Differential chemokine activation of CC chemokine receptor 1-regulated pathways: ligand selective activation of Gα 14-coupled pathways

Clozapine reduces chemokine-mediated migration of lymphocytes by targeting NF-κB and AKT phosphorylation

Multiple sclerosis is a disease characterised by demyelination of axons in the central nervous system. The atypical antipsychotic drug clozapine has been shown to attenuate disease severity in experimental autoimmune encephalomyelitis (EAE), a mouse model that is useful for the study of multiple sclerosis. However, the mechanism of action by which clozapine reduces disease in EAE is poorly understood. To better understand how clozapine exerts its protective effects, we investigated the underlying signalling pathways by which clozapine may reduce immune cell migration by evaluating chemokine and dopamine receptor-associated signalling pathways. We found that clozapine inhibits migration of immune cells by reducing chemokine production in microglia cells by targeting NF-κB phosphorylation and promoting an anti-inflammatory milieu. Furthermore, clozapine directly targets immune cell migration by changing Ca²⁺ levels within immune cells and reduces the phosphorylation of signalling protein AKT. Linking these pathways to the antagonising effect of clozapine on dopamine and serotonin receptors, we provide insight into how clozapine alters immune cells migration by directly targeting the underlying migration-associated pathways.

Biased agonism at chemokine receptors

In the human chemokine system, interactions between the approximately 50 known endogenous chemokine ligands and 20 known chemokine receptors (CKRs) regulate a wide range of cellular functions and biological processes including immune cell activation and homeostasis, development, angiogenesis, and neuromodulation. CKRs are a family of G protein-coupled receptors (GPCR), which represent the most common and versatile class of receptors in the human genome and the targets of approximately one third of all Food and Drug Administration-approved drugs. Chemokines and CKRs bind with significant promiscuity, as most CKRs can be activated by multiple chemokines and most chemokines can activate multiple CKRs. While these ligand-receptor interactions were previously regarded as redundant, it is now appreciated that many chemokine:CKR interactions display biased agonism, the phenomenon in which different ligands binding to the same receptor signal through different pathways with different efficacies, leading to distinct biological effects. Notably, these biased responses can be modulated through changes in ligand, receptor, and or the specific cellular context (system). In this review, we explore the biochemical mechanisms, functional consequences, and therapeutic potential of biased agonism in the chemokine system. An enhanced understanding of biased agonism in the chemokine system may prove transformative in the understanding of the mechanisms and consequences of biased signaling across all GPCR subtypes and aid in the development of biased pharmaceuticals with increased therapeutic efficacy and safer side effect profiles.

Clozapine reduces infiltration into the CNS by targeting migration in experimental autoimmune encephalomyelitis

Background

Atypical antipsychotic agents, such as clozapine, are used to treat schizophrenia and other psychiatric disorders by a mechanism that is believed to involve modulating the immune system. Multiple sclerosis is an immune-mediated neurological disease, and recently, clozapine was shown to reduce disease severity in an animal model of MS, experimental autoimmune encephalomyelitis (EAE). However, the mode of action by which clozapine reduces disease in this model is poorly understood.

Methods

Because the mode of action by which clozapine reduces neuroinflammation is poorly understood, we used the EAE model to elucidate the in vivo and in vitro effects of clozapine.

Results

In this study, we report that clozapine treatment reduced the infiltration of peripheral immune cells into the central nervous system (CNS) and that this correlated with reduced expression of the chemokines CCL2 and CCL5 transcripts in the brain and spinal cord. We assessed to what extent immune cell populations were affected by clozapine treatment and we found that clozapine targets the expression of chemokines by macrophages and primary microglia. Furthermore, in addition to decreasing CNS infiltration by reducing chemokine expression, we found that clozapine directly inhibits chemokine-induced migration of immune cells. This direct target on the immune cells was not mediated by a change in receptor expression on the immune cell surface but by decreasing downstream signaling via these receptors leading to a reduced migration.

Conclusions

Taken together, our study indicates that clozapine protects against EAE by two different mechanisms; first, by reducing the chemoattractant proteins in the CNS; and second, by direct targeting the migration potential of peripheral immune cells.

