Z-DNA-forming sequences generate large-scale deletions in mammalian cells.
Z-DNA-forming sequences generate large-scale deletions in mammalian cells.
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DOI：
10.1073/pnas.0511084103
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发表时间：
2006-02
影响因子：
11.1
通讯作者：
Guliang Wang;Laura A. Christensen;K. Vasquez
中科院分区：
文献类型：
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作者：
Guliang Wang;Laura A. Christensen;K. Vasquez
自发性染色体断裂经常发生在基因组热点，在没有DNA损伤的情况下，并可能导致易位相关的人类疾病。在人类肿瘤中，染色体断裂点通常位于嘌呤-嘧啶Z-DNA形成序列附近。然而，尚不清楚Z-DNA是否在这些染色体断裂的产生中起作用。在这里，我们表明，Z-DNA形成序列在细菌和哺乳动物细胞中诱导高水平的遗传不稳定性。在哺乳动物细胞中，Z-DNA形成序列诱导附近的双链断裂，导致95%的突变体发生大规模缺失。哺乳动物细胞中的这些Z-DNA诱导的双链断裂并不局限于特定的序列，而是分散在400 bp的区域，与人类疾病中的染色体断裂点一致。这一观察结果与大肠杆菌中产生的突变相反，大肠杆菌中产生的突变主要是重复序列内的小缺失。我们发现，在哺乳动物细胞提取物中复制会增加小缺失的频率。令人惊讶的是，在哺乳动物细胞中产生的大规模缺失至少部分是不依赖复制的，并且可能是由Z-DNA形成序列周围的修复加工裂解引发的。这些结果表明，哺乳动物细胞处理Z-DNA形成序列的方式与细菌截然不同。我们的数据表明，Z-DNA形成序列可能是白血病和淋巴瘤中发现的基因易位的致病因素，某些细胞条件，如转录活跃可能会增加Z-DNA相关的遗传不稳定性的风险。
Spontaneous chromosomal breakages frequently occur at genomic hot spots in the absence of DNA damage and can result in translocation-related human disease. Chromosomal breakpoints are often mapped near purine-pyrimidine Z-DNA-forming sequences in human tumors. However, it is not known whether Z-DNA plays a role in the generation of these chromosomal breakages. Here, we show that Z-DNA-forming sequences induce high levels of genetic instability in both bacterial and mammalian cells. In mammalian cells, the Z-DNA-forming sequences induce double-strand breaks nearby, resulting in large-scale deletions in 95% of the mutants. These Z-DNA-induced double-strand breaks in mammalian cells are not confined to a specific sequence but rather are dispersed over a 400-bp region, consistent with chromosomal breakpoints in human diseases. This observation is in contrast to the mutations generated in Escherichia coli that are predominantly small deletions within the repeats. We found that the frequency of small deletions is increased by replication in mammalian cell extracts. Surprisingly, the large-scale deletions generated in mammalian cells are, at least in part, replication-independent and are likely initiated by repair processing cleavages surrounding the Z-DNA-forming sequence. These results reveal that mammalian cells process Z-DNA-forming sequences in a strikingly different fashion from that used by bacteria. Our data suggest that Z-DNA-forming sequences may be causative factors for gene translocations found in leukemias and lymphomas and that certain cellular conditions such as active transcription may increase the risk of Z-DNA-related genetic instability.