Figure 1. The effect of oxidative stress on cell survival. At low levels of oxidative stress, p21 activates the Nrf2-dependent antioxidant response which protects cells from ROS induced cellular damage. At moderate levels of oxidative stress, p21 induces cell cycle arrest to allow time for DNA repair. At high levels of oxidative stress, Nrf2 is destroyed and the Nrf2-dependent pro-survival response is inhibited and the pro-apoptotic response is initiated activating apoptosis.