351
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Triantafilou M, Gamper FGJ, Haston RM, Mouratis MA, Morath S, Hartung T, Triantafilou K. Membrane sorting of toll-like receptor (TLR)-2/6 and TLR2/1 heterodimers at the cell surface determines heterotypic associations with CD36 and intracellular targeting. J Biol Chem 2006; 281:31002-11. [PMID: 16880211 DOI: 10.1074/jbc.m602794200] [Citation(s) in RCA: 353] [Impact Index Per Article: 18.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Toll-like receptors (TLRs) are receptors of the innate immune system responsible for recognizing pathogen-associated molecular patterns. TLR2 seems to be the most promiscuous TLR receptor able to recognize the most diverse set of pathogen-associated patterns. Its promiscuity has been attributed to its unique ability to heterodimerize with TLRs 1 and 6 and, most recently, to its association with CD36 in response to diacylated lipoproteins. Thus, it seems that TLR2 forms receptor clusters in response to different microbial ligands. In this study we investigated TLR2 cell surface heterotypic interactions in response to different ligands as well as internalization and intracellular trafficking. Our data show that TLR2 forms heterodimers with TLR1 and TLR6 and that these heterodimer pre-exist and are not induced by the ligand. Upon stimulation by the specific ligand, these heterodimers are recruited within lipid rafts. In contrast, heterotypic associations of TLR2/6 with CD36 are not preformed and are ligand-induced. All TLR2 receptor clusters accumulate in lipid rafts and are targeted to the Golgi apparatus. This localization and targeting is ligand-specific. Activation occurs at the cell surface, and the observed trafficking is independent of signaling.
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Affiliation(s)
- Martha Triantafilou
- Infection and Immunity Group, School of Life Sciences, University of Sussex, Falmer, Brighton, BN1 9QG, United Kingdom
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352
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Powers KA, Szászi K, Khadaroo RG, Tawadros PS, Marshall JC, Kapus A, Rotstein OD. Oxidative stress generated by hemorrhagic shock recruits Toll-like receptor 4 to the plasma membrane in macrophages. ACTA ACUST UNITED AC 2006; 203:1951-61. [PMID: 16847070 PMCID: PMC2118368 DOI: 10.1084/jem.20060943] [Citation(s) in RCA: 161] [Impact Index Per Article: 8.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Abstract
Oxidative stress generated by ischemia/reperfusion is known to prime inflammatory cells for increased responsiveness to subsequent stimuli, such as lipopolysaccharide (LPS). The mechanism(s) underlying this effect remains poorly elucidated. These studies show that alveolar macrophages recovered from rodents subjected to hemorrhagic shock/resuscitation expressed increased surface levels of Toll-like receptor 4 (TLR4), an effect inhibited by adding the antioxidant N-acetylcysteine to the resuscitation fluid. Consistent with a role for oxidative stress in this effect, in vitro H2O2 treatment of RAW 264.7 macrophages similarly caused an increase in surface TLR4. The H2O2-induced increase in surface TLR4 was prevented by depleting intracellular calcium or disrupting the cytoskeleton, suggesting the involvement of receptor exocytosis. Further, fluorescent resonance energy transfer between TLR4 and the raft marker GM1 as well as biochemical analysis of the raft components demonstrated that oxidative stress redistributes TLR4 to lipid rafts in the plasma membrane. Preventing the oxidant-induced movement of TLR4 to lipid rafts using methyl-β-cyclodextrin precluded the increased responsiveness of cells to LPS after H2O2 treatment. Collectively, these studies suggest a novel mechanism whereby oxidative stress might prime the responsiveness of cells of the innate immune system.
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Affiliation(s)
- Kinga A Powers
- Department of Surgery, St. Michael's Hospital and University Health Network, Toronto, Ontario, Canada
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353
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Blanco LP, DiRita VJ. Bacterial-associated cholera toxin and GM1 binding are required for transcytosis of classical biotype Vibrio cholerae through an in vitro M cell model system. Cell Microbiol 2006; 8:982-98. [PMID: 16681839 DOI: 10.1111/j.1462-5822.2005.00681.x] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
Abstract
To elucidate mechanisms involved in M cell uptake and transcytosis of Vibrio cholerae, we used an in vitro model of human M-like cells in a Caco-2 monolayer. Interspersed among the epithelial monolayer of Caco-2 cells we detect cells that display M-like features with or without prior lymphocyte treatment and we have established key parameters for V. cholerae transcytosis in this model. Cholera toxin (CT) mutants lacking the A subunit alone or both the A and B subunits were deficient for transcytosis. We explored this finding further and showed that expression of both subunits is required for binding by whole V. cholerae to immobilized CT receptor, the glycosphingolipid GM1. Confocal microscopy showed CT associated with transcytosing bacteria, and transcytosis was inhibited by pre-incubation with GM1 before infection. Finally, heat treatment of the bacterial cells caused a loss of binding to GM1 that was correlated with a significant decrease in uptake and transcytosis by the monolayer. Our data support a model in which the ability of bacteria to interact with GM1 in a CT-dependent fashion plays a critical role in transcytosis of V. cholerae by M cells.
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Affiliation(s)
- Luz P Blanco
- Unit for Laboratory Animal Medicine, University of Michigan Medical School, Ann Arbor, MI, USA
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354
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Dolganiuc A, Bakis G, Kodys K, Mandrekar P, Szabo G. Acute ethanol treatment modulates Toll-like receptor-4 association with lipid rafts. Alcohol Clin Exp Res 2006; 30:76-85. [PMID: 16433734 DOI: 10.1111/j.1530-0277.2006.00003.x] [Citation(s) in RCA: 72] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
BACKGROUND Alcohol, a substance that is most frequently abused, suppresses innate immune responses to microbial pathogens. The host senses pathogens via Toll-like receptors (TLRs). Recent studies indicate that alcohol affects TLR signaling. METHODS Here, we hypothesized that acute alcohol treatment may interfere with early steps of membrane-associated TLR2 and TLR4 signaling at the level of lipid rafts. Human monocytes and Chinese hamster ovary (CHO) cells, transfected with human TLR2, TLR4, or CD14, were stimulated with peptidoglycan (PGN, TLR2 ligand) or lipopolysaccharide (LPS, TLR4 ligand) with or without alcohol (50 mM) and analyzed for cytokine production (enzyme-linked immunosorbent assay), nuclear factor-kappaB (NF-kappaB) activation (electrophoretic mobility shift assay), membrane fluidity (fluorescent pyrene eximer formation), and partition of cellular membrane into cholesterol-rich, detergent-resistant domains (DRMs; Western blot). RESULTS We determined that both TLR2 and TLR4 were located outside the rafts; flotillin, a DRM marker, was resident in the rafts, while CD14 was equally distributed in and outside the rafts in a steady-state condition. PGN forced TLR2 to migrate into DRMs. Engagement of TLR4 and CD14 with LPS induced their migration into the rafts. Alcohol prevented TLR4 partitioning; however, it did not affect TLR2 migration into the rafts. Furthermore, alcohol downregulated TLR4-induced, but not TLR2-induced, NF-kappaB activation and cytokine production in monocytes. We found that alcohol increased membrane fluidity and depleted cellular cholesterol in CHO cells without affecting cell viability. CONCLUSIONS These data demonstrate for the first time that alcohol disturbs TLR4 and CD14 association with lipid rafts. We propose that alcohol-induced effects on lipid rafts may contribute to modulation of TLR4-CD14-triggered early cellular responses.
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Affiliation(s)
- Angela Dolganiuc
- Department of Medicine, University of Massachusetts Medical School, Worcester, Massachusetts 01605-2324, USA
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355
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Rowe DC, McGettrick AF, Latz E, Monks BG, Gay NJ, Yamamoto M, Akira S, O’Neill LA, Fitzgerald KA, Golenbock DT. The myristoylation of TRIF-related adaptor molecule is essential for Toll-like receptor 4 signal transduction. Proc Natl Acad Sci U S A 2006; 103:6299-304. [PMID: 16603631 PMCID: PMC1458872 DOI: 10.1073/pnas.0510041103] [Citation(s) in RCA: 207] [Impact Index Per Article: 10.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/18/2005] [Indexed: 11/18/2022] Open
Abstract
TRIF-related adaptor molecule (TRAM) is the fourth Toll/IL-1 resistance domain-containing adaptor to be described that participates in Toll-like receptor (TLR) signaling. TRAM functions exclusively in the TLR4 pathway. Here we show by confocal microscopy that TRAM is localized in the plasma membrane and the Golgi apparatus, where it colocalizes with TLR4. Membrane localization of TRAM is the result of myristoylation because mutation of a predicted myristoylation site in TRAM (TRAM-G2A) brought about dissociation of TRAM from the membrane and its relocation to the cytosol. Further, TRAM, but not TRAM-G2A, was radiolabeled with [3H]myristate in vivo. Unlike wild-type TRAM, overexpression of TRAM-G2A failed to elicit either IFN regulatory factor 3 or NF-kappaB signaling. Moreover, TRAM-G2A was unable to reconstitute LPS responses in bone marrow-derived macrophages from TRAM-deficient mice. These observations provide clear evidence that the myristoylation of TRAM targets it to the plasma membrane, where it is essential for LPS responses through the TLR4 signal transduction pathway, and suggest a hitherto unappreciated manner in which LPS responses can be regulated.
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Affiliation(s)
- Daniel C. Rowe
- *Division of Infectious Disease and Immunology, Department of Medicine, University of Massachusetts Medical School, Worcester, MA 01605
| | | | - Eicke Latz
- *Division of Infectious Disease and Immunology, Department of Medicine, University of Massachusetts Medical School, Worcester, MA 01605
| | - Brian G. Monks
- *Division of Infectious Disease and Immunology, Department of Medicine, University of Massachusetts Medical School, Worcester, MA 01605
| | - Nicholas J. Gay
- Department of Biochemistry, University of Cambridge, Cambridge CB2 1YP, United Kingdom; and
| | - Masahiro Yamamoto
- Department of Host Defense, Research Institute for Microbial Diseases, Osaka University, Osaka 565-0871, Japan
| | - Shizuo Akira
- Department of Host Defense, Research Institute for Microbial Diseases, Osaka University, Osaka 565-0871, Japan
| | - Luke A. O’Neill
- Department of Biochemistry, Trinity College, Dublin 2, Ireland
| | - Katherine A. Fitzgerald
- *Division of Infectious Disease and Immunology, Department of Medicine, University of Massachusetts Medical School, Worcester, MA 01605
| | - Douglas T. Golenbock
- *Division of Infectious Disease and Immunology, Department of Medicine, University of Massachusetts Medical School, Worcester, MA 01605
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356
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Lee HS, Wolfert MA, Zhang Y, Boons GJ. The 2-aminogluconate isomer of rhizobium sin-1 lipid A can antagonize TNF-alpha production induced by enteric LPS. Chembiochem 2006; 7:140-8. [PMID: 16317789 DOI: 10.1002/cbic.200500298] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
The naturally occurring lipopolysaccharide (LPS) from Rhizobium sin-1, a nitrogen-fixing bacterial species, can prevent the induction of the tumor necrosis factor TNF-alpha induced by enteric LPS. The proximal saccharide moiety of R. sin-1 lipid A can exist in two forms, namely as a 2-aminogluconolactone or 2-aminogluconate. As it is unknown which of these forms is responsible for the antagonistic properties of R. sin-1 lipid A, compound 4 was prepared, and its inflammatory properties were studied. This compound contains a methyl ether at the C-5 hydroxyl, which prevents lactonization and therefore is ideally suited to determine whether the 2-aminogluconate possesses antagonistic properties. Compound 4 was synthesized by a highly convergent approach with a key disaccharide building block functionalized with a set of orthogonal protecting groups. The novel synthetic compound lacks proinflammatory properties, as indicated by an absence of TNF-alpha protein production. This compound was, however, able to antagonize the production of TNF-alpha induced by enteric LPS; this indicates that the 2-aminogluconate form of R. sin-1 lipid A is responsible for its biological properties.
