Systematic identification of anticancer drug targets reveals a nucleus-to-mitochondria ROS-sensing pathway

Multiple anticancer drugs have been proposed to cause cell death, in part, by increasing the steady-state levels of cellular reactive oxygen species (ROS). However, for most of these drugs, exactly how the resultant ROS function and are sensed is poorly understood. It remains unclear which proteins the ROS modify and their roles in drug sensitivity/resistance. To answer these questions, we examined 11 anticancer drugs with an integrated proteogenomic approach identifying not only many unique targets but also shared ones-including ribosomal components, suggesting common mechanisms by which drugs regulate translation. We focus on CHK1 that we find is a nuclear H2O2 sensor that launches a cellular program to dampen ROS. CHK1 phosphorylates the mitochondrial DNA-binding protein SSBP1 to prevent its mitochondrial localization, which in turn decreases nuclear H2O2. Our results reveal a druggable nucleus-to-mitochondria ROS-sensing pathway-required to resolve nuclear H2O2 accumulation and mediate resistance to platinum-based agents in ovarian cancers.

CX3CR1 deficiency leads to impairment of immune surveillance in the epididymis

Mononuclear phagocytes (MPs) play an active role in the immunological homeostasis of the urogenital tract. In the epididymis, a finely tuned balance between tolerance to antigenic sperm and immune activation is required to maintain epididymal function while protecting sperm against pathogens and stressors. We previously characterized a subset of resident MPs that express the CX3CR1 receptor, emphasizing their role in antigen sampling and processing during sperm maturation and storage in the murine epididymis. Bacteria-associated epididymitis is the most common cause of intrascrotal inflammation and frequently leads to reproductive complications. Here, we examined whether the lack of functional CX3CR1 in homozygous mice (CX3CR1EGFP/EGFP, KO) alters the ability of MPs to initiate immune responses during epididymitis induced by LPS intravasal-epididymal injection. Confocal microscopy revealed that CX3CR1-deficient MPs located in the initial segments of the epididymis displayed fewer luminal-reaching membrane projections and impaired antigen capture activity. Moreover, flow cytometry showed a reduction of epididymal KO MPs with a monocytic phenotype under physiological conditions. In contrast, flow cytometry revealed an increase in the abundance of MPs with a monocytic signature in the distal epididymal segments after an LPS challenge. This was accompanied by the accumulation of CD103+ cells in the interstitium, and the prevention or attenuation of epithelial damage in the KO epididymis during epididymitis. Additionally, CX3CR1 deletion induced downregulation of Gja1 (connexin 43) expression in KO MPs. Together, our study provides evidence that MPs are gatekeepers of the immunological blood-epididymis barrier and reveal the role of the CX3CR1 receptor in epididymal mucosal homeostasis by inducing MP luminal protrusions and by regulating the monocyte population in the epididymis at steady state as well as upon infection. We also uncover the interaction between MPs and CD103+ dendritic cells, presumably through connexin 43, that enhance immune responses during epididymitis. Our study may lead to new diagnostics and therapies for male infertility and epididymitis by identifying immune mechanisms in the epididymis.

Condensates induced by transcription inhibition localize active chromatin to nucleoli

The proper function of the genome relies on spatial organization of DNA, RNA, and proteins, but how transcription contributes to the organization is unclear. Here, we show that condensates induced by transcription inhibition (CITIs) drastically alter genome spatial organization. CITIs are formed by SFPQ, NONO, FUS, and TAF15 in nucleoli upon inhibition of RNA polymerase II (RNAPII). Mechanistically, RNAPII inhibition perturbs ribosomal RNA (rRNA) processing, releases rRNA-processing factors from nucleoli, and enables SFPQ to bind rRNA. While accumulating in CITIs, SFPQ/TAF15 remain associated with active genes and tether active chromatin to nucleoli. In the presence of DNA double-strand breaks (DSBs), the altered chromatin compartmentalization induced by RNAPII inhibition increases gene fusions in CITIs and stimulates the formation of fusion oncogenes. Thus, proper RNAPII transcription and rRNA processing prevent the altered compartmentalization of active chromatin in CITIs, suppressing the generation of gene fusions from DSBs.

High Histone Deacetylase 2/3 Expression in Non-Functioning Pituitary Tumors

Epigenetic modification of chromatin is involved in non-malignant pituitary neoplasia by causing abnormal expression of tumor suppressors and oncogenes. These changes are potentially reversible, suggesting the possibility of targeting tumor cells by restoring the expression of epigenetically silenced tumor suppressors. The role of the histone deacetylase (HDAC) family in pituitary tumorigenesis is not known. We report that HDAC2 and 3, Class I HDAC members, are highly expressed in clinically non-functioning pituitary adenomas (NFPAs) compared to normal pituitary (NP) samples as determined by RT-PCR and immunohistochemical staining (IHC). Treatment of a human NFPA derived folliculostellate cell line, PDFS, with the HDAC3 inhibitor RGFP966 for 96 hours resulted in inhibition of cell proliferation by 70%. Furthermore, the combination of RGFP966 with a methyltransferase/DNMT inhibitor, 5’-aza-2’-deoxycytidine, led to the restoration of the expression of several tumor suppressor genes, including STAT1, P16, PTEN, and the large non-coding RNA tumor suppressor MEG3, in PDFS cells. Our data support the hypothesis that both histone modification and DNA methylation are involved in the pathogenesis of human NFPAs and suggest that targeting HDACs and DNA methylation can be incorporated into future therapies.

Sprouting Angiogenesis in Human Pituitary Adenomas

Introduction

Angiogenesis in pituitary tumors is not fully understood, and a better understanding could help inform new pharmacologic therapies, particularly for aggressive pituitary tumors.

Materials and Methods

219 human pituitary tumors and 12 normal pituitary glands were studied. Angiogenic genes were quantified by an angiogenesis qPCR array and a TaqMan probe-based absolute qPCR. Angiogenesis inhibition in pituitary tumors was evaluated in vitro with the endothelial tube formation assay and in vivo in RbΔ19 mice.

Results

71 angiogenic genes, 40 of which are known to be involved in sprouting angiogenesis, were differentially expressed in pituitary tumors. Expression of endothelial markers CD31, CD34, and ENG was significantly higher in pituitary tumors, by 5.6, 22.3, and 8.2-fold, respectively, compared to in normal pituitary tissue. There was no significant difference in levels of the lymphatic endothelial marker LYVE1 in pituitary tumors compared with normal pituitary gland tissue. Pituitary tumors also expressed significantly higher levels of angiogenesis growth factors, including VEGFA (4.2-fold), VEGFB (2.2), VEGFC (19.3), PGF (13.4), ANGPT2 (9.2), PDGFA (2.7), PDGFB (10.5) and TGFB1 (3.8) compared to normal pituitary tissue. Expression of VEGFC and PGF was highly correlated with the expression of endothelial markers in tumor samples, including CD31, CD34, and ENG (endoglin, a co-receptor for TGFβ). Furthermore, VEGFR inhibitors inhibited angiogenesis induced by human pituitary tumors and prolonged survival of RbΔ19 mice.