The Angiotensin Receptor Blocker Losartan Suppresses Growth of Pulmonary Metastases via AT1R-Independent Inhibition of CCR2 Signaling and Monocyte Recruitment

Inflammatory monocytes have been shown to play key roles in cancer metastasis through promotion of tumor cell extravasation, growth, and angiogenesis. Monocyte recruitment to metastases is mediated primarily via the CCL2-CCR2 chemotactic axis. Thus, disruption of this axis represents an attractive therapeutic target for the treatment of metastatic disease. Losartan, a type I angiotensin II receptor (AT1R) antagonist, has been previously shown to have immunomodulatory actions involving monocyte and macrophage activity. However, the exact mechanisms accounting for these effects have not been fully elucidated. Therefore, we investigated the effects of losartan and its primary metabolite on CCL2-mediated monocyte recruitment and CCR2 receptor function using mouse tumor models and in vitro human monocyte cultures. We show, in this study, that losartan and its metabolite potently inhibit monocyte recruitment through the noncompetitive inhibition of CCL2-induced ERK1/2 activation, independent of AT1R activity. Studies in experimental metastasis models demonstrated that losartan treatment significantly reduced the metastatic burden in mice, an effect associated with a significant decrease in CD11b⁺/Ly6C⁺-recruited monocytes in the lungs. Collectively, these results indicate that losartan can exert antimetastatic activity by inhibiting CCR2 signaling and suppressing monocyte recruitment and therefore suggest that losartan (and potentially other AT1R blocker drugs) could be repurposed for use in cancer immunotherapy.

Molecular Mechanisms of Biased and Probe-Dependent Signaling at CXC-Motif Chemokine Receptor CXCR3 Induced by Negative Allosteric Modulators

Our recent explorations of allosteric modulators with improved properties resulted in the identification of two biased negative allosteric modulators, BD103 (N-1-{[3-(4-ethoxyphenyl)-4-oxo-3,4-dihydropyrido[2,3-d]pyrimi-din2yl]ethyl}-4-(4-fluorobutoxy)-N-[(1-methylpiperidin-4-yl)methyl}]butanamide) and BD064 (5-[(N-{1-[3-(4-ethoxyphenyl)-4-oxo-3,4-dihydropyrido[2,3-d]pyrimidin-2-yl]ethyl-2-[4-fluoro-3-(trifluoromethyl)phenyl]acetamido)methyl]-2-fluorophenyl}boronic acid), that exhibited probe-dependent inhibition of CXC-motif chemokine receptor CXCR3 signaling. With the intention to elucidate the structural mechanisms underlying their selectivity and probe dependence, we used site-directed mutagenesis combined with homology modeling and docking to identify amino acids of CXCR3 that contribute to modulator binding, signaling, and transmission of cooperativity. With the use of allosteric radioligand RAMX3 ([³H]N-{1-[3-(4-ethoxyphenyl)-4-oxo-3,4-dihydropyrido[2,3-d]pyrimidin-2-yl]ethyl}-2-[4-fluoro-3-(trifluoromethyl)phenyl]-N-[(1-methylpiperidin-4-yl)methyl]acetamide), we identified that F131^3.32 and Y308^7.43 contribute specifically to the binding pocket of BD064, whereas D186^4.60 solely participates in the stabilization of binding conformation of BD103. The influence of mutations on the ability of negative allosteric modulators to inhibit chemokine-mediated activation (CXCL11 and CXCL10) was assessed with the bioluminescence resonance energy transfer-based cAMP and β-arrestin recruitment assay. Obtained data revealed complex molecular mechanisms governing biased and probe-dependent signaling at CXCR3. In particular, F131^3.32, S304^7.39, and Y308^7.43 emerged as key residues for the compounds to modulate the chemokine response. Notably, D186^4.60, W268^6.48, and S304^7.39 turned out to play a role in signal pathway selectivity of CXCL10, as mutations of these residues led to a G protein-active but β-arrestin-inactive conformation. These diverse effects of mutations suggest the existence of ligand- and pathway-specific receptor conformations and give new insights in the sophisticated signaling machinery between allosteric ligands, chemokines, and their receptors, which can provide a powerful platform for the development of new allosteric drugs with improved pharmacological properties.

Epigenetic Modification of the CCL5/CCR1/ERK Axis Enhances Glioma Targeting in Dedifferentiation-Reprogrammed BMSCs

The success of stem cell-mediated gene therapy in cancer treatment largely depends on the specific homing ability of stem cells. We have previously demonstrated that after in vitro induction of neuronal differentiation and dedifferentiation, bone marrow stromal cells (BMSCs) revert to a primitive stem cell population (De-neu-BMSCs) distinct from naive BMSCs. We report here that De-neu-BMSCs express significantly higher levels of chemokines, and display enhanced homing abilities to glioma, the effect of which is mediated by the activated CCL5/CCR1/ERK axis. Intriguingly, we find that the activated chemokine axis in De-neu-BMSCs is epigenetically regulated by histone modifications. On the therapeutic front, we show that De-neu-BMSCs elicit stronger homing and glioma-killing effects together with cytosine deaminase/5-fluorocytosine compared with unmanipulated BMSCs in vivo. Altogether, the current study provides an insight into chemokine regulation in BMSCs, which may have more profound effects on BMSC function and their application in regenerative medicine and cancer targeting.

