title: Sublethal doses of β-amyloid peptide abrogate DNA-dependent protein kinase activity.
abstract: Accumulation of DNA damage and deficiency in DNA repair potentially contribute to the progressive neuronal loss in neurodegenerative disorders, including Alzheimer disease (AD). In multicellular eukaryotes, double strand breaks (DSBs), the most lethal form of DNA damage, are mainly repaired by the nonhomologous end joining pathway, which relies on DNA-PK complex activity. Both the presence of DSBs and a decreased end joining activity have been reported in AD brains, but the molecular player causing DNA repair dysfunction is still undetermined. β-Amyloid (Aβ), a potential proximate effector of neurotoxicity in AD, might exert cytotoxic effects by reactive oxygen species generation and oxidative stress induction, which may then cause DNA damage. Here, we show that in PC12 cells sublethal concentrations of aggregated Aβ(25-35) inhibit DNA-PK kinase activity, compromising DSB repair and sensitizing cells to nonlethal oxidative injury. The inhibition of DNA-PK activity is associated with down-regulation of the catalytic subunit DNA-PK (DNA-PKcs) protein levels, caused by oxidative stress and reversed by antioxidant treatment. Moreover, we show that sublethal doses of Aβ(1-42) oligomers enter the nucleus of PC12 cells, accumulate as insoluble oligomeric species, and reduce DNA-PK kinase activity, although in the absence of oxidative stress. Overall, these findings suggest that Aβ mediates inhibition of the DNA-PK-dependent nonhomologous end joining pathway contributing to the accumulation of DSBs that, if not efficiently repaired, may lead to the neuronal loss observed in AD.
authors.affiliation: Istituto di Ricovero e Cura a Carattere Scientifico San Raffaele Pisana, Rome 00166, Italy.
authors.forename: Alessio
authors.initials: A
authors.lastname: Cardinale
authors.forename: Mauro
authors.initials: M
authors.lastname: Racaniello
authors.forename: Serena
authors.initials: S
authors.lastname: Saladini
authors.forename: Giovanna
authors.initials: G
authors.lastname: De Chiara
authors.forename: Cristiana
authors.initials: C
authors.lastname: Mollinari
authors.forename: Maria Chiara
authors.initials: MC
authors.lastname: de Stefano
authors.forename: Maurizio
authors.initials: M
authors.lastname: Pocchiari
authors.forename: Enrico
authors.initials: E
authors.lastname: Garaci
authors.forename: Daniela
authors.initials: D
authors.lastname: Merlo
mesh_terms: D000544:Alzheimer Disease / Q000235:genetics / Q000378:metabolism; D016229:Amyloid beta-Peptides / Q000494:pharmacology*; D000818:Animals; D053903:DNA Breaks, Double-Stranded / Q000187:drug effects*; D004260:DNA Repair / Q000187:drug effects*; D051747:DNA-Activated Protein Kinase / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D009687:Nuclear Proteins / Q000235:genetics / Q000378:metabolism*; D018384:Oxidative Stress; D016716:PC12 Cells; D055503:Protein Multimerization; D051381:Rats
chemical_list: D016229:Amyloid beta-Peptides; D009687:Nuclear Proteins; D051747:DNA-Activated Protein Kinase; C497263:PRKDC protein, human