Silibinin induces apoptosis by caspase activation, down-regulating Bcl-2 and activating YAP/p53 in renal cell carcinoma

Silibinin, a flavanone in milk thistle, has been shown effective anticancer effects in various kinds of human tumors. In the present study, we investigated whether and how silibinin induces cell apoptosis in human renal cell carcinoma (RCC) cells. We found that silibinin could markedly inhibit the growth of 786-O and ACHN RCC cells by MTT assay and cell apoptosis by flow cytometric analysis. Moreover, using laser scanning confocal microscope, we found 786-O and ACHN showed typical pyknosis and nuclei splitting after treatment with 150 μM silibinin for 24 h. Meanwhile, it was found that silibinin activated cleaved caspase 3 and cleaved PARP and decreased expression of Bcl-2 in 786-O and ACHN cells by western blotting analysis. Furthermore, we found that silibinin could increase YAP and p53 expression in a time-dependent manner, but the induction of p53 was about 2 h behind the induction of YAP. Additionally, knockdown of YAP could not cause the p53 protein overexpression by silibinin treatment. Taken together, our study provided the first evidence that silibinin is imparted strong inhibitory, and apoptotic effects on RCC cells through increasing YAP/p53 index. Silibinin merits further investigation as an apoptosis inducer as well as a novel RCC chemo therapeutic agent in the clinical setting.