Mono (S) hydroxy fatty acids: novel ligands for cytosolic actin

Exposure to cigarette smoke extract and lipopolysaccharide modifies cytoskeleton organization in bronchial epithelial cells

The integrity of the respiratory epithelium is crucial for airway homeostasis. Tobacco smoke exposure and recurrent infections of the airways play a crucial role in the progression and in the decline of the respiratory function in chronic obstructive pulmonary disease (COPD). The aim of this study was to detect differentially expressed proteins in a bronchial epithelial cell line (16-HBE) stimulated with cigarette smoke extract (CSE) and lipopolysaccharide (LPS), a constituent of gram-negative bacteria, alone and/or in combination, by using two-dimensional electrophoresis (2DE) analysis coupled with matrix-assisted laser desorption/ionization time-of-flight mass spectrometry. Western blot analysis was applied to confirm the expression of significantly modulated proteins. Flow cytometry and immunofluorescence were used to assess F-actin polimerization by phalloidin method. Fourteen proteins, with significant (p < 0.05) changes in intensity, were identified at various experimental points: 6 were up-regulated and 8 were down-regulated. As expected, bioinformatic analysis revealed that most of these proteins are involved in anti-oxidant and immune responses and in cytoskeleton stability. Western blot analysis confirmed that: Proteasome activator complex subunit 2 (PSME2), Peroxiredoxin-6 (PRDX6), Annexin A5 (ANXA5) and Heat shock protein beta-1 (HSPB1) were reduced and Coactosin-like protein (COTL-1) was increased by co-exposure of CSE and LPS. Furthermore, LPS and CSE increased actin polimerization. In conclusion, although further validation studies are needed, our findings suggest that, CSE and LPS could contribute to the progressive deterioration of lung function, altering the expression of proteins involved in metabolic processes and cytoskeleton rearrangement in bronchial epithelial cells.

Actin filaments-A target for redox regulation

Actin and its ability to polymerize into dynamic filaments is critical for the form and function of cells throughout the body. While multiple proteins have been characterized as affecting actin dynamics through noncovalent means, actin and its protein regulators are also susceptible to covalent modifications of their amino acid residues. In this regard, oxidation-reduction (Redox) intermediates have emerged as key modulators of the actin cytoskeleton with multiple different effects on cellular form and function. Here, we review work implicating Redox intermediates in post-translationally altering actin and discuss what is known regarding how these alterations affect the properties of actin. We also focus on two of the best characterized enzymatic sources of these Redox intermediates-the NADPH oxidase NOX and the flavoprotein monooxygenase MICAL-and detail how they have both been identified as altering actin, but share little similarity and employ different means to regulate actin dynamics. Finally, we discuss the role of these enzymes and redox signaling in regulating the actin cytoskeleton in vivo and highlight their importance for neuronal form and function in health and disease. © 2016 Wiley Periodicals, Inc.

Mammalian lipoxygenases and their biological relevance

Lipoxygenases (LOXs) form a heterogeneous class of lipid peroxidizing enzymes, which have been implicated not only in cell proliferation and differentiation but also in the pathogenesis of various diseases with major public health relevance. As other fatty acid dioxygenases LOXs oxidize polyunsaturated fatty acids to their corresponding hydroperoxy derivatives, which are further transformed to bioactive lipid mediators (eicosanoids and related substances). On the other hand, lipoxygenases are key players in the regulation of the cellular redox homeostasis, which is an important element in gene expression regulation. Although the first mammalian lipoxygenases were discovered 40 years ago and although the enzymes have been well characterized with respect to their structural and functional properties the biological roles of the different lipoxygenase isoforms are not completely understood. This review is aimed at summarizing the current knowledge on the physiological roles of different mammalian LOX-isoforms and their patho-physiological function in inflammatory, metabolic, hyperproliferative, neurodegenerative and infectious disorders. This article is part of a Special Issue entitled "Oxygenated metabolism of PUFA: analysis and biological relevance".

