Atypical chemokine receptors

Intracellular GPCR modulators enable precision pharmacology

G-protein-coupled receptors (GPCRs) have proven to be the most successful target class for drug discovery but their complicated signal transduction pathways cause difficulties for drug development. Recently, ligands have been identified that engage an intracellular binding site which promotes pathway biased signal in cooperation with orthosteric ligands. Here, we explore the topic of biased signaling and intracellular modulators to understand their application for precision pharmacology of Class A or Rhodopsin-Like GPCRs.

G protein-coupled receptor GPR182 negatively regulates sprouting angiogenesis via modulating CXCL12-CXCR4 axis signaling

Angiogenesis is a critical process for tumor progression, regulated by various signaling pathways. Although antiangiogenic therapies targeting the VEGF pathway have shown potential, their effectiveness is inconsistent across different tumor types. GPR182, an endothelial cell-specific G protein-coupled receptor, is frequently downregulated in hypervascular tumors, but its specific role in angiogenesis has not been well defined. Our study reveals that GPR182 expression is markedly reduced in hepatocellular carcinoma (HCC) and inversely correlates with CD31, a pan-endothelial marker. In zebrafish embryos, Gpr182 deficiency resulted in enhanced angiogenic sprouting and hypervascularization, and GPR182-deficient human umbilical vein endothelial cells (HUVECs) showed increased migration and proliferation. At the molecular level, GPR182 acts as a decoy receptor, binding CXCL12 and regulating its gradient, which in turn suppresses CXCR4-mediated angiogenesis. The pharmacological blockade of CXCR4 with AMD3100 corrected the abnormal angiogenic phenotype in Gpr182-deficient zebrafish embryos and in the livers of a zebrafish HCC model. This work uncovers GPR182 as a negative regulator of angiogenesis, a key process in tumor growth and metastasis, and proposes that targeting GPR182 may offer a novel therapeutic approach for antiangiogenic strategies in cancer treatment.

A patent review of CXCR7 modulators (2019-present)

INTRODUCTION

Atypical chemokine receptor 3 (ACKR3) (formerly CXCR7) regulates various biological processes through its ligands and is closely associated with numerous diseases, including inflammation, cancer, cardiovascular diseases (CVDs), pain, and neurological disorders. Therefore, ACKR3 has emerged as a potential target for disease treatment.

AREAS COVERED

This review summarizes the ACKR3 modulators published in patents from 2019 to 2024 using data from Google Patents, the European Patent Office, and the World Intellectual Property Organization's online databases. This includes information on their chemical structures, syntheses, activities, and developmental stages.

EXPERT OPINION

ACKR3 agonists gained traction as a treatment for cardiovascular and pain conditions. WW-12, which was derived from the chemical modifications of conolidine, became a novel small-molecule pain modulator by activating ACKR3, which in turn boosted endogenous opioid peptides for the classical opioid receptors.ACKR3 antagonist ACT-1004-1239 from Idorsia Pharmaceuticals Ltd. has demonstrated the ability to treat cancer, acute lung injury/ARDS, and autoimmune diseases, including multiple sclerosis. The outcomes of these clinical trials will direct the development and indications of future ACKR3 modulators.

Emerging concepts in the molecular cell biology and functions of mammalian erythrocytes

Erythrocytes, or red blood cells, are essential components of vertebrate blood, comprising approximately 45% of human blood volume. Their distinctive features, including small size, biconcave shape, extended lifespan (∼115 days), and lack of a nucleus or other membrane-bound organelles, make them unique among mammalian cell types. Traditionally regarded as passive carriers of oxygen and carbon dioxide, erythrocytes were long thought to function merely as hemoglobin-filled sacs, incapable of gene expression or roles beyond gas transport. However, advancements in molecular biology have revealed a more complex picture. Recent studies have identified various RNA types within erythrocytes, demonstrated globin mRNA translation, and uncovered miRNA-mediated defenses against Plasmodium infection. Beyond gas exchange, erythrocytes play critical roles in regulating regional blood flow via nitric oxide, contribute to innate immunity through toll-like receptors, transport amino acids between tissues, and maintain water homeostasis. Furthermore, emerging technologies have repurposed erythrocytes as drug-delivery vehicles, opening new avenues for therapeutic applications. This review highlights these recent discoveries and explores the expanding functional landscape of erythrocytes, shedding light on their multifaceted roles in physiology and medicine.

Structural visualization of small molecule recognition by CXCR3 uncovers dual-agonism in the CXCR3-CXCR7 system

Chemokine receptors are critically involved in multiple physiological and pathophysiological processes related to immune response mechanisms. Most chemokine receptors are prototypical GPCRs although some also exhibit naturally-encoded signaling-bias toward β-arrestins (βarrs). C-X-C type chemokine receptors, namely CXCR3 and CXCR7, constitute a pair wherein the former is a prototypical GPCR while the latter exhibits selective coupling to βarrs despite sharing a common natural agonist: CXCL11. Moreover, CXCR3 and CXCR7 also recognize small molecule agonists suggesting a modular orthosteric ligand binding pocket. Here, we determine cryo-EM structures of CXCR3 in an Apo-state and in complex with small molecule agonists biased toward G-proteins or βarrs. These structural snapshots uncover an allosteric network bridging the ligand-binding pocket to intracellular side, driving the transducer-coupling bias at this receptor. Furthermore, structural topology of the orthosteric binding pocket also allows us to discover and validate that selected small molecule agonists of CXCR3 display robust agonism at CXCR7. Collectively, our study offers molecular insights into signaling-bias and dual agonism in the CXCR3-CXCR7 system with therapeutic implications.

The 129 strain-derived passenger mutations in ACKR1-deficient mice alter the expression of PYHIN and Fc-gamma receptor genes

Most genetically modified mice have been produced using 129 strain-derived embryonic stem cells. Despite ample backcrosses with other strains, these may retain characteristics for 129 passenger mutations, leading to confounding phenotypes unrelated to targeted genes. Here we show that widely used Ackr1-/-129ES mice have approximately 6 Mb of the 129-derived genome retained adjacently to the Ackr1 locus on chromosome 1, including several characteristic polymorphisms. These most notably affect the expression of PYHIN and Fc-gamma receptor genes in myeloid cells, resulting in the overproduction of IL-1β by activated macrophages and the loss of Fc-gamma receptors on myeloid progenitor cells. Therefore, caution is warranted when interpreting Ackr1-/-129ES mouse phenotypes as being solely due to the ACKR1 deficiency. Our findings call for a careful reevaluation of data from previous studies using Ackr1-/-129ES mice and underscore the limitations and pitfalls inherent to mouse models produced using traditional genetic engineering techniques involving 129 embryonic stem cells.

Unraveling the Multifaceted Roles of Atypical Chemokine Receptors in Breast Cancer

Breast cancer (BC) remains one of the most prevalent and deadly malignancies among women globally. A deeper understanding of the molecular mechanisms driving BC progression and metastasis is essential for the development of effective therapeutic strategies. While traditional chemokine receptors are well known for their roles in immune cell migration and positioning, atypical chemokine receptors (ACKRs) have recently gained attention as key modulators in cancer-related processes. Unlike conventional receptors, ACKRs-comprising ACKR1, ACKR2, ACKR3, and ACKR4-primarily function by scavenging chemokines, regulating their availability, and modulating receptor signaling in a ligand-independent manner. This review aims to elucidate the roles of ACKRs in BC, focusing on their influence on the tumor microenvironment (TME), cancer cell proliferation, survival, metastasis, and angiogenesis. Additionally, we will explore the potential of ACKRs as diagnostic and prognostic markers and assess their viability as therapeutic targets. By synthesizing recent research findings and highlighting future research directions, this review seeks to provide a comprehensive understanding of the significance of ACKRs in BC and underscore the need for continued investigation into their therapeutic potential.

Molecular regulators of chemotaxis in human hematopoietic stem cells

Hematopoietic stem cells (HSCs), essential for lifelong blood cell regeneration, are clinically utilized to treat various hematological disorders. These cells originate in the aorta-gonad-mesonephros region, expand in the fetal liver, and mature in the bone marrow. Chemotaxis, involving gradient sensing, polarization, and migration, directs HSCs and is crucial for their homing and mobilization. The molecular regulation of HSC chemotaxis involves chemokines, chemokine receptors, signaling pathways, and cytoskeletal proteins. Recent advances in understanding these regulatory mechanisms have deepened insights into HSC development and hematopoiesis, offering new avenues for therapeutic innovations. Strategies including glucocorticoid receptor activation, modulation of histone acetylation, stimulation of nitric oxide signaling, and interference with m6A RNA modification have shown potential in enhancing CXCR4 expression, thereby improving the chemotactic response and homing capabilities of human HSCs. This review synthesizes current knowledge on the molecular regulation of human HSC chemotaxis and its implications for health and disease.

