EARLY AND LATE EVENTS IN FC-EPSILON-RI SIGNAL-TRANSDUCTION IN HUMAN CULTURED MAST-CELLS

Protein tyrosine phosphorylation and other biochemical events have bee n shown to occur after cross-linking of Fc epsilon RI in rodent mast c ells. To investigate the mechanism of Fc epsilon RI signal transductio n in human mast cells, we used human cultured mast cells (HCMC) genera ted from cord blood cells in the presence of recombinant human stem ce ll factor and IL-6. We found that on cross-linking of Fc epsilon RI: 1 ) HCMC released histamine; 2) rapid tyrosine phosphorylation of multip le cellular substrates, including Syk, HS1, c-Cbl, ERK-1,and ERK-2, wa s observed; 3) intracellular Ca2+ and inositol phosphate production we re increased within the first minute after Fc epsilon RI cross-linking ; and 4) genistein, a tyrosine kinase inhibitor, inhibited both protei n tyrosine phosphorylation and histamine release in a dose-dependent m anner. These results were consistent with previous studies in rodent m ast cells. In contrast, no tyrosine phosphorylation of phospholipase C gamma 1 and Btk (Bruton's tyrosine kinase) were observed in our exper imental conditions. These results suggest that the greater part of the early and late signaling events in HCMC is similar to those obtained with rodent mast cells and indicated that the requirement of tyrosine phosphorylation in the activation process of each of the signaling mol ecules might be different in HCMC and rodent mast cells. Our finding i ndicates that HCMC may be useful for analysis of Fc epsilon RI-mediate d signal transduction in human mast cells.