Identification of an alternative G{alpha}q-dependent chemokine receptor signal transduction pathway in dendritic cells and granulocytes

Exacerbating effects of single-dose acute ethanol exposure on neuroinflammation and amelioration by GPR110 (ADGRF1) activation

BACKGROUND

Neuroinflammation is a widely studied phenomenon underlying various neurodegenerative diseases. Earlier study demonstrated that pharmacological activation of GPR110 in both central and peripheral immune cells cooperatively ameliorates neuroinflammation caused by systemic lipopolysaccharide (LPS) administration. Ethanol consumption has been associated with exacerbation of neurodegenerative and systemic inflammatory conditions. The goal of this study is to determine the effects of single-dose acute ethanol exposure and GPR110 activation on the neuro-inflammation mechanisms.

METHODS

For in vivo studies, GPR110 wild type (WT) and knockout (KO) mice at 10-12 weeks of age were given an oral gavage of ethanol (3 g/kg) or maltose (5.4 g/kg) at 1-4 h prior to the injection of LPS (1 mg/kg, i.p.) followed by the GPR110 ligand, synaptamide (5 mg/kg). After 2-24 h, brains were collected for the analysis of gene expression by RT-PCR or protein expression by western blotting and enzyme-linked immunosorbent assay (ELISA). Microglial activation was assessed by western blotting and immunohistochemistry. For in vitro studies, microglia and peritoneal macrophages were isolated from adult WT mice and treated with 25 mM ethanol for 4 h and then with LPS (100 ng/ml) followed by 10 nM synaptamide for 2 h for gene expression and 12 h for protein analysis.

RESULTS

Single-dose exposure to ethanol by gavage before LPS injection upregulated pro-inflammatory cytokine expression in the brain and plasma. The LPS-induced Iba-1 expression in the brain was significantly higher after ethanol pretreatment in both WT and GPR110KO mice. GPR110 ligand decreased the mRNA and/or protein expression of these cytokines and Iba-1 in the WT but not in GPR110KO mice. In the isolated microglia and peritoneal macrophages, ethanol also exacerbated the LPS-induced expression of pro-inflammatory cytokines which was mitigated at least partially by synaptamide. The expression of an inflammasome marker NLRP3 upregulated by LPS was further elevated with prior exposure to ethanol, especially in the brains of GPR110KO mice. Both ethanol and LPS reduced adenylate cyclase 8 mRNA expression which was reversed by the activation of GPR110. PDE4B expression at both mRNA and protein level in the brain increased after ethanol and LPS treatment while synaptamide suppressed its expression in a GPR110-dependent manner.

CONCLUSION

Single-dose ethanol exposure exacerbated LPS-induced inflammatory responses. The GPR110 ligand synaptamide ameliorated this effect of ethanol by counteracting on the cAMP system, the common target for synaptamide and ethanol, and by regulating NLRP3 inflammasome.

Functional Analysis of CXCR3 Splicing Variants and Their Ligands Using NanoBiT-Based Molecular Interaction Assays

CXCR3 regulates leukocyte trafficking, maturation, and various pathophysiological conditions. Alternative splicing generates three CXCR3 isoforms in humans. Previous studies investigated the roles of CXCR3 isoforms, and some biochemical data are not correlated with biological relevance analyses. RT-PCR analyses indicate that most cells express all three splicing variants, suggesting that they may mutually affect the chemokine binding and cellular responses of other splicing variants. Here, we performed an integrative analysis of the functional relations among CXCR3 splicing variants and their chemokine-dependent signaling using NanoBiT live cell protein interaction assays. The results indicated that the CXCR3 N-terminal region affected cell surface expression levels and ligand-dependent activation. CXCR3A was efficiently expressed in the plasma membrane and responded to I-TAC, IP-10, and MIG chemokines. By contrast, CXCR3B had low plasma membrane expression and mediated I-TAC-stimulated cellular responses. CXCR3Alt was rarely expressed on the cell surface and did not mediate any cell responses to the tested chemokines; however, CXCR3Alt negatively affected the plasma membrane expression of CXCR3A and CXCR3B and their chemokine-stimulated cellular responses. Jurkat cells express endogenous CXCR3, and exogenous CXCR3A expression enhanced chemotactic activity in response to I-TAC, IP-10, and MIG. By contrast, exogenous expression of CXCR3B and CXCR3Alt eliminated or reduced the CXCR3A-induced chemotactic activity. The PF-4 chemokine did not activate any CXCR3-mediated cellular responses. NanoBiT technology are useful to integrative studies of CXCR3-mediated cell signaling, and expand our knowledge of the cellular responses mediated by molecular interactions among the splicing variants, including cell surface expression, ligand-dependent receptor activation, and chemotaxis.

Extracellular vesicles from pristane-treated CD38-deficient mice express an anti-inflammatory neutrophil protein signature, which reflects the mild lupus severity elicited in these mice

In CD38-deficient (Cd38-/-) mice intraperitoneal injection of pristane induces a lupus-like disease, which is milder than that induced in WT mice, showing significant differences in the inflammatory and autoimmune processes triggered by pristane. Extracellular vesicles (EV) are present in all body fluids. Shed by cells, their molecular make-up reflects that of their cell of origin and/or tissue pathological situation. The aim of this study was to analyze the protein composition, protein abundance, and functional clustering of EV released by peritoneal exudate cells (PECs) in the pristane experimental lupus model, to identify predictive or diagnostic biomarkers that might discriminate the autoimmune process in lupus from inflammatory reactions and/or normal physiological processes. In this study, thanks to an extensive proteomic analysis and powerful bioinformatics software, distinct EV subtypes were identified in the peritoneal exudates of pristane-treated mice: 1) small EV enriched in the tetraspanin CD63 and CD9, which are likely of exosomal origin; 2) small EV enriched in CD47 and CD9, which are also enriched in plasma-membrane, membrane-associated proteins, with an ectosomal origin; 3) small EV enriched in keratins, ECM proteins, complement/coagulation proteins, fibrin clot formation proteins, and endopetidase inhibitor proteins. This enrichment may have an inflammation-mediated mesothelial-to-mesenchymal transition origin, representing a protein corona on the surface of peritoneal exudate EV; 4) HDL-enriched lipoprotein particles. Quantitative proteomic analysis allowed us to identify an anti-inflammatory, Annexin A1-enriched pro-resolving, neutrophil protein signature, which was more prominent in EV from pristane-treated Cd38-/- mice, and quantitative differences in the protein cargo of the ECM-enriched EV from Cd38-/- vs WT mice. These differences are likely to be related with the distinct inflammatory outcome shown by Cd38-/- vs WT mice in response to pristane treatment. Our results demonstrate the power of a hypothesis-free and data-driven approach to transform the heterogeneity of the peritoneal exudate EV from pristane-treated mice in valuable information about the relative proportion of different EV in a given sample and to identify potential protein markers specific for the different small EV subtypes, in particular those proteins defining EV involved in the resolution phase of chronic inflammation.

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.

Co-receptor signaling in the pathogenesis of neuroHIV

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

Heterotrimeric G Protein Subunit Gαq Is a Master Switch for Gβγ-Mediated Calcium Mobilization by Gi-Coupled GPCRs

Mechanisms that control mobilization of cytosolic calcium [Ca²⁺]_i are key for regulation of numerous eukaryotic cell functions. One such paradigmatic mechanism involves activation of phospholipase Cβ (PLCβ) enzymes by G protein βγ subunits from activated Gα_i-Gβγ heterotrimers. Here, we report identification of a master switch to enable this control for PLCβ enzymes in living cells. We find that the Gα_i-Gβγ-PLCβ-Ca²⁺ signaling module is entirely dependent on the presence of active Gα_q. If Gα_q is pharmacologically inhibited or genetically ablated, Gβγ can bind to PLCβ but does not elicit Ca²⁺ signals. Removal of an auto-inhibitory linker that occludes the active site of the enzyme is required and sufficient to empower "stand-alone control" of PLCβ by Gβγ. This dependence of Gi-Gβγ-Ca²⁺ on Gα_q places an entire signaling branch of G-protein-coupled receptors (GPCRs) under hierarchical control of Gq and changes our understanding of how Gi-GPCRs trigger [Ca²⁺]_i via PLCβ enzymes.

