title: Syk-dependent phosphorylation of microtubules in activated B-lymphocytes.
abstract: Syk is a protein-tyrosine kinase that is essential for B-lymphocyte development and B-cell signaling. Syk phosphorylates tubulin on tyrosine both in vitro and in intact lymphocytes. Here we show that (alpha)-tubulin present within the cytoskeletal microtubule network was phosphorylated in a Syk-dependent manner following the activation of B-cells by engagement of the B-cell antigen receptor or by treatment with the phosphotyrosine phosphatase inhibitor, pervanadate. Immunofluorescence staining of microtubule cytoskeletons and western blotting studies with antibodies to phosphotyrosine confirmed the phosphorylation of polymerized tubulin in Syk-expressing, but not Syk-deficient, cells. At low concentrations of pervanadate, centrosomes appeared to be preferentially tyrosine-phosphorylated. Tubulin phosphorylated to a high stoichiometry on tyrosine assembled into microtubules in vitro, and preassembled microtubules were also phosphorylated by Syk kinase in vitro. Thus, Syk has the capacity to interact with microtubule networks within the B-lymphocyte and catalyzes the phosphorylation of the (alpha)-tubulin subunit. Syk-dependent phosphorylation of microtubules may affect the ability of the microtubule cytoskeleton to serve as a platform upon which signaling complexes are assembled.
authors.affiliation: Department of Biological Sciences and Department of Medicinal Chemistry and Molecular Pharmacology, Purdue University, West Lafayette, Indiana 47907, USA.
authors.forename: S
authors.initials: S
authors.lastname: Faruki
authors.forename: R L
authors.initials: RL
authors.lastname: Geahlen
authors.forename: D J
authors.initials: DJ
authors.lastname: Asai
mesh_terms: D000818:Animals; D000888:Antibodies, Anti-Idiotypic / Q000494:pharmacology; D001402:B-Lymphocytes / Q000187:drug effects / Q000378:metabolism* / Q000648:ultrastructure; D001704:Biopolymers / Q000378:metabolism; D002460:Cell Line; D018385:Centrosome / Q000187:drug effects / Q000378:metabolism; D002645:Chickens; D003599:Cytoskeleton / Q000187:drug effects / Q000378:metabolism / Q000648:ultrastructure; D004791:Enzyme Inhibitors / Q000494:pharmacology; D004792:Enzyme Precursors / Q000187:drug effects / Q000378:metabolism* / Q000502:physiology; D017353:Gene Deletion; D047908:Intracellular Signaling Peptides and Proteins; D008213:Lymphocyte Activation; D008870:Microtubules / Q000187:drug effects / Q000378:metabolism*; D010766:Phosphorylation; D019000:Phosphotyrosine / Q000378:metabolism; D017027:Protein Tyrosine Phosphatases / Q000037:antagonists & inhibitors; D011505:Protein-Tyrosine Kinases / Q000187:drug effects / Q000378:metabolism* / Q000502:physiology; D015398:Signal Transduction / Q000502:physiology; D000072377:Syk Kinase; D014404:Tubulin / Q000187:drug effects / Q000378:metabolism*; D014638:Vanadates / Q000494:pharmacology
chemical_list: D000888:Antibodies, Anti-Idiotypic; D001704:Biopolymers; D004791:Enzyme Inhibitors; D004792:Enzyme Precursors; D047908:Intracellular Signaling Peptides and Proteins; D014404:Tubulin; C044203:anti-IgM; C076715:pervanadate; D019000:Phosphotyrosine; D014638:Vanadates; D011505:Protein-Tyrosine Kinases; D000072377:Syk Kinase; D017027:Protein Tyrosine Phosphatases