RESUMO
The Mre11/Rad50/Nbs1 complex initiates double-strand break repair by homologous recombination (HR). Loss of Mre11 or its nuclease activity in mouse cells is known to cause genome aberrations and cellular senescence, although the molecular basis for this phenotype is not clear. To identify the origin of these defects, we characterized Mre11-deficient (MRE11-/-) and nuclease-deficient Mre11 (MRE11-/H129N) chicken DT40 and human lymphoblast cell lines. These cells exhibit increased spontaneous chromosomal DSBs and extreme sensitivity to topoisomerase 2 poisons. The defects in Mre11 compromise the repair of etoposide-induced Top2-DNA covalent complexes, and MRE11-/- and MRE11-/H129N cells accumulate high levels of Top2 covalent conjugates even in the absence of exogenous damage. We demonstrate that both the genome instability and mortality of MRE11-/- and MRE11-/H129N cells are significantly reversed by overexpression of Tdp2, an enzyme that eliminates covalent Top2 conjugates; thus, the essential role of Mre11 nuclease activity is likely to remove these lesions.
Assuntos
Antígenos de Neoplasias/genética , Quebras de DNA de Cadeia Dupla/efeitos dos fármacos , DNA Topoisomerases Tipo II/genética , Proteínas de Ligação a DNA/genética , DNA/genética , Proteínas Nucleares/genética , Reparo de DNA por Recombinação/efeitos dos fármacos , Fatores de Transcrição/genética , Hidrolases Anidrido Ácido , Animais , Antígenos de Neoplasias/metabolismo , Proteínas de Ciclo Celular/genética , Proteínas de Ciclo Celular/metabolismo , Morte Celular/efeitos dos fármacos , Linhagem Celular Tumoral , Galinhas , DNA/metabolismo , Enzimas Reparadoras do DNA/genética , Enzimas Reparadoras do DNA/metabolismo , DNA Topoisomerases Tipo II/metabolismo , Proteínas de Ligação a DNA/deficiência , Proteínas de Ligação a DNA/metabolismo , Etoposídeo/farmacologia , Regulação da Expressão Gênica , Instabilidade Genômica/efeitos dos fármacos , Humanos , Linfócitos/citologia , Linfócitos/efeitos dos fármacos , Linfócitos/metabolismo , Proteína Homóloga a MRE11 , Mutação , Proteínas Nucleares/metabolismo , Diester Fosfórico Hidrolases , Proteínas de Ligação a Poli-ADP-Ribose , Transdução de Sinais , Inibidores da Topoisomerase II/farmacologia , Fatores de Transcrição/metabolismoRESUMO
The removal of boron from model wastewater using PAdeCS, a material derived from waste concrete, was studied. Three different types of boron removal methods were examined: adsorption with untreated PAdeCS, adsorption with heat-treated ettringite-enriched PAdeCS, and coagulation-sedimentation method by mixing untreated PAdeCS as a calcium source and aluminum sulfate as an aluminum and sulfate ion source for the formation of ettringite. The highest boron removal performance was observed for the coagulation-sedimentation method, where the boron concentration in the model wastewater decreased rapidly from 100 mg/L to the level below the Japanese effluent standard at 10 mg/L when the weight ratio of PAdeCS addition into water is 4.0% with aluminum sulfate, of which the added amount corresponds to the stoichiometric condition for the formation of ettringite (Ca:Al:SO4 2- = 6:2:3). The heat-treated ettringite-enriched PAdeCS also showed higher boron removal performances compared with untreated PAdeCS. The dependency of the boron removal capacity on the aqueous boron concentration can be expressed by the Langmuir equation for all the cases. The maximum capacity (q m) values were 1.83, 3.39, and 3.02 mg/g-solid for adsorption with untreated PAdeCS, adsorption with heat-treated ettringite-enriched PAdeCS, and coagulation-sedimentation, respectively. These capacities were higher or comparable with the ones reported in the literature.