Mechanisms of internalization and recycling of the chemokine receptor, CCR5

Identifying CCR5 coreceptor populations permissive for HIV-1 entry and productive infection: implications for in vivo studies

Background

The chemokine receptor CCR5 is the major coreceptor for HIV-1 cell entry. We previously observed that not all CCR5 mAbs reduce HIV-1 infection, suggesting that only some CCR5 populations are permissive for HIV-1 entry. This study aims to better understand the relevant conformational states of the cellular coreceptor, CCR5, involved in HIV entry. We hypothesized that CCR5 assumes multiple configurations during normal cycling on the plasma membrane, but only particular forms facilitate HIV-1 infection.

Methods

To this end, we quantified different CCR5 populations using six CCR5 monoclonal antibodies (mAbs) with different epitope specificities and visualized them with super-resolution microscopy. We quantified each surface CCR5 population before and after HIV-1 infection.

Results

Based on CCR5 conformational changes, down-modulation, and trafficking rates (internalization and recycling kinetics), we were able to distinguish among heterogeneous CCR5 populations and thus which populations might best be targeted to inhibit HIV-1 entry. We assume that a decreased surface presence of a particular CCR5 subpopulation following infection means that it has been internalized due to HIV-1 entry, and that it therefore represents a highly relevant target for future antiviral therapy strategies. Strikingly, this was most true for antibody CTC8, which targets the N-terminal region of CCR5 and blocks viral entry more efficiently than it blocks chemokine binding.

Conclusions

Defining the virus-host interactions responsible for HIV-1 transmission, including specific coreceptor populations capable of establishing de novo infections, is essential for the development of an HIV-1 vaccine. This study hopefully will facilitate further development of inhibitors to block CCR5 usage by HIV-1, as well as inform future HIV-1 vaccine design.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12967-022-03243-8.

Regulation of CXCR6 Expression on Adipocytes and Osteoblasts Differentiated from Human Adipose Tissue-Derived Mesenchymal Stem Cells

Human mesenchymal stem cells derived from adipose tissue (hADMSCs) are a desirable candidate in regenerative medicine. hADMSCs secrete growth factors, cytokines, and chemokines and also express various receptors that are important in cell activation, differentiation, and migration to injured tissue. We showed that the expression level of chemokine receptor CXCR6 was significantly increased by ~2.5-fold in adipogenic-differentiated cells (Ad), but not in osteogenic-differentiated cells (Os) when compared with hADMSCs. However, regulation of CXCR6 expression on hADMSCs by using lentiviral particles did not affect the differentiation potential of hADMSCs. Increased expression of CXCR6 on Ad was mediated by both receptor recycling, which was in turn regulated by secretion of CXCL16, and de novo synthesis. The level of soluble CXCL16 was highly increased in both Ad and Os in particular, which inversely correlates with the expression on a transmembrane-bound form of CXCL16 that is cleaved by disintegrin and metalloproteinase. We concluded that the expression of CXCR6 is regulated by receptor degradation or recycling when it is internalized by interaction with CXCL16 and by de novo synthesis of CXCR6. Overall, our study may provide an insight into the molecular mechanisms of the CXCR6 reciprocally expressed on differentiated cells from hADMSCs.

Analysis of Chemokine Receptor Trafficking by Site-Specific Biotinylation

Chemokine receptors undergo internalization and desensitization in response to ligand activation. Internalized receptors are either preferentially directed towards recycling pathways (e.g. CCR5) or sorted for proteasomal degradation (e.g. CXCR4). Here we describe a method for the analysis of receptor internalization and recycling based on specific Bir A-mediated biotinylation of an acceptor peptide coupled to the receptor, which allows a more detailed analysis of receptor trafficking compared to classical antibody-based detection methods. Studies on constitutive internalization of the chemokine receptors CXCR4 (12.1% ± 0.99% receptor internalization/h) and CCR5 (13.7% ± 0.68%/h) reveals modulation of these processes by inverse (TAK779; 10.9% ± 0.95%/h) or partial agonists (Met-CCL5; 15.6% ± 0.5%/h). These results suggest an actively driven internalization process. We also demonstrate the advantages of specific biotinylation compared to classical antibody detection during agonist-induced receptor internalization, which may be used for immunofluorescence analysis as well. Site-specific biotinylation may be applicable to studies on trafficking of transmembrane proteins, in general.

Actin- and clathrin-dependent mechanisms regulate interferon gamma release after stimulation of human immune cells with respiratory syncytial virus

Background

Respiratory syncytial virus (RSV) can cause recurrent and severe respiratory tract infections. Cytoskeletal proteins are often involved during viral infections, either for cell entry or the initiation of the immune response. The importance of actin and clathrin dynamics for cell entry and the initiation of the cellular immune response against RSV in human immune cells is not known yet. The aim of this study was to investigate the role of actin and clathrin on cell entry of RSV and the subsequent effect on T cell activation and interferon gamma release in human immune cells.

