title: Involvement of the drug efflux protein TolC in mutagenicity induced by MNNG or Trp-P-2.
abstract: In the development of mutation assay systems, a number of approaches have been performed with a particular view to improve sensitivity. The inhibition of mutagen-efflux from tester bacteria might lead to increased mutagenic activity as the concentration of mutagen increases inside the cell. In this study, we constructed a series of Escherichia coli CC strains lacking the TolC protein to determine if mutation is actually enhanced by the inhibition of mutagen reflux. TolC is an outer-membrane protein that forms part of an excretion system in E. coli. The frequency of induction of mutations by N-methyl-N'-nitro-N-nitrosoguanidine (MNNG), N-ethyl-N'-nitro-N-nitrosoguanidine (ENNG) and ethyl methanesulfonate (EMS) were significantly higher in TolC-deficient strain KA796-1/CC102 than in TolC-proficient strains, especially that of MNNG was seven times higher and detected at lower doses than in the parent strain. In a KA796-1/CC108 TolC-deficient strain, mutation induced by Trp-P-2 was detected at significant levels, even at low doses that did not induce detectable levels of mutation in the parent strain KA796/CC108. When the wild-type E. coli tolC gene was introduced into a strain lacking the gene, TolC function was restored and the frequency of induction by MNNG became similar to that of the wild-type. In contrast, introduction of a mutant tolC gene did not complement the TolC deficiency and the frequency of MNNG-induced mutations remained high. These results suggest that some mutagens are excreted at least in part via the TolC system, and that the lack of functional TolC increases the susceptibility of bacteria to many mutagens.
authors.affiliation: Faculty of Pharmaceutical Sciences, Okayama University, Tsushima, Okayama 700-8530, Japan.
authors.forename: Eizo
authors.initials: E
authors.lastname: Takahashi
authors.forename: Keinosuke
authors.initials: K
authors.lastname: Okamoto
authors.forename: Sakae
authors.initials: S
authors.lastname: Arimoto
authors.forename: Hiroyasu
authors.initials: H
authors.lastname: Yamanaka
authors.forename: Tomoe
authors.initials: T
authors.lastname: Negishi
mesh_terms: D001425:Bacterial Outer Membrane Proteins / Q000235:genetics*; D001692:Biological Transport; D002243:Carbolines / Q000633:toxicity; D004926:Escherichia coli / Q000187:drug effects / Q000235:genetics* / Q000378:metabolism; D029968:Escherichia coli Proteins / Q000235:genetics*; D005020:Ethyl Methanesulfonate / Q000633:toxicity; D017353:Gene Deletion; D015870:Gene Expression; D005816:Genetic Complementation Test; D026901:Membrane Transport Proteins / Q000172:deficiency / Q000235:genetics*; D008769:Methylnitronitrosoguanidine / Q000031:analogs & derivatives* / Q000633:toxicity*; D009152:Mutagenicity Tests / Q000592:standards; D009153:Mutagens / Q000633:toxicity*
chemical_list: D001425:Bacterial Outer Membrane Proteins; D002243:Carbolines; D029968:Escherichia coli Proteins; D026901:Membrane Transport Proteins; D009153:Mutagens; C073126:tolC protein, E coli; D008769:Methylnitronitrosoguanidine; C013525:ENNG; C019133:3-amino-1-methyl-5H-pyrido(4,3-b)indole; D005020:Ethyl Methanesulfonate