Expression of the rat peroxisomal 3-ketoacyl-CoA thiolase gene B is induced by peroxisome proliferators. Although a sequence element like a peroxisome proliferator-activated receptor (PPAR)-binding site is located in the promoter region of this gene, we previously found that this element is competent for the activation by hepatocyte nuclear factor-4, but not functional with PPARalpha. We describe here a new peroxisome proliferator-response element located in the intron 3 (+1422/+1434) that binds in vitro the PPARalpha/retinoid X receptor alpha heterodimer and confers the induction by PPARalpha in transfection assays. We propose a model of regulation of the rat thiolase B gene involving those elements in the promoter and intron 3.
