UMMS Affiliation

Department of Biochemistry and Molecular Biology; Program in Molecular Medicine

Publication Date


Document Type



1-Phosphatidylinositol 3-Kinase; *Adaptor Proteins, Signal Transducing; Antigens, CD3; Base Sequence; Blotting, Western; GRB2 Adaptor Protein; Lymphocyte Activation; Membrane Proteins; Molecular Sequence Data; Phosphotransferases (Alcohol Group Acceptor); Precipitin Tests; Protein Binding; Proteins; Proto-Oncogene Proteins; Proto-Oncogene Proteins c-cbl; Receptors, Antigen, T-Cell; Recombinant Fusion Proteins; *Signal Transduction; Son of Sevenless Proteins; T-Lymphocytes; *Ubiquitin-Protein Ligases


Life Sciences | Medicine and Health Sciences


T-cell receptor (TCR) cross-linking increases tyrosine phosphorylation of multiple proteins, only a few of which have been identified. One of the most rapidly tyrosine-phosphorylated polypeptides is the 120-kDa product of the proto-oncogene c-cbl, a cytosolic and cytoskeletal protein containing multiple proline-rich motifs that are potential binding sites for proteins containing Src homology 3 (SH3) domains. We report here that in cultured Jurkat T cells, Cbl is coprecipitated with antibody against the adapter protein Grb2. Upon activation of Jurkat T cells via the TCR-CD3 complex, we find that high-affinity binding of Cbl requires the N-terminal SH3 domain of GST-Grb2 fusion protein but after cross-linking of the TCR-CD3 and CD4 receptors, Cbl binds equally to its SH2 domain. Grb2 antisera also precipitated p85 from serum-starved cells, while TCR activation increased p85 and tyrosine-phosphorylated Cbl but not Cbl protein in Grb2 immunocomplexes. Phosphatidylinositol (PI) 3-kinase activity was immunoprecipitated from serum-starved cells with Cbl and to a lesser extent with Grb2 antisera, and TCR cross-linking increased this activity severalfold. The PI 3-kinase activity associated with Cbl amounted to 5 to 10% of the total cellular activity that could be precipitated by p85 antisera. The Ras exchange factor Son-of-sevenless 1 (Sos-1) was not found in anti-Cbl immunoprecipitates from activated cells, and Cbl was not detectable in anti-Sos-1 precipitates, supporting the likelihood that Sos-Grb2 and Cbl-Grb2 are present as distinct complexes. Taken together, these data suggest that Cbl function in Jurkat T cells involves its constitutive association with Grb2 and its recruitment of PI 3-kinase in response to TCR activation.


Mol Cell Biol. 1995 Jul;15(7):3571-8.

Journal/Book/Conference Title

Molecular and cellular biology

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Link to Article in PubMed

PubMed ID




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