Stimulation of macrophage Fc gamma RIIIA activates the receptor-associated protein tyrosine kinase Syk and induces phosphorylation of multiple proteins including p95Vav and p62/GAP-associated protein.
The role of tyrosine phosphorylation during signal transduction by the phagocytic macrophage (Mphi) FcR Fc gamma RIIIA was investigated. Cross-linking Fc gamma RIIIA on pulmonary Mphi or cultured monocytes used as in vitro model for differentiated Mphi induced rapid and transient phosphorylation of multiple protein substrates. The lymphocyte/mast cell 72-kDa protein tyrosine kinase (PTK) designated PTK72 or Syk, whose expression in Mphi was previously unknown, was identified as a major substrate by immunoprecipitation and phosphopeptide mapping. Activation of Fc gamma RIIIA stimulated a fourfold increase in Syk kinase activity assessed by autophosphorylation. Under mild lysis conditions several specific proteins were co-precipitated with the gamma subunit of Fc gamma RIIIA. Tyrosine kinase activity was also co-precipitated with gamma, as shown by in vitro phosphorylation of gamma. One of these kinases was identified as Syk by phosphopeptide mapping, suggesting a physical association between this PTK and the receptor. Two additional phosphoproteins induced by Fc gamma RIIIA cross-linking were identified: the hematopoietic proto-oncogene product p95Vav, previously implicated in B lymphocyte and mast cell signaling; and p62, a protein associated with p21Ras-GAP. Our results also establish that there are important functional similarities in signal transduction between a phagocytic Mphi FcR and other multi-subunit Ig gene family receptors in diverse cell lineages.
Darby
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Graduate Group in Immunology, University of Pennsylvania, Philadelphia 19104.
Geahlen
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Schreiber
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D018797:Cell Cycle Proteins; D002478:Cells, Cultured; D004792:Enzyme Precursors / Q000378:metabolism*; D020690:GTPase-Activating Proteins; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins; D008264:Macrophages / Q000378:metabolism*; D009000:Monocytes / Q000378:metabolism; D010766:Phosphorylation; D011505:Protein-Tyrosine Kinases / Q000378:metabolism*; D011506:Proteins / Q000378:metabolism*; D000090063:Proto-Oncogene Mas; D011518:Proto-Oncogene Proteins / Q000378:metabolism*; D051567:Proto-Oncogene Proteins c-vav; D017452:Receptors, IgG / Q000502:physiology*; D015398:Signal Transduction; D000072377:Syk Kinase
D018797:Cell Cycle Proteins; D004792:Enzyme Precursors; D020690:GTPase-Activating Proteins; D047908:Intracellular Signaling Peptides and Proteins; C000715470:MAS1 protein, human; D011506:Proteins; D000090063:Proto-Oncogene Mas; D011518:Proto-Oncogene Proteins; D051567:Proto-Oncogene Proteins c-vav; D017452:Receptors, IgG; C496618:VAV1 protein, human; D011505:Protein-Tyrosine Kinases; C000606896:SYK protein, human; D000072377:Syk Kinase