B cell antigen receptor signaling induces the formation of complexes containing the Crk adapter proteins.
Crk proteins are Src homology (SH) 2/SH3-containing adapter proteins that can mediate the formation of signaling complexes. We show that engaging the B cell antigen receptor (BCR) on the RAMOS B cell line caused both Crk-L and Crk II to associate with several tyrosine-phosphorylated proteins. We identified two of these phosphoproteins as Cas and Cbl and showed that both bound to the Crk SH2 domain after BCR engagement. BCR ligation also increased the amount of Crk proteins in the particulate fraction of the cells and induced the formation of Crk.Cas and Crk.Cbl complexes in the particulate fraction. We propose that tyrosine phosphorylation of membrane-associated Cas and Cbl creates binding sites for the Crk SH2 domain and recruits Crk complexes to cellular membranes. Thus, Crk proteins may participate in BCR signaling by using their SH2 domains to direct the interactions and subcellular localization of proteins that bind to their SH3 domains. In RAMOS cells, we found that the SH3 domains of Crk-L and Crk II bound C3G. Since C3G activates Rap, a negative regulator of the Ras pathway, Crk proteins may participate in regulation of Ras signaling by the BCR.
Ingham
R J
RJ
Department of Microbiology and Immunology, University of British Columbia, Vancouver, British Columbia V6T 1Z3, Canada. mgold@unixg.ubc.ca
Krebs
D L
DL
Barbazuk
S M
SM
Turck
C W
CW
Hirai
H
H
Matsuda
M
M
Gold
M R
MR
D048868:Adaptor Proteins, Signal Transducing; D017209:Apoptosis; D029563:Cellular Apoptosis Susceptibility Protein; D066246:ErbB Receptors / Q000378:metabolism; D029968:Escherichia coli Proteins; D051380:GRB2 Adaptor Protein; D006801:Humans; D009687:Nuclear Proteins / Q000378:metabolism*; D011505:Protein-Tyrosine Kinases / Q000378:metabolism; D011506:Proteins / Q000378:metabolism; D011518:Proto-Oncogene Proteins / Q000378:metabolism*; D050737:Proto-Oncogene Proteins c-crk; D015800:Protozoan Proteins; D011947:Receptors, Antigen, B-Cell / Q000502:physiology*; D015398:Signal Transduction; D014157:Transcription Factors / Q000378:metabolism; D014407:Tumor Cells, Cultured; D018909:src Homology Domains
D048868:Adaptor Proteins, Signal Transducing; C082869:CRKL protein; C097229:Cbl protein, E coli; D029563:Cellular Apoptosis Susceptibility Protein; D029968:Escherichia coli Proteins; D051380:GRB2 Adaptor Protein; C495948:GRB2 protein, human; D009687:Nuclear Proteins; D011506:Proteins; D011518:Proto-Oncogene Proteins; D050737:Proto-Oncogene Proteins c-crk; D015800:Protozoan Proteins; D011947:Receptors, Antigen, B-Cell; D014157:Transcription Factors; D066246:ErbB Receptors; D011505:Protein-Tyrosine Kinases