Mutator Phenotype and DNA Double-Strand Break Repair in BLM Helicase-Deficient Human Cells.
Mutator Phenotype and DNA Double-Strand Break Repair in BLM Helicase-Deficient Human Cells.
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BLM解旋酶缺陷型人类细胞中的突变器表型和DNA双链破裂修复。
DOI：
10.1128/mcb.00443-16
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发表时间：
2016-12-01
影响因子：
5.3
通讯作者：
Honma M
中科院分区：
文献类型：
--
作者：
Suzuki T;Yasui M;Honma M
Bloom综合征（BS）是一种BLM基因的常染色体隐性遗传疾病，易患各种癌症。为了研究BS细胞中DNA双链断裂（DSB）的突变表型和遗传后果，我们通过破坏BLM基因开发了BLM解旋酶缺陷的人类细胞。由于同源重组（HR）或非同源末端连接（NHEJ）而具有杂合性缺失（洛）的细胞可以在有或没有定点DSB诱导的情况下恢复。BLM细胞表现出高频率的自发等位基因间HR与交叉，但也发生了非交叉事件与长道基因转换。尽管存在高度等位基因间HR事件，但BLM细胞主要通过自发缺失产生半合子洛。这些表型在DSB修复过程中表现出来。NHEJ和HR均适当修复BLM细胞中的DSB，分别导致半合子和纯合子LOH。然而，洛缺失的程度在BLM细胞中加剧，如大的缺失和长链基因转换与交叉所证明的。BLM解旋酶抑制HR修复过程中分支迁移的延长和双霍利迪连接（HJs）的交叉，并且该酶的缺陷导致双HJs的塌陷、异常延长和/或优选的对交叉的解析，从而导致大规模的洛缺失。这种机制是BS中癌症易感性的基础。
Bloom syndrome (BS), an autosomal recessive disorder of the BLM gene, predisposes sufferers to various cancers. To investigate the mutator phenotype and genetic consequences of DNA double-strand breaks (DSBs) in BS cells, we developed BLM helicase-deficient human cells by disrupting the BLM gene. Cells with a loss of heterozygosity (LOH) due to homologous recombination (HR) or nonhomologous end joining (NHEJ) can be restored with or without site-directed DSB induction. BLM cells exhibited a high frequency of spontaneous interallelic HR with crossover, but noncrossover events with long-tract gene conversions also occurred. Despite the highly interallelic HR events, BLM cells predominantly produced hemizygous LOH by spontaneous deletion. These phenotypes manifested during repair of DSBs. Both NHEJ and HR appropriately repaired DSBs in BLM cells, resulting in hemizygous and homozygous LOHs, respectively. However, the magnitude of the LOH was exacerbated in BLM cells, as evidenced by large deletions and long-tract gene conversions with crossover. BLM helicase suppresses the elongation of branch migration and crossover of double Holliday junctions (HJs) during HR repair, and a deficiency in this enzyme causes collapse, abnormal elongation, and/or preferable resolution to crossover of double HJs, resulting in a large-scale LOH. This mechanism underlies the predisposition for cancer in BS.