Chemokines and chemokine receptors: Potential therapeutic targets in systemic lupus erythematosus

Systemic lupus erythematosus (SLE) is an autoimmune disease that affects connective tissue and can lead to multisystem organ damage. Chemokines are a class of small proteins that interact with receptors and participate in a variety of physiological functions, including cell growth, differentiation, apoptosis and distribution. They also play important roles in pathological processes, such as the inflammatory response, wound repair, tumor formation and metastasis. Previous studies have shown that the levels of chemokines and their receptors are elevated in the blood and inflamed tissues of SLE patients. In addition, chemokine ligand-receptor interactions control the recruitment of leukocytes into tissues, suggesting that chemokines and their receptors may be biomarkers and therapeutic targets for SLE. This review summarizes the causative role of chemokines and their receptors in SLE, as well as their clinical values and challenges as potential biomarkers and therapeutic targets.

Chemokine expression profile of an innate granuloma

Granulomas are defined by the presence of organized layers of immune cells that include macrophages. Granulomas are often characterized as a way for the immune system to contain an infection and prevent its dissemination. We recently established a mouse infection model where Chromobacterium violaceum induces the innate immune system to form granulomas in the liver. This response successfully eradicates the bacteria and returns the liver to homeostasis. Here, we sought to characterize the chemokines involved in directing immune cells to form the distinct layers of a granuloma. We use spatial transcriptomics to investigate the spatial and temporal expression of all CC and CXC chemokines and their receptors within this granuloma response. The expression profiles change dynamically over space and time as the granuloma matures and then resolves. To investigate the importance of monocyte-derived macrophages in this immune response, we studied the role of CCR2 during C. violaceum infection. Ccr2-/- mice had negligible numbers of macrophages, but large numbers of neutrophils, in the C. violaceum-infected lesions. In addition, lesions had abnormal architecture resulting in loss of bacterial containment. Without CCR2, bacteria disseminated and the mice succumbed to the infection. This indicates that macrophages are critical to form a successful innate granuloma in response to C. violaceum.

Atypical chemokine receptor 2 expression is directly regulated by hypoxia inducible factor-1 alpha in cancer cells under hypoxia

Lack of significant and durable clinical benefit from anti-cancer immunotherapies is partly due to the failure of cytotoxic immune cells to infiltrate the tumor microenvironment. Immune infiltration is predominantly dependent on the chemokine network, which is regulated in part by chemokine and atypical chemokine receptors. We investigated the impact of hypoxia in the regulation of Atypical Chemokine Receptor 2 (ACKR2), which subsequently regulates major pro-inflammatory chemokines reported to drive cytotoxic immune cells into the tumor microenvironment. Our in silico analysis showed that both murine and human ACKR2 promoters contain hypoxia response element (HRE) motifs. Murine and human colorectal, melanoma, and breast cancer cells overexpressed ACKR2 under hypoxic conditions in a HIF-1α dependent manner; as such overexpression was abrogated in melanoma cells expressing non-functional deleted HIF-1α. We also showed that decreased expression of ACKR2 in HIF-1α-deleted cells under hypoxia was associated with increased CCL5 levels. Chromatin immunoprecipitation data confirmed that ACKR2 is directly regulated by HIF-1α at its promoter in B16-F10 melanoma cells. This study provides new key elements on how hypoxia can impair immune infiltration in the tumor microenvironment.

Novel Small-Molecule Atypical Chemokine Receptor 3 Agonists: Design, Synthesis, and Pharmacological Evaluation for Antiplatelet Therapy

ACKR3, an atypical chemokine receptor, has been associated with prothrombotic events and the development of cardiovascular events. We designed, synthesized, and evaluated a series of novel small molecule ACKR3 agonists. Extensive structure-activity relationship studies resulted in several promising agonists with potencies ranging from the low micromolar to nanomolar range, for example, 23 (EC50 = 111 nM, Emax = 95%) and 27 (EC50 = 69 nM, Emax = 82%) in the β-arrestin-recruitment assay. These compounds are selective for ACKR3 versus ACKR2, CXCR3, and CXCR4. Several agonists were subjected to investigations of their P-selectin expression reduction in the flow cytometry experiments. In particular, compounds 23 and 27 showed the highest potency for platelet aggregation inhibition, up to 80% and 97%, respectively. The most promising compounds, especially 27, exhibited good solubility, metabolic stability, and no cytotoxicity, suggesting a potential tool compound for the treatment of platelet-mediated thrombosis.

Molecular mechanism of distinct chemokine engagement and functional divergence of the human Duffy antigen receptor

The Duffy antigen receptor is a seven-transmembrane (7TM) protein expressed primarily at the surface of red blood cells and displays strikingly promiscuous binding to multiple inflammatory and homeostatic chemokines. It serves as the basis of the Duffy blood group system in humans and also acts as the primary attachment site for malarial parasite Plasmodium vivax and pore-forming toxins secreted by Staphylococcus aureus. Here, we comprehensively profile transducer coupling of this receptor, discover potential non-canonical signaling pathways, and determine the cryoelectron microscopy (cryo-EM) structure in complex with the chemokine CCL7. The structure reveals a distinct binding mode of chemokines, as reflected by relatively superficial binding and a partially formed orthosteric binding pocket. We also observe a dramatic shortening of TM5 and 6 on the intracellular side, which precludes the formation of the docking site for canonical signal transducers, thereby providing a possible explanation for the distinct pharmacological and functional phenotype of this receptor.

Chemokine expression profile of an innate granuloma

Granulomas are defined by the presence of organized layers of immune cells that include macrophages. Granulomas are often characterized as a way for the immune system to contain an infection and prevent its dissemination. We recently established a mouse infection model where Chromobacterium violaceum induces the innate immune system to form granulomas in the liver. This response successfully eradicates the bacteria and returns the liver to homeostasis. Here, we sought to characterize the chemokines involved in directing immune cells to form the distinct layers of a granuloma. We use spatial transcriptomics to investigate the spatial and temporal expression of all CC and CXC chemokines and their receptors within this granuloma response. The expression profiles change dynamically over space and time as the granuloma matures and then resolves. To investigate the importance of monocyte-derived macrophages in this immune response, we studied the role of CCR2 during C. violaceum infection. Ccr2 -/- mice had negligible numbers of macrophages, but large numbers of neutrophils, in the C. violaceum-infected lesions. In addition, lesions had abnormal architecture resulting in loss of bacterial containment. Without CCR2, bacteria disseminated and the mice succumbed to the infection. This indicates that macrophages are critical to form a successful innate granuloma in response to C. violaceum.

Chemokine CCL19 and Its Receptors CCR7 and CCRL1 in Chronic Rhinosinusitis

Background

CCL19 has been shown to predict disease severity in COVID-19 and treatment response in rheumatoid arthritis. CCL19 can exert both pro- and anti-inflammatory effects and is elevated in chronic rhinosinusitis (CRS). However, its role in CRS remains unknown. This study sought to determine the transcriptional changes in CCL19, its receptors, and associated cytokines and their association with disease severity in CRS.

Methods

A clinical database of control subjects and patients with CRS was examined. Lund-Kennedy, Lund-Mackay, Sinonasal Outcomes Test 22 (SNOT-22), and rhinosinusitis disability index (RSDI) scores were collected at enrollment. mRNA was extracted from sinonasal tissues and subjected to multiplex gene expression analysis. Gene transcript differences between patients with CRS and controls were compared and correlated with disease severity metrics. Immunohistochemical analyses of CCL19, CCR7, and CCRL1 were conducted to compare differences in protein expression between cohorts. A subgroup analysis was performed to compare transcriptional and protein expression difference between patients with (CRSwNP) and without (CRSsNP) nasal polyps and controls.

