The SH3 domain-binding T cell tyrosyl phosphoprotein p120. Demonstration of its identity with the c-cbl protooncogene product and in vivo complexes with Fyn, Grb2, and phosphatidylinositol 3-kinase

• Published in: The Journal of biological chemistry 1995-08, Vol.270 (32), p.19141-19150
• Main Authors: Fukazawa, T, Reedquist, K A, Trub, T, Soltoff, S, Panchamoorthy, G, Druker, B, Cantley, L, Shoelson, S E, Band, H
• Format: Article
• Language: English
• Subjects: Adaptor Proteins, Signal Transducing; Amino Acid Sequence; GRB2 Adaptor Protein; Humans; Lymphocyte Activation; Molecular Sequence Data; Phosphatidylinositol 3-Kinases; Phosphorylation; Phosphotransferases (Alcohol Group Acceptor) - metabolism; Proteins - metabolism; Proto-Oncogene Proteins - metabolism; Proto-Oncogene Proteins c-abl - isolation & purification; Proto-Oncogene Proteins c-abl - metabolism; Proto-Oncogene Proteins c-fyn; Receptors, Antigen, T-Cell - physiology; Tyrosine - metabolism
• ISSN: 0021-9258
• DOI: 10.1074/jbc.270.32.19141

Previously, we have identified p120 as a Fyn/Lck SH3 and SH2 domain-binding protein that is tyrosine phosphorylated rapidly after T cell receptor triggering. Here, we used direct protein purification, amino acid sequence analysis, reactivity with antibodies, and two-dimensional gel analyses to identify p120 as the human c-cbl protooncogene product. We demonstrate in vivo complexes of p120cbl with Fyn tyrosine kinase, the adaptor protein Grb2, and the p85 subunit of phosphatidylinositol (PI) 3-kinase. The association of p120cbl with Fyn and the p85 subunit of PI 3-kinase (together with PI 3-kinase activity) was markedly increased by T cell activation, consistent with in vitro binding of p120cbl to their SH2 as well as SH3 domains. In contrast, a large fraction of p120cbl was associated with Grb2 prior to activation, and this association did not change upon T cell activation. In vitro, p120cbl interacted with Grb2 exclusively through its SH3 domains. These results demonstrate a novel Grb2-p120cbl signaling complex in T cells, distinct from the previously analyzed Grb2-Sos complex. The association of p120cbl with ubiquitous signaling proteins strongly suggests a general signal transducing function for this enigmatic protooncogene with established leukemogenic potential but unknown physiological function.