Shikonin induces programmed necrosis-like cell death through the formation of receptor interacting protein 1 and 3 complex.

An alternative cell demise programmed necrosis has also been proposed when apoptotic machinery is impaired or blocked during tumor necrosis factor alpha (TNFα) stimulation. Shikonin (SKN), an herbal extract from the Chinese plant, has been reported to induce either apoptosis or necrosis depending on cell types or its concentrations. In this presentation, SKN caused cell death of NIH3T3 in a dose-dependent manner. Intriguingly, SKN-mediated cell death was in part protected by necrostatin-1 (Nec-1), a specific inhibitor of programmed necrosis, but not zVAD a pan-caspase inhibitor. SKN directly mediated cell death via receptor interacting protein1 and 3 (RIP1-RIP3) complex formation, which is required for TNFα-mediated programmed necrosis. Additionally, SKN-caused cell death was reversed by a reactive oxygen species (ROS) scavenger N-acetylcysteine (NAC) whereas TNFα-mediated necrosis was successfully protected by butylated hydroxyanisole (BHA), implying that ROS may be differentially derived from death inducing agents. Concurrently with the protective effect of the ROS scavenger or Nec-1 on TNFα or SKN, the RIP1-RIP3 complex was significantly affected in the presence of those agents. Here, it is highlighted that SKN as well as TNFα can directly mediate cell death via a pronecrotic complex, but ROS were generated via different routes depending on cell death-inducing agents.