title: Point mutation of a tyrosine in the linker region of Syk results in a gain of function.
abstract: The protein tyrosine kinase Syk plays an essential role in Fc epsilon RI-mediated histamine release in mast cells by regulating the phosphorylation of other proteins. We investigated the functional role of a putative Syk phosphorylation site, Tyr317. This tyrosine in the linker region of Syk is a possible site for binding by the negative regulator Cbl. Syk with Tyr317 mutated to Phe (Y317F) was expressed in a Syk-negative variant of the RBL-2H3 mast cells. Compared with cells expressing wild-type Syk, expression of the Y317F mutant resulted in an increase in the Fc epsilon RI-mediated tyrosine phosphorylation of phospholipase C-gamma and a dramatic enhancement of histamine release. The in vivo Fc epsilon RI-induced tyrosine phosphorylation of wild-type Syk and that of the Y317F mutant were similar. Although the Fc epsilon RI-induced tyrosine phosphorylation of total cellular proteins was enhanced in the cells expressing the Y317F Syk, the phosphorylation of some other molecules, including the receptor subunits, Vav and mitogen-activated protein kinase, was not increased. The Fc epsilon RI-induced phosphorylation of Cbl was downstream of Syk kinase activity and was unchanged by expression of the Y317F mutation. These data indicate that Tyr317 in the linker region of Syk functions to negatively regulate the signals leading to degranulation.
authors.affiliation: Receptors and Signal Transduction Section, Oral Infection and Immunity Branch, National Institutes of Dental and Craniofacial Research, Bethesda, MD 20892, USA. ks190b@nih.gov
authors.forename: K
authors.initials: K
authors.lastname: Sada
authors.forename: J
authors.initials: J
authors.lastname: Zhang
authors.forename: R P
authors.initials: RP
authors.lastname: Siraganian
mesh_terms: D000818:Animals; D004792:Enzyme Precursors / Q000235:genetics* / Q000378:metabolism* / Q000502:physiology; D006636:Histamine Release; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins; D007527:Isoenzymes / Q000378:metabolism; D020935:MAP Kinase Signaling System / Q000235:genetics; D050722:Oncogene Protein v-cbl; D010446:Peptide Fragments / Q000235:genetics* / Q000378:metabolism* / Q000502:physiology; D010649:Phenylalanine / Q000235:genetics; D051966:Phospholipase C gamma; D010766:Phosphorylation; D017354:Point Mutation; D011505:Protein-Tyrosine Kinases / Q000235:genetics* / Q000378:metabolism* / Q000502:physiology; D051381:Rats; D017455:Receptors, IgE / Q000502:physiology; D015682:Retroviridae Proteins, Oncogenic / Q000378:metabolism; D000072377:Syk Kinase; D014162:Transfection; D014407:Tumor Cells, Cultured; D010738:Type C Phospholipases / Q000378:metabolism; D014443:Tyrosine / Q000235:genetics* / Q000378:metabolism / Q000502:physiology
chemical_list: D004792:Enzyme Precursors; D047908:Intracellular Signaling Peptides and Proteins; D007527:Isoenzymes; D050722:Oncogene Protein v-cbl; D010446:Peptide Fragments; D017455:Receptors, IgE; D015682:Retroviridae Proteins, Oncogenic; D014443:Tyrosine; D010649:Phenylalanine; D011505:Protein-Tyrosine Kinases; C000606896:SYK protein, human; D000072377:Syk Kinase; C000606898:Syk protein, rat; D010738:Type C Phospholipases; D051966:Phospholipase C gamma