title: Fc epsilon RI aggregation induces tyrosine phosphorylation of a novel 72 kDa protein downstream of Syk.
abstract: Tyrosine phosphorylation of proteins is critical for the Fc epsilon RI-induced signal transduction that leads to the release of inflammatory mediators from mast cells. Here we report the isolation of a monoclonal antibody, mAb BD2, to a 72 kDa protein that becomes rapidly tyrosine phosphorylated after Fc epsilon RI aggregation. By immunoprecipitation, immunoblotting and/or protease digestion this 72 kDa protein was different from the previously identified 68-76 kDa tyrosine phosphorylated proteins Btk, paxillin, SLP-76 or Syk. The phosphorylation of this 72 kDa protein was detectable within 15 sec after receptor aggregation and was independent of Ca2+ influx or the activation of protein kinase C. By in vitro kinase reaction, the 72 kDa protein did not autophosphorylate, which suggests that it is not a kinase, but is associated with a 140 kDa protein that was strongly phosphorylated. Studies in Syk deficient and Syk transfected variants of the RBL-2H3 cells demonstrated that the tyrosine phosphorylation of this 72 kDa protein was downstream of Syk. These data indicate that the 72 kDa protein precipitated by mAb BD2 is a novel phosphoprotein involved in Fc epsilon RI signaling.
authors.affiliation: Receptors and Signal Transduction Section, OIIB, National Institute of Dental Research, Bethesda, Maryland 20892, USA.
authors.forename: M M
authors.initials: MM
authors.lastname: Hamawy
authors.forename: C
authors.initials: C
authors.lastname: Fischler
authors.forename: J
authors.initials: J
authors.lastname: Zhang
authors.forename: R P
authors.initials: RP
authors.lastname: Siraganian
mesh_terms: D000818:Animals; D000911:Antibodies, Monoclonal / Q000302:isolation & purification / Q000378:metabolism; D000918:Antibody Specificity; D000936:Antigen-Antibody Complex / Q000378:metabolism; D004792:Enzyme Precursors / Q000378:metabolism*; D047908:Intracellular Signaling Peptides and Proteins; D015471:Leukemia, Basophilic, Acute; D051379:Mice; D008807:Mice, Inbred BALB C; D008970:Molecular Weight; D010750:Phosphoproteins / Q000276:immunology / Q000378:metabolism; D010766:Phosphorylation; D011505:Protein-Tyrosine Kinases / Q000378:metabolism*; D051381:Rats; D011940:Receptor Aggregation; D017455:Receptors, IgE / Q000378:metabolism* / Q000502:physiology; D015398:Signal Transduction; D000072377:Syk Kinase; D014407:Tumor Cells, Cultured; D014443:Tyrosine / Q000378:metabolism*
chemical_list: D000911:Antibodies, Monoclonal; D000936:Antigen-Antibody Complex; D004792:Enzyme Precursors; D047908:Intracellular Signaling Peptides and Proteins; D010750:Phosphoproteins; D017455:Receptors, IgE; D014443:Tyrosine; D011505:Protein-Tyrosine Kinases; D000072377:Syk Kinase; C000606897:Syk protein, mouse; C000606898:Syk protein, rat