Structure and expression of two highly related genes encoding SCM-1/human lymphotactin

Upregulated X-C motif chemokine ligand 2 (XCL2) is associated with poor prognosis and increased immune infiltration in clear cell renal cell carcinoma

BACKGROUND

Clear cell renal cell carcinoma (ccRCC) is one of the most popular malignant carcinomas in the genitourinary system. As a novel tumor-related gene, X-C Motif Chemokine Ligand 2 (XCL2) was up-regulated in ccRCC. The current study aims to reveal the functional activity of XCL2 in ccRCC.

METHODS

The transcriptome profiling, clinical parameters, and simple nucleotide variation profiles of ccRCC samples were obtained from the Cancer Genome Atlas (TCGA) database. The survival analysis, multivariate/univariate Cox analysis, correlation analysis, gene set enrichment analysis (GSEA), and tumor mutation burden (TMB) analysis were performed. Next, immune cell infiltration and immune functions were analyzed. Finally, the functions of XCL2 were investigated in Caki-1 and 786-O cells.

RESULTS

Upregulated XCL2 was associated with worse overall survival of ccRCC and correlated to age, grade, stage, and T stage. Age, grade, and XCL2 were independent prognostic factors. Significant enrichment in apoptosis, DNA replication, and immune response was demonstrated by GSEA. XCL2 was not only tightly associated with immune cell infiltration, but also significantly linked with several immune functions. Moreover, patients, who had higher XCL2 expression, owned higher levels of TMB. Interestingly, XCL2 was positively correlated with common immune checkpoints. In vitro, XCL2 could inhibit apoptosis, and promote proliferation, migration, invasion, and epithelial-mesenchymal transition (EMT) of Caki-1 and 786-O cells.

CONCLUSIONS

In general, the current study suggested that XCL2 may participate in the progression of ccRCC. Importantly, XCL2 may be a potential new target of immunotherapy.

Role of Chemokines in the Pathogenesis of Visceral Leishmaniasis

Abstract:

Visceral leishmaniasis (VL; also known as kala-azar), caused by the protozoan parasite Leishmania donovani is characterized by the inability of the host to generate an effective immune response. The manifestations of the disease depends on involvement of various immune components such as activation of macrophages, cell mediated immunity, secretion of cytokines and chemokines, etc. Macrophages are the final host cells for Leishmania parasites to multiply, and they are the key to a controlled or aggravated response that leads to clinical symptoms. The two most common macrophage phenotypes are M1 and M2. The pro-inflammatory microenvironment (mainly by IL-1β, IL-6, IL-12, IL-23, and TNF-α cytokines) and tissue injury driven by classically activated macrophages (M1-like) and wound healing driven by alternatively activated macrophages (M2-like) in an anti-inflammatory environment (mainly by IL-10, TGF-β, chemokine ligand (CCL)1, CCL2, CCL17, CCL18, and CCL22). Moreover, on polarized Th cells, chemokine receptors are expressed differently. Typically, CXCR3 and CCR5 are preferentially expressed on polarized Th1 cells, whereas CCR3, CCR4 and CCR8 have been associated with the Th2 phenotype. Further, the ability of the host to produce a cell-mediated immune response capable of regulating and/or eliminating the parasite is critical in the fight against the disease. Here, we review the interactions between parasites and chemokines and chemokines receptors in the pathogenesis of VL.

Role of chemokines in hepatocellular carcinoma (Review)

Hepatocellular carcinoma (HCC) is a prevalent malignant tumor worldwide, with an unsatisfactory prognosis, although treatments are improving. One of the main challenges for the treatment of HCC is the prevention or management of recurrence and metastasis of HCC. It has been found that chemokines and their receptors serve a pivotal role in HCC progression. In the present review, the literature on the multifactorial roles of exosomes in HCC from PubMed, Cochrane library and Embase were obtained, with a specific focus on the functions and mechanisms of chemokines in HCC. To date, >50 chemokines have been found, which can be divided into four families: CXC, CX3C, CC and XC, according to the different positions of the conserved N‑terminal cysteine residues. Chemokines are involved in the inflammatory response, tumor immune response, proliferation, invasion and metastasis via modulation of various signaling pathways. Thus, chemokines and their receptors directly or indirectly shape the tumor cell microenvironment, and regulate the biological behavior of the tumor. In addition, the potential application of chemokines in chemotaxis of exosomes as drug vehicles is discussed. Exosomes containing chemokines or expressing receptors for chemokines may improve chemotaxis to HCC and may thus be exploited for targeted drug delivery.

Role of inflammatory chemokines in hypertension

Hypertension is associated with immune cells activation and their migration into the kidney, vasculature, heart and brain. These inflammatory mechanisms are critical for blood pressure regulation and mediate target organ damage, creating unique novel targets for pharmacological modulation. In response to angiotensin II and other pro-hypertensive stimuli, the expression of several inflammatory chemokines and their receptors is increased in the target organs, mediating homing of immune cells. In this review, we summarize the contribution of key inflammatory chemokines and their receptors to increased accumulation of immune cells in target organs and effects on vascular dysfunction, remodeling, oxidative stress and fibrosis, all of which contribute to blood pressure elevation. In particular, the role of CCL2, CCL5, CXCL8, CXCL9, CXCL10, CXCL11, CXCL16, CXCL1, CX3CL1, XCL1 and their receptors in the context of hypertension is discussed. Recent studies have tested the efficacy of pharmacological or genetic targeting of chemokines and their receptors on the development of hypertension. Promising results indicate that some of these pathways may serve as future therapeutic targets to improve blood pressure control and prevent target organ consequences including kidney failure, heart failure, atherosclerosis or cognitive impairment.

Rat cytomegalovirus-encoded γ-chemokine vXCL1 is a highly adapted, species-specific agonist for rat XCR1-positive dendritic cells

Dendritic cells (DCs) expressing the chemokine receptor XCR1 are specialized in antigen cross-presentation to control infections with intracellular pathogens. XCR1-positive (XCR1⁺) DCs are attracted by XCL1, a γ-chemokine secreted by activated CD8⁺ T cells and natural killer cells. Rat cytomegalovirus (RCMV) is the only virus known to encode a viral XCL1 analog (vXCL1) that competes for XCR1 binding with the endogenous chemokine. Here we show that vXCL1 from two different RCMV strains, as well as endogenous rat XCL1 (rXCL1) bind to and induce chemotaxis exclusively in rat XCR1⁺ DCs. Whereas rXCL1 activates the XCR1 Gi signaling pathway in rats and humans, both of the vXCL1s function as species-specific agonists for rat XCR1. In addition, we demonstrate constitutive internalization of XCR1 in XCR1-transfected HEK293A cells and in splenic XCR1⁺ DCs. This internalization was independent of β-arrestin 1 and 2 and was enhanced after binding of vXCL1 and rXCL1; however, vXCL1 appeared to be a stronger agonist. These findings suggest a decreased surface expression of XCR1 during DC cultivation at 37°C, and subsequent impairment of chemotactic activity and XCR1⁺ DC function.