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Affiliation(s)
- Hyi-Seung Lee
- Complex Carbohydrate Research Center, The University of Georgia, 315 Riverbend Road, Athens, GA 30602, USA
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357
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Zhao H, Loh HH, Law PY. Adenylyl cyclase superactivation induced by long-term treatment with opioid agonist is dependent on receptor localized within lipid rafts and is independent of receptor internalization. Mol Pharmacol 2006; 69:1421-32. [PMID: 16415176 DOI: 10.1124/mol.105.020024] [Citation(s) in RCA: 66] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023] Open
Abstract
Long-term opioid agonist treatment results in adenylyl cyclase superactivation. A recent "RAVE" theory implicates a direct correlation between the ability of agonist to induce receptor internalization and the magnitude of adenylyl cyclase superactivation. We decided to test such a theory by examining the adenylyl cyclase superactivation after long-term activation of mu-opioid receptor (MOR) in an EcR293 cell model. We examined the magnitudes of adenylyl cyclase superactivation in the presence of naloxone after long-term treatment with morphine, etorphine, and methadone, three agonists reported to have differential activities in promoting MOR internalization. It can be shown that the magnitudes of adenylyl cyclase superactivation after treating with these three agonists, although different, were dependent on MOR density. Blunting MOR internalization with the dominant-negative mutant of dynamin, K44E, did not alter the magnitude of either morphine- or etorphine-induced adenylyl cyclase superactivation. In the presence of diprenorphine, the magnitude of adenylyl cyclase superactivation after etorphine treatment was identical to that observed with morphine. It could be demonstrated further that adenylyl cyclase superactivation is dependent on the cell surface-located MOR. Sucrose gradient fractionation demonstrated the colocalization of MOR and adenylyl cyclase V/VI with caveolin-1, a marker for lipid rafts. After long-term agonist treatment, the majority of MOR remained at the lipid rafts. Methyl-beta-cyclodextrin (MbetaCD) completely blunted the adenylyl cyclase superactivation and agonist-induced receptor internalization. These MbetaCD actions were reversed by incubating the cells with cholesterol. Thus, the adenylyl cyclase superactivation is not dependent on agonist-induced receptor internalization. Rather, the location of MOR at lipid rafts is an absolute requirement for the observed adenylyl cyclase superactivation.
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Affiliation(s)
- Hui Zhao
- Department of Pharmacology, 6-120 Jackson Hall, Medical School, University of Minnesota, 321 Church St. S.E., Minneapolis, MN 55455-0217, USA
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358
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Kay JG, Murray RZ, Pagan JK, Stow JL. Cytokine Secretion via Cholesterol-rich Lipid Raft-associated SNAREs at the Phagocytic Cup. J Biol Chem 2006; 281:11949-54. [PMID: 16513632 DOI: 10.1074/jbc.m600857200] [Citation(s) in RCA: 88] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022] Open
Abstract
Lipopolysaccharide-activated macrophages rapidly synthesize and secrete tumor necrosis factor alpha (TNFalpha) to prime the immune system. Surface delivery of membrane carrying newly synthesized TNFalpha is controlled and limited by the level of soluble N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE) proteins syntaxin 4 and SNAP-23. Many functions in immune cells are coordinated from lipid rafts in the plasma membrane, and we investigated a possible role for lipid rafts in TNFalpha trafficking and secretion. TNFalpha surface delivery and secretion were found to be cholesterol-dependent. Upon macrophage activation, syntaxin 4 was recruited to cholesterol-dependent lipid rafts, whereas its regulatory protein, Munc18c, was excluded from the rafts. Syntaxin 4 in activated macrophages localized to discrete cholesterol-dependent puncta on the plasma membrane, particularly on filopodia. Imaging the early stages of TNFalpha surface distribution revealed these puncta to be the initial points of TNFalpha delivery. During the early stages of phagocytosis, syntaxin 4 was recruited to the phagocytic cup in a cholesterol-dependent manner. Insertion of VAMP3-positive recycling endosome membrane is required for efficient ingestion of a pathogen. Without this recruitment of syntaxin 4, it is not incorporated into the plasma membrane, and phagocytosis is greatly reduced. Thus, relocation of syntaxin 4 into lipid rafts in macrophages is a critical and rate-limiting step in initiating an effective immune response.
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Affiliation(s)
- Jason G Kay
- Institute for Molecular Bioscience, University of Queensland, Brisbane, Queensland 4072, Australia
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359
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Okutani D, Lodyga M, Han B, Liu M. Src protein tyrosine kinase family and acute inflammatory responses. Am J Physiol Lung Cell Mol Physiol 2006; 291:L129-41. [PMID: 16581827 DOI: 10.1152/ajplung.00261.2005] [Citation(s) in RCA: 140] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023] Open
Abstract
Acute inflammatory responses are one of the major underlying mechanisms for tissue damage of multiple diseases, such as ischemia-reperfusion injury, sepsis, and acute lung injury. By use of cellular and molecular approaches and transgenic animals, Src protein tyrosine kinase (PTK) family members have been identified to be essential for the recruitment and activation of monocytes, macrophages, neutrophils, and other immune cells. Src PTKs also play a critical role in the regulation of vascular permeability and inflammatory responses in tissue cells. Importantly, animal studies have demonstrated that small chemical inhibitors for Src PTKs attenuate tissue injury and improve survival from a variety of pathological conditions related to acute inflammatory responses. Further investigation may lead to the clinical application of these inhibitors as drugs for ischemia-reperfusion injury (such as stroke and myocardial infarction), sepsis, acute lung injury, and multiple organ dysfunction syndrome.
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Affiliation(s)
- Daisuke Okutani
- Thoracic Surgery Research Laboratory, University Health Network Toronto General, Ontario, Canada
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360
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Wang R, Kovalchin JT, Muhlenkamp P, Chandawarkar RY. Exogenous heat shock protein 70 binds macrophage lipid raft microdomain and stimulates phagocytosis, processing, and MHC-II presentation of antigens. Blood 2006; 107:1636-42. [PMID: 16263790 DOI: 10.1182/blood-2005-06-2559] [Citation(s) in RCA: 86] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023] Open
Abstract
The extracellular presence of endotoxin-free heat shock protein 70 (HSP70) enhances the rate and capacity of macrophage-mediated phagocytosis at 6 times the basal rate. It is protein-specific, dose- and time-dependent and involves the internalization of inert microspheres, Gram-positive and -negative bacteria and fungi. Structurally, exogenous HSP70 binds the macrophage plasma membrane, specifically on its lipid raft-microdomain. Disruption of lipid rafts, HSP70-LR interaction, or denaturing HSP70 abrogates the HSP-mediated increase in phagocytosis. Further, HSP70-mediated phagocytosis directly enhances the processing and presentation of internalized antigens via the endocytic MHC class-II pathway to CD4+ T lymphocytes. Modulating the HSP70-LR interaction presents an opportunity to intervene at the level of host-pathogen interface: a therapeutic tool for emerging infections, especially when conventional treatment with antibiotics is ineffective (antibiotic resistance) or unavailable (rapidly spreading, endemic). These results identify a new role for HSP70, a highly conserved molecule in stimulating phagocytosis: a primordial macrophage function, thereby influencing both innate and adaptive immune responses.
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Affiliation(s)
- Ruibo Wang
- Division of Plastic Surgery, University of Connecticut Health Center MC 1601, 263 Farmington Ave, Farmington CT 06030-1601, USA
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361
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Seyberth T, Voss S, Brock R, Wiesmüller KH, Jung G. Lipolanthionine Peptides Act as Inhibitors of TLR2-Mediated IL-8 Secretion. Synthesis and Structure−Activity Relationships. J Med Chem 2006; 49:1754-65. [PMID: 16509590 DOI: 10.1021/jm050585d] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Lipoproteins from gram-positive and -negative bacteria, mycoplasma, and shorter synthetic lipopeptide analogues activate cells of the innate immune system via the Toll-like receptor TLR2/TLR1 or TLR2/TLR6 heterodimers. For this reason, these compounds constitute highly active adjuvants for vaccines either admixed or covalently linked. The lanthionine scaffold has structural similarity with the S-(2,3-dihydroxypropyl)cysteine core structure of the lipopeptides. Therefore, lanthionine-based lipopeptide amides were synthesized and probed for activity as potential TLR2 agonists or antagonists. A collection of analytically defined lipolanthionine peptide amides exhibited an inhibitory effect of the TLR2-mediated IL-8 secretion when applied in high molar excess to the agonistic synthetic lipopeptide Pam3Cys-Ser-(Lys)4-OH. Structure-activity relationships revealed the influence of the chirality of the two alpha-carbon atoms, the chain lengths of the attached fatty acids and fatty amines, and the oxidation level of the sulfur atom on the inhibitory activity of the lipolanthionine peptide amides.
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Affiliation(s)
- Tobias Seyberth
- Institute of Organic Chemistry, University of Tübingen, 72076 Tübingen, Germany
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362
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Olsson S, Sundler R. The role of lipid rafts in LPS-induced signaling in a macrophage cell line. Mol Immunol 2006; 43:607-12. [PMID: 15904959 DOI: 10.1016/j.molimm.2005.04.011] [Citation(s) in RCA: 92] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/24/2005] [Indexed: 01/15/2023]
Abstract
The significance of lipid rafts in lipopolysaccharide (LPS) signaling in macrophages was studied through isolation of them by gradient centrifugation and subsequent visualization of signal molecules using antibodies. LPS signaling is initiated by binding to Toll-like receptor-4 (TLR4) and the co-receptor CD-14, leading to activation of downstream targets, such as MAP kinases. In this study, we show that LPS causes translocation of CD-14 and MAP kinases (ERK-2 and p38) to lipid rafts in the macrophage cell line RAW 264.7. The adaptor proteins MyD88 and Gab-2, on the other hand, were not detected in the lipid raft fractions. These results indicate that lipid rafts play a role in LPS-induced signaling in macrophages.