Methods

Peripheral blood mononuclear cells and purified monocytes were isolated from healthy adults and stimulated in vitro with RSV. Actin and clathrin dynamics were inhibited with respectively cytochalasin D and chlorpromazine. T cell receptor signaling was inhibited with cyclosporin A. Flow cytometry was used to determine the role of actin and clathrin on cell entry and T cell activation by RSV. Enzyme-linked immunosorbent assays were used to investigate the contribution of actin and clathrin on the release of interferon gamma.

Results

Cell entry, virus gene transcription and interferon gamma release are actin-dependent. Post-endocytic processes like the increased expression of major histocompatibility complex II on monocytes , T cell activation and the release of interferon gamma are clathrin-dependent. Finally, T cell receptor signaling affects T cell activation, whereas soluble interleukin 18 is dispensable.

Conclusion

Analysis of cell entry and interferon gamma release after infection with RSV reveals the importance of actin- and clathrin-dependent signaling in human immune cells. Insights into the cellular biology of the human immune response against respiratory syncytial virus will provide a better understanding of disease pathogenesis and may prove useful in the development of preventive strategies.

Immature human dendritic cells enhance their migration through KCa3.1 channel activation

Migration capacity is essential for dendritic cells (DCs) to present antigen to T cells for the induction of immune response. The DC migration is supposed to be a calcium-dependent process, while not fully understood. Here, we report a role of the KCa3.1/IK1/SK4 channels in the migration capacity of both immature (iDC) and mature (mDC) human CD14(+)-derived DCs. KCa3.1 channels were shown to control the membrane potential of human DC and the Ca(2+) entry, which is directly related to migration capacities. The expression of migration marker such as CCR5 and CCR7 was modified in both types of DCs by TRAM-34 (100nM). But, only the migration of iDC was decreased by use of both TRAM-34 and KCa3.1 siRNA. Confocal analyses showed a close localization of CCR5 with KCa3.1 in the steady state of iDC. Finally, the implication of KCa3.1 seems to be limited to the migration capacities as T cell activation of DCs appeared unchanged. Altogether, these results demonstrated that KCa3.1 channels have a pro-migratory effect on iDC migration. Our findings suggest that KCa3.1 in human iDC play a major role in their migration and constitute an attractive target for the cell therapy optimization.

CXCL16 upregulates RANKL expression in rheumatoid arthritis synovial fibroblasts through the JAK2/STAT3 and p38/MAPK signaling pathway

OBJECTIVE

To explore the influence of chemokine, CXCL16, on the expression of the receptor activator nuclear factor κB ligand (RANKL) in rheumatoid arthritis (RA) fibroblast-like synoviocytes (RA-FLS).

METHODS

The expression of CXCL16/CXCR6 and RANKL in RA or osteoarthritis (OA) patient synovia was examined by Western blot and immunohistochemistry. The serum concentration of CXCL16 and RANKL was measured by enzyme-linked immunosorbent assay (ELISA). RA-FLS were treated with recombinant CXCL16, and RANKL mRNA and protein were measured using PCR, Western blot and ELISA.

RESULTS

The synovial expression of CXCL16, CXCR6, and RANKL was higher in RA patients than in patients with OA. The serum CXCL16 and RANKL levels were higher in RA patients compared with OA patients and healthy controls. CXCL16 correlated with erythrocyte sedimentation rate, C reactive protein, disease activity, serum rheumatoid factor, and RANKL. RA-FLS treated with CXCL16 showed markedly increased expression of RANKL. When STAT3 or p38 activation was blocked by an inhibitor, CXCL16 failed to upregulate RANKL expression. In contrast, inhibiting the Akt or Erk pathway did not achieve the same effect.

CONCLUSIONS

CXCL16 upregulates RANKL expression in RA-FLS and these effects are mainly mediated by the JAK2/STAT3 and p38/MAPK signaling pathways.

Anti-infective peptide IDR-1002 augments monocyte chemotaxis towards CCR5 chemokines

Innate defense regulator (IDR) peptides are a class of immunomodulators which enhance and modulate host innate immune responses against microbial pathogens. While IDR-mediated protection against a range of bacterial pathogens is dependent on enhanced monocyte recruitment to the site of infection, the mechanisms through which they increase monocyte trafficking remain unclear. In this study, anti-infective peptide IDR-1002 was shown to enhance monocyte chemotaxis towards chemokines CCL3 and CCL5. This enhancement correlated with the selective upregulation of CCR5 surface expression by peptide-treated monocytes. It was found that IDR-1002 enhancement of monocyte chemotaxis was fully dependent on CCR5 function. Furthermore, IDR-1002 enhanced chemokine-induced monocyte p38 MAPK phosphorylation in a CCR5-dependent fashion. Overall, these results indicate that peptide IDR-1002 can selectively influence monocyte recruitment by host chemokines through the regulation of chemokine receptors.

