Dual Phosphorylation of Phosphoinositide 3-Kinase Adaptor Grb2-Associated Binder 2 Is Responsible for Superoxide Formation Synergistically Stimulated by Fcγ and Formyl-Methionyl-Leucyl-Phenylalanine Receptors in Differentiated THP-1 Cells

Outer membrane vesicles from X-ray-irradiated Pseudomonas aeruginosa alleviate lung injury caused by P. aeruginosa infection-mediated sepsis

Pseudomonas aeruginosa infection causes pneumonia and sepsis. Previous research found that X-ray radiation can induce P. aeruginosa to release outer membrane vesicles (OMVs) of relatively consistent sizes. This study found that OMVs derived from X-ray-irradiated P. aeruginosa can significantly inhibit lung leakage, inflammatory cell infiltrating into lung, and the production of pro-inflammatory cytokines, IL-1β and TNFα caused by P. aeruginosa infection under preventive and therapeutic administration conditions. Under the same conditions, OMVs also significantly alleviated pathological characteristics of lung injury, including pulmonary edema, pulmonary hemorrhage, and alveolar wall thickening. OMVs also significantly reduced bacterial burdens in peritoneal cavity, accompanied by a reduction in the number of viable bacteria capable of forming bacterial colonies. Pretreating macrophages and neutrophils with OMVs enhances their bactericidal ability. When bacteria were cocultured with treated cells, the number of viable bacteria capable of forming bacterial colonies was significantly reduced. OMVs themselves have not been shown to cause any lung injury or affect bacterial viability. Therefore, OMVs derived from X-ray-irradiated P. aeruginosa may not only be applied in prevention and treatment of diseases associated with P. aeruginosa infection, but also served as an excellent vaccine development platform.

Saikosaponin a contributed to CCIN treatment by promoting neutrophil bactericidal activity via activation CBL-dependent ERK pathway

BACKGROUND

Despite granulocyte colony-stimulating factor (GCSF) is widely used in clinical, cancer chemotherapy induced neutropenia (CCIN) infection and infection-related mortality is high for lack of functionally mature neutrophils. Generating functional neutrophils is new therapeutic approaches to reduce CCIN-associated infection and mortality. Saikosaponin a (SSA) is one of the major bioactive components of Radix Bupleuri (RB) and exerts immunoregulatory effects.

PURPOSE

The present study aims to investigate the efficacy and mechanism of SSA in CCIN therapy.

METHODS

SSA was applied both in vitro and in vivo to assess the efficacy of CCIN therapy. The differentiation of neutrophils was measured by Nitroblue tetrazolium (NBT) reduction assay and Giemsa staining assay. The neutrophil differentiation related real-time transcription factors were detected by quantitative PCR (RT-qPCR) and Western Blot. Bacteria killing assay was used to assess the ability of fighting infection. Network pharmacology was employed to explore the mechanism network, and the predicted pathways were validated by Western Blot.

RESULTS

We found that SSA contributed to generate functional mature neutrophils which capable of fighting infection both in vitro and in vivo. Network pharmacology prediction showed 55 pathways were predicted involved in SSA against CCIN. Further validation showed that CBL-ERK1/2 pathway was activated by SSA, which could upregulate PU.1 and CEBPβ expression leading to neutrophil differentiation.

CONCLUSIONS

Our findings suggest a natural regimen SSA regenerates microbicidal neutrophils to effectively reduce CCIN-associated infection via activating CBL-ERK1/2 pathway, providing a rationale for future therapeutic approaches.

Saikosaponin d contributed to cancer chemotherapy induced neutropenia therapy by promoting neutrophil differentiation via activation CBL-dependent ERK pathway

Cancer chemotherapy induced neutropenia (CCIN) is one of the most common toxicity caused by cytotoxic anticancer agents. Despite granulocyte colony-stimulating factor (GCSF) is widely used in clinical practice, the infection and infection-related mortality rate is still high for lack of functionally mature neutrophils. Saikosaponin d (SSD) is one of the major bioactive constituents of Radix Bupleuri (RB), which exerts immune-modulatory properties. We explored the function of SSD in CCIN therapy, we found that SSD contributed to generate functional mature neutrophils which capable of fighting infection both in vitro and in vivo. Network pharmacology was employed to explore the mechanism, 61 signal pathways might play an important role in CCIN treatment. Western Blot was employed to further confirm the potential pathway involved. We found CBL-ERK1/2 pathway was activated by SSD, followed by upregulating PU.1 and CEBPβ expression and leading to neutrophil differentiation. Our findings suggest a natural regimen SSD which could regenerate microbicidal neutrophils to effectively reduce CCIN-associated infection via activating CBL-ERK1/2, providing a rationale for future therapeutic approaches.

