Rat Mast Cell Line Research Articles

Novel IgE crosslinking-induced luciferase expression method using human-rat chimeric IgE receptor-carrying mast cells

BackgroundThe measurement of antigen-specific serum IgE is common in clinical assessments of type I allergies. However, the interaction between antigens and IgE won't invariably trigger mast cell activation. We previously developed the IgE crosslinking-induced luciferase expression (EXiLE) method using the RS-ATL8 mast cell line; however, the method may not be sensitive enough in some cases. MethodsIn this study, we introduced an NF-AT-regulated luciferase reporter gene into the RBL-2H3 rat mast cell line and expressed a chimeric high-affinity IgE receptor (FcεRI) α chain gene, comprising an extracellular domain from humans and transmembrane/intracellular domains from rats. ResultsWe generated multiple clones expressing the chimeric receptor. Based on their responsiveness and proliferation, we selected the HuRa-40 clone. This cell line exhibited significantly elevated human α chain expression compared to RS-ATL8 cells, demonstrating a 10-fold enhancement of antigen-specific reactivity. Reproducibility across different batches and operators was excellent. Moreover, we observed a detectable response inhibition by an anti-allergy drugs (omalizumab and cyclosporin A). ConclusionsHuRa-40 cells—which carry the human-rat chimeric IgE receptor—comprise a valuable reporter cell line for the EXiLE method. Their versatility extends to various applications and facilitates high-throughput screening of anti-allergy drugs.

Suppression of Mast Cell Activation by GPR35: GPR35 Is a Primary Target of Disodium Cromoglycate.

Mast cell stabilizers, including disodium cromoglycate (DSCG), were found to have potential as the agonists of an orphan G protein-coupled receptor, GPR35, although it remains to be determined whether GPR35 is expressed in mast cells and involved in suppression of mast cell degranulation. Our purpose in this study is to verify the expression of GPR35 in mast cells and to clarify how GPR35 modulates the degranulation. We explored the roles of GPR35 using an expression system, a mast cell line constitutively expressing rat GPR35, peritoneal mast cells, and bone marrow-derived cultured mast cells. Immediate allergic responses were assessed using the IgE-mediated passive cutaneous anaphylaxis (PCA) model. Various known GPR35 agonists, including DSCG and newly designed compounds, suppressed IgE-mediated degranulation. GPR35 was expressed in mature mast cells but not in immature bone marrow-derived cultured mast cells and the rat mast cell line. Degranulation induced by antigens was significantly downmodulated in the mast cell line stably expressing GPR35. A GPR35 agonist, zaprinast, induced a transient activation of RhoA and a transient decrease in the amount of filamentous actin. GPR35 agonists suppressed the PCA responses in the wild-type mice but not in the GPR35-/- mice. These findings suggest that GPR35 should prevent mast cells from undergoing degranulation induced by IgE-mediated antigen stimulation and be the primary target of mast cell stabilizers. SIGNIFICANCE STATEMENT: The agonists of an orphan G protein-coupled receptor, GPR35, including disodium cromoglycate, were found to suppress degranulation of rat and mouse mature mast cells, and their antiallergic effects were abrogated in the GPR35-/- mice, indicating that the primary target of mast cell stabilizers should be GPR35.

Light‐driven Activation of NADP(H) Oxidase 5

Ultraviolet band A (UVA) light irradiation has been shown to induce cytosolic calcium oscillations in the isolated rat peritoneal mast cells via activation of NADPH oxidase (NOX). It has been clarified that UVA-triggered calcium oscillations in mast cells (isolated rat peritoneal mast cells, rat mast cell line RBL-2H3, mouse bone marrow-derived mast cells) was due to NOX2 activation. To elucidate whether UVA light irradiation would also activate NOX5, a monomeric isoform of the NOX family of oxidases not requiring transmembrane p22 or cytosolic subunits for activity and not endogenously expressed in rodents, NOX5 was expressed ectopically in CHO-K1 cells, and the effect of UVA irradiation or photodynamic action on cytosolic calcium concentration was monitored with Fura-2 fluorescent calcium imaging. It was found that NOX5 expressed ectopically in CHO-K1 cells was activated by UVA (LED 380 nm) light irradiation to induce persistent cytosolic calcium oscillations. Blue LED (450 nm) light irradiation of CHO-K1 cells expressing protein photosensitizer miniSOG-NOX5 fusion protein triggered also persistent cytosolic calcium oscillations which were completely blocked by NOX inhibitor diphenyleneiodonium (DPI), and inhibited by singlet oxygen quencher Trolox C. Sulphonated aluminium phthalocyanine (SALPC) photodynamically activated the heterologously expressed NOX5 in CHO-K1 cells to trigger similarly cytosolic calcium oscillations, which were completely inhibited by DPI. These data suggest that both UVA light irradiation and 1O2 generation with photodynamic action could activate NOX5, to ultimately trigger calcium oscillations. It is therefore possible now to realize light-driven NOX5 activation for cell-type or subcellular organelle specific generation of superoxide anion.