The Signaling Duo CXCL12 and CXCR4: Chemokine Fuel for Breast Cancer Tumorigenesis

Simple Summary

Breast cancer remains the most common malignancy in women. In this review, we explore the role of the CXCL12/CXCR4 pathway in breast cancer. We show that the CXCL12/CXCR4 cascade is involved in nearly every aspect of breast cancer tumorigenesis including proliferation, cell motility and distant metastasis. Moreover, we summarize current knowledge about the CXCL12/CXCR4-targeted therapies. Due to the critical roles of this pathway in breast cancer and other malignancies, we believe that audiences in different fields will find this overview helpful.

Abstract

The CXCL12/CXCR4 signaling pathway has emerged in the recent years as a key player in breast cancer tumorigenesis. This pathway controls many aspects of breast cancer development including cancer cell proliferation, motility and metastasis to all target organs. Moreover, the CXCL12/CXCR4 cascade affects both immune and stromal cells, creating tumor-supporting microenvironment. In this review, we examine state-of-the-art knowledge about detrimental roles of the CXCL12/CXCR4 signaling, discuss its therapeutic potential and suggest further research directions beneficial both for basic research and personalized medicine in breast cancer.

Kinetic Analysis of the Early Signaling Steps of the Human Chemokine Receptor CXCR4

G protein–coupled receptors (GPCRs) are biologic switches that transduce extracellular stimuli into intracellular responses in the cell. Temporally resolving GPCR transduction pathways is key to understanding how cell signaling occurs. Here, we investigate the kinetics and dynamics of the activation and early signaling steps of the CXC chemokine receptor (CXCR) 4 in response to its natural ligands CXC chemokine ligand (CXCL) 12 and macrophage migration inhibitory factor (MIF), using Förster resonance energy transfer–based approaches. We show that CXCR4 presents a multifaceted response to CXCL12, with receptor activation (≈0.6 seconds) followed by a rearrangement in the receptor/G protein complex (≈1 seconds), a slower dimer rearrangement (≈1.7 seconds), and prolonged G protein activation (≈4 seconds). In comparison, MIF distinctly modulates every step of the transduction pathway, indicating distinct activation mechanisms and reflecting the different pharmacological properties of these two ligands. Our study also indicates that CXCR4 exhibits some degree of ligand-independent activity, a relevant feature for drug development.

An Overview on G Protein-coupled Receptor-induced Signal Transduction in Acute Myeloid Leukemia

BACKGROUND

Acute Myeloid Leukemia (AML) is a genetically heterogeneous disease characterized by uncontrolled proliferation of precursor myeloid-lineage cells in the bone marrow. AML is also characterized by patients with poor long-term survival outcomes due to relapse. Many efforts have been made to understand the biological heterogeneity of AML and the challenges to develop new therapies are therefore enormous. G Protein-coupled Receptors (GPCRs) are a large attractive drug-targeted family of transmembrane proteins, and aberrant GPCR expression and GPCR-mediated signaling have been implicated in leukemogenesis of AML. This review aims to identify the molecular players of GPCR signaling, focusing on the hematopoietic system, which are involved in AML to help developing novel drug targets and therapeutic strategies.

METHODS

We undertook an exhaustive and structured search of bibliographic databases for research focusing on GPCR, GPCR signaling and expression in AML.

RESULTS AND CONCLUSION

Many scientific reports were found with compelling evidence for the involvement of aberrant GPCR expression and perturbed GPCR-mediated signaling in the development of AML. The comprehensive analysis of GPCR in AML provides potential clinical biomarkers for prognostication, disease monitoring and therapeutic guidance. It will also help to provide marker panels for monitoring in AML. We conclude that GPCR-mediated signaling is contributing to leukemogenesis of AML, and postulate that mass spectrometrybased protein profiling of primary AML cells will accelerate the discovery of potential GPCR related biomarkers for AML.

GPR110 (ADGRF1) mediates anti-inflammatory effects of N-docosahexaenoylethanolamine

Background

Neuroinflammation is a widely accepted underlying condition for various pathological processes in the brain. In a recent study, synaptamide, an endogenous metabolite derived from docosahexaenoic acid (DHA, 22:6n-3), was identified as a specific ligand to orphan adhesion G-protein-coupled receptor 110 (GPR110, ADGRF1). Synaptamide has been shown to suppress lipopolysaccharide (LPS)-induced neuroinflammation in mice, but involvement of GPR110 in this process has not been established. In this study, we investigated the possible immune regulatory role of GPR110 in mediating the anti-neuroinflammatory effects of synaptamide under a systemic inflammatory condition.

Methods

For in vitro studies, we assessed the role of GPR110 in synaptamide effects on LPS-induced inflammatory responses in adult primary mouse microglia, immortalized murine microglial cells (BV2), primary neutrophil, and peritoneal macrophage by using quantitative PCR (qPCR) and enzyme-linked immunosorbent assay (ELISA) as well as neutrophil migration and ROS production assays. To evaluate in vivo effects, wild-type (WT) and GPR110 knock-out (KO) mice were injected with LPS intraperitoneally (i.p.) or TNF intravenously (i.v.) followed by synaptamide (i.p.), and expression of proinflammatory mediators was measured by qPCR, ELISA, and western blot analysis. Activated microglia in the brain and NF-kB activation in cells were examined microscopically after immunostaining for Iba-1 and RelA, respectively.

Results

Intraperitoneal (i.p.) administration of LPS increased TNF and IL-1β in the blood and induced pro-inflammatory cytokine expression in the brain. Subsequent i.p. injection of the GPR110 ligand synaptamide significantly reduced LPS-induced inflammatory responses in wild-type (WT) but not in GPR110 knock-out (KO) mice. In cultured microglia, synaptamide increased cAMP and inhibited LPS-induced proinflammatory cytokine expression by inhibiting the translocation of NF-κB subunit RelA into the nucleus. These effects were abolished by blocking synaptamide binding to GPR110 using an N-terminal targeting antibody. GPR110 expression was found to be high in neutrophils and macrophages where synaptamide also caused a GPR110-dependent increase in cAMP and inhibition of LPS-induced pro-inflammatory mediator expression. Intravenous injection of TNF, a pro-inflammatory cytokine that increases in the circulation after LPS treatment, elicited inflammatory responses in the brain which were dampened by the subsequent injection (i.p.) of synaptamide in a GPR110-dependent manner.

Conclusion

Our study demonstrates the immune-regulatory function of GPR110 in both brain and periphery, collectively contributing to the anti-neuroinflammatory effects of synaptamide under a systemic inflammatory condition. We suggest GPR110 activation as a novel therapeutic strategy to ameliorate inflammation in the brain as well as periphery.

