Similarities and differences in RANTES- and (AOP)-RANTES-triggered signals: implications for chemotaxis

Molecular Role of HIV-1 Human Receptors (CCL5-CCR5 Axis) in neuroAIDS: A Systematic Review

Chronic HIV-1 infection can cause neurological illness, also known as HIV-associated neurocognitive disorders (HAND). The elevated level of pro-inflammatory cytokines and chemokines, such as C-C Chemokine Ligand 5 (CCL5/RANTES), is one of the ways of causing HIV-1-mediated neuroinflammation. C-C Chemokine Receptor 5 (CCR5) is the main coreceptor for viral entry into host cells and for mediating induction of CCL5/RANTES. CCR5 and CCL5 are part of a correlated axis of immune pathways used for effective protection against the HIV-1 virus. The purpose of this paper was to review the literary knowledge about the immunopathological relationship between this immune complex and neuroAIDS. A systematic review of the literature was conducted based on the selection and search of articles, available in English, Spanish, or Portuguese in the time frame of 1990-2022, of primary and secondary types in the PUBMED, Science Direct, SciELO, and LILACS databases through descriptors (MeSH) together with "AND": "CCR5"; "CCL5"; "neurological manifestations"; or "HIV". The methodological quality of the articles was assessed using the JBI Checklists and the PRISMA 2020 writing guidelines were followed. A total of 36 articles were included in the final composition of the review. The main cells of the CNS affected by neuroAIDS are: neurons; microglia; astrocytes; and oligodendrocytes. Molecular devices and their associations with cellular injuries have been described from the entry of the virus into the host's CNS cell to the generation of mental disorders. Furthermore, divergent results were found about the levels of CCL5/RANTES secretion and the generation of immunopathogenesis, while all condensed research for CCR5 indicated that elevation of this receptor causes more neurodegenerative manifestations. Therefore, new therapeutic and interventional strategies can be conditioned on the immunological direction proposed in this review for the disease.

Moving through a changing world: Single cell migration in 2D vs. 3D

Migration of single adherent cells is frequently observed in the developing and adult organism and has been the subject of many studies. Yet, while elegant work has elucidated molecular and mechanical cues affecting motion dynamics on a flat surface, it remains less clear how cells migrate in a 3D setting. In this review, we explore the changing parameters encountered by cells navigating through a 3D microenvironment compared to cells crawling on top of a 2D surface, and how these differences alter subcellular structures required for propulsion. We further discuss how such changes at the micro-scale impact motion pattern at the macro-scale.

Co-receptor signaling in the pathogenesis of neuroHIV

The HIV co-receptors, CCR5 and CXCR4, are necessary for HIV entry into target cells, interacting with the HIV envelope protein, gp120, to initiate several signaling cascades thought to be important to the entry process. Co-receptor signaling may also promote the development of neuroHIV by contributing to both persistent neuroinflammation and indirect neurotoxicity. But despite the critical importance of CXCR4 and CCR5 signaling to HIV pathogenesis, there is only one therapeutic (the CCR5 inhibitor Maraviroc) that targets these receptors. Moreover, our understanding of co-receptor signaling in the specific context of neuroHIV is relatively poor. Research into co-receptor signaling has largely stalled in the past decade, possibly owing to the complexity of the signaling cascades and functions mediated by these receptors. Examining the many signaling pathways triggered by co-receptor activation has been challenging due to the lack of specific molecular tools targeting many of the proteins involved in these pathways and the wide array of model systems used across these experiments. Studies examining the impact of co-receptor signaling on HIV neuropathogenesis often show activation of multiple overlapping pathways by similar stimuli, leading to contradictory data on the effects of co-receptor activation. To address this, we will broadly review HIV infection and neuropathogenesis, examine different co-receptor mediated signaling pathways and functions, then discuss the HIV mediated signaling and the differences between activation induced by HIV and cognate ligands. We will assess the specific effects of co-receptor activation on neuropathogenesis, focusing on neuroinflammation. We will also explore how the use of substances of abuse, which are highly prevalent in people living with HIV, can exacerbate the neuropathogenic effects of co-receptor signaling. Finally, we will discuss the current state of therapeutics targeting co-receptors, highlighting challenges the field has faced and areas in which research into co-receptor signaling would yield the most therapeutic benefit in the context of HIV infection. This discussion will provide a comprehensive overview of what is known and what remains to be explored in regard to co-receptor signaling and HIV infection, and will emphasize the potential value of HIV co-receptors as a target for future therapeutic development.

CCR5: Established paradigms and new frontiers for a 'celebrity' chemokine receptor

Because of the level of attention it received due to its role as the principal HIV coreceptor, CCR5 has been described as a 'celebrity' chemokine receptor. Here we describe the development of CCR5 inhibitory strategies that have been developed for HIV therapy and which are now additionally being considered for use in HIV prevention and cure. The wealth of CCR5-related tools that have been developed during the intensive investigation of CCR5 as an HIV drug target can now be turned towards the study of CCR5 as a model chemokine receptor. We also summarize what is currently known about the cell biology and pharmacology of CCR5, providing an update on new areas of investigation that have emerged in recent research. Finally, we discuss the potential of CCR5 as a drug target for diseases other than HIV, discussing the evidence linking CCR5 and its natural chemokine ligands with inflammatory diseases, particularly neuroinflammation, and certain cancers. These pathologies may provide new uses for the strategies for CCR5 blockade originally developed to combat HIV/AIDS.

GRK2 mediates TCR-induced transactivation of CXCR4 and TCR-CXCR4 complex formation that drives PI3Kγ/PREX1 signaling and T cell cytokine secretion

The immune system includes abundant examples of biologically-relevant cross-regulation of signaling pathways by the T cell antigen receptor (TCR) and the G protein-coupled chemokine receptor, CXCR4. TCR ligation induces transactivation of CXCR4 and TCR-CXCR4 complex formation, permitting the TCR to signal via CXCR4 to activate a phosphatidylinositol 3,4,5-trisphosphate-dependent Rac exchanger 1 protein (PREX1)-dependent signaling pathway that drives robust cytokine secretion by T cells. To understand this receptor heterodimer and its regulation, we characterized the molecular mechanisms required for TCR-mediated TCR-CXCR4 complex formation. We found that the cytoplasmic C-terminal domain of CXCR4 and specifically phosphorylation of Ser-339 within this region were required for TCR-CXCR4 complex formation. Interestingly, siRNA-mediated depletion of G protein-coupled receptor kinase-2 (GRK2) or inhibition by the GRK2-specific inhibitor, paroxetine, inhibited TCR-induced phosphorylation of CXCR4-Ser-339 and TCR-CXCR4 complex formation. Either GRK2 siRNA or paroxetine treatment of human T cells significantly reduced T cell cytokine production. Upstream, TCR-activated tyrosine kinases caused inducible tyrosine phosphorylation of GRK2 and were required for the GRK2-dependent events of CXCR4-Ser-339 phosphorylation and TCR-CXCR4 complex formation. Downstream of TCR-CXCR4 complex formation, we found that GRK2 and phosphatidylinositol 3-kinase γ (PI3Kγ) were required for TCR-stimulated membrane recruitment of PREX1 and for stabilization of cytokine mRNAs and robust cytokine secretion. Together, our results identify a novel role for GRK2 as a target of TCR signaling that is responsible for TCR-induced transactivation of CXCR4 and TCR-CXCR4 complex formation that signals via PI3Kγ/PREX1 to mediate cytokine production. Therapeutic regulation of GRK2 or PI3Kγ may therefore be useful for limiting cytokines produced by T cell malignancies or autoimmune diseases.