Conclusion

Human pituitary tumors are characterized by more active angiogenesis than normal pituitary gland tissue in a manner consistent with sprouting angiogenesis. Angiogenesis in pituitary tumors is regulated mainly by PGF and VEGFC, not VEGFA and VEGFB. Angiogenesis inhibitors, such as the VEGFR2 inhibitor cabozantinib, may merit further investigation as therapies for aggressive human pituitary tumors.

Exercise hormone irisin is a critical regulator of cognitive function

Identifying secreted mediators that drive the cognitive benefits of exercise holds great promise for the treatment of cognitive decline in ageing or Alzheimer's disease (AD). Here, we show that irisin, the cleaved and circulating form of the exercise-induced membrane protein FNDC5, is sufficient to confer the benefits of exercise on cognitive function. Genetic deletion of Fndc5/irisin (global Fndc5 knock-out (KO) mice; F5KO) impairs cognitive function in exercise, ageing and AD. Diminished pattern separation in F5KO mice can be rescued by delivering irisin directly into the dentate gyrus, suggesting that irisin is the active moiety. In F5KO mice, adult-born neurons in the dentate gyrus are morphologically, transcriptionally and functionally abnormal. Importantly, elevation of circulating irisin levels by peripheral delivery of irisin via adeno-associated viral overexpression in the liver results in enrichment of central irisin and is sufficient to improve both the cognitive deficit and neuropathology in AD mouse models. Irisin is a crucial regulator of the cognitive benefits of exercise and is a potential therapeutic agent for treating cognitive disorders including AD.

A cross-nearest neighbor/Monte Carlo algorithm for single-molecule localization microscopy defines interactions between p53, Mdm2, and MEG3

The functions of long noncoding (lnc)RNAs, such as MEG3, are defined by their interactions with other RNAs and proteins. These interactions, in turn, are shaped by their subcellular localization and temporal context. Therefore, it is important to be able to analyze the relationships of lncRNAs while preserving cellular architecture. The ability of MEG3 to suppress cell proliferation led to its recognition as a tumor suppressor. MEG3 has been proposed to activate p53 by disrupting the interaction of p53 with mouse double minute 2 homolog (Mdm2). To test this mechanism in the native cellular context, we employed two-color direct stochastic optical reconstruction microscopy, a single-molecule localization microscopy technique, to detect and quantify the localizations of p53, Mdm2, and MEG3 in U2OS cells. We developed a new cross-nearest neighbor/Monte Carlo algorithm to quantify the association of these molecules. Proof of concept for our method was obtained by examining the association between FKBP1A and mTOR, MEG3 and p53, and Mdm2 and p53. In contrast to previous models, our data support a model in which MEG3 modulates p53 independently of the interaction with Mdm2.

The Upregulation of Molecules Related to Tumor Immune Escape in Human Pituitary Adenomas

Human pituitary adenomas are one of the most common intracranial neoplasms. Although most of these tumors are benign and can be treated medically or by transsphenoidal surgery, a subset of these tumors are fast-growing, aggressive, recur, and remain a therapeutic dilemma. Because antibodies against immune checkpoint receptors PD-1 and CLTA-4 are now routinely used for cancer treatment, we quantified the expression of mRNA coding for PD-1, CLTA-4, and their ligands, PD-L1, PD-L2, CD80, and CD86 in human pituitary adenomas and normal pituitary glands, with the ultimate goal of exploiting immune checkpoint therapy in aggressive pituitary adenomas. Aggressive pituitary adenomas demonstrated an increased expression of PD-L2, CD80, and CD86 in compared to that of normal human pituitary glands. Furthermore, aggressive pituitary tumors demonstrated significantly higher levels of CD80 and CD86 compared to non-aggressive tumors. Our results establish a rationale for studying a potential role for immune checkpoint inhibition therapy in the treatment of pituitary adenomas.

Thioredoxin Interacting Protein Is Required for a Chronic Energy-Rich Diet to Promote Intestinal Fructose Absorption

Increased consumption of fats and added sugars has been associated with an increase in metabolic syndromes. Here we show that mice chronically fed an energy-rich diet (ERD) with high fat and moderate sucrose have enhanced the absorption of a gastrointestinal fructose load, and this required expression of the arrestin domain protein Txnip in the intestinal epithelial cells. ERD feeding induced gene and protein expression of Glut5, and this required the expression of Txnip. Furthermore, Txnip interacted with Rab11a, a small GTPase that facilitates the apical localization of Glut5. We also demonstrate that ERD promoted Txnip/Glut5 complexes in the apical intestinal epithelial cell. Our findings demonstrate that ERD facilitates fructose absorption through a Txnip-dependent mechanism in the intestinal epithelial cell, suggesting that increased fructose absorption could potentially provide a mechanism for worsening of metabolic syndromes in the setting of a chronic ERD.

Two- and three-color STORM analysis reveals higher-order assembly of leukotriene synthetic complexes on the nuclear envelope of murine neutrophils

Over the last several years it has become clear that higher order assemblies on membranes, exemplified by signalosomes, are a paradigm for the regulation of many membrane signaling processes. We have recently combined two-color direct stochastic optical reconstruction microscopy (dSTORM) with the (Clus-DoC) algorithm that combines cluster detection and colocalization analysis to observe the organization of 5-lipoxygenase (5-LO) and 5-lipoxygenase-activating protein (FLAP) into higher order assemblies on the nuclear envelope of mast cells; these assemblies were linked to leukotriene (LT) C4 production. In this study we investigated whether higher order assemblies of 5-LO and FLAP included cytosolic phospholipase A2 (cPLA2) and were linked to LTB4 production in murine neutrophils. Using two- and three-color dSTORM supported by fluorescence lifetime imaging microscopy we identified higher order assemblies containing 40 molecules (median) (IQR: 23, 87) of 5-LO, and 53 molecules (62, 156) of FLAP monomer. 98 (18, 154) molecules of cPLA2 were clustered with 5-LO, and 77 (33, 114) molecules of cPLA2 were associated with FLAP. These assemblies were tightly linked to LTB4 formation. The activation-dependent close associations of cPLA2, FLAP, and 5-LO in higher order assemblies on the nuclear envelope support a model in which arachidonic acid is generated by cPLA2 in apposition to FLAP, facilitating its transfer to 5-LO to initiate LT synthesis.