The lectin ArtinM activates RBL-2H3 mast cells without inducing degranulation.

Mast cells are connective tissue resident cells with morphological and functional characteristics that contribute to their role in allergic and inflammatory processes, host defense and maintenance of tissue homeostasis. Mast cell activation results in the release of pro-inflammatory mediators which are largely responsible for the physiological functions of mast cells. The lectin ArtinM, extracted from Artocarpus heterophyllus (jackfruit), binds to D-manose, thus inducing degranulation of mast cells. ArtinM has several immunomodulatory properties including acceleration of wound healing, and induction of cytokine release. The aim of the present study was to investigate the role of ArtinM in the activation and proliferation of mast cells. The rat mast cell line RBL-2H3 was used throughout this study. At a low concentration (0.25μg/mL), ArtinM induced mast cell activation and the release of IL-6 without stimulating the release of pre-formed or newly formed mediators. Additionally, when the cells were activated by ArtinM protein tyrosine phosphorylation was stimulated. The low concentration of ArtinM also activated the transcription factor NFkB, but not NFAT. ArtinM also affected the cell cycle and stimulated cell proliferation. Therefore, ArtinM may have therapeutic applications by modulating immune responses due to its ability to activate mast cells and promote the release of newly synthesized mediators. Additionally, ArtinM could have beneficial effects at low concentrations without degranulating mast cells and inducing allergic reactions.

The Establishment of EXiLE test for House Dust Mite Allergy

Successful allergen immunotherapy (AIT) is associated with an increase in the production of allergen-specific IgG antibodies including IgG4 which may contribute to IgE-blocking factor (IgE-BF) activity. Recently, in vitro allergy test method was reported as EXiLE (IgE crosslinking-induced luciferase expression) test using a luciferase-reporting humanized rat mast cell line. However, to understand immunomodulation effect after AIT, this functional assay has not been fully validated. This study is aimed to investigate effect of IgE-BFs induced by house dust mite (HDM)-AIT on EXiLE test. HDM allergic rhinitis patients’ sera before- and after-AIT were used. EXiLE test was performed as previously reported (Allergol. Int, 2012). Briefly, RS-ATL8 cells were plated into the wells of a 96 well-plate and incubated with diluted serum overnight. The cells were stimulated with allergen (HDM, 0.1-1000 ng/mL) without washing. Then, luciferase substrate was added to the cells, and chemiluminescence was measured. The data was expressed as luciferase expression (LE) levels which were represented as the fold increase compared with the allergen untreated conditions (baseline), and EC50 value was calculated by fitting a dose response curve. The optimal incubation time was 3hr with HDM (0.1-1000 ng/mL). The LE levels showed significant correlation with the value of Der p specific-IgE (r2>0.95). EC50 of LE levels in sera after-AIT was shifted from that in sera before-AIT (p=0.01) EXiLE test was validated using the HDM allergic rhinitis sera. This test can be utilized for immunomodulation effect induced by AIT.

Non-digestible oligosaccharides scFOS/lcFOS facilitate safe subcutaneous immunotherapy for peanut allergy

