IDENTIFICATION OF A PEROXISOME PROLIFERATOR-RESPONSIVE ELEMENT UPSTREAM OF THE HUMAN PEROXISOMAL FATTY ACYL-COENZYME-A OXIDASE GENE

Peroxisome proliferators cause a rapid and coordinated transcriptional activation of genes encoding the enzymes of the peroxisomal beta-oxid ation pathway in rats and mice. Cis-acting peroxisome proliferator res ponsive elements (PPREs) have been identified in the 5'-flanking regio n of H2O2-producing rat acyl-CoA oxidase (ACOX) gene and in other gene s inducible by peroxisome proliferators. To gain more insight into the purported nonresponsiveness of human liver cells to peroxisome prolif erator-induced increases in peroxisome volume density and in the activ ity of the beta-oxidation enzyme system, we have previously cloned the human ACOX gene, the first and rate-limiting enzyme of the peroxisoma l beta-oxidation system. We now present information on a regulatory el ement for the peroxisome proliferator-activated receptor (PPAR)/retino id X receptor (RXR) heterodimers. The PPRE, consists of AGGTCA C TGGTC A, which is a direct repeat of hexamer half-sites interspaced by a sin gle nucleotide (DR1 motif). It is located at - 1918 to - 1906 base pai rs upstream of the transcription initiation site of this human ACOX ge ne. This PPRE specifically binds to baculovirus-expressed recombinant rat PPAR alpha/RXR alpha heterodimers. In transient transfection exper iments, the maximum induction of luciferase expression by ciprofibrate and/or 9-cis-retinoic acid is dependent upon cotransfection of expres sion plasmids for PPAR alpha and RXR alpha. The functionality of this human ACOX promoter was further demonstrated by linking it to a beta-g alactosidase reporter gene or to a rat urate oxidase cDNA and establis hing stably transfected African green monkey kidney (CV1) cell lines e xpressing reporter protein, The human ACOX promoter has been found to be responsive to peroxisome proliferators in CV1 cells stably expressi ng PPAR alpha, whereas only a basal level of promoter activity is dete cted in stably transfected cells lacking PPAR alpha. The presence of a PPRE in the promoter of this human peroxisomal ACOX gene and its resp onsiveness to peroxisome proliferators suggests that factors other tha n the PPRE in the 5'-flanking sequence of the human ACOX gene may acco unt for differences, if any, in the pleiotropic responses of humans to peroxisome proliferators.