Post-translational modification and regulation of actin

Many of the best-studied actin regulatory proteins use non-covalent means to modulate the properties of actin. Yet, actin is also susceptible to covalent modifications of its amino acids. Recent work is increasingly revealing that actin processing and its covalent modifications regulate important cellular events. In addition, numerous pathogens express enzymes that specifically use actin as a substrate to regulate their hosts' cells. Actin post-translational alterations have been linked to different normal and disease processes and the effects associated with metabolic and environmental stressors. Herein, we highlight specific co-translational and post-translational modifications of actin and discuss the current understanding of the role that these modifications play in regulating actin.

Essential fatty acids and their metabolites as modulators of stem cell biology with reference to inflammation, cancer, and metastasis

Stem cells are pluripotent and expected to be of benefit in the management of coronary heart disease, stroke, diabetes mellitus, cancer, and Alzheimer's disease in which pro-inflammatory cytokines are increased. Identifying endogenous bioactive molecules that have a regulatory role in stem cell survival, proliferation, and differentiation may aid in the use of stem cells in various diseases including cancer. Essential fatty acids form precursors to both pro- and anti-inflammatory molecules have been shown to regulate gene expression, enzyme activity, modulate inflammation and immune response, gluconeogenesis via direct and indirect pathways, function directly as agonists of a number of G protein-coupled receptors, activate phosphatidylinositol 3-kinase/Akt and p44/42 mitogen-activated protein kinases, and stimulate cell proliferation via Ca(2+), phospholipase C/protein kinase, events that are also necessary for stem cell survival, proliferation, and differentiation. Hence, it is likely that bioactive lipids play a significant role in various diseases by modulating the proliferation and differentiation of embryonic stem cells in addition to their capacity to suppress inflammation. Ephrin Bs and reelin, adhesion molecules, and microRNAs regulate neuronal migration and cancer cell metastasis. Polyunsaturated fatty acids and their products seem to modulate the expression of ephrin Bs and reelin and several adhesion molecules and microRNAs suggesting that bioactive lipids participate in neuronal regeneration and stem cell proliferation, migration, and cancer cell metastasis. Thus, there appears to be a close interaction among essential fatty acids, their bioactive products, and inflammation and cancer growth and its metastasis.

15-Lipoxygenase-2 gene regulation by its product 15-(S)-hydroxyeicosatetraenoic acid through a negative feedback mechanism that involves peroxisome proliferator-activated receptor gamma

An inverse relationship exists between the expression of 15-lipoxygenase-2 (15-LOX-2) and peroxisome proliferator-activated receptor gamma (PPARgamma) in normal prostate epithelial cells (PrECs) compared with their expression in prostate carcinoma cells (PC-3). The reason for this difference, however, is unknown. We hypothesized that this inverse expression partly involves the 15-LOX-2 promoter and 15-S-hydroxyeicosatetraenoic acid (15-(S)-HETE), a product of 15-LOX-2 that binds to PPARgamma. We identified an active steroid nuclear receptor half-site present in the 15-LOX-2 promoter fragment F-5 (-618/+177) that can interact with PPARgamma. After forced expression of wild-type PPARgamma, 15-(S)-HETE (1 microM) decreased F-5 reporter activity in PrECs whereas forced expression of 15-LOX-2 resulted in 15-(S)-HETE production which enhanced F-5 activity in PC-3. In contrast, the expression of dominant-negative PPARgamma reversed the transcriptional activation of F-5 by enhancing it 202-fold in PrEC or suppressing it in PC-3; the effect in PC-3 was positively increased 150-fold in the presence of 15-(S)-HETE (1 microM). Peroxisome proliferator-activated receptor gamma interacted with 15-LOX-2 promoter sequences in pulldown experiments using biotinylated 15-LOX-2 (-560/-596 bp) oligonucleotides. In gelshift analyses PPARgamma and orphan receptor RORalpha were shown to interact with the F-5 fragment in PC-3 cells. These data suggest that crosstalk mechanisms exist between the 15-LOX-2 gene and PPARgamma to counterbalance expression and help explain the inverse relationship of these genes in normal versus cancer cells.

