Sage E, Le Doan T, Boyer V, Helland D E, Kittler L, Helene C, Moustacchi E
CNRS UA 1292, Institut Curie, Paris, France.
J Mol Biol. 1989 Sep 20;209(2):297-314. doi: 10.1016/0022-2836(89)90278-7.
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)
利用DNA测序方法研究了几种呋喃香豆素（包括3 - 乙氧羰基补骨脂素（3 - CPs）、8 - 甲氧基补骨脂素（8 - MOP）、5 - 甲氧基补骨脂素（5 - MOP）和白芷素）对DNA的光敏作用。3 - CPs诱导鸟嘌呤残基的光氧化，导致DNA中出现碱不稳定位点（通过热哌啶揭示），而8 - MOP、5 - MOP和白芷素则不会。当G位于GG双峰的5'侧时，会优先发生光氧化，这可能反映了在这种情况下G部分更容易接近。通过自由基（I型）和单线态氧（II型）起作用的机制都参与了3 - CPs对G残基的光氧化。光氧化的G残基的产生与光加合物的形成无关，单线态氧或自由基的清除剂不会抑制3 - CPs与DNA的光结合。这使我们提出，共价光加合物源自插入的激发敏化剂分子，而G的光氧化是通过涉及结合的3 - CPs的电子转移反应或通过向分子氧的能量转移产生的，从而产生随后与鸟嘌呤碱基反应的单线态氧。对这两种类型的DNA损伤进行定量分析表明，在我们的条件下，3 - CPs加紫外线在DNA中产生的体外光氧化G残基至少与光加合物的程度相同。一种小牛胸腺氧化还原内切酶，等同于大肠杆菌的内切酶III，对氧化性DNA损伤具有特异性，可识别并在光氧化G残基的位点切割DNA。该酶的切割程度与热哌啶观察到的程度相近，并随着激发氧物种寿命改变时产生的光氧化G残基数量而变化。氧化还原内切酶不会切割用8 - MOP、5 - MOP或白芷素加紫外线处理的DNA。大肠杆菌的外切酶III和内切酶IV也参与氧化性DNA损伤的修复，可将经3 - CPs处理的DNA的复制形式I转化为复制形式II。这表明这些酶识别的损伤是类脱嘌呤损伤。鉴于3 - CPs的低毒性和低致突变性，3 - CPs光动力效应诱导的DNA光氧化产物可能会被DNA修复系统有效处理。很明显，3 - CPs光诱导了几类DNA损伤，包括氧化损伤。（摘要截短至400字）
