One-step immunopurification and lectinochemical characterization of the Duffy atypical chemokine receptor from human erythrocytes

Duffy antigen/receptor for chemokines (DARC) is a glycosylated seven-transmembrane protein acting as a blood group antigen, a chemokine binding protein and a receptor for Plasmodium vivax malaria parasite. It is present on erythrocytes and endothelial cells of postcapillary venules. The N-terminal extracellular domain of the Duffy glycoprotein carries Fy(a)/Fy(b) blood group antigens and Fy6 linear epitope recognized by monoclonal antibodies. Previously, we have shown that recombinant Duffy protein expressed in K562 cells has three N-linked oligosaccharide chains, which are mainly of complex-type. Here we report a one-step purification method of Duffy protein from human erythrocytes. DARC was extracted from erythrocyte membranes in the presence of 1% n-dodecyl-β-D-maltoside (DDM) and 0.05% cholesteryl hemisuccinate (CHS) and purified by affinity chromatography using immobilized anti-Fy6 2C3 mouse monoclonal antibody. Duffy glycoprotein was eluted from the column with synthetic DFEDVWN peptide containing epitope for 2C3 monoclonal antibody. In this single-step immunoaffinity purification method we obtained highly purified DARC, which migrates in SDS-polyacrylamide gel as a major diffuse band corresponding to a molecular mass of 40-47 kDa. In ELISA purified Duffy glycoprotein binds anti-Duffy antibodies recognizing epitopes located on distinct regions of the molecule. Results of circular dichroism measurement indicate that purified DARC has a high content of α-helical secondary structure typical for chemokine receptors. Analysis of DARC glycans performed by means of lectin blotting and glycosidase digestion suggests that native Duffy N-glycans are mostly triantennary complex-type, terminated with α2-3- and α2-6-linked sialic acid residues with bisecting GlcNAc and α1-6-linked fucose at the core.

High-level production, solubilization and purification of synthetic human GPCR chemokine receptors CCR5, CCR3, CXCR4 and CX3CR1

Chemokine receptors belong to a class of integral membrane G-protein coupled receptors (GPCRs) and are responsible for transmitting signals from the extracellular environment. However, the structural changes in the receptor, connecting ligand binding to G-protein activation, remain elusive for most GPCRs due to the difficulty to produce them for structural and functional studies. We here report high-level production in E.coli of 4 human GPCRs, namely chemokine receptors (hCRs) CCR5, CCR3, CXCR4 and CX3CR1 that are directly involved in HIV-1 infection, asthma and cancer metastasis. The synthetic genes of CCR5, CCR3, CXCR4 and CX3CR1 were synthesized using a two-step assembly/amplification PCR method and inserted into two different kinds of expression systems. After systematic screening of growth conditions and host strains, TB medium was selected for expression of pEXP-hCRs. The low copy number pBAD-DEST49 plasmid, with a moderately strong promoter tightly regulated by L-arabinose, proved helpful for reducing toxicity of expressed membrane proteins. The synthetic Trx-hCR fusion genes in the pBAD-DEST49 vector were expressed at high levels in the Top10 strain. After a systematic screen of 96 detergents, the zwitterionic detergents of the Fos-choline series (FC9-FC16) emerged as the most effective for isolation of the hCRs. The FC14 was selected both for solubilization from bacterial lysates and for stabilization of the Trx-hCRs during purification. Thus, the FC-14 solubilized Trx-hCRs could be purified using size exclusion chromatography as monomers and dimers with the correct apparent MW and their alpha-helical content determined by circular dichroism. The identity of two of the expressed hCRs (CCR3 and CCR5) was confirmed using immunoblots using specific monoclonal antibodies. After optimization of expression systems and detergent-mediated purification procedures, we achieved large-scale, high-level production of 4 human GPCR chemokine receptor in a two-step purification, yielding milligram quantities of CCR5, CCR3, CXCR4 and CX3CR1 for biochemical, biophysical and structural analysis.