Chemokine receptor trafficking coordinates neutrophil clustering and dispersal at wounds in zebrafish

Immune cells congregate at specific loci to fight infections during inflammatory responses, a process that must be transient and self-resolving. Cell dispersal promotes resolution, but it remains unclear how transition from clustering to dispersal is regulated. Here we show, using quantitative live imaging in zebrafish, that differential ligand-induced trafficking of chemokine receptors such as Cxcr1 and Cxcr2 orchestrates the state of neutrophil congregation at sites of tissue damage. Through receptor mutagenesis and biosensors, we show that Cxcr1 promotes clustering at wound sites, but is promptly desensitized and internalized, which prevents excess congregation. By contrast, Cxcr2 promotes bidirectional motility and is sustained at the plasma membrane. Persistent plasma membrane residence of Cxcr2 prolongs downstream signaling and is required for sustained exploratory motion conducive to dispersal. Thus, differential trafficking of two chemokine receptors allows coordination of antagonistic cell behaviors, promoting a self-resolving migratory response.

Inflammatory responses must be induced and resolved timely to serve protection from pathogens without inducing excessive tissue damage. Here the authors use live imaging in zebrafish to show that the intracellular trafficking of two chemokine receptors, Cxcr1 and Cxcr2, is differentially regulated on activated neutrophils to control their clustering and dispersal, respectively.

Context-Dependent Signaling of CXC Chemokine Receptor 4 and Atypical Chemokine Receptor 3

G protein-coupled receptors (GPCRs) are regulated by complex molecular mechanisms, both in physiologic and pathologic conditions, and their signaling can be intricate. Many factors influence their signaling behavior, including the type of ligand that activates the GPCR, the presence of interacting partners, the kinetics involved, or their location. The two CXC-type chemokine receptors, CXC chemokine receptor 4 (CXCR4) and atypical chemokine receptor 3 (ACKR3), both members of the GPCR superfamily, are important and established therapeutic targets in relation to cancer, human immunodeficiency virus infection, and inflammatory diseases. Therefore, it is crucial to understand how the signaling of these receptors works to be able to specifically target them. In this review, we discuss how the signaling pathways activated by CXCR4 and ACKR3 can vary in different situations. G protein signaling of CXCR4 depends on the cellular context, and discrepancies exist depending on the cell lines used. ACKR3, as an atypical chemokine receptor, is generally reported to not activate G proteins but can broaden its signaling spectrum upon heteromerization with other receptors, such as CXCR4, endothelial growth factor receptor, or the α ₁-adrenergic receptor (α ₁-AR). Also, CXCR4 forms heteromers with CC chemokine receptor (CCR) 2, CCR5, the Na⁺/H⁺ exchanger regulatory factor 1, CXCR3, α ₁-AR, and the opioid receptors, which results in differential signaling from that of the monomeric subunits. In addition, CXCR4 is present on membrane rafts but can go into the nucleus during cancer progression, probably acquiring different signaling properties. In this review, we also provide an overview of the currently known critical amino acids involved in CXCR4 and ACKR3 signaling.

The Role of the CXCL12/CXCR4/ACKR3 Axis in Autoimmune Diseases

Chemokine receptors are members of the G protein-coupled receptor superfamily. These receptors are intimately involved in cell movement, and thus play a critical role in several physiological and pathological situations that require the precise regulation of cell positioning. CXCR4 is one of the most studied chemokine receptors and is involved in many functions beyond leukocyte recruitment. During embryogenesis, it plays essential roles in vascular development, hematopoiesis, cardiogenesis, and nervous system organization. It has been also implicated in tumor progression and autoimmune diseases and, together with CD4, is one of the co-receptors used by the HIV-1 virus to infect immune cells. In contrast to other chemokine receptors that are characterized by ligand promiscuity, CXCR4 has a unique ligand-stromal cell-derived factor-1 (SDF1, CXCL12). However, this ligand also binds ACKR3, an atypical chemokine receptor that modulates CXCR4 functions and is overexpressed in multiple cancer types. The CXCL12/CXCR4/ACKR3 axis constitutes a potential therapeutic target for a wide variety of inflammatory diseases, not only by interfering with cell migration but also by modulating immune responses. Thus far, only one antagonist directed against the ligand-binding site of CXCR4, AMD3100, has demonstrated clinical relevance. Here, we review the role of this ligand and its receptors in different autoimmune diseases.

CD38 knockout suppresses tumorigenesis in mice and clonogenic growth of human lung cancer cells

The ectodomain of the plasma membrane ectoenzyme CD38 functions as both an NAD glycohydrolase and an ADP-ribosyl cyclase by catalyzing, respectively, the conversion of NAD to nicotinamide and ADP-ribose or cyclic ADP-ribose. CD38 is attracting particular attention in cancer therapy. An anti-CD38 monoclonal antibody (daratumumab) was approved for treatment of patients with multiple myeloma. However, the role of CD38 in non-hematological malignancies has not been explored. Previously, we reported that ADP-ribose-acceptor hydrolase (ARH)-1 deficiency in mice was associated with tumor development. In the present study, we found that in wild-type and ARH1-deficient mice deletion of the CD38 gene reduced tumor formation. Significant reductions in tumor number were observed in lymphomas, adenocarcinomas and hemangio/histolytic sarcomas. Consistent with a role for CD38 in tumorigenesis, CRISPR/Cas9-based knockout of CD38 in A549 human adenocarcinoma cells inhibited anchorage-independent cell growth, cell invasion and xenograft growth in nude mice. CD38 mRNA and protein expression were evaluated in human lung cancer cell lines and in human lung cancer specimens. CD38 overexpression in tumor cells was identified in 11 of 27 patient samples. In addition, some human lung cancer cell lines had dramatically higher CD38 mRNA and protein expression than normal cells. Consistent with these observations, search of the Oncomine database showed that some human lung adenocarcinomas had higher CD38 mRNA levels compared to normal lung tissues. In total, our data are consistent with the conclusion that CD38 plays a role in murine and human lung tumorigenesis and that anti-CD38 treatment may have therapeutic potential in lung cancer.

G protein subtype-specific signaling bias in a series of CCR5 chemokine analogs

Chemokines and some chemical analogs of chemokines prevent cellular HIV-1 entry when bound to the HIV-1 coreceptors C-C chemokine receptor 5 (CCR5) or C-X-C chemokine receptor 4 (CXCR4), which are G protein-coupled receptors (GPCRs). The ideal HIV-1 entry blocker targeting the coreceptors would display ligand bias and avoid activating G protein-mediated pathways that lead to inflammation. We compared CCR5-dependent activation of second messenger pathways in a single cell line. We studied two endogenous chemokines [RANTES (also known as CCL5) and MIP-1α (also known as CCL3)] and four chemokine analogs of RANTES (5P12-, 5P14-, 6P4-, and PSC-RANTES). We found that CCR5 signaled through both G_i/o and G_q/11 IP₁ accumulation and Ca²⁺ flux arose from G_q/11 activation, rather than from Gβγ subunit release after G_i/o activation as had been previously proposed. The 6P4- and PSC-RANTES analogs were superagonists for G_q/11 activation, whereas the 5P12- and 5P14-RANTES analogs displayed a signaling bias for G_i/o These results demonstrate that RANTES analogs elicit G protein subtype-specific signaling bias and can cause CCR5 to couple preferentially to G_q/11 rather than to G_i/o signaling pathways. We propose that G protein subtype-specific signaling bias may be a general feature of GPCRs that can couple to more than one G protein family.

Loss of Gαq impairs regulatory B-cell function

Background

Recent studies have shown a crucial role of Gαq in immune regulation, but how Gαq modulates regulatory B-cell (Breg) function is still unclear. We address this here.

