Withoff S, Keith W N, Knol A J, Coutts J C, Hoare S F, Mulder N H, de Vries E G
Department of Internal Medicine, University Hospital Groningen, The Netherlands.
Br J Cancer. 1996 Aug;74(4):502-7. doi: 10.1038/bjc.1996.393.
A panel of doxorubicin-resistant sublines of the human small-cell lung carcinoma cell line GLC4 displays decreasing DNA topoisomerase II alpha (TopoII alpha) mRNA levels with increasing resistance. In the present study we describe how this decrease may be regulated. No significant differences in TopoII alpha mRNA stability or gene arrangement were found, using mRNA slot-blotting and Southern blotting, in the most resistant cell line compared with the parental cell line. To investigate if TopoII alpha gene copy loss contributed to the mRNA decrease, fluorescence in situ hybridisation using a TopoII alpha-specific probe was performed. During doxorubicin resistance development, the composition of the population in each cell line shifted with increasing resistance, from a population in which most cells contain three TopoII alpha gene copies (GLC4) to a population in which most cells contain only two copies. A partial revertant of the most resistant cell line displayed a shift back to the original situation. We conclude that the TopoII alpha gene copy number decrease per cell line is in good agreement with the decreased TopoII alpha mRNA and protein levels, and TopoII activity levels in these cell lines which were described previously.
人小细胞肺癌细胞系GLC4的一组阿霉素耐药亚系显示，随着耐药性增加，DNA拓扑异构酶IIα（TopoIIα）mRNA水平降低。在本研究中，我们描述了这种降低可能是如何被调控的。使用mRNA斑点杂交和Southern杂交，在最耐药的细胞系与亲代细胞系之间，未发现TopoIIα mRNA稳定性或基因排列存在显著差异。为了研究TopoIIα基因拷贝数缺失是否导致mRNA降低，使用TopoIIα特异性探针进行了荧光原位杂交。在阿霉素耐药性发展过程中，每个细胞系中群体的组成随着耐药性增加而发生变化，从大多数细胞含有三个TopoIIα基因拷贝的群体（GLC4）转变为大多数细胞仅含有两个拷贝的群体。最耐药细胞系的部分回复突变体显示出向原始状态的转变。我们得出结论，每个细胞系中TopoIIα基因拷贝数的减少与这些细胞系中先前描述的TopoIIα mRNA和蛋白质水平以及TopoII活性水平的降低高度一致。
