Examination of Ligand-Dependent Coactivator Recruitment by Peroxisome Proliferator-Activated Receptor-α (PPARα)

The ligand-dependent recruitment of coactivators to peroxisome proliferator-activated receptor-α (PPARα) was examined. PPAR-binding protein (PBP), PPARγ coactivator-1α (PGC-1α), steroid receptor coactivator-1 (SRC-1), and CBP/p300-interacting transactivator with ED-rich tail 2 (CITED2) affected PPARα activity in the presence of Wy-14,643. The effects on PPARα activity in light of increased or decreased expression of these coactivators were qualitatively different depending on the ligand examined. Diminished expression of PGC-1α, SRC-1, or PBP by RNAi plasmids affected natural or synthetic agonist activity whereas only Wy-14,643 was affected by decreased PGC-1α. The interaction of PPARα with an LXXLL-containing peptide library showed ligand-specific patterns, indicative of differences in conformational change. The association of coactivators to PPARα occurs predominantly via the carboxyl-terminus and mutating (456)LHPLL to (456)LHPAA resulted in a dominant-negative construct. This research confirms that coactivator recruitment to PPARα is ligand-dependent and that selective receptor modulators (SRMs) of this important protein are likely

Regulation of Peroxisome Proliferator-Activated Receptors by E6-Associated Protein

Peroxisome proliferator-activated receptors (PPARs) are nuclear receptors (NRs) that regulate genes involved in lipid and glucose metabolism. PPAR activity is regulated by interactions with cofactors and of interest are cofactors with ubiquitin ligase activity. The E6-associated protein (E6-AP) is an E3 ubiquitin ligase that affects the activity of other NRs, although its effects on PPARs have not been examined. E6-AP inhibited the ligand-independent transcriptional activity of PPARα and PPARβ, with marginal effects on PPARγ, and decreased basal mRNA levels of PPARα target genes. Inhibition of PPARα activity required the ubiquitin ligase function of E6-AP, but occurred in a proteasome-independent manner. PPARα interacted with E6-AP, and in mice treated with PPARα agonist clofibrate, mRNA and protein levels of E6-AP were increased in wildtype, but not in PPARα null mice, indicating a PPARα-dependent regulation. These studies suggest coordinate regulation of E6-AP and PPARα, and contribute to our understanding of the role of PPARs in cellular metabolism

Walnut oil increases cholesterol efflux through inhibition of stearoyl CoA desaturase 1 in THP-1 macrophage-derived foam cells

Extent: 13p.Background: Walnuts significantly decrease total and low-density lipoprotein cholesterol in normo- and hypercholesterolemic individuals. No study to date has evaluated the effects of walnuts on cholesterol efflux, the initial step in reverse cholesterol transport, in macrophage-derived foam cells (MDFC). The present study was conducted to investigate the mechanisms by which walnut oil affects cholesterol efflux. Methods: The extract of English walnuts (walnut oil) was dissolved in DMSO and applied to cultured THP-1 MDFC cells (0.5 mg/mL). THP-1 MDFC also were treated with human sera (10%, v:v) taken from subjects in a walnut feeding study. Cholesterol efflux was examined by liquid scintillation counting. Changes in gene expression were quantified by real time PCR. Results: Walnut oil treatment significantly increased cholesterol efflux through decreasing the expression of the lipogenic enzyme stearoyl CoA desaturase 1 (SCD1) in MDFC. Alpha-linolenic acid (ALA), the major n-3 polyunsaturated fatty acids found in walnuts, recaptured SCD1 reduction in MDFC, a mechanism mediated through activation of nuclear receptor farnesoid-X-receptor (FXR). Postprandial serum treatment also increased cholesterol efflux in MDFC. When categorized by baseline C-reactive protein (CRP; cut point of 2 mg/L), subjects in the lower CRP sub-group benefited more from dietary intervention, including a more increase in cholesterol efflux, a greater reduction in SCD1, and a blunted postprandial lipemia. Conclusion: In conclusion, walnut oil contains bioactive molecules that significantly improve cholesterol efflux in MDFC. However, the beneficial effects of walnut intake may be reduced by the presence of a pro-inflammatory state.Jun Zhang, Jessica A Grieger, Penny M Kris-Etherton, Jerry T Thompson, Peter J Gillies, Jennifer A Fleming and John P Vanden Heuve

Beef in an Optimal Lean Diet study: effects on lipids, lipoproteins, and apolipoproteins123

Background: A Step I diet with lean beef compared with lean white meat both decrease LDL cholesterol. To our knowledge, no studies have evaluated a low–saturated fatty acid (SFA) (<7% calories) diet that contains lean beef

Regulation of Peroxisome Proliferator–Activated Receptor-α by MDM2

Peroxisome proliferator–activated receptor-alpha (PPARα) belongs to the nuclear receptor (NR) family of transcription factors and regulates lipid and glucose metabolism. Like other NRs, the regulation of gene expression by PPARα depends on cofactor recruitment to the transcription complex and multiple protein-protein interactions. In this study, Murine Double Minute 2 (MDM2), an E3 ubiquitin ligase, is identified as a PPARα-interacting protein that regulates PPARα transcriptional activity. MDM2 modulated the transcriptional activity of PPARα and PPARβ/δ, but not PPARγ in reporter assays. Knockdown of MDM2 by small interfering RNA in rat hepatoma cells inhibited ligand-induced mRNA levels of several PPARα target genes involved in lipid metabolism. MDM2 associated with PPARα on target gene promoters, and this association increased in response to Wy14,643 treatment. MDM2 interacted with PPARα and this interaction occurred with the A/B domain of PPARα. Coexpression of MDM2 increased PPARα ubiquitination and the E3 ubiquitin ligase activity of MDM2 affected PPARα protein expression and transcriptional activity. MDM2 expression was decreased in response to clofibrate in wild-type (WT), but not in PPARα null mice, indicating a PPARα-dependent regulation. These studies identify a role for MDM2 in regulating PPARα-mediated pathways of lipid metabolism

Role of Peroxisome Proliferator-Activated Receptor β/δ and B-Cell Lymphoma-6 in Regulation of Genes Involved in Metastasis and Migration in Pancreatic Cancer Cells

PPARβ/δ is a ligand-activated transcription factor that regulates various cellular functions via induction of target genes directly or in concert with its associated transcriptional repressor, BCL-6. Matrix remodeling proteinases are frequently over-expressed in pancreatic cancer and are involved with metastasis. The present study tested the hypothesis that PPARβ/δ is expressed in human pancreatic cancer cells and that its activation could regulate MMP-9, decreasing cancer cells ability to transverse the basement membrane. In human pancreatic cancer tissue there was significantly higher expression of MMP-9 and PPARβ/δ, and lower levels of BCL-6 mRNA. PPARβ/δ activation reduced the TNFα-induced expression of various genes implicated in metastasis and reduced the invasion through a basement membrane in cell culture models. Through the use of short hairpin RNA inhibitors of PPARβ/δ, BCL-6, and MMP-9, it was evident that PPARβ/δ was responsible for the ligand-dependent effects whereas BCL-6 dissociation upon GW501516 treatment was ultimately responsible for decreasing MMP-9 expression and hence invasion activity. These results suggest that PPARβ/δ plays a role in regulating pancreatic cancer cell invasion through regulation of genes via ligand-dependent release of BCL-6 and that activation of the receptor may provide an alternative therapeutic method for controlling migration and metastasis