Disparate effects of 12-lipoxygenase and 12-hydroxyeicosatetraenoic acid in vascular endothelial and smooth muscle cells and in cardiomyocytes

The expression and activity of the arachidonic acid-metabolizing enzyme leukocyte-type 12-lipoxygenase (12-LO) are augmented in cultured vascular endothelial and smooth muscle cells exposed to high glucose concentrations and in blood vessels of diabetic animals. The product of this enzyme, 12-hydroxyeicosatetraenoic acid (12-HETE), evokes two types of interactions in these cells: on one hand it acts as a pro-inflammatory factor that contributes to the initiation and progression of atherosclerotic lesions. Yet on the other, it protects the same cells against deleterious effects of high levels of intracellular glucose by downregulating the glucose transport system in the cells. In addition, it has been shown that 12-LO and 12-HETE support insulin-dependent glucose transporter-4 translocation to the plasma membrane by maintaining intact actin fiber network in the cardiomyocytes. Here we focus on the disparate cellular interactions by which 12-LO and 12-HETE affect the glucose transport system in vascular endothelial and smooth muscle cells and in cardiomyocytes.

Monomethyl branched-chain fatty acids play an essential role in Caenorhabditis elegans development

Monomethyl branched-chain fatty acids (mmBCFAs) are commonly found in many organisms from bacteria to mammals. In humans, they have been detected in skin, brain, blood, and cancer cells. Despite a broad distribution, mmBCFAs remain exotic in eukaryotes, where their origin and physiological roles are not understood. Here we report our study of the function and regulation of mmBCFAs in Caenorhabditis elegans, combining genetics, gas chromatography, and DNA microarray analysis. We show that C. elegans synthesizes mmBCFAs de novo and utilizes the long-chain fatty acid elongation enzymes ELO-5 and ELO-6 to produce two mmBCFAs, C15ISO and C17ISO. These mmBCFAs are essential for C. elegans growth and development, as suppression of their biosynthesis results in a growth arrest at the first larval stage. The arrest is reversible and can be overcome by feeding the arrested animals with mmBCFA supplements. We show not only that the levels of C15ISO and C17ISO affect the expression of several genes, but also that the activities of some of these genes affect biosynthesis of mmBCFAs, suggesting a potential feedback regulation. One of the genes, lpd-1, encodes a homolog of a mammalian sterol regulatory element-binding protein (SREBP 1c). We present results suggesting that elo-5 and elo-6 may be transcriptional targets of LPD-1. This study exposes unexpected and crucial physiological functions of C15ISO and C17ISO in C. elegans and suggests a potentially important role for mmBCFAs in other eukaryotes.

Arachidonate 5-lipoxygenase

In this article, it has been attempted to review data primarily on the activation of human 5-lipoxygenase, in vitro and in the cell. First, structural properties and enzyme activities are described. This is followed by the activating factors: Ca2+, membranes, ATP, and lipid hydroperoxide. Also, studies on phosphorylation of 5-lipoxygenase, interaction with other proteins, and the intracellullar mobility of 5-lipoxygenase, are reviewed.

Eicosanoids and the regulation of cardiac glucose transport

Intact actin microfilaments are necessary for insulin-regulated GLUT4 translocation from intracellular pools to the plasma membrane. Products of the lipoxygenase (LO) pathway were shown to be implicated in the regulation of actin cytoskeleton rearrangement. The aim of this study was to examine the role of these LO products for cardiac insulin signaling and glucose uptake, GLUT4 translocation, and actin-based cytoskeleton structure. Exposure of cardiomyocytes to esculetin or NDGA, two structurally different LO inhibitors, induced a complete inhibition of insulin-stimulated glucose uptake, whereas control cells showed a threefold stimulation by insulin. Addition of 12(S)-HETE rendered the NDGA-treated cells insulin-sensitive. Early insulin signaling was not changed in cells exposed to LO inhibitors. Cell surface biotinylation of control cells showed a twofold increase of GLUT4 at the cell surface after insulin stimulation. In contrast, the LO inhibitors induced a complete inhibition of insulin-stimulated GLUT4 translocation. Labeling of the F-actin cytoskeleton revealed a prominent disassembly of actin fibers in cells exposed to the LO inhibitors. In conclusion, we show here that products of the LO reaction participate in the organization of the actin network in ventricular cardiomyocytes. Inhibition of LO blocks GLUT4 translocation without affecting insulin signaling events. These data suggest that products of the LO reaction participate in the regulation of glucose transport by contribution to a rearrangement of actin cytoskeletal elements.

