Inhibition Of Melanoma Growth By GSDME-dependent Pyroptosis

Various types of tumor cells produce higher levels of reactive oxygen species(ROS)than normal cells.Tumor cells strive to scavenge excessive ROS by their antioxidant systems to maintain pro-tumorigenic signaling and apoptotic resistance.Once the tumor cells fail to maintain the balance of ROS level,the anti-tumor signaling pathway will be activated and causing oxidative stress induced-cancer cell death.Although iron is essential for cell growth and homeostasis,it is potentially toxic to cells and tissues.The role of iron and ROS in cell death has been controversial.Therefore,it is necessary to study how iron and ROS cause cell death,and whether they can be use in cancer treatment.Pyroptosis is a newly discovered programmed death mediated by gasdermin family proteins including GSDMD and GSDME.In previous studies,we have shown that iron activates ROS signaling in melanoma cells,inducing Tom20dependent GSDME-mediated pyroptosis.However,how Tom20 senses ROS and activates downstream caspases and whether the combination of iron and ros-inducing drugs can be used to treat melanoma are still unclear.In this study,we demonstrate that the mitochondrial membrane protein Tom20 senses iron and ROS-inducing drug stimulation in melanoma cells A375.It was found that iron-activated ROS oxidized the cysteine residues of Tom20 protein and induced Tom20 oligomerization,which significantly enhanced the interaction between Tom20 and Bax,the bcl-2 family protein,thereby promoting Bax translocation to mitochondria to induce the release of cytochrome C to the cytoplasm,led to the activation of caspase9 and caspase-3.Finally,GSDME was cleaved and activated by caspase-3,and resulted in pyroptosis.In subcutaneous xenograft tumor model and lung metastatic model,the combination treatment of iron and ROS-inducing drugs could inhibit the growth and metastasis of melanoma,the inhibitory effect was GSDME-dependent with GSDME cleavage.However,the combination treatment of iron and ROS-inducing drugs showed no obvious effects on the body weight,spleen weight and intestinal tract of mice,indicating less toxicity in mice.To sum up,this study not only proves that iron-activated ROS can induce pyroptosis in melanoma cells through the novel Tom20-bax-caspase-GSDME pathway,but also suggests that iron can be used as a sensitizer to effectively inhibit the growth and metastasis of melanoma,which has referential significance for the treatment of melanoma.