Gnb isoforms control a signaling pathway comprising Rac1, Plcβ2, and Plcβ3 leading to LFA-1 activation and neutrophil arrest in vivo

RNAi library screening reveals Gβ1, Casein Kinase 2 and ICAP-1 as novel regulators of LFA-1-mediated T cell polarity and migration

The αLβ2 integrin LFA-1 plays a key role in T-cell adhesion to the endothelial vasculature and migration into both secondary lymphoid organs and peripheral tissues via interactions with its target protein ICAM-1, but the pathways that regulate LFA-1-mediated T-cell polarity and migration are not fully understood. In this study we screened two RNAi libraries targeting G protein-coupled receptors (GPCR)/GPCR-associated proteins and kinases in a HuT 78 T cell line model of LFA-1-stimulated T-cell migration. Based on staining of the actin cytoskeleton, multiple parameters to measure cell morphology were used to assess the contribution of 1109 genes to LFA-1-mediated T-cell polarity and migration. These RNAi screens identified a number of both novel and previously identified genes that either increased or decreased the polarity and migratory capacity of these cells. Following multiparametric analysis, hierarchical clustering and pathway analysis, three of these genes were characterized in further detail using primary human T cells, revealing novel roles for the heterotrimeric G protein subunit Gβ1 and Casein Kinase 2 in LFA-1-mediated T-cell polarity and migration in vitro. Our studies also highlighted a new role for ICAP-1, an adaptor protein previously described to be associated with β1 integrins, in β2 integrin LFA-1-directed migration in T cells. Knockdown of ICAP-1 expression in primary T cells revealed a role in cell polarity, cell velocity and transmigration towards SDF-1 for this adaptor protein. This study therefore uncovers new roles for GPCR/GPCR-associated proteins and kinases in T-cell migration and provides potential novel targets for modulation of the T-cell immune response.

A multidimensional recommendation framework for identifying biological targets to aid the diagnosis and treatment of liver metastasis in patients with colorectal cancer

The quest to understand the molecular mechanisms of tumour metastasis and identify pivotal biomarkers for cancer therapy is increasing in importance. Single-omics analyses, constrained by their focus on a single biological layer, cannot fully elucidate the complexities of tumour molecular profiles and can thus overlook crucial molecular targets. In response to this limitation, we developed a multiobjective recommendation system (RJH-Metastasis 1.0) anchored in a multiomics knowledge graph to integrate genome, transcriptome, and proteome data and corroborative literature evidence and then conducted comprehensive analyses of colorectal cancer with liver metastasis (CRCLM). A total of 25 key genes significantly associated with CRCLM were recommended by our system, and GNB1, GATAD2A, GBP2, MACROD1, and EIF5B were further highlighted. Specifically, GNB1 presented fewer mutations but elevated RNA transcription and protein expression in CRCLM patients. The role of GNB1 in promoting the malignant behaviours of colon cancer cells was demonstrated via in vitro and in vivo studies. Aberrant expression of GNB1 could be regulated by METTL1-driven m7G modification. METTL1 knockdown decreased m7G modification in the 3' UTR of GNB1, increasing its mRNA transcription and translation during liver metastasis. Furthermore, GNB1 induced the formation of an immunosuppressive microenvironment by promoting the CLEC2C-KLRB1 interaction between memory B cells and KLRB1+PD-1+CD8+ cells. GNB1 expression and the efficacy of PD-1 antibody-based treatment in CRCLM patients were significantly correlated. In summary, our recommendation system can be used for effective exploration of key molecules in colorectal cancer, among which GNB1 was identified as a critical CRCLM promoter and immunotherapy biomarker in colorectal cancer patients.

IL-13 and IL-17A activate β1 integrin through an NF-kB/Rho kinase/PIP5K1γ pathway to enhance force transmission in airway smooth muscle

Integrin activation resulting in enhanced adhesion to the extracellular matrix plays a key role in fundamental cellular processes. Although integrin activation has been extensively studied in circulating cells such as leukocytes and platelets, much less is known about the regulation and functional impact of integrin activation in adherent cells such as smooth muscle. Here, we show that two different asthmagenic cytokines, IL-13 and IL-17A, activate type I and IL-17 cytokine receptor families, respectively, to enhance adhesion of airway smooth muscle. These cytokines also induce activation of β1 integrins detected by the conformation-specific antibody HUTS-4. Moreover, HUTS-4 binding is increased in the smooth muscle of patients with asthma compared to nonsmokers without lung disease, suggesting a disease-relevant role for integrin activation in smooth muscle. Indeed, integrin activation induced by the β1-activating antibody TS2/16, the divalent cation manganese, or the synthetic peptide β1-CHAMP that forces an extended-open integrin conformation dramatically enhances force transmission in smooth muscle cells and airway rings even in the absence of cytokines. We demonstrate that cytokine-induced activation of β1 integrins is regulated by a common pathway of NF-κB-mediated induction of RhoA and its effector Rho kinase, which in turn stimulates PIP5K1γ-mediated synthesis of PIP2 at focal adhesions, resulting in β1 integrin activation. Taken together, these data identify a pathway by which type I and IL-17 cytokine receptor family stimulation induces functionally relevant β1 integrin activation in adherent smooth muscle and help to explain the exaggerated force transmission that characterizes chronic airway diseases such as asthma.

