TP53 and cancer: After hypoxia-mediated DNA double-strand breaks, the MRE11-RAD50-NBS1 (MRN) complex activates ATM and is autophosphorylated at serine 367 (ser367), serine 1893 (ser1893), serine 1981 (ser1981), and serine 2996 (ser2996), thereby inducing MRE11-RAD50-NBS1 (MRN) complex-associated recruitment of various complex phosphorylation cascades, such as p53 (cancer suppressor), CHK1, and CHK2, to the DNA DSB sites.