Induction of apoptosis by shikonin through a
ROS/JNK-mediated process in Bcr/Abl-positive chronic myelogenous
leukemia (CML) cells
Xin Mao1,*, Chun Rong Yu1,*, Wen Hua Li1 and Wen Xin Li1
1State Key Laboratory of Virology, College of Life Sciences, Wuhan University, Wuhan 430072, China
Abstract This study examined the signaling events induced by shikonin that lead to the induction of apoptosis in Bcr/Abl-positive chronic myelogenous leukemia (CML) cells (e.g., K562, LAMA84). Treatment of K562 cells with shikonin (e.g., 0.5 μM) resulted in profound induction of apoptosis accompanied by rapid generation of reactive oxygen species (ROS), striking activation of c-Jun-N-terminal kinase (JNK) and p38, marked release of the mitochondrial proteins cytochrome c and Smac/DIABLO, activation of caspase-9 and -3, and cleavage of PARP. Scavenging of ROS completely blocked all of the above-mentioned events (i.e., JNK and p38 phosphorylation, cytochrome c and Smac/DIABLO release, caspase and PARP cleavage, as well as the induction of apoptosis) following shikonin treatment. Inhibition of JNK and knock-down of JNK1 significantly attenuated cytochrome c release, caspase cleavage and apoptosis, but did not affect shikonin-mediated ROS production. Additionally, inhibition of caspase activation completely blocked shikonin-induced apoptosis, but did not appreciably modify shikonin-mediated cytochrome c release or ROS generation. Altogether, these findings demonstrate that shikonin-induced oxidative injury operates at a proximal point in apoptotic signaling cascades, and subsequently activates the stress-related JNK pathway, triggers mitochondrial dysfunction, cytochrome c release, and caspase activation, and leads to apoptosis. Our data also suggest that shikonin may be a promising agent for the treatment of CML, as a generator of ROS.
.Shikonin (C16H16O5) is a natural naphthoquinone derivative compound that is present in the root tissues of the traditional Chinese medical herb Lithospermum erythrorhizon. This herb is found throughout China, including in Southern Yun Nan, Northern Dong Bei, Western Xin Jiang and Tibet. Lithospermum erythrorhizon was first recorded in a 2000-year-old Chinese medical material dictionary “Materia Medica of Deity of Agriculture”, also called “Shen Nong Ben Cao Jing” 1. This dictionary was compiled around the time of the Qin (225 BC–206 BC) and Han (206 BC–220 AD) dynasties.