YxxM motifs in BCAP are required for activation of PI3K/Akt in response to CD19 stimulation.

Wild-type and its derived mutant DT40 cells expressing mouse CD19 were stimulated and subsequently analyzed as described in Figures 1 and 2. (A) CD19-induced Akt activation. (B) Tyrosine phosphorylation of BCAP and its association with p85. The positions of the multiple chicken BCAP species, long (100 and 98 kd) and short (72 and 70 kd) isoforms, are indicated by brackets. As a negative control experiment, BCAP-deficient DT40 cells were also analyzed. (C) Generation of PI(3,4,5)P₃. Cells loaded with [³²P]orthophosphate were incubated with or without 50 nM wortmannin for 10 minutes and subsequently stimulated. PI(3,4,5)P₃ generation was analyzed as described in “Materials and methods.” Fold increases of PI(3,4,5)P₃levels normalized to total phospholipids after CD19 stimulation are shown. The results are shown as mean ± SE of 3 independent experiments.