Steroids 68 (2003) 685–691 Transcriptional regulation of farnesyl pyrophosphate synthase by liver X receptors Junichi Fukuchi, Ching Song, Andrew L. Ko, Shutsung Liao ∗ Department of Biochemistry and Molecular Biology, The Ben May Institute for Cancer Research, The University of Chicago, Box MC 6027, 5841 South Maryland Avenue, Chicago, IL 60637, USA Received 24 April 2003; received in revised form 11 June 2003; accepted 16 June 2003 Abstract Liver X receptors (LXRs) are members of the nuclear receptor superfamily that are involved in cholesterol and lipid metabolism. In addition to liver, the brain is another site where LXRs may control cholesterol homeostasis. In the brain, the regulation of cholesterol homeostasis is independent from other parts of the body, and its disturbance is associated with neurodegenerative disorders, such as Alzheimer’s disease. We have used PCR-based suppressive subtractive cloning to identify new LXR target genes in brain cells. In this report, we show that farnesyl pyrophosphate synthase (FPPS) is a new target gene for LXR in astrocytes and neurons. Farnesyl pyrophosphate is an obligate intermediate for de novo cholesterol synthesis and a substrate for protein farnesylation. Stimulation of FPPS mRNA synthesis by an LXR agonist, Hypocholamide, was observed in several cell lines from the central nervous system. We identified a single putative direct repeat 4 (DR4) LXR response element in the FPPS promoter. In a reporter gene assay, LXR transactivated a reporter gene bearing a truncated FPPS promoter containing this DR4 cis-element but not if the DR4 element was mutated. Using gel-mobility shift assay, we further demonstrated the direct interaction between the LXR/retinoid X receptor (RXR) heterodimer and the response element. Taken together, our results indicate that LXRs directly regulate FPPS gene expression, and thus may play a role in modulating cholesterol synthesis in the brain. © 2003 Elsevier Inc. All rights reserved. Keywords: LXR; FPPS; Cholesterol; Brain 1. Introduction A number of nuclear receptors have been identified as key regulators of cholesterol homeostasis [1,2]. The liver X receptors (LXRs) bind to oxidized forms of cholesterol and activate target gene expression. LXR has a relatively restricted expression pattern (liver, kidney, intestine, adi- pose tissue, and adrenals), whereas LXR is ubiquitously expressed and so was also named ubiquitous receptor or UR [3–7]. LXR and LXR show a high degree of amino acid similarity (78%). It has been proposed that they share identical target genes [8]. LXRs bind DNA as obligate het- erodimers with retinoid X receptor (RXR) that are activated by their endogenous ligand, 9-cis-retinoic acid. LXR/RXR binds with high affinity to a DNA sequence called direct re- peat 4 (DR4). Studies with mice lacking LXR have revealed a physiological role for LXR [9]. These mice fail to adapt metabolically when challenged with high cholesterol diets and accumulate cholesterol in the liver. The first gene dis- ∗ Corresponding author. Tel.: +1-773-702-6999; fax: +1-773-834-1770. E-mail address: sliao@huggins.bsd.uchicago.edu (S. Liao). covered as an LXR target, rodent cholesterol 7-hydroxylase (CYP7A1) is a rate-limiting enzyme in the conversion of cholesterol to bile acids [10]. Other LXR target genes in- volved in lipid metabolism include the human cholesteryl ester transfer protein [11] which translocates cholesteryl esters between lipoprotein fractions and the ATP-binding cassette transporters, ABCA1 [12–14] and ABCG1 [15], which are implicated in the efflux of cellular free cholesterol. Apolipoprotein E (ApoE) is also one of the target genes [16] and is an important modulator of atherogenesis. In addition, sterol regulatory element-binding protein 1c (SREBP-1c), a transcription factor known to regulate the expression of li- pogenic enzymes, is regulated by LXRs through LXR re- sponse elements in its promoter [17–19]. The hypothesis that LXRs can sense cholesterol levels and mediate the induc- tion of genes within cholesterol metabolic pathways makes LXRs attractive pharmaceutical targets [20,21]. On the other hand, cholesterol is not only a major lipid component of mammalian cell membrane [22], but also plays a key role in synaptogenesis and is essential for optimal release of neurotransmitter [23]. Virtually all of the cholesterol present in the brain is derived from in situ 0039-128X/$ – see front matter © 2003 Elsevier Inc. All rights reserved. doi:10.1016/S0039-128X(03)00100-4