Transcriptomic analyses of chemokines reveal that down-regulation of XCR1 is associated with advanced hepatocellular carcinoma

Chemokines are essential coordinators of cellular migration and cell-cell interactions, therefore considerable attention has been paid to the application of chemokines to cancer immunotherapy. In this study, we screened for the expression levels of 58 human chemokines/chemokine receptors in hepatocellular carcinoma (HCC) by using samples from the TCGA LIHC cohort and found 16 consistently down-regulated and 11 up-regulated chemokine genes in HCC compared with normal samples. Furthermore, the expressions of XCR1 were verified by Western blot in liver cancer cell lines. We used CCK8, plate cloning formation, scratch-wound and transwell analysis to measure the ability of proliferation, metastasis and invasion, respectively. Protein expression was analyzed by cell immunofluorescence and western-blot. We found that silencing XCR1 promoted, while overexpressing XCR1 inhibited, HCC cell migration and invasion in vitro, its mechanism may involve in inhibition of Epithelial Mesenchymal Transition (EMT). However, the overexpression of XCR1 in HCCLM3 in vitro can restrain the growth partially due to the inhibition of MAPK and PI3K/AKT signaling pathway. Gene Set Enrichment Analysis (GSEA) showed that high expression of XCR1 is positively associated with EMT, which is closely associated with tumor migration and invasion. Our study provides the basis for further investigation of the molecular mechanism by which down-regulation of XCR1 promotes the development and progression of HCC.

Cytokine Expression of Stem Cells Originating from the Apical Complex and Coronal Pulp of Immature Teeth

INTRODUCTION

The aim of this study was to measure and compare the expression levels of cytokines from developing apical complex cells (DACCs) and dental pulp stem cells (DPSCs) of the immature tooth.

METHODS

DPSC-conditioned medium (CM) and DACCs-CM were obtained from human young teeth, and 174 cytokines secreted from each CM were identified and compared. A cytokine membrane array and enzyme-linked immunosorbent assay were used to measure and compare the expression levels of the cytokines. Immunocytochemistry targeting insulin-like growth factor-1 and neurotrophin-3 was additionally performed.

RESULTS

There were statistically significant differences in the expression levels of 25 cytokines: 22 and 3 were expressed more strongly in DPSCs-CM and DACCs-CM, respectively. Odontoblast differentiation-related cytokines were more strongly expressed in DPSCs-CM, while cell-proliferation-related cytokines were more strongly expressed in DACCs-CM. Proinflammatory and anti-inflammatory cytokines were predominantly expressed in DPSCs-CM and DACCs-CM, respectively.

CONCLUSIONS

DPSCs may exert a stronger paracrine effect than DACCs on regeneration of the dentin-pulp complex, in terms of odontoblast differentiation.

A Novel α9 Integrin Ligand, XCL1/Lymphotactin, Is Involved in the Development of Murine Models of Autoimmune Diseases

The integrin α9β1 is a key receptor involved in the development of autoimmune diseases. However, the detailed mechanism for the association of α9β1 integrin with its ligands remains unclear. In this study, we introduce XCL1/lymphotactin, a member of the chemokine family, as a novel ligand for α9 integrin. Using α9 integrin-overexpressing NIH3T3 cells and endogenously α9 integrin-expressing human rhabdomyosarcoma cells, the interaction between XCL1 and α9 integrin was confirmed by pull-down assays. XCL1 enhanced α9 integrin-dependent cell migration of these cells, thus acting on α9 integrin as a chemoattractant. We also analyzed the in vivo function of XCL1 in the development of anti-type II collagen Ab-induced inflammatory arthritis (CAIA) in BALB/c mice and experimental autoimmune encephalomyelitis in C57BL/6 mice, because α9 integrin is involved in these autoimmune disease models. In CAIA, recombinant XCL1 aggravated the disease and this exacerbation was inhibited by an anti-α9 integrin Ab. An XCL1-neutralizing Ab produced in this study also ameliorated CAIA. Furthermore, the XCL1-neutralizing Ab abrogated the disease progression in experimental autoimmune encephalomyelitis. Therefore, to our knowledge this study provides the first in vitro and in vivo evidence that the interaction between XCL1 and α9 integrin has an important role for autoimmune diseases.

Progress in research on C-chemokine XCL1

XCL1, also known as lymphotactin, is the only known member of the C-type-chemokine family, which is produced mainly by CD8⁺ T cells and natural killer cells. XCL1 has a unique amino acid sequence feature and two interchangeable conformations, which makes XCL1 different from other chemokines in structure and function. The XCL1-specific receptor, XCR1, is a member of the G-protein-coupled receptor family and plays an important role in the negative selection of T cells in the thymus and in the initiation of cross-antigen presentation and mediation of cytotoxic immune responses. XCL1 can regulate the balance of the immune system and maintain intestinal immune homeostasis, and it is involved in a variety of diseases such as autoimmune diseases, nephritis, tuberculosis and human immunodeficiency virus infection. In recent years, the selective expression of XCR1 on CD8⁺ DCs with strong cross antigen-presention ability has been proved, which has led to studies using XCL1 for mucosal immunization, antitumor immunotherapy and targeted vaccine development.

A Requirement for Metamorphic Interconversion in the Antimicrobial Activity of Chemokine XCL1

Chemokines make up a superfamily of ∼50 small secreted proteins (8-12 kDa) involved in a host of physiological processes and disease states, with several previously shown to have direct antimicrobial activity comparable to that of defensins in efficacy. XCL1 is a unique metamorphic protein that interconverts between the canonical chemokine fold and a novel all-β-sheet dimer. Phylogenetic analysis suggests that, within the chemokine family, XCL1 is most closely related to CCL20, which exhibits antibacterial activity. The in vitro antimicrobial activity of WT-XCL1 and structural variants was quantified using a radial diffusion assay (RDA) and in solution bactericidal assays against Gram-positive and Gram-negative species of bacteria. Comparisons of WT-XCL1 with variants that limit metamorphic interconversion showed a loss of antimicrobial activity when restricted to the conserved chemokine fold. These results suggest that metamorphic folding of XCL1 is required for potent antimicrobial activity.

