RESUMEN
Progressive accumulation of DNA damage is causally involved in cellular senescence and organismal aging. The DNA damage kinase ATM plays a central role in maintaining genomic stability. ATM mutations cause the genetic disorder ataxia telangiectasia, which is primarily characterized by progressive neurodegeneration and cancer susceptibility. Although the importance of ATM function to protect against oxidative DNA damage and during aging is well described, the mechanism of ATM activation by these stimuli is not known. Here we identify ATM interactor (ATMIN) as an essential component of the ATM signaling pathway in response to oxidative stress and aging. Embryos lacking ATMIN (atmin(Δ/Δ)) died in utero and showed increased numbers of cells positive for phosphorylated histone H2aX, indicative of increased DNA damage. atmin(Δ/Δ) mouse embryonic fibroblasts accumulated DNA damage and prematurely entered senescence when cultured at atmospheric oxygen levels (20%), but this defect was rescued by addition of an antioxidant and also by culturing cells at physiological oxygen levels (3%). In response to acute oxidative stress, atmin(Δ/Δ) mouse embryonic fibroblasts showed slightly lower levels of ATM phosphorylation and reduced ATM substrate phosphorylation. Conditional deletion of ATMIN in the murine nervous system (atmin(ΔN)) resulted in reduced numbers of dopaminergic neurons, as does ATM deficiency. ATM activity was observed in old, but not in young, control mice, but aging-induced ATM signaling was impaired by ATMIN deficiency. Consequently, old atmin(ΔN) mice showed accumulation of DNA damage in the cortex accompanied by gliosis, resulting in increased mortality of aging mutant mice. These results suggest that ATMIN mediates ATM activation by oxidative stress, and thereby ATMIN protects the aging brain by preventing accumulation of DNA damage.
Asunto(s)
Envejecimiento/metabolismo , Proteínas Portadoras/metabolismo , Proteínas de Ciclo Celular/metabolismo , Corteza Cerebral/metabolismo , Daño del ADN/fisiología , Proteínas de Unión al ADN/metabolismo , Proteínas Nucleares/metabolismo , Estrés Oxidativo/fisiología , Proteínas Serina-Treonina Quinasas/metabolismo , Proteínas Supresoras de Tumor/metabolismo , Envejecimiento/genética , Envejecimiento/patología , Animales , Antioxidantes/metabolismo , Proteínas de la Ataxia Telangiectasia Mutada , Proteínas Portadoras/genética , Proteínas de Ciclo Celular/genética , Células Cultivadas , Senescencia Celular/genética , Corteza Cerebral/embriología , Corteza Cerebral/patología , Proteínas de Unión al ADN/genética , Pérdida del Embrión/genética , Pérdida del Embrión/metabolismo , Pérdida del Embrión/patología , Embrión de Mamíferos/metabolismo , Embrión de Mamíferos/patología , Fibroblastos/metabolismo , Fibroblastos/patología , Histonas/genética , Histonas/metabolismo , Ratones , Ratones Mutantes , Neuronas/metabolismo , Neuronas/patología , Proteínas Nucleares/genética , Oxígeno/metabolismo , Fosforilación/genética , Proteínas Serina-Treonina Quinasas/genética , Factores de Transcripción , Proteínas Supresoras de Tumor/genéticaRESUMEN
Ataxia telangiectasia mutated (ATM) protein kinase activation by DNA double-strand breaks (DSBs) requires the Mre11-Rad50-NBS1 (MRN) complex, whereas ATM interactor (ATMIN) protein is required for ATM signaling induced by changes in chromatin structure. We show here that NBS1 and ATMIN proteins compete for ATM binding and that this mechanism controls ATM function. DSB-induced ATM substrate phosphorylation was increased in atmin mutant cells. Conversely, NBS1 deficiency resulted in increased ATMIN-dependent ATM signaling. Thus, the absence of one cofactor increased flux through the alternative pathway. Notably, ATMIN deficiency rescued the cellular lethality of NBS1-deficient cells, and NBS1/ATMIN double deficiency resulted in complete abrogation of ATM signaling and profound radiosensitivity. Hence, ATMIN and NBS1 mediate all ATM signaling by DSBs, and increased ATMIN-dependent ATM signaling explains the different phenotypes of nbs1- and atm-mutant cells. Thus, the antagonism and redundancy of ATMIN and NBS1 constitute a crucial regulatory mechanism for ATM signaling and function.