IL-13 and IL-17A Activate β1 Integrin through an NF-kB/Rho kinase/PIP5K1γ pathway to Enhance Force Transmission in Airway Smooth Muscle

Integrin activation resulting in enhanced adhesion to the extracellular matrix plays a key role in fundamental cellular processes. Although G-protein coupled receptor-mediated integrin activation has been extensively studied in non-adherent migratory cells such as leukocytes and platelets, much less is known about the regulation and functional impact of integrin activation in adherent stationary cells such as airway smooth muscle. Here we show that two different asthmagenic cytokines, IL-13 and IL-17A, activate type I and IL-17 cytokine receptor families respectively, to enhance adhesion of muscle to the matrix. These cytokines also induce activation of β1 integrins as detected by the conformation-specific antibody HUTS-4. Moreover, HUTS-4 binding is significantly increased in the smooth muscle of patients with asthma compared to healthy controls, suggesting a disease-relevant role for aberrant integrin activation. Indeed, we find integrin activation induced by a β1 activating antibody, the divalent cation manganese, or the synthetic peptide β1-CHAMP, dramatically enhances force transmission in collagen gels, mouse tracheal rings, and human bronchial rings even in the absence of cytokines. We further demonstrate that cytokine-induced activation of β1 integrins is regulated by a common pathway of NF-κB-mediated induction of RhoA and its effector Rho kinase, which in turn stimulates PIP5K1γ-mediated synthesis of PIP2 resulting in β1 integrin activation. Taken together, these data identify a previously unknown pathway by which type I and IL-17 cytokine receptor family stimulation induces functionally relevant β1 integrin activation in adherent smooth muscle and help explain the exaggerated force transmission that characterizes chronic airways diseases such as asthma.

Nexinhib20 Inhibits Neutrophil Adhesion and β2 Integrin Activation by Antagonizing Rac-1-Guanosine 5'-Triphosphate Interaction

Neutrophils are critical for mediating inflammatory responses. Inhibiting neutrophil recruitment is an attractive approach for preventing inflammatory injuries, including myocardial ischemia-reperfusion (I/R) injury, which exacerbates cardiomyocyte death after primary percutaneous coronary intervention in acute myocardial infarction. In this study, we found out that a neutrophil exocytosis inhibitor Nexinhib20 inhibits not only exocytosis but also neutrophil adhesion by limiting β2 integrin activation. Using a microfluidic chamber, we found that Nexinhib20 inhibited IL-8-induced β2 integrin-dependent human neutrophil adhesion under flow. Using a dynamic flow cytometry assay, we discovered that Nexinhib20 suppresses intracellular calcium flux and β2 integrin activation after IL-8 stimulation. Western blots of Ras-related C3 botulinum toxin substrate 1 (Rac-1)-GTP pull-down assays confirmed that Nexinhib20 inhibited Rac-1 activation in leukocytes. An in vitro competition assay showed that Nexinhib20 antagonized the binding of Rac-1 and GTP. Using a mouse model of myocardial I/R injury, Nexinhib20 administration after ischemia and before reperfusion significantly decreased neutrophil recruitment and infarct size. Our results highlight the translational potential of Nexinhib20 as a dual-functional neutrophil inhibitory drug to prevent myocardial I/R injury.

Genome-scale CRISPR screening reveals that C3aR signaling is critical for rapid capture of fungi by macrophages

The fungal pathogen Histoplasma capsulatum (Hc) invades, replicates within, and destroys macrophages. To interrogate the molecular mechanisms underlying this interaction, we conducted a host-directed CRISPR-Cas9 screen and identified 361 genes that modify macrophage susceptibility to Hc infection, greatly expanding our understanding of host gene networks targeted by Hc. We identified pathways that have not been previously implicated in Hc interaction with macrophages, including the ragulator complex (involved in nutrient stress sensing), glycosylation enzymes, protein degradation machinery, mitochondrial respiration genes, solute transporters, and the ER membrane complex (EMC). The highest scoring protective hits included the complement C3a receptor (C3aR), a G-protein coupled receptor (GPCR) that recognizes the complement fragment C3a. Although it is known that complement components react with the fungal surface, leading to opsonization and release of small peptide fragments such as C3a, a role for C3aR in macrophage interactions with fungi has not been elucidated. We demonstrated that whereas C3aR is dispensable for macrophage phagocytosis of bacteria and latex beads, it is critical for optimal macrophage capture of pathogenic fungi, including Hc, the ubiquitous fungal pathogen Candida albicans, and the causative agent of Valley Fever Coccidioides posadasii. We showed that C3aR localizes to the early phagosome during Hc infection where it coordinates the formation of actin-rich membrane protrusions that promote Hc capture. We also showed that the EMC promotes surface expression of C3aR, likely explaining its identification in our screen. Taken together, our results provide new insight into host processes that affect Hc-macrophage interactions and uncover a novel and specific role for C3aR in macrophage recognition of fungi.

