Proliferation of fibroblasts is vital for adequate wound healing but is probably also involved in different hyperproliferative disorders such as atherosclerosis and cancer. The regeneration of tissue usually starts with coagulation, involving release of mitogenic and inflammatory factors from activated platelets. This study focuses on the role of eicosanoids in the proliferative effects of platelets on human fibroblasts. We show that the phospholipase A2 inhibitor 7,7-dimethyl-5,8-eicosadienoic acid (DMDA), the combined cyclooxygenase (COX) and lipoxygenase (LOX) inhibitor 5,8,11,14-eicosatetraynoic acid (ETYA) and the LOX inhibitor 5,8,11-eicosatriynoic acid (ETI) block the platelet-induced proliferation of serum starved subconfluent human fibroblasts. Anti-proliferative effects were also obtained by specific inhibition of 5-LOX with 5,6-dehydro arachidonic acid (5,6-dAA), whereas the 12-LOX inhibitor cinnamyl-3,4-dihydroxy-α-cyanocinnamate (CDC) did not affect the platelet-stimulated growth of fibroblasts. The expression of 5-LOX was analyzed by reverse-transcriptase-mediated PCR (RT-PCR), Western blotting and HPLC. 5-LOX message and protein was detected in fibroblasts but not in platelets. Incubation with platelets markedly increased, already after one hour, the expression of 5-LOX in the fibroblast culture. The increased 5-LOX activity was associated with an elevated level of the 5-LOX metabolite 5-hydroxyeicosatetraenoic acid (5-HETE) reaching its maximum after 1-2 hours of co-incubation of fibroblasts and platelets. The 5-HETE production was reduced by the inhibitors DMDA, ETYA and ETI. In conclusion, this study suggests that platelet-stimulated proliferation of fibroblasts is mediated by an increased 5-LOX activity, which supports recent findings indicating a crucial role for this enzyme in proliferative disorders such as atherosclerosis. © 2006 Schattauer GmbH, Stuttgart.
Polyunsaturated fatty acids (PUFAs) have beneficial effects on epileptic seizures and cardiac arrhythmia. We report that ω-3 and ω-6 all-cis-PUFAs affected the voltage dependence of the Shaker K channel by shifting the conductance versus voltage and the gating charge versus voltage curves in negative direction along the voltage axis. Uncharged methyl esters of the PUFAs did not affect the voltage dependence, whereas changes of pH and charge mutations on the channel surface affected the size of the shifts. This suggests an electrostatic effect on the channel's voltage sensors. Monounsaturated and saturated fatty acids, as well as trans-PUFAs did not affect the voltage dependence. This suggests that fatty acid tails with two or more cis double bonds are required to place the negative carboxylate charge of the PUFA in a position to affect the channel's voltage dependence. We propose that charged lipophilic compounds could play a role in regulating neuronal excitability by electrostatically affecting the channel's voltage sensor. We believe this provides a new approach for pharmacological treatment that is voltage sensor pharmacology. © 2008 by the Biophysical Society.
Voltage-gated ion channels regulate the electric activity of excitable tissues, such as the heart and brain. Therefore, treatment for conditions of disturbed excitability is often based on drugs that target ion channels. In this study of a voltage-gated K channel, we propose what we believe to be a novel pharmacological mechanism for how to regulate channel activity. Charged lipophilic substances can tune channel opening, and consequently excitability, by an electrostatic interaction with the channels voltage sensors. The direction of the effect depends on the charge of the substance. This was shown by three compounds sharing an arachiclonyl backbone but bearing different charge: arachidonic acid, methyl arachidonate, and arachidonyl amine. Computer simulations of membrane excitability showed that small changes in the voltage dependence of Na and K channels have prominent impact on excitability and the tendency for repetitive firing. For instance, a shift in the voltage dependence of a K channel with -5 or +5 mV corresponds to a threefold increase or decrease in K channel density, respectively. We suggest that electrostatic tuning of ion channel activity constitutes a novel and powerful pharmacological approach with which to affect cellular excitability.