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Affiliation(s)
- Sandra Olsson
- Department of Experimental Medical Research, Lund University, BMC, B12, SE 22184 Lund, Sweden
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363
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Nebl T, De Veer MJ, Schofield L. Stimulation of innate immune responses by malarial glycosylphosphatidylinositol via pattern recognition receptors. Parasitology 2006; 130 Suppl:S45-62. [PMID: 16281992 DOI: 10.1017/s0031182005008152] [Citation(s) in RCA: 74] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
The glycosylphosphatidylinositol (GPI) anchor of Plasmodium falciparum is thought to function as a critical toxin that contributes to severe malarial pathogenesis by eliciting the production of proinflammatory responses by the innate immune system of mammalian hosts. Analysis of the fine structure of P. falciparum GPI suggests a requirement for the presence of both core glycan and lipid moieties in the recognition and signalling of parasite glycolipids by host immune cells. It has been demonstrated that GPI anchors of various parasitic protozoa can mediate cellular immune responses via members of the Toll-like family of pattern recognition receptors (TLRs). Recent studies indicate that GPI anchors of P. falciparum and other protozoa are preferentially recognized by TLR-2, involving the MyD88-dependent activation of specific signalling pathways that mediate the production of proinflammatory cytokines and nitric oxide from host macrophages in vitro. However, the contribution of malaria GPI toxin to severe disease syndromes and the role of specific TLRs or other pattern recognition receptors in innate immunity in vivo is only just beginning to be characterized. A better understanding of the molecular mechanisms underlying severe malarial pathogenesis may yet lead to substantial new insights with important implications for the development of novel therapeutics for malaria treatment.
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Affiliation(s)
- T Nebl
- The Walter and Eliza Hall Institute of Medical Research, Victoria, Australia
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364
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Blanco AM, Vallés SL, Pascual M, Guerri C. Involvement of TLR4/type I IL-1 receptor signaling in the induction of inflammatory mediators and cell death induced by ethanol in cultured astrocytes. THE JOURNAL OF IMMUNOLOGY 2006; 175:6893-9. [PMID: 16272348 DOI: 10.4049/jimmunol.175.10.6893] [Citation(s) in RCA: 201] [Impact Index Per Article: 10.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
Activated astroglial cells are implicated in neuropathogenesis of many infectious and inflammatory diseases of the brain. A number of inflammatory mediators and cytokines have been proposed to play a key role in glial cell-related brain damage. Cytokine production seems to be initiated by signaling through TLR4/type I IL-1R (IL-1RI) in response to their ligands, LPS and IL-1beta, playing vital roles in innate host defense against infections, inflammation, injury, and stress. We have shown that glial cells are stimulated by ethanol, up-regulating cytokines and inflammatory mediators associated with TLR4 and IL-1RI signaling pathways in brain, suggesting that ethanol may contribute to brain damage via inflammation. We explore the possibility that ethanol, in the absence of LPS or IL-1beta, triggers signaling pathways and inflammatory mediators through TLR4 and/or IL-1RI activation in astrocytes. We show in this study that ethanol, at physiologically relevant concentrations, is capable of inducing rapid phosphorylation within 10 min of IL-1R-associated kinase, ERK1/2, stress-activated protein kinase/JNK, and p38 MAPK in astrocytes. Then an activation of NF-kappaB and AP-1 occurs after 30 min of ethanol treatment along with an up-regulation of inducible NO synthase and cyclooxygenase-2 expression. Finally, we note an increase in cell death after 3 h of treatment. Furthermore, by using either anti-TLR4- or anti-IL-1RI-neutralizing Abs, before and during ethanol treatment, we inhibit ethanol-induced signaling events, including NF-kappaB and AP-1 activation, inducible NO synthase, and cyclooxygenase-2 up-regulation and astrocyte death. In summary, these findings indicate that both TLR4 and IL-1RI activation occur upon ethanol treatment, and suggest that signaling through these receptors mediates ethanol-induced inflammatory events in astrocytes and brain.
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Affiliation(s)
- Ana M Blanco
- Unidad de Patología Celular, Centro de Investigación Príncipe Felipe, Valencia, Spain
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365
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Abstract
Acute inflammatory responses are one of the major underlying mechanisms for tissue damage of multiple diseases, such as sepsis and acute lung injury. Inflammatory mediators released from a variety of cells in response to acute inflammations can interact with immune cells, microvascular endothelial cells and other tissue cells, to elicit a series of intracellular signaling reactions where activation of Src protein tyrosine kinase (PTK) family members is involved. Using cellular and molecular approaches and transgenic animals, Src PTK family members have been identified to be essential for the recruitment and activation of monocytes, macrophages, neutrophils and other immune cells. Src PTK family members also play a critical role in the regulation of vascular permeability and inflammatory responses in tissue cells. Importantly, animal studies have demonstrated that small chemical inhibitors for Src PTKs attenuated acute lung injury. Further investigation may lead to the clinical application of these inhibitors as drugs for acute lung injury.
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Affiliation(s)
- Daisuke Okutani
- Department of Cancer and Thoracic Surgery, Okayama University Graduate School of Medicine and Dentistry
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366
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Tang PS, Tsang ME, Lodyga M, Bai XH, Miller A, Han B, Liu M. Lipopolysaccharide accelerates caspase-independent but cathepsin B-dependent death of human lung epithelial cells. J Cell Physiol 2006; 209:457-67. [PMID: 16894574 DOI: 10.1002/jcp.20751] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
Caspase-independent cell death has drawn increasing attention. In the present study, we found that lipopolysaccharide (LPS) accelerated spontaneous death of human lung epithelial A549 cells in a serum- and cell density-dependent manner: while serum starvation has been demonstrated to induce apoptosis in the same cell line, LPS-induced cell death was only observed in the presence of serum; in addition, the cell death was not observed when the cells were seeded at 10- or 100-fold lower density. The apoptotic features were demonstrated by TUNEL assay, DNA laddering and Annexin V staining. However, treatment of cells with two commonly used pan-caspase inhibitors, zVAD.fmk or BOC-D.fmk, failed to block cell death. In contrast, two cathepsin B inhibitors, Ca074-Me or N-1845, reduced cell death significantly. A time-dependent activation of cathepsin B, but not caspase 3, was observed in both control and LPS-treated cells. Although LPS did not further activate cathepsin B or its release, it increased expression and translocation of apoptosis inducing factor from mitochondria to the nucleus, and increased release of cytochrome c from mitochondria. LPS-induced cell death was significantly attenuated by either N-acetyl-L-cysteine or pyrrolidine-dithiocarbamate, both free radical scavengers. Disruption of lipid raft formation with filipin or methyl-beta-cyclodextrin also reduced apoptosis significantly, suggesting that lipid raft-dependent signaling is essential. These data imply that confluent cells undergo spontaneous cell death mediated by cathepsin B; LPS may accelerate this caspase-independent cell death through release of mitochondrial contents and reactive oxygen species.
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Affiliation(s)
- Peter S Tang
- Division of Cellular and Molecular Biology, University Health Network Toronto General Research Institute, Toronto, Ontario, Canada
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367
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Abstract
Sepsis is the systemic immune response to severe bacterial infection. The innate immune recognition of bacterial and viral products is mediated by a family of transmembrane receptors known as Toll-like receptors (TLRs). In endothelial cells, exposure to lipopolysaccharide (LPS), a major cell wall constituent of Gram-negative bacteria, results in endothelial activation through a receptor complex consisting of TLR4, CD14 and MD2. Recruitment of the adaptor protein myeloid differentiation factor (MyD88) initiates an MyD88-dependent pathway that culminates in the early activation of nuclear factor-kappaB (NF-kappaB) and the mitogen-activated protein kinases. In parallel, a MyD88-independent pathway results in a late-phase activation of NF-kappaB. The outcome is the production of various proinflammatory mediators and ultimately cellular injury, leading to the various vascular sequelae of sepsis. This review will focus on the signaling pathways initiated by LPS binding to the TLR4 receptor in endothelial cells and the coordinated regulation of this pathway.
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Affiliation(s)
- Shauna M Dauphinee
- Department of Medical Biophysics, British Columbia Cancer Agency, Vancouver, British Columbia, Canada
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368
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Wang XM, Kim HP, Song R, Choi AMK. Caveolin-1 confers antiinflammatory effects in murine macrophages via the MKK3/p38 MAPK pathway. Am J Respir Cell Mol Biol 2005; 34:434-42. [PMID: 16357362 PMCID: PMC2644205 DOI: 10.1165/rcmb.2005-0376oc] [Citation(s) in RCA: 126] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022] Open
Abstract
Caveolin-1 has been reported to regulate apoptosis, lipid metabolism, and endocytosis in macrophages. In the present study, we demonstrate that caveolin-1 can act as a potent immunomodulatory molecule. We first observed caveolin-1 expression in murine alveolar macrophages by Western blotting and immunofluorescence microscopy. Loss-of-function experiments using small interfering RNA showed that down regulating caveolin-1 expression in murine alveolar and peritoneal macrophages increased LPS-induced proinflammatory cytokine TNF-alpha and IL-6 production but decreased anti-inflammatory cytokine IL-10 production. Gain-of-function experiments demonstrated that overexpression of caveolin-1 in RAW264.7 cells decreased LPS-induced TNF-alpha and IL-6 production and augmented IL-10 production. p38 mitogen-activated protein kinase (MAPK) phosphorylation was increased by overexpressing caveolin-1 in RAW264.7 cells, whereas c-Jun N-terminal kinase, extracellular signal-regulated kinase MAPK, and Akt phosphorylation were inhibited. The antiinflammatory modulation of LPS-induced cytokine production by caveolin-1 was significantly abrogated by the administration of p38 inhibitor SB203580 in RAW264.7 cells. Peritoneal macrophages isolated from MKK3 null mice did not demonstrate any modulation of LPS-induced cytokine production by caveolin-1. LPS-induced activation of NF-kappaB and AP-1 determined by electrophoretic mobility shift assay were significantly reduced by overexpressing caveolin-1 in RAW264.7 cells. The reductions were attenuated by the administration of p38 inhibitor SB203580. Taken together, our data suggest that caveolin-1 acts as a potent immunomodulatory effector molecule in immune cells and that the regulation of LPS-induced cytokine production by caveolin-1 involves the MKK3/p38 MAPK pathway.
