Amplification of the human dihydrofolate reductase gene via double minutes is initiated by chromosome breaks
Amplification of the human dihydrofolate reductase gene via double minutes is initiated by chromosome breaks
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DOI：
10.1073/pnas.130194897
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发表时间：
2000-07-05
影响因子：
11.1
通讯作者：
Hamlin, JL
中科院分区：
文献类型：
--
作者：
Singer, MJ;Mesner, LD;Hamlin, JL
DNA序列扩增是人类肿瘤基因组不稳定性最常见的表现之一。我们之前已经证明，中国仓鼠细胞中二氢叶酸还原酶（DHFR）基因的扩增是由染色体断裂启动的，随后是产生大量染色体内重复的桥-断裂-融合循环；这些最终通过未知的过程修剪成更小、更同质的单位，表现为同质染色染色体区域（HSR）。然而，在大多数人类肿瘤细胞中，扩增的DNA序列承载在不稳定的染色体外双分钟（DM）上，这表明不同的扩增机制在运作。在这项研究中，我们分离出了大量独立的甲氨蝶呤抗性人类细胞系，所有这些细胞系都含有携带 DHFR 的 DM。令人惊讶的是，除了其中一个之外，所有这些细胞系都部分或完全丧失了亲本携带 DHFR 的染色体之一。少数细胞群中的细胞显示出扩增过程中可能存在的瞬时中间体，包括最初的 HSR、其随后的断裂、含有 DHFR 的片段的出现，以及最后的 DM。我们的研究表明，HSR 和 DM 都是由染色体断裂引发的，但细胞类型在额外序列最终如何处理和/或维持方面有所不同。
DNA sequence amplification is one of the most frequent manifestations of genomic instability in human tumors. We have shown previously that amplification of the dihydrofolate reductase (DHFR) gene in Chinese hamster cells is initiated by chromosome breaks, followed by bridge-breakage-fusion cycles that generate large intrachromosomal repeats; these are ultimately trimmed by an unknown process to smaller, more homogenous units manifested as homogenously staining chromosome regions (HSRs), However, in most human tumor cells, amplified DNA sequences are borne on unstable, extrachromosomal double minutes (DMs), which suggests the operation of a different amplification mechanism. In this study, we have isolated a large number of independent methotrexate-resistant human cell lines, all of which contained DHFR-bearing DMs, Surprisingly, all but one of these also had suffered partial or complete loss of one of the parental DHFR-bearing chromosomes. Cells in a few populations displayed what could be transient intermediates in the amplification process, including an initial HSR, its subsequent breakage, the appearance of DHFR-containing fragments, and, finally, DMs, Our studies suggest that HSRs and DMs both are initiated by chromosome breaks, but that cell types differ in how the extra sequences ultimately are processed and/or maintained.