Methods

CD19⁺IL-10⁺ Bregs of wild-type (WT) and Gnaq^−/− mice were analyzed by flow cytometry after stimulation by lipopolysaccharide. The WT and Gnaq^−/− Bregs were isolated and cocultured with WT CD4⁺CD25⁻ T cells in the presence of T-activator, and the proliferation of T cells and differentiation of regulatory T cells (Tregs) were analyzed by flow cytometry. We used inhibitors of PI3 kinase (PI3K), extracellular regulated protein kinases 1/2 (Erk1/2), and p38 mitogen-activated protein kinase (p38 MAPK) to detect the pathways involved in the regulation of Gαq on Breg differentiation, which were confirmed by western blot analysis. Furthermore, the expression level of Gαq was assessed by quantitative real-time PCR in peripheral blood mononuclear cells (PBMCs) from healthy controls and rheumatoid arthritis patients. The frequency of CD19⁺CD24^hiCD38^hi B cells in PBMCs was detected by flow cytometry, and the association of the Gαq mRNA expression level and the frequency of CD19⁺CD24^hiCD38^hi B cells was analyzed by Spearman test.

Results

The differentiation of CD19⁺IL-10⁺ Bregs was inhibited in the Gnaq^−/− mice. In addition, Gαq depletion showed an impaired suppressive function of Bregs on T-cell proliferation, which might be due to the decreased Treg expansion. Mechanically, our data demonstrated that the PI3K, Erk1/2, and p38 MAPK signaling pathways were required for regulation of Gαq on Bregs, and blockage of these signaling pathways impaired Breg differentiation. Consistent with our previous studies, we also found a decreased frequency of CD19⁺CD24^hiCD38^hi Bregs in rheumatoid arthritis patients. As expected, a significantly positive correlation was investigated between CD19⁺CD24^hiCD38^hi Bregs with Gαq mRNA expression.

Conclusions

Our results indicate that Gαq plays a critical role in the differentiation and immunosuppression of Bregs, and it may provide a new therapeutic target for autoimmune diseases.

Electronic supplementary material

The online version of this article (10.1186/s13075-018-1682-0) contains supplementary material, which is available to authorized users.

Regulator of G protein signaling 5 restricts neutrophil chemotaxis and trafficking

Neutrophils are white blood cells that are mobilized to damaged tissues and to sites of pathogen invasion, providing the first line of host defense. Chemokines displayed on the surface of blood vessels promote migration of neutrophils to these sites, and tissue- and pathogen-derived chemoattractant signals, including N-formylmethionylleucylphenylalanine (fMLP), elicit further migration to sites of infection. Although nearly all chemoattractant receptors use heterotrimeric G proteins to transmit signals, many of the mechanisms lying downstream of chemoattractant receptors that either promote or limit neutrophil motility are incompletely defined. Here, we show that regulator of G protein signaling 5 (RGS5), a protein that modulates G protein activity, is expressed in both human and murine neutrophils. We detected significantly more neutrophils in the airways of Rgs5^-/- mice than WT counterparts following acute respiratory virus infection and in the peritoneum in response to injection of thioglycollate, a biochemical proinflammatory stimulus. RGS5-deficient neutrophils responded with increased chemotaxis elicited by the chemokines CXC motif chemokine ligand 1 (CXCL1), CXCL2, and CXCL12 but not fMLP. Moreover, adhesion of these cells was increased in the presence of both CXCL2 and fMLP. In summary, our results indicate that RGS5 deficiency increases chemotaxis and adhesion, leading to more efficient neutrophil mobilization to inflamed tissues in mice. These findings suggest that RGS5 expression and activity in neutrophils determine their migrational patterns in the complex microenvironments characteristic of inflamed tissues.

Expression of Gαq Is Decreased in Lymphocytes from Primary Sjögren's Syndrome Patients and Related to Increased IL-17A Expression

Primary Sjögren's syndrome (pSS) is a rheumatic disease characterized by the destruction of salivary and lacrimal glands, and its pathogenesis mechanism remains unclear. Gαq is the α-subunit of the heterotrimeric Gq protein. Researches demonstrated that Gαq was involved in the pathogenesis regulation of several rheumatic diseases. This study explored the role of Gαq in pSS. Gαq mRNA levels in peripheral blood mononuclear cells (PBMCs) from 39 patients and 26 healthy controls (HCs) were investigated using real-time PCR. IL-17A serum concentrations in 22 pSS patients and 23 HCs were tested by ELISA, and the clinical significance of Gαq was analyzed. The association of Gαq with interleukin-17A (IL-17A) expression was also analyzed in patients with pSS. We showed that Gαq expression in PBMCs from patients with pSS was significantly lower than that in PBMCs from HCs. Gαq expression level was closely associated with pSS disease activity. Furthermore, a negative association was also found in IL-17A and Gαq expression level. These data suggest that Gαq is involved in pSS pathogenesis regulation, possibly due to its regulation of Th17. These results provide new insights into the pSS pathogenesis mechanism involving abnormal Th17 regulation.

CD38 promotes pristane-induced chronic inflammation and increases susceptibility to experimental lupus by an apoptosis-driven and TRPM2-dependent mechanism

In this study, we investigated the role of CD38 in a pristane-induced murine model of lupus. CD38-deficient (Cd38-/-) but not ART2-deficient (Art2-/-) mice developed less severe lupus compared to wild type (WT) mice, and their protective phenotype consisted of (i) decreased IFN-I-stimulated gene expression, (ii) decreased numbers of peritoneal CCR2hiLy6Chi inflammatory monocytes, TNF-α-producing Ly6G+ neutrophils and Ly6Clo monocytes/macrophages, (iii) decreased production of anti-single-stranded DNA and anti-nRNP autoantibodies, and (iv) ameliorated glomerulonephritis. Cd38-/- pristane-elicited peritoneal exudate cells had defective CCL2 and TNF-α secretion following TLR7 stimulation. However, Tnf-α and Cxcl12 gene expression in Cd38-/- bone marrow (BM) cells was intact, suggesting a CD38-independent TLR7/TNF-α/CXCL12 axis in the BM. Chemotactic responses of Cd38-/- Ly6Chi monocytes and Ly6G+ neutrophils were not impaired. However, Cd38-/- Ly6Chi monocytes and Ly6Clo monocytes/macrophages had defective apoptosis-mediated cell death. Importantly, mice lacking the cation channel TRPM2 (Trpm2-/-) exhibited very similar protection, with decreased numbers of PECs, and apoptotic Ly6Chi monocytes and Ly6Clo monocytes/macrophages compared to WT mice. These findings reveal a new role for CD38 in promoting aberrant inflammation and lupus-like autoimmunity via an apoptosis-driven mechanism. Furthermore, given the implications of CD38 in the activation of TRPM2, our data suggest that CD38 modulation of pristane-induced apoptosis is TRPM2-dependent.

Cinacalcet Rectifies Hypercalcemia in a Patient With Familial Hypocalciuric Hypercalcemia Type 2 (FHH2) Caused by a Germline Loss-of-Function Gα11 Mutation

