Characterization of a response element for peroxisomal proliferator activated receptor (PPRE) in human muscle-type carnitine palmitoyltransferase I

Abstract

Peroxisome proliferator-activated receptors (PPARs) play a key role in lipid metabolism by regulating the transcription of genes involved in fatty acid oxidation. This study identifies and characterizes a functional peroxisome proliferator response element (PPRE) in the 5′ flanking region of the human muscle-type carnitine palmitoyltransferase I (MCPT I) gene. Electrophoretic mobility shift assays revealed strong binding of PPAR–RXR heterodimers to this element, whereas individual receptors did not show significant binding. Transient transfection experiments in CV1 cells demonstrated that PPARα and PPARγ, but not PPARδ, activated the MCPT I promoter in the presence of fatty acid ligands. Furthermore, insertion of the MCPT I PPRE into a normally unresponsive thymidine kinase promoter conferred PPAR responsiveness, and site-directed mutagenesis of the DR-1 core abolished activation. These results demonstrate that MCPT I is a direct PPAR target gene. In addition, competition with other nuclear receptors such as COUP-TF and HNF-4 modulates PPRE activity, indicating a complex regulatory network. Together with previous findings on HMG-CoA synthase and other lipid-metabolism genes, these data support a model in which free fatty acids regulate their own oxidation through transcriptional control in both hepatic and extrahepatic tissues. This mechanism highlights the central role of PPARs in coordinating energy metabolism.