Loss of Bloom syndrome protein destabilizes human gene cluster architecture
Loss of Bloom syndrome protein destabilizes human gene cluster architecture
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DOI：
10.1093/hmg/ddp282
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发表时间：
2009-09-15
影响因子：
3.5
通讯作者：
Pierce, Andrew J.
中科院分区：
文献类型：
--
作者：
Killen, Michael W.;Stults, Dawn M.;Pierce, Andrew J.
布鲁姆综合征在多种组织类型中具有很强的恶性肿瘤倾向。Bloom综合征患者（BLM）蛋白在该疾病中作为Holliday连接溶解酶的生化功能缺陷，缺乏功能性BLM的人类细胞显示出10倍的姐妹染色单体交换率升高。总的来说，这些现象表明，有丝分裂重组失调驱动了这些个体癌症发展的基因组不稳定性。在这里，我们使用物理分析高度重复，高度自相似的人类核糖体RNA基因簇作为失调同源重组的前哨生物标志物，以证明BLM蛋白功能的丧失导致自发分子水平基因组重组的显著增加。对野生型人细胞系衍生的单细胞亚克隆群体的分析表明，基因簇结构通常在有丝分裂中非常忠实地保存下来，但在BLMs衍生的细胞系中，基因簇结构非常不稳定，以至于不同亚克隆群体的基因簇结构基本上无法相互识别。不同的RecQ解旋酶（WRN蛋白与早衰Werner综合征有关）缺陷的人类细胞不表现出基因簇不稳定性（GCI）表型，这表明BLM蛋白特异性地抑制了这种重组介导的基因组不稳定性，而不是一般的RecQ解旋酶。共济失调-毛细血管扩张缺陷细胞系也显示rDNA GCI升高，尽管没有达到BLM缺陷细胞的程度。人类基因组中大量低拷贝重复序列之间的重组失调介导的基因组重组可能被证明是驱动人类癌症发生和发展的基因组不稳定的重要附加机制。
Bloom syndrome confers strong predisposition to malignancy in multiple tissue types. The Bloom syndrome patient (BLM) protein defective in the disease biochemically functions as a Holliday junction dissolvase and human cells lacking functional BLM show 10-fold elevated rates of sister chromatid exchange. Collectively, these phenomena suggest that dysregulated mitotic recombination drives the genomic instability underpinning the development of cancer in these individuals. Here we use physical analysis of the highly repeated, highly self-similar human ribosomal RNA gene clusters as sentinel biomarkers for dysregulated homologous recombination to demonstrate that loss of BLM protein function causes a striking increase in spontaneous molecular level genomic restructuring. Analysis of single-cell derived sub-clonal populations from wild-type human cell lines shows that gene cluster architecture is ordinarily very faithfully preserved under mitosis, but is so unstable in cell lines derived from BLMs as to make gene cluster architecture in different sub-clonal populations essentially unrecognizable one from another. Human cells defective in a different RecQ helicase, the WRN protein involved in the premature aging Werner syndrome, do not exhibit the gene cluster instability (GCI) phenotype, indicating that the BLM protein specifically, rather than RecQ helicases generally, holds back this recombination-mediated genomic instability. An ataxia-telangiectasia defective cell line also shows elevated rDNA GCI, although not to the extent of BLM defective cells. Genomic restructuring mediated by dysregulated recombination between the abundant low-copy repeats in the human genome may prove to be an important additional mechanism of genomic instability driving the initiation and progression of human cancer.