G-protein subunit α-11 (Gα₁₁ ) couples the calcium-sensing receptor (CaSR) to phospholipase C (PLC)-mediated intracellular calcium (Ca²⁺_i ) and mitogen-activated protein kinase (MAPK) signaling, which in the parathyroid glands and kidneys regulates parathyroid hormone release and urinary calcium excretion, respectively. Heterozygous germline loss-of-function Gα₁₁ mutations cause familial hypocalciuric hypercalcemia type 2 (FHH2), for which effective therapies are currently not available. Here, we report a novel heterozygous Gα₁₁ germline mutation, Phe220Ser, which was associated with hypercalcemia in a family with FHH2. Homology modeling showed the wild-type (WT) Phe220 nonpolar residue to form part of a cluster of hydrophobic residues within a highly conserved cleft region of Gα₁₁ , which binds to and activates PLC; and predicted that substitution of Phe220 with the mutant Ser220 polar hydrophilic residue would disrupt PLC-mediated signaling. In vitro studies involving transient transfection of WT and mutant Gα₁₁ proteins into HEK293 cells, which express the CaSR, showed the mutant Ser220 Gα₁₁ protein to impair CaSR-mediated Ca²⁺_i and extracellular signal-regulated kinase 1/2 (ERK) MAPK signaling, consistent with diminished activation of PLC. Furthermore, engineered mutagenesis studies demonstrated that loss of hydrophobicity within the Gα₁₁ cleft region also impaired signaling by PLC. The loss-of-function associated with the Ser220 Gα₁₁ mutant was rectified by treatment of cells with cinacalcet, which is a CaSR-positive allosteric modulator. Furthermore, in vivo administration of cinacalcet to the proband harboring the Phe220Ser Gα₁₁ mutation, normalized serum ionized calcium concentrations. Thus, our studies, which report a novel Gα₁₁ germline mutation (Phe220Ser) in a family with FHH2, reveal the importance of the Gα₁₁ hydrophobic cleft region for CaSR-mediated activation of PLC, and show that allosteric CaSR modulation can rectify the loss-of-function Phe220Ser mutation and ameliorate the hypercalcemia associated with FHH2. © 2017 The Authors. Journal of Bone and Mineral Research Published by Wiley Periodicals Inc.

The 17,18-epoxyeicosatetraenoic acid-G protein-coupled receptor 40 axis ameliorates contact hypersensitivity by inhibiting neutrophil mobility in mice and cynomolgus macaques

BACKGROUND

Metabolites of eicosapentaenoic acid exert various physiologic actions. 17,18-Epoxyeicosatetraenoic acid (17,18-EpETE) is a recently identified new class of antiallergic and anti-inflammatory lipid metabolite of eicosapentaenoic acid, but its effects on skin inflammation and the underlying mechanisms remain to be investigated.

OBJECTIVE

We evaluated the effectiveness of 17,18-EpETE for control of contact hypersensitivity in mice and cynomolgus macaques. We further sought to reveal underlying mechanisms by identifying the responsible receptor and cellular target of 17,18-EpETE.

METHODS

Contact hypersensitivity was induced by topical application of 2,4-dinitrofluorobenzene. Skin inflammation and immune cell populations were analyzed by using flow cytometric, immunohistologic, and quantitative RT-PCR analyses. Neutrophil mobility was examined by means of imaging analysis in vivo and neutrophil culture in vitro. The receptor for 17,18-EpETE was identified by using the TGF-α shedding assay, and the receptor's involvement in the anti-inflammatory effects of 17,18-EpETE was examined by using KO mice and specific inhibitor treatment.

RESULTS

We found that preventive or therapeutic treatment with 17,18-EpETE ameliorated contact hypersensitivity by inhibiting neutrophil mobility in mice and cynomolgus macaques. 17,18-EpETE was recognized by G protein-coupled receptor (GPR) 40 (also known as free fatty acid receptor 1) and inhibited chemoattractant-induced Rac activation and pseudopod formation in neutrophils. Indeed, the antiallergic inflammatory effect of 17,18-EpETE was abolished in the absence or inhibition of GPR40.

CONCLUSION

17,18-EpETE inhibits neutrophil mobility through GPR40 activation, which is a potential therapeutic target to control allergic inflammatory diseases.

Gαq Regulates the Development of Rheumatoid Arthritis by Modulating Th1 Differentiation

The Gαq-containing G protein, an important member of G_q/11 class, is ubiquitously expressed in mammalian cells. Gαq has been found to play an important role in immune regulation and development of autoimmune disease such as rheumatoid arthritis (RA). However, how Gαq participates in the pathogenesis of RA is still not fully understood. In the present study, we aimed to find out whether Gαq controls RA via regulation of Th1 differentiation. We observed that the expression of Gαq was negatively correlated with the expression of signature Th1 cytokine (IFN-γ) in RA patients, which suggests a negative role of Gαq in differentiation of Th1 cells. By using Gαq knockout (Gnaq-/-) mice, we demonstrated that loss of Gαq led to enhanced Th1 cell differentiation. Gαq negative regulated the differentiation of Th1 cell by modulating the expression of T-bet and the activity of STAT4. Furthermore, we detected the increased ratio of Th1 cells in Gnaq-/- bone marrow (BM) chimeras spontaneously developing inflammatory arthritis. In conclusion, results presented in the study demonstrate that loss of Gαq promotes the differentiation of Th1 cells and contributes to the pathogenesis of RA.

Modulation of Chemokine Receptor Function by Cholesterol: New Prospects for Pharmacological Intervention

Chemokine receptors are seven transmembrane-domain receptors belonging to class A of G-protein-coupled receptors (GPCRs). The receptors together with their chemokine ligands constitute the chemokine system, which is essential for directing cell migration and plays a crucial role in a variety of physiologic and pathologic processes. Given the importance of orchestrating cell migration, it is vital that chemokine receptor signaling is tightly regulated to ensure appropriate responses. Recent studies highlight a key role for cholesterol in modulating chemokine receptor activities. The steroid influences the spatial organization of GPCRs within the membrane bilayer, and consequently can tune chemokine receptor signaling. The effects of cholesterol on the organization and function of chemokine receptors and GPCRs in general include direct and indirect effects (Fig. 1). Here, we review how cholesterol and some key metabolites modulate functions of the chemokine system in multiple ways. We emphasize the role of cholesterol in chemokine receptor oligomerization, thereby promoting the formation of a signaling hub enabling integration of distinct signaling pathways at the receptor-membrane interface. Moreover, we discuss the role of cholesterol in stabilizing particular receptor conformations and its consequence for chemokine binding. Finally, we highlight how cholesterol accumulation, its deprivation, or cholesterol metabolites contribute to modulating cell orchestration during inflammation, induction of an adaptive immune response, as well as to dampening an anti-tumor immune response.

Decreased Gαq expression in T cells correlates with enhanced cytokine production and disease activity in systemic lupus erythematosus

Aberrant T cell immune responses appear central to the development of systemic lupus erythematosus (SLE). We previously reported that Gαq, the alpha subunit of Gq, regulates T and B cell immune responses, promoting autoimmunity. To address whether Gαq contributes to the pathogenesis of SLE, Gαq mRNA expression was studied using real time-PCR in PBMCs and T cells from SLE patients as well as age- and sex-matched healthy controls. Our results showed that Gαq mRNA expression was decreased in PBMCs and T cells from SLE patients compared to healthy individuals. Correlation analyses showed that Gαq expression in T cells from SLE patients was associated with disease severity (as per SLE Disease Activity Index), the presence of lupus nephritis, and expression of Th1, Th2 and Th17 cytokines. In keeping with clinical results, T-helper cell subsets (Th1, Th2 and Th17) were over-represented in Gαq knockout mice. In addition, Gαq expression in SLE T cells was negatively correlated with the expression of Bcl-2, an anti-apoptotic gene, and positively correlated with the expression of Bax, a pro-apoptotic gene. These data suggest that reduced Gαq levels in T cells may promote enhanced and prolonged T cell activation, contributing to the clinical manifestations of SLE.

