title: High frequency of genomic deletions induced by Me-lex, a sequence selective N3-adenine methylating agent, at the Hprt locus in Chinese hamster ovary cells.
abstract: We have investigated the mutagenicity induced at the Hprt locus in Chinese hamster ovary (CHO) cells treated with increasing concentrations of Me-lex, a minor groove selective methylating agent that efficiently generates more than 90-95% of 3-MeA DNA adducts. Me-lex treatment was cytotoxic but weakly mutagenic, resulting in up to 7-fold induction above background in the Hprt mutation frequency. The molecular nature of 43 Hprt mutations induced by Me-lex was determined by sequence analysis of the Hprt cDNA and genomic analysis of the gene locus. Base pair substitutions represented about 25% of Me-lex induced mutations. The mutation spectrum revealed a high percentage of genomic deletions (51%) comprising single/multiple exon(s) and even the loss of the complete locus. When the distribution of mutations among different classes was considered, the difference between the spontaneous and Me-lex induced CHO spectra was statistically significant (p<0.012), indicating that the sites where mutations occurred were Me-lex specific. Based upon these results we hypothesize that a large proportion of mutations may result from the processing of 3-MeA, the main adduct induced by Me-lex, within A/T rich sequences in non-coding regions of the Hprt gene. The processing of these lesions by DNA polymerases could result in recombination and genomic deletions, thus representing a severe threat for genome integrity.
authors.affiliation: Molecular Mutagenesis and DNA Repair Unit, Department of Epidemiology and Prevention, National Cancer Research Institute (IST), L.go R. Benzi, 10, 16132 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: 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 / Q000494:pharmacology; D000818:Animals; D001483:Base Sequence; D016466:CHO Cells; D006224:Cricetinae; D003412:Cricetulus; D019175:DNA Methylation; D007041:Hypoxanthine Phosphoribosyltransferase / Q000235:genetics; D009153:Mutagens; D017384:Sequence Deletion
chemical_list: D009153:Mutagens; C025946:3-methyladenine; D007041:Hypoxanthine Phosphoribosyltransferase; D000225:Adenine