Results

Thirty-eight subjects (control group, n=7; CRS group, n=31) were included in this study. CCRL1 (p=0.0093) and CCR7 (p=0.017) levels were significantly elevated in CRS compared to those in controls. CCL19 (p=0.038) and CCR7 (p=0.0097) levels were elevated in CRSwNP and CCRL1 was elevated in CRSsNP (p=0.0004). CCR7 expression was significantly elevated in sinonasal epithelial cells in CRSwNP (p=0.04). CCL19 expression was positively correlated with TNFA expression (p<0.0002). CCL19 and CCR7 expression was positively correlated with SNOT-22 and RSDI scores (p<0.05).

Conclusion

CCL19 and CCR7 may modulate TNF-α-driven pro-inflammatory signaling and contribute to increased disease severity in CRS. Mechanistic studies are required to further elucidate the role of CCRL1 in CRS.

Atypical chemokine receptor 4 (ACKR4/CCX-CKR): A comprehensive exploration across physiological and pathological landscapes in contemporary research

Atypical chemokine receptor 4 (ACKR4), also known as CCX-CKR, is a member of the chemokine receptor family that lacks typical G protein signaling activity. Instead, ACKR4 functions as a scavenger receptor that can bind and internalize a wide range of chemokines, influencing their availability and activity in the body. ACKR4 is involved in various physiological processes, such as immune cell trafficking and the development of thymus, spleen, and lymph nodes. Moreover, ACKR4 has been implicated in several pathological conditions, including cancer, heart and lung diseases. In cancer, ACKR4 plays a complex role, acting as a tumor suppressor or promoter depending on the type of cancer and the stage of the disease. For instance, ACKR4 may inhibit the growth and metastasis of breast cancer, but it may also promote the progression of hepatocellular carcinoma and gastric cancer. In inflammatory situations, ACKR4 has been found to modulate the recruitment and activation of immune cells, contributing to the pathogenesis of diseases such as myocardial infraction and pulmonary sarcoidosis. The study of ACKR4 is still ongoing, and further research is needed to fully understand its role in different physiological and pathological contexts. Nonetheless, ACKR4 represents a promising target for the development of novel therapeutic strategies for various diseases.

Atypical chemokine receptors in cancer

Atypical chemokine receptors (ACKRs) are a group of seven-transmembrane spanning serpentine receptors that are structurally homologous to classical G-protein-coupled receptors and bind cognate chemokines with high affinities but do not signal via G-proteins or mediate cell migration. However, ACKRs efficiently modify the availability and function of chemokines in defined microanatomical environments, can signal via intracellular effectors other than G-proteins, and play complex roles in physiology and disease, including in cancer. In this review, we summarize the findings on the diverse contributions of individual ACKRs to cancer development, progression, and tumor-host interactions. We discuss how changes in ACKR expression within tumor affect cancer growth, tumor vascularization, leukocyte infiltration, and metastasis formation, ultimately resulting in differential disease outcomes. Across many studies, ACKR3 expression was shown to support tumor growth and dissemination, whereas ACKR1, ACKR2, and ACKR4 in tumors were more likely to contribute to tumor suppression. With few notable exceptions, the insights on molecular and cellular mechanisms of ACKRs activities in cancer remain sparse, and the intricacies of their involvement are not fully appreciated. This is particularly true for ACKR1, ACKR2 and ACKR4. A better understanding of how ACKR expression and functions impact cancer should pave the way for their future targeting by new and effective therapies.

Pharmacological Characterization and Radiolabeling of VUF15485, a High-Affinity Small-Molecule Agonist for the Atypical Chemokine Receptor ACKR3

Atypical chemokine receptor 3 (ACKR3), formerly referred to as CXCR7, is considered to be an interesting drug target. In this study, we report on the synthesis, pharmacological characterization and radiolabeling of VUF15485, a new ACKR3 small-molecule agonist, that will serve as an important new tool to study this β-arrestin-biased chemokine receptor. VUF15485 binds with nanomolar affinity (pIC50 = 8.3) to human ACKR3, as measured in [125I]CXCL12 competition binding experiments. Moreover, in a bioluminescence resonance energy transfer-based β-arrestin2 recruitment assay VUF15485 acts as a potent ACKR3 agonist (pEC50 = 7.6) and shows a similar extent of receptor activation compared with CXCL12 when using a newly developed, fluorescence resonance energy transfer-based ACKR3 conformational sensor. Moreover, the ACKR3 agonist VUF15485, tested against a (atypical) chemokine receptor panel (agonist and antagonist mode), proves to be selective for ACKR3. VUF15485 labeled with tritium at one of its methoxy groups ([3H]VUF15485), binds ACKR3 saturably and with high affinity (K d = 8.2 nM). Additionally, [3H]VUF15485 shows rapid binding kinetics and consequently a short residence time (<2 minutes) for binding to ACKR3. The selectivity of [3H]VUF15485 for ACKR3, was confirmed by binding studies, whereupon CXCR3, CXCR4, and ACKR3 small-molecule ligands were competed for binding against the radiolabeled agonist. Interestingly, the chemokine ligands CXCL11 and CXCL12 are not able to displace the binding of [3H]VUF15485 to ACKR3. The radiolabeled VUF15485 was subsequently used to evaluate its binding pocket. Site-directed mutagenesis and docking studies using a recently solved cryo-EM structure propose that VUF15485 binds in the major and the minor binding pocket of ACKR3. SIGNIFICANCE STATEMENT: The atypical chemokine receptor atypical chemokine receptor 3 (ACKR3) is considered an interesting drug target in relation to cancer and multiple sclerosis. The study reports on new chemical biology tools for ACKR3, i.e., a new agonist that can also be radiolabeled and a new ACKR3 conformational sensor, that both can be used to directly study the interaction of ACKR3 ligands with the G protein-coupled receptor.

Molecular insights into atypical modes of β-arrestin interaction with seven transmembrane receptors

β-arrestins (βarrs) are multifunctional proteins involved in signaling and regulation of seven transmembrane receptors (7TMRs), and their interaction is driven primarily by agonist-induced receptor activation and phosphorylation. Here, we present seven cryo-electron microscopy structures of βarrs either in the basal state, activated by the muscarinic receptor subtype 2 (M2R) through its third intracellular loop, or activated by the βarr-biased decoy D6 receptor (D6R). Combined with biochemical, cellular, and biophysical experiments, these structural snapshots allow the visualization of atypical engagement of βarrs with 7TMRs and also reveal a structural transition in the carboxyl terminus of βarr2 from a β strand to an α helix upon activation by D6R. Our study provides previously unanticipated molecular insights into the structural and functional diversity encoded in 7TMR-βarr complexes with direct implications for exploring novel therapeutic avenues.

Chemokines: A key driver for inflammation in protozoan infection

Chemokines belong to the group of small proteins within the cytokine family having strong chemo-attractant properties. In most cases, the strong immuno-modulatory role of chemokines is crucial for generating the immune response against pathogens in various protozoan diseases. In this review, we have given a brief update on the classification, characterization, homeostasis, transcellular migration, and immuno-modulatory role of chemokines. Here we will evaluate the potential role of chemokines and their regulation in various protozoan diseases. There is a significant direct relationship between parasitic infection and the recruitment of effector cells of the immune response. Chemokines play an indispensable role in mediating several defense mechanisms against infection, such as leukocyte recruitment and the generation of innate and cell-mediated immunity that aids in controlling/eliminating the pathogen. This process is controlled by the chemotactic movement of chemokines induced as a primary host immune response. We have also addressed that chemokine expressions during infection are time-dependent and orchestrated in a systematic pattern that ultimately assists in generating a protective immune response. Taken together, this review provides a systematic understanding of the complexity of chemokines profiles during protozoan disease conditions and the rationale of targeting chemokines for the development of therapeutic strategies.

The Role of Atypical Chemokine Receptors in Neuroinflammation and Neurodegenerative Disorders

Neuroinflammation is associated with several neurodegenerative disorders, including Alzheimer's disease (AD), Parkinson's disease (PD), and multiple sclerosis (MS). Neuroinflammation provides protection in acute situations but results in significant damage to the nervous system if chronic. Overexpression of chemokines within the brain results in the recruitment and activation of glial and peripheral immune cells which can propagate a cascading inflammatory response, resulting in neurodegeneration and the onset of neurodegenerative disorders. Recent work has identified the role of atypical chemokine receptors (ACKRs) in neurodegenerative conditions. ACKRs are seven-transmembrane domain receptors that do not follow canonical G protein signaling, but regulate inflammatory responses by modulating chemokine abundance, location, and availability. This review summarizes what is known about the four ACKRs and three putative ACKRs within the brain, highlighting their known expression and discussing the current understanding of each ACKR in the context of neurodegeneration. The ability of ACKRs to alter levels of chemokines makes them an appealing therapeutic target for neurodegenerative conditions. However, further work is necessary to understand the expression of several ACKRs within the neuroimmune system and the effectiveness of targeted drug therapies in the prevention and treatment of neurodegenerative conditions.

