Chemokine receptor CCR5 functionally couples to inhibitory G proteins and undergoes desensitization

Ligand-Dependent Mechanisms of C-C Chemokine Receptor 5 (CCR5) Trafficking Revealed by APEX2 Proximity Labeling Proteomics

CC chemokine receptor 5 (CCR5) contributes to inflammatory responses by driving cell migration and scavenging chemokine to shape directional chemokine gradients. A drug against CCR5 has been approved for blocking HIV entry into cells. However, targeting CCR5 for the treatment of inflammatory diseases and cancer has had limited success because of the complex biology and pharmacology of this receptor. CCR5 is activated by many natural and engineered chemokines that elicit distinct receptor signaling and trafficking responses, including some that sequester the receptor inside the cell. The sequestration phenomenon may be therapeutically exploitable, but the mechanisms by which different ligands traffic CCR5 to different cellular locations are poorly understood. Here we employed live cell ascorbic acid peroxidase proximity labeling and quantitative mass spectrometry proteomics for unbiased discovery of temporally resolved protein neighborhoods of CCR5 following stimulation with its endogenous agonist, CCL5, and two CCL5 variants that promote intracellular retention of the receptor. Along with targeted pharmacological assays, the data reveals distinct ligand-dependent CCR5 trafficking patterns with temporal resolution. All three chemokines internalize CCR5 via β-arrestin- dependent, clathrin-mediated endocytosis but to different extents, with different kinetics and with varying dependencies on GPCR kinase subtypes. The agonists differ in their ability to target the receptor to lysosomes for degradation, as well as to the Golgi compartment and the trans-Golgi network, and these trafficking patterns translate into distinct levels of ligand scavenging. The results provide insight into the molecular mechanisms behind CCR5 intracellular sequestration and suggest actionable patterns for the development of chemokine-based CCR5 targeting molecules.

Significance Statement

CCR5 plays a crucial role in the immune system and is important in numerous physiological and pathological processes such as inflammation, cancer and HIV transmission. Along with its functional diversity, different CCR5 ligands can induce distinct receptor signaling responses and trafficking behaviors; the latter includes intracellular receptor sequestration which offers a potential therapeutic strategy for inhibiting CCR5 function. Using time-resolved proximity labeling proteomics and targeted pharmacological experiments, this study reveals the molecular basis for receptor sequestration including information that can be exploited for the development of CCR5 targeting molecules that promote retention of the receptor inside the cell.

The intricate role of CCL5/CCR5 axis in Alzheimer disease

The morbidity and mortality associated with Alzheimer disease (AD), one of the most common neurodegenerative diseases, are increasing each year. Although both amyloid β and tau proteins are known to be involved in AD pathology, their detailed functions in the pathogenesis of the disease are not fully understood. There is increasing evidence that neuroinflammation contributes to the development and progression of AD, with astrocytes, microglia, and the cytokines and chemokines they secrete acting coordinately in these processes. Signaling involving chemokine (C-C motif) ligand 5 (CCL5) and its main receptor C-C chemokine receptor 5 (CCR5) plays an important role in normal physiologic processes as well as pathologic conditions such as neurodegeneration. In recent years, many studies have shown that the CCL5/CCR5 axis plays a major effect in the pathogenesis of AD, but there are also a few studies that contradict this. In short, the role of CCL5/CCR5 axis in the pathogenesis of AD is still intricate. This review summarizes the structure, distribution, physiologic functions of the CCL5/CCR5 axis, and the progress in understanding its involvement in the pathogenesis of AD.

Pertussis toxin suppresses dendritic cell-mediated delivery of B. pertussis into lung-draining lymph nodes

The adenylate cyclase (ACT) and the pertussis (PT) toxins of Bordetella pertussis exert potent immunomodulatory activities that synergize to suppress host defense in the course of whooping cough pathogenesis. We compared the mouse lung infection capacities of B. pertussis (Bp) mutants (Bp AC⁻ or Bp PT^–) producing enzymatically inactive toxoids and confirm that ACT action is required for maximal bacterial proliferation in the first days of infection, whereas PT action is crucial for persistence of B. pertussis in mouse lungs. Despite accelerated and near complete clearance from the lungs by day 14 of infection, the PT⁻ bacteria accumulated within the lymphoid tissue of lung-draining mediastinal lymph nodes (mLNs). In contrast, the wild type or AC⁻ bacteria colonized the lungs but did not enter into mLNs. Lung infection by the PT⁻ mutant triggered an early arrival of migratory conventional dendritic cells with associated bacteria into mLNs, where the PT⁻ bacteria entered the T cell-rich paracortex of mLNs by day 5 and proliferated in clusters within the B-cell zone (cortex) of mLNs by day 14, being eventually phagocytosed by infiltrating neutrophils. Finally, only infection by the PT⁻ bacteria triggered an early production of anti-B. pertussis serum IgG antibodies already within 14 days of infection. These results reveal that action of the pertussis toxin blocks DC-mediated delivery of B. pertussis bacteria into mLNs and prevents bacterial colonization of mLNs, thus hampering early adaptive immune response to B. pertussis infection.

Of the three classical Bordetella species causing respiratory infections in mammals, only the human-specialized whooping cough agent B. pertussis produces the pertussis toxin (PT) as its major virulence factor. Human pertussis is an acute respiratory illness and the pleiotropic activities of pertussis toxin account for the characteristic systemic manifestations of the disease, such as hyperleukocytosis, histamine sensitization, hyperinsulinemia, or inflammatory lung pathology. We found that PT activity inhibits the migration of infected dendritic cells from the lungs into the draining mediastinal lymph nodes (mLNs). This prevents mLN infection by bacteria evading from migratory cells and delivery of bacterial antigens into mLNs. As a result, the induction of adaptive serum antibody responses to infection is delayed. We thus propose that PT action serves to create a time window for proliferation of B. pertussis on airway mucosa to facilitate transmission of the pathogen among humans.

CCR5 as a Coreceptor for Human Immunodeficiency Virus and Simian Immunodeficiency Viruses: A Prototypic Love-Hate Affair

CCR5, a chemokine receptor central for orchestrating lymphocyte/cell migration to the sites of inflammation and to the immunosurveillance, is involved in the pathogenesis of a wide spectrum of health conditions, including inflammatory diseases, viral infections, cancers and autoimmune diseases. CCR5 is also the primary coreceptor for the human immunodeficiency viruses (HIVs), supporting its entry into CD4⁺ T lymphocytes upon transmission and in the early stages of infection in humans. A natural loss-of-function mutation CCR5-Δ32, preventing the mutated protein expression on the cell surface, renders homozygous carriers of the null allele resistant to HIV-1 infection. This phenomenon was leveraged in the development of therapies and cure strategies for AIDS. Meanwhile, over 40 African nonhuman primate species are long-term hosts of simian immunodeficiency virus (SIV), an ancestral family of viruses that give rise to the pandemic CCR5 (R5)-tropic HIV-1. Many natural hosts typically do not progress to immunodeficiency upon the SIV infection. They have developed various strategies to minimize the SIV-related pathogenesis and disease progression, including an array of mechanisms employing modulation of the CCR5 receptor activity: (i) deletion mutations abrogating the CCR5 surface expression and conferring resistance to infection in null homozygotes; (ii) downregulation of CCR5 expression on CD4⁺ T cells, particularly memory cells and cells at the mucosal sites, preventing SIV from infecting and killing cells important for the maintenance of immune homeostasis, (iii) delayed onset of CCR5 expression on the CD4⁺ T cells during ontogenetic development that protects the offspring from vertical transmission of the virus. These host adaptations, aimed at lowering the availability of target CCR5⁺ CD4⁺ T cells through CCR5 downregulation, were countered by SIV, which evolved to alter the entry coreceptor usage toward infecting different CD4⁺ T-cell subpopulations that support viral replication yet without disruption of host immune homeostasis. These natural strategies against SIV/HIV-1 infection, involving control of CCR5 function, inspired therapeutic approaches against HIV-1 disease, employing CCR5 coreceptor blocking as well as gene editing and silencing of CCR5. Given the pleiotropic role of CCR5 in health beyond immune disease, the precision as well as costs and benefits of such interventions needs to be carefully considered.

