Biomedical subjects
B Moser
Publications and source records attributed to B Moser.
TYMSTR, a putative chemokine receptor selectively expressed in activated T cells, exhibits HIV-1 coreceptor function.
BACKGROUND: Chemokines bind to specific receptors and mediate leukocyte migration to sites of inflammation. Recently, some chemokine receptors, notably CXCR4 and CCR5, have been shown to be essential fusion factors on target cells for infection by human immunodeficiency virus (HIV); the chemokines bound by these receptors have also been shown to act as potent inhibitors of HIV infection. Here, we describe the isolation of a novel, putative chemokine receptor. RESULTS: We have isolated the cDNA for a putative human chemokine receptor, which we have termed TYMSTR (T-lymphocyte-expressed seven-transmembrane domain receptor). The TYMSTR gene is localized to human chromosome 3 and encodes a protein that has a high level of identity with chemokine receptors. TYMSTR mRNA was selectively expressed in interleukin-2-stimulated T lymphocytes but not in freshly isolated lymphocytes and leukocytes or related cell lines. The natural ligand for TYMSTR was not identified among 32 human chemokines and other potential ligands. Cells co-expressing TYMSTR and human CD4 fused with cells expressing envelope glycoproteins of macrophage (M)-tropic HIV-1 as well as T-cell line (T)-tropic HIV-1 isolates. Addition of infectious, T-tropic HIV-1 particles to TYMSTR/CD4-expressing cells resulted in viral entry and proviral DNA formation. CONCLUSIONS: Our findings demonstrate that TYMSTR, in combination with CD4, mediates HIV-1 fusion and entry. The high-level expression of TYMSTR in CD4(+) T lymphocytes and the selectivity of this receptor for T-tropic and M-tropic HIV-1 strains indicates that TYMSTR might function as HIV coreceptor at both early and late stages of infection.
Identification of CCR8, the receptor for the human CC chemokine I-309.
The nucleotide sequence for a putative chemokine receptor, termed TER1, ChemR1, or CKR-L1, was recently obtained by a polymerase chain reaction-based cloning technique. It encodes a protein of 355 amino acids that shows 32-45% sequence identity with human chemokine receptors. The gene was localized on human chromosome 3p21-24, the site for the genes for the five known CC chemokine receptors, suggesting that the natural ligand may be a CC chemokine. We have stably expressed this receptor in murine pre-B cells 300-19 and have tested their responsiveness to 20 human chemokines and some other potential agonists. The CC chemokine I-309 was the only agonist that selectively induced intracellular Ca2+ mobilization and chemotaxis in receptor-transfected 300-19 cells. Stromal cell-derived factor 1, which binds to murine CXCR4 expressed in parental as well as transfected 300-19 cells, served as positive control in the functional screening. The interaction of I-309 with TER1 was of high affinity as shown by 125I-I-309 binding (Kd of 1.2 nM) and transient [Ca2+]i changes at subnanomolar concentrations of agonist. Migration responses in receptor-transfected 300-19 cells was typically bimodal with maximal activity at 10 nM of I-309. These data demonstrate that TER1 (ChemR1 or CKR-L1) is the receptor for I-309, and we propose to call this receptor CCR8 in agreement with the current nomenclature for chemokine receptors. The expression of CCR8 in blood leukocytes and lymphocytes was analyzed by Northern blot. No transcripts were found in RNA from freshly isolated blood neutrophils, monocytes, cultured macrophages, and phytohemagglutinin-stimulated T lymphocytes, and a faint hybridization signal corresponding to the RNA species of 4 kb was obtained only with RNA from interleukin-2-treated T lymphocytes. CCR8 is unusual for its selectivity for a single chemokine, previously shown only for CXCR1 and CXCR4, which bind interleukin-8 and stromal cell-derived factor 1, respectively. Identification of the receptor for I-309 represents a significant progress in determining the function of I-309 in inflammation and disease.
The chemokine SDF-1, stromal cell-derived factor 1, attracts early stage B cell precursors via the chemokine receptor CXCR4.