Allosteric Modulation of Chemoattractant Receptors

Chemoattractants control selective leukocyte homing via interactions with a dedicated family of related G protein-coupled receptor (GPCR). Emerging evidence indicates that the signaling activity of these receptors, as for other GPCR, is influenced by allosteric modulators, which interact with the receptor in a binding site distinct from the binding site of the agonist and modulate the receptor signaling activity in response to the orthosteric ligand. Allosteric modulators have a number of potential advantages over orthosteric agonists/antagonists as therapeutic agents and offer unprecedented opportunities to identify extremely selective drug leads. Here, we resume evidence of allosterism in the context of chemoattractant receptors, discussing in particular its functional impact on functional selectivity and probe/concentration dependence of orthosteric ligands activities.

Biased agonism at chemokine receptors: obstacles or opportunities for drug discovery?

Chemokine receptors are typically promiscuous, binding more than one ligand, with the ligands themselves often expressed in different spatial localizations by multiple cell types. This is normally a tightly regulated process; however, in a variety of inflammatory disorders, dysregulation results in the excessive or inappropriate expression of chemokines that drives disease progression. Biased agonism, the phenomenon whereby different ligands of the same receptor are able to preferentially activate one signaling pathway over another, adds another level of complexity to an already complex system. In this minireview, we discuss the concept of biased agonism within the chemokine family and report that targeting single signaling axes downstream of chemokine receptors is not only achievable, but may well present novel opportunities to target chemokine receptors, allowing the fine tuning of receptor responses in the context of allergic inflammation and beyond.

An intact helical domain is required for Gα14 to stimulate phospholipase Cβ

Background

Stimulation of phospholipase Cβ (PLCβ) by the activated α-subunit of G_q (Gα_q) constitutes a major signaling pathway for cellular regulation, and structural studies have recently revealed the molecular interactions between PLCβ and Gα_q. Yet, most of the PLCβ-interacting residues identified on Gα_q are not unique to members of the Gα_q family. Molecular modeling predicts that the core PLCβ-interacting residues located on the switch regions of Gα_q are similarly positioned in Gα_z which does not stimulate PLCβ. Using wild-type and constitutively active chimeras constructed between Gα_z and Gα₁₄, a member of the Gα_q family, we examined if the PLCβ-interacting residues identified in Gα_q are indeed essential.

Results

Four chimeras with the core PLCβ-interacting residues composed of Gα_z sequences were capable of binding PLCβ2 and stimulating the formation of inositol trisphosphate. Surprisingly, all chimeras with a Gα_z N-terminal half failed to functionally associate with PLCβ2, despite the fact that many of them contained the core PLCβ-interacting residues from Gα₁₄. Further analyses revealed that the non-PLCβ2 interacting chimeras were capable of interacting with other effector molecules such as adenylyl cyclase and tetratricopeptide repeat 1, indicating that they could adopt a GTP-bound active conformation.

Conclusion

Collectively, our study suggests that the previously identified PLCβ-interacting residues are insufficient to ensure productive interaction of Gα₁₄ with PLCβ, while an intact N-terminal half of Gα₁₄ is apparently required for PLCβ interaction.

Electronic supplementary material

The online version of this article (doi:10.1186/s12900-015-0043-3) contains supplementary material, which is available to authorized users.