CCR5 is a potential therapeutic target for cancer

INTRODUCTION

Chemokines and their cognate receptors play a major role in modulating inflammatory responses. Depending on their ligand binding, chemokine receptors can stimulate both immune activating and inhibitory signaling pathways. The CC chemokine receptor 5 (CCR5) promotes immune responses by recruiting immune cells to the sites of inflammation/tumor, and is involved in stimulating tumor cell proliferation, invasion and migration through various mechanisms. Moreover, CCR5 also contributes to an immune-suppressive tumor microenvironment by recruiting regulatory T cells and myeloid-derived suppressor cells facilitating tumor development and progression. In summary, cells expressing CCR5 modulate immune response and tumor progression. Expression of CCR5 is increased in various malignancies and associated with poor outcome. Experimental data show promising efficacy signals with CCR5 antagonists in preclinical tumor models. Therefore, CCR5 has been recognized as a potential therapeutic target for cancer.

AREAS COVERED

In this review, we focus on the role of CCR5 in cancer progression and discuss its impact and potential as a therapeutic target for cancer.

EXPERT OPINION

Beyond immune-checkpoint inhibitors, potentially synergistic immune-modulatory drugs such as CCR5 antagonists are a promising approach to enlarge our treatment armamentarium against cancer.

Human CCR5Δ32 (rs333) polymorphism has no influence on severity and mortality of influenza A(H1N1)pdm09 infection in Brazilian patients from the post pandemic period

BACKGROUND

Influenza is an acute and highly contagious viral respiratory infection that causes significant morbidity and mortality. The identification of host genetic factors associated with susceptibility and severity of influenza virus infection is of paramount importance. Previous studies evaluating the potential involvement of the CCR5Δ32 polymorphism (rs333), a 32 base pair deletion in CC motif chemokine receptor 5 (CCR5) gene, in severity and mortality of influenza A(H1N1)pdm09 infected individuals have been reported, but their results are quite conflicting.

OBJECTIVES

The aim of this study was the evaluation of the CCR5Δ32 frequency in individuals with mild, severe and fatal influenza A(H1N1)pdm09 infection and its putative association with clinical and epidemiologic data.

PATIENTS/METHODS

A total of 432 individuals were included in this study and classified according to their clinical status, into the following groups: influenza like illness (ILI) (n = 153); severe acute respiratory infection (SARI) (n = 173) and fatal (n = 106) cases. The samples were collected in the post pandemic period, from 2012 to 2018. Individuals were further stratified according to their clinical and epidemiological data. The CCR5Δ32 variant was genotyped by PCR amplification and a subset of samples was further submitted to Sanger sequencing.

RESULTS

The different clinical groups (ILI, SARI and fatal) presented similar distribution of wt/wt and wt/Δ32 genotypes and CCR5Δ32 allele frequencies. Genotype Δ32/Δ32 was not detected in our study. Additionally, no association between wt/wt and wt/Δ32 genotypes and dyspnea, a clinical factor for influenza complications was found. Similarly, no significant differences in the distribution of wt/wt and wt/Δ32 genotypes and CCR5Δ32 variant allele frequencies were observed in samples from the different Brazilian geographical regions.

CONCLUSIONS

The CCR5Δ32 variant does not influence the susceptibility to influenza A(H1N1)pdm09 severe disease or mortality in individuals from Brazil.

Frequency of the CCR5-delta32 allele in Brazilian populations: A systematic literature review and meta-analysis

The CCR5 is a chemokine receptor widely expressed by several immune cells that are engaged in inflammatory responses. Some populations have individuals exhibiting a 32bp deletion in the CCR5 gene (CCR5-delta32) that produces a truncated non-functional protein not expressed on the cell surface. This polymorphism, known to be associated with susceptibility to infectious and inflammatory diseases, such as osteomyelitis, pre-eclampsia, systemic lupus erythematous, juvenile idiopathic arthritis, rheumatoid arthritis and HIV/AIDS, is more commonly found in European populations with average frequency of 10%. However, it is also possible to observe a significant frequency in other world populations, such as the Brazilian one. We performed a systematic review and meta-analysis of CCR5-delta32 genetic association studies in Brazilian populations throughout the country to estimate the frequency of this polymorphism. We also compared CCR5-delta32 frequencies across Brazilian regions. The systematic literature reviewed studies involving delta32 allele in Brazilian populations published from 1995 to 2015. Among the reviewed literature, 25 studies including 30 Brazilian populations distributed between the North, Northeast, South and Southeast regions were included in our meta-analysis. We observed an overall allelic frequency of 4% (95%-CI, 0.03-0.05), that was considered moderate and, notably, higher than some European populations, such as Cyprus (2.8%), Italy (3%) and Greece (2.4%). Regarding the regional frequency comparisons between North-Northeast (N-NE) and South-Southeast (S-SE) regions, we observed an allelic frequency of 3% (95%-CI, 0.02-0.04) and 4% (95%-CI, 0.03-0.05), respectively. The populations from S-SE regions had a slightly higher CCR5-delta32 frequency than N-NE regions (OR=1.41, p=0.002). Although there are several studies about the CCR5-delta32 polymorphism and its effect on the immune response of some infectious diseases, this report is the first meta-analysis study that provides a descriptive study of the distribution of CCR5-delta32 allele in Brazilian population.

Critical roles of chemokine receptor CCR5 in regulating glioblastoma proliferation and invasion

Glioblastoma (GBM) is the most prevalent malignant primary brain tumor in adults and exhibits a spectrum of aberrantly aggressive phenotype. Tumor cell proliferation and invasion are critically regulated by chemokines and their receptors. Recent studies have shown that the chemokine CCL5 and its receptor CCR5 play important roles in tumor invasion and metastasis. Nonetheless, the roles of the CCR5 in GBM still remain unclear. The present study provides the evidence that the chemokine receptor CCR5 is highly expressed and associated with poor prognosis in human GBM. Mechanistically, CCL5-CCR5 mediates activation of Akt, and subsequently induces proliferation and invasive responses in U87 and U251 cells. Moreover, down-regulation of CCR5 significantly inhibited the growth of glioma in U87 tumor xenograft mouse model. Finally, high CCR5 expression in GBM is correlated with increased p-Akt expression in patient samples. Together, these findings suggest that the CCR5 is a critical molecular event associated with gliomagenesis.

HIV-associated neuropathogenesis: a systems biology perspective for modeling and therapy

Despite the development of powerful antiretroviral drugs, HIV-1 associated neurological disorders (HAND) will affect approximately half of those infected with HIV-1. Combined anti-retroviral therapy (cART) targets viral replication and increases T-cell counts, but it does not always control macrophage polarization, brain infection or inflammation. Moreover, it remains difficult to identify those at risk for HAND. New therapies that focus on modulating host immune response by making use of biological pathways could prove to be more effective than cART for the treatment of neuroAIDS. Additionally, while numerous HAND biomarkers have been suggested, they are of little use without methods for appropriate data integration and a systems-level interpretation. Machine learning, could be used to develop multifactorial computational models that provide clinicians and researchers with the ability to identify which factors (in what combination and relative importance) are considered important to outcome.

CCR5 conformations are dynamic and modulated by localization, trafficking and G protein association

CCR5 acts as the principal coreceptor during HIV-1 transmission and early stages of infection. Efficient HIV-1 entry requires a series of processes, many dependent on the conformational state of both viral envelope protein and cellular receptor. Monoclonal antibodies (MAbs) are able to identify different CCR5 conformations, allowing for their use as probes to distinguish CCR5 populations. Not all CCR5 MAbs are able to reduce HIV-1 infection, suggesting the use of select CCR5 populations for entry. In the U87.CD4.CCR5-GFP cell line, we used such HIV-1-restricting MAbs to probe the relation between localization, trafficking and G protein association for individual CCR5 conformations. We find that CCR5 conformations not only exhibit different localization and abundance patterns throughout the cell, but that they also display distinct sensitivities to endocytosis inhibition. Using chemokine analogs that vary in their HIV-1 inhibitory mechanisms, we also illustrate that responses to ligand engagement are conformation-specific. Additionally, we provide supporting evidence for the select sensitivity of conformations to G protein association. Characterizing the link between the function and dynamics of CCR5 populations has implications for understanding their selective targeting by HIV-1 and for the development of inhibitors that will block CCR5 utilization by the virus.

C-C chemokine receptor type five (CCR5): An emerging target for the control of HIV infection

When HIV was initially discovered as the causative agent of AIDS, many expected to find a vaccine within a few years. This has however proven to be elusive; it has been approximately 30 years since HIV was first discovered, and a suitable vaccine is still not in effect. In 2009, a paper published by Hutter et al. reported on a bone marrow transplant performed on an HIV positive individual using stem cells that were derived from a donor who was homozygous for a mutation in the CCR5 gene known as CCR5 delta-32 (Δ32) (Hütter et al., 2009). The HIV positive individual became HIV negative and remained free of viral detection after transplantation despite having halted anti-retroviral (ARV) treatment. This review will focus on CCR5 as a key component in HIV immunity and will discuss the role of CCR5 in the control of HIV infection.

