Pentacyclic triterpenoids, including ursolic acid (UA), are bioactive compounds with multiple biological activities involving anti-inflammatory effects. However, the mode of their action on mast cells, key players in the early stages of allergic inflammation, and underlying molecular mechanisms remain enigmatic. To better understand the effect of UA on mast cell signaling, here we examined the consequences of short-term treatment of mouse bone marrow-derived mast cells with UA. Using IgE-sensitized and antigen- or thapsigargin-activated cells, we found that 15 min exposure to UA inhibited high affinity IgE receptor (FcεRI)-mediated degranulation, calcium response, and extracellular calcium uptake. We also found that UA inhibited migration of mouse bone marrow-derived mast cells toward antigen but not toward prostaglandin E2 and stem cell factor. Compared to control antigen-activated cells, UA enhanced the production of tumor necrosis factor-α at the mRNA and protein levels. However, secretion of this cytokine was inhibited. Further analysis showed that UA enhanced tyrosine phosphorylation of the SYK kinase and several other proteins involved in the early stages of FcεRI signaling, even in the absence of antigen activation, but inhibited or reduced their further phosphorylation at later stages. In addition, we show that UA induced changes in the properties of detergent-resistant plasma membrane microdomains and reduced antibody-mediated clustering of the FcεRI and glycosylphosphatidylinositol-anchored protein Thy-1. Finally, UA inhibited mobility of the FcεRI and cholesterol. These combined data suggest that UA exerts its effects, at least in part, via lipid-centric plasma membrane perturbations, hence affecting the functions of the FcεRI signalosome.

• Keywords
• immunoglobulin E, lipid raft, mast cell, plasma membrane, signal transduction, tumor necrosis factor, tyrosine kinase,
• MeSH
• Antigens metabolism   MeSH
• Cell Degranulation MeSH
• Ursolic Acid MeSH
• Lipids pharmacology   MeSH
• Mast Cells metabolism   MeSH
• Mice MeSH
• Receptors, IgE * metabolism   MeSH
• Triterpenes * pharmacology   metabolism   MeSH
• Calcium metabolism   MeSH
• Animals MeSH
• Check Tag
• Mice MeSH
• Animals MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Names of Substances
• Antigens MeSH
• Lipids MeSH
• Receptors, IgE * MeSH
• Triterpenes * MeSH
• Calcium MeSH

A better understanding of the molecular mechanisms leading to mast cell migration and chemotaxis is the long-term goal in mast cell research and is essential for comprehension of mast cell function in health and disease. Various techniques have been developed in recent decades for in vitro and in vivo assessment of mast cell motility and chemotaxis. In this chapter, three microscopy assays facilitating real-time quantification of mast cell chemotaxis and migration are described, focusing on individual cell tracking and data analysis.

• Keywords
• Cell migration, Cell tracking, Chemoattractant, Chemokine, Chemotaxis, Mast cells,
• MeSH
• Cell Migration Assays methods   MeSH
• Biological Assay methods   MeSH
• Cell Tracking methods   MeSH
• Chemotaxis physiology   MeSH
• Fibronectins metabolism   MeSH
• Humans MeSH
• Mast Cells cytology   physiology   MeSH
• Microscopy methods   MeSH
• Mice MeSH
• Computer Systems MeSH
• Cell Movement physiology   MeSH
• Environment, Controlled MeSH
• Sepharose MeSH
• Software MeSH
• Animals MeSH
• Check Tag
• Humans MeSH
• Mice MeSH
• Animals MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Names of Substances
• Fibronectins MeSH
• Sepharose MeSH

