Activation of NF-kappa B transcription factor in human neutrophils by sulphatides and L-selectin cross-linking

Modulation of the Functional State of Mouse Neutrophils by Selenium Nanoparticles In Vivo

This study aimed to discover the immunomodulatory effect of selenium nanoparticles (SeNPs) on the functional state of neutrophils in vivo. Intraperitoneal injections of SeNPs (size 100 nm) 2.5 mg/kg/daily to BALB/c mice for a duration of 7-28 days led to the development of an inflammatory reaction, which was registered by a significant increase in the number of neutrophils released from the peritoneal cavity, as well as their activated state, without additional effects. At the same time, subcutaneous injections of the same SeNPs preparations at concentrations of 0.1, 0.5, and 2.5 mg/kg, on the contrary, modulated the functional state of neutrophils depending on the concentration and duration of SeNPs administration. With the use of fluorescence spectroscopy, chemiluminescence, biochemical methods, and PCR analysis, it was found that subcutaneous administration of SeNPs (0.1, 0.5, and 2.5 mg/kg) to mice for a short period of time (7-14 days) leads to modification of important neutrophil functions (adhesion, the number of migrating cells into the peritoneal cell cavity, ROS production, and NET formation). The obtained results indicated the immunostimulatory and antioxidant effects of SeNPs in vivo during short-term administration, while the most pronounced immunomodulatory effects of SeNPs were observed with the introduction of a low concentration of SeNPs (0.1 mg/kg). Increase in the administration time of SeNPs (0.1 mg/kg or 2.5 mg/kg) up to 28 days led to a decrease in the adhesive abilities of neutrophils and suppression of the expression of mRNA of adhesive molecules, as well as proteins involved in the generation of ROS, with the exception of NOX2; there was a tendency to suppress gene expression pro-inflammatory factors, which indicates the possible manifestation of immunosuppressive and anti-inflammatory effects of SeNPs during their long-term administration. Changes in the expression of selenoproteins also had features depending on the concentration and duration of the administered SeNPs. Selenoprotein P, selenoprotein M, selenoprotein S, selenoprotein K, and selenoprotein T were the most sensitive to the introduction of SeNPs into the mouse organism, which indicates their participation in maintaining the functional status of neutrophils, and possibly mediated the immunomodulatory effect of SeNPs.

Protocol for visualizing conditional interaction between transmembrane and cytoplasmic proteins

This protocol visualizes dynamic interaction between a transmembrane protein and an intracellular protein induced by clusterization/oligomerization of the transmembrane protein. Association-dissociation of the intracellular region of the transmembrane protein with cytoplasmic protein(s) is detected by proximity ligation assay. Since a transmembrane protein often resists extraction, biochemical analysis of its dynamic interaction with cytoplasmic effectors is cumbersome. This protocol quantitatively visualizes protein-protein interaction occurring in the membrane periphery, providing a powerful tool to elucidate signal transduction across the membrane.

For complete details on the use and execution of this protocol, please refer to Ooki et al. (2019).

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Antibody-mediated cross-linking induces functional clustering of membrane protein

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PLA can visualize extracellular-signal-dependent intracellular protein interaction

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This protocol is applicable for the analysis of dynamic protein network formation

Brain glycolipids suppress T helper cells and inhibit autoimmune demyelination

The CNS is considered an immune privileged site because its repertoire of highly immunogenic molecules remains unseen by the immune system under normal conditions. However, the mechanism underlying the inhibition of immune reactions within the CNS environment is not known, particularly in regions containing myelin, which contains several potent proteins and lipids that are invariably recognized as foreign by immune system cells. Sulfatides constitute a major component of myelin glycolipids and are known to be capable of raising an immune response. In this study, the effect of sulfatides on mouse T cell function and differentiation was analyzed in vitro and in vivo. We found profound inhibition of sulfatide-dependent T cell proliferation which was particularly pronounced in naive T helper (Th) cells. The inhibitory effect of sulfatides on T cell function was CD1d-independent and was not related to apoptosis or necrosis but did involve the induction of anergy as confirmed by the upregulation of early growth response 2 transcription factor. A glycolipid 3-sulfate group was essential for the T cell suppression, and the T cell inhibition was galectin-4-dependent. Sulfatide stimulation in vitro led to prominent suppression of Th17 differentiation, and this was related to a decrease in susceptibility to disease in a mouse model of multiple sclerosis, experimental autoimmune encephalomyelitis. Thus, we have defined a novel mechanism of negative regulation of T cell function by endogenous brain-derived glycolipids, a family of molecules traditionally deemphasized in favor of myelin proteins in studies of CNS autoimmunity.

