Ethanol-induced apoptosis in human liver adenocarcinoma cells (SK-Hep1): Fas- and mitochondria-mediated pathways and interaction with MAPK signaling system

- Ethanol-induced apoptosis in SK-Hep1 cells was mediated by Fas and mitochondria.
- Above-mentioned two pathways were both triggered by oxidative stress mediated by ROS.
- p38 MAPK and JNK were promoting mitochondria-mediated ethanol-induced apoptosis.
- ROS generation preceded DISC formation and MAPK action in ethanol-induced apoptosis.
- Interaction between apoptosis and MAPK signaling systems was shown in SK-Hep1 cells.

For studying molecular mechanisms regulating the fate of ethanol-treated hepatocytes, involvement of Fas in ethanol-induced apoptosis was examined in human liver adenocarcinoma (SK-Hep1) cells in which the function of Fas-associated death domain (FADD) protein was knocked down by transfection. In FADD-knocked down cells, while ethanol-induced increase in generation of reactive oxygen species (ROS) was unaffected, apoptosis was significantly suppressed, demonstrating the involvement of Fas in ethanol-induced hepatocyte apoptosis more directly than in the past reports. On the other hand, effects of mitogen-activated protein kinase (MAPK), which is well known to determine the fate of various cells, on ethanol-induced apoptosis have not been examined in SK-Hep1 cells. Of three major MAPKs, only p38 MAPK and JNK were found activated by 200 mM ethanol treatment. When cells were incubated with inhibitors of p38 MAPK and JNK, ethanol-induced apoptosis was decreased while ROS generation was unaffected, and examination of pro-apoptotic Bax and anti-apoptotic Bcl-2 levels showed decrease of the former and increase of the latter. We concluded that oxidative stress inflicted by ROS triggered Fas-mediated and mitochondria-mediated apoptotic pathways in ethanol-treated SK-Hep1 cells, and that p38 MAPK and JNK were promoting mitochondrial pathway, suggesting interaction between apoptosis and MAPK signaling systems.