Anti-apoptotic Effects of Human Wharton's Jelly-derived Mesenchymal Stem Cells on Skeletal Muscle Cells Mediated via Secretion of XCL1

The role of Wharton's jelly-derived human mesenchymal stem cells (WJ-MSCs) in inhibiting muscle cell death has been elucidated in this study. Apoptosis induced by serum deprivation in mouse skeletal myoblast cell lines (C2C12) was significantly reduced when the cell lines were cocultured with WJ-MSCs. Antibody arrays indicated high levels of chemokine (C motif) ligand (XCL1) secretion by cocultured WJ-MSCs and XCL1 protein treatment resulted in complete inhibition of apoptosis in serum-starved C2C12 cells. Apoptosis of C2C12 cells and loss of differentiated C2C12 myotubes induced by lovastatin, another muscle cell death inducer, was also inhibited by XCL1 treatment. However, XCL1 treatment did not inhibit apoptosis of cell lines other than C2C12. When XCL1-siRNA pretreated WJ-MSCs were cocultured with serum-starved C2C12 cells, apoptosis was not inhibited, thus confirming that XCL1 is a key factor in preventing C2C12 cell apoptosis. We demonstrated the therapeutic effect of XCL1 on the zebrafish myopathy model, generated by knock down of a causative gene ADSSL1. Furthermore, the treatment of XCL1 resulted in significant recovery of the zebrafish skeletal muscle defects. These results suggest that human WJ-MSCs and XCL1 protein may act as promising and novel therapeutic agents for treatment of myopathies and other skeletal muscle diseases.

Structural and agonist properties of XCL2, the other member of the C-chemokine subfamily

Known for its unusual metamorphic native state structure, XCL1 has been the focus of most efforts to elucidate the structural, functional, and physiological properties of chemokines in the C subfamily. By comparison, its closely related paralog XCL2 remains virtually uncharacterized. Based on the importance of the chemokine N-terminus in receptor activation, it was hypothesized that two amino acid differences in XCL2 would alter its agonist activity relative to XCL1 for their shared receptor XCR1. This present study reveals several properties of XCL2 that were unexamined until now. Structurally, XCL1 and XCL2 are very similar, exchanging between the monomeric chemokine fold and an unrelated dimeric state under physiological NaCl and temperature conditions. Ca(2+) flux, chemotaxis, and heparin binding assays showed that the monomer form of XCL2 is responsible for G protein-coupled receptor activation while the dimeric form is important for GAG binding. Despite their high structural similarity, XCL2 displays a slightly higher affinity for heparin than XCL1. Because their in vitro functional profiles are virtually identical, distinct physiological roles for XCL1 and XCL2 are probably encoded at the level of expression.

International Union of Basic and Clinical Pharmacology. [corrected]. LXXXIX. Update on the extended family of chemokine receptors and introducing a new nomenclature for atypical chemokine receptors

Sixteen years ago, the Nomenclature Committee of the International Union of Pharmacology approved a system for naming human seven-transmembrane (7TM) G protein-coupled chemokine receptors, the large family of leukocyte chemoattractant receptors that regulates immune system development and function, in large part by mediating leukocyte trafficking. This was announced in Pharmacological Reviews in a major overview of the first decade of research in this field [Murphy PM, Baggiolini M, Charo IF, Hébert CA, Horuk R, Matsushima K, Miller LH, Oppenheim JJ, and Power CA (2000) Pharmacol Rev 52:145-176]. Since then, several new receptors have been discovered, and major advances have been made for the others in many areas, including structural biology, signal transduction mechanisms, biology, and pharmacology. New and diverse roles have been identified in infection, immunity, inflammation, development, cancer, and other areas. The first two drugs acting at chemokine receptors have been approved by the U.S. Food and Drug Administration (FDA), maraviroc targeting CCR5 in human immunodeficiency virus (HIV)/AIDS, and plerixafor targeting CXCR4 for stem cell mobilization for transplantation in cancer, and other candidates are now undergoing pivotal clinical trials for diverse disease indications. In addition, a subfamily of atypical chemokine receptors has emerged that may signal through arrestins instead of G proteins to act as chemokine scavengers, and many microbial and invertebrate G protein-coupled chemokine receptors and soluble chemokine-binding proteins have been described. Here, we review this extended family of chemokine receptors and chemokine-binding proteins at the basic, translational, and clinical levels, including an update on drug development. We also introduce a new nomenclature for atypical chemokine receptors with the stem ACKR (atypical chemokine receptor) approved by the Nomenclature Committee of the International Union of Pharmacology and the Human Genome Nomenclature Committee.

Cytomegalovirus expresses the chemokine homologue vXCL1 capable of attracting XCR1+ CD4- dendritic cells

Cytomegaloviruses (CMV) have developed various strategies to escape the immune system of the host. One strategy involves the expression of virus-encoded chemokines to modulate the host chemokine network. We have identified in the English isolate of rat CMV (murid herpesvirus 8 [MuHV8]) an open reading frame encoding a protein homologous to the chemokine XCL1, the only known C chemokine. Viral XCL1 (vXCL1), a glycosylated protein of 96 amino acids, can be detected 13 h postinfection in the supernatant of MuHV8-infected rat embryo fibroblasts. vXCL1 exclusively binds to CD4(-) rat dendritic cells (DC), a subset of DC that express the corresponding chemokine receptor XCR1. Like endogenous rat XCL1, vXCL1 selectively chemoattracts XCR1(+) CD4(-) DC. Since XCR1(+) DC in mice and humans have been shown to excel in antigen cross-presentation and thus in the induction of cytotoxic CD8(+) T lymphocytes, the virus has apparently hijacked this gene to subvert cytotoxic immune responses. The biology of vXCL1 offers an interesting opportunity to study the role of XCL1 and XCR1(+) DC in the cross-presentation of viral antigens.

Combining genetic mapping with genome-wide expression in experimental autoimmune encephalomyelitis highlights a gene network enriched for T cell functions and candidate genes regulating autoimmunity

The experimental autoimmune encephalomyelitis (EAE) is an autoimmune disease of the central nervous system commonly used to study multiple sclerosis (MS). We combined clinical EAE phenotypes with genome-wide expression profiling in spleens from 150 backcross rats between susceptible DA and resistant PVG rat strains during the chronic EAE phase. This enabled correlation of transcripts with genotypes, other transcripts and clinical EAE phenotypes and implicated potential genetic causes and pathways in EAE. We detected 2285 expression quantitative trait loci (eQTLs). Sixty out of 599 cis-eQTLs overlapped well-known EAE QTLs and constitute positional candidate genes, including Ifit1 (Eae7), Atg7 (Eae20-22), Klrc3 (eEae22) and Mfsd4 (Eae17). A trans-eQTL that overlaps Eae23a regulated a large number of small RNAs and implicates a master regulator of transcription. We defined several disease-correlated networks enriched for pathways involved in cell-mediated immunity. They include C-type lectins, G protein coupled receptors, mitogen-activated protein kinases, transmembrane proteins, suppressors of transcription (Jundp2 and Nr1d1) and STAT transcription factors (Stat4) involved in interferon signaling. The most significant network was enriched for T cell functions, similar to genetic findings in MS, and revealed both established and novel gene interactions. Transcripts in the network have been associated with T cell proliferation and differentiation, the TCR signaling and regulation of regulatory T cells. A number of network genes and their family members have been associated with MS and/or other autoimmune diseases. Combining disease and genome-wide expression phenotypes provides a link between disease risk genes and distinct molecular pathways that are dysregulated during chronic autoimmune inflammation.