Molecular Cloning and Characterization of a Highly Selective Chemokine-binding Protein from the Tick Rhipicephalus sanguineus

Ticks are blood-feeding parasites that secrete a number of immuno-modulatory factors to evade the host immune response. Saliva isolated from different species of ticks has recently been shown to contain chemokine neutralizing activity. To characterize this activity, we constructed a cDNA library from the salivary glands of the common brown dog tick, Rhipicephalus sanguineus. Pools of cDNA clones from the library were transfected into HEK293 cells, and the conditioned media from the transfected cells were tested for chemokine binding activity by chemical cross-linking to radiolabeled CCL3 followed by SDS-PAGE. By de-convolution of a single positive pool of 270 clones, we identified a full-length cDNA encoding a protein of 114 amino acids, which after signal peptide cleavage was predicted to yield a mature protein of 94 amino acids that we called Evasin-1. Recombinant Evasin-1 was produced in HEK293 cells and in insect cells. Using surface plasmon resonance we were able to show that Evasin-1 was exquisitely selective for 3 CC chemokines, CCL3 and CCL4 and the closely related chemokine CCL18, with K(D) values of 0.16, 0.81, and 3.21 nm, respectively. The affinities for CCL3 and CCL4 were confirmed in competition receptor binding assays. Analysis by size exclusion chromatography demonstrated that Evasin-1 was monomeric and formed a 1:1 complex with CCL3. Thus, unlike the other chemokine-binding proteins identified to date from viruses and from the parasitic worm Schistosoma mansoni, Evasin-1 is highly specific for a subgroup of CC chemokines, which may reflect a specific role for these chemokines in host defense against parasites.

Solubilization, stabilization, and purification of chemokine receptors using biosensor technology

Establishing solubilization conditions for membrane-associated receptors is often a tedious empirical process. Here we describe a novel application of SPR biosensor technology to screen solubilization conditions automatically and to assess receptor activity directly. We focus on two chemokine receptors, CXCR4 and CCR5, which are important in HIV cell invasion. The autosampler in Biacore 3000 permitted whole cells expressing C-terminally tagged receptors to be automatically lysed under a given solubilization condition and the lysates to be injected over an antibody surface. The total amount of solubilized receptor could be quantitated from the antibody capture level, whereas the amount of active receptor could be quantitated using a subsequent injection of conformationally sensitive antibody or protein. Using this approach, we identified detergent/lipid/buffer combinations that enhanced and maintained receptor activity. We also used the biosensor to demonstrate CD4-dependent binding of gp120 to solubilized CCR5 and to develop affinity chromatography-based purification methods that increased receptor activity more than 300%. Together, these results illustrate the benefits of using the biosensor as a tool for isolating functional membrane receptors and for analyzing ligand/receptor interactions.

Purification and biochemical characterization of the D6 chemokine receptor

There is much interest in chemokine receptors as therapeutic targets in diseases such as AIDS, autoimmune and inflammatory disorders, and cancer. Hampering such studies is the lack of accurate three-dimensional structural models of these molecules. The CC-chemokine receptor D6 is expressed at exceptionally high levels in heterologous transfectants. Here we report the purification and biochemical characterization of milligram quantities of D6 protein from relatively small cultures of transfected mammalian cells. Importantly, purified D6 retains full functional activity, shown by displaceable binding of 125I-labelled MIP-1beta (macrophage inflammatory protein-1beta) and by complete binding of the receptor to a MIP-1alpha affinity column. In addition, we show that D6 is decorated on the N-terminus by N-linked glycosylation. Mutational analysis reveals that this glycosylation is dispensable for ligand binding and high expression in transfected cells. Metabolic labelling has revealed the receptor to also be sulphated and phosphorylated. Phosphorylation is ligand independent and is not enhanced by ligand binding and internalization, suggesting similarities with the viral chemokine receptor homologue US28. Like US28, an analysis of the full cellular complement of D6 in transfected cells indicates that >80% is found associated with intracellular vesicular structures. This may account for the high quantities of D6 that can be synthesized in these cells. These unusual properties of D6, and the biochemical characterization described here, leads the way towards work aimed at generating the three-dimensional structure of this seven-transmembrane-spanning receptor.