The organization of leukotriene biosynthesis on the nuclear envelope revealed by single molecule localization microscopy and computational analyses

The initial steps in the synthesis of leukotrienes are the translocation of 5-lipoxygenase (5-LO) to the nuclear envelope and its subsequent association with its scaffold protein 5-lipoxygenase-activating protein (FLAP). A major gap in our understanding of this process is the knowledge of how the organization of 5-LO and FLAP on the nuclear envelope regulates leukotriene synthesis. We combined single molecule localization microscopy with Clus-DoC cluster analysis, and also a novel unbiased cluster analysis to analyze changes in the relationships between 5-LO and FLAP in response to activation of RBL-2H3 cells to generate leukotriene C₄. We identified the time-dependent reorganization of both 5-LO and FLAP into higher-order assemblies or clusters in response to cell activation via the IgE receptor. Clus-DoC analysis identified a subset of these clusters with a high degree of interaction between 5-LO and FLAP that specifically correlates with the time course of LTC₄ synthesis, strongly suggesting their role in the initiation of leukotriene biosynthesis.

Diabetes regulates fructose absorption through thioredoxin-interacting protein

Metabolic studies suggest that the absorptive capacity of the small intestine for fructose is limited, though the molecular mechanisms controlling this process remain unknown. Here we demonstrate that thioredoxin-interacting protein (Txnip), which regulates glucose homeostasis in mammals, binds to fructose transporters and promotes fructose absorption by the small intestine. Deletion of Txnip in mice reduced fructose transport into the peripheral bloodstream and liver, as well as the severity of adverse metabolic outcomes resulting from long-term fructose consumption. We also demonstrate that fructose consumption induces expression of Txnip in the small intestine. Diabetic mice had increased expression of Txnip in the small intestine as well as enhanced fructose uptake and transport into the hepatic portal circulation. The deletion of Txnip in mice abolished the diabetes-induced increase in fructose absorption. Our results indicate that Txnip is a critical regulator of fructose metabolism and suggest that a diabetic state can promote fructose uptake.

Coordinated regulation of bidirectional COPI transport at the Golgi by CDC42

The Golgi complex plays a central role in the intracellular sorting of secretory proteins ^1,2. Anterograde transport through the Golgi has been explained by the movement of Golgi cisternae, known as cisternal maturation ^3–5. Because this explanation is now appreciated to be incomplete ⁶, interest has developed in understanding tubules that connect the Golgi cisternae ^7–9. Here, we find that the Coat Protein I (COPI) complex sorts anterograde cargoes into these tubules. Moreover, the small GTPase cdc42 regulates bidirectional Golgi transport by targeting the dual functions of COPI in cargo sorting and carrier formation. Cdc42 also directly imparts membrane curvature in promoting COPI tubule formation. Our findings further reveal that COPI tubular transport complements cisternal maturation in explaining how anterograde Golgi transport is achieved, and that bidirectional COPI transport is modulated by environmental cues through cdc42.

The CD200-CD200R1 inhibitory signaling pathway: immune regulation and host-pathogen interactions

The CD200:CD200R1 inhibitory signaling pathway has been implicated in playing a prominent role in limiting inflammation in a wide range of inflammatory diseases. CD200R1 signaling inhibits the expression of proinflammatory molecules including tumor necrosis factor, interferons, and inducible nitric oxide synthase in response to selected stimuli. Unsurprisingly, due to the regulatory role that CD200R1 plays in multiple inflammatory pathways, an increasing number of parasitic, bacterial, and viral pathogens exploit this pathway to suppress host defenses. A complete understanding of the pathways regulated by CD200R1 signaling and the diverse mechanisms that pathogens have evolved to manipulate the CD200:CD200R1 pathway can help identify clinical situations where targeting this interaction can be of therapeutic benefit. In this review, we compare CD200R1 to other pathogen-targeted inhibitory receptors and highlight how this signaling pathway is utilized by a diverse number of pathogens and, therefore, may represent a novel targeting strategy for the treatment of infectious diseases.

CD47 plays a critical role in T-cell recruitment by regulation of LFA-1 and VLA-4 integrin adhesive functions

CD47 plays an important but incompletely understood role in the innate and adaptive immune responses. CD47, also called integrin-associated protein, has been demonstrated to associate in cis with β1 and β3 integrins. Here we test the hypothesis that CD47 regulates adhesive functions of T-cell α4β1 (VLA-4) and αLβ2 (LFA-1) in in vivo and in vitro models of inflammation. Intravital microscopy studies reveal that CD47(-/-) Th1 cells exhibit reduced interactions with wild-type (WT) inflamed cremaster muscle microvessels. Similarly, murine CD47(-/-) Th1 cells, as compared with WT, showed defects in adhesion and transmigration across tumor necrosis factor-α (TNF-α)-activated murine endothelium and in adhesion to immobilized intercellular adhesion molecule 1 (ICAM-1) and vascular cell adhesion protein 1 (VCAM-1) under flow conditions. Human Jurkat T-cells lacking CD47 also showed reduced adhesion to TNF-α-activated endothelium and ICAM-1 and VCAM-1. In cis interactions between Jurkat T-cell β2 integrins and CD47 were detected by fluorescence lifetime imaging microscopy. Unexpectedly, Jurkat CD47 null cells exhibited a striking defect in β1 and β2 integrin activation in response to Mn(2+) or Mg(2+)/ethylene glycol tetraacetic acid treatment. Our results demonstrate that CD47 associates with β2 integrins and is necessary to induce high-affinity conformations of LFA-1 and VLA-4 that recognize their endothelial cell ligands and support leukocyte adhesion and transendothelial migration.

A new short-term mouse model of chronic obstructive pulmonary disease identifies a role for mast cell tryptase in pathogenesis

BACKGROUND

Cigarette smoke-induced chronic obstructive pulmonary disease (COPD) is a life-threatening inflammatory disorder of the lung. The development of effective therapies for COPD has been hampered by the lack of an animal model that mimics the human disease in a short timeframe.

OBJECTIVES

We sought to create an early-onset mouse model of cigarette smoke-induced COPD that develops the hallmark features of the human condition in a short time-frame. We also sought to use this model to better understand pathogenesis and the roles of macrophages and mast cells (MCs) in patients with COPD.

METHODS

Tightly controlled amounts of cigarette smoke were delivered to the airways of mice, and the development of the pathologic features of COPD was assessed. The roles of macrophages and MC tryptase in pathogenesis were evaluated by using depletion and in vitro studies and MC protease 6-deficient mice.

RESULTS

After just 8 weeks of smoke exposure, wild-type mice had chronic inflammation, mucus hypersecretion, airway remodeling, emphysema, and reduced lung function. These characteristic features of COPD were glucocorticoid resistant and did not spontaneously resolve. Systemic effects on skeletal muscle and the heart and increased susceptibility to respiratory tract infections also were observed. Macrophages and tryptase-expressing MCs were required for the development of COPD. Recombinant MC tryptase induced proinflammatory responses from cultured macrophages.

