Luteolin promotes degradation in signal transducer and activator of transcription 3 in human hepatoma cells: An implication for the antitumor potential of flavonoids
Luteolin promotes degradation in signal transducer and activator of transcription 3 in human hepatoma cells: An implication for the antitumor potential of flavonoids
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DOI：
10.1158/0008-5472.can-05-4062
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发表时间：
2006-05-01
期刊：
影响因子：
11.2
通讯作者：
Sata, Michio
中科院分区：
文献类型：
--
作者：
Selvendiran, Karuppaiyah;Koga, Hironori;Sata, Michio
在这项研究中，我们已经调查了潜在的分子机制，在体外和体内的人肝癌细胞的叶黄素的强效促凋亡作用，专注于信号转导和转录激活因子3（STAT 3）/Fas信号。木犀草素处理HLF肝癌细胞后出现明显的凋亡，并呈时间和剂量依赖性。与木犀草素激活caspase-8一致，鉴定了功能性Fas/CD 95的表达增强。与增加的Fas/CD 95表达一致，在木犀草素处理的细胞中，在20分钟内发现了STAT 3的Tyr（705）磷酸化的急剧减少，这是一种已知的Fas/CD 95转录的负调节因子，导致STAT 3的靶基因产物如细胞周期蛋白D1、存活素、Bcl-xL和血管内皮生长因子的下调。有趣的是，STAT 3的快速下调与Tyr（705）磷酸化STAT 3的加速泛素依赖性降解一致，而不是Ser（727）磷酸化的STAT 3，STAT 3活性的另一种调节剂。木犀草素处理后，Ser（727）-磷酸化的STAT 3的表达水平逐渐降低，随后是CDK 5活性形式的快速和明确的下调，CDK 5可以在Ser（727）磷酸化STAT 3。STAT 3的过表达导致对毛地黄黄酮的抗性，表明STAT 3是毛地黄黄酮的关键靶点。在用HAK-1B肝癌细胞移植瘤的裸鼠中，毛地黄黄酮以剂量依赖的方式显著抑制肿瘤的生长。这些数据表明，毛地黄黄酮通过双途径靶向STAT 3-泛素依赖性降解Tyr（705）-磷酸化的STAT 3和通过失活CDK 5逐渐下调Ser（727）-磷酸化的STAT 3，从而通过上调Fas/CD 95触发凋亡。
In this study, we have investigated the underlying molecular mechanism for the potent proapoptotic effect of luteotin on human hepatoma cells both in vitro and in vivo, focusing on the signal transducer and activator of transcription 3 (STAT3)/Fas signaling. A clear apoptosis was found in the luteolin-treated HLF hepatoma cells in a time- and dosage-dependent manner. In concert with the caspase-8 activation by luteolin, an enhanced expression in functional Fas/CD95 was identified. Consistent with the increased Fas/CD95 expression, a drastic decrease in the Tyr(705) phosphorylation of STAT3, a known negative regulator of Fas/CD95 transcription, was found within 20 minutes in the luteolin-treated cells, leading to down-regulation in the target gene products of STAT3, such as cyclin D1, survivin, Bcl-xL, and vascular endothelial growth factor. Of interest, the rapid down-regulation in STAT3 was consistent with an accelerated ubiquitin-dependent degradation in the Tyr(705) phosphorylated STAT3, but not the Ser(727) -phosphorylated one, another regulator of STAT3 activity. The expression level of Ser(727)- phosphorylated STAT3 was gradually decreased by the luteolin treatment, followed by a fast and clear down-regulation in the active forms of CDK5, which can phosphorylate STAT3 at Ser(727). An overexpression in STAT3 led to resistance to luteolin, suggesting that STAT3 was a critical target of luteolin. In nude mice with xenografted tumors using HAK-1B hepatoma cells, luteolin significantly inhibited the growth of the tumors in a dosage-dependent manner. These data suggested that luteolin targeted STAT3 through dual pathways-the ubiquitin-dependent degradation in Tyr(705)-phosphorylated STAT3 and the gradual down-regulation in Ser(727)-phosphorylated STAT3 through inactivation of CDK5, thereby triggering apoptosis via up-regulation in Fas/CD95.