C5a mutants are potent antagonists of the C5a receptor (CD88) and of C5L2: position 69 is the locus that determines agonism or antagonism

The anaphylatoxin C5a exerts a plethora of biologic activities critical in the pathogenesis of systemic inflammatory diseases. Recently, we reported on a C5a mutant, jun/fos-A8, as a potent antagonist for the human and mouse C5a receptor (CD88). Addressing the molecular mechanism accounting for CD88 receptor antagonism by site-directed mutagenesis, we found that a positively charged amino acid at position 69 is crucial. Replacements by either hydrophobic or negatively charged amino acids switched the CD88 antagonist jun/fos-A8 to a CD88 agonist. In addition to CD88, the seven-transmembrane receptor C5L2 has recently been found to provide high affinity binding sites for C5a and its desarginated form, C5adesArg74. A jun/fos-A8 mutant in which the jun/ fos moieties and amino acids at positions 71-73 were deleted, A8Delta71-73, blocked C5a and C5adesArg74 binding to CD88 and C5L2. In contrast, the cyclic C5a C-terminal analog peptide AcF-[OP-d-ChaWR] inhibited binding of the two anaphylatoxins to CD88 but not to C5L2, suggesting that the C5a core segment is important for high affinity binding to C5L2. Both receptors are coexpressed on human monocytes and the human mast cell line HMC-1; however, C5L2 expression on monocytes is weaker as compared with HMC-1 cells and highly variable. In contrast, no C5L2 expression was found on human neutrophils. A8Delta71-73 is the first antagonist that blocks C5a and C5adesArg74 binding to both C5a receptors, CD88 and C5L2, making it a valuable tool for studying C5L2 functions and for blocking the biological activities of C5a and C5adesArg74 in mice and humans.

Identification of keratinocyte proteins that mark subsets of cells in the epidermal stratum basale: comparisons with the intestinal epithelium

Rapid renewing epithelia such as the epidermis and the intestinal epithelium are maintained by proliferation of undifferentiated stem cells located at specific locations. Recent experiments indicate that stem cells from adult organs might be able to populate tissues other than their tissue of origin. Such findings open the possibility that adult stem cells from different tissues might share common markers. We investigated this by two different approaches. In a first approach we compared the expression profiles from epidermal and intestinal epithelial cells at various stages of differentiation. We found that 108 of 1,176 genes analyzed were expressed above background in either keratinocytes or enterocytes and, among these, only 16 genes were expressed in both cell types. Of these 16 genes expressed in both cell types, only five displayed the same shift in expression level during cellular differentiation. Interestingly, all five genes were downregulated during cellular differentiation and represented ubiquitously expressed genes. In the second approach we analyzed the expression of the CC chemokine receptor 6 (CCR6), which we have recently identified as an early differentiation marker of epidermal cells, in the intestine. This analysis demonstrates that the CCR6 protein is found in enterocytes at later stages of differentiation.

Variations in eosinophil chemokine responses: an investigation of CCR1 and CCR3 function, expression in atopy, and identification of a functional CCR1 promoter

We previously showed in a small group of donors that eosinophils from a subgroup of individuals responded equipotently to CC chemokine ligand (CCL)11/eotaxin and CCL3/macrophage-inflammatory protein-1alpha in assays of eosinophil shape change (CCL3/macrophage-inflammatory protein-1alpha-highly responsive (MHR) donors). In this study, we investigated the functional role of CCL3 in eosinophil responses in 73 donors. MHR donors, identified by their eosinophil shape change responses, represented approximately 19% of the donor pool. Eosinophils from these donors showed increased eosinophil CCR1 expression and also underwent CCL3-mediated chemotaxis and up-regulation of CD11b. All MHR donors gave a history of atopy-associated diseases. In a further study, we prospectively recruited 110 subjects, subdivided into nonatopics or atopics, and investigated expression of CCR1 and CCR3 on eosinophils, basophils, monocytes, and neutrophils. Eosinophil CCR1 expression was non-normally distributed in atopics, although higher CCR1 expression levels were not predictive of a diagnosis of atopy or atopic disease. We identified the CCR1 promoter and investigated its function. We found a minimal promoter within 177 bp of the transcription start site, and an upstream enhancer region that facilitated expression in leukocyte cell lines. Collectively, these data demonstrate that MHR individuals form an important subgroup that, when associated with a diagnosis of allergic disease, may require tailored therapy to modulate eosinophil recruitment. Identification of a functional CCR1 promoter will facilitate the study of possible genetic determinants underlying this potentially important clinical phenotype.