The lymphotactin receptor is expressed in epithelial ovarian carcinoma and contributes to cell migration and proliferation

Chemokine receptor-ligand interactions are important to support functioning of both normal and pathologic cells. The expression and function of chemokine receptors in epithelial ovarian carcinoma (EOC) is largely unknown. Here, we report that the lymphotactin receptor (XCR1) was expressed in primary and metastatic human epithelial ovarian carcinoma (EOC) specimens and cell lines. In contrast, expression of XCR1 was not detected in the normal ovary or in human normal ovarian surface epithelial cells. Our data indicate that XCL1 and XCL2 are either present in the malignant ascites or expressed by the ovarian carcinoma cells. The addition of lymphotactin (XCL1 and XCL2) stimulated migration and proliferation of XCR1-positive cells. Reduction of XCR1 expression in ovarian carcinoma cell line SKOV-3 resulted in abrogated diaphragm and peritoneal wall tumor formation and in reduced frequency of colonic, splenetic, and liver nodules in an in vivo xenograft mouse model. Taken together, our data suggest that XCR1 is expressed early during the course of tumorigenic transformation and contributes towards increased cell migration and proliferation, which can facilitate the prometastatic behavior of EOC cells.

The Role of XCR1 and its Ligand XCL1 in Antigen Cross-Presentation by Murine and Human Dendritic Cells

Recently, the chemokine receptor XCR1 has been found to be exclusively expressed on a subset of dendritic cell (DC) known to be involved in antigen cross-presentation. This review aims to summarize the known biology of the XCR1 receptor and its chemokine ligand XCL1, both in the mouse and the human. Further, any involvement of this receptor–ligand pair in antigen uptake, cross-presentation, and induction of innate and adaptive cytotoxic immunity is explored. The concept of antigen delivery to DC via the XCR1 receptor is discussed as a vaccination strategy for selective induction of cytotoxic immunity against certain pathogens or tumors.

XCL1 and XCR1 in the immune system

XCL1, a C class chemokine also known as lymphotactin, is produced by T, NK, and NKT cells during infectious and inflammatory responses, whereas XCR1, the receptor of XCL1, is expressed by a dendritic cell subpopulation. The XCL1-XCR1 axis plays an important role in dendritic-cell-mediated cytotoxic immune response. It has been also shown that XCL1 and XCR1 are constitutively expressed in the thymus and regulate the thymic establishment of self-tolerance and the generation of regulatory T cells. This review summarizes the expression and function of XCL1 and XCR1 in the immune system.

Tumor microenvironment modifications induced by soluble VEGF receptor expression in a rat liver metastasis model

Vascular endothelial growth factor is a potent pro-angiogenic growth factor which is also known to alter tumor microenvironment by inhibiting dendritic cell differentiation and promoting accumulation of myeloid-derived suppressor cells. In the present study, we analyzed the modifications induced by intratumoral expression of sFLT-1, a soluble VEGF receptor, in a rat metastatic colon carcinoma model. We generated colon cancer cell lines stably expressing sFLT-1 or a mock construct. Human umbilical vein endothelial cells cultured with conditioned medium from sFLT-1-expressing tumor cells exhibit a significantly decreased survival, demonstrating the functionality of the secreted sFLT-1. Invivo, sFLT-1 expression induced a 30% decrease in microvessel density in 15-day old experimental liver metastasis from colon carcinoma. Tumor growth was inhibited by 63% and 52% in left and right liver lobes respectively within 25days. In these tumors, sFLT-1 expression was associated with a decreased myeloid cell infiltration and a modification in the expression of several cytokines/chemokines. Altogether, these results suggest that VEGF trapping by sFLT-1 intratumoral expression results in reduced vascularization, tumor growth inhibition and modification of immune tumor microenvironment.

Expressions of lymphotactin and its receptor, XCR, in Lewis rats with experimental autoimmune anterior uveitis

BACKGROUND

To demonstrate the expression of lymphotactin and its receptor (XCR) in the iris/ciliary body and popliteal lymph node, and to clarify their roles in experimental autoimmune anterior uveitis (EAAU).

METHODS

Uveitis was induced in Lewis rats by injection of melanin-associated antigen into the peritoneum and footpad. At defined time points, mRNA expression levels of lymphotactin and XCR in the iris/ciliary body and popliteal lymph node were measured by semiquantitative polymerase chain reaction. Lymphotactin levels in aqueous humor and serum after immunization were determined by enzyme-linked immunosorbent assay. In a separate experiment, an NF-κB inhibitor, pyrrolidine dithiocarbamate (PDTC; 200 mg/kg/day), was injected daily into the intraperitoneum after immunization. Cellular sources of lymphotactin were determined by immunhistochemical staining and flow cytometry.

RESULTS

Lymphotactin mRNA was upregulated in the iris/ciliary body with a peak level at day 14, which is in line with the disease course. XCR mRNA was expressed maximally and then declined gradually from days 5 to 21. With an expression pattern similar to that of mRNA expression, lymphotactin in aqueous humor had attracted corresponding numbers of leukocytes. PDTC markedly inhibited the expression of lymphotactin in aqueous humor and serum. Immunohistochemical staining and flow cytometry analysis revealed that the expression of lymphotactin was detected in infiltrated inflammatory cells, dominantly CD8+ T cells, and increased along with inflammation.

CONCLUSIONS

The lymphotactin and XCR interaction might direct distinct lymphocytes subsets to inflammatory sites. Lymphotactin could regulate the inflammatory process. Lymphotactin expression may be modulated, at least in part, through the NF-κB signaling pathway.

Comprehensive assessment of chemokine expression profiles by flow cytometry

The chemokines are a large family of mainly secreted molecules involved in the regulation of numerous physiological and pathophysiological processes. Despite many years of investigation, the precise cellular sources of most chemokines have remained incompletely defined as a consequence of the limited availability of suitable reagents to visualize the expression of chemokine proteins at the single-cell level. Here, we developed a simple flow cytometry-based assay using commercially available chemokine-specific antibodies for efficient cell-associated detection of 37 of 39 murine chemokines. To demonstrate the utility of this methodology, we used it to reevaluate the nature of homeostatic chemokines in the hematopoietic compartment, to delineate the complete chemokine profiles of NK cells and B cells in response to major polyclonal stimuli, and to assess the chemokine response of DCs to bacterial infection. The versatility of this analytical methodology was further demonstrated by its application to selected human chemokines and should greatly facilitate any future investigation into chemokine biology at large.

