Tyrosine phosphorylation of B-cell adaptor for phosphoinositide 3-kinase is required for Akt activation in response to CD19 engagement

CD19 is a coreceptor that amplifies signaling Initiated by antigen cross-linking of the B-cell antigen receptor (BCR). CD19 can also signal independently of BCR coligation. This study shows that (B) under bar-(c) under bar ell adaptor for phosphoinositide 3-kinase (BCAP), previously characterized as a substrate of the tyrosine kinases upon BCR engagement, Is phosphorylated by cross-linking of CD19. Tyrosine phosphorylation of BCAP, mediated by Lyn, provides binding site(s) for phosphoinositide 3-kinase (PI3K), thereby participating in Akt activation. Thus, these results provide evidence that BCAP serves as an adaptor molecule for CD19 to activate the PI3K pathway In B cells. (Blood. 2002;99: 584-589) (C) 2002 by The American Society of Hematology.