inositol-1-4-5-trisphosphate and Mast-Cell-Sarcoma

Genetic ablation of the B cell surface glycoprotein CD19 severely impairs the humoral immune response. This requirement is thought to reflect a critical role of CD19 in signal transduction that occurs upon antigen C3dg coligation of antigen receptors with CD19 containing type 2 complement receptors (CR2). Here we show that CD19 plays a key accessory role in B cell antigen receptor signaling independent of CR2 coligation and define molecular circuitry by which this function is mediated. While CD19 is not required for antigen-mediated activation of receptor proximal tyrosines kinases, it is critical for activation of phosphatidylinositol 3-kinase (PI3-kinase). PI3-Kinase activation is dependent on phosphorylation of CD19 Y484 and Y515. Antigen-induced CD19-dependent PI3-kinase activation is required for normal phosphoinositide hydrolysis and Ca2+ mobilization responses. Thus, CD19 functions as a B cell antigen receptor accessory molecule that modifies antigen receptor signaling in a qualitative manner.

Topics: Androstadienes; Animals; Antigens, CD19; Binding Sites; Calcium; DNA, Complementary; Enzyme Inhibitors; Extracellular Space; Humans; Inositol 1,4,5-Trisphosphate; Intracellular Fluid; Mast-Cell Sarcoma; Mice; Mutagenesis, Site-Directed; Phosphatidylinositol 3-Kinases; Phosphorylation; Protein Processing, Post-Translational; Protein-Tyrosine Kinases; Receptors, Antigen, B-Cell; Recombinant Fusion Proteins; Signal Transduction; Spleen; Tumor Cells, Cultured; Wortmannin