Katiyar Santosh K, Roy Anshu M, Baliga Manjeshwar S
Department of Dermatology, University of Alabama at Birmingham, 1670 University Boulevard, Volker Hall 557, P.O. Box 202, Birmingham, AL 35294, USA.
Mol Cancer Ther. 2005 Feb;4(2):207-16.
Silymarin, a plant flavonoid, has been shown to inhibit skin carcinogenesis in mice. However, the mechanism responsible for the anti-skin carcinogenic effects of silymarin is not clearly understood. Here, we report that treatment of JB6 C141 cells (preneoplastic epidermal keratinocytes) and p53+/+ fibroblasts with silymarin and silibinin (a major constituent of silymarin) resulted in a dose-dependent inhibition of cell viability and induction of apoptosis in an identical manner. Silymarin-induced apoptosis was determined by fluorescence staining (8-64% apoptosis) and flow cytometry (12-76% apoptosis). The silymarin-induced apoptosis was primarily p53 dependent because apoptosis occurred to a much greater extent in the cells expressing wild-type p53 (p53+/+, 9-61%) than in p53-deficient cells (p53-/-, 6-20%). The induction of apoptosis in JB6 C141 cells was associated with increased expression of the tumor suppressor protein, p53, and its phosphorylation at Ser15. The constitutive expression of antiapoptotic proteins Bcl-2 and Bcl-xl were decreased after silymarin treatment, whereas the expression of the proapoptotic protein Bax was increased. There was a shift in Bax/Bcl-2 ratio in favor of apoptotic signal in silymarin-treated cells, which resulted in increased levels of cytochrome c release, apoptotic protease-activating factor-1, and cleaved caspase-3 and poly(ADP-ribose) polymerase in JB6 C141 cells. The shift in Bax/Bcl-2 ratio was more prominent in p53+/+ fibroblasts than in p53-/- cells. Silymarin-induced apoptosis was blocked by the caspase inhibitor (Z-VAD-FMK) in JB6 C141 cells which suggested the role of caspase activation in the induction of apoptosis. These observations show that silymarin-induced apoptosis is primarily p53 dependent and mediated through the activation of caspase-3.
水飞蓟素是一种植物类黄酮，已被证明可抑制小鼠皮肤癌的发生。然而，水飞蓟素抗皮肤癌作用的机制尚不清楚。在此，我们报告，用水飞蓟素和水飞蓟宾（水飞蓟素的主要成分）处理JB6 C141细胞（癌前表皮角质形成细胞）和p53+/+成纤维细胞，会以相同方式导致细胞活力呈剂量依赖性抑制并诱导细胞凋亡。通过荧光染色（凋亡率为8 - 64%）和流式细胞术（凋亡率为12 - 76%）测定水飞蓟素诱导的细胞凋亡。水飞蓟素诱导的细胞凋亡主要依赖p53，因为在表达野生型p53的细胞（p53+/+，凋亡率为9 - 61%）中，细胞凋亡的程度比p53缺陷细胞（p53-/-，凋亡率为6 - 20%）大得多。JB6 C141细胞中细胞凋亡的诱导与肿瘤抑制蛋白p53的表达增加及其在Ser15位点的磷酸化有关。水飞蓟素处理后，抗凋亡蛋白Bcl-2和Bcl-xl的组成型表达降低，而促凋亡蛋白Bax的表达增加。在水飞蓟素处理的细胞中，Bax/Bcl-2比值发生变化，有利于凋亡信号，这导致JB6 C141细胞中细胞色素c释放、凋亡蛋白酶激活因子-1以及裂解的caspase-3和聚（ADP-核糖）聚合酶水平升高。在p53+/+成纤维细胞中，Bax/Bcl-2比值的变化比在p53-/-细胞中更明显。在JB6 C141细胞中，水飞蓟素诱导的细胞凋亡被caspase抑制剂（Z-VAD-FMK）阻断，这表明caspase激活在细胞凋亡诱导中起作用。这些观察结果表明，水飞蓟素诱导的细胞凋亡主要依赖p53，并通过caspase-3的激活介导。