Protein engineering of the chemokine CCL20 prevents psoriasiform dermatitis in an IL-23-dependent murine model

Psoriasis is a chronic inflammatory skin disease characterized by the infiltration of T cell and other immune cells to the skin in response to injury or autoantigens. Conventional, as well as unconventional, γδ T cells are recruited to the dermis and epidermis by CCL20 and other chemokines. Together with its receptor CCR6, CCL20 plays a critical role in the development of psoriasiform dermatitis in mouse models. We screened a panel of CCL20 variants designed to form dimers stabilized by intermolecular disulfide bonds. A single-atom substitution yielded a CCL20 variant (CCL20 S64C) that acted as a partial agonist for the chemokine receptor CCR6. CCL20 S64C bound CCR6 and induced intracellular calcium release, consistent with G-protein activation, but exhibited minimal chemotactic activity. Instead, CCL20 S64C inhibited CCR6-mediated T cell migration with nominal impact on other chemokine receptor signaling. When given in an IL-23-dependent mouse model for psoriasis, CCL20 S64C prevented psoriatic inflammation and the up-regulation of IL-17A and IL-22. Our results validate CCR6 as a tractable therapeutic target for psoriasis and demonstrate the value of CCL20 S64C as a lead compound.

The role of the human Duffy antigen receptor for chemokines in malaria susceptibility: current opinions and future treatment prospects

The Duffy antigen receptor for chemokine (DARC) is a nonspecific receptor for several proinflammatory cytokines. It is homologous to the G-protein chemokine receptor superfamily, which is suggested to function as a scavenger in many inflammatory-and proinflammatory-related diseases. G-protein chemokine receptors are also known to play a critical role in infectious diseases; they are commonly used as entry vehicles by infectious agents. A typical example is the chemokine receptor CCR5 or CXCR4 used by HIV for infecting target cells. In malaria, DARC is considered an essential receptor that mediates the entry of the human and zoonotic malaria parasites Plasmodium vivax and Plasmodium knowlesi into human reticulocytes and erythrocytes, respectively. This process is mediated through interaction with the parasite ligand known as the Duffy binding protein (DBP). Most therapeutic strategies have been focused on blocking the interaction between DBP and DARC by targeting the parasite ligand, while strategies targeting the receptor, DARC, have not been intensively investigated. The rapid increase in drug resistance and the lack of new effective drugs or a vaccine for malaria constitute a major threat and a need for novel therapeutics to combat disease. This review explores strategies that can be used to target the receptor. Inhibitors of DARC, which block DBP-DARC interaction, can potentially provide an effective strategy for preventing malaria caused by P. vivax.

Use of Resonance Energy Transfer Techniques for In Vivo Detection of Chemokine Receptor Oligomerization

Since the first reports on chemokine function, much information has been generated on the implications of these molecules in numerous physiological and pathological processes, as well as on the signaling events activated through their binding to receptors. As is the case for other G protein-coupled receptors, chemokine receptors are not isolated entities that are activated following ligand binding; rather, they are found as dimers and/or higher order oligomers at the cell surface, even in the absence of ligands. These complexes form platforms that can be modified by receptor expression and ligand levels, indicating that they are dynamic structures. The analysis of the conformations adopted by these receptors at the membrane and their dynamics is thus crucial for a complete understanding of the function of the chemokines. We focus here on the methodology insights of new techniques, such as those based on resonance energy transfer for the analysis of chemokine receptor conformations in living cells.

CCR5 susceptibility to ligand-mediated down-modulation differs between human T lymphocytes and myeloid cells

CCR5 is a chemokine receptor expressed on leukocytes and a coreceptor used by HIV-1 to enter CD4(+) T lymphocytes and macrophages. Stimulation of CCR5 by chemokines triggers internalization of chemokine-bound CCR5 molecules in a process called down-modulation, which contributes to the anti-HIV activity of chemokines. Recent studies have shown that CCR5 conformational heterogeneity influences chemokine-CCR5 interactions and HIV-1 entry in transfected cells or activated CD4(+) T lymphocytes. However, the effect of CCR5 conformations on other cell types and on the process of down-modulation remains unclear. We used mAbs, some already shown to detect distinct CCR5 conformations, to compare the behavior of CCR5 on in vitro generated human T cell blasts, monocytes and MDMs and CHO-CCR5 transfectants. All human cells express distinct antigenic forms of CCR5 not detected on CHO-CCR5 cells. The recognizable populations of CCR5 receptors exhibit different patterns of down-modulation on T lymphocytes compared with myeloid cells. On T cell blasts, CCR5 is recognized by all antibodies and undergoes rapid chemokine-mediated internalization, whereas on monocytes and MDMs, a pool of CCR5 molecules is recognized by a subset of antibodies and is not removed from the cell surface. We demonstrate that this cell surface-retained form of CCR5 responds to prolonged treatment with more-potent chemokine analogs and acts as an HIV-1 coreceptor. Our findings indicate that the regulation of CCR5 is highly specific to cell type and provide a potential explanation for the observation that native chemokines are less-effective HIV-entry inhibitors on macrophages compared with T lymphocytes.

Chemokine receptor oligomerization and allostery

Oligomerization of chemokine receptors has been reported to influence many aspects of receptor function through allosteric communication between receptor protomers. Allosteric interactions within chemokine receptor hetero-oligomers have been shown to cause negative cooperativity in the binding of chemokines and to inhibit receptor activation in the case of some receptor pairs. Other receptor pairs can cause enhanced signaling and even activate entirely new, hetero-oligomer-specific signaling complexes and responses downstream of receptor activation. Many mechanisms contribute to these effects including direct allosteric coupling between the receptors, G protein-mediated allostery, G protein stealing, ligand sequestration, and recruitment of new intracellular proteins by exposing unique binding interfaces on the oligomerized receptors. These effects present both challenges as well as exciting opportunities for drug discovery. One of the most difficult challenges will involve determining if and when hetero-oligomers versus homomeric receptors are involved in specific disease states.

HIV-1 resistance to maraviroc conferred by a CD4 binding site mutation in the envelope glycoprotein gp120

Maraviroc (MVC) is a CCR5 antagonist that inhibits HIV-1 entry by binding to the coreceptor and inducing structural alterations in the extracellular loops. In this study, we isolated MVC-resistant variants from an HIV-1 primary isolate that arose after 21 weeks of tissue culture passage in the presence of inhibitor. gp120 sequences from passage control and MVC-resistant cultures were cloned into NL4-3 via yeast-based recombination followed by sequencing and drug susceptibility testing. Using 140 clones, three mutations were linked to MVC resistance, but none appeared in the V3 loop as was the case with previous HIV-1 strains resistant to CCR5 antagonists. Rather, resistance was dependent upon a single mutation in the C4 region of gp120. Chimeric clones bearing this N425K mutation replicated at high MVC concentrations and displayed significant shifts in 50% inhibitory concentrations (IC(50)s), characteristic of resistance to all other antiretroviral drugs but not typical of MVC resistance. Previous reports on MVC resistance describe an ability to use a drug-bound form of the receptor, leading to reduction in maximal drug inhibition. In contrast, our structural models on K425 gp120 suggest that this resistant mutation impacts CD4 interactions and highlights a novel pathway for MVC resistance.