CONCLUSION

A short-term mouse model of cigarette smoke-induced COPD was developed in which the characteristic features of the disease were induced more rapidly than in existing models. The model can be used to better understand COPD pathogenesis, and we show a requirement for macrophages and tryptase-expressing MCs.

The nuclear membrane leukotriene synthetic complex is a signal integrator and transducer

Leukotrienes are bioactive signaling molecules derived from arachidonic acid that initiate and amplify innate immunity. A single structure, the leukotriene synthetic complex, on the nuclear membrane of neutrophils integrates and transduces extracellular signals to generate the chemotactic lipid LTB₄.

Leukotrienes (LTs) are lipid-signaling molecules derived from arachidonic acid (AA) that initiate and amplify inflammation. To initiate LT formation, the 5-lipoxygenase (5-LO) enzyme translocates to nuclear membranes, where it associates with its scaffold protein, 5-lipoxygenase–activating protein (FLAP), to form the core of the multiprotein LT synthetic complex. FLAP is considered to function by binding free AA and facilitating its use as a substrate by 5-LO to form the initial LT, LTA₄. We used a combination of fluorescence lifetime imaging microscopy, cell biology, and biochemistry to identify discrete AA-dependent and AA-independent steps that occur on nuclear membranes to control the assembly of the LT synthetic complex in polymorphonuclear leukocytes. The association of AA with FLAP changes the configuration of the scaffold protein, enhances recruitment of membrane-associated 5-LO to form complexes with FLAP, and controls the closeness of this association. Granulocyte monocyte colony–stimulating factor provides a second AA-independent signal that controls the closeness of 5-LO and FLAP within complexes but not the number of complexes that are assembled. Our results demonstrate that the LT synthetic complex is a signal integrator that transduces extracellular signals to modulate the interaction of 5-LO and FLAP.

Joint tissues amplify inflammation and alter their invasive behavior via leukotriene B4 in experimental inflammatory arthritis

Mechanisms by which mesenchymal-derived tissue lineages participate in amplifying and perpetuating synovial inflammation in arthritis have been relatively underinvestigated and are therefore poorly understood. Elucidating these processes is likely to provide new insights into the pathogenesis of multiple diseases. Leukotriene B(4) (LTB(4)) is a potent proinflammatory lipid mediator that initiates and amplifies synovial inflammation in the K/BxN model of arthritis. We sought to elucidate mechanisms by which mesenchymal-derived fibroblast-like synoviocytes (FLSs) perpetuate synovial inflammation. We focused on the abilities of FLSs to contribute to LTB(4) synthesis and to respond to LTB(4) within the joint. Using a series of bone marrow chimeras generated from 5-lipoxygenase(-/-) and leukotriene A(4) (LTA(4)) hydrolase(-/-) mice, we demonstrate that FLSs generate sufficient levels of LTB(4) production through transcellular metabolism in K/BxN serum-induced arthritis to drive inflammatory arthritis. FLSs-which comprise the predominant lineage populating the synovial lining-are competent to metabolize exogenous LTA(4) into LTB(4) ex vivo. Stimulation of FLSs with TNF increased their capacity to generate LTB(4) 3-fold without inducing the expression of LTA(4) hydrolase protein. Moreover, LTB(4) (acting via LTB(4) receptor 1) was found to modulate the migratory and invasive activity of FLSs in vitro and also promote joint erosion by pannus tissue in vivo. Our results identify novel roles for FLSs and LTB(4) in joints, placing LTB(4) regulation of FLS biology at the center of a previously unrecognized amplification loop for synovial inflammation and tissue pathology.

20-HETE mediates ozone-induced, neutrophil-independent airway hyper-responsiveness in mice

Background

Ozone, a pollutant known to induce airway hyper-responsiveness (AHR), increases morbidity and mortality in patients with obstructive airway diseases and asthma. We postulate oxidized lipids mediate in vivo ozone-induced AHR in murine airways.

Methodology/Principal Findings

Male BALB/c mice were exposed to ozone (3 or 6 ppm) or filtered air (controls) for 2 h. Precision cut lung slices (PCLS; 250 µm thickness) containing an intrapulmonary airway (∼0.01 mm² lumen area) were prepared immediately after exposure or 16 h later. After 24 h, airways were contracted to carbachol (CCh). Log EC₅₀ and E_max values were then calculated by measuring the airway lumen area with respect to baseline. In parallel studies, dexamethasone (2.5 mg/kg), or 1-aminobenzotriazol (ABT) (50 mg/kg) were given intraperitoneal injection to naïve mice 18 h prior to ozone exposure. Indomethacin (10 mg/kg) was administered 2 h prior. Cell counts, cytokine levels and liquid chromatography-mass spectrometry (LC-MS) for lipid analysis were assessed in bronchoalveolar lavage (BAL) fluid from ozone exposed and control mice. Ozone acutely induced AHR to CCh. Dexamethasone or indomethacin had little effect on the ozone-induced AHR; while, ABT, a cytochrome P450 inhibitor, markedly attenuated airway sensitivity. BAL fluid from ozone exposed animals, which did not contain an increase in neutrophils or interleukin (IL)-6 levels, increased airway sensitivity following in vitro incubation with a naïve PCLS. In parallel, significant increases in oxidized lipids were also identified using LC-MS with increases of 20-HETE that were decreased following ABT treatment.

Conclusions/Significance

These data show that ozone acutely induces AHR to CCh independent of inflammation and is insensitive to steroid treatment or cyclooxygenase (COX) inhibition. BAL fluid from ozone exposed mice mimicked the effects of in vivo ozone exposure that were associated with marked increases in oxidized lipids. 20-HETE plays a pivotal role in mediating acute ozone-induced AHR.

