Figure 2.

Origins and effects of cellular reactive oxygen species (ROS). ROS are generated by complex I and III of the electron transport chain in the mitochondria and by NADPH oxidase (NOX) enzymes located at the cytoplasmic membrane (PM). ROS disrupt cellular processes by oxidizing the cysteine (Cys) residues of various proteins and damaging nucleic acids. Oxidation by ROS could cause the inactivation of phosphatases, activation of kinases and transcription factors (TF), and genomic alterations, leading to enhanced cellular proliferation and survival. ROS production is counteracted by the generation of antioxidants, such as superoxide dismutase (SOD), glutathione peroxidase (GPX), peroxiredoxin (PRX), thioredoxin (TRX), and catalase. In cancers, redox homeostasis is modified to favor ROS tolerance. OM: outer mitochondrial membrane. IM: inner mitochondrial membrane. NM: nuclear membrane.