Nuclear phosphoinositide-specific phospholipase C β1 controls cytoplasmic CCL2 mRNA levels in HIV-1 gp120-stimulated primary human macrophages

HIV-1 envelope glycoprotein gp120 induces, independently of infection, the release of CCL2 from macrophages. In turn, this chemokine acts as an autocrine factor enhancing viral replication. In this study, we show for the first time that phosphoinositide-specific phospholipase C (PI-PLC) is required for the production of CCL2 triggered by gp120 in macrophages. Using a combination of confocal laser-scanner microscopy, pharmacologic inhibition, western blotting and fluorescence-activated cell sorter analysis, we demonstrate that gp120 interaction with CCR5 leads to nuclear localization of the PI-PLC β1 isozyme mediated by mitogen-activated protein kinase ERK-1/2. Notably, phosphatidylcholine-specific phospholipase C (PC-PLC), previously reported to be required for NF-kB-mediated CCL2 production induced by gp120 in macrophages, drives both ERK1/2 activation and PI-PLC β1 nuclear localization induced by gp120. PI-PLC β1 activation through CCR5 is also triggered by the natural chemokine ligand CCL4, but independently of ERK1/2. Finally, PI-PLC inhibition neither blocks gp120-mediated NF-kB activation nor overall accumulation of CCL2 mRNA, whereas it decreases CCL2 transcript level in the cytoplasm. These results identify nuclear PI-PLC β1 as a new intermediate in the gp120-triggered PC-PLC-driven signal transduction pathway leading to CCL2 secretion in macrophages. The finding that a concerted gp120-mediated signaling involving both PC- and PI-specific PLCs is required for the expression of CCL2 in macrophages suggests that this signal transduction pathway may also be relevant for the modulation of viral replication in these cells. Thus, this study may contribute to identify novel targets for therapeutic intervention in HIV-1 infection.

New approaches in the treatment of HIV/AIDS - focus on maraviroc and other CCR5 antagonists

Treatment of HIV-1 infection has produced dramatic success for many patients. Nevertheless, viral resistance continues to limit the efficacy of currently available agents in many patients. The CCR5 antagonists are a new class of antiretroviral agents that target a necessary coreceptor for viral entry of many strains of HIV-1. Recently, the first agent within this class, maraviroc, was approved by a number of regulatory agencies, including the Food and Drug Administration. Herein we review the role of the CCR5 receptor in HIV-1 infection and potential methods to target it in anti-HIV-1 therapy. We review the various categories of agents and discuss specific agents that have progressed to clinical study. We discuss in detail the recently approved, first in class CCR5 antagonist, maraviroc, and discuss aspects of resistance to CCR5 antagonism and the potential role of CCR5 antagonism in the management of HIV-1 infection.

Glioblastoma: synergy of growth promotion between CCL5 and NK-1R can be thwarted by blocking CCL5 with miraviroc, an FDA approved anti-HIV drug and blocking NK-1R with aprepitant, an FDA approved anti-nausea drug

WHAT IS KNOWN AND BACKGROUND

Two receptor signaling pathways that are commonly active in facilitating glioblastoma growth and invasion- that of CCR5 and neurokinin (NK)-1R- have small molecule inhibitors that are FDA approved and marketed to treat other conditions. The anti-HIV drug, maraviroc, inhibits human CCR5's ligand from binding, and hence blocks CCR5 stimulation. The anti-nausea drug aprepitant blocks substance P signaling at NK-1R.

AIMS AND OBJECTIVE

We propose on the basis of molecular insights that a combination of the two drugs is likely to be useful in the treatment of glioblastoma.

COMMENT

After stimulation by their respective ligands both CCR5 and NK-1R, through intermediaries, phosphorylate and thereby activate ERK1/2, triggering in turn migratory and mitotic events. Neurokinin-1R second messenger signaling also happens to serine phosphorylate CCR5. Phosphorylated CCR5 exhibits amplified activity after agonist ligation. Therefore, aprepitant and maraviroc combined treatment is expected to exert synergestic inhibition of growth enhancing signaling in glioblastoma. Inhibiting an amplifier is equivalent to amplifying an inhibitor. Since the two suggested drugs are non-cytotoxic they are envisioned as adjunctive treatments to current standard temozolomide, radiation, and bevacizumab, all to be used after debulking primary resection.

WHAT IS NEW AND CONCLUSION

Our analysis makes the case for a well-designed trial of the proposed combination in the treatment of glioblastoma.

The chemokine receptor CCR5 in the central nervous system

The expression and the role of the chemokine receptor CCR5 have been mainly studied in the context of HIV infection. However, this protein is also expressed in the brain, where it can be crucial in determining the outcome in response to different insults. CCR5 expression can be deleterious or protective in controlling the progression of certain infections in the CNS, but it is also emerging that it could play a role in non-infectious diseases. In particular, it appears that, in addition to modulating immune responses, CCR5 can influence neuronal survival. Here, we summarize the present knowledge about the expression of CCR5 in the brain and highlight recent findings suggesting its possible involvement in neuroprotective mechanisms.

An arrestin-dependent multi-kinase signaling complex mediates MIP-1beta/CCL4 signaling and chemotaxis of primary human macrophages

MIP-1beta/CCL4 is a principal regulator of macrophage migration and signals through CCR5. Several protein kinases are linked to CCR5 in macrophages including the src kinase Lyn, PI3K, focal adhesion related kinase Pyk2, and members of the MAPK family, but whether and how these kinases regulate macrophage chemotaxis are not known. To define the role of these signaling molecules, we examined the functions and interactions of endogenous proteins in primary human macrophages. Using siRNA gene silencing and pharmacologic inhibition, we show that chemotaxis in response to CCR5 stimulation by MIP-1beta requires activation of Pyk2, PI3K p85, and Lyn, as well as MAPK ERK. MIP-1beta activation of CCR5 triggered translocation of Pyk2 and PI3K p85 from the cytoplasm to colocalize with Lyn at the plasma membrane with formation of a multimolecular complex. We show further that arrestins were recruited into the complex, and arrestin down-regulation impaired complex formation and macrophage chemotaxis toward MIP-1beta. Together, these results identify a novel mechanism of chemokine receptor regulation of chemotaxis and suggest that arrestins may serve as scaffolding proteins linking CCR5 to multiple downstream signaling molecules in a biologically important primary human cell type.

RANTES modulates the release of glutamate in human neocortex

The effects of the recombinant chemokine human RANTES (hRANTES) on the release of glutamate from human neocortex glutamatergic nerve endings were investigated. hRANTES facilitated the spontaneous release of d [(3)H]D-aspartate ([(3)H]DASP-) by binding Pertussis toxin-sensitive G-protein-coupled receptors (GPCRs), whose activation caused Ca(2+) mobilization from inositol trisphosphate-sensitive stores and cytosolic tyrosine kinase-mediated phosphorylations. Facilitation of release switched to inhibition when the effects of hRANTES on the 12 mM K(+)-evoked [(3)H]D-ASP exocytosis were studied. Inhibition of exocytosis relied on activation of Pertussis toxin-sensitive GPCRs negatively coupled to adenylyl cyclase. Both hRANTES effects were prevented by met-RANTES, an antagonist at the chemokine receptors (CCRs) of the CCR1, CCR3, and CCR5 subtypes. Interestingly, human neocortex glutamatergic nerve endings seem to possess all three receptor subtypes. Blockade of CCR1 and CCR5 by antibodies against the extracellular domain of CCRs prevented both the hRANTES effect on [(3)H]D-ASP release, whereas blockade of CCR3 prevented inhibition, but not facilitation, of release. The effects of RANTES on the spontaneous and the evoked release of [(3)H]D-ASP were also observed in experiments with mouse cortical synaptosomes, which may therefore represent an appropriate animal model to study RANTES-induced effects on neurotransmission. It is concluded that glutamate transmission can be modulated in opposite directions by RANTES acting at distinct CCR receptor subtypes coupled to different transduction pathways, consistent with the multiple and sometimes contrasting effects of the chemokine.

