title: Cleavage of the BRCT tandem domains of nibrin by the 657del5 mutation affects the DNA damage response less than the Arg215Trp mutation.
abstract: The Nijmegen breakage syndrome (NBS) is a genetic disorder caused by mutations in NBN gene and characterized by chromosomal instability and hypersensitivity to ionizing radiations (IR). The N-terminus of nibrin (NBN) contains a tandem breast cancer 1 (BRCA1) carboxy-terminal (BRCT) domain that represents one of the major mediators of phosphorylation-dependent protein-protein interactions in processes related to cell cycle checkpoint and DNA repair functions. Patients with NBS compound heterozygous for the 657del5 hypomorphic mutation and for the Arg215Trp missense mutation (corresponding to the 643C>T gene mutation) display a clinical phenotype more severe than that of patients homozygous for the 657del5 mutation. Here, we show that both the 657del5 and Arg215Trp mutations, occurring within the tandem BRCT domains of NBN, although not altering the assembly of the MRE11/RAD50/NBN (MRN) complex, affect the MRE11 IR-induced nuclear foci (IRIF) formation and the DNA double-strand break (DSB) signaling via the phosphorylation of both ataxia-telangiectasia-mutated (ATM) kinase and ATM downstream targets (e.g., SMC1 and p53). Remarkably, data obtained indicate that the cleavage of the BRCT tandem domains of NBN by the 657del5 mutation affects the DNA damage response less than the Arg215Trp mutation. Indeed, the 70-kDa NBN fragment, arising from the 657del5 mutation, maintains the capability to interact with MRE11 and γ-H2AX and to form IRIF. Altogether, the role of the tandem BRCT domains of NBN in the localization of the MRN complex at the DNA DSB and in the activation of the damage response is highlighted.
authors.affiliation: Department of Biology, University Roma Tre, Roma, Italy.
authors.forename: Gina
authors.initials: G
authors.lastname: Mendez
authors.forename: Domenica
authors.initials: D
authors.lastname: Cilli
authors.forename: Francesco
authors.initials: F
authors.lastname: Berardinelli
authors.forename: Mara
authors.initials: M
authors.lastname: Viganotti
authors.forename: Paolo
authors.initials: P
authors.lastname: Ascenzi
authors.forename: Caterina
authors.initials: C
authors.lastname: Tanzarella
authors.forename: Antonio
authors.initials: A
authors.lastname: Antoccia
authors.forename: Alessandra
authors.initials: A
authors.lastname: di Masi
mesh_terms: D017766:Acid Anhydride Hydrolases; D064007:Ataxia Telangiectasia Mutated Proteins; D019313:BRCA1 Protein / Q000235:genetics*; D059447:Cell Cycle Checkpoints / Q000235:genetics; D018797:Cell Cycle Proteins / Q000235:genetics* / Q000378:metabolism; D002461:Cell Line, Transformed; D002868:Chromosomal Proteins, Non-Histone / Q000235:genetics / Q000378:metabolism; D053903:DNA Breaks, Double-Stranded; D045643:DNA Repair Enzymes / Q000235:genetics / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism; D015870:Gene Expression; D005838:Genotype; D006579:Heterozygote; D006720:Homozygote; D006801:Humans; D000076228:MRE11 Homologue Protein; D009154:Mutation; D049932:Nijmegen Breakage Syndrome / Q000235:genetics* / Q000378:metabolism / Q000473:pathology; D009687:Nuclear Proteins / Q000235:genetics* / Q000378:metabolism; D010641:Phenotype; D010766:Phosphorylation; D017346:Protein Serine-Threonine Kinases / Q000235:genetics / Q000378:metabolism; D017434:Protein Structure, Tertiary; D015398:Signal Transduction; D016159:Tumor Suppressor Protein p53 / Q000235:genetics / Q000378:metabolism; D025521:Tumor Suppressor Proteins / Q000235:genetics / Q000378:metabolism; D000098550:Structural Maintenance of Chromosome Protein 1
chemical_list: D019313:BRCA1 Protein; C492913:BRCA1 protein, human; D018797:Cell Cycle Proteins; D002868:Chromosomal Proteins, Non-Histone; D004268:DNA-Binding Proteins; C121766:MRE11 protein, human; C112156:NBN protein, human; D009687:Nuclear Proteins; D016159:Tumor Suppressor Protein p53; D025521:Tumor Suppressor Proteins; D000098550:Structural Maintenance of Chromosome Protein 1; C576324:ATM protein, human; D064007:Ataxia Telangiectasia Mutated Proteins; D017346:Protein Serine-Threonine Kinases; D000076228:MRE11 Homologue Protein; D017766:Acid Anhydride Hydrolases; C112158:RAD50 protein, human; D045643:DNA Repair Enzymes