Polymorphonuclear neutrophil activation by Src phosphorylation contributes to HLA-A2 antibody-induced transfusion-related acute lung injury

Human leukocyte antigen (HLA)-A2 antibody contributes to the pathogenesis of transfusion-related acute lung injury (TRALI) via polymorphonuclear neutrophil (PMN) activation, but the signaling pathways involved this process remain largely undefined. In this study, we sought to study the signaling pathways involved in the pathogenesis of HLA-A2-induced TRALI. Lipopolysaccharide (LPS), and the plasma from the HLA-A2 antibody-positive donors were utilized to establish a rat model of TRALI. Human pulmonary endothelial cells (HPMECs) were in vitro co-cultured with HLA-A2 antibody-treated PMNs and then treated with LPS to induce a cytotoxicity model. The effects of HLA-A2 antibody on HPMEC injury were evaluated in this model. Besides, dasatinib was used to block the Src phosphorylation to explore whether Src involved in the TRALI or HPMEC injury induced by HLA-A2 antibody. The HLA-A2 antibody plus LPS induced TRALI and stimulated PMN activation in rats. HLA-A2 antibody-induced TRALI could be attenuated via depletion of PMN. HLA-A2 antibody activated NF-κB and NLRP3 inflammasome. In addition, HLA-A2 antibody aggravated the HPMEC injuries and the release of PMN surfaces makers, but dasatinib treatment reversed this effect, indicating that HLA-A2 antibody activated PMNs and exacerbated TRALI by stimulating phosphorylation of Src followed by activation of NF-κB and NLRP3 inflammasome, which was validated in vivo. In summary, HLA-A2 induced PMNs by activating NF-κB/NLRP3 inflammasome via phosphorylated-Src elevation, thereby exacerbating TRALI. This study highlights promising target for the treatment of antibody-mediated TRALI.

Neutrophils in acute inflammation: current concepts and translational implications

Modulation of neutrophil recruitment and function is crucial for targeting inflammatory cells to sites of infection to combat invading pathogens while, at the same time, limiting host tissue injury or autoimmunity. The underlying mechanisms regulating recruitment of neutrophils, 1 of the most abundant inflammatory cells, have gained increasing interest over the years. The previously described classical recruitment cascade of leukocytes has been extended to include capturing, rolling, adhesion, crawling, and transmigration, as well as a reverse-transmigration step that is crucial for balancing immune defense and control of remote organ endothelial leakage. Current developments in the field emphasize the importance of cellular interplay, tissue environmental cues, circadian rhythmicity, detection of neutrophil phenotypes, differential chemokine sensing, and contribution of distinct signaling components to receptor activation and integrin conformations. The use of therapeutics modulating neutrophil activation responses, as well as mutations causing dysfunctional neutrophil receptors and impaired signaling cascades, have been defined in translational animal models. Human correlates of such mutations result in increased susceptibility to infections or organ damage. This review focuses on current advances in the understanding of the regulation of neutrophil recruitment and functionality and translational implications of current discoveries in the field with a focus on acute inflammation and sepsis.

Decoding the signaling profile of hematopoietic progenitor kinase 1 (HPK1) in innate immunity: a proteomic approach

Signaling via β₂ integrins (CD11/CD18) as well as T and B cell receptors involves similar pathways. However, the activation of the same signaling molecule can result in opposing effects. One such example is the hematopoietic progenitor kinase 1 (HPK1), which negatively regulates T and B cell activation but enforces neutrophil adhesion via β₂ integrins. This difference may be defined by specific HPK1 interacting networks in different leukocyte subsets which have already been described in the adaptive immune system. Here, we set out to identify interacting proteins of HPK1 in neutrophil-like differentiated HL-60 cells exposed to immobilized fibrinogen and left non-activated or Mn²⁺ -activated to allow β₂ integrin-dependent adhesion. Co-immunoprecipitation experiments followed by mass spectrometry led to the identification of 115 HPK1-interacting proteins. 58 proteins were found only in non-activated cells and 39 proteins only in Mn²⁺ -activated adherent cells. From these results we decoded a pre-existing signaling cluster of HPK1 in non-activated cells encompassing proteins essential for β₂ integrin-mediated signaling during neutrophil trafficking, namely DNAX-activation protein 12 (DAP12), spleen tyrosine kinase (Syk) and Rac1. Thus, our study provides novel insights into the complex architecture of the signaling processes during neutrophil activation and the complex signaling profile of HPK1 in leukocytes. This article is protected by copyright. All rights reserved.