Chemokines in neuroectodermal cancers: the crucial growth signal from the soil

Although chemokines and their receptors were initially identified as regulators of cell trafficking during inflammation and immune response, they have emerged as crucial players in all stages of tumor development, primary growth, migration, angiogenesis, and establishment as metastases in distant target organs. Neuroectodermal tumors regroup neoplasms originating from the embryonic neural crest cells, which display clinical and biological similarities. These tumors are highly malignant and rapidly progressing diseases that disseminate to similar target organs such as bone marrow, bone, liver and lungs. There is increasing evidence that interaction of several chemokine receptors with corresponding chemokine ligands are implicated in the growth and invasive characteristics of these tumors. In this review we summarize the current knowledge on the role of CXCL12 chemokine and its CXCR4 and CXCR7 receptors in the progression and survival of neuroectodermal tumors, with particular emphasis on neuroblastoma, the most typical and enigmatic neuroectodermal childhood tumor.

Galphai protein-dependant extracellular signal-regulated kinase-1/2 activation is required for HIV-1 reverse transcription

BACKGROUND

HIV-1 triggers infection through interaction with the CD4 receptor and the chemokine receptors, CCR5 or CXCR4, on host cells. The involvement of signaling via the chemokine receptors in viral infection remains an issue of debate. We have previously reported that Galphai1 is involved in the signaling triggered by R5 HIV-1 strains through CCR5 binding to facilitate viral replication in unstimulated peripheral blood mononuclear cells. In this study, we pursued the identification of the downstream signaling molecules in CCR5-mediated infection. We also questioned whether CXCR4 using HIV-1 strains induce the same signaling mechanism.

METHODS

We analyzed by western blotting the coreceptor-mediated activation of various mitogen-acitvated protein kinases, including extracellular signal-regulated kinase (ERK)1/2, p38 and c-jun N-terminal kinase in non-stimulated human peripheral blood mononuclear cells. The involvement of Galphai protein in ERK1/2 activation was tested using pertussis toxin. Using real-time PCR, we studied the role of ERK1/2 in the life cycle of HIV-1.

RESULTS

We found that pertussis toxin inhibited the replication of X4 as well as R5 strains. Furthermore, both strains activated a pertussis toxin-sensitive mitogen-activated protein kinase pathway involving mitogen-activated protein kinase kinases-1/2 and ERK1/2. The inhibition of ERK1/2 activation by U0126 and PD98059 blocked both R5 and X4 HIV-1 replication. Furthermore, ERK1/2 activity was required for the completion of HIV-1 reverse transcription.

CONCLUSION

Our results show that R5 and X4 HIV-1 strains induce the same Galphai-dependent ERK pathway that facilitates reverse transcription. The identification of the signaling pathway required for optimal viral replication sheds a new light on HIV physiopathology and opens new therapeutic possibilities.

Signaling mechanism of HIV-1 gp120 and virion-induced IL-1beta release in primary human macrophages

HIV-1 envelope glycoprotein gp120 induces, independently of infection, the release of proinflammatory cytokines, including IL-1beta from macrophages, that are implicated in the pathogenesis of HIV-associated dementia. However, the signal transduction pathways involved have not been fully defined. Previously, our laboratory reported that soluble gp120 activates multiple protein kinases in primary human monocyte-derived macrophages, including the Src family kinase Lyn, PI3K, and the focal adhesion-related proline-rich tyrosine kinase Pyk2. In this study we showed that gp120 induces IL-1beta release from macrophages in a time- and concentration-dependent manner through binding to the chemokine receptor CCR5 and coupling to G(i)alpha protein. Using pharmacological inhibitors and small interfering RNA gene knockdown, we demonstrated that concomitant activation of Lyn, Pyk2, and class IA PI3K are required for gp120-induced IL-1beta production. By coimmunoprecipitation and immunofluorescence confocal microscopy, we showed that CCR5 activation by gp120 triggered the assembly of a signaling complex involving endogenous Lyn, PI3K, and Pyk2 and is associated with PI3K and Pyk2 translocation from the cytoplasm to the membrane where they colocalized with Lyn. Finally, we demonstrated that virion-associated gp120 induced similar response, as structurally intact whole virions also triggered IL-1beta release and re-localization of PI3K and Pyk2. This study identifies a novel signaling mechanism for HIV-1-induced IL-1beta production by primary human macrophages that may be involved in the neuropathogenesis of HIV-associated dementia.

CCR5 internalisation and signalling have different dependence on membrane lipid raft integrity

The chemokine receptor, CCR5, acts as a co-receptor for human immunodeficiency virus entry into cells. CCR5 has been shown to be targeted to cholesterol- and sphingolipid-rich membrane microdomains termed lipid rafts or caveolae. Cholesterol is essential for CCL4 binding to CCR5 and for keeping the conformational integrity of the receptor. Filipin treatment leads to loss of caveolin-1 from the membrane and therefore to a collapse of the caveolae. We have found here that sequestration of membrane cholesterol with filipin did not affect receptor signalling, however a loss of ligand-induced internalisation of CCR5 was observed. Cholesterol extraction with methyl-beta-cyclodextrin (MCD) reduced signalling through CCR5 as measured by release of intracellular Ca(2+) and completely abolished the inhibition of forskolin-stimulated cAMP accumulation with no effect on internalisation. Pertussis toxin (PTX) treatment inhibited the intracellular release of calcium that is transduced via Galphai G-proteins. Depletion of cholesterol destroyed microdomains in the membrane and switched CCR5/G-protein coupling to a PTX-independent G-protein. We conclude that cholesterol in the membrane is essential for CCR5 signalling via the Galphai G-protein subunit, and that integrity of lipid rafts is not essential for effective CCR5 internalisation however it is crucial for proper CCR5 signal transduction via Galphai G-proteins.

RANTES and human sperm fertilizing ability: effect on acrosome reaction and sperm/oocyte fusion

Beta-chemokine, regulated on activation and normally T-cell expressed and presumably secreted (RANTES), is present in both the male and female genital tract fluids where its levels increase in diseases related to infertility, such as endometriosis and male genital tract infections. beta-Chemokine receptors (CCR3 and CCR5) are expressed on freshly ejaculated human sperm cells and a sperm chemoattractant effect for RANTES has been reported. No information exists on other possible roles of RANTES on sperm functions involved in the fertilization process. In the present study, the exposure of sperm suspensions to high concentrations of the chemokine, comparable to those observed in inflammatory diseases, significantly decreased the stimulatory effect exerted by progesterone on sperm/oocyte fusion, evaluated by means of the hamster egg penetration test. Accordingly, a large proportion of spermatozoa preincubated under capacitating conditions with high concentrations of RANTES underwent a premature acrosome reaction (AR) that prevented subsequent progesterone-induced AR. Finally, sperm samples exposed to the same high levels of chemokine showed a significant increase in the intracellular levels of cAMP, which is involved in capacitation and AR dynamics. These results indicate a negative interference of high levels of RANTES on the sperm fertilizing ability, thereby suggesting a potential contribution of this chemokine to subfertility associated with endometriosis and genital tract inflammatory diseases.

Interleukin-8 stimulates cell proliferation in non-small cell lung cancer through epidermal growth factor receptor transactivation

Interleukin-8 (IL-8; CXCL8) is a cytokine of the CXC chemokine family that is involved in neutrophil recruitment and activation. In addition, IL-8 has been implicated in a wide variety of other processes, including angiogenesis and metastasis in lung cancer. Lung adenocarcinoma and muco-epidermoid carcinoma cells produce substantial amounts of IL-8, and express both CXCR1 and CXCR2 IL-8 receptors. We hypothesized that IL-8 stimulates proliferation of non-small cell lung cancer cells, involving transactivation of the epidermal growth factor receptor (EGFR). The EGFR plays a central role in regulating cell proliferation and it has been therefore implicated in lung cancer. Both EGFR ligands and transactivation of the receptor may lead to downstream signalling events, including mitogen-activated protein kinase (MAPK) activation. Transactivation of the EGFR has been shown to occur in response to ligands of various G-protein coupled receptors (GPCRs) and involves metalloproteinase-mediated release of membrane bound EGFR ligands. The aim of the present study was to investigate the effect of IL-8 on proliferation of lung adenocarcinoma and muco-epidermoid carcinoma cells, and to explore the mechanisms leading to this proliferation in two different non-small cell lung cancer cell lines (A549 and NCI-H292). In both NSCLC cell lines, we observed that IL-8 stimulates epithelial cell proliferation in a dose-dependent manner. The ability of IL-8 to increase cell proliferation was blocked both by an inhibitor of EGFR tyrosine kinase, by a specific anti-EGFR blocking antibody and by a panmetalloproteinase inhibitor. Similar results were obtained using the GPCR inhibitor pertussis toxin. Inhibition of the MAPK p42/44 (ERK1/2) also blocked the mitogenic effect of IL-8, while a p38 MAPK inhibitor did not affect IL-8-induced cell proliferation. These results suggest that IL-8 increases cell proliferation in NSCLC cell lines via transactivation of the EGFR and that this mechanism involves metalloproteinase activity.