In the bone marrow, progenitor (pro-) and precursor (pre-) B cells depend on close contact with stromal cells for growth and maturation. Stromal cell-derived factor 1 (SDF-1), also known as pre-B cell growth-stimulating factor, is produced by bone marrow stromal cells and was reported to act together with interleukin-7 as co-mitogen for pre-B cells. SDF-1 was recently shown to be a chemokine which is chemotactic for different types of leukocytes and acts via the chemokine receptor CXCR4. Using sorted B220+ bone marrow cells and several B cell lines characteristic for different stages of B lymphopoiesis, we now show that SDF-1 is a potent attractant for pro- and pre-B cells, but is inactive on B cells at later stages of development. In early B cell precursors, SDF-1 induced intracellular Ca2+ mobilization and in vitro migration with a potency and efficacy similar to that observed for chemokines acting on blood leukocytes. These responses were mediated via CXCR4 as they could be inhibited by an antireceptor antibody. SDF-1 is the first chemokine shown to act on early-stage B cell precursors. Mice lacking SDF-1 die perinatally and show a severe deficiency in B lymphopoiesis. We propose that SDF-1 released from the stromal cells exerts its critical hematopoietic function by selectively attracting and confining early B cell precursors within the bone marrow microenvironment that provides the necessary factors for growth and differentiation.
LHRH receptors and LHRH receptor-bearing cells in pituitaries of streptozocin diabetic male rats.
Streptozocin (STZ)-diabetic rats have low hypothalamic luteotropic hormone-releasing hormone (LHRH) secretion and various alterations of gonadotrope cells, among which low luteotropic hormone (LH) secretion. Possible causes for the gonadotrope disorders may be low hypothalamic LHRH secretion alone or combined with reduced (a) number of LHRH receptor sites, or (b) receptor to ligand affinity, or (c) of LHRH receptor-bearing cells. To clarify this question we determined by saturation and competition binding Bmax, KD and KA of the LHRH receptor sites and counted the receptor-bearing cells in pituitary glands of control and STZ-diabetic adult male rats. We found a single receptor class, the Bmax was strongly reduced in diabetic animals whereas both KD and KA were similar in the two groups. The number of LHRH receptor-bearing cells in diabetic animals was increased. Therefore a reduced number of receptor sites per gonadotrope cell occurs in our model. Since in the STZ-diabetic male rats the number of gonadotropes is increased, a higher number of receptor-bearing cells was observed. We conclude that the reduced LH secretion from the diabetic pituitary gland might be due to a reduced number of LHRH receptor sites in the pituitary gland. The increased number of receptor-bearing cells might partially compensate for this change.
The HIV-1 life cycle is blocked at two different points in mature dendritic cells.
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Chemokines and HIV: a remarkable synergism.
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Human chemokines: an update.
Interleukin 8, the first chemokine to be characterized, was discovered nearly ten years ago. Today, more than 30 human chemokines are known. They are often upregulated in inflammation and act mainly on leukocytes inducing migration and release responses. The present review deals largely with the new developments of the last three years. Several structural studies have shown that most chemokines form dimers. The dimers, however, dissociate upon dilution, and the monomers constitute the biologically active form. Chemokine activities are mediated by seven-transmembrane-domain, G protein coupled receptors, five of which were discovered in the past three years. The primary receptor-binding domain of all chemokines is near the NH2 terminus, and antagonists can be obtained by truncation or substitutions in this region. Major progress has been made in the understanding of chemokine actions on T lymphocytes that respond to several CC chemokines but also to IP10 and Mig, two CXC chemokines that selectively attract T cells via a novel receptor. Effects of chemokines on angiogenesis and tumor growth have been reported, but the data are still contradictory and the mechanisms unknown. Of considerable interest is the recent discovery that some chemokines function as HIV-suppressive factors by interacting with chemokine receptors which, together with CD4, were recognized as the binding sites for HIV-1.
Efficient interaction of HIV-1 with purified dendritic cells via multiple chemokine coreceptors.
HIV-1 actively replicates in dendritic cell (DC)-T cell cocultures, but it has been difficult to demonstrate substantial infection of purified mature DCs. We now find that HIV-1 begins reverse transcription much more efficiently in DCs than T cells, even though T cells have higher levels of CD4 and gp120 binding. DCs isolated from skin or from blood precursors behave similarly. Several M-tropic strains and the T-tropic strain IIIB enter DCs efficiently, as assessed by the progressive formation of the early products of reverse transcription after a 90-min virus pulse at 37 degrees C. However, few late gag-containing sequences are detected, so that active viral replication does not occur. The formation of these early transcripts seems to follow entry of HIV-1, rather than binding of virions that contain viral DNA. Early transcripts are scarce if DCs are exposed to virus on ice for 4 h, or for 90 min at 37 degrees C, conditions which allow virus binding. Also the early transcripts once formed are insensitive to trypsin. The entry of a M-tropic isolates is blocked by the chemokine RANTES, and the entry of IIIB by SDF-1. RANTES interacts with CCR5 and SDF-1 with CXCR4 receptors. Entry of M-tropic but not T-tropic virus is ablated in DCs from individuals who lack a functional CCR5 receptor. DCs express more CCR5 and CXCR4 mRNA than T cells. Therefore, while HIV-1 does not replicate efficiently in mature DCs, viral entry can be active and can be blocked by chemokines that act on known receptors for M- and T-tropic virus.