A Broad-Spectrum Chemokine-Binding Protein of Bovine Papular Stomatitis Virus Inhibits Neutrophil and Monocyte Infiltration in Inflammatory and Wound Models of Mouse Skin

Bovine papular stomatitis virus (BPSV) is a Parapoxvirus that induces acute pustular skin lesions in cattle and is transmissible to humans. Previous studies have shown that BPSV encodes a distinctive chemokine-binding protein (CBP). Chemokines are critically involved in the trafficking of immune cells to sites of inflammation and infected tissue, suggesting that the CBP plays a role in immune evasion by preventing immune cells reaching sites of infection. We hypothesised that the BPSV-CBP binds a wide range of inflammatory chemokines particularly those involved in BPSV skin infection, and inhibits the recruitment of immune cells from the blood into inflamed skin. Molecular analysis of the purified protein revealed that the BPSV-CBP is a homodimeric polypeptide with a MW of 82.4 kDa whilst a comprehensive screen of inflammatory chemokines by surface plasmon resonance showed high-affinity binding to a range of chemokines within the CXC, CC and XC subfamilies. Structural analysis of BPSV-CBP, based on the crystal structure of orf virus CBP, provided a probable explanation for these chemokine specificities at a molecular level. Functional analysis of the BPSV-CBP using transwell migration assays demonstrated that it potently inhibited chemotaxis of murine neutrophils and monocytes in response to CXCL1, CXCL2 as well as CCL2, CCL3 and CCL5 chemokines. In order to examine the effects of CBP in vivo, we used murine skin models to determine its impact on inflammatory cell recruitment such as that observed during BPSV infection. Intradermal injection of BPSV-CBP blocked the influx of neutrophils and monocytes in murine skin in which inflammation was induced with lipopolysaccharide. Furthermore, intradermal injection of BPSV-CBP into injured skin, which more closely mimics BPSV lesions, delayed the influx of neutrophils and reduced the recruitment of MHC-II+ immune cells to the wound bed. Our findings suggest that the CBP could be important in pathogenesis of BPSV infections.

Chemokine Receptor Signaling and the Hallmarks of Cancer

The chemokines are a family of chemotactic cytokines that mediate their activity by acting on seven-transmembrane-spanning G protein-coupled receptors. Both the ability of the chemokines and their receptors to form homo- and heterodimers and the promiscuity of the chemokine-chemokine receptor interaction endow this protein family with enormous signaling plasticity and complexity that are not fully understood at present. Chemokines were initially identified as essential regulators of homeostatic and inflammatory trafficking of innate and adaptive leucocytes from lymphoid organs to tissues. Chemokines also mediate the host response to cancer. Nevertheless, chemokine function in this response is not limited to regulating leucocyte infiltration into the tumor microenvironment. It is now known that chemokines and their receptors influence most-if not all-hallmark processes of cancer; they act on both neoplastic and untransformed cells in the tumor microenvironment, including fibroblasts, endothelial cells (blood and lymphatic), bone marrow-derived stem cells, and, obviously, infiltrating leucocytes. This review begins with an overview of chemokine and chemokine receptor structure, to better define how chemokines affect the proliferation, survival, stemness, and metastatic potential of neoplastic cells. We also examine the main mechanisms by which chemokines regulate tumor angiogenesis and immune cell infiltration, emphasizing the pro- and antitumorigenic activity of this protein superfamily in these interrelated processes.

Gq-Coupled Receptors in Autoimmunity

Heterotrimeric G proteins can be divided into Gi, Gs, Gq/11, and G12/13 subfamilies according to their α subunits. The main function of G proteins is transducing signals from G protein coupled receptors (GPCRs), a family of seven transmembrane receptors. In recent years, studies have demonstrated that GPCRs interact with Gq, a member of the Gq/11 subfamily of G proteins. This interaction facilitates the vital role of this family of proteins in immune regulation and autoimmunity, particularly for Gαq, which is considered the functional α subunit of Gq protein. Therefore, understanding the mechanisms through which Gq-coupled receptors control autoreactive lymphocytes is critical and may provide insights into the treatment of autoimmune disorders. In this review, we summarize recent advances in studies of the role of Gq-coupled receptors in autoimmunity, with a focus on their pathologic role and downstream signaling.

Common and biased signaling pathways of the chemokine receptor CCR7 elicited by its ligands CCL19 and CCL21 in leukocytes

Chemokines are pivotal regulators of cell migration during continuous immune surveillance, inflammation, homeostasis, and development. Chemokine binding to their 7-transmembrane domain, G-protein-coupled receptors causes conformational changes that elicit intracellular signaling pathways to acquire and maintain an asymmetric architectural organization and a polarized distribution of signaling molecules necessary for directional cell migration. Leukocytes rely on the interplay of chemokine-triggered migration modules to promote amoeboid-like locomotion. One of the most important chemokine receptors for adaptive immune cell migration is the CC-chemokine receptor CCR7. CCR7 and its ligands CCL19 and CCL21 control homing of T cells and dendritic cells to areas of the lymph nodes where T cell priming and the initiation of the adaptive immune response occur. Moreover, CCR7 signaling also contributes to T cell development in the thymus and to lymphorganogenesis. Although the CCR7-CCL19/CCL21 axis evolved to benefit the host, inappropriate regulation or use of these proteins can contribute or cause pathobiology of chronic inflammation, tumorigenesis, and metastasis, as well as autoimmune diseases. Therefore, it appears as the CCR7-CCL19/CCL21 axis is tightly regulated at numerous intersections. Here, we discuss the multiple regulatory mechanism of CCR7 signaling and its influence on CCR7 function. In particular, we focus on the functional diversity of the 2 CCR7 ligands, CCL19 and CCL21, as well as on their impact on biased signaling. The understanding of the molecular determinants of biased signaling and the multiple layers of CCR7 regulation holds the promise for potential future therapeutic intervention.

Comprehensive analysis of chemokine-induced cAMP-inhibitory responses using a real-time luminescent biosensor

Chemokine receptors are members of the G-protein-coupled receptor (GPCR) family coupled to members of the Gi class, whose primary function is to inhibit the cellular adenylate cyclase. We used a cAMP-related and PKA-based luminescent biosensor (GloSensor™ F-22) to monitor the real-time downstream response of chemokine receptors, especially CX3CR1 and CXCR4, after activation with their cognate ligands CX3CL1 and CXCL12. We found that the amplitudes and kinetic profiles of the chemokine responses were conserved in various cell types and were independent of the nature and concentration of the molecules used for cAMP prestimulation, including either the adenylate cyclase activator forskolin or ligands mediating Gs-mediated responses like prostaglandin E2 or beta-adrenergic agonist. We conclude that the cAMP chemokine response is robustly conserved in various inflammatory conditions. Moreover, the cAMP-related luminescent biosensor appears as a valuable tool to analyze the details of Gi-mediated cAMP-inhibitory cellular responses, even in native conditions and could help to decipher their precise role in cell function.

Gαq controls rheumatoid arthritis via regulation of Th17 differentiation

Gαq, the α-subunit of Gq protein, is ubiquitously expressed in mammalian cells. It initially attracted attention for its physiological significance in cardiovascular system. In recent years, studies have also indicated the important roles of Gαq in regulating immunity, supplying us a new insight into the mechanism of immune regulation. T helper type 17 (Th17) cells are potent inducers of tissue inflammation. Many studies have shown that Th17 cells are major effector cells in the pathogenesis of many experimental autoimmune diseases and human inflammatory conditions such as rheumatoid arthritis (RA). One of our previous studies has shown that Gαq negatively controls the disease activity of RA. However, how Gαq controls the pathogenesis of autoimmune disease is not clear. Whether this effect is via the regulation of Th17 differentiation is still not known. We aimed to find out the role of Gαq in control of Th17 differentiation. We investigated the relationship between Gαq and Th17 in RA patients. We then investigated the mechanism of how Gαq regulated Th17 differentiation by using Gnaq(-/-) mice. We observed that the expression of Gαq was negatively associated with interleukin-17A expression in RA patients, indicating that Gαq negatively controlled the differentiation of Th17 cells. By using Gnaq(-/-) mice, we demonstrated that Gαq inhibited the differentiation of Th17 cell via regulating the activity of extracellular signal-regulated kinase-1/2 to control the expression of STAT3 (signal transducer and activator of transcription 3) and RORα (RAR-related orphan receptor-α). These data suggest the possibility of targeting Gαq to develop a novel therapeutic regimen for autoimmune disease.

