Esculetin induces apoptosis in human colon cancer cells by inducing endoplasmic reticulum stress

Colorectal cancer has become more common in many regions of the world. Recently, we showed that esculetin, a natural coumarin, induces apoptosis in HT-29 colon cancer cells via the reactive oxygen species-mediated mitochondrial pathway. The present study examined whether esculetin induces apoptosis in HT-29 colon cancer cells by inducing endoplasmic reticulum (ER) stress. We found that esculetin induced characteristic signs of ER stress, confirmed by ER staining, mitochondrial calcium overload and expression of ER stress-related proteins (i.e. glucose regulated protein 78, phosphorylated ribonucleic acid-dependent protein kinase-like ER kinase, phosphorylated inositol requiring enzyme 1, phosphorylated eukaryotic initiation factor-2α, spliced X-box binding protein 1 and cleaved activating transcription factor 6). Esculetin also induced the expression of the CCAAT/enhancer-binding protein-homologous protein (CHOP) and pro-apoptotic factors caspase-12. Moreover, transfection of colon cancer cells with a small interfering ribonucleic acid targeting CHOP attenuated esculetin-induced apoptosis. Taken together, these results suggest that the ER stress response plays an important role in esculetin-induced apoptosis in human colon cancer cells.