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Affiliation(s)
- Xiao Mei Wang
- Division of Pulmonary, Allergy, and Critical Care Medicine, University of Pittsburgh School of Medicine, 3459 Fifth Avenue, MUH 628, Pittsburgh, PA 15213, USA
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369
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Hadley JS, Wang JE, Foster SJ, Thiemermann C, Hinds CJ. Peptidoglycan of Staphylococcus aureus upregulates monocyte expression of CD14, Toll-like receptor 2 (TLR2), and TLR4 in human blood: possible implications for priming of lipopolysaccharide signaling. Infect Immun 2005; 73:7613-9. [PMID: 16239565 PMCID: PMC1273841 DOI: 10.1128/iai.73.11.7613-7619.2005] [Citation(s) in RCA: 46] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023] Open
Abstract
Previous studies have indicated that peptidoglycan (PepG) from gram-positive bacteria can exert a priming effect on the innate immune response to lipopolysaccharide (LPS) from gram-negative bacteria. Here, we hypothesized that this priming effect may be preceded by enhanced expression of monocyte CD14, Toll-like receptor 2 (TLR2), and TLR4. In an ex vivo whole human blood model, we observed a substantial synergy between LPS and PepG in the release of tumor necrosis factor alpha and interleukin-1beta (IL-1beta) over the 24-h experimental period, whereas the effect on IL-8 and IL-10 release was more time dependent. The priming effect of PepG on cytokine release was preceded by a rapid upregulation of CD14, TLR2, and TLR4 expression on monocytes: at 3 hours there was a twofold increase in CD14 expression (P < 0.03), a fivefold increase in TLR2 expression (P < 0.03), and a twofold increase in TLR4 expression (P < 0.03). CD14 and TLR2 remained upregulated throughout the experimental period following exposure to PepG (P < 0.05). Only a transient upregulation of these monocyte receptors was observed following treatment with LPS or LPS plus PepG. In conclusion, the synergistic effect of LPS and PepG on cytokine release is preceded by a reciprocal upregulation of TLR2 and TLR4 by both bacterial cell wall components.
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Affiliation(s)
- J S Hadley
- Department of Experimental Medicine, Nephrology and Critical Care, William Harvey Research Institute, Barts and The London, Queen Mary School of Medicine and Dentistry, London, United Kingdom.
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370
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Shuto T, Kato K, Mori Y, Viriyakosol S, Oba M, Furuta T, Okiyoneda T, Arima H, Suico MA, Kai H. Membrane-anchored CD14 is required for LPS-induced TLR4 endocytosis in TLR4/MD-2/CD14 overexpressing CHO cells. Biochem Biophys Res Commun 2005; 338:1402-9. [PMID: 16263085 DOI: 10.1016/j.bbrc.2005.10.102] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/28/2005] [Accepted: 10/16/2005] [Indexed: 10/25/2022]
Abstract
Lipopolysaccharide (LPS) induces inflammatory activation through TLR4 (toll-like receptor-4)/MD-2 (myeloid differentiation-2)/CD14 (cluster of differentiation-14) complex. Although optimal LPS signaling is required to activate our innate immune systems against gram-negative bacterium, excessive amount of LPS signaling develops a detrimental inflammatory response in gram-negative bacterial infections. Downregulation of surface TLR4 expression is one of the critical mechanisms that can restrict LPS signaling. Here, we found that membrane-anchored CD14 is required for LPS-induced downregulation of TLR4 and MD-2 in CHO cells. Moreover, pretreatment of the cells with sterol-binding agent filipin reduced LPS-induced TLR4 downregulation, suggesting the involvement of caveolae-mediated endocytosis pathway. Involvement of caveolae in LPS-induced TLR4 endocytosis was further confirmed by immunoprecipitation. Thus, our data indicate that caveolae-dependent endocytosis pathway is involved in LPS-induced TLR4 downregulation and that this is dependent on membrane-anchored CD14 expression.
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Affiliation(s)
- Tsuyoshi Shuto
- Department of Molecular Medicine, Kumamoto University, Kumamoto 862-0973, Japan
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371
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Tytell M. Release of heat shock proteins (Hsps) and the effects of extracellular Hsps on neural cells and tissues. Int J Hyperthermia 2005; 21:445-55. [PMID: 16048841 DOI: 10.1080/02656730500041921] [Citation(s) in RCA: 66] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/25/2022] Open
Abstract
Hsps were long thought to be cytoplasmic proteins with functions restricted to the intra-cellular compartment. However, an increasing number of observations show that they can be released into the extra-cellular space and can then have a wide variety of affects on other cells. The mechanism of release remains unknown, but may involve the shedding of exosomes, which are vesicles containing cytoplasmic constituents. In the nervous system, it appears that glial cells can release the 70 kD Hsps and that neurons exposed to extra-cellular Hsps are more likely to survive injury than their naïve counterparts. These phenomena have great potential significance in the development of neuroprotective therapeutic strategies utilizing the heat shock protein response.
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Affiliation(s)
- M Tytell
- Department of Neurobiology and Anatomy, Wake Forest University School of Medicine, Winston-Salem, NC 27157, USA.
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372
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Cuschieri J, Bulger E, Garcia I, Maier RV. Oxidative-induced calcium mobilization is dependent on annexin VI release from lipid rafts. Surgery 2005; 138:158-64. [PMID: 16153422 DOI: 10.1016/j.surg.2005.03.018] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/07/2005] [Revised: 03/23/2005] [Accepted: 03/25/2005] [Indexed: 02/04/2023]
Abstract
BACKGROUND Oxidative stress results in macrophage reprogramming through the formation of focal adhesion-like complexes on lipid rafts. Although the cellular mechanisms responsible for this reprogramming remain unknown, oxidative stress is known to result in a transient increase in intracellular calcium. This transient flux is thought to occur through the membrane dissociation of the calcium-bound protein annexin VI. The purpose of this study is to clarify the source of the calcium, and determine if it is responsible for the formation of focal adhesion-like complexes during oxidative stress through the activation of calcium/calmodulin dependent protein kinase II (CaMK II). METHODS THP-1 cells were stimulated with hydrogen peroxide. Selected cells were pretreated with methyl beta-cyclodextrin (MbetaCD), a cholesterol-depleting agent; 1,2-bis aminophenoxy ethane-N,N,N',N'-tetraacetic acid, an intracellular calcium chelator; or autocamtide 2-related inhibitory peptide, a CaMK II inhibitor. Intracellular calcium flux was determined by a Fluo-3 technique. Lipid raft and cellular protein were extracted and analyzed for active CaMK II, annexin VI, and components of focal adhesion-like complexes. RESULTS Hydrogen peroxide exposure led to mobilization of annexin VI from lipid rafts to the cytosol, which was followed by an increase in cytosolic calcium, phosphorylation of CaMK II, and formation of focal adhesion-like complexes. Cholesterol depletion from lipid rafts attenuated all of these effects. 1,2-bis Aminophenoxy ethane-N,N,N',N'-tetraacetic acid and autocamtide 2-related inhibitory peptide pretreatment attenuated CaMK II phopshorylation and formation of focal ahdesionlike complexes. CONCLUSIONS Macrophage reprogramming during oxidative stress occurs through the cytosolic mobilization of annexin VI from lipid rafts. As a result, bound calcium dissociates, resulting in the activation of CaMK II and the formation of focal adhesion-like complexes.
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373
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Abstract
Glycosylation of proteins has proven extremely important in a variety of cellular processes, including enzyme trafficking, tissue homing and immune functions. In the past decade, increasing interest in carbohydrate-mediated mechanisms has led to the identification of novel carbohydrate-recognizing receptors expressed on cells of the immune system. These non-enzymatic lectins contain one or more carbohydrate recognition domains (CRDs) that determine their specificity. In addition to their cell adhesion functions, lectins now also appear to play a major role in pathogen recognition. Depending on their structure and mode of action, lectins are subdivided in several groups. In this review, we focus on the calcium (Ca(2+))-dependent lectin group, known as C-type lectins, with the dendritic cell-specific ICAM-3 grabbing non-integrin (DC-SIGN) as a prototype type II C-type lectin organized in microdomains, and their role as pathogen recognition receptors in sensing microbes. Moreover, the cross-talk of C-type lectins with other receptors, such as Toll-like receptors, will be discussed, highlighting the emerging model that microbial recognition is based on a complex network of interacting receptors.
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Affiliation(s)
- Alessandra Cambi
- Department of Tumor Immunology, Nijmegen Centre for Molecular Life Sciences, Radboud University, Nijmegen, the Netherlands
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374
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Vigh L, Escribá PV, Sonnleitner A, Sonnleitner M, Piotto S, Maresca B, Horváth I, Harwood JL. The significance of lipid composition for membrane activity: New concepts and ways of assessing function. Prog Lipid Res 2005; 44:303-44. [PMID: 16214218 DOI: 10.1016/j.plipres.2005.08.001] [Citation(s) in RCA: 159] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
In the last decade or so, it has been realised that membranes do not just have a lipid-bilayer structure in which proteins are embedded or with which they associate. Structures are dynamic and contain areas of heterogeneity which are vital for their formation. In this review, we discuss some of the ways in which these dynamic and heterogeneous structures have implications during stress and in relation to certain human diseases. A particular stress is that of temperature which may instigate adaptation in poikilotherms or appropriate defensive responses during fever in mammals. Recent data emphasise the role of membranes in sensing temperature changes and in controlling a regulatory loop with chaperone proteins. This loop seems to need the existence of specific membrane microdomains and also includes association of chaperone (heat stress) proteins with the membrane. The role of microdomains is then discussed further in relation to various human pathologies such as cardiovascular disease, cancer and neurodegenerative diseases. The concept of modifying membrane lipids (lipid therapy) as a means for treating such pathologies is then introduced. Examples are given when such methods have been shown to have benefit. In order to study membrane microheterogeneity in detail and to elucidate possible molecular mechanisms that account for alteration in membrane function, new methods are needed. In the second part of the review, we discuss ultra-sensitive and ultra-resolution imaging techniques. These include atomic force microscopy, single particle tracking, single particle tracing and various modern fluorescence methods. Finally, we deal with computing simulation of membrane systems. Such methods include coarse-grain techniques and Monte Carlo which offer further advances into molecular dynamics. As computational methods advance they will have more application by revealing the very subtle interactions that take place between the lipid and protein components of membranes - and which are so essential to their function.
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Affiliation(s)
- Làszló Vigh
- Institute of Biochemistry, Biological Research Center, Hungarian Academy of Sciences, H-6726 Szeged, Hungary
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375
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Bausero MA, Gastpar R, Multhoff G, Asea A. Alternative mechanism by which IFN-gamma enhances tumor recognition: active release of heat shock protein 72. JOURNAL OF IMMUNOLOGY (BALTIMORE, MD. : 1950) 2005; 175:2900-12. [PMID: 16116176 PMCID: PMC1762097 DOI: 10.4049/jimmunol.175.5.2900] [Citation(s) in RCA: 134] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
IFN-gamma exhibits differential effects depending on the target and can induce cellular activation and enhance survival or mediate cell death via activation of apoptotic pathways. In this study, we demonstrate an alternative mechanism by which IFN-gamma enhances tumor recognition, mediated by the active release of Hsp72. We demonstrate that stimulation of 4T1 breast adenocarcinoma cells and K562 erythroleukemic cells with IFN-gamma triggers the cellular stress response, which results in the enhanced expression of total Hsp72 expression without a significant increase in cell death. Intracellular expression of Hsp72 was abrogated in cells stably transfected with a mutant hsf-1 gene. IFN-gamma-induced Hsp72 expression correlated with enhanced surface expression and consequent release of Hsp72 into the culture medium. Pretreatment of tumors with compounds known to the block the classical protein transport pathway, including monensin, brefeldin A, tunicamycin, and thapsigargin, did not significantly block Hsp72 release. However, pretreatment with intracellular calcium chelator BAPTA-AM or disruption of lipid rafts using methyl beta-cyclodextrin completely abrogated IFN-gamma-induced Hsp72 release. Biochemical characterization revealed that Hsp72 is released within exosomes and has the ability to up-regulate CD83 expression and stimulate IL-12 release by naive dendritic cells. Pretreatment with neutralizing mAb or depletion of Hsp72 completely abrogated its chaperokine function. Taken together, these findings are indicative of an additional previously unknown mechanism by which IFN-gamma promotes tumor surveillance and furthers our understanding of the central role of extracellular Hsp72 as an endogenous adjuvant and danger signal.
