Murine double minute (MDM2) is an E3 ligase that promotes ubiquitination and 
degradation of tumor suppressor protein 53 (p53). MDM2-mediated regulation of 
p53 has been investigated as a classical tumorigenesis pathway. Here, we 
describe TRIAD1 as a novel modulator of the p53-MDM2 axis that induces p53 
activation by inhibiting its regulation by MDM2. Ablation of TRIAD1 attenuates 
p53 levels activity upon DNA damage, whereas ectopic expression of TRIAD1 
promotes p53 stability by inhibiting MDM2-mediated ubiquitination/degradation. 
Moreover, TRIAD1 binds to the C-terminus of p53 to promote its dissociation from 
MDM2. These results implicate TRIAD1 as a novel regulatory factor of p53-MDM2.