Chemokine receptor oligomerization: a further step toward chemokine function

A broad array of biological responses including cell polarization, movement, immune and inflammatory responses, as well as prevention of HIV-1 infection, are triggered by the chemokines, a family of secreted and structurally related chemoattractant proteins that bind to class A-specific seven-transmembrane receptors linked to G proteins. Chemokines and their receptors should not be considered isolated entities, as they act in complex networks. Chemokines bind as oligomers, or oligomerize after binding to glycosaminoglycans on endothelial cells, and are then presented to their receptors on target cells, facilitating the generation of chemoattractant gradients. The chemokine receptors form homo- and heterodimers, as well as higher order structures at the cell surface. These structures are dynamic and are regulated by receptor expression and ligand levels. Complexity is even greater, as in addition to regulation by cytokines and decoy receptors, chemokine and receptor levels are affected by proteolytic cleavage and other protein modifications. This complex scenario should be considered when analyzing chemokine biology and the ability of their antagonists to act in vivo. Strategies based on blocking or stabilizing ligand and receptor dimers could be alternative approaches that might have broad therapeutic potential.

Mechanisms regulating chemokine receptor activity

Co-ordinated movement and controlled positioning of leucocytes is key to the development, maintenance and proper functioning of the immune system. Chemokines and their receptors play an essential role in these events by mediating directed cell migration, often referred to as chemotaxis. The chemotactic property of these molecules is also thought to contribute to an array of pathologies where inappropriate recruitment of specific chemokine receptor-expressing leucocytes is observed, including cancer and inflammatory diseases. As a result, chemokine receptors have become major targets for therapeutic intervention, and during the past 15 years much research has been devoted to understanding the regulation of their biological activity. From these studies, processes which govern the availability of functional chemokine receptors at the cell surface have emerged as playing a central role. In this review, we summarize and discuss current knowledge on the molecular mechanisms contributing to the regulation of chemokine receptor surface expression, from gene transcription and protein degradation to post-translational modifications, multimerization, intracellular transport and cross-talk.

HIV-1 Entry, Inhibitors, and Resistance

Entry inhibitors represent a new class of antiretroviral agents for the treatment of infection with HIV-1. While resistance to other HIV drug classes has been well described, resistance to this new class is still ill defined despite considerable clinical use. Several potential mechanisms have been proposed: tropism switching (utilization of CXCR4 instead of CCR5 for entry), increased affinity for the coreceptor, increased rate of virus entry into host cells, and utilization of inhibitor-bound receptor for entry. In this review we will address the development of attachment, fusion, and coreceptor entry inhibitors and explore recent studies describing potential mechanisms of resistance.

CCR5 monoclonal antibodies for HIV-1 therapy

PURPOSE OF REVIEW

To summarize emerging clinical and preclinical data pertaining to the use of CCR5 monoclonal antibodies (mAbs) as therapies for HIV-1 infection. The epitope specificity of CCR5 mAbs is discussed in relation to its critical impact on antiviral activity and CCR5 antagonism. We compare and contrast mAbs and small-molecule CCR5 antagonists in terms of their binding and antiviral properties. Two CCR5 mAbs have entered clinical testing and have successfully completed proof-of-concept studies in HIV-infected individuals, providing initial information on the potential therapeutic utility of these agents.

RECENT FINDINGS

New studies support the view that the most potent antiviral CCR5 mAbs recognize the second extracellular loop of CCR5 either exclusively or in combination with the amino terminus. Studies have revealed fundamental differences in how mAbs and small molecules bind CCR5 and inhibit HIV-1. CCR5 mAbs and small-molecule CCR5 antagonists have demonstrated consistent antiviral synergy and limited or no viral cross-resistance in independent studies. Single intravenous infusions of CCR5 mAbs significantly reduced HIV-1 RNA levels in infected individuals for 2-3 weeks without appreciable toxicity.

SUMMARY

CCR5 mAbs have demonstrated broad and potent antiviral activity in vitro. Clinical studies have established CCR5 mAbs as potent antiretroviral agents with prolonged activity following a single dose. CCR5 mAbs represent both a distinct class of CCR5 inhibitor and a novel approach to HIV-1 therapy.

The prostate specific membrane antigen regulates the expression of IL-6 and CCL5 in prostate tumour cells by activating the MAPK pathways

The interleukin-6 (IL-6) and the chemokine CCL5 are implicated in the development and progression of several forms of tumours including that of the prostate. The expression of the prostate specific membrane antigen (PSMA) is augmented in high-grade and metastatic tumors. Observations of the clinical behaviour of prostate tumors suggest that the increased secretion of IL-6 and CCL5 and the higher expression of PSMA may be correlated. We hypothesized that PSMA could be endowed with signalling properties and that its stimulation might impact on the regulation of the gene expression of IL-6 and CCL5. We herein demonstrate that the cross-linking of cell surface PSMA with specific antibodies activates the small GTPases RAS and RAC1 and the MAPKs p38 and ERK1/2 in prostate carcinoma LNCaP cells. As downstream effects of the PSMA-fostered RAS-RAC1-MAPK pathway activation we observed a strong induction of NF-κB activation associated with an increased expression of IL-6 and CCL5 genes. Pharmacological blockade with specific inhibitors revealed that both p38 and ERK1/2 participate in the phenomenon, although a major role exerted by p38 was evident. Finally we demonstrate that IL-6 and CCL5 enhanced the proliferative potential of LNCaP cells synergistically and in a dose-dependent manner and that CCL5 functioned by receptor-mediated activation of the STAT5-Cyclin D1 pro-proliferative pathway. The novel functions attributable to PSMA which are described in the present report may have profound influence on the survival and proliferation of prostate tumor cells, accounting for the observation that PSMA overexpression in prostate cancer patients is related to a worse prognosis.

Imaging techniques: new insights into chemokine/chemokine receptor biology at the immune system

Our current knowledge of molecular and cellular responses in vivo is based mainly on event reconstruction from time-freeze observations. Conventional biochemical and genetic methods consider the cell as an individual entity and ligand/receptor pairs as isolated systems. In addition, the data refer to the average behavior of a pool of cells and/or receptors removed from their real-life context. The use of new technologies, particularly real-time imaging approaches, is showing us that biological responses are highly dynamic and extremely dependent on the context in which they take place, and therefore much more diverse than initially envisaged. This review focuses on the mechanistic insights that new imaging techniques, such as those based on resonance energy transfer and two-photon microscopy, contribute to our understanding of how receptors work within a single cell, and how cells work within a tissue. Cell movement is a complex and regulated process; it has a key role in embryogenesis, organogenesis, wound-healing and tumor invasion. Nonetheless, it is in immune system homeostasis and response that cell movement becomes essential. For this reason, immunology is being radically transformed and enriched by these new approaches. We will discuss the use of these techniques for studying chemokine/chemokine receptors and their role in the immune system function, and comment on the potential contribution to the design of therapeutic strategies.

Chemokine-idiotype fusion DNA vaccines are potentiated by bivalency and xenogeneic sequences

V regions of monoclonal Ig express an exquisite B-cell tumor–specific antigen called idiotype (Id). Id is a weak antigen and it is important to improve immunogenicity of Id vaccines. Chemokine receptors are expressed on antigen-presenting cells (APCs) and are promising targets for Id vaccines. Here we compare monomeric and dimeric forms of MIP-1α and RANTES that target Id to APCs in a mouse B lymphoma (A20) and a multiple myeloma model (MOPC315). MIP-1α was more potent than RANTES. The dimeric proteins were more potent than monomeric equivalents in short-term assays. When delivered in vivo by intramuscular injection of plasmids followed by electroporation, dimeric proteins efficiently primed APCs in draining lymph nodes for activation and proliferation of Id-specific CD4+ T cells. Good anti-Id antibody responses were obtained, and mice immunized only once were 60% to 80% protected in both tumor models. CD8+ T cells contributed to the protection. Antibody responses and tumor protection were reduced when the human Ig hinge = CH3 dimerization motif was replaced with syngeneic mouse counterparts, indicating that tumor-protective responses were dependent on xenogeneic sequences. The results suggest that bivalency and foreign sequences combine to increase the efficiency of chemokine-Id DNA vaccines.