Cytochrome P-450 4F18 is the leukotriene B4 omega-1/omega-2 hydroxylase in mouse polymorphonuclear leukocytes: identification as the functional orthologue of human polymorphonuclear leukocyte CYP4F3A in the down-regulation of responses to LTB4

Leukotriene B(4) (LTB(4)) is a potent chemoattractant for polymorphonuclear leukocytes (PMN) and other cells. Human PMN inactivate LTB(4) by omega-oxidation catalyzed by cytochrome P-450 (CYP) 4F3A. The contribution of the enzymatic inactivation of LTB(4) by CYP4Fs to down-regulating functional responses of cells to LTB(4) is unknown. To elucidate the role of CYP4F-mediated inactivation of LTB(4) in terminating the responses of PMN to LTB(4) and to identify a target for future genetic studies in mice, we have identified the enzyme that catalyzes the omega-1 and omega-2 oxidation of LTB(4) in mouse myeloid cells as CYP4F18. As determined by mass spectrometry, this enzyme catalyzes the conversion of LTB(4) to 19-OH LTB(4) and to a lesser extent 18-OH LTB(4). Inhibition of CYP4F18 resulted in a marked increase in calcium flux and a 220% increase in the chemotactic response of mouse PMN to LTB(4). CYP4F18 expression was induced in bone marrow-derived dendritic cells by bacterial lipopolysaccharide, a ligand for TLR4, and by poly(I.C), a ligand for TLR3. However, when bone marrow-derived myeloid dendritic cells trafficked to popliteal lymph nodes from paw pads, the expression of CYP4F18 was down-regulated. The results identify CYP4F18 as a critical protein in the regulation of LTB(4) metabolism and functional responses in mouse PMN and identify it as the functional orthologue of human PMN CYP4F3A.

The membrane organization of leukotriene synthesis

Cell signaling leading to the formation of leukotriene (LT)C(4) requires the localization of the four key biosynthetic enzymes on the outer nuclear membrane and endoplasmic reticulum. Whether any macromolecular organization of these proteins exists is unknown. By using fluorescence lifetime imaging microscopy and biochemical analysis, we demonstrate the presence of two distinct multimeric complexes that regulate the formation of LTs in RBL-2H3 cells. One complex consists of multimers of LTC(4) synthase and the 5-lipoxygenase activating protein (FLAP). The second complex consists of multimers of FLAP. Surprisingly, all LTC(4) synthase was found to be in association with FLAP. The results indicate that the formation of LTC(4) and LTB(4) may be determined by the compartmentalization of biosynthetic enzymes in discrete molecular complexes.

Myeloid expression of cytochrome P450 4F3 is determined by a lineage-specific alternative promoter

The cytochrome P450 4F3 (CYP4F3) gene encodes two functionally distinct enzymes that differ only by the selection of exon 4 (CYP4F3A) or exon 3 (CYP4F3B). CYP4F3A inactivates leukotriene B4, a reaction that has significance for controlling inflammation. CYP4F3B converts arachidonic acid to 20-hydroxyeicosatetraenoic acid, a potent activator of protein kinase C. We have previously shown that mRNAs coding for CYP4F3A and CYP4F3B are generated from distinct transcription start sites in neutrophils and liver. We therefore investigated mechanisms that regulate the cell-specific expression of these two isoforms. Initially, we analyzed the distribution of CYP4F3 in human leukocytes and determined a lineage-specific pattern of isoform expression. CYP4F3A is expressed in myeloid cells and is coordinate with myeloid differentiation markers such as CD11b and myeloperoxidase during development in the bone marrow. In contrast, CYP4F3B expression is restricted to a small population of CD3+ T lymphocytes. We identified distinct transcriptional features in myeloid, lymphoid, and hepatic cells that indicate the presence of multiple promoters in the CYP4F3 gene. The hepatic promoter depends on a cluster of hepatocyte nuclear factor sites 123-155 bp upstream of the initiator ATG codon. The myeloid promoter spans 400 bp in a region 468-872 bp upstream of the ATG codon; it is associated with clusters of CACCT sites and can be activated by ZEB-2, a factor primarily characterized as a transcriptional repressor in cells that include lymphocytes. ZEB-2 interacts with C-terminal binding protein and Smads, and this would provide opportunities for integrating environmental signals in myelopoiesis and inflammation.

Membrane localization and topology of leukotriene C4 synthase

Leukotriene C(4) (LTC(4)) synthase conjugates LTA(4) with GSH to form LTC(4). Determining the site of LTC(4) synthesis and the topology of LTC(4) synthase may uncover unappreciated intracellular roles for LTC(4), as well as how LTC(4) is transferred to its export carrier, the multidrug resistance protein-1. We have determined the membrane localization of LTC(4) synthase by immunoelectron microscopy. In contrast to the closely related five-lipoxygenase-activating protein, LTC(4) synthase is distributed in the outer nuclear membrane and peripheral endoplasmic reticulum but is excluded from the inner nuclear membrane. We have combined immunofluorescence with differential membrane permeabilization to determine the topology of LTC(4) synthase. The active site of LTC(4) synthase is localized in the lumen of the nuclear envelope and endoplasmic reticulum. These results indicate that the synthesis of LTB(4) and LTC(4) occurs in different subcellular locations and suggests that LTC(4) must be returned to the cytoplasmic side of the membrane for export by multidrug resistance protein-1. The differential localization of two very similar integral membrane proteins suggests that mechanisms other than size-dependent exclusion regulate their passage to the inner nuclear membrane.

Covalent linkage of prosthetic heme to CYP4 family P450 enzymes

An extensive body of research on the structural properties of cytochrome P450 enzymes has established that these proteins possess a b-type heme prosthetic group which is noncovalently bound at the active site. Coordinate, electrostatic, and hydrogen bond interactions between the protein backbone and heme functional groups are readily overcome upon mild acid treatment of the enzyme, which releases free heme from the protein. In the present study, we have used a combination of HPLC, LC/ESI-MS, and SDS-PAGE techniques to demonstrate that members of the mammalian CYP4B, CYP4F, and CYP4A subfamilies bind their heme in an unusually tight manner. HPLC chromatography of CYP4B1 on a POROS R2 column under mild acidic conditions caused dissociation of less than one-third of the heme from the protein. Moreover, heme was not substantially removed from CYP4B1 under electrospray or electrophoresis conditions that readily release the prosthetic group from other non-CYP4 P450 isoforms. This was evidenced by an intact protein mass value of 59,217 +/- 3 amu for CYP4B1 (i.e., apoprotein plus heme) and extensive staining of this approximately 60 kDa protein with tetramethylbenzidine/H(2)O(2) following SDS-PAGE. In addition, treatment of CYP4B1, CYP4F3, and CYP4A5/7 with strong base generated a new, chromatographically distinct, polar heme species with a mass of 632.3 amu rather than 616.2 amu. This mass shift is indicative of the incorporation of an oxygen atom into the heme nucleus and is consistent with the presence of a novel covalent ester linkage between the protein backbone of the CYP4 family of mammalian P450s and their heme catalytic center.