Background: Mucosal mast cells (MC) are key players in IgE-mediated food allergy (FA). The evidence on the interaction between gut microbiota, MC and susceptibility to FA is contradictory. Objective: We tested the hypothesis that commensal bacteria are essential for MC migration to the gut and their maturation impacting the susceptibility to FA. Methods: The development and severity of FA symptoms was studied in sensitized germ-free (GF), conventional (CV), and mice mono-colonized with L. plantarum WCFS1 or co-housed with CV mice. MC were phenotypically and functionally characterized. Results: Systemic sensitization and oral challenge of GF mice with ovalbumin led to increased levels of specific IgE in serum compared to CV mice. Remarkably, despite the high levels of sensitization, GF mice did not develop diarrhea or anaphylactic hypothermia, common symptoms of FA. In the gut, GF mice expressed low levels of the MC tissue-homing markers CXCL1 and CXCL2, and harbored fewer MC which exhibited lower levels of MC protease-1 after challenge. Additionally, MC in GF mice were less mature as confirmed by flow-cytometry and their functionality was impaired as shown by reduced edema formation after injection of degranulation-provoking compound 48/80. Co-housing of GF mice with CV mice fully restored their susceptibility to develop FA. However, this did not occur when mice were mono-colonized with L. plantarum. Conclusion: Our results demonstrate that microbiota-induced maturation and gut-homing of MC is a critical step for the development of symptoms of experimental FA. This new mechanistic insight into microbiota-MC-FA axis can be exploited in the prevention and treatment of FA in humans.

• Keywords
• commensal bacteria, food allergy, germ-free, mast cells, mouse models,
• MeSH
• Biomarkers MeSH
• Cell Differentiation genetics   immunology   MeSH
• Cytokines metabolism   MeSH
• Cell Degranulation genetics   immunology   MeSH
• Germ-Free Life MeSH
• Mast Cells immunology   metabolism   MeSH
• Metagenome MeSH
• Metagenomics methods   MeSH
• Microbiota * immunology   MeSH
• Disease Models, Animal MeSH
• Mice MeSH
• Disease Susceptibility MeSH
• Food Hypersensitivity etiology   metabolism   pathology   MeSH
• RNA, Ribosomal, 16S MeSH
• Gastrointestinal Microbiome MeSH
• Animals MeSH
• Check Tag
• Mice MeSH
• Female MeSH
• Animals MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Names of Substances
• Biomarkers MeSH
• Cytokines MeSH
• RNA, Ribosomal, 16S MeSH

Protein 4.1R, a member of the 4.1 family, functions as a bridge between cytoskeletal and plasma membrane proteins. It is expressed in T cells, where it binds to a linker for activation of T cell (LAT) family member 1 and inhibits its phosphorylation and downstream signaling events after T cell receptor triggering. The role of the 4.1R protein in cell activation through other immunoreceptors is not known. In this study, we used 4.1R-deficient (4.1R-KO) and 4.1R wild-type (WT) mice and explored the role of the 4.1R protein in the high-affinity IgE receptor (FcεRI) signaling in mast cells. We found that bone marrow mast cells (BMMCs) derived from 4.1R-KO mice showed normal growth in vitro and expressed FcεRI and c-KIT at levels comparable to WT cells. However, 4.1R-KO cells exhibited reduced antigen-induced degranulation, calcium response, and secretion of tumor necrosis factor-α. Chemotaxis toward antigen and stem cell factor (SCF) and spreading on fibronectin were also reduced in 4.1R-KO BMMCs, whereas prostaglandin E2-mediated chemotaxis was not affected. Antibody-induced aggregation of tetraspanin CD9 inhibited chemotaxis toward antigen in WT but not 4.1R-KO BMMCs, implying a CD9-4.1R protein cross-talk. Further studies documented that in the absence of 4.1R, antigen-mediated phosphorylation of FcεRI β and γ subunits was not affected, but phosphorylation of SYK and subsequent signaling events such as phosphorylation of LAT1, phospholipase Cγ1, phosphatases (SHP1 and SHIP), MAP family kinases (p38, ERK, JNK), STAT5, CBL, and mTOR were reduced. Immunoprecipitation studies showed the presence of both LAT1 and LAT2 (LAT, family member 2) in 4.1R immunocomplexes. The positive regulatory role of 4.1R protein in FcεRI-triggered activation was supported by in vivo experiments in which 4.1R-KO mice showed the normal presence of mast cells in the ears and peritoneum, but exhibited impaired passive cutaneous anaphylaxis. The combined data indicate that the 4.1R protein functions as a positive regulator in the early activation events after FcεRI triggering in mast cells.