Naloxone acts as a potent analgesic in transgenic mouse models of sickle cell anemia

Sickle cell anemia is a common genetic disorder in African Americans. Opioid analgesics are traditionally the treatment for the severe pain associated with this disease. Here we reveal that the opioid antagonist naloxone possesses potent analgesic activity in two transgenic mouse models of sickle cell anemia (NY1DD and hBERK1) and not in their respective controls (ICR-CD1 and C57BL/6J) when administered by three parenteral routes [intracerebroventricular (i.c.v.), intrathecal, and subcutaneous]. In the NY1DD mice, naloxone (i.c.v.) possessed approximately 300-fold greater potency than morphine (i.c.v.). Other opioid antagonists (naltrexone, norbinaltorphimine, and naltrindole) were substantially less effective in producing analgesia. Naloxone and morphine were synergistic in NY1DD mice, suggesting different receptor systems. Microarray analysis suggested naloxone-induced down-regulation of the CC chemokine receptor (CCR)5 in NY1DD mice but not in control mice. Pretreatment of control mice with CC chemokine ligand 5 [CCL5 (RANTES)] enabled naloxone to produce analgesia similar to that observed in NY1DD mice. Mu opioid receptor knockout mice treated similarly also displayed analgesia. That the effect of CCL5 was specifically related to CCR5 and/or CCR1 activation was demonstrated by antagonism of analgesia with the chemokine antagonist methionylated RANTES. Similar antagonism of naloxone-induced analgesia also was observed when NY1DD mice were pretreated with methionylated RANTES. These results indicate that CCR5/CCR1 receptors are directly or indirectly involved in analgesia produced by naloxone. The present study suggests that naloxone may be clinically useful in the treatment of pain associated with sickle cell disease and other disorders involving inflammation.

Structural basis for the interaction of CCR5 with a small molecule, functionally selective CCR5 agonist

The chemokine receptor CCR5 is an attractive target for HIV-1 drug development, as individuals whose cells lack surface CCR5 expression are highly resistant to HIV-1 infection. CCR5 ligands, such as CCL5/RANTES, effectively inhibit HIV-1 infection by competing for binding opportunities to the CCR5 and inducing its internalization. However, the inherent proinflammatory activity of the chemotactic response of CCR5 ligands has limited their clinical use. In this study, we found that a novel small molecule, functionally selective CCR5 agonist, 2,2-dichloro-1-(triphenylphosphonio)vinyl formamide perchlorate (YM-370749), down-modulates CCR5 from the cell surface without inducing a chemotactic response and inhibits HIV-1 replication. In molecular docking studies of YM-370749 and a three-dimensional model of CCR5 based on the rhodopsin crystal structure as well as binding and functional studies using various CCR5 mutants, the amino acid residues necessary for interaction with YM-370749 were marked. These results provide a structural basis for understanding the activation mechanism of CCR5 and for designing functionally selective agonists as a novel class of anti-HIV-1 agents.

Genetic variants of RANTES are associated with serum RANTES level and protection for type 1 diabetes

RANTES (regulated on activation, normal T-cell expressed and secreted) is a T-helper type 1 (Th1) chemokine that promotes T-cell activation and proliferation. RANTES is genetically associated with asthma, sarcoidosis and multiple sclerosis. The concentration of RANTES is increased at inflammation sites in different autoimmune diseases. Type 1 diabetes (T1D) is a Th1-mediated disease with complex genetic predisposition. We tested RANTES as a candidate gene for association with T1D using three single-nucleotide polymorphism (SNP) variants (rs4251719, rs2306630 and rs2107538) to capture haplotype information. The minor alleles of all SNPs were transmitted less frequently to T1D offspring (transmission rates 37.3% (P=0.002), 38.7% (P=0.007) and 41.0% (P=0.01)) and were less frequently present in patients compared to controls (P=0.009, 0.03 and 0.04, respectively). A similar protective effect was observed for the haplotype carrying three minor alleles (transmission disequilibrium test (TDT): P=0.003; odds ratio (OR)=0.55; confidence interval (CI): 0.37-0.83; case/control: P=0.03; OR=0.74; CI: 0.55-0.98). Both patients and controls carrying the protective haplotype express significantly lower serum levels of RANTES compared to non-carriers. Subsequently, we tested a cohort of 310 celiac disease patients, but failed to detect association. RANTES SNPs are significantly associated with RANTES serum concentration and development of T1D. The rs4251719*A-rs2306630*A-rs2107538*A haplotype associated with low RANTES production confers protection from T1D. Our data imply that RANTES is associated with T1D both genetically and functionally, and contributes to diabetes-prone Th1 cytokine profile.

Vaccinia virus activation of CCR5 invokes tyrosine phosphorylation signaling events that support virus replication

Vaccinia virus, a poxvirus, produces structurally distinct forms of virions for which the immediate events following cell entry are ill-defined. We provide evidence that intracellular mature virus (IMV) enters both permissive and nonpermissive T-cell lines and that introduction of CCR5 into nonpermissive mouse fibroblasts or human primary T cells renders the cells permissive for vaccinia replication. Notably, T cells expressing CCR5 in which tyrosine 339 in the intracellular region is replaced by phenylalanine no longer support virus replication or virus-inducible activation of specific host cell signaling effectors IRS-2, Grb2, and Erk1/2. We show that following IMV entry into the cell, the intact but not the tyrosine-deficient CCR5 is rapidly internalized and colocalizes with virus. This colocalization precedes virus-inducible signaling and replication.

Macaque trophoblast migration toward RANTES is inhibited by cigarette smoke-conditioned medium

Trophoblast migration within the endometrium and uterine vasculature is essential for normal placental and fetal development. We previously demonstrated that macaque trophoblasts express the chemokine receptor CCR5 and that this receptor mediates trophoblast migration toward RANTES (regulated upon activation normal T-cell expressed and secreted). In the present paper we have used primary cultures of early gestation macaque trophoblasts to test the hypothesis that tobacco smoke inhibits trophoblast migration as the result of dysregulation of the RANTES/CCR5 chemotactic axis. Early gestation macaque trophoblasts were incubated in the absence or presence of cigarette smoke-conditioned medium (CSM). Cell migration was quantified using migration chambers. CCR5 and G protein receptor kinase 2 (GRK2) expression was measured by immunofluorescence microscopy and Western blotting. cAMP levels were measured by enzyme-linked immunosorbent assay. Trophoblast migration toward RANTES was reduced when cells were incubated in CSM. Trophoblasts also showed reduced expression of CCR5, increased levels of cAMP, and increased expression of GRK2. Finally, the secretion of RANTES by uterine endothelial cells was reduced by exposing the cells to CSM. These results support the idea that cigarette smoke constituents inhibit directional trophoblast migration by causing increased desensitization of trophoblast CCR5 and inhibiting the secretion of RANTES by endothelial cells.

The attraction of chemokines as a target for specific anti-inflammatory therapy

Since the identification of the first chemotactic cytokines 20 years ago, the field has mushroomed, with the discovery of approximately 40 ligands, which interact with 20 different cell surface receptors. At the time of writing this review, a PubMed trawl using the word 'chemokine' will recover over 28,000 manuscripts. In this article, we will give a short history of the discovery of chemokines and provide examples of the potential for therapeutic targeting of the chemokine network in inflammatory disease.

