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Martinez P.,Telomeres and Telomerase Group | Thanasoula M.,Telomeres and Telomerase Group | Carlos A.R.,CR UK MRC Gray Institute for Radiation Oncology and Biology | Gomez-Lopez G.,Bioinformatics Core Unit | And 6 more authors.
Nature Cell Biology

Rap1 is a component of the shelterin complex at mammalian telomeres, but its in vivo role in telomere biology has remained largely unknown to date. Here we show that Rap1 deficiency is dispensable for telomere capping but leads to increased telomere recombination and fragility. We generated cells and mice deleted for Rap1; mice with Rap1 deletion in stratified epithelia were viable but had shorter telomeres and developed skin hyperpigmentation in adulthood. By performing chromatin immunoprecipitation coupled with ultrahigh-throughput sequencing, we found that Rap1 binds to both telomeres and to extratelomeric sites through the (TTAGGG) 2 consensus motif. Extratelomeric Rap1-binding sites were enriched at subtelomeric regions, in agreement with preferential deregulation of subtelomeric genes in Rap1-deficient cells. More than 70% of extratelomeric Rap1-binding sites were in the vicinity of genes, and 31% of the genes deregulated in Rap1-null cells contained Rap1-binding sites, suggesting a role for Rap1 in transcriptional control. These findings place a telomere protein at the interface between telomere function and transcriptional regulation. © 2010 Macmillan Publishers Limited. All rights reserved. Source

Badie S.,CR UK MRC Gray Institute for Radiation Oncology and Biology | Carlos A.R.,CR UK MRC Gray Institute for Radiation Oncology and Biology | Carlos A.R.,Gulbenkian Institute | Folio C.,CR UK MRC Gray Institute for Radiation Oncology and Biology | And 5 more authors.
EMBO Journal

Loss of telomere protection occurs during physiological cell senescence and ageing, due to attrition of telomeric repeats and insufficient retention of the telomere-binding factor TRF2. Subsequently formed telomere fusions trigger rampant genomic instability leading to cell death or tumorigenesis. Mechanistically, telomere fusions require either the classical non-homologous end-joining (C-NHEJ) pathway dependent on Ku70/80 and LIG4, or the alternative non-homologous end-joining (A-NHEJ), which relies on PARP1 and LIG3. Here, we show that the tumour suppressor BRCA1, together with its interacting partner CtIP, both acting in end resection, also promotes end-joining of uncapped telomeres. BRCA1 and CtIP do not function in the ATM-dependent telomere damage signalling, nor in telomere overhang removal, which are critical for telomere fusions by C-NHEJ. Instead, BRCA1 and CtIP act in the same pathway as LIG3 to promote joining of de-protected telomeres by A-NHEJ. Our work therefore ascribes novel roles for BRCA1 and CtIP in end-processing and fusion reactions at uncapped telomeres, underlining the complexity of DNA repair pathways that act at chromosome ends lacking protective structures. Moreover, A-NHEJ provides a mechanism of previously unanticipated significance in telomere dysfunction-induced genome instability. © 2015 The Authors. Published under the terms of the CC BY 4.0 license. Source

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