The effects of CCR5 inhibition on regulatory T-cell recruitment to colorectal cancer

BACKGROUND

Regulatory T cells (Treg) are enriched in human colorectal cancer (CRC) where they suppress anti-tumour immunity. The chemokine receptor CCR5 has been implicated in the recruitment of Treg from blood into CRC and tumour growth is delayed in CCR5-/- mice, associated with reduced tumour Treg infiltration.

METHODS

Tissue and blood samples were obtained from patients undergoing resection of CRC. Tumour-infiltrating lymphocytes were phenotyped for chemokine receptors using flow cytometry. The presence of tissue chemokines was assessed. Standard chemotaxis and suppression assays were performed and the effects of CCR5 blockade were tested in murine tumour models.

RESULTS

Functional CCR5 was highly expressed by human CRC infiltrating Treg and CCR5(high) Treg were more suppressive than their CCR5(low) Treg counterparts. Human CRC-Treg were more proliferative and activated than other T cells suggesting that local proliferation could provide an alternative explanation for the observed tumour Treg enrichment. Pharmacological inhibition of CCR5 failed to reduce tumour Treg infiltration in murine tumour models although it did result in delayed tumour growth.

CONCLUSIONS

CCR5 inhibition does not mediate anti-tumour effects as a consequence of inhibiting Treg recruitment. Other mechanisms must be found to explain this effect. This has important implications for anti-CCR5 therapy in CRC.

High-throughput flow cytometry compatible biosensor based on fluorogen activating protein technology

Monitoring the trafficking of multiple proteins simultaneously in live cells is of great interest because many receptor proteins are found to function together with others in the same cell. However, existing fluorescent labeling techniques have restricted the mechanistic study of functional receptor pairs. We have expanded a hybrid system combining fluorogen-activating protein (FAP) technology and high-throughput flow cytometry to a new type of biosensor that is robust, sensitive, and versatile. This provides the opportunity to study multiple trafficking proteins in the same cell. Human beta2 adrenergic receptor (β2AR) fused with FAP AM2.2 and murine C-C chemokines receptor type 5 fused with FAP MG13 was chosen for our model system. The function of the receptor and the binding between MG13 and fluorogen MG-2p have been characterized by flow cytometry and confocal microscopy assays. The binding of fluorogen and the FAP pair is highly specific, while both FAP-tagged fusion proteins function similarly to their wild-type counterparts. The system has successfully served as a counter screen assay to eliminate false positive compounds identified in a screen against NIH Molecular Libraries Small Molecule Repository targeting regulators of the human β2AR.

NHERF1 regulates gp120-induced internalization and signaling by CCR5, and HIV-1 production

The scaffolding protein Na(+) /H(+) exchanger regulator factor 1 (NHERF1) plays an important role in the trafficking of G protein-coupled receptors. We previously demonstrated that NHERF1 is involved in chemokine receptor CCR5 homodimer internalization and signal transduction. Given the importance of CCR5 internalization during HIV-1 infection, we evaluated NHERF1's contribution in HIV-1 infection. We challenged human osteosarcoma cells coexpressing CD4 and CCR5 cells expressing either NHERF1 fragment domains or WT NHERF1 with an HIV-1 strain to examine the effects of NHERF1 on HIV-1 entry and replication. WT NHERF1 potentiates HIV-1 envelope gp120-induced CCR5 internalization, and promotes the replication of HIV-1. In order to better understand how NHERF1 affects signal transduction, different domains of NHERF1 were overexpressed in cells to analyze their effect on the different signaling pathways. Here, we show that NHERF1 can associate with CCR5, and promote activation of the gp120-induced MAPK/ERK, focal adhesion kinase and RhoA (Ras homolog gene family member A) signaling pathways. NHERF1 overexpression also increases HIV-1 host cell migration triggered by gp120 via focal adhesion kinase (FAK) signaling. Finally, NHERF1 enhanced actin filament rearrangement in host cells, an important step in post-entry HIV-1 replication events. While postsynaptic density 95/disk-large/zonula occludens 2 (PDZ2) appears to be the major contributor in those events, other domains also participate in the regulation of gp120-induced signaling pathways. Altogether, our results suggest a very important role of the scaffold NHERF1 in the regulation of HIV-1 entry and replication.

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.

The role of chemokines and their receptors in angiogenesis

Chemokines are a vertebrate-specific group of small molecules that regulate cell migration and behaviour in diverse contexts. So far, around 50 chemokines have been identified in humans, which bind to 18 different chemokine receptors. These are members of the seven-transmembrane receptor family. Initially, chemokines were identified as modulators of the immune response. Subsequently, they were also shown to regulate cell migration during embryonic development. Here, we discuss the influence of chemokines and their receptors on angiogenesis, or the formation of new blood vessels. We highlight recent advances in our understanding of how chemokine signalling might directly influence endothelial cell migration. We furthermore examine the contributions of chemokine signalling in immune cells during this process. Finally, we explore possible implications for disease settings, such as chronic inflammation and tumour progression.