HIV blocked by chemokine antagonist.
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Chemokine receptor specific for IP10 and mig: structure, function, and expression in activated T-lymphocytes.
A human receptor that is selective for the CXC chemokines IP10 and Mig was cloned and characterized. The receptor cDNA has an open reading frame of 1104-bp encoding a protein of 368 amino acids with a molecular mass of 40,659 dalton. The sequence includes seven putative transmembrane segments characteristic of G-protein coupled receptors. It shares 40.9 and 40.3% identical amino acids with the two IL-8 receptors, and 34.2-36.9% identity with the five known CC chemokine receptors. The IP10/Mig receptor is highly expressed in IL-2-activated T lymphocytes, but is not detectable in resting T lymphocytes. B lymphocytes, monocytes and granulocytes. It mediates Ca2+ mobilization and chemotaxis in response to IP10 and Mig, but does not recognize the CXC-chemokines IL-8, GRO alpha, NAP-2, GCP-2. ENA78, PF4, the CC-chemokines MCP-1, MCP-2, MCP-3, MCP-4, MIP-1 alpha, MIP-1 beta. RANTES, 1309, eotaxin, nor lymphotactin. The exclusive expression in activated T-lymphocytes is of high interest since the receptors for chemokines which have been shown so far to attract lymphocytes, e.g., MCP-1, MCP-2, MCP-3, MIP-1 alpha, MIP-1 beta, and RANTES, are also found in monocytes and granulocytes. The present observations suggest that the IP10/Mig receptor is involved in the selective recruitment of effector T cells.
The CXC chemokine SDF-1 is the ligand for LESTR/fusin and prevents infection by T-cell-line-adapted HIV-1.
A putative chemokine receptor that we previously cloned and termed LESTR has recently been shown to function as a co-receptor (termed fusin) for lymphocyte-tropic HIV-1 strains. Cells expressing CD4 became permissive to infection with T-cell-line-adapted HIV-1 strains of the syncytium-inducing phenotype after transfection with LESTR/fusin complementary DNA. We report here the indentification of a human chemokine of the CXC type, stromal cell-derived factor 1 (SDF-1), as the natural ligand for LESTR/fusin, and we propose the term CXCR-4 for this receptor, in keeping with the new chemokine-receptor nomenclature. SDF-1 activates Chinese hamster ovary (CHO) cells transfected with CXCR-4 cDNA as well as blood leukocytes and lymphocytes. In cell lines expressing CXCR-4 and CD4, and in blood lymphocytes, SDF-1 is a powerful inhibitor of infection by lymphocyte-tropic HIV-1 strains, whereas the CC chemokines RANTES, MIP-1 alpha and MIP-1 beta, which were shown previously to prevent infection with primary, monocyte-tropic viruses, are inactive. In combination with CC chemokines, which block the infection with monocyte/macrophage-tropic viruses, SDF-1 could help to decrease virus load and prevent the emergence of the syncytium-inducing viruses which are characteristic of the late stages of AIDS.
Interleukin-2 regulates CC chemokine receptor expression and chemotactic responsiveness in T lymphocytes.
Several studies have shown that CC chemokines attract T lymphocytes, and that CD45RO+, memory phenotype cells are considered to be the main responders. The results, however, have often been contradictory and the role of lymphocyte activation and proliferation has remained unclear. Using CD45RO+ blood lymphocytes cultured under different stimulatory conditions, we have now studied chemotaxis as well as chemokine receptor expression. Expression of the RANTES/MIP-1 alpha receptor (CC-CKR1) and the MCP-1 receptor (CC-CKR2) was highly correlated with migration toward RANTES, MCP-1, and other CC chemokines, and was strictly dependent on the presence of IL-2 in the culture medium. Migration and receptor expression were rapidly downregulated when IL-2 was withdrawn, but were fully restored when IL-2 was added again. The effect of IL-2 could be partially mimicked by IL-4, IL-10, or IL-12, but not by IL-13, IFN gamma, IL-1 beta, TNF-alpha, or by exposure to anti-CD3, anti-CD28 or phytohemagglutinin. Activation of fully responsive lymphocytes through the TCR/CD3 complex and CD28 antigen actually had the opposite effect. It rapidly downregulated receptor expression and consequent migration even in the presence of IL-2. In contrast to the effects on CC chemokine receptors, stimulation of CD45RO+ T lymphocytes with IL-2 neither induced the expression of the CXC chemokine receptors, IL8-R1 and IL8-R2, nor chemotaxis to IL-8. The prominent role of IL-2 in CC chemokine responsiveness of lymphocytes suggests that IL-2-mediated expansion is a prerequisite for the recruitment of antigen-activated T cells into sites of immune and inflammatory reactions.
