Purification and characterization of recombinant histidine-tagged human platelet 12-lipoxygenase expressed in a baculovirus/insect cell system

An adaptable in silico ensemble model of the arachidonic acid cascade

Eicosanoids are a family of bioactive lipids, including derivatives of the ubiquitous fatty acid arachidonic acid (AA). The intimate involvement of eicosanoids in inflammation motivates the development of predictive in silico models for a systems-level exploration of disease mechanisms, drug development and replacement of animal models. Using an ensemble modelling strategy, we developed a computational model of the AA cascade. This approach allows the visualisation of plausible and thermodynamically feasible predictions, overcoming the limitations of fixed-parameter modelling. A quality scoring method was developed to quantify the accuracy of ensemble predictions relative to experimental data, measuring the overall uncertainty of the process. Monte Carlo ensemble modelling was used to quantify the prediction confidence levels. Model applicability was demonstrated using mass spectrometry mediator lipidomics to measure eicosanoids produced by HaCaT epidermal keratinocytes and 46BR.1N dermal fibroblasts, treated with stimuli (calcium ionophore A23187), (ultraviolet radiation, adenosine triphosphate) and a cyclooxygenase inhibitor (indomethacin). Experimentation and predictions were in good qualitative agreement, demonstrating the ability of the model to be adapted to cell types exhibiting differences in AA release and enzyme concentration profiles. The quantitative agreement between experimental and predicted outputs could be improved by expanding network topology to include additional reactions. Overall, our approach generated an adaptable, tuneable ensemble model of the AA cascade that can be tailored to represent different cell types and demonstrated that the integration of in silico and in vitro methods can facilitate a greater understanding of complex biological networks such as the AA cascade.

Evaluation of ω-alkynyl-labeled linoleic and arachidonic acids as substrates for recombinant lipoxygenase pathway enzymes

ω-Alkynyl-fatty acids can be used as probes for covalent binding to intracellular macromolecules. To inform future in vivo studies, we determined the rates of reaction of ω-alkynyl-labeled linoleate with recombinant enzymes of the skin 12R-lipoxygenase (12R-LOX) pathway involved in epidermal barrier formation (12R-LOX, epidermal lipoxygenase-3 (eLOX3), and SDR9C7). We also examined the reactivity of ω-alkynyl-arachidonic acid with representative lipoxygenase enzymes employing either "carboxyl end-first" substrate binding (5S-LOX) or "tail-first" (platelet-type 12S-LOX). ω-Alkynyl-linoleic acid was oxygenated by 12R-LOX at 62 ± 9 % of the rate compared to linoleic acid, the alkynyl-9R-HPODE product was isomerized by eLOX3 at only 43 ± 1 % of the natural substrate, whereas its epoxy alcohol product was converted to epoxy ketone linoleic by an NADH-dependent dehydrogenase (SDR9C7) with 91 ± 1 % efficiency. The results suggest the optimal approach will be application of the 12R-LOX/eLOX3-derived epoxyalcohol, which should be most efficiently incorporated into the pathway and allow subsequent analysis of covalent binding to epidermal proteins. Regarding the orientation of substrate binding in LOX catalysis, our results and previous reports suggest the ω-alkynyl group has a stronger inhibitory effect on tail-first binding, as might be expected. Beyond slowing the reaction, however, we found that the tail-first binding and transformation of ω-alkynyl-arachidonic acid by platelet-type 12S-LOX results in almost complete enzyme inactivation, possibly due to reactive intermediates blocking the enzyme active site. Overall, the results reinforce the conclusion that ω-alkynyl-fatty acids are suitable for selected applications after appropriate reactivity is established.

Synthesis of two new lipid mediators from docosahexaenoic acid by combinatorial catalysis involving enzymatic and chemical reaction

Omega-3 polyunsaturated fatty acids (PUFAs) have been known to have beneficial effects in the prevention of various diseases. Recently, it was identified that the bioactivities of omega-3 are related to lipid mediators, called pro-resolving lipid mediators (SPMs), converted from PUFAs, so they have attracted much attention as potential pharmaceutical targets. Here, we aimed to build an efficient production system composed of enzymatic and chemical catalysis that converts docosahexaenoic acid (DHA) into lipid mediators. The cyanobacterial lipoxygenase, named Osc-LOX, was identified and characterized, and the binding poses of enzyme and substrates were predicted by ligand docking simulation. DHA was converted into three lipid mediators, a 17S-hydroxy-DHA, a 7S,17S-dihydroxy-DHA (RvD5), and a 7S,15R-dihydroxy-16S,17S-epoxy-DPA (new type), by an enzymatic reaction and deoxygenation. Also, two lipid mediators, 7S,15R,16S,17S-tetrahydroxy-DPA (new type) and 7S,16R,17S-trihydroxy-DHA (RvD2), were generated from 7S,15R-dihydroxy-16S,17S-epoxy-DPA by a chemical reaction. Our study suggests that discovering new enzymes that have not been functionally characterized would be a powerful strategy for producing various lipid mediators. Also, this combination catalysis approach including biological and chemical reactions could be an effective production system for the manufacturing lipid mediators.

Eosinophils synthesize trihydroxyoctadecenoic acids (TriHOMEs) via a 15-lipoxygenase dependent process

Trihydroxyoctadecenoic acids (TriHOMEs) are linoleic acid-derived lipid mediators reported to be dysregulated in obstructive lung disease. In contrast to many other oxylipins, TriHOME biosynthesis in humans is still poorly understood. The association of TriHOMEs with inflammation prompted the current investigation into the ability of human granulocytes to synthesize the 16 different 9,10,13-TriHOME and 9,12,13-TriHOME isomers and of the TriHOME biosynthetic pathway. Following incubation with linoleic acid, eosinophils and (to a lesser extent) the mast cell line LAD2, but not neutrophils, formed TriHOMEs. Stereochemical analysis revealed that TriHOMEs produced by eosinophils predominantly evidenced the 13(S) configuration, suggesting 15-lipoxygenase (15-LOX)-mediated synthesis. TriHOME formation was blocked following incubation with the 15-LOX inhibitor BLX-3887 and was shown to be largely independent of soluble epoxide hydrolase and cytochrome P450 activities. TriHOME synthesis was abolished when linoleic acid was replaced with 13-HODE, but increased in incubations with 13-HpODE, indicating the intermediary role of epoxy alcohols in TriHOME formation. In contrast to eosinophils, LAD2 cells formed TriHOMEs having predominantly the 13(R) configuration, demonstrating that there are multiple synthetic routes for TriHOME formation. These findings provide for the first-time insight into the synthetic route of TriHOMEs in humans and expand our understanding of their formation in inflammatory diseases.