Biased signaling at chemokine receptors

The ability of G protein-coupled receptors (GPCRs) to activate selective signaling pathways according to the conformation stabilized by bound ligands (signaling bias) is a challenging concept in the GPCR field. Signaling bias has been documented for several GPCRs, including chemokine receptors. However, most of these studies examined the global signaling bias between G protein- and arrestin-dependent pathways, leaving unaddressed the potential bias between particular G protein subtypes. Here, we investigated the coupling selectivity of chemokine receptors CCR2, CCR5, and CCR7 in response to various ligands with G protein subtypes by using bioluminescence resonance energy transfer biosensors monitoring directly the activation of G proteins. We also compared data obtained with the G protein biosensors with those obtained with other functional readouts, such as β-arrestin-2 recruitment, cAMP accumulation, and calcium mobilization assays. We showed that the binding of chemokines to CCR2, CCR5, and CCR7 activated the three Gαi subtypes (Gαi1, Gαi2, and Gαi3) and the two Gαo isoforms (Gαoa and Gαob) with potencies that generally correlate to their binding affinities. In addition, we showed that the binding of chemokines to CCR5 and CCR2 also activated Gα12, but not Gα13. For each receptor, we showed that the relative potency of various agonist chemokines was not identical in all assays, supporting the notion that signaling bias exists at chemokine receptors.

RANTES (CCL5) reduces glucose-dependent secretion of glucagon-like peptides 1 and 2 and impairs glucose-induced insulin secretion in mice

Type 2 diabetes is associated with elevated circulating levels of the chemokine RANTES and with decreased plasma levels of the incretin hormone glucagon-like peptide 1 (GLP-1). GLP-1 is a peptide secreted from intestinal L-cells upon nutrient ingestion. It enhances insulin secretion from pancreatic β-cells and protects from β-cell loss but also promotes satiety and weight loss. In search of chemokines that may reduce GLP-1 secretion we identified RANTES and show that it reduces glucose-stimulated GLP-1 secretion in the human enteroendocrine cell line NCI-H716, blocked by the antagonist Met-RANTES, and in vivo in mice. RANTES exposure to mouse intestinal tissues lowers transport function of the intestinal glucose transporter SGLT1, and administration in mice reduces plasma GLP-1 and GLP-2 levels after an oral glucose load and thereby impairs insulin secretion. These data show that RANTES is involved in altered secretion of glucagon-like peptide hormones most probably acting through SGLT1, and our study identifies the RANTES-receptor CCR1 as a potential target in diabetes therapy.

Bias in chemokine receptor signalling

Chemokine receptors are widely expressed on a variety of immune cells and play a crucial role in normal physiology as well as in inflammatory and infectious diseases. The existence of 23 chemokine receptors and 48 chemokine ligands guarantees a tight control and fine-tuning of the immune system. Here, we discuss the multiple regulatory mechanisms of chemokine signalling at a systemic, cellular, and molecular level. In particular, we focus on the impact of biased signalling at the receptor level; an emerging concept in molecular pharmacology. An improved understanding of these mechanisms may provide a framework for more effective drug discovery and development at a target class that is so relevant for immune function.

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.

CCR1/CCL5 interaction promotes invasion of taxane-resistant PC3 prostate cancer cells by increasing secretion of MMPs 2/9 and by activating ERK and Rac signaling

Castration-refractory prostate cancer (CRPC) is treated with taxane-based chemotherapy, but eventually becomes drug resistant. It is thus essential to identify novel therapeutic targets for taxane resistance in CRPC patients. We investigated the role of the chemokine (C-C motif) receptor 1 (CCR1) and its ligand, chemokine (C-C motif) ligand 5 (CCL5), in taxane-resistant CRPC using paclitaxel-resistant prostate cancer cells (PC3PR) established from PC3 cells. We found that the expression levels of CCR1 mRNA and protein were up-regulated in PC3PR cells compared to PC3 cells. In order to investigate the role of increased CCR1 in PC3PR cells, we stimulated cells with CCL5, one of the chemokine ligands of CCR1. In CCL5-stimulated PC3PR cells, siRNA-mediated knockdown of CCR1 expression reduced phosphorylation of ERK1/2 and Rac1/cdc42. Furthermore, CCR1 knockdown and MEK1/2 inhibition decreased CCL5-stimulated secretion of MMPs 2 and 9, which play important roles in cancer cell invasion and metastasis. In the Matrigel invasion assay, knockdown of CCR1 and inhibition of the ERK and Rac signaling pathways significantly decreased the number of invading cells. Finally, the serum CCL5 protein level as measured by ELISA was not different among the three groups of patients: those with negative prostate biopsy, those at initial diagnosis of prostate cancer, and those with taxane-resistant prostate cancer. These results demonstrated for the first time that the interaction of CCR1 with CCL5 caused by increased expression of CCR1 promotes invasion of PC3PR cells by increasing secretion of MMPs 2 and 9 and by activating ERK and Rac signaling. Our findings suggest that CCR1 could be a novel therapeutic target for taxane-resistant CRPC.