[No abstract available]
Lewis lung carcinoma cells contain specific high-affinity binding sites for the eicosanoid 12(S)-hydroxy-5,8,10,14-eicosatetraenoic acid [12(S)-HETE]. These binding sites have a cytosolic/nuclear localization and contain the heat shock proteins hsp70 and hsp90 as components of a high molecular weight cytosolic binding complex. The ligand binding subunit of this complex is a protein with an apparent molecular mass of ÿ50 kDa as judged by gel permeation chromatography. In this report, we present data showing that the 50-kDa 12(S)-HETE binding protein interacts as a homodimer with steroid receptor coactivator-1 (SRC-1) in the presence of 12(S)-HETE. Two putative interaction domains were mapped. One of these (amino acids 701-781) was within the nuclear receptor interaction domain in SRC-1 required for binding of various steroid and thyroid hormone receptors. It contains the most C-terminal of the three copies of LXXLL motif present in the nuclear receptor interaction domain. The second interaction domain was present in the N-terminal part of SRC-1 (amino acids 1-221). This region has two LXXLL motifs, one does not bind and the other binds only weakly to steroid and thyroid hormone receptors. Glutathione S-transferase (GST) pulldown experiments and far Western analyses demonstrated that the N-terminal region of SRC-1 (amino acids 1-212) alone does not bind the 50-kDa 12(S)-HETE binding protein, whereas GST/?SRC-11-1138 ligand-dependently pulled down a protein of ÿ50 kDa in size. Our results suggest that the 50-kDa 12(S)-HETE binding protein is a receptor that may signal through interaction with a nuclear receptor coactivator protein.
Mammalian lipoxygenases (LOXs) are categorized with respect to their positional specificity of arachidonic acid oxygenation. Site-directed mutagenesis identified sequence determinants for the positional specificity of these enzymes, and a critical amino acid for the stereoselectivity was recently discovered. To search for sequence determinants of murine (12R)-LOX, we carried out multiple amino acid sequence alignments and found that Phe390, Gly441, Ala455, and Val631 align with previously identified positional determinants of S-LOX isoforms. Multiple site-directed mutagenesis studies on Phe390 and Ala455 did not induce specific alterations in the reaction specificity, but yielded enzyme species with reduced specific activities and stereo random product patterns. Mutation of Gly441 to Ala, which caused drastic alterations in the reaction specificity of other LOX isoforms, failed to induce major alterations in the positional specificity of mouse (12R)-LOX, but markedly modified the enantioselectivity of the enzyme. When Val631, which aligns with the positional determinant He593 of rabbit 15-LOX, was mutated to a less space-filling residue (Ala or Gly), we obtained an enzyme species with augmented catalytic activity and specifically altered reaction characteristics (major formation of chiral (11R)-hydroxyeicosatetraenoic acid methyl ester). The importance of Val631 for the stereo control of murine (12R)-LOX was confirmed with other substrates such as methyl linoleate and 20-hydroxyeicosatetraenoic acid methyl ester. These data identify Val 631 as the major sequence determinant for the specificity of murine (12R)-LOX. Furthermore, we conclude that substrate fatty acids may adopt different catalytically productive arrangements at the active site of murine (12R)-LOX and that each of these arrangements may lead to the formation of chiral oxygenation products. © 2005 by The American Society for Biochemistry and Molecular Biology, Inc.
Leukotriene C-4 is a potent inflammatory mediator formed from arachidonic acid and glutathione. 5-Lipoxygenase (540), 5-lipoxygenase activating protein (FLAP) and leukotriene C-4 synthase (LTC4S) participate in its biosynthesis. We report evidence from in situ hybridization experiments that FLAP mRNA is abundantly expressed in fetal mouse liver from e11.5 until delivery. In contrast very little or no FLAP mRNA was detected in adult liver. The fetal expression in liver was not uniform but occurred in patches. Cells from e15.5 livers were fractionated by fluorescence activated cell sorting into hepatocytes and other CD45(-) cells and CD45(+) hematopoietic cells. The latter were further separated into immature (Lin(-)) and mature (Lin(+)) cells and analyzed for FLAP mRNA content by quantitative RT-PCR. FLAP mRNA expression was confined to CD45(+) cells and the mature cells had approximately 4-fold higher FLAP mRNA levels compared to the immature cells.
