Slow repair of bulky DNA adducts along the nontranscribed strand of the human p53 gene may explain the strand bias of transversion mutations in cancers
Slow repair of bulky DNA adducts along the nontranscribed strand of the human p53 gene may explain the strand bias of transversion mutations in cancers
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DOI：
10.1038/sj.onc.1201647
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发表时间：
1998-03-12
期刊：
影响因子：
8
通讯作者：
Tang, MS
中科院分区：
文献类型：
--
作者：
Denissenko, MF;Pao, A;Tang, MS
利用UvrABC切割结合连接介导的聚合酶链式反应(LMPCR)，我们已经证明沿着人p53基因的非转录链形成苯并(A)芘二醇环氧化物(BPDE)加合物具有高度的选择性；优先结合的位置与在人类肺癌中发现的主要突变热点一致。序列依赖的加合物的形成和修复都可能对肿瘤组织中的这些突变热点起作用。为了测试这种可能性，我们扩展了我们之前的研究，绘制了P53基因转录链中BPDE加合物的分布，并量化了正常人类成纤维细胞中该基因两条DNA链的单个外显子5、7和8受损碱基的修复率。我们发现：(I)在两条链上，BPDE加合物优先在CpG序列上形成，(Ii)在转录的DIVA链中BPDE加合物的修复始终快于非转录链中加合物的修复，而非转录链中主要损伤热点(密码子157、248和273处的鸟嘌呤)的修复速度比其他损伤位置的修复速度慢两到四倍。这些结果有力地表明，优先加合物形成和缓慢修复都导致了157、248和273密码子突变的热点，而大量加合物修复的链偏向是在人类癌症中观察到的P53基因G到T颠换突变的链偏向的主要原因。
Using UvrABC incision in combination with ligation-mediated PCR (LMPCR) we have previously shown that benzo(a)pyrene diol epoxide (BPDE) adduct formation along the nontranscribed strand of the human p53 gene is highly selective; the preferential binding sites coincide with the major mutation hotspots found in human lung cancers. Both sequence-dependent adduct formation and repair may contribute to these mutation hotspots in tumor tissues. To test this possibility, we have extended our previous studies by mapping the BPDE adduct distribution in the transcribed strand of the p53 gene and quantifying the rates of repair for individual damaged bases in exons 5, 7, and 8 for both DNA strands of this gene in normal human fibroblasts. We found that: (i) on both strands, BPDE adducts preferentially form at CpG sequences, and (ii) repair of BPDE adducts in the transcribed DIVA strand is consistently faster than repair of adducts in the nontranscribed strand, while repair at the major damage hotspots (guanines at codons 157, 248 and 273) in the nontranscribed strand is two to four times slower than repair at other damage sites. These results strongly suggest that both preferential adduct formation and slow repair lead to hotspots for mutations at codons 157, 248 and 273, and that the strand bias of bulky adduct repair is primarily responsible for the strand bias of G to T transversion mutations observed in the p53 gene in human cancers.