TRIAD1 Is a Novel Transcriptional Target of p53 and Regulates Nutlin‐3a‐Induced Cell Death

ABSTRACT Nutlin‐3a is a non‐genotoxic, p53‐activating, MDM2 inhibitor being investigated as an anticancer agent. Although Nutlin‐3a selectively antagonizes the ubiquitin E3 ligase activity of MDM2, its efficacy is not entirely regulated by MDM2 levels in cancer cells. Here, we report that the cytotoxic effects of Nutlin‐3a are regulated by TRIAD1 via a positive feedback loop with p53. We found that Nutlin‐3a enhanced TRIAD1 transcription in a p53‐dependent manner. Using in silico analysis and promoter luciferase assays, we demonstrated that p53‐mediated transcription of TRIAD1 is mediated by a p53 consensus sequence in the TRIAD1 promoter region. Silencing TRIAD1 expression in wild‐type p53 (p53WT) cancer cells suppressed Nutlin‐3a‐mediated p53 activation and p53 target gene expression. These effects were enhanced in TRIAD1‐overexpressing p53WT cancer cells, but not in p53‐deficient cancer cells. Furthermore, TRIAD1 knockdown significantly reduced the growth inhibitory and cytotoxic effects of Nutlin‐3a in p53WT cancer cells, as demonstrated by cell viability assays, cell cycle analysis, clonogenic growth, and soft‐agar colony forming assays. Together, these data indicate that TRIAD1 regulates Nutlin‐3a‐mediated p53 activation and the cytotoxic activity of Nutlin‐3a. J. Cell. Biochem. 118: 1733–1740, 2017. © 2016 Wiley Periodicals, Inc. In this manuscript, we, for the first time, demonstrated that TRIAD1 has a positive feedback loop with tumor suppressive factor p53 and is involved in Nutlin‐3a‐induced p53 activation and its cytotoxic effects.