Molecular cloning and functional characterization of mouse coactosin-like protein

Coactosin was first isolated from Dictyostelium discoideum and, as reported, human coactosin-like protein (CLP) was identified in a yeast two-hybrid screen using 5-lipoxygenase (5LO) as a bait. A mouse CLP (mCLP) cDNA clone was identified among EMBL/GenBank EST sequences. The derived amino acid sequence (142 residues) was 95.1% identical with human CLP. Here, we also show that mCLP interacts with actin and 5LO in the two-hybrid system. High-speed cosedimentation assays and GST-binding assays confirmed these protein interactions. In chemical cross-linking experiments, one molecule of mCLP was covalently linked to either one subunit of actin or one molecule of 5LO. The mCLP-F-actin and mCLP-5LO associations were pH-insensitive and Ca(2+)-independent. However, association with actin was best observed at low salt concentrations, while association with 5LO was favored by salt, indicating different binding characteristics.

Endogenous anti-inflammatory mediators from arachidonate in human neutrophils

Eicosanoids have been historically involved in the pathogenesis of various inflammatory diseases. Lipoxins (LXs) and epi-LXs show physiological effects relevant to inflammation regulation. In this study, we focused on LX precursors based on the hypothesis that their entrance and metabolism into the cell may facilitate their targeting at the inflammation site. Because compound chirality is of considerable importance in the efficacy of therapeutic agents, our aim was to study the anti-inflammatory effects of various epimers of LXA(4) precursors compared to LXA(4). Blood polymorphonuclear cells (PMNs) were incubated with 15(S)- or 15(R)-hydroxyeicosatetraenoic acid (HETE), 14(R)-,15(S)-, or 14(S),15(S)-diHETE, and LXA(4) and then stimulated with the calcium ionophore A23187. We found that 15(R)-HETE rather than 15(S)-HETE was preferentially metabolized and that 15-epi-LXs were produced in larger amounts than LXs. In contrast, when PMNs were incubated with the diastereoisomers of 14,15(S)-diHETE, 14-epi-LXB(4) was produced in lower amounts than LXB(4). Enantiomers of 15-HETE and diastereoisomers of 14,15-diHETE and LXA(4) were able to significantly decrease LTB(4) release by PMNs. These results suggest a potential resolution of the inflammatory process through endogenous anti-inflammatory mediators released by the way of trans-cellular metabolism.

PGF(2alpha), a prostanoid released by endothelial cells activated by hypoxia, is a chemoattractant candidate for neutrophil recruitment

Despite increasing evidence supporting the involvement of neutrophils in ischemic and postischemic damages, the mechanisms underlying the early recruitment of these cells are not completely understood. In this report, the effects of conditioned media from hypoxic endothelial cells on neutrophil chemotaxis were investigated by biochemical and morphological studies. We showed that conditioned media collected from several endothelial cell origins submitted to hypoxia as well as ischemic rat liver perfusion liquids have a chemotactic activity for neutrophils. The role of various chemoattractant molecules like HETEs, platelet-activating factor, and cytokines such as interleukin-8 and interleukin-1 was examined in the same model. Chemotactic peptide contribution was ruled out as boiled conditioned media still trigger chemotaxis. However, cell treatment with cyclooxygenase inhibitors, neutralization of PGF(2alpha) biological activity with polyclonal antibodies, and the neutrophil preincubation with a specific PGF(2alpha) antagonist, all dramatically inhibited neutrophil chemotaxis. A strong chemoattractant effect of pure exogenous PGF(2alpha) or of a synthetic analog was also observed. The major effect of PGF(2alpha) on neutrophil chemotaxis was confirmed ex vivo in a rat liver perfusion ischemic model. These results suggest that PGF(2alpha), a prostanoid abundantly released by the endothelium of hypoxic or ischemic tissues, is a chemoattractant molecule that might be involved in the early recruitment of neutrophils in ischemic organs.