Peptide, Peptidomimetic and Small-molecule Drug Discovery Targeting HIV-1 Host-cell Attachment and Entry through gp120, gp41, CCR5 and CXCR4+

This review highlights selected examples of peptide, peptidomimetic and small-molecule drug discovery targeting HIV-1 to advance novel anti-HIV pharmaceuticals that inhibit initial stages of the viral cycle; namely, attachment and entry. Some of these approaches have culminated in the development of peptide-based drugs, while other have exploited peptides as enabling tools toward the identification of small-molecule lead compounds. Both of these conceptually different approaches have facilitated lead optimization of molecules with complementary and often surprising anti-HIV pharmacological properties, supporting their role in pharmaceutical development. Furthermore, such molecules enabled mechanistic elucidation of viral attachment and entry and provided additional insights toward achieving the desired drug profile.

A single amino acid change and truncated TM are sufficient for simian immunodeficiency virus to enter cells using CCR5 in a CD4-independent pathway

Entry of HIV and SIV into susceptible cells is mediated by CD4 and chemokine receptors, which act as coreceptors. To study cell entry of SIV, we constructed a cell line, xKLuSIV, derived from non-susceptible human K562 cells, that express the firefly luciferase reporter gene under control of a minimal SIV long terminal repeat (LTR). Using these susceptible cells, we studied the entry of a well-characterized molecularly cloned macrophage-tropic SIV. xKLuSIV cells that express rhesus macaque CD4 and/or the rhesus chemokine receptor CCR5 are susceptible to infection with the macrophage-tropic, neurovirulent strain SIV/17E-Fr, but only xKLuSIV cells expressing both CCR5 and CD4 were susceptible to infection by the macrophage-tropic, non-neurovirulent strain SIV/17E-Cl. CCR5-dependent, CD4-independent infection by SIV/17E-Fr was abrogated by pre-incubation of the cells with AOP-RANTES, a ligand for CCR5. In addition to viral entry occurring by a CD4-independent mechanism, neutralization of SIV/17E-Fr with rhesus mAbs from 3 different neutralization groups blocked entry into x KLuSIV cells by both CD4-dependent and -independent mechanisms. Triggering the env glycoprotein of SIV-17 EFr with soluble CD4 had no significant effect in infectivity, but triggering of the same glycoprotein of SIV/17E-Cl allowed it to enter cells in a CD4-independent fashion. Using mutant molecular clones, we studied the determinants for CD4 independence, all of which are confined to the env gene. We report here that truncation of the TM at amino acid 764 and changing a single amino acid (R751G) in the SIV envelope transmembrane protein (TM) conferred the observed CD4-independent phenotype. Our data suggest that the envelope from the neurovirulent SIV/17E-Fr interacts with CCR5 in a CD4-independent manner, and changes in the TM protein of this virus are important components that contribute to neurovirulence in SIV.

The role of chemokines and extracellular matrix components in the migration of T lymphocytes into three-dimensional substrata

The role of chemokines and their interactions with extracellular matrix components (ECM) or the capacity of T cells to migrate into and accumulate within three-dimensional (3D) collagen type 1 substrata was studied. We examined the influence of chemokines and fibronectin on the infiltration properties of non-infiltrative (do not migrate into 3D substrata) and spontaneously infiltrative (migrate into 3D substrata) T-cell lines. Infiltrative and non-infiltrative T-acute lymphocytic leukaemic cell lines exhibited no consistent differences with respect to the expression of various chemokine receptors or beta(1)-integrins. Chemokines presented inside the collagen increased the depth of migration of infiltrative T-cell lines, but did not render non-infiltrative T-cell lines infiltrative, although they augmented the attachment of non-infiltrative T-cell lines to the upper surface of the collagen. The presence of fibronectin inside the collagen did not render non-infiltrative T-cell lines infiltrative, but markedly augmented the migration of 'infiltrative' T-cell lines into collagen. Both infiltrative and non-infiltrative T-cell lines showed migratory responses to chemokines in Boyden assays (migration detected on 2D substrata). These results indicate that the process of T-cell infiltration/migration into 3D substrata depends on a tissue penetration mechanism distinguishable from migration on 2D substrata and that the basic capacity of T cells to infiltrate is independent of chemokines and ECM components applied as attractants.

Heterophilic interactions of platelet factor 4 and RANTES promote monocyte arrest on endothelium

The chemokines platelet factor 4 (PF4) and RANTES (regulated on activation normal T cell expressed and secreted) are secreted by activated platelets and influence multiple cell types and biologic processes. For instance, PF4 inhibits progenitor cell proliferation and angiogenesis, while platelet-derived RANTES is involved in vascular recruitment of monocytes. However, little is known about functional interactions of PF4 and RANTES. Here we show that the presence of PF4 enhanced the arrest of RANTES-stimulated monocytes and monocytic cells on activated endothelial cells under flow conditions, while binding of PF4 to the monocyte surface was increased by RANTES. Both RANTES-triggered arrest and PF4 binding involved monocytic chondroitin sulfate. Ligand blots and surface plasmon resonance revealed a robust heterophilic interaction of PF4 with RANTES but not with RANTES variants defective in higher order oligomerization. The tetrameric mutant E26A bound to the monocyte surface without increasing PF4 binding, and monocyte arrest induced by E26A-RANTES was not enhanced by PF4. Stimulation of monocytes with supernatants of activated platelets triggered arrest involving RANTES and PF4, as shown by inhibition studies. Our results suggest that heterophilic interactions with PF4 require structural motifs important in RANTES oligomerization and amplify RANTES-triggered effects on monocyte adhesion. This may have implications for the modulation of inflammatory recruitment by platelet-derived chemokines.

Activation of formyl peptide receptor-like 1 by WKYMVm induces serine phosphorylation of STAT3, which inhibits its tyrosine phosphorylation and nuclear translocation induced by hydrogen peroxide

Signal transducer and activator of transcription 3 (STAT3) is an important transcription factor that modulates the expression of several genes. The activation of STAT3 accompanies tyrosine phosphorylation and its translocation to the nucleus. Formyl peptide receptor like 1 (FPRL1) is an important classical chemoattractant receptor. In this study, we observed that the stimulation of FPRL1 by Trp-Lys-Tyr-Met-Val-D-Met (WKYMVm) caused serine phosphorylation but not tyrosine phosphorylation of STAT3 in a pertussis toxin-sensitive manner. Moreover, downstream of FPRL1 stimulation, phospholipase D (PLD) activity was dramatically increased. n-butanol, a well-known phosphatidic acid (PA) acceptor, completely inhibited WKYMVm-induced STAT3 serine phosphorylation. Moreover, the exogenous addition of PA mimicked STAT3 phosphorylation by WKYMVm. We also found that WKYMVm stimulated extracellular signal regulated kinase (ERK), and that ERK activity is required for STAT3 serine phosphorylation. This WKYMVm-induced ERK activation was inhibited by n-butanol, whereas ERK activation was also induced by the addition of exogenous PA. In terms of the functional aspects of the WKYMVm-induced serine phosphorylation of STAT3, we found that hydrogen peroxide-stimulated STAT3 activation was blocked by pretreating WKYMVm. Taken together, we found that WKYMVm stimulated FPRL1, and that this resulted in STAT3 serine phosphorylation via PLD-mediated ERK activation, and that the serine phosphorylation of STAT3 blocked hydrogen peroxide-induced STAT3 activity.

