/PARP-1−/− MEFs regarding Robertsonian-like fusions (0.04 vs. 0 per metaphase), dicentric fusions (0.04 vs. 0.04 per metaphase), or telomere associations (0.08 vs. 0 per metaphase), as well as aneuploidies (0.16 vs. 0.24 per metaphases). Thus, these data argue against a role of PARP-1 in controlling telomere length and telomere capping.


Impact of telomerase ablation on organismal viability, aging, and tumorigenesis in mice lacking the DNA repair proteins PARP-1, Ku86, or DNA-PKcs.

Espejel S, Klatt P, Ménissier-de Murcia J, Martín-Caballero J, Flores JM, Taccioli G, de Murcia G, Blasco MA - J. Cell Biol. (2004)

Telomere length in MEFs derived from successive generations of telomerase-deficient mice lacking PARP-1. Telomere length distribution in primary MEFs from littermate mice of the indicated genotypes. One telomere fluorescence unit (TFU) corresponds to 1 kb of TTAGGG repeats (Zijlmans et al., 1997). The respective genotype, average telomere length, and SD are indicated. Note that SD and not SEM is shown. In addition, the total number of telomeres analyzed and the number of signal-free ends, i.e., telomeres that do not contain any detectable TTAGGG signal as determined by the Q-FISH technique (detection limit is 150 bp), are given. The vertical dashed line is shown to facilitate comparisons between genotypes.
© Copyright Policy
Related In: Results  -  Collection

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getmorefigures.php?uid=PMC2172587&req=5

fig1: Telomere length in MEFs derived from successive generations of telomerase-deficient mice lacking PARP-1. Telomere length distribution in primary MEFs from littermate mice of the indicated genotypes. One telomere fluorescence unit (TFU) corresponds to 1 kb of TTAGGG repeats (Zijlmans et al., 1997). The respective genotype, average telomere length, and SD are indicated. Note that SD and not SEM is shown. In addition, the total number of telomeres analyzed and the number of signal-free ends, i.e., telomeres that do not contain any detectable TTAGGG signal as determined by the Q-FISH technique (detection limit is 150 bp), are given. The vertical dashed line is shown to facilitate comparisons between genotypes.
Mentions: As outlined above, functional interactions between telomerase and the DNA-PK complex (Ku86 and DNA-PKcs) in telomere length maintenance have been already established (Espejel et al., 2002a,b). However, the role of PARP-1 in telomere maintenance remains controversial (d'Adda di Fagagna et al., 1999; Samper et al., 2001; Bailey and Goodwin, 2004). In particular, the question of whether PARP-1 impacts on telomere erosion and chromosomal instability in telomerase-deficient cells in vivo has not been clarified. To this end, we generated successive generations (G1–G4) of mice doubly deficient for PARP-1 and telomerase, Terc−/−/PARP-1−/− mice, and compared telomere length in mouse embryonic fibroblasts (MEFs) derived from these mice to that of the corresponding Terc−/− controls. Comparisons were always made between littermate mice. As shown in Fig. 1, PARP-1 deficiency did not significantly accelerate telomere shortening in increasing Terc−/− generations. Total telomere length reduction along four successive generations of Terc deficiency was 18.2 and 17.9 kb in the presence or absence of PARP-1, respectively. Consistent with this fact, the percentage of critically short telomeres, i.e., chromosomes without detectable TTAGGG repeats, in MEFs from late generation (G4) Terc−/− mice was comparable in the absence (17.8%) or presence (14.7%) of PARP-1 (Fig. 1). Such signal-free ends provoke end-to-end fusions between chromosomes, chromosome breaks, as well as aneuploidies. Specifically, we did not observe significant differences between G4 Terc−/−/PARP-1+/+ and G4 Terc−/−/PARP-1−/− MEFs regarding Robertsonian-like fusions (0.04 vs. 0 per metaphase), dicentric fusions (0.04 vs. 0.04 per metaphase), or telomere associations (0.08 vs. 0 per metaphase), as well as aneuploidies (0.16 vs. 0.24 per metaphases). Thus, these data argue against a role of PARP-1 in controlling telomere length and telomere capping.

Bottom Line: First, we show that abrogation of PARP-1 in the absence of telomerase does not affect the rate of telomere shortening, telomere capping, or organismal viability compared with single telomerase-deficient controls.In contrast, mice doubly deficient for telomerase and either Ku86 or DNA-PKcs manifest accelerated loss of organismal viability compared with single telomerase-deficient mice.These results support the notion that absence of telomerase and short telomeres in combination with DNA repair deficiencies accelerate the aging process without impacting on tumorigenesis.

View Article: PubMed Central - PubMed

Affiliation: Molecular Oncology Program, Spanish National Cancer Center (CNIO), E-28029 Madrid, Spain.

ABSTRACT
The DNA repair proteins poly(ADP-ribose) polymerase-1 (PARP-1), Ku86, and catalytic subunit of DNA-PK (DNA-PKcs) have been involved in telomere metabolism. To genetically dissect the impact of these activities on telomere function, as well as organismal cancer and aging, we have generated mice doubly deficient for both telomerase and any of the mentioned DNA repair proteins, PARP-1, Ku86, or DNA-PKcs. First, we show that abrogation of PARP-1 in the absence of telomerase does not affect the rate of telomere shortening, telomere capping, or organismal viability compared with single telomerase-deficient controls. Thus, PARP-1 does not have a major role in telomere metabolism, not even in the context of telomerase deficiency. In contrast, mice doubly deficient for telomerase and either Ku86 or DNA-PKcs manifest accelerated loss of organismal viability compared with single telomerase-deficient mice. Interestingly, this loss of organismal viability correlates with proliferative defects and age-related pathologies, but not with increased incidence of cancer. These results support the notion that absence of telomerase and short telomeres in combination with DNA repair deficiencies accelerate the aging process without impacting on tumorigenesis.

Show MeSH
Related in: MedlinePlus