RESUMO
CTCF is an essential epigenetic regulator mediating chromatin insulation, long-range regulatory interactions, and the organization of large topological domains in the nucleus. Phenotypes of CTCF haploinsufficient mutations in humans, knockout in mice, and depletion in cells are often consistent with impaired genome stability, but a role of CTCF in genome maintenance has not been fully investigated. Here, we report that CTCF maintains genome stability, is recruited to sites of DNA damage, and promotes homologous recombination repair of DNA double-strand breaks (DSBs). CTCF depletion increased chromosomal instability, marked by chromosome breakage and end fusions, elevated genotoxic stress-induced genomic DNA fragmentation, and activated the ataxia telangiectasia mutated (ATM) kinase. We show that CTCF could be recruited to drug-induced 53BP1 foci and known fragile sites, as well as to I-SceI endonuclease-induced DSBs. Laser irradiation analysis revealed that this recruitment depends on ATM, Nijmegen breakage syndrome (NBS), and the zinc finger DNA-binding domain of CTCF. We demonstrate that CTCF knockdown impaired homologous recombination (HR) repair of DSBs. Consistent with this, CTCF knockdown reduced the formation of γ-radiation-induced Rad51 foci, as well as the recruitment of Rad51 to laser-irradiated sites of DNA lesions and to I-SceI-induced DSBs. We further show that CTCF is associated with DNA HR repair factors MDC1 and AGO2, and directly interacts with Rad51 via its C terminus. These analyses establish a direct, functional role of CTCF in DNA repair and provide a potential link between genome organization and genome stability.
Assuntos
Fator de Ligação a CCCTC/metabolismo , Dano ao DNA , Instabilidade Genômica , Osteossarcoma/genética , Reparo de DNA por Recombinação , Neoplasias Ósseas/genética , Neoplasias Ósseas/metabolismo , Neoplasias Ósseas/patologia , Fator de Ligação a CCCTC/antagonistas & inibidores , Fator de Ligação a CCCTC/genética , Humanos , Osteossarcoma/metabolismo , Osteossarcoma/patologia , RNA Interferente Pequeno/genética , Rad51 Recombinase/genética , Rad51 Recombinase/metabolismo , Células Tumorais CultivadasRESUMO
Fluorination was confirmed to be the most effective route to introduce localized spins in graphene. However, adatoms clustering in perfect graphene lead to a low efficiency. In this study, we report experimental evidence of the generation of localized spin magnetic moments on defective graphene (reduced graphene oxide) through fluorination. More interstingly, the result shows that defects help increase the efficiency of the fluorination with regard to the density of magnetic moments created. Fluorinated reduced graphene oxide can have a high magnetic moment of 3.187 × 10(-3) µB per carbon atom and a high efficiency of 8.68 × 10(-3) µB per F atom. It may be attributed to the many vacancies, which hinder the clustering of F atoms, and introduce many magnetic edge adatoms.
