Engagement of CD19 on mouse B cells induces tyrosine phosphorylation of BCAP and its association with PI3K p85.
Splenic B cells (4 × 107) were stimulated by CD19 cross-linking as in Figure 1A or by BCR cross-linking using goat anti–mouse IgM F(ab′)2 fragment (15 μg/mL) and subjected to the following analyses. (A) Immunoprecipitates with anti-CD19 Ab were separated on 7.5% SDS-PAGE and analyzed by Western blotting with antiphosphotyrosine mAb 4G10 (upper panel), anti-CD19 Ab (middle panel), or anti-p85 Ab (lower panel). (B) Immunoprecipitates with anti-BCAP Ab were separated on 7.5% SDS-PAGE and analyzed by Western blotting with antiphosphotyrosine mAb 4G10 (upper panel), anti-BCAP Ab (middle panel), or anti-p85 Ab (lower panel). The positions of the multiple mouse BCAP species, long (100 and 98 kd) and short (72 and 70 kd) isoforms, are indicated by brackets.