BackgroundImproving the safety of subcutaneous immunotherapy (SCIT) for food allergy is necessary to reduce side effects and achieve long-term tolerance. We determined the effect of dietary supplementation with 1% non-digestible short- and long-chain fructo-oligosaccharides (scFOS/lcFOS) on safety and efficacy of SCIT using a peanut allergy mouse model.MethodsAfter sensitization, mice received a scFOS/lcFOS or control diet for the rest of the study. To study safety of SCIT, mice were dosed with a single subcutaneous injection of peanut extract (PE) or PBS. To study efficacy, mice were dosed subcutaneously (SCIT, 3 times/week) with PE or PBS for 3 weeks. Hereafter, acute allergic skin responses, anaphylactic shock symptoms and body temperature were assessed. To study the mechanism in vitro, the human IgE receptor (FcεRI)-transfected rat mast cell (RBL) line was sensitized with an oligoclonal pool of chimeric human (chu)IgE antibodies against bovine β-lactoglobulin (BLG) and incubated with the oligosaccharides before exposure to BLG to assess direct the effect on degranulation.ResultsscFOS/lcFOS reduced anaphylaxis caused by a single PE SCIT dose. scFOS/lcFOS alone also reduced the acute allergic skin response. Moreover, scFOS/lcFOS supplementation resulted in lower MMCP-1 levels in serum after PE SCIT dose compared to control diet, while antibody levels were not affected by the diet. In vitro incubation with scFOS/lcFOS at 0.5% suppressed the degranulation of IgE-sensitized RBL cells. However, dietary supplementation with scFOS/lcFOS did not improve the efficacy of SCIT.ConclusionsWe show that scFOS/lcFOS diet improves the safety of SCIT, as evidenced by lower anaphylactic responses without compromising the efficacy in a mouse model for peanut allergy. This effect is likely to result from the suppression of mast cell effector function.

Histamine uptake mediated by plasma membrane monoamine transporter and organic cation transporters in rat mast cell lines

The resources of released histamine from activated mast cells, as initial effectors of allergic disease, include not only endogenous prepackaged histamine and newly synthesized histamine, but also histamine that is obtained through the de novo reuptake pathway. To investigate the de novo histamine production pathway, a mast cell line, RBL-2H3 Sc98 in which endogenous histamine production is lacking and only the de novo histamine release pathway via transporters is maintained, was used to dissect histamine reuptake in the present study. Histamine content measurements indicated that RBL-2H3 Sc98 cells took up extracellular histamine for storage in granules and subsequent release after stimulation by an antigen. Profiling and inhibition analysis of possible transporters suggested that the plasma membrane monoamine transporter and organic cation transporter 1 may be candidate transporters for histamine uptake from extracellular spaces, and that vesicular monoamine transporter 2 was responsible for intracellular vesicle uptake. These results may provide the foundation to understand the contribution of exogenous histamine to outward histamine release that is mediated by mechanisms other than conventional exocytosis.

C2 Domains of Munc13-4 Are Crucial for Ca2+-Dependent Degranulation and Cytotoxicity in NK Cells.

In the immune system, degranulation/exocytosis from lymphocytes is crucial for life through facilitating eradication of infected and malignant cells. Dysfunction of the NK cell exocytosis process has been implicated with devastating immune diseases, such as familial hemophagocytic lymphohistiocytosis, yet the underlying molecular mechanisms of such processes have remained elusive. In particular, although the lytic granule exocytosis from NK cells is strictly Ca2+-dependent, the molecular identity of the Ca2+ sensor has yet to be identified. In this article, we show multiple lines of evidence in which point mutations in aspartic acid residues in both C2 domains of human Munc13-4, whose mutation underlies familial hemophagocytic lymphohistiocytosis type 3, diminished exocytosis with dramatically altered Ca2+ sensitivity in both mouse primary NK cells as well as rat mast cell lines. Furthermore, these mutations within the C2 domains severely impaired NK cell cytotoxicity against malignant cells. Total internal reflection fluorescence microscopy analysis revealed that the mutations strikingly altered Ca2+ dependence of fusion pore opening of each single granule and frequency of fusion events. Our results demonstrate that both C2 domains of Munc13-4 play critical roles in Ca2+-dependent exocytosis and cytotoxicity by regulating single-granule membrane fusion dynamics in immune cells.

Ginsenoside Rg3 suppresses mast cell–mediated allergic inflammation via mitogen-activated protein kinase signaling pathway

