title: A sensitized genetic system for the analysis of murine B lymphocyte signal transduction pathways dependent on Bruton's tyrosine kinase.
abstract: Modifier screens have been powerful genetic tools to define signaling pathways in lower organisms. The identification of modifier loci in mice has begun to allow a similar dissection of mammalian signaling pathways. Transgenic mice (Btk(lo)) expressing 25% of endogenous levels of Bruton's tyrosine kinase (Btk) have B cell functional responses between those of wild-type and Btk(-/-) mice. We asked whether reduced dosage or complete deficiency of genes previously implicated as Btk regulators would modify the Btk(lo) phenotype. We used two independent assays of Btk-dependent B cell function. Proliferative response to B cell antigen receptor cross-linking in vitro was chosen as an example of a relatively simple, well-defined signaling system. In vivo response to type II T-independent antigens (TI-II) measures complex interactions among multiple cell types over time and may identify additional Btk pathways. All modifiers identified differentially affected these two assays, indicating that Btk mediates these processes via distinct mechanisms. Loss of Lyn, PTEN (phosphatase and tensin homolog), or SH2-containing inositol phosphatase suppressed the Btk(lo) phenotype in vitro but not in vivo, whereas CD19 and the p85alpha form of phosphoinositide 3-kinase behaved as Btk(lo) enhancers in vivo but not in vitro. Effects of Lyn, PTEN, or p85alpha haploinsufficiency were observed. Haploinsufficiency or complete deficiency of protein kinase C beta, Fyn, CD22, Galphaq, or Galpha11 had no detectable effect on the function of Btk(lo) B cells. A transgenic system creating a reduction in dosage of Btk can therefore be used to identify modifier loci that affect B cell responses and quantitatively rank their contribution to Btk-mediated processes.
authors.affiliation: Department of Microbiology, Immunology, and Molecular Genetics, and Howard Hughes Medical Institute, University of California, Los Angeles, CA 90095, USA.
authors.forename: A B
authors.initials: AB
authors.lastname: Satterthwaite
authors.forename: F
authors.initials: F
authors.lastname: Willis
authors.forename: P
authors.initials: P
authors.lastname: Kanchanastit
authors.forename: D
authors.initials: D
authors.lastname: Fruman
authors.forename: L C
authors.initials: LC
authors.lastname: Cantley
authors.forename: C D
authors.initials: CD
authors.lastname: Helgason
authors.forename: R K
authors.initials: RK
authors.lastname: Humphries
authors.forename: C A
authors.initials: CA
authors.lastname: Lowell
authors.forename: M
authors.initials: M
authors.lastname: Simon
authors.forename: M
authors.initials: M
authors.lastname: Leitges
authors.forename: A
authors.initials: A
authors.lastname: Tarakhovsky
authors.forename: T F
authors.initials: TF
authors.lastname: Tedder
authors.forename: R
authors.initials: R
authors.lastname: Lesche
authors.forename: H
authors.initials: H
authors.lastname: Wu
authors.forename: O N
authors.initials: ON
authors.lastname: Witte
mesh_terms: D000077329:Agammaglobulinaemia Tyrosine Kinase; D000818:Animals; D018941:Antigens, CD19 / Q000502:physiology; D001402:B-Lymphocytes / Q000502:physiology*; D051379:Mice; D008807:Mice, Inbred BALB C; D008810:Mice, Inbred C57BL; D008822:Mice, Transgenic; D051059:PTEN Phosphohydrolase; D019869:Phosphatidylinositol 3-Kinases / Q000502:physiology; D000072183:Phosphatidylinositol-3,4,5-Trisphosphate 5-Phosphatases; D010744:Phosphoric Monoester Hydrolases / Q000502:physiology; D011493:Protein Kinase C / Q000502:physiology; D011505:Protein-Tyrosine Kinases / Q000502:physiology*; D011947:Receptors, Antigen, B-Cell / Q000502:physiology; D015398:Signal Transduction; D025521:Tumor Suppressor Proteins
chemical_list: D018941:Antigens, CD19; D011947:Receptors, Antigen, B-Cell; D025521:Tumor Suppressor Proteins; D019869:Phosphatidylinositol 3-Kinases; D011505:Protein-Tyrosine Kinases; D000077329:Agammaglobulinaemia Tyrosine Kinase; C000625949:BTK protein, human; C000625951:Btk protein, mouse; D011493:Protein Kinase C; D010744:Phosphoric Monoester Hydrolases; D051059:PTEN Phosphohydrolase; C098706:INPPL1 protein, human; D000072183:Phosphatidylinositol-3,4,5-Trisphosphate 5-Phosphatases