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Affiliation(s)
- Maria A Bausero
- Center for Molecular Stress Response, Boston University Medical Center and Boston University School of Medicine, Boston, MA 02118, USA
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376
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Lepper PM, Triantafilou M, Schumann C, Schneider EM, Triantafilou K. Lipopolysaccharides from Helicobacter pylori can act as antagonists for Toll-like receptor 4. Cell Microbiol 2005; 7:519-28. [PMID: 15760452 DOI: 10.1111/j.1462-5822.2005.00482.x] [Citation(s) in RCA: 76] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
Infection with Helicobacter pylori, a Gram-negative bacterium, is strongly associated with gastric ulcers and adenocarcinoma. The mechanisms by which the innate immune system recognizes H. pylori lipopolysaccharide (LPS) remain unclear. Contradictory reports exist that suggest that Toll-like receptors are involved. In this study we evaluated the interactions of Toll-like receptors with LPS from different strains of H. pylori. Using reporter cell lines, as well as HEK293 cells transfected with either CD14 and TLR4, or CD14 and TLR2, we show that H. pylori LPS-induced cell activation is mediated through TLR2. In addition, for the first time, we report that LPS from some H. pylori strains are able to antagonize TLR4. The antagonistic activity of H. pylori LPS from certain strains, as well as the activation via TLR2, might give H. pylori an advantage over the host that may be associated with the clinical outcome of H. pylori infection.
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Affiliation(s)
- Philipp M Lepper
- Department of Medical Microbiology and Hygiene, University of Ulm, 89075 Ulm, Germany
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377
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Karsan A, Blonder J, Law J, Yaquian E, Lucas DA, Conrads TP, Veenstra T. Proteomic analysis of lipid microdomains from lipopolysaccharide-activated human endothelial cells. J Proteome Res 2005; 4:349-57. [PMID: 15822910 DOI: 10.1021/pr049824w] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
The endothelium plays a critical role in orchestrating the inflammatory response seen during sepsis. Many of the inflammatory effects of Gram-negative sepsis are elicited by lipopolysaccharide (LPS), a glycolipid component of bacterial cell walls. Lipid-rich microdomains have been shown to concentrate components of the LPS signaling system. However, much remains to be learned about which proteins are constituents of lipid microdomains, and how these are regulated following cell activation. Progress in this area would be accelerated by employing global proteomic analyses, but the hydrophobicity of membrane proteins presents an analytical barrier to the effective application of such approaches. Herein, we describe a method to isolate detergent-resistant membranes from endothelial cells, and prepare these samples for proteomic analysis in a way that is compatible with subsequent separations and mass spectrometric (MS) analysis. In the application of these sample preparation and MS analyses, 358 proteins from the lipid-rich microdomains of LPS-activated endothelial cell membranes have been identified of which half are classified as membrane proteins by Gene Ontology. We also demonstrate that the sample preparation method used for solubilization and trypsin digestion of lipid-rich microdomains renders the membrane spanning sequences of transmembrane proteins accessible for endoproteolytic hydrolysis. This analysis sets the analytical foundation for an in-depth probing of LPS signaling in endothelial cells.
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Affiliation(s)
- Aly Karsan
- Department of Medical Biophysics and Pathology and Laboratory Medicine, British Columbia Cancer Agency, Vancouver, British Columbia, Canada V5Z 1L3.
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378
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Abstract
Toll-like receptors (TLRs) constitute an archetypal pattern recognition system. Their sophisticated biology underpins the ability of innate immunity to discriminate between highly diverse microbial pathogens and self. However, the remarkable progress made in describing this biology has also revealed new immunological systems and processes previously hidden to investigators. In particular, TLRs appear to have a fundamental role in the generation of clonal adaptive immune responses, non-infectious disease pathogenesis and even in the maintenance of normal mammalian homeostasis. Although an understanding of TLRs has answered some fundamental questions at the host-pathogen interface, further issues, particularly regarding therapeutic modulation of these receptors, have yet to be resolved.
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Affiliation(s)
- P A Hopkins
- Gram-Positive Molecular Pathogenesis Group, Department of Infectious Diseases, Division of Investigative Science, Faculty of Medicine, Imperial College, London, UK.
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379
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Cluff CW, Baldridge JR, Stöver AG, Evans JT, Johnson DA, Lacy MJ, Clawson VG, Yorgensen VM, Johnson CL, Livesay MT, Hershberg RM, Persing DH. Synthetic toll-like receptor 4 agonists stimulate innate resistance to infectious challenge. Infect Immun 2005; 73:3044-52. [PMID: 15845512 PMCID: PMC1087352 DOI: 10.1128/iai.73.5.3044-3052.2005] [Citation(s) in RCA: 90] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
A compound family of synthetic lipid A mimetics (termed the aminoalkyl glucosaminide phosphates [AGPs]) was evaluated in murine infectious disease models of protection against challenge with Listeria monocytogenes and influenza virus. For the Listeria model, intravenous administration of AGPs was followed by intravenous bacterial challenge 24 h later. Spleens were harvested 2 days postchallenge for the enumeration of CFU. For the influenza virus model, mice were challenged with virus via the intranasal/intrapulmonary route 48 h after intranasal/intrapulmonary administration of AGPs. The severity of disease was assessed daily for 3 weeks following challenge. Several types of AGPs provided strong protection against influenza virus or Listeria challenge in wild-type mice, but they were inactive in the C3H/HeJ mouse, demonstrating the dependence of the AGPs on toll-like receptor 4 (TLR4) signaling for the protective effect. Structure-activity relationship studies showed that the activation of innate immune effectors by AGPs depends primarily on the lengths of the secondary acyl chains within the three acyl-oxy-acyl residues and also on the nature of the functional group attached to the aglycon component. We conclude that the administration of synthetic TLR4 agonists provides rapid pharmacologic induction of innate resistance to infectious challenge by two different pathogen classes, that this effect is mediated via TLR4, and that structural differences between AGPs can have dramatic effects on agonist activity in vivo.
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380
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Kuipers HF, Biesta PJ, Groothuis TA, Neefjes JJ, Mommaas AM, van den Elsen PJ. Statins Affect Cell-Surface Expression of Major Histocompatibility Complex Class II Molecules by Disrupting Cholesterol-Containing Microdomains. Hum Immunol 2005; 66:653-65. [PMID: 15993711 DOI: 10.1016/j.humimm.2005.04.004] [Citation(s) in RCA: 66] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/03/2005] [Revised: 04/07/2005] [Accepted: 04/11/2005] [Indexed: 11/18/2022]
Abstract
Statins, the main therapy for hypercholesterolemia, are currently considered as possible immunomodulatory agents. Statins inhibit the production of proinflammatory cytokines and reduce the expression of several immunoregulatory molecules, including major histocompatibility complex class II (MHC-II) molecules. In this study, we investigated the mechanism by which simvastatin reduces the membrane expression of MHC-II molecules on several human cell types. We demonstrate that the reduction of MHC-II membrane expression by simvastatin correlates with disruption of cholesterol-containing microdomains, which transport and concentrate MHC-II molecules to the cell surface. In addition, we demonstrate that statins reduce cell-surface expression of other immunoregulatory molecules, which include MHC-I, CD3, CD4, CD8, CD28, CD40, CD80, CD86, and CD54. Our observations indicate that the downregulation of MHC-II at the cell surface contributes to the immunomodulatory properties of statins and is achieved through disruption of cholesterol-containing microdomains, which are involved in their intracellular transport.
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Affiliation(s)
- Hedwich F Kuipers
- Division of Molecular Biology, Department of Immunohematology and Blood Transfusion, Leiden University Medical Center, Leiden, The Netherlands
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381
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Abstract
Over the last few years, dramatic increases in our knowledge about diffusely adhering Escherichia coli (DAEC) pathogenesis have taken place. The typical class of DAEC includes E. coli strains harboring AfaE-I, AfaE-II, AfaE-III, AfaE-V, Dr, Dr-II, F1845, and NFA-I adhesins (Afa/Dr DAEC); these strains (i) have an identical genetic organization and (ii) allow binding to human decay-accelerating factor (DAF) (Afa/Dr(DAF) subclass) or carcinoembryonic antigen (CEA) (Afa/Dr(CEA) subclass). The atypical class of DAEC includes two subclasses of strains; the atypical subclass 1 includes E. coli strains that express AfaE-VII, AfaE-VIII, AAF-I, AAF-II, and AAF-III adhesins, which (i) have an identical genetic organization and (ii) do not bind to human DAF, and the atypical subclass 2 includes E. coli strains that harbor Afa/Dr adhesins or others adhesins promoting diffuse adhesion, together with pathogenicity islands such as the LEE pathogenicity island (DA-EPEC). In this review, the focus is on Afa/Dr DAEC strains that have been found to be associated with urinary tract infections and with enteric infection. The review aims to provide a broad overview and update of the virulence aspects of these intriguing pathogens. Epidemiological studies, diagnostic techniques, characteristic molecular features of Afa/Dr operons, and the respective role of Afa/Dr adhesins and invasins in pathogenesis are described. Following the recognition of membrane-bound receptors, including type IV collagen, DAF, CEACAM1, CEA, and CEACAM6, by Afa/Dr adhesins, activation of signal transduction pathways leads to structural and functional injuries at brush border and junctional domains and to proinflammatory responses in polarized intestinal cells. In addition, uropathogenic Afa/Dr DAEC strains, following recognition of beta(1) integrin as a receptor, enter epithelial cells by a zipper-like, raft- and microtubule-dependent mechanism. Finally, the presence of other, unknown virulence factors and the way that an Afa/Dr DAEC strain emerges from the human intestinal microbiota as a "silent pathogen" are discussed.
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Affiliation(s)
- Alain L Servin
- Institut National de la Santé et de la Recherche Médicale, Unité 510, Faculté de Pharmacie Paris XI, Châtenay-Malabry, France.