Leukotrienes (LT) are potent pro-inflammatory mediators formed from arachidonic acid (AA) in reactions catalyzed by 5-lipoxygenase and either leukotriene A4 hydrolase or leukotriene C4 synthase. 5-lipoxygenase activating protein (FLAP) is also required. We have previously reported expression of FLAP in the hematopoietic compartment of the fetal liver raising questions regarding the role of leukotrienes in hematopoietic regulation. Here we report evidence from in situ hybridization, immunohistochemistry and qRT-PCR experiments that the complete LT biosynthesis machinery is abundantly expressed in hematopoietic cells of the fetal mouse liver from e11.5 until birth. FACS sorting of hematopoietic cells from e15.5 liver and adult bone marrow into different subpopulations followed by quantitative RT-PCR analysis showed that expression was confined mainly to myeloid cells but also detected in hematopoietic stem and progenitor cells. Analysis of FLAP knockout mice showed that a lack of this gene abolished LT and reduced 5(S)- hydroxyeicosa-6E,8Z,11Z,14Z-tetraenoic acid (HETE) production. Furthermore, decreased relative numbers of B-lymphocytes and increased numbers of T-lymphocytes were observed in peripheral blood and increased numbers of common lymphoid progenitor cells were observed in BM. Taken together these findings suggest that production of LTs can occur in cells of the fetal and adult hematopoietic compartments and that deficiency of the FLAP gene (and leukotrienes) may affect lymphocyte maturation.
Leukotriene C-4 is a potent inflammatory mediator formed from arachidonic acid and glutathione. 5-Lipoxygenase (5-LO), 5-lipoxygenase activating protein (FLAP) and leukotriene C-4 synthase (LTC4S) participate in its biosynthesis. We report evidence that LTC4S interacts in vitro with both FLAP and 5-LO and that these interactions involve distinct parts of LTC4S. FLAP bound to the N-terminal part/first hydrophobic region of LTC4S. This part did not bind 5-LO which bound to the second hydrophilic loop of LTC4S. Fluorescent FLAP- and LTC4S-fusion proteins co-localized at the nuclear envelope. Furthermore, GFP-FLAP and GFP-LTC4S co-localized with a fluorescent ER marker. In testing HEK293/T or COS-7 cells GFP-5-LO was found mainly in the nuclear matrix. Upon stimulation with calcium ionophore, GFP-5-LO translocated to the nuclear envelope allowing it to interact with FLAP and LTC4S. Direct interaction of 5-LO and LTC4S in ionophore-stimulated (but not un-stimulated) cells was demonstrated by BRET using GFP-5-LO and Rluc-LTC4S.
Leukotriene C4 synthase is a key enzyme in leukotriene biosynthesis. Its gene has been cloned and mapped to mouse chromosome 11. Expression occurs in cells of myeloid origin and also in the choroid plexus, the hypothalamus and the medial eminence of mouse brain. In this study a vector that expresses enhanced green fluorescent protein (eGFP) under the control of the mouse leukotriene C4 synthase promoter was constructed and used to study promoter activity in different cell lines. Specific eGFP expression was observed in human monocytic leukemia (THP-1) and rat basophilic leukemia (RBL-1) myeloid cells which both express leukotriene C4 synthase, but not in human embryonic kidney (HEK293/T) epithelial cells which do not express this enzyme. In the myeloid cells, but not in the epithelial cells, we observed that the leukotriene C4 synthase promoter activity was stimulated by 12-O-tetradecanoylphorbol-13-acetate and all-trans-retinoic acid. In contrast dimethyl sulfoxide did not affect promoter activity. © 2007 Elsevier Inc. All rights reserved.
