Posttranscriptional Regulation of Bruton's Tyrosine Kinase Expression in Antigen Receptor-Stimulated Splenic B Cells

• Published in: Proceedings of the National Academy of Sciences - PNAS 2000-03, Vol.97 (6), p.2737-2742
• Main Authors: Nisitani, S, Satterthwaite, A B, Akashi, K, Weissman, I L, Witte, O N, Wahl, M I
• Format: Article
• Language: English
• Subjects: Agammaglobulinaemia Tyrosine Kinase; Animals; Antibodies; B lymphocytes; B-Lymphocytes - immunology; B-Lymphocytes - metabolism; Biological Sciences; Bone marrow; Bone Marrow - immunology; Bone Marrow - metabolism; Bone marrow cells; Bruton's tyrosine kinase; Cell Division - immunology; Cellular immunity; DNA Nucleotidylexotransferase - biosynthesis; DNA-Binding Proteins; Flow Cytometry; Hematopoietic Stem Cells - immunology; Hematopoietic Stem Cells - metabolism; Histograms; Humans; Immunoglobulin M - metabolism; ionomycin; Lymphocytes; Mice; Mice, Inbred BALB C; Mice, Knockout; Mutation; Nuclear Proteins; Phosphatidylinositol 3-Kinases - metabolism; Protein-Tyrosine Kinases - biosynthesis; Protein-Tyrosine Kinases - genetics; Protein-Tyrosine Kinases - immunology; Proto-Oncogene Proteins c-bcl-2 - biosynthesis; Receptors, Antigen - metabolism; RNA Processing, Post-Transcriptional; Signal Transduction; Spleen - immunology; Spleen - metabolism; Stem cells; T lymphocytes; Up regulation
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.050583597

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, post-transcriptional 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.