SH2 domains, but not membrane localization of Syk, are critical for FcεRI-induced histamine release.

Syk-negative cells and cells expressing the different forms of Syk were cultured overnight with antigen-specific IgE and then stimulated with antigen or with calcium ionophore A23187. Maximum antigen-induced histamine release is presented as a percentage of that with 1 μM A23187. Results are the mean values ± SE from 3 independent experiments. There was no antigen-induced release above background with the parental B2, myr-SykDK, and the myr-SykΔS cloned lines. The difference in antigen-induced release between the Syk WT and myr-Syk cell lines was statistically significant (.05 per t test). The A23187-induced average release as a percentage of the total cellular histamine content in the different cell lines was 67% (Syk-negative B2), 67% (Syk WT-1), 67% (Syk WT 5), 76% (myr-Syk A18), 78% (myr-Syk A28), 76% (myr-SykDK B4), 63% (myr-SykDK B7), 84% (myr-SykΔS E12), and 83% (myr-SykΔS E15). In nonstimulated cells incubated for 45 minutes, the histamine release as a percentage of the total cellular content was as follows: 4% (Syk-negative B2), 4% (Syk WT 1), 4% (Syk WT 5), 4% (myr-Syk A18), 3% (myr-Syk A28), 3% (myr-SykDK B4), 5% (myr-SykDK B7), 3% (myr-SykΔS E12), and 4% (myr-SykΔS E15).