Unravelling the Influence of Host Genetic Factors on Malaria Susceptibility in Asian Populations

Malaria is a deadly blood-borne disease caused by a Plasmodium parasite. Infection results in various forms of malaria, including an asymptomatic state, uncomplicated disease, or severe disease. Severe malaria (SM) is particularly prevalent among young children and is a significant cause of mortality. SM is associated with the sequestration of parasitized erythrocytes in the microvasculature of vital host organs, disrupting the normal functioning of the immune system. Although the exact mechanisms of malaria pathogenesis are yet to be fully understood, researchers have been investigating the role of host genetics in determining the severity of the disease and the outcome of infection. The objective of this study is to identify specific host genes that have been examined for their association with malaria in Asian populations and pinpoint those most likely to influence susceptibility. Through an extensive screening process, a total of 982 articles were initially identified, and after careful review, 40 articles discussing 68 genes were included in this review. By constructing a network of protein-protein interactions (PPIs), we identified six key proteins (TNF, IL6, TLR4, IL1β, IL10, and IL8) that exhibited substantial interactions (more than 30 edges), suggesting their potential as significant targets for influencing malaria susceptibility. Notably, these six proteins have been previously identified as crucial components of the immune response, associated with malaria susceptibility, and capable of affecting different clinical forms of the disease. Identifying genes that contribute to malaria susceptibility or resistance holds the promise of enhancing the diagnosis and treatment of this debilitating illness. Such knowledge has the potential to pave the way for more targeted and effective strategies in combating malaria, particularly in Asian populations where controlling Plasmodium vivax is challenging, and India contributes the highest number of cases. By understanding the genetic factors underlying malaria vulnerability, we can develop interventions that are tailored to the specific needs of Asian populations, ultimately leading to better outcomes in the fight against this disease.

Structural Space of the Duffy Antigen/Receptor for Chemokines' Intrinsically Disordered Ectodomain 1 Explored by Temperature Replica-Exchange Molecular Dynamics Simulations

Plasmodium vivax malaria affects 14 million people each year. Its invasion requires interactions between the parasitic Duffy-binding protein (PvDBP) and the N-terminal extracellular domain (ECD1) of the host's Duffy antigen/receptor for chemokines (DARC). ECD1 is highly flexible and intrinsically disordered, therefore it can adopt different conformations. We computationally modeled the challenging ECD1 local structure. With T-REMD simulations, we sampled its dynamic behavior and collected its most representative conformations. Our results suggest that most of the DARC ECD1 domain remains in a disordered state during the simulated time. Globular local conformations are found in the analyzed local free-energy minima. These globular conformations share an α-helix spanning residues Ser18 to Ser29 and in many cases they comprise an antiparallel β-sheet, whose β-strands are formed around residues Leu10 and Ala49. The formation of a parallel β-sheet is almost negligible. So far, progress in understanding the mechanisms forming the basis of the P. vivax malaria infection of reticulocytes has been hampered by experimental difficulties, along with a lack of DARC structural information. Our collection of the most probable ECD1 structural conformations will help to advance modeling of the DARC structure and to explore DARC-ECD1 interactions with a range of physiological and pathological ligands.

Molecular insights into intrinsic transducer-coupling bias in the CXCR4-CXCR7 system

Chemokine receptors constitute an important subfamily of G protein-coupled receptors (GPCRs), and they are critically involved in a broad range of immune response mechanisms. Ligand promiscuity among these receptors makes them an interesting target to explore multiple aspects of biased agonism. Here, we comprehensively characterize two chemokine receptors namely, CXCR4 and CXCR7, in terms of their transducer-coupling and downstream signaling upon their stimulation by a common chemokine agonist, CXCL12, and a small molecule agonist, VUF11207. We observe that CXCR7 lacks G-protein-coupling while maintaining robust βarr recruitment with a major contribution of GRK5/6. On the other hand, CXCR4 displays robust G-protein activation as expected but exhibits significantly reduced βarr-coupling compared to CXCR7. These two receptors induce distinct βarr conformations even when activated by the same agonist, and CXCR7, unlike CXCR4, fails to activate ERK1/2 MAP kinase. We also identify a key contribution of a single phosphorylation site in CXCR7 for βarr recruitment and endosomal localization. Our study provides molecular insights into intrinsic-bias encoded in the CXCR4-CXCR7 system with broad implications for drug discovery.

GPR182 is a broadly scavenging atypical chemokine receptor influencing T-independent immunity

Immune responses highly depend on the effective trafficking of immune cells into and within secondary lymphoid organs (SLOs). Atypical chemokine receptors (ACKRs) scavenge chemokines to eliminate them from the extracellular space, thereby generating gradients that guide leukocytes. In contrast to canonical chemokine receptors, ACKRs do not induce classical intracellular signaling that results in cell migration. Recently, the closest relative of ACKR3, GPR182, has been partially deorphanized as a potential novel ACKR. We confirm and extend previous studies by identifying further ligands that classify GPR182 as a broadly scavenging chemokine receptor. We validate the "atypical" nature of the receptor, wherein canonical G-protein-dependent intracellular signaling is not activated following ligand stimulation. However, β-arrestins are required for ligand-independent internalization and chemokine scavenging whereas the C-terminus is in part dispensable. In the absence of GPR182 in vivo, we observed elevated chemokine levels in the serum but also in SLO interstitium. We also reveal that CXCL13 and CCL28, which do not bind any other ACKR, are bound and efficiently scavenged by GPR182. Moreover, we found a cooperative relationship between GPR182 and ACKR3 in regulating serum CXCL12 levels, and between GPR182 and ACKR4 in controlling CCL20 levels. Furthermore, we unveil a new phenotype in GPR182-KO mice, in which we observed a reduced marginal zone (MZ), both in size and in cellularity, and thus in the T-independent antibody response. Taken together, we and others have unveiled a novel, broadly scavenging chemokine receptor, which we propose should be named ACKR5.

Chemokine-targeted nanoparticles: stimulation of the immune system in cancer immunotherapy

Surgery, chemotherapy, radiation therapy, and immunotherapy are potential therapeutic choices for many malignant and metastatic cancers. Despite adverse side effects and pain, surgery and chemotherapy continue to be the most common cancer treatments. However, patients treated with immunotherapy had better cancer control than those who got other treatments. There are two methods to activate immunological pathways: systemically and locally. To modify the tumor microenvironment (TME), the former uses systemic cytokine/chemokine (CK) delivery, whilst the latter uses immunological checkpoints or small molecule inhibitors. Organic and inorganic nanomaterials (NMs) enhanced the efficacy of cancer immunotherapy. NMs can transmit drugs, peptides, antigens, antibodies, whole cell membranes, etc. Surface-modified NMs precisely target and enter the tissues. The inner core of surface-modified NMs is composed of chemicals with limited bioavailability and biocompatibility, resulting in prolonged blood retention and decreased renal clearance. These platforms hinder or prevent many immune cell activities and modify the TME, enhancing the efficiency of cancer immunotherapy. By inhibiting CK/CK receptor signaling, cell migration and other immune responses could be controlled. Developing CK-targeted nanoparticles (NPs) that inhibit CK signaling or take advantage of the ligand-receptor connection is possible. Surface chemical modification of NMs with CKs or specific peptides has several medicinal applications, including tissue-specific drug delivery and limited cell migration in cancer-afflicted conditions. This review covers current developments in the role of different groups of CK-loaded NP in tumor therapy targeting immune cells and cancer. It also covers the role of NP targeting CK signaling which aids in immunogenic cell death (ICD) and induction of antitumor immunity. In addition, CK gene silencing and its capacity to prevent cancer metastasis as well as inhibition of immune cell migration to modulate the TME are discussed.

