Farnesyl pyrophosphate regulates adipocyte functions as an endogenous PPARγ agonist.

The cholesterol biosynthetic pathway produces not only sterols but also non-sterol mevalonate metabolites involved in isoprenoid synthesis. Mevalonate metabolites affect transcriptional and post-transcriptional events that in turn affect various biological processes including energy metabolism. In the present study, we examine whether mevalonate metabolites activate PPARγ (peroxisome-proliferator-activated receptor γ), a ligand-dependent transcription factor playing a central role in adipocyte differentiation. In the luciferase reporter assay using both GAL4 chimaera and full-length PPARγ systems, a mevalonate metabolite, FPP (farnesyl pyrophosphate), which is the precursor of almost all isoprenoids and is positioned at branch points leading to the synthesis of other longer-chain isoprenoids, activated PPARγ in a dose-dependent manner. FPP induced the in vitro binding of a co-activator, SRC-1 (steroid receptor co-activator-1), to GST (glutathione transferase)-PPARγ. Direct binding of FPP to PPARγ was also indicated by docking simulation studies. Moreover, the addition of FPP up-regulated the mRNA expression levels of PPARγ target genes during adipocyte differentiation induction. In the presence of lovastatin, an HMG-CoA (3-hydroxy-3-methylglutaryl-CoA) reductase inhibitor, both intracellular FPP levels and PPARγ-target gene expressions were decreased. In contrast, the increase in intracellular FPP level after the addition of zaragozic acid, a squalene synthase inhibitor, induced PPARγ-target gene expression. The addition of FPP and zaragozic acid promotes lipid accumulation during adipocyte differentiation. These findings indicated that FPP might function as an endogenous PPARγ agonist and regulate gene expression in adipocytes.

Development of a novel PPARγ ligand screening system using pinpoint fluorescence-probed protein.

The activation of peroxisome-proliferator-activated receptor-γ (PPARγ), which plays a central role in adipocyte differentiation, depends on ligand-dependent co-activator recruitment. In this study, we developed a novel method of PPARγ ligand screening by measuring the increase in fluorescent polarization accompanied by the interaction of a fluorescent co-activator and PPARγ. Sterol receptor co-activator-1 (SRC-1), a major PPARγ co-activator, was probed by fluorescent TAMRA by the Amber codon fluorescence probe method. Polarization was increased by adding PPARγ ligands to a solution containing labeled SRC-1 (designated TAMRA-SRC-S) and PPARγ. The disassociation constants (Kd) of the PPARγ synthesized ligands, pioglitazone (221 nM), troglitazone (83.0 nM), and 15-deoxy-Δ12,14-prostaglandin J(2) (15d-ΔPGJ(2)) (156 nM), were determined by this method. Farnesol (2.89 µM) and bixin (21.1 µM), which we have reported to be PPARγ ligands, increased the fluorescent polarization. Their Kd values were in agreement with the ED(50) values obtained in the luciferase assay. The results indicate that the method is valuable for screening natural PPARγ ligands.

Incorporation of fluorescent non-natural amino acids into N-terminal tag of proteins in cell-free translation and its dependence on position and neighboring codons.

Fluorescence labeling is a useful technique for structural and functional analyses of proteins. In a previous study, we developed position-specific incorporation of visible wavelength fluorescent non-natural amino acids carrying relatively small BODIPY fluorophores into proteins, in response to a four-base codon CGGG. Here, we have expanded this position-specific fluorescence labeling method to include relatively large non-natural amino acids carrying photostable rhodamine dyes. TAMRA-linked aminophenylalanine was synthesized and attached to a tRNA having a four-base anticodon, and its incorporation into proteins was examined in an Escherichia coli cell-free translation system. TAMRA-labeled amino acids were successfully incorporated into proteins, although incorporation was allowed only at the N-terminal region. Insertion of two codons encoding a stop codon in the +1 frame before four-base codon suppressed the expression of non-labeled proteins that may have been produced by spontaneous +1 frameshift upstream of the four-base codon. Alternation of the incorporation position affected the expression level of the TAMRA-labeled protein. In addition, alternation of upstream and downstream codons affected the efficiency and accuracy of TAMRA-labeled amino acid incorporation. Based on these results, a novel tag peptide was developed; it contained the four-base codon at the 9th position with optimized upstream and downstream codons. This tag peptide was effective for producing proteins with various fluorescent labels at the N-terminal region.