Na+/H+ exchanger regulatory factor-1 is involved in chemokine receptor homodimer CCR5 internalization and signal transduction but does not affect CXCR4 homodimer or CXCR4-CCR5 heterodimer

Chemokine receptors are members of the G protein-coupled receptor (GPCR) family. CCR5 is also the principal co-receptor for macrophage-tropic strains of human immunodeficiency virus, type 1 (HIV-1), and efforts have been made to develop ligands to inhibit HIV-1 infection by promoting CCR5 receptor endocytosis. Given the nature of GPCRs and their propensity to form oligomers, one can consider ligand-based therapies as unselective in terms of the oligomeric composition of complexes. For example, a ligand targeting a CCR5 homomer could likely induce signal transduction on a heteromeric CCR5-CXCR4. Other avenues could therefore be explored. We identified a receptor adaptor interacting specifically with one receptor complex but not others. NHERF1, an adaptor known for its role in desensitization, internalization, and regulation of the ERK signaling cascade for several GPCRs, interacts via its PDZ2 domain with the CCR5 homodimer but not with the CXCR4-CCR5 heterodimer or CXCR4 homodimer. To further characterize this interaction, we also show that NHERF1 increases the CCR5 recruitment of arrestin2 following stimulation. NHERF1 is also involved in CCR5 internalization, as we demonstrate that co-expression of constructs bearing the PDZ2 domain can block CCR5 internalization. We also show that NHERF1 potentiates RANTES (regulated on activation normal T cell expressed and secreted)-induced ERK1/2 phosphorylation via CCR5 activation and that this activation requires NHERF1 but not arrestin2. Taken together, our results suggest that oligomeric receptor complexes can associate specifically with partners and that in this case NHERF1 could represent an interesting new target for the regulation of CCR5 internalization and potentially HIV infection.

The molecular mechanisms of traditional Chinese medicine ZHENG syndromes on pancreatic tumor growth

BACKGROUND

Traditional Chinese medicine (TCM) syndromes (ZHENG in Chinese) are the abstraction from the comprehensive analysis of clinical information gained by the four main diagnostic TCM methods: observation, listening, questioning, and pulse analyses. Proper TCM diagnosis is the most important principle to guide the prescribing of Chinese herbs.

OBJECTIVE

To evaluate the specific effect of TCM ZHENG on tumor growth and to examine the molecular mechanisms underlying ZHENG and tumor growth.

METHODS

The authors established subcutaneous tumor models of pancreatic cancer ZHENG syndromes of Damp heat (Shi-Re) and Spleen deficiency (Pi-Xu). Tissue samples of the subcutaneous transplanted tumors from each model were studied versus control tumors. CCR5 and CXCR4 proteins in these tissues were assayed by immunohistochemical staining. The expression of CCR5/CCL5/CCL4/CCL3 and CXCR4/SDF-1 mRNA was investigated by reverse transcriptase-polymerase chain reaction (RT-PCR). SDF-1, CCL4, CCL5, and CCL3, which are ligands of CXCR4 and CCR5, were examined by ELISA.

RESULTS

The study found that tumor models with different ZHENG were successfully established in each group; the tumor growth of Shi-Re group was slower than that of the control group. It was found that there was a significant difference in CCR5 mRNA expression levels among the Pi-Xu, Shi-Re, and control groups. The results of immunohistochemistry staining revealed that the positive rate of CCR5 protein in Shi-Re group, Pi-Xu group, and control group was 25.00%, 53.33%, 83.33%, respectively. The Shi-Re group expressed the lowest levels of CCL5 and CCL4.

CONCLUSION

The results of the study suggest that the existence of TCM ZHENG may influence the tumor growth in pancreatic cancer, which might be mediated by the expression of CCR5/CCL5/CCL4. This finding may lead to the development of TCM ZHENG as a prognostic indicator in pancreatic tumor growth.

Analysis of second messenger pathways stimulated by different chemokines acting at the chemokine receptor CCR5

The chemokine receptor, CCR5, responds to several chemokines leading to changes in activity in several signalling pathways. Here, we investigated the ability of different chemokines to provide differential activation of pathways. The effects of five CC chemokines acting at CCR5 were investigated for their ability to inhibit forskolin-stimulated 3'-5'-cyclic adenosine monophosphate (cAMP) accumulation and to stimulate Ca(2+) mobilisation in Chinese hamster ovary (CHO) cells expressing CCR5. Macrophage inflammatory protein 1alpha (D26A) (MIP-1alpha (D26A), CCL3 (D26A)), regulated on activation, normal T-cell expressed and secreted (RANTES, CCL5), MIP-1beta (CCL4) and monocyte chemoattractant protein 2 (MCP-2, CCL8) were able to inhibit forskolin-stimulated cAMP accumulation, whilst MCP-4 (CCL13) could not elicit a response. CCL3 (D26A), CCL4, CCL5, CCL8 and CCL13 were able to stimulate Ca(2+) mobilisation through CCR5, although CCL3 (D26A) and CCL5 exhibited biphasic concentration-response curves. The Ca(2+) responses induced by CCL4, CCL5, CCL8 and CCL13 were abolished by pertussis toxin, whereas the response to CCL3 (D26A) was only partially inhibited by pertussis toxin, indicating G(i/o)-independent signalling induced by this chemokine. Although the rank order of potency of chemokines was similar between the two assays, certain chemokines displayed different pharmacological profiles in cAMP inhibition and Ca(2+) mobilisation assays. For instance, whilst CCL13 could not inhibit forskolin-stimulated cAMP accumulation, this chemokine was able to induce Ca(2+) mobilisation via CCR5. It is concluded that different chemokines acting at CCR5 can induce different pharmacological responses, which may account for the broad spectrum of chemokines that can act at CCR5.