Identification of the tetraspanin CD82 as a new barrier to xenotransplantation

Significant immunological obstacles are to be negotiated before xenotransplantation becomes a clinical reality. An initial rejection of transplanted vascularized xenograft is attributed to Galα1,3Galβ1,4GlcNAc-R (Galα1,3-Gal)-dependent and -independent mechanisms. Hitherto, no receptor molecule has been identified that could account for Galα1,3-Gal-independent rejection. In this study, we identify the tetraspanin CD82 as a receptor molecule for the Galα1,3-Gal-independent mechanism. We demonstrate that, in contrast to human undifferentiated myeloid cell lines, differentiated cell lines are capable of recognizing xenogeneic porcine aortic endothelial cells in a calcium-dependent manner. Transcriptome-wide analysis to identify the differentially expressed transcripts in these cells revealed that the most likely candidate of the Galα1,3-Gal-independent recognition moiety is the tetraspanin CD82. Abs to CD82 inhibited the calcium response and the subsequent activation invoked by xenogeneic encounter. Our data identify CD82 on innate immune cells as a major "xenogenicity sensor" and open new avenues of intervention to making xenotransplantation a clinical reality.

α-Enolase of Streptococcus pneumoniae induces formation of neutrophil extracellular traps

Streptococcus pneumoniae is the most common causative agent of community-acquired pneumonia throughout the world, with high morbidity and mortality rates. A major feature of pneumococcal pneumonia is abundant neutrophil infiltration. In this study, we identified S. pneumoniae α-enolase as a neutrophil binding protein in ligand blot assay and mass spectrometry findings. Scanning electron microscopic and fluorescence microscopic analyses also revealed that S. pneumoniae α-enolase induces formation of neutrophil extracellular traps, which have been reported to bind and kill microbes. In addition, cytotoxic assay results showed that α-enolase dose-dependently increased the release of extracellular lactate dehydrogenase from human neutrophils as compared with untreated neutrophils. Furthermore, an in vitro cell migration assay using Chemotaxicell culture chambers demonstrated that α-enolase possesses neutrophil migrating activity. Interestingly, bactericidal assay findings showed that α-enolase increased neutrophil extracellular trap-dependent killing of S. pneumoniae in human blood. Moreover, pulldown assay and mass spectrometry results identified myoblast antigen 24.1D5 as an α-enolase-binding protein on human neutrophils, whereas flow cytometric analysis revealed that 24.1D5 was expressed on human neutrophils, but not on human monocytes or T cells. Together, our results indicate that α-enolase from S. pneumoniae increases neutrophil migrating activity and induces cell death of human neutrophils by releasing neutrophil extracellular traps. Furthermore, we found that myoblast antigen 24.1D5, which expressed on the surface of neutrophils, bound to α-enolase of S. pneumoniae.

Secondary metabolites from the roots of Neolitsea daibuensis and their anti-inflammatory activity

Bioassay-guided fractionation of the roots of Neolitsea daibuensis afforded three new β-carboline alkaloids, daibucarbolines A-C (1-3), three new sesquiterpenoids, daibulactones A and B (4 and 5) and daibuoxide (6), and 20 known compounds. The structures of 1-6 were determined by spectroscopic analysis and single-crystal X-ray diffraction. Daibucarboline A (1), isolinderalactone (7), 7-O-methylnaringenin (8), and prunetin (9) exhibited moderate iNOS inhibitory activity, with IC₅₀ values of 18.41, 0.30, 19.55, and 10.50 μM, respectively.