Activation of NK cells by CC chemokines. Chemotaxis, Ca2+ mobilization, and enzyme release.
The responses of cloned human NK cells (ERNK57) to seven CC chemokines (monocyte chemotactic protein-1 (MCP-1), MCP-2, MCP-3, RANTES (regulated on activation, normal T cell expressed and secreted), macrophage inflammatory protein-1 alpha (MIP-1 alpha), MIP-1 beta, and 1309) and two CXC chemokines (IL-8 and IP-10) were studied. Except for 1309, all CC chemokines induced chemotaxis of the NK cells in vitro, whereas the CXC chemokines were inactive. Maximal activity was obtained at 1 nM for MCP-1 and 10 to 100 nM for the other CC chemokines. The response showed a typically bimodal concentration dependence in all cases, except for RANTES, which induced a linear increase of migration over the concentration range of 0.1 to 1000 nM. A transient rise of the cytosolic-free Ca2+ concentration ([Ca2+]i), which is characteristic for chemokine-stimulated leukocytes, was observed in NK cells after stimulation with all six active chemokines. Since granule exocytosis is required for NK cell-dependent target killing, the effect of CC chemokines on exocytosis was tested. All CC chemokines that induced chemotaxis and [Ca2+]i changes also induced the release of granzyme A and N-acetyl-beta-D-glucosaminidase from cloned and blood NK cells, as well as CD8+ T cells after pretreatment with cytochalasin B. Maximum release was obtained from NK cells, and amounted to 35% and 13% of the total content of granzyme A and N-acetyl-beta-D-glucosaminidase, respectively. The capacity of cloned NK cells and CD8+ T cells to respond to chemokines depended on the time in culture after stimulation with PHA in the presence of irradiated feeder cells, and maximum responses were observed after 10 to 16 days. Our results demonstrate that CC chemokines activate NK cells, and are, therefore, not only attractants for monocytes, T lymphocytes, and eosinophil and basophil granulocytes.
Expression of high- and low-affinity receptors for C3a on the human mast cell line, HMC-1.
The proteolytic cleavage product of complement component 3, (C3a), is like C4a and C5a, is a potent anaphylatoxin and induces the production of inflammatory mediators in phagocytes. Notably, mast cells respond to C3a with the release of vasoactive substances, including histamine. We have examined the function and receptor binding of C3a in a human leukemic mast cell line, HMC-1. Similar to chemoattractant agonists in leukocytes, C3a induced rapid cytosolic free calcium concentration increases in HMC-1 cells. EGTA did not diminish this response, indicating that mobilizable Ca2+ was from intracellular stores. Receptors of C3a in HMC-1 cells couple in part to Bordetella pertussis toxin-sensitive G-proteins and, therefore, appear to belong to the family of serpentine receptors that require G-proteins for signal transduction. HMC-1 cells express two types of C3a receptors, C3aR1 and C3aR2, that were shown to bind 125I-C3a with high-(Kd1 = 2.1-4.8 nM) or low-affinity (Kd2 = 30-150 nM), and both receptors are expressed at high level: 3 x 10(5)-6 x 10(5) C3aR1/cell and 5 x 10(5)-2.3 x 10(6) C3aR2/cell. Results from cross-linking experiments with 125I-C3a fully agree with the presence of two different classes of C3a receptors in HMC-1 cells. Two membrane proteins with apparent molecular masses of 54-61 kDa (p57) and 86-107 kDa (p97) could be covalently modified with 125I-C3a, and this cross-linking was inhibited with an excess of unlabeled C3a. Many of the known agonists for leukocytes including 13 chemokines (IL-8, NAP-2, GRO alpha, ENA-78, IP10, PF4, MCP-1, 2 and 3, RANTES, MIP-1 alpha, MIP-1 beta and I309), three neuropeptides (neuropeptide Y, somatostatin and calcitonin), as well as C5a, did not activate HMC-1 cells, indicating that C3a is one of a few protein ligands for which this cell line expresses specific receptors. The apparent selectivity for C3a and the abundant expression of C3a receptors make the HMC-1 cell line an excellent choice for the cloning of the receptor genes.