The Biosynthesis of Enzymatically Oxidized Lipids

Enzymatically oxidized lipids are a specific group of biomolecules that function as key signaling mediators and hormones, regulating various cellular and physiological processes from metabolism and cell death to inflammation and the immune response. They are broadly categorized as either polyunsaturated fatty acid (PUFA) containing (free acid oxygenated PUFA "oxylipins", endocannabinoids, oxidized phospholipids) or cholesterol derivatives (oxysterols, steroid hormones, and bile acids). Their biosynthesis is accomplished by families of enzymes that include lipoxygenases (LOX), cyclooxygenases (COX), cytochrome P450s (CYP), and aldo-keto reductases (AKR). In contrast, non-enzymatically oxidized lipids are produced by uncontrolled oxidation and are broadly considered to be harmful. Here, we provide an overview of the biochemistry and enzymology of LOXs, COXs, CYPs, and AKRs in humans. Next, we present biosynthetic pathways for oxylipins, oxidized phospholipids, oxysterols, bile acids and steroid hormones. Last, we address gaps in knowledge and suggest directions for future work.

Magnetic immobilization of a quorum sensing signal hydrolase, AiiA

Magnetic immobilization of quorum sensing (QS) signal hydrolases provides a convenient solution for quenching QS process that is essential for bacterial biofilm formation and antimicrobial resistance. In the present study, a QS signal hydrolase, AiiA, was fused with a magnetic protein, MagR, and expressed in Escherichia coli. Magnetic immobilization of AiiA was achieved on Fe₃ O₄ -SiO₂ iron beads and was confirmed via SDS-PAGE, zeta potential measurement, FTIR spectrometry, and SEM analysis. The magnetic immobilized AiiA exhibited activity in degrading the quorum sensing signal, C6-HSL. This study opens a new avenue to actively immobilize enzymes via magnetic interaction and quench quorum sensing.

Probing the Electrostatic and Steric Requirements for Substrate Binding in Human Platelet-Type 12-Lipoxygenase

Human platelet ALOX12 (hALOX12 or h12-LOX) has been implicated in a variety of human diseases. The present study investigates the active site of hALOX12 to more thoroughly understand how it positions the substrate and achieves nearly perfect regio- and stereospecificities (i.e., 100 ± 5% of the 12(S)-hydroperoxide product), utilizing site-directed mutagenesis. Specifically, we have determined that Arg402 is not as important in substrate binding as previously seen for hALOX15 but that His596 may play a role in anchoring the carboxy terminal of the arachidonic acid during catalysis. In addition, Phe414 creates a π-stacking interaction with a double bond of arachidonic acid (Δ¹¹), and Ala417/Val418 define the bottom of the cavity. However, the influence of Ala417/Val418 on the profile is markedly less for hALOX12 than that seen in hALOX15. Mutating these two residues to larger amino acids (Ala417Ile/Val418Met) only increased the generation of 15-HpETE by 24 ± 2%, but conversely, smaller residues at these positions converted hALOX15 to almost 100% hALOX12 reactivity [Gan et al. (1996) J. Biol. Chem. 271, 25412-25418]. However, we were able to increase 15-HpETE to 46 ± 3% by restricting the width of the active site with the Ala417Ile/Val418Met/Ser594Thr mutation, indicating both depth and width of the active site are important. Finally, residue Leu407 is shown to play a critical role in positioning the substrate correctly, as seen by the increase of 15-HpETE to 21 ± 1% for the single Leu407Gly mutant. These results outline critical differences between the active site requirements of hALOX12 relative to hALOX15 and explain both their product specificity and inhibitory differences.

Minireview: 12-Lipoxygenase and Islet β-Cell Dysfunction in Diabetes

The insulin producing islet β-cells have increasingly gained attention for their role in the pathogeneses of virtually all forms of diabetes. Dysfunction, de-differentiation, and/or death of β-cells are pivotal features in the transition from normoglycemia to hyperglycemia in both animal models of metabolic disease and humans. In both type 1 and type 2 diabetes, inflammation appears to be a central cause of β-cell derangements, and molecular pathways that modulate inflammation or the inflammatory response are felt to be prime targets of future diabetes therapy. The lipoxygenases (LOs) represent a class of enzymes that oxygenate cellular polyunsaturated fatty acids to produce inflammatory lipid intermediates that directly and indirectly affect cellular function and survival. The enzyme 12-LO is expressed in all metabolically active tissues, including pancreatic islets, and has received increasing attention for its role in promoting cellular inflammation in the setting of diabetes. Genetic deletion models of 12-LO in mice reveal striking protection from metabolic disease and its complications and an emerging body of literature has implicated its role in human disease. This review focuses on the evidence supporting the proinflammatory role of 12-LO as it relates to islet β-cells, and the potential for 12-LO inhibition as a future avenue for the prevention and treatment of metabolic disease.

Lipoxygenase-catalyzed transformation of epoxy fatty acids to hydroxy-endoperoxides: a potential P450 and lipoxygenase interaction

Herein, we characterize a generally applicable transformation of fatty acid epoxides by lipoxygenase (LOX) enzymes that results in the formation of a five-membered endoperoxide ring in the end product. We demonstrated this transformation using soybean LOX-1 in the metabolism of 15,16-epoxy-α-linolenic acid, and murine platelet-type 12-LOX and human 15-LOX-1 in the metabolism of 14,15-epoxyeicosatrienoic acid (14,15-EET). A detailed examination of the transformation of the two enantiomers of 15,16-epoxy-α-linolenic acid by soybean LOX-1 revealed that the expected primary product, a 13S-hydroperoxy-15,16-epoxide, underwent a nonenzymatic transformation in buffer into a new derivative that was purified by HPLC and identified by UV, LC-MS, and ¹H-NMR as a 13,15-endoperoxy-16-hydroxy-octadeca-9,11-dienoic acid. The configuration of the endoperoxide (cis or trans side chains) depended on the steric relationship of the new hydroperoxy moiety to the enantiomeric configuration of the fatty acid epoxide. The reaction mechanism involves intramolecular nucleophilic substitution (SNi) between the hydroperoxy (nucleophile) and epoxy group (electrophile). Equivalent transformations were documented in metabolism of the enantiomers of 14,15-EET by the two mammalian LOX enzymes, 15-LOX-1 and platelet-type 12-LOX. We conclude that this type of transformation could occur naturally with the co-occurrence of LOX and cytochrome P450 or peroxygenase enzymes, and it could also contribute to the complexity of products formed in the autoxidation reactions of polyunsaturated fatty acids.

A high throughput screen identifies potent and selective inhibitors to human epithelial 15-lipoxygenase-2

Lipoxygenase (LOX) enzymes catalyze the hydroperoxidation of arachidonic acid and other polyunsaturated fatty acids to hydroxyeicosatetraenoic acids with varying positional specificity to yield important biological signaling molecules. Human epithelial 15­lipoxygenase­2 (15-LOX-2) is a highly specific LOX isozyme that is expressed in epithelial tissue and whose activity has been correlated with suppression of tumor growth in prostate and other epithelial derived cancers. Despite the potential utility of an inhibitor to probe the specific role of 15-LOX-2 in tumor progression, no such potent/specific 15­LOX­2 inhibitors have been reported to date. This study employs high throughput screening to identify two novel, specific 15­LOX­2 inhibitors. MLS000545091 is a mixed-type inhibitor of 15-LOX-2 with a K_i of 0.9+/−0.4 µM and has a 20-fold selectivity over 5-LOX, 12-LOX, 15-LOX-1, COX-1, and COX-2. MLS000536924 is a competitive inhibitor with a K_i of 2.5+/−0.5 µM and also possesses 20-fold selectivity toward 15-LOX-2 over the other oxygenases, listed above. Finally, neither compound possesses reductive activity towards the active-site ferrous ion.