Alternative splicing determines the function of CYP4F3 by switching substrate specificity

Diversity of cytochrome P450 function is determined by the expression of multiple genes, many of which have a high degree of identity. We report that the use of alternate exons, each coding for 48 amino acids, generates isoforms of human CYP4F3 that differ in substrate specificity, tissue distribution, and biological function. Both isoforms contain a total of 520 amino acids. CYP4F3A, which incorporates exon 4, inactivates LTB4 by omega-hydroxylation (Km = 0.68 microm) but has low activity for arachidonic acid (Km = 185 microm); it is the only CYP4F isoform expressed in myeloid cells in peripheral blood and bone marrow. CYP4F3B incorporates exon 3 and is selectively expressed in liver and kidney; it is also the predominant CYP4F isoform in trachea and tissues of the gastrointestinal tract. CYP4F3B has a 30-fold higher Km for LTB4 compared with CYP4F3A, but it utilizes arachidonic acid as a substrate for omega-hydroxylation (Km = 22 microm) and generates 20-HETE, an activator of protein kinase C and Ca2+/calmodulin-dependent kinase II. Homology modeling demonstrates that the alternative exon has a position in the molecule which could enable it to contribute to substrate interactions. The results establish that tissue-specific alternative splicing of pre-mRNA can be used as a mechanism for changing substrate specificity and increasing the functional diversity of cytochrome P450 genes.

Differential localization of 5- and 15-lipoxygenases to the nuclear envelope in RAW macrophages

Leukotriene formation is initiated in myeloid cells by an increase in intracellular calcium and translocation of 5-lipoxygenase from the cytoplasm to the nuclear envelope where it can utilize arachidonic acid. Monocyte- macrophages and eosinophils also express 15-lipoxygenase, which converts arachidonic acid to 15(S)-hydroxyeicosatetraenoic acid. Enhanced green fluorescent 5-lipoxygenase (5-LO) and 15-lipoxygenase (15-LO) fusion proteins were expressed in the cytoplasm of RAW 264.7 macrophages. Only 5-lipoxygenase translocated to the nuclear envelope after cell stimulation, suggesting that differential subcellular compartmentalization can regulate the generation of leukotrienes versus 15(S)-hydroxyeicosatetraenoic acid in cells that possess both lipoxygenases. A series of truncation mutants of 5-LO were created to identify putative targeting domains; none of these mutants localized to the nuclear envelope. The lack of targeting of 15-LO was then exploited to search for specific targeting motifs in 5-LO, by creating 5-LO/15-LO chimeric molecules. The only chimera that could sustain nuclear envelope translocation was one which involved replacement of the N-terminal 237 amino acids with the corresponding segment of 15-LO. Significantly, no discrete targeting domain could be identified in 5-LO, suggesting that sequences throughout the molecule are required for nuclear envelope localization.

Expression of the CYP4F3 gene. tissue-specific splicing and alternative promoters generate high and low K(m) forms of leukotriene B(4) omega-hydroxylase

Cytochrome P450 4F3 (CYP4F3) catalyzes the inactivation of leukotriene B(4) by omega-oxidation in human neutrophils. To understand the regulation of CYP4F3 expression, we analyzed the CYP4F3 gene and cloned a novel isoform (CYP4F3B) that is expressed in fetal and adult liver, but not in neutrophils. The CYP4F3 gene contains 14 exons and 13 introns. The cDNAs for CYP4F3A (the neutrophil isoform) and CYP4F3B have identical coding regions, except that they contain exons 4 and 3, respectively. Both exons code for amino acids 66-114 but share only 27% identity. When expressed in COS-7 cells, the K(m) of CYP4F3B was determined to be 26-fold higher than the K(m) of CYP4F3A using leukotriene B(4) as a substrate. 5'-Rapid amplification of cDNA end studies reveal that the CYP4F3A and CYP4F3B transcripts have 5'-termini derived from different parts of the gene and are initiated from distinct transcription start sites located 519 and 71 base pairs (bp), respectively, from the ATG initiation codon. A consensus TATA box is located 27 bp upstream of the CYP4F3B transcription start site, and a TATA box-like sequence is located 23 bp upstream of the CYP4F3A transcription start site. The data indicate that the tissue-specific expression of functionally distinct CYP4F3 isoforms is regulated by alternative promoter usage and mutually exclusive exon splicing.

Glutathione conjugates recognize the Rossmann fold of glyceraldehyde-3-phosphate dehydrogenase

Leukotriene (LT) C4 and other glutathione conjugates are synthesized intracellularly and then move to the plasma membrane for export. The intracellular proteins that bind these molecules and the significance of these interactions are poorly understood. To identify the binding sites of membrane-associated proteins that recognize these molecules, we utilized photoaffinity probes to label the inner leaflet of erythrocytes. The predominant molecule labeled with S-(p-nitrobenzyl)glutathione-[125I]4-azidosalicylic acid (PNBG-[125I]ASA) or LTC4-[125I]4-azidosalicylic acid (LTC4-[125I]ASA) was 38 kDa. The protein was labeled with PNBG-[125I]ASA, electroblotted to polyvinylidene difluoride membranes, digested in situ with lysyl endopeptidase, and two radiolabeled peptides isolated by reverse phase-high performance liquid chromatography. These contained an identity of 7/11 with amino acids 119-129, and 11/11 with amino acids 67-77 of human liver glyceraldehyde-3-phosphate dehydrogenase (GAPDH), respectively. Photoaffinity labeling with PNBG-[125I]ASA was blocked completely by 100 microM ATP and greater than 50% with 100 microM NAD+. LTC4-[125I]ASA binding to the NAD+ site was confirmed by V8 protease digestion of purified GAPDH labeled with LTC4-[125I]ASA or PNBG-[125I]ASA, with both labels localized to the 6.8-kDa N-terminal fragment. Photoaffinity labeling of HL-60 cells with LTC4-125I-ASA identified GAPDH as the predominant cytoplasmic binding protein in these cells. These data indicate that GAPDH is a membrane-associated and cytoplasmic protein which binds glutathione conjugates including LTC4.

Purification of human leukotriene C4 synthase

Leukotriene (LT) C4 synthase, the enzyme that catalyzes the conjugation of LTA4 with reduced glutathione to form LTC4, was purified to homogeneity from the KG-1 myeloid cell line after solubilization of the microsomes utilizing a combination of 0.4% sodium deoxycholate and 0.4% Triton X-102. The solubilized enzyme was then applied to an S-hexyl-glutathione-agarose column that was eluted by the use of 7.5 mM probenecid. After removal of the probenecid by sequential concentration and dilution in an Amicon concentrator, the enzyme was additionally purified and concentrated by binding to and elution from approximately 75 mg of S-hexyl-glutathione-agarose. The enzyme was further resolved by electrophoresis with a nondenaturing Tris-glycine gel, and the LTC4 synthase activity was localized to slices 3 and 4. When the remainder of the eluate from the nondenaturing gel was precipitated by acetone and analyzed by 14% SDS/PAGE with silver staining, a single protein band of 18 kDa was associated with LTC4 synthase activity and was not present in the eluates of slices lacking activity. The overall recovery was 12.5%. In a separate preliminary purification, in which the yield was only approximately 1%, the eluates of the nondenaturing gel had also revealed a single protein of 18 kDa by SDS/PAGE, which was present only in the eluates with LTC4 synthase activity. These data identify LTC4 synthase as a protein of 18 kDa, a size consistent with its membership in the microsomal glutathione S-transferase family.

