Fig. 2

P53 is the most important regulator in DNA damage. P53 is a substrate for both the ATM and ATR kinases, as well as for CHK1 and CHK2. Phosphorylation of p53 allows its interaction with transcriptional cofactors, transcribes and activates its target genes for extensive cell responses, such as cell cycle arrest, DNA repair, apoptosis and senescence. When DNA damage is difficult to be repaired, it will induce cell apoptosis, senescence, or mitotic catastrophe. The final death pathway depends on the function of checkpoints and the status of p53