AlkB influences the chloroacetaldehyde-induced mutation spectra and toxicity in the pSP189 supF shuttle vector.
2-Chloroacetaldehyde (CAA), a metabolite of the carcinogen vinyl chloride, reacts with DNA to form cyclic etheno ()-lesions. AlkB, an iron-/alpha-ketoglutarate-dependent dioxygenase, repairs 1, N (6)-ethenodeoxyadenosine (A) and 3, N (4)-ethenodeoxycytidine (C) in site-specifically modified single-stranded viral genomes in vivo and also protects the E. coli genome from the toxic effects of CAA. We examined the role of AlkB as a cellular defense against CAA by characterizing the frequencies, types, and distributions of mutations induced in the double-stranded supF gene of pSP189 damaged in vitro and replicated in AlkB-proficient (AlkB (+)) and AlkB-deficient (AlkB (-)) E. coli. AlkB reduced mutagenic potency and increased the survival of CAA-damaged plasmids. Toxicity and mutagenesis data were benchmarked to levels of -adducts and DNA strand breaks measured by LC-MS/MS and a plasmid nicking assay. CAA treatment caused dose-dependent increases in A, C, and 1, N (2)-ethenodeoxyguanosine (1, N (2)-G) and small increases in strand breaks and abasic sites. Mutation frequency increased in plasmids replicated in both AlkB (+) and AlkB (-) cells; however, at the maximum CAA dose, the mutation frequency was 5-fold lower in AlkB (+) than in AlkB (-) cells, indicating that AlkB protected the genome from CAA lesions. Most induced mutations in AlkB (-) cells were G:C to A:T transitions, with lesser numbers of G:C to T:A transversions and A:T to G:C transitions. G:C to A:T and A:T to G:C transitions were lower in AlkB (+) cells than in AlkB (-) cells. Mutational hotspots at G122, G123, and G160 were common to both cell types. Three additional hotspots were found in AlkB (-) cells (C133, T134, and G159), with a decrease in mutation frequency and change in mutational signature in AlkB (+) cells. These results suggest that the AlkB protein contributes to the elimination of exocyclic DNA base adducts, suppressing the toxic and mutagenic consequences induced by this damage and contributing to genetic stability.
Department of Biological Engineering, Center for Environmental Health Sciences, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, MA 02139, USA.
Min Young
MY
Kim
Xinfeng
X
Zhou
James C
JC
Delaney
Koli
K
Taghizadeh
Peter C
PC
Dedon
John M
JM
Essigmann
Gerald N
GN
Wogan
D000079:Acetaldehyde / Q000031:analogs & derivatives / Q000494:pharmacology; D001483:Base Sequence; D002853:Chromatography, Liquid; D004249:DNA Damage / Q000187:drug effects* / Q000502:physiology; D004252:DNA Mutational Analysis; D004269:DNA, Bacterial / Q000187:drug effects*; D004305:Dose-Response Relationship, Drug; D004926:Escherichia coli / Q000235:genetics; D029968:Escherichia coli Proteins / Q000494:pharmacology*; D016153:Genes, Suppressor; D005822:Genetic Vectors; D016678:Genome; D013058:Mass Spectrometry; D006899:Mixed Function Oxygenases / Q000494:pharmacology*; D008969:Molecular Sequence Data; D016296:Mutagenesis; D010957:Plasmids
D004269:DNA, Bacterial; D029968:Escherichia coli Proteins; C004656:chloroacetaldehyde; D006899:Mixed Function Oxygenases; C466427:AlkB protein, E coli; D000079:Acetaldehyde