Compared with controls, nuclear DNA damage response was higher (P ≤ 0.001) in diabetic subjects with increased accumulation of phospho-ataxia-telangiectasia (ATM), γ-H2AX, along with active recruitment of repair proteins (Mre11, Rad50, and Nbs1).
These include members of the Mre11 complex (Mre11/Rad50/Nbs1) and ataxia-telangiectasia (A-T) mutated (ATM), mutated in the human genetic disorder A-T.
In particular, defects in the DNA damage sensor, the Mre11-RAD50-NBS1 complex, also lead to syndromes with neurological deficits and overlapping phenotypes to A-T.
Therefore, the pleiotropic A-T-related systemic and cellular defects observed in NBS1m/m mice are due to the disruption of the adapter function of NBS1 in mediating ATM activities.
Other "A-T variants" include: (1) Nijmegen breakage syndrome (NBS) or nibrin/Nbs1 deficiency, with microcephaly and mental retardation but without ataxia, apraxia, or telangiectasia, and 2) A-T(Fresno), a phenotype that combines features of both NBS and A-T, with mutations in the ATM gene.
The complex containing the Mre11, Rad50, and Nbs1 proteins (MRN) is essential for the cellular response to DNA double-strand breaks, integrating DNA repair with the activation of checkpoint signaling through the protein kinase ATM (ataxia telangiectasia mutated).
Ataxia-Telangiectasia (A-T) and Nijmegen breakage syndrome (NBS) are recessive genetic diseases with similar cellular phenotypes that are caused by mutations in the recently described ATM (encoding ATM) and NBS1 (encoding p95) genes, respectively.
The similarities and differences in cellular phenotype between irradiated NBS and AT cells are discussed in terms of the functional properties of the signaling pathways downstream of AT involving the NBS1 and TP53 proteins.
Ionizing radiation activates the ataxia telangiectasia kinase (ATM)-dependent and NBS1-dependent phosphorylation of FANCD2, resulting in an S-phase checkpoint.
Mutations of the ATM and NBS1 genes are responsible for the inherited Ataxia-Telangiectasia and Nijmegen Breakage Syndrome, both of which are associated with a predisposition to cancer.