BackgroundGinsenoside Rg3 (G-Rg3) is the major bioactive ingredient of Panax ginseng and has many pharmacological effects, including antiadipogenic, antiviral, and anticancer effects. However, the effect of G-Rg3 on mast cell–mediated allergic inflammation has not been investigated. MethodThe antiallergic effects of G-Rg3 on allergic inflammation were evaluated using the human and rat mast cell lines HMC-1 and RBL-2H3. Antiallergic effects of G-Rg3 were detected by measuring cyclic adenosine monophosphate (cAMP), detecting calcium influx, and using real-time reverse transcription polymerase chain reaction, enzyme-linked immunosorbent assay, Western blotting, and in vivo experiments. ResultsG-Rg3 decreased histamine release from activated mast cells by enhancing cAMP levels and calcium influx. Proinflammatory cytokine production was suppressed by G-Rg3 treatment via regulation of the mitogen-activated protein kinases/nuclear factor-kappa B and receptor-interacting protein kinase 2 (RIP2)/caspase-1 signaling pathway in mast cells. Moreover, G-Rg3 protected mice against the IgE-mediated passive cutaneous anaphylaxis reaction and compound 48/80-induced anaphylactic shock. ConclusionG-Rg3 may serve as an alternative therapeutic agent for improving allergic inflammatory disorders.

Phospholipid scramblase 1 amplifies anaphylactic reactions in vivo.

Mast cells are critical actors of hypersensitivity type I (allergic) reactions by the release of vasoactive and proinflammatory mediators following their activation by aggregation of the high-affinity receptor for immunoglobulin E (FcεRI). We have previously identified Phospholipid Scramblase 1 (PLSCR1) as a new molecular intermediate of FcεRI signaling that amplifies degranulation of the rat mast cell line RBL-2H3. Here we characterized primary mast cells from Plscr1-/- mice. The absence of PLSCR1 expression did not impact mast cell differentiation as evidenced by unaltered FcεRI expression, general morphology, amount of histamine stored and expression of FcεRI signal effector molecules. No detectable mast cell deficiency was observed in Plscr1-/- adult mice. In dose-response and time-course experiments, primary cultures of mast cells (bone marrow-derived mast cells and peritoneal cell-derived mast cells) generated from Plscr1-/- mice exhibited a reduced release of β-hexosaminidase upon FcεRI engagement as compared to their wild-type counterparts. In vivo, Plscr1-/- mice were protected in a model of passive systemic anaphylaxis when compared to wild-type mice, which was consistent with an observed decrease in the amounts of histamine released in the serum of Plscr1-/- mice during the reaction. Therefore, PLSCR1 aggravates anaphylactic reactions by increasing FcεRI-dependent mast cell degranulation. PLSCR1 could be a new therapeutic target in allergy.

Adaptor protein-3: A key player in RBL-2H3 mast cell mediator release.

Mast cell (MC) secretory granules are Lysosome-Related Organelles (LROs) whose biogenesis is associated with the post-Golgi secretory and endocytic pathways in which the sorting of proteins destined for a specific organelle relies on the recognition of sorting signals by adaptor proteins that direct their incorporation into transport vesicles. The adaptor protein 3 (AP-3) complex mediates protein trafficking between the trans-Golgi network (TGN) and late endosomes, lysosomes, and LROs. AP-3 has a recognized role in LROs biogenesis and regulated secretion in several cell types, including many immune cells such as neutrophils, natural killer cells, and cytotoxic T lymphocytes. However, the relevance of AP-3 for these processes in MCs has not been previously investigated. AP-3 was found to be expressed and distributed in a punctate fashion in rat peritoneal mast cells ex vivo. The rat MC line RBL-2H3 was used as a model system to investigate the role of AP-3 in mast cell secretory granule biogenesis and mediator release. By immunofluorescence and immunoelectron microscopy, AP-3 was localized both to the TGN and early endosomes indicating that AP-3 dependent sorting of proteins to MC secretory granules originates in these organelles. ShRNA mediated depletion of the AP-3 δ subunit was shown to destabilize the AP-3 complex in RBL-2H3 MCs. AP-3 knockdown significantly affected MC regulated secretion of β-hexosaminidase without affecting total cellular enzyme levels. Morphometric evaluation of MC secretory granules by electron microscopy revealed that the area of MC secretory granules in AP-3 knockdown MCs was significantly increased, indicating that AP-3 is involved in MC secretory granule biogenesis. Furthermore, AP-3 knockdown had a selective impact on the secretion of newly formed and newly synthesized mediators. These results show for the first time that AP-3 plays a critical role in secretory granule biogenesis and mediator release in MCs.