Background
Leukotrienes are potent inflammatory mediators, which in a number of studies have been found to be associated with ischemic stroke pathology: gene variants affecting leukotriene synthesis, including the FLAP (ALOX5AP) gene, have in human studies shown correlation to stroke incidence, and animal studies have demonstrated protective properties of various leukotriene-disrupting drugs. However, no study has hitherto described a significant effect of a genetic manipulation of the leukotriene system on ischemic stroke. Therefore, we decided to compare the damage from focal cerebral ischemia between wild type and FLAP knockout mice. Damage was evaluated by infarct staining and a functional test after middle cerebral artery occlusion in 20 wild type and 20 knockout male mice.
Results
Mortality-adjusted median infarct size was 18.4 (3.2-76.7) mm3 in the knockout group, compared to 72.0 (16.7-174.0) mm3 in the wild type group (p < 0.0005). There was also a tendency of improved functional score in the knockout group (p = 0.068). Analysis of bone marrow cells confirmed that knockout animals had lost their ability to form leukotrienes.
Conclusions
Since the local inflammatory reaction after ischemic stroke is known to contribute to the brain tissue damage, the group difference seen in the current study could be a consequence of a milder inflammatory reaction in the knockout group. Our results add evidence to the notion that leukotrienes are important in ischemic stroke, and that blocked leukotriene production ameliorates cerebral damage.
Microsomal glutathione transferase (mGT) specifically binds leukotriene C4 synthase in the presence of Mg2+ ion (Söderström et al., Protein Expression and Purification (1995) 6, 352-356). To investigate if this interaction occurs in vivo we screened a human lung cDNA library with a bait vector encoding human mGT in the yeast two-hybrid system. One of the five positive clones obtained encoded leukotriene C4 synthase. This clone was expressed in two heterologous systems. The recombinant protein cross-reacted with a guinea pig antibody raised against a Keyhole limpet hemocyanin coupled synthetic peptide corresponding to amino acids 141-150 of human leukotriene C4 synthase.
We have previously shown that the two membrane bound enzymes leukotriene C synthase and microsomal glutathione S-transferase interact in vitro and in vivo. Rat basophilic leukemia cells and murine mastocytoma cells, two well-known sources of leukotriene C synthase, both expressed microsomal glutathione S-transferase as determined by Western blot analyses. Several human tissues were found to contain both leukotriene C synthase and microsomal glutathione S-transferase mRNA. These data suggest that the interaction may be physiologically important. To study this further, expression vectors encoding the two enzymes were cotransfected into mammalian cells and the subcellular localization of the enzymes was determined by indirect immunofluorescence using confocal laser scanning microscopy. The results showed that leukotriene C synthase and microsomal glutathione S-transferase were both localized on the nuclear envelope and adjacent parts of the endoplasmic reticulum. Image overlay demonstrated virtually identical localization. We also observed that coexpression substantially reduced the catalytic activity of each enzyme suggesting that a mechanism involving protein–protein interaction may contribute to the regulation of LTC4 production.
Leukotrienes (LTs) are biologically active compounds derived from arachidonic acid which have important pathophysiological roles in asthma and inflammation. The cysteinyl leukotriene LTC4 and its metabolites LTD4 and LTE4 stimulate bronchoconstriction, airway mucous formation and generalized edema formation. LTC4 is formed by addition of glutathione to LTA4, catalyzed by the integral membrane protein, LTC4 synthase (LTCS). We now report the use of bioluminescence resonance energy transfer (BRET) to demonstrate that LTCS forms homo-oligomers in living cells. Fusion proteins of LTCS and Renilla luciferase (Rluc) and a variant of green fluorescent protein (GFP), respectively, were prepared. High BRET signals were recorded in transiently transfected human embryonic kidney (HEK 293) cells co-expressing Rluc/LTCS and GFP/LTCS. Homo-oligomer formation in living cells was verified by co-transfection of a plasmid expressing non-chimeric LTCS. This resulted in dose-dependent attenuation of the BRET signal. Additional evidence for oligomer formation was obtained in cell-free assays using glutathione S-transferase (GST) pull-down assay. To map interaction domains for oligomerization, GFP/LTCS fusion proteins were prepared with truncated variants of LTCS. The results obtained identified a C-terminal domain (amino acids 114–150) sufficient for oligomerization of LTCS. Another, centrally located, interaction domain appeared to exist between amino acids 57–88. The functional significance of LTCS homo-oligomer formation is currently being investigated.
