Shikonin induces cell death by inhibiting glycolysis in human testicular cancer I-10 and seminoma TCAM-2 cells

Abstract

To investigate the pattern of shikonin-induced cell death in testicular cancer cell I-10 and seminoma TCAM-2 cells and explore the possible mechanism in light of mitochondrial function and glycolysis. I-10 cells treated with 0, 1.2, 1.4 and 1.6 μmol/L shikonin and TCAM-2 cells treated with 0, 0.5, 1 and 1.5 μmol/L shikonin were examined for mitochondrial membrane potential and production of reactive oxygen species (ROS) using JC-1 kit and ROS kit, respectively. The levels of intracellular lactic acid in the cells were detected using a lactic acid kit. The inhibitory effect of shikonin on the proliferation of the cells was assessed with MTT assay. The death patterns of the cells were observed by transmission electron microscopy, and annexin V-FITC/PI double staining was used to detect cell apoptosis. Western blotting was used to detect the relative expression levels of the apoptotic proteins Bax, Bcl-2, and cleaved caspase-3, the autophagy- related protein LC3B and glycolysis- related proteins PKM2, GLUT1 and HK2. MTT assay showed that shikonin significantly inhibited the proliferation of I-10 and TCAM-2 cells in a time- and dose-dependent manner (P < 0.05). The IC50 values of shikonin in I-10 cells at 24, 48, and 72 h were 1.8, 1.36 and 1.16 μmol/L, as compared with 2.37, 0.8 and 0.41 μmol/L in TCAM-2 cells, respectively. Shikonin treatment significantly reduced mitochondrial membrane potential, increased ROS levels and lower the level of lactic acid in both I-10 and TCAM-2 cells (P < 0.05). Transmission electron microscopy and annexin V-FITC/PI double staining demonstrated that shikonin induced apoptosis and excessive autophagy in I-10 and TCAM-2 cells (P < 0.05). In both I-10 and TCAM cells, shikonin treatment significantly down- regulated the expressions of Bax, Bcl-2, cleaved caspase-3, PKM2, GLUT1 and HK2, and up-regulated the expression of autophagy-related protein LC3B (P < 0.05). Shikonin can inhibit the proliferation, induce apoptosis and increase autophagy in both I-10 and TCAM-2 cells probably by affecting energy metabolism of the cells.