ACKR4a induces autophagy to block NF-κB signaling and apoptosis to facilitate Vibrio harveyi infection

Autophagy and apoptosis are two recognized mechanisms of resistance to bacterial invasion. However, bacteria have likewise evolved the ability to evade immunity. In this study, we identify ACKR4a, a member of an atypical chemokine receptor family, as a suppressor of the NF-κB pathway, which cooperates with Beclin-1 to induce autophagy to inhibit NF-κB signaling and block apoptosis, facilitating Vibrio harveyi infection. Mechanistically, V. harveyi-induced Ap-1 activates ACKR4a transcription and expression. ACKR4a forms a complex with Beclin-1 and MyD88, respectively, inducing autophagy and transporting MyD88 into the lysosome for degradation to suppress inflammatory cytokine production. Meanwhile, ACKR4a-induced autophagy blocks apoptosis by inhibiting caspase8. This study proves for the first time that V. harveyi uses both autophagy and apoptosis to evade innate immunity, suggesting that V. harveyi has evolved the ability to against fish immunity.

The dual-function chemokine receptor CCR2 drives migration and chemokine scavenging through distinct mechanisms

C-C chemokine receptor 2 (CCR2) is a dual-function receptor. Similar to other G protein-coupled chemokine receptors, it promotes monocyte infiltration into tissues in response to the chemokine CCL2, and, like atypical chemokine receptors (ACKRs), it scavenges chemokine from the extracellular environment. CCR2 therefore mediates CCL2-dependent signaling as a G protein-coupled receptor (GPCR) and also limits CCL2 signaling as a scavenger receptor. We investigated the mechanisms underlying CCR2 scavenging, including the involvement of intracellular proteins typically associated with GPCR signaling and internalization. Using CRISPR knockout cell lines, we showed that CCR2 scavenged by constitutively internalizing to remove CCL2 from the extracellular space and recycling back to the cell surface for further rounds of ligand sequestration. This process occurred independently of G proteins, GPCR kinases (GRKs), β-arrestins, and clathrin, which is distinct from other "professional" chemokine scavenger receptors that couple to GRKs, β-arrestins, or both. These findings set the stage for understanding the molecular regulators that determine CCR2 scavenging and may have implications for drug development targeting this therapeutically important receptor.

Physiology of chemokines in the cancer microenvironment

Chemokines are chemotactic cytokines whose canonical functions govern movement of receptor-expressing cells along chemical gradients. Chemokines are a physiological system that is finely tuned by ligand and receptor expression, ligand or receptor oligomerization, redundancy, expression of atypical receptors, and non-GPCR binding partners that cumulatively influence discrete pharmacological signaling responses and cellular functions. In cancer, chemokines play paradoxical roles in both the directed emigration of metastatic, receptor-expressing cancer cells out of the tumor as well as immigration of tumor-infiltrating immune cells that culminate in a tumor-unique immune microenvironment. In the age of precision oncology, strategies to effectively harness the power of immunotherapy requires consideration of chemokine gradients within the unique spatial topography and temporal influences with heterogeneous tumors. In this article, we review current literature on the diversity of chemokine ligands and their cellular receptors that detect and process chemotactic gradients and illustrate how differences between ligand recognition and receptor activation influence the signaling machinery that drives cellular movement into and out of the tumor microenvironment. Facets of chemokine physiology across discrete cancer immune phenotypes are contrasted to existing chemokine-centered therapies in cancer.

Evaluation of Atypical Chemokine Receptor Expression in T Cell Subsets

Chemokines are molecules that pertain to a family of small cytokines and can generate cell chemotaxis through the interaction with their receptors. Chemokines can trigger signaling via conventional G-protein-coupled receptors or through atypical chemokine receptors. Currently, four atypical chemokine receptors have been are described (ACKR1, ACKR2, ACKR3 and ACKR4). ACKRs are expressed in various cells and tissues, including T lymphocytes. These receptors' main function is related to the internalization and degradation of chemokines, as well as to the inflammation control. However, the expression of these receptors in human T lymphocytes is unclear in the literature. The objective of this study was to evaluate the expression of ACKRs in different subpopulations of T lymphocytes. For this, peripheral blood from healthy donors was used to analyze the expression of ACKR2, ACKR3 and ACKR4 by immunophenotyping CD4, CD8 T lymphocytes and, in their subsets, naive, transition and memory. Results obtained in this study demonstrated that ACKR2, ACKR3 and ACKR4 receptors were expressed by T lymphocytes subsets in different proportions. These receptors are highly expressed in the cytoplasmic milieu of all subsets of T lymphocytes, therefore suggesting that their expression in plasma membrane is regulated after transcription, and it must be dependent on a stimulus, which was not identified in our study. Thus, regarding ACKRs function as scavenger receptors, at least for the ACKR3, this function does not impair the chemotaxis exert for their ligand compared to the typical counterpart receptor.

G-Protein-Coupled Receptors in Rheumatoid Arthritis: Recent Insights into Mechanisms and Functional Roles

Rheumatoid arthritis (RA) is a chronic inflammatory disease that leads to joint damage and even disability. Although there are various clinical therapies for RA, some patients still have poor or no response. Thus, the development of new drug targets remains a high priority. In this review, we discuss the role of G-protein-coupled receptors (GPCRs), including chemokine receptors, melanocortin receptors, lipid metabolism-related receptors, adenosine receptors, and other inflammation-related receptors, on mechanisms of RA, such as inflammation, lipid metabolism, angiogenesis, and bone destruction. Additionally, we summarize the latest clinical trials on GPCR targeting to provide a theoretical basis and guidance for the development of innovative GPCR-based clinical drugs for RA.

The Extended N-Terminal Domain Confers Atypical Chemokine Receptor Properties to CXCR3-B

The chemokine receptor CXCR3 plays a critical role in immune cell recruitment and activation. CXCR3 exists as two main isoforms, CXCR3-A and CXCR3-B, resulting from alternative splicing. Although the two isoforms differ only by the presence of an N-terminal extension in CXCR3-B, they have been attributed divergent functional effects on cell migration and proliferation. CXCR3-B is the more enigmatic isoform and the mechanisms underlying its function and signaling remain elusive. We therefore undertook an in-depth cellular and molecular comparative study of CXCR3-A and CXCR3-B, investigating their activation at different levels of the signaling cascades, including G protein coupling, β-arrestin recruitment and modulation of secondary messengers as well as their downstream gene response elements. We also compared the subcellular localization of the two isoforms and their trafficking under resting and stimulated conditions along with their ability to internalize CXCR3-related chemokines. Here, we show that the N-terminal extension of CXCR3-B drastically affects receptor features, modifying its cellular localization and preventing G protein coupling, while preserving β-arrestin recruitment and chemokine uptake capacities. Moreover, we demonstrate that gradual truncation of the N terminus leads to progressive recovery of surface expression and G protein coupling. Our study clarifies the molecular basis underlying the divergent effects of CXCR3 isoforms, and emphasizes the β-arrestin-bias and the atypical nature of CXCR3-B.

Double life: How GRK2 and β-arrestin signaling participate in diseases

G-protein coupled receptor (GPCR) kinases (GRKs) and β-arrestins play key roles in GPCR and non-GPCR cellular responses. In fact, GRKs and arrestins are involved in a plethora of pathways vital for physiological maintenance of inter- and intracellular communication. Here we review decades of research literature spanning from the discovery, identification of key structural elements, and findings supporting the diverse roles of these proteins in GPCR-mediated pathways. We then describe how GRK2 and β-arrestins partake in non-GPCR signaling and briefly summarize their involvement in various pathologies. We conclude by presenting gaps in knowledge and our prospective on the promising pharmacological potential in targeting these proteins and/or downstream signaling. Future research is warranted and paramount for untangling these novel and promising roles for GRK2 and arrestins in metabolism and disease progression.

ACKR3 regulates platelet activation and ischemia-reperfusion tissue injury

Platelet activation plays a critical role in thrombosis. Inhibition of platelet activation is a cornerstone in treatment of acute organ ischemia. Platelet ACKR3 surface expression is independently associated with all-cause mortality in CAD patients. In a novel genetic mouse strain, we show that megakaryocyte/platelet-specific deletion of ACKR3 results in enhanced platelet activation and thrombosis in vitro and in vivo. Further, we performed ischemia/reperfusion experiments (transient LAD-ligation and tMCAO) in mice to assess the impact of genetic ACKR3 deficiency in platelets on tissue injury in ischemic myocardium and brain. Loss of platelet ACKR3 enhances tissue injury in ischemic myocardium and brain and aggravates tissue inflammation. Activation of platelet-ACKR3 via specific ACKR3 agonists inhibits platelet activation and thrombus formation and attenuates tissue injury in ischemic myocardium and brain. Here we demonstrate that ACKR3 is a critical regulator of platelet activation, thrombus formation and organ injury following ischemia/reperfusion.