Leukotrienes (LTs) are fatty acid derivatives formed by oxygenation of arachidonic acid via the 5-lipoxygenase (5-LO) pathway. Upon activation of inflammatory cells 5-LO is translocated to the nuclear envelope (NE) where it converts arachidonic acid to the unstable epoxide LTA4. LTA4 is further converted to LTC4 by conjugation with glutathione, a reaction catalyzed by the integral membrane protein LTC4 synthase (LTC4S), which is localized on the NE and endoplasmic reticulum (ER). We now report the mapping of regions of LTC4S that are important for its subcellular localization. Multiple constructs encoding fusion proteins of green fluorescent protein (GFP) as the N-terminal part and various truncated variants of human LTC4S as C-terminal part were prepared and transfected into HEK 293/T or COS-7 cells. Constructs encoding hydrophobic region 1 of LTC4S (amino acids 6–27) did not give distinct membrane localized fluorescence. In contrast hydrophobic region 2 (amino acids 60–89) gave a localization pattern similar to that of full length LTC4S. Hydrophobic region 3 (amino acids 114–135) directed GFP to a localization indistinguishable from that of full length LTC4S. A minimal directing sequence, amino acids 117–132, was identified by further truncation. The involvement of the hydrophobic regions in the homo-oligomerization of LTC4S was investigated using bioluminescence resonance energy transfer (BRET) analysis in living cells. BRET data showed that hydrophobic regions 1 and 3 each allowed oligomerization to occur. These regions most likely form transmembrane helices, suggesting that homo-oligomerization of LTC4S is due to helix–helix interactions in the membrane.
The ability of three distinct types of human cytosolic glutathione transferase to catalyze the formation of leukotriene C4 from glutathione and leukotriene A4 has been demonstrated. The near-neutral transferase (mu) was the most efficient enzyme with Vmax= 180 nmol X min-1 X mg-1 and Km= 160 microM. The Vmax and Km values for the basic (alpha-epsilon) and the acidic (pi) transferases were 66 and 24 nmol X min-1 X mg-1 and 130 and 190 microM, respectively. The synthetic methyl ester derivative of leukotriene A4 was somewhat more active as a substrate for all the three forms of the enzyme.
Leukotriene (LT)C4 synthase is a membrane-bound, specific glutathione transferase which catalyzes the transformation of LTA4 to LTC4. It was originally shown to be present in rodent mastocytoma and basophilic leukemia cells as well as in macrophages. Recently, expression of human LTC4 synthase was demonstrated in platelets (Söderström, M., et al. (1992) Arch. Biochem. Biophys. 294, 70-74). The present report describes the induction of LTC4 synthase activity during differentiation of human erythroleukemia (HEL) cells by the protein kinase C stimulator 12-O-tetradecanoyl phorbol 13-acetate (TPA), ligands of the steroid-thyroid hormone receptor superfamily: all-trans-retinoic acid (RA) and 1 alpha, 25-dihydroxy-vitamin D3 and in addition dimethylsulfoxide (DMSO). TPA was the most powerful inducer of enzyme activity followed by 1 alpha, 25-dihydroxy-vitamin D3 and DMSO. RA did not induce LTC4 synthase activity.
