The HumanADFPGene Is a Direct Liver-X-Receptor (LXR) Target Gene and Differentially Regulated by Synthetic LXR Ligands

Abstract

Expression of adipocyte differentiation-related protein (ADFP), residing on the surface of lipid droplets, correlates to hepatic fat storage. In the context of consequences and treatment of metabolic disorders, including hepatic steatosis, it is imperative to gain knowledge about the regulation of the human ADFP gene. The nuclear receptor liver-X-receptor (LXR) is a key regulator of hepatic fatty acid biosynthesis and cholesterol homeostasis as well as a potential drug target. Here, we report that two synthetic LXR ligands differently regulate human ADFP expression. The partialpropoxy]benzeneacetic acid hydrochloride (GW3965) significantly induces ADFP expression in human primary hepatocytes, whereas the full agonist N- (2,2,2-trifluoroethyl)-N-[4-[2,2,2-trifluoro-1-hydroxy-1(trifluoromethyl)ethyl]phenyl] benzenesulfonamide (T0901317) does not. Bioinformatics analysis revealed several potential LXR response elements (LXREs) in the human ADFP gene. By using chromatin immunoprecipitation and luciferase reporter assays, we show that LXR, upon stimulation with GW3965, directly regulates human ADFP transcription by binding to LXREs located in the 3Ј-untranslated and the 5Ј-flanking regions. The ligand-stimulated LXR recruitment was associated with recruitment of RNA polymerase II and the coactivators cAMP response element-binding protein-binding protein/ p300 to the promoter region demonstrating that the identified LXREs are functional and able to induce transcription. Moreover, our results show that sequence identity of the hexamer repeats in DR4 elements is not sufficient to determine whether the element binds LXR or not. The partial agonist GW3965 specifically regulates ADFP gene transcription, and our data prove that the two synthetic LXR agonists, commonly used in experimental research, can differentially regulate gene expression. This has implications for pharmaceutical targeting of LXR.

Activation of liver X receptor promotes fatty acid synthesis in goat mammary epithelial cells via modulation of SREBP1 expression

“…Perilipin 2 and perilipin 3 are 2 milk fat droplet proteins (Ogg et al, 2004;Ma and Corl, 2012); perilipin 2 is reported to be colocalized on the surface of lipid droplets (McIntosh et al, 2012) and is essential for the formation of milk fat lipid droplets and lactation, as demonstrated in mice (Russell et al, 2011). Studies to date have revealed that PLIN2 is mainly regulated transcriptionally by PPAR and LXR in monogastrics (Fan et al, 2009;Kotokorpi et al, 2010;Kang et al, 2015), indicating that the regulatory role of SREBP1 in milk fat droplet formation or secretion is not as strong as fatty acid synthesis, desaturation, elongation, and TAG synthesis. Using the free web-based tool Lasagna (Lee and Huang, 2013), we analyzed the promoter region of sheep PLIN2 for SREBP1 and LXR (NR1H2: RXR in Jaspar core matrices) response elements.…”

Cancer-Preventive Rexinoid Modulates Neutral Lipid Contents of Mammary Epithelial Cells through a Peroxisome Proliferator-Activated Receptor γ-Dependent Mechanism

“…ADFP is localized at the surface of lipid droplets in adipocytes and a variety of other cells, including fibroblasts, macrophages, hepatocytes, and mammary epithelial cells (Brasaemle et al, 1997), and stimulates lipid accumulation when overexpressed (Imamura et al, 2002). It has been determined that the human ADFP gene is a direct LXR target (Kotokorpi et al, 2010); because an RXR/LXR heterodimer might be activated through the RXR partner, ADFP could potentially be up-regulated by rexinoids. It is noteworthy that knockdown of either LXR␣ or LXR␤ was unable to block lipid droplet formation in HMECs (data not shown), which suggests that the induction of ADFP is not the driving force behind the accumulation of lipid droplets in HMECs.…”

Bioinformatics and Drug Discovery

“…The last approach is facilitated by the availability of extensively compiled and curated databases of known regulatory motifs [21][22][23] weight matrix (PWM) to find the genomic location of a known motif, Gibbs sampler for de novo motif discovery [24,25] and support vector machines [26,27] that can be used to extract differences between two groups of sequences (e.g., motif-present and motif-absent) and to use the resulting information to detect/scan motifs in genomes. The regulatory motifs could be response elements of nuclear receptors whose identification often leads to refinement of drug targets [28]. Such studies are facilitated by software such as DAMBE [29] which, when given an annotated genomic sequence, can extract coding sequences, rRNAs, tRNAs, introns, exons, 5' and 3' splice sites, upstream or downstream sequences of gene features, etc., with just a few mouse clicks.…”