CCR1-mediated STAT3 tyrosine phosphorylation and CXCL8 expression in THP-1 macrophage-like cells involve pertussis toxin-insensitive Gα(14/16) signaling and IL-6 release

Agonists of CCR1 contribute to hypersensitivity reactions and atherosclerotic lesions, possibly via the regulation of the transcription factor STAT3. CCR1 was demonstrated to use pertussis toxin-insensitive Gα(14/16) to stimulate phospholipase Cβ and NF-κB, whereas both Gα(14) and Gα(16) are also capable of activating STAT3. The coexpression of CCR1 and Gα(14/16) in human THP-1 macrophage-like cells suggests that CCR1 may use Gα(14/16) to induce STAT3 activation. In this study, we demonstrated that a CCR1 agonist, leukotactin-1 (CCL15), could indeed stimulate STAT3 Tyr(705) and Ser(727) phosphorylation via pertussis toxin-insensitive G proteins in PMA-differentiated THP-1 cells, human erythroleukemia cells, and HEK293 cells overexpressing CCR1 and Gα(14/16). The STAT3 Tyr(705) and Ser(727) phosphorylations were independent of each other and temporally distinct. Subcellular fractionation and confocal microscopy illustrated that Tyr(705)-phosphorylated STAT3 translocated to the nucleus, whereas Ser(727)-phosphorylated STAT3 was retained in the cytosol after CCR1/Gα(14) activation. CCL15 was capable of inducing IL-6 and IL-8 (CXCL8) production in both THP-1 macrophage-like cells and HEK293 cells overexpressing CCR1 and Gα(14/16). Neutralizing Ab to IL-6 inhibited CCL15-mediated STAT3 Tyr(705) phosphorylation, whereas inhibition of STAT3 activity abolished CCL15-activated CXCL8 release. The ability of CCR1 to signal through Gα(14/16) provides a linkage for CCL15 to regulate IL-6/STAT3-signaling cascades, leading to expression of CXCL8, a cytokine that is involved in inflammation and the rupture of atherosclerotic plaque.

Pharmacological modulation of chemokine receptor function

G protein-coupled chemokine receptors and their peptidergic ligands are interesting therapeutic targets due to their involvement in various immune-related diseases, including rheumatoid arthritis, multiple sclerosis, inflammatory bowel disease, chronic obstructive pulmonary disease, HIV-1 infection and cancer. To tackle these diseases, a lot of effort has been focused on discovery and development of small-molecule chemokine receptor antagonists. This has been rewarded by the market approval of two novel chemokine receptor inhibitors, AMD3100 (CXCR4) and Maraviroc (CCR5) for stem cell mobilization and treatment of HIV-1 infection respectively. The recent GPCR crystal structures together with mutagenesis and pharmacological studies have aided in understanding how small-molecule ligands interact with chemokine receptors. Many of these ligands display behaviour deviating from simple competition and do not interact with the chemokine binding site, providing evidence for an allosteric mode of action. This review aims to give an overview of the evidence supporting modulation of this intriguing receptor family by a range of ligands, including small molecules, peptides and antibodies. Moreover, the computer-assisted modelling of chemokine receptor-ligand interactions is discussed in view of GPCR crystal structures. Finally, the implications of concepts such as functional selectivity and chemokine receptor dimerization are considered.

Therapeutic potential of CCR1 antagonists for multiple myeloma

The chemokine receptor CCR1 has been the target of intensive research for nearly two decades. Small-molecule antagonists were first reported in 1998 and, since then, many inhibitors for CCR1 have been brought forth. Yet, with all the money and time spent, to date, no small-molecule antagonists have successfully moved past Phase II clinical trials. With the current advancement of CCR1 antagonists by Bristol-Myers Squibb and Chemocentrix, there has been renewed interest. In this review, we present an overview of CCR1, its activating ligands, methods of signaling, and downstream response. We discuss studies that indicate CCR1 plays an important role in multiple myeloma and the underlying molecular mechanisms. Finally, we present an overview of the clinical and preclinical compounds for CCR1. We address individual structures, discuss their pharmacological précis, and summarize the published evidence to assess their value for use in multiple myeloma.