The benzamide derivative N-[1-(7-tert-Butyl-1H-indol-3-ylmethyl)-2-(4-cyclopropanecarbonyl-3-methyl-piperazin-1-yl)-2-oxo-ethyl]-4-nitro-benzamide (SP-10) reduces HIV-1 infectivity in vitro by modifying actin dynamics

Current treatments for patients infected with HIV are suboptimal. There is a need for new HIV therapies that act through different mechanisms than current treatments. We investigated the in vitro efficacy, safety and mechanism of action of the benzamide derivative N-[1-(7-tert-Butyl-1H-indol-3-ylmethyl)-2-(4-cyclopropanecarbonyl-3-methyl-piperazin-1-yl)-2-oxo-ethyl]-4-nitro-benzamide (SP-10), a potential new HIV treatment. When HIV-1-responsive engineered HeLa cells were pre-incubated for 48 h with either SP-10 or zidovudine (AZT), SP-10 was able to inhibit viral replication at much lower concentrations (IC50 = 0.036 nM) than AZT (IC50 = 27.4 nM). In contrast to AZT, SP-10 also inhibited replication of the multidrug-resistant HIV-1 strain MDR-769 in the HeLa cell model. In co-incubation experiments, SP-10 also inhibited the CCR5-sensitive HIV-1 BaL virus replication in human peripheral blood mononuclear cells. SP-10 displayed very low toxicity compared with current antiviral treatments. Confocal laser scanning microscopy and immunoprecipitation studies showed that SP-10 reduced the expression of CD4 and CCR5 on the surface of the host cell. SP-10 also reduced the level of gp120 binding to the cell surface. Confocal laser scanning microscopy studies showed that SP-10 blocked the formation of actin filaments (F-actin) and altered actin accumulation near the cell surface. These promising results suggest that SP-10 has a novel mechanism of action that enables effective inhibition of HIV-1 binding and cell entry. Further development of SP-10 as a new HIV treatment appears warranted.

RSV-infected airway epithelial cells cause biphasic up-regulation of CCR1 expression on human monocytes

Respiratory syncytial virus (RSV) infection can cause extensive airway inflammation, which is orchestrated by chemokines and their receptors. RSV-infected epithelial cells secrete many cytokines and chemokines, but little is known about regulation of chemokine receptors on target cells. We investigated the effects of conditioned media (CM) from RSV-infected epithelial cells on monocyte CCR1, CCR2, and CCR5 expression. RSV-CM but not control-CM stimulated a biphasic increase in cell-surface CCR1, and levels peaked at 36 h and 96 h poststimulation. Similar CCR1 up-regulation occurred on monocyte-derived macrophages. Cytochlasin D and colchicine blocked both peaks of expression, demonstrating requirement of a functional cytoskeleton. Intracellular staining revealed little internal sequestration of CCR1 protein, and CCR1 up-regulation was inhibited by actinomycin D and cycloheximide, indicating that both waves of RSV-CM-induced surface CCR1 expression were dependent on de novo transcription and protein synthesis. Cytokine-neutralizing experiments showed that the effects of RSV-CM were decreased by blocking TNF-alpha (percent inhibition=51+/-2.3% at 36 h peak and 42+/-7.7% at 96 h peak) and to a lesser extent, IL-1 (percent inhibition=32+/-7.2% at 36 h and 23+/-2.9% at 96 h). In summary, RSV-CM causes a biphasic up-regulation of surface CCR1 on monocytes, which is dependent on an intact cytoskeleton, requires new gene transcription and protein synthesis, and is mediated in part by the proinflammatory cytokines TNF-alpha and IL-1.

