Three Members of the Human Pyruvate Dehydrogenase Kinase Gene Family Are Direct Targets of the Peroxisome Proliferator-activated Receptor β/δ

Abstract

The nuclear receptors peroxisome proliferator-activated receptors (PPARs) are known for their critical role in the metabolic syndrome. Here, we show that they are direct regulators of the family of pyruvate dehydrogenase kinase ( PDK) genes, whose products act as metabolic homeostats in sensing hunger and satiety levels in key metabolic tissues by modulating the activity of the pyruvate dehydrogenase complex. Mis-regulation of this tightly controlled network may lead to hyperglycemia. In human embryonal kidney cells we found the mRNA expression of PDK2, PDK3 and PDK4 to be under direct primary control of PPAR ligands, and in normal mouse kidney tissue Pdk2 and Pdk4 are PPAR targets. Both, treatment of HEK cells with PPARβ/δ-specific siRNA and the genetic disruption of the Pparβ/δ gene in mouse fibroblasts resulted in reduced expression of Pdk genes and abolition of induction by PPARβ/δ ligands. These findings suggest that PPARβ/δ is a key regulator of PDK genes, in particular the PDK4/ Pdk4 gene. In silico analysis of the human PDK genes revealed two candidate PPAR response elements in the PDK2 gene, five in the PDK3 gene and two in the PDK4 gene, but none in the PDK1 gene. For seven of these sites we could demonstrate both PPARβ/δ ligand responsiveness in context of their chromatin region and simultaneous association of PPARβ/δ with its functional partner proteins, such as retinoid X receptor, co-activator and mediator proteins and phosphorylated RNA polymerase II. In conclusion, PDK2, PDK3 and PDK4 are primary PPARβ/δ target genes in humans underlining the importance of the receptor in the control of metabolism.