Potent and selective inhibitors of human reticulocyte 12/15-lipoxygenase as anti-stroke therapies

A key challenge facing drug discovery today is variability of the drug target between species, such as with 12/15-lipoxygenase (12/15-LOX), which contributes to ischemic brain injury, but its human and rodent isozymes have different inhibitor specificities. In the current work, we have utilized a quantitative high-throughput (qHTS) screen to identify compound 1 (ML351), a novel chemotype for 12/15-LOX inhibition that has nanomolar potency (IC₅₀ = 200 nM) against human 12/15-LOX and is protective against oxidative glutamate toxicity in mouse neuronal HT22 cells. In addition, it exhibited greater than 250-fold selectivity versus related LOX isozymes, was a mixed inhibitor, and did not reduce the active-site ferric ion. Lastly, 1 significantly reduced infarct size following permanent focal ischemia in a mouse model of ischemic stroke. As such, this represents the first report of a selective inhibitor of human 12/15-LOX with demonstrated in vivo activity in proof-of-concept mouse models of stroke.

A mutation interfering with 5-lipoxygenase domain interaction leads to increased enzyme activity

5-Lipoxygenase (5-LOX) catalyzes two steps in conversion of arachidonic acid to proinflammatory leukotrienes. Lipoxygenases, including human 5-LOX, consist of an N-terminal C2-like β-sandwich and a catalytic domain. We expressed the 5-LOX domains separately, these were found to interact in the yeast two-hybrid system. The 5-LOX structure suggested association between Arg(101) in the β-sandwich and Asp(166) in the catalytic domain, due to electrostatic interaction as well as hydrogen bonds. Indeed, mutagenic replacements of these residues led to loss of two-hybrid interaction. Interestingly, when Arg(101) was mutated to Asp in intact 5-LOX, enzyme activity was increased. Thus, higher initial velocity of the reaction (vinit) and increased final amount of products were monitored for 5-LOX-R101D, at several different assay conditions. In the 5-LOX crystal structure, helix α2 and adjacent loops (including Asp(166)) of the 5-LOX catalytic domain has been proposed to form a flexible lid controlling access to the active site, and lid movement would be determined by bonding of lid residues to the C2-like β-sandwich. The more efficient catalysis following disruption of the R101-D166 ionic association supports the concept of such a flexible lid in human 5-LOX.

Synthesis and structure-activity relationship studies of 4-((2-hydroxy-3-methoxybenzyl)amino)benzenesulfonamide derivatives as potent and selective inhibitors of 12-lipoxygenase

Human lipoxygenases (LOXs) are a family of iron-containing enzymes which catalyze the oxidation of polyunsaturated fatty acids to provide the corresponding bioactive hydroxyeicosatetraenoic acid (HETE) metabolites. These eicosanoid signaling molecules are involved in a number of physiologic responses such as platelet aggregation, inflammation, and cell proliferation. Our group has taken a particular interest in platelet-type 12-(S)-LOX (12-LOX) because of its demonstrated role in skin diseases, diabetes, platelet hemostasis, thrombosis, and cancer. Herein, we report the identification and medicinal chemistry optimization of a 4-((2-hydroxy-3-methoxybenzyl)amino)benzenesulfonamide-based scaffold. Top compounds, exemplified by 35 and 36, display nM potency against 12-LOX, excellent selectivity over related lipoxygenases and cyclooxygenases, and possess favorable ADME properties. In addition, both compounds inhibit PAR-4 induced aggregation and calcium mobilization in human platelets and reduce 12-HETE in β-cells.

Lipoxygenase pathways in Homo neanderthalensis: functional comparison with Homo sapiens isoforms

Lipoxygenases (LOX) have been implicated in biosynthesis of pro- and anti-inflammatory mediators, and a previous report suggested compromised leukotriene signaling in H. neanderthalensis. To search for corresponding differences in leukotriene biosynthesis, we screened the Neandertal genome for LOX genes and found that, as modern humans, this archaic hominid contains six LOX genes (nALOX15, nALOX12, nALOX5, nALOX15B, nALOX12B, and nALOXE3) and one pseudogene. In the Neandertal genome, 60-75% of the amino acids of the different human LOX isoforms have been identified, and the degree of identity varies between 96 and 99%. Most functional amino acids (iron ligands, specificity determinants, calcium and ATP-binding sites, membrane-binding determinants, and phosphorylation sites) are well conserved in the Neandertal LOX isoforms, and expression of selected neandertalized human LOX mutants revealed no major functional defects. However, in nALOX12 and nALOXE3, two premature stop codons were found, leading to inactive enzyme species. These data suggest that ALOX15, ALOX5, ALOX15B, and ALOX12B should have been present as functional enzymes in H. neanderthalensis and that in contrast to lower nonhuman primates (M. mulatta) and other mammals (mice, rats), this ancient hominid expressed a 15-lipoxygenating ALOX15. Expression of ALOXE3 and ALOX12 was compromised, which might have caused problems in epidermal differentiation.

Investigations of human platelet-type 12-lipoxygenase: role of lipoxygenase products in platelet activation

Human platelet-type 12-lipoxygenase (12-LOX) has recently been shown to play an important role in regulation of human platelet function by reacting with arachidonic acid (AA). However, a number of other fatty acids are present on the platelet surface that, when cleaved from the phospholipid, can be oxidized by 12-LOX. We sought to characterize the substrate specificity of 12-LOX against six essential fatty acids: AA, dihomo-γ-linolenic acid (DGLA), eicosapentaenoic acid (EPA), α-linolenic acid (ALA), eicosadienoic acid (EDA), and linoleic acid (LA). Three fatty acids were comparable substrates (AA, DGLA, and EPA), one was 5-fold slower (ALA), and two showed no reactivity with 12-LOX (EDA and LA). The bioactive lipid products resulting from 12-LOX oxidation of DGLA, 12-(S)-hydroperoxy-8Z,10E,14Z-eicosatrienoic acid [12(S)-HPETrE], and its reduced product, 12(S)-HETrE, resulted in significant attenuation of agonist-mediated platelet aggregation, granule secretion, αIIbβ3 activation, Rap1 activation, and clot retraction. Treatment with DGLA similarly inhibited PAR1-mediated platelet activation as well as platelet clot retraction. These observations are in surprising contrast to our recent work showing 12(S)-HETE is a prothrombotic bioactive lipid and support our hypothesis that the overall effect of 12-LOX oxidation of fatty acids in the platelet is dependent on the fatty acid substrates available at the platelet membrane.

