MiR-657/ATF2 Signaling Pathway Has a Critical Role in Spatholobus suberectus Dunn Extract-Induced Apoptosis in U266 and U937 Cells

Though Spatholobus suberectus Dunn (SSD) has been reported to have anti-virus, anti-osteoclastogenesis, and anti-inflammation activities, its underlying anti-cancer mechanism has never been elucidated in association with the role of miR-657 in endoplasmic reticulum (ER) stress-related apoptosis to date. SSD treatment exerted cytotoxicity in U266 and U937 cells in a dose-dependent manner. Also, apoptosis-related proteins such as PARP, procaspase-3, and Bax were regulated by SSD treatment. Furthermore, Terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) assay revealed that a number of apoptotic bodies were increased by SSD. Interestingly, the ER stress-related proteins such as p-ATF2 and CHOP were elevated by SSD. Interestingly, reactive oxygen species (ROS) generation and cytotoxicity by SSD treatment were significantly reduced by N-Acetyl-L-cysteine (NAC). Among the microRNAs (miRNAs) regulated by SSD treatment, miR-657 was most significantly reduced by SSD treatment. However, an miR-657 mimic reversed SSD-induced apoptosis by the attenuation of the expression of p-ATF2, CHOP, and PARP cleavage. Overall, these findings provide scientific evidence that miR657 is an onco-miRNA targeting the ER stress signal pathway and SSD induces apoptosis via the inhibition of miR-657, ROS, and the activation of p-ATF2 and CHOP as a potent anti-cancer agent for myeloid-originated hematological cancer.