A common signaling pathway leading to degranulation in mast cells and its regulation by CCR1-ligand.

BACKGROUND: Signal transduction pathways mediated by various receptors expressed on mast cells are thought to be complex, and inhibitory signals that turn off activating signals are not known. METHODS: Upstream signaling cascades mediated by several known receptors in bone marrow-derived mast cells that lead to degranulation and mediator release were studied by immunoblotting and immunoprecipitation. Small interfering RNAs and knockout mice were used to confirm findings. RESULTS: All ligands tested including IgE/Ag, SCF, HSP70, CCL3, and its valiant eMIP induced phosphorylation of linker for activation of T cells (LAT), which triggered their receptor-mediated downstream signaling cascades that controlled degranulation and mediator release. Phosphorylation of lymphocyte-specific protein kinase (Lck) was induced by each ligand, which commonly played an indispensable role in LAT phosphorylation. In contrast, phosphorylation of spleen tyrosine kinase was additionally induced in cells stimulated only with IgE/Ag and SCF, which is also associated with LAT phosphorylation in part. Degranulation and mediator release induced by IgE/Ag, SCF, or HSP70 were enhanced by nanomolar doses of CCR1 ligands CCL3 and eMIP via enhanced LAT phosphorylation. On the other hand, micromolar doses of CCR1 ligand inhibited degranulation and mediator release from mast cells stimulated with IgE/Ag, SCF, or HSP70 by de-phosphorylation of phosphorylated Lck with Src homology region 2 domain-containing phosphatase-1. CONCLUSIONS: Linker for activation of T cells plays a central role in signal transduction pathways in mast cells stimulated with any ligand tested. Dose-dependent alternate costimulation and inhibition of CCR1 ligands in IgE/Ag-, SCF-, or HSP70-stimulated mast cells occur at the level of Lck-LAT phosphorylation.

The orphan nuclear receptor NR4A1 promotes FcεRI-stimulated mast cell activation and anaphylaxis by counteracting the inhibitory LKB1/AMPK axis.

BACKGROUND: Nuclear receptor subfamily 4 group A member 1 (NR4A1), an orphan nuclear receptor, has been implicated in several biological events such as metabolism, apoptosis, and inflammation. Recent studies indicate a potential role for NR4A1 in mast cells, yet its role in allergic responses remains largely unknown. OBJECTIVES: The aim of this study was to clarify the role of NR4A1 in mast cell activation and anaphylaxis. METHODS: To evaluate the function of NR4A1 in mast cells, the impacts of siRNA knockdown, gene knockout, adenoviral overexpression, and pharmacological inhibition of NR4A1 on FcεRI signaling and effector functions in mouse bone marrow-derived mast cells (BMMCs) in vitro and on anaphylactic responses in vivo were evaluated. RESULTS: Knockdown or knockout of NR4A1 markedly suppressed degranulation and lipid mediator production by FcεRI-crosslinked BMMCs, while its overexpression augmented these responses. Treatment with a NR4A1 antagonist also blocked mast cell activation to a similar extent as NR4A1 knockdown or knockout. Moreover, mast cell-specific NR4A1-deficient mice displayed dampened anaphylactic responses in vivo. Mechanistically, NR4A1 promoted FcεRI signaling by counteracting the liver kinase B1 (LKB1)/adenosine monophosphate-activated protein kinase (AMPK) axis. Following FcεRI crosslinking, NR4A1 bound to the LKB1/AMPK complex and sequestered it in the nucleus, thereby promoting FcεRI downstream signaling pathways. Silencing or knockout of LKB1/AMPK largely abrogated the effect of NR4A1 on mast cell activation. Additionally, NR4A1 facilitated spleen tyrosine kinase activation independently of LKB1/AMPK. CONCLUSIONS: Nuclear receptor subfamily 4 group A member 1 positively regulates mast cell activation by antagonizing the LKB1-AMPK-dependent negative regulatory axis. This finding may provide a novel therapeutic strategy for the development of anti-allergic compounds.

Author Correction: Sirt1 negatively regulates FcεRI-mediated mast cell activation through AMPK- and PTP1B-dependent processes.

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

Sauchinone suppresses FcεRI-mediated mast cell signaling and anaphylaxis through regulation of LKB1/AMPK axis and SHP-1-Syk signaling module.