The B-lymphoid Grb2 interaction code

The growth factor receptor-bound protein 2 (Grb2) is a ubiquitously expressed and evolutionary conserved adapter protein possessing a plethora of described interaction partners for the regulation of signal transduction. In B lymphocytes, the Grb2-mediated scaffolding function controls the assembly and subcellular targeting of activating as well as inhibitory signalosomes in response to ligation of the antigen receptor. Also, integration of simultaneous signals from B-cell coreceptors that amplify or attenuate antigen receptor signal output relies on Grb2. Hence, Grb2 is an essential signal integrator. The key question remains, however, of how pathway specificity can be maintained during signal homeostasis critically required for the balance between immune cell activation and tolerance induction. Here, we summarize the molecular network of Grb2 in B cells and introduce a proteomic approach to elucidate the interactome of Grb2 in vivo.

Function, regulation and pathological roles of the Gab/DOS docking proteins

Since their discovery a little more than a decade ago, the docking proteins of the Gab/DOS family have emerged as important signalling elements in metazoans. Gab/DOS proteins integrate and amplify signals from a wide variety of sources including growth factor, cytokine and antigen receptors as well as cell adhesion molecules. They also contribute to signal diversification by channelling the information from activated receptors into signalling pathways with distinct biological functions. Recent approaches in protein biochemistry and systems biology have revealed that Gab proteins are subject to complex regulation by feed-forward and feedback phosphorylation events as well as protein-protein interactions. Thus, Gab/DOS docking proteins are at the centre of entire signalling subsystems and fulfil an important if not essential role in many physiological processes. Furthermore, aberrant signalling by Gab proteins has been increasingly linked to human diseases from various forms of neoplasia to Alzheimer's disease.

In this review, we provide a detailed overview of the structure, effector functions, regulation and evolution of the Gab/DOS family. We also summarize recent findings implicating Gab proteins, in particular the Gab2 isoform, in leukaemia, solid tumours and other human diseases.

Cell cycle regulation by oncogenic tyrosine kinases in myeloid neoplasias: from molecular redox mechanisms to health implications

Neoplastic expansion of myeloid cells is associated with specific genetic changes that lead to chronic activation of signaling pathways, as well as altered metabolism. It has become increasingly evident that transformation relies on the interdependency of both events. Among the various genetic changes, the oncogenic BCR-ABL tyrosine kinase in patients with Philadelphia chromosome positive chronic myeloid leukemia (CML) has been a focus of extensive research. Transformation by this oncogene is associated with elevated levels of intracellular reactive oxygen species (ROS). ROS have been implicated in processes that promote viability, cell growth, and regulation of other biological functions such as migration of cells or gene expression. Currently, the BCR-ABL inhibitor imatinib mesylate (Gleevec) is being used as a first-line therapy for the treatment of CML. However, BCR-ABL transformation is associated with genomic instability, and disease progression or resistance to imatinib can occur. Imatinib resistance is not known to cause or significantly alter signaling requirements in transformed cells. Elevated ROS are crucial for transformation, making them an ideal additional target for therapeutic intervention. The underlying mechanisms leading to elevated oxidative stress are reviewed, and signaling mechanisms that may serve as novel targeted approaches to overcome ROS-dependent cell growth are discussed.

Tuberin: a stimulus-regulated tumor suppressor protein controlled by a diverse array of receptor tyrosine kinases and G protein-coupled receptors

Tuberin, a tumor suppressor protein, is involved in various cellular functions including survival, proliferation, and growth. It has emerged as an important effector regulated by receptor tyrosine kinases (RTKs) and G protein-coupled receptors (GPCRs). Regulation of tuberin by RTKs and GPCRs is highly complex and dependent on the type of receptors and their associated signaling molecules. Apart from Akt, the first kinase recognized to phosphorylate and inactivate tuberin upon growth factor stimulation, an increasing number of kinases upstream of tuberin have been identified. Furthermore, recruitment of different scaffolding adaptor components to the activated receptors appears to play an important role in the regulation of tuberin activity. More recently, the differential regulation of tuberin by various G protein family members have also been intensively studied, it appears that G proteins can both facilitate (e.g., G(i/o)) as well as inhibit (e.g., G(q)) tuberin phosphorylation. In the present review, we attempt to summarize our emerging understandings of the roles of RTKs, GPCRs, and their cross-talk on the regulation of tuberin.

