Mouse γ-butyrobetaine dioxygenase is regulated by peroxisome proliferator-activated receptor α through a PPRE located in the proximal promoter

Convincing evidence from studies with peroxisome proliferator-activated receptor (PPAR)alpha-deficient mice suggested that the carnitine biosynthetic enzyme gamma-lputyrobetaine dioxygenase (BBD) is regulated by PPAR alpha. However, the identification of BBD as a direct PPAR alpha target gene as well as its exact regulation remained to be demonstrated. In silico-analysis of the mouse BBD promoter revealed seven putative peroxisome proliferator response elements (PPRE) with high similarity to the consensus PPRE. Luciferase reporter gene assays using mutated and non-mutated serial 5'-truncation BBD promoter reporter constructs revealed that one PPRE located at -75 to -87 relative to the transcription start site in the proximal BBD promoter is probably functional. Using gel. shift assays we observed in vitro-binding of PPAR alpha/RXR alpha heterodimer to this PPRE confirming that it is functional. In conclusion, the present study clearly shows that mouse BBD is a direct PPAR alpha target gene and that transcriptional up-regulation of mouse BBD by PPARa is likely mediated by binding of the PPAR alpha/RXR heterodimer to one PPRE located in its proximal promoter region. The results confirm emerging evidence from recent studies that PPAR alpha plays a key role in the regulation of carnitine homeostasis by controlling genes involved in both, carnitine synthesis and carnitine uptake. (C) 2011 Elsevier Inc. All rights reserved.