Surfactin induces autophagy, apoptosis, and cell cycle arrest in human oral squamous cell carcinoma

Objectives: To investigate the anticancer effects and underlying mechanisms of surfactin on human oral squamous cell carcinoma (OSCC). Materials and Methods: The capacity of surfactin to induce apoptosis, autophagy, and cell cycle arrest of two different human OSCC cell lines was investigated by cell viability, acridine orange staining, and cell cycle regulatory protein expression, respectively. The signaling network underlying these processes were determined by the analysis of reactive oxygen species (ROS) generation, nicotinamide adenine dinucleotide phosphate (NADPH) oxidase activity, endoplasmic reticulum (ER) stress-related protein levels, calcium release, mitogen-activated protein kinases activation, and cell cycle regulatory protein expression through corresponding reagents and experiments under various experimental conditions using specific pharmaceutical inhibitors or small interfering RNAs. Results: Surfactin was able to induce apoptosis through NADPH oxidase/ROS/ER stress/calcium-downregulated extracellular signal-regulated kinases 1/2 pathway. Surfactin could also lead to autophagy that shared the common regulatory signals with apoptosis pathway until calcium node. Cell cycle arrest at G₂/M phase caused by surfactin was demonstrated through p53 and p21 accumulation combined p34^cdc2, phosphorylated p34^cdc2, and cyclin B1 inhibition, which was regulated by NADPH oxidase-derived ROS. Conclusion: Surfactin could induce apoptosis, autophagy, and cell cycle arrest in ROS-dependent manner, suggesting a multifaced anticancer agent for OSCC.