CCL3, acting via the chemokine receptor CCR5, leads to independent activation of Janus kinase 2 (JAK2) and Gi proteins

The interaction of the chemokine receptor, CCR5, expressed in recombinant cells, with different G proteins was investigated and CCR5 was found to interact with Gi, Go and Gq species. Interaction with Gi leads to G protein activation, whereas Gq does not seem to be activated. Additionally, CCR5 activation also leads to phosphorylation of Janus kinase 2 (JAK2). Activation of JAK2 is independent of Gi or Gq activation. Gi protein activation was not prevented by inhibition of JAK, showing that heterotrimeric G protein activation and activation of the JAK/signal transducer and activator of transcription (STAT) pathway are independent of each other.

Mutational analysis of the R33-encoded G protein-coupled receptor of rat cytomegalovirus: identification of amino acid residues critical for cellular localization and ligand-independent signalling

The rat cytomegalovirus (RCMV) R33 gene encodes a G protein-coupled receptor (GPCR), pR33, which possesses agonist-independent, constitutive signalling activity. To characterize this activity further, we generated a series of point and deletion mutants of pR33. Both expression of and signalling by the mutants was evaluated. Several point mutants were generated that contained modifications in the NRY motif. This motif, at aa 130–132 of pR33, is the counterpart of the common DRY motif of GPCRs, which is known to be involved in G protein coupling. We found that mutation of the asparagine residue within the NRY motif of pR33 (N130) to aspartic acid resulted in a mutant (N130D) with similar signalling characteristics to the wild-type (WT) protein, indicating that N130 is not the determinant of constitutive activity of pR33. Interestingly, a mutant carrying an alanine at aa 130 (N130A) was severely impaired in Gq/11-mediated, constitutive activation of phospholipase C, whereas it displayed similar levels of activity to pR33 in Gi/0-mediated signalling. Another protein that contained a modified NRY motif, R131A, did not show constitutive activity, whereas mutants Y132F and Y132A displayed similar activities to the WT receptor. This indicated that residue R131 is critical for pR33 function in vitro, whereas Y132 is not. Finally, we identified two consecutive arginines within the C-terminal tails of both pR33 and its homologue from human CMV, pUL33, which are important for correct cell-surface expression of these receptors.

Chemokine receptor expression and in vivo signaling pathways in the joints of rats with adjuvant-induced arthritis

OBJECTIVE

This study was undertaken to characterize the role of CC chemokines and their receptors in rat adjuvant-induced arthritis (AIA), a model for rheumatoid arthritis (RA). Furthermore, we investigated the signaling pathways associated with CC receptors as well as the cell type distribution of the receptors.

METHODS

Using TaqMan real-time reverse transcription-polymerase chain reaction, Western blot analysis, and immunohistochemistry, we defined chemokine and chemokine receptor messenger RNA (mRNA) expression, CC chemokine receptor (CCR) protein activation during the disease course, CCR-associated signaling pathways, and immunopositive CCR5, phosphorylated signal transducer and activator of transcription 1 (p-STAT-1), and p-STAT-3 cells in rat AIA versus control joints.

RESULTS

We showed significant up-regulation of CCR1, CCR2, CCR5, and macrophage inflammatory protein 1beta/CCL4 mRNA in AIA on post-adjuvant injection day 18, coincident with peak inflammation. Additionally, increases in tyrosine phosphorylation of CCR1 (days 14, 18, 21, and 24), CCR2 (days 14 and 18), and CCR5 (days 14, 18, and 21) were detected in AIA rats compared with control (nonarthritic) rats. JAK-1, STAT-1, and STAT-3 were associated with CCR1 and were highly tyrosine phosphorylated on days 14 and 18. Moreover, CCR2 was associated with JAK-2, STAT-1, and STAT-3 on day 18. The association of STAT-1 and STAT-3 with CCR5 on days 18 and 21 correlated with JAK-1 phosphorylation and binding on day 18. However, the activation of JNK was not associated with CCR5 activation in rat AIA. Immunohistochemical analysis demonstrated that the expression of CCR5, p-STAT-1, and p-STAT-3 was detected on synovial lining cells, macrophages, and endothelial cells in arthritic rat ankles on post-adjuvant injection day 18. While the majority of the CCR5 and p-STAT-1 immunostaining was on synovial lining cells and macrophages, p-STAT-3 was predominantly expressed on endothelial cells.

CONCLUSION

CCR1, CCR2, and CCR5 mRNA expression and tyrosine phosphorylation increased with peak inflammation in the AIA model. CCR1, CCR2, and CCR5 tyrosine phosphorylation are associated with the JAK/STAT-1/STAT-3 pathway at different stages of rat AIA, as well as with macrophage and endothelial cell infiltration. However, their signaling activation overlaps with peak inflammation. Up-regulation and activation of CCRs may play a role in macrophage and endothelial cell infiltration in rat AIA joints in addition to activating the associated signaling pathways. The downstream intermediate signaling proteins associated with CC receptors may be used as potential tools to control inflammation in RA.

Chemokine-induced cell death in CCR5-expressing neuroblastoma cells

CCR5 is expressed in neurons but its function in this cellular context is hitherto poorly understood. We have generated CCR5-expressing SH-SY5Y neuroblastoma cells. CCR5 ligands induced cell death in these cells, but not in control neuroblastoma cells or in CCR5-expressing fibroblasts. CCR5-dependent killing of neuroblastoma cells occurred through apoptosis, since it was accompanied by caspase-3 activation and could be prevented by a caspase-3 inhibitor. Finally, cell killing by activated microglia was more rapid and extensive in CCR5-expressing neuroblastoma cells than in control cells. In summary, CCR5 may act as a death receptor in cells of neuronal lineage and therefore be involved in inflammatory neurodegeneration.

Human Cytomegalovirus Chemokine Receptor US28-induced Smooth Muscle Cell Migration Is Mediated by Focal Adhesion Kinase and Src

The human cytomegalovirus-encoded chemokine receptor US28 induces arterial smooth muscle cell (SMC) migration; however, the underlying mechanisms involved in this process are unclear. We have previously shown that US28-mediated SMC migration occurs by a ligand-dependent process that is sensitive to protein-tyrosine kinase inhibitors. We demonstrate here that US28 signals through the non-receptor protein-tyrosine kinases Src and focal adhesion kinase (FAK) and that this activity is necessary for US28-mediated SMC migration. In the presence of RANTES (regulated on activation normal T cell expressed and secreted), US28 stimulates the production of a FAK.Src kinase complex. Interestingly, Src co-immunoprecipitates with US28 in a ligand-dependent manner. This association occurs earlier than the formation of the FAK.Src kinase complex, suggesting that US28 activates Src before FAK. US28 binding to RANTES also promotes the formation of a Grb2.FAK complex, which is sensitive to treatment with the Src inhibitor PP2, further highlighting the critical role of Src in US28 activation of FAK. Human cytomegalovirus US28-mediated SMC migration is inhibited by treatment with PP2 and through the expression of either of two dominant negative inhibitors of FAK (F397Y and NH2-terminal amino acids 1-401). These findings demonstrate that activation of FAK and Src plays a critical role in US28-mediated signaling and SMC migration.

Signal transduction events regulating integrin function and T cell migration: new functions and complexity

Integrin receptors facilitate T cell function by mediating adhesive events critical for T cell trafficking and recognition of foreign antigen, including interactions with vascular endothelium, extracellular matrix components, and antigen-presenting cells. Consequently, the functional activity of integrin receptors is acutely regulated by various intracellular signals delivered by other cell surface receptors, resulting in rapid changes in T cell adhesion and migration. This review highlights recent insights into our understanding of the signaling events by which the CD3/T cell receptor complex and chemokine receptors regulate integrin function and T cell migration. These studies highlight novel functions for several signaling molecules, including the tyrosine kinases Itk and ZAP-70, and the adapter protein SLAP-130/Fyb. In addition, analysis of the regulation of integrin function and chemokine-mediated migration has highlighted the critical role that spatial localization of signaling molecules plays in signal transduction, and the importance of the actin cytoskeleton in T cell function.