Discovery of potent and selective inhibitors of human platelet-type 12- lipoxygenase

We report the discovery of novel small molecule inhibitors of platelet-type 12-human lipoxygenase, which display nanomolar activity against the purified enzyme, using a quantitative high-throughput screen (qHTS) on a library of 153607 compounds. These compounds also exhibit excellent specificity, >50-fold selectivity vs the paralogues, 5-human lipoxygenase, reticulocyte 15-human lipoxygenase type-1, and epithelial 15-human lipoxygenase type-2, and >100-fold selectivity vs ovine cyclooxygenase-1 and human cyclooxygenase-2. Kinetic experiments indicate this chemotype is a noncompetitive inhibitor that does not reduce the active site iron. Moreover, chiral HPLC separation of two of the racemic lead molecules revealed a strong preference for the (-)-enantiomers (IC(50) of 0.43 ± 0.04 and 0.38 ± 0.05 μM) compared to the (+)-enantiomers (IC(50) of >25 μM for both), indicating a fine degree of selectivity in the active site due to chiral geometry. In addition, these compounds demonstrate efficacy in cellular models, which underscores their relevance to disease modification.

Discovery of potent and selective inhibitors of human reticulocyte 15-lipoxygenase-1

There are a variety of lipoxygenases in the human body (hLO), each having a distinct role in cellular biology. Human reticulocyte 15-lipoxygenase-1 (15-hLO-1), which catalyzes the dioxygenation of 1,4-cis,cis-pentadiene-containing polyunsaturated fatty acids, is implicated in a number of diseases including cancer, atherosclerosis, and neurodegenerative conditions. Despite the potential therapeutic relevance of this target, few inhibitors have been reported that are both potent and selective. To this end, we have employed a quantitative high-throughput (qHTS) screen against ∼74000 small molecules in search of reticulocyte 15-hLO-1 selective inhibitors. This screen led to the discovery of a novel chemotype for 15-hLO-1 inhibition, which displays nM potency and is >7500-fold selective against the related isozymes, 5-hLO, platelet 12-hLO, epithelial 15-hLO-2, ovine cyclooxygenase-1, and human cyclooxygenase-2. In addition, kinetic experiments were performed which indicate that this class of inhibitor is tight binding, reversible, and appears not to reduce the active-site ferric ion.

Purification by Strep-Tactin affinity chromatography of a delete envelope gp51 protein of Bovine Leukaemia virus expressed in Sf21 insect cells

Bovine leukaemia virus (BLV) causes disease in cattle and it is related to human T lymphotrofic viruses HTLV-1 and HTLV-2. The objective of this study was to express and purify deleted and stable forms of the gp51 envelope glycoprotein of BLV using a baculovirus system. Two forms of the gp51 were synthesised: one comprised the gp51 N-terminal 174 amino acids and a single 6xHis tag (Delta(175-268)gp51-His) and the second form contained the same amino acid sequence and a C-terminal Strep-tag II in addition to the 6xHis tag (Delta(175-268)gp51-STH). The two proteins were expressed and purified by immobilized metal-affinity chromatography (IMAC) or by Strep-Tactin column. The Strep-Tactin technology was more efficient than IMAC method and achieved a high pure recombinant deleted gp51. In addition the Delta(175-268)gp51-STH protein was further concentrated by IMAC. This purified antigen could be used for the isolation of immunoreactive molecules and to develop a competitive ELISA test.

A cell-based assay for screening lipoxygenase inhibitors

Lipoxygenases (LOX) form a family of lipid peroxidizing enzymes within the plant and animal kingdoms. In humans, six functional lipoxygenase isoforms have been identified. 5-LOX, "platelet-type" 12-LOX (p12-LOX) and 15-LOX type 1 (15-LOX1), originally identified in leukocytes, platelets, and reticulocytes, respectively, generate lipid mediators involved in host cellular functions and in the pathophysiology of asthma, cardiovascular diseases, and cancer. The pharmaceutical industry has reinvigorated their programs to develop novel LOX inhibitors in view of recent findings. However, high throughput LOX screening assays to test novel agents against these intracellular enzymes are limited. We describe a cell-based 96-well microplate fluorescence assay tested against several existing LOX inhibitors, and validate the assay by comparing known IC(50) values and HPLC analysis, which may provide a useful screen for novel LOX inhibitors.

Using enzyme assays to evaluate the structure and bioactivity of sponge-derived meroterpenes

Enzyme screening of crude sponge extracts prioritized a 2005 Papua New Guinea collection of Hyrtios sp. for further study. The MeOH extract contained puupehenone and four puupehenone analogues (1, 2, 3, 5, and 7) along with a new diastereomer, 20-epi-hydroxyhaterumadienone (4), and a new analogue, 15-oxo-puupehenoic acid (6). The drimane terpene core of 4 and 6 was rapidly dereplicated, and the modified Mosher's method identified 4, while 1D and 2D NMR techniques were used to solve 6. These compounds plus noteworthy repository natural products and standards were tested against three lipoxygenase isozymes, human 5-, 12-, and 15-lipoxygenases. Significant potency and selectivity profiles were exhibited in the human 5-lipoxygenase assay by puupehenone (1) and jaspaquinol (9) and structural factors responsible for activity identified.

Mechanistic investigations of human reticulocyte 15- and platelet 12-lipoxygenases with arachidonic acid

Human reticulocyte 15-lipoxygenase-1 (15-hLO-1) and human platelet 12-lipoxygenase (12-hLO) have been implicated in a number of diseases, with differences in their relative activity potentially playing a central role. In this work, we characterize the catalytic mechanism of these two enzymes with arachidonic acid (AA) as the substrate. Using variable-temperature kinetic isotope effects (KIE) and solvent isotope effects (SIE), we demonstrate that both k(cat)/K(M) and k(cat) for 15-hLO-1 and 12-hLO involve multiple rate-limiting steps that include a solvent-dependent step and hydrogen atom abstraction. A relatively low k(cat)/K(M) KIE of 8 was determined for 15-hLO-1, which increases to 18 upon the addition of the allosteric effector molecule, 12-hydroxyeicosatetraenoic acid (12-HETE), indicating a tunneling mechanism. Furthermore, the addition of 12-HETE lowers the observed k(cat)/K(M) SIE from 2.2 to 1.4, indicating that the rate-limiting contribution from a solvent sensitive step in the reaction mechanism of 15-hLO-1 has decreased, with a concomitant increase in the C-H bond abstraction contribution. Finally, the allosteric binding of 12-HETE to 15-hLO-1 decreases the K(M)[O(2)] for AA to 15 microM but increases the K(M)[O(2)] for linoleic acid (LA) to 22 microM, such that the k(cat)/K(M)[O(2)] values become similar for both substrates (approximately 0.3 s(-1) microM(-1)). Considering that the oxygen concentration in cancerous tissue can be less than 5 microM, this result may have cellular implications with respect to the substrate specificity of 15-hLO-1.

