title: Cross-linking of B cell receptor-related MB-1 molecule induces protein tyrosine phosphorylation in early B lineage cells.
abstract: Cross-linking of surface B cell Ag receptor (BCR) induces tyrosine phosphorylation of BCR-associated components through a receptor-mediated signal transmission pathway. B cell-specific mb-1 and B29 genes encode the alpha/beta components of the BCR-associated complex in mature sIgM+ B cells. Here, we studied the involvement of the mb-1 gene product, MB-1, in the BCR-related structure of immature B cells. Affinity-purified anti-MB-1 antibody coprecipitated mu chain/20-kDa/15-kDa proteins together with monomer MB-1 and Ig-alpha/Ig-beta heterodimer components from digitonin lysates of the pre-B cell line 18.81. The monomer MB-1 and Ig-alpha in the pre-B cell line were shown to migrate with identical patterns in nonequilibrium pH gradient gel electrophoresis/SDS-PAGE. Western blot analysis showed that MB-1 protein is coprecipitated with mu chain from the pre-B cell line. We studied the tyrosine phosphorylation response of bone marrow B lineage cells as well as spleen B cells after cross-linking of BCR-related components with anti-mu, anti-kappa, and anti-MB-1 antibodies. We identified the activation of tyrosine kinase by direct cross-linking of MB-1 expressed on the surface of early B lineage cells. Anti-mu antibody stimulation induced the activation of tyrosine kinase in early (5- to 10-min) and late (30- to 120-min) responses in bone marrow early B lineage cells. Anti-MB-1 mAb (11-18-5) induced the late response exclusively but anti-kappa antibody induced only the early response. These results clearly indicate that MB-1 acts in the BCR-mediated signal transmission in early B lineage cells. To explore the molecular mechanism of protein tyrosine phosphorylation in bone marrow B lineage cells, we studied associated components of the BCR complex by using an in vitro kinase reaction and observed the phosphorylation of a 60-kDa protein in pre-B cell lines. The 60-kDa phosphoprotein coprecipitated with MB-1 and the BCR-related complex is very similar to the Src-type Fyn tyrosine kinase or a Fyn-related protein.
authors: Department of Immunology, Saga Medical School, Japan.
authors: T
authors: T
authors: Matsuo
authors: J
authors: J
authors: Nomura
authors: K
authors: K
authors: Kuwahara
authors: H
authors: H
authors: Igarashi
authors: S
authors: S
authors: Inui
authors: M
authors: M
authors: Hamaguchi
authors: M
authors: M
authors: Kimoto
authors: N
authors: N
authors: Sakaguchi
mesh_terms: D000818:Animals; D000911:Antibodies, Monoclonal / Q000276:immunology; D015703:Antigens, CD; D001402:B-Lymphocytes / Q000378:metabolism*; D051925:CD79 Antigens; D002118:Calcium / Q000378:metabolism; D002460:Cell Line; D005260:Female; D006412:Hematopoietic Stem Cells / Q000378:metabolism*; D007075:Immunoglobulin M / Q000502:physiology; D008562:Membrane Glycoproteins / Q000502:physiology*; D051379:Mice; D008810:Mice, Inbred C57BL; D008811:Mice, Inbred DBA; D010750:Phosphoproteins / Q000032:analysis; D010766:Phosphorylation; D011505:Protein-Tyrosine Kinases / Q000032:analysis; D011506:Proteins / Q000378:metabolism*; D011518:Proto-Oncogene Proteins / Q000032:analysis; D051076:Proto-Oncogene Proteins c-fyn; D011817:Rabbits; D011947:Receptors, Antigen, B-Cell / Q000502:physiology*; D014443:Tyrosine / Q000378:metabolism*
chemical_list: D000911:Antibodies, Monoclonal; D015703:Antigens, CD; D051925:CD79 Antigens; C497882:Cd79a protein, mouse; D007075:Immunoglobulin M; D008562:Membrane Glycoproteins; D010750:Phosphoproteins; D011506:Proteins; D011518:Proto-Oncogene Proteins; D011947:Receptors, Antigen, B-Cell; D014443:Tyrosine; D011505:Protein-Tyrosine Kinases; C494960:Fyn protein, mouse; D051076:Proto-Oncogene Proteins c-fyn; D002118:Calcium