IL-12 and IL-10 production are differentially regulated by phosphatidylinositol 3-kinase in mast cells

The cellular mechanisms that directly regulate the production of pro- and anti-inflammatory cytokines after lipopolysaccharide (LPS) stimulation in mast cells are currently unresolved. The aim of this study was to clarify the role of phosphatidylinositol 3-kinase (PI3K) in the production of IL-12 and IL-10 in mouse bone marrow-derived mast cells (BMMCs), stimulated with Escherichia coli-derived LPS. LPS activates the PI3K signalling pathway; analysis of cytokine production following LPS stimulation of BMMCs revealed that inhibition of the PI3K pathway differentially regulated IL-10 and IL-12 syntheses. IL-12 production was enhanced, whereas IL-10 levels were suppressed. Inhibition of LPS-mediated activation of the PI3K pathway resulted in a pronounced reduction of NF-κB activity that was dependent on IκBα phosphorylation. These findings demonstrate a regulatory function for PI3K in modulating IL-10 and IL-12 production in mast cells and provide insight into how engagement of the PI3K pathway affects the induction of key immunoregulatory cytokines that control both qualitative and quantitative aspects of early inflammation.

Signaling through L-selectin mediates enhanced chemotaxis of lymphocyte subsets to secondary lymphoid tissue chemokine

L-selectin functions as an important adhesion molecule that mediates tethering and rolling of lymphocytes by binding to high endothelial venule (HEV)-expressed ligands during recirculation. Subsequent lymphocyte arrest and transmigration require activation through binding of HEV-decorated homeostatic chemokines such as secondary lymphoid tissue chemokine (SLC; CCL21) to its counterreceptor, CCR7. Importantly, L-selectin also functions as a signaling molecule. In this study, signaling induced by ligation of L-selectin using mAb or endothelial cell-expressed ligand significantly enhanced the chemotaxis of murine T cells and B cells to SLC but not to other homeostatic chemokines. Consistent with the expression levels of L-selectin in different lymphocyte subsets, L-selectin-mediated enhancement of chemotaxis to SLC was observed for all naive lymphocytes and effector/memory CD8(+) T cells, whereas only a subpopulation of effector/memory CD4(+) T cells responded. During in vivo mesenteric lymph node migration assays, the absence of L-selectin on lymphocytes significantly attenuated both their ability to migrate out of the HEV and their chemotaxis away from the vessel wall. Notably, ligation of L-selectin and/or CCR7 did not result in increased CCR7 expression levels, internalization, or re-expression. Pharmacologic inhibitor studies showed that L-selectin-mediated enhanced chemotaxis to SLC required intact intracellular kinase function. Furthermore, treatment of lymphocytes with the spleen tyrosine kinase family inhibitor piceatannol reduced their ability to migrate across the HEV in peripheral lymph nodes. Therefore, these results suggest that "cross-talk" in the signaling pathways initiated by L-selectin and CCR7 provides a novel mechanism for functional synergy between these two molecules during lymphocyte migration.

Synthetic isoforms of endogenous sulfatides differently modulate indoleamine 2,3-dioxygenase in antigen presenting cells

AIMS

To investigate whether sulfatides modulate indoleamine 2,3-dioxygenase (IDO)1, a fine-tuned enzymatic mechanism for controlling immune responses, gene expression/function in antigen presenting cells (APC). The relationship between structure and activity (SAR) of newly synthesized sulfatide isoforms (C16:0, C18:0, C22:0, C24:1) was also evaluated.

