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.
SummarySepsis is an often lethal syndrome resulting from maladaptive immune and metabolic responses to infection, compromising host homeostasis. Disease tolerance is a defense strategy against infection that preserves host homeostasis without exerting a direct negative impact on pathogens. Here, we demonstrate that induction of the iron-sequestering ferritin H chain (FTH) in response to polymicrobial infections is critical to establish disease tolerance to sepsis. The protective effect of FTH is exerted via a mechanism that counters iron-driven oxidative inhibition of the liver glucose-6-phosphatase (G6Pase), and in doing so, sustains endogenous glucose production via liver gluconeogenesis. This is required to prevent the development of hypoglycemia that otherwise compromises disease tolerance to sepsis. FTH overexpression or ferritin administration establish disease tolerance therapeutically. In conclusion, disease tolerance to sepsis relies on a crosstalk between adaptive responses controlling iron and glucose metabolism, required to maintain blood glucose within a physiologic range compatible with host survival.
BRCA2 is a key component of the homologous recombination (HR) pathway of DNA repair, acting as the loader of RAD51 recombinase at sites of double-strand breaks. Here, we demonstrate that BRCA2 associates with telomeres during S/G2 and facilitates RAD51 loading onto telomeres. Conditional Brca2 deletion and Rad51 inhibition in mouse embryonic fibroblasts (MEFs), but not Brca1 inactivation, led to telomere shortening and accumulation of fragmented telomeric signals, a hallmark of telomere fragility associated with replication defects. This suggests that BRCA2-mediated HR reactions contribute to telomere length maintenance by facilitating telomere replication and implies an essential role for BRCA2 in telomere integrity during unchallenged cell proliferation. Mouse mammary tumors lacking Brca2 accumulated telomere dysfunction-induced foci. BRCA2-mutated human breast tumors had shorter telomeres than BRCA1-mutated ones, suggesting that the genomic instability observed in BRCA2-deficient tumors is due in part to telomere dysfunction.
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