Peroxisome proliferator-activated receptor-delta upregulates 14-3-3 epsilon in human endothelial cells via CCAAT/enhancer binding protein-beta

Abstract

Peroxisome proliferator-activated receptor delta (PPARdelta) agonists are promising new agents for treatment of the metabolic syndrome. Although they possess antiatherosclerotic properties in vivo and promote endothelial cell survival, their mechanism of action is incompletely understood. 14-3-3epsilon is a critical component of the endothelial cell antiapoptotic machinery, which is essential to maintain homeostasis of the vascular wall. To test the hypothesis that PPARdelta targets 14-3-3epsilon in endothelial cells, we studied the response of the gene that encodes 14-3-3epsilon in humans, YWHAE, to PPARdelta ligands (L-165,041 and GW501516). We found that PPARdelta activates YWHAE promoter in a concentration and time-dependent manner. Consistent with these findings, L-165,041 increased 14-3-3epsilon mRNA and protein level, whereas PPARdelta small interfering RNA suppressed both basal and L-165,041-dependent YWHAE transcription and 14-3-3epsilon protein expression. Surprisingly, PPAR response elements in YWHAE promoter were not required for upregulation by PPARdelta, whereas a CCAAT/enhancer binding protein (C/EBP) site located at -160/-151 bp regulated both basal and PPARdelta-dependent promoter activity. Intriguingly, activation or knock down of endogenous PPARdelta regulated C/EBPbeta protein expression. Chromatin immunoprecipitation assays demonstrated that L-165,041 determines the localization of C/EBPbeta to the region spanning this C/EBP response element, whereas sequential chromatin immunoprecipitation analysis revealed that C/EBPbeta and PPARdelta form a transcriptional activating complex on this C/EBP site. Our work uncovers a novel role for C/EBPbeta as a mediator of PPARdelta-dependent 14-3-3epsilon gene regulation in human endothelial cells and provides insight into the mechanism by which PPARdelta agonists may be beneficial in atherosclerosis.