[Show abstract][Hide abstract] ABSTRACT: The peptide F2L was previously characterized as a high-affinity natural agonist for the human formyl peptide receptor (FPR) 3. F2L is an acetylated 21-aa peptide corresponding with the N terminus of the intracellular heme-binding protein 1 (HEBP1). In the current work, we have investigated which proteases were able to generate the F2L peptide from its precursor HEBP1. Structure-function analysis of F2L identified three amino acids, G(3), N(7), and S(8), as the most important for interaction of the peptide with FPR3. We expressed a C-terminally His-tagged form of human HEBP1 in yeast and purified it to homogeneity. The purified protein was used as substrate to identify proteases generating bioactive peptides for FPR3-expressing cells. A conditioned medium from human monocyte-derived macrophages was able to generate bioactivity from HEBP1, and this activity was inhibited by pepstatin A. Cathepsin D was characterized as the protease responsible for HEBP1 processing, and the bioactive product was identified as F2L. We have therefore determined how F2L, the specific agonist of FPR3, is generated from the intracellular protein HEBP1, although it is unknown in which compartment the processing by cathepsin D occurs in vivo.
The Journal of Immunology 06/2011; 187(3):1475-85. DOI:10.4049/jimmunol.1003545 · 5.36 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: F2L (formylpeptide receptor (FPR)-like (FPRL)-2 ligand), a highly conserved acetylated peptide derived from the amino-terminal cleavage of heme-binding protein, is a potent chemoattractant for human monocytes and dendritic cells, and inhibits LPS-induced human dendritic cell maturation. We recently reported that F2L is able to activate the human receptors FPRL-1 and FPRL2, two members of the FPR family, with highest selectivity and affinity for FPRL2. To facilitate delineation of mechanisms of F2L action in vivo, we have now attempted to define its mouse receptors. This is complicated by the nonequivalence of the human and mouse FPR gene families (three vs at least eight members, respectively). When cell lines were transfected with plasmids encoding the eight mouse receptors, only the one expressing the receptor Fpr2 responded to F2L (EC(50) approximately 400 nM for both human and mouse F2L in both calcium flux and cAMP inhibition assays). This value is similar to F2L potency at human FPRL1. Consistent with this, mouse neutrophils, which like macrophages and dendritic cells express Fpr2, responded to human and mouse F2L in both calcium flux and chemotaxis assays with EC(50) values similar to those found for Fpr2-expressing cell lines ( approximately 500 nM). Moreover, neutrophils from mice genetically deficient in Fpr2 failed to respond to F2L. Thus, Fpr2 is a mouse receptor for F2L, and can be targeted for the study of F2L action in mouse models.
The Journal of Immunology 03/2007; 178(3):1450-6. DOI:10.4049/jimmunol.178.3.1450 · 5.36 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The formyl peptide receptor (FPR) family is involved in host defence against pathogens, but also in sensing internal molecules that may constitute signals of cellular dysfunction. It includes three subtypes in human and other primates. FPR responds to formyl peptides derived from bacterial and mitochondrial proteins. FPRL1 displays a large array of exogenous and endogenous ligands, including the chemokine variant sCKbeta8-1, the neuroprotective peptide humanin, and lipoxin A4. Two high affinity agonists (F2L and humanin) were recently described for FPRL2. In mouse, eight FPR-related receptors have been described. Fpr1 is the ortholog of human FPR, while fpr2 appears to share many ligands with human FPRL1. Altogether, the physiological role of the FPR family is still incompletely understood, due in part to the large variety of ligands, the redundancy with other chemoattractant agents, and the lack of clear orthologs between human and mouse receptors. Newly developed tools will allow to study further this family of receptors.