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382
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Kim HS, Desveaux D, Singer AU, Patel P, Sondek J, Dangl JL. The Pseudomonas syringae effector AvrRpt2 cleaves its C-terminally acylated target, RIN4, from Arabidopsis membranes to block RPM1 activation. Proc Natl Acad Sci U S A 2005; 102:6496-501. [PMID: 15845764 PMCID: PMC1088372 DOI: 10.1073/pnas.0500792102] [Citation(s) in RCA: 199] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/30/2005] [Indexed: 11/18/2022] Open
Abstract
Plant pathogenic Pseudomonas syringae deliver type III effector proteins into the host cell, where they function to manipulate host defense and metabolism to benefit the extracellular bacterial colony. The activity of these virulence factors can be monitored by plant disease resistance proteins deployed to "guard" the targeted host proteins. The Arabidopsis RIN4 protein is targeted by three different type III effectors. Specific manipulation of RIN4 by each of them leads to activation of either the RPM1 or RPS2 disease resistance proteins. The type III effector AvrRpt2 is a cysteine protease that is autoprocessed inside the host cell where it activates RPS2 by causing RIN4 disappearance. RIN4 contains two sites related to the AvrRpt2 cleavage site (RCS1 and RCS2). We demonstrate that AvrRpt2-dependent cleavage of RIN4 at RCS2 is functionally critical in vivo. This event leads to proteasome-mediated elimination of all but a membrane-embedded approximately 6.4-kDa C-terminal fragment of RIN4. One or more of three consecutive cysteines in this C-terminal fragment are required for RIN4 localization; these are likely to be palmitoylation and/or prenylation sites. AvrRpt2-dependent cleavage at RCS2, and release of the remainder of RIN4 from the membrane, consequently prevents RPM1 activation by AvrRpm1 or AvrB. RCS2 is contained within the smallest tested fragment of RIN4 that binds AvrB in vitro. Thus, at least two bacterial virulence factors target the same domain of RIN4, a approximately 30-aa plant-specific signature sequence found in a small Arabidopsis protein family that may be additional targets for these bacterial virulence factors.
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Affiliation(s)
- Han-Suk Kim
- Department of Biology, CB 3280, University of North Carolina, Chapel Hill, NC 27599, USA
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383
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Gaus K, Rodriguez M, Ruberu KR, Gelissen I, Sloane TM, Kritharides L, Jessup W. Domain-specific lipid distribution in macrophage plasma membranes. J Lipid Res 2005; 46:1526-38. [PMID: 15863834 DOI: 10.1194/jlr.m500103-jlr200] [Citation(s) in RCA: 86] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Lipid rafts, defined as cholesterol- and sphingolipid-rich domains, provide specialized lipid environments understood to regulate the organization and function of many plasma membrane proteins. Growing evidence of their existence, protein cargo, and regulation is based largely on the study of isolated lipid rafts; however, the consistency and validity of common isolation methods is controversial. Here, we provide a detailed and direct comparison of the lipid and protein composition of plasma membrane "rafts" prepared from human macrophages by different methods, including several detergent-based isolations and a detergent-free method. We find that detergent-based and detergent-free methods can generate raft fractions with similar lipid contents and a biophysical structure close to that previously found on living cells, even in cells not expressing caveolin-1, such as primary human macrophages. However, important differences between isolation methods are demonstrated. Triton X-100-resistant rafts are less sensitive to cholesterol or sphingomyelin depletion than those prepared by detergent-free methods. Moreover, we show that detergent-based methods can scramble membrane lipids during the isolation process, reorganizing lipids previously in sonication-derived nonraft domains to generate new detergent-resistant rafts. The role of rafts in regulating the biological activities of macrophage plasma membrane proteins may require careful reevaluation using multiple isolation procedures, analyses of lipids, and microscopic techniques.
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Affiliation(s)
- Katharina Gaus
- Centre for Vascular Research at the School of Medical Sciences, University of New South Wales, and Department of Haematology, Prince of Wales Hospital, Sydney, NSW Australia.
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384
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Abstract
Phagocytosis requires receptor-mediated recognition of particles, usually in the guise of infectious agents and apoptotic cells. Phagosomes fuse with lysosomes to generate phagolysosomes, which play a key role in enzymatic digestion of the internalized contents into component parts. Recent findings indicate that a simple paradigm of a single cognate receptor interaction that guides the phagosome to phagolysosome formation belies the complexity of combinatorial receptor recognition and diversity of phagosome function. In fact, phagosomes are comprised of hundreds of proteins that play a key role in deciphering the contents of the phagosome and in defining host response. In this review we discuss how the challenge of recognizing diverse molecular patterns is met by combinatorial interactions between phagocytic receptors. Furthermore, these combinations are dynamic and both sculpt the balance between a proinflammatory or anti-inflammatory response and direct phagosome diversity. We also indicate an important role for genetically tractable model organisms in defining key components of this evolutionarily conserved process.
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Affiliation(s)
- Lynda M Stuart
- Laboratory of Developmental Immunology, Massachusetts General Hospital and Harvard Medical School, Boston, MA 02114, USA
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385
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Manukyan M, Triantafilou K, Triantafilou M, Mackie A, Nilsen N, Espevik T, Wiesmüller KH, Ulmer AJ, Heine H. Binding of lipopeptide to CD14 induces physical proximity of CD14, TLR2 and TLR1. Eur J Immunol 2005; 35:911-21. [PMID: 15714590 DOI: 10.1002/eji.200425336] [Citation(s) in RCA: 124] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Abstract
Lipoproteins or lipopeptides (LP) are bacterial cell wall components detected by the innate immune system. For LP, it has been shown that TLR2 is the essential receptor in cellular activation. However, molecular mechanisms of LP recognition are not yet clear. We used a FLAG-labeled derivative of the synthetic lipopeptide N-palmitoyl-S-[2,3-bis(palmitoyloxy)-(2R,S)-propyl]-(R)-cysteinyl-seryl-(lysyl)(3)-lysine (Pam(3)CSK(4)) to study the roles of CD14, TLR2 and TLR1 in binding and signaling of LP and their molecular interactions in human cells. The activity of Pam(3)CSK(4)-FLAG was TLR2 dependent, whereas the binding was enabled by CD14, as evaluated by flow cytometry and confocal microscopy. Using FRET and FRAP imaging techniques to study molecular associations, we could show that after Pam(3)CSK(4)-FLAG binding, CD14 and Pam(3)CSK(4)-FLAG associate with TLR2 and TLR1, and TLR2 is targeted to a low-mobility complex. Thus, LP binding to CD14 is the first step in the LP recognition, inducing physical proximity of CD14 and LP with TLR2/TLR1 and formation of the TLR2 signaling complex.
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Affiliation(s)
- Maria Manukyan
- Department of Immunology and Cell Biology, Research Center Borstel, Borstel, Germany
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386
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Jimenez de Bagues MP, Maria-Pilar JDB, Dudal S, Dornand J, Gross A. Cellular bioterrorism: how Brucella corrupts macrophage physiology to promote invasion and proliferation. Clin Immunol 2005; 114:227-38. [PMID: 15721833 DOI: 10.1016/j.clim.2004.07.010] [Citation(s) in RCA: 55] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/19/2004] [Accepted: 07/22/2004] [Indexed: 01/18/2023]
Abstract
Brucellosis is a worldwide human zoonosis caused by intracellular bacteria of the genus Brucella. Virulence factors play an important role in allowing Brucella infection and proliferation within macrophages. Brucella enters macrophages through lipid raft microdomains, avoids phagolysosome fusion, and inhibits TNF-alpha secretion and apoptosis. Furthermore, Brucella can perturb bactericidal activity in macrophages by influencing the host cell response to its advantage through its LPS or by activating the cAMP/PKA pathway. To date, small steps have been taken in defining and understanding the virulence factors of Brucella used in macrophage subversion, but further investigation is required to fully explain virulence and persistence.
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Affiliation(s)
- Maria-Pilar Jimenez de Bagues
- Unidad de Sanidad Animal, Servicio de Investigación Agroalimentaria, Diputación General de Aragón, Ap. 727. 50080 Zaragoza, Spain
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387
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Kishore SP, Bungum MK, Platt JL, Brunn GJ. Selective suppression of Toll-like receptor 4 activation by chemokine receptor 4. FEBS Lett 2005; 579:699-704. [PMID: 15670831 DOI: 10.1016/j.febslet.2004.12.047] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/23/2004] [Revised: 11/24/2004] [Accepted: 12/20/2004] [Indexed: 11/29/2022]
Abstract
The response of Toll-like receptor 4 (TLR4) to lipopolysaccharide (LPS) is thought vital for resisting infection. Since aberrant TLR4 signaling may initiate inflammatory conditions such as the sepsis syndrome, we sought a component of normal cells that might provide local control of TLR4 activation. We found that antibodies that block chemokine receptor 4 (CXCR4) function enhanced TLR4 signaling, while increased expression of CXCR4 or addition of the CXCR4 ligand SDF-1 suppressed TLR4 signaling induced by LPS. These findings suggest that CXCR4 could exert local control of TLR4 and suggest the possibility of new therapeutic approaches to suppression of TLR4 function.
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Affiliation(s)
- Sandeep P Kishore
- Transplantation Biology, Mayo Clinic, 200 First Street SW, Medical Sciences 2-66, Rochester, MN 55905, USA
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388
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Triantafilou M, Morath S, Mackie A, Hartung T, Triantafilou K. Lateral diffusion of Toll-like receptors reveals that they are transiently confined within lipid rafts on the plasma membrane. J Cell Sci 2005; 117:4007-14. [PMID: 15286178 DOI: 10.1242/jcs.01270] [Citation(s) in RCA: 121] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The innate immune system utilises pattern recognition receptors in order to recognise microbial conserved molecular patterns. The family of Toll-like receptors (TLRs) has been shown to act as the main pattern recognition receptors for the innate immune system. Using biochemical as well as fluorescence imaging techniques, TLR2 and TLR4 were found to be recruited within microdomains upon stimulation by bacterial products. Furthermore their lateral diffusion in the cell membrane as determined by fluorescence recovery after photobleaching revealed that upon stimulation by bacterial products TLRs encounter barriers to their lateral movement, thus supporting the notion that specialised domains on the plasma membrane facilitate the innate recognition.
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Affiliation(s)
- Martha Triantafilou
- Infection and Immunity Group, School of Life Sciences, University of Sussex, Falmer, Brighton, BN1 9QG, UK
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389
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Hajishengallis G, Tapping RI, Martin MH, Nawar H, Lyle EA, Russell MW, Connell TD. Toll-like receptor 2 mediates cellular activation by the B subunits of type II heat-labile enterotoxins. Infect Immun 2005; 73:1343-9. [PMID: 15731031 PMCID: PMC1064972 DOI: 10.1128/iai.73.3.1343-1349.2005] [Citation(s) in RCA: 63] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The type II heat-labile enterotoxins (LT-IIa and LT-IIb) of Escherichia coli have an AB5 subunit structure similar to that of cholera toxin (CT) and other type I enterotoxins, despite significant differences in the amino acid sequences of their B subunits and different ganglioside receptor specificities. LT-II holotoxins and their nontoxic B subunits display unique properties as immunological adjuvants distinct from those of CT and its B subunits. In contrast to type II holotoxins, the corresponding pentameric B subunits, LT-IIaB and LT-IIbB, stimulated cytokine release in both human and mouse cells dependent upon Toll-like receptor 2 (TLR2). Induction of interleukin-1beta (IL-1beta), IL-6, IL-8, or tumor necrosis factor alpha in human THP-1 cells by LT-IIaB or LT-IIbB was inhibited by anti-TLR2 but not by anti-TLR4 antibody. Furthermore, transient expression of TLR1 and TLR2 in human embryonic kidney 293 cells resulted in activation of a nuclear factor-kappaB-dependent luciferase gene in response to LT-IIaB or LT-IIbB. Moreover, peritoneal macrophages from TLR2-deficient mice failed to respond to LT-IIaB or LT-IIbB, in contrast to wild-type or TLR4-deficient cells. These results demonstrate that besides their established binding to gangliosides, the B subunits of type II enterotoxins also interact with TLR2. Although a ganglioside-nonbinding mutant (T34I) of LT-IIaB effectively induced cytokine release, a phenotypically similar point mutation (T13I) in LT-IIbB abrogated cytokine induction, suggesting a variable requirement for gangliosides as coreceptors in TLR2 agonist activity. TLR2-dependent activation of mononuclear cells by type II enterotoxin B subunits appears to be a novel mechanism whereby these molecules may exert their immunomodulatory and adjuvant activities.