• Keywords
• 4.1R protein, chemotaxis, degranulation, mast cell, passive cutaneous anaphylaxis,
• MeSH
• Chemotaxis immunology   MeSH
• Cell Degranulation immunology   MeSH
• Mast Cells immunology   metabolism   MeSH
• Microfilament Proteins immunology   metabolism   MeSH
• Mice, Inbred C57BL MeSH
• Mice, Knockout MeSH
• Mice MeSH
• Passive Cutaneous Anaphylaxis immunology   MeSH
• Receptors, IgE immunology   metabolism   MeSH
• Animals MeSH
• Check Tag
• Mice MeSH
• Animals MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Names of Substances
• Epb41 protein, mouse MeSH Browser
• Microfilament Proteins MeSH
• Receptors, IgE MeSH

C-terminal Src kinase (CSK) is a major negative regulator of Src family tyrosine kinases (SFKs) that play critical roles in immunoreceptor signaling. CSK is brought in contiguity to the plasma membrane-bound SFKs via binding to transmembrane adaptor PAG, also known as CSK-binding protein. The recent finding that PAG can function as a positive regulator of the high-affinity IgE receptor (FcεRI)-mediated mast cell signaling suggested that PAG and CSK have some non-overlapping regulatory functions in mast cell activation. To determine the regulatory roles of CSK in FcεRI signaling, we derived bone marrow-derived mast cells (BMMCs) with reduced or enhanced expression of CSK from wild-type (WT) or PAG knockout (KO) mice and analyzed their FcεRI-mediated activation events. We found that in contrast to PAG-KO cells, antigen-activated BMMCs with CSK knockdown (KD) exhibited significantly higher degranulation, calcium response, and tyrosine phosphorylation of FcεRI, SYK, and phospholipase C. Interestingly, FcεRI-mediated events in BMMCs with PAG-KO were restored upon CSK silencing. BMMCs with CSK-KD/PAG-KO resembled BMMCs with CSK-KD alone. Unexpectedly, cells with CSK-KD showed reduced kinase activity of LYN and decreased phosphorylation of transcription factor STAT5. This was accompanied by impaired production of proinflammatory cytokines and chemokines in antigen-activated cells. In line with this, BMMCs with CSK-KD exhibited enhanced phosphorylation of protein phosphatase SHP-1, which provides a negative feedback loop for regulating phosphorylation of STAT5 and LYN kinase activity. Furthermore, we found that in WT BMMCs SHP-1 forms complexes containing LYN, CSK, and STAT5. Altogether, our data demonstrate that in FcεRI-activated mast cells CSK is a negative regulator of degranulation and chemotaxis, but a positive regulator of adhesion to fibronectin and production of proinflammatory cytokines. Some of these pathways are not dependent on the presence of PAG.

• Keywords
• C-terminal Src kinase, LYN, SHP-1, STAT5, cytokines, degranulation, mast cell, phosphoprotein associated with glycosphingolipid-enriched microdomains,
• MeSH
• Analysis of Variance MeSH
• Bone Marrow Cells physiology   MeSH
• CSK Tyrosine-Protein Kinase MeSH
• Cytokines metabolism   MeSH
• Cell Degranulation MeSH
• Fibronectins metabolism   MeSH
• Phosphoproteins metabolism   MeSH
• Phosphorylation MeSH
• Genetic Vectors MeSH
• HEK293 Cells MeSH
• Humans MeSH
• Mast Cells physiology   MeSH
• Membrane Proteins metabolism   MeSH
• Intercellular Signaling Peptides and Proteins MeSH
• Mice, Inbred C57BL MeSH
• Mice, Knockout MeSH
• Mice MeSH
• Receptors, IgE metabolism   MeSH
• Signal Transduction immunology   MeSH
• src-Family Kinases metabolism   physiology   MeSH
• STAT5 Transcription Factor metabolism   MeSH
• Tyrosine metabolism   MeSH
• Protein Tyrosine Phosphatase, Non-Receptor Type 6 metabolism   MeSH
• Calcium metabolism   MeSH
• Animals MeSH
• Check Tag
• Humans MeSH
• Mice MeSH
• Animals MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Names of Substances
• CSK Tyrosine-Protein Kinase MeSH
• CSK protein, human MeSH Browser
• Cytokines MeSH
• Fibronectins MeSH
• Phosphoproteins MeSH
• lyn protein-tyrosine kinase MeSH Browser
• Membrane Proteins MeSH
• Intercellular Signaling Peptides and Proteins MeSH
• Pag protein, mouse MeSH Browser
• Pag1 protein, mouse MeSH Browser
• Ptpn6 protein, mouse MeSH Browser
• Receptors, IgE MeSH
• src-Family Kinases MeSH
• STAT5 Transcription Factor MeSH
• Tyrosine MeSH
• Protein Tyrosine Phosphatase, Non-Receptor Type 6 MeSH
• Calcium MeSH