Oxidative metabolism of a fatty acid amide hydrolase-regulated lipid, arachidonoyltaurine

A novel class of lipids, N-acyltaurines, was recently discovered in fatty acid amide hydrolase knockout mice. In some peripheral tissues, such as liver and kidney, N-acyltaurines with long, polyunsaturated acyl chains are most prevalent. Polyunsaturated fatty acids are converted to a variety of signaling molecules by cyclooxygenases (COXs) and lipoxygenases (LOXs). The ability of COXs and LOXs to oxygenate arachidonoyltaurine was evaluated to gain insight into the potential metabolic fate of N-acyltaurines. Although arachidonoyltaurine was a poor substrate for COXs, mammalian 12 S- and 15 S-LOXs oxygenated arachidonoyltaurine with similar or better efficiency than arachidonic acid. Products of arachidonoyltaurine oxygenation were characterized by liquid chromatography-tandem mass spectrometry (LC-MS/MS). The positional specificity of single oxygenation was retained for 15 S-LOXs. However, platelet-type 12 S-LOX produced 12- and 15-hydroxyeicosatetraenoyltaurines (HETE-Ts). Furthermore, LOXs generated dihydroxyeicosatetraenoyltaurines (diHETE-Ts). Metabolism of arachidonoyltaurine by murine resident peritoneal macrophages (RPMs) was also profiled. Arachidonoyltaurine was rapidly taken up and converted primarily to 12-HETE-T. Over prolonged incubations, RPMs also generated small amounts of diHETE-T. Oxidative metabolism of polyunsaturated N-acyltaurines may represent a pathway for the generation or termination of novel signaling molecules.

Oxidation of 2-Cys-peroxiredoxins by arachidonic acid peroxide metabolites of lipoxygenases and cyclooxygenase-2

Human peroxiredoxins serve dual roles as anti-oxidants and regulators of H(2)O(2)-mediated cell signaling. The functional versatility of peroxiredoxins depends on progressive oxidation of key cysteine residues. The sulfinic or sulfonic forms of peroxiredoxin lose their peroxidase activity, which allows cells to accumulate H(2)O(2) for signaling or pathogenesis in inflammation, cancer, and other disorders. We report that arachidonic acid lipid hydroperoxide metabolites of 5-, 12-, 15-lipoxygenase-1, and cyclooxygenase-2 oxidize the 2-Cys-peroxiredoxins 1, 2, and 3 to their sulfinic and sulfonic forms. When added exogenously to cells, 5-, 12- and 15-hydroperoxy-eicosatetraenoic acids also over-oxidized peroxiredoxins. Our results suggest that lipoxygenases and cyclooxygenases may affect 2-Cys peroxiredoxin signaling, analogous to NADPH oxidases in the "floodgate" model (Wood, Z. A., Poole, L. B, and Karplus P. A. (2003) Science 300, 600-653). Peroxiredoxin-dependent mechanisms may modulate the receptor-dependent actions of autocoids derived from cellular lipoxygenase and cyclooxygenase catalysis.

Oxidative metabolism of lipoamino acids and vanilloids by lipoxygenases and cyclooxygenases

The lipoamino acids and endovanilloids have multiple roles in nociception, pain, and inflammation, yet their biological reactivity has not been fully characterized. Cyclooxygenases (COXs) and lipoxygenases (LOs) oxygenate polyunsaturated fatty acids to generate signaling molecules. The ability of COXs and LOs to oxygenate arachidonyl-derived lipoamino acids and vanilloids was investigated. COX-1 and COX-2 were able to minimally metabolize many of these species. However, the lipoamino acids were efficiently oxygenated by 12S- and 15S-LOs. The kinetics and products of oxygenation by LOs were characterized. Whereas 15S-LOs retained positional specificity of oxygenation with these novel substrates, platelet-type 12S-LO acted as a 12/15-LO. Fatty acid oxygenases may play an important role in the metabolic inactivation of lipoamino acids or vanilloids or may convert them to bioactive derivatives.

Synthetic curcuminoids modulate the arachidonic acid metabolism of human platelet 12-lipoxygenase and reduce sprout formation of human endothelial cells

Platelet 12-lipoxygenase (P-12-LOX) is overexpressed in different types of cancers, including prostate cancer, and the level of expression is correlated with the grade of this cancer. Arachidonic acid is metabolized by 12-LOX to 12(S)-hydroxyeicosatetraenoic acid [12(S)-HETE], and this biologically active metabolite is involved in prostate cancer progression by modulating cell proliferation in multiple cancer-related pathways inducing angiogenesis and metastasis. Thus, inhibition of P-12-LOX can reduce these two processes. Several lipoxygenase inhibitors are known, including plant and mammalian lipoxygenases, but only a few of them are known inhibitors of P-12-LOX. Curcumin is one of these lipoxygenase inhibitors. Using a homology model of the three-dimensional structure of human P-12-LOX, we did computational docking of synthetic curcuminoids (curcumin derivatives) to identify inhibitors superior to curcumin. Docking of the known inhibitors curcumin and NDGA to P-12-LOX was used to optimize the docking protocol for the system in study. Over 75% of the compounds of interest were successfully docked into the active site of P-12-LOX, many of them sharing similar binding modes. Curcuminoids that did not dock into the active site did not inhibit P-12-LOX. From a set of the curcuminoids that were successfully docked and selected for testing, two were found to inhibit human lipoxygenase better than curcumin. False-positive curcuminoids showed high LogP (theoretical) values, indicating poor water solubility, a possible reason for lack of inhibitory activity or/and nonrealistic binding. Additionally, the curcuminoids inhibiting P-12-LOX were tested for their ability to reduce sprout formation of endothelial cells (in vitro model of angiogenesis). We found that only curcuminoids inhibiting human P-12-LOX and the known inhibitor NDGA reduced sprout formation. Only limited inhibition of sprout formation at approximately IC(50) concentrations has been seen. At IC(50), a substantial amount of 12-HETE can be produced by lipoxygenase, providing a stimulus for angiogenic sprouting of endothelial cells. Increasing the concentration of lipoxygenase inhibitors above IC(50), thus decreasing the concentration of 12(S)-HETE produced, greatly reduced sprout formation for all inhibitors tested. This universal event for all tested lipoxygenase inhibitors suggests that the inhibition of sprout formation was most likely due to the inhibition of human P-12-LOX but not other cancer-related pathways.

Construction of a tagging system for subcellular localization of proteins encoded by open reading frames

We have previously characterized a monoclonal antibody (SC1D7) that is directed to maltose-binding protein (MBP) of Escherichia coli and other closely related enteric bacteria. SC1D7 does not cross-react with proteins in eucaryotes and appears to be a highly specific tool in immunochemical analyses. To better map the epitope, we took advantage of an available plasmid, pMAL-c2, that encodes the E. coli MBP-coding sequence and constructed plasmids to express MBP fragments. A construct containing the N-terminal portion of MBP does not react with SC1D7, whereas a second construct expressing glutathione S-transferase fused with the C-terminal half of MBP does react with SC1D7. To precisely define the epitope, random peptides displayed on M13 were used to react with SC1D7. Sequences of reactive peptides were aligned, and a consensus sequence of XDXRIPX was deduced. This sequence matches MBP with an amino acid stretch of KDPRIAA. To consolidate the mapping result, a sequence encoding this epitope was inserted into an expression vector and the resulting recombinant protein did react with SC1D7. Thereafter, this epitope was incorporated into a eucaryotic expression plasmid containing a previously defined hepatitis delta virus epitope for protein tagging. This two-epitope-tagging vector is useful in various molecular analyses. We demonstrate its usage for localization of a bacterial virulence factor in host cells. This vector should be applicable for high-throughput characterization of new open reading frames found in genome sequencing.