Inflammatory cytokines modulate chemokine production patterns of HepG2 cells toward initially inclined direction

AIM

Human hepatocytes are known to express an array of inflammatory cytokines and chemokines. In this study, we examined the potential roles of hepatocytes in regulating immune responses in the liver, by assessing the induction of Th1- or Th2-specific chemokines in HepG2 cells after various inflammatory stimulations.

METHODS

HepG2 cells were stimulated with IL-1alpha, IFN-gamma, IL-4, IL-10, and/or CCL2, harvested at several time points, and served for the analyses of cytokine/chemokine mRNA expressions by semi-quantitative RT-PCR.

RESULTS

(i) IL-1alpha up-regulated mRNA levels of CXCL8, CXCL10, and CCL2. IFN-gamma increased those of CXCL9, CXCL10, and CCL5, while IL-4 or IL-10 had no effect. (ii) Addition of IL-4 to the culture of IFN-gamma-stimulated cells, down-regulated CXCL9 and CXCL10 mRNA levels. (iii) Addition of IFN-gamma to the culture of IL-1alpha-stimulated cells, further up-regulated CXCL9 and CXCL10 mRNA levels. Addition of IL-4 decreased CXCL8 and CXCL10 levels, and increased CCL2 level in IL-1alpha-stimulated cells. (iv) CCL2 induced IL-4 mRNA expression.

CONCLUSIONS

IFN-gamma augmented mRNA expression of Th1-specific chemokines (CXCL9 and CXCL10) in HepG2 cells. IL-4 had no effect on those of Th2-spesific chemokines (CCL17 and CCL22); however, it was supposed to augment Th2 response indirectly through the induction of CCL2 under the inflammatory condition. The findings suggest that hepatocytes have ability to promote immune responses in the liver toward the direction, initially determined by the cytokine balances in the local inflammatory region.

Differential expression of the CXCR3 ligands in chronic hepatitis C virus (HCV) infection and their modulation by HCV in vitro

To investigate chemokine expression networks in chronic hepatitis C virus (HCV) infection, we used microarray analysis to determine chemokine expression in human infection and in chimpanzees experimentally infected with HCV. The CXCR3 chemokine family was highly expressed in both human and chimpanzee infection. CXCL10 was the only CXCR3 chemokine elevated in the serum, suggesting that it may neutralize any CXCR3 chemokine gradient established between the periphery and liver by CXCL11 and CXCL9. Thus, CXCR3 chemokines may not be responsible for recruitment of T lymphocytes but may play a role in positioning these cells within the liver. The importance of the CXCR3 chemokines, in particular CXCL11, was highlighted by replicating HCV (JFH-1) to selectively upregulate its expression in response to gamma interferon (IFN-gamma) and tumor necrosis factor alpha (TNF-alpha). This selective upregulation was confirmed at the transcriptional level by using the CXCL11 promoter driving the luciferase reporter gene. This synergistic increase in expression was not a result of HCV protein expression but the nonspecific innate response to double-stranded RNA (dsRNA), as both in vitro-transcribed HCV RNA and the dsRNA analogue poly(I:C) increased CXCL11 expression and promoter activity. Furthermore, we show that CXCL11 is an IRF3 (interferon regulatory factor 3) response gene whose expression is selectively enhanced by IFN-gamma and TNF-alpha. In conclusion, the CXCR3 chemokines are the most significantly expressed chemokines in chronic hepatitis C and most likely play a role in positioning T cells in the liver. Furthermore, HCV can selectively increase CXCL11 expression in response to IFN-gamma and TNF-alpha stimulation that may play a role in the pathogenesis of HCV-related liver disease.

Mycobacterium tuberculosis antigen Wag31 induces expression of C-chemokine XCL2 in macrophages

Tuberculosis is still a major threat to human health. To date, only approximately half of the proteins encoded by Mycobacterium tuberculosis H37Rv have been assigned specific functions. Wag31 (Rv2145c) is one of the bacterial proteins whose function is mostly unknown. Using a modified split-ubiquitin membrane yeast two-hybrid system, we screened a macrophage cDNA library with Wag31 as bait and identified XCL2, a C-subfamily chemokine, as a binding partner for Wag31. More importantly, Wag31 was found to specifically stimulate XCL2 expression in macrophages. The results from this study demonstrate that expression of C-chemokine is not restricted to certain types of T cells and natural killer cells. Because C-chemokine is chemotactic for CD8+ and CD4+ T cells, our novel findings could provide a new mechanism by which the bacteria induce cell-mediated immunity and by which Wag31 could be a potential target for controlling M. tuberculosis infection.

The chemokine and chemokine receptor superfamilies and their molecular evolution

The human chemokine superfamily currently includes at least 46 ligands, which bind to 18 functionally signaling G-protein-coupled receptors and two decoy or scavenger receptors. The chemokine ligands probably comprise one of the first completely known molecular superfamilies. The genomic organization of the chemokine ligand genes and a comparison of their sequences between species shows that tandem gene duplication has taken place independently in the mouse and human lineages of some chemokine families. This means that care needs to be taken when extrapolating experimental results on some chemokines from mouse to human.

Favorable prognosis of renal cell carcinoma with increased expression of chemokines associated with a Th1-type immune response

The potential role of chemokines in clinical tumors remains poorly understood. Recent investigations have shown the differential expression of chemokine receptors on lymphocytes mediating Th1- and Th2-type immune responses. We examined Th1- and Th2-associated cytokines and chemokines, as well as the expression of their receptors in tumor-infiltrating lymphocytes in renal cell carcinoma (RCC). Sixty-seven patients with sporadic RCC were analyzed for the expression of Th1- and Th2-associated genes using real-time polymerase chain reaction. Tumor infiltration by CXC chemokine receptor 3 (CXCR3)-positive and CC chemokine receptor 5 (CCR5)-positive cells was detected by immunohistochemistry and by flow cytometry. The expression of Th1-associated genes was significantly increased in tumors compared to normal kidney tissues. The expression of interferon-gamma correlated positively with that of Th1 chemokines. Tumors expressing higher Th1 chemokines did not recur after curative surgery. Multivariate analysis showed that increased monokine induced by interferon (IFN)-gamma (MIG) expression was an independent favorable prognostic factor. Immunohistochemistry showed that the degree of CXCR3-positive cell infiltration significantly correlated with IFN-gamma inducible protein 10, MIG and IFN-gamma-inducible T cell a chemoattractant expression (I-TAC). Flow cytometric analysis showed increased expression of CXCR3 and CCR5 in tumor-infiltrating T lymphocytes compared to that in peripheral blood T cells. These results suggest that upregulation of the Th1-type immune response in RCC tumors with a favorable prognosis may be mediated by Th1-associated chemokines. Integrity of the Th1-type immune response seems to be required for tumor regression, suggesting that detection and correction of a defect in the Th1-type response cascade would thus be one of the main targets for tailor-made immunotherapy and gene therapy in RCC.

