ATM and cancer: In response to the damage caused by ionizing radiation, activated ATM phosphorylates P53, separates the binding of P53 to the negative regulator MDM2, causes cell cycle arrest, and promotes the binding of FBXW7 to P53, thus mediating the degradation of p53 to ensure that the accumulated p53 is restored to basal levels; this allows cancer cells to resume normal cell cycle progression and confers radioresistance [136].