Sauchinone, the biologically active lignan of Saururus chinensis, has been reported to have anti-inflammatory, antitumor, antioxidant, and hepatoprotective properties. However, little is known about the effect of sauchinone on FcεRI-mediated mast cell activation. The aim of this study was to evaluate the anti-allergic activity of sauchinone and the underlying mechanism using mouse bone marrow-derived mast cells (BMMCs) and the mast cell-mediated passive cutaneous anaphylaxis (PCA) model. Sauchinone markedly suppressed FcεRI-mediated activation of positive signaling mediators, including Syk, linker for activation of T cells (LAT), phospholipase C (PLC)γ, mitogen-activated protein (MAP) kinases, Akt, IκB kinase (IKK), and intracellular Ca2+, and increased the activation of negative signaling mediators, including liver kinase B (LKB)1/AMP-activated protein kinase (AMPK) and Src homology 2 domain-containing protein tyrosine phosphatase (SHP)-1. Interestingly, sauchinone increased the interaction between SHP-1 and Syk. Consequently, sauchinone significantly suppressed FcεRI-mediated BMMC degranulation and synthesis of eicosanoids and cytokines. These inhibitory effects of sauchinone were diminished in BMMCs treated with siRNAs targeting LKB1, AMPKα2, or SHP-1, and in BMMCs isolated from AMPKα2-deficient mice. In addition, administration of sauchinone markedly suppressed the IgE-mediated PCA reaction in wild-type mice, and this inhibitory effect was significantly reduced in AMPKα2-/- mice. Taken together, these data suggest that sauchinone suppresses FcεRI-mediated mast cell activation and anaphylaxis through modulation of the LKB1/AMPK and SHP-1/Syk pathways. Therefore, sauchinone might be a potential therapeutic agent for the treatment of allergic inflammatory diseases.

Tanshinone IIA suppresses FcεRI-mediated mast cell signaling and anaphylaxis by activation of the Sirt1/LKB1/AMPK pathway.

AMP-activated protein kinase (AMPK) and its upstream mediators liver kinase B1 (LKB1) and sirtuin 1 (Sirt1) are generally known as key regulators of metabolism. We have recently reported that the AMPK pathway negatively regulates mast cell activation and anaphylaxis. Tanshinone IIA (Tan IIA), an active component of Salvia miltiorrhiza extract that is currently used for the treatment of cardiovascular and cerebrovascular diseases, shows anti-diabetic activity and improves insulin resistance in db/db mice through activation of AMPK. The aim of this study was to evaluate the anti-allergic activity of Tan IIA in vivo and to investigate the underlying mechanism in vitro in the context of AMPK signaling. The anti-allergic effect of Tan IIA was evaluated using mouse bone marrow-derived mast cells (BMMCs) from AMPKα2-/- or Sirt1-/- mice, or BMMCs transfected with siRNAs specific for AMPKα2, LKB1, or Sirt1. AMPKα2-/- and Sirt1-/- mice were used to confirm the anti-allergic effect of Tan IIA in anaphylaxis in vivo. Tan IIA dose-dependently inhibited FcεRI-mediated degranulation and production of eicosanoids and cytokines in BMMCs. These inhibitory effects were diminished by siRNA-mediated knockdown or genetic deletion of AMPKα2 or Sirt1. Moreover, Tan IIA inhibited a mast cell-mediated local passive anaphylactic reaction in wild-type mice, but not in AMPKα2-/- or Sirt1-/- mice. In conclusion, Tan IIA suppresses FcεRI-mediated mast cell activation and anaphylaxis through activation of the inhibitory Sirt1-LKB1-AMPK pathway. Thus, Tan IIA may be useful as a new therapeutic agent for mast cell-mediated allergic diseases.

Jellyfish extract induces apoptotic cell death through the p38 pathway and cell cycle arrest in chronic myelogenous leukemia K562 cells.

Jellyfish species are widely distributed in the world's oceans, and their population is rapidly increasing. Jellyfish extracts have several biological functions, such as cytotoxic, anti-microbial, and antioxidant activities in cells and organisms. However, the anti-cancer effect of Jellyfish extract has not yet been examined. We used chronic myelogenous leukemia K562 cells to evaluate the mechanisms of anti-cancer activity of hexane extracts from Nomura's jellyfish in vitro. In this study, jellyfish are subjected to hexane extraction, and the extract is shown to have an anticancer effect on chronic myelogenous leukemia K562 cells. Interestingly, the present results show that jellyfish hexane extract (Jellyfish-HE) induces apoptosis in a dose- and time-dependent manner. To identify the mechanism(s) underlying Jellyfish-HE-induced apoptosis in K562 cells, we examined the effects of Jellyfish-HE on activation of caspase and mitogen-activated protein kinases (MAPKs), which are responsible for cell cycle progression. Induction of apoptosis by Jellyfish-HE occurred through the activation of caspases-3,-8 and -9 and phosphorylation of p38. Jellyfish-HE-induced apoptosis was blocked by a caspase inhibitor, Z-VAD. Moreover, during apoptosis in K562 cells, p38 MAPK was inhibited by pretreatment with SB203580, an inhibitor of p38. SB203580 blocked jellyfish-HE-induced apoptosis. Additionally, Jellyfish-HE markedly arrests the cell cycle in the G0/G1 phase. Therefore, taken together, the results imply that the anti-cancer activity of Jellyfish-HE may be mediated apoptosis by induction of caspases and activation of MAPK, especially phosphorylation of p38, and cell cycle arrest at the Go/G1 phase in K562 cells.