[Show abstract][Hide abstract] ABSTRACT: Chemotaxis of dendritic cells (DCs) and monocytes is a key step in the initiation of an adequate immune response. Formyl peptide receptor (FPR) and FPR-like receptor (FPRL)1, two G protein-coupled receptors belonging to the FPR family, play an essential role in host defense mechanisms against bacterial infection and in the regulation of inflammatory reactions. FPRL2, the third member of this structural family of chemoattractant receptors, is characterized by its specific expression on monocytes and DCs. Here, we present the isolation from a spleen extract and the functional characterization of F2L, a novel chemoattractant peptide acting specifically through FPRL2. F2L is an acetylated amino-terminal peptide derived from the cleavage of the human heme-binding protein, an intracellular tetrapyrolle-binding protein. The peptide binds and activates FPRL2 in the low nanomolar range, which triggers intracellular calcium release, inhibition of cAMP accumulation, and phosphorylation of extracellular signal-regulated kinase 1/2 mitogen-activated protein kinases through the G(i) class of heterotrimeric G proteins. When tested on monocytes and monocyte-derived DCs, F2L promotes calcium mobilization and chemotaxis. Therefore, F2L appears as a new natural chemoattractant peptide for DCs and monocytes, and the first potent and specific agonist of FPRL2.
Journal of Experimental Medicine 02/2005; 201(1):83-93. DOI:10.1084/jem.20041277 · 13.91 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Dendritic cells (DCs) and macrophages are professional antigen-presenting cells (APCs) that play key roles in both innate and adaptive immunity. ChemR23 is an orphan G protein-coupled receptor related to chemokine receptors, which is expressed specifically in these cell types. Here we present the characterization of chemerin, a novel chemoattractant protein, which acts through ChemR23 and is abundant in a diverse set of human inflammatory fluids. Chemerin is secreted as a precursor of low biological activity, which upon proteolytic cleavage of its COOH-terminal domain, is converted into a potent and highly specific agonist of ChemR23, the chemerin receptor. Activation of chemerin receptor results in intracellular calcium release, inhibition of cAMP accumulation, and phosphorylation of p42-p44 MAP kinases, through the Gi class of heterotrimeric G proteins. Chemerin is structurally and evolutionary related to the cathelicidin precursors (antibacterial peptides), cystatins (cysteine protease inhibitors), and kininogens. Chemerin was shown to promote calcium mobilization and chemotaxis of immature DCs and macrophages in a ChemR23-dependent manner. Therefore, chemerin appears as a potent chemoattractant protein of a novel class, which requires proteolytic activation and is specific for APCs.
Journal of Experimental Medicine 11/2003; 198(7):977-85. DOI:10.1084/jem.20030382 · 13.91 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Human chemokine receptor (HCR) is a putative chemokine receptor sharing high similarity with CCR1, CCR2, CCR3 and CCR5. Its gene is located within the main cluster of CC-chemokine receptor genes, in the 3p21 region of the human genome. We generated monoclonal antibodies directed at human HCR, and studied its distribution in human leukocyte populations and cell lines, and its regulation following maturation or activation of these populations. In peripheral blood leukocytes, HCR is expressed on CD4+ and CD8+ T lymphocytes, including most memory and part of naive cells, but is absent from B cells. Expression of HCR was enhanced following stimulation of T cells by OKT3 and IL-2. HCR is present on monocytes and macrophages. Monocyte-derived dendritic cells harbored HCR, and expression was enhanced following stimulation by lipopolysaccharides, poly (I:C), IFN-gamma or CD40L. Neutrophils strongly expressed HCR. A similar distribution was found in bone marrow,and HCR was also expressed in CD34+ precursors. Expression of HCR and its regulation were confirmed by real-time PCR. In a panel of human tissues, we found abundant HCR transcripts in thymus, spleen, lymph nodes and lung. This large distribution across leukocyte populations, and the up-regulation during DC maturation, represent a new profile among chemokine receptors. We speculate that HCR responds to inflammatory chemokines, and might be involved in the interaction between antigen presenting and T cells, and in hematopoiesis.