Identification of key genes responsible for cytokine-induced erythroid and myeloid differentiation and switching of hematopoietic stem cells by RAGE

We utilized a unique culture system to analyze the expression patterns of gene, protein, and cell surface antigen, and the biological process of the related genes in erythroid and myeloid differentiation and switching of hematopoietic stem cells (HSCs) in response to cytokine alterations. Gene-specific fragments (266) identified from five populations of cytokine-stimulated HSCs were categorized into three groups: (1) expressed specifically in a single cell population; (2) expressed in two cell populations, and (3) expressed in three or more populations. Of 145 defined cDNAs, three (2%) were novel genes. Protein two-dimensional gel electrophoresis and flow cytometry analyses showed overlapped and distinguished protein expression profiles in the cell populations studied. Biological process mapping of mRNAs expressed in erythroid and myeloid lineages indicated that mRNAs shared by both lineages attended 'core processes,' whereas genes specifically expressed in either lineage alone were related to specific processes or cellular maturation. Data from this study support the hypothesis that committed HSCs (E14 or G14) cells can still be redirected to develop into myeloid or erythroid cells when erythropoietin (EPO) is replaced with granulocyte-colony stimulating factor (G-CSF) under erythroid-cultured condition or G-CSF with EPO in myeloid-cultured environment, respectively. Our results suggest that genes or proteins co-expressed in erythroid and myeloid lineages may be essential for the lineage maintenance and switching in hematopoiesis.

Mutational analysis of the mechanism of negative regulation by SRC homology 2 domain-containing protein tyrosine phosphatase substrate-1 of phagocytosis in macrophages

Src homology 2 domain-containing protein tyrosine phosphatase substrate-1 (SHPS-1) is a transmembrane protein predominantly expressed in macrophages. The binding of CD47 on RBCs to SHPS-1 on macrophages is implicated in inhibition of phagocytosis of the former cells by the latter. We have now shown that forced expression in mouse RAW264.7 macrophages of a mutant version (SHPS-1-4F) of mouse SHPS-1, in which four tyrosine phosphorylation sites are replaced by phenylalanine, markedly promoted Fc gammaR-mediated phagocytosis of mouse RBCs or SRBCs. Forced expression of another mutant form (SHPS-1-deltaCyto) of mouse SHPS-1, which lacks most of the cytoplasmic region, did not promote such phagocytosis. Similarly, forced expression of a rat version of SHPS-1-4F, but not that of rat wild-type SHPS-1 or SHPS-1-deltaCyto, in RAW264.7 cells enhanced Fc gammaR-mediated phagocytosis of RBCs. Tyrosine phosphorylation of endogenous SHPS-1 as well as its association with Src homology 2 domain-containing protein tyrosine phosphatase-1 were not markedly inhibited by expression of SHPS-1-4F. Furthermore, the attachment of IgG-opsonized RBCs to RAW264.7 cells was markedly increased by expression of SHPS-1-4F, and this effect did not appear to be mediated by the interaction between CD47 and SHPS-1. These data suggest that inhibition by SHPS-1 of phagocytosis in macrophages is mediated, at least in part, in a manner independent of the transinteraction between CD47 and SHPS-1. In addition, the cytoplasmic region as well as tyrosine phosphorylation sites in this region of SHPS-1 appear indispensable for this inhibitory action of SHPS-1. Moreover, SHPS-1 may regulate the attachment of RBCs to macrophages by an as yet unidentified mechanism.

Simultaneous measurement of superoxide generation and intracellular Ca2+ concentration reveals the effect of extracellular Ca2+ on rapid and transient contents of superoxide generation in differentiated THP-1 cells

We invented a simultaneous measuring instrument of fluorescence and chemiluminescence, realizing the analysis of chronological correlation between change in intracellular Ca2+ concentration ([Ca2+]i) and superoxide generation. A human monocytic cell line, THP-1, differentiated to be neutrophil-like cells generated superoxide with increase in intracellular Ca2+ concentration when stimulated with formyl-methionyl-leucyl-phenylalanine (fMLP) whereas PMA, phorbol ester-stimulated superoxide response occurred without change in [Ca2+]i. The cells treated with TMB-8, an intracellular Ca2+ antagonist, generated superoxide rapidly as well as transiently with transient [Ca2+]i elevation after stimulation with fMLP, whereas EGTA-treated cells generated superoxide slowly as well as persistently with transient [Ca2+]i elevation after the stimulation. These results suggest that the rapid and transient contents of superoxide generation are specific for Ca2+ influx from the extracellular domain. Verapamil, voltage-dependent Ca2+ channel blocker, dose-dependently inhibited fMLP-stimulated extracellular Ca2+ influx and superoxide generation without affecting PMA-stimulated superoxide generation. Other channel blockers tested, nifedipine and diltiazem, similarly inhibited these fMLP-stimulated responses. Numerical analysis of the values of the response curves elucidated that TMB-8 or the channel blocker reveals or eliminates the same contents of superoxide generation by the antagonism of intracellular Ca2+ release or extracellular Ca2+ influx, respectively. Taking these results together, the characteristic extracellular Ca2+ influx essential for superoxide generation was first revealed by the simultaneous measurement of superoxide generation and change in [Ca2+]i.

