Reactive Oxygen Species‐Mediated Activation of AMP‐Activated Protein Kinase and c‐Jun N‐terminal Kinase Plays a Critical Role in Beta‐Sitosterol‐Induced Apoptosis in Multiple Myeloma U266 cells

Although beta‐sitosterol has been well known to have anti‐tumor activity in liver, lung, colon, stomach, breast and prostate cancers via cell cycle arrest and apoptosis induction, the underlying mechanism of anti‐cancer effect of beta‐sitosterol in multiple myeloma cells was never elucidated until now. Thus, in the present study, the role of reactive oxygen species (ROS) in association with AMP‐activated protein kinase (AMPK) and c‐Jun N‐terminal kinase (JNK) pathways was demonstrated in beta‐sitosterol‐treated multiple myeloma U266 cells. Beta‐sitosterol exerted cytotoxicity, increased sub‐G₁ apoptotic population and activated caspase‐9 and ‐3, cleaved poly (ADP‐ribose) polymerase (PARP) followed by decrease in mitochondrial potential in U266 cells. Beta‐sitosterol promoted ROS production, activated AMPK, acetyl‐CoA carboxylase (ACC) and JNK in U266 cells. Also, beta‐sitosterol attenuated the phosphorylation of AKT, mammalian target of rapamycin and S6K, and the expression of cyclooxygenase‐2 and VEGF in U266 cells. Conversely, AMPK inhibitor compound C and JNK inhibitor SP600125 suppressed apoptosis induced by beta‐sitosterol in U266 cells. Furthermore, ROS scavenger N‐acetyl L‐cysteine attenuated beta‐sitosterol‐mediated sub‐G₁ accumulation, PARP cleavage, JNK and AMPK activation in U266 cells. Overall, these findings for the first time suggest that ROS‐mediated activation of cancer metabolism‐related genes such as AMPK and JNK plays an important role in beta‐sitosterol‐induced apoptosis in U266 multiple myeloma cells. Copyright © 2013 John Wiley & Sons, Ltd.