Mast cells play crucial roles in both innate and adaptive arms of the immune system. Along with basophils, mast cells are essential effector cells for allergic inflammation that causes asthma, allergic rhinitis, food allergy and atopic dermatitis. Mast cells are usually increased in inflammatory sites of allergy and, upon activation, release various chemical, lipid, peptide and protein mediators of allergic reactions. Since antigen/immunoglobulin E (IgE)-mediated activation of these cells is a central event to trigger allergic reactions, innumerable studies have been conducted on how these cells are activated through cross-linking of the high-affinity IgE receptor (FcεRI). Development of mature mast cells from their progenitor cells is under the influence of several growth factors, of which the stem cell factor (SCF) seems to be the most important. Therefore, how SCF induces mast cell development and activation via its receptor, KIT, has been studied extensively, including a cross-talk between KIT and FcεRI signaling pathways. Although our understanding of the signaling mechanisms of the FcεRI and KIT pathways is far from complete, pharmaceutical applications of the knowledge about these pathways are underway. This review will focus on recent progresses in FcεRI and KIT signaling and chemotaxis.

• Keywords
• Chemotaxis, IgE receptor, KIT receptor, Mast cell, Plasma membrane, Signal transduction,
• MeSH
• Chemotaxis * drug effects   MeSH
• Humans MeSH
• Mast Cells cytology   drug effects   MeSH
• Signal Transduction * drug effects   MeSH
• Animals MeSH
• Check Tag
• Humans MeSH
• Animals MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Review MeSH
• Research Support, N.I.H., Extramural MeSH

The transmembrane adaptor protein PAG/CBP (here, PAG) is expressed in multiple cell types. Tyrosine-phosphorylated PAG serves as an anchor for C-terminal SRC kinase, an inhibitor of SRC-family kinases. The role of PAG as a negative regulator of immunoreceptor signaling has been examined in several model systems, but no functions in vivo have been determined. Here, we examined the activation of bone marrow-derived mast cells (BMMCs) with PAG knockout and PAG knockdown and the corresponding controls. Our data show that PAG-deficient BMMCs exhibit impaired antigen-induced degranulation, extracellular calcium uptake, tyrosine phosphorylation of several key signaling proteins (including the high-affinity IgE receptor subunits, spleen tyrosine kinase, and phospholipase C), production of several cytokines and chemokines, and chemotaxis. The enzymatic activities of the LYN and FYN kinases were increased in nonactivated cells, suggesting the involvement of a LYN- and/or a FYN-dependent negative regulatory loop. When BMMCs from PAG-knockout mice were activated via the KIT receptor, enhanced degranulation and tyrosine phosphorylation of the receptor were observed. In vivo experiments showed that PAG is a positive regulator of passive systemic anaphylaxis. The combined data indicate that PAG can function as both a positive and a negative regulator of mast cell signaling, depending upon the signaling pathway involved.

• MeSH
• Anaphylaxis genetics   MeSH
• Bone Marrow Cells metabolism   physiology   MeSH
• CSK Tyrosine-Protein Kinase MeSH
• Cell Degranulation MeSH
• Type C Phospholipases metabolism   MeSH
• Phosphoproteins genetics   MeSH
• Phosphorylation MeSH
• Intracellular Signaling Peptides and Proteins metabolism   MeSH
• Syk Kinase MeSH
• RNA, Small Interfering MeSH
• Mast Cells metabolism   physiology   MeSH
• Membrane Proteins genetics   MeSH
• Mice, Inbred C57BL MeSH
• Mice, Knockout MeSH
• Mice MeSH
• Proto-Oncogene Proteins c-fyn biosynthesis   MeSH
• Proto-Oncogene Proteins c-kit metabolism   MeSH
• Receptors, IgE metabolism   MeSH
• RNA Interference MeSH
• Signal Transduction MeSH
• src-Family Kinases biosynthesis   metabolism   MeSH
• Protein-Tyrosine Kinases metabolism   MeSH
• Calcium metabolism   MeSH
• Animals MeSH
• Check Tag
• Mice MeSH
• Animals MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Names of Substances
• CSK Tyrosine-Protein Kinase MeSH
• Type C Phospholipases MeSH
• Phosphoproteins MeSH
• Fyn protein, mouse MeSH Browser
• Intracellular Signaling Peptides and Proteins MeSH
• Syk Kinase MeSH
• lyn protein-tyrosine kinase MeSH Browser
• RNA, Small Interfering MeSH
• Membrane Proteins MeSH
• Pag1 protein, mouse MeSH Browser
• Proto-Oncogene Proteins c-fyn MeSH
• Proto-Oncogene Proteins c-kit MeSH
• Receptors, IgE MeSH
• src-Family Kinases MeSH
• Syk protein, mouse MeSH Browser
• Protein-Tyrosine Kinases MeSH
• Calcium MeSH