Pivotal role of the CCL5/CCR5 interaction for recruitment of endothelial progenitor cells in mouse wound healing

BM-derived endothelial progenitor cells (EPCs) are critical and essential for neovascularization in tissue repair and tumorigenesis. EPCs migrate from BM to tissues via the bloodstream, but specific chemotactic cues have not been identified. Here we show in mice that the absence of CCR5 reduced vascular EPC accumulation and neovascularization, but not macrophage recruitment, and eventually delayed healing in wounded skin. When transferred into Ccr5-/- mice, Ccr5+/+ BM cells, but not Ccr5-/- cells, accumulated in the wound site, were incorporated into the vasculature, and restored normal neovascularization. Consistent with these observations, CCL5 induced in vitro EPC migration in a CCR5-dependent manner. Moreover, expression of VEGF and TGF-β was substantially diminished at wound sites in Ccr5-/- mice, which suggests that EPCs are important not only as the progenitors of endothelial cells, but also as the source of growth factors during tissue repair. Taken together, these data identify the CCL5/CCR5 interaction as what we believe to be a novel molecular target for modulation of neovascularization and eventual tissue repair.

CCL5 induces a pro-inflammatory profile in microglia in vitro

The chemokine receptors CCR1, CCR2, CCR3, CCR5, and CXCR2 have been found to be expressed on microglia in many neurodegenerative diseases, such as multiple sclerosis and Alzheimer's disease. There is emerging evidence that chemokines, besides chemoattraction, might directly modulate reactive profiles of microglia. To address this hypothesis we have investigated the effects of CCL2, CCL3, CCL5, and CXCL1 on cytokine and growth factor production, NO synthesis, and phagocytosis in non-stimulated and lipopolysaccharide-stimulated primary rat microglia. The respective receptors CCR1, CCR5, and CXCR2 were shown to be functionally expressed on microglia. All tested chemokines stimulated chemotaxis whereas only CCL5 increased NO secretion and attenuated IL-10 as well as IGF-1 production in activated microglia. Based on these findings we propose that besides its chemoattractant function CCL5 has a modulatory effect on activated microglia.

Cord blood chemokines differentiate between spontaneous and elective preterm births in singleton pregnancies

BACKGROUND

Signals originating from both maternal and fetal compartments participate in the preterm labor process.

OBJECTIVE

To investigate whether cord blood immunoproteins predict spontaneous preterm labor.

METHODS

Cord blood from 125 very preterm (gestational age <32weeks) singleton infants and 33 term infants was collected after birth and analyzed for 107 immunoproteins on microarrays. Immunoproteins from spontaneous preterm births (SPTB) were compared to immunoproteins from preterm births without labor. The placentas were studied for histology and immunohistochemistry. The data was modeled by classification and regression trees (CART) analysis.

RESULTS

In preterm births, low CCL16 level predicted SPTB with a sensitivity of 94.7%, and specificity of 46.9%. According to logistic regression analysis, low CCL16 (OR 57.9), histologic chorioamnitis (OR 33.6), and high CCL23 (OR 44.6) were independent risk factors of SPTB. Cord blood CCL16 was higher in preterm births without labor and in term births than in SPTBs. CCL16 and its signaling receptor CCR1 were visualized in syncytiotrophoblast and cytotrophoblast cells of placental villi.

CONCLUSION

Low umbilical cord blood chemokine CCL16 associates with spontaneous preterm birth. Further studies are required to show whether CCL16 is involved in spontaneous preterm labor or in placental disease necessitating elective preterm delivery.

Chapter 5. Multiple approaches to the study of chemokine receptor homo- and heterodimerization

Chemokines belong to a family of structurally related chemoattractant proteins that bind to specific seven-transmembrane receptors linked to G proteins. They are implicated in a variety of biologic responses ranging from cell polarization, movement, immune and inflammatory responses, as well as prevention of HIV-1 infection and cancer metastasis. Recent evidence indicates that chemokine receptors can adopt several conformations at the cell membrane. Chemokine receptor homo- and heterodimers preexist on the cell surface, even in the absence of ligands. Chemokine binding stabilizes specific receptor conformations and activates distinct signaling cascades. Analysis of the conformations adopted by the receptors at the membrane and their dynamics is crucial for a complete understanding of the function of these inflammatory mediators. We focus here on conventional biochemical and genetic methods, as well as on new imaging techniques such as those based on resonance energy transfer, discussing their advantages, disadvantages, and possible complementarity in the analysis of chemokine receptor dimerization.