The multiple function of Grb2 associated binder (Gab) adaptor/scaffolding protein in immune cell signaling

The Grb2 associated binder (Gab) adaptor/scaffolding protein family comprises conserved proteins: mammalian Gab1, Gab2 and Gab3, Drosophila Dos and Caenorhabditis elegans Soc1. Gab adaptors are involved in multiple signaling pathways mediated by receptor- and non-receptor protein tyrosine kinases (PTKs), and become phosphorylated upon stimulation by growth factors-, cytokines-, Ig Fc- and antigen receptors. Through its phosphorylated tyrosine containing motifs, proline-rich sequences and pleckstrin homologue (PH) domain Gab adaptors may generate an interacting platform for proteins with SH2 and SH3 domains and may transfer these molecules to the plasma membrane, thereby contributing to their activation. This review will concentrate on the function of mammalian Gab proteins in the signal transduction triggered by immune receptors.

Pertussis toxin-sensitive Gi/o proteins are involved in nerve growth factor-induced pro-survival Akt signaling cascade in PC12 cells

In Galpha(z)-deficient mice, survival of sympathetic neurons is significantly attenuated in the presence of pertussis toxin (PTX). This suggests that G(i/o) proteins may have distinct roles in neuronal survival. Here, we investigated the possible involvement of G(i/o) proteins in nerve growth factor (NGF)-induced pro-survival phosphatidylinositol-3-kinase (PI3K)/Akt signaling in rat pheochromocytoma PC12 cells. Treatment of PC12 cells with NGF increased the Akt phosphorylation level in a time- and dose-dependent manner. The NGF-dependent Akt activation was partially attenuated by PTX or overexpression of regulators of G protein signaling Z1 (RGSZ1) and Galpha-interacting protein (GAIP)), indicating the participation of G(i/o) proteins. In contrast, epidermal growth factor (EGF)-mediated Akt phosphorylation was unaffected by PTX or RGSZ1 and GAIP. Expression of PTX-resistant mutants of Galpha(i1), Galpha(i3), Galpha(oA), and Galpha(oB), but not Galpha(i2), abolished the inhibitory effect of PTX on NGF-induced Akt activation. The use of transducin as a Gbetagamma scavenger further revealed that Gbetagamma subunits rather than Galpha(i/o) acted as the signal transducer. The activation profiles of Akt-regulated downstream effectors such as Bad, IKK, and nuclear factor-kappaB (NFkappaB) were also examined. NGF-stimulated phosphorylation of Bad and IKK and transcriptional activity of NFkappaB were indeed sensitive to treatments with PTX. This is the first study that demonstrates the involvement of G(i/o) proteins in NGF-induced Akt signaling.