Molecular cloning and functional characterization of Cynomolgus monkey (Macaca fascicularis) CC chemokine receptor, CCR3

We have cloned and performed the first functional characterization of the chemokine receptor, CCR3, of Cynomolgus monkey (Macaca fascicularis). The deduced amino acid sequence of the cloned Cynomolgus CCR3 was found to be more similar to that of a previously-reported Rhesus (Macaca mulatta) CCR3 (99.4%) than that of a reported Cynomolgus CCR3 (98.0%). Stably-transfected Cynomolgus CCR3 bound human eotaxin (CCL11) with similar kinetics (Kd 240 pM) and was responsive to human CCR3 ligands (eotaxin [CCL11], eotaxin-2 [CCL24], and MCP4 [CCL13]) in Ca(2+) mobilization and chemotaxis assays, thus provides a useful alternative species model system for the analysis of modulators of eotaxin--CCR3 induced signaling and activation.

Functional expression of chemokine receptor 2 by normal human eosinophils

BACKGROUND

Within the granulocytes, the CC chemokines preferentially activate basophils and eosinophils on binding to chemokine receptors (CCRs). In vivo administration of neutralizing anti-monocyte chemoattractant protein 1 (MCP-1) antibodies can block accumulation of eosinophils in the lungs of antigen-challenged animals.

OBJECTIVE

We studied a panel of chemokines for chemotactic activity in normal human eosinophils from healthy donors with a special focus on MCP-1, identified the respective receptor required for the biological response of eosinophils, and investigated mediators used for signal transduction.

METHODS

Cells were enriched by magnetic cell sorting. Receptor expression in eosinophils was shown by RT-PCR and fluorescence-activated cell sorting. The biological response was tested in chemotaxis and calcium mobilization assays.

RESULTS

Eosinophils have detectable mRNA for CCR2, and the receptor protein is expressed on cell surfaces. MCP-1 induces chemotaxis and calcium mobilization in eosinophils. The chemotactic activity of MCP-1 revealed a double-peaked dose-response curve; one of the peaks is abolished by addition of a blocking antibody to CCR2, but it is insensitive to blocking of CCR1 or CCR3. Specific enzyme inhibitors ruled out signaling characteristics of CCR2 in eosinophils.

CONCLUSION

Normal human eosinophils express functional CCR2 on cell surfaces.

Chemokine receptor expression profile of eosinophils at inflamed tissue sites: Decreased CCR3 and increased CXCR4 expression by lung eosinophils

BACKGROUND

To date, most studies dealing with eosinophil chemokine receptors have used eosinophils isolated from peripheral blood. During the movement of eosinophils from the peripheral blood to inflamed tissue sites, microenvironmental signals might alter their expression of chemokine receptors. However, little is known about the profile of expression of chemokine receptors by eosinophils at inflamed tissue sites in human beings.

OBJECTIVE

The purpose of this study was to determine whether eosinophils that have migrated into inflamed tissues exhibit a profile of chemokine receptor expression that is qualitatively and/or quantitatively different from that of eosinophils in peripheral locations.

METHODS

We studied simultaneously the expression and function of chemokine receptors in eosinophils in both bronchoalveolar lavage fluid (BALF) and peripheral blood specimens of 7 patients with eosinophilic lung diseases.

RESULTS

De novo expression of CCR2, CCR4, and CCR5 was not detected at either the protein or the mRNA level. However, surface expression of CCR3 was decreased and CXCR4 was conversely increased with statistical significance in BALF eosinophils. Moreover, the changes in CCR3 and CXCR4 expression were reflected in the altered migratory response to their ligands. On the other hand, the levels of CXCR1, CXCR2, CXCR3, and CCR1 were virtually unchanged in BALF eosinophils, and these receptors did not have functional significance.

