Luteolin induces apoptosis through endoplasmic reticulum stress and mitochondrial dysfunction in Neuro-2a mouse neuroblastoma cells

Abstract

Luteolin, a dietary flavonoid, induces apoptosis in various types of cancer cells. However, its role in neuroblastoma and the underlying mechanisms remain to be elucidated. In the present study, we investigated the molecular mechanisms of the anti-cancer effect of luteolin in Neuro-2a mouse neuroblastoma cells. Luteolin induced apoptotic cell death and activation of caspase-12, -9, and -3, and knockdown of caspase-12 by siRNA transfection reduced luteolin-induced cell death. Luteolin also induced expression of endoplasmic reticulum (ER) stress-associated proteins, including C/EBP homologous protein (CHOP) and glucose-regulated proteins (GRP) 94 and 78, cleavage of ATF6α, and phosphorylation of eIF2α. CHOP knockdown or ER stress inhibitor, 4-phenylbutyric acid, reduced luteolin-induced cell death. These results suggest involvement of ER stress in luteolin-induced neuroblastoma cell death. We then showed that luteolin induced accumulation of reactive oxygen species and that the anti-oxidant N-acetylcysteine reduced luteolin-induced cell death and expression of CHOP and GRP78. We also demonstrated rapid reduction of mitochondrial membrane potential by luteolin, and N-acetylcysteine, as well as 4-phenylbutyric acid or CHOP siRNA transfection ameliorated luteolin-induced late loss, but not early loss of mitochondrial membrane potential. Finally, we showed that luteolin induced activation of mitogen-activated protein kinases such as JNK, p38, and ERK, and inhibitors of mitogen-activated protein kinases reduced luteolin-induced cell death and CHOP expression, as well as mitochondrial Bax translocation and cytochrome c release. Collectively, our results suggest that luteolin induces apoptosis through ER stress and mitochondrial dysfunction in Neuro-2a mouse neuroblastoma cells.