Regulated upon activation, normal T cell expressed and secreted (RANTES) and monocyte chemotactic protein 1 in follicular fluid accumulate differentially in patients with and without endometriosis undergoing in vitro fertilization

OBJECTIVE

To compare the amount of regulated upon activation, normal T cell expressed and secreted (RANTES) and monocyte chemotactic protein 1 (MCP-1) in follicular fluid (FF) of patients with and without endometriosis and to determine their oocyte fertilization and pregnancy rates.

DESIGN

Case-control study.

SETTING

Department of Obstetrics and Gynecology, University Hospital Schleswig-Holstein, Campus Luebeck, Germany.

PATIENT(S)

Thirty-two women with endometriosis stages I-IV and 28 women without endometriosis, both groups surgically and histologically confirmed.

INTERVENTION(S)

Diagnostic laparoscopy, IVF-ET.

MAIN OUTCOME MEASURE(S)

RANTES and MCP-1 levels in follicular fluid, measured by ELISA, and oocyte fertilization and pregnancy rates.

RESULT(S)

Follicular response and days of gonadotropin stimulation were similar between the two groups. The levels of RANTES in FF from patients with endometriosis were significantly higher (460.4 +/- 90.3 pg/mL) compared with concentrations in patients with tubal infertility (243.8 +/- 70.9 pg/mL; P<.05). In contrast, MCP-1 concentrations in FF from women with endometriosis (330.0 +/- 29.2 pg/mL) were lower than in women with tubal infertility (420.5 +/- 46.6 pg/mL; P<.05). Oocyte fertilization rates in the endometriosis group (54%) were significantly lower than those of the tubal infertility group (73%; P<.05), as were the pregnancy rates (19% vs. 35%, respectively; P<.01).

CONCLUSION(S)

Women with endometriosis-associated infertility have a poor IVF outcome. Immune cell recruitment into the ovary might affect follicular function and lead to impaired oocyte quality.

CCL5 evokes calcium signals in microglia through a kinase-, phosphoinositide-, and nucleotide-dependent mechanism

Microglia, the resident macrophages of the CNS, are responsible for the innate immune response in the brain and participate in the pathogenesis of certain neurodegenerative disorders. Chemokines initiate activation and migration of microglia. The beta-chemokine CCL5 induces an elevation in intracellular calcium concentration ([Ca(2+)](i)) in human microglia. Here, we examined the signal transduction pathway linking activation of chemokine receptor CCR5 to an elevation in [Ca(2+)](i) in cultured microglia by using pharmacological approaches in combination with Fura-2-based digital imaging. The CCL5-induced response required Janus kinase (Jak) activity and the stimulation of an inhibitory G protein. Multiple downstream signaling pathways were involved, including phosphatidylinositol 3-kinase (PI3K), Bruton's tyrosine kinase (Btk), and phospholipase C (PLC)-mediated release of Ca(2+) from inositol 1,4,5-trisphosphate (IP(3))-sensitive stores. Activation of both the kinase and the lipase pathways was required for eliciting the Ca(2+) response. However, the majority of the [Ca(2+)](i) increase was derived from sources activated by NAD metabolites. Cyclic ADP-ribose (cADPR) evoked Ca(2+) release from intracellular stores, and ADPR evoked Ca(2+) influx via a nimodipine-sensitive channel. Thus, a multistep cascade couples CCR5 activation to Ca(2+) increases in human microglia. Because changes in [Ca(2+)](i) affect chemotaxis, secretion, and gene expression, pharmacologic modulation of this pathway may alter inflammatory and degenerative processes in the CNS.

Macrophage inflammatory protein 1alpha inhibits postentry steps of human immunodeficiency virus type 1 infection via suppression of intracellular cyclic AMP

Primary isolates of human immunodeficiency virus type 1 (HIV-1) predominantly use chemokine receptor CCR5 to enter target cells. The natural ligands of CCR5, the beta-chemokines macrophage inflammatory protein 1alpha (MIP-1alpha), MIP-1beta, and RANTES, interfere with HIV-1 binding to CCR5 receptors and decrease the amount of virions entering cells. Although the inhibition of HIV-1 entry by beta-chemokines is well documented, their effects on postentry steps of the viral life cycle and on host cell components that control the outcome of infection after viral entry are not well defined. Here, we show that all three beta-chemokines, and MIP-1alpha in particular, inhibit postentry steps of the HIV-1 life cycle in primary lymphocytes, presumably via suppression of intracellular levels of cyclic AMP (cAMP). Productive HIV-1 infection of primary lymphocytes requires cellular activation. Cell activation increases intracellular cAMP, which is required for efficient synthesis of proviral DNA during early steps of viral infection. Binding of MIP-1alpha to cognate receptors decreases activation-induced intracellular cAMP levels through the activation of inhibitory G proteins. Furthermore, inhibition of one of the downstream targets of cAMP, cAMP-dependent PKA, significantly inhibits synthesis of HIV-1-specific DNA without affecting virus entry. These data reveal that beta-chemokine-mediated inhibition of virus replication in primary lymphocytes combines inhibitory effects at the entry and postentry levels and imply the involvement of beta-chemokine-induced signaling in postentry inhibition of HIV-1 infection.

Chemokine receptor CCR5: insights into structure, function, and regulation

CC chemokine receptor 5 (CCR5) is a seven-transmembrane, G protein-coupled receptor (GPCR) which regulates trafficking and effector functions of memory/effector T-lymphocytes, macrophages, and immature dendritic cells. It also serves as the main coreceptor for the entry of R5 strains of human immunodeficiency virus (HIV-1, HIV-2). Chemokine binding to CCR5 leads to cellular activation through pertussis toxin-sensitive heterotrimeric G proteins as well as G protein-independent signalling pathways. Like many other GPCR, CCR5 is regulated by agonist-dependent processes which involve G protein coupled receptor kinase (GRK)-dependent phosphorylation, beta-arrestin-mediated desensitization and internalization. This review discusses recent advances in the elucidation of the structure and function of CCR5, as well as the complex mechanisms that regulate CCR5 signalling and cell surface expression.

Agonist-induced endocytosis of CC chemokine receptor 5 is clathrin dependent

The signaling activity of several chemokine receptors, including CC chemokine receptor 5 (CCR5), is in part controlled by their internalization, recycling, and/or degradation. For CCR5, agonists such as the chemokine CCL5 induce internalization into early endosomes containing the transferrin receptor, a marker for clathrin-dependent endocytosis, but it has been suggested that CCR5 may also follow clathrin-independent routes of internalization. Here, we present a detailed analysis of the role of clathrin in chemokine-induced CCR5 internalization. Using CCR5-transfected cell lines, immunofluorescence, and electron microscopy, we demonstrate that CCL5 causes the rapid redistribution of scattered cell surface CCR5 into large clusters that are associated with flat clathrin lattices. Invaginated clathrin-coated pits could be seen at the edge of these lattices and, in CCL5-treated cells, these pits contain CCR5. Receptors internalized via clathrin-coated vesicles follow the clathrin-mediated endocytic pathway, and depletion of clathrin with small interfering RNAs inhibits CCL5-induced CCR5 internalization. We found no evidence for CCR5 association with caveolae during agonist-induced internalization. However, sequestration of cholesterol with filipin interferes with agonist binding to CCR5, suggesting that cholesterol and/or lipid raft domains play some role in the events required for CCR5 activation before internalization.