Modulation of chemokine receptor activity through dimerization and crosstalk

Chemokines are small, secreted proteins that bind to the chemokine receptor subfamily of class A G protein-coupled receptors. Collectively, these receptor-ligand pairs are responsible for diverse physiological responses including immune cell trafficking, development and mitogenic signaling, both in the context of homeostasis and disease. However, chemokines and their receptors are not isolated entities, but instead function in complex networks involving homo- and heterodimer formation as well as crosstalk with other signaling complexes. Here the functional consequences of chemokine receptor activity, from the perspective of both direct physical associations with other receptors and indirect crosstalk with orthogonal signaling pathways, are reviewed. Modulation of chemokine receptor activity through these mechanisms has significant implications in physiological and pathological processes, as well as drug discovery and drug efficacy. The integration of signals downstream of chemokine and other receptors will be key to understanding how cells fine-tune their response to a variety of stimuli, including therapeutics.

Mechanisms of chemokine and antigen-dependent T-lymphocyte navigation

T-lymphocyte trafficking is targeted to specific organs by selective molecular interactions depending on their differentiation and functional properties. Specific chemokine receptors have been associated with organ-specific trafficking of memory and effector T-cells, as well as the recirculation of naïve T-cells to secondary lymphoid organs. In addition to the acquisition of tissue-selective integrins and chemokine receptors, an additional level of specificity for T-cell trafficking into the tissue is provided by specific recognition of antigen displayed by the endothelium involving the TCRs (T-cell antigen receptors) and co-stimulatory receptors. Activation of PI3K (phosphoinositide 3-kinase) is a robust signalling event shared by most chemokine receptors as well as the TCR and co-stimulatory receptors, contributing to several aspects of T-lymphocyte homing as well as actin reorganization and other components of the general migratory machinery. Accordingly, inhibition of PI3K has been considered seriously as a potential therapeutic strategy by which to combat various T-lymphocyte-dependent pathologies, including autoimmune and inflammatory diseases, as well as to prevent transplant rejection. However, there is substantial evidence for PI3K-independent mechanisms that facilitate T-lymphocyte migration. In this regard, several other signalling-pathway components, including small GTPases, PLC (phospholipase C) and PKC (protein kinase C) isoforms, have also been implicated in T-lymphocyte migration in response to chemokine stimulation. The present review will therefore examine the PI3K-dependent and -independent signal-transduction pathways involved in T-cell migration during distinct modes of T-cell trafficking in response to either chemokines or the TCR and co-stimulatory molecules.

Chemokine receptor dimerization and chemotaxis

A broad array of biological responses ranging from cell polarization, movement, immune and inflammatory responses, as well as prevention of HIV-1 infection, are triggered by the chemokines, a family of structurally related chemoattractant proteins that bind to specific seven-transmembrane receptors linked to G proteins. Although it was initially believed that chemokine receptors act as monomeric entities, it has now been shown that they function as oligomers. Chemokine receptor homo- and heterodimers are found on the cell membrane; binding to their ligands stabilizes specific receptor conformations and activates distinct signaling cascades. Thorough analysis of the conformations adopted by the receptors at the membrane is therefore a prerequisite for understanding the function of these inflammatory mediators. For study of the chemokine receptor conformations at the cell surface, we focus here on conventional biochemical and genetic methods, as well as on new imaging techniques such as those based on resonance energy transfer; we also evaluate in vitro and in vivo methods to determine certain chemokine receptor functions.

MLN3897, a novel CCR1 inhibitor, impairs osteoclastogenesis and inhibits the interaction of multiple myeloma cells and osteoclasts

The interaction between osteoclasts (OCs) and multiple myeloma (MM) cells plays a key role in the pathogenesis of MM-related osteolytic bone disease (OBD). MM cells promote OC formation and, in turn, OCs enhance MM cell proliferation. Chemokines are mediators of MM effects on bone and vice versa; in particular, CCL3 enhances OC formation and promotes MM cell migration and survival. Here, we characterize the effects of MLN3897, a novel specific antagonist of the chemokine receptor CCR1, on both OC formation and OC-MM cell interactions. MLN3897 demonstrates significant impairment of OC formation (by 40%) and function (by 70%), associated with decreased precursor cell multinucleation and down-regulation of c-fos signaling. OCs secrete high levels of CCL3, which triggers MM cell migration; conversely, MLN3897 abrogates its effects by inhibiting Akt signaling. Moreover, MM cell-to-OC adhesion was abrogated by MLN3897, thereby inhibiting MM cell survival and proliferation. Our results therefore show novel biologic sequelae of CCL3 and its inhibition in both osteoclastogenesis and MM cell growth, providing the preclinical rationale for clinical trials of MLN3897 to treat OBD in MM.