Identification of genes involved in Ca2+ ionophore A23187-mediated apoptosis and demonstration of a high susceptibility for transcriptional repression of cell cycle genes in B lymphoblasts from a patient with Scott syndrome

Background

In contrast to other agents able to induce apoptosis of cultured cells, Ca²⁺ ionophore A23187 was shown to elicit direct activation of intracellular signal(s). The phenotype of the cells derived from patients having the hemorrhagic disease Scott syndrome, is associated with an abnormally high proportion of apoptotic cells, both in basal culture medium and upon addition of low ionophore concentrations in long-term cultures. These features are presumably related to the mutation also responsible for the defective procoagulant plasma membrane remodeling. We analyzed the specific transcriptional re-programming induced by A23187 to get insights into the effect of this agent on gene expression and a defective gene regulation in Scott cells.

Results

The changes in gene expression upon 48 hours treatment with 200 nM A23187 were measured in Scott B lymphoblasts compared to B lymphoblasts derived from the patient's daughter or unrelated individuals using Affymetrix microarrays. In a similar manner in all of the B cell lines, results showed up-regulation of 55 genes, out of 12,000 represented sequences, involved in various pathways of the cell metabolism. In contrast, a group of 54 down-regulated genes, coding for histones and proteins involved in the cell cycle progression, was more significantly repressed in Scott B lymphoblasts than in the other cell lines. These data correlated with the alterations of the cell cycle phases in treated cells and suggested that the potent effect of A23187 in Scott B lymphoblasts may be the consequence of the underlying molecular defect.

Conclusion

The data illustrate that the ionophore A23187 exerts its pro-apoptotic effect by promoting a complex pattern of genetic changes. These results also suggest that a subset of genes participating in various steps of the cell cycle progress can be transcriptionally regulated in a coordinated fashion. Furthermore, this research brings a new insight into the defect in cultured Scott B lymphoblasts, leading to hypothesize that a mutated gene plays a role not only in membrane remodeling but also in signal transduction pathway(s) leading to altered transcriptional regulation of cell cycle genes.

HIGH EXPRESSION OF CHEMOKINE GENE AS A FAVORABLE PROGNOSTIC FACTOR IN RENAL CELL CARCINOMA

PURPOSE

The presence and potential role of chemokines in clinical tumors remain poorly understood. Chemokines are a large family of chemoattractant cytokines with several members that are also able to regulate angiogenesis. We hypothesized that chemokines may have an important role in regulating tumor growth in renal cell carcinoma (RCC). To begin to test this hypothesis chemokine gene expression and its influence on prognosis, cellular infiltration and angiogenesis in RCC were examined.

MATERIALS AND METHODS

A total of 51 patients with sporadic RCC were analyzed for the expression of the 7 chemokine genes interleukin-8, gamma-interferon inducible protein-10 (IP-10), monokine induced by gamma-interferon (MIG), macrophage chemoattractant protein-1, macrophage inflammatory protein (MIP)-1alpha, MIP-1beta, and regulated and activated normal T cells excreted and secreted (RANTES) using semiquantitative reverse transcriptasepolymerase chain reaction. Lymphocyte infiltration and microvessel density were determined immunohistochemically by staining CD8 and CD34 cells, respectively.

RESULTS

: The expression of IP-10, MIG, MIP-1beta and RANTES was significantly increased in tumor compared to normal kidney tissues. The expression of IP-10, MIG and MIP-1beta showed an inverse correlation with tumor size. Stages 1 to 3 tumors expressing high levels of IP-10, MIG, MIP-1beta and RANTES did not recur after curative surgery. Intratumor expression of IP-10, MIG and MIP-1beta showed a positive correlation with the degree of CD8 cell infiltrating in the tumor and an inverse correlation with microvessel density.

CONCLUSIONS

These results suggest that IP-10, MIG and MIP-1beta are expressed at high levels in tumors that rarely recur after surgery. The antitumorigenic effect of IP-10, MIG and MIP-1beta may result from the recruitment of lymphocyte infiltration and/or inhibition of angiogenesis in RCC. The amplification of chemokine expression by immunotherapy or gene therapy may be a practical and effective strategy to promote tumor regression.

The origin of a developmentally regulated Igh replicon is located near the border of regulatory domains for Igh replication and expression

The 3' Ig heavy chain locus (Igh) regulatory region is the most downstream known element of the murine Igh gene cluster. We report here that the nearest non-Igh genes-Crip, Crp2, and Mta1-are located approximately 70 kb further downstream and are beyond the end of the domain of Igh transcriptional regulation. We have localized an origin of replication in MEL cells to a 3-kb segment located between the 3' Igh regulatory region and Crip. Sequences downstream of this origin are replicated by forks that move in both directions. Sequences upstream of this origin (Igh-C, -D, and -J) are replicated in a single direction through a 500-kb segment in which no active bidirectional origins can be detected. We propose that this origin may lie at or near the end of the Igh regulation domain.

Chemokines in immunity

Chemokines are a superfamily of small, heparin-binding cytokines that induce directed migration of various types of leukocytes through interactions with a group of seven-transmembrane G protein-coupled receptors. At present, over 40 members have been identified in humans. Until a few years ago, chemokines were mainly known as potent attractants for leukocytes such as neutrophils and monocytes, and were thus mostly regarded as the mediators of acute and chronic inflammatory responses. They had highly complex ligand-receptor relationships and their genes were regularly mapped on chromosomes 4 and 17 in humans. Recently, novel chemokines have been identified in rapid succession, mostly through application of bioinformatics on expressed sequence tag databases. A number of surprises have followed the identification of novel chemokines. They are constitutively expressed in lymphoid and other tissues with individually characteristic patterns. Most of them turned out to be highly specific for lymphocytes and dendritic cells. They have much simpler ligand-receptor relationships, and their genes are mapped to chromosomal loci different from the traditional chemokine gene clusters. Thus, the emerging chemokines are functionally and genetically quite different from the classical "inflammatory chemokines" and may be classified as "immune (system) chemokines" because of their profound importance in the genesis, homeostasis and function of the immune system. The emergence of immune chemokines has brought about a great deal of impact on the current immunological research, leading us to a better understanding on the fine traffic regulation of lymphocytes and dendritic cells. The immune chemokines and their receptors are also likely to be important future targets for therapeutic intervention of our immune responses.