Heterodimerization and cross-desensitization between the mu-opioid receptor and the chemokine CCR5 receptor

Cross-desensitization between micro-opioid receptor agonists and CC chemokines was shown to occur in immune cells and in the central nervous system. However, these cells do not permit examination of potential mechanisms at cellular levels due to low levels and mixed populations of receptors. In this study, we investigated possible interactions and biochemical mechanisms of cross-desensitization between the mu-opioid and chemokine CCR5 receptors coexpressed in Chinese hamster ovary (CHO) cells. Hemagglutinin (HA)-tagged micro-opioid receptor coimmunoprecipitated with FLAG (Asp-Tyr-Lys-Asp-Asp-Asp-Asp-Lys)-tagged chemokine receptor CCR5 in cells expressing the two receptors, but not in a mixture of cells transfected with one of the two receptors, indicating that the two receptors form heterodimers. Treatment with the mu-opioid receptor agonist DAMGO ([D-Ala(2), N-Me-Phe(4), Gly(5)-ol]-enkephalin), the chemokine RANTES (Regulated on Activation, Normal T cell-Expressed and -Secreted) (CCL5), or both, did not affect the level of coimmunoprecipitation. DAMGO and RANTES (CCL5) induced chemotaxis in CHO cells coexpressing both receptors, and preincubation with either DAMGO or RANTES (CCL5) profoundly inhibited chemotaxis caused by the other. DAMGO pretreatment enhanced phosphorylation of the chemokine CCR5 receptor and reduced RANTES (CCL5)-promoted [35S]GTP gamma S binding. Conversely, RANTES (CCL5) preincubation slightly increased phosphorylation of the mu-opioid receptor and significantly reduced DAMGO-induced [35S]GTP gamma S binding. These results indicate that activation of either receptor affected G protein coupling of the other, likely due to enhanced phosphorylation of the receptor. Heterodimerization between the two receptors may contribute to the observed cross-desensitization.

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.

HIV-1 gp120 chemokine receptor-mediated signaling in human macrophages

The chemokine receptors CCR5 and CXCR4 serve as the cellular receptors in conjunction with CD4 for HIV-1 entry and infection of target cells. Although the virus has subverted these molecules for its own use, their natural function is to respond to activation and migration signals delivered by extracellular chemokines. A principal research objective of our laboratory is to understand the consequences of virus-chemokine receptor interactions for cellular function, as well as for entry and infection. We hypothesized that CXCR4-using (X4) and CCR5-using (R5) HIV-1 strains might elicit signals through the chemokine receptors that result in aberrant function and/or regulate virus entry or postentry steps of infection. We have focused on primary human macrophages, which express both CXCR4 and CCR5, because macrophages are a principal target for HIV-1 in vivo, inappropriate macrophage activation appears to play a major role in the pathogenesis of certain sequelae of AIDS, such as HIV encephalopathy, and macrophage infection is regulated at several steps subsequent to entry in ways that are linked to envelope- receptor interactions. This review summarizes our recent findings regarding the mechanisms of chemokine-receptor signaling in macrophages, the role of viral envelope glycoproteins in eliciting macrophage signals, and how these activation pathways may participate in macrophage infection and affect cell functions apart from infection.

The [35S]GTPgammaS binding assay: approaches and applications in pharmacology

Receptors of the of seven transmembrane spanning, heterotrimeric G protein coupled family (GPCR) play crucial roles in regulating physiological functions and consequently are targets for the action of many classes of drugs. Activation of receptor by agonist leads to the dissociation of GDP from Galpha of the Galphabetagamma heterotrimer, followed by the binding of GTP to Galpha and subsequent modulation of downstream effectors. The G protein heterotrimer is reformed by GTPase activity of the Galpha subunit, forming Galpha-GDP and so allowing Galpha and Gbetagamma to recombine. The [35S]GTPgammaS assay measures the level of G protein activation following agonist occupation of a GPCR, by determining the binding of the non-hydrolyzable analog [35S]GTPgammaS to Galpha subunits. Thus, the assay measures a functional consequence of receptor occupancy at one of the earliest receptor-mediated events. The assay allows for traditional pharmacological parameters of potency, efficacy and antagonist affinity, with the advantage that agonist measures are not subjected to amplification or other modulation that may occur when analyzing parameters further downstream of the receptor. In general the assay is experimentally more feasible for receptors coupled to the abundant G(i/o) proteins. Nevertheless, [35S]GTPgammaS binding assays are used with GPCRs that couple to the G(s) and G(q) families of G proteins, especially in artificial expression systems, or using receptor-Galpha constructs or immunoprecipitation of [35S]GTPgammaS-labeled Galpha. The relative simplicity of the assay has made it very popular and its use is providing insights into contemporary pharmacological topics including the roles of accessory proteins in signaling, constitutive activity of receptors and agonist specific signaling.

HIV coreceptors: role of structure, posttranslational modifications, and internalization in viral-cell fusion and as targets for entry inhibitors

The human immunodeficiency virus (HIV) envelope glycoprotein forms trimers on the virion surface, with each monomer consisting of two subunits, gp120 and gp41. The gp120 envelope component binds to CD4 on target cells and undergoes conformational changes that allow gp120 to interact with certain G-protein-coupled receptors (GPCRs) on the same target membranes. The GPCRs that function as HIV coreceptors were found to be chemokine receptors. The primary coreceptors are CCR5 and CXCR4, but several other chemokine receptors were identified as "minor coreceptors", indicating their ability support entry of some HIV strains in tissue cultures. Formation of the tri-molecular complexes stabilizes virus binding and triggers a series of conformational changes in gp41 that facilitate membrane fusion and viral cell entry. Concerted efforts are underway to decipher the specific interactions between gp120/CD4, gp120/coreceptors, and their contributions to the subsequent membrane fusion process. It is hoped that some of the transient conformational intermediates in gp120 and gp41 would serve as targets for entry inhibitors. In addition, the CD4 and coreceptors are primary targets for several classes of inhibitors currently under testing. Our review summarizes the current knowledge on the interactions of HIV gp120 with its receptor and coreceptors, and the important properties of the chemokine receptors and their regulation in primary target cells. We also summarize the classes of coreceptor inhibitors under development.

Negative role of cAMP-dependent protein kinase A in RANTES-mediated transcription of proinflammatory mediators through Raf

The chemokine RANTES (regulated on activation normal T cell expressed and secreted) is expressed in several inflammatory diseases of the central nervous system and is a powerful stimulus for astrocyte production of proinflammatory mediators. The mechanism of RANTES-mediated astrocyte activation was investigated. RANTES stimulation decreased both intracellular cyclic AMP (cAMP) levels and cAMP-dependent protein kinase A (PKA) activity in cultures of primary mouse astrocytes. H-89, a potent inhibitor of PKA, mimicked RANTES-mediated chemokine and cytokine transcription. RANTES treatments activated Raf-1 kinase activity, and conversely a dominant negative Raf and a Raf-1 inhibitor blocked RANTES-induced chemokine transcription. Transfection with a constitutively active Raf was sufficient to induce transcription of proinflammatory mediators. The combined data indicate that Raf-1 is required for RANTES-mediated astrocyte activation. Decreases of cAMP and PKA activity contributed to the transcription of proinflammatory mediators by cross-talk with the Raf-1/mitogen-activated protein kinase pathway. The results identify an upstream signaling pathway for amplification of proinflammatory mediators in the central nervous system.

Functional reconstitution of the HIV receptors CCR5 and CD4 in liposomes

Reconstitution of membrane proteins allows their study in a membrane environment that can be manipulated at will. Because membrane proteins have diverse biophysical properties, reconstitution methods have so far been developed for individual proteins on an ad hoc basis. We developed a postinsertion reconstitution method for CCR5, a G protein coupled receptor, with seven transmembrane alpha helices and small ecto- and endodomains. A His6-tagged version of CCR5 was expressed in mammalian cells, purified using the detergent N-dodecyl-beta-d-maltoside (DDM) and reconstituted into preformed liposomal membranes saturated with DDM, removing the detergent with hydrophobic polystyrene beads. We then attempted to incorporate CD4, a protein with a single transmembrane helix and a large hydrophilic ectodomain into liposomal membranes, together with CCR5. Surprisingly, reconstitution of this protein was also achieved by the method. Both proteins were found to be present together in individual liposomes. The reconstituted CCR5 was recognized by several monoclonal antibodies, recognized its natural ligand, and CD4 bound a soluble form of gp120, a subunit of the HIV fusion protein that uses CD4 as a receptor. Moreover, cells expressing the entire fusion protein of HIV bound to the liposomes, indicating that the proteins were intact and that most of them were oriented right side out. Thus, functional coreconstitution of two widely different proteins can be achieved by this method, suggesting that it might be useful for other proteins.

Hypoxic-ischemic injury induces macrophage inflammatory protein-1alpha expression in immature rat brain

BACKGROUND AND PURPOSE

Macrophage inflammatory protein (MIP)-1alpha is a well-characterized monocyte chemoattractant; its role in regulating monocyte and microglial recruitment and activation in the injured neonatal brain is unknown. We evaluated the impact of acute hypoxic-ischemic (HI) brain injury on the expression of MIP-1alpha in neonatal rat brain.

