FcεRI cross-linking-induced actin assembly mediates calcium signalling in RBL-2H3 mast cells

Abstract

To determine the role of actin assembly in the Ca2+ signalling of mast cells activated by cross-linking of FcεRI, we examined the effects of cytochalasin D, an inhibitor of actin polymerization. In the RBL-2H3 cells, F-actin content was increased by sensitization with anti-dinitrophenol (DNP) IgE. In these cells, cytochalasin D induced oscillatory increases in cytosolic Ca2+ ([Ca2+]i); these increase were inhibited by jasplakinolide, a stabilizer of actin filaments. In the IgE-sensitized RBL-2H3 cells, DNP-human serum albumin (DNP-HSA) augmented actin assembly. DNP-HSA also increased the production of IP3, [Ca2+]i and degranulation. Cytochalasin D enhanced all of these DNP-HSA-induced effects. In a Ca2+-free solution, DNP-HSA induced a transient increase in [Ca2+]i, and this increase was accelerated by cytochalasin D. After cessation of the DNP-HSA-induced Ca2+ release, the re-addition of Ca2+ induced a sustained increase in [Ca2+]i through capacitative Ca2+ entry (CCE), and this increase was enhanced by cytochalasin D. The effect of cytochalasin D in enhancing the CCE activity was prevented by xestospongin C. In contrast, neither the Ca2+ release nor the CCE activation that was induced by thapsigargin was affected by cytochalasin D. These results suggest that actin de-polymerization stimulates the FcεRI-mediated signalling to augment the release of Ca2+ from the endoplasmic reticulum in RBL-2H3 cells.