Identification of viral macrophage inflammatory protein (vMIP)-II as a ligand for GPR5/XCR1

Lymphotactin is unique among chemokines in that it contains only two of four conserved cysteines and may possess a structure less constrained than other chemokines. The viral chemokine vMIP-II, which presumably has a structure similar to that of CC chemokines has been shown to inhibit many chemokine receptors, but its activity at GPR5/XCR1 has not been described. Interestingly, vMIP-II (but not vMIP-I) was found to be a potent antagonist of lymphotactin activity at GPR5/XCR1, extending the range of chemokine classes that this viral protein is known to inhibit to include the C class chemokine. In addition, we have extended previous analyses of GPR5/XCR1 expression and show that this receptor is expressed in leukocyte cells previously shown to be responsive to lymphotactin.

An Activation-Responsive Element in Single C Motif-1/Lymphotactin Promoter Is a Site of Constitutive and Inducible DNA-Protein Interactions Involving Nuclear Factor of Activated T Cell

Single C motif-1 (SCM-1)/lymphotactin is a C-type chemokine whose expression is activation dependent, cyclosporin A sensitive and restricted to CD8+ T cells, double-negative thymocytes, γδ-type T cells, and NK cells. In humans, there are two highly homologous genes encoding SCM-1α and SCM-1β. Here we examined the regulatory mechanism of the SCM-1 genes. The luciferase reporter gene under the control of the 5′ flanking region of 0.7 kb was strongly induced upon activation with anti-CD3 or PHA plus PMA only in SCM-1-producer T cell lines through a cyclosporin A-sensitive mechanism. An element termed E1 located at −108 to −95 nt relative to the major transcription start site was found to be critical for the promoter activity. In electrophoretic mobility shift assays using the E1 oligonucleotide as probe, nuclear extracts from unstimulated T and B cell lines formed a constitutive complex termed complex I, while nuclear extracts from stimulated SCM-1-producer T cell lines formed a higher mobility complex termed complex II with a concomitant decrease in complex I. The shift from complex I to complex II seen only in SCM-1-producer T cell lines upon activation was completely suppressed by cyclosporin A. Both complexes were critically dependent on the NF-AT core sequence TTTCC in the E1 element and were partially supershifted by anti-NF-ATp. One-hybrid assays in yeast isolated NF-ATp as an E1 binding protein, and transfection of NF-ATp into T and B cell lines strongly enhanced the activation-dependent SCM-1 promoter activity. Collectively, a unique mechanism involving NF-ATp appears to regulate the cell type-specific and activation-dependent expression of the SCM-1 genes.

Molecular cloning of mXCR1, the murine SCM-1/lymphotactin receptor

Single C motif-1 (SCM-1)/lymphotactin is a C-type member of the chemokine superfamily. Previously, we identified its specific receptor XCR1. Here we isolated the murine homologue of XCR1 (mXCR1). To demonstrate its biological activity, we produced recombinant mouse SCM-1 by the baculovirus expression system. B300-19 murine pre-B cells expressing mXCR1 responded to mSCM-1 in chemotactic and calcium-mobilization assays. mXCR1 mRNA was weakly expressed in spleen and lung of normal C57BL/6 mice. In spleen, CD8+ cells and NK1.1+ cells were found to express mXCR1. Identification of mXCR1 will now allow us to study the role of this unique cytokine system in the mouse models of inflammation and immunity.

Expression of SCM-1alpha/lymphotactin and SCM-1beta in natural killer cells is upregulated by IL-2 and IL-12

Recruitment of lymphocytes is an important feature of the host immune response against pathogens. However, the mechanisms by which lymphocytes are attracted are not yet fully understood. Recently, the cDNA of a lymphocyte-specific chemokine, lymphotactin (Lptn), was isolated from murine and human T cells and was also found to be expressed in murine NK cells and human NK cell clones. This study investigated the influence of interleukin (IL)-2 and IL-12 on the expression of Lptn, also known as SCM (single cysteine motif)-1alpha, and SCM-1beta, a 97% homolog of Lptn, in freshly isolated human NK cells and the human NK cell line NK-92. Northern blot analysis and RT-PCR confirmed that nonactivated human NK cells expressed both genes at low level. After activation with IL-2 or IL-12, the expression of both Lptn and SCM-1beta was upregulated within hours. NK-92 cells maintained in medium supplemented with IL-2 constitutively expressed SCM-1 mRNA. However, after 24 h of IL-2 starvation and subsequent culturing at various IL-2 concentrations, the expression of Lptn/SCM-1alpha was upregulated in a dose-dependent manner, whereas the expression of SCM-1beta remained consistently high. These observations indicate that NK cells, in addition to T lymphocytes, express Lptn/SCM-1alpha and SCM-1beta after cytokine activation. The upregulation of these chemokines in NK cells on activation likely acts to increase the number of effector cells reaching the site of an immune response such as inflammation.

Characterization of genetically altered, interleukin 2-independent natural killer cell lines suitable for adoptive cellular immunotherapy

NK-92 is a highly cytotoxic natural killer (NK) tumor cell line that possesses properties that make it an excellent candidate for adoptive cellular immunotherapy. However, the cytotoxicity of NK cells is dependent on cytokines such as interleukin 2 (IL-2). Although NK-92 cells maintain cytotoxicity for a time after withdrawal of IL-2, clinical use will probably require prolonged treatment with fully activated cells to eliminate disease effectively. The ability to support cytotoxic cells with exogenously administered IL-2 is limited by associated toxicity. Therefore, we describe the transfection of the IL-2-dependent NK-92 cell line with human IL-2 (hIL-2) cDNA by particle-mediated gene transfer to create two IL-2-independent variants, NK-92MI and NK-92 CI, and describe their characterization and comparison with parental cells. Both variants were shown to contain, express, and synthesize the hIL-2 cDNA. IL-2 synthesis was higher in NK-92MI cells compared with NK-92CI cells, with no expression in parental cells. Functionally, the cytotoxicity of all three cell lines was similar and coincubation with IL-2-independent variants did not affect hematopoietic progenitor cells. NK-92MI and NK-92CI cells were more radiosensitive than NK-92 cells, with proliferation inhibited at lower radiation doses and increased morality and decreased cytotoxicity compared with parental cells. Data presented here show that we have created by particle-mediated gene transfer two IL-2-independent variants of NK-92 that are identical to parental cells in virtually all respects, including high cytotoxic activity. The nonviral transfection of these cells makes them suitable for clinical applications. These IL-2-independent cells should allow prolonged treatment with fully active natural killer cells without the need for exogenous IL-2 support.

CK-1, a putative chemokine of rainbow trout (Oncorhynchus mykiss)

Chemokines are small inducible proteins that direct the migration of leukocytes. While chemokines are well characterised in mammals, they have yet to be identified in fish. We have isolated a cDNA clone from rainbow trout (Oncorhynchus mykiss) which encodes a protein (CK-1) having structural features typical of chemokines. Amino-acid residues that define the beta-chemokines of mammals are conserved in CK-1, including the paired cysteine motif, CC. Further similarities are shared with the C6 subfamily of beta-chemokines. In contrast, the organisation of the CK-1 gene is closer to that of mammalian alpha-chemokine genes than beta-chemokine genes. The CK-1 gene is present in all four salmonid species examined and the nucleotide sequences of the exons are highly conserved. CK-1 has characteristics in common with mammalian alpha and beta-chemokine genes, suggesting that this salmonid chemokine gene preserves traits once present in the ancestral chemokine gene from which modern mammalian chemokine genes evolved.