Immune microenvironment-related gene mapping predicts immunochemotherapy response and prognosis in diffuse large B-cell lymphoma

Diffuse large B-cell lymphoma (DLBCL) is the most common subtype of non-Hodgkin's lymphoma (NHL). The R-CHOP immunochemotherapy regimen is the first-line treatment option for DLBCL patients and has greatly improved the prognosis of DLBCL, making it a curable disease. However, drug resistance or relapse is the main challenge for current DLBCL treatment. Studies have shown that the tumor microenvironment plays an important role in the onset, development, and responsiveness to drugs in DLBCL. Here, we used the CIBERSORT algorithm to resolve the composition of the immune microenvironment of 471 DLBCL patients from the GEO database. We found that activated memory CD4+ T cells and γδ T cells were significantly associated with immunochemotherapy response. Weighted gene co-expression networks (WGCNA) were constructed using differentially expressed genes from immunochemotherapy responders and non-responders. The module most associated with these two types of T cells was defined as hub module. Enrichment analysis of the hub module showed that baseline immune status was significantly stronger in responders than in non-responders. A protein-protein interaction (PPI) network was constructed for hub module to identify hub genes. After survival analysis, five prognosis-related genes (CD3G, CD3D, GNB4, FCHO2, GPR183) were identified and all these genes were significantly negatively associated with PD1. Using our own patient cohort, we validated the efficacy of CD3G and CD3D in predicting immunochemotherapy response. Our study showed that CD3G, CD3D, GNB4, FCHO2, and GPR183 are involved in the regulation of the immune microenvironment of DLBCL. They can be used as biomarkers for predicting immunochemotherapy response and potential therapeutic targets in DLBCL.

TAS2R16 Activation Suppresses LPS-Induced Cytokine Expression in Human Gingival Fibroblasts

Sustained and non-resolved inflammation is a characteristic of periodontitis. Upon acute inflammation, gingival fibroblasts release cytokines to recruit immune cells to counter environmental stimuli. The intricate regulation of pro-inflammatory signaling pathways, such as NF-κB, is necessary to maintain periodontal homeostasis. Nonetheless, how inflammation is resolved has not yet been elucidated. In this study, 22 subtypes of taste receptor family 2 (TAS2Rs), as well as the downstream machineries of Gα-gustducin and phospholipase C-β2 (PLCβ2), were identified in human gingival fibroblasts (HGFs). Various bitter agonists could induce an intensive cytosolic Ca²⁺ response in HGFs. More importantly, TAS2R16 was expressed at a relatively high level, and its agonist, salicin, showed robust Ca²⁺ evocative effects in HGFs. Activation of TAS2R16 signaling by salicin inhibited the release of lipopolysaccharide (LPS)-induced pro-inflammatory cytokines, at least in part, by repressing LPS-induced intracellular cAMP elevation and NF-κB p65 nuclear translocation in HGFs. These findings indicate that TAS2Rs activation in HGFs may mediate endogenous pro-inflammation resolution by antagonizing NF-κB signaling, providing a novel paradigm and treatment target for the better management of periodontitis.

The CC and CXC chemokine receptors in turbot (Scophthalmus maximus L.) and their response to Aeromonas salmonicida infection

Chemokines are crucial regulators of cell mobilization for development, homeostasis, and immunity. Chemokines signal through binding to chemokine receptors, a superfamily of seven-transmembrane domain G-coupled receptors. In the present study, eleven CC chemokine receptors (CCRs) and seven CXC chemokine receptors (CXCRs) were identified from turbot genome. Phylogenetic and syntenic analyses were performed to annotate these genes, indicating the closest relationship between the turbot chemokine receptors and their counterparts of Japanese flounders (Paralichthys olivaceus). Evolutionary analyses revealed that the tandem duplications of CCR8 and CXCR3, the whole genome duplications of CCR6, CCR9, CCR12, and CXCR4, and the teleost-specific CCR12 led to the expansion of turbot chemokine receptors. In addition, turbot chemokine receptors were ubiquitously expressed in nine examined healthy tissues, with high expression levels observed in spleen, gill, and head kidney. Moreover, most turbot chemokine receptors were significantly differentially expressed in spleen and gill after Aeromonas salmonicida infection, and exhibited general down-regulations at early time points and then gradually up-regulated. Finally, protein-protein interaction network (PPI) analyses indicated that chemokine receptors interacted with a few immune-related genes such as interleukins, Grk genes, CD genes, etc. These results should be valuable for comparative immunological studies and provide insights for further functional characterization of chemokine receptors in turbots.

Mitofusin-2 regulates leukocyte adhesion and β2 integrin activation

Neutrophils are critical for inflammation and innate immunity, and their adhesion to vascular endothelium is a crucial step in neutrophil recruitment. Mitofusin-2 (MFN2) is required for neutrophil adhesion, but molecular details are unclear. Here, we demonstrated that β₂ -integrin-mediated slow-rolling and arrest, but not PSGL-1-mediated cell rolling, are defective in MFN2-deficient neutrophil-like HL60 cells. This adhesion defect is associated with reduced expression of fMLP (N-formylmethionyl-leucyl-phenylalanine) receptor FPR1 as well as the inhibited β₂ integrin activation, as assessed by conformation-specific monoclonal antibodies. MFN2 deficiency also leads to decreased actin polymerization, which is important for β2 integrin activation. Mn²⁺ -induced cell spreading is also inhibited after MFN2 knockdown. MFN2 deficiency limited the maturation of β2 integrin activation during the neutrophil-directed differentiation of HL60 cells, which is indicated by CD35 and CD87 markers. MFN2 knockdown in β2-integrin activation-matured cells (CD87^high population) also inhibits integrin activation, indicating that MFN2 directly affects β2 integrin activation. Our study illustrates the function of MFN2 in leukocyte adhesion and may provide new insights into the development and treatment of MFN2 deficiency-related diseases.