The N-terminal "beta-barrel" domain of 5-lipoxygenase is essential for nuclear membrane translocation

5-Lipoxygenase is the key enzyme in the formation of leukotrienes, which are potent lipid mediators of asthma pathophysiology. This enzyme translocates to the nuclear envelope in a calcium-dependent manner for leukotriene biosynthesis. Eight green fluorescent protein (GFP)-lipoxygenase constructs, representing the major human and mouse enzymes within this family, were constructed and their cDNAs transfected into human embryonic kidney 293 cells. Of these eight lipoxygenases, only the 5-lipoxygenase was clearly nuclear localized and translocated to the nuclear envelope upon stimulation with the calcium ionophore. The N-terminal "beta -barrel" domain of 5-lipoxygenase, but not the catalytic domain, was necessary and sufficient for nuclear envelope translocation. The GFP-N-terminal 5-lipoxygenase domain translocated faster than GFP-5-lipoxygenase. beta-Barrel/catalytic domain chimeras with 12- and 15-lipoxygenase indicated that only the N-terminal domain of 5-lipoxygenase could carry out this translocation function. Mutations of iron atom binding ligands (His550 or deletion of C-terminal isoleucine) that disrupt nuclear localization do not alter translocation capacity indicating distinct determinants of nuclear localization and translocation. Moreover, data show that GFP-5-lipoxygenase beta-barrel containing constructs can translocate to the nuclear membrane whether cytoplasmic or nuclear localized. Thus, the predicted beta-barrel domain of 5-lipoxygenase may function like the C2 domain within protein kinase C and cytosolic phospholipase A(2) with unique determinants that direct its localization to the nuclear envelope.

Characterization of the murine epidermal 12/15-lipoxygenase

The murine lipoxygenase (LO) family consists of at least seven members classified according to the HETE (hydroxyeicosatetraenoic acid) metabolite generated during arachidonic acid metabolism and the site of tissue expression. At present there are four 12-lipoxygenases that are functionally distinct, vary in cell and tissue distribution, catalytic activity and each are products of separate, linked genes. They are "platelet-type" 12-LO (P-12LO), "leukocyte-type" 12-LO (L-12LO), "epidermal-type" 12-LO (e-12LO) and the most recently discovered 12(R)-LO. In this report we characterize e-12LO, which was overexpressed in the baculovirus/insect cell expression system. The enzyme functions as a dual specificity 12/15-lipoxygenase with a 12-HETE/15-HETE product ratio of approximately 6:1 with arachidonic acid as substrate. Several other polyunsaturated fatty acids served as substrates for e-12LO such as gamma-linolenic, dihomo-gamma-linolenic and eicosapentaenoic acids. A green fluorescent protein/e-12LO fusion protein was localized to the cytosol of transfected HEK 293 cells. The e-12LO gene was expressed in mouse oocytes and early embryos. Western blot analysis revealed high level expression in postnatal day 3 mouse epidermal lysates. Together these data suggest that e-12LO plays a role in normal epidermal function and as yet an undiscovered role in early development.

The N-terminal domain of 5-lipoxygenase binds calcium and mediates calcium stimulation of enzyme activity

Human 5-lipoxygenase (5-LO) is a key enzyme in the conversion of arachidonic acid into leukotrienes and lipoxins, mediators and modulators of inflammation. In this study, we localized a stimulatory Ca(2+)-binding site to the N-terminal region of the enzyme. Thus, in a (45)Ca(2+) overlay assay, the N-terminal 128 amino acids of recombinant human 5-LO (fused to glutathione S-transferase) bound radioactive calcium to about the same extent as intact 5-LO. The glutathione S-transferase fusion protein of the C-terminal part of 5-LO (amino acids 120-673) showed much weaker binding. A model of a putative 5-LO N-terminal domain was calculated based on the structure of rabbit reticulocyte 15-LO. This model resembles beta-sandwich C2 domains of other Ca(2+)-binding proteins. Comparison of our model with the C2 domain of cytosolic phospholipase A(2) suggested a number of amino acids, located in the loops that connect the beta-strands, as potential Ca(2+) ligands. Indeed, mutations particularly in loop 2 (N43A, D44A, and E46A) led to decreased Ca(2+) binding and a requirement for higher Ca(2+) concentrations to stimulate enzyme activity. Our data indicate that an N-terminal beta-sandwich of 5-LO functions as a C2 domain in the calcium regulation of enzyme activity.

Immobilised metal affinity chromatography of beta-galactosidase from unclarified Escherichia coli homogenates using expanded bed adsorption

The development of an expanded bed process for the direct extraction and partial purification of beta-galactosidase from unclarified Escherichia coli homogenates using its natural affinity for metal loaded STREAMLINE Chelating is described. Small packed beds were used to determine the effect of chelated metal ion (Cu2+, Ni2+, Co2+ or Zn2+), loading pH and ionic strength on the selective binding capacity, and recovery of beta-galactosidase from clarified homogenates. An elution protocol was developed using the competitive displacer, imidazole, to recover beta-galactosidase in 87% yield and 3.4-fold purification. These results were then used to develop a separation for the recovery of beta-galactosidase from unclarified homogenates in a 2.5-cm diameter expanded bed. Although Ni2+ loaded STREAMLINE Chelating had a 5% dynamic capacity for beta-galactosidase of just 118 U ml(-1) (0.39 mg ml(-1)), the low capacity was thought to be due to the large size of the target (464,000) relative to the exclusion limit of the macroporous adsorbent. Despite this low capacity, Ni2 STREAMLINE Chelating was used successfully to recover beta-galactosidase from an unclarified homogenate in 86.4% yield and at 5.95-fold purification. The degree of purification relative to a commercial standard, as assessed using the purification factor and sodium dodecyl sulphate-polyacrylamide gel electrophoresis was high suggesting that this pseudo-affinity procedure compared favourably with alternative methods.

