Sequence-selective depurination, DNA interstrand cross-linking and DNA strand break formation associated with alkylated DNA.
Sequence-selective depurination, DNA interstrand cross-linking and DNA strand break formation associated with alkylated DNA.
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DOI：
10.1093/carcin/13.3.425
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发表时间：
1992-03
期刊：
影响因子：
4.7
通讯作者：
A. S. Prakash;N. Gibson
中科院分区：
文献类型：
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作者：
A. S. Prakash;N. Gibson
DNA被氯乙基亚硝基脲（CNU）在鸟嘌呤N7位置的烷基化已被证明以序列选择性方式发生。在这份报告中，我们发现，这些烷基化位点的脱嘌呤发生两个不同的动力学组件-GG序列脱嘌呤30分钟内暴露于CNU，而脱嘌呤在GT序列是第一次观察到1小时后，并继续增加16小时后药物暴露。这些脱嘌呤位点转化为DNA链断裂，并构成鸟嘌呤N7烷基化的总位点的不到10%。发现亚精胺减少5 '-GG-3'序列中的烷基化，但增加5 '-GTC-3'序列中的烷基化。这些发现表明，大多数由CNU形成的鸟嘌呤N7烷基化是稳定的，与一个次要的加合物负责缓慢的脱嘌呤事件。我们建议，由CNU诱导的快速脱嘌呤发生从初始鸟嘌呤O 6烷基化，然后通过鸟嘌呤O 6-N7环化中间体脱嘌呤。我们还建议，由此产生的脱嘌呤位点可能会导致DNA链间交联（ISC）。为了支持这些假设，我们证明：（i）用单烷基化剂硫酸二甲酯修饰的DNA在脱嘌呤后形成DNA ISC;（ii）鞣花酸增强鸟嘌呤N7烷基化的水平，并改变三种双官能氯乙基化剂CNU、米托唑胺和甲基3-羟乙基化酶所显示的序列选择性模式。（2-氯乙基）-4-氧代咪唑并[5，1-d]-1，2，3，5-四嗪-8-羧酸酯，但不与氮芥反应;（iii）鞣花酸对用单官能烷基化剂N-甲基-N-亚硝基脲、N-乙基-N-亚硝基脲和甲磺酸甲酯观察到的烷基化频率没有影响;（iv）鞣花酸增加CNU诱导的脱嘌呤和链断裂形成的频率，而不影响脱嘌呤的序列选择性模式。
Alkylation of DNA by chloroethylnitrosourea (CNU) at the guanine N7 position has been shown to occur in a sequence-selective fashion. In this report we find that the depurination of these alkylated sites occurs with two distinct kinetic components--GG sequences depurinate within 30 min of exposure to CNU, while depurination at GT sequences is first observed after 1 h and continues to increase 16 h after drug exposure. These apurinic sites are converted to DNA strand breaks and constitute less than 10% of the total sites of guanine N7 alkylation. Spermidine was found to decrease alkylation in 5'-GG-3' sequences but increases alkylation at 5'-GTC-3' sequences. These findings suggest that the majority of the guanine N7 alkylations formed by CNU are stable, with a minor adduct being responsible for the slow depurination event. We propose that the rapid depurination induced by CNU occurs from an initial guanine O6 alkylation, which then depurinates via a guanine O6-N7 cyclized intermediate. We also propose that the resulting apurinic sites may lead to DNA interstrand cross-linking (ISC). In support of these hypotheses we show that (i) DNA modified with the monoalkylating agent dimethylsulfate forms DNA ISC upon depurination; (ii) ellagic acid enhances the level of guanine N7 alkylation and alters the pattern of sequence selectivity shown by three bifunctional chloroethylating agents CNU, mitozolomide and methyl 3-(2-chloroethyl)-4-oxoimidazo[5,1-d]-1,2,3,5-tetrazine-8-ca rboxylate but not with nitrogen mustard; (iii) ellagic acid has no effect upon the frequency of alkylation observed with the monofunctional alkylators N-methyl-N-nitrosourea, N-ethyl-N-nitrosourea and methylmethanesulfonate; (iv) ellagic acid increases the frequency of depurination and strand break formation induced by CNU without affecting the sequence-selective pattern of depurination.