Silibinin inhibits constitutive and TNFα-induced activation of NF-αB and sensitizes human prostate carcinoma DU145 cells to TNFα-induced apoptosis
Silibinin inhibits constitutive and TNFα-induced activation of NF-αB and sensitizes human prostate carcinoma DU145 cells to TNFα-induced apoptosis
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DOI：
10.1038/sj.onc.1205240
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发表时间：
2002-03-07
期刊：
影响因子：
8
通讯作者：
Agarwal, R
中科院分区：
文献类型：
--
作者：
Dhanalakshmi, S;Singh, RP;Agarwal, R
前列腺癌（PCA）是美国男性最常见的侵袭性恶性肿瘤之一，然而，迄今为止在其治疗方面取得的成功有限。即使是最有效的药物（如TNFalpha）也无法杀死人PCA细胞，这可能是由于NF-kappaB的组成性激活，随后激活了大量抗凋亡基因。在这种情况下，强凋亡剂TNFalpha进一步诱导NF-kappaB活化，而不是诱导细胞凋亡。在最近的几项研究中，我们已经在各种实验肿瘤模型和细胞培养系统中证明了水飞蓟素及其成分水飞蓟宾素的防癌和抗癌作用。在这里，我们研究了水飞蓟宾是否能有效抑制人PCA细胞中组成型NF-kappaB的激活，这将有助于克服tnfy不敏感。我们的研究表明水飞蓟宾能有效抑制晚期人前列腺癌DU145细胞NF-kappaB的组成性激活。与此一致的是，NF-kappaB的p65和p50亚基的核水平也降低了。在评估这一作用的分子机制的研究中，水飞蓟宾处理导致IkappaBalpha水平显著升高，同时磷酸化IkappaBalpha水平降低。激酶试验显示水飞蓟宾剂量依赖性地降低IKKalpha激酶活性。水飞蓟宾对IKKalpha的影响似乎是直接的，正如体外激酶测定所证明的那样，免疫沉淀的IKKalpha与水飞蓟宾一起孵育。这表明水飞蓟宾对IKKalpha和下游效应物的抑制作用并不一定需要上游事件。其他研究表明，水飞蓟宾还通过IkappaBalpha途径抑制tnfalpha诱导的NF-kappaB活化，并随后使DU145细胞对tnfa诱导的凋亡敏感。这些结果表明水飞蓟宾素可以提高晚期PCA中基于tnfalpha的化疗的有效性。
Prostate cancer (PCA) is one of the most common invasive malignancies of men in the US, however, there have been Limited successes so far in its therapy. Even most potent agents (e.g. TNFalpha) are ineffective in killing human PCA cells possibly due to constitutive activation of NF-kappaB that subsequently activates a large number of anti-apoptotic genes. In such a scenario, strong apoptotic agent TNFalpha, further induces NF-kappaB activation rather than inducing apoptosis. In several recent studies, we have demonstrated both cancer preventive and anti-cancer efficacy of silymarin and its constituent silibinin in a variety of experimental tumor models and cell culture systems. Here we examined whether silibinin is effective in inhibiting constitutive NF-kappaB activation in human PCA cells, which would help in overcoming TNFY-insensitivity. Our studies reveal that silibinin effectively inhibits constitutive activation of NF-kappaB in advanced human prostate carcinoma DU145 cells. Consistent with this, nuclear levels of p65 and p50 sub-units of NF-kappaB were also reduced. In the studies assessing molecular mechanism of this effect, silibinin treatment resulted in a significant increase in the level of IkappaBalpha with a concomitant decrease in phospho-IkappaBalpha. Kinase assays revealed that silibinin dose-dependently decreases IKKalpha kinase activity. The effect of silibinin on IKKalpha seemed to be direct as evidenced by the in vitro kinase assay, where immunoprecipitated IKKalpha was incubated with silibinin. This shows that silibinin does not necessarily need an upstream event to bring about its inhibitory effect on IKKalpha and downstream effectors. Additional studies showed that silibinin also inhibits TNFalpha-induced activation of NF-kappaB via IkappaBalpha pathway and subsequently sensitizes DU145 cells to TNFa-induced apoptosis. These results indicate that silibinin could be used to enhance the effectiveness of TNFalpha-based chemotherapy in advanced PCA.