title: Posttranscriptional regulation of Bruton's tyrosine kinase expression in antigen receptor-stimulated splenic B cells.
abstract: Mutation of Bruton's tyrosine kinase (Btk) causes human X-linked agammaglobulinemia and murine X-linked immunodeficiency syndrome (xid). Quantitative aspects of B lymphocyte development and function have been demonstrated to depend on Btk level in vivo by using a murine transgenic model system. A sensitive intracellular immunofluorescent assay was developed to measure Btk protein on a per cell basis to test the hypothesis that its dosage is dynamically regulated during B cell development or functional responses. Marrow-derived hematopoietic stem cells, common lymphoid progenitor cells, and developing B and myeloid lineages expressed Btk protein at comparable levels. Resting peripheral B lineage cells had a significantly lower amount of Btk than marrow-derived cells in both wild-type and xid mice. Activation of the B cell antigen receptor up-regulated Btk protein level 10-fold within several hours by a phosphatidylinositol 3-kinase-dependent, posttranscriptional mechanism. In contrast, the protein level of Btk R28C in activated B lymphocytes from xid mice remained low. Bypass of the antigen receptor signaling pathways by treatment of cells with phorbol myristic acid and ionomycin rescued up-regulation of Btk protein in xid splenic B cells. These combined results suggest that certain receptor signals mediated by Btk regulate the level of expression of Btk protein in responding B lymphocytes to potentiate signal transduction. Dynamic regulation of Btk protein dosage is an additional mechanism to modulate B lymphocyte immune functions.
authors.affiliation: Department of Microbiology, Immunology, and Molecular Genetics, and Howard Hughes Medical Institute, University of California at Los Angeles, Los Angeles, CA 90095, USA.
authors.forename: S
authors.initials: S
authors.lastname: Nisitani
authors.forename: A B
authors.initials: AB
authors.lastname: Satterthwaite
authors.forename: K
authors.initials: K
authors.lastname: Akashi
authors.forename: I L
authors.initials: IL
authors.lastname: Weissman
authors.forename: O N
authors.initials: ON
authors.lastname: Witte
authors.forename: M I
authors.initials: MI
authors.lastname: Wahl
mesh_terms: D000077329:Agammaglobulinaemia Tyrosine Kinase; D000818:Animals; D001402:B-Lymphocytes / Q000276:immunology / Q000378:metabolism*; D001853:Bone Marrow / Q000276:immunology / Q000378:metabolism; D002455:Cell Division / Q000276:immunology; D004253:DNA Nucleotidylexotransferase / Q000096:biosynthesis; D004268:DNA-Binding Proteins; D005434:Flow Cytometry; D006412:Hematopoietic Stem Cells / Q000276:immunology / Q000378:metabolism; D006801:Humans; D007075:Immunoglobulin M / Q000378:metabolism; D051379:Mice; D008807:Mice, Inbred BALB C; D018345:Mice, Knockout; D009154:Mutation; D009687:Nuclear Proteins; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D011505:Protein-Tyrosine Kinases / Q000096:biosynthesis* / Q000235:genetics / Q000276:immunology; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000096:biosynthesis; D012323:RNA Processing, Post-Transcriptional; D011946:Receptors, Antigen / Q000378:metabolism*; D015398:Signal Transduction; D013154:Spleen / Q000276:immunology / Q000378:metabolism*; D015854:Up-Regulation
chemical_list: D004268:DNA-Binding Proteins; D007075:Immunoglobulin M; D009687:Nuclear Proteins; D019253:Proto-Oncogene Proteins c-bcl-2; C499311:RAG2 protein, human; C499308:Rag2 protein, mouse; D011946:Receptors, Antigen; C064655:V(D)J recombination activating protein 2; D019869:Phosphatidylinositol 3-Kinases; D011505:Protein-Tyrosine Kinases; D000077329:Agammaglobulinaemia Tyrosine Kinase; C000625949:BTK protein, human; C000625951:Btk protein, mouse; D004253:DNA Nucleotidylexotransferase