Siegelin Markus D, Reuss David E, Habel Antje, Herold-Mende Christel, von Deimling Andreas
Department of Neuropathology, University Hospital Heidelberg, Im Neuenheimer Feld 220, 69120 Heidelberg, Germany.
Mol Cancer Ther. 2008 Nov;7(11):3566-74. doi: 10.1158/1535-7163.MCT-08-0236.
Resistance to tumor necrosis factor-related apoptosis-inducing ligand (TRAIL/Apo2L) limits its potential as a drug for cancer therapy. Here, we report that kaempferol, a bioactive plant flavonoid, sensitizes U251 and U87 glioma cells to TRAIL-mediated apoptosis. In contrast, U373 cells are not affected by kaempferol treatment. Treatment of kaempferol alone for 24 h did not induce apoptosis in the cell lines. We provide evidence that TRAIL-induced apoptosis is partially driven by kaempferol-mediated reduction of survivin protein levels. On kaempferol treatment, proteasomal degradation of survivin was observed. Inhibition of proteasomal degradation with MG132 in kaempferol-treated cells restored survivin protein levels in both glial cell lines. Consequently, overexpression of survivin attenuated TRAIL-kaempferol-induced apoptosis. In addition, we show that kaempferol mediates down-regulation of phosphorylated Akt, thereby further reducing survivin protein level. Furthermore, the blockage of the serine/threonine kinase Akt activity by kaempferol is important for inhibition of survivin because active phosphorylated Akt enhances the stability of survivin. However, we also show that the combined treatment of TRAIL and kaempferol induces cleavage (activation) of caspase-8, thereby exerting a proapoptotic effect independent of survivin known not to inhibit caspase-8 activation. Other effects induced by kaempferol were suppression of X-linked inhibitor of apoptosis proteins as the antiapoptotic members of the Bcl-2 family, Bcl-2, Bcl-xL, and Mcl-1 in a concentration-dependent manner. In summary, we showed that suppression of survivin is an essential mechanism in TRAIL-kaempferol-mediated apoptosis.
对肿瘤坏死因子相关凋亡诱导配体（TRAIL/Apo2L）的耐药性限制了其作为癌症治疗药物的潜力。在此，我们报告了山奈酚，一种具有生物活性的植物黄酮类化合物，可使U251和U87胶质瘤细胞对TRAIL介导的凋亡敏感。相比之下，U373细胞不受山奈酚处理的影响。单独用山奈酚处理24小时未在这些细胞系中诱导凋亡。我们提供的证据表明，TRAIL诱导的凋亡部分是由山奈酚介导的生存素蛋白水平降低所驱动。在山奈酚处理后，观察到生存素的蛋白酶体降解。用MG132抑制山奈酚处理细胞中的蛋白酶体降解可恢复两种胶质细胞系中的生存素蛋白水平。因此，生存素的过表达减弱了TRAIL-山奈酚诱导的凋亡。此外，我们表明山奈酚介导磷酸化Akt的下调，从而进一步降低生存素蛋白水平。此外，山奈酚对丝氨酸/苏氨酸激酶Akt活性的阻断对于生存素的抑制很重要，因为活性磷酸化Akt可增强生存素的稳定性。然而，我们还表明，TRAIL和山奈酚的联合处理可诱导半胱天冬酶-8的切割（激活），从而发挥独立于已知不抑制半胱天冬酶-8激活的生存素的促凋亡作用。山奈酚诱导的其他效应是以浓度依赖的方式抑制凋亡蛋白的X连锁抑制剂，即Bcl-2家族的抗凋亡成员Bcl-2、Bcl-xL和Mcl-1。总之，我们表明生存素的抑制是TRAIL-山奈酚介导的凋亡中的一个重要机制。