Sirt1 negatively regulates FcεRI-mediated mast cell activation through AMPK- and PTP1B-dependent processes.

Sirt1, a key regulator of metabolism and longevity, has recently been implicated in the regulation of allergic reactions, although the underlying mechanism remains unclear. Here we show that Sirt1 negatively regulates FcεRI-stimulated mast cell activation and anaphylaxis through two mutually regulated pathways involving AMP-activated protein kinase (AMPK) and protein tyrosine phosphatase 1B (PTP1B). Mast cell-specific knockout of Sirt1 dampened AMPK-dependent suppression of FcεRI signaling, thereby augmenting mast cell activation both in vitro and in vivo. Sirt1 inhibition of FcεRI signaling also involved an alternative component, PTP1B, which attenuated the inhibitory AMPK pathway and conversely enhanced the stimulatory Syk pathway, uncovering a novel role of this phosphatase. Moreover, a Sirt1 activator resveratrol stimulated the inhibitory AMPK axis, with reciprocal suppression of the stimulatory PTP1B/Syk axis, thus potently inhibiting anaphylaxis. Overall, our results provide a molecular explanation for the beneficial role of Sirt1 in allergy and underscore a potential application of Sirt1 activators as a new class of anti-allergic agents.

15,16-Dihydrotanshinone I suppresses IgE-Ag stimulated mouse bone marrow-derived mast cell activation by inhibiting Syk kinase.

ETHNOPHARMACOLOGICAL RELEVANCE: 15,16-Dihydrotanshinone I (DHT-I), isolated from the dried root of Salvia miltiorrhiza Bung, which is traditionally used to treat cardiovascular and inflammatory diseases agent in Chinese medicine. DHT-I has been reported to have a broad range of biological activities, including antibacterial activity, and has been used to treat circulatory disorders, hepatitis, inflammation, cancer, and neurodegenerative diseases. AIM OF THE STUDY: The aim of this study was to evaluate the anti-allergic inflammatory effects of DHT-I on degranulation and on the generation of eicosanoids, such as, prostaglandin D2 (PGD2) and leukotriene C4 (LTC4), in IgE/Ag-stimulated bone marrow-derived mast cells (BMMCs). MATERIALS AND METHODS: The anti-allergic inflammatory activity of DHT-I was evaluated using BMMCs. The effects of DHT-I on mast cell activation were investigated by following degranulation and eicosanoid generation using ELISA and immunoblotting and immunoprecipitation techniques. RESULTS: DHT-I at a concentration of 20µM markedly inhibited degranulation and the generation of PGD2 and LTC4 in IgE/Ag-stimulated BMMCs (about 90% inhibitions, respectively). Analyses of FcεRI-mediated signaling pathways demonstrated that DHT-I inhibited the phosphorylations of spleen tyrosine kinase (Syk) and linker for activation of T cells (LAT), and inhibited downstream signaling process, including [Ca(2+)]i mobilization induced by the phosphorylation of phospholipase Cγ1 (PLCγ1), and the activations of mitogen-activated protein kinases (MAPKs) and the Akt-nuclear factor-κB (NF-κB) pathway. CONCLUSIONS: DHT-1 inhibits the release of allergic inflammatory mediators from IgE/Ag-stimulated mast cells by suppressing a FcεRI-mediated Syk-dependent signal pathway. This result suggests DHT-I offers a novel developmental basis for drugs targeting allergic inflammatory diseases.

Isothiocyanates inhibit the invasion and migration of C6 glioma cells by blocking FAK/JNK-mediated MMP-9 expression.

Isothiocyanates (ITCs) derived from cruciferous vegetables, including benzyl isothiocyanate (BITC), phenethyl isothiocyanate (PEITC) and sulforaphane (SFN), exhibit preventative effects against various types of cancers. Yet, the inhibitory effects of ITCs on C6 glioma cell invasion and migration have not been reported. Thus, we aimed to analyze ITC-regulated MMP-9 activation, a crucial enzyme of cancer metastasis that degrades the extracellular matrix, in C6 glioma cells to investigate the inhibitory effects on cancer invasion and migration by ITCs. In the present study, we found that ITCs specifically suppressed PMA-induced MMP-9 secretion and protein expression. The inhibitory effects of ITCs on PMA-induced MMP-9 expression were found to be associated with the inhibition of MMP-9 transcription levels through suppression of nuclear translocation of NF-κB and activator protein-1 (AP-1). It was also confirmed that ITCs decreased MMP-9-mediated signaling such as FAK and JNK, whereas they had no effect on the phosphorylation of ERK and p38. Moreover, wound-healing and Τranswell invasion assays showed that ITCs inhibited the migration and invasion of C6 glioma cells. These results suggest that ITCs could be potential agents for the prevention of C6 glioma cell migration and invasion by decreasing FAK/JNK-mediated MMP-9 expression.