Functions as a central linker protein, downstream of the B-cell receptor (BCR), bridging the SYK kinase to a multitude of signaling pathways and regulating biological outcomes of B-cell function and development. Plays a role in the activation of ERK/EPHB2, MAP kinase p38 and JNK. Modulates AP1 activation. Important for the activation of NF-kappa-B and NFAT. Plays an important role in BCR-mediated PLCG1 and PLCG2 activation and Ca(2+) mobilization and is required for trafficking of the BCR to late endosomes. However, does not seem to be required for pre-BCR-mediated activation of MAP kinase and phosphatidyl-inositol 3 (PI3) kinase signaling. May be required for the RAC1-JNK pathway. Plays a critical role in orchestrating the pro-B cell to pre-B cell transition. May play an important role in BCR-induced B-cell apoptosis. Associates with PLCG1, VAV1 and NCK1 in a B-cell antigen receptor-dependent fashion. Interacts with VAV3, PLCG2 and GRB2 (By similarity). Interacts through its SH2 domain with CD79A. Interacts (via SH2 domain) with SYK; phosphorylated and activated by SYK. Interacts (via SH2 domain) with SCIMP; this interaction is dependent on phosphorylation of SCIMP 'Tyr-120' (PubMed:21930792, PubMed:28290451). BCR activation results in the translocation to membrane fraction. Expressed in the spleen and weakly in thymus, no expression was seen in liver, testis, or brain. Expressed in B-cell lines representing different developmental stages from the pre-B to the plasma cell stage, but not in a T-cell or a fibroblast cell line. Following BCR activation, phosphorylated on tyrosine residues by SYK and LYN. When phosphorylated, serves as a scaffold to assemble downstream targets of antigen activation, including PLCG1, VAV1, GRB2 and NCK1. Phosphorylation of Tyr-84, Tyr-178 and Tyr-189 facilitates PLCG1 binding. Phosphorylation of Tyr-72 facilitates VAV1 and NCK1 binding. Phosphorylation is required for both Ca(2+) and MAPK signaling pathways (By similarity). Phosphorylation of Tyr-96 is required for the binding of BTK.