CONCLUSION

Eosinophils at inflamed tissue sites exhibited an expression profile qualitatively similar to that in peripheral locations, except for decreased CCR3 and increased CXCR4 expression. Our results suggest that CCR3 is primarily and CXCR4 is cooperatively involved in eosinophil accumulation at inflamed tissue sites.

Chemokine receptor expression by human syncytiotrophoblast

Despite their potential importance in placental HIV infection and placental immune function, nothing is known about the expression of chemokine receptors by human syncytiotrophoblast cells. Immunocytochemical analysis revealed that primary cultures of term syncytiotrophoblast cells express CCR1, CCR3, CXCR4, and CCR6. Immunohistochemical examination of cryosections of term placental villous tissue confirmed the expression of CCR3, CXCR4, and CCR6 by trophoblast cells. The primary syncytiotrophoblast cultures showed no reactivity with antibodies against CCR5. In the villous tissue sections, CCR5 was detected in stromal cells and blood vessel walls but was not found in trophoblast cells. RT-PCR analysis of RNA extracted from cultured syncytiotrophoblast cells confirmed that the cells express message for CCR1, CCR3, CXCR4, CCR6 and CCR10. No transcripts corresponding to CCR2b, CCR5, or CCR8 were detected. Other experiments showed that exposure of syncytiotrophoblast cells to soluble SDF-1alpha elicited a calcium mobilization response, consistent with the expression of functional CXCR4. Thus, human syncytiotrophoblast cells express CXCR4, a known co-receptor for TCL-tropic HIV-1 isolates but do not express CCR5, the major co-receptor for M-tropic isolates. In addition to implications for the maternal-fetal transmission of HIV, the expression of chemokine receptors by syncytiotrophoblast cells could be important in other aspects of placental immune function.

Cutting edge: identification of the orphan receptor G-protein-coupled receptor 2 as CCR10, a specific receptor for the chemokine ESkine

A number of orphan G-protein coupled receptors (GPR) have been reported as putative chemokine receptors. One previously reported orphan receptor is an incomplete PCR clone, called GPR2. Here we report the cloning of full-length human (h)GPR2 and mouse (m)GPR2 cDNAs, and the identification of GPR2 as a receptor for a novel CC chemokine called ESkine. hGPR2 is expressed at high levels in testis and small intestine, and at lower levels in other tissues. mGPR2 was expressed at high levels in small intestine, colon, lymph nodes, and Peyer's patches and at lower levels in thymus and spleen. Stimulation of L1.2/hGPR2 transfectants with hESkine induced their migration and resulted in intracellular calcium mobilization. These results provide evidence that GPR2 is a specific receptor for ESkine. We propose that GPR2 be renamed as CCR10. The expression pattern of mGPR2/CCR10 suggests that it may play a role in the homing/trafficking of leukocytes within intestinal and lymphoid environments.

Cutting edge: identification of a novel chemokine receptor that binds dendritic cell- and T cell-active chemokines including ELC, SLC, and TECK

Searching for new receptors of dendritic cell- and T cell-active chemokines, we used a combination of techniques to interrogate orphan chemokine receptors. We report here on human CCX CKR, previously represented only by noncontiguous expressed sequence tags homologous to bovine PPR1, a putative gustatory receptor. We employed a two-tiered process of ligand assignment, where immobilized chemokines constructed on stalks (stalkokines) were used as bait for adhesion of cells expressing CCX CKR. These cells adhered to stalkokines representing ELC, a chemokine previously thought to bind only CCR7. Adhesion was abolished in the presence of soluble ELC, SLC (CCR7 ligands), and TECK (a CCR9 ligand). Complete ligand profiles were further determined by radiolabeled ligand binding and competition with >80 chemokines. ELC, SLC, and TECK comprised high affinity ligands (IC50 <15 nM); lower affinity ligands include BLC and vMIP-II (IC50 <150 nM). With its high affinity for CC chemokines and homology to CC receptors, we provisionally designate this new receptor CCR10.

