Chemical Probes That Differentially Modulate Peroxisome Proliferator-activated Receptor α and BLTR, Nuclear and Cell Surface Receptors for Leukotriene B4

Abstract

Peroxisome proliferator-activated receptor ␣ (PPAR␣) is a nuclear receptor for various fatty acids, eicosanoids, and hypolipidemic drugs. In the presence of ligand, this transcription factor increases expression of target genes that are primarily associated with lipid homeostasis. We have previously reported PPAR␣ as a nuclear receptor of the inflammatory mediator leukotriene B 4 (LTB 4 ) and demonstrated an anti-inflammatory function for PPAR␣ in vivo (Devchand, P. R., Keller, H., Peters, J. M., Vazquez, M., Gonzalez, F. J., and Wahli, W. (1996) Nature 384, 39 -43). LTB 4 also has a cell surface receptor (BLTR) that mediates proinflammatory events, such as chemotaxis and chemokinesis (Yokomizo, T., Izumi, T., Chang, K., Takuwa, Y., and Shimizu, T. (1997) Nature 387, 620 -624). In this study, we report on chemical probes that differentially modulate activity of these two LTB 4 receptors. The compounds selected were originally characterized as synthetic BLTR effectors, both agonists and antagonists. Here, we evaluate the compounds as effectors of the three PPAR isotypes (␣, ␤, and ␥) by transient transfection assays and also determine whether the compounds are ligands for these nuclear receptors by coactivator-dependent receptor ligand interaction assay, a semifunctional in vitro assay. Because the compounds are PPAR␣ selective, we further analyze their potency in a biological assay for the PPAR␣-mediated activity of lipid accumulation. These chemical probes will prove invaluable in dissecting processes that involve nuclear and cell surface LTB 4 receptors and also aid in drug discovery programs.Hormones and nutrient-derived molecules, such as retinoids and fatty acid derivatives, are important signals in many biological processes. Dysregulation or disruption of their signaling pathways can manifest in various ways, with defects that range in severity, rate of onset, and organ systems affected. For instance, a prolonged disturbance of lipid homeostasis is often associated with many late-onset inflammatory conditions, obesity, diabetes, and cardiovascular disease. In order to efficiently treat and prevent these prominent metabolic problems, a better understanding of the mechanisms involved in lipid regulation is required.Intracellular targets for lipid mediators have been postulated for many years (1). However, it is only recently that we have seen the emergence of reports describing nuclear receptors for fatty acids and their derivatives (see Refs. 2 and 3 and references therein). Particular attention has focused on a group of ligand-activated transcription factors called peroxisome proliferator-activated receptors (PPARs).1 The three PPAR isotypes (␣, ␤/␦, and ␥) form a distinct subclass of the nuclear hormone receptor superfamily (4). The functional complex is a heterodimer of PPAR and the retinoid X acid receptor (RXR) that binds to a consensus sequence in the promoter of target genes and can up-regulate transcription in the presence of a PPAR ligand. Although the PPAR target genes identified so far, are gener...

Regulatory effects of arachidonate 5-lipoxygenase on hepatic microsomal TG transfer protein activity and VLDL-triglyceride and apoB secretion in obese mice

“…Although more studies are needed to clarify this issue, the existence of distinct uptake systems for LTB 4 and LTD 4 at the sinusoidal membrane of hepatocytes has been previously demonstrated (45). Moreover, in addition to cell surface receptors, LTB 4 is known to bind to nuclear receptors (46). In summary, our results indicate that 5-LO products directly modulate two key steps in lipid transport within the hepatic cells: the expression of key genes involved in the uptake of free fatty acids (i.e., L-FABP) and the secretion of VLDL-TG and apoB under the control of MTP activity (Fig.…”

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“…Emerging evidence suggests that various lipid mediators are ligands for PPARs, a family of nuclear receptors that can act as transcription factors. In particular, studies by Devchand et al (45,46) have suggested that LTB 4 is a ligand for PPAR␣ and that activation of PPAR␣ by LTB 4 may function to limit the inflammatory response. Since LTB 4 levels were reduced in the allografts in 5lo Ϫ/Ϫ recipients, our findings raise the possibility that interruption of LTB 4 activation of PPAR␣ in this setting might contribute to accellerated graft rejection.…”

Immunohistochemical localization of guinea‐pig leukotriene B4 12‐hydroxydehydrogenase/15‐ketoprostaglandin 13‐reductase

“…LTB 4 12-HD catalyzes the conversion of LTB 4 into 12-keto-LTB 4 in the presence of NADP 1 , and plays an important role in inactivating LTB 4 . The cDNA contained an ORF of 987 bp that encodes a protein of 329 amino-acid residues with a 78% identity with porcine LTB 4 12-HD. The amino acids in the putative NAD 1 …”

“…We have cloned cDNA for leukotriene B 4 12-hydroxydehydrogenase (LTB 4 12-HD)/15-ketoprostaglandin 13-reductase (PGR) from guinea-pig liver. LTB 4 12-HD catalyzes the conversion of LTB 4 into 12-keto-LTB 4 in the presence of NADP 1 , and plays an important role in inactivating LTB 4 .…”