β2 integrin activation and signal transduction in leukocyte recruitment

Leukocyte recruitment is a critical step in the pathogenesis of inflammatory and immunological responses. Cell adhesion molecules (CAMs) are involved in controlling cell movements and the recruitment process, and the integrin family of CAMs plays a key role. During cell movement, integrin function is dynamically and precisely regulated. However, this balance might be broken under pathological conditions. Thus, the functional regulation and molecular mechanisms of integrins related to diseases are often a focus of research. Integrin β2 is one of the most commonly expressed integrins in leukocytes that mediate leukocyte adhesion and migration, and it plays an important role in immune responses and inflammation. In this review, we focus on specific functions of integrin β2 in leukocyte recruitment, the conformational changes and signal transduction of integrin β2 activation, the similarities between murine and human factors, and how new insights into these processes can inform future therapies for inflammation and immune diseases.

Full spectrum of clonal haematopoiesis-driver mutations in chronic heart failure and their associations with mortality

Aims

Somatic mutations in haematopoietic stem cells can lead to the clonal expansion of mutated blood cells, known as clonal haematopoiesis (CH). Mutations in the most prevalent driver genes DNMT3A and TET2 with a variant allele frequency (VAF) ≥ 2% have been associated with atherosclerosis and chronic heart failure of ischemic origin (CHF). However, the effects of mutations in other driver genes for CH with low VAF (<2%) on CHF are still unknown.

Methods and results

Therefore, we analysed mononuclear bone marrow and blood cells from 399 CHF patients by deep error‐corrected targeted sequencing of 56 genes and associated mutations with the long‐term mortality in these patients (3.95 years median follow‐up). We detected 1113 mutations with a VAF ≥ 0.5% in 347 of 399 patients, and only 13% had no detectable CH. Despite a high prevalence of mutations in the most frequently mutated genes DNMT3A (165 patients) and TET2 (107 patients), mutations in CBL, CEBPA, EZH2, GNB1, PHF6, SMC1A, and SRSF2 were associated with increased death compared with the average death rate of all patients. To avoid confounding effects, we excluded patients with DNMT3A‐related, TET2‐related, and other clonal haematopoiesis of indeterminate potential (CHIP)‐related mutations with a VAF ≥ 2% for further analyses. Kaplan–Meier survival analyses revealed a significantly higher mortality in patients with mutations in either of the seven genes (53 patients), combined as the CH‐risk gene set for CHF. Baseline patient characteristics showed no significant differences in any parameter including patient age, confounding diseases, severity of CHF, or blood cell parameters except for a reduced number of platelets in patients with mutations in the risk gene set in comparison with patients without. However, carrying a mutation in any of the risk genes remained significant after multivariate cox regression analysis (hazard ratio, 3.1; 95% confidence interval, 1.8–5.4; P < 0.001), whereas platelet numbers did not.

Conclusions

Somatic mutations with low VAF in a distinct set of genes, namely, in CBL, CEBPA, EZH2, GNB1, PHF6, SMC1A, and SRSF2, are significantly associated with mortality in CHF, independently of the most prevalent CHIP‐mutations in DNMT3A and TET2. Mutations in these genes are prevalent in young CHF patients and comprise an independent risk factor for the outcome of CHF, potentially providing a novel tool for risk assessment in CHF.

Natural Killer Cell Integrins and Their Functions in Tissue Residency

Integrins are transmembrane receptors associated with adhesion and migration and are often highly differentially expressed receptors amongst natural killer cell subsets in microenvironments. Tissue resident natural killer cells are frequently defined by their differential integrin expression compared to other NK cell subsets, and integrins can further localize tissue resident NK cells to tissue microenvironments. As such, integrins play important roles in both the phenotypic and functional identity of NK cell subsets. Here we review the expression of integrin subtypes on NK cells and NK cell subsets with the goal of better understanding how integrin selection can dictate tissue residency and mediate function from the nanoscale to the tissue environment.

ArhGAP15, a RacGAP, Acts as a Temporal Signaling Regulator of Mac-1 Affinity in Sterile Inflammation

During inflammation, leukocyte recruitment has to be tightly controlled to prevent overwhelming leukocyte infiltration, activation, and, consequently, organ damage. A central regulator of leukocyte recruitment is Rac1. In this study, we analyzed the effects of the RacGAP ArhGAP15 on leukocyte recruitment. Using ArhGAP15-deficient mice, reduced neutrophil adhesion and transmigration in the TNF-α-inflamed cremaster muscle and a prolongation of chemokine-dependent leukocyte adhesion could be observed. In a murine model of sterile kidney injury, reduced neutrophil infiltration, and serum creatinine levels were apparent. Further in vitro and in vivo analyses revealed a defective intravascular crawling capacity, resulting from increased affinity of the β₂-integrin Mac-1 after prolonged chemokine stimulation of neutrophils. LFA-1 activity regulation was not affected. Summarizing, ArhGAP15 specifically regulates Mac-1, but not LFA-1, and affects leukocyte recruitment by controlling postadhesion strengthening and intravascular crawling in a Mac-1-dependent manner. In conclusion, ArhGAP15 is involved in the time-dependent regulation of leukocyte postadhesion in sterile inflammation.