MAIN METHODS

CD1d-transfected THP-1 human cells were used as APC and treated with increasing concentrations (0.01-10μΜ) of each compound for an appropriate period of time. The gene expression and the enzymatic activity of IDO1 were examined using reverse transcription-polymerase chain reaction (RT-PCR) and high performance liquid chromatography (HPLC). Compound-untreated cells were taken as negative, while 1000U/ml interferon (IFN)-γ-treated cells as positive controls.

KEY FINDINGS

Not all sulfatides induced the same effect: the basal IDO1 expression was significantly reduced (-48 ± 3% at 0.01μΜ) by C16:0 sulfatide, while it was increased by C18:0 or C24:1 sulfatide (+87 ± 7% and +50 ± 5% at 1μΜ, respectively) over negative controls; C22:0 sulfatide resulted ineffective at all concentrations tested. These effects functionally correlated with changes in IDO1 activity: l-kynurenine contents in the culture media were significantly reduced by C16:0 sulfatide (-29 ± 4% at 0.01μM), while it was increased by C18:0 or C24:1 sulfatide (+61 ± 8% and +48 ± 4% at 1μM, respectively) over negative controls. C22:0 sulfatide resulted ineffective at all concentration tested.

SIGNIFICANCE

The overall data demonstrate that specific sulfatide isoforms differently modulate IDO1 in APC. The sulfatide-induced effects are structurally dependent on the length/saturation of their fatty acid chain.

Critical role of Lck in L-selectin signaling induced by sulfatides engagement

Recruitment of leukocytes onto inflamed tissues is an important physiological event, in which L-selectin plays an essential role in initial leukocyte capture and at the same time, triggers cell signaling. Lck is a member of the Src family of protein tyrosine kinases and is critical for T cell activation triggered by receptor ligation. Here, we demonstrated that Lck was associated directly with and phosphorylated the L-selectin cytoplasmic tail upon L-selectin engagement with sulfatides. Through the direct interaction with ZAP-70 and c-Abl via its Src homology 2 (SH2) and SH3 domains, Lck organized a signaling complex at the cytoplasmic tail of L-selectin. In the cells with Lck knockdown by small interfering RNA treatment, L-selectin signaling was suppressed dramatically, as indicated by reduced phosphorylation of c-Abl and ZAP-70. Re-expression of wild-type or constitutively active but not kinase-dead murine Lck rescued the phosphorylation completely, but the SH2 domain mutant or the SH3/SH2 double mutant of murine Lck had no effect. These results suggest that Lck plays a critical role in L-selectin signaling upon sulfatides stimulation.

L-selectin ligation-induced CSF-1 gene transcription is regulated by AP-1 in a c-Abl kinase-dependent manner

L-selectin is a cell adhesion molecule that plays an important role both in mediating the initial capture and subsequent rolling of leukocytes along the endothelial cells and in the signal transduction for leukocyte activation. In our previous studies, we reported that L-selectin ligation could increase macrophage colony-stimulating factor (CSF)-1 gene transcription, in which c-Abl acts as a crucial cytoplasmic kinase. Here we investigated the function of the nuclear c-Abl kinase in the CSF-1 gene transcriptional events triggered by L-selectin ligation. We determined that c-Abl kinase recruits to the nucleus following L-selectin ligation, and the nuclear c-Abl kinase can phosphorylate c-Jun and regulate activator protein (AP)-1 activity. Furthermore, the activated c-Abl kinase interacts with AP-1 and forms a complex in the CSF-1 promoter region to regulate CSF-1 gene transcription in the L-selectin ligation-activated cells. These results indicate that nuclear c-Abl kinase can activate CSF-1 gene transcription by regulating AP-1 activity in the signaling events induced by L-selectin ligation.

