Tanshinone IIA (Tan-IIA) was isolated from Salviae Miltiorrhizae Radix. Our previous studies showed that Tan-IIA induced apoptosis in human colon cancer colo 205 cells, but the molecular mechanisms of the effect of Tan-IIA on human colon cancer were not clearly elucidated. The protein expression of ErbB-2 was up-regulated and activated in human and experimental colon cancers. In the present study, the effects of Tan-IIA on the protein expression of ErbB-2 in colo 205 cells were investigated. In vitro, colo 205 cells were treated with various concentrations of Tan-IIA (1, 2 and 5 μg/ ml) for 24 h, and the protein expression of TNF-α, ErbB-2 and caspase-3 was assayed by Western blotting. For the in vivo studies, male SCID mice were xenografted with colo 205 cells, and from day 10, Tan IIA (20 mg/kg/day, dissolved in corn oil) was administered by oral feeding for 30 days. As a control, mice with xenografted tumors were separately treated with corn oil (0.1 ml/10 g body weight). Expression of TNF-α, ErbB-2 and caspase-3 proteins was measured by Western blot analysis. Our results showed that Tan-IIA down-regulated the protein expression of ErbB-2 and up-regulated TNF-α and caspase-3 in colo 205 cells in vitro. In a colo 205 xenograft model, treatment with Tan-IIA caused up-regulation of TNF-α, caspase-3 and down-regulation of ErbB-2 protein expression as compared to the controls. Based on these observations, one possible molecular mechanisms by which Tan-IIA inhibits the proliferation of colo 205 cells is through the down-regulation of ErbB-2 protein expression and the up-regulation of the protein expression of TNF-α and caspase-3.

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