Engineered telomere degradation models dyskeratosis congenita

Laboratory for Cell Biology and Genetics, The Rockefeller University, New York, New York 10065, USA.
Genes & Development (Impact Factor: 10.8). 08/2008; 22(13):1773-85. DOI: 10.1101/gad.1679208
Source: PubMed


Dyskeratosis congenita (DC) is an inherited bone marrow failure syndrome characterized by cutaneous symptoms, including hyperpigmentation and nail dystrophy. Some forms of DC are caused by mutations in telomerase, the enzyme that counteracts telomere shortening, suggesting a telomere-based disease mechanism. However, mice with extensively shortened telomeres due to telomerase deficiency do not develop the characteristics of DC, raising questions about the etiology of DC and/or mouse models for human telomere dysfunction. Here we describe mice engineered to undergo telomere degradation due to the absence of the shelterin component POT1b. When combined with reduced telomerase activity, POT1b deficiency elicits several characteristics of DC, including hyperpigmentation and fatal bone marrow failure at 4-5 mo of age. These results provide experimental support for the notion that DC is caused by telomere dysfunction, and demonstrate that key aspects of a human telomere-based disease can be modeled in the mouse.

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    • "synthetic peptide into X-DC3 human patient lymphocytes resulted in both increased telomerase activity and decreased DNA damage. On the other hand the consequences of A353V-X-DC mutation on DNA damage resemble to those found in cells with mutations in Tin2 and Pot1, which are structural components of telomeres [38] [39]. "
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    ABSTRACT: The predominant X-linked form of Dyskeratosis congenita results from mutations in DKC1, which encodes dyskerin, a protein required for ribosomal RNA modification that is also a component of the telomerase complex. We have previously found that expression of an internal fragment of dyskerin (GSE24.2) rescues telomerase activity in X-linked dyskeratosis congenita (X-DC) patient cells. Here we have found that an increased basal and induced DNA damage response occurred in X-DC cells in comparison with normal cells. DNA damage that is also localized in telomeres results in increased heterochromatin formation and senescence. Expression of a cDNA coding for GSE24.2 rescues both global and telomeric DNA damage. Furthermore, transfection of bacterial purified or a chemically synthesized GSE24.2 peptide is able to rescue basal DNA damage in X-DC cells. We have also observed an increase in oxidative stress in X-DC cells and expression of GSE24.2 was able to diminish it. Altogether our data indicated that supplying GSE24.2, either from a cDNA vector or as a peptide reduces the pathogenic effects of Dkc1 mutations and suggests a novel therapeutic approach.
    Full-text · Article · Jul 2014 · PLoS ONE
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    • "Both mouse Pot1 homologs promote chromosome end protection, as G-strand overhangs lengthen in Pot1b−/− cells, and end-to-end chromosome fusions occur as a result of telomere deprotection in both Pot1a−/− and Pot1b−/− cells (He et al. 2006, 2009; Hockemeyer et al. 2006, 2008; Wu et al. 2006). However, disparate cellular and telomere phenotypes have been reported. "
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    ABSTRACT: Telomeres are composed of simple tandem DNA repeats that protect the ends of linear chromosomes from replicative erosion or inappropriate DNA damage response mechanisms. The mammalian Protection Of Telomeres (POT1) protein interacts with single-stranded telomeric DNA and can exert positive and negative effects on telomere length. Of four distinct POT1 homologs in the roundworm Caenorhabditis elegans, deficiency for POT-1 or POT-2 resulted in progressive telomere elongation that occurred because both proteins negatively regulate telomerase. We created a POT-1::mCherry fusion protein that forms discrete foci at C. elegans telomeres, independent of POT-2, allowing for live analysis of telomere dynamics. Transgenic pot-1::mCherry repressed telomerase in pot-1 mutants. Animals deficient for pot-1, but not pot-2, displayed mildly enhanced telomere erosion rates in the absence of the telomerase reverse transcriptase, trt-1. However, trt-1; pot-1 double mutants exhibited delayed senescence in comparison to trt-1 animals, and senescence was further delayed in trt-1; pot-2; pot-1 triple mutants, some of which survived robustly in the absence of telomerase. Our results indicate that POT-1 and POT-2 play independent roles in suppressing a telomerase-independent telomere maintenance pathway but may function together to repress telomerase.
    Full-text · Article · Feb 2013 · G3-Genes Genomes Genetics
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    • "By 8 weeks of age, some K14-Cre;TRF2f/f mice developed multiple distinct bends in the tail resembling the crinkled mouse phenotype which exhibits stem cell depletion (32; Fig. 1A,B). Older K14-Cre;TRF2f/f mice developed nail dystrophy which has been described in mouse models of dyskeratosis congenita exhibiting stem cell depletion resulting from short telomeres (33,34; Fig. 1C). These phenotypes were not observed in K14-Cre;TRF2+/+ mice. "
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    ABSTRACT: To examine the role of telomeric repeat-binding factor 2 (TRF2) in epithelial tumorigenesis, we characterized conditional loss of TRF2 expression in the basal layer of mouse epidermis. These mice exhibit some characteristics of dyskeratosis congenita, a human stem cell depletion syndrome caused by telomere dysfunction. The epidermis in conditional TRF2 null mice exhibited DNA damage response and apoptosis, which correlated with stem cell depletion. The stem cell population in conditional TRF2 null epidermis exhibited shorter telomeres than those in control mice. Squamous cell carcinomas induced in conditional TRF2 null mice developed with increased latency and slower growth due to reduced numbers of proliferating cells as the result of increased apoptosis. TRF2 null epidermal stem cells were found in both primary and metastatic tumors. Despite the low-grade phenotype of the conditional TRF2 null primary tumors, the number of metastatic lesions was similar to control cancers. Basal cells from TRF2 null tumors demonstrated extreme telomere shortening and dramatically increased numbers of telomeric signals by fluorescence in situ hybridization due to increased genomic instability and aneuploidy in these cancers. DNA damage response signals were detected at telomeres in TRF2 null tumor cells from these mice. The increased genomic instability in these tumors correlated with eightfold expansion of the transformed stem cell population compared with that in control cancers. We concluded that genomic instability resulting from loss of TRF2 expression provides biological advantages to the cancer stem cell population.Oncogene advance online publication, 26 November 2012; doi:10.1038/onc.2012.555.
    Full-text · Article · Nov 2012 · Oncogene
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