CCR9A and CCR9B: two receptors for the chemokine CCL25/TECK/Ck beta-15 that differ in their sensitivities to ligand

We isolated cDNAs for a chemokine receptor-related protein having the database designation GPR-9-6. Two classes of cDNAs were identified from mRNAs that arose by alternative splicing and that encode receptors that we refer to as CCR9A and CCR9B. CCR9A is predicted to contain 12 additional amino acids at its N terminus as compared with CCR9B. Cells transfected with cDNAs for CCR9A and CCR9B responded to the chemokine CC chemokine ligand 25 (CCL25)/thymus-expressed chemokine (TECK)/chemokine beta-15 (CK beta-15) in assays for both calcium flux and chemotaxis. No other chemokines tested produced responses specific for the cDNA-transfected cells. mRNA for CCR9A/B is expressed predominantly in the thymus, coincident with the expression of CCL25, and highest expression for CCR9A/B among thymocyte subsets was found in CD4+CD8+ cells. mRNAs encoding the A and B forms of the receptor were expressed at a ratio of approximately 10:1 in immortalized T cell lines, in PBMC, and in diverse populations of thymocytes. The EC50 of CCL25 for CCR9A was lower than that for CCR9B, and CCR9A was desensitized by doses of CCL25 that failed to silence CCR9B. CCR9 is the first example of a chemokine receptor in which alternative mRNA splicing leads to proteins of differing activities, providing a mechanism for extending the range of concentrations over which a cell can respond to increments in the concentration of ligand. The study of CCR9A and CCR9B should enhance our understanding of the role of the chemokine system in T cell biology, particularly during the stages of thymocyte development.

Pertussis toxin-sensitive signal controls the trafficking of thymocytes across the corticomedullary junction in the thymus

We investigated a role of chemokines in thymocyte trafficking. Genes encoding stromal cell-derived factor-1 and its receptor CXCR4 were detected in the cortex by in situ hybridization. Early immigrant cells did not express CXCR4, whereas their descendant CD44+CD25+CD4-CD8- cells did. CXCR4 expression was down-modulated when CD4+CD8+ double-positive cells became CD4+CD8- or CD4-CD8+ single-positive (SP) cells. Positively selected CD69+CD3intermediate cells gained CCR4, of which ligand, thymus activation-regulated chemokine, was expressed in the medulla. At the next developmental stage, CD69-CD3high cells lost CCR4 but gained CCR7. These results suggest that thymocytes use different chemokines along with their development. Blockade of chemokine receptor-mediated signaling by pertussis toxin perturbed the normal distribution of SP cells and resulted in the accumulation of SP cells in the cortex. Thus, a pertussis toxin-sensitive event controls the trafficking of SP cells across the corticomedullary junction.

Macrophage-inflammatory protein-1alpha receptor expression on normal and chronic myeloid leukemia CD34+ cells

We have assessed expression of MIP-1alpha binding sites on the surface of CD34+ cells from normal bone marrow (NBM) and chronic myeloid leukemia (CML) peripheral blood. This study has highlighted a small subpopulation of CD34+ (15.7 +/- 6.2% in NBM and 9 +/- 4% in CML), which has specific macrophage-inflammatory protein-1alpha (MIP-1alpha) cell surface binding sites. Further phenotypic characterization of the receptor-bearing cells has shown that they do not express the Thy-1 Ag, suggesting that they are committed progenitor cells rather than CD34+ Thy+ stem cells. However, more than 80% of methanol-fixed CD34+ cells do bind MIP-1alpha, suggesting that these cells may possess a pool of internal receptors, although we were unable to induce cell surface expression by cytokine stimulation. The percentage of these CD34+, MIP-1alpha-R+ cells present in the CD34 compartment of NBM is significantly higher than in CML, implicating lack of binding sites as part of the mechanism for the loss of response to this chemokine seen in CML. Specific Ab to the MIP-1alpha receptor implicated in HIV infection, CCR5, revealed that very few CD34+ cells expressed these receptors and that expression was confined to the CD34+ Thy- progenitor population. Data presented in this work suggest that active binding sites for the stem cell growth inhibitor MIP-1alpha are not constitutively expressed on the surface of most resting primitive multipotent cells, and that these cells are not potential targets for HIV-1 infection through CCR5.

