title: 3-Amino-1,4-dimethyl-5H-pyrido[4,3-b]indole (Trp-P-1) inhibits the binding activity of T4 endonuclease V to UV-damaged DNA.
abstract: 3-Amino-1,4-dimethyl-5H-pyrido[4,3-b]indole (Trp-P-1) is a mutagen/carcinogen derived from cooked foods which enhances the induction of mutations and chromosome aberrations by UV without microsomal activation. These co-mutagenic effects are considered to arise from inhibition of DNA excision repair at the incision step. However, the inhibition mechanism has not been clarified. In this study we show, using agarose gel electrophoresis, that Trp-P-1 inhibits incision by T4 endonuclease V, which cleaves DNA at the site of cyclobutane dimers. Trp-P-1 also inhibits the binding of this enzyme to UV-damaged DNA in a gel shift assay. In addition, the results of DNA unwinding assay with topoisomerase I suggest that Trp-P-1 intercalates into DNA molecules. The known intercalators ethidium bromide and acriflavine demonstrate similar effects in these experiments. However, 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP), which showed no co-mutagenic effects in our previous study, does not demonstrate such effects. These results suggest that Trp-P-1 changes DNA conformation by intercalation, causing inhibition of binding of repair enzymes to UV-damaged DNA, and this in turn leads to inhibition of DNA excision repair and to co-mutagenic effects.
authors.affiliation: School of Food and Nutritional Sciences, University of Shizuoka, Japan.
authors.forename: K
authors.initials: K
authors.lastname: Shimoi
authors.forename: R
authors.initials: R
authors.lastname: Miyamura
authors.forename: T
authors.initials: T
authors.lastname: Mori
authors.forename: T
authors.initials: T
authors.lastname: Todo
authors.forename: E
authors.initials: E
authors.lastname: Ohtsuka
authors.forename: K
authors.initials: K
authors.lastname: Wakabayashi
authors.forename: N
authors.initials: N
authors.lastname: Kinae
mesh_terms: D002243:Carbolines / Q000633:toxicity*; D004247:DNA / Q000378:metabolism* / Q000528:radiation effects*; D004249:DNA Damage; D004264:DNA Topoisomerases, Type I / Q000378:metabolism / Q000494:pharmacology; D004278:DNA, Superhelical / Q000187:drug effects; D043224:Deoxyribonuclease (Pyrimidine Dimer); D004706:Endodeoxyribonucleases / Q000037:antagonists & inhibitors* / Q000378:metabolism*; D004996:Ethidium / Q000494:pharmacology; D007093:Imidazoles / Q000494:pharmacology; D007364:Intercalating Agents / Q000633:toxicity*; D009153:Mutagens / Q000633:toxicity*; D009690:Nucleic Acid Conformation / Q000528:radiation effects; D011740:Pyrimidine Dimers / Q000378:metabolism; D014466:Ultraviolet Rays; D014764:Viral Proteins
chemical_list: D002243:Carbolines; D004278:DNA, Superhelical; D007093:Imidazoles; D007364:Intercalating Agents; D009153:Mutagens; D011740:Pyrimidine Dimers; D014764:Viral Proteins; D004247:DNA; C049584:2-amino-1-methyl-6-phenylimidazo(4,5-b)pyridine; D004706:Endodeoxyribonucleases; C470698:endonuclease V, phage T4; D043224:Deoxyribonuclease (Pyrimidine Dimer); D004264:DNA Topoisomerases, Type I; D004996:Ethidium; C019132:3-amino-1,4-dimethyl-5H-pyrido(4,3-b)indole