METHODS

To elicit forebrain ischemic injury, 7-day-old (P7) rats underwent right carotid ligation, followed by 2.5 hours of 8% oxygen exposure. We used an enzyme-linked immunosorbent assay and immunohistochemistry to detect MIP-1alpha; double-labeling immunofluorescence assays were analyzed with confocal microscopy to identify cellular sources of MIP-1alpha. Immunocytochemistry assays were also used to detect 2 MIP-1alpha receptors, CCR1 and CCR5.

RESULTS

We found marked increases in tissue concentrations of MIP-1alpha in the HI cerebral hemisphere, peaking from 8 to 72 hours after lesioning. Immunocytochemistry assays revealed that MIP-1alpha was constitutively expressed in physiologically activated microglia; from 8 to 120 hours after lesioning, MIP-1alpha immunoreactive monocytes and microglia accumulated in the lesion territory. In immunoreactive cells, MIP-1alpha was diffusely distributed throughout the cytoplasm at early post-HI time intervals; by 72 hours, MIP-1alpha immunoreactivity was typically concentrated adjacent to the nucleus, a pattern indicative of active MIP-1alpha production. In P7 to P12 brain, many cells expressed MIP-1alpha receptors; both CCR1 and CCR5 immunoreactivity were localized to endothelium and ependyma; CCR1-immunoreactive astrocytes and neurons and CCR5-immunoreactive microglia were also identified.

CONCLUSIONS

These data implicate MIP-1alpha as a mediator of the complex and sustained inflammatory response initiated by perinatal HI braininjury.

Expression of functional chemokine receptors by rat cerebellar neurons

In this study, we examined chemokine receptor expression and function in rat cerebellar neurons. Calcium imaging experiments demonstrated that a wide variety of chemokines elicited [Ca(2+)](i) transients in acutely isolated and cultured cerebellar Purkinje and granule neurons. In many cases, these chemokine responses were pertussis toxin (PTX) insensitive. In addition, chemokines activated the Ca(2+) and cAMP-dependent transcription factor CREB and the extracellular response kinases ERK1/ERK2. Chemokines increased the survival of Purkinje neurons deprived of their trophic support. Thus, the presence of chemokine receptors and the signaling pathways they activate suggest that chemokines play a role in the control of cerebellar neuron survival and development and may mediate communication between the CNS and the immune system.

HIV-1 gp120 and chemokine activation of Pyk2 and mitogen-activated protein kinases in primary macrophages mediated by calcium-dependent, pertussis toxin-insensitive chemokine receptor signaling

Human immunodeficiency virus type 1 (HIV-1) uses the chemokine receptors CCR5 and CXCR4 as coreceptors for entry. It was recently demonstrated that HIV-1 glycoprotein 120 (gp120) elevated calcium and activated several ionic signaling responses in primary human macrophages, which are important targets for HIV-1 in vivo. This study shows that chemokine receptor engagement by both CCR5-dependent (R5) and CXCR4-dependent (X4) gp120 led to rapid phosphorylation of the focal adhesion-related tyrosine kinase Pyk2 in macrophages. Pyk2 phosphorylation was also induced by macrophage inflammatory protein-1beta (MIP-1beta) and stromal cell-derived factor-1alpha, chemokine ligands for CCR5 and CXCR4. Activation was blocked by EGTA and by a potent blocker of calcium release-activated Ca++ (CRAC) channels, but was insensitive to pertussis toxin (PTX), implicating CRAC-mediated extracellular Ca++ influx but not Galpha(i) protein-dependent mechanisms. Coreceptor engagement by gp120 and chemokines also activated 2 members of the mitogen-activated protein kinase (MAPK) superfamily, c-Jun amino-terminal kinase/stress-activated protein kinase and p38 MAPK. Furthermore, gp120-stimulated macrophages secreted the chemokines monocyte chemotactic protein-1 and MIP-1beta in a manner that was dependent on MAPK activation. Thus, the gp120 signaling cascade in macrophages includes coreceptor binding, PTX-insensitive signal transduction, ionic signaling including Ca++ influx, and activation of Pyk2 and MAPK pathways, and leads to secretion of inflammatory mediators. HIV-1 Env signaling through these pathways may contribute to dysregulation of uninfected macrophage functions, new target cell recruitment, or modulation of macrophage infection.

Differential expression of chemokine receptors on peripheral blood, synovial fluid, and synovial tissue monocytes/macrophages in rheumatoid arthritis

OBJECTIVE

Since it is likely that monocytes utilize chemokines to migrate to the rheumatoid arthritis (RA) joint, we investigated the expression of C-C chemokine receptors (CCR) 1-6 and C-X-C receptor 3 (CXCR3) in the peripheral blood (PB), synovial fluid (SF), and synovial tissue of patients with RA as well as in the PB of normal subjects.

METHODS

We compared chemokine receptor expression on CD14+ monocytes from normal PB, RA PB, and RA SF using 2-color flow cytometry. Correlations with patient clinical data were determined. Chemokine and receptor expression were investigated in RA synovial tissue by immunohistochemistry and 2-color immunofluorescence to identify CD68+ macrophages.

RESULTS

Most normal PB monocytes expressed CCR1 (87%) and CCR2 (84%), but not CCRs 3, 4, 5, or 6 or CXCR3. RA PB monocytes expressed CCR1 (56%) and CCR2 (76%), with significantly more expressing CCR3 (18%), CCR4 (38%), and CCR5 (17%) compared with normal PB monocytes. Significantly fewer SF monocytes from RA patients expressed CCR1 (17%), CCR2 (24%), and CCR4 (6%) while significantly more expressed CCR3 (35%) and CCR5 (47%) compared with RA and normal PB monocytes; CCR6 and CXCR3 were rarely detected. Clinically, the erythrocyte sedimentation rate was inversely correlated with the expression of CCR1 and CCR4 by RA PB, and CCR5 expression by RA SF was correlated with the SF white blood cell count. CCR1-, CCR2-, and CCR5-immunoreactive cells were found in RA synovial tissue and colocalized with CD68+ macrophages. RA synovial tissue RANTES (regulated upon activation, normally T cell expressed and secreted chemokine)- and monocyte chemoattractant protein 1-immunoreactive cells colocalized with CCR1 and CCR2, respectively, on serial sections. Macrophage inflammatory protein 1alpha (MIP-1alpha) was principally restricted to vascular endothelium, and MIP-1beta+ macrophages were found throughout the sections.

CONCLUSION

Monocytes mainly express CCR1 and CCR2 in normal and RA PB, CCR3 and CCR5 in RA PB and RA SF, and CCR4 in RA PB. The differential expression of chemokine receptors suggests that certain receptors aid in monocyte recruitment from the circulation while others are important in monocyte retention in the joint.

Intracellular signaling events at the leading edge of migrating cells

Cell migration is an important facet of the life cycle of immune and other cell types. A complex set of events must take place at the leading edge of motile cells before these cells can migrate. Chemokines induce the motility of various cell types by activating multiple intracellular signaling pathways. These include the activation of chemokine receptors, which are coupled to the heterotrimeric G proteins. The release of G beta gamma subunits from chemokine receptors results in the recruitment to the plasma membrane, with subsequent activation of various down-stream signaling molecules. Among these molecules are the pleckstrin homology domain-containing proteins and the phosphoinositide 3-kinase gamma which phosphorylates phospholipids and activates members of the GTP exchange factors (GEFs). These GEFs facilitate the exchange of GTP for GDP in members of GTPases. The latter are important for reorganizing the cell cytoskeleton, and in inducing chemotaxis. Chemokines also induce the mobilization of intracellular calcium from intracellular stores. Second messengers such as inositol 1,4,5 trisphosphate, and cyclic adenosine diphosphate ribose are among those induced by chemokines. In addition, the G beta gamma subunits recruit members of the G protein-coupled receptor kinases, which phosphorylate chemokine receptors, resulting in desensitization and termination of the motility signals. This review will discuss the intracellular signaling pathways induced by chemokines, particularly those activated at the leading edge of migrating cells which lead to cell polarization, cytoskeleton reorganization and motility.