Nucleoside 5′-O-monophosphorothioates as modulators of the P2Y14 receptor and mast cell degranulation

Mast cells (MCs) are long-lived resident cells known for their substantial role in antigen-induced anaphylaxis and other immunoglobulin E-mediated allergic reactions as well as tumor promotion. MCs' activation results in the release of pro-inflammatory factors such as histamine, tryptase, tumor necrosis factor or carboxypeptidase A stored in secretory granules. IgE-dependent hypersensitivity has been thought to be the major pathway mediating degranulation of mast cells, but the P2Y14 nucleotide receptor activated by UDP-glucose (UDPG) may also enhance this process. In this study we identified thymidine 5'-O-monophosphorothioate (TMPS) as a molecule inhibiting UDPG-induced degranulation in a rat mast cell line (RBL-2H3). Additionally, TMPS diminished UDPG-evoked intracellular calcium mobilization in a stable HEK293T cell line overexpressing the P2Y14 receptor. Therefore, we demonstrate that the use of thymidine 5'-O-monophosphorothioate might be a novel anti-inflammatory approach based on preventingmast cell activation.

The novel H2 S donor 4-carboxy-phenyl isothiocyanate inhibits mast cell degranulation and renin release by decreasing intracellular calcium.

Hydrogen sulfide (H2 S) modulates many pathophysiological processes, including inflammation and allergic reactions, in which mast cells act as major effector cells. IgE receptor (FcεRI) cross linking leads to an increase in intracellular calcium ([Ca+2 ]i ), a critical step in mast cell degranulation. The aim of this study was to investigate the role of H2 S in [Ca+2 ]i -dependent mast cell activation. We investigated the effects of H2 S, either endogenously produced or released by the slow H2 S donor 4-carboxy-phenyl isothiocyanate (PhNCS-COOH), on antigenic- and non-antigenic degranulation of native murine mast cells, and human and rat (RBL-2H3) mast cell lines. We measured the release of specific mast cell degranulation markers (β-hexosaminidase and renin), as well as changes in [Ca+2 ]i and phosphorylation of proteins downstream of FcεRI activation. Endogenously produced H2 S inhibited antigen-induced degranulation in RBL-2H3. Similarly, H2 S released by PhNCS-COOH (10-300μM) reduced, in a concentration-dependent manner, antigenic and non-antigenic degranulation and renin release in all mast cell types. Notably, PhNCS-COOH also prevented in a concentration-dependent mode the increase in [Ca+2 ]i elicited by Ca+2 ionophore, thapsigargin and FcεRI activation. Moreover, PhNCS-COOH attenuated the phosphorylation of Syk, cPLA-2 and PLCγ1 in antigen-stimulated RBL-2H3 cells. Collectively, our results demonstrate that, by attenuating the phosphorylation of proteins downstream of FcεRI cross-linking on mast cells, H2 S diminishes [Ca+2 ]i availability and thus mast cell degranulation and renin release. These findings suggest that PhNCS-COOH could be a strategic therapeutic tool in mast cell-mediated allergic conditions.

Effects of a Moderately Lower Temperature on the Proliferation and Degranulation of Rat Mast Cells.

Mast cells are traditionally considered as key effector cells in IgE-mediated allergic diseases. However, the roles of mast cells have also been implicated in diverse physiological and pathological processes. Mast cells are distributed in various organs and tissues of various species. Some of the organs and tissues, such as testis, skin, and the upper part of the respiratory tract, have a temperature that is lower than the body's core temperature. The purpose of the present study was to investigate the effects of a lower temperature on the proliferation and degranulation of rat mast cells. Here, we demonstrate that cell growth was retarded at 35°C compared to 37°C for both rat peritoneal mast cells (RPMC) and RBL-2H3, a rat mast cell line. Furthermore, RPMC became more susceptible to degranulation at 35°C compared to 37°C. In contrast, degranulation of RBL-2H3 was not as sensitive to temperature change as RPMC. The functionality of mast cells in unique organs with a lower temperature warrants further analysis.

Different Results of IgE Binding- and Crosslinking-Based Allergy Tests Caused by Allergen Immobilization.