A thermostable dolichol phosphoryl mannose synthase responsible for glycoconjugate synthesis of the hyperthermophilic archaeon Pyrococcus horikoshii.

Dolichol phosphoryl mannose synthase (DPM synthase) is an essential enzyme in the synthesis of N- and O-linked glycoproteins and the glycosylphosphatidyl-inositol anchor. An open reading frame, PH0051, from the hyperthermophilic archaeon Pyrococcus horikoshii encodes a DPM synthase ortholog, PH0051p. A full-length version of PH0051p was produced using an E. coli in vitro translation system and its thermostable activity was confirmed with a DPM synthesis assay, although the in vitro productivity was not sufficient for further characterization. Then, a yeast expression vector coding for the N-terminal catalytic domain of PH0051p was constructed. The N-terminal domain, named DPM(1-237), was successfully expressed, and turned out to be a membrane-bound form in Saccharomyces cerevisiae cells, even without its hydrophobic C-terminal domain. The membrane-bound DPM(1-237) was solubilized with a detergent and purified to homogeneity. The purified DPM(1-237) showed thermostability at up to 75 degrees C and an optimum temperature of 60 degrees C. The truncated mutant DPM(1-237) required Mg(2+) and Mn(2+) ions as cofactors the same as eukaryotic DPM synthases. By site-directed mutagenesis, Asp(89) and Asp(91) located at the most conserved motif, DXD, were confirmed as the catalytic residues, the latter probably bound to a cofactor, Mg(2+). DPM(1-237) was able to utilize both acceptor lipids, dolichol phosphate and the prokaryotic carrier lipid C(55)-undecaprenyl phosphate, with Km values of 1.17 and 0.59 microM, respectively. The DPM synthase PH0051p seems to be a key component of the pathway supplying various lipid-linked phosphate sugars, since P. horikoshii could synthesize glycoproteins as well as the membrane-associated PH0051p in vivo.

Incorporation of beta-amyloid protein through the bovine ileal epithelium before and after weaning: model for orally transmitted amyloidoses.

To determine the mechanism of bovine intestinal incorporation of the pathogen, and the pathogenesis of prion protein in the early stage, cows suckling and weaning were orally given a fusion protein of Abeta-EGFP. Abeta-EGFP was incorporated through the villous columnar epithelial cells and accumulated in crypt patches in the ileum of suckling cows. The sites of the uptake and accumulation of Abeta-EGFP are very close to the peripheral nervous system; however, such uptake of Abeta-EGFP was not observed in 6-month-old post-weaning cows. The present study, therefore, suggests that the weaning period is very important for the risk of transmission.

Phytol directly activates peroxisome proliferator-activated receptor alpha (PPARalpha) and regulates gene expression involved in lipid metabolism in PPARalpha-expressing HepG2 hepatocytes.

The peroxisome proliferator-activated receptor (PPAR) is one of the indispensable transcription factors for regulating lipid metabolism in various tissues. In our screening for natural compounds that activate PPAR using luciferase assays, a branched-carbon-chain alcohol (a component of chlorophylls), phytol, has been identified as a PPARalpha-specific activator. Phytol induced the increase in PPARalpha-dependent luciferase activity and the degree of in vitro binding of a coactivator, SRC-1, to GST-PPARalpha. Moreover, the addition of phytol upregulated the expression of PPARalpha-target genes at both mRNA and protein levels in PPARalpha-expressing HepG2 hepatocytes. These findings indicate that phytol is functional as a PPARalpha ligand and that it stimulates the expression of PPARalpha-target genes in intact cells. Because PPARalpha activation enhances circulating lipid clearance, phytol may be important in managing abnormalities in lipid metabolism.