The interleukin-8 receptor B and CXC chemokines can mediate transendothelial migration of human skin homing T cells.
We studied the involvement of chemokines that bind to G protein-coupled receptors in the migration of skin homing T cells across a bilayer vascular construct (BVC) consisting of a fibroblast matrix underneath an activated endothelial (EC) monolayer. Based on the expression of the cutaneous lymphocyte-associated antigen (CLA), a skin homing receptor, CD45R0+ T cells freshly isolated from blood or HUT-78 cutaneous T lymphoma cells were separated into CLA+ and CLA- subpopulations. These T cells were incubated on interleukin (IL)-1 beta and tumor necrosis factor-alpha-activated EC, and the number of transmigrated cells was determined. The chemokine IL-8 was selectively involved in the enhanced migration of CLA+ T cells across activated EC as demonstrated by blocking antibody to IL-8 but not to GRO-alpha, MCP-1 and RANTES. Identical results were obtained with both human umbilical vein EC (HUVEC) and microvascular skin EC (HDMEC). Pertussis toxin selectively inhibited the enhanced transendothelial migration (TEM) of CLA+ T cells, suggesting that CLA-dependent TEM depends on Gi protein-transmitted signals. Moreover, the IL-8 receptor B (IL-8RB) appeared to be functionally involved in TEM, as demonstrated by receptor desensitization with the CXC chemokines IL-8 and GRO-alpha and by blocking the IL-8RB with specific monoclonal antibodies. Although only the IL-8RB was involved in CLA-dependent TEM, mRNA encoding IL-8RA and IL-8RB was expressed by both CLA+ and CLA- T cells. This correlated with IL-8RA and IL-8RB surface expression on these cells. Thus, the IL-8RB is selectively functional in TEM of T cells expressing the skin homing receptor CLA. Our results demonstrate a critical role for IL-8 and possibly other IL-8RB ligands in addition to the IL-8RB in TEM and suggest the involvement of these molecules in the homing of specific T cells to inflamed skin.
Sequential regulation of alpha 4 beta 1 and alpha 5 beta 1 integrin avidity by CC chemokines in monocytes: implications for transendothelial chemotaxis.
Leukocyte emigration possibly requires dynamic regulation of integrin adhesiveness for endothelial and extracellular matrix ligands. Adhesion assays on purified vascular cell adhension molecule (VCAM)-1, fibronectin, and fibronectin fragments revealed distinct kinetic patterns for the regulation of very late antigen (VLA)-4 (alpha 4 beta 1) and VLA-5 (alpha 5 beta 1) avidity by the CC chemokines monocyte inflammatory protein (MIP)-1 alpha, RANTES (regulated on activation, normal T expressed and secreted), or monocyte chemoattractant protein (MCP)-1 in monocytes. CC chemokines induced early activation and subsequent deactivation of VLA-4, whereas upregulation of VLA-5 avidity occurred later and persisted. Controlled detachment assays in shear flow suggested that adhesive strength of VLA-4 for VCAM-1 or the 40-kD fragment of fibronectin (FN40) is more rapidly increased and subsequently reduced by MCP-1 than by MIP-1 alpha, and confirmed late and sustained activation of the adhesive strength of VLA-5 for the 120-kD fragment of fibronectin (FN120). Mn2+ or the stimulating beta 1 mAb TS2/16 strongly and stably enhanced monocyte binding to VCAM-1 or fibronectin, and locked beta 1 integrins in a high avidity state, which was not further modulated by CC chemokines. Mn2+ and mAb TS2/16 inhibited CC chemokine-induced transendothelial migration, particularly chemotaxis across stimulated endothelium that involved VLA-4 and VCAM-1. VLA-4 on Jurkat cells is of constitutively high avidity and interfered with migration across barriers expressing VCAM-1. Low but not high site densities of VCAM-1 or FN40 promoted, while FN120 impaired, beta 1 integrin-dependent monocyte chemotaxis to MCP-1 across filters coated with these substrates. Thus, we show that CC chemokines can differentially and selectively regulate avidity of integrins sharing common beta subunits. Transient activation and deactivation of VLA-4 may serve to facilitate transendothelial diapedesis, whereas late and prolonged activation of VLA-5 may mediate subsequent interactions with the basement membrane and extracellular matrix.
Hiking sticks in mountaineering.
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