Effects of p53 in the intracellular oxidant system. According to a new model of p53-dependent regulation of ROS, p53 acts on the intracellular antioxidant system in both unstressed and low-stressed cells through the up-regulation of a series of genes (indicated in light gray boxes), including Gpx1, Mn-SOD2 and catalase. GPX catalyzes the oxidation of GSH into GSSG; Mn-SOD2 is localized in mitochondria and catalyzes the dismutation of superoxide () into oxygen and hydrogen peroxide (H2O2), whereas catalase catalyzes the decomposition of H2O2 to water and oxygen. When high levels of stress are present, p53 induces the transcription of several pro-oxidant as well as pro-apoptotic genes, such as bax (in dark gray circle), with the consequent release of cytochrome c from mitochondria, activation of caspases and induction of apoptosis.
