Identification of a peroxisome-proliferator-activated-receptor response element in the apolipoprotein E gene control region

Apolipoprotein E (apoE) is a protein involved in reverse cholesterol transp ort. Among other tissues, apoE is expressed in macrophages where its expres sion increases when macrophages develop into foam cells. It has been recent ly shown that peroxisome-proliferator-activated receptor gamma (PPAR gamma) is involved in this conversion. Northern-blot analysis was carried out in the macrophage cell line THP I to determine whether apoE mRNA levels were r egulated by ciglitazone, a PPAR gamma inducer, The results indicated that t reatment with ciglitazone doubled the levels of apoE mRNA. To identify a po ssible PPARy response element (PPRE), several portions of apoE gene control region were used to construct luciferase reporter plasmids. In U-87 MG cel ls, a 185 bp fragment located in the apoE/apoCl intergenic region was suffi cient to induce a 10-fold increase in the luciferase activity of the extrac t of cells co-transfected with a PPARy expression plasmid. Subsequent analy sis revealed the presence of a sequence with a high level of sequence simil arity to the consensus PPRE. Mutations in this sequence resulted in a lack of functionality both in transient transfection and in electrophoretic-mobi lity-shift assays. These results demonstrated the presence of a functional PPRE in the apoE/apoCl intergenic region. These results have implications f or the regulation of apoE gene expression and could be relevant for underst anding the anti-atherogenic effect of thiazolidinediones.