Negative regulation of phagocytosis in macrophages by the CD47-SHPS-1 system

Src homology 2 domain-containing protein tyrosine phosphatase (SHP) substrate-1 (SHPS-1) is a transmembrane protein that is expressed predominantly in macrophages. Its extracellular region interacts with the transmembrane ligand CD47 expressed on the surface of adjacent cells, and its cytoplasmic region binds the protein tyrosine phosphatases SHP-1 and SHP-2. Phagocytosis of IgG- or complement-opsonized RBCs by peritoneal macrophages derived from mice that express a mutant SHPS-1 protein that lacks most of the cytoplasmic region was markedly enhanced compared with that apparent with wild-type macrophages. This effect was not observed either with CD47-deficient RBCs as the phagocytic target or in the presence of blocking Abs to SHPS-1. Depletion of SHPS-1 from wild-type macrophages by RNA interference also promoted FcgammaR-mediated phagocytosis of wild-type RBCs. Ligation of SHPS-1 on macrophages by CD47 on RBCs promoted tyrosine phosphorylation of SHPS-1 and its association with SHP-1, whereas tyrosine phosphorylation of SHPS-1 was markedly reduced in response to cross-linking of FcgammaRs. Treatment with inhibitors of PI3K or of Syk, but not with those of MEK or Src family kinases, abolished the enhancement of FcgammaR-mediated phagocytosis apparent in macrophages from SHPS-1 mutant mice. In contrast, FcgammaR-mediated tyrosine phosphorylation of Syk, Cbl, or the gamma subunit of FcR was similar in macrophages from wild-type and SHPS-1 mutant mice. These results suggest that ligation of SHPS-1 on macrophages by CD47 promotes the tyrosine phosphorylation of SHPS-1 and thereby prevents the FcgammaR-mediated disruption of the SHPS-1-SHP-1 complex, resulting in inhibition of phagocytosis. The inhibition of phagocytosis by the SHPS-1-SHP-1 complex may be mediated at the level of Syk or PI3K signaling.

Involvement of G i/o proteins in nerve growth factor-stimulated phosphorylation and degradation of tuberin in PC-12 cells and cortical neurons

Tuberin is a critical translation regulator whose role in nerve growth factor (NGF)-promoted neuronal survival has not been documented. In the present study, we examined the ability of NGF to regulate tuberin in PC-12 cells and primary cortical neurons. Incubation of serum-deprived cells with NGF stimulated tuberin phosphorylation and induced proteosome-mediated tuberin degradation. Inhibition of the phosphatidylinositol-3-kinase (PI3K) by wortmannin or overexpression of the kinase dead Akt mutant completely blocked the NGF-induced tuberin phosphorylation and degradation. It is interesting that the NGF-induced tuberin phosphorylation was partially blocked by pertussis toxin or overexpression of regulators of G protein signaling (regulator of G protein signaling Z1 and Galpha-interacting protein), suggesting the participation of G(i/o) proteins. The use of transducin as a Gbetagamma scavenger indicated that Gbetagamma subunits rather than Galpha(i/o) acted as the signal transducer. Epidermal growth factor can similarly induce tuberin phosphorylation and degradation via a PI3K/Akt pathway in PC-12 cells, but these responses were insensitive to pertussis toxin treatment. Treatment of PC-12 cells with a specific agonist to the G(i)-coupled alpha(2)-adrenoceptor also stimulated tuberin phosphorylation transiently, further demonstrating the involvement of G(i/o) signaling in tuberin regulation in PC-12 cells. Finally, overexpression of nonphosphorylable tuberin attenuated NGF-promoted survival of PC-12 cells, suggesting that the phosphorylation and degradation of tuberin are important for NGF-promoted cell survival. Together, this study demonstrates the regulatory effect of NGF and G(i/o) signaling on tuberin.

Activation of the PI3K/mTOR pathway by BCR-ABL contributes to increased production of reactive oxygen species

BCR-ABL oncoprotein-expressing cells are associated with a relative increase of intracellular reactive oxygen species (ROS), which is thought to play a role in transformation. Elevated ROS levels in BCR-ABL-transformed cells were found to be blocked by the mitochondrial complex I inhibitor rotenone as well as the glucose transport inhibitor phloretin, suggesting that the source of increased ROS might be related to increased glucose metabolism. The glucose analog 2-deoxyglucose (2-DOG) reduced ROS to levels found in non-BCR-ABL-transformed cells and inhibited cell growth alone or in cooperation with imatinib mesylate (Gleevec). A mutant of BCR-ABL that is defective in transformation of myeloid cells, Tyr177Phe, was also found to be defective in raising intracellular ROS levels. Glucose metabolism in BCR-ABL-transformed cells is likely to be mediated by activation of the phosphatidylinositol-3'-kinase (PI3K) pathway, which is regulated through this site. Inhibition of PI3K or mTOR led to a significant decrease in ROS levels. Overall, our results suggest that elevated levels of ROS in BCR-ABL-transformed cells are secondary to a transformation-associated increase in glucose metabolism and an overactive mitochondrial electron transport chain and is specifically regulated by PI3K. Finally, these results hint at novel targets for drug development that may aid traditional therapy.