title: A novel nonsense mutation in the APTX gene associated with delayed DNA single-strand break removal fails to enhance sensitivity to different genotoxic agents.
abstract: APTX is the gene involved in ataxia with oculomotor apraxia type 1 (AOA1), a recessive disorder with early-onset cerebellar ataxia, oculomotor apraxia and peripheral neuropathy. The encoded protein, aprataxin, is a DNA repair protein processing the products of abortive ligations, 5'-adenylated DNA. We describe a novel nonsense mutation in APTX, c.892C>T (p.Gln298X), segregating in two AOA1 patients and leading to the loss of aprataxin protein in patient's cells. These cells, while exhibiting reduced catalase activity, are not hypersensitive to toxicity elicited by H(2)O(2) exposure at either physiologic or ice-bath temperature. On the other hand, the rate of repair of DNA single-strand-breaks (SSBs) induced in both conditions is always significantly slower in AOA1 cells. By using the alkylating agent methyl methane sulphonate (MMS) we confirmed the association of the APTX mutation with a DNA repair defect in the absence of detectable changes in susceptibility to toxicity. These results, while consistent with a role of aprataxin in the repair of SSBs induced by H(2)O(2), or MMS, demonstrate that other mechanisms may be recruited in AOA1 cells to complete the repair process, although at a slower rate. Lack of hypersensitivity to the oxidant, or MMS, also implies that delayed repair is not per se a lethal event.
authors.affiliation: E. Medea Scientific Institute, Laboratory of Molecular Biology, Bosisio Parini, Italy.
authors.forename: Claudia
authors.initials: C
authors.lastname: Crimella
authors.forename: Orazio
authors.initials: O
authors.lastname: Cantoni
authors.forename: Andrea
authors.initials: A
authors.lastname: Guidarelli
authors.forename: Chiara
authors.initials: C
authors.lastname: Vantaggiato
authors.forename: Andrea
authors.initials: A
authors.lastname: Martinuzzi
authors.forename: Mara
authors.initials: M
authors.lastname: Fiorani
authors.forename: Catia
authors.initials: C
authors.lastname: Azzolini
authors.forename: Genny
authors.initials: G
authors.lastname: Orso
authors.forename: Nereo
authors.initials: N
authors.lastname: Bresolin
authors.forename: Maria Teresa
authors.initials: MT
authors.lastname: Bassi
mesh_terms: D001072:Apraxias / Q000235:genetics; D001260:Ataxia Telangiectasia / Q000235:genetics; D001483:Base Sequence; D002524:Cerebellar Ataxia / Q000151:congenital; D018389:Codon, Nonsense / Q000235:genetics*; D004247:DNA / Q000235:genetics / Q000378:metabolism; D053904:DNA Breaks, Single-Stranded; D004249:DNA Damage / Q000235:genetics; D004260:DNA Repair; D004268:DNA-Binding Proteins / Q000235:genetics*; D006801:Humans; D006861:Hydrogen Peroxide / Q000633:toxicity; D034141:Hypoalbuminemia / Q000235:genetics; D008741:Methyl Methanesulfonate / Q000633:toxicity; D009153:Mutagens / Q000633:toxicity*; D009687:Nuclear Proteins / Q000235:genetics*; D016877:Oxidants / Q000633:toxicity; D010375:Pedigree; D013132:Spinocerebellar Degenerations / Q000235:genetics
chemical_list: C438188:APTX protein, human; D018389:Codon, Nonsense; D004268:DNA-Binding Proteins; D009153:Mutagens; D009687:Nuclear Proteins; D016877:Oxidants; D004247:DNA; D008741:Methyl Methanesulfonate; D006861:Hydrogen Peroxide