The physicochemical nature of allergen molecules differ from the liquid phase to the solid phase. However, conventional allergy tests are based on the detection of immunoglobulin (Ig)E binding to immobilized allergens. We recently developed an in vitro allergy testing method using a luciferase-reporting humanized rat mast cell line to detect IgE crosslinking-induced luciferase expression (EXiLE test). The aim of the present study was to evaluate the effects of antigen immobilization on the results of different in vitro allergy tests using two anti-ovalbumin (OVA) antibodies (Abs), E-C1 and E-G5, with different properties in the OVA-induced allergic reaction. Both Abs showed clear binding to OVA with an enzyme-linked immunosorbent assay and by BIAcore analysis. However, only E-C1 potentiated EXiLE response for the liquid-phase OVA. On the other hand, OVA immobilized on solid-phase induced EXiLE responses in both E-C1 Ab- and E-G5 Ab-sensitized mast cells. Western blotting of OVA indicated that E-C1 Ab binds both to OVA monomers and dimers, unlike E-G5 Ab, which probably binds only to the OVA dimer. These results suggest that antigen immobilization enhanced IgE crosslinking ability through multimerization of allergen molecules in the solid phase, resulting in an increase in false positives in IgE binding-based conventional in vitro allergy tests. These findings shed light on the physicochemical nature of antigens as an important factor for the development and evaluation of in vitro allergy tests and suggest that mast cell activation-based allergy testing with liquid-phase allergens is a promising strategy to evaluate the physiological interactions of IgE and allergens.

Licarin A is a candidate compound for the treatment of immediate hypersensitivity via inhibition of rat mast cell line RBL-2H3 cells.

We previously demonstrated that some phenylpropanoids are capable of inhibiting activated mast cells. This study evaluated the anti-allergic effects of licarin A, a neolignan isolated from various plants, on antigen-stimulated rat mast cell line. The inhibitory effects of licarin A on histamine release, tumour necrosis factor-α (TNF-α) and prostaglandin D2 (PGD2) production, and cyclooxygenase-2 (COX-2) expression in dinitrophenyl-human serum albumin (DNP-HSA) rat basophilic leukemia cells (DNP-HSA-stimulated RBL-2H3 cells), were investigated by spectrofluorometry, ELISA and immunoblotting. Licarin A significantly and dose-dependently reduced TNF-α production (IC50 12.6 ± 0.3 μm) in DNP-HSA-stimulated RBL-2H3 cells. Furthermore, the levels of PGD2 secretion in DNP-HSA-stimulated cells pretreated with licarin A were lower than those stimulated with DNP-HSA alone (positive control). Treatment with licarin A at 20 μm produced slight suppression of DNP-HSA-induced increases in COX-2 mRNA and protein levels. We identified several signalling pathways that mediated these pharmacological effects. Licarin A treatment tended to reduce phosphorylated protein kinase C alpha/beta II (PKCα/βII) and p38 mitogen-activated protein kinase (MAPK) protein levels. Our results demonstrate that licarin A reduces TNF-α and PGD2 secretion via the inhibition of PKCα/βII and p38 MAPK pathways; this compound may be useful for attenuating immediate hypersensitivity.

Dectin-1-mediated Signaling Leads to Characteristic Gene Expressions and Cytokine Secretion via Spleen Tyrosine Kinase (Syk) in Rat Mast Cells

Dectin-1 recognizes β-glucan and plays important roles for the antifungal immunity through the activation of spleen tyrosine kinase (Syk) in dendritic cells or macrophages. Recently, expression of Dectin-1 was also identified in human and mouse mast cells, although its physiological roles were largely unknown. In this report, rat mast cell line RBL-2H3 was analyzed to investigate the molecular mechanism of Dectin-1-mediated activation and responses of mast cells. Treatment of cells with Dectin-1-specific agonist curdlan induced tyrosine phosphorylation of cellular proteins and the interaction of Dectin-1 with the Src homology 2 domain of Syk. These responses depended on tyrosine phosphorylation of the hemi-immunoreceptor tyrosine-based activation motif in the cytoplasmic tail of Dectin-1, whereas they were independent of the γ-subunit of high-affinity IgE receptor. DNA microarray and real-time PCR analyses showed that Dectin-1-mediated signaling stimulated gene expression of transcription factor Nfkbiz and inflammatory cytokines, such as monocyte chemoattractant protein-1, IL-3, IL-4, IL-13, and tumor necrosis factor (TNF)-α. The response was abrogated by pretreatment with Syk inhibitor R406. These results suggest that Syk is critical for Dectin-1-mediated activation of mast cells, although the signaling differs from that triggered by FcϵRI activation. In addition, these gene expressions induced by curdlan stimulation were specifically observed in mast cells, suggesting that Dectin-1-mediated signaling of mast cells offers new insight into the antifungal immunity.