Downregulation of CCR5 expression on cells by recombinant adenovirus containing antisense CCR5, a possible measure to prevent HIV-1 from entering target cells

Chemokine (C-C motif) receptor 5 (CCR5) is one of the major co-receptors for the macrophage (M)-tropic HIV-1. To prevent HIV-1 from entering into target cells, we inhibited CCR5 expression on target cell surface by recombinant adenovirus containing anti-sense CCR5 cDNA. A fragment of 653 bp cDNA located in the 5' region of CCR5 cDNA was reversely inserted into pAdTrack-CMV. Recombinant adenovirus containing antisense CCR5 cDNA (Ad-antiR5) was obtained by homologous recombination of resultant plasmid with the adenoviral backbone plasmid pAdEasy-2 in E. coli BJ5183 and then packed in AD-293 cells. Rate of positive CCR5 on U937 cell surface measured by flow cytometry was decreased from 89.53% to 1.88% after U937 cells infected with Ad-antiR5 for 24 hours, and this reduction lasted at least for 10 days. After challenged with HIV-1, the U937 cells infected with Ad-antiR5 produced much less p24 antigen in cultured medium than those infected with control recombinant adenovirus and the uninfected cells. The recombinant adenovirus had no effect on chemotactic activity and proliferation of the U937 cells. Therefore, the recombinant adenovirus containing anti-sense CCR5 cDNA can down-regulate CCR5 expression on U937 cells and protect the cells from HIV-1 infection without effects on their chemotaxis activity and proliferation function.

CCR5 expression on monocytes and T cells: modulation by transmigration across the blood-brain barrier in vitro

Observational studies in multiple sclerosis (MS) demonstrated altered expression of chemokine receptors (CkRs) on comparable populations of mononuclear cells (e.g. CD4(+)/CD45RO(+) T-cells) in brain sections compared with blood. These findings raised questions about the regulation of CkRs on trafficking cells. Regulatory processes for CkRs are complex: examples include down-regulation following ligand engagement during migration and either up- or down-regulation following activation. Additionally, CkRs that mediate transmigration without being down-regulated will be selectively enriched on migrating cells in the inflammatory site. Finally, CkRs may act as functionally neutral markers of activated cells capable of undergoing transmigration. Clarifying CkR regulation may aid in the selection and application of antagonists for treating neuroinflammation. Mechanisms of receptor regulation during transmigration cannot be studied by descriptive methods. We evaluated CCR5 expression on CD14(+) monocytes and CD3(+) T-cells following CCL5-driven transmigration through an in vitro blood-brain barrier (IVBBB), as both T-cells and monocytes in MS lesions express CCR5. CCR5 expression was augmented on non-migrating CD14(+) but not CD3(+) cells, suggesting selective activation of monocytes by incubation in contact with endothelial cells. As proposed from observational studies, CCR5 was enriched on monocytes that migrated spontaneously in the absence of exogenous chemokine. Addition of the CCR5 ligand CCL5 to the lower chamber led to enhanced CD3(+) T-cell migration. Interestingly, CCR5 was down-regulated on both CD14(+) monocytes and CD3(+) T cells during CCL5-driven migration. These results are distinct from those obtained in comparable studies of CCR2 and CXCR3, suggesting that the specifics for CkR expression should be studied for individual receptors on each leukocyte subpopulation during the design of strategies for pharmacological blockade in neuroinflammation.

Opposite fate of endocytosed CCR7 and its ligands: recycling versus degradation

The chemokine receptor CCR7 and its ligands CCL19 and CCL21 play a crucial role for the homing of lymphocytes and dendritic cells to secondary lymphoid tissues. Nevertheless, how CCR7 senses the gradient of chemokines and how migration is terminated are poorly understood. In this study, we demonstrate that CCR7(-GFP) is endocytosed into early endosomes containing transferrin receptor upon CCL19 binding, but less upon CCL21 triggering. Internalization of CCR7 was independent of lipid rafts but relied on dynamin and Eps15 and was inhibited by hypertonic sucrose, suggesting clathrin-dependent endocytosis. After chemokine removal, internalized CCR7 recycled back to the plasma membrane and was able to mediate migration again. In contrast, internalized CCL19 was sorted to lysosomes for degradation, showing opposite fate for endocytosed CCR7 and its ligand.

Mu opioid receptor-effector coupling and trafficking in dorsal root ganglia neurons

Morphine induces profound analgesic tolerance in vivo despite inducing little internalization of the mu opioid receptor (muOR). Previously proposed explanations suggest that this lack of internalization could either lead to prolonged signaling and associated compensatory changes in downstream signaling systems, or that the receptor is unable to recycle and resensitize and so loses efficacy, either mechanism resulting in tolerance. We therefore examined, in cultured neurons, the relationship between muOR internalization and desensitization in response to two agonists, D-Ala2, N-MePhe4, Gly5-ol-enkephalin (DAMGO) and morphine. In addition, we studied the chimeric mu/delta opioid receptor (mu/ partial differentialOR) which could affect internalization and desensitization in neurons. Dorsal root ganglia neurons from muOR knockout mice were transduced with an adenovirus expressing either receptor and their respective internalization, desensitization and trafficking profiles determined. Both receptors desensitized equally, measured by Ca2+ current inhibition, during the first 5 min of agonist exposure to DAMGO or morphine treatment, although the mu/partial differentialOR desensitized more extensively. Such rapid desensitization was unrelated to internalization as DAMGO, but not morphine, internalized both receptors after 20 min. In response to DAMGO the mu/partial differentialOR internalized more rapidly than the muOR and was trafficked through Rab4-positive endosomes and lysosomal-associated membrane protein-1-labeled lysosomes whereas the muOR was trafficked through Rab4 and Rab11-positive endosomes. Chronic desensitization of the Ca2+ current response, after 24 h of morphine or DAMGO incubation, was seen in the DAMGO, but not morphine-treated, muOR-expressing cells. Such persistence of signaling after chronic morphine treatment suggests that compensation of downstream signaling systems, rather than loss of efficacy due to poor receptor recycling, is a more likely mechanism of morphine tolerance in vivo. In contrast to the muOR, the mu/partial differentialOR showed equivalent desensitization whether morphine or DAMGO treated, but internalized further with DAMGO than morphine. Such ligand-independent desensitization could be a result of the observed higher rate of synthesis and degradation of this chimeric receptor.