Leukotriene C4 is a potent mediator of allergic and inflammatory reactions, and is formed from arachidonic acid and glutathione through the sequential action of 5-lipoxygenase and leukotriene C4 synthase (LTCS). These enzymes are predominantly expressed in cells of myeloid lineage. In this report, we have investigated LTCS mRNA expression in mouse brain. Expression was demonstrated using RT-PCR and RNase protection assays. In situ hybridization experiments showed exclusive staining of the choroid plexus of all brain ventricles. This expression pattern may provide a mechanism for the generation of LTC4 on the cerebral side of the blood-brain barrier and suggests a possible novel regulator function of LTC4 in the formation of cerebrospinal fluid.
Leukotriene C4 synthesis was studied in preparations from mouse mastocytoma cells. Enzymic conjugation of leukotriene A4 with glutathione was catalysed by both the cytosol and the microsomal fraction. The specific activity of the microsomal fraction (7.8 nmol/min per mg of protein) was 17 times that of the cytosol fraction. The cytosol fraction of the mastocytoma cells contained two glutathione transferases, which were purified to homogeneity and characterized. A microsomal glutathione transferase was purified from mouse liver; this enzyme was shown by immunoblot analysis to be present in the mastocytoma microsomal fraction at a concentration one-tenth or less of that in the liver microsomal fraction. Both the cytosolic and the microsomal glutathione transferases in the mastocytoma cells were identified with enzymes previously characterized, by determining specific activities with various substrates, sensitivities to inhibitors, reactions with antibodies, and physical properties. The purified microsomal glutathione transferase from liver was inactive with leukotriene A4 or its methyl ester as substrate. The cytosolic enzymes displayed activity with leukotriene A4, but their specific activities and intracellular concentrations were too low to account for the leukotriene C4 formation in the mastocytoma cells. The microsomal fraction of the cells contained an enzyme distinguishable by various criteria from the previously studied glutathione transferases. This membrane-bound enzyme, leukotriene C synthase (leukotriene A4:glutathione S-leukotrienyltransferase), appears to carry the main responsibility for the biosynthesis of leukotriene C4.
Leukotriene C4 is considered to play a major role in several important pathophysiological conditions, e.g., allergy, asthma, and shock. The present investigation demonstrates the presence in human platelets of a membrane-associated enzyme catalyzing the final step in the biosynthesis of leukotriene C4. This leukotriene C4 synthase was shown to be distinct from previously characterized "microsomal" and soluble glutathione transferases. The latter enzymes did not contribute significantly to the leukotriene A4 conjugating activity in platelets. As determined with leukotriene C4 synthase of a crude membrane fraction from human platelets, the Km value was 7 microM and the V value was 0.56 nmol x min-1 x mg-1 with leukotriene A4 as substrate. The enzyme was 20-fold more efficient with leukotriene A4 than with leukotriene A5 and 30-fold more efficient than with the unphysiological derivative leukotriene A4 methyl ester, as measured by the corresponding V/Km values; 14,15-leukotriene A4 was not a substrate. Platelets should be a useful source for the purification and further characterization of human leukotriene C4 synthase.
The chapter presents a study on leukotriene C4 (LTC4) synthase, discussing the characterization in mouse mastocytoma cells. LTC4 is formed by conjugation of leukotriene A4 (LTA4) with glutathione (GSH). In biological systems, the reaction is catalyzed by a membrane-bound enzyme, leukotriene C4 synthase (EC 2.5.1.37). Cytosolic glutathione transferases, in particular, members of the class Mu, have been shown to catalyze formation of LTC4.The most efficient isoenzymes are transferase 6-6 isolated from rat brain, transferase 4-4 from rat liver, and transferase μ from human liver. The name leukotriene C4 synthase, used for the enzyme described in this chapter, has been adopted to distinguish the enzyme from the above glutathione transferases, which display broad substrate specificity. Reports from three groups of investigators have shown that LTC4 formation in rat basophilic leukemia cells is catalyzed by a membrane-bound enzyme. Leukotriene C4 synthase activity has been described and an enzyme partially purified from the microsomal fraction of guinea pig lung. The formation of LTC4 is especially high in mouse mastocytoma cells, the source from which LTC4 was first isolated. The partial purification of leukotriene C4 synthase from this source is described in the chapter.