Chemotaxis, a process leading to movement of cells toward increasing concentrations of chemoattractants, is essential, among others, for recruitment of mast cells within target tissues where they play an important role in innate and adaptive immunity. Chemotaxis is driven by chemoattractants, produced by various cell types, as well as by intrinsic cellular regulators, which are poorly understood. In this study we prepared a new mAb specific for the tetraspanin CD9. Binding of the antibody to bone marrow-derived mast cells triggered activation events that included cell degranulation, Ca(2+) response, dephosphorylation of ezrin/radixin/moesin (ERM) family proteins, and potent tyrosine phosphorylation of the non-T cell activation linker (NTAL) but only weak phosphorylation of the linker for activation of T cells (LAT). Phosphorylation of the NTAL was observed with whole antibody but not with its F(ab)(2) or Fab fragments. This indicated involvement of the Fcγ receptors. As documented by electron microscopy of isolated plasma membrane sheets, CD9 colocalized with the high-affinity IgE receptor (FcεRI) and NTAL but not with LAT. Further tests showed that both anti-CD9 antibody and its F(ab)(2) fragment inhibited mast cell chemotaxis toward antigen. Experiments with bone marrow-derived mast cells deficient in NTAL and/or LAT revealed different roles of these two adaptors in antigen-driven chemotaxis. The combined data indicate that chemotaxis toward antigen is controlled in mast cells by a cross-talk among FcεRI, tetraspanin CD9, transmembrane adaptor proteins NTAL and LAT, and cytoskeleton-regulatory proteins of the ERM family.

• MeSH
• Adaptor Proteins, Signal Transducing metabolism   MeSH
• Tetraspanin 29 physiology   MeSH
• Fusion Regulatory Protein 1, Light Chains metabolism   MeSH
• Antigens metabolism   MeSH
• Models, Biological MeSH
• Cell Membrane metabolism   MeSH
• Chemotaxis MeSH
• Cytoskeleton metabolism   MeSH
• Phosphoproteins metabolism   MeSH
• Phosphorylation MeSH
• Glucuronidase metabolism   MeSH
• Immunoglobulin Fab Fragments chemistry   MeSH
• Rats MeSH
• Mast Cells cytology   MeSH
• Membrane Proteins metabolism   MeSH
• Mice, Inbred C57BL MeSH
• Mice MeSH
• Rats, Wistar MeSH
• Receptors, IgE metabolism   MeSH
• Amino Acid Transport System y+ metabolism   MeSH
• Tyrosine chemistry   MeSH
• Calcium metabolism   MeSH
• Protein Binding MeSH
• Animals MeSH
• Check Tag
• Rats MeSH
• Mice MeSH
• Animals MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Names of Substances
• Adaptor Proteins, Signal Transducing MeSH
• Tetraspanin 29 MeSH
• Fusion Regulatory Protein 1, Light Chains MeSH
• Antigens MeSH
• Phosphoproteins MeSH
• Glucuronidase MeSH
• Immunoglobulin Fab Fragments MeSH
• Lat protein, mouse MeSH Browser
• Lat protein, rat MeSH Browser
• Membrane Proteins MeSH
• Receptors, IgE MeSH
• SLC7A8 protein, mouse MeSH Browser
• Slc7a8 protein, rat MeSH Browser
• Amino Acid Transport System y+ MeSH
• Tyrosine MeSH
• Calcium MeSH