The Gab1 Protein Is a Docking Site for Multiple Proteins Involved in Signaling by the B Cell Antigen Receptor

• Published in: The Journal of biological chemistry Vol. 273; no. 46; pp. 30630 - 30637
• Main Authors: Ingham, Robert J., Holgado-Madruga, Marina, Siu, Charity, Wong, Albert J., Gold, Michael R.
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 13.11.1998; American Society for Biochemistry and Molecular Biology
• Subjects: Adaptor Proteins, Signal Transducing; Adaptor Proteins, Vesicular Transport; Binding Sites; GRB2 Adaptor Protein; Humans; Intracellular Signaling Peptides and Proteins; Phosphatidylinositol 3-Kinases - metabolism; Phosphoproteins - metabolism; Phosphorylation; Protein Binding; Protein Sorting Signals - physiology; Protein Tyrosine Phosphatase, Non-Receptor Type 11; Protein Tyrosine Phosphatase, Non-Receptor Type 6; Protein Tyrosine Phosphatases - metabolism; Proteins - metabolism; Receptors, Antigen, B-Cell - physiology; SH2 Domain-Containing Protein Tyrosine Phosphatases; Shc Signaling Adaptor Proteins; Src Homology 2 Domain-Containing, Transforming Protein 1; src Homology Domains; Tumor Cells, Cultured; Tyrosine - metabolism
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.273.46.30630

Gab1 is a member of the docking/scaffolding protein family which includes IRS-1, IRS-2, c-Cbl, p130cas, and p62dok. These proteins contain a variety of protein-protein interaction motifs including multiple tyrosine residues that when phosphorylated can act as binding sites for Src homology 2 (SH2) domain-containing signaling proteins. We show in the RAMOS human B cell line that Gab1 is tyrosine-phosphorylated in response to B cell antigen receptor (BCR) engagement. Moreover, tyrosine phosphorylation of Gab1 correlated with the binding of several SH2-containing signaling proteins to Gab1 including Shc, Grb2, phosphatidylinositol 3-kinase, and the SHP-2 tyrosine phosphatase. Far Western analysis showed that the SH2 domains of Shc, SHP-2, and the p85 subunit of phosphatidylinositol 3-kinase could bind directly to tyrosine-phosphorylated Gab1 isolated from activated RAMOS cells. In contrast, the Grb2 SH2 domain did not bind directly to Gab1 but instead to the Shc and SHP-2 associated with Gab1. We also show that Gab1 is present in the membrane-enriched particulate fraction of RAMOS cells and that Gab1/signaling protein complexes are found in this fraction after BCR engagement. Thus, tyrosine-phosphorylated Gab1 may recruit cytosolic signaling proteins to cellular membranes where they can act on membrane-bound targets. This may be a critical step in the activation of multiple BCR signaling pathways.