The deficiency of Gαq leads to enhanced T-cell survival

We have previously reported that Gαq, the α subunit of the Gq protein, had important roles in dendritic cell migration, B-cell survival and autoimmunity. In this study, we showed that the deficiency of Gαq led to enhanced T-cell survival. Cultured Gnaq(-/-) T cells exhibited survival advantages both in medium alone and in the presence of anti-CD3 stimulation. Gnaq(-/-) T cells still exhibited a survival advantage when they were cultured in the presence of interleukin (IL)-2 or IL-7. Gnaq(-/-) T cells were more resistant to activation-induced cell death (AICD) in vitro. The survival advantage of Gnaq(-/-) T cells was further confirmed by transferring T cells into syngeneic hosts in vivo. Gαq deficiency might promote T-cell survival by upregulated Bcl-xL expression and downregulated Fas and FasL expressions. Furthermore, upon T-cell receptor (TCR) ligation, Akt activity was increased in Gnaq(-/-) T cells in comparison with wild-type (WT) T cells. The survival advantage of Gnaq(-/-) T cells was significantly attenuated after adding Akt inhibitor. Taken together, our data demonstrated a negative role of Gαq in regulating T-cell survival.

Ectoenzymes in leukocyte migration and their therapeutic potential

Inflammation causes or accompanies a huge variety of diseases. Migration of leukocytes from the blood into the tissues, in the tissues, and from the tissues to lymphatic vasculature is crucial in the formation and resolution of inflammatory infiltrates. In addition to classical adhesion and activation molecules, several other molecules are known to contribute to the leukocyte traffic. Several of them belong to ectoenzymes, which are cell surface molecules having catalytically active sites outside the cell. We will review here how several ectoenzymes present on leukocytes or endothelial cell surface function as adhesins and/or modulate the extravasation cascade through their enzymatic activities. Moreover, their therapeutic potential as immune modulators in different experimental inflammation models and in clinical trials will be discussed.

Role of G protein-coupled receptors in control of dendritic cell migration

Dendritic cells (DCs) are highly efficient antigen-presenting cells. The migratory properties of DCs give them the capacity to be a sentinel of the body and the vital role in the induction and regulation of adaptive immune responses. Therefore, it is important to understand the mechanisms in control of migration of DCs to lymphoid and nonlymphoid tissues. This may provide us novel insight into the clinical treatment of diseases such as autoimmune disease, infectious disease, and tumor. The chemotactic G protein-coupled receptors (GPCR) play a vital role in control of DCs migration. Here, we reviewed the recent advances regarding the role of GPCR in control of migration of subsets of DCs, with a focus on the chemokine receptors. Understanding subsets of DCs migration could provide a rational basis for the design of novel therapies in various clinical conditions.

The regulating function of heterotrimeric G proteins in the immune system

Heterotrimeric guanine nucleotide-binding proteins (G proteins), which consist of an α-, a β- and a γ-subunit, have crucial roles as molecular switches in the regulation of the downstream effector molecules of multiple G protein-coupled receptor signalling pathways, such as phospholipase C and adenylyl cyclase. According to the structural and functional similarities of their α-subunits, G proteins can be divided into four subfamilies: Gαs, Gαi/o, Gαq/11 and Gα12/13. Most of the α- and the βγ-subunits are abundantly expressed on the surface of immune cells. Recent studies have demonstrated that G proteins are a group of important immunomodulatory factors that regulate the migration, activation, survival, proliferation, differentiation and cytokine secretion of immune cells. In this review, we summarise the recent findings on the functions of G proteins in immune regulation and autoimmunity.

HIV-1 Nef impairs heterotrimeric G-protein signaling by targeting Gα(i2) for degradation through ubiquitination

The HIV Nef protein is an important pathogenic factor that modulates cell surface receptor trafficking and impairs cell motility, presumably by interfering at multiple steps with chemotactic receptor signaling. Here, we report that a dominant effect of Nef is to trigger AIP4 E3 ligase-mediated Gα(i2) ubiquitination, which leads to Gα(i2) endolysosomal sequestration and destruction. The loss of the Gα(i2) subunit was demonstrable in many cell types in the context of gene transfection, HIV infection, or Nef protein transduction. Nef directly interacts with Gα(i2) and ternary complexes containing AIP4, Nef, and Gα(i2) form. A substantial reversal of Gα(i2) loss and a partial recovery of impaired chemotaxis occurred following siRNA knockdown of AIP4 or NEDD4 or by inhibiting dynamin. The N-terminal myristoyl group, (62)EEEE(65) motif, and (72)PXXP(75) motif of Nef are critical for this effect to occur. Nef expression does not affect a Gq(i5) chimera where the five C-terminal residues of Gq are replaced with those of Gα(i2). Lysine at position 296 of Gα(i2) was identified as the critical determinant of Nef-induced degradation. By specifically degrading Gα(i2), Nef directly subverts leukocyte migration and homing. Impaired trafficking and homing of HIV Nef-expressing lymphocytes probably contributes to early immune dysfunction following HIV infection.

GPCR activation of Ras and PI3Kc in neutrophils depends on PLCb2/b3 and the RasGEF RasGRP4

The molecular mechanisms by which receptors regulate the Ras Binding Domains of the PIP3-generating, class I PI3Ks remain poorly understood, despite their importance in a range of biological settings, including tumorigenesis, activation of neutrophils by pro-inflammatory mediators, chemotaxis of Dictyostelium and cell growth in Drosophila. We provide evidence that G protein-coupled receptors (GPCRs) can stimulate PLCb2/b3 and diacylglycerol- dependent activation of the RasGEF, RasGRP4 in neutrophils. The genetic loss of RasGRP4 phenocopies knock-in of a Ras-insensitive version of PI3Kc in its effects on PI3Kc-dependent PIP3 accumulation, PKB activation, chemokinesis and reactive oxygen species (ROS) formation. These results establish a new mechanism by which GPCRs can stimulate Ras, and the broadly important principle that PLCs can control activation of class I PI3Ks.

The Gαq/11 proteins contribute to T lymphocyte migration by promoting turnover of integrin LFA-1 through recycling

The role of Gαi proteins coupled to chemokine receptors in directed migration of immune cells is well understood. In this study we show that the separate class of Gαq/11 proteins is required for the underlying ability of T cells to migrate both randomly and in a directed chemokine-dependent manner. Interfering with Gαq or Gα11 using dominant negative cDNA constructs or siRNA for Gαq causes accumulation of LFA-1 adhesions and stalled migration. Gαq/11 has an impact on LFA-1 expression at plasma membrane level and also on its internalization. Additionally Gαq co-localizes with LFA-1- and EEA1-expressing intracellular vesicles and partially with Rap1- but not Rab11-expressing vesicles. However the influence of Gαq is not confined to the vesicles that express it, as its reduction alters intracellular trafficking of other vesicles involved in recycling. In summary vesicle-associated Gαq/11 is required for the turnover of LFA-1 adhesion that is necessary for migration. These G proteins participate directly in the initial phase of recycling and this has an impact on later stages of the endo-exocytic pathway.

