Rat sterol carrier protein-X expression is induced by a peroxisome proliferator-activated receptor

Sterol carrier protein-X is a peroxisomal protein which has 3-oxoacyl coenzyme A thiolase activity and, thus, appears to be involved in the /3-oxidation of fatty acids (FA). To define a mechanism through which FAs may regulate SCPx, we hypothesize that SCPx is transcriptionally controlled via a peroxisome proliferator-activated receptor (PPAR). PPAR, acting as a heterodimer with the retinoid-X-receptor (RXR), has been shown to bind to a peroxisome proliferator response element (PPRE) in genes encoding FA-metabo!izing peroxisomal enzymes. To address this, a clone containing the 5' promoter region of SCPx was isolated from an arrayed PI rat genomic library and 2 kb of 51 ATG flanking region was sequenced. Within this TATA-less promoter, a chimeric PPRE sequence was identified at nucleotides -121 to -133 relative to the ATG. A 935 bp region containing this putative PPRE was subcloned into a chloramphenicol acetyltransferase (CAT) reporter plasmid (pPROXCAT) which was cotransfected into 1A4 bladder carcinoma cells +/- expression plasmids containing PPAR and/or RXR cDNAs. These constructs were then used to determine whether the putative SCPx PPRE was activated by PPAR and/or RXR in CAT assays. Results indicate that pPROX-CAT cotransfected with PPAR alone stimulated CAT activity 4-fold while RXR alone activated CAT 5-fold. When both PPAR and RXR were cotransfected with pPROX-CAT, activity increased 16-fold. Deletion fragments of the 935 bp SCPx promoter indicate that a 104 bp fragment void of the PPRE did not. induce CAT expression whereas all larger fragments containing the PPRE induced CAT activity at least 4-fold over background. This study is the first to demonstrate PPAR activation of the SCPx promoter and to localize the PPRE within the SCPx promoter region. Supported by AHA-PDF#9405014 (RBI)fc AHA-GIA#9501360 (MPM).