title: Paired immunoglobulin-like receptor B (PIR-B) inhibits BCR-induced activation of Syk and Btk by SHP-1.
abstract: Coligation of paired immunoglobulin-like receptor B (PIR-B) with B cell antigen receptor (BCR) blocks antigen-induced B cell activation. This inhibition is mediated in part by recruitment of SHP-1 and SHP-2 to the phosphorylated ITIMs in the cytoplasmic domain of PIR-B; however the molecular target(s) of these phosphatases remain elusive. Here we show that PIR-B ligation inhibits the BCR-induced tyrosine phosphorylation of Igalpha/Igbeta, Syk, Btk and phospholipase C (PLC)-gamma2. Overexpression of a catalytically inactive form of SHP-1 prevents the PIR-B-mediated inhibition of tyrosine phosphorylation of Syk, Btk, and PLC-gamma2. Dephosphorylation of Syk and Btk mediated by SHP-1 leads to a decrease of their kinase activity, which in turn inhibits tyrosine phosphorylation of PLC-gamma2. Furthermore, we define a requirement for Lyn in mediating tyrosine phosphorylation of PIR-B. Based on these results, we propose a model of PIR-B-mediated inhibitory signaling in which coligation of PIR-B and BCR results in phosphorylation of ITIMs by Lyn, subsequent recruitment of SHP-1, and a resulting inhibition of the BCR-induced inositol 1,4,5-trisphosphate generation by dephosphorylation of Syk and Btk.
mesh_terms: D000077329:Agammaglobulinaemia Tyrosine Kinase; D000818:Animals; D020013:Calcium Signaling / Q000502:physiology; D002460:Cell Line; D004789:Enzyme Activation; D004792:Enzyme Precursors / Q000378:metabolism*; D007295:Inositol Phosphates / Q000378:metabolism; D047908:Intracellular Signaling Peptides and Proteins; D007527:Isoenzymes / Q000037:antagonists & inhibitors; D051379:Mice; D008954:Models, Biological; D051966:Phospholipase C gamma; D010766:Phosphorylation; D011499:Protein Processing, Post-Translational / Q000502:physiology*; D054592:Protein Tyrosine Phosphatase, Non-Receptor Type 11; D053824:Protein Tyrosine Phosphatase, Non-Receptor Type 6; D017027:Protein Tyrosine Phosphatases / Q000502:physiology*; D011505:Protein-Tyrosine Kinases / Q000378:metabolism*; D011947:Receptors, Antigen, B-Cell / Q000276:immunology*; D017452:Receptors, IgG / Q000235:genetics; D011971:Receptors, Immunologic / Q000235:genetics / Q000502:physiology*; D011993:Recombinant Fusion Proteins / Q000502:physiology; D000072377:Syk Kinase; D014162:Transfection; D010738:Type C Phospholipases / Q000037:antagonists & inhibitors; D019061:src-Family Kinases / Q000378:metabolism