ACKR3 is a critical regulator of platelet-mediated thrombosis and organ injury following ischemia/reperfusion. Platelet ACKR3 surface expression is independently associated with all-cause mortality in patients with cardiovascular diseases.

Mechanosensitive ACKR4 scavenges CCR7 chemokines to facilitate T cell de-adhesion and passive transport by flow in inflamed afferent lymphatics

T cell migration via afferent lymphatics to draining lymph nodes (dLNs) depends on expression of CCR7 in T cells and CCL21 in the lymphatic vasculature. Once T cells have entered lymphatic capillaries, they slowly migrate into contracting collecting vessels. Here, lymph flow picks up, inducing T cell detachment and rapid transport to the dLNs. We find that the atypical chemokine receptor 4 (ACKR4), which binds and internalizes CCL19 and CCL21, is induced by lymph flow in endothelial cells lining lymphatic collectors, enabling them to scavenge these chemokines. In the absence of ACKR4, migration of T cells to dLNs in TPA-induced inflammation is significantly reduced. While entry into capillaries is not impaired, T cells accumulate in the ACKR4-deficient dermal collecting vessel segments. Overall, our findings identify an ACKR4-mediated mechanism by which lymphatic collectors facilitate the detachment of lymph-borne T cells in inflammation and their transition from crawling to free-flow toward the dLNs.

ACKR1 favors transcellular over paracellular T-cell diapedesis across the blood-brain barrier in neuroinflammation in vitro

The migration of CD4+ effector/memory T cells across the blood-brain barrier (BBB) is a critical step in MS or its animal model, EAE. T-cell diapedesis across the BBB can occur paracellular, via the complex BBB tight junctions or transcellular via a pore through the brain endothelial cell body. Making use of primary mouse brain microvascular endothelial cells (pMBMECs) as in vitro model of the BBB, we here directly compared the transcriptome profile of pMBMECs favoring transcellular or paracellular T-cell diapedesis by RNA sequencing (RNA-seq). We identified the atypical chemokine receptor 1 (Ackr1) as one of the main candidate genes upregulated in pMBMECs favoring transcellular T-cell diapedesis. We confirmed upregulation of ACKR1 protein in pMBMECs promoting transcellular T-cell diapedesis and in venular endothelial cells in the CNS during EAE. Lack of endothelial ACKR1 reduced transcellular T-cell diapedesis across pMBMECs under physiological flow in vitro. Combining our previous observation that endothelial ACKR1 contributes to EAE pathogenesis by shuttling chemokines across the BBB, the present data support that ACKR1 mediated chemokine shuttling enhances transcellular T-cell diapedesis across the BBB during autoimmune neuroinflammation.

Emerging Roles of the Atypical Chemokine Receptor 3 (ACKR3) in Cardiovascular Diseases

Chemokines, and their receptors play a crucial role in the pathophysiology of cardiovascular diseases (CVD). Chemokines classically mediate their effects by binding to G-protein-coupled receptors. The discovery that chemokines can also bind to atypical chemokine receptors (ACKRs) and initiate alternative signaling pathways has changed the paradigm regarding chemokine-related functions. Among these ACKRs, several studies have highlighted the exclusive role of ACKR3, previously known as C-X-C chemokine receptor type 7 (CXCR7), in CVD. Indeed, ACKR3 exert atheroprotective, cardioprotective and anti-thrombotic effects through a wide range of cells including endothelial cells, platelets, inflammatory cells, fibroblasts, vascular smooth muscle cells and cardiomyocytes. ACKR3 functions as a scavenger receptor notably for the pleiotropic chemokine CXCL12, but also as a activator of different pathways such as β-arrestin-mediated signaling or modulator of CXCR4 signaling through the formation of ACKR3-CXCR4 heterodimers. Hence, a better understanding of the precise roles of ACKR3 may pave the way towards the development of novel and improved therapeutic strategies for CVD. Here, we summarize the structural determinant characteristic of ACKR3, the molecules targeting this receptor and signaling pathways modulated by ACKR3. Finally, we present and discuss recent findings regarding the role of ACKR3 in CVD.

Involvement of various chemokine/chemokine receptor axes in trafficking and oriented locomotion of mesenchymal stem cells in multiple sclerosis patients

Multiple sclerosis (MS) is a specific type of chronic immune-mediated disease in which the immune responses are almost run against the central nervous system (CNS). Despite intensive research, a known treatment for MS disease yet to be introduced. Thus, the development of novel and safe medications needs to be considered for the disease management. Application of mesenchymal stem cells (MSCs) as an emerging approach was recruited forthe treatment of MS. MSCs have several sources and they can be derived from the umbilical cord, adipose tissue, and bone marrow. Chemokines are low molecular weight proteins that their functional activities are achieved by binding to the cell surface G protein-coupled receptors (GPCRs). Chemokine and chemokine receptors are of the most important and effective molecules in MSC trafficking within the different tissues in hemostatic and non-hemostatic circumstances. Chemokine/chemokine receptor axes play a pivotal role in the recruitment and oriented trafficking of immune cells both towards and within the CNS and it appears that chemokine/chemokine receptor signaling may be the most important leading mechanisms in the pathogenesis of MS. In this article, we hypothesized that the chemokine/chemokine receptor axes network have crucial and efficacious impacts on behavior of the MSCs, nonetheless, the exact responsibility of these axes on the targeted tropism of MSCs to the CNS of MS patients yet remained to be fully elucidated. Therefore, we reviewed the ability of MSCs to migrate and home into the CNS of MS patients via expression of various chemokine receptors in response to chemokines expressed by cells of CNS tissue, to provide a great source of knowledge.

The dimeric form of CXCL12 binds to atypical chemokine receptor 1

The pleiotropic chemokine CXCL12 is involved in diverse physiological and pathophysiological processes, including embryogenesis, hematopoiesis, leukocyte migration, and tumor metastasis. It is known to engage the classical receptor CXCR4 and the atypical receptor ACKR3. Differential receptor engagement can transduce distinct cellular signals and effects as well as alter the amount of free, extracellular chemokine. CXCR4 binds both monomeric and the more commonly found dimeric forms of CXCL12, whereas ACKR3 binds monomeric forms. Here, we found that CXCL12 also bound to the atypical receptor ACKR1 (previously known as Duffy antigen/receptor for chemokines or DARC). In vitro nuclear magnetic resonance spectroscopy and isothermal titration calorimetry revealed that dimeric CXCL12 bound to the extracellular N terminus of ACKR1 with low nanomolar affinity, whereas the binding affinity of monomeric CXCL12 was orders of magnitude lower. In transfected MDCK cells and primary human Duffy-positive erythrocytes, a dimeric, but not a monomeric, construct of CXCL12 efficiently bound to and internalized with ACKR1. This interaction between CXCL12 and ACKR1 provides another layer of regulation of the multiple biological functions of CXCL12. The findings also raise the possibility that ACKR1 can bind other dimeric chemokines, thus potentially further expanding the role of ACKR1 in chemokine retention and presentation.

G-protein-coupled receptors as therapeutic targets for glioblastoma

Glioblastoma multiforme (GBM) is the most common and aggressive primary brain tumour in adults. Treatments include surgical resection, radiotherapy, and chemotherapy. Despite this, the prognosis remains poor, with an impacted quality of life during treatment coupled with brain tumour recurrence; thus, new treatments are desperately needed. In this review, we focus on recent advances in G-protein-coupled receptor (GPCR) targets. To date, the most promising targets are the chemokine, cannabinoid, and dopamine receptors, but future work should further examine the melanocortin receptor-4 (MC4R), adhesion, lysophosphatidic acid (LPA) and smoothened (Smo) receptors to initiate new drug-screening strategies and targeted delivery of safe and effective GBM therapies.