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Affiliation(s)
- George Hajishengallis
- Department of Microbiology, Immunology, and Parasitology, Louisiana State University, Health Sciences Center, New Orleans, LA 70119, USA.
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390
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Lentschat A, Karahashi H, Michelsen KS, Thomas LS, Zhang W, Vogel SN, Arditi M. Mastoparan, a G Protein Agonist Peptide, Differentially Modulates TLR4- and TLR2-Mediated Signaling in Human Endothelial Cells and Murine Macrophages. THE JOURNAL OF IMMUNOLOGY 2005; 174:4252-61. [PMID: 15778388 DOI: 10.4049/jimmunol.174.7.4252] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
Previous studies have implicated a role for heterotrimeric G protein-coupled signaling in B cells, monocytes, and macrophages stimulated with LPS and have shown that G proteins coimmunoprecipitate with membrane-bound CD14. In this study, we have extended these observations in human dermal microvessel endothelial cells (HMEC) that lack membrane-bound CD14 and in murine macrophages to define further the role of heterotrimeric G proteins in TLR signaling. Using the wasp venom-derived peptide, mastoparan, to disrupt G protein-coupled signaling, we identified a G protein-dependent signaling pathway in HMEC stimulated with TLR4 agonists that is necessary for the activation of p38 phosphorylation and kinase activity, NF-kappaB and IL-6 transactivation, and IL-6 secretion. In contrast, HMEC activation by TLR2 agonists, TNF-alpha, or IL-1beta was insensitive to mastoparan. In the murine macrophage cell line, RAW 264.7, and in primary murine macrophages, G protein dysregulation by mastoparan resulted in significant inhibition of LPS-induced signaling leading to both MyD88-dependent and MyD88-independent gene expression, while TLR2-mediated gene expression was not significantly inhibited. In addition to inhibition of TLR4-mediated MAPK phosphorylation in macrophages, mastoparan blunted IL-1R-associated kinase-1 kinase activity induced by LPS, but not by TLR2 agonists, yet failed to affect phosphorylation of Akt by phosphoinositol-3-kinase induced by either TLR2- or TLR4-mediated signaling. These data confirm the importance of heterotrimeric G proteins in TLR4-mediated responses in cells that use either soluble or membrane-associated CD14 and reveal a level of TLR and signaling pathway specificity not previously appreciated.
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Affiliation(s)
- Arnd Lentschat
- Department of Microbiology and Immunology, University of Maryland, Baltimore, MD 21201, USA
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391
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Benhnia MREI, Wroblewski D, Akhtar MN, Patel RA, Lavezzi W, Gangloff SC, Goyert SM, Caimano MJ, Radolf JD, Sellati TJ. Signaling through CD14 attenuates the inflammatory response to Borrelia burgdorferi, the agent of Lyme disease. THE JOURNAL OF IMMUNOLOGY 2005; 174:1539-48. [PMID: 15661914 DOI: 10.4049/jimmunol.174.3.1539] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
Lyme disease is a chronic inflammatory disorder caused by the spirochetal bacterium, Borrelia burgdorferi. In vitro evidence suggests that binding of spirochetal lipoproteins to CD14, a pattern recognition receptor expressed on monocytes/macrophages and polymorphonuclear cells, is a critical requirement for cellular activation and the subsequent release of proinflammatory cytokines that most likely contribute to symptomatology and clinical manifestations. To test the validity of this notion, we assessed the impact of CD14 deficiency on Lyme disease in C3H/HeN mice. Contrary to an anticipated diminution in pathology, CD14(-/-) mice exhibited more severe and persistent inflammation than did CD14(+/+) mice. This disparity reflects altered gene regulation within immune cells that may engender the higher bacterial burden and serum cytokine levels observed in CD14(-/-) mice. Comparing their in vitro stimulatory activity, live spirochetes, but not lysed organisms, were a potent CD14-independent stimulus of cytokine production, triggering an exaggerated response by CD14(-/-) macrophages. Collectively, our in vivo and in vitro findings support the provocative notion that: 1) pattern recognition by CD14 is entirely dispensable for elaboration of an inflammatory response to B. burgdorferi, and 2) CD14-independent signaling pathways are inherently more destructive than CD14-dependent pathways. Continued study of CD14-independent signaling pathways may provide mechanistic insight into the inflammatory processes that underlie development of chronic inflammation.
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392
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Affiliation(s)
- Gregor Rothe
- Bremer Zentrum für Laboratoriumsmedizin GmbH, D-28205 Bremen, Germany
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393
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Triantafilou M, Triantafilou K. Heat-shock protein 70 and heat-shock protein 90 associate with Toll-like receptor 4 in response to bacterial lipopolysaccharide. Biochem Soc Trans 2005; 32:636-9. [PMID: 15270695 DOI: 10.1042/bst0320636] [Citation(s) in RCA: 123] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
Mammalian responses to bacterial LPS (lipopolysaccharide) from the outer membrane of Gram-negative bacteria can lead to an uncontrolled inflammatory response that can be deadly for the host. It has been shown that the innate immune system employs at least three cell surface receptors, CD14, TLR4 (Toll-like receptor 4) and MD-2, in order to recognize bacterial LPS. In our previous work we have found that Hsps (heat-shock proteins) are also involved in the innate recognition of bacterial products. Their presence on the cell surface, as well as their involvement in the innate recognition process, are poorly understood. In the present study we have investigated the association of TLR4 with Hsp70 and Hsp90 following LPS stimulation, both on the cell surface and intracellularly. Our results show that Hsp70 and Hsp90 form a cluster with TLR4 within lipid microdomains following LPS stimulation. In addition, Hsp70 and Hsp90 seem to be involved in TLR4/LPS trafficking and targeting to the Golgi apparatus, since upon LPS stimulation we found that both Hsps are targeted to the Golgi along with TLR4. The present study sheds new light into the involvement of Hsps in the innate immune response.
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Affiliation(s)
- M Triantafilou
- Infection and Immunity Group, University of Sussex, School of Life Sciences, Falmer, Brighton, BN1 9QG, UK
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394
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Motoyama K, Arima H, Nishimoto Y, Miyake K, Hirayama F, Uekama K. Involvement of CD14 in the inhibitory effects of dimethyl-α-cyclodextrin on lipopolysaccharide signaling in macrophages. FEBS Lett 2005; 579:1707-14. [PMID: 15757665 DOI: 10.1016/j.febslet.2005.01.076] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/22/2004] [Revised: 01/17/2005] [Accepted: 01/31/2005] [Indexed: 12/11/2022]
Abstract
The potential use of alpha-cyclodextrin and its hydrophilic alpha-cyclodextrin derivatives (alpha-CyDs) as antagonists against lipopolysaccharide (LPS), which stimulates the nitric oxide (NO) and tumor necrosis factor-alpha (TNF-alpha) production as well as nuclear factor-kappaB (NF-kappaB) activation in macrophages was examined. Of three alpha-CyDs used in the present study, 2,6-di-O-methyl-alpha-CyD (DM-alpha-CyD) had greater inhibitory activity than did the other CyDs against NO and TNF-alpha production through an impairment of gene expression in macrophage cell lines and primary macrophages stimulated with LPS and lipid A in a concentration-dependent manner. Concomitantly, DM-alpha-CyD inhibited NF-kappaB translocation into nucleus. These inhibitory effects of DM-alpha-CyD could be attributed to the release of CD14 from lipid rafts caused by an efflux of phospholipids, but not cholesterol. These results suggest that DM-alpha-CyD may have promise as a potent and unique antagonist for excess activation of macrophages stimulated with LPS.
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Affiliation(s)
- Keiichi Motoyama
- Graduate School of Pharmaceutical Sciences, Kumamoto University, 5-1, Oe-honmachi, Kumamoto 862-0973, Japan
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395
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An H, Xu H, Zhang M, Zhou J, Feng T, Qian C, Qi R, Cao X. Src homology 2 domain-containing inositol-5-phosphatase 1 (SHIP1) negatively regulates TLR4-mediated LPS response primarily through a phosphatase activity- and PI-3K-independent mechanism. Blood 2005; 105:4685-92. [PMID: 15701712 DOI: 10.1182/blood-2005-01-0191] [Citation(s) in RCA: 115] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023] Open
Abstract
Src homology 2 (SH2) domain-containing inositol-5-phosphatase 1 (SHIP1) plays important roles in negatively regulating the activation of immune cells primarily via the phosphoinositide 3-kinase (PI-3K) pathway by catalyzing the PI-3K product PtdIns-3,4,5P3 (phosphatidylinositol-3,4,5-triphosphate) into PtdIns-3,4P2. However, the role of SHIP1 in Toll-like receptor 4 (TLR4)-mediated lipopolysaccharide (LPS) response remains unclear. Here we demonstrate that SHIP1 negatively regulates LPS-induced inflammatory response via both phosphatase activity-dependent and -independent mechanisms in macrophages. SHIP1 becomes tyrosine phosphorylated and up-regulated upon LPS stimulation in RAW264.7 macrophages. SHIP1-specific RNA-interfering and SHIP1 overexpression experiments demonstrate that SHIP1 inhibits LPS-induced tumor necrosis factor alpha (TNF-alpha) and interleukin 6 (IL-6) production by negatively regulating the LPS-induced combination between TLR4 and myeloid differentiation factor 88 (MyD88); activation of Ras (p21(ras) protein), PI-3K, extracellular signal-regulated kinase 1/2 (ERK1/2), p38, and c-Jun NH2-terminal kinase (JNK); and degradation of IkappaB-alpha. SHIP1 also significantly inhibits LPS-induced mitogen-activated protein kinase (MAPK) activation in TLR4-reconstitited COS7 cells. Although SHIP1-mediated inhibition of PI-3K is dependent on its phosphatase activity, phosphatase activity-disrupted mutant SHIP1 remains inhibitory to LPS-induced TNF-alpha production. Neither disrupting phosphatase activity nor using the PI-3K pathway inhibitor LY294002 or wortmannin could significantly block SHIP1-mediated inhibition of LPS-induced ERK1/2, p38, and JNK activation and TNF-alpha production, demonstrating that SHIP1 inhibits LPS-induced activation of MAPKs and cytokine production primarily by a phosphatase activity- and PI-3K-independent mechanism.
