Taniguchi Hiroya, Yoshida Tatsushi, Horinaka Mano, Yasuda Takashi, Goda Ahmed E, Konishi Masako, Wakada Miki, Kataoka Keisho, Yoshikawa Toshikazu, Sakai Toshiyuki
Department of Molecular-Targeting Cancer Prevention, Graduate School of Medical Science, Kyoto Prefectural University of Medicine, Kawaramachi-Hirokoji, Kyoto, Japan.
Cancer Res. 2008 Nov 1;68(21):8918-27. doi: 10.1158/0008-5472.CAN-08-1120.
Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) is one of the most promising candidates for new cancer therapeutics. A current problem is that some cancers still remain resistant to TRAIL. We show for the first time that a naturally occurring flavonoid, baicalein, overcomes TRAIL resistance in cancer cells. The combination of baicalein and TRAIL effectively induced apoptosis in TRAIL-resistant colon cancer SW480 cells. Baicalein up-regulated the expression of death receptor 5 (DR5) among TRAIL receptors at the mRNA and protein levels. Suppression of this up-regulation with small interfering RNA (siRNA) efficiently reduced the apoptosis induced by TRAIL and baicalein, suggesting that the sensitization was mediated through DR5 induction. Moreover, baicalein also overcame TRAIL resistance with DR5 up-regulation in prostate cancer PC3 cells. Of note, the combination of TRAIL and baicalein hardly induced apoptosis in normal human cells, such as blood cells and hepatocytes. Baicalein increased DR5 promoter activity, and this enhanced activity was diminished by mutation of a CCAAT/enhancer-binding protein homologous protein (CHOP)-binding site in SW480 cells. In SW480 cells, CHOP siRNA blocked both functions of baicalein. CHOP expression was induced by baicalein in SW480 cells; however, in PC3 cells, baicalein scarcely induced CHOP and mutation of the CHOP-binding site did not abrogate the DR5 promoter activation by baicalein. Interestingly, baicalein induced reactive oxygen species (ROS) and a ROS scavenger prevented DR5 expression and TRAIL sensitization in PC3 but not SW480 cells. These results indicate that, using two different pathways, baicalein exposes cancer surveillance of TRAIL and overcomes TRAIL resistance in cancer cells.
肿瘤坏死因子相关凋亡诱导配体(TRAIL)是新型癌症治疗药物中最具潜力的候选药物之一。目前存在的一个问题是,一些癌症对TRAIL仍具有抗性。我们首次表明,一种天然存在的黄酮类化合物黄芩素能够克服癌细胞对TRAIL的抗性。黄芩素与TRAIL联合使用可有效诱导TRAIL抗性结肠癌细胞SW480凋亡。黄芩素在mRNA和蛋白质水平上调了TRAIL受体中死亡受体5(DR5)的表达。用小干扰RNA(siRNA)抑制这种上调可有效减少TRAIL和黄芩素诱导的凋亡,这表明这种致敏作用是通过DR5诱导介导的。此外,黄芩素在前列腺癌PC3细胞中也通过上调DR5克服了TRAIL抗性。值得注意的是,TRAIL与黄芩素联合使用几乎不会诱导正常人细胞(如血细胞和肝细胞)凋亡。黄芩素增加了DR5启动子活性,而SW480细胞中CCAAT/增强子结合蛋白同源蛋白(CHOP)结合位点的突变减弱了这种增强的活性。在SW480细胞中,CHOP siRNA阻断了黄芩素的两种功能。黄芩素在SW480细胞中诱导了CHOP表达;然而,在PC3细胞中,黄芩素几乎不诱导CHOP表达,且CHOP结合位点的突变并未消除黄芩素对DR5启动子的激活作用。有趣的是,黄芩素诱导了活性氧(ROS)的产生,并且一种ROS清除剂可阻止PC3细胞中DR5的表达和TRAIL致敏作用,但对SW480细胞无效。这些结果表明,黄芩素通过两种不同的途径揭示了TRAIL对癌症的监测作用,并克服了癌细胞对TRAIL的抗性。