Miao Ze-Hong, Ding Jian
Division of Anti-tumor Pharmacology, State Key Laboratory of Drug Research, Shanghai Institute of Materia Medica, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai 201203, People's Republic of China.
Cancer Res. 2003 Aug 1;63(15):4527-32.
Expression of mdr-1 is complex and highly regulated. Several lines of evidence indirectly suggest that transcription factor c-Jun may negatively regulate human mdr-1 gene expression. We recently found that salvicine, a novel topoisomerase II inhibitor, is cytotoxic for multidrug resistance (MDR) tumor cells and down-regulates mdr-1 expression in MDR K562/A02 cells. Salvicine also stimulates a significant increase in the level of c-jun mRNA in HL60 cells. This study investigated the relationship between c-Jun activation and down-regulation of mdr-1 expression by salvicine in K562/A02 cells. Reverse-transcription PCR and Western blotting analyses revealed that salvicine suppressed mdr-1 expression in MDR cells and promoted c-jun expression in both MDR and parental K562 cells. Moreover, levels of c-jun expression were enhanced by salvicine before reduction of mdr-1 expression in K562/A02 cells. Furthermore, c-jun antisense oligodeoxynucleotides prevented salvicine-stimulated enhancement of c-Jun protein and reduction of mdr-1 gene expression, but did not affect the increase in c-jun mRNA levels. Salvicine promoted phosphorylation of c-Jun-N-terminal kinase and c-Jun protein in MDR K562/A02 and parental K562 cells. Electrophoretic mobility shift assay analysis showed that salvicine enhanced DNA binding activity of transcription factor activator protein 1. Additionally, c-jun antisense oligodeoxynucleotides also inhibited salvicine-induced apoptosis and cytotoxicity in MDR and parental K562 cells. A possible pathway emerges from these results: salvicine stimulates c-Jun-N-terminal kinase phosphorylation and activation, resulting in c-Jun phosphorylation and activation. Activated c-Jun promotes expression of c-jun itself, represses mdr-1 transcription, and triggers pro-apoptotic signals, resulting in low mdr-1 expression and cell death. The present results demonstrate that transcription factor c-Jun plays a principal role in down-regulation of mdr-1 expression and induction of apoptosis in salvicine-treated human MDR K562/A02 cells, providing new insights into the complicated mechanisms regulating mdr-1 expression. The findings also suggest that c-Jun might be a potential drug target for circumventing tumor MDR.
多药耐药基因1（mdr-1）的表达复杂且受到高度调控。多条证据间接表明，转录因子c-Jun可能对人类mdr-1基因表达起负调控作用。我们最近发现，新型拓扑异构酶II抑制剂沙尔威辛对多药耐药（MDR）肿瘤细胞具有细胞毒性，并能下调MDR K562/A02细胞中的mdr-1表达。沙尔威辛还能显著刺激HL60细胞中c-jun mRNA水平的升高。本研究调查了沙尔威辛在K562/A02细胞中激活c-Jun与下调mdr-1表达之间的关系。逆转录聚合酶链反应（RT-PCR）和蛋白质免疫印迹分析显示，沙尔威辛抑制MDR细胞中的mdr-1表达，并促进MDR和亲本K562细胞中c-jun的表达。此外，在K562/A02细胞中，mdr-1表达降低之前，沙尔威辛可增强c-jun的表达水平。此外，c-jun反义寡脱氧核苷酸可阻止沙尔威辛刺激的c-Jun蛋白增强和mdr-1基因表达降低，但不影响c-jun mRNA水平的升高。沙尔威辛可促进MDR K562/A02细胞和亲本K562细胞中c-Jun氨基末端激酶和c-Jun蛋白的磷酸化。电泳迁移率变动分析表明，沙尔威辛增强了转录因子激活蛋白1的DNA结合活性。此外，c-jun反义寡脱氧核苷酸还可抑制沙尔威辛诱导的MDR和亲本K562细胞凋亡及细胞毒性。这些结果揭示了一条可能的途径：沙尔威辛刺激c-Jun氨基末端激酶磷酸化和激活，导致c-Jun磷酸化和激活。激活的c-Jun促进c-jun自身的表达，抑制mdr-1转录，并触发促凋亡信号，导致mdr-1低表达和细胞死亡。目前的结果表明，转录因子c-Jun在沙尔威辛处理的人类MDR K562/A02细胞中mdr-1表达下调和凋亡诱导中起主要作用，为调控mdr-1表达的复杂机制提供了新的见解。这些发现还表明，c-Jun可能是克服肿瘤MDR的潜在药物靶点。
