Histone modifications affect differential regulation of TGF-beta/SMAD3-induced Nox4 by p53
Wednesday, September 14, 2016 — Poster Session I
- HE Boudreau
- A Korzeniowska
- TL Leto
Recent studies suggest p53 plays an important role in TGF-beta-mediated cell signaling and migration. Previously, we showed wild-type (WT) and mutant (mt) forms of p53 differentially regulate reactive oxygen species (ROS) generation by NADPH oxidase-4 (Nox4): WT-p53 suppresses TGF-beta-induced Nox4, ROS production, and cell migration, whereas several tumor-associated p53-mt proteins enhance Nox4 expression and cell migration by TGF-beta/SMAD3-dependent mechanisms. Here we examined the basis of human Nox4 promoter regulation by p53 and SMAD3. By deletion analysis of the Nox4 promoter, we identified two critical SMAD3 binding elements (SBEs) required for mutant p53-induced promoter activity between -3975 and -4760 bp relative to the transcription start site. Conversely, promoter activity was abolished by dose-dependent expression of p53-WT. Expression of active SMAD3 resulted in robust Nox4 promoter activity, which was abolished when co-expressed with p53-WT. Moreover, mutations in the transactivation domain of p53 relieved the repressive effects of WT-p53, further supporting a model in which WT-p53 acts as a direct repressor of the Nox4 promoter. Interestingly, other evidence suggests WT and mt p53 also act through epigenetic mechanisms to differentially affect Nox4 expression. The repressive effect by p53-WT on Nox4 was relieved upon treatment with histone deacetylase (HDAC) inhibitors or HDAC2 silencing. Finally, overexpression of p300, a known p53-mt-binding transcriptional co-regulator and histone acetyltranserfase (HAT), enhanced p53-mt-mediated Nox4 promoter activity and cell migration, whereas HAT-inactive p300-mt reduced these effects. Collectively, these results provide insight into regulation and epigenetic control of Nox4 by TGF-beta/SMAD3 and p53 that may influence metastatic activities in advanced cancers.
Category: Cancer Biology