Identification of single C motif-1/lymphotactin receptor XCR1

Single C motif-1 (SCM-1)/lymphotactin is a member of the chemokine superfamily, but retains only the 2nd and 4th of the four cysteine residues conserved in other chemokines. In humans, there are two highly homologous SCM-1 genes encoding SCM-1alpha and SCM-1beta with two amino acid substitutions. To identify a specific receptor for SCM-1 proteins, we produced recombinant SCM-1alpha and SCM-1beta by the baculovirus expression system and tested them on murine L1.2 cells stably expressing eight known chemokine receptors and three orphan receptors. Both proteins specifically induced migration in cells expressing an orphan receptor, GPR5. The migration was chemotactic and suppressed by pertussis toxin, indicating coupling to a Galpha type of G protein. Both proteins also induced intracellular calcium mobilization in GPR5-expressing L1.2 cells with efficient mutual cross desensitization. SCM-1alpha bound specifically to GPR5-expressing L1.2 cells with a Kd of 10 nM. By Northern blot analysis, GPR5 mRNA of about 5 kilobases was detected strongly in placenta and weakly in spleen and thymus among various human tissues. Identification of a specific receptor for SCM-1 would facilitate our investigation on its biological function. Following the set rule for the chemokine receptor nomenclature, we propose to designate GPR5 as XCR1 from XC chemokine receptor-1.

The T cell-directed CC chemokine TARC is a highly specific biological ligand for CC chemokine receptor 4

Thymus and activation-regulated chemokine (TARC) is a recently identified CC chemokine that is expressed constitutively in thymus and transiently in stimulated peripheral blood mononuclear cells. TARC functions as a selective chemoattractant for T cells that express a class of receptors binding TARC with high affinity and specificity. To identify the receptor for TARC, we produced TARC as a fusion protein with secreted alkaline phosphatase (SEAP) and used it for specific binding. By stably transfecting five orphan receptors and five known CC chemokine receptors (CCR1 to -5) into K562 cells, we found that TARC-SEAP bound selectively to cells expressing CCR4. TARC-SEAP also bound to K562 cells stably expressing CCR4 with a high affinity (Kd = 0.5 nM). Only TARC and not five other CC chemokines (MCP-1 (monocyte chemoattractant protein-1), RANTES (regulated upon activation, normal T cells expressed and secreted), MIP-1alpha (macrophage inflammatory protein-1alpha), MIP-1beta, and LARC (liver and activation-regulated chemokine)) competed with TARC-SEAP for binding to CCR4. TARC but not RANTES or MIP-1alpha induced migration and calcium mobilization in 293/EBNA-1 cells stably expressing CCR4. K562 cells stably expressing CCR4 also responded to TARC in a calcium mobilization assay. Northern blot analysis revealed that CCR4 mRNA was expressed strongly in human T cell lines and peripheral blood T cells but not in B cells, natural killer cells, monocytes, or granulocytes. Taken together, TARC is a specific functional ligand for CCR4, and CCR4 is the specific receptor for TARC selectively expressed on T cells.

Identification of CCR6, the specific receptor for a novel lymphocyte-directed CC chemokine LARC

Liver and activation-regulated chemokine (LARC) is a recently identified CC chemokine that is expressed mainly in the liver. LARC functions as a selective chemoattractant for lymphocytes that express a class of receptors specifically binding to LARC with high affinity. To identifiy the receptor for LARC, we examined LARC-induced calcium mobilization in cells stably expressing five CC chemokine receptors (CCR1-CCR5) and five orphan seven-transmembrane receptors. LARC specifically induced calcium flux in K562 cells as well as 293/EBNA-1 cells stably expressing an orphan receptor GPR-CY4. LARC induced migration in 293/EBNA-1 cells stably expressing GPR-CY4 with a bi-modal dose-response curve. LARC fused with secreted alkaline phosphatase (LARC-SEAP) bound specifically to Raji cells stably expressing GPR-CY4 with a Kd of 0.9 nM. Only LARC but not five other CC chemokines (MCP-1, RANTES, MIP-1alpha, MIP-1beta, and TARC) competed with LARC-SEAP for binding to GPR-CY4. By Northern blot analysis, GPR-CY4 mRNA was expressed mainly in spleen, lymph nodes, Appendix, and fetal liver among various human tissues. Among various leukocyte subsets, GPR-CY4 mRNA was detected in lymphocytes (CD4(+) and CD8(+) T cells and B cells) but not in natural killer cells, monocytes, or granulocytes. Expression of GPR-CY4 mRNA in CD4(+) and CD8(+) T cells was strongly up-regulated by IL-2. Taken together, GPR-CY4 is the specific receptor for LARC expressed selectively on lymphocytes, and LARC is a unique functional ligand for GPR-CY4. We propose GPR-CY4 to be designated as CCR6.

Molecular cloning of a novel human CC chemokine liver and activation-regulated chemokine (LARC) expressed in liver. Chemotactic activity for lymphocytes and gene localization on chromosome 2

Partial overlapping cDNA sequences likely to encode a novel human CC chemokine were identified from the GenBank Expressed Sequence Tag data base. Using these sequences, we isolated full-length cDNA encoding a protein of 96 amino acid residues with 20-28% identity to other CC chemokines. By Northern blot, this chemokine was mainly expressed in liver among various tissues and strongly induced in several human cell lines by phorbol myristate acetate. We thus designated this chemokine as LARC from Liver and Activation-Regulated Chemokine. We mapped the LARC gene close to the chromosomal marker D2S159 at chromosome 2q33-q37 by somatic cell and radiation hybrid mappings and isolated two yeast artificial chromosome clones containing the LARC gene from this region. To prepare LARC, we subcloned the cDNA into a baculovirus vector and expressed it in insect cells. The secreted protein started at Ala-27 and was significantly chemotactic for lymphocytes. At a concentration of 1 microg/ml, it also showed a weak chemotactic activity for granulocytes. Unlike other CC chemokines, however, LARC was not chemotactic for monocytic THP-1 cells or blood monocytes. LARC tagged with secreted alkaline phosphatase-(His)6 bound specifically to lymphocytes, the binding being competed only by LARC and not by other CC or CXC chemokines. Scatchard analysis revealed a single class of receptors for LARC on lymphocytes with a Kd of 0.4 nM and 2100 sites/cell. Collectively, LARC is a novel CC chemokine, which may represent a new group of CC chemokines localized on chromosome 2.