Figure 3.

The enzymatic activity of Syk is required for BCR-induced activation of Akt/PKB. (A) Wild-type and mutant DT40 cells were stimulated with mouse anti-chicken IgM Ab for 30 minutes. Akt/PKB was immunoprecipitated and subjected to an in vitro kinase assay. The change in Akt kinase activity in anti-Ig stimulated vs. unstimulated wild-type, and the indicated mutant DT40 cells is presented as the change in arbitrary PhosphorImager units. (B) Cells were stimulated as in A, and the phosphorylation state of Akt/PKB was determined by immunoprecipitation with anti-Akt Ab followed by immunoblotting with anti-Akt Ab. (C) DT40 Syk⁻ cells transfected with wild-type and catalytically inactive mutant of Syk were stimulated with M4. The phosphorylation states of Akt/PKB were determined as described in A.