N-ACETYL-L-CYSTEINE INHIBITS ANTIGEN-MEDIATED SYK, BUT NOT LYN TYROSINE KINASE ACTIVATION IN MAST-CELLS

High affinity IgE receptors (alpha beta gamma(2)) mediate the activati on of the non-receptor tyrosine kinases Lyn and Syk. Here we show that the antioxidant drug N-acetyl-L-cysteine (NAG) inhibits antigen-media ted Syk activation whereas Lyn activation and phosphorylation of beta and gamma is maintained. Furthermore, NAC inhibits antigen-mediated ca lcium mobilization and exocytosis in a dose-dependent manner, but does not inhibit ionomycin-induced exocytosis. These data support a model in which the activation of Lyn is responsible for receptor phosphoryla tion and precedes the activation of Syk, The inhibition of Syk activat ion by NAC may be relevant to B and T cell antigen receptors, which ar e also linked to Syk/ZAP70 tyrosine kinases.