Differential characteristics of human 15-lipoxygenase isozymes and a novel splice variant of 15S-lipoxygenase

The lipoxygenases (LOs) are a family of nonheme iron dioxygenases that catalyse the insertion of molecular oxygen into polyunsaturated fatty acids. Five members of this gene family have been described in man, 5-LO, 12S-LO, 12R-LO, 15-LO and 15S-LO. Using partially purified recombinant 15S-LO enzyme and cells constitutively expressing this protein, we have compared the activity, substrate specificity, kinetic characteristics and regulation of this enzyme to that previously reported for 15-LO. 15S-LO has a threefold higher Km, similar Vmax and increased specificity of oxygenation for arachidonic acid, and a similar Km but decreased Vmax for linoleic acid in comparison to 15-LO. Unlike 15-LO, 15S-LO is not suicide inactivated by the products of fatty acid oxygenation. However, in common with other LOs, 15S-LO activity is regulated through calcium-dependent association of the enzyme with the membrane fraction of cells. In addition, whilst independently cloning the recently described 15S-LO, we identified a splice variant containing an in-frame 87-bp deletion corresponding to amino acids 401-429 inclusive. Modelling of the 15S-LO and subsequent studies with partially purified recombinant protein suggest that the deleted region comprises a complete alpha-helix flanking the active site of the enzyme resulting in decreased specificity of oxygenation and affinity for fatty acid substrates. Alternative splicing of 15S-LO would therefore provide a further level of regulation of fatty acid metabolism. These results demonstrate that there are substantial differences in the enzyme characteristics and regulation of the 15-LO isozymes which may reflect differing roles for the proteins in vivo.

Parameters influencing human mu opioid receptor over-expression in baculovirus-infected insect cells

The cDNA encoding the human mu opioid receptor (hMOR) was cloned in the baculovirus Autographa californica (AcMNPV) under the control of the polyhedrin promoter. We investigated the influence of different molecular constructions on receptor expression levels: the receptor was fused either to an amino- or a carboxy-terminal histidine tag (hMOR-N-His and hMOR-C-His respectively), or to the cleavable sequence signal of the baculovirus gp64 glycoprotein (gp-hMOR and gp-hMOR-C-His). Two cell lines, Spodoptera frugiperda (Sf9) and Trichoplusia ni (BTI-TN-5B1-4), in combination with three different culture media were also tested for their ability to produce maximal protein expression. Molecular constructions and culture conditions were both shown to influence substantially protein production. The best results were obtained using cells adapted to serum-free medium combined with constructions in fusion with the endogenous signal sequence of the baculovirus gp64 protein. Those conditions led to maximal expression and shortened the time required for receptor production. We also showed that an amino-terminal location of a hexahistidine tag was more detrimental to the expression level than a carboxy-terminal position.

Determinants of 5-lipoxygenase nuclear localization using green fluorescent protein/5-lipoxygenase fusion proteins

5-Lipoxygenase catalyzes the first two steps in the biosynthesis of leukotrienes, potent extracellular mediators of inflammation and allergic disorders. The unanticipated observation of 5-lipoxygenase in the nucleus of some cell types including bone marrow-derived mast cells (Chen, X. S., Naumann, T. A., Kurre, U., Jenkins, N. A., Copeland, N. G., and Funk, C. D. (1995) J. Biol. Chem. 270, 17993-17999) has raised speculation about intranuclear actions of leukotrienes or the enzyme itself. To explore the entry of 5-lipoxygenase into the nucleus we have transfected various cell types with expression vectors encoding native 5-lipoxygenase and green fluorescent protein/5-lipoxygenase (GFP-5LO) fusion proteins. 5-Lipoxygenase and green fluorescent protein/5-lipoxygenase co-localized with the nuclear DNA stain Hoechst 33258 in each cell type. The three main basic regions of 5-lipoxygenase were incapable of acting as "classical" nuclear localization signal sequences. Mutations that abolished enzyme activity/non-heme iron resulted in proteins that would no longer enter the nucleus. An NH2-terminal 5-lipoxygenase fragment of 80 residues was sufficient for directing nuclear localization of green fluorescent protein but not cytosolic pyruvate kinase. The combined data suggest that 5-lipoxygenase enters the nucleus not by a classical nuclear localization signal but by a non-conventional signal located in the predicted beta-barrel domain that may be masked by structural alterations.

Intra- and extracellular expression of rabbit reticulocyte 15-lipoxygenase in the Baculovirus/insect cell system

Rabbit reticulocyte 15-lipoxygenase was expressed as intracellular enzyme and as export protein in High Five cells. While intracellular expression in the baculovirus/insect cell system was already reported for various mammalian lipoxygenases, we have developed a strategy for secretion of this cytosolic enzyme using the signal sequence of human interleukin-2. Expression levels of 10 mg/liter (intracellular strategy) and 18 mg/liter (extracellular strategy) were obtained. The recombinant enzyme expressed as intracellular protein was purified to apparent homogeneity by anion-exchange chromatography on a Mono-Q column with an overall recovery of 80% enzyme activity. For the final enzyme preparation, a specific linoleic acid oxygenase activity of 16.7 micromol 13-hydroperoxyoctadeca-9,11-dieic acid formation mg-1 min-1 was determined, which corresponds to a molecular turnover number of 21 s-1. Similar turnover rates have been reported for the native rabbit 15-lipoxygenase. Extracellularly expressed recombinant 15-lipoxygenase exhibited a heterogeneity in anion-exchange chromatography. Three major peaks of 15-lipoxygenase activity were eluted from a Mono-Q column and the relative amounts of these isoforms varied from batch to batch of enzyme expression. One of the major isoenzymes which cochromatographed with the native 15-lipoxygenase was purified to homogeneity from the cell-free culture supernatant and exhibited a specific activity of 5.1 micromol 13-hydroperoxyoctadeca-9,11-dienoic acid formation mg-1 min-1 (turnover rate of 6.1 s-1). The recombinant enzyme species were characterized with respect to their protein-chemical and enzymatic properties and no differences to the native rabbit 15-lipoxygenase were detected.

Expression and characterization of human glutamate-cysteine ligase

Glutamate-cysteine ligase (GLCL) catalyzes the rate-limiting step in glutathione biosynthesis. GLCL comprises regulatory (GLCLR) and catalytic (GLCLC) subunits. To understand better the structure-function relationship of GLCL subunits and holoenzyme, human GLCLR and GLCLC genes were inserted into the baculovirus genome. Recombinant hGLCLR andhGLCLC were produced in cells infected with recombinant baculoviruses, and homogeneous hGLCL subunits and holoenzyme were purified from cell lysates with a Ni-NTA resin. Purified recombinant hGLCL holoenzyme was catalytically more active than hGLCLC with L-glutamate, L-alpha-aminobutyrate, and ATP as substrates. The selectivity of purified hGLCL holoenzyme for L-glutamate, L-alpha-aminobutyrate, or L-cysteine was significantly higher than for hGLCLC. Glutathione was a noncompetitive inhibitor for both hGLCL holoenzyme and hGLCLC. hGLCLC was more sensitive to inhibition by glutathione than hGLCL holoenzyme. Deletion of the first 25 amino acid residues at the amino terminus of GLCLC dramatically decreased GLCL activity, indicating that the amino terminus of GLCLC is required for full catalytic activity. Expressed and purified hGLCL provides a useful tool to investigate glutathione biosynthesis in vitro.

