Syk plays a crucial role in the transduction of oxidative stress signaling. In this paper, we investigated the roles of Src homology 2 (SH 2) domains of Syk in oxidative stress signaling, using Syk-negative DT 40 cells expressing the N- or C-terminal SH 2 domain mutant [mSH2(N) or mSH2(C)] of Syk. Tyrosine phosphorylation of Syk in cells expressing mSH2(N) Syk after H2O2 treatment was higher than that in cells expressing wildtype Syk or mSH2(C) Syk. The tyrosine phosphorylation of wild-type Syk and mSH2(C) Syk, but not that of mSH2(N), was sensitive to PP 2, a specific inhibitor of Src-family protein-tyrosine kinase. In oxidative stress, the C-terminal SH 2 domain of Syk was demonstrated to be required for induction of tyrosine phosphorylation of cellular proteins, phospholipase C (PLC)-γ2 phosphorylation, inositol 1, 4, 5-triphosphate (IP 3) generation, Ca2+ release from intracellular stores, and c-Jun N-terminal kinase activation. In contrast, in mSH2(N) Syk-expressing cells, tyrosine phosphorylation of intracellular proteins including PLC-γ2 was markedly induced in oxidative stress. The enhanced phosphorylation of mSH 2(N)Syk and PLC-γ2, however, did not link to Ca2+ mobilization from intracellular pools and IP3 generation. Thus, the N- and C-terminal SH 2 domains of Syk possess distinctive functions in oxidative stress signaling.
The Japanese Biochemical Society