Histone Deacetylase Regulates IL‐4 Gene Expression in Mast Cells by Oxidative Stress

Objectives: Many pro-inflammatory cytokines are regulated by acetylation and deacetylation of core histone. Since dysregulation of Th2 cytokine production is a key for the pathogenesis of allergic diseases, we examined the role of histone deacetylase (HDAC) on expression of IL-4 gene in mast cells. We also examined whether oxidative stress has some impact on HDAC activity. Methods: RBL-2H3 cells, a rat mast cell line, were sensitized overnight with DNP-specific IgE. The cells were then treated with HDAC inhibitors (trichostatin A) for 15 min and stimulated with DNP-antigen. After 2 hour incubation, total RNA was isolated to determine the level of IL-4 gene transcription by real-time reverse transcriptase polymerase chain reaction (Taqman system). After incubated with H2O2 for 0 to 24 hours, HDAC activity was measured in nuclear extracts obtained from the RBL-2H3 cells with HDAC Fluorescent activity assay kit (BIOMOL) as well as the detection of IL-4 mRNA. Results: IL-4 mRNA expression was induced with antigen in IgE-sensitized RBL-2H3 cells. Pretreatment of trichostatin A and H2O2 enhanced IL-4 mRNA expression with dose-dependent manner. There is 5-fold induction of IL-4 mRNA by HDAC inhibitors. HDAC activity of RBL-2H3 cells were reduced with H2O2 treatment. Conclusions: Our results suggest that oxidative stress may up-regulate IL-4 gene expression in mast cell via decrease of HDAC activity.

Transcriptional regulation and proteolytic processing of perlecan in mast cells lead to the production of forms that contain the alpha2/beta1 integrin binding site: roles in wound healing and tissue regeneration (544.3)

This study demonstrated that primary human mast cells as well as the rat and human mast cell lines, RBL‐2H3 and HMC‐1, produce the heparan sulfate proteoglycan (HSPG), perlecan, with a Mr of 640kDa as well as smaller molecular weight species of 300 and 130kDa. Utilizing domain‐specific antibodies and N‐terminal sequencing we confirmed that both forms contained the C‐terminal module of the protein core, which were generated by mast cell‐derived proteases. Fractions from mast cell cultures that were enriched for these fragments were shown to bind endothelial cells via the alpha2/beta1 integrin and stimulate the migration of cells in “scratch assays”. Both of these activities were inhibited by incubation with antibodies reactive to the C‐terminus of the perlecan protein core. This study showed that the transcriptional regulation of the HSPG2 gene is more complex than first thought, particularly in mast cells. Domain specific RT‐PCR experiments demonstrated that these cells were capable of splicing the perlecan gene (HSPG2) and when we performed quantitative PCR experiments, we demonstrated that the C‐terminal region was over‐represented compared to the N‐terminal region. This together with the data demonstrating proteolytic processing suggest that the C‐terminal region of perlecan, which contains the alpha2/beta1 integrin binding site may have downstream biological functions that regulate angiogenesis and matrix turnover and thereby promote wound healing and tissue regenerative processes.

Escherichia coli Exposure Inhibits Exocytic SNARE‐Mediated Membrane Fusion in Mast Cells

Mast cells orchestrate the allergic response through the release of proinflammatory mediators, which is driven by the fusion of cytoplasmic secretory granules with the plasma membrane. During this process, SNARE proteins including Syntaxin4, SNAP23 and VAMP8 play a key role. Following stimulation, the kinase IKKβ interacts with and phosphorylates the t-SNARE SNAP23. Phosphorylated SNAP23 then associates with Syntaxin4 and the v-SNARE VAMP8 to form a ternary SNARE complex, which drives membrane fusion and mediator release. Interestingly, mast cell degranulation is impaired following exposure to bacteria such as Escherichia coli. However, the molecular mechanism(s) by which this occurs is unknown. Here, we show that E. coli exposure rapidly and additively inhibits degranulation in the RBL-2H3 rat mast cell line. Following co-culture with E. coli, the interaction between IKKβ and SNAP23 is disrupted, resulting in the hypophosphorylation of SNAP23. Subsequent formation of the ternary SNARE complex between SNAP23, Syntaxin4 and VAMP8 is strongly reduced. Collectively, these results demonstrate that E. coli exposure inhibits the formation of VAMP8-containing exocytic SNARE complexes and thus the release of VAMP8-dependent granules by interfering with SNAP23 phosphorylation.