Peroxisome proliferator-activated receptor-δ upregulates 14-3-3ε in human endothelial cells via CCAAT/enhancer binding protein-β

Peroxisome proliferator-activated receptor delta (PPAR delta) 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. 14-3-3 epsilon 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 PPAR delta targets 14-3-3 epsilon in endothelial cells, we studied the response of the gene that encodes 14-3-3 epsilon in humans, YWHAE, to PPAR delta ligands (L-165,041 and GW501516). We found that PPAR delta activates YWHAE promoter in a concentration and time-dependent manner. Consistent with these findings, L-165,041 increased 14-3-3 epsilon mRNA and protein level, whereas PPAR delta small interfering RNA suppressed both basal and L-165,041-dependent YWHAE transcription and 14-3-3 epsilon protein expression. Surprisingly, PPAR response elements in YWHAE promoter were not required for upregulation by PPAR delta, whereas a CCAAT/enhancer binding protein (C/EBP) site located at -160/-151 bp regulated both basal and PPAR delta-dependent promoter activity. Intriguingly, activation or knock down of endogenous PPAR delta regulated C/EBP beta protein expression. Chromatin immunoprecipitation assays demonstrated that L-165,041 determines the localization of C/EBP beta to the region spanning this C/EBP response element, whereas sequential chromatin immunoprecipitation analysis revealed that C/EBP beta and PPAR delta form a transcriptional activating complex on this C/EBP site. Our work uncovers a novel role for C/EBP beta as a mediator of PPAR delta-dependent 14-3-3 epsilon gene regulation in human endothelial cells and provides insight into the mechanism by which PPAR delta agonists may be beneficial in atherosclerosis.