Endoplasmic reticulum stress triggered by Soyasapogenol B promotes apoptosis and autophagy in colorectal cancer

Colorectal cancer (CRC) is a common human malignancy which accounts for 600,000 deaths annually at the global level. Soyasapogenol B (Soy B), an ingredient of soybean, has been found to exert anti-proliferative activities in vitro in human breast cancer cells. The current study aimed to evaluate the efficacy of Soy B in suppressing CRC.The effect of Soy B on cell viability was assessed using the Cell Counting Kit-8 (CCK-8) assay. The effect of Soy B on cell proliferation was determined using colony formation assay. The percentage of apoptotic cells was determined by the TUNEL assay and flow cytometry following Annexin V-FITC/Propidium Iodide (PI) double staining. JC-1 staining was performed to examine the change in mitochondrial membrane potential. Autophagy was examined by acridine orange staining and mRFP-GFP-LC3 adenovirus transfection. Caspase-12 activities were determined by ELISA kit. Western blotting was used to determine the expression of relevant proteins. To investigate the role of autophagy in the pro-death and pro-apoptotic activities of Soy B, autophagy inhibitors Bafilomycin A1 (Baf-A1) and Atg5 siRNA were utilized. TUDCA and CHOP shRNA were utilized to block ER stress. Moreover, a CRC xenograft murine model was used to analyze the therapeutic efficacy of Soy B in vivo.Soy B treatment decreased the number of viable cells and colonies formed in CRC cell lines. Moreover, Soy B treatment promoted the apoptotic cell death via the intrinsic pathway and autophagy which positively contributed to cell death and apoptosis. In addition, our results showed that ER stress, triggered by Soy B, mediated apoptosis and autophagy. In vivo results revealed that Soy B could suppress tumor growth, which was associated with increased ER stress, accompanied with apoptosis and autophagy induction.Soy B was able to promote cell death in vitro and in vivo. Our findings highlight the possibility of utilizing Soy B as a chemotherapeutic agent to prevent and treat CRC.