Eijdems E W, De Haas M, Coco-Martin J M, Ottenheim C P, Zaman G J, Dauwerse H G, Breuning M H, Twentyman P R, Borst P, Baas F
Division of Molecular Biology, The Netherlands Cancer Institute, Amsterdam.
Int J Cancer. 1995 Mar 3;60(5):676-84. doi: 10.1002/ijc.2910600518.
Some multidrug resistant cell lines over-express the gene encoding the multidrug-resistance-associated protein (MRP). In all cell lines reported thus far, over-expression is associated with gene amplification. We have studied the predominant mechanisms of MRP over-expression in 4 human lung-cancer cell lines that cover a range of drug-resistance levels, and we have analyzed the MRP amplicon. In the SW-1573-derived, weakly resistant cell line 30.3M, MRP mRNA is elevated 3-fold in the absence of gene amplification. Run-on analysis shows that the increased MRP gene expression in this cell line is due to transcriptional activation. In the highly resistant GLC4/ADR and COR-L23/R cells, MRP gene amplification predominates, whereas in the moderately resistant MOR/R cells, gene amplification is combined with a mechanism resulting in an additional increase in the level of MRP mRNA. Fluorescence in situ hybridization shows that, in the GLC4/ADR cells, amplified MRP sequences are present both in double minute chromosomes (DM) and in homogeneously staining regions (HSR). By pulsed-field gel electrophoresis we show that the MRP-containing DM are 1 Mb in length. Chromosome-16-specific repetitive sequences adjacent to the MRP gene are also present in the DM and HSR, compatible with the involvement of these sequences in recombination events underlying MRP gene amplification. Our results show that low levels of drug resistance may arise by transcriptional activation of the MRP gene, whereas at high levels of drug resistance amplification of the MRP gene predominates, possibly facilitated by the presence of recombination-prone sequences.
一些多药耐药细胞系过度表达编码多药耐药相关蛋白（MRP）的基因。在迄今为止报道的所有细胞系中，过度表达与基因扩增相关。我们研究了4种涵盖不同耐药水平的人肺癌细胞系中MRP过度表达的主要机制，并分析了MRP扩增子。在源自SW - 1573的低耐药细胞系30.3M中，在没有基因扩增的情况下，MRP mRNA升高了3倍。核转录分析表明，该细胞系中MRP基因表达的增加是由于转录激活。在高耐药的GLC4/ADR和COR - L23/R细胞中，MRP基因扩增占主导，而在中度耐药的MOR/R细胞中，基因扩增与一种导致MRP mRNA水平额外增加的机制相结合。荧光原位杂交显示，在GLC4/ADR细胞中，扩增的MRP序列存在于双微体染色体（DM）和均匀染色区（HSR）中。通过脉冲场凝胶电泳我们表明，含有MRP的DM长度为1 Mb。与MRP基因相邻的16号染色体特异性重复序列也存在于DM和HSR中，这与这些序列参与MRP基因扩增背后的重组事件相一致。我们的结果表明，低水平的耐药可能通过MRP基因的转录激活产生，而在高水平耐药时，MRP基因扩增占主导，可能由易发生重组的序列的存在所促进。