A novel affinity chromatography purification for human leukotriene C4 synthase is described. It is based on a specific interaction between leukotriene C4 synthase and microsomal glutathione S-transferase which occurs in the presence of magnesium ion. Microsomal glutathione S-transferase was immobilized on NHS-activated Sepharose 4B and used as an affinity matrix. Microsomes from 12-O-tetradecanoyl phorbol 13-acetate-treated human erythroleukemia cells were solubilized with taurocholic acid and applied on the affinity matrix at 0.1 M Mg2+ concentration. After washing with a buffer containing Mg2+, the enzyme was eluted with a glutathione-containing buffer lacking Mg2+. This facile one-step procedure gave a 166-fold purification of leukotriene C4 synthase with a yield of 44%. Analyses of proteins specifically adsorbed to the affinity matrix revealed components with apparent molecular weights of 18, 37, 48, and 60 kDa.
Incubation of RAW 264.7 murine macrophages with 9,15-dihydroxy-11-oxo-, (5Z,9alpha,13E,15(S))-Prosta-5,13-dien-1-oic acid [prostaglandin D(2) (PGD(2))] induced formation of considerable peroxisome proliferator-activated receptor-gamma (PPARgamma) activity [Nature 391 (1998) 79]. Because PGD(2) itself is a poor PPARgamma ligand, we incubated RAW 264.7 macrophage cultures with prostaglandin D(2) for 24 h and studied the ability of the metabolites formed to activate PPARgamma. PGD(2) products were extracted and fractionated by reverse phase high-performance liquid chromatography. Chemical identification was achieved by UV spectroscopy, gas-liquid chromatography/mass spectrometry and chemical syntheses of reference compounds. PGD(2) was converted to eight products, six of which were identified. Ligand-induced interaction of PPARgamma with steroid receptor coactivator-1 was determined by glutathione-S-transferase pull-down assays and PPARgamma activation was investigated by transient transfection of RAW 264.7 macrophages. In addition to the previously known ligand 11-oxo-(5Z,9,12E,14Z)-Prosta-5,9,12,14-tetraen-1-oic acid (15-deoxy-delta(12,14)-PGJ(2)), a novel PPARgamma ligand and activator viz. 9-hydroxy-11-oxo-, (5Z,9alpha,12E,14Z)-Prosta-5,12,14-trien-1-oic acid (15-deoxy-delta(12,14)-PGD(2)) was identified. The biological significance of these results is currently under investigation.
Peroxisome proliferator-activated receptor gamma (PPAR?) colocalizes with oxidized low-density lipoprotein (LDL) in foam cells in atherosclerotic lesions. We have explored a potential role of oxidized fatty acids in LDL as PPAR? activators. LDL from patients suffering from intermittent claudication due to atherosclerosis was analyzed using HPLC and gas chromatography/mass spectrophotometry and found to contain 9-hydroxy-and 13-hydroxyoctadecadienoic acid (9- and 13-HODE), as well as 5-hydroxy-, 12-hydroxy- and 15-hydroxyeicosatetraenoic acid (5-, 12- and 15-HETE respectively). PPAR? was potently activated by 13(S)-HODE and 15(S)-HETE, as judged by transient transfection assays in macrophages or CV-1 cells. 5(S)- and 12(S)-HETE as well as 15-deoxy-?12,14 -prostaglandin J2 also activated PPAR? but were less potent. Interestingly, the effect of the lipoxygenase products 13(S -HODE and 15(S)-HETE as well as of the drug rosiglitazone were preferentially enhanced by the coactivator CREB-binding protein, whereas the effect of the cyclooxygenase product 15-deoxy-?12,14-prostaglandin J2 was preferentially enhanced by steroid receptor coactivator-1. We interpret these results, which may have relevance to the pathogenesis of atherosclerosis, to indicate that the lipoxygenase products on the one hand and the cyclooxygenase product on the other exert specific effects on the transcription of target genes through differential coactivator recruitment by PPAR?/9-cis retinoic acid receptor heterodimer complexes.