Expression of ACKR4 demarcates the "peri-marginal sinus," a specialized vascular compartment of the splenic red pulp

The spleen comprises defined microanatomical compartments that uniquely contribute to its diverse host defense functions. Here, we identify a vascular compartment within the red pulp of the spleen delineated by expression of the atypical chemokine receptor 4 (ACKR4) in endothelial cells. ACKR4-positive vessels form a three-dimensional sinusoidal network that connects via shunts to the marginal sinus and tightly surrounds the outer perimeter of the marginal zone. Endothelial cells lining this vascular compartment express ACKR4 as part of a distinct gene expression profile. We show that T cells enter the spleen largely through this peri-marginal sinus and initially localize extravascularly around these vessels. In the absence of ACKR4, homing of T cells into the spleen and subsequent migration into T cell areas is impaired, and organization of the marginal zone is severely affected. Our data delineate the splenic peri-marginal sinus as a compartment that supports spleen homing of T cells.

Differential Involvement of ACKR3 C-Tail in β-Arrestin Recruitment, Trafficking and Internalization

Background: The atypical chemokine receptor 3 (ACKR3) belongs to the superfamily of G protein-coupled receptors (GPCRs). Unlike classical GPCRs, this receptor does not activate G proteins in most cell types but recruits β-arrestins upon activation. ACKR3 plays an important role in cancer and vascular diseases. As recruitment of β-arrestins is triggered by phosphorylation of the C-terminal tail of GPCRs, we studied the role of different potential phosphorylation sites within the ACKR3 C-tail to further delineate the molecular mechanism of internalization and trafficking of this GPCR. Methods: We used various bioluminescence and fluorescence resonance energy transfer-based sensors and techniques in Human Embryonic Kidney (HEK) 293T cells expressing WT or phosphorylation site mutants of ACKR3 to measure CXCL12-induced recruitment of β-arrestins and G-protein-coupled receptor kinases (GRKs), receptor internalization and trafficking. Results: Upon CXCL12 stimulation, ACKR3 recruits both β-arrestin 1 and 2 with equivalent kinetic profiles. We identified interactions with GRK2, 3 and 5, with GRK2 and 3 being important for β-arrestin recruitment. Upon activation, ACKR3 internalizes and recycles back to the cell membrane. We demonstrate that β-arrestin recruitment to the receptor is mainly determined by a single cluster of phosphorylated residues on the C-tail of ACKR3, and that residue T³⁵² and in part S³⁵⁵ are important residues for β-arrestin1 recruitment. Phosphorylation of the C-tail appears essential for ligand-induced internalization and important for differential β-arrestin recruitment. GRK2 and 3 play a key role in receptor internalization. Moreover, ACKR3 can still internalize when β-arrestin recruitment is impaired or in the absence of β-arrestins, using alternative internalization pathways. Our data indicate that distinct residues within the C-tail of ACKR3 differentially regulate CXCL12-induced β-arrestin recruitment, ACKR3 trafficking and internalization.

C-C Chemokine receptor-like 2 (CCRL2) acts as coreceptor for human immunodeficiency virus-2

INTRODUCTION

Most of the typical chemokine receptors (CKRs) have been identified as coreceptors for a variety of human and simian immunodeficiency viruses (HIVs and SIVs). This study evaluated CCRL2 to examine if it was an HIV/SIV coreceptor.

METHODS

The Human glioma cell line, NP-2, is normally resistant to infection by HIV and SIV. The cell was transduced with amplified cluster of differentiation 4 (CD4) as a receptor and CCR5, CXCR4 and CCRL2 as coreceptor candidates to produce NP-2/CD4/coreceptor cells (). The cells were infected with multiplicity of infection (MOI) 1.0. Infected cells were detected by indirect immunofluorescence assay (IFA). Multinucleated giant cells (MGC) in syncytia were quantified by Giemsa staining. Proviral DNA was detected by polymerase chain reaction (PCR), and reverse transcriptase (RT) activity was measured.

RESULTS

IFA detected viral antigens of the primary isolates, HIV-1HAN2 and HIV-2MIR in infected NP-2/CD4/CCRL2 cells, indicated CCRL2 as a functional coreceptor. IFA results were confirmed by the detection of proviral DNA and measurement of RT-activity in the spent cell supernatants. Additionally, MGC was detected in HIV-2MIR-infected NP-2/CD4/CCCRL2 cells. HIV-2MIR were found more potent users of CCRL2 than HIV-1HAN2. Moreover, GWAS studies, gene ontology and cell signaling pathways of the HIV-associated genes show interaction of CCRL2 with HIV/SIV envelope protein.

CONCLUSIONS

In vitro experiments showed CCRL2 to function as a newly identified coreceptor for primary HIV-2 isolates conveniently. The findings contribute additional insights into HIV/SIV transmission and pathogenesis. However, its in vivo relevance still needs to be evaluated. Confirming in vivo relevance, ligands of CCRL2 can be investigated as potential targets for HIV entry-inhibitor drugs.

CXCR7: a β-arrestin-biased receptor that potentiates cell migration and recruits β-arrestin2 exclusively through Gβγ subunits and GRK2

BACKGROUND

Some chemokine receptors referred to as atypical chemokine receptors (ACKRs) are thought to non-signaling decoys because of their inability to activate typical G-protein signaling pathways. CXCR7, also known as ACKR3, binds to only two chemokines, SDF-1α and I-TAC, and recruits β-arrestins. SDF-1α also binds to its own conventional receptor, CXCR4, involving in homeostatic modulation such as development and immune surveillance as well as pathological conditions such as inflammation, ischemia, and cancers. Recently, CXCR7 is suggested as a key therapeutic target together with CXCR4 in such conditions. However, the molecular mechanisms underlying cellular responses and functional relation with CXCR7 and CXCR4 have not been elucidated, despite massive studies. Therefore, we aimed to reveal the molecular networks of CXCR7 and CXCR4 and compare their effects on cell migration.

METHODS

Base on structural complementation assay using NanoBiT technology, we characterized the distinct mechanisms underlying β-arrestin2 recruitment by both CXCR4 and CXCR7. Crosslinking and immunoprecipitation were conducted to analyze complex formation of the receptors. Gene deletion using CRISPR and reconstitution of the receptors were applied to analysis of ligand-dependent ERK phosphorylation and cell migration. All experiments were performed in triplicate and repeated more than three times. Unpaired Student's t-tests or ANOVA using PRISM5 software were employed for statistical analyses.

RESULTS

Ligand binding to CXCR7 does not result in activation of typical signaling pathways via Gα subunits but activation of GRK2 via βγ subunits and receptor phosphorylation with subsequent β-arrestin2 recruitment. In contrast, CXCR4 induced Gα_i activation and recruited β-arrestin2 through C-terminal phosphorylation by both GRK2 and GRK5. SDF-1α-stimulated ERK phosphorylation was facilitated by CXCR4, but not CXCR7. Heterodimerization of CXCR4 and CXCR7 was not confirmed in this study, while homodimerization of them was verified by crosslinking experiment and NanoBiT assay. Regarding chemotaxis, SDF-1α-stimulated cell migration was mediated by both CXCR4 and CXCR7.

CONCLUSION

This study demonstrates that SDF-1α-stimulated CXCR7 mediates β-arrestin2 recruitment via different molecular networking from that of CXCR4. CXCR7 may be neither a simple scavenger nor auxiliary receptor but plays an essential role in cell migration through cooperation with CXCR4.

The DARC-null trait is associated with moderate modulation of NK cell profiles and unaltered cytolytic T cell profiles in black South Africans

The Duffy Antigen Receptor for Chemokines (DARC)-null trait, common among persons of African descent and associated with lower absolute neutrophil counts (ANCs), may be linked to increased risk to certain infections including HIV-1 but the underlying causes are poorly understood. We hypothesized that DARC-null-linked neutropenia may negatively impact neutrophil immunoregulatory modulation of other immune cells such as natural killer (NK) and CD8+ T cells leading to altered phenotype, functionality and homeostatic activity of these immune cells. HIV-1 uninfected (n = 20) and HIV-1 chronically infected (n = 19) participants were assessed using multi-parametric flow cytometry to determine NK and CD8+ T cell counts, phenotypic profiles, and cytokine production and degranulation. Annexin V and carboxyfluorescein succinimidyl ester (CFSE) staining were used to examine NK cell survival and NK cell and CD8+ T cell proliferation respectively. Participants were genotyped for the DARC-null polymorphism using allelic discrimination assays and ANCs were measured by full blood count. In HIV uninfected individuals, a reduction of total NK cell counts was noted in the absence of DARC and this correlated with lower ANCs. HIV uninfected DARC-null subjects displayed a less mature NK cell phenotype. However, this did not translate to differences in NK cell activation or effector functionality by DARC state. Whilst HIV-1 infected subjects displayed NK cell profiling that is typical of HIV infection, no differences were noted upon DARC stratification. Similarly, CD8+ T cells from HIV infected individuals displayed phenotypic and functional modulation that is characteristic of HIV infection, but profiling was unaffected by the DARC-null variant irrespective of HIV status. Overall, the data suggests that the DARC-null polymorphism and lower ANCs does not impede downstream cytolytic cell priming and functionality.