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.

CDK9/cyclin T1: a host cell target for antiretroviral therapy

Hijacking of the host cell’s signal transduction machinery has been increasingly regarded as an important strategy for facilitating virus propagation. The positive-transcription elongation factor (P-TEFb) complex, cyclin-dependent kinase (CDK)9/cyclin T1, is an example of such an attack by HIV. Upon infection of cells, the HIV protein transactivator of transcription (Tat) forms a highly specific complex with the two host cell proteins CDK9 and cyclin T1. This complex ensures phosphorylation of the native CDK9 substrate, RNA polymerase II, leading to productive elongation of viral RNA in the host cell. Although challenging, inhibition of CDK9 activity with small molecules is a therapeutically valid strategy to inhibit HIV replication. Other than direct antiviral agents, that inhibit HIV replication through a direct interaction with viral proteins, CDK9 inhibitors might not suffer from the emergence of resistant virus strains. This review outlines the advantages and prospects of selective CDK9 inhibitors in the management of HIV infections.

Ezrin directly interacts with the alpha1b-adrenergic receptor and plays a role in receptor recycling

Using the yeast two-hybrid system, we identified ezrin as a protein interacting with the C-tail of the alpha1b-adrenergic receptor (AR). The interaction was shown to occur in vitro between the receptor C-tail and the N-terminal portion of ezrin, or Four-point-one ERM (FERM) domain. The alpha1b-AR/ezrin interaction occurred inside the cells as shown by the finding that the transfected alpha1b-AR and FERM domain or ezrin could be coimmunoprecipitated from human embryonic kidney 293 cell extracts. Mutational analysis of the alpha1b-AR revealed that the binding site for ezrin involves a stretch of at least four arginines on the receptor C-tail. The results from both receptor biotinylation and immunofluorescence experiments indicated that the FERM domain impaired alpha1b-AR recycling to the plasma membrane without affecting receptor internalization. The dominant negative effect of the FERM domain, which relies on its ability to mask the ezrin binding site for actin, was mimicked by treatment of cells with cytochalasin D, an actin depolymerizing agent. A receptor mutant (DeltaR8) lacking its binding site in the C-tail for ezrin displayed delayed receptor recycling. These findings identify ezrin as a new protein directly interacting with a G protein-coupled receptor and demonstrate the direct implication of ezrin in GPCR trafficking via an actin-dependent mechanism.

Regulation of LFA-1 activity through cytoskeleton remodeling and signaling components modulates the efficiency of HIV type-1 entry in activated CD4+ T lymphocytes

Besides interactions between the viral envelope glycoproteins with cell surface receptors, interactions between cell-derived molecules incorporated onto virions and their ligand could also modulate HIV type-1 (HIV-1) entry inside CD4(+) T lymphocytes. Although incorporation of host ICAM-1 within HIV-1 increases both virus attachment and fusion, the precise mechanism through which this phenomenon is occurring is still unclear. We demonstrate in this study that activation of primary human CD4(+) T lymphocytes increases LFA-1 affinity and avidity states, two events promoting the early events of the HIV-1 replication cycle through interactions between virus-embedded host ICAM-1 and LFA-1 clusters. Confocal analyses suggest that HIV-1 is concentrated in microdomains rich in LFA-1 clusters that also contain CD4 and CXCR4 molecules. Experiments performed with specific inhibitors revealed that entry of HIV-1 in activated CD4(+) T cells is regulated by LFA-1-dependent ZAP70, phospholipase Cgamma1, and calpain enzymatic activities. By using laboratory and clinical strains of HIV-1 produced in primary human cells, we demonstrate the importance of the LFA-1 activation state and cluster formation in the initial step of the virus life cycle. Overall, these data provide new insights into the complex molecular events involved in HIV-1 binding and entry.

C-C Chemokine Receptor 5 Gene Variants in Relation to Lung Disease in Sarcoidosis

RATIONALE

Genetic factors are likely to influence the clinical course and pattern of sarcoidosis, a granulomatous disease of unknown origin.

OBJECTIVES

We tested this hypothesis for C-C chemokine receptor 5 (CCR5), a molecule involved in recruitment and activation of mononuclear cells.

