IgG-Mediated Signal Transduction in Canine Mastocytoma-Derived Cells

Publisher Website
Google Scholar
Abstract
Background: We have reported canine cutaneous mastocytoma-derived cells named CM-MC sensitized with monomeric IgG released histamine upon anti-IgG stimulation. However, IgG or IgE-mediated signal transduction in the cells remains to be examined. Methods: Monomeric IgG-binding to cells was measured by flow cytometry using FITC-anti-IgG. IgG-mediated protein tyrosine phosphorylation was studied by Western blotting using anti-phosphotyrosine antibody. We monitored the intracellular Ca2+ concentration ([Ca2+]i) when IgG-primed cells were activated with anti-canine IgG. Release of Ca2+ from intracellular stores was analyzed with thapsigargin in the absence of extracellular Ca2+. The Ca2+ entry via store-operated Ca2+ channel from the external environment was characterized using Ba2+, Ni2+ and EGTA. Cells sensitized with canine serum abundant in IgG and IgE or heat-inactivated serum were activated by anti-canine IgG or anti-canine IgE. The effect of extracellular Ca2+ and reaction time on IgG-mediated histamine release was examined. Staurosporine and ER-27319 were used to clarify the IgG-mediated protein tyrosine phosphorylation. Results: Abundant IgG-binding sites on the cell were detected by FACS analysis. Anti-IgG induced rapid protein tyrosine phosphorylation and [Ca2+]i elevation. When extracellular Ca2+ was excluded by EGTA, a mild and transient increase in [Ca2+]i was observed, indicating the release of Ca2+ from anti-IgG-sensitive intracellular Ca2+ stores. The constant Ba2+ entry from external environment proved the Ca2+ influx occurred mainly via a store-operated Ca2+ channel which was inhibited by Ni2+ and EGTA. Canine serum-sensitized cells showed a rapid and sustained increase in [Ca2+]i upon both anti-IgG and anti-IgE stimulation. The [Ca2+]i elevation induced by anti-IgE was decreased in the cells sensitized with heat-inactivated serum. Histamine release from CM-MCs was absolutely dependent on extracellular Ca2+, and reached equilibrium within 5 min. Staurosporine inhibited the tyrosine phosphorylation of 38-, 65-, 70-, 80-kD proteins. ER-27319 inhibited the tyrosine phosphorylation of 38- and 70-kD proteins. Staurosporine also inhibited IgG-mediated [Ca2+]i elevation and histamine release in a dose-dependent manner. Conclusions: Canine cutaneous mastocytoma-derived (CM-MC) cells were activated by both IgG- and IgE-mediated mechanisms. IgG-mediated protein tyrosine phosphorylation and Ca2+ influx were similar to those mediated by IgE. CM-MC cells are useful for the study of allergic inflammation caused by IgG-dependent mechanisms.