Dong J, Naito M, Tsuruo T
Institute of Molecular and Cellular Biosciences, The University of Tokyo, Bunkyo-ku, Japan.
Oncogene. 1997 Aug 7;15(6):639-47. doi: 10.1038/sj.onc.1201237.
Human monocytic leukemia U937 cells readily undergo apoptosis when they are treated with TNF-alpha, anti-Fas antibody and anticancer drugs such as etoposide and Ara-C. To study the mechanism of apoptosis, we developed a novel apoptosis-resistant variant, UC, from U937 cells. The UC cells showed resistance to apoptosis induced by TNF-alpha, anti-Fas antibody, etoposide and Ara-C. Somatic cell hybridization between U937 and UC showed that apoptosis-resistance to TNF-alpha in UC was genetically recessive and resistance to etoposide was dominant, suggesting that UC has at least two different mutations functionally involved in apoptosis. Mechanistic analysis revealed that UC cells expressed reduced amounts of c-Myc. Transfection of the c-myc gene into UC cells restored the sensitivity of the cells to undergo apoptosis induced by TNF-alpha and anti-Fas, which attributes apoptosis-resistance in this circumstance to the reduced expression of c-Myc. On the other hand, c-myc transfection into UC cells could not restore their sensitivity to etoposide- and Ara-C-induced apoptosis, arguing against the role of c-myc in chemotherapy-induced apoptosis. However, treating the parental U937 cells with antisense oligonucleotides designed to reduce c-Myc expression rendered the cells resistant to etoposide-induced as well as to TNF-alpha-induced apoptosis. These results indicate that the reduced expression of c-Myc in UC is strongly associated with the resistance to etoposide-induced apoptosis. Our finding that c-myc transfection into UC could not restore the sensitivity to etoposide-induced apoptosis, suggests UC could have a second mutation that confers resistance to etoposide-induced apoptosis in a genetically dominant manner. Taken together, our present results indicate that c-Myc plays a role in cellular susceptibility to death receptor-mediated and chemotherapy-induced apoptosis.
人单核细胞白血病U937细胞在用肿瘤坏死因子-α（TNF-α）、抗Fas抗体以及抗癌药物如依托泊苷和阿糖胞苷处理时容易发生凋亡。为了研究凋亡机制，我们从U937细胞中培育出一种新型的抗凋亡变体UC。UC细胞对TNF-α、抗Fas抗体、依托泊苷和阿糖胞苷诱导的凋亡具有抗性。U937和UC之间的体细胞杂交表明，UC对TNF-α的凋亡抗性是遗传隐性的，而对依托泊苷的抗性是显性的，这表明UC至少有两个在功能上参与凋亡的不同突变。机制分析显示，UC细胞中c-Myc的表达量减少。将c-myc基因转染到UC细胞中可恢复细胞对TNF-α和抗Fas诱导凋亡的敏感性，这表明在这种情况下凋亡抗性归因于c-Myc表达的降低。另一方面，将c-myc转染到UC细胞中并不能恢复它们对依托泊苷和阿糖胞苷诱导凋亡的敏感性，这表明c-myc在化疗诱导的凋亡中不起作用。然而，用设计用于降低c-Myc表达的反义寡核苷酸处理亲代U937细胞，使细胞对依托泊苷诱导的凋亡以及TNF-α诱导的凋亡产生抗性。这些结果表明，UC中c-Myc表达的降低与对依托泊苷诱导凋亡的抗性密切相关。我们发现将c-myc转染到UC中不能恢复对依托泊苷诱导凋亡的敏感性，这表明UC可能有第二个以遗传显性方式赋予对依托泊苷诱导凋亡抗性的突变。综上所述，我们目前的结果表明c-Myc在细胞对死亡受体介导和化疗诱导凋亡的易感性中起作用。