c-Abl is required for the signaling transduction induced by L-selectin ligation

Lymphocyte recruitment onto inflamed tissues requires cells tethering to and rolling on vascular surfaces under flow. L-selectin is constitutively expressed on leukocytes to mediate the leukocytes' initial capture and subsequent rolling along the vessel. Apart from its adhesive function, engagement of L-selectin also results in cell activation, which is related to the completed signaling transduction. Here we show that ligation of L-selectin with its mAb increases c-Abl kinase activity, and that the activated c-Abl kinase can be recruited to and phosphorylate the cytoplasmic domain of L-selectin. In addition, the activated c-Abl kinase can regulate Zap70 kinase by increasing the phosphorylation of the Y319 site of Zap70 kinase and connect with Zap70 kinase through its SH2 domain. These results indicate that c-Abl kinase plays an important role in accepting and transferring the upstream activation events induced by L-selectin ligation.

Up-regulation of leukocyte CXCR4 expression by sulfatide: An L-selectin-dependent pathway on CD4+ T cells

CXCR4 plays significant roles in immune and inflammatory responses and is important for selective recruitment of leukocytes. We previously showed that CXCR4 surface expression of human lymphocytes was affected by sulfatide, an in vivo ligand for L-selectin. Increased CXCR4 expression was shown to promote biologically relevant functions such as integrin-dependent adhesion and transmigration. Here, we show that sulfatide-induced CXCR4 up-regulation also occurs on other leukocyte subsets in humans and mice. B cells and CD4(+)CD25(+) T cells had the highest CXCR4 up-regulation after sulfatide stimulation. Transfection of L-selectin was sufficient for K562 cells to acquire sulfatide-induced CXCR4 up-regulation, while analysis of L-selectin knockout mice revealed that this response was critically L-selectin dependent only for CD4(+) T cells, suggesting an alternative pathway in CD8(+) T cells and B cells. Sulfatide triggered several intracellular signaling events in CD4(+) T cells, but only tyrosine kinase activation, including members of the Src family, were essential for L-selectin to CXCR4 signaling. CXCR4 up-regulation was rapid, enhanced CXCL12-induced signaling and increased chemotaxis toward CXCL12, and therefore has potentially important roles in vivo. Thus, the response to CXCL12 depends in part on tissue expression of sulfatide and, specifically in CD4(+) T cells, also depends on the surface level of L-selectin.

L-selectin: adhesion, signalling and its importance in pathologic posttraumatic endotoxemia and non-septic inflammation

The leucocyte expressed surface-bound L-selectin belongs to the selectin family of adhesion molecules. It exhibits adhesive as well as signalling functions. Mainly, it is of importance in lymphocyte homing and in the extravasation of leucocytes into the surrounding tissue during inflammation. Acting in the initial step of the cell adhesion cascade, L-selectin is responsible for the rolling of leucocytes on endothelial layers. Therefore, L-selectin is thought to be an adequate target for pharmacological interventions. Beneath the discussion of the molecules' general features like molecule structure and its regulation, the review focuses firstly on L-selectin in the context of posttraumatic inflammatory disorders, and secondly on the importance of L-selectin specific signalling events.

Mutagenesis of the Ezrin-Radixin-Moesin Binding Domain of L-selectin Tail Affects Shedding, Microvillar Positioning, and Leukocyte Tethering

L-selectin is a cell adhesion molecule that mediates the initial capture (tethering) and subsequent rolling of leukocytes along ligands expressed on endothelial cells. We have previously identified ezrin and moesin as novel binding partners of the 17-amino acid L-selectin tail, but the biological role of this interaction is not known. Here we identify two basic amino acid residues within the L-selectin tail that are required for binding to ezrin-radixinmoesin (ERM) proteins: arginine 357 and lysine 362. L-selectin mutants defective for ERM binding show reduced localization to microvilli and decreased phorbol 12-myristate 13-acetate-induced shedding of the L-selectin ectodomain. Cells expressing these L-selectin mutants have reduced tethering to the L-selectin ligand P-selectin glycoprotein ligand-1, but rolling velocity on P-selectin glycoprotein ligand-1 is not affected. These results suggest that ERM proteins are required for microvillar positioning of L-selectin and that this is important both for leukocyte tethering and L-selectin shedding.