5-Lipoxygenase interacts with coactosin-like protein

We have recently identified coactosin-like protein (CLP) in a yeast two-hybrid screen using 5-lipoxygenase (5LO) as a bait. In this report, we demonstrate a direct interaction between 5LO and CLP. 5LO associated with CLP, which was expressed as a glutathione S-transferase fusion protein, in a dose-dependent manner. Coimmunoprecipitation experiments using epitope-tagged 5LO and CLP proteins transiently expressed in human embryonic kidney 293 cells revealed the presence of CLP in 5LO immunoprecipitates. In reciprocal experiments, 5LO was detected in CLP immunoprecipitates. Non-denaturing polyacrylamide gel electrophoresis and cross-linking experiments showed that 5LO binds CLP in a 1:1 molar stoichiometry in a Ca(2+)-independent manner. Site-directed mutagenesis suggested an important role for lysine 131 of CLP in mediating 5LO binding. In view of the ability of CLP to bind 5LO and filamentous actin (F-actin), we determined whether CLP could physically link 5LO to actin filaments. However, no F-actin-CLP.5LO ternary complex was observed. In contrast, 5LO appeared to compete with F-actin for the binding of CLP. Moreover, 5LO was found to interfere with actin polymerization. Our results indicate that the 5LO-CLP and CLP-F-actin interactions are mutually exclusive and suggest a modulatory role for 5LO in actin dynamics.

5-lipoxygenase is phosphorylated by p38 kinase-dependent MAPKAP kinases

5-lipoxygenase (5-LO) catalyzes the initial steps in the formation of leukotrienes, a group of inflammatory mediators derived from arachidonic acid (AA). Here we describe that activation of p38 mitogen-activated protein kinase in human polymorphonuclear leukocytes and in Mono Mac 6 cells leads to activation of downstream kinases, which can subsequently phosphorylate 5-LO in vitro. Different agents activated the 5-LO kinase activities, including stimuli for cellular leukotriene biosynthesis (A23187, thapsigargin, N-formyl-leucyl-phenylalanine), compounds that up-regulate the capacity for leukotriene biosynthesis (phorbol 12-myristate 13-acetate, tumor necrosis factor alpha, granulocyte/macrophage colony-stimulating factor), and well known p38 stimuli as sodium arsenite and sorbitol. For all stimuli, 5-LO kinase activation was counteracted by SB203580 (3 microM or less), an inhibitor of p38 kinase. At least two p38-dependent 5-LO kinase activities were found. Based on migration properties in in-gel kinase assays and immunoreactivity, one of these was identified as mitogen-activated protein kinase-activated protein kinase 2 (MAPKAP kinase 2). The other appeared to be MAPKAP kinase 3; however, it could not be excluded that also other p38-dependent kinases contributed. When polymorphonuclear leukocytes were incubated with sodium arsenite (strong activator of 5-LO kinases), platelet-activating factor and exogenous AA, there was a 4-fold increase in 5-LO activity as compared with incubations with only platelet-activating factor and AA. This indicates that 5-LO phosphorylation can be one factor determining cellular 5-LO activity.

Interaction of 5-lipoxygenase with cellular proteins

5-Lipoxygenase (5LO) plays a pivotal role in cellular leukotriene synthesis. To identify proteins interacting with human 5LO, we used a two-hybrid approach to screen a human lung cDNA library. From a total of 1.5 x 10(7) yeast transformants, nine independent clones representing three different proteins were isolated and found to specifically interact with 5LO. Four 1.7- to 1.8-kb clones represented a 16-kDa protein named coactosin-like protein for its significant homology with coactosin, a protein found to be associated with actin in Dictyostelium discoideum. Coactosin-like protein thus may provide a link between 5LO and the cytoskeleton. Two other yeast clones of 1.5 kb encoded transforming growth factor (TGF) type beta receptor-I-associated protein 1 partial cDNA. TGF type beta receptor-I-associated protein 1 recently has been reported to associate with the activated form of the TGF beta receptor I and may be involved in the TGF beta-induced up-regulation of 5LO expression and activity observed in HL-60 and Mono Mac 6 cells. Finally, three identical 2.1-kb clones contained the partial cDNA of a human protein with high homology to a hypothetical helicase K12H4. 8 from Caenorhabditis elegans and consequently was named DeltaK12H4. 8 homologue. Analysis of the predicted amino acid sequence revealed the presence of a RNase III motif and a double-stranded RNA binding domain, indicative of a protein of nuclear origin. The identification of these 5LO-interacting proteins provides additional approaches to studies of the cellular functions of 5LO.