The protein-tyrosine kinase csk is involved in signaling through the FceRI

Csk plays a role in the signal transduction of several immunologie receptors, including the TCR and BCR. This study was undertaken to examine whether Csk has a function in signal transduction through the high affinity receptor for IgE, FctRI. RBL cells (a rat mast cell line) were activated with anti-DNP IgE plus DNP-HSA conjugate. Anti-Csk antibodies and recombinant fusion proteins were used to identify tyrosine-phosphorylated proteins that associate with Csk. One protein of 60 kD (p60) was found to associate with the SH2 domain of Csk in vitro after stimulation of the RBL cells. This association was not observed when a Csk-SH2 domain with mutations in the phosphotyrosine-binding FLVRES motif was used. p60 phosphorylation reached a maximum after 2 minutes of stimulation and remained high while the receptors were aggregated. Disaggregation of the receptors by monovalent hapten resulted in rapid dephosphorylation of p60. The phosphorylation of p60 was only detected after activation by IgE and antigen and not by stimulation with PMA and/or ionomycin. p60 coprecipitated with Csk from RBL cells and was phosphorylated in vitro by kinases in the immunoprecipitate. It has been demonstrated that Csk associates with a GAPassociated protein of 60 kD (GAPpoO) in Src transformed fibroblasts. Our investigations do not, however, suggest that Csk associates with GAPpoO in RBL cells. Our data show that Csk is involved in FceRI signal transduction anrl a«nriate<i with a vet imiHpnrifiprl nhnsnhnnrnrein nf 60 IcD nnnn rccentnr aggregation.