β2 Integrins-Multi-Functional Leukocyte Receptors in Health and Disease

β2 integrins are heterodimeric surface receptors composed of a variable α (CD11a-CD11d) and a constant β (CD18) subunit and are specifically expressed by leukocytes. The α subunit defines the individual functional properties of the corresponding β2 integrin, but all β2 integrins show functional overlap. They mediate adhesion to other cells and to components of the extracellular matrix (ECM), orchestrate uptake of extracellular material like complement-opsonized pathogens, control cytoskeletal organization, and modulate cell signaling. This review aims to delineate the tremendous role of β2 integrins for immune functions as exemplified by the phenotype of LAD-I (leukocyte adhesion deficiency 1) patients that suffer from strong recurrent infections. These immune defects have been largely attributed to impaired migratory and phagocytic properties of polymorphonuclear granulocytes. The molecular base for this inherited disease is a functional impairment of β2 integrins due to mutations within the CD18 gene. LAD-I patients are also predisposed for autoimmune diseases. In agreement, polymorphisms within the CD11b gene have been associated with autoimmunity. Consequently, β2 integrins have received growing interest as targets in the treatment of autoimmune diseases. Moreover, β2 integrin activity on leukocytes has been implicated in tumor development.

Intravascular adhesion and recruitment of neutrophils in response to CXCL1 depends on their TRPC6 channels

Abstract

Here we report a novel role for TRPC6, a member of the transient receptor potential (TRPC) channel family, in the CXCL1-dependent recruitment of murine neutrophil granulocytes. Representing a central element of the innate immune system, neutrophils are recruited from the blood stream to a site of inflammation. The recruitment process follows a well-defined sequence of events including adhesion to the blood vessel walls, migration, and chemotaxis to reach the inflammatory focus. A common feature of the underlying signaling pathways is the utilization of Ca²⁺ ions as intracellular second messengers. However, the required Ca²⁺ influx channels are not yet fully characterized. We used WT and TRPC6^−/− neutrophils for in vitro and TRPC6^−/− chimeric mice (WT mice with WT or TRPC6^−/− bone marrow cells) for in vivo studies. After renal ischemia and reperfusion injury, TRPC6^−/− chimeric mice had an attenuated TRPC6^−/− neutrophil recruitment and a better outcome as judged from the reduced increase in the plasma creatinine concentration. In the cremaster model CXCL1-induced neutrophil adhesion, arrest and transmigration were also decreased in chimeric mice with TRPC6^−/− neutrophils. Using atomic force microscopy and microfluidics, we could attribute the recruitment defect of TRPC6^−/− neutrophils to the impact of the channel on adhesion to endothelial cells. Mechanistically, TRPC6^−/− neutrophils exhibited lower Ca²⁺ transients during the initial adhesion leading to diminished Rap1 and β₂ integrin activation and thereby reduced ICAM-1 binding. In summary, our study reveals that TRPC6 channels in neutrophils are crucial signaling modules in their recruitment from the blood stream in response to CXCL1.

Key point

Neutrophil TRPC6 channels are crucial for CXCL1-triggered activation of integrins during the initial steps of neutrophil recruitment.

Blood flow guides sequential support of neutrophil arrest and diapedesis by PILR-β1 and PILR-α

Arrest of rapidly flowing neutrophils in venules relies on capturing through selectins and chemokine-induced integrin activation. Despite a long-established concept, we show here that gene inactivation of activating paired immunoglobulin-like receptor (PILR)-β1 nearly halved the efficiency of neutrophil arrest in venules of the mouse cremaster muscle. We found that this receptor binds to CD99, an interaction which relies on flow-induced shear forces and boosts chemokine-induced β₂-integrin-activation, leading to neutrophil attachment to endothelium. Upon arrest, binding of PILR-β1 to CD99 ceases, shifting the signaling balance towards inhibitory PILR-α. This enables integrin deactivation and supports cell migration. Thus, flow-driven shear forces guide sequential signaling of first activating PILR-β1 followed by inhibitory PILR-α to prompt neutrophil arrest and then transmigration. This doubles the efficiency of selectin-chemokine driven neutrophil arrest by PILR-β1 and then supports transition to migration by PILR-α.

DDX3 Participates in Translational Control of Inflammation Induced by Infections and Injuries

Recent studies have suggested that DDX3 functions in antiviral innate immunity, but the underlying mechanism remains elusive. We previously identified target mRNAs whose translation is controlled by DDX3. Pathway enrichment analysis of these targets indicated that DDX3 is involved in various infections and inflammation. Using immunoblotting, we confirmed that PACT, STAT1, GNB2, Rac1, TAK1, and p38 mitogen-activated protein kinase (MAPK) proteins are downregulated by DDX3 knockdown in human monocytic THP-1 cells and epithelial HeLa cells. Polysome profiling revealed that DDX3 knockdown reduces the translational efficiency of target mRNAs. We further demonstrated DDX3-mediated translational control of target mRNAs by luciferase reporter assays. To examine the effects of DDX3 knockdown on macrophage migration and phagocytosis, we performed in vitro cell migration assay and flow cytometry analysis of the uptake of green fluorescent protein-expressing Escherichia coli in THP-1 cells. The DDX3 knockdown cells exhibited impaired macrophage migration and phagocytosis. Moreover, we used a human cytokine antibody array to identify the cytokines affected by DDX3 knockdown. Several chemokines were decreased considerably in DDX3 knockdown THP-1 cells after lipopolysaccharide or poly(I·C) stimulation. Lastly, we demonstrated that DDX3 is crucial for the recruitment of phagocytes to the site of inflammation in transgenic zebrafish.

