Physical and Functional Association of Src-related Protein Tyrosine Kinases with Fc Gamma RII in Monocytic THP-1 Cells

Aggregation of Fc gamma RII (CD 32), a low affinity receptor for immunoglobulin G (IgG), on the monocytic cell line THP-1 induces protein tyrosine kinase (PTK) activity. Several distinct cellular proteins, including Fc gamma RII itself, are phosphorylated on tyrosine following cross-linking of the receptor. Fc gamma RII lacks intrinsic PTK activity. In this report we demonstrate that a kinase activity was coprecipitated with Fc gamma RII in THP-1 cells. The kinetics of the receptor-associated kinase activity paralleled the appearance of tyrosine phosphorylation events observed following Fc gamma RII activation of THP-1 cells. Several proteins were associated with the receptor. Reimmunoprecipitation analysis demonstrated that lyn gene products were among the proteins coprecipitated with Fc gamma RII. p59hck (Hck) and p56lyn (Lyn) were the most abundant Src-related PTKs (Src-PTKs) in THP-1 cells. Enzymatic activity of both kinases, as measured by an in vitro kinase assay, was increased following specific cross-linking of Fc gamma RII. Furthermore, Fc gamma RII was specifically associated with both enzymes following its engagement and served as a substrate for both of these kinases. The association of Fc gamma RII with Src-PTK was specific for Fc gamma RII activation of THP-1 cells, since activation of cells via the high affinity Fc gamma receptor, Fc gamma RI (CD 64), did not result in association of Fc gamma RII with Hck or Lyn. Our data demonstrate a functional and physical association of Fc gamma RII with Hck and Lyn consistent with the involvement of Src-PTK in Fc gamma RII-mediated signal transduction.