European Journal of Immunology 02/2002; 32(2):494-501. DOI:10.1002/1521-4141(200202)32:2<494::AID-IMMU494>3.0.CO;2-Y · 4.52 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: CCR5 is a functional receptor for MIP-1alpha, MIP-1beta, RANTES (regulated on activation normal T cell expressed), MCP-2, and MCP-4 and constitutes the main coreceptor for macrophage tropic human and simian immunodeficiency viruses. By using CCR5-CCR2b chimeras, we have shown previously that the second extracellular loop of CCR5 is the major determinant for chemokine binding specificity, whereas the amino-terminal domain plays a major role for human immunodeficiency virus type 1 (HIV-1) and simian immunodeficiency virus coreceptor function. In the present work, by using a panel of truncation and alanine-scanning mutants, we investigated the role of specific residues in the CCR5 amino-terminal domain for chemokine binding, functional response to chemokines, HIV-1 gp120 binding, and coreceptor function. Truncation of the amino-terminal domain resulted in a progressive decrease of the binding affinity for chemokines, which correlated with a similar drop in functional responsiveness. Mutants lacking residues 2-13 exhibited fairly weak responses to high concentrations (500 nM) of RANTES or MIP-1beta. Truncated mutants also exhibited a reduction in the binding affinity for R5 Env proteins and coreceptor activity. Deletion of 4 or 12 residues resulted in a 50 or 80% decrease in coreceptor function, respectively. Alanine-scanning mutagenesis identified several charged and aromatic residues (Asp-2, Tyr-3, Tyr-10, Asp-11, and Glu-18) that played an important role in both chemokine and Env high affinity binding. The overlapping binding site of chemokines and gp120 on the CCR5 amino terminus, as well as the involvement of these residues in the epitopes of monoclonal antibodies, suggests that these regions are particularly exposed at the receptor surface.
[Show abstract][Hide abstract] ABSTRACT: The functional and structural characteristics of two previously described "loss-of-function" mutants of the thyrotropin receptor (TSHR) gene were analyzed by transient transfection in COS cells. Both mutations (Pro162Ala, Ile167Asn) are located in the putative extracellular hormone-binding domain of the receptor. The following parameters were analyzed: expression of native receptor on the cell surface (as measured by binding of labeled thyrotropin [TSH] to intact cells, or flow cytometry of intact cells); total TSHR expression (measured by flow cytometry of permeabilized cells); response to TSH measured as cyclic adenosine monophosphate (cAMP) accumulation. The total cellular expression of both mutant receptors was similar. Cell surface expression of Pro162A1a mutant was reduced about twofold and the EC50 for TSH stimulation was increased twofold. In contrast, the Ile167Asn mutant did not reach the cell surface and the intracellularly expressed mutant protein did not react with a monoclonal antibody (BA8) recognizing only the native TSHR. Based on the current model of the three-dimensional structure of the TSHR, the Pro162Ala substitution maps at the surface of the molecule, while the Ile167Asn mutation affects a residue whose side chain contributes to the hydrophobic core characteristic of proteins harboring leucine repeat motifs. These results are consistent with Ile167Asn causing a gross destabilization of receptor structure incompatible with its normal routing through the intracellular membrane system of the cell.
[Show abstract][Hide abstract] ABSTRACT: CCR5 was first characterized as a receptor for MIP-1alpha, MIP-1beta, and RANTES, and was rapidly shown to be the main coreceptor for M-tropic human immunodeficiency virus (HIV)-1 strains and simian immunodeficiency virus (SIV). Chemokines constitute a rapidly growing family of proteins and receptor-chemokine interactions are known to be promiscuous and redundant. We have therefore tested whether other CC-chemokines could bind to and activate CCR5. All CC-chemokines currently available were tested for their ability to compete with [(125)I]-MIP-1beta binding on a stable cell line expressing recombinant CCR5, and/or to induce a functional response in these cells. We found that in addition to MIP-1beta, MIP-1alpha, and RANTES, five other CC-chemokines could compete for [(125)I]-MIP-1beta binding: MCP-2, MCP-3, MCP-4, MCP-1, and eotaxin binding was characterized by IC(50) values of 0.22, 2.14, 5.89, 29.9, and 21.7 nmol/L, respectively. Among these ligands, MCP-3 had the remarkable property of binding CCR5 with high affinity without eliciting a functional response, MCP-3 could also inhibit the activation of CCR5 by MIP-1beta and may therefore be considered as a natural antagonist for CCR5. It was unable to induce significant endocytosis of the receptor. Chemokines that could compete with high affinity for MIP-1beta binding could also compete for monomeric gp120 binding, although with variable potencies; maximal gp120 binding inhibition was 80% for MCP-2, but only 30% for MIP-1beta. MCP-3 could compete efficiently for gp120 binding but was, however, found to be a weak inhibitor of HIV infection, probably as a consequence of its inability to downregulate the receptor.
