title: Activation-induced association of a 145-kDa tyrosine-phosphorylated protein with Shc and Syk in B lymphocytes and macrophages.
abstract: Engagement of many cell surface receptors results in tyrosine phosphorylation of an overlapping set of protein substrates. Some proteins, such as the adaptor protein Shc, and a frequently observed Shc-associated protein, p145, are common substrates in a variety of receptor signaling pathways and are thus of special interest. Tyrosine-phosphorylated Shc and p145 coprecipitated with anti-Shc antibodies following B cell antigen receptor (BCR) cross-linking or interleukin-4 (IL-4) receptor activation in B cells, and after lipopolysaccharide (LPS) treatment or IgG Fc receptor (Fc gamma R) cross-linking in macrophages. In the case of BCR stimulation, we have shown that this represented the formation of an inducible complex. Furthermore, in response to LPS activation or Fc gamma R cross-linking of macrophages and BCR cross-linking (but not IL-4 treatment) of B cells, we observed a similar tyrosine-phosphorylated p145 protein associated with the tyrosine kinase Syk. We did not detect any Shc associated with Syk, indicating that a trimolecular complex of Shc, Syk, and p145 was not formed in significant amounts. By several criteria, the Syk-associated p145 was very likely the same protein as the previously identified Shc-associated p145. The Syk-associated p145 and the Shc-associated p145 exhibited identical mobility by SDS-polyacrylamide gel electrophoresis and identical patterns of induced tyrosine phosphorylation. The p145 protein that coprecipitated with either Shc or Syk bound to a GST-Shc fusion protein. In addition, a monoclonal antibody developed against Shc-associated p145 also immunoblotted the Syk-associated p145. The observations that p145 associated with both Shc and Syk proteins, in response to stimulation of a variety of receptors, suggest that it plays an important role in coordinating early signaling events.
authors.affiliation: G. W. Hooper Foundation, University of California, San Francisco 94143-0552, USA.
authors.forename: M T
authors.initials: MT
authors.lastname: Crowley
authors.forename: S L
authors.initials: SL
authors.lastname: Harmer
authors.forename: A L
authors.initials: AL
authors.lastname: DeFranco
mesh_terms: D000818:Animals; D001402:B-Lymphocytes / Q000378:metabolism*; D002460:Cell Line; D004792:Enzyme Precursors / Q000378:metabolism*; D006801:Humans; D015847:Interleukin-4 / Q000494:pharmacology; D047908:Intracellular Signaling Peptides and Proteins; D008070:Lipopolysaccharides / Q000494:pharmacology; D008213:Lymphocyte Activation; D008264:Macrophages / Q000378:metabolism*; D008565:Membrane Proteins / Q000378:metabolism*; D051379:Mice; D010766:Phosphorylation; D011505:Protein-Tyrosine Kinases / Q000378:metabolism*; D015398:Signal Transduction; D000072377:Syk Kinase; D014443:Tyrosine / Q000378:metabolism*
chemical_list: D004792:Enzyme Precursors; D047908:Intracellular Signaling Peptides and Proteins; D008070:Lipopolysaccharides; D008565:Membrane Proteins; D015847:Interleukin-4; D014443:Tyrosine; D011505:Protein-Tyrosine Kinases; C000606896:SYK protein, human; D000072377:Syk Kinase; C000606897:Syk protein, mouse