The mechanism of leukotriene B4 export from human polymorphonuclear leukocytes

Recently, we characterized the export of leukotriene (LT) C4 from human eosinophils as a carrier-mediated process (Lam, B. K., Owen, W. F., Jr., Austen, K. F., and Soberman, R. J. (1989) J. Biol. Chem. 264, 12885-12889). To determine whether a similar mechanism regulates the release of leukotriene B4 (LTB4), human polymorphonuclear leukocytes (PMN) were preloaded with LTB4 by incubation with 25 microM leukotriene A4 (LTA4) at 0 degrees C for 60 min. PMN converted LTA4 to LTB4 in a time-dependent manner as determined by resolution of products by reverse-phase high performance liquid chromatography and quantitation by integrated optical density. When PMN preloaded with LTB4 were resuspended in buffer at 37 degrees C for 0-90 s, there occurred a time-dependent release of LTB4 but little formation or release of 20-hydroxy-LTB4 and 20-carboxy-LTB4. When PMN were preloaded with increasing amounts of intracellular LTB4 by incubation with 3.1-50.0 microM LTA4 and were then resuspended in buffer at 37 degrees C for 20 s, there occurred a concentration-dependent and saturable release of LTB4 with a Km of 798 pmol/10(7) cells and a Vmax of 383 pmol/10(7) cells/20 s. The release of LTB4 was temperature-sensitive with a Q10 of 3.0 and an energy of activation of 19.9 kcal/mol. The rate of LTB4 release at 37 degrees C is about 50 times the rate of 20-carboxy-LTB4 release. PMN preloaded with LTB4 and resuspended at 0 degree C for 1-60 min in the presence of 30 microM LTA5 progressively converted LTA5 to LTB5. The rate of LTB4 release at 0 degree C was inhibited over the entire time period, peaking at about 50% at 30 min. These results indicate that the release of LTB4 from PMN is a carrier-mediated process that is distinct from its biosynthesis.

A morphometric study of normodense and hypodense human eosinophils that are derived in vivo and in vitro

Hypodense eosinophils were obtained from two patients with the idiopathic hyperosinophilic syndrome (IHES), and hypodense eosinophils were derived by culturing normodense human eosinophils from control donors in the presence of endothelial cells alone, granulocyte/macrophage-colony-stimulating factor (GM-CSF) alone, or GM-CSF and fibroblasts. These eosinophils were examined ultrastructurally and stereologically for alterations in the volume density (Vv) of their electron-dense granules, the Vv of their lucent granules, the Vv of their lipid droplets, the numerical density of their granules with respect to cytoplasm (Nv), and the plasma membrane surface area-to-cell volume ratio (Sv) that might account for their decreased sedimentation density. The hypodense eosinophils that were obtained from the two patients with IHES exhibited a one-third reduction in granule Vv relative to normodense eosinophils from control donors, primarily because of a decrease in granule size. The culture-derived hypodense eosinophils exhibited 10% to 16% decreases in their granule Vv, significant increases in their lucent granules, and a approximately 7.5% decrease in their Sv. Calculation of the cell volume from cross-sectional area measurements showed that the eosinophils that had been cocultured with fibroblasts in the presence of GM-CSF increased their volume by approximately 15%. The eosinophils that had been cocultured with endothelial cells exocytosed some of their granules. In conclusion, a composite of factors including cell swelling, a decrease in the volume of the cytoplasm occupied by granules, and an increase in granule lucency contributes to the hypodense phenotype in vitro, but only cell swelling and hypogranulation are seen in cells from patients with IHES. The latter could reflect the response of 'primed' hypodense eosinophils in vivo to pertinent tissue ligands.

Docosahexaenoic acid, a constituent of rodent fetal serum and fish oil diets, inhibits acquisition of macrophage tumoricidal function

Macrophage (M phi) activation is deficient in the fetus and neonate, at times when the serum concentration of docosahexaenoic acid (DHA; 22:6n3) is approximately 10-fold higher than in the adult. We tested the effects of highly purified DHA on M phi activation in vitro. M phi were stimulated with rIFN-gamma plus either of two second or "triggering" signals, LPS or heat-killed Listeria monocytogenes. M phi activation was assayed as the lysis of P815 mastocytoma cells, which are resistant to TNF-alpha. DNA inhibited the activation of peritoneal M phi and the M phi line RAW264.7 in a dose-dependent manner at concentrations between 20 and 160 microM. These concentrations are found in fetal and neonatal rodent sera. Another polyunsaturated fatty acid, arachidonic acid (20:4n6), was much less inhibitory. In contrast to its profound effect on tumoricidal activation, DHA did not inhibit phagocytosis and catabolism of 125I-heat-killed Listeria monocytogenes. Increasing the rIFN-gamma or second signals reduced the inhibition of tumoricidal activation by DHA but not M phi incorporation of 14C-DHA. When the rIFN-gamma and second signals were separated in time, DHA was far more inhibitory if delivered with the triggering signal than if delivered with the rIFN-gamma. However, the incorporation of 14C-DHA was the same under these two conditions. In M phi treated with DHA during LPS stimulation, the inhibition was time-dependent, requiring more than 2 h. Although DHA inhibits cyclooxygenase activity, its inhibition of M phi activation was not reversed with the following cyclooxygenase products: PGE2, a stable TXA2 analog (U-46, 619) or a stable PGI2 analog (Iloprost). Although DHA is metabolized by lipoxygenases, the inhibition was not reversed by the lipoxygenase inhibitors 5, 8, 11, 14-eicosatetraynoic acid and nordihydroguaiaretic acid. Altogether, the data indicate that DHA, at concentrations present in fetal and neonatal sera, inhibits M phi activation and may contribute to the previously observed deficits in M phi function in the fetus and neonate.

