title: Redistribution of Bruton's tyrosine kinase by activation of phosphatidylinositol 3-kinase and Rho-family GTPases.
abstract: Bruton's tyrosine kinase (Btk) is a member of the Tec family of protein tyrosine kinases (PTK) characterized by an N-terminal pleckstrin homology domain (PH) thought to directly interact with phosphoinositides. We report here that wild-type (wt) and also a gain-of-function mutant of Btk are redistributed following a wide range of receptor-mediated stimuli through phosphatidylinositol 3-kinase (PI 3-K) activation. Employing chimeric Btk with green fluorescent protein in transient transfections resulted in Btk translocation to the cytoplasmic membrane of live cells through various forms of upstream PI 3-K activation. The redistribution was blocked by pharmacological and biological inhibitors of PI 3-K. A gain-of-function mutant of Btk was found to be a potent inducer of lamellipodia and/or membrane ruffle formation. In the presence of constitutively active forms of Rac1 and Cdc42, Btk is co-localized with actin in these regions. Formation of the membrane structures was blocked by the dominant negative form of N17-Rac1. Therefore, Btk forms a link between a vast number of cell surface receptors activating PI 3-K and certain members of the Rho-family of small GTPases. In the chicken B cell line, DT40, cells lacking Btk differed from wt cells in the actin pattern and showed decreased capacity to form aggregates, further suggesting that cytoskeletal regulation mediated by Btk may be of physiological relevance.
authors.affiliation: Department of Biosciences, Novum Karolinska Institutet, SE-141 57 Huddinge, Sweden.
authors.forename: B F
authors.initials: BF
authors.lastname: Nore
authors.forename: L
authors.initials: L
authors.lastname: Vargas
authors.forename: A J
authors.initials: AJ
authors.lastname: Mohamed
authors.forename: L J
authors.initials: LJ
authors.lastname: Brandén
authors.forename: C M
authors.initials: CM
authors.lastname: Bäckesjö
authors.forename: T C
authors.initials: TC
authors.lastname: Islam
authors.forename: P T
authors.initials: PT
authors.lastname: Mattsson
authors.forename: K
authors.initials: K
authors.lastname: Hultenby
authors.forename: B
authors.initials: B
authors.lastname: Christensson
authors.forename: C I
authors.initials: CI
authors.lastname: Smith
mesh_terms: D000077329:Agammaglobulinaemia Tyrosine Kinase; D000818:Animals; D001692:Biological Transport; D002460:Cell Line; D054377:Chemokine CXCL12; D019743:Chemokines, CXC / Q000494:pharmacology; D002645:Chickens; D003599:Cytoskeleton / Q000737:chemistry; D004789:Enzyme Activation; D019869:Phosphatidylinositol 3-Kinases / Q000502:physiology*; D011505:Protein-Tyrosine Kinases / Q000378:metabolism*; D020741:rho GTP-Binding Proteins / Q000502:physiology*; D019061:src-Family Kinases / Q000502:physiology
chemical_list: D054377:Chemokine CXCL12; D019743:Chemokines, CXC; D019869:Phosphatidylinositol 3-Kinases; D011505:Protein-Tyrosine Kinases; D000077329:Agammaglobulinaemia Tyrosine Kinase; D019061:src-Family Kinases; D020741:rho GTP-Binding Proteins