IgE alone-induced actin assembly modifies calcium signaling and degranulation in RBL-2H3 mast cells.
In the mast cell signaling pathways, the binding of immunoglobulin E (IgE) to FcepsilonRI, its high-affinity receptor, is generally thought to be a passive step. In this study, we examined the effect of IgE alone, that is, without antigen stimulation, on the degranulation in mast cells. Monomeric IgE (500-5,000 ng/ml) alone increased cytosolic Ca2+ level ([Ca2+]i) and induced degranulation in rat basophilic leukemia (RBL)-2H3 mast cells. Monomeric IgE (5,000 ng/ml) alone also increased [Ca2+]i and induced degranulation in bone marrow-derived mast cells. Interestingly, monomeric IgE (5-50 ng/ml) alone, in concentrations too low to induce degranulation, increased filamentous actin content in RBL-2H3 mast cells. We next examined whether actin dynamics affect the IgE alone-induced RBL-2H3 mast cell activation pathways. Cytochalasin D inhibited the ability of IgE alone (50 ng/ml) to induce de novo actin assembly. In cytochalasin D-treated cells, IgE (50 ng/ml) alone increased [Ca2+]i and induced degranulation. We have summarized the current findings into two points. First, IgE alone increases [Ca2+]i and induces degranulation in mast cells. Second, IgE, at concentrations too low to increase either [Ca2+]i or degranulation, significantly induces actin assembly, which serves as a negative feedback control in the mast cell Ca2+ signaling and degranulation.
D000199:Actins / Q000187:drug effects* / Q000378:metabolism / Q000502:physiology*; D000818:Animals; D002118:Calcium / Q000378:metabolism; D020013:Calcium Signaling / Q000502:physiology*; D015550:Cell Degranulation / Q000187:drug effects / Q000502:physiology*; D045744:Cell Line, Tumor; D007073:Immunoglobulin E / Q000494:pharmacology*; D007425:Intracellular Membranes / Q000378:metabolism; D008407:Mast Cells / Q000187:drug effects / Q000502:physiology*; D009994:Osmolar Concentration; D051381:Rats
D000199:Actins; D007073:Immunoglobulin E; D002118:Calcium