Kuo M T, Vyas R C, Jiang L X, Hittelman W N
Department of Molecular Pathology, University of Texas M. D. Anderson Cancer Center, Houston 77030.
Mol Cell Biol. 1994 Aug;14(8):5202-11. doi: 10.1128/mcb.14.8.5202-5211.1994.
Recent studies of several drug-resistant Chinese hamster cell lines suggested that a breakage-fusion-bridge mechanism is frequently involved in the amplification of drug resistance genes. These observations underscore the importance of chromosome breakage in the initiation of DNA amplification in mammalian cells. However, the mechanism of this breakage is unknown. Here, we propose that the site of chromosome breakage consistent with the initial event of P-glycoprotein (P-gp) gene amplification via the breakage-fusion-bridge cycle in three independently established multidrug-resistant CHO cells was located at 1q31. This site is a major chromosome fragile site that can be induced by methotrexate and aphidicolin treatments. Pretreatments of CHO cells with methotrexate or aphidicolin enhanced the frequencies of resistance to vinca alkaloid and amplification of the P-gp gene. These observations suggest that chromosome fragile sites play a pivotal role in DNA amplification in mammalian cells. Our data are also consistent with the hypothesis that gene amplification can be initiated by stress-induced chromosome breakage that is independent of modes of action of cytotoxic agents. Drug-resistant variants may arise by their growth advantage due to overproduction of cellular target molecules via gene amplification.
最近对几种耐药性中国仓鼠细胞系的研究表明，断裂-融合-桥接机制经常参与耐药基因的扩增。这些观察结果强调了染色体断裂在哺乳动物细胞DNA扩增起始中的重要性。然而，这种断裂的机制尚不清楚。在此，我们提出，在三个独立建立的多药耐药CHO细胞系中，与通过断裂-融合-桥接循环进行P-糖蛋白（P-gp）基因扩增的初始事件一致的染色体断裂位点位于1q31。该位点是一个主要的染色体脆弱位点，可通过甲氨蝶呤和阿非迪霉素处理诱导产生。用甲氨蝶呤或阿非迪霉素预处理CHO细胞可提高对长春花生物碱的耐药频率以及P-gp基因的扩增频率。这些观察结果表明，染色体脆弱位点在哺乳动物细胞的DNA扩增中起关键作用。我们的数据也与以下假设一致，即基因扩增可由应激诱导的染色体断裂引发，而这与细胞毒性剂的作用方式无关。耐药变体可能因其通过基因扩增导致细胞靶分子过度产生而具有生长优势而产生。
