Apoptosis is induced by shikonin through the mitochondrial signaling pathway

The aim of the present study was to investigate the effects of shikonin (SHI) on the induction of apoptosis in human TT medullary thyroid carcinoma cells, and to explore the role of mitochondrial signaling in this process. MTT, Annexin V-phycoerythrin/7-aminoactinomycin D staining, electron microscopy and JC-1 probe staining were performed to analyze mitochondrial membrane potential, and western blot analysis was used to examine the activation of the mitochondrial signaling pathway, and the changes in mitochondrial apoptosis pathway-associated protein expression. Following culture for 24-72 h, treatment with various concentrations of SHI inhibited the proliferation of TT cells, in a dose- and time-dependent manner. Transmission electron microscopy demonstrated the presence of typical apoptotic structures, as well as mitochondrial structural changes. The expression levels of apoptosis-associated proteins caspase-9, caspase-3 and poly adenosine triphosphate ribose polymerase increased in a dose-dependent manner following treatment with SHI. In addition, the mitochondrial membrane potential of the experimental group was significantly decreased, and the mitochondrial apoptosis pathway-associated proteins were altered. A possible mechanism underlying SHI-induced apoptosis through the mitochondrial signaling pathway is the regulation of B cell lymphoma 2 (Bcl-2)/Bcl-2-associated protein X expression levels, resulting in the decrease in mitochondrial membrane potential and the activation of the caspase-9/caspase-3 enzyme-associated reactions.