Sager R, Gadi I K, Stephens L, Grabowy C T
Proc Natl Acad Sci U S A. 1985 Oct;82(20):7015-9. doi: 10.1073/pnas.82.20.7015.
During selection for methotrexate resistance, tumorigenic CHEF/16 cells and derivatives from CHEF/16 tumors underwent amplification of the dihydrofolate reductase gene (DHFR) at accelerated rates compared with closely related nontumorigenic CHEF/18 cells. "Dot blot" analysis showed that the CHEF/16 cells contained many more copies of the DHFR gene than did the CHEF/18 cells, when assayed at similar elevated levels of methotrexate resistance. Chromosome analysis of cell samples taken at several time points during amplification revealed large differences between the nontumorigenic CHEF/18 cells and the two tumorigenic cell lines. The tumorigenic cells developed few chromosome rearrangements over a 4-log increase in methotrexate resistance, other than increased length of a single chromosome, which was shown by in situ hybridization to contain most or all of the amplified DHFR gene copies. In contrast, the CHEF/18 cells underwent complex, progressive changes in almost every chromosome, and in situ hybridization suggested a dispersed pattern of gene amplification. The data support the hypothesis that unregulated amplification is a pathological process, occurring readily in neoplastic but rarely in normal cells, that together with other chromosomal disturbances contributes to the rapid evolution and progression of cancer.
在选择对甲氨蝶呤耐药的细胞过程中，致瘤性CHEF/16细胞及其肿瘤衍生细胞与密切相关的非致瘤性CHEF/18细胞相比，二氢叶酸还原酶基因（DHFR）以更快的速度扩增。“斑点印迹”分析表明，在检测到相似的甲氨蝶呤耐药升高水平时，CHEF/16细胞所含的DHFR基因拷贝数比CHEF/18细胞多得多。对扩增过程中几个时间点采集的细胞样本进行染色体分析，结果显示非致瘤性CHEF/18细胞与两种致瘤性细胞系之间存在巨大差异。在甲氨蝶呤耐药性增加4个对数的过程中，致瘤性细胞除了一条单一染色体长度增加外，几乎没有发生染色体重排，原位杂交显示该染色体包含大部分或所有扩增的DHFR基因拷贝。相比之下，CHEF/18细胞在几乎每一条染色体上都发生了复杂的、渐进性的变化，原位杂交提示基因扩增呈分散模式。这些数据支持了这样一种假说，即不受调控的扩增是一种病理过程，在肿瘤细胞中容易发生而在正常细胞中很少发生，它与其他染色体紊乱一起导致了癌症的快速演变和进展。