STAT3 Cooperates With Phospholipid Scramblase 2 to Suppress Type I Interferon Response

Type I interferon (IFN-I) is a pluripotent cytokine that modulates innate and adaptive immunity. We have previously shown that STAT3 suppresses IFN-I response in a manner dependent on its N-terminal domain (NTD), but independent of its DNA-binding and transactivation ability. Using the yeast two-hybrid system, we have identified phospholipid scramblase 2 (PLSCR2) as a STAT3 NTD-binding partner and a suppressor of IFN-I response. Overexpression of PLSCR2 attenuates ISRE-driven reporter activity, which is further aggravated by co-expression of STAT3. Moreover, PLSCR2 deficiency enhances IFN-I-induced gene expression and antiviral activity without affecting the activation or nuclear translocation of STAT1 and STAT2 or the assembly of ISGF3 complex. Instead, PLSCR2 impedes promoter occupancy by ISGF3, an effect further intensified by the presence of STAT3. Moreover, palmitoylation of PLSCR2 is required for its binding to STAT3 and for this suppressive activity. In addition to STAT3, PLSCR2 also interacts with STAT2, which facilitates the suppressive effect on ISGF3-mediated transcriptional activity. Together, these results define the role of a novel STAT3–PLSCR2 axis in fine-tuning IFN-I response.

A suppressive role of guanine nucleotide-binding protein subunit beta-4 inhibited by DNA methylation in the growth of anti-estrogen resistant breast cancer cells

BACKGROUND

Breast cancer is the most common malignancy in women worldwide. Although the endocrine therapy that targets estrogen receptor α (ERα) signaling has been well established as an effective adjuvant treatment for patients with ERα-positive breast cancers, long-term exposure may eventually lead to the development of acquired resistance to the anti-estrogen drugs, such as fulvestrant and tamoxifen. A better understanding of the mechanisms underlying antiestrogen resistance and identification of the key molecules involved may help in overcoming antiestrogen resistance in breast cancer.

METHODS

The whole-genome gene expression and DNA methylation profilings were performed using fulvestrant-resistant cell line 182R-6 and tamoxifen-resistant cell line TAMR-1 as a model system. In addition, qRT-PCR and Western blot analysis were performed to determine the levels of mRNA and protein molecules. MTT, apoptosis and cell cycle analyses were performed to examine the effect of either guanine nucleotide-binding protein beta-4 (GNB4) overexpression or knockdown on cell proliferation, apoptosis and cell cycle.

RESULTS

Among 9 candidate genes, GNB4 was identified and validated by qRT-PCR as a potential target silenced by DNA methylation via DNA methyltransferase 3B (DNMT3B). We generated stable 182R-6 and TAMR-1 cell lines that are constantly expressing GNB4 and determined the effect of the ectopic GNB4 on cell proliferation, cell cycle, and apoptosis of the antiestrogen-resistant cells in response to either fulvestrant or tamoxifen. Ectopic expression of GNB4 in two antiestrogen resistant cell lines significantly promoted cell growth and shortened cell cycle in the presence of either fulvestrant or tamoxifen. The ectopic GNB4 induced apoptosis in 182R-6 cells, whereas it inhibited apoptosis in TAMR-1 cells. Many regulators controlling cell cycle and apoptosis were aberrantly expressed in two resistant cell lines in response to the enforced GNB4 expression, which may contribute to GNB4-mediated biologic and/or pathologic processes. Furthermore, knockdown of GNB4 decreased growth of both antiestrogen resistant and sensitive breast cancer cells.

CONCLUSION

GNB4 is important for growth of breast cancer cells and a potential target for treatment.

Splice-Aware Multiple Sequence Alignment of Protein Isoforms

Multiple sequence alignment (MSA) is a classic problem in computational genomics. In typical use, MSA software is expected to align a collection of homologous genes, such as orthologs from multiple species or duplication-induced paralogs within a species. Recent focus on the importance of alternatively-spliced isoforms in disease and cell biology has highlighted the need to create MSAs that more effectively accommodate isoforms. MSAs are traditionally constructed using scoring criteria that prefer alignments with occasional mismatches over alignments with long gaps. Alternatively spliced protein isoforms effectively contain exon-length insertions or deletions (indels) relative to each other, and demand an alternative approach. Some improvements can be achieved by making indel penalties much smaller, but this is merely a patchwork solution. In this work we present Mirage, a novel MSA software package for the alignment of alternatively spliced protein isoforms. Mirage aligns isoforms to each other by first mapping each protein sequence to its encoding genomic sequence, and then aligning isoforms to one another based on the relative genomic coordinates of their constitutive codons. Mirage is highly effective at mapping proteins back to their encoding exons, and these protein-genome mappings lead to extremely accurate intra-species alignments; splice site information in these alignments is used to improve the accuracy of inter-species alignments of isoforms. Mirage alignments have also revealed the ubiquity of dual-coding exons, in which an exon conditionally encodes multiple open reading frames as overlapping spliced segments of frame-shifted genomic sequence.

