As shown in Figure 2A, the silibinin-induced ROS generation

was blocked by the calpain inhibitor with potency similar to that of catalase. Figure 2 Role of calpain and PKC in ROS generation Selleckchem Smoothened Agonist and cell death induced by silibinin. (A) Effect of inhibitors of calpain and PKC on silibinin-induced ROS generation. Cells were exposed to 30 μM silibinin in the presence or absence of 0.5 μM calpain inhibitor (CHO), 1 μM GF 109203X (GF), 1 μM rottlerin (Ro), and 800 units/ml catalase (Cat) and ROS generation was estimated by measuring changes in DCF fluorescence using FACS analysis. Data are mean ± SEM of five independent experiments performed in duplicate. *p < 0.05 compared with silibinin alone. (B) Effect of PKC inhibitors on silibinin-induced cell death. Cells were exposed to 30 μM silibinin in the presence or absence of 1 μM GF 109203X (GF) and 1 μM rottlerin (Ro) and cell viability was measured by MTT assay. Data are mean ± SEM of four independent experiments performed in duplicate. *p < 0.05 compared with silibinin alone. (C) Effect of silibinin on PKCδ activation. Cells were exposed to 30 μM silibinin

for various times and PKCδ phosphorylation was estimated by Western blot analysis. (D) Effect of calpain inhibitor on PKCδ phosphorylation. Cells were exposed to 30 μM silibinin for 10 min in the presence or absence of 0.5 U0126 μM calpain inhibitor (CHO) and PKCδ phosphorylation was estimated by Western blot analysis. PKCs are a family of serine/threonine kinases which are involved Methocarbamol in tumor formation and progression [14]. PKC isoforms cooperate or exert opposite effects on the process of apoptosis [15, 16]. PKC isoforms such as PKCα, ε, and ξ inhibit apoptosis, whereas PKCδ is involved in the process of apoptosis [16, 17]. Although previous studies

have shown that flavonoids can induce activation of PKC [18, 19], it is unclear whether PKC is involved in the signaling cascade of silibinin-induced cell death. Although PKCs are activated by ROS [20, 21], it has been reported that PKC activation can also cause ROS generation [22, 23]. Therefore, we examined involvement of PKC in the silibinin-induced ROS generation. The general PKC inhibitor GF 109203X and the selective PKCδ inhibitor rottlerin blocked the ROS generation (Figure 2A). The silibinin-induced cell death was also prevented by the general PKC inhibitor GF 109203X and rottlerin (Figure 2B), AZD8931 research buy indicating that silibinin induces ROS generation and cell death through PKC activation. We next examined whether silibinin induces PKCδ phosphorylation, an index of PKCδ activation. Silibinin induced a transient phosphorylation of PKCδ after 10 min of treatment, which was inhibited by treatment of calpain inhibitor (Figure 2C and 2D), suggesting that PKCδ may be a downstream of calpain in the silibinin-induced cell death.