Sterol regulatory element binding protein binds to a cis element in the promoter of the farnesyl diphosphate synthase gene.

Abstract

Sterol-regulated transcription of the gene for rat farnesyl diphosphate (FPP) synthase (geranyl-diphosphate:isopentenyl-diphosphate geranyltranstransferase, EC 2.5.1.10) is dependent in part on the binding of the ubiquitous transcription factor NF-Y to a 6-bp element within the proximal promoter. Current studies identify a second element in this promoter that is also required for sterol-regulated transcription in vivo. Mutation of three nucleotides (CAC) within this element blocks the 8-fold induction of FPP synthase promoter-reporter genes that normally occurs when the transfected cells are incubated in medium deprived of sterols. Gel mobility-shift assays demonstrate that the transcriptionally active 68-kDa fragment of the sterol regulatory element (SRE-1)-binding protein assays (SREBP-1) binds to an oligonucleotide containing the wild-type sequence but not to an oligonucleotide in which the CAC has been mutated. DNase 1 protection pattern (footprint) analysis indicates that SREBP-1 binds to nucleotides that include the CAC. Both the in vivo and in vitro assays are affected by mutagenesis of nucleotides adjacent to the CAC. Coexpression of SREBP with a wild-type FPP synthase promoter-reporter gene in CV-1 cells results in very high levels of reporter activity that is sterol-independent. In contrast, the reporter activity remained low when the promoter contained a mutation in the CAC trinucleotide. We conclude that sterol-regulated transcription of FPP synthase is controlled in part by the interaction of SREBP with a binding site that we have termed SRE-3. Identification of this element may prove useful in the identification of other genes that are both regulated by SREBP and involved in lipid biosynthesis.