Docosahexaenoic acid, a constituent of rodent fetal serum and fish oil diets, inhibits acquisition of macrophage tumoricidal function

Macrophage (M phi) activation is deficient in the fetus and neonate, at times when the serum concentration of docosahexaenoic acid (DHA; 22:6n3) is approximately 10-fold higher than in the adult. We tested the effects of highly purified DHA on M phi activation in vitro. M phi were stimulated with rIFN-gamma plus either of two second or "triggering" signals, LPS or heat-killed Listeria monocytogenes. M phi activation was assayed as the lysis of P815 mastocytoma cells, which are resistant to TNF-alpha. DNA inhibited the activation of peritoneal M phi and the M phi line RAW264.7 in a dose-dependent manner at concentrations between 20 and 160 microM. These concentrations are found in fetal and neonatal rodent sera. Another polyunsaturated fatty acid, arachidonic acid (20:4n6), was much less inhibitory. In contrast to its profound effect on tumoricidal activation, DHA did not inhibit phagocytosis and catabolism of 125I-heat-killed Listeria monocytogenes. Increasing the rIFN-gamma or second signals reduced the inhibition of tumoricidal activation by DHA but not M phi incorporation of 14C-DHA. When the rIFN-gamma and second signals were separated in time, DHA was far more inhibitory if delivered with the triggering signal than if delivered with the rIFN-gamma. However, the incorporation of 14C-DHA was the same under these two conditions. In M phi treated with DHA during LPS stimulation, the inhibition was time-dependent, requiring more than 2 h. Although DHA inhibits cyclooxygenase activity, its inhibition of M phi activation was not reversed with the following cyclooxygenase products: PGE2, a stable TXA2 analog (U-46, 619) or a stable PGI2 analog (Iloprost). Although DHA is metabolized by lipoxygenases, the inhibition was not reversed by the lipoxygenase inhibitors 5, 8, 11, 14-eicosatetraynoic acid and nordihydroguaiaretic acid. Altogether, the data indicate that DHA, at concentrations present in fetal and neonatal sera, inhibits M phi activation and may contribute to the previously observed deficits in M phi function in the fetus and neonate.

Identification of an aldehyde dehydrogenase in the microsomes of human polymorphonuclear leukocytes that metabolizes 20-aldehyde leukotriene B4

We have previously reported that cytochrome P-450LTB in the microsomes of human polymorphonuclear leukocytes (PMN) catalyzes three omega-oxidations of leukotriene B4 (LTB4), leading to the sequential formation of 20-OH-LTB4, 20-CHO-LTB4, and 20-COOH-LTB4 (Soberman, R.J., Sutyak, J.P., Okita, R.T., Wendelborn, D.F., Roberts, L.J., II, and Austen, K. F. (1988) J. Biol. Chem. 263, 7996-8002). The identification of the novel final intermediate, 20-CHO-LTB4, allowed direct analysis of its metabolism by PMN microsomes in the presence of adenine nucleotide cofactors. Microsomes in the presence of 100 microM NAD+ or 100 microM NADP+ converted 1.0 microM 20-CHO-LTB4 to 20-COOH-LTB4 with a Km of 2.4 +/- 0.8 microM (mean +/- S.E., n = 4) and a Vmax of 813.9 +/- 136.6 pmol.min-1.mg-1, for NAD+, as compared to 0.12 microM and 5.0 pmol.min-1.mg-1 (n = 2) for NADPH as a cofactor. The conversion of 1.0 microM of 20-CHO-LTB4 to 20-COOH-LTB4 in the presence of saturating concentrations (1.0 mM) of both NAD+ and NADP+ was not greater than the reaction in the presence of 1.0 mM of each cofactor separately, indicating that NAD+ and NADP+ were cofactors for the same enzyme. Antibody to cytochrome P-450 reductase did not inhibit the conversion of 20-CHO-LTB4 to 20-COOH-LTB4. When 1.0 microM 20-OH-LTB4 was added to microsomes in the presence of NADPH, approximately three-fourths of the product formed (63.7 +/- 5.1 pmol; mean +/- S.E., n = 3) was 20-CHO-LTB4 and approximately one-fourth (21.3 +/- 3.9 pmol; mean +/- S.E., n = 3) was 20-COOH-LTB4. In the presence of both NADPH and NAD+, only 20-COOH-LTB4 (85.5 +/- 9.9 pmol; mean +/- S.E., n = 3) was formed. PMN microsomes also contain an NADH-dependent aldehyde reductase which converts 20-CHO-LTB4 to 20-OH-LTB4, a member of the LTB4 family of molecules with biological activity. Based upon kinetic, cofactor and inhibition data, microsomal aldehyde dehydrogenase preferentially regulates the final and irreversible inactivation step in the LTB4 metabolic sequence.

The identification of a distinct export step following the biosynthesis of leukotriene C4 by human eosinophils

We have examined the requirements for the export of leukotriene C4 (LTC4) from cultured human eosinophils. To define saturability and kinetics of LTC4 export, eosinophils were interacted with leukotriene A4 (LTA4) at 37 degrees C, and the methanolic extracts of the cell-associated and extracellular compartments were then analyzed for LTC4 content by reverse phase high performance liquid chromatography with on-line monitoring of absorbance at 280 nm. When LTA4 was added at concentrations from 0 to 100 microM for 10 min at 37 degrees C, the amount of LTC4 released extracellularly became constant at an LTA4 concentration of 7.5 microM or greater even though the amount of intracellular LTC4 continued to increase. When eosinophils were incubated with 50 microM LTA4 for 0-60 min at 37 degrees C and then held at 0 degrees C for the remainder of the 60-min interval, 54.2 and 77.3% (n = 3), respectively, of the total LTC4 was released extracellularly after 15 and 30 min of incubation at 37 degrees C. Eosinophils incubated with 50 microM LTA4 at 0 degrees C for 1 h synthesized 290 pmol of LTC4 (n = 3) which was approximately half-maximal, all of which was retained intracellularly. We utilized the time and temperature dependence of LTC4 export to preload eosinophils with both LTC4 and leukotriene C5 (LTC5) by sequentially supplying them with specific substrates. With increasing concentrations of intracellular LTC5, there was dose-dependent inhibition of the subsequent release of LTC4 at 37 degrees C, with the sum of the released glutathionyl leukotrienes remaining constant. In addition, only minimal competition for LTC4 release occurred when cells were preloaded with both LTC4 and the conjugate of 1-chloro-2,4-dinitrobenzene and reduced glutathione, S-(dinitrophenyl)glutathione. The criteria of saturability, time dependence of LTC4 release at 37 degrees C, competition of LTC4 with LTC5 for release, and the inhibition of LTC4 release at 0 degrees C establish the export of LTC4 from cells as a novel and specific biochemical step distinct from both LTA4 uptake and the conjugation of LTA4 with reduced glutathione by LTC4 synthase to form LTC4.

Interleukin 5 and phenotypically altered eosinophils in the blood of patients with the idiopathic hypereosinophilic syndrome

We report that the hypodense eosinophil population in three patients with corticosteroid-unresponsive IHES was uniquely long lived ex vivo in the absence of exogenous cytokines. Serum or plasma from these patients conferred prolonged viability ex vivo to normodense eosinophils from reference donors and converted them to a functionally activated hypodense phenotype. In that antibody against IL-5 neutralized this activity in IHES serum, excessive quantities of this cytokine may account for the characteristic eosinophilia and long-lived, functionally augmented eosinophil phenotype in this disorder.