METHODS

In addition to the known CCR5 Delta 32 insertion/deletion, we evaluated a further eight single-nucleotide polymorphisms in 106 British patients and 142 British unaffected subjects, and second-setted the results in 112 Dutch patients and 169 healthy Dutch control subjects.

MEASUREMENTS AND MAIN RESULTS

In the British population, the frequency of one of the identified haplotypes (HHC) was strongly associated with the presence of parenchymal disease (radiographic stage >or= II versus stages 0 and I) at presentation (odds ratio [OR], 5.2; 95% confidence interval [CI], 1.96-13.7; corrected p = 0.02), at 2 (OR, 6.6; 95% CI, 2.5-17.6; corrected p = 0.006), and at 4 years follow-up (OR, 6.8; 95% CI, 2.5-18.0; corrected p = 0.0045). In the Dutch population, the same association was seen at 2 (OR, 6.7; 95% CI, 2.8-16.4; corrected p = 0.002), and 4 years follow-up (OR, 9.0; 95% CI, 3.5-23.1; corrected p = 0.0009).

CONCLUSIONS

No association between the CCR5 haplotype HHC and susceptibility to sarcoidosis was observed, indicating that this relevant gene only operates after disease induction. In summary, we report a strong association between CCR5 haplotype HHC and persistent lung involvement in sarcoidosis.

Chemokine receptor internalization and intracellular trafficking

The internalization and intracellular trafficking of chemokine receptors have important implications for the cellular responses elicited by chemokine receptors. The major pathway by which chemokine receptors internalize is the clathrin-mediated pathway, but some receptors may utilize lipid rafts/caveolae-dependent internalization routes. This review discusses the current knowledge and controversies regarding these two different routes of endocytosis. The functional consequences of internalization and the regulation of chemokine receptor recycling will also be addressed. Modifications of chemokine receptors, such as palmitoylation, ubiquitination, glycosylation, and sulfation, may also impact trafficking, chemotaxis and signaling. Finally, this review will cover the internalization and trafficking of viral and decoy chemokine receptors.

JM4 is a four-transmembrane protein binding to the CCR5 receptor

The CC chemokine receptor 5 (CCR5) is a major co-receptor for human immunodeficiency virus (HIV) and CCR5 mutants lacking the carboxy (C)-terminus interfere with HIV infection. Therefore, we analysed the C-terminus of CCR5 and here describe Jena-Muenchen 4 (JM4), a novel CCR5-interacting protein. JM4 is membrane-associated, co-precipitates with CCR5, and is ubiquitously expressed. It shares about 62% sequence similarity with JWA and glutamate transporter-associated protein 3-18 (GTRAP3-18), a regulator of an amino acid transporter. JWA, like JM4, is a four-transmembrane protein, which binds to the CCR5 receptor. Furthermore, JM4, JWA, and GTRAP3-18 co-localise and heterodimerise indicating a functional relationship. JM4 co-localises with calnexin in the endoplasmic reticulum and with the mannose 6-phosphate receptor in the Golgi. JM4 and GTRAP3-18 harbor a Rab-acceptor motif, indicating a function in vesicle formation at the Golgi complex. In conclusion, we describe a CCR5-interacting protein, which is suggested to function in trafficking and membrane localisation of the receptor, possibly also other receptors or amino acid transporters.

Proteomics analysis of human astrocytes expressing the HIV protein Tat

Astrocyte infection in HIV has been associated with rapid progression of dementia in a subset of HIV/AIDS patients. Astrogliosis and microglial activation are observed in areas of axonal and dendritic damage in HIVD. In HIV-infected astrocytes, the regulatory gene tat is over expressed and mRNA levels for Tat are elevated in brain extracts from individuals with HIV-1 dementia. Tat can be detected in HIV-infected astrocytes in vivo. The HIV-1 protein Tat transactivates viral and cellular gene expression, is actively secreted mainly from astrocytes, microglia and macrophages, into the extracellular environment, and is taken up by neighboring uninfected cells such as neurons. The HIV-1 protein Tat released from astrocytes reportedly produces trimming of neurites, mitochondrial dysfunction and cell death in neurons, while protecting its host, the astrocyte. We utilized proteomics to investigate protein expression changes in human astrocytes intracellularly expressing Tat (SVGA-Tat). By coupling 2D fingerprinting and identification of proteins by mass spectrometry, we identified phosphatase 2A, isocitrate dehydrogenase, nuclear ribonucleoprotein A1, Rho GDP dissociation inhibitor alpha, beta-tubulin, crocalbin like protein/calumenin, and vimentin/alpha-tubulin to have decreased protein expression levels in SVGA-Tat cells compared to the SVGA-pcDNA cells. Heat shock protein 70, heme oxygenase-1, and inducible nitric oxide synthase were found to have increased protein expression in SVGA-Tat cells compared to controls by slotblot technique. These findings are discussed with reference to astrocytes serving as a reservoir for the HIV virus and how Tat promotes survival of the astrocytic host.