Role of the Syk autophosphorylation site and SH2 domains in B cell antigen receptor signaling.
To explore the mechanism(s) by which the Syk protein tyrosine kinase participates in B cell antigen receptor (BCR) signaling, we have studied the function of various Syk mutants in B cells made Syk deficient by homologous recombination knockout. Both Syk SH2 domains were required for BCR-mediated Syk and phospholipase C (PLC)-gamma 2 phosphorylation, inositol 1,4,5-triphosphate release, and Ca2+ mobilization. A possible explanation for this requirement was provided by findings that recruitment of Syk to tyrosine-phosphorylated immunoglobulin (Ig) alpha and Ig beta requires both Syk SH2 domains. A Syk mutant in which the putative autophosphorylation site (Y518/Y519) of Syk was changed to phenylalanine was also defective in signal transduction; however, this mutation did not affect recruitment to the phosphorylated immunoreceptor family tyrosine-based activation motifs (ITAMs). These findings not only confirm that both SH2 domains are necessary for Syk binding to tyrosine-phosphorylated Ig alpha and Ig beta but indicate that this binding is necessary for Syk (Y518/519) phosphorylation after BCR ligation. This sequence of events is apparently required for coupling the BCR to most cellular protein tyrosine phosphorylation, to the phosphorylation and activation of PLC-gamma 2, and to Ca2+ mobilization.
D000595:Amino Acid Sequence; D001402:B-Lymphocytes / Q000276:immunology*; D002118:Calcium / Q000378:metabolism; D002478:Cells, Cultured; D004792:Enzyme Precursors / Q000378:metabolism*; D015544:Inositol 1,4,5-Trisphosphate / Q000378:metabolism; D047908:Intracellular Signaling Peptides and Proteins; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D010455:Peptides / Q000737:chemistry; D010766:Phosphorylation; D011505:Protein-Tyrosine Kinases / Q000378:metabolism*; D011947:Receptors, Antigen, B-Cell / Q000378:metabolism*; D015398:Signal Transduction; D013329:Structure-Activity Relationship; D000072377:Syk Kinase; D018909:src Homology Domains
D004792:Enzyme Precursors; D047908:Intracellular Signaling Peptides and Proteins; D010455:Peptides; D011947:Receptors, Antigen, B-Cell; D015544:Inositol 1,4,5-Trisphosphate; D011505:Protein-Tyrosine Kinases; D000072377:Syk Kinase; D002118:Calcium