title: The Ig-alpha ITAM is required for efficient differentiation but not proliferation of pre-B cells.
abstract: Signals from the pre-B cell receptor (pre-BCR) mediated by the cytoplasmic tails of Ig-alpha/Ig-beta are essential for developing B cells. To analyze the role of Ig-alpha ITAM and non-ITAM tyrosines in pre-BCR signaling, we reconstituted individual tyrosine mutants of Ig-alpha in src homology 2 domain-containing leukocyte protein of 65 kDa (SLP-65)/Ig-alpha double-deficient pre-B cells. We show that the Ig-alpha mutants led to comparable pre-BCR expression on the cell surface, while the pre-BCR-induced tyrosine phosphorylation was different. We further show that the reconstitution of Ig-alpha and the resulting pre-BCR expression led to enrichment of the pre-BCR-expressing cells in vitro irrespective of the introduced Ig-alpha mutation. We show that, even though the enrichment rate increased by lowering the IL-7 concentration, residual amounts of IL-7 were required for optimal enrichment. Our results indicate that surface IL-7 receptor expression is modulated by the pre-BCR, thereby increasing the IL-7 sensitivity of the respective cells. In contrast to the comparable pre-B cell proliferation, however, the Ig-alpha mutants differed in their capacity to induce calcium flux and activate efficient pre-B cell differentiation. Together, our data suggest that ITAM tyrosines and Y204 are required for efficient pre-B cell differentiation but not proliferation.
authors.affiliation: Institute for Biologie III, Albert Ludwigs-University of Freiburg, Freiburg, Germany.
authors.forename: Bettina
authors.initials: B
authors.lastname: Storch
authors.forename: Sonja
authors.initials: S
authors.lastname: Meixlsperger
authors.forename: Hassan
authors.initials: H
authors.lastname: Jumaa
mesh_terms: D048868:Adaptor Proteins, Signal Transducing / Q000096:biosynthesis / Q000235:genetics; D020816:Amino Acid Motifs / Q000235:genetics; D000818:Animals; D016175:B-Lymphocyte Subsets / Q000166:cytology* / Q000276:immunology / Q000378:metabolism; D051925:CD79 Antigens / Q000172:deficiency / Q000235:genetics / Q000502:physiology*; D002454:Cell Differentiation / Q000235:genetics / Q000276:immunology*; D049109:Cell Proliferation; D002478:Cells, Cultured; D008562:Membrane Glycoproteins / Q000096:biosynthesis / Q000235:genetics / Q000502:physiology; D051379:Mice; D008807:Mice, Inbred BALB C; D016297:Mutagenesis, Site-Directed; D010766:Phosphorylation; D054420:Pre-B Cell Receptors; D011947:Receptors, Antigen, B-Cell / Q000096:biosynthesis / Q000235:genetics / Q000502:physiology; D015398:Signal Transduction / Q000235:genetics / Q000276:immunology; D013234:Stem Cells / Q000166:cytology* / Q000276:immunology* / Q000378:metabolism; D014443:Tyrosine / Q000235:genetics
chemical_list: D048868:Adaptor Proteins, Signal Transducing; C113939:B cell linker protein; D051925:CD79 Antigens; C497882:Cd79a protein, mouse; D008562:Membrane Glycoproteins; D054420:Pre-B Cell Receptors; D011947:Receptors, Antigen, B-Cell; D014443:Tyrosine