Oxidative DNA damage photo-induced by 3-carbethoxypsoralen and other furocoumarins. Mechanisms of photo-oxidation and recognition by repair enzymes.
DNA photosensitization by several furocoumarins (including 3-carbethoxypsoralen (3-CPs), 8-methoxypsoralen (8-MOP), 5-methoxypsoralen (5-MOP) and angelicin was investigated by using DNA sequencing methodology. 3-CPs induces photo-oxidation of guanine residues leading to alkali-labile sites in DNA (revealed by hot piperidine), whereas 8-MOP, 5-MOP and angelicin do not. There is a preferential photo-oxidation of G when located on the 5' side of GG doublets, likely to reflect a better accessibility of the G moiety in such a context. Mechanisms operating via both radicals (type I) and singlet oxygen (type II) are involved in the photo-oxidation of G residues by 3-CPs. Photo-oxidized G residues are produced independently of the formation of photoadducts, and scavengers of singlet oxygen or radicals do not inhibit photobinding of 3-CPs to DNA. This leads us to propose that covalent photoadducts arise from the intercalated excited sensitizer molecules, whereas G photo-oxidations are produced either by electron transfer reactions involving bound 3-CPs or by energy transfer to molecular oxygen, thereby producing singlet oxygen that subsequently reacts with guanine bases. Quantification of both types of DNA lesions indicated that in vitro photo-oxidized G residues are produced in DNA by 3-CPs plus ultraviolet light at least to the same extent as photoadducts, under our conditions. A calf thymus redoxyendonuclease, equivalent to the endonuclease III of Escherichia coli, specific for oxidative DNA damages, recognizes and cleaves DNA at sites of photo-oxidized G residues. The extent of the cleavage by this enzyme was close to that observed by hot piperidine and followed the amount of photo-oxidized G residues produced when the lifetime of excited oxygen species is modified. The redoxyendonuclease did not incise DNA treated with 8-MOP, 5-MOP or angelicin plus ultraviolet light. The exonuclease III and endonuclease IV of E. coli also involved in the repair of oxidative DNA damage, convert the replicative form I of 3-CPs-treated DNA to replicative form II. This suggests that the lesions recognized by these enzymes are apurinic-like lesions. In view of the low toxicity and mutagenicity of 3-CPs, DNA photo-oxidation products induced by the photodynamic effect of 3-CPs are likely to be efficiently taken care of by the DNA repair system(s). It is clear that 3-CPs photo-induces several classes of DNA damage, including oxidative damage.(ABSTRACT TRUNCATED AT 400 WORDS)
Sage
E
E
CNRS UA 1292, Institut Curie, Paris, France.
Le Doan
T
T
Boyer
V
V
Helland
D E
DE
Kittler
L
L
Helene
C
C
Moustacchi
E
E
D001483:Base Sequence; D004249:DNA Damage; D043603:DNA-(Apurinic or Apyrimidinic Site) Lyase; D043223:Deoxyribonuclease IV (Phage T4-Induced); D004706:Endodeoxyribonucleases; D004926:Escherichia coli; D029968:Escherichia coli Proteins; D005090:Exodeoxyribonucleases; D011564:Furocoumarins; D008027:Light; D008969:Molecular Sequence Data; D010084:Oxidation-Reduction; D010100:Oxygen; D010880:Piperidines
D029968:Escherichia coli Proteins; D011564:Furocoumarins; D010880:Piperidines; C032727:piperidine; C017104:3-carbethoxypsoralen; D004706:Endodeoxyribonucleases; D005090:Exodeoxyribonucleases; C020133:exodeoxyribonuclease III; D043223:Deoxyribonuclease IV (Phage T4-Induced); C468972:endonuclease IV, E coli; D043603:DNA-(Apurinic or Apyrimidinic Site) Lyase; D010100:Oxygen