[Show abstract][Hide abstract] ABSTRACT: CCR5 is the major coreceptor for macrophage-tropic human immunodeficiency virus type I (HIV-1). For most G-protein-coupled receptors that have been tested so far, the disulfide bonds linking together the extracellular loops (ECL) are required for maintaining the structural integrity necessary for ligand binding and receptor activation. A natural mutation affecting Cys20, which is thought to form a disulfide bond with Cys269, has been described in various human populations, although the consequences of this mutation for CCR5 function are not known. Using site-directed mutagenesis, we mutated the four extracellular cysteines of CCR5 singly or in combination to investigate their role in maintaining the structural conformation of the receptor, its ligand binding and signal transduction properties, and its ability to function as a viral coreceptor. Alanine substitution of any single Cys residue reduced surface expression levels by 40-70%. However, mutation of Cys101 or Cys178, predicted to link ECL1 and ECL2 of the receptor, abolished recognition of CCR5 by a panel of conformation sensitive anti-CCR5 antibodies. The effects of the mutations on receptor expression and conformation were partially temperature-sensitive, with partial restoration of receptor expression and conformation achieved by incubating cells at 32 degrees C. All cysteine mutants were unable to bind detectable levels of MIP-1beta, and did not respond functionally to CCR5 agonists. Surprisingly, all cysteine mutants did support infection by R5 strains of HIV, though at reduced levels. These results indicate that both disulfide bonds of CCR5 are necessary for maintaining the structural integrity of the receptor necessary for ligand binding and signaling. Env binding and the mechanisms of HIV entry appear much less sensitive to alterations of CCR5 conformation.
[Show abstract][Hide abstract] ABSTRACT: Whether they are of low or high histopathological grade, human astrocytic tumors are characterized by a marked propensity to diffuse into large areas of normal brain parenchyma. This invasion relates mainly to cell motility, which enables individual cell migration to take place. The present study characterizes in vitro the gastrin-mediated effects on both the growth (cell proliferation vs. cell death) and motility dynamics of the human U87 and U373 glioblastoma cell lines. A computer-assisted phase-contrast microscope was used to track the number of mitoses versus cell deaths every 4 min over a 72-h period and so to quantitatively describe the trajectories of living U373 and U87 cells growing on plastic supports in culture media both with and without the addition of 0.1, 5, or 100 nM gastrin. While 5 or 100 nM gastrin only weakly (p < .05 to p < .01) increased cell proliferation in the U87 cell line and not in U373 one, it very significantly (p < .001) inhibited the amount of cell death at 5 and 100 nM in both the U87 and U373 lines. In addition, 5 nM gastrin markedly inhibited cell mobility in U87 (p < .00001) and U373 (p < .0001) glioblastoma models. All these data strongly suggest that gastrin plays a major role in the biological behavior of the in vitro U87 and U373 human glioblastoma cell lines in matters concerning their levels of cell motility and growth dynamics.
Journal of Neurobiology 12/1998; 37(3):373-82. DOI:10.1002/(SICI)1097-4695(19981115)37:33.0.CO;2-H · 3.84 Impact Factor