Sos, Vav, and C3G participate in B cell receptor-induced signaling pathways and differentially associate with Shc-Grb2, Crk, and Crk-L adaptors.
B cell antigen receptor (BCR)-mediated signal transduction controls B cell proliferation and differentiation. The BCR activates Ras, presumably by the formation of a Shc-Grb2 adaptor complex, which recruits the Grb2-associated guanine nucleotide exchange factor Sos to the plasma membrane. In order to reveal additional BCR-induced signaling events involving the Grb2 ... adaptor, we undertook the isolation of Grb2-binding proteins. Using the yeast two-hybrid system and bacterial fusion proteins, Vav and C3G were identified as Grb2 binders. Vav is a putative nucleotide exchange factor and a target for BCR-induced tyrosine phosphorylation. C3G exerts nucleotide exchange activity on the Ras-related Rap1 protein. While Sos binds to both Grb2 Src homology-3 (SH3) domains, Vav was found to associate selectively with the carboxyl-terminal SH3 domain, while C3G bound selectively to the amino-terminal SH3 domain of bacterially expressed Grb2. Despite the association of Vav with Grb2 in vitro, we could not demonstrate an interaction between endogenous Vav and Grb2 molecules in primary B cells. Instead, Vav was found to inducibly associate with the Grb2-related adaptor protein Crk upon BCR stimulation. C3G did not bind to either Grb2, Shc, or Crk in vivo. Instead, C3G was found in association with the Crk-L adaptor, both before and after BCR stimulation. We show that Crk-L also participates in BCR signaling, since it inducibly interacts with tyrosine-phosphorylated Cbl. We conclude that, in addition to Sos, Vav and C3G play a role in BCR-mediated signal transduction. These guanine nucleotide exchange factors selectively associate with Grb2, Crk, and Crk-L, respectively, which may serve to direct them to different target molecules. Since Cbl binds to Grb2, Crk, as well as Crk-L, we hypothesize that Cbl may affect the function of all three exchangers.
Mesh Terms:
Adaptor Proteins, Signal Transducing, Adaptor Proteins, Vesicular Transport, Amino Acid Sequence, B-Lymphocytes, Base Sequence, Cell Cycle Proteins, Cells, Cultured, DNA Primers, GRB2 Adaptor Protein, Guanine Nucleotide Exchange Factors, Humans, Membrane Proteins, Molecular Sequence Data, Nuclear Proteins, Proteins, Proto-Oncogene Proteins, Proto-Oncogene Proteins c-crk, Proto-Oncogene Proteins c-vav, Receptors, Antigen, B-Cell, Shc Signaling Adaptor Proteins, Signal Transduction, Son of Sevenless Proteins, ras Guanine Nucleotide Exchange Factors
Adaptor Proteins, Signal Transducing, Adaptor Proteins, Vesicular Transport, Amino Acid Sequence, B-Lymphocytes, Base Sequence, Cell Cycle Proteins, Cells, Cultured, DNA Primers, GRB2 Adaptor Protein, Guanine Nucleotide Exchange Factors, Humans, Membrane Proteins, Molecular Sequence Data, Nuclear Proteins, Proteins, Proto-Oncogene Proteins, Proto-Oncogene Proteins c-crk, Proto-Oncogene Proteins c-vav, Receptors, Antigen, B-Cell, Shc Signaling Adaptor Proteins, Signal Transduction, Son of Sevenless Proteins, ras Guanine Nucleotide Exchange Factors
J. Biol. Chem.
Date: Apr. 12, 1996
PubMed ID: 8621483
View in: Pubmed Google Scholar
Download Curated Data For This Publication
897
Switch View:
- Interactions 3