Chemokine-mediated inflammation: Identification of a possible regulatory role for CCR2

The chemokine receptor CCR2 binds four pro-inflammatory monocyte chemoattractant proteins, designated MCP1/CCL2, MCP2/CCL8, MCP3/CCL7 and MCP4/CCL13. This study demonstrates the important biology of this receptor during the response to the chemokine milieu. Competitive chemotaxis and calcium flux assays were performed utilising mixtures of chemokines to assess a hierarchal arrangement of chemokine prepotency; these demonstrated that the MCP2-CCR2 interaction is able to supersede signals generated by RANTES, another pro-inflammatory chemokine, or the homeostatic chemokine SDF1. These observations were validated using three physiologically relevant monocytic cell lines. Having identified the importance of CCR2, experiments were then performed to examine the signal transduction processes coupled to this receptor. G protein coupling was initially examined; Cholera toxin reduced the chemotactic response to MCP2 (p<0.001), whilst the response to the other MCP chemokines remained normal. The response to MCP2 was uniquely inhibited by elevated concentrations of cAMP and, unlike MCP1, 3 and 4 (p<0.05), MCP2 failed to inhibit adenylate cyclase. Expression of dominant negative H-ras demonstrated that each MCP chemokine required active ras in order to elicit ERK activation and a chemotactic response. Unlike MCP1, MCP2 failed to induce nuclear translocation of activated ERK1 or subsequent induction of c-Myc expression. Akt activation also showed ligand-specific differences, with MCP2 producing a delayed response compared to the other MCP chemokines. Together these data highlight the importance of CCR2 and suggest that it is a powerful tool for fine tuning the immune response.

T lymphocytes on the move: chemokines, PI 3-kinase and beyond

The ordered, directional migration of T lymphocytes is a key process in development, immune surveillance and the immune response. Chemokines have an important role in the guidance of T lymphocytes and activate several members of the phosphoinositide 3-kinase (PI 3-kinase) family, which contribute to various aspects of the migratory machinery in many cell systems. However, the role of PI 3-kinase in T-cell movement is unclear, and its importance has been largely dismissed. Over the past two years, there has been exciting progress in our appreciation not only of the finer details of PI 3-kinase involvement in T-cell migration, but also of other signalling events that probably influence T-cell migration in response to recognized chemoattractants. These aspects of T-cell migration are the subject of this review.

Chemokines, sphingosine-1-phosphate, and cell migration in secondary lymphoid organs

Secondary lymphoid organs serve as hubs for the adaptive immune system, bringing together antigen, antigen-presenting cells, and lymphocytes. Two families of G protein-coupled receptors play essential roles in lymphocyte migration through these organs: chemokine receptors and sphingosine-1-phosphate (S1P) receptors. Chemokines expressed by lymphoid stromal cells guide lymphocyte and dendritic cell movements during antigen surveillance and the initiation of adaptive immune responses. S1P receptor-1 is required for lymphocyte egress from thymus and secondary lymphoid organs and is downregulated by the immunosuppressive drug FTY720. Here, we review the steps associated with the initiation of adaptive immune responses in secondary lymphoid organs, highlighting the roles of chemokines and S1P.

Expression and regulation of CC class chemokines in the dystrophic (mdx) diaphragm

In the murine (mdx) model of Duchenne muscular dystrophy, dystrophic changes are much more severe in the diaphragm than in limb muscles, and the diaphragm more closely resembles the human disease phenotype. Chemokines could play a central role in governing such phenotypic differences, as inflammation is an important disease modifier. Here we report that CC chemokine receptors (CCRs 1, 2, 3, 5) and ligands (macrophage inflammatory protein-1alpha, RANTES) are expressed at higher levels in dystrophic than in wild-type muscles across age groups (6, 12, and 24 wk). Moreover, chemokine ligand expression and muscle inflammation are significantly higher in dystrophic diaphragms than in limb muscles of the same animals. In vitro, CCR1 is constitutively expressed by cultured primary diaphragmatic myotubes. Stimulation of myotubes by proinflammatory cytokines (tumor necrosis factor-alpha, interleukin-1alpha, interferon-gamma) found within the in vivo dystrophic muscle environment, upregulates CCR1 in mdx and wild-type cultures, and also increases expression of its ligand RANTES to a significantly greater degree in the mdx group. Taken together, our results suggest that CC chemokines may play an important role in sustaining inflammation within the mdx diaphragm, which could help account for its more severe phenotype and also offer a target for therapeutic intervention in Duchenne patients.