Differential signaling of formyl peptide receptor-like 1 by Trp-Lys-Tyr-Met-Val-Met-CONH2 or lipoxin A4 in human neutrophils

Classical chemoattractant receptors are of fundamental importance to immune responses. The two major roles of such receptors are the modulation of chemotaxis and the generation of reactive oxygen species. The formyl peptide receptor-like 1 (FPRL1) can be stimulated by two different ligands, Trp-Lys-Tyr-Met-Val-Met-CONH2 (WKYMVM) and lipoxin A4 (LXA4). Although leukocyte chemotaxis mediated by activated FPRL1 has been reported, the role of FPRL1 in superoxide generation remains to be studied. In this study, we examined the effect of WKYMVM or LXA4 on chemotactic migration and superoxide generation in human neutrophils. WKYMVM and LXA4 stimulated neutrophil chemotaxis via tyrosine phosphorylation events. In terms of reactive oxygen species generation, WKYMVM but not LXA4 stimulated superoxide generation in neutrophils. To understand this difference on superoxide generation via the same receptor, FPRL1, we compared the signaling pathways downstream of FPRL1 by the two different ligands. At first, we confirmed that both WKYMVM and LXA4 caused intracellular calcium ([Ca2+]i) increase in a pertussis toxin-sensitive manner and that these ligands competitively inhibited each other with respect to [Ca2+]i increase in neutrophils. This result suggests that WKYMVM and LXA4 share the same receptor, FPRL1. By investigating cellular signaling by WKYMVM and LXA4, we found that WKYMVM but not LXA4 induced extracellular signal-regulated protein kinases (ERKs), c-Jun NH2-terminal kinase, and phospholipase A2 (PLA2) activation. We also found that ERK-mediated cytosolic PLA2 activity is essential for superoxide generation. These results indicate that the activation of FPRL1 by the two different ligands can induce differential cellular signaling and unique functional consequences in human neutrophils.

Agonist-independent desensitization and internalization of the human platelet-activating factor receptor by coumermycin-gyrase B-induced dimerization

Platelet-activating factor (PAF) is a phospholipid with potent and diverse physiological actions, particularly as a mediator of inflammation. We have reported previously that mutant G protein-coupled receptors (GPCRs) affect the functional properties of coexpressed wild-type human PAF receptor (hPAFR) (Le Gouill, C., Parent, J. L., Caron, C. A., Gaudreau, R., Volkov, L., Rola-Pleszczynski, M., and Stankova, J. (1999) J. Biol. Chem. 274, 12548-12554). Increasing evidence suggests that dimerization of GPCRs may play an important role in the regulation of their biological activity. Additional data have also suggested that dimerization may be important in the subsequent internalization of the delta-opioid receptor. To investigate the specific role of dimerization in the internalization process of GPCRs, we generated a fusion protein of hPAFR and bacterial DNA gyrase B (GyrB), dimerized through the addition of coumermycin. We found that dimerization potentiates PAF-induced internalization of hPAFR-GyrB in Chinese hamster ovary cells stably expressing c-Myc-hPAFR-GyrB. Coumermycin-driven dimerization was also sufficient to induce an agonist-independent sequestration process in an arrestin- and clathrin-independent manner. Moreover, the protein kinase C inhibitors staurosporine and GF109203X blocked the coumermycin-induced desensitization of hPAFR-GyrB, suggesting the implication of protein kinase C in the molecular mechanism mediating the agonist-independent desensitization of the receptor. Taken together, these findings suggest a novel mechanism of GPCR desensitization and internalization triggered by dimerization.

Recent progress in discovery of small-molecule CCR5 chemokine receptor ligands as HIV-1 inhibitors

This review addresses key pharmacology and virology issues relevant in discovery and development of CCR5 antagonists as anti-HIV drugs, such as target validation, receptor internalization, allosterism, viral resistance and tropism. Recent progress in the discovery and development of CCR5 antagonists, SAR and clinical status are reviewed. Finally, modeling-based structure of CCR5 is discussed in the context of a small-molecule antagonism of the CCR5 receptor.

CC chemokine ligand 5/RANTES chemokine antagonists aggravate glomerulonephritis despite reduction of glomerular leukocyte infiltration

The chemokine CC chemokine ligand (CCL)5/RANTES as well as its respective receptor CCR5 mediate leukocyte infiltration during inflammation and are up-regulated early during the course of glomerulonephritis (GN). We tested the effects of the two CCL5/RANTES blocking analogs, Met-RANTES and amino-oxypentane-RANTES, on the course of horse apoferritin (HAF)-induced GN. HAF-injected control mice had proliferative GN with mesangial immune complex deposits of IgG and HAF. Daily i.p. injections of Met-RANTES or amino-oxypentane-RANTES markedly reduced glomerular cell proliferation and glomerular macrophage infiltration, which is usually associated with less glomerular injury and proteinuria in HAF-GN. Surprisingly, however, HAF-GN mice treated with both analogs showed worse disease with mesangiolysis, capillary obstruction, and nephrotic range albuminuria. These findings were associated with an enhancing effect of the CCL5/RANTES analogs on the macrophage activation state, characterized by a distinct morphology and increased inducible NO synthetase expression in vitro and in vivo, but a reduced uptake of apoptotic cells in vivo. The humoral response and the Th1/Th2 balance in HAF-GN and mesangial cell proliferation in vitro were not affected by the CCL5/RANTES analogs. We conclude that, despite blocking local leukocyte recruitment, chemokine analogs can aggravate some specific disease models, most likely due to interactions with systemic immune reactions, including the removal of apoptotic cells and inducible NO synthetase expression.

Chemokines: attractive mediators of the immune response

An effective inflammatory immune response first requires the recruitment of cells to the site of inflammation and then their appropriate activation and regulation. Chemokines are critical in this response since they are both chemotactic and immunoregulatory molecules. In this regard, the interaction between CCL5 and CCR5 may be critical in regulating T cell functions, by mediating their recruitment and polarization, activation, and differentiation. Various tyrosine phosphorylation signaling cascades can be engaged following chemokine receptor aggregation on T cells, including the Jak-Stat pathway, FAK activation, the MAP kinase pathway, PI3-kinase activation, and transactivation of the T cell receptor. This review will address specific aspects related to chemokine-T cell interactions and the molecular signaling mechanisms that influence T cell function in an inflammatory immune response.

Two mechanisms for human immunodeficiency virus type 1 inhibition by N-terminal modifications of RANTES

C-C chemokine receptor 5 (CCR5) is the primary coreceptor for human immunodeficiency virus type 1 (HIV-1) infection. Native chemokines that bind to CCR5 inhibit HIV-1 infection, albeit weakly, but chemically modified chemokines inhibit infection more efficiently. We have investigated the inhibitory mechanism of three N-terminally modified RANTES variants (AOP-, NNY-, and PSC-RANTES) with the MT-2 human T-cell line stably expressing either native or mutated CCR5. The RANTES analogues showed the same rank order (PSC > NNY > AOP) in their capacity to induce prolonged CCR5 internalization, inhibit surface reexpression, and prevent HIV-1 infection on MT-2 cells expressing wild-type CCR5 or CCR5 with four C-terminal serine phosphorylation sites mutated to alanine. None of the RANTES analogues caused internalization of a C-terminal cytoplasmic domain deletion mutant of CCR5, and each derivative had equal potency in inhibiting HIV-1 infection of MT-2 cells expressing this mutant. We conclude that the C-terminal cytoplasmic residues of CCR5 are necessary for receptor sequestration by RANTES analogues but that the process and the relative activity of each derivative are not dependent upon phosphorylation of the C-terminal serine residues. Two mechanisms of antiviral activity are demonstrated: receptor blockade and receptor sequestration. Potency correlates with the ability to induce CCR5 sequestration but not with receptor binding, suggesting that sequestration may make the greater contribution to antiviral activity.