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Affiliation(s)
- Huazhang An
- Institute of Immunology, Second Military Medical University, Shanghai, People's Republic of China
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396
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Zeyda M, Säemann MD, Stuhlmeier KM, Mascher DG, Nowotny PN, Zlabinger GJ, Waldhäusl W, Stulnig TM. Polyunsaturated fatty acids block dendritic cell activation and function independently of NF-kappaB activation. J Biol Chem 2005; 280:14293-301. [PMID: 15684433 DOI: 10.1074/jbc.m410000200] [Citation(s) in RCA: 108] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023] Open
Abstract
Polyunsaturated fatty acids (PUFAs) modulate immune responses leading to clinically significant beneficial effects in a variety of inflammatory disorders. PUFA effects on T cells have been extensively studied, but their influence on human dendritic cells (DCs), which are the most potent antigen-presenting cells and play a key role in initiating immune responses, has not been elucidated so far. Here we show that PUFAs of the n-3 and n-6 series (arachidonic and eicosapentaenoic acid) affect human monocyte-derived DC differentiation and inhibit their activation by LPS, resulting in altered DC surface molecule expression and diminished cytokine secretion. Furthermore, the potency to stimulate T cells was markedly inhibited in PUFA-treated DCs. The PUFA-mediated block in LPS-induced DC activation is reflected by diminished TNF-alpha, IL-12p40, CD40, and COX-2 mRNA levels. Strikingly, typical LPS-induced signaling events such as degradation of IkappaB and activation of NF-kappaB were not affected by PUFAs, even though DC membrane lipid composition was markedly altered. Arachidonic and eicosapentaenoic acid both altered DC prostaglandin production, but inhibitors of cyclooxygenases and lipoxygenases did not abolish PUFA effects, indicating that the observed PUFA actions on DCs were independent of autoregulation via eicosanoids. These data demonstrate a unique interference with DC activation and function that could significantly contribute to the well known anti-inflammatory effects of PUFAs.
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Affiliation(s)
- Maximilian Zeyda
- Clinical Divisions of Endocrinology and Metabolism, Medical University of Vienna, Währinger Gürtel 18-20, A-1090 Vienna, Austria
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397
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Moreno C, Merino J, Ramírez N, Echeverría A, Pastor F, Sánchez-Ibarrola A. Lipopolysaccharide needs soluble CD14 to interact with TLR4 in human monocytes depleted of membrane CD14. Microbes Infect 2005; 6:990-5. [PMID: 15345230 DOI: 10.1016/j.micinf.2004.05.010] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/20/2004] [Accepted: 05/25/2004] [Indexed: 01/19/2023]
Abstract
Toll-like receptors recognize specific patterns of microbial components and regulate the activation of both innate and adaptive immunity. TLR4 recognizes lipopolysaccharide (LPS) in monocytes/macrophages with the help of other molecules like CD14 and MD-2, which indicates that the functional LPS receptor forms a large complex. The functional relationship between the components has been the subject of debate, as have the modifications induced by the ligand in the expression of some of these components. Moreover, as for other members of this family of receptors, the possible direct interaction of receptors and their ligands is a matter of discussion. In this paper we address the question of whether the expression of some of the components influences the expression of the rest. Human monocytes in which CD14 has been downregulated through interference in the turnover of the molecule at the Golgi level, show normal membrane TLR4 expression, when compared with control cells. On the other hand, LPS alters membrane TLR4 expression by monocytes devoid of membrane CD14 only in the presence of human serum. The effect of serum is blocked by anti-CD14 monoclonal antibodies, which strongly suggests a functional role for soluble CD14/LPS complexes in the interaction with TLR4. Our data add information on the relationship between the components of the LPS receptor and the characteristics of the interaction of LPS and TLR4 in cells devoid of membrane CD14.
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Affiliation(s)
- Cristina Moreno
- Department of Immunology, Clínica Universitaria, Faculty of Medicine, University of Navarra, 31008 Pamplona, Spain
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398
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Mueller M, Brandenburg K, Dedrick R, Schromm AB, Seydel U. Phospholipids Inhibit Lipopolysaccharide (LPS)-Induced Cell Activation: A Role for LPS-Binding Protein. THE JOURNAL OF IMMUNOLOGY 2005; 174:1091-6. [PMID: 15634934 DOI: 10.4049/jimmunol.174.2.1091] [Citation(s) in RCA: 56] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
The inhibition of LPS-induced cell activation by specific antagonists is a long-known phenomenon; however, the underlying mechanisms are still poorly understood. It is commonly accepted that the membrane-bound receptors mCD14 and TLR4 are involved in the activation of mononuclear cells by LPS and that activation may be enhanced by soluble LPS-binding protein (LBP). Hexaacylated Escherichia coli lipid A has the highest cytokine-inducing capacity, whereas lipid A with four fatty acids (precursor IVa, synthetic compound 406) is endotoxically inactive, but expresses antagonistic activity against active LPS. Seeking to unravel basic molecular principles underlying antagonism, we investigated phospholipids with structural similarity to compound 406 with respect to their antagonistic activity. The tetraacylated diphosphatidylglycerol (cardiolipin, CL) exhibits high structural similarity to 406, and our experiments showed that CL strongly inhibited LPS-induced TNF-alpha release when added to the cells before stimulation or as a CL/LPS mixture. Also negatively charged and to a lesser degree zwitterionic diacyl phospholipids inhibited LPS-induced cytokine production. Using Abs against LBP, we could show that the activation of cells by LPS was dependent on the presence of cell-associated LBP, thus making LBP a possible target for the antagonistic action of phospholipids. In experiments investigating the LBP-mediated intercalation of LPS and phospholipids into phospholipid liposomes mimicking the macrophage membrane, we could show that preincubation of soluble LBP with phospholipids leads to a significant reduction of LPS intercalation. In summary, we show that LBP is a target for the inhibitory function of phospholipids.
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Affiliation(s)
- Mareile Mueller
- Department of Immunochemistry and Biochemical Microbiology, Division of Biophysics, Leibniz-Center for Medicine and Biosciences, Research Center Borstel, Borstel, Germany
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399
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West AP, Dancho BA, Mizel SB. Gangliosides inhibit flagellin signaling in the absence of an effect on flagellin binding to toll-like receptor 5. J Biol Chem 2005; 280:9482-8. [PMID: 15632166 DOI: 10.1074/jbc.m411875200] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
A recent study (Ogushi, K., Wada, A., Niidome, T., Okuda, T., Llanes, R., Nakayama, M., Nishi, Y., Kurazono, H., Smith, K. D., Aderem, A., Moss, J., and Hirayama, T. (2004) J. Biol. Chem. 279, 12213-12219) concluded that gangliosides serve as co-receptors for flagellin signaling via toll-like receptor 5 (TLR5). In view of several findings in this study that were inconsistent with a role for gangliosides as co-receptors, we re-examined this important issue. Using TLR5-negative RAW 264.7 cells and a TLR5-enhanced yellow fluorescent protein chimera, we established an assay for specific binding of flagellin to cells. Inhibition of clatherin-mediated internalization of flagellin.TLR5-enhanced yellow fluorescent protein complexes did not impair flagellin activation of IRAK-1. Thus flagellin signal occurs at the cell surface and not intracellularly. Exogenous addition of mixed gangliosides (GM1, GD1a, and GT1b) as well as GD1a itself inhibited flagellin-induced interleukin-1 receptor-associated kinase activation as well as tumor necrosis factor alpha production in HeNC2, THP-1, and RAW 264.7 cells. Gangliosides inhibited flagellin signaling in the absence of an effect on flagellin binding to TLR5. Depletion of gangliosides in RAW 264.7 cells did not alter the concentration dependence or magnitude of flagellin signaling as measured by interleukin-1 receptor-associated kinase activation or tumor necrosis factor alpha production. Our findings are consistent with the conclusions that gangliosides are not essential co-receptors for flagellin and that the inhibitory effect of gangliosides is mediated by at least one mechanism that is distinct from any effect on the binding of flagellin to TLR5.
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Affiliation(s)
- A Phillip West
- Department of Microbiology and Immunology, Wake Forest University School of Medicine, Winston-Salem, North Carolina 27157, USA
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Wysoczynski M, Reca R, Ratajczak J, Kucia M, Shirvaikar N, Honczarenko M, Mills M, Wanzeck J, Janowska-Wieczorek A, Ratajczak MZ. Incorporation of CXCR4 into membrane lipid rafts primes homing-related responses of hematopoietic stem/progenitor cells to an SDF-1 gradient. Blood 2005; 105:40-48. [PMID: 15328152 DOI: 10.1182/blood-2004-04-1430] [Citation(s) in RCA: 198] [Impact Index Per Article: 9.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023] Open
Abstract
We found that supernatants of leukapheresis products (SLPs) of patients mobilized with granulocyte-colony-stimulating factor (G-CSF) or the various components of SLPs (fibrinogen, fibronectin, soluble vascular cell adhesion molecule-1 [VCAM-1], intercellular adhesion molecule-1 [ICAM-1], and urokinase plasminogen activator receptor [uPAR]) increase the chemotactic responses of hematopoietic stem/progenitor cells (HSPCs) to stromal-derived factor-1 (SDF-1). However, alone they do not chemoattract HSPCs, but they do increase or prime the cells' chemotactic responses to a low or threshold dose of SDF-1. We observed that SLPs increased calcium flux, phosphorylation of mitogen-activated protein kinase (MAPK) p42/44 and AKT, secretion of matrix metalloproteinases, and adhesion to endothelium in CD34+ cells. Furthermore, SLPs increased SDF-dependent actin polymerization and significantly enhanced the homing of human cord blood (CB)- and bone marrow (BM)-derived CD34+ cells in a NOD/SCID mouse transplantation model. Moreover, the sensitization or priming of cell chemotaxis to an SDF-1 gradient was dependent on cholesterol content in the cell membrane and on the incorporation of the SDF-1 binding receptor CXCR4 and the small GTPase Rac-1 into membrane lipid rafts. This colocalization of CXCR4 and Rac-1 in lipid rafts facilitated guanosine triphosphate (GTP) binding/activation of Rac-1. Hence, we postulate that CXCR4 could be primed by various factors related to leukapheresis and mobilization that increase its association with membrane lipid rafts, allowing the HSPCs to better sense the SDF-1 gradient. This may partially explain why HSPCs from mobilized peripheral blood leukapheresis products engraft more quickly in patients than do those from BM or CB. Based on our findings, we suggest that the homing of HSPCs is optimal when CXCR4 is incorporated in membrane lipid rafts and that ex vivo priming of HSPCs with some of the SLP-related molecules before transplantation could increase their engraftment.
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Affiliation(s)
- Marcin Wysoczynski
- Stem Cell Biology Program, James Graham Brown Cancer Center, University of Louisville, KY 40202, USA
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