Dictyopteris undulata Extract Induces Apoptosis via Induction of Endoplasmic Reticulum Stress in Human Colon Cancer Cells

BACKGROUND Induction of endoplasmic reticulum (ER) stress-mediated apoptosis in cancer cells represents an alternative approach for cancer therapy. The objective of this study was to elucidate whether ethanol extract of the marine brown alga Dictyopteris undulata can induce apoptosis, via ER stress, in human colon adenocarcinoma cells. METHODS Anti-proliferative activity was evaluated by the colony forming assay. ER stress response was evaluated using flow cytometry and confocal imaging after Rhod2 and ER tracker staining. The expression of ER stress-related proteins was assessed by Western blotting. RESULTS D. undulata extract (DUE) inhibited colony forming ability in SW480 cells. Furthermore, DUE induced characteristic signs of ER stress: mitochondrial Ca(2+) overloading, ER staining, expression of ER stress-related proteins, phosphorylation of RNA-dependent protein kinase-like ER kinase and inositol requiring enzyme 1, cleavage of activating transcription factor 6, and induction of the pro-apoptotic factors, CCAAT/enhancer-binding protein-homologous protein (CHOP) and caspase-12. Moreover, down-regulation of CHOP by siCHOP RNA attenuated DUE-induced apoptosis. CONCLUSIONS The ER stress response plays an important role in DUE-induced apoptosis in human colon cancer cells.