title: XRCC1 deficiency influences the cytotoxicity and the genomic instability induced by Me-lex, a specific inducer of N3-methyladenine.
abstract: Me-lex is a sequence-specific alkylating agent synthesized to preferentially (>90%) generate N3-methyladenine (3-mA) in the minor groove of double-strand DNA, in A-T rich regions. In this paper we investigated the effect of XRCC1 deficiency in the processing of 3-mA adducts generated by Me-lex, through the molecular analysis of the Hprt mutations and the evaluation of cytogenetic end points such as sister chromatid exchanges (SCEs), micronuclei (MN) and nucleus fragmentation. EM-C11 cells, deficient in XRCC1 activity, showed a 2.5-fold higher sensitivity to the toxicity of Me-lex compared to the DNA repair proficient parental CHO-9 cells, but were not hyper mutable. The spontaneous mutation spectrum at the Hprt locus generated in EM-C11 cells revealed a high percentage of genomic deletions. After Me-lex treatment, the percentage of genomic deletions did not increase, but a class of mutations which appeared to target regulatory regions of the gene significantly increased (p=0.0277), suggesting that non-coding Hprt genomic sequences represent a strong target for the rare mutations induced by Me-lex. The number of SCEs per chromosome increased 3-fold above background in 50mucapital EM, Cyrillic Me-lex treated CHO-9 cells, while at higher Me-lex concentrations a sharp increase in the percentage of MN and fragmented nuclei was observed. In EM-C11 cells the background level of SCEs (0.939+/-0.182) was approximately 10-fold higher than in CHO-9 (0.129+/-0.027) and higher levels of multinucleated cells and MN were also found. In EM-C11, even low doses of Me-lex (25microM) led to a significant increase in genomic damage. These results indicate that XRCC1 deficiency can lead to genomic instability even in the absence of an exogenous genotoxic insult and low levels of Me-lex-induced lesions, i.e., 3-mA and/or a BER intermediate, can exacerbate this instability.
authors.affiliation: Department of Epidemiology and Prevention, National Cancer Research Institute, Genova, Italy.
authors.forename: Debora
authors.initials: D
authors.lastname: Russo
authors.forename: Gilberto
authors.initials: G
authors.lastname: Fronza
authors.forename: Laura
authors.initials: L
authors.lastname: Ottaggio
authors.forename: Paola
authors.initials: P
authors.lastname: Monti
authors.forename: Chiara
authors.initials: C
authors.lastname: Perfumo
authors.forename: Alberto
authors.initials: A
authors.lastname: Inga
authors.forename: Prema
authors.initials: P
authors.lastname: Iyer
authors.forename: Barry
authors.initials: B
authors.lastname: Gold
authors.forename: Paola
authors.initials: P
authors.lastname: Menichini
mesh_terms: D000225:Adenine / Q000031:analogs & derivatives / Q000378:metabolism; D000477:Alkylating Agents / Q000494:pharmacology*; D000818:Animals; D016466:CHO Cells; D006224:Cricetinae; D003412:Cricetulus; D004249:DNA Damage / Q000235:genetics*; D004268:DNA-Binding Proteins / Q000235:genetics*; D042822:Genomic Instability / Q000235:genetics*; D009153:Mutagens / Q000494:pharmacology*; D009429:Netropsin / Q000031:analogs & derivatives* / Q000494:pharmacology; D017384:Sequence Deletion; D000076105:X-ray Repair Cross Complementing Protein 1
chemical_list: D000477:Alkylating Agents; D004268:DNA-Binding Proteins; D009153:Mutagens; D000076105:X-ray Repair Cross Complementing Protein 1; C110963:methyl lexitropsin; C025946:3-methyladenine; D009429:Netropsin; D000225:Adenine
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