Rho family GTPases are required for activation of Jak/STAT signaling by G protein-coupled receptors

As do cytokine receptors and receptor tyrosine kinases, G protein-coupled receptors (GPCRs) signal to Janus kinases (Jaks) and signal transducers and activators of transcription (STATs). However, the early biochemical events linking GPCRs to this signaling pathway have been unclear. Here we show that GPCR-stimulated Rac activity and the subsequent generation of reactive oxygen species are necessary for activating tyrosine phosphorylation of Jaks and STAT-dependent transcription. The requirement for Rac activity can be overcome by addition of hydrogen peroxide. Expression of activated mutants of Rac1 is sufficient to activate Jak2 and STAT-dependent transcription, and the activation of Jak2 correlates with the ability of Rac1 to bind to NADPH oxidase subunit p67(phox). We further show that GPCR agonists stimulate tyrosine phosphorylation of STAT1 and STAT3 proteins in a Rac-dependent manner. The tyrosine phosphorylation of STAT3 is biphasic; the first peak of phosphorylation is weak and correlates with rapid activation of Jaks by GPCRs, whereas the second peak is stronger and requires the synthesis of an autocrine factor. Rho also plays an essential role in the induction of STAT transcriptional activity. Our results highlight a novel role for Rho GTPases in mediating the regulatory effects of GPCRs on STAT-dependent gene expression.

Analysis of ligand-stimulated CC chemokine receptor 5 (CCR5) phosphorylation in intact cells using phosphosite-specific antibodies

Human CC chemokine receptor 5 (CCR5), a member of the superfamily of G protein-coupled receptors, regulates the activation and directed migration of leukocytes and serves as the main coreceptor for the entry of R5 tropic strains of human immunodeficiency viruses. We have previously shown that RANTES/CCL5 binding to CCR5 induces GPCR kinase (GRK)- and protein kinase C (PKC)-mediated phosphorylation of four distinct C-terminal serine residues. To study these phosphorylation events in vivo, we have generated monoclonal antibodies, which specifically react only with either phosphorylated or nonphosphorylated CCR5. These phosphosite-specific antibodies reveal that following ligand stimulation of the receptor serine 337 is exclusively phosphorylated by a PKC-mediated mechanism, while GRKs phosphorylate serine 349. GRK-mediated receptor phosphorylation proceeds in a regular time-dependent manner (t(12) approximately 2 min) with an apparent EC(50) of 5 nm. In contrast, PKC phosphorylates serine 337 at 50-fold lower concentrations and in a very rapid, albeit transient manner. Protein phosphatases that are active at neutral pH and are inhibited by okadaic acid rapidly dephosphorylate phosphoserine 337, but less efficiently phosphoserine 349, in intact cells and in an in vitro assay. Immunofluorescence microscopy demonstrates that phosphorylated receptors accumulate in a perinuclear compartment, which resembles recycling endosomes. This study is the first to analyze in detail the spatial and temporal dynamics of GRK- versus PKC-mediated phosphorylation of a G protein-coupled receptor and its subsequent dephosphorylation on the level of individual phosphorylation sites.

CCR7-mediated physiological lymphocyte homing involves activation of a tyrosine kinase pathway

Homing of blood-borne lymphocytes to peripheral lymph nodes (PLNs) is a multistep process dependent on the sequential engagement of L-selectin, which mediates lymphocyte rolling along the luminal surface of high endothelial venules (HEVs), followed by activation of lymphocyte integrins and transmigration through HEVs. Within lymphoid tissue, B and T lymphocytes then migrate toward specific microenvironments such as B-cell follicles and the paracortex, respectively. The lymphocyte-expressed chemokine receptor CCR7 is playing an important role during this process, as its HEV-presented ligands CCL19 and CCL21 can trigger rapid integrin activation under flow in addition to inducing a chemotactic response, which may participate in transmigration and/or interstitial migration. Here, we report that Tyrphostin (Tyr) AG490, a pharmacological inhibitor of Janus family tyrosine kinases (Jaks), blocked the chemotactic response of primary mouse lymphocytes to CCL19 and CCL21 in a dose-dependent manner. Furthermore, Tyr AG490 inhibited rapid CCL21-mediated up-regulation of alpha4 and beta2 integrin adhesiveness in static adhesion assays and under physiological flow, whereas adhesion induced by phorbol myristate acetate remained unaltered. Using intravital microscopy of subiliac PLNs in mice, we found that adoptively transferred Tyr AG490-treated lymphocytes adhered significantly less in HEVs compared with control cells, although L-selectin-mediated rolling was similar in both samples. Finally, we observed rapid Jak2 phosphorylation in CCL21-stimulated primary mouse lymphocytes. Thus, our study suggests a role for Jak tyrosine kinases during CCR7-mediated lymphocyte recirculation.

Slit proteins, potential endogenous modulators of inflammation

Recent studies suggest that molecules important for guiding neuronal migration and axon path-finding also play a role in modulating leukocyte chemotaxis. Neuronal migration and leukocyte chemotaxis may share some common regulatory mechanisms. Intracellular signal transduction mechanisms guiding neuronal migration and leukocyte chemotaxis are beginning to be elucidated. Studying molecular mechanisms modulating cell migration may provide new insights into understanding of endogenous inhibitors of inflammation.

Constitutive activation and endocytosis of the complement factor 5a receptor: evidence for multiple activated conformations of a G protein-coupled receptor

Serpentine receptors relay hormonal or sensory stimuli to heterotrimeric guanine nucleotide-binding proteins (G proteins). In most G protein-coupled receptors (GPCRs), binding of the agonist ligand elicits both stimulation of the G protein and endocytosis of the receptor. We have begun to address whether these responses reflect the same sets of conformational changes in the receptor using constitutively active mutants of the human complement factor 5a receptor (C5aR). Two different mutant receptors both constitutively activate G protein-mediated responses, but one (F251A) is endocytosed only in response to ligand stimulation, while the other (NQ) is constitutively internalized in the absence of ligand. Both the constitutive and ligand-dependent endocytosis are accompanied by recruitment of beta-arrestin to the receptor. An inactivating mutation (N296A) complements the NQ mutation, producing a receptor that is activated only upon exposure to agonist; this revertant receptor (NQ/N296A) is nevertheless constitutively endocytosed. Thus one mutant (F251A) requires agonist for triggering endocytosis but not for activation of the downstream G protein signal, while another (NQ/N296A) behaves in the opposite fashion. Dissociation of two responses normally dependent on agonist binding indicates that the corresponding functions of an activated GPCR reflect different sets of changes in the receptor's conformation.

Chemokine receptors and neural function

Numerous studies have demonstrated that chemokines play an integral role in diseases marked by inflammation. Recently, it has also been shown that chemokines and their receptors are widely expressed in the central nervous system by all types of cells, including neurons. The functions of neuronal chemokine receptors have yet to be fully defined. However, there are indications that neuronal chemokine receptors play an integral role in the development of the nervous system, in the regulation of neuronal excitability and in the signal transduction pathways that regulate neuronal survival. This review explores these topics and discusses the overall impact that chemokines may have on neuronal function.