Identification of amino acids involved in the binding of hMIP-1 alpha to CC-CKR1, a MIP-1 alpha receptor found on neutrophils

Human macrophage inflammatory protein-1alpha (hMIP-1alpha) and human macrophage inflammatory protein-1beta (hMIP-1beta) are chemokines involved in a diverse range of immunological effects. Both hMIP-1alpha and hMIP-1beta are involved in the activation of monocytes and THP-1 cells probably through a common receptor(s). However, only hMIP-1alpha can bind to neutrophils with high affinity, presumably through CC-CKR1 (CKR1). Since the structure of these two proteins is highly conserved, non-conserved amino acids must define the disparate binding patterns that these two proteins exhibit. Measurements of binding, chemotaxis and calcium influx conducted with hMIP-1alpha and hMIP-1beta chimeric proteins and mutants show that two amino acids (37K and 43L) are important in the binding and signaling of hMIP-1alpha through CKR1. Furthermore, we also show that mutations of the three charged amino acids at the C-terminus of hMIP-1alpha and hMIP-1beta (amino acids 61, 65 and 67), do not adversely affect the binding to THP-1 cells.

Cloning of two chemokine receptor homologs (CXC-R4 and CC-R7) in rainbow trout Oncorhynchus mykiss

Two rainbow trout chemokine receptors have been sequenced, with homology to CXC-R4 and CC-R7 molecules. The CXC-R4 sequence consisted of 1681 nucleotides, which translated into a mature protein of 357 amino acids, with 80.7% similarity to human CXC-R4. The CC-R7 sequence consisted of 2287 nucleotides, which translated into a 368-amino acid mature protein with 64.5% similarity to human CC-R7. Both sequences contained seven hydrophobic regions, representing the seven transmembrane domains (TM) typical of G-protein-coupled receptors. Extracellular cysteines, transmembrane prolines, and the DRY motif immediately following TM3 were conserved. Phylogenetic tree analysis revealed a tight clustering of trout CXC-R4 with CXC-R3-5 genes. Trout CC-R7 clustered with CC-R6-7 and CXC-R1-2. Reverse transcriptase-polymerase chain reaction analysis demonstrated a wide tissue distribution of CXC-R4 and CC-R7 message in trout, being present in head-kidney leukocytes, blood, gill, brain, spleen, and liver.

Identification of CCR8 as the specific receptor for the human beta-chemokine I-309: cloning and molecular characterization of murine CCR8 as the receptor for TCA-3

Chemokine receptor-like 1 (CKR-L1) was described recently as a putative seven-transmembrane human receptor with many of the structural features of chemokine receptors. To identify the ligand of CKR-L1, we have studied chemokine-induced calcium mobilization in 293 cells transfected with CKR-L1. Of 20 different chemokines tested, only I-309 was able to elicit a significant calcium mobilization. In addition, I-309 induced the transfectants to migrate in vitro. As expected for chemokine receptor-mediated effects, pertussis toxin, but not cholera toxin, inhibited both the calcium flux and migration of the CKR-L1 transfectants in response to I-309. All of these data support the conclusion that I-309 is a functional ligand for CKR-L1. According to the current chemokine receptor nomenclature, we have designated this gene as CCR8. The murine CCR8 (mCCR8) gene was cloned, and its predicted amino acid sequence showed a 71% identity with that of human CCR8. As human CCR8, mCCR8 is expressed in thymus. Both I-309 and its murine homologue TCA-3 were able to induce calcium mobilization in transiently transfected 293-EBNA cells expressing mCCR8. The affinity of the binding of 125I-labeled TCA-3 to mCCR8 was high (Kd approximately 2 nM); the binding was prevented completely by an excess of cold TCA-3, and only partially competed (40%) by I-309. The identification of I-309 and TCA-3 as the functional ligands for CCR8 receptors will help to unravel the role of these proteins in physiologic and pathologic situations.