Control of Cytoskeletal Dynamics by β-Arrestin1/Myosin Vb Signaling Regulates Endosomal Sorting and Scavenging Activity of the Atypical Chemokine Receptor ACKR2

The atypical chemokine receptor ACKR2, formerly named D6, is a scavenger chemokine receptor with a non-redundant role in the control of inflammation and immunity. The scavenging activity of ACKR2 depends on its trafficking properties, which require actin cytoskeleton rearrangements downstream of a β-arrestin1-Rac1-PAK1-LIMK1-cofilin-dependent signaling pathway. We here demonstrate that in basal conditions, ACKR2 trafficking properties require intact actin and microtubules networks. The dynamic turnover of actin filaments is required to sustain ACKR2 constitutive endocytosis, while both actin and microtubule networks are involved in processes regulating ACKR2 constitutive sorting to rapid, Rab4-dependent and slow, Rab11-dependent recycling pathways, respectively. After chemokine engagement, ACKR2 requires myosin Vb activity to promote its trafficking from Rab11-positive recycling endosomes to the plasma membrane, which sustains its scavenging activity. Other than cofilin phosphorylation, induction of the β-arrestin1-dependent signaling pathway by ACKR2 agonists also leads to the rearrangement of microtubules, which is required to support the myosin Vb-dependent ACKR2 upregulation and its scavenging properties. Disruption of the actin-based cytoskeleton by the apoptosis-inducing agent staurosporine results in impaired ACKR2 internalization and chemokine degradation that is consistent with the emerging scavenging-independent activity of the receptor in apoptotic neutrophils instrumental for promoting efficient efferocytosis during the resolution of inflammation. In conclusion, we provide evidence that ACKR2 activates a β-arrestin1-dependent signaling pathway, triggering both the actin and the microtubule cytoskeletal networks, which control its trafficking and scavenger properties.

The Role of Selected Chemokines and Their Receptors in the Development of Gliomas

Among heterogeneous primary tumors of the central nervous system (CNS), gliomas are the most frequent type, with glioblastoma multiforme (GBM) characterized with the worst prognosis. In their development, certain chemokine/receptor axes play important roles and promote proliferation, survival, metastasis, and neoangiogenesis. However, little is known about the significance of atypical receptors for chemokines (ACKRs) in these tumors. The objective of the study was to present the role of chemokines and their conventional and atypical receptors in CNS tumors. Therefore, we performed a thorough search for literature concerning our investigation via the PubMed database. We describe biological functions of chemokines/chemokine receptors from various groups and their significance in carcinogenesis, cancer-related inflammation, neo-angiogenesis, tumor growth, and metastasis. Furthermore, we discuss the role of chemokines in glioma development, with particular regard to their function in the transition from low-grade to high-grade tumors and angiogenic switch. We also depict various chemokine/receptor axes, such as CXCL8-CXCR1/2, CXCL12-CXCR4, CXCL16-CXCR6, CX3CL1-CX3CR1, CCL2-CCR2, and CCL5-CCR5 of special importance in gliomas, as well as atypical chemokine receptors ACKR1-4, CCRL2, and PITPMN3. Additionally, the diagnostic significance and usefulness of the measurement of some chemokines and their receptors in the blood and cerebrospinal fluid (CSF) of glioma patients is also presented.

A Single-Cell Transcriptional Roadmap of the Mouse and Human Lymph Node Lymphatic Vasculature

Single-cell transcriptomics promise to revolutionize our understanding of the vasculature. Emerging computational methods applied to high-dimensional single-cell data allow integration of results between samples and species and illuminate the diversity and underlying developmental and architectural organization of cell populations. Here, we illustrate these methods in the analysis of mouse lymph node (LN) lymphatic endothelial cells (LEC) at single-cell resolution. Clustering identifies five well-delineated subsets, including two medullary sinus subsets not previously recognized as distinct. Nearest neighbor alignments in trajectory space position the major subsets in a sequence that recapitulates the known features and suggests novel features of LN lymphatic organization, providing a transcriptional map of the lymphatic endothelial niches and of the transitions between them. Differences in gene expression reveal specialized programs for (1) subcapsular ceiling endothelial interactions with the capsule connective tissue and cells; (2) subcapsular floor regulation of lymph borne cell entry into the LN parenchyma and antigen presentation; and (3) pathogen interactions and (4) LN remodeling in distinct medullary subsets. LEC of the subcapsular sinus floor and medulla, which represent major sites of cell entry and exit from the LN parenchyma respectively, respond robustly to oxazolone inflammation challenge with enriched signaling pathways that converge on both innate and adaptive immune responses. Integration of mouse and human single-cell profiles reveals a conserved cross-species pattern of lymphatic vascular niches and gene expression, as well as specialized human subsets and genes unique to each species. The examples provided demonstrate the power of single-cell analysis in elucidating endothelial cell heterogeneity, vascular organization, and endothelial cell responses. We discuss the findings from the perspective of LEC functions in relation to niche formations in the unique stromal and highly immunological environment of the LN.

ACKR4 Recruits GRK3 Prior to β-Arrestins but Can Scavenge Chemokines in the Absence of β-Arrestins

Chemokines are essential for guiding cell migration. Atypical chemokine receptors (ACKRs) contribute to the cell migration process by binding, internalizing and degrading local chemokines, which enables the formation of confined gradients. ACKRs are heptahelical membrane spanning molecules structurally related to G-protein coupled receptors (GPCRs), but seem to be unable to signal through G-proteins upon ligand binding. ACKR4 internalizes the chemokines CCL19, CCL21, and CCL25 and is best known for shaping functional CCL21 gradients. Ligand binding to ACKR4 has been shown to recruit β-arrestins that has led to the assumption that chemokine scavenging relies on β-arrestin-mediated ACKR4 trafficking, a common internalization route taken by class A GPCRs. Here, we show that CCL19, CCL21, and CCL25 readily recruited β-arrestin1 and β-arrestin2 to human ACKR4, but found no evidence for β-arrestin-dependent or independent ACKR4-mediated activation of the kinases Erk1/2, Akt, or Src. However, we demonstrate that β-arrestins interacted with ACKR4 in the steady-state and contributed to the spontaneous trafficking of the receptor in the absence of chemokines. Deleting the C-terminus of ACKR4 not only interfered with the interaction of β-arrestins, but also with the uptake of fluorescently labeled cognate chemokines. We identify the GPCR kinase GRK3, and to a lesser extent GRK2, but not GRK4, GRK5, and GRK6, to be recruited to chemokine-stimulated ACKR4. We show that GRK3 recruitment proceded the recruitment of β-arrestins upon ACKR4 engagement and that GRK2/3 inhibition partially interfered with steady-state interaction and chemokine-driven recruitment of β-arrestins to ACKR4. Overexpressing β-arrestin2 accelerated the uptake of fluorescently labeled CCL19, indicating that β-arrestins contribute to the chemokine scavenging activity of ACKR4. By contrast, cells lacking β-arrestins were still capable to take up fluorescently labeled CCL19 demonstrating that β-arrestins are dispensable for chemokine scavenging by ACKR4.

Chemokines and chemokine receptors: A new strategy for breast cancer therapy

Chemokines and chemokine receptors not only participate in the development of tissue differentiation, hematopoiesis, inflammation, and immune regulation but also play an important role in the process of tumor development. The role of chemokines and chemokine receptors in tumors has been emphasized in recent years. More and more studies have shown that chemokines and chemokine receptors are closely related to the occurrence, angiogenesis, metastasis, drug resistance, and immunity of breast cancer. Here, we review recent progression on the roles of chemokines and chemokine receptors in breast cancer, and discuss the possible mechanism in breast cancer that might facilitate the development of new therapies by targeting chemokines as well as chemokine receptors. Chemokines and chemokine receptors play an important role in the occurrence and development of breast cancer. In-depth study of chemokines and chemokine receptors can provide intervention targets for breast cancer biotherapy. The regulation of chemokines and chemokine receptors may become a new strategy for breast cancer therapy.