Mechanochemical modeling of neutrophil migration based on four signaling layers, integrin dynamics, and substrate stiffness

Directional neutrophil migration during human immune responses is a highly coordinated process regulated by both biochemical and biomechanical environments. In this paper, we developed an integrative mathematical model of neutrophil migration using a lattice Boltzmann-particle method built in-house to solve the moving boundary problem with spatiotemporal regulation of biochemical components. The mechanical features of the cell cortex are modeled by a series of spring-connected nodes representing discrete cell-substrate adhesive sites. The intracellular signaling cascades responsible for cytoskeletal remodeling [e.g., small GTPases, phosphoinositide-3-kinase (PI3K), and phosphatase and tensin homolog] are built based on our previous four-layered signaling model centered on the bidirectional molecular transport mechanism and implemented as reaction-diffusion equations. Focal adhesion dynamics are determined by force-dependent integrin-ligand binding kinetics and integrin recycling and are thus integrated with cell motion. Using numerical simulations, the model reproduces the major features of cell migration in response to uniform and gradient biochemical stimuli based on the quantitative spatiotemporal regulation of signaling molecules, which agree with experimental observations. The existence of multiple types of integrins with different binding kinetics could act as an adaptation mechanism for substrate stiffness. Moreover, cells can perform reversal, U-turn, or lock-on behaviors depending on the steepness of the reversal biochemical signals received. Finally, this model is also applied to predict the responses of mutants in which PTEN is overexpressed or disrupted.

The ITIM Domain-Containing NK Receptor Ly49Q Impacts Pulmonary Infection by Mediating Neutrophil Functions

Pulmonary infection is a frequent pathology associated with excessive neutrophil infiltration. Ly49Q, an ITIM domain-bearing receptor expressed on different leukocytes, has been recently reported to impact neutrophil migration and polarization. Utilizing a murine model of Klebsiella pneumoniae-induced pulmonary infection in combination with additional in vivo and in vitro assays, we show that Ly49Q is critically involved in different steps of the leukocyte adhesion cascade. Ly49Q deficiency is associated with a reduced rolling velocity, impaired crawling capacity, and diminished transmigration. We show that overactivation of the neutrophil β₂ integrins Mac-1 and LFA-1 is responsible for increased adhesion and reduced neutrophil transmigration, resulting in a strongly impaired immune defense against pulmonary infection. Structure function analysis in vitro and in vivo demonstrated that different domains of Ly49Q are important for its function. In summary, Ly49Q regulates integrin activation and neutrophil recruitment and is required for an adequate immune response in pulmonary infection.

Gβ1 is required for neutrophil migration in zebrafish

Signaling mediated by G protein-coupled receptors (GPCRs) is essential for the migration of cells toward chemoattractants. The recruitment of neutrophils to injured tissues in zebrafish larvae is a useful model for studying neutrophil migration and trafficking in vivo. Indeed, the study of this process led to the discovery that PI3Kγ is required for the polarity and motility of neutrophils, features that are necessary for the directed migration of these cells to wounds. However, the mechanism by which PI3Kγ is activated remains to be determined. Here we show that signaling by specifically the heterotrimeric G protein subunit Gβ1 is critical for neutrophil migration in response to wounding. In embryos treated with small-molecule inhibitors of Gβγ signaling, neutrophils failed to migrate to wound sites. Although both the Gβ1 and Gβ4 isoforms are expressed in migrating neutrophils, only deficiency for the former (morpholino-based knockdown) interfered with the directed migration of neutrophils towards wounds. The Gβ1 deficiency also impaired the ability of cells to change cell shape and reduced their general motility, defects that are similar to those in neutrophils deficient for PI3Kγ. Transplantation assays showed that the requirement for Gβ1 in neutrophil migration is cell autonomous. Finally, live imaging revealed that Gβ1 is required for polarized activation of PI3K, and for the actin dynamics that enable neutrophil migration. Collectively, our data indicate that Gβ1 signaling controls proper neutrophil migration by activating PI3K and modulating actin dynamics. Moreover, they illustrate a role for a specific Gβ isoform in chemotaxis in vivo.

Leukocyte arrest: Biomechanics and molecular mechanisms of β2 integrin activation

Integrins are a group of heterodimeric transmembrane receptors that play essential roles in cell-cell and cell-matrix interaction. Integrins are important in many physiological processes and diseases. Integrins acquire affinity to their ligand by undergoing molecular conformational changes called activation. Here we review the molecular biomechanics during conformational changes of integrins, integrin functions in leukocyte biorheology (adhesive functions during rolling and arrest) and molecules involved in integrin activation.