title: Tyrosine phosphorylation of components of the B-cell antigen receptors following receptor crosslinking.
abstract: Crosslinking membrane immunoglobulin (mIg), the B-cell antigen receptor, stimulates tyrosine phosphorylation of a number of proteins. Since many receptors are phosphorylated after ligand binding, we asked if components of the mIg receptor complexes were tyrosine-phosphorylated after mIg crosslinking. Both mIgM and mIgD are noncovalently associated with at least two other proteins. mIgM is associated with the MB-1 protein, which is disulfide-linked to a protein designated Ig-beta. mIgD is not associated with MB-1 but is with IgD-alpha, which is also disulfide-linked to Ig-beta. Using immunoprecipitation with a specific anti-MB-1 antiserum followed by anti-phosphotyrosine immunoblotting, we found that crosslinking mIgM stimulated tyrosine phosphorylation of MB-1, Ig-beta, and a previously unidentified 54-kDa polypeptide associated with MB-1. In mature splenic B cells that express both mIgM and mIgD, mIgM crosslinking stimulated tyrosine phosphorylation of the 32-kDa MB-1 protein, whereas mIgD crosslinking stimulated tyrosine phosphorylation of MB-1-related proteins of 33 and 34 kDa. The 32-kDa MB-1 protein was only associated with mIgM, whereas the 33- and 34-kDa MB-1-related proteins were specifically associated with mIgD and are most likely IgD-alpha. Thus, crosslinking either mIgM or mIgD stimulated tyrosine phosphorylation only of the MB-1-related proteins associated with that receptor.
authors.affiliation: Department of Microbiology and Immunology, University of California, San Francisco.
authors.forename: M R
authors.initials: MR
authors.lastname: Gold
authors.forename: L
authors.initials: L
authors.lastname: Matsuuchi
authors.forename: R B
authors.initials: RB
authors.lastname: Kelly
authors.forename: A L
authors.initials: AL
authors.lastname: DeFranco
mesh_terms: D000818:Animals; D015703:Antigens, CD; D001402:B-Lymphocytes / Q000378:metabolism*; D051925:CD79 Antigens; D015180:Electrophoresis, Gel, Two-Dimensional; D007072:Immunoglobulin D / Q000378:metabolism; D007075:Immunoglobulin M / Q000378:metabolism*; D066298:In Vitro Techniques; D046911:Macromolecular Substances; D008562:Membrane Glycoproteins / Q000378:metabolism*; D051379:Mice; D019000:Phosphotyrosine; D011940:Receptor Aggregation; D011947:Receptors, Antigen, B-Cell / Q000378:metabolism*; D011961:Receptors, Fc / Q000378:metabolism*; D015398:Signal Transduction; D014443:Tyrosine / Q000031:analogs & derivatives* / Q000378:metabolism
chemical_list: D015703:Antigens, CD; D051925:CD79 Antigens; C497882:Cd79a protein, mouse; D007072:Immunoglobulin D; D007075:Immunoglobulin M; D046911:Macromolecular Substances; D008562:Membrane Glycoproteins; D011947:Receptors, Antigen, B-Cell; D011961:Receptors, Fc; C035311:immunoglobulin M receptor; D019000:Phosphotyrosine; D014443:Tyrosine