title: Influences of base excision repair defects on the lethality and mutagenicity induced by Me-lex, a sequence-selective N3-adenine methylating agent.
abstract: Due to its minor groove selectivity, Me-lex preferentially generates N3-methyladenine (3-MeA) adducts in double-stranded DNA. We undertook a genetic approach in yeast to establish the influence of base excision repair (BER) defects on the processing of Me-lex lesions on plasmid DNA that harbors the p53 cDNA as target. We constructed a panel of isogenic strains containing a reporter gene to test p53 function and the following gene deletions: deltamag1, deltaapn1apn2, and deltaapn1apn2mag1. When compared with the wild-type strain, a decrease in survival was observed in deltamag1, deltaapn1apn2, and deltaapn1apn2mag1. The Me-lex-induced mutation frequency increased in the following order: wild type < deltamag1< deltaapn1apn2 = deltaapn1apn2mag1. A total of 77 mutants (23 in wild type, 31 in deltamag1, and 23 in deltaapn1apn2) were sequenced. Eighty-one independent mutations (24 in wild type, 34 in deltamag1, and 23 in deltaapn1apn2) were detected. The majority of base pair substitutions were AT-targeted in all strains (14/23, 61% in wild type; 20/34, 59%, in deltamag1; and 14/23, 61%, in deltaapn1apn2). The Mag1 deletion was associated with a significant decrease of GC > AT transitions when compared with both the wild-type and the AP endonuclease mutants. This is the first time that the impact of Mag1 and/or AP endonuclease defects on the mutational spectra caused by 3-MeA has been determined. The results suggest that 3-MeA is critical for Me-lex cytotoxicity and that its mutagenicity is slightly elevated in the absence of Mag1 glycosylase activity but significantly higher in the absence of AP endonuclease activity.
authors.affiliation: Mutagenesis Laboratory, National Cancer Research Institute (IST), L.go R. Benzi, 10, 16132-Genova, Italy.
authors.forename: Paola
authors.initials: P
authors.lastname: Monti
authors.forename: Paola
authors.initials: P
authors.lastname: Campomenosi
authors.forename: Yari
authors.initials: Y
authors.lastname: Ciribilli
authors.forename: Raffaella
authors.initials: R
authors.lastname: Iannone
authors.forename: Alberto
authors.initials: A
authors.lastname: Inga
authors.forename: Dharini
authors.initials: D
authors.lastname: Shah
authors.forename: Gina
authors.initials: G
authors.lastname: Scott
authors.forename: Philip A
authors.initials: PA
authors.lastname: Burns
authors.forename: Paola
authors.initials: P
authors.lastname: Menichini
authors.forename: Angelo
authors.initials: A
authors.lastname: Abbondandolo
authors.forename: Barry
authors.initials: B
authors.lastname: Gold
authors.forename: Gilberto
authors.initials: G
authors.lastname: Fronza
mesh_terms: D000225:Adenine / Q000378:metabolism; D001483:Base Sequence; D004247:DNA / Q000378:metabolism; D019175:DNA Methylation; D004260:DNA Repair / Q000187:drug effects; D018076:DNA, Complementary / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D017353:Gene Deletion; D016158:Genes, p53; D005822:Genetic Vectors; D006801:Humans; D007700:Kinetics; D008969:Molecular Sequence Data; D016296:Mutagenesis; D009153:Mutagens; D009429:Netropsin / Q000031:analogs & derivatives*; D010957:Plasmids / Q000378:metabolism; D011401:Promoter Regions, Genetic
chemical_list: D018076:DNA, Complementary; D009153:Mutagens; C110963:methyl lexitropsin; D009429:Netropsin; D004247:DNA; D000225:Adenine