Beta-chemokines and human immunodeficiency virus type-1 proteins evoke intracellular calcium increases in human microglia

Activation of beta-chemokine receptors, co-receptors for human immunodeficiency virus type-1 (HIV-1), stimulates movement and secretion in microglia, possibly through a Ca(2+)-dependent mechanism. We studied chemokine activation of Ca(2+) signaling processes in microglia. Human fetal microglia were grown in primary culture and chemokine-induced increases in intracellular calcium concentration ([Ca(2+)](i)) were measured in single cells using indo-1-based microfluorimetry. Application of 50 ng/ml regulated on activation, normal T expressed and secreted (RANTES; 120 s) evoked responses in 26% of the microglia (187/719 cells). [Ca(2+)](i) increased from a basal level of 66+/-6 nM to peak at 268+/-23 nM (n=187). Chemokine-evoked responses rapidly desensitized as indicated by the rapid return to basal [Ca(2+)](i) levels in the maintained presence of RANTES. The removal of extracellular Ca(2+) or stimulation in the presence of Ni(2+) (2mM) or La(3+) (100 microM) blocked the RANTES-elicited [Ca(2+)](i) increase. The L-type calcium channel antagonist nimodipine (10 microM) inhibited the RANTES-mediated increase in [Ca(2+)](i) by 80+/-16%. Thus, the RANTES-evoked calcium transient appears to result from Ca(2+) influx with little if any release from intracellular stores. Application of gp120(clade) (E) and gp120(CM235) (50 ng/ml) neither mimicked nor antagonized the RANTES-evoked response. Application of 50 ng/ml eotaxin (120 s) evoked an increase in [Ca(2+)](i) in 13% of the human microglia in culture (61/469 cells). The HIV-1 regulatory protein Tat (50 ng/ml) increased the [Ca(2+)](i) in a subset of eotaxin-responsive cells (16/30). The L-type calcium channel antagonist nimodipine (3 microM) inhibited eotaxin- and Tat-mediated increases in [Ca(2+)](i) by 88+/-6% and 93+/-6%, respectively. Thus, activation of CCR3 appears to evoke Ca(2+) influx through L-type Ca(2+) channels.These results indicate that beta-chemokines, RANTES and eotaxin, activate a nimodipine sensitive Ca(2+) influx pathway in human fetal microglia. HIV-1 Tat protein mimicked chemokine-mediated Ca(2+) signaling and may modulate the migratory and secretory responses of microglia.

TNF-alpha-induced secretion of C-C chemokines modulates C-C chemokine receptor 5 expression on peripheral blood lymphocytes

Peripheral blood lymphocytes express CCR5, a chemokine receptor for immune cell migration and calcium signaling that serves as an important coreceptor for the HIV. After in vitro stimulation, CCR5 expression is dramatically increased on mature T lymphocytes, especially on the CD45RO+ memory subset. In this study, we report that TNF-alpha delays the surface expression of CCR5 on PBLs after activation and diminishes CCR5 irrespective of its initial level. Functional loss of CCR5 is reflected in a decreased capability of the treated cells to migrate and signal calcium after MIP-1beta stimulation. The effect is mediated via the p80 type II TNF receptor (TNFR2), which induces NF-kappaB among other factors, leading to an enhanced secretion of the chemokines macrophage-inflammatory protein-1alpha, macrophage-inflammatory protein-1beta, and RANTES. Expression of these chemokines directly down-regulates CCR5. These findings reveal a new regulatory mechanism utilized by activated peripheral T cells to modulate their chemotaxis and potentially other functions mediated by CCR5, including the infection of T lymphocytes by macrophage-tropic HIV strains.

Human NK cells express CC chemokine receptors 4 and 8 and respond to thymus and activation-regulated chemokine, macrophage-derived chemokine, and I-309

NK cells respond to various chemokines, suggesting that they express receptors for these chemokines. In this paper, we show that IL-2-activated NK (IANK) cells express CC chemokine receptor 4 (CCR4) and CCR8, as determined by flow cytometric, immunoblot, and RNase protection assays. Macrophage-derived chemokine (MDC), the ligand for CCR4, induces the phosphorylation of CCR4 within 0.5 min of activating IANK cells with this ligand. This is corroborated with the recruitment of G protein-coupled receptor kinases 2 and 3 and their association with CCR4 in IANK cell membranes. Also, CCR4 is internalized between 5 and 45 min but reappears in the membranes after 60 min of stimulation with MDC. MDC, thymus and activation-regulated chemokine (TARC), and I-309 induce the chemotaxis of IANK cells, an activity that is inhibited upon pretreatment of these cells with pertussis toxin, suggesting that receptors for these chemokines are coupled to pertussis toxin-sensitive G proteins. In the calcium release assay, cross-desensitization experiments showed that TARC completely desensitizes the calcium flux response induced by MDC or I-309, whereas both MDC and I-309 partially desensitize the calcium flux response induced by TARC. These results suggest that TARC utilizes CCR4 and CCR8. Our results are the first to show that IL-2-activated NK cells express CCR4 and CCR8, suggesting that these receptors are not exclusive for Th2 cells.

Acquisition of HIV type 1 resistance by beta-chemokine-producing CD4+ T cells

The CD4+ T cell is a major target cell type for human immunodeficiency virus type 1 (HIV-1) infection. In this study, we provide evidence that the susceptibility to HIV-1 infection is variable in individual CD4+ T cells. Five CD4+ T cell clones were isolated from an HIV-1-seronegative donor and were investigated for their susceptibility to HIV-1 infection. Four CD4+ T cell clones were resistant to infection by a macrophage-tropic (R5) HIV-1 isolate whereas one clone was fully permissive. The level of susceptibility to HIV-1 correlated inversely with beta-chemokine production, including RANTES (regulated on activation, normally T cell expressed and secreted), macrophage inflammatory protein 1alpha (MIP-1alpha), and MIP-1beta. Resistance to HIV-1 infection was abrogated by the combined use of neutralizing antibodies against these three beta-chemokines. Interestingly, a complete inhibition of HIV-1 infection was observed in peripheral blood mononuclear cells on infection induced by adding the culture supernatant or a small number of HIV-1-resistant cell clones. Our results suggest the presence of a clonal self-defense mechanism within the CD4+ T cell population in vivo that involves the secretion of beta-chemokines.

Chemokines and allergic disease

Understanding the chemokine network has become one of the great challenges for researchers interested in inflammatory mechanisms and inflammation-based diseases. The complexity and diversity of the system provide not only a daunting task for its comprehension but also numerous opportunities for development of new, targeted therapies. It is now certain that chemokines are involved as important mediators of allergic inflammation; the fine details and scope of their roles are now under investigation. Presumably, because of distinct pressures on the immune systems of people living in different geographic regions, genetic variation of ligands, receptors, and regulatory regions in the network have emerged. Establishing the roles of these polymorphisms in determining disease susceptibility or progression among individuals and in distinct ethnic groups will provide a basis for improved understanding and treatment of allergic diseases.

Anti-HIV agent trichosanthin enhances the capabilities of chemokines to stimulate chemotaxis and G protein activation, and this is mediated through interaction of trichosanthin and chemokine receptors

Trichosanthin (TCS), an active protein component isolated from a traditional Chinese medicinal herb Trichosanthes kirilowii, has been shown to inhibit HIV infection and has been applied in clinical treatment of AIDS. The recent development that chemokines and chemokine receptors play important roles in HIV infection led us to investigate the possible functional interaction of TCS with chemokines and their receptors. This study demonstrated that TCS greatly enhanced both RANTES (regulated upon activation, normal T cell expressed and secreted)- and stromal cell-derived factor (SDF)-1 alpha-stimulated chemotaxis (EC50 approximately equal to 1 nM) in leukocytes (THP-1, Jurkat, and peripheral blood lymphocyte cells) and activation of pertussis toxin-sensitive G proteins (EC50 approximately equal to 20 nM). TCS also significantly augmented chemokine-stimulated activation of chemokine receptors CCR5 and CXCR4 as well as CCR1, CCR2B, CCR3, and CCR4 transiently expressed in HEK293 cells. A mutant TCS with 4,000-fold lower ribosome-inactivating activity showed similar augmentation activity as wild-type TCS. Moreover, flow cytometry demonstrated that the specific association of TCS to the cell membranes required the presence of chemokine receptors, and laser confocal microscopy reveals that TCS was colocalized with chemokine receptors on the membranes. The results from TCS-Sepharose pull-down and TCS and chemokine receptor coimmunoprecipitation and cross-linking experiments demonstrated association of TCS with CCR5. Thus, our data clearly demonstrated that TCS synergizes activities of chemokines to stimulate chemotaxis and G protein activation, and the effects of TCS are likely to be mediated through its interaction with chemokine receptors.