Role of G protein-coupled receptors in inflammation

G protein-coupled receptors (GPCRs) play important roles in inflammation. Inflammatory cells such as polymorphonuclear leukocytes (PMN), monocytes and macrophages express a large number of GPCRs for classic chemoattractants and chemokines. These receptors are critical to the migration of phagocytes and their accumulation at sites of inflammation, where these cells can exacerbate inflammation but also contribute to its resolution. Besides chemoattractant GPCRs, protease activated receptors (PARs) such as PAR1 are involved in the regulation of vascular endothelial permeability. Prostaglandin receptors play different roles in inflammatory cell activation, and can mediate both proinflammatory and anti-inflammatory functions. Many GPCRs present in inflammatory cells also mediate transcription factor activation, resulting in the synthesis and secretion of inflammatory factors and, in some cases, molecules that suppress inflammation. An understanding of the signaling paradigms of GPCRs in inflammatory cells is likely to facilitate translational research and development of improved anti-inflammatory therapies.

Gastrin-releasing peptide receptor (GRPR) mediates chemotaxis in neutrophils

Neutrophil migration to inflamed sites is crucial for both the initiation of inflammation and resolution of infection, yet these cells are involved in perpetuation of different chronic inflammatory diseases. Gastrin-releasing peptide (GRP) is a neuropeptide that acts through G protein coupled receptors (GPCRs) involved in signal transmission in both central and peripheral nervous systems. Its receptor, gastrin-releasing peptide receptor (GRPR), is expressed by various cell types, and it is overexpressed in cancer cells. RC-3095 is a selective GRPR antagonist, recently found to have antiinflammatory properties in arthritis and sepsis models. Here we demonstrate that i.p. injection of GRP attracts neutrophils in 4 h, and attraction is blocked by RC-3095. Macrophage depletion or neutralization of TNF abrogates GRP-induced neutrophil recruitment to the peritoneum. In vitro, GRP-induced neutrophil migration was dependent on PLC-β2, PI3K, ERK, p38 and independent of Gαi protein, and neutrophil migration toward synovial fluid of arthritis patients was inhibited by treatment with RC-3095. We propose that GRPR is an alternative chemotactic receptor that may play a role in the pathogenesis of inflammatory disorders.

Ca2+ signaling in the regulation of dendritic cell functions

Dendritic cells (DCs) are highly versatile antigen-presenting cells critically involved in both innate and adaptive immunity as well as maintenance of self-tolerance. DC function is governed by Ca(2+) signaling, which directs the DC responses to diverse antigens, including Toll-like receptor ligands, intact bacteria, and microbial toxins. Ca(2+)-sensitive DC functions include DC activation, maturation, migration, and formation of immunological synapses with T cells. Moreover, alterations of cytosolic Ca(2+) trigger immune suppression or switch off DC activity. Ca(2+) signals are generated by the orchestration of Ca(2+) transport processes across plasma, endoplasmic reticulum, and inner mitochondrial membrane. These processes include active pumping of Ca(2+), Ca(2+)/Na(+) antiport, and electrodiffusion through Ca(2+)-permeable channels or uniporters. Ca(2+) channels in the plasma membrane such as Ca(2+) release-activated Ca(2+) or L-type Ca(2+) channels are tightly regulated by the membrane potential which in turn depends on the activity of voltage-gated K(+) or Ca(2+)-activated nonselective cation channels. The rapidly growing knowledge on the function and regulation of these membrane transport proteins provides novel insight into pathophysiological mechanisms underlying dysfunction of the immune system and opens novel therapeutic opportunity to favorably influence the function of the immune system.

A critical role of Gbetagamma in tumorigenesis and metastasis of breast cancer

A growing body of evidence indicates that G protein-coupled receptors (GPCRs) are involved in breast tumor progression and that targeting GPCRs may be a novel adjuvant strategy in cancer treatment. However, due to the redundant role of multiple GPCRs in tumor development, it may be necessary to target a common signaling component downstream of these receptors to achieve maximum efficacy. GPCRs transmit signals through heterotrimeric G proteins composed of Gα and Gβγ subunits. Here we evaluated the role of Gβγ in breast tumor growth and metastasis both in vitro and in vivo. Our data show that blocking Gβγ signaling with Gα(t) or small molecule inhibitors blocked serum-induced breast tumor cell proliferation as well as tumor cell migration induced by various GPCRs in vitro. Moreover, induced expression of Gα(t) in MDA-MB-231 cells inhibited primary tumor formation and retarded growth of existing breast tumors in nude mice. Blocking Gβγ signaling also dramatically reduced the incidence of spontaneous lung metastasis from primary tumors and decreased tumor formation in the experimental lung metastasis model. Additional studies indicate that Gβγ signaling may also play a role in the generation of a tumor microenvironment permissive for tumor progression, because the inhibition of Gβγ signaling attenuated leukocyte infiltration and angiogenesis in primary breast tumors. Taken together, our data demonstrate a critical role of Gβγ signaling in promoting breast tumor growth and metastasis and suggest that targeting Gβγ may represent a novel therapeutic approach for breast cancer.

MCP-1/CCR2B-dependent loop upregulates MUC5AC and MUC5B in human airway epithelium

Cigarette smoke represents a major risk factor for the development of chronic obstructive pulmonary disease (COPD), a respiratory condition associated with airflow obstruction, mucus hypersecretion, chronic inflammation, and upregulation of inflammatory mediators such as the monocyte chemotactic protein-1 (MCP-1). MCP-1 through its receptor CCR2 induces chemotaxis and activates (44/42)MAPK, a kinase known to play a key role in mucin regulation in bronchial epithelium. In the present study we used differentiated primary cultures of normal human bronchial epithelial (NHBE) cells to test whether MCP-1 through its receptor CCR2 induces mucin upregulation. We have provided evidence that NHBE cells release MCP-1 to the epithelial surface and express the CCR2B isoform of the receptor mainly at the apical pole. In addition, we found that MCP-1 has a novel function in airway epithelium, increasing the two major airway mucins MUC5AC and MUC5B, an effect mediated, at least in part, by a cascade of events initiated by interaction of its receptor CCR2B with G(q) subunits in caveolae, followed by PLCβ, PKC, and (44/42)MAPK activation. We also have shown that MCP-1 is able to induce its own expression using the same receptor but through a different pathway that involves RhoA GTPase. Furthermore, we found that a single exposure to MCP-1 is enough to induce MCP-1 secretion and sustained mucin upregulation up to 7 days after initial exposure, an effect mediated by CCR2B as confirmed using short hairpin RNA. These results agree with our data in smoker's airway epithelium, where CCR2B is present in MUC5AC- and MUC5B-expressing cells and augmented MCP-1 expression is associated with increased MUC5AC and MUC5B immunolabeling, suggesting that the mechanisms described in primary cell cultures in the present study are operative in vivo. Therefore, therapeutic approaches targeting MCP-1/CCR2B may be useful in preventing not only influx of inflammatory cells to the airways but also mucus hypersecretion and goblet cell hyperplasia.

G alpha q-containing G proteins regulate B cell selection and survival and are required to prevent B cell-dependent autoimmunity

Survival of mature B cells is regulated by B cell receptor and BAFFR-dependent signals. We show that B cells from mice lacking the G_αq subunit of trimeric G proteins (Gnaq^−/− mice) have an intrinsic survival advantage over normal B cells, even in the absence of BAFF. Gnaq^−/− B cells develop normally in the bone marrow but inappropriately survive peripheral tolerance checkpoints, leading to the accumulation of transitional, marginal zone, and follicular B cells, many of which are autoreactive. Gnaq^−/− chimeric mice rapidly develop arthritis as well as other manifestations of systemic autoimmune disease. Importantly, we demonstrate that the development of the autoreactive B cell compartment is the result of an intrinsic defect in Gnaq^−/− B cells, resulting in the aberrant activation of the prosurvival factor Akt. Together, these data show for the first time that signaling through trimeric G proteins is critically important for maintaining control of peripheral B cell tolerance induction and repressing autoimmunity.