Detection of low-affinity adhesion ligands by linking recombinant cell adhesion molecules in uniform orientation to a fluorescently labelled dextran molecule by means of hexahistidine tagging: the case of multimeric CD40

Cell-cell interactions involve highly polyvalent associations between receptors on adjacent cells. In order to mimic this process, we have prepared a highly polyvalent form of CD40 attached to a dextran backbone. This was accomplished by engineering a hexahistidine tag on the C-terminus of the CD40 and binding, in a uniform orientation, up to 100 molecules of hexahistidine CD40 by metal chelation to a single fluorescently tagged dextran molecule. The advantage of this 'multimeric' CD40 is that it would be expected to bind to any counterstructure with a significantly higher avidity compared to monomeric CD40. The multimeric CD40 bound with high affinity to stably transfected mouse fibroblasts expressing CD40L. The multimeric ligand also bound to the activated T cell clone, D10, but did not bind to resting cells, showing that it bound to the physiological ligand. Using this system, we found no evidence to support the claim [Heath et al., 1993. Cell. Immunol. 152, 468.] that the A20 cells have a counterstructure for CD40, and propose that the high binding of CD40 observed in this study may have been due to an exposed hexahistidine tag on the molecule. This multimeric technology has considerable potential for detecting low-affinity interactions between cell adhesion receptors and ligands. The uniform orientation of the molecules on the dextran is an advantage over previous systems and permits the preparation of heterogeneous, multimeric ligands which more closely mimic the conditions at the cell surface.

Increased platelet sensitivity to ADP in mice lacking platelet-type 12-lipoxygenase

Arachidonic acid metabolism is one of several mechanisms culminating in the production of an agonist for platelet activation and recruitment. Although the proaggregatory role of thromboxane A2, a product of the aspirin-inhibitable cyclooxygenase, is well established, relatively little is known regarding the biological importance of arachidonic acid metabolism via the 12-lipoxygenase (P-12LO) pathway to 12-hydro(pero)xyeicosatetraenoic acid. We observed that platelets obtained from mice in which the P-12LO gene has been disrupted by gene targeting (P-12LO-/-) exhibit a selective hypersensitivity to ADP, manifested as a marked increase in slope and percent aggregation in ex vivo assays and increased mortality in an ADP-induced mouse model of thromboembolism. The hyperresponsiveness to ADP is independent of dense granule release, cyclooxygenase-derived eicosanoid synthesis, and protein kinase C activity. The addition of 12-hydroxyeicosatetraenoic acid to P-12LO-/- platelet-rich plasma rescues the hyperresponsive phenotype resulting in a diminished ADP-induced aggregation profile. The enhanced ADP sensitivity of P-12LO-/- mice appears to reveal a mechanism by which a product of the P-12LO pathway suppresses platelet activation by ADP.

Characterization of delta, kappa, and mu human opioid receptors overexpressed in baculovirus-infected insect cells

The cDNAs encoding human delta (hDOR), kappa (hKOR) and micro (hMOR) opioid receptors were cloned in the baculovirus Autographa californica (AcMNPV) under the control of the polyhedrin promoter with or without an amino-terminal hexahistidine tag. Expression levels were optimized in Spodoptera frugiperda (Sf9) cells and were in the following order hMOR > hDOR > hKOR. The receptors bound antagonists with affinity values similar to those published previously for the receptors expressed in mammalian cells. They also retained selectivity toward specific antagonists. The three receptors bound peptidic agonists with low affinity, suggesting that they might not be functionally coupled to intracellular effectors. Introduction of an amino-terminal hexahistidine tag decreased the levels of expression markedly. Only hMOR-his was expressed at a level allowing binding study, but no difference could be detected in the affinities of both agonists and antagonists compared with the nontagged protein. hMOR expression was also optimized in High Five cells leading to a further increase in protein production. The pharmacological profile was similar to the one obtained when the receptor was expressed in Sf9 cells. Our results show that the baculovirus expression system is suitable for large scale production of human opioid receptors.

Requirement for epidermal growth factor receptor tyrosine kinase and for 12-lipoxygenase activity in the expression of 12-lipoxygenase in human epidermoid carcinoma cells

We studied the dependency of basal 12-lipoxygenase (12-LOX; arachidonate:oxygen 12-oxidoreductase, EC 1.13.11.31) expression and activity on functional protein tyrosine kinase of the epidermal growth factor receptor (EGF-R) and on 12-LOX activity in human A431 epidermoid carcinoma cells. Treatment of cells with inhibitors of high specificity for EGF-R tyrosine kinase, namely PD 153035 and 4,5-dianilinophthalimide (DAPH1), decreased cellular 12-LOX at mRNA, protein, and activity levels in a time- and dose-dependent manner, with PD 153035 being effective at concentrations below 1 microM. After 24-hr incubation with 10 microM PD 153035 or DAPH1, 12-LOX activity dropped to 14% (39%), and 12-LOX protein to 25% (24%) of control level. Inhibition of 12-LOX activity by the compound N-benzyl-N-hydroxy-5-phenylpentanamide (BHPP) also resulted in a substantial decrease in 12-LOX protein expression. 12-LOX mRNA levels were diminished or undetectable by reverse transcription-polymerase chain reaction after cell treatment with these inhibitors. Our results suggest that basal 12-LOX expression in A431 tumor cells largely depends on functional EGF-R tyrosine kinase, and that 12-LOX activity is required in the EGF-elicited intracellular signaling maintaining the expression of 12-LOX.

Lipoxygenase activity in heart cells

Arachidonic acid (AA) metabolism via the lipoxygenase (LOX) pathway in rat hearts and in cultured rat cardiomyocytes was investigated using 1-[14C]AA. LOX activity was detected in the microsomal fraction, in the high speed supernatant prepared from rat hearts and in rat cardiomyocyte supernatant. LOX products from all fractions comigrated in thin layer chromatography as 12-hydroxyeicosatetraenoic acid (12-HETE) and 15-HETE. Enzyme linked immunosorbent assay for 12-HETE showed its formation by the microsomal fraction, the ammonium sulfate (AS) pellet, and by rat cardiomyocyte supernatant, while radioimmunoassay for 15-HETE showed its formation only by the AS pellet. The properties of LOX in each fraction are reported here.

Expression and characterization of recombinant alpha-galactosidase in baculovirus-infected insect cells

A cDNA encoding coffee bean alpha-galactosidase was subcloned into baculovirus expression vectors, pVL-1393 and pAc-GP67B, for intracellular and extracellular expression in Spodoptera frugiperda (Sf9) insect cells, respectively. The expressed protein (recombinant alpha-galactosidase) was immunologically reactive with antisera raised against its native counterpart isolated from coffee beans and was biologically active towards the substrate p-nitrophenyl alpha-galactopyranoside. The subcellular distribution of recombinant alpha-galactosidase expressed from different vectors was analyzed by Western blotting, immunofluorescent labeling, and electron microscopy. In addition, recombinant alpha-galactosidase was compared to the native enzyme with respect to glycosylation, thermostability, and pH profile. Furthermore, a recombinant alpha-galactosidase molecule with a His6 tag